WO2003011675A1

WO2003011675A1 - Back up hydraulic system for steer-by-wire system

Info

Publication number: WO2003011675A1
Application number: PCT/NL2002/000523
Authority: WO
Inventors: Johannes Haaye Van Der Kamp; Johannes Andrianus Maria Duits
Original assignee: Ab Skf
Priority date: 2001-08-03
Filing date: 2002-08-02
Publication date: 2003-02-13
Also published as: NL1018699C2

Abstract

Back up hydraulic system for providing hydraulic fluid to a steer-by-wire system. The steer-by-wire system comprises a hydraulic steering actuator (21), a hydraulic pump (31) driven by an engine (29), and an electronically controlled valve (24) controlling fluid flow to the hydraulic steering actuator (21). The back up hydraulic system comprises a back up pump (189, and a back-up supply duct (19) for coupling the back up pump (18) to a supply duct (27) of the hydraulic steering actuator (21). Furthermore, a back up controller (16) may be provided for driving the electric motor (15), the back up controller (16) being arranged to detect a malfunction of the engine (29).

Description

Back up hydraulic system for steer-by-wire system

The present invention relates to a back up supply system for providing back up hydraulic power to a steer-by- wire system. More particularly, the present invention relates to a back up hydraulic system for providing hydraulic fluid to a steer-by-wire system, the steer-by-wire system comprising a hydraulic steering actuator, a hydraulic pump driven by an engine, and an electronically controlled valve controlling fluid flow to the hydraulic steering actuator.

Such a back up hydraulic system is known from German Patent DE-C-195 46 723. In this document, a back up hydraulic system is present using a direct hydraulic link between the steering device and the steering actuator which is used in case of failure of the main hydraulic system for the hydraulic steering actuator.

German patent application DE-A-199 34740 describes an electromagnetic valve for application in a hydraulic steering actuator system, e.g. of a fork lift truck. Hydraulic fluid is pressurised by an engine of the vehicle and supplied to the actuator controlling the angular position of steered wheels of the vehicle via a steering valve. The electromagnetic valve allows to correct the relation between the absolute position of the steering wheel and the steered wheels.

More and more, present steering systems are replaced by steer-by-wire controls, in which there is no direct mechanical coupling between a steering wheel and steered wheels of a vehicle, such as a fork lift truck. Usually, these steer-by- wire systems comprise a hydraulically driven steering actuator and a directional valve for controlling the steering actuator, in which the directional valve is controlled by an electric signal. A disadvantage encountered with the known steer-by-wire system, is that when the engine driving the hydraulic fluid pump fails, also the hydraulic pressure drops and no steering of the vehicle is possible.

The present invention seeks to provide a back up system for a steer-by-wire system having a hydraulically driven actuator, which allows continued steering capability after an engine failure. According to the present invention, a back up hydraulic system is provided according to the preamble defined above, in which the back up hydraulic system comprises a back up pump, and a back-up supply duct for coupling the back up pump to a supply duct of the hydraulic steering actuator. This back up system allows to steer the vehicle even after failure of the engine driving the pump which provides the hydraulic power for the steer-by- wire actuator. In this manner, a fail-safe steer-by-wire system may be provided.

In an embodiment of the present system, the back up pump is driven by an electric motor, supplied by a battery, such as the vehicle battery. Although this only provides a limited capacity for driving the electric motor, it may be sufficient to safely stop the vehicle.

The back up pump may take hydraulic fluid from the main hydraulic fluid sump, but also, the back up hydraulic system may comprise a back up sump for providing back up hydraulic fluid. The back up sump may comprise enough hydraulic fluid to last a limited amount of time or steering actuation to bring the vehicle to a safe and controlled stop.

In a further embodiment, the back up supply duct is connectable to the supply duct via a one way safety valve. This ensures that normal operation of the steer-by- wire system is not influenced by the back up system.

In an further embodiment, the back up hydraulic system further comprises a back up controller for driving the back up pump, the back up controller being arranged to detect a malfunction of the engine. The detection of a malfunction of the engine may be implemented in a number of different ways, e.g. by direct engine monitoring or by monitoring the hydraulic fluid pressure in the steer-by-wire system. Alternatively, the back up controller is arranged to detect a malfunction of the engine by monitoring proper operation of the steer-by- wire system. When e.g. a steering input to a steering wheel is not followed by the correct actuation of the steered wheels (as monitored by a steer-by-wire control unit), a failure in the steer-by-wire system may be assumed that necessitates a start of the back up hydraulic system.

