阅读说明：本技术 用于控制驱动力矩的方法和用于执行该方法的传动系组件 (Method for controlling a drive torque and drive train assembly for carrying out the method ) 是由 P·奥伯京纳 H·尼森 M·赫克 T·加斯曼 于 2018-03-12 设计创作，主要内容包括：本发明涉及一种用于控制电动机的驱动力矩的方法,该电动机用于驱动机动车的传动系。对驱动力矩的控制如此根据车速来进行,使得当车速低于所预设的阈值时,控制电动机(7)处于高的转矩-模式下,并且当车速高于所预设阈值时,控制电动机(7)处于低的转矩-模式下。本发明还涉及一种用于执行该方法的传动系组件。(The invention relates to a method for controlling the drive torque of an electric motor for driving a drive train of a motor vehicle. The drive torque is controlled as a function of the vehicle speed in such a way that the electric motor (7) is controlled in a high torque mode when the vehicle speed is below a predetermined threshold value and in a low torque mode when the vehicle speed is above the predetermined threshold value. The invention also relates to a drive train assembly for carrying out the method.)

1. Method for controlling a motor torque of an electric motor in a drive train (3) of a motor vehicle, wherein the drive train (3) comprises a first side shaft (15) for driving a first vehicle wheel (17), a second side shaft (16) for driving a second vehicle wheel (18), a controllable first friction clutch (20) associated with the first side shaft (15), and a controllable second friction clutch (20') associated with the second side shaft (16), and a drive (21) arranged on a power path between the electric motor (7) and at least one of the first and second friction clutches (20, 20');

the method comprises the following steps:

monitoring a drive rotational speed value representing a rotational speed (n21) of the drive element (21);

monitoring a first rotation speed value representing a rotation speed (n17) of the first vehicle wheel (17);

monitoring a second rotational speed value representing a rotational speed (n18) of the second vehicle wheel (18);

determining a transmittable first clutch torque (T20) for the first friction clutch (20) as a function of the first rotational speed value relative to the drive rotational speed value; and is

Determining a transmittable second clutch torque (T20') for the second friction clutch (20') as a function of the second rotational speed value relative to the driven rotational speed value;

monitoring a vehicle-speed value representative of a vehicle speed (v) and comparing said vehicle-speed value with a preset speed threshold (v _ lim);

if the vehicle-speed value is below a preset speed threshold (v _ lim):

controlling the electric motor (7) in a high-torque mode in such a way that a motor torque generated by the electric motor (7) is provided as required;

if the vehicle-speed value is higher than the preset speed threshold (v _ lim):

the electric motor (7) is controlled in the low-torque mode in such a way that the motor torque (Tm) generated by the electric motor (7) is less than 50% of the maximum generatable torque (Tm _ max) of the electric motor (7) plus the double of the smaller of the first and second transmittable clutch torques (T20, T20').

2. Method according to claim 1, characterized in that as a further step it is provided:

monitoring a lateral acceleration variable representative of a lateral acceleration (Alat) of the motor vehicle, and generating a lateral acceleration signal,

wherein the electric motor (7) is controlled as a function of the lateral acceleration signal in such a way that

Controlling the electric motor (7) in a high torque-mode if the lateral acceleration signal is above a defined lateral acceleration threshold;

controlling the electric motor (7) in a low torque mode if the lateral acceleration signal is below a defined lateral acceleration threshold.

3. The method of claim 2, wherein the lateral acceleration signal is applied to determine at least one of:

a motor torque (Tm) of the electric motor (7), a rated rotational speed (n7) of the electric motor (7), a transmittable first clutch torque (T20) of the first clutch (20) and a transmittable second clutch torque (T20') of the second clutch (20').

4. Method according to any one of claims 1 to 3, characterized in that the motor vehicle has a driven front axle (6) and a rear axle (4), wherein the drive train (3) which can be driven by the electric motor (7) is associated with the rear axle (4),

wherein, as further steps, provision is made for:

the difference in rotational speed between a first side shaft (9) and a second side shaft (10) of the front axle (6) is determined, and

controlling the electric motor (7) according to the difference in rotational speed such that

Controlling the electric motor (7) in a high torque mode when the rotational speed difference is below a defined rotational speed difference threshold; and is

Controlling the electric motor (7) in a low torque mode when the rotational speed difference is above the defined rotational speed difference threshold.

5. Method according to any of claims 1 to 4, characterized in that as a further step it is provided:

monitoring wheel speed variables representative of wheel speeds (n11, n12, n18, n19) of the motor vehicle and generating wheel speed signals, wherein the wheel speed signals are applied to determine at least one of: a motor torque (Tm) of the electric motor (7), a rated rotational speed (n7) of the electric motor (7), a transmittable first clutch torque (T20) of the first clutch (20) and a transmittable second clutch torque (T20') of the second clutch (20').

6. Method according to any of claims 1 to 5, characterized in that as a further step it is provided:

monitoring a steering variable representative of a steering angle (α) for the motor vehicle and generating a steering signal, wherein the steering signal is applied to determine at least one of: a motor torque (Tm) of the electric motor (7), a rated rotational speed (n7) of the electric motor (7), a transmittable first clutch torque (T20) of the first clutch (20) and a transmittable second clutch torque (T20') of the second clutch (20').

7. Method according to one of claims 1 to 6, characterized in that, for determining the transmittable first clutch torque (T20), the rotational speed (n21) of the first clutch input part (21) is compared with the rotational speed (n22) of the first clutch output part (22); and is

In order to determine the transmittable second clutch torque (T20'), the rotational speed (n21') of the second clutch input part (21') is compared with the rotational speed (n22') of the second clutch output part (22 ').

