Electrohydraulic steering system for a vehicle and vehicle

Abstract

The invention relates to an electrohydraulic steering system (1a) for a vehicle, comprising a steering angle sensor (150), a steering control device (29) that is signal-connected to the steering angle sensor (150), a steering cylinder (75) that is connected to one or more wheels (70) of the vehicle, and a steering unit (50) that is mechanically connected to the steering control device (29) and hydraulically connected to the steering cylinder (75). The steering control device (29) comprises an electric actuator (29a) that is configured to actuate the steering unit (50) based on a steering angle setpoint received from the steering angle sensor (150) in order to adjust a steering angle of the vehicle.

Description

The present invention relates to an electrohydraulic steering system for a vehicle and to a vehicle having an electrohydraulic steering system.BACKGROUND OF THE INVENTIONMobile working machines, in particular tractors, can be equipped with hydrostatic steering without a mechanical steering linkage between the steering wheel and the steered wheels. In this case, the steering wheel can be connected via a steering column to a steering assembly (so-called Orbitrol), which, corresponding to a movement of the steering wheel, conducts a specific amount of hydraulic fluid to a steering cylinder on the steered wheels of the mobile working machine. A required pressure for steering the wheels by means of the steering cylinder can be provided by a hydraulic pump which can be driven by a drive motor of the mobile working machine, for example by an internal combustion engine. The hydraulic pump, the steering assembly and the steering cylinder can be connected in particular to flexible hydraulic lines. Steering systems of this type are distinguished by high power transmission at low costs.However, they have the disadvantage that there is no fixed angular relationship between the steering wheel angle and the wheel steering angle, that is to say that a "12 o'clock position" of the steering wheel does not mean a straight-ahead running of the vehicle and that there is no feedback on the steering forces on the steering wheel. In addition, a separate hydraulic circuit is required for automatic steering of the mobile work machine, as a result of which the outlay and costs for the steering system increase.Disclosure of the InventionAccording to the invention, an electrohydraulic steering system for a vehicle and a vehicle having an electrohydraulic steering system having the features of the independent patent claims are proposed. Advantageous embodiments are the subject matter of the dependent claims and of the following description.The invention makes it possible to improve a driving behavior of a vehicle with hydraulic steering and to dispense with an additional hydraulic circuit for automatic steering.An electrohydraulic steering system according to the invention comprises a steering angle sensor and a steering control device which is connected to the steering angle sensor by signal technology. The signal connection can be, for example, a cable-bound connection, in particular a CAN bus (controller area network). By means of the signal connection, in particular a steering angle setpoint value can be transmitted from the steering angle sensor to the steering control device. It is also possible for further variables, such as steering angle speed and / or steering angle acceleration, to be sent to the steering control device.According to one specific embodiment, the steering angle sensor may include an actuating element and at least one steering angle sensor. The actuating element can be, for example, a steering wheel or a joystick with which a driver can specify / set a steering angle which can be detected / measured by the steering angle sensor as a steering angle setpoint value. The term "steering angle" is to be understood here as meaning the angle of engagement at the actuating element. The actuating element is in particular not mechanically coupled to the steering assembly, i.e. the invention relates substantially to a so-called steer-by-wire function ("steering by means of cable").For this purpose, the steering angle sensor can be attached, for example, to a steering column connected to the actuating element and determine the angle of rotation / angle of deflection thereof, for example by means of a angle of rotation sensor such as a GMR sensor (Giant Magneto Resistance) or a Hall sensor. In this case, in embodiments of the invention, a force feedback actuator can also be attached to the steering column, which generates haptic feedback in a known manner as a function of steering forces occurring at the actuating element.Alternatively or additionally, the steering angle sensor may be included in a controller of the vehicle. This may be the case in particular with an autonomously driving vehicle that is automatically steered by the vehicle controller (automatic steering). In this case, the steering angle sensor can be integrated in the vehicle controller in particular as software. In the case of a vehicle that is not driving autonomously, for example, a driver assistance system, such as a lane keeping assistant, can cause automatic steering as a vehicle control and specify a steering angle setpoint value.The electro-hydraulic steering system also includes a steering cylinder connected to one or more wheels of the vehicle and a steering assembly (Orbitrol) mechanically connected to the steering controller and hydraulically connected to the steering cylinder, the steering controller including an electric actuator that actuates