阅读说明：本技术 液力减速器系统和控制液力减速器系统的方法 (Hydrodynamic retarder system and method for controlling a hydrodynamic retarder system ) 是由 J·范丁格恩 J·A·贝德特 H·涅维汉 于 2018-04-25 设计创作，主要内容包括：本公开涉及一种用于变速器的可控液力减速器系统(10),包括电子控制器单元(ECU)(38),用于通过调节减速器出口压力来选择和控制制动扭矩。该系统可以包括算法,以计算减速器出口压力设定点或表格或制动扭矩曲线或廓形,从而允许ECU(38)计算或查找减速器RT出口压力、车辆或转子速度与由操作者选择的制动扭矩曲线之间的函数关系,以提供所选的RT出口压力。所公开的系统仍然还可以包括冷却系统或利用车辆发动机冷却系统。在一个实施例中,冷却器(32)可以在变速器和可控减速器(27)之间共享,并且可以被调节以适应冷却要求。ECU(38)还可以独立于冷却系统对RT出口压力进行调节以解决短期和长期RT过热保护。ECU(38)可以编程为避免选择可能导致系统快速过热的RT出口压力设定点。本文公开的比例控制RT系统还可以通过进一步将过热校正因子应用于RT出口压力设定点来解决长期过热。(The present disclosure relates to a controllable hydrodynamic retarder system (10) for a transmission including an Electronic Controller Unit (ECU) (38) for selecting and controlling braking torque by adjusting retarder outlet pressure. The system may include an algorithm to calculate a retarder outlet pressure set point or table or a brake torque curve or profile to allow the ECU (38) to calculate or look up a functional relationship between the retarder RT outlet pressure, vehicle or rotor speed, and the brake torque curve selected by the operator to provide the selected RT outlet pressure. The disclosed system may still further include or utilize a vehicle engine cooling system. In one embodiment, a cooler (32) may be shared between the transmission and the controllable retarder (27) and may be adjusted to accommodate cooling requirements. The ECU (38) may also regulate RT outlet pressure independently of the cooling system to account for short and long term RT overheating protection. The ECU (38) may be programmed to avoid selecting an RT outlet pressure set point that may cause rapid system overheating. The proportional control RT system disclosed herein can also account for long term overheating by further applying an overheating correction factor to the RT outlet pressure set point.)

1. A hydrodynamic retarder system (10), in particular for a motor vehicle, comprising:

a hydrodynamic retarder (27), the hydrodynamic retarder (27) comprising a rotor and a stator and having an inlet (27a) and an outlet (27 b);

a retarder proportional valve (29), the retarder proportional valve (29) in fluid communication with the retarder outlet, the retarder proportional valve (29) configured to control a retarder outlet pressure; and

an Electronic Control Unit (ECU) (38);

wherein the ECU (38) is configured to determine a Retarder (RT) outlet pressure set point based on at least one or both of a current rotor speed and a desired braking torque; and is

Wherein the ECU (38) is configured to control the retarder proportional valve (29) based on the retarder outlet pressure setpoint such that the retarder proportional valve (29) provides a retarder outlet pressure within the retarder outlet pressure setpoint range.

2. A hydraulic retarder system (10) according to claim 1, characterized in that the ECU (38) is configured to determine the retarder outlet pressure set point based on the current rotor speed and on the desired braking torque.

3. A hydraulic retarder system (10) according to any of the preceding claims, characterized in that the hydraulic retarder system (10) further comprises a table stored in the ECU (38), the table comprising one or more rotor speed values and one or more desired braking torque values, and the table providing the retarder outlet pressure set point as a function of the one or more rotor speed values and the one or more desired braking torque values.

4. A hydraulic retarder system (10) according to any of the preceding claims, characterized in that the hydraulic retarder system (10) further comprises an input device, wherein the ECU (38) is configured to determine the desired braking torque based on or further based on an input signal provided by an operator via the input device.

5. A hydraulic retarder system (10) according to any of the preceding claims, characterized in that the hydraulic retarder system (10) further comprises one or more vehicle sensors, wherein the ECU (38) is configured to determine the outlet pressure set point based on or further based on one or more vehicle sensor signals provided by the one or more vehicle sensors.

6. A hydraulic retarder system (10) according to claim 5, characterized in that the one or more vehicle sensors comprise at least one or each of a temperature sensor (36) for measuring retarder fluid temperature, in particular at retarder outlet, a pressure sensor for measuring retarder fluid pressure, in particular at retarder outlet, an inclination sensor for measuring inclination angle, and a vehicle speed sensor for measuring vehicle speed.

7. A hydrodynamic retarder system (10) according to any of the preceding claims, further comprising:

a fluid reservoir (12);

a cooler (32); and

at least one cooler flow valve (30), the at least one cooler flow valve (30) selectively fluidly connecting the retarder proportional valve (29) with either of the cooler (32) and the fluid reservoir (12).

8. A hydrodynamic retarder system (10) as defined in claim 7, characterized in that the at least one cooler flow valve (30) is configured to: the at least one chiller flow valve (30) fluidly connects the retarder proportional valve (29) with the chiller (32) if the retarder outlet pressure is above a first pressure threshold; and wherein the at least one cooler flow valve (30) is configured to: the at least one cooler flow valve (30) fluidly connects the retarder proportional valve (29) with the fluid reservoir (12) such that fluid from the retarder proportional valve (29) bypasses the cooler (32) if the retarder outlet pressure is lower than a second pressure threshold that is equal to or less than the first pressure threshold.

9. A hydrodynamic retarder system (10) according to any of claims 7 and 8, further comprising:

a torque converter (22) and one or more transmission lubrication channels (21) in fluid communication with the fluid reservoir (12);

wherein the at least one cooler flow valve (30) selectively fluidly connects the torque converter (22) with any of the cooler (32) and the one or more transmission lubrication passages (21).

10. A hydrodynamic retarder system (10) as defined in claim 9, characterized in that the at least one cooler flow valve (30) is configured to: if the retarder outlet pressure is above a first pressure threshold, the at least one cooler flow valve (30) fluidly connects the torque converter (22) with the one or more fluid lubrication passages such that fluid from the torque converter (22) bypasses the cooler (32); and wherein the at least one cooler flow valve (30) is configured to: the at least one cooler flow valve (30) fluidly connects the torque converter (22) with the cooler (32) if the retarder outlet pressure is lower than a second pressure threshold that is equal to or less than the first pressure threshold.