8. Method according to one of claims 1 to 7, characterized in that the motor torque of the electric motor (7) is positive, wherein the electric motor (7) is adjusted to the maximum producible drive torque in a high torque mode; alternatively, the first and second electrodes may be,

the motor torque of the electric motor (7) is negative, wherein the electric motor (7) is set to a maximum producible braking torque in a high torque mode.

9. Drive assembly for a motor vehicle, comprising:

a drive train (3) with an electric motor (7), a first side shaft (15) for driving a first vehicle wheel (17), a second side shaft (16) for driving a second vehicle wheel (18), a controllable first friction clutch (20) for regulating a torque transmittable by the first side shaft (15), a controllable second friction clutch (20') for regulating a torque transmittable by the second side shaft (16), and a drive (21) arranged in a power path between the electric motor (7) and at least one of the first and second friction clutches (20, 20');

-first sensing means (25) for determining a first rotation speed value representative of a rotation speed (n17) of said first vehicle wheel (17);

-second sensing means (25') for determining a second rotation speed value representative of the rotation speed (n18) of said second vehicle wheel (18);

a drive speed sensor (38, 39) for determining a drive speed value representing the speed of rotation of the drive element (21); and

at least one control unit (ECU) for controlling the electrical machine (7);

characterized in that the control unit (ECU) is arranged to perform the method according to any one of claims 1 to 8.

10. The drive assembly according to claim 9, characterized in that the first friction clutch (20) has a first outer disc carrier drivingly connected with the electric motor (7) and a first inner disc carrier drivingly connected with the first side shaft (15), and,

the second friction clutch (20') has a second outer disk carrier drivingly connected to the electric motor (7) and a second inner disk carrier drivingly connected to the second side shaft (16),

the first outer disk carrier and the second outer disk carrier are connected to one another in a rotationally fixed manner, in particular are designed in one piece.

11. Drive assembly according to claim 9 or 10, characterized in that the drive train (3) with the electric motor (7) is associated with a rear axle (4) of the motor vehicle, wherein a drive train (5) for driving a front axle (6) of the motor vehicle is also provided, which is mechanically separated from the drive train (3) of the rear axle (4).

12. The drive assembly according to any one of claims 9 to 11, characterized in that the first friction clutch (20) and the second friction clutch (20') are steplessly variably controllable between an open position, in which no torque is transmitted, and a closed position, in which full torque is transmitted, respectively.

Technical Field

The invention relates to a method for controlling the drive torque of an electric motor in a drive train of a motor vehicle. The invention also relates to a drive train assembly for carrying out such a method.

Background

Motor vehicles are known which have a first drivetrain with a first drive source for driving a first drive axle (antreibessachse) and a second drivetrain with a second drive source for driving a second drive axle. These drive sources may differ from one another, for example one of the two drive sources may be designed as an internal combustion engine and the other as an electrical machine. This drive concept is also referred to as "hybrid drive". The electric machine and the internal combustion engine can drive the motor vehicle individually or jointly in a superimposed manner.

On the power path (leistungspeed), the electrical machine may be followed by a transmission (Getriebe) which converts the rotary motion generated by the electrical machine from fast to slow, and a power distribution unit (leistungsverzwigung seinheit) which distributes the introduced rotary motion to the two sideshafts.

EP 2353916B 1 discloses a method for actuating a clutch arrangement of a motor vehicle drive train, which has two friction clutches with a common input arrangement connected to a drive unit. The first friction clutch has a first output assembly connected with the first drive axle, and the second friction clutch has a second output assembly connected with the second drive axle. These output shafts are each drivingly connected to an associated vehicle wheel. When different friction values of the driving-lane surfaces of the first or second vehicle wheel are detected, the two friction clutches are actuated in such a way that the drive torques of the two vehicle wheels are limited to the drive torques of the driving wheels having the lower friction values that can be transmitted to the driving lane.

DE 102015118759 a1 discloses a method for controlling the drive torque and the drive speed in a drive train assembly of a motor vehicle, which has two drive trains separated from each other. The first driveline is driven by the internal combustion engine. The second drive train is driven by the electric machine. In the method, the rotational speeds of the first and second drive axles are monitored, a setpoint rotational speed of the electrical machine for driving the second drive axle is determined, the electrical machine is controlled in a setpoint rotational speed mode as a function of the rotational speeds of these drive axles, a setpoint torque for driving the second drive axle is determined as a function of the rotational speeds of the two drive axles, and the clutch in the second drive train is controlled in a setpoint torque mode as a function of the rotational speeds of the first and second drive axles.

DE 102014221055 a1 discloses a motor vehicle having a first drive machine in the form of an internal combustion engine for driving a first drive axle and a second drive machine in the form of an electric motor for driving a second drive axle. A drive control device is provided which is set to control the first and second drive machines in accordance with a rated torque as a control variable. In this case, the drive torque setpoint variable is converted into suitable control signals for operating the first and second drive machines.

A control device for a drive train of a motor vehicle is known from US 2016/0356370 a 1. The controller is configured to reduce the drive torque when slip of a driving wheel of the first axle (Schlupf) exceeds a predetermined threshold. The controller controls the torque applied to the wheels of the second axle and identifies when there is a different slip at the wheels, at which of the wheels the slip exceeds a predetermined threshold. The torque adjustment is then performed by means of the controller.

