METHOD FOR OPERATING A HYDROSTATIC VEHICLE STEERING SYSTEM

Description

[0001] The invention relates to a method for operating a hydrostatic vehicle steering system.

[0002] The use of hydrostatic vehicle steering systems allows for comfortable steering of even heavy commercial vehicles, such as agricultural tractors, but also other vehicles from the agricultural, forestry or construction machinery sector.

[0003] In its basic design, such a hydrostatic vehicle steering system comprises a steering handle designed as a steering wheel. This handle rotates a steering metering valve in the form of an orbitrol, which is supplied with pressurized hydraulic fluid from a high-pressure hydraulic pump. This orbitrol then actuates a connected steering cylinder to adjust the vehicle's steerable wheels. The orbitrol's function is limited to regulating the hydraulic flow towards the steering cylinder, while the high-pressure hydraulic pump provides the hydraulic pressure, and thus the hydraulic energy. In this way, sufficient steering forces can be generated, even for heavy vehicles.

[0004] In addition, steering assistance systems are becoming increasingly important, as are known primarily from the automotive sector, for example, to support the driver in staying within a predetermined lane. In the latter case, haptically perceptible operating or hand torques are usually transmitted to a steering column connected to a steering wheel, in such a way that the driver receives an unambiguous indication of the direction of any necessary steering correction.

[0005] Unlike steering systems used in automobiles, hydrostatic vehicle steering systems do not have a mechanical linkage between the steering wheel and the steerable wheels. This, in turn, leads to special considerations when such a hydrostatic steering system is to be operated in conjunction with various steering assistance systems.

[0006] The features of the generic term "independent claim" are disclosed in document EP2896547A1.

[0007] The object of the present invention is therefore to provide a method for operating a hydrostatic vehicle steering system that is optimized for use with different steering assistance systems.

[0008] This problem is solved by a method for operating a hydrostatic vehicle steering system with the features of claim 1.

[0009] Advantageous further developments of the method according to the invention are set out in the dependent claims.

[0010] In the method for operating a hydrostatic vehicle steering system, the steering system comprises an input shaft rotatable by means of a steering handle, an output shaft for rotary actuation of a steering metering valve which serves for the hydraulic control of a steering cylinder interacting with steerable vehicle wheels, a coupling device for establishing a detachable rotary connection between the input and output shafts, and an actuator for applying a predetermined steering torque to the output shaft. In a first operating mode intended for manual steering operation, the coupling device automatically assumes a closed clutch position under the action of a restoring spring force. In a second operating mode intended for autonomous steering operation, it is moved into an open clutch position at the instigation of a control unit, against the action of the restoring spring force.

[0011] In the first operating mode, intended for manual steering, steering inputs are made by an operator via the steering handle, which is typically designed as a steering wheel. In this mode, the actuator, through a targeted application of a corresponding steering torque to the output shaft and thus to the input shaft (which is rotaryally connected to it via the coupling device), generates a haptically perceptible actuation or hand torque at the steering handle in a "feedback assistance mode" controlled by the control unit. This serves, for example, to (i) indicate a steering correction to be made via the steering handle, (ii) provide feedback on steering torques acting on the steerable vehicle wheels due to driving conditions, and / or (iii) generate steering resistance dependent on the steering angle and, if applicable, other parameters. Conversely, it is also possible to use a control unit in a mode that... "Emergency Assistance Mode"In the event of a hydraulic failure of the hydrostatic vehicle steering system, active power steering assistance can be implemented. The steering torque generated by the actuator can be detected by a torque sensor assigned to the output shaft and fed back to the control unit to form a control loop.

[0012] In other words, in the first operating mode, the actuator is preferentially controlled by the control unit in the sense of providing haptically perceptible steering feedback and / or reducing the steering forces required by the operator.

[0013] The second operating mode, however, is reserved for autonomous steering operation. In this mode, the actuator can be controlled by the control unit according to steering commands issued by an autonomous vehicle control system, for example, according to a trajectory to be followed by the vehicle. The separation of the rotary connection between the input and output shafts, achieved by opening the coupling device, ensures in such a mode "Driving assistance mode", that the steering handle does not move in a manner that is disruptive to the operator. The steering handle can be fixed in place by means of a passive or control unit-activated braking element to prevent free rotation of the input shaft in the second operating mode.