11. A hydrodynamic retarder system (10) according to any of claims 7-10, characterized in that the at least one cooler flow valve (30) comprises at least one hydraulic actuator in fluid communication with the retarder outlet and configured to control the control position of the at least one cooler flow valve (30) based on a retarder outlet pressure; and/or wherein the at least one cooler flow valve (30) comprises an electromagnet in communication with the ECU (38) and is configured to control a control position of the at least one cooler flow valve (30) based on an electromagnetic signal received from the ECU (38).

12. A hydraulic retarder system (10) according to any of the preceding claims, characterized in that the retarder proportional valve (29) comprises a hydraulic actuator fluidly connected to a first pilot valve (28), the first pilot valve (28) comprising an electromagnet in communication with the ECU (38) and configured to control the control position of the first pilot valve (28) based on an electromagnetic signal received from the ECU (38); and/or wherein the retarder proportional valve (29) comprises a solenoid in communication with the ECU (38) and is configured to control a control position of the retarder proportional valve (29) based on a solenoid signal received from the ECU (38).

13. A hydrodynamic retarder system (10) according to any of the preceding claims, further comprising:

a fluid reservoir (12);

a retarder pump (16), the retarder pump (16) being in fluid communication with the fluid reservoir (12); and

a retarder on/off valve (24), the retarder on/off valve (24) configured to selectively fluidly connect the retarder pump (16) with the retarder inlet.

14. A hydraulic retarder system (10) according to claim 12, characterized in that the retarder on/off valve (24) comprises a hydraulic actuator selectively fluidly connected to another fluid pump through a second pilot valve (34), the second pilot valve (34) comprising a solenoid in communication with the ECU (38) and being configured to control the control position of the second pilot valve (34) based on electromagnetic signals received from the ECU (38); and/or wherein the retarder on/off valve (24) comprises a solenoid in communication with the ECU (38) and configured to control a control position of the retarder on/off valve (24) based on a solenoid signal received from the ECU (38).

15. A method of controlling a hydraulic retarder system (10), in particular for a transmission of a motor vehicle, comprising:

a hydrodynamic retarder (27), the hydrodynamic retarder (27) comprising a rotor and a stator and having an inlet and an outlet;

a retarder proportional valve (29), the retarder proportional valve (29) in fluid communication with the retarder outlet, the retarder proportional valve (29) configured to control a retarder outlet pressure; and

an Electronic Control Unit (ECU) (38);

the method comprises the following steps:

determining a retarder outlet pressure set point based on at least one or both of a current rotor speed and a desired braking torque; and

controlling the retarder proportional valve (29) based on the retarder outlet pressure setpoint such that the retarder proportional valve (29) provides a retarder outlet pressure within the retarder outlet pressure setpoint.

Technical Field

The present disclosure relates generally to vehicle brake assist known as retarder systems and methods. In particular, the system and method relate to hydrodynamic retarders, and more particularly to an integrated hydrodynamic transmission and retarder system. More specifically, the systems and methods disclosed herein relate to an integrated hydrotransmission and ratio-controllable retarder system.

Background

In a hydrodynamic transmission, in particular for a motor vehicle, a retarder may be connected directly or indirectly to the transmission input or output shaft or any other transmission shaft to assist braking of, for example, a motor vehicle incorporating the transmission by slowing down the rotation of the transmission shaft. The decelerator may utilize friction and vibration loss of a movable blade or impeller of a rotor connected to a driving shaft and a fixed blade or impeller of a stator connected to a frame of the decelerator. The chamber housing the vanes may be filled or evacuated with fluid. The annular fluid flow within the chamber acts on the blades of the rotor, slowing rotation of the rotor and drive shaft and producing vehicle braking. Such a reduction of the transmission shaft is extremely useful when the brake is in heavy use during downhill driving. The moving blades may be attached to a propeller shaft or a separate rotor connected to the propeller shaft, either directly or through a gear or gearbox, to further slow the propeller shaft and assist in braking of the vehicle. The retarder system may use standard transmission fluid (gear oil), engine oil, or a separate fluid, fluid mixture, or oil.

When vehicle braking assistance or a retarder is required, fluid, typically transmission fluid or oil, is pumped into the retarder chamber and friction and shock losses of the blades or impellers connected to or part of the drive shaft will cause the vehicle to retarder. The on/off retarder may be filled or emptied. For a proportional controlled retarder, the degree of deceleration may be varied in several ways, including adjusting the fill level of the retarder chamber, the retarder inlet pressure, the retarder outlet pressure within the retarder chamber, or the extension of the gap between the rotor and the stator.

Friction and impact cause the fluid to heat up. The superheated fluid will degrade rapidly, reducing viscosity and performance, and require a higher frequency of replacement intervals, and may reduce the life of the seal. To prevent overheating, a fluid may be circulated through the cooling system. The cooling system may be integrated into the engine cooling system of the vehicle, or a separate cooling system specific to the transmission and/or retarder may be used. For example, the cooling system may include an air-to-oil heat exchanger. After passing through the cooling system, the cooled fluid may be returned to an oil or fluid reservoir before being recirculated. Indeed, cooling of the transmission fluid may be required even in situations where a retarder is not used due to high demands placed on the transmission system, such as in off-highway vehicles. In some integrated hydrodynamic transmission and retarder systems, particularly in a proportional-controlled hydrodynamic retarder, cooling of the working fluid or transmission fluid is performed by a cooling system integrated into the engine cooling system of the vehicle, which includes an oil-to-engine coolant heat exchanger to dissipate heat from the fluid or oil into the electric motor cooling circuit of the vehicle.

A proportional control hydraulic retarder is a retarder capable of providing a selectable, predetermined and/or variable braking torque or retarding force. Such a proportional control retarder system may also have a cooling system separate or independent from the engine cooling system, or integrated in the engine cooling system. In some known proportional control retarders, a heat exchanger is used to dissipate heat from a fluid into the motor cooling circuit of the vehicle. To save space and/or minimize cost, these known systems typically do not use a pump to circulate oil between the retarder and the cooler. Instead, such systems typically use the retarder itself as a turbo pump to provide a pressure head to create flow through the retarder and the cooler. During retarder activation, the valve allows fluid to enter the retarder chamber while air is released, for example, through a breather. The cooling flow rate is determined by the balance between the retarder head and the head losses in the pipes or channels, valves and heat exchangers. As a result, these components have narrow tolerances and cannot be easily changed without affecting the flow rate and therefore the cooling function. Indeed, in many cases, the limited ability to change components, and thus flow rate, may be the reason for integrating the heat exchanger into the retarder system.