An electric drive for driving a drive axle of a motor vehicle is known from WO 2017157479 a 1. The electric drive comprises an electric machine with a motor shaft, a transmission unit with a transmission shaft which can be driven in rotation by the motor shaft, and a double clutch unit. The dual clutch unit comprises a clutch housing, which can be driven in rotation by the transmission shaft, and two disk packs (Lamellenpaket), which can each be actuated by means of a respective actuator in order to transmit a torque to a respective sideshaft. Such a double clutch assembly (which is also marketed by the applicant under the name "Twinster" clutch) enables a variable distribution of torque to the two output shafts. Depending on the driving situation, the torques at the wheels inside or outside the curve can be individually adjusted, which leads to an improved driving dynamics or rather driving stability as a whole. This control principle is also referred to as active or variable Torque distribution or "Torque vector".

However, in driving situations in which the traction forces at the left and right wheels differ significantly (which are also referred to as "μ -split" situations), the variable torque distribution can lead to an undesirable yaw moment (Giermometment) about the vertical axis of the vehicle. Today, all-wheel drive assemblies with a double clutch unit in the drive axle use a complex control strategy (Regelstrategie) in order to avoid such critical yaw moments, in particular at high speeds. The basic approach in this case is to apply a first control strategy for maximum traction at low speeds ("select-high strategy") and a second control strategy for optimum driving stability at high speeds ("select-low strategy").

In all-wheel drive systems with an electric drive and a double clutch for variable torque distribution, the torque distribution between the two vehicle wheels can be controlled by means of the double clutch.

Disclosure of Invention

The object of the present invention is to provide a method for controlling the drive torque of an electric motor for a drive train of a motor vehicle, by means of which high driving stability is ensured both at high speeds and at low speeds. The invention also has for its object to provide a corresponding drive train assembly with which such a control method can be carried out.

The solution consists in a method for controlling the drive torque of an electric motor in a drive train of a motor vehicle, wherein the drive train comprises a first side shaft for driving a first vehicle wheel, a second side shaft for driving a second vehicle wheel, a controllable first friction clutch associated with the first side shaft, a controllable second friction clutch associated with the second side shaft, and a drive arranged in a power path between the electric motor and at least one of the two friction clutches; the method comprises the following steps: monitoring a drive speed value representative of a speed of rotation of the drive member; monitoring a first speed value representative of a speed of rotation of a first vehicle wheel; monitoring a second speed value representative of a speed of a second vehicle wheel; determining a transmittable first clutch torque for the first friction clutch as a function of the drive rotational speed value and the first rotational speed value; determining a transmittable second clutch torque for the second friction clutch as a function of the drive rotational speed value and the second rotational speed value; monitoring a vehicle-speed value representative of a vehicle speed and comparing the vehicle-speed value with a preset speed threshold; and if the vehicle-speed value is below a preset speed threshold: the electric motor is controlled in the high-torque mode in such a way that the motor torque generated by the electric motor is provided as required; and if the vehicle-speed value is higher than a preset speed threshold: the electric motor is controlled in the low-torque mode in such a way that the motor torque generated by the electric motor is less than double the smaller of the first and second transmittable clutch torques plus an additional torque which is less than 50% of the maximum generatable torque of the electric motor.

The advantage of this method is that high driving stability is ensured, in particular even at high speeds of the vehicle, wherein friction losses in the drive train are minimized by controlling the motor torque of the electric motor in the low-torque mode. This is achieved by limiting the motor torque provided by the electric motor if a driving situation ("μ -split") with different friction values between the two wheels is identified above a speed threshold. The power input into the friction clutch associated with the wheels with greater slip or a lower friction value relative to the traffic lane is correspondingly reduced to the drive torque that can be transmitted to the traffic lane. The energy input into the respective friction clutch is therefore also low, so that this method contributes to an increase in the energy efficiency during operation of the drive train. A further advantage is that the method can be carried out for any time when driving situations ("μ -split") occur with different friction values between the two vehicle wheels, since the heat input into the friction clutch is smaller and accordingly no thermal cut-off takes place as the transferable drive torque decreases.

By means of the method, the drive train behaves like a decoupled differential transmission when the electric motor is controlled in the low-torque mode, which differential transmission has a balancing effect between the two sideshafts with respect to the transferable rotational motion.

The rotational speed of the drive is sensed, which can in principle be any arbitrary component in the power path between the electric motor and the friction clutch. It is decisive that the determined drive rotational speed value can be taken into account as a reference value for determining the rotational speed difference between the input and the output of the clutch. For example, the drive element can be a motor shaft of an electric motor, a drive shaft connected thereto, a gear, a clutch input or a drive element connected rotationally fixed thereto. According to an exemplary embodiment, for determining the transmittable first clutch torque, the rotational speed of the clutch input can be compared with the rotational speed of the first clutch output, and for determining the transmittable second clutch torque, the rotational speed of the clutch input can be compared with the rotational speed of the second clutch output. The two clutch input parts have the same rotational speed and can also be designed in one piece, according to one possible embodiment.

The additional torque can be provided to provide a certain traction at the wheels with greater slip, however in an order of magnitude in which the yaw torque that is possible is not critical and can be handled well in terms of driving stability. In particular, it is provided that the additional torque is less than 50%, in particular less than 30%, and sometimes less than 10%, of the maximum motor torque that can be generated by the electric motor. For the design of the additional torque, a plurality of possibilities are conceivable, which can be used individually or in a supplementary manner. In a simple embodiment, the additional moment can be determined as a constant value (k), which can be, for example, between 5Nm and 150Nm, wherein the upper limit can also be lower, for example 100Nm or 50 Nm. In the event of a control intervention, the motor torque (Tm) provided by the electric motor is therefore limited to twice the transmittable drive torque (T20low) of the wheels having a low friction value relative to the roadway plus the constant value (k) (Tm <2 × T20low + k). According to another possibility, the additional torque (Tx) can be variably adjusted, preferably as a function of the vehicle speed. In this case, it is provided in particular that the additional torque is set to a lower value at higher vehicle speeds than at lower vehicle speeds. It is also possible to adjust the additional torque as a function of the determined transmittable clutch torque. In particular, the additional torque can be set to a fraction of the difference between the first and second transmittable clutch torques, for example to a value of less than a quarter of the torque difference.

