阅读说明：本技术 液压系统以及控制作业机械的液压系统的方法 (Hydraulic system and method of controlling hydraulic system of working machine ) 是由 博·维格霍尔姆 约翰·霍尔曼 帕特里克·斯特纳 于 2019-04-26 设计创作，主要内容包括：一种用于作业机械的液压系统(100),该系统包括：第一电机(102),连接到第一液压机(104)；第二电机(106),连接到第二液压机(108),第二液压机的输出侧(110)被连接到第一液压机的输入侧(116)；至少一个液压消耗器(118),通过供应管线(120)液压联接到第一液压机的输出侧(114),并且该至少一个液压消耗器(118)被构造成由第一液压机提供动力；以及阀装置(130),布置在液压消耗器与第一液压机和第二液压机之间,其中该阀装置被构造成基于来自第一液压机的请求输出压力,以控制从所述液压消耗器到第一液压机的输入侧或到第二液压机的输入侧中的任一者的液压流体的回流。(A hydraulic system (100) for a work machine, the system comprising: a first electric machine (102) connected to a first hydraulic machine (104); a second electric machine (106) connected to a second hydraulic machine (108), an output side (110) of the second hydraulic machine being connected to an input side (116) of the first hydraulic machine; at least one hydraulic consumer (118) hydraulically coupled to the output side (114) of the first hydraulic machine by a supply line (120), and the at least one hydraulic consumer (118) is configured to be powered by the first hydraulic machine; and a valve arrangement (130) arranged between the hydraulic consumer and the first and second hydraulic machines, wherein the valve arrangement is configured to control a return flow of hydraulic fluid from the hydraulic consumer to either one of an input side of the first hydraulic machine or an input side of the second hydraulic machine based on a requested output pressure from the first hydraulic machine.)

1. A hydraulic system (100) for a work machine, the system comprising:

a first electric machine (102), the first electric machine (102) being connected to a first hydraulic machine (104);

a second electric machine (106), the second electric machine (106) being connected to a second hydraulic machine (108), an output side (110) of the second hydraulic machine being connected to an input side (116) of the first hydraulic machine;

at least one hydraulic consumer (118), the at least one hydraulic consumer (118) being hydraulically coupled to the output side (114) of the first hydraulic machine by a supply line (120), and the at least one hydraulic consumer (118) being configured to be powered by the first hydraulic machine; and

a valve arrangement (130), the valve arrangement (130) being arranged between the hydraulic consumer and the first and second hydraulic machines, wherein the valve arrangement is configured to: controlling a return flow of hydraulic fluid from the hydraulic consumer to either an input side of the first hydraulic machine or an input side of the second hydraulic machine based on a requested output pressure from the first hydraulic machine.

2. The hydraulic system according to claim 1, wherein the valve arrangement comprises at least one controllable pressure reducing valve (130).

3. The hydraulic system of claim 1, wherein the controllable pressure relief valve is an electronically controlled pressure relief valve.

4. The hydraulic system of any preceding claim, wherein the valve arrangement is configured to: directing the return flow to an input side of the second hydraulic machine if a requested output pressure from the first hydraulic machine exceeds a threshold pressure.

5. The hydraulic system of claim 4, wherein the valve arrangement is configured to: directing the return flow to an input side of the first hydraulic machine if a requested output pressure from the first hydraulic machine is below a threshold pressure.

6. The hydraulic system of claim 4 or 5, wherein the threshold pressure is a maximum output pressure of the first hydraulic machine.

7. The hydraulic system of any preceding claim, wherein the second hydraulic machine is configured to provide a pressure to the input side of the first hydraulic machine corresponding to a pressure difference between the requested output pressure and a threshold pressure of the first hydraulic machine.

8. The hydraulic system of any preceding claim, wherein the first and second hydraulic machines are configured to: such that the combined output pressure from the first and second hydraulic machines is equal to the maximum possible requested pressure from the first hydraulic machine.

9. The hydraulic system according to any one of the preceding claims, wherein said at least one hydraulic consumer is one of a steering cylinder, a lift cylinder and a tilt cylinder of a work machine.