In other known proportional control hydraulic retarder systems, a relatively small pump may be used to provide the retarder fill flow. In the event that faster filling is required, an accumulator system may be added. Known proportional control hydrodynamic retarders can generally be controlled in several ways.

U.S. patent No. 3,987,874, the entire contents of which are incorporated herein, discloses controlling retarder inlet pressure to control the braking torque applied to the rotor, wherein high inlet pressures typically result in higher braking torque being applied to the transmission.

Control of retarder outlet pressure is disclosed in U.S. patent No. 3,774,734, wherein higher outlet pressure generally results in higher braking torque, the entire contents of which are incorporated herein.

U.S. patent No. 5,771,997, the entire contents of which are incorporated herein, discloses controlling fill levels in a retarder to control braking torque, with higher fill levels generally resulting in higher braking torque.

U.S. patent No. 4,864,872, which is incorporated herein in its entirety, discloses controlling the extension of the gap between the rotor and the stator, wherein reducing the extension of the gap generally results in higher braking torque.

And U.S. patent No. 3,863,739, which is incorporated herein in its entirety, discloses braking torque related to retarder performance and rotor speed. At a given retarder inlet pressure, the braking torque applied by the retarder increases as the rotor speed increases.

Accordingly, there is a need for a hydrodynamic retarder system comprising a hydrodynamic retarder which can be more flexibly integrated with different cooling systems and which preferably provides improved control of the braking torque applied via the hydrodynamic retarder, and a corresponding method of operating the system.

Disclosure of Invention

A hydrodynamic retarder system and a method of operation capable of providing these functions are defined in the independent claims. Particular embodiments are described in the dependent claims.

Therefore, a hydrodynamic retarder system, in particular for a transmission of a motor vehicle, is currently proposed. The proposed hydrodynamic retarder system comprises:

a hydrodynamic Retarder (RT) comprising a rotor and a stator and having an inlet and an outlet;

a Reducer (RT) proportional valve in fluid communication with the Reducer (RT) outlet, the RT proportional valve configured to control RT outlet pressure; and

an Electronic Control Unit (ECU);

wherein the ECU is configured to determine a Retarder (RT) outlet pressure set point based on at least one or both of a current rotor speed and a desired braking torque; and is

Wherein the ECU is configured to control the RT proportional valve based on the RT outlet pressure set point such that the RT proportional valve provides a RT outlet pressure within a range of the RT outlet pressure set point or within a predetermined range.

Furthermore, a method of controlling a hydraulic RT system is proposed, the method comprising the steps of:

determining a RT outlet pressure set point based on at least one or both of a current speed of a rotor of the hydraulic RT and a desired braking torque; and

the RT proportional valve is controlled based on the RT outlet pressure set point such that the RT proportional valve provides a RT outlet pressure within a range of the RT outlet pressure set point.

The presently proposed system and method may address interchangeability of cooling systems, variability of brake torque curves applied by the RT, overheating, and other issues not previously considered. In particular, a hydraulic transmission including the presently proposed hydraulic RT system may potentially provide selectable braking torque functionality while maintaining a high degree of freedom in transmission cooling system selection.

The ECU may be configured or programmed to determine the RT outlet pressure set point based on the current rotor speed and based on the desired brake torque.

The hydraulic RT system may further include a table stored in the ECU. For example, the ECU may include a memory device for storing the table. For example, the memory device may include an electronically readable device, a magnetically readable device, or an optically readable device. The table may include one or more rotor speed values. Additionally or alternatively, the table may include one or more desired brake torque values. The table may provide a RT outlet pressure set point that varies as a function of at least one or both of the one or more rotor speed values and the one or more desired brake torque values.

In other words, the table may include a braking torque curve showing the relationship between vehicle or rotor/propeller shaft speed, retarder outlet pressure and braking torque applied by the retarder. This relationship may be formulated as an algorithm, a brake torque table, a curve or a profile. These may be tailored to the particular configuration of the vehicle based on factors such as retarder size and blade or impeller shape, vehicle weight, total transmission system drag, typical drop-off values, and other parameters. Algorithms, tables or brake torque curves or profiles that can indicate the extent of brake torque relative to rotor speed and/or vehicle speed and retarder outlet pressure can be used by an electronic controller in the vehicle to provide a proportionally controllable retarder.

The operator or driver of the vehicle into which the hydraulic RT system may be incorporated is typically unable to accurately judge or determine the degree to which RT will apply braking torque based on RT outlet pressure and/or based on the speed of the vehicle. In particular, the braking torque applied by RT generally increases with increasing rotor speed, following a characteristic curve in which each point on the curve may require or represent a particular minimum outlet pressure, which may also increase with increasing rotor speed. Thus, for a particular RT outlet pressure, the braking torque generally follows a characteristic curve for increasing the rotor speed to a rotor speed for which the requested minimum outlet pressure is equal to the applied outlet pressure, and from that point onwards the braking torque applied by RT generally remains approximately constant for further increasing the rotor speed. As disclosed herein, the ability to transition between a series of prescribed or stored braking torque curves, where each curve may include a braking torque that strictly increases with increasing rotor speed, may improve drivability of the vehicle and improve safety as compared to control strategies that include directly controlling RT outlet pressure without regard to other variables such as rotor speed. Furthermore, the combination of high RT outlet pressure and high RT capacity/high brake torque settings can result in rapid overheating of retarder fluid. The table stored in the ECU may include brake torque curves designed to avoid such combinations.

The ECU may be configured or programmed to control or regulate RT outlet pressure via the RT proportional valve, for example, using feedback control.

The hydraulic RT system may further include an input device, particularly an input device in communication with the ECU. The input device may include, but is not limited to, at least one or each of a pedal, a lever, a knob, a switch, a joystick, a touch screen, a microphone, or a camera, for example. The ECU may be configured or programmed to determine the desired braking torque based on, or further based on, input signals provided by an operator via the input device. For example, the operator may select a particular braking torque setting, such as a desired braking torque value, which may include a desired percentage of the maximum applicable braking torque or a desired braking torque profile.

The hydraulic RT system may further include one or more vehicle sensors in communication with the ECU. The ECU may then be configured to determine the outlet pressure set point based on, or further based on, one or more vehicle sensor signals provided by one or more vehicle sensors.