In control engineering, controlling the motor torque in the low or high torque mode means that the torque is the reference variable (setpoint value) to be set for controlling the electric motor. Depending on the driving state of the motor vehicle, the torque of the electric motor required for the desired driving dynamics is determined and the electric motor accordingly supplies the electric machine torque introduced into the drive train. In this case, in the high-torque mode, the maximum motor torque is available as required, i.e., without torque limitation, and is introduced into the drive train. The tractive effort requirement depends on the respective driving situation, for example on the gradient present and/or the desired vehicle acceleration. In the low-torque mode, the motor torque of the electric motor is limited to a limit value that corresponds to double the minimum transmissible clutch torque of the two wheels, as described above. In the select-low mode, the motor torque is determined at least on the basis of the rotational speeds of the two wheels of the electromechanically driven axle and the rotational speed of the electric motor or of a component which is drivingly connected thereto. The component can be, for example, a clutch input, in particular an outer disk carrier (aussenlamellentractor) which is drivingly connected to an electric motor. The motor torque can be calculated, for example, by means of an Electronic Control Unit (ECU). The control of the two friction clutches can be effected by means of the same or another electronic control unit.

The electric motor converts energy and can be operated in motoring operation or generating operation, wherein the motor torque can be positive or negative, respectively, depending on whether the vehicle is in coasting or towing operation. The control of the motor torque of the electric motor can accordingly involve two operating modes. In the motor mode or traction mode, the electric motor converts electrical energy into mechanical energy, so that the drive axle or the two sideshafts of the motor vehicle can be driven. The motor torque is positive, so that the method in the low torque mode involves a maximum drive torque that can be transmitted by the electric motor to the vehicle wheels, as described above. In generator operation or coasting operation, the electric machine converts mechanical energy into electrical energy, which can then be stored in a battery. The motor torque is negative, so that the method in the low torque mode involves a maximum transmission of the braking torque from the wheels to the electric motor, as described above. It is possible to recover the braking energy of the motor vehicle, which is also referred to as regeneration.

As a further method step, it may be provided that a lateral acceleration variable representing a lateral acceleration of the motor vehicle is monitored and a lateral acceleration signal is generated, which can be used as an input variable for controlling the electric motor. In particular, the lateral acceleration signal can be used to determine the motor torque and/or the rotational speed of the electric motor. Furthermore, the lateral acceleration signal can also be taken into account for controlling the setpoint torque to be transmitted by the two friction clutches. According to one possible embodiment, the electric motor can be controlled in a high torque mode if the lateral acceleration signal is above a defined lateral acceleration threshold value; and/or the electric motor may be controlled in the low torque mode if the lateral acceleration signal is below the set lateral acceleration threshold. The consideration of the lateral acceleration signal can optionally be carried out. That is, the motor torque can be controlled in the low torque mode if only the condition that the vehicle speed is above the preset speed threshold or, in addition, the condition that the lateral acceleration signal is above the defined lateral acceleration threshold is met. The lateral acceleration threshold value may be in particular between 2m/s²And 4m/s²Example ofE.g. 3m/s²。

The method mentioned is suitable for motor vehicles with only one driven drive train or for motor vehicles with two driven drive trains that are mechanically separated from one another. By mechanically decoupled is meant that the first and second drive trains are designed separately and that no force transmission component is provided between the two drive trains. The electric motor is used only for driving one drive train or one transaxle, while the other drive source is used only for driving the other drive train or the other transaxle.

In a motor vehicle with two drive trains, the front axle can be driven by a front drive source and the rear axle by an electric motor, it can be provided that a rotational speed difference between two wheels of the front axle is determined and the electric motor is controlled as a function of the rotational speed difference of the front axle wheels in such a way that the electric motor is controlled in the high-torque mode when the rotational speed difference falls below a defined rotational speed difference threshold value; and controlling the electric motor in the low torque mode when the rotational speed difference is above a defined rotational speed difference threshold. The consideration of the speed difference for selecting between the low-torque mode and the high-torque mode can optionally be carried out, that is to say in addition to the consideration of the vehicle speed value and, if appropriate, of the lateral acceleration signal. The rotational speed difference threshold value may be in particular between 20U/min and 40U/min and is, for example, 30U/min. It can generally be provided that the electric motor is operated for driving the rear axle if the axle speed of the front axle is greater than the axle speed of the rear axle.

In order to determine the axle speed, at least one signal representing the speed of the respective vehicle axle can be detected. For calculating the axle rotational speed, for example, the average wheel rotational speed of the right and left wheels of the respective axle or, when a differential is used in the front axle, the rotational speed of the differential housing can also be used. The electric motor can optionally be set to a nominal speed in the activated state in such a way that the vehicle axle driven by the electric motor can be driven at a higher speed than the vehicle axle driven by the internal combustion engine. Furthermore, it can be provided that the electric motor is switched on for driving the rear axle when the motor vehicle is driving in a curve, wherein the nominal rotational speed of the electric motor is then preferably set such that the rear axle can be driven at a greater rotational speed than the front axle.