10. A work machine comprising a system according to any of the preceding claims.

11. A method for controlling a hydraulic system (100) of a work machine, the system comprising:

a first electric machine (102), the first electric machine (102) being connected to a first hydraulic machine (104);

a second electric machine (106), the second electric machine (106) being connected to a second hydraulic machine (108), an output side (110) of the second hydraulic machine being connected to an input side (116) of the first hydraulic machine;

at least one hydraulic consumer (118), the at least one hydraulic consumer (118) being hydraulically coupled to the output side (114) of the first hydraulic machine by a supply line (120), and the at least one hydraulic consumer (118) being configured to be powered by the first hydraulic machine; and

a valve arrangement (130), the valve arrangement (130) being arranged between the hydraulic consumer and the first and second hydraulic machines, wherein the method comprises:

controlling the valve arrangement to direct a return flow of hydraulic fluid from the hydraulic consumer to either the input side of the first hydraulic machine or to the input side of the second hydraulic machine based on a requested output pressure from the first hydraulic machine.

12. The method of claim 11, further comprising:

receiving (300) a requested pressure to be provided by the first hydraulic machine;

controlling (304) the valve arrangement to direct a return flow of the hydraulic fluid from the hydraulic consumer to an input side of the first hydraulic machine if (302) the requested pressure is below a threshold pressure; and

controlling (306) the valve arrangement to direct a return flow of the hydraulic fluid from the hydraulic consumer to the input side of the second hydraulic machine and to control the second hydraulic machine to provide a pressurised flow to the input side of the first hydraulic machine if (302) the requested pressure is above a threshold pressure.

13. The method of claim 12, further comprising: for a requested pressure above the threshold pressure, the valve arrangement is controlled using a ramp to gradually redirect flow from the input side of the first hydraulic machine to the input side of the second hydraulic machine.

14. The method of claim 12 or 13, further comprising: for a requested pressure above the threshold pressure, controlling the second hydraulic machine to gradually increase the output pressure of the second hydraulic machine to a pressure corresponding to a difference between the requested pressure and the threshold pressure of the first hydraulic machine.

15. A method as claimed in any of claims 12 to 14, in which the threshold pressure is the maximum output pressure of the first hydraulic machine.

Technical Field

The present disclosure relates to a hydraulic system and a method for controlling a hydraulic system of a work machine. In particular, the method and system relate to a hybrid drive system including an internal combustion engine and a plurality of electric machines.

The invention is suitable for working machines in the field of industrial construction machines or construction equipment, in particular wheel loaders. Although the invention will be described in relation to a wheel loader, the invention is not limited to this particular machine, but may also be used in other work machines, such as articulated haulers, excavators and backhoe loaders.

Background

In connection with heavy transport, for example in construction work, work machines are often used. Work machines may be operated with large and heavy loads in areas where there is no road, such as for transportation associated with road or tunnel construction, sand pits, mines, and the like.

The work machines typically employ hydraulic systems to power functions such as steering and lifting. The hydraulic system may be powered, for example, by an internal combustion engine via a power take-off connected to an output shaft of the engine.

To improve the fuel efficiency of the work machine, a hybrid hydraulic system may be used. One approach that has received attention is to provide a hydraulic hybrid power system that includes an electric machine for powering the hydraulic system. By combining the electric machine with an energy storage, energy can be recovered and stored during certain operations for use when needed.

A typical wheel loader operation includes simultaneous operation with two major subsystems of the motion system-the transmission system and the work hydraulic system. Since both systems are directly coupled to the engine shaft, there may be problems with the interaction between the systems.

Therefore, further improvements in the efficiency of hybrid hydraulic systems are desired.

Disclosure of Invention

It is an object of the present invention to provide an improved electric hybrid hydraulic system for a work machine.