The one or more vehicle sensors may include, but are not limited to, at least one or each of temperature sensors for measuring RT fluid temperature, such as for measuring RT fluid temperature at RT outlet, in RT chamber, in cooler, in one or more transmission cooling channels, or in fluid reservoir; a pressure sensor for measuring the RT fluid pressure, in particular for measuring the RT fluid pressure at the RT outlet; a tilt sensor for measuring a tilt angle of a transmission to which the hydraulic RT system can be coupled, or of a vehicle to which the hydraulic RT system can be incorporated, in particular of RT; and a speed sensor, in particular for measuring the speed of the RT rotor, the speed of the propeller shaft or the speed of the vehicle to which the hydraulic RT system can be coupled.

The hydraulic RT system can include at least one or each of a fluid reservoir, a cooler, and at least one cooler flow valve. At least one cooler flow valve may be configured to selectively fluidly connect the RT proportional valve with either of the cooler and the fluid reservoir. For example, at least one cooler flow valve may have a first control position and a second control position. The at least one cooler flow valve may be configured to: when it is switched to the first control position, it directs fluid from the RT proportional valve to the fluid reservoir, for example in such a way that fluid from the RT proportional valve bypasses the cooler. And the at least one cooler flow valve may be configured to: when it is switched to the second control position, it directs fluid from the RT proportional valve to the chiller. After passing through the cooler, the fluid may then be directed from the cooler to, for example, a reservoir.

The at least one cooler flow valve may be biased to the first control position, for example, by a biasing member, which may comprise a resilient biasing member such as a spring. For example, the at least one cooler flow valve may be configured such that if the RT outlet pressure is above a first pressure threshold, the at least one cooler flow valve is switched to a second control position fluidly connecting the RT proportional valve with the cooler. And the at least one cooler flow valve may be configured to: if the RT outlet pressure is lower than a second pressure threshold that is equal to or less than the first pressure threshold, the at least one cooler flow valve is fluidly switched to a first control position that connects the RT proportional valve with the fluid tank.

For example, the at least one chiller flow valve may include at least one hydraulic actuator in fluid communication with the RT outlet. The hydraulic actuator may then be configured to control a control position of the at least one cooler flow valve based on the RT outlet pressure. For example, a hydraulic actuator of the cooler flow valve may apply the RT outlet pressure to a spool of the cooler flow valve and may bias the cooler flow valve toward a second control position of the cooler flow valve. For example, an outlet pressure applied to the cooler flow valve via a hydraulic actuator of the cooler flow valve may bias the cooler flow valve toward the first control position against a biasing member of the cooler flow valve as described above. Additionally or alternatively, the at least one cooler flow valve may include a solenoid in communication with the ECU, wherein the solenoid is configured to control a control position of the at least one cooler flow valve based on a solenoid signal received from the ECU. For example, the ECU may be in communication with a pressure sensor for measuring RT outlet pressure, and may control a control position of the cooler flow valve via an electromagnet of the cooler flow valve based on RT outlet pressure measured or sensed using the pressure sensor.

The hydraulic RT system may further include a torque converter and/or one or more transmission lubrication channels. The torque converter may be in fluid communication with the fluid reservoir, for example, via a transmission pump. And one or more transmission lubrication passages may be in fluid communication with the fluid reservoir. The at least one cooler flow valve may be configured to selectively fluidly connect the torque converter with any of the cooler and the one or more transmission lubrication passages. For example, the at least one cooler flow valve may be configured to: when it is switched to the first control position, it directs fluid from the torque converter to the cooler. From the cooler, the fluid may then be further directed to one or more transmission lubrication passages. And fluid may be further directed from the one or more transmission lubrication passages to a fluid reservoir. And the at least one cooler flow valve may be configured to: when it is switched to the second control position, it directs fluid from the torque converter to one or more transmission lubrication passages, for example, so that fluid from the torque converter bypasses a cooler.

The at least one cooler flow valve may be configured to: if the RT outlet pressure is above the first pressure threshold, at least one cooler flow valve fluidly connects the torque converter with one or more fluid lubrication passages such that fluid from the torque converter bypasses the cooler. And the at least one cooler flow valve may be configured to: at least one cooler flow valve fluidly connects the torque converter with the cooler if the RT outlet pressure is lower than a second pressure threshold that is equal to or less than the first pressure threshold.

The RT proportional valve may include a first hydraulic actuator. The first hydraulic actuator of the RT proportional valve may bias the RT proportional valve toward a closed position in which the RT proportional valve increases the RT outlet pressure. The first hydraulic actuator of the RT proportional valve may be fluidly connected to the first pilot valve. The first pilot valve may selectively fluidly connect the first hydraulic actuator of the RT proportional valve with the fluid reservoir, such as via one of the RT pump or the transmission pump as described above. That is, the control position of the first pilot valve may control or regulate the hydraulic pressure applied to the spool of the RT proportional valve via the first hydraulic actuator of the RT proportional valve. The first pilot valve may include a solenoid in communication with the ECU and configured to control a control position of the first pilot valve based on an electromagnetic signal received from the ECU. For example, the ECU may be in communication with a pressure sensor for measuring RT outlet pressure, and may be configured to control a control position of the first pilot valve based on the measured RT outlet pressure.

The RT proportional valve may further include a second hydraulic actuator. The second hydraulic actuator of the RT proportional valve may bias the RT proportional valve toward an open position in which the RT proportional valve reduces the RT outlet pressure. The second hydraulic actuator of the RT proportional valve may be fluidly connected or selectively fluidly connected to the RT outlet. That is, the RT proportional valve may be configured such that the RT outlet pressure biases the RT proportional valve toward an open position in which the RT proportional valve reduces the RT outlet pressure.

Additionally or alternatively, the RT proportional valve may be electrically controlled. For example, the RT proportional valve may include a solenoid in communication with the ECU and configured to control a control position of the RT proportional valve based on a solenoid signal received from the ECU. For example, the ECU may be in communication with a pressure sensor for measuring RT outlet pressure, and may be configured to control a control position of the RT proportional valve based on the measured RT outlet pressure.

The RT proportional valve may further comprise a biasing member, in particular a resilient biasing member such as a spring. The biasing member of the RT proportional valve may be configured to bias the RT proportional valve toward an open position.

The hydraulic RT system can further include a fluid reservoir, an RT pump in fluid communication with the fluid reservoir, and an RT on/off valve configured to selectively fluidly connect the RT pump with the RT inlet to selectively fill the hydraulic RT.