In a further embodiment, the steer-by-wire system further comprises an accumulator positioned between the electrically controlled valve and the pump for storing an amount of pressurized hydraulic fluid. This makes it possible to make a limited number of steering movements in case the engine providing hydraulic pressure is not working, until the pressure of the hydraulic fluid in the accumulator falls below a certain level. In a further embodiment, the steer-by-wire system further comprises a one way valve positioned between the electrically controlled valve and the pump. This one way valve helps maintaining the hydraulic pressure in the electronically controlled valve. In a further embodiment the electronically controlled valve comprises redundant electrical coils and corresponding control devices. These redundant components increase the reliability of the system, as in general, the electrical components have a lower reliability than the hydraulic components.

In a further embodiment of the back up hydraulic system, the hydraulic system further comprises filters to clean the hydraulic fluid. This minimises the risk of hydraulic failures due to sticky valves.

In an even further embodiment, the invention also relates to a back up hydraulic system in which the back up hydraulic system is used in a vehicle comprising at least one wheel, the back up pump being driven using energy taken from the at least one wheel. This provides a reliable vehicle, that can still be safely steered when all other energy supplies for the hydraulic systems fail, as long as the vehicle is moving. The present invention will now be explained in further detail using an exemplary embodiment, with reference to the accompanying drawing, in which

Fig. 1 shows a schematic diagram of a complete steer-by- wire system in which the back up supply according to the present invention is used; Fig. 2 shows a schematic diagram of the hydraulic system of the system of Fig. 1; and

Fig. 3 shows a schematic diagram of a complete steer-by- wire system and a back up supply according to an alternative embodiment of the present invention.

A steer-by- wire system uses a steer-by- wire controller 12 to convert a rotation or angle position of a steering wheel 11 of a vehicle, such as a fork lift truck, into an electrical signal. Via signal lead 14, the electrical signal is supplied to an electrically controlled valve 24 of a hydraulic steering actuator 21, which mechanically controls the angular position of steered wheels 20 of the vehicle. A wheel position sensor 13 determines the actual (absolute) position of the steered wheels 20, and supplies a feedback signal to the steer-by-wire controller 12.

The steering actuator 21 comprises a piston 22 and two hydraulic lines 23, 25, which are controlled by the valve 24. Hydraulic fluid is pressurised by a pump 31, mechanically driven by the engine 29 of the vehicle, which may be a combustion engine or an electrical engine. Hydraulic pressure is also delivered to other vehicle systems 33 by means of pump 32. The hydraulic fluid is taken from a sump or reservoir 28, and via the pump 31 the hydraulic fluid is transported to the valve 24 via supply duct 27. Depending on the position of the valve, the hydraulic fluid flows to the left or right chamber of the hydraulic actuator 21 via ducts 25 and 23, respectively to drive the piston 22 of the actuator 21. Fluid from the other side of the actuator flows via the valve 24 and a return duct 26 back to the sump 28.

When the engine 29 of the vehicle fails, the pump 31 will no longer pressurise the hydraulic fluid, and thus no actuation of the actuator 21 is possible, although the steer- by- wire controller 12 still provides a control signal to the valve 24.

In order to be able to still steer the vehicle when the engine 29 fails, the present invention provides a back up system, comprising an electric motor 15, which drives a back up pump 18. The back up pump 18 pressurises hydraulic fluid from a back up sump 17, and provides the pressurised fluid to the supply duct 27 via duct 19 and safety valve 34. The back up pump 18 is driven by the batteries of the vehicle, and thus provides a limited capability to enable steering of the vehicle after engine failure. The back up pump 18 can also be driven with energy taken from one or more wheels of the vehicle. This means that as long as the vehicle is moving it will be possible to perform steering actions. This energy can for instance be transformed into electrical energy (e.g. using a dynamo) to feed the electrical engine 15, but it is also possible to use the rotational movement of the wheels of the vehicle to directly drive the back up pump 18.

The back up sump 17 also has only a limited capacity to provide hydraulic fluid. This may be overcome by having the back up pump 18 draw hydraulic fluid from the main sump 28. For reasons of reliability, the electric motor 15 and/or back up pump 18 may be provided redundantly.

Fig. 2 shows a schematic diagram of the hydraulic system of the system described above. In Fig. 2, elements with the same function are indicated by the same reference numeral as in Fig. 1. The valve 24 may be integrated into a manifold 40 provided close to the actuator 21. The manifold 40 comprises connections for the supply and return duct 27, 26, and for the ducts 23, 25 to the actuator 21. In addition, the manifold comprises a connection for the back up supply duct 19. The safety valve 34 may also be provided in the manifold 40. In addition to the (electrically controlled) valve 24, the manifold further comprises a number of safety features, such as shock valves 41, 42 and suction valves 43, 44, as well as bypass valve 45.

The electric motor 15 is controlled by a back up controller 16. The back up controller 16 monitors the correct functioning of the engine 29. The back up controller 16 may implement this function by receiving a signal 35 from other vehicle systems monitoring the engine 29, or receiving an engine failure signal from the engine directly.