According to a first aspect of the present disclosure, a hydraulic system for a work machine is provided. This hydraulic system includes: a first motor connected to a first hydraulic machine; a second motor, the first motor being connected to a second hydraulic machine, an output side of the second hydraulic machine being connected to an input side of the first hydraulic machine; at least one hydraulic consumer hydraulically coupled to an output side of the first hydraulic machine by a supply line and configured to be powered by the first hydraulic machine; and a valve arrangement arranged between the hydraulic consumer and the first and second hydraulic machines, wherein the valve arrangement is configured to: controlling a return flow of hydraulic fluid from the hydraulic consumer to either an input side of the first hydraulic machine or an input side of a second hydraulic machine based on a requested output pressure from the first hydraulic machine.

The first electric machine is connected to the first hydraulic machine, meaning that the output shaft of the electric machine is mechanically connected to the input shaft of the hydraulic machine, so that the electric machine can act as either a motor powering the hydraulic machine or as a generator generating electric power received by the hydraulic machine. The same applies to the second electric motor and the second hydraulic machine. It may also be provided that the first and second electric machines are connected to a power source and/or an energy storage.

The invention is based on the recognition that, on the basis of the requested pressure, it is decided by configuring the valve arrangement whether the return flow is directed to the first hydraulic machine or to the second hydraulic machine, which can support the first hydraulic machine when required. This has the advantage that the first and second hydraulic machines and the first and second electric machines can be designed to meet the maximum torque and pressure requirements of the hydraulic consumer as a sum of two component groups, rather than individually. The described system can therefore be manufactured using smaller components, i.e. components having a lower capacity than using only one set of components, thereby providing advantages in terms of system installation and integration.

Furthermore, the described system provides flexibility in that it is also able to provide additional hydraulic flow from the second hydraulic machine to the first hydraulic machine if the hydraulic consumer needs, i.e. if the return flow is not sufficient for the first hydraulic machine to provide the requested flow. Another advantage of the described system is that it provides redundancy in the hydraulic system, which means that if one of the first and second electric machines or first and second hydraulic machines fails, the hydraulic system can still operate even though its capacity may be reduced. This may help the operator to complete the task and arrive at the repair site in a safe manner without additional assistance or field repair.

According to the invention, the second hydraulic machine may be considered to provide a pressure lift to the first hydraulic machine, whereas from a motor perspective the second hydraulic machine may be considered to provide a torque lift to the first hydraulic machine.

According to an embodiment of the invention, the valve means may comprise at least one controllable pressure reducing valve. Thus, the valve arrangement may be controlled by controlling the threshold pressure of the controllable pressure reducing valve to direct flow to the input side of the first or second hydraulic machine. The controllable pressure reducing valve may for example be an electrically controlled pressure reducing valve. It should be noted, however, that the valve device may be constructed in a number of different ways while still achieving the described effects. However, a controllable reduced pressure may be advantageous because it is easy to use and the reduced pressure may be controlled mechanically or electronically.

According to one embodiment of the invention, the valve arrangement is configured to direct the return flow to the input side of the second hydraulic machine if the requested output pressure from the first hydraulic machine exceeds a threshold pressure. The threshold pressure may for example be the maximum output pressure of the first hydraulic machine. The threshold pressure may also be set so that the first electric machine and the first hydraulic machine can operate at the highest possible efficiency. Thus, when the pressure request from the hydraulic consumer is above a threshold pressure, the return flow may be redirected to the input side of the second hydraulic machine. The second hydraulic machine is then operated to raise the pressure and a pressurised flow is provided to the input side of the first hydraulic machine, which in turn raises the pressure to a level requested by the hydraulic consumer. Thus, the first hydraulic machine is supported by the second hydraulic machine to provide an output pressure above a threshold pressure.

According to one embodiment of the invention, the second hydraulic machine is configured to provide a pressure to the input side of the first hydraulic machine corresponding to a pressure difference between the requested output pressure and a threshold pressure of the first hydraulic machine. The requested pressure is thus provided by the combined pressure of the first and second hydraulic machines. The pressure provided by the second hydraulic machine may also take into account any pressure losses in the first hydraulic machine.

According to an embodiment of the invention, the at least one hydraulic consumer may be one of a steering cylinder, a lifting cylinder and a tilting cylinder of the work machine. Thus, the described hydraulic system may be used in a work machine, such as a wheel loader, and its advantages lead to a more efficient operation of the work machine. There is also provided a work machine comprising a hydraulic system according to any of the preceding embodiments.