The RT on/off valve may include a first hydraulic actuator. The first hydraulic actuator of the RT on/off valve may bias the RT on/off valve toward an open position in which the RT on/off valve fluidly connects the RT inlet with the RT pump such that the RT pump may fill the hydraulic RT. The first hydraulic actuator of the RT on/off valve may be selectively fluidly connected to a fluid pump, such as the transmission pump described above via a second pilot valve. The second pilot valve may include a solenoid in communication with the ECU and configured to control a control position of the second pilot valve based on an electromagnetic signal received from the ECU. For example, the ECU may be configured or programmed to fluidly connect a first hydraulic actuator of the RT on/off valve with the fluid pump to switch the RT on/off valve to an open position and to fill the hydraulic RT based on an input command provided by an operator or based on sensor signals provided by one or more vehicle sensors.

The RT on/off valve may further include a second hydraulic actuator. A second hydraulic actuator of the RT on/off valve may bias the RT on/off valve toward a closed position in which the RT on/off valve fluidly isolates the RT inlet from the RT pump such that the RT pump may not be filled with hydraulic RT. The second hydraulic actuator of the RT on/off valve may be fluidly connected or selectively fluidly connected to the RT inlet.

Additionally or alternatively, the RT on/off valve may be electrically controlled. For example, the RT on/off valve may include a solenoid in communication with the ECU and configured to control a control position of the RT on/off valve based on a solenoid signal received from the ECU. For example, the ECU may be configured or programmed to control the control position of the RT on/off valve based on input commands provided by an operator or based on sensor signals provided by one or more vehicle sensors.

The RT on/off valve may further comprise a biasing member, in particular a resilient biasing member such as a spring. The biasing member of the RT on/off valve may be configured to bias the RT on/off valve toward a closed position in which the RT on/off valve fluidly isolates the RT inlet from the RT pump such that the RT pump may not be filled with hydraulic RT.

The ECU may be configured or programmed to control the braking torque by adjusting the RT outlet pressure. For example, the ECU may be configured or programmed to calculate using an algorithm, or use a table or braking torque curve or profile, to look up a functional relationship between retarder RT outlet pressure, vehicle or rotor speed, and the braking torque curve selected by the operator to provide a selected RT outlet pressure within certain limits. The ECU may also be configured to regulate RT outlet pressure to address short and long term RT overheating protection regardless of whether fluid from the RT is directed to the cooling system.

The ECU may be configured or programmed such that the operator may select a braking torque profile that gives a particular degree or capacity of braking torque, such as between 0% or other minimum settings such as 25% and 100% or other maximum values such as 90%. The minimum setting may be represented by a minimum braking torque curve and the maximum setting may be represented by a maximum braking torque curve, and the change in braking capability may provide a linear or other interpolation between these curves. The ECU may then be configured to use an algorithm, table, or other braking profile/production profile to select the appropriate RT outlet pressure for the current rotor speed to achieve the selected braking torque profile. For example, the ECU may be configured or programmed to include a processor connected to an electronic memory that stores algorithms, tables, or brake curves or profiles to calculate or obtain the RT outlet pressure set point from a brake torque curve selected by the operator and vehicle or rotor speed. In this way, the ECU may be configured or programmed to communicate the obtained RT outlet pressure set point directly or indirectly to the RT proportional valve, which may regulate the RT outlet pressure required to provide the selected braking torque.

Furthermore, because the controllable or proportional RT systems disclosed herein may be configured to be set, controlled, and/or adjusted accordingly, undesirably high braking torques and rapid overheating may be substantially reduced or prevented. In other words, the ECU may be configured or programmed to adjust or disallow selection of a braking torque profile that may result in extremely high braking torque under certain vehicle operating conditions, such as high rotor speed and high RT outlet pressure. For example, the ECU may be configured or programmed to avoid selecting an RT outlet pressure set point that may result in rapid overheating of the hydraulic RT system. In other words, at high rotor speeds and high RT outlet pressure, the ECU may be configured to regulate RT outlet pressure to prevent the operator-selected high braking torque from causing extremely high braking torque and rapid overheating. For example, a high brake torque setting selected by the operator will typically result in the ECU calculating or obtaining a high RT outlet pressure set point at low to medium rotor speeds and/or RT outlet pressure conditions, since overheating will not occur under such conditions. However, at high rotor speeds and/or RT outlet pressures, the ECU may be programmed to adjust or disallow the RT outlet pressure set point which may lead to rapid overheating. For example, the RT outlet pressure set point that can cause rapid overheating can be programmed in an algorithm or identified in a brake torque table, curve or profile.

However, it is understood that after prolonged use of RT, even with the appropriate braking profile or braking torque setting, overheating of RT fluid beyond the cooler capacity may still result, which may also lead in time to RT overheating referred to as long term overheating. The presently proposed hydraulic RT system may be configured to address such long term heating by further applying an superheat correction factor to the RT outlet pressure set point. For example, the ECU may be connected to one or more temperature sensors that measure the fluid temperature, or may take into account the time of effective operation of the retarder to estimate long term overheating, and may adjust the RT outlet pressure set point.

The hydraulic RT system may include a temperature sensor in/at the retarder outlet fluid flow, and the ECU may be configured or programmed to apply a correction factor to the RT outlet pressure set point based on the measured temperature, for example, using an algorithm, a brake torque meter, or a brake torque curve. The correction factor may be stored in a look-up table or calculated by the processor using a correction factor formula to adjust the RT outlet pressure set point. The ECU may be configured or programmed to communicate with a RT proportional valve that regulates the RT outlet pressure. Additionally or alternatively, the ECU may be configured or programmed to lower the outlet pressure set point based on temperature values measured with other temperature sensors, such as a sump or torque converter outlet temperature sensor.

Drawings

These and further benefits of the presently disclosed systems and methods are described in the following detailed description and illustrated in the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of an embodiment of a hydrodynamic transmission and retarder system, independent of a cooler;

FIG. 2 shows a table of retarder outlet pressure set points in bar (bar) given retarder braking capability in percent (horizontal axis) given rotor speed (vertical axis);

FIG. 3 shows a table of retarder outlet pressure set points in bar (bar) given retarder braking capability in percent (horizontal axis) given rotor speed (vertical axis), subject to a correction factor to prevent long term overheating of a particular cooling system; and

FIG. 4 shows a graph of retarder capacity correction factor based on measurements of temperature RT outlet.