According to one method, a wheel speed variable representative of a wheel speed of the motor vehicle can be monitored and a corresponding wheel speed signal generated therefrom. These wheel speed signals can be used to determine the motor torque of the electric motor, the nominal rotational speed of the electric motor, the nominal torque of the first friction clutch and/or the nominal torque of the second friction clutch.

The control of the driving dynamics of a motor vehicle is particularly important when driving in curves, wherein the vehicle speed also plays a critical role. In this case, it can be provided as a further method step that a steering variable representative of the steering angle for the vehicle wheels is monitored and a corresponding steering signal is generated. The steering signal can then be used to adjust the motor torque and/or the motor speed of the electric motor and/or the respective setpoint torques of the two friction clutches in order to influence the driving dynamics of the motor vehicle.

As a further method step, an accelerator pedal variable representative of an accelerator pedal position of the motor vehicle may be monitored and an accelerator pedal signal generated, wherein the accelerator pedal signal may be used to set a motor torque and/or a motor speed of the electric motor and/or a respective setpoint torque of the two friction clutches.

It goes without saying that individual, a plurality or all of the mentioned method steps can be carried out. That is, the steering signal, the lateral acceleration signal, the accelerator pedal signal, and/or the wheel speed signal may be applied to control the motor torque or the motor speed, either individually or in combination. This applies correspondingly to the control of the torque which can be transmitted by the two friction clutches. It is also conceivable to detect other variables and to use them for determining control variables, such as the longitudinal acceleration, yaw rate and/or other signals that can be taken into account of the motor vehicle.

According to a method, which may also be referred to as a regeneration mode, both friction clutches can be closed when the motor vehicle is in coasting mode. In this context, coasting is understood as a driving situation in which the electric motor is dragged (pushed) by the vehicle. In this way, the electric motor is driven by the wheels of the second drive axle and operates in generator operation. The electric motor converts the mechanical energy introduced by the drive axle into electrical energy, which can be stored in a battery connected to the electric motor.

According to another method, which may also be referred to as a cruise mode (Segelmodus), when the motor vehicle is operated in cruise mode, the two friction clutches can be disengaged, so that the electric motor is decoupled from the wheels of the drive train. The term "cruise" shall at present include the following functions: during driving, the primary drive source (internal combustion engine) is decoupled from the associated drive train without braking it. In cruise operation, the electric motor can accordingly also be decoupled from the sideshafts (this takes place by disengaging the clutch) and, if appropriate, switched off.

The solution of the above object is also a drive assembly for a motor vehicle, comprising: a drive train with an electric motor, a first side shaft for driving a first vehicle wheel, a second side shaft for driving a second vehicle wheel, a controllable first friction clutch associated with the first side shaft, a controllable second friction clutch associated with the second side shaft, and a drive arranged on a power path between the electric motor and at least one of the two friction clutches; a first sensor means for determining a first rotational speed value representing a rotational speed of the first side shaft; a second sensor means for determining a second rotational speed value representing the rotational speed of the second side shaft; a drive speed sensor for determining a drive speed value representing a speed of rotation of the drive member; and at least one control unit for controlling the electrical machine; wherein the control unit is configured to perform a method according to one or more of the above embodiments.

The same advantages as with the method according to the invention result from the use of the drive assembly, so that reference is made to the above description for this purpose. It goes without saying that all features relating to the method can be transferred to the product, whereas all features relating to the product can be transferred to the method. By operating the electric motor at high speed in the low torque mode, a high driving stability is ensured, wherein at the same time friction losses are reduced. Each of the two sideshafts has associated with it a friction clutch which regulates the torque which can be transmitted in each case by the associated sideshaft. The friction clutch can be arranged in the power path between the electric motor and the first or second side shaft or can also be arranged within the respective side shaft.

An electromechanically driven drivetrain may have a transmission unit which distributes the torque introduced by the electric motor to two output parts. For example, the transmission unit may comprise a bevel gear transmission (winkeltriib) or an end-gear transmission. The transmission unit can be designed as an input transmission, i.e. with a fixed transmission ratio between the transmission input and the transmission output. Alternatively, the transmission unit can also have a controllable shift stage, with which the rotational movement introduced by the electric motor can be converted into a different output rotational speed.

According to one embodiment, the first friction clutch comprises a first outer disc carrier drivingly connected to the electric motor and a first inner disc carrier drivingly connected to the first side shaft. Accordingly, the second friction clutch has a second outer disc carrier drivingly connected to the electric motor and a second inner disc carrier drivingly connected to the second side shaft. The first outer disk carrier and the second outer disk carrier are preferably connected to one another in a rotationally fixed manner, in particular are designed in one piece.

It is provided that the first friction clutch and the second friction clutch can be variably controlled in each case steplessly between an open position (in which no torque is transmitted) and a closed position (in which full torque is transmitted). The clutch torque or drive torque required at the right and left wheels can thus be adjusted as required.

Drawings

Preferred embodiments are described below with reference to the accompanying drawings. Wherein:

fig. 1 schematically shows a drive train assembly of a motor vehicle for controlling a motor torque of an electric motor;

fig. 2 schematically shows a flow chart for carrying out the method according to the invention for controlling the motor torque of an electric motor in a drive train of a motor vehicle.

Detailed Description

Fig. 1 and 2, which are described jointly below, show a mechanical drive train assembly 2 of a motor vehicle. The drive train assembly 2 comprises a first drive train 3 with a first drive axle 4 and a second drive train 5 with a second drive axle 6.

The first drive train 3 can be driven by a first drive unit 7, which is designed in the form of an electrical machine. The second drive train 5 can be driven by a second drive unit 8, which is designed in particular in the form of an internal combustion engine, wherein another drive source, such as an electric machine, is also conceivable. The second drive unit 8 can be followed by a shift transmission (Schaltgetriebe)13, by means of which the motor torque is converted into a drive torque or the motor speed is converted into a drive rotational speed.