Also, the steer-by- wire controller 12 maybe arranged to provide an engine fail signal via signal lead 36. When the steer-by- wire controller 12 monitors that a steer-by- wire input signal does not result in a deflection of the steered wheels 20, it may be assumed that hydraulic pressure is absent because a failure of the engine has occurred. Also, the hydraulic pressure may be monitored to provide a signal when hydraulic pressure is below a predetermined threshold. Consequently, the steer-by- wire controller may then send a signal to the back up controller 16 to supply back up hydraulic fluid to the actuator 21. By having a separate back up system for providing hydraulic fluid to the actuator

21, it is ascertained that the vehicle may be steered in case of an engine failure. The capacity of the vehicle batteries and of the back up sump 17 should be at least enough to be able to bring the vehicle to a controlled stop. In this manner, a simple and cost- effective back up system is provided adding the to safety level of the vehicle. Safety can be further increased by adding an accumulator 50 to the steer-by-wire system. The accumulator 50 is preferably positioned between the electrically controlled valve 24 and the pump 31, as is shown in figure 3. When the engine 29 is running, the accumulator 50 will store some of the hydraulic fluid under pressure. In case of a failure of the engine 29, the accumulator 50 will maintain enough hydraulic pressure to enable a few steering movements. If more steering movements are required to bring the vehicle to a safe stop, the back up system, as discussed above, could come into action.

Figure 3 also shows a one way valve 51 positioned between the electrically controlled valve 24 and the pump 31, that is preferably used in combination with the accumulator 50. This one way valve 51 increases the performance of the accumulator 50, as will readily be understood by a person skilled in the art.

An embodiment using such a one way valve 51 and an accumulator 50 also allows to take energy saving measures, such as turning engine 29 off when no steering actions are performed. As soon as a steering movement is performed, the engine 29 can be switched on. This may take some time, but during this time period steering movements are enabled by the pressure maintained by the one way valve 51 and the accumulator 50.

The electronically controlled valve 24 is controlled with electrical coils and corresponding control devices. These electrical components are known to be less reliable then hydraulic components. Safety could even further be increased by adding redundant electrical coils and corresponding control devices.

Pollution of the oil used in the hydraulic system could cause sticky valves, increasing the chances of a failing hydraulic system. This risk could be minimised by using one or more filters, that are known to a person skilled in the art.

Claims

1. Back up hydraulic system for providing hydraulic fluid to a steer-by-wire system, the steer-by- wire system comprising a hydraulic steering actuator (21), a hydraulic pump (31) driven by an engine (29), and an electronically controlled valve (24) controlling fluid flow to the hydraulic steering actuator (21), the back up hydraulic system comprising a back up pump (18) and a back-up supply duct (19) for coupling the back up pump (18) to a supply duct (27) of the hydraulic steering actuator (21).

2. Back up hydraulic system according to claim 1 , in which the back up pump

(18) is driven by an electric motor (15), supplied by a battery.

3. Back up hydraulic system according to claim 1 or 2, further comprising a back up sump (17) for providing back up hydraulic fluid.

4. Back up hydraulic system according to claim 1, 2 or 3, in which the back up supply duct (19) is connectable to the supply duct (27) via one way safety valve (34).

5. Back up hydraulic system according to one of the proceeding claims, further comprising a back up controller (16) for driving the back up pump (18), the back up controller (16) being arranged to detect a malfunction of the engine (29).

6. Back up hydraulic system according to claim 5, in which the back up controller (16) is arranged to detect a malfunction of the engine (29) by monitoring hydraulic fluid pressure.

7. Back up hydraulic system according to claim 5 or 6, in which the back up controller (16) is aπanged to detect a malfunction of the engine (29) by monitoring proper operation of the steer-by- wire system.

8. Back up hydraulic system according to one of the proceeding claims, in which the steer-by-wire system further comprises an accumulator (50) positioned between the electrically controlled valve (24) and the pump (31) for storing an amount of pressurized hydraulic fluid.

9. Back up hydraulic system according to claim 8, in which the steer-by-wire system further comprises a one way valve (51) positioned between the electrically controlled valve (24) and the pump (31).

10. Back up hydraulic system according to one of the proceeding claims, in which the electronically controlled valve (24) comprises redundant electrical coils and coπesponding control devices.

11. Back up hydraulic system according to one of the proceeding claims, in which the hydraulic system further comprises filters to clean the hydraulic fluid.

12. Back up hydraulic system according to one of the proceeding claims, in which the back up hydraulic system is used in a vehicle comprising at least one wheel, the back up pump (18) being driven using energy taken from the at least one wheel.