Detailed Description

It is to be understood that the invention may assume various alternative components, orientations and configurations, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the specification are simply exemplary embodiments of the inventive concepts disclosed and defined herein. Hence, specific dimensions, directions or other physical characteristics relating to the various embodiments disclosed herein are not to be considered as limiting, unless the context clearly dictates otherwise.

FIG. 1 illustrates one embodiment of a hydraulic transmission having a controllable or proportional retarder system 10. In this embodiment, the system 10 may have two pumps, namely, an RT pump 16 for supplying fluid flow to the retarder circuit and a Transmission (TM) pump 14 for supplying fluid flow to the transmission. In another embodiment, the system 10 may have a single fluid pump for supplying fluid to the parallel fluid circuits. In such a system, the single pump may be a larger capacity pump that provides fluid, and may be a dual flow pump that allows the same or different flow rates. For example, pumps 14 and 16 may be positive displacement pumps and may have the same or similar nominal flow rates. The system 10 may use various fluids to provide lubrication and torque converter and retarder functions, such as transmission fluid, hydraulic fluid, or other acceptable fluids or oils.

The transmission circuit may include a TM pump 14 that provides fluid flow to the primary regulator valve 18 at an appropriate fluid flow pressure to operate the clutch and Retarder (RT)27 via RT pilot valves 34, 28. For example, transmission circuit fluid may flow from the fluid reservoir 12 to the primary regulator valve 18, to the torque converter 22, to the cooler flow valve 30, to the transmission lubrication passage 21, and back to the fluid reservoir 12.

The retarder circuit may include RT pump 16, RT on/off valve 24, vent check valve 26, RT 27, RT proportional valve 29, cooler flow valve 30, and reservoir 12.

In the embodiment illustrated in FIG. 1, the cooler flow valve 30 may receive fluid flow from the retarder circuit and the transmission circuit and may direct fluid flow to the cooler 32 according to the cooling needs of the system 10. When RT 27 is not in use or when RT outlet pressure indicates low pressure and therefore low heat, the cooler flow valve 30 may direct fluid flow from the torque converter 22 in the transmission circuit to the cooler 32 and then to the transmission lubrication passage 21 and back to the sump 12, as shown in fig. 1.

The two RT pilot pressure valves 34, 28 may be part of the transmission valve control 20. One of the two RT pilot pressure valves 34, 28, i.e. the RT pilot on/off valve 34, can control the state or position of the RT on/off valve 24 to start or stop RT 27, while the other pilot pressure valve, i.e. the RT pilot proportional valve 28, can control the state or position of the RT proportional valve 29 to regulate the pressure on the RT outlet connection. In an alternative embodiment, the control of valves 24, 29 may be accomplished directly by an ECU controlled solenoid (solenoid) without the use of pilot pressure valves 34, 28.

When the vehicle is powered off, the RT on/off valve 24 may be in the closed position by the action of a spring force. The RT on/off valve 24 remains in the closed position until a solenoid or other force pushes the RT on/off valve 24 against a spring force to an open position. Once the vehicle is de-energized, the spring force may return the RT on/off valve 24 to the closed position. Alternatively, the RT on/off valve 24 may be returned to the closed position manually by an operator or automatically by an automated system. In the closed position, RT on/off valve 24 directs fluid flow from RT pump 16 directly into reservoir 12. For example, a portion of the fluid may be directed through the aerosol valve. In the embodiment of the system 10 shown in fig. 1, the back pressure is low to minimize drag losses, but sufficient back pressure may also be applied to supply the aerosol valve. From this state, RT pump 16 provides fluid flow from reservoir 12 through RT on/off valve 24 and back to the reservoir, switching RT on/off valve 24 to the open position by manual or automatic systems, fluid flow is directed to retarder 27 through RT inlet 27a, and the retarder cavity is filled. The fluid in the reducer chamber creates an annular flow of oil that acts on movable vanes or impellers that are part of or connected to the drive shaft, thereby creating a braking action or torque. A vent check valve 26 may be provided to prevent any leakage of the fill flow. The RT on/off valve 24 may be configured to be controlled by moving a spool of the RT on/off valve 24 by the action of the RT pilot on/off valve 34.

By deactivating RT 27 by moving RT on/off valve 24 to a closed position after operation of RT 27, RT 27 may potentially be vented due to rotor centrifugal force. The rotation of the bladed or bladed rotor in the retarder cavity can be used as a turbo pump pumping the remaining fluid in the retarder cavity and/or in the RT circuit between the RT on/off valves 24 and RT 27 to the tank 12. During evacuation, the breather 26 in the inlet line may be used to fill the RT 27 with air. RT proportional valve 29 and cooler flow valve 30 may be in a position to connect RT outlet 27b with tank 12 without any throttling for rapid evacuation. A retarder spray valve may be provided to provide an oil mist to cool and slow the air flow in the retarder cavity, thereby reducing the air resistance of the empty retarder.

The degree of braking torque applied to the propeller shaft may be set to follow a particular braking torque profile, also referred to as retarder capacity. The braking torque profile may be operator controlled, as opposed to an uncontrollable retarder or an on/off retarder, where the degree of braking torque provided by the retarder follows a fixed braking profile depending on vehicle and/or drive axle speed and possibly other less important factors. The degree of braking torque may be set by an operator adjusting settings of an Electronic Control Unit (ECU) 38. The ECU38 preferably communicates with a vehicle CAN bus and/or a human machine interface and/or a multimedia interface. The braking torque or degree of braking torque set by the vehicle operator may also potentially be overwritten by a backup automatic system configured to prevent overheating or to correct or avoid unsafe conditions.

To initiate the function of RT 27 to provide braking torque, the ECU may move RT pilot on/off valve 34 from a closed position to an open position against the spring bias to flow fluid through RT 27 to create braking torque against the rotor or drive shaft. The RT pilot on/off valve 34 may be turned on manually by the operator of the vehicle through a lever or pedal or other means or using an automated system such as one that senses vehicle braking parameters, such as one that senses brake engagement, brake friction, brake overheating, and/or one that senses the incline and decline encountered by the vehicle and/or senses vehicle or engine speed or speed increase.