It can be seen that the first drive axle 3 forms the rear axle of the motor vehicle and the second drive axle 6 forms the front axle of the motor vehicle, wherein the opposite arrangement is also possible. The two drive trains 3, 5 are mechanically decoupled from one another, i.e. no force transmission is possible between the two drive trains. The electric machine 7 is used only for driving the first drive axle 4, while the drive source 8 is used only for driving the second drive axle 6. A variant embodiment is also possible in which only one vehicle axle is driven.

The front axle 6 comprises an axle differential 37, which distributes the incoming drive torque uniformly to the right and left front axles 9, 10 of the motor vehicle. The two sideshafts 9, 10 each comprise, at their transmission-side end and at their wheel-side end, a constant velocity revolute joint (not shown) which makes it possible to transmit a torque to the wheels 11, 12 of the motor vehicle in the event of an angular movement.

The electromechanically driven drive train 3 comprises a right-hand sideshaft 15 for driving a right-hand wheel 17, a left-hand sideshaft 16 for driving a left-hand wheel 18, a controllable first friction clutch 20 in the power path between the electric motor 7 and the right-hand sideshaft 15, and a controllable second friction clutch 20' in the power path between the electric motor 7 and the left-hand sideshaft 16. In the present embodiment, the rotational movement generated by the electric motor 7 is introduced uniformly via the optional bevel gear 14 into the two clutch input parts 21, 21 'of the two friction clutches 20, 20'. The output parts 22, 22 'of the two clutches 20, 20' are connected with the respective sideshafts 15, 16 for transmitting torque. At the outer end, the two sideshafts 15, 16 are connected with wheels 17, 18 of the drive axle 4.

According to a variant embodiment, which is not shown, the two friction clutches can also be designed as clutch units with a common clutch input and two clutch outputs which can be rotated independently of one another. In this case, the common clutch input is drivingly connected to the electric motor, while the right-hand clutch output is drivingly connected to the right-hand sideshaft and the left-hand clutch output is drivingly connected to the left-hand sideshaft. The common clutch input can be designed in particular as an outer disk carrier; the clutch output is accordingly designed as an inner disk carrier.

The transmission and distribution of torque to the two sideshafts 17, 18 is controlled by means of two friction clutches 20, 20'. No axle differential is provided. The two clutch input parts 21, 21' are rigidly connected to one another so that they rotate at the same rotational speed n4, n 21. In order to set different drive torques at the two vehicle wheels 17, 18, the clutches 20, 20' can be actuated individually. The two clutches 20, 20' are each actuated by an associated actuating unit 34, 34', with which an axial force for closing the respective clutch 20, 20' can be applied to the friction pack of the clutch. The actuating units 34, 34' can be designed as hydraulic actuating units, which are supplied with hydraulic pressure by a pump 35. It goes without saying that other forms of actuating unit are also possible, such as electromechanical actuators (e.g. with ball ramp assemblies), or electromagnetic actuators.

The actuating unit of the clutch 20, 20 'and the electric machine 7 are controlled by an Electronic Control Unit (ECU) which sends corresponding control currents to the clutch 20, 20' or the electric machine 7 via lines. For the transmission of electrical signals to and from the control unit (ECU), a serial bus assembly 23 is provided, which CAN be embodied, for example, as a CAN (Controller Area Network) bus. The interface, protocol and circuit technology for transmitting signals on the CAN bus are known and need not be described in detail. It goes without saying that, as an alternative to the bus assembly, separate wiring of the different electrical components of the vehicle with the control unit (ECU) can also be provided.

Different driving states can be achieved with the two clutches 20, 20'. The drive torques for driving the two sideshafts 15, 16 of the respective transaxle 4 can be individually and variably adjusted as a function of the measured demand (setpoint torque). Furthermore, the two sideshafts 15, 16 and the electrical machine 7 can be connected to each other or disconnected from each other as required by means of clutches 20, 20'. The clutches 20, 20' are designed as friction clutches, which enable a continuously variable adjustment of the clutch torques transmittable between the respective clutch input 21, 21' and the associated clutch output 22, 22 '. In the completely closed state, the side shafts 15, 16 are connected to one another in a rotationally fixed manner, so that they rotate at the same rotational speed n 4. In the disengaged state of the two clutches 20, 20', the two sideshafts 15, 16 are mechanically decoupled from the electric motor 7, so that no torque is transmitted between the electric motor 7 and the wheels 17, 18. Between the closed position and the open position, the clutches 20, 20' can be adjusted steplessly to any intermediate position, so that the torques transmitted to the right-hand and left- hand sideshafts 15, 16 can be adjusted and controlled individually here. For this purpose, the control unit (ECU) determines the setpoint torques (T20, T20') for the respective clutch 20, 20'.

The control unit (ECU) comprises a process-controlled microprocessor and an electronic memory, in which a control program is stored. Corresponding control signals for the actuation units 34, 34 'of the clutches 20, 20' and the electric machine 7 are generated by the microprocessor as a function of the instructions of the control program. In order to generate corresponding control signals, the control unit (ECU) relies on information about various operating parameters of the motor vehicle. To this end, the control unit (ECU) can access various signals representative of these operating parameters via the bus assembly 23.