According to a second aspect of the present invention, there is provided a method for controlling a hydraulic system of a work machine, the system comprising: a first motor connected to a first hydraulic machine; a second motor, the first motor being connected to a second hydraulic machine, the output side of the second hydraulic machine being connected to the input side of the first hydraulic machine; at least one hydraulic consumer hydraulically coupled to an output side of the first hydraulic machine by a supply line and configured to be powered by the first hydraulic machine; and a valve arrangement arranged between the hydraulic consumer and the first and second hydraulic machines. The method comprises the following steps: based on the requested output pressure from the first hydraulic machine, a valve arrangement is controlled to direct a return flow of hydraulic fluid from the hydraulic consumer to the input side of the first hydraulic machine or the input side of the second hydraulic machine.

According to an embodiment of the invention, the method may further comprise: receiving a requested pressure to be provided by a first hydraulic machine; controlling a valve arrangement to direct a return flow of the hydraulic fluid from the hydraulic consumer to an input side of the first hydraulic machine if the requested pressure is below a threshold pressure; and if the requested pressure is above the threshold pressure, controlling the valve arrangement to direct a return flow of said hydraulic fluid from the hydraulic consumer to the input side of the second hydraulic machine, and controlling the second hydraulic machine to provide a pressurised flow to the input side of the first hydraulic machine. Thus, based on the requested pressure from the first hydraulic machine, the valve arrangement is controlled such that the return flow is only directed to the second hydraulic machine when the requested pressure exceeds a threshold pressure.

According to an embodiment of the invention, the method further comprises, for a requested pressure above a threshold pressure, using a ramp control valve arrangement to gradually redirect flow from the input side of the first hydraulic machine to the input side of the second hydraulic machine. By controlling the operation of the valve means to gradually redirect the flow, a smooth transition can be achieved without sudden pressure changes. This may improve both the operational safety of the hydraulic consumer and the comfort of the operator of the hydraulic system. In a similar manner, the valve arrangement may also be controlled to provide a smooth transition when redirecting the return flow from the input of the second hydraulic machine to the input of the first hydraulic machine.

Further effects and features of this second aspect of the invention are largely analogous to those described above in connection with the first aspect of the invention.

Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.

Drawings

With reference to the accompanying drawings, the following is a more detailed description of embodiments of the invention cited as examples.

In the figure:

figure 1 is a schematic diagram of a hydraulic system according to an embodiment of the present invention,

figure 2 is a schematic diagram of a hydraulic system according to an embodiment of the present invention,

FIG. 3 is a flowchart outlining the steps of a method of controlling a hydraulic system according to an embodiment of the present invention, and

FIG. 4 is a schematic illustration of a work machine including a hydraulic system according to an embodiment of the present disclosure.

Detailed Description

In this detailed description, various embodiments of the hydraulic system and the method for controlling the hydraulic system according to the invention are mainly discussed with reference to a hydraulic hybrid system in a wheel loader, wherein the hydraulic consumers are shown as hydraulic cylinders. It should be noted, however, that this by no means limits the scope of the invention, as the described hydraulic system is equally applicable to other applications and other types of work machines.

Fig. 1 schematically illustrates a hydraulic system 100 for a work machine, such as a wheel loader. The hydraulic system 100 includes a first electric machine 102 connected to a first hydraulic machine 104 and a second electric machine 106 connected to a second hydraulic machine 108, wherein an output side 110 of the second hydraulic machine 108 is connected to an input side 116 of the first hydraulic machine 104. The first and second hydraulic machines 104, 108 are shown here as fixed displacement hydraulic machines. However, the system may also be operated using a variable displacement hydraulic machine. If a variable displacement hydraulic machine is used, it is also necessary to provide control signals to the machine to control the pressure provided.