the steering assembly based on a steering angle command received from the steering angle sensor to adjust a steering angle of the vehicle.In other words, the steering control device receives a steering angle target value that can be specified either by a driver by means of the actuating element or by the vehicle controller, and then actuates the steering assembly by means of the electric actuator in order to supply hydraulic energy for setting the steering angle to the steering cylinder in accordance with the steering angle target value. In this way, a further hydraulic circuit for automatic steering can be dispensed with, since in this case, too, the steering control device actuates the steering assembly in order to set the desired steering angle via the steering cylinder.According to an embodiment, the electro-hydraulic steering system may include a hydraulic pump for providing the hydraulic energy for operating the steering cylinder. In particular, the hydraulic pump can provide hydraulic fluid at a predetermined pressure to the steering unit, which hydraulic fluid can be conveyed by the steering unit into a first or a second working chamber of the steering cylinder as a function of the steering angle setpoint value.According to an embodiment, the steering control device may include a first control unit and a second control unit. In this case, the first control unit can be connected to the steering angle sensor by means of a first signal line and the second control unit can be connected to the steering angle sensor by means of a second signal line. The first and second signal lines can be, in particular, a first and second CAN bus. In this way, in the event of failure of one of the two signal lines and / or one of the two control units, recourse can be had to the respective other.In order to further increase the reliability of the steering control device, the electric actuator can comprise a first drive and a second drive, wherein the first and / or the second drive can be controlled by the first and the second control unit. In particular, each of the two control units can control both the first and the second drive of the electric actuator. The first and / or the second drive can be connected to an output element of the electric actuator, which can mechanically connect the steering control device to the steering assembly. In particular, the electric actuator can each contain an electric motor as first and second drive, wherein the two electric motors can have, for example, a common output shaft as output element. It is also possible for each of the two drives to have a separate output element and to be connected via a transmission. A drive power of the first and second drives can be selected such that the steering assembly can be actuated with only one of the two drives in order to be able to actuate the steering assembly by means of the other in the event of failure of one of the two drives.According to one embodiment, a mechanical transmission ratio can be arranged between the steering control device and the steering assembly, which transmission ratio can be connected on the one hand to the output element of the electric actuator of the steering control device and on the other hand to an input element of the steering assembly. The output element of the electric actuator can be an output shaft, for example, and the input element of the steering assembly can be an input shaft, for example. The mechanical transmission ratio can be, for example, a worm gear. Any other type of transmission suitable for transmitting a force / torque from the electric actuator to the steering assembly is likewise possible.According to one specific embodiment, the steering control device and / or the steering assembly may be configured to operate the steering cylinder, in particular in an emergency steering operation. An emergency steering operation is to be understood here as a steering operation in which no hydraulic energy is transmitted from the hydraulic pump to the steering cylinder, for example on account of a failure of the hydraulic pump and / or a hydraulic line between the hydraulic pump and the steering assembly. In this case, for example, an emergency steering pump functionality integrated in the steering assembly can be driven by the electric actuator in order to convey hydraulic fluid to the steering cylinder for operation thereof.According to one embodiment, the electrohydraulic steering system can comprise a position sensor for determining an actual steering angle value. The position sensor can be arranged, for example, on / in the steering cylinder and determine the actual steering angle value, for example, based on a measured position of the steering cylinder. For this purpose, for example, a relationship between steering cylinder position and steering angle can be determined and stored in a characteristic curve, e.g., in the first and / or second control unit. It is also possible that one or more position sensors are attached to one or more tie rods of the vehicle and the actual steering angle value is determined on the basis of one or more wheel angle angles.In this case, the steering control device may receive an actual steering angle value from the position sensor, and may control the steering angle based on a comparison between the target steering angle value and the actual steering angle value. For this purpose, the position sensor can be connected for example by signal technology to the first and / or the second control unit. The signal connection can be a radio connection or, in particular, a cable connection.Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.It is understood that the features mentioned above and those still to be explained below can be used not only in the respectively specified combination, but also in other combinations or alone, without departing from the scope of the present invention.The invention is schematically illustrated in the drawings on the basis of an exemplary embodiment and is described in detail below with reference to the drawings. In the drawings, like elements are denoted by like reference numerals. Therefore, repetitive description is omitted as appropriate.DESCRIPTION OF THE FIGURESFIG. 1 schematically shows a hydrostatic steering system not according to the invention. FIG. 2 schematically shows an electrohydraulic steering system according to an exemplary embodiment of the invention. FIG. 3 schematically shows a second exemplary embodiment of the electrohydraulic steering system. FIG. 4 schematically shows a third exemplary embodiment of the electrohydraulic steering system.Detailed Description of the DrawingsFIG. 1 schematically shows a hydrostatic steering system 1, not according to the invention, having a steering wheel 10, which is mechanically connected via a steering column 21 to a steering assembly 50 in the form of an orbitrol. A steering angle sensor for detecting a rotation angle / steering angle of the steering column is mounted on the steering column 21. The steering assembly 50 is furthermore connected to a steering cylinder 75 by means of two flexible hydraulic lines 55. A first hydraulic line 55 is connected to a first working chamber 75a and a second hydraulic line 55 is connected to a second working chamber 75b of the steering cylinder 75. The steering cylinder 75 is mechanically connected to a steered axle 76 of a vehicle, not shown in detail, to which two wheels 70 are attached.The steering assembly 50 is supplied with hydraulic fluid by a hydraulic pump 40, which is driven by an internal combustion engine 30, via a further flexible hydraulic line 54. The hydrostatic steering system 1 shown in FIG. 1 also has a separate emergency steering pump 25 and a priority valve 26 which is arranged between the two pumps 40, 25 connected in parallel and the steering assembly 50, and connects either the hydraulic pump 40 or the emergency steering pump 25 to the latter. The emergency steering pump 25 can be, for example, an electrically driven pump which can be used when the internal combustion engine 30 is not active, for example when the vehicle is towed, or there is a failure of the hydraulic pump 40.When the steering wheel 10 is moved leftward or rightward, the steering unit 50 supplies a larger amount of hydraulic fluid into the first working space 75a (leftward steering) or the second working space 75b (rightward steering) of the steering cylinder 75 according to the rotational direction, thereby moving the wheels 70 in the corresponding direction.In addition, the steering system 1 shown has a separate hydraulic circuit for automatically steering the vehicle, which includes a vehicle controller 22, a bypass valve 24 and a bypass controller 23. The bypass valve 24 is connected in parallel with the steering unit 50 and is connected via two further flexible hydraulic lines 55 ato the working chambers of the steering cylinder 75. Hydraulic fluid is supplied from the hydraulic pump 40 or the emergency steering pump 25 via a further flexible hydraulic line 54 awhich is connected to the hydraulic line 54. The vehicle controller 22 is connected in terms of signal technology to the steering angle sensor 20 and the bypass controller receives a signal from a position sensor 60 which detects a position of the steering cylinder 75 (indicated by the arrows between the steering angle sensor 20 and the vehicle controller 22 and also the position sensor 60 and the bypass controller 23).In this case, a desired steering angle is specified by means of the vehicle controller 22, and the bypass valve 23 is set by the bypass controller 22 in such a way that the working spaces 75 a, 75 bof the steering cylinder 75 are acted upon with hydraulic fluid in accordance with the specified steering angle (indicated by the arrows between the vehicle controller 22, the bypass controller 23 and the bypass valve 24). The set steering angle is monitored or regulated by means of the position sensor 60. When a driver enters the steering operation through an operation of the steering wheel 10, the vehicle controller 22 receives a corresponding signal from the steering angle sensor 20 and turns off the automatic steering.It will be appreciated that in the hydrostatic steering system shown in Figure 1, a plurality of hydraulic components are required to provide the described steering functions. It will also be appreciated that the steering system responds only to movements of the steering wheel, but the absolute position of the steering wheel has no relation to the wheel steering angle.FIG. 2 shows, in contrast, an electrohydraulic steering system 1 aaccording to an exemplary embodiment of the invention, which can implement these steering functions with a significantly reduced number of components. For this purpose, the steering wheel 10 is no longer directly connected to the steering assembly 50 via the steering column 21, but rather a steering control device 29 and a mechanical transmission 28, e.g. a worm gear 28, are connected upstream of the steering assembly 50. Instead of the steering wheel 10, a joystick or any other suitable actuating element 10 can also be used.Thus, in the present case, the steering wheel 10 and the steering angle sensor 20, which determines the angle of rotation / steering angle of the steering column 21, form a steering