In particular, rotational speed sensors 24, 24' are provided; 25. 25' which provide information about the respective rotational speed n11, n12, n18, n19 of each of the wheels 11, 12, 18, 19. From the measured rotational speeds, the control unit (ECU) can calculate an axle rotational speed n4 of the motor-driven vehicle axle 4 or an axle rotational speed n6 of the second vehicle axle 6. A speed sensor 38 can also be provided for monitoring a signal representing the speed n21 of the clutch input 21. A speed sensor 36 may additionally be provided for monitoring a signal representing the speed n6 of the differential housing of the differential 37 of the second vehicle axle 6. Based on the sensed rotational speed n11, n12 of the front wheels 11, 12 or the rotational speed n6 of the differential carrier 37, it can be detected when one of these front wheels enters a slip state, so that the driving dynamics can then be influenced in a regulated manner by means of a control unit (ECU).

It is also provided that the control unit (ECU) accesses at least one motor signal representative of the provided motor torque (T8) and/or the motor rotational speed (n8) of the drive unit 8. The motor signal is transmitted by a schematically illustrated motor sensor 26 to the bus assembly 23. Furthermore, a control unit (ECU) has access to the steering angle signal. The steering angle signal is provided by a steering angle sensor 27 which detects the turning position of the steered wheel 28 of the motor vehicle or of a steering column carrying the steered wheel 28. The rotational position of the steering wheel or of the steering column is a measure for the steering angle of the motor vehicle, which is denoted by α, i.e. the angular difference between the front wheel and the position directly in front.

As a further input signal for the control unit (ECU), a pedal position signal can be used, which specifies the position of an accelerator pedal 30 of the motor vehicle by means of a pedal sensor 29. It can also be provided that the control unit (ECU) has access to one or more acceleration signals of the motor vehicle which are representative for a lateral acceleration Alat of the motor vehicle about a vertical axis or for a longitudinal acceleration of the motor vehicle. To this end, an acceleration sensor 31 is symbolically depicted, which is likewise connected to the control unit (ECU) via the bus assembly 23.

It may also be provided that the control unit (ECU) accesses further signals, for example a gear signal, which detects the gear in which the transmission is switched. Furthermore, the control unit (ECU) can determine the speed of the motor vehicle in a manner known per se.

The particularity of the present control concept is that the electric machine 7 is controlled in the torque mode depending on the vehicle speed. In this case, it is provided in particular that, when the wheel speed falls below a predefined speed threshold v _ lim, the electric motor 7 is controlled in a high torque mode, in which the motor torque Tm supplied is not limited or is set as a function of the requested demand (Tm = Tm _ max). In contrast, when the vehicle speed is higher than the preset speed threshold value, the electric motor 7 is controlled in the low torque mode in such a way that the motor torque Tm generated by the electric motor 7 is limited to a lower limit value Tm _ lim relative to the maximum motor torque. The limited motor torque Tm _ lim is less than or equal to double the smaller (T20low) of the first and second transferable clutch torques (T20', T20) plus an additional torque (Tx), i.e. Tm _ lim ≦ 2 × T20low + Tx). The additional torque Tx can in particular be less than or equal to 50% of the maximum generatable torque Tm _ max of the electric motor 7. The clutch torques T20', T20 transmittable by the friction clutches 20, 20' are determined as a function of the rotational speed values n17, n18 of the two vehicle wheels 17, 18 of the electromechanically driven axle 4, respectively, in proportion to the rotational speed n21 of the clutch input 21, 21 '.

Further details are set forth below with the aid of the flow chart according to fig. 2.

It can be seen that as input variables I for controlling the motor torque Tm of the electric motor 7, the rotational speed n21 of the clutch input part 21, 21', the rotational speeds n17, n18 of the wheels 17, 18, the vehicle speed v, the steering angle signal α and the lateral acceleration signal Alat are taken into account. The latter two signal values, i.e. the steering angle signal α and the lateral acceleration signal Alat, are selectable here.

In step S10, it is determined whether a slip is likely to occur between one of the two wheels 17, 18 of the electromechanically driven axle 4 and the drive member 21 upstream of the friction clutch 20, 20' on the power path. For this purpose, the difference between the rotational speed n17 of the right wheel 17 and the rotational speed n21 of the clutch input 21 or the difference between the rotational speed n18 of the left wheel 18 and the rotational speed n21 of the clutch input 21' can be taken into account. The rotational speed n21 of the respective clutch input 21, 21' or of the components connected thereto is detected by means of the rotational speed sensor 38. According to a variant embodiment, the two friction clutches 20, 20' can also be designed as a single structural unit. The two clutch input parts 21, 21' can be embodied in one piece, in particular in the form of an outer disk carrier. In this case, the inner disk carrier is connected to the respective side shaft in a rotationally fixed manner. It goes without saying that, when calculating the slip, the rotational speed difference between the right and left wheels 17, 18, which is likely to occur due to a curve, is taken into account or calculated.

In a further step S20, the clutch torque T20 which can be transmitted by the right-hand clutch 20 is calculated as a function of the rotational speed difference between the rotational speed n17 of the right-hand vehicle wheel 17 and the rotational speed n21 of the clutch input section 21. Accordingly, the clutch torque T20 'which can be transmitted by the left clutch 20' is calculated as a function of the rotational speed difference between the rotational speed n18 of the left vehicle wheel 18 and the rotational speed n21 'of the clutch input section 21'. The first and second clutch portions 21, 21 'are rigidly connected to each other and thus have the same rotational speed (n21= n 21').

The vehicle speed v and optionally other values such as the lateral acceleration Alat and/or a possible difference in rotational speed between the two wheels 11, 12 of the front axle 6 are continuously monitored.