The degree of braking torque, i.e. the required or desired braking profile/curve or retarder capacity, may be set by the operator by means of the same lever or pedal or other means. Additionally or alternatively, the degree of braking torque may be selected using a separate selector means. When RT 27 is active, ECU38 may sense lever or pedal position or a selector to obtain a desired degree of braking torque, and may obtain vehicle speed or rotor speed from vehicle sensors. ECU38 may then determine an RT outlet pressure set point that provides the desired degree of braking torque. For example, ECU38 may include a processor and algorithms stored in electronic memory or memory to calculate the RT outlet set point. Additionally or alternatively, the processor may look up the RT outlet pressure set point from a brake curve profile, table or graph stored in electronic memory or storage.

An example of a brake torque table is shown in fig. 2, which shows the relationship between rotor speed (n-RT in RPM), brake torque (RT capacity in 10% increments) and RT outlet pressure (the pressure values in the table, measured in bar). An example of the effect of possible long term over-temperature protection on the outlet pressure set point is shown in fig. 3. In fig. 3, those RT outlet pressure set point values that are reduced relative to the corresponding RT outlet pressure set point values shown in fig. 2 to prevent long term overheating are labeled with the letter "x". For example, in the table shown in FIG. 2, the RT outlet pressure set point associated with a rotor speed of 2200rpm and a brake torque capacity of 90% is 10.0 bar. In contrast, in the table shown in fig. 3, the corresponding value of the RT outlet pressure set point associated with a rotor speed of 2200rpm and a braking maximum torque of 90% is reduced to 6.9 bar.

Once the ECU38 determines the RT outlet pressure set point, the ECU38 can send the appropriate current to the RT pilot proportional valve 28, which RT pilot proportional valve 28 moves the corresponding solenoid that applies or releases fluid pressure to the RT proportional valve 29. The position of RT proportional valve 29 is changed based on the fluid pressure to apply the desired RT outlet pressure.

Once the ECU38 senses the retarder activation signal and calculates or obtains the brake torque setting and vehicle or rotor speed, the ECU38 may send the appropriate current to the RT pilot on/off valve 34, which RT pilot on/off valve 34 moves the corresponding solenoid that applies fluid pressure to the RT on/off valve 24. Thus, the RT on/off valve 24 is pushed to the lower position. This directs fluid flow to RT inlet 27a, filling the retarder cavity and initiating the retarder braking action. The vent check valve 26 prevents any leakage of the fill flow. In an alternative embodiment, ECU38 may be configured or programmed to send electrical control signals directly to RT on/off valve 24 equipped with a solenoid to move the valve position to and from the open and closed positions. It will be appreciated that in the latter embodiment, the RT on/off valve 24 comprises a solenoid actuated valve rather than a fluid pressure controlled valve.

The RT pilot proportional valve 28 may regulate an RT proportional valve 29, the RT proportional valve 29 fluidly connected to the retarder outlet 27 b. The RT proportional valve 29 can regulate the throttling of the fluid exiting the retarder outlet to ensure that the retarder outlet pressure remains within a specified range of the pressure set point. In an alternative embodiment, ECU38 may be configured or programmed to control RT proportional valve 29 by sending an electrical signal directly to RT proportional valve 29 equipped with a solenoid. For example, a pressure sensor 36 may be provided to communicate the RT outlet pressure to RT pilot proportional valve 28 or to ECU 38. It will be appreciated that in the latter embodiment, RT proportional valve 29 comprises an electrically controlled valve rather than a fluid pressure controlled valve.

RT proportional valve 29 may be configured such that fluid from RT proportional valve 29 can be selectively directed to tank 12 or cooler 32 via cooler flow valve 30, for example, as a function of RT outlet pressure. For example, the cooler flow valve 30 may be biased, such as by a spring, to a valve position that directs flow to the sump 12 until the biasing force is overcome to move a valve spool of the cooler flow valve 30 to direct fluid flow to the cooler 32 and only then to the sump 12. In the embodiment of system 10 shown in fig. 1, when the RT outlet pressure exceeds a pressure from about 1.5 bar to about 5.5 bar, preferably from about 2 bar to about 3 bar, the spool of RT proportional valve 29 is moved to direct fluid flow to cooler 32 and only then to tank 12. In this position, the cooler flow valve 30 directs fluid flow from the transmission circuit directly to the transmission lubrication passage 21 and sump 12 without passing through the cooler 12. It is contemplated that the predetermined pressure that determines the position of the cooler flow valve 30 may be adjusted by varying the spring, which may be required in the event of very high cooler pressure losses.

The pressure at the RT outlet 27b may determine the position of the cooler flow valve 30. For example, the cooler flow valve 30 may include a hydraulic actuator in fluid communication or selective fluid communication with the RT outlet 27 b. In another embodiment, the position of the cooler flow valve 30 is directly controlled by an electromagnet that receives current from the ECU 38. The ECU38 sends a current based on the RT outlet pressure set point or based on a sensor measuring RT outlet pressure or based on other means.

Fluid flow from RT proportional valve 29 may flow to a cooler flow valve 30, which cooler flow valve 30 may receive fluid flow from the retarder and transmission circuits. As described above, when RT 27 is not in use or is not in use at a sufficiently high RT outlet pressure, fluid flow from the transmission circuit, particularly from the torque converter 22, to the cooler flow valve 30 may be directed to the cooler 32, while retarder circuit flow may be directed to bypass the cooler 32. Although it is preferred to direct the retarder circuit flow to the chiller 32 once the RT 27 is started, the RT outlet pressure may not typically be high enough to overcome chiller pressure losses. Thus, when RT 27 is in use and when RT outlet pressure is sufficiently high, the cooler flow valve 30 directs flow from the retarder circuit to the cooler 32, and the transmission circuit flow is directed around the cooler 32.

The cooler flow valve 30 may be controlled by a pressure sensor disposed in or around the valve, or the cooler flow valve 30 may be controlled by the ECU38 and a pressure sensor disposed in the retarder circuit and in communication with the ECU 38. It is conceivable that the predetermined pressure determining the flow to the cooling valve 30 can be adjusted by changing the spring of the cooling flow valve 30, which may be required in the case of very high cooler pressure losses.