angle sensor 150, which transmits a steering angle setpoint value to the steering control device 29. For this purpose, the steering control device 29 is connected by signal technology to the steering angle sensor 20 (indicated by the arrow between the steering angle sensor 20 and the steering control device 29) and additionally comprises an electric actuator 29 a(see FIG. 4 ) which actuates the steering assembly 50 via the mechanical transmission 28 in accordance with a steering angle setpoint value received from the steering angle sensor 20.In addition to the steering angle sensor 20, in the present example a force feedback actuator 27 is attached to the steering column 21, which generates haptic feedback in a known manner as a function of steering forces occurring at the steering wheel 10. The steering forces can be determined in particular by the steering control device 29 and sent to the force feedback actuator 27 (indicated by the arrow between the steering control device 29 and the force feedback actuator 27).In addition, the steering controller 29 receives an actual steering angle value from the position sensor 60 to control the steering angle based on a comparison between the target steering angle value and the actual steering angle value (indicated by the arrow between the position sensor 60 and the steering controller 29). For this purpose, the position sensor 60 can be arranged, for example, on / in the steering cylinder 75 and determine the actual steering angle value, for example, on the basis of a measured position of the steering cylinder 75.In the event of a failure of the hydraulic pump 40, the electric actuator 29 aof the steering control device 29 can drive the steering assembly 50 for carrying out an emergency steering pump functionality in order to convey hydraulic fluid to the steering cylinder 75 for operation thereof. Therefore, a separate emergency steering pump 25 and a priority valve 26 can be dispensed with. Furthermore, no separate hydraulic circuit is required for automatically steering the vehicle, as will be clear from FIG. 2.FIG. 3 schematically shows a second exemplary embodiment of the electrohydraulic steering system 1 b, in which the vehicle controller 22 forms / comprises the steering angle sensor 150 and transmits a steering angle setpoint value to the steering control device 29 for automatic steering of the vehicle (indicated by the arrow between the vehicle controller 22 and the steering control device 29). In this case, e.g. the (in any case only optional) force feedback actuator 27 can be omitted, since no feedback about the steering forces to the steering wheel 10 is required, but all other components of the electrohydraulic steering system 1 bare identical to that shown in FIG. 2.It is clear that by using the steering control device 29, the steering cylinder 75 can also be actuated by the steering unit 50 in the case of automatic steering. Therefore, no bypass valve 24 with a corresponding bypass control 22 is necessary, and the flexible lines 54 a, 55 acan likewise be omitted.It is understood that the first and second embodiments may be combined so that a steering angle target value may be transmitted from the vehicle controller 22 to the steering control device 29 both by means of the actuator 10 and the steering angle sensor 20 and automatically.FIG. 4 schematically shows a third exemplary embodiment of the electrohydraulic steering system 1 c, which enables increased fault safety by using redundant components.In this embodiment, the steering wheel 10, as well as a first steering angle sensor 20- 1 and a second steering angle sensor 20- 2 mounted on the steering column 21 connected to the steering wheel 10, constitute the steering angle sensor 150. The first and second steering angle sensors 20- 1, 20- 2 are connected to first and second control units 201- 1, 201- 2 of the steering control device 29 via a first signal line 200- 1 and a second signal line 200- 2, respectively. In particular, the first and second signal lines 200- 1, 200- 2 can each be a CAN bus (controller area network). In this case, a steering angle setpoint value determined by means of the first steering angle sensor 20- 1 can be sent to the respective control unit 201- 1, 201- 2 via the first CAN bus 200- 1 and a steering angle setpoint value determined by means of the second steering angle sensor 20- 2 via the second CAN bus 200- 2. It is also possible for further variables determined by means of the first and second steering angle sensors 20- 1, 20- 2, such as steering angle speed and / or steering angle acceleration, to be transmitted via the first and second CAN buses 200- 1, 200- 2 to the first and second control units 201- 1, 201- 2. Alternatively or additionally, the vehicle controller 22 shown in FIG. 2 can serve as a steering angle sensor 150 in that, for example, a driver assistance function is contained therein which specifies a steering angle setpoint value.An actual steering angle value is sent from the position sensor 60 to each of the two control units 201- 1, 201- 2 of the steering control device 29 in the present case, so that a regulation of the steering angle is still possible even in the event of failure of one of the two control units 201- 1, 201- 2.In the present exemplary embodiment, the steering control device 29 comprises, in addition to the two control units 201- 1, 201- 2, the electric actuator 29 a, which in turn has a first and a second drive 202- 1, 202- 2, wherein the first drive 202- 1 is actuated by the first control unit 201- 1 and the second drive 202- 2 is actuated by the second control unit 201- 2. The first and second drives 202- 