Depending on whether the vehicle speed value representative for the vehicle speed v is above or below the defined speed threshold value v _ lim and, if appropriate, depending on whether the measured lateral acceleration signal Alat is above or below the defined lateral acceleration threshold value Alat _ lim and, if appropriate, depending on whether the rotational speed difference Δ n6 between the right and left wheels 11, 12 of the front axle 6 (so-called μ -split driving state) is above or below the defined rotational speed difference Δ n6_ lim, a distinction is then made in step S30 between: whether the electric motor 7 is operated in the high torque mode ("high selected") or in the low torque mode ("low selected").

If the vehicle speed v is below (-) a preset threshold value v _ lim, which may be, for example, between 50 and 70km/h, the electric motor 7 is controlled in the high torque mode so that the supplied motor torque (Tm) is not limited (Tm = Tm _ max). This pattern, which may also be referred to as "select high", is shown in the left branch S40 of fig. 2. In this operating mode, the two friction clutches 20, 20' can be adjusted accordingly such that they transmit the maximum clutch torque. The maximum transmittable clutch torque corresponds at least substantially to the drive torque transmittable to the road by the relevant vehicle wheels 17, 18.

If the vehicle speed is higher than a preset threshold value of (+) the motor torque Tm of the electric motor 7 is limited to a limit value T _ lim (Tm = T _ lim). This situation is shown in the right branch of fig. 2. The limited electric machine torque (Tm _ lim) depends on the transmittable clutch torques (T20', T20) of the clutches 20, 20' whose associated vehicle wheels 17, 18 have a lower traction force relative to the roadway. In step S50, the following case distinction is made: whether there are differently transmittable clutch torques T20', T20 between the two friction clutches 20, 20' due to slip, or which transmittable clutch torques T20', T20 are smaller due to the slip being likely larger.

In particular, the limited motor torque (Tm _ lim) is less than or equal to twice the smaller of the first and second transferable clutch torques (T20', T20) (T20low) plus an additional torque Tx, i.e. Tm _ lim ≦ 2 × T20low + Tx. The additional torque Tx can be determined on the basis of different possibilities, in particular less than 50% of the maximum generatable torque Tm _ max of the electric motor 7, i.e. Tm _ lim ≦ 2 × T20low +0.5Tm _ max.

If there is slip at the right wheel 17, i.e. the transmittable clutch torque T20 of the right friction clutch 20 is smaller than the transmittable clutch torque T20 'of the left friction clutch 20', a limit value for the motor torque Tm is determined as a function of the transmittable clutch torque T20 of the right friction clutch 20. Here, Tm _ lim =2 × T20+ Tx is applied. This possibility is shown in the left sub-branch S60. If a slip is respectively present at the left vehicle wheel 18, i.e. the transmittable clutch torque T20 'of the left friction clutch 20' is smaller than the transmittable clutch torque T20 of the right friction clutch 20, the limit value for the electric machine torque Tm is determined as a function of the transmittable clutch torque T20 'of the left friction clutch 20'. Here, Tm _ lim =2 × T20' + Tx is applied. This possibility is shown in the right sub-branch S70. The end of the method is depicted with S80.

The additional moment Tx can be provided to provide a certain traction at the wheels 17, 18 with greater slip, however in an order of magnitude in which the possible yaw moment is not critical and is well controllable in terms of driving stability. In order to determine the additional torque Tx in particular, several possibilities are conceivable. In a simple embodiment, the additional torque can be determined as a constant value k, which can be, for example, between 5Nm and 150Nm, i.e. Tx = k. In the event of a control intervention, the motor torque Tm provided by the electric motor 7 is therefore limited to double the transmittable drive torque T20low of the wheels 17, 18 having a lower friction value relative to the roadway, plus the constant value k, i.e. Tm < Tm _ lim =2xT20low + Tx). It is also possible to variably adjust the additional torque, preferably as a function of the vehicle speed. In this case, it can be provided in particular that the additional torque is set to a lower value at higher vehicle speeds than at lower vehicle speeds. In particular, the additional torque is set to be less than or equal to 50% of the maximum motor torque of the electric motor 7.

The method can be carried out not only in traction mode, i.e. the electric motor 7 converts electrical energy into mechanical energy in order to drive the vehicle, but also in overrun mode, i.e. the electric motor 7 converts mechanical energy into electrical energy in order to brake the vehicle.

The advantage of this method is that high driving stability is ensured, in particular even at high speeds of the vehicle, wherein friction losses in the drive train are minimized by controlling the motor torque Tm of the electric motor 7 in the low torque mode. The power input into the friction clutch associated with the wheels 17, 18 with greater slip or a lower friction value relative to the traffic lane is correspondingly reduced to the drive torque that can be transmitted to the traffic lane. The energy input into the respective friction clutch 20, 20' is therefore also low, so that this method contributes to an increase in the energy efficiency during operation of the drive train.

List of reference numerals:

2 drive train assembly

3 first drive train

4 first drive axle

5 second drive train

6 second drive axle

7 electric machine/motor

8 driving source

9 side shaft

10 side shaft

11 wheel

12 wheel

13 speed variator

14 bevel gear transmission part

15 side shaft

16 side shaft

17 differential case

18 wheel

19 wheel

20. 20' clutch

21 Clutch input part

22 Clutch output

23 bus module

24 rotation speed sensor

25 speed sensor

26 motor sensor

27 steering angle sensor

28 steering wheel

29 pedal sensor

30 accelerator pedal

31 acceleration sensor

32 output section

33 output part

34 operating unit

35 Pump

36 revolution speed sensor

37-axle differential

38 revolution speed transducer

39 motor sensor

Alat lateral acceleration

Alpha steering angle

ECU electronic control unit

I input signal

n number of revolutions

S10-S80 steps

T torque

v-velocity.