The hydraulic system 100 further comprises at least one hydraulic consumer 118, which at least one hydraulic consumer 118 is hydraulically coupled to the output side 114 of the first hydraulic machine 104 via a supply line 120 and is configured to be powered by the first hydraulic machine 104. The hydraulic consumer 118 is here represented by a hydraulic cylinder 118, the hydraulic cylinder 118 having a piston side 126 connected to the output side 114 of the first hydraulic machine 104 and a piston-rod side 125 connected to a first return line 122, which first return line 122 hydraulically couples the hydraulic consumer 118 to the input side 116 of the first hydraulic machine 104 via a valve arrangement 130.

The valve arrangement 130 is arranged between the hydraulic consumers 118 and the respective input sides 116, 112 of the first and second hydraulic machines 104, 108. The valve arrangement 130 is configured to control the return flow of hydraulic fluid from the hydraulic consumer 118 to either the input side 116 of the first hydraulic machine 104 or the input side 112 of the second hydraulic machine 108 based on the requested output pressure from the first hydraulic machine 104.

As shown in fig. 1, the valve arrangement 130 includes a controllable pressure relief valve 132, which controllable pressure relief valve 132 may be provided in the form of an electrically controlled pressure relief valve 132. The valve arrangement 130 is advantageously configured to direct the return flow to the input side 112 of the second hydraulic machine 108 if the requested output pressure from the first hydraulic machine 104 exceeds a threshold pressure, which may be the maximum output pressure of the first hydraulic machine 104.

The requested pressure from the first hydraulic machine 104 may be based on a requested function from the vehicle operator, such as turning the wheel loader, lifting a load, or any other operation requiring hydraulic power. The request is converted to a pressure to be provided by the first hydraulic machine 104 and the valve arrangement 130 is controlled based on a comparison between the requested pressure and a threshold pressure of the first hydraulic machine 108.

The valve arrangement 130 further comprises a check valve 134, which check valve 134 is arranged between the return line 122 from the hydraulic consumer 118 and the input side 116 of the first hydraulic machine 104. When the controllable pressure relief valve 132 is closed, the check valve 134 allows flow from the return line to the first hydraulic machine. Thus, the pressure required to open the controllable pressure relief valve 132 can be controlled such that flow from the return line is directed to either of the first and second hydraulic machines 104, 108.

As further shown in fig. 1, the hydraulic system includes a check valve 136 disposed between the input side 112 of the second hydraulic machine 108 and the hydraulic fluid supply 124, wherein the check valve 136 is configured to allow the second hydraulic machine 108 to access hydraulic fluid from the hydraulic fluid supply 124. As shown in fig. 1, the check valve 136 is arranged to prevent hydraulic fluid from flowing from the first return line 122 to the hydraulic fluid supply 124. The hydraulic fluid supply 124 is shown here as a hydraulic tank 124.

In fig. 2, the hydraulic system 200 is further illustrated as comprising: a first pressure detection means 202, the first pressure detection means 202 being arranged to determine the pressure in the supply line 120; and a second pressure detecting means 204, the second pressure detecting means 204 being arranged to determine the pressure at the input side of the first hydraulic machine. The first and second pressure detection means 202, 204 may for example be pressure sensors arranged in the supply line 120 and the first return line 122, respectively.

For example, the hydraulic consumer, embodied here as hydraulic cylinder 118, may be a steering cylinder, a lift cylinder, or a tilt cylinder of a work machine. Furthermore, by providing each hydraulic consumer with a controllable pressure relief valve, the valve arrangement 130 can easily be expanded with additional valves to accommodate additional hydraulic consumers. Fig. 2 also shows a directional control valve 208 disposed between the hydraulic cylinder 118 and the rest of the hydraulic system 100.

Fig. 2 further shows a first power electronic control unit 210 and a second power electronic control unit 212 for controlling said first motor 102 and second motor 106, respectively. The first 210 and second 212 electronic power control units are in turn controlled by the hydraulic system control unit 214, which hydraulic system control unit 214 is arranged and configured to control the overall function of the hydraulic system 100. The control unit 214 may include a microprocessor, microcontroller, programmable digital signal processor, or other programmable device. The control unit 214 may also or alternatively comprise an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device or a digital signal processor. Where the control unit 214 comprises a programmable device such as the microprocessor, microcontroller or programmable digital signal processor described above, the processor may also comprise computer executable code which controls the operation of the programmable device. Furthermore, the control unit may be embodied as a dedicated control unit for the hydraulic system, or the desired functions may be provided by one or more general Electronic Control Units (ECUs).