1, 202- 2 may be, in particular, electric motors 202- 1, 202- 2.In normal operation, for example, one of the two branches 20- 1 to 202- 1 can be used, and if this branch fails, it is switched over to the other branch 20- 2 to 202- 2.A signal connection (indicated by the two arrows between the two control units 201- 1, 201- 2) exists between the first and second control units 201- 1, 201- 2, which signal connection makes it possible, for example, to monitor each other and / or to detect a failure of a branch.In order to supply voltage to all electrical components of the electrohydraulic steering system 1 aaccording to the exemplary embodiment shown, said system comprises two voltage sources 250- 1, 250- 2, each of which is capable of supplying the electrical components with sufficient voltage / current. Thus, a function of the electrical components (steering angle sensors 20- 1, 20- 2, control units 201- 1, 201- 2, drives 202- 1, 202- 2, etc.) is also given in the event of failure of one of the two voltage sources 250- 1, 250- 2.The first and second drives 202- 1, 202- 2 in the present case have a common output element 222, which can be a common output shaft 222, for example. It is also possible for each of the two drives 202- 1, 202- 2 to have a separate output element 222. The output element 222 shown is connected to the mechanical transmission 28 which, in turn, can engage with an input element (not shown) of the steering assembly 50 in order to actuate the latter in such a way that the steering angle setpoint value determined by the steering angle sensors 20- 1, 20- 2 is set by means of the steering cylinder 75. A drive power of each individual one of the two drives 202- 1, 202- 2 may be sufficient in particular to actuate the steering assembly 50 and an emergency steering pump functionality contained therein. This ensures that the steering assembly can still be actuated by the other even in the event of failure of one drive 202- 1, 202- 2.It becomes clear that in the present exemplary embodiment all electrical components and lines of the electrohydraulic steering system 1 care designed to be redundant, so that an increased reliability is provided even without a mechanical connection between actuating element 10 and steering assembly 50.

Claims

An electrohydraulic steering system (1a, 1b, 1c) for a vehicle comprising - a steering angle transmitter (150); - a steering control device (29) which is connected signal-wise to the steering angle transmitter (150); - a steering cylinder (75) which is connected to one or more wheels (70) of the vehicle; and - a steering assembly (50) which is mechanically connected to the steering control device (29) and hydraulically connected to the steering cylinder (75), wherein the steering control device (29) comprises an electric actuator (29a) which is configured to actuate the steering assembly (50) based on a steering angle setpoint value received from the steering angle transmitter (150) in order to set a steering angle of the vehicle.The electro-hydraulic steering system (1a, 1b, 1c) of claim 1, further comprising a hydraulic pump (40) for providing the hydraulic energy for operating the steering cylinder (75).The electrohydraulic steering system (1a, 1b, 1c) according to claim 1 or 2, wherein the steering angle sensor (150) comprises an actuator (10) and at least one steering angle sensor (20).The electro-hydraulic steering system (1a, 1b, 1c) of claim 3, wherein the actuator (10) is not mechanically coupled to the steering assembly (50).The electro-hydraulic steering system (1a, 1b, 1c) of any preceding claim, wherein the steering angle sensor (150) is included in a controller (22) of the vehicle.Electrohydraulic steering system (1a, 1b, 1c) according to one of the preceding claims, wherein the steering control device (29) comprises a first control unit (201-1) and a second control unit (201-2), and wherein the first control unit (201-1) is connected to the steering angle sensor (150) by means of a first signal line (200-1) and the second control unit (201-2) is connected to the steering angle sensor (150) by means of a second signal line (200-2).Electrohydraulic steering system (1a, 1b, 1c) according to Claim 5, wherein the electric actuator (29a) of the steering control device (29) comprises a first drive (202-1) and a second drive (202-2) and an output element (222) which is connected to the first drive (202-1) and / or to the second drive (202-2), and wherein the first and the second control unit (201-1, 201-2) are configured to control the first and / or the second drive (202-1, 202-2) of the electric actuator (29a).Electrohydraulic steering system (1a, 1b, 1c) according to one of the preceding claims, wherein a mechanical transmission (28) is arranged between the steering control device (29) and the steering assembly (50), which transmission is connected on the one hand to the output element (222) of the electric actuator (29a) of the steering control device (29) and on the other hand to an input element of the steering assembly (50).Electrohydraulic steering system (1a, 1b, 1c) according to one of the preceding claims, wherein the steering control device (29) and / or the steering assembly (50) are configured to operate the steering cylinder (75), in particular in an emergency steering operation.Electrohydraulic steering system (1a, 1b, 1c) according to one of the preceding claims, further comprising a position sensor (60) for determining an actual steering angle value.A vehicle comprising an electro-hydraulic steering system (1a, 1b, 1c) according to any of the preceding claims.

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