In the case where the flow rates in both the TM and RT circuits are similar or about the same, the chiller can be switched from the TM circuit to the RT circuit without a large pressure gradient. Thus, once the RT outlet pressure exceeds a particular cooler flow valve pressure threshold, the cooler 32 may be positioned in the circuit containing the largest heat source. Thus, the presently disclosed hydraulic retarder system may receive coolers and piping components with relatively high head losses up to a pressure threshold of the cooler flow valve. These components can be switched without affecting the retarder control function. For example, in the system 10 shown in FIG. 1, the cooler 32 and fluid lines may be selected according to desired preferences as long as the head loss is below the pressure threshold of the cooler flow valve 30. The pressure threshold may be determined, for example, by a spring of the cooler flow valve 30. Even the threshold pressure can be increased as needed by changing the chiller flow valve spring, which may be required in the case of very high chiller and pipeline head losses. However, this may result in some discontinuities/steps in the brake torque curve and/or increased fluid reservoir fluid temperature under some operating conditions.

The presently disclosed system may be configured to control overheating in the system regardless of the function of the chiller. In particular, a controllable retarder system for a transmission as disclosed herein may provide both short term and long term over-temperature protection independent of a cooler. Short term rapid overheating may occur when RT 27 is engaged during high vehicle speeds or rotor speeds paired with high brake torque capability and/or already high RT outlet pressure. This rapid overheating can lead to damage to the seals or other components.

By rejecting any calculated or derived RT outlet pressure set point that may result in rapid overheating, short term RT overheating may be prevented or significantly reduced by ECU38 and the brake torque algorithm, table, curve or profile. For example, when the operator selects a high brake torque setting and the retarder 27 is activated while the vehicle or rotor is traveling or spinning at high speed, the algorithm will make a calculation or the table will use the high RT outlet pressure set point to indicate. However, since this RT outlet pressure set point may cause rapid overheating, the ECU may be programmed to apply a correction factor to lower the pressure set point, or may not allow the set point to be used if it exceeds a particular value based on the conditions.

Long-term RT overheating, which may occur when the retarder has been in use for an extended period of time and generates heat above the chiller capacity, can be avoided or significantly reduced by the present system. In one embodiment, a correction factor for the RT outlet pressure set point may be applied, which may be determined by ECU38 based on the RT outlet temperature. The shaded area on the table shown in figure 3 represents the reduced RT outlet pressure set point to prevent a long term overheating condition.

A temperature sensor also connected to the ECU may cause the ECU to apply a correction factor to lower the outlet pressure set point from that determined by an algorithm, table or curve to prevent long term overheating due to long term retarder use. In one embodiment, a temperature sensor 36 may be included in or adjacent to the fluid flow exiting the retarder fluid outlet to prevent overheating of the fluid. In one embodiment, the ECU38 receives temperature data to adjust the retarder through control of the RT outlet pressure according to fig. 4, which shows the degree or percentage of reduction of the RT outlet pressure set point.

As one example, in the case where the temperature at the retarder outlet varies from 160 ℃ to 165 ℃, the retarder outlet pressure may be multiplied by a correction factor from 1 to 0. The temperature is below 160 deg.c and the correction factor may be 1, which means that there is no outlet pressure correction. Thus, the retarder outlet temperature is kept below 165 ℃, at least in steady state conditions.

While the invention has been described with reference to illustrative embodiments, it is to be understood that the description is not to be construed in a limiting sense. Rather, various changes and modifications may be made to the illustrative embodiments without departing from the true spirit and scope of the invention as defined by the following claims. Furthermore, it will be understood that any changes and modifications will be recognized by those skilled in the art as an equivalent to one or more elements recited in the following claims, and shall be covered by the full breadth of their claims as permitted by law.

In addition, the present disclosure may relate or otherwise relate to one or more of the following aspects:

1. a controllable hydrodynamic retarder for a transmission, comprising:

(a) a fluid reservoir for holding a volume of fluid;

(b) a retarder on/off valve selectively moving from a closed position restricting fluid flow from the sump to the retarder to an open position to direct fluid from the sump to the retarder when the retarder is activated; a retarder drawing fluid from a reservoir via a turbo-pump action;

(c) the retarder having an outlet for fluid flow out of the retarder and to a retarder proportional valve;

(d) the retarder proportional valve in fluid communication with the retarder outlet for regulating the retarder outlet pressure according to a retarder outlet pressure set point and for directing a flow of fluid to the cooler; and

(e) an electronic controller unit operatively connected to the retarder on/off valve, the retarder proportional valve and to the vehicle bus for obtaining vehicle characteristics of the rotor speed and brake torque settings, the electronic controller configured to calculate or obtain a retarder outlet pressure set point upon retarder activation, move the retarder on/off valve to an open position, and control the retarder proportional valve position to provide a retarder outlet pressure within the retarder outlet pressure set point.

2. A controllable hydrodynamic retarder for a transmission of aspect 1, further comprising a pump in fluid communication with the sump for pumping fluid from the sump to a retarder on/off valve, wherein the retarder on/off valve is movable from a closed position, directing fluid flow from the pump to the sump by the electronic controller unit, to an open position, directing fluid flow to the retarder.

3. A controllable hydrodynamic retarder for a transmission of aspect 2, further comprising a cooler flow valve in fluid communication between the retarder proportional valve and the cooler for directing fluid flow from the retarder proportional valve to the cooler or the sump.

4. A controllable hydrodynamic retarder for the transmission of aspect 3, further comprising: a transmission pump in fluid communication with the sump for pumping fluid through the transmission circuit including the transmission lubrication passage and out to the cooler flow valve, wherein the cooler flow valve is configured to direct fluid flow from the transmission circuit to the cooler and to direct fluid flow from the retarder proportional valve to the sump and bypass the cooler unless the transmission outlet pressure exceeds a predetermined pressure at which the cooler flow valve directs fluid flow from the transmission proportional valve to the cooler and from the transmission circuit to the sump and bypasses the cooler.

5. A controllable hydrodynamic retarder for a transmission of aspect 4, wherein the cooler flow valve is spring biased in a first position directing fluid flow from the retarder proportional valve to a sump and directing fluid flow from the transmission circuit to the cooler, wherein if fluid flow from the retarder proportional valve exceeds a predetermined fluid pressure, the cooler flow valve is moved to a second position directing fluid flow from the retarder proportional valve to the cooler and then to the sump.

6. A controllable hydrodynamic retarder for the transmission of aspect 4, wherein the cooler flow valve is controlled by an electromagnet that receives current directly from the ECU.

7. A controllable hydrodynamic retarder for the transmission of aspect 4, wherein the position of the cooler flow valve is controlled by a pilot pressure from a pilot pressure valve controlled by the ECU, which determines the cooler valve position based on a retarder outlet pressure set point or based on a pressure sensor signal.