FIG. 3 is a flow chart summarizing the steps of a method according to an embodiment of the invention. The method will be described with reference to the hydraulic system 100 shown in fig. 1 and 2. In general, the method comprises: based on the requested output pressure from the first hydraulic machine 104, the valve arrangement 130 is controlled to direct a return flow of hydraulic fluid from the hydraulic consumer 118 to either of the input side 116 of the first hydraulic machine 104 and the input side 112 of the second hydraulic machine.

In more detail, the method comprises: receiving 300 a requested pressure to be provided by the first hydraulic machine 104; and determines 302 whether the requested pressure is below or above a threshold pressure for the first hydraulic machine 104. If the requested pressure is below the threshold pressure, the method includes: the valve arrangement 130 is controlled 304 to direct a return flow of hydraulic fluid from the hydraulic consumer 118 to the input side 116 of the first hydraulic machine 104. This means that the pressure request can be fulfilled by the first hydraulic machine 104 and no pressure increase from the second hydraulic machine 108 is required.

If the requested pressure is above the threshold pressure 302, the method includes: the valve arrangement 130 is controlled 306 to direct a return flow of hydraulic fluid from the hydraulic consumer 118 to the input side 112 of the second hydraulic machine 108 and to control the second hydraulic machine 108 to provide a pressurised flow to the input side 116 of the first hydraulic machine 104. Thus, the output pressure from the first hydraulic machine 104 is the combined pressure of the first and second hydraulic machines 104, 108.

The valve arrangement 130 is advantageously configured to provide a gradual and smooth transition when the return flow changes from flowing to the input side 116 of the first hydraulic machine 104 to flowing to the input side 112 of the second hydraulic machine 108, i.e. when the requested pressure increases. The gradual transition has the effect that the hydraulic consumer will not experience a sudden change in supply pressure, which in turn will allow a smooth movement of the hydraulic cylinder. The pressure of the second hydraulic machine 108 may be increased using a ramp that coincides with the transition ramp of the valve arrangement so that the flow of the first hydraulic machine 104 is similarly inclined to provide a smooth pressure increase for the hydraulic consumer 118.

Figure 4 shows a frame-steered work machine in the form of a wheel loader 401. The body of the wheel loader 401 comprises a front body part 402 and a rear body part 403, which parts each have an axle 412, 413 for driving a pair of wheels. The rear body portion 403 includes a cab 414. The body parts 402, 403 are connected to each other such that they can be pivoted relative to each other about a vertical axis by means of two first actuators, in the form of hydraulic cylinders 404, 405, arranged between the two parts. The hydraulic cylinders 404, 405 are thus arranged on both sides of the horizontal centre line of the vehicle in the direction of travel of the vehicle in order to turn the wheel loader 401.

The wheel loader 401 comprises equipment 411 for handling objects or material. The apparatus 411 comprises: a load-arm unit 406, also referred to as a linkage; and a device 407 in the form of a bucket mounted on the load-arm unit 406. A first end of the load-arm unit 406 is pivotally connected to the front vehicle section 402. The device 407 is pivotally connected to a second end of the load-arm unit 406.

The load-arm unit 406 may be raised and lowered relative to the front vehicle part 402 of the vehicle by means of two second actuators in the form of two hydraulic cylinders 408, 409, each of which is connected at one end to the front vehicle part 402 and at the other end to the load-arm unit 406. The bucket 407 may be tilted relative to the load-arm unit 406 by means of a third actuator in the form of a hydraulic cylinder 410, which is connected at one end to the front car part 402 and at the other end to the bucket 407 by means of a link arm system 415.

It is to be understood that the invention is not limited to the embodiments described above and shown in the drawings; on the contrary, the skilled person will recognise that many variations and modifications are possible within the scope of the appended claims.