[0014] The aforementioned driving assistance mode can be implemented in agricultural tractors from the manufacturer John Deere, for example, through the use of a so-called AutoTrac steering system.

[0015] It should also be noted that the vehicle steering system is designed to be fail-safe, as the clutch mechanism automatically returns to its first operating mode, intended for manual steering, in the event of a malfunction, due to the restoring spring force. This ensures that the operator can steer the vehicle even under such circumstances.

[0016] As a result, the inventive method for operating a hydrostatic vehicle steering system allows the requirements of different steering assistance systems that use the actuator to be met.

[0017] The actuator is, for example, an electric geared motor controlled by the control unit. It is conceivable that a slip clutch or similar device is integrated into the geared motor, allowing the operator, in the first operating mode, to influence the vehicle's steering at any time by turning the steering handle and thus the steering metering valve, regardless of the actuator's operating state. Alternatively, the motor torque of the geared motor could be limited to a value that the operator can overcome via the steering handle, or a device for switching off the geared motor could be provided for this purpose.

[0018] To ensure that the operator always retains control over the vehicle's steering, the clutch unit can also switch from the second operating mode to the first operating mode in the event of manual steering input via the steering handle and / or a pressure drop in the hydraulic supply for the steering metering valve. The latter corresponds to the emergency assist mode intended for a failure of the hydrostatic steering system's hydraulic supply. In this case, the control unit can automatically switch to the first operating mode, receiving signals from an angle sensor that detects rotation at the steering handle or the steering system's input shaft.evaluates a pressure sensor for monitoring the delivery pressure of a high-pressure hydraulic pump encompassed by the hydraulic source.

[0019] According to the invention, the coupling device is moved into the open coupling position upon initiation of a switching signal generated by an actuating arrangement only if the first and second release signals transmitted by the control unit are simultaneously present at the actuating arrangement. The AND gate thus formed largely prevents the rotary connection established between the input and output shafts by means of the coupling device from being unintentionally disconnected.

[0020] Initially, it is conceivable that the coupling device is electrically actuated, whereby, in the de-energized state, it automatically assumes the closed coupling position under the action of a restoring spring force of an electrically controlled switching mechanism. The actuating arrangement could comprise a series connection of first and second electrical normally closed contacts, which, upon the activation of the first and second release signals, are moved to a closed position to generate an electrical switching signal that controls the switching mechanism. These electrical normally closed contacts, particularly those designed as components of associated relays, are characterized by the fact that, in the unactuated state, they automatically assume an open position under the action of a restoring spring force.This enables a failsafe function that ensures the coupling device remains in its closed position in the event of a failure of one of the two relays or a faulty trigger signal. The coupling device only moves to its open position if both normally closed contacts simultaneously close and the output electrical switching signal reaches a voltage value suitable for actuating the coupling device or the switching mechanism. The relays can be electromechanical or semiconductor.

[0021] Alternatively, the function described above can also be implemented if the coupling device is hydraulically pressure-actuated, whereby, in a pressureless state, it automatically assumes the closed coupling position under the action of a restoring spring force of a hydraulically controlled switching mechanism. For this purpose, the actuating arrangement can comprise a parallel connection of first and second hydraulic 3 / 2-way valves, whose valve outlets are connected to each other. To generate a hydraulic switching signal that controls the switching mechanism, these valves are moved from a rest position connecting the valve outlets to a hydraulic reservoir to an operating position connecting the valve outlets to the hydraulic source upon the initiation of the first and second release signals.If one of the two 3 / 2-way valves is in its rest position, pressure build-up at the valve outlets is prevented due to the pressure relief connection to the hydraulic reservoir. This also implements a failsafe function, ensuring that the coupling remains in its closed position in the event of a failure of one of the two 3 / 2-way valves or a faulty release signal.

[0022] As a result, the coupling device is only moved into its open coupling position if both 3 / 2-way valves are simultaneously in their operating position and the hydraulic switching signal applied to the valve outlets assumes a pressure value suitable for actuating the coupling device or the switching mechanism.

[0023] The actual actuation of the relays or the 3 / 2-way valves by the control unit is preferably carried out electrically, in the latter case by using a corresponding solenoid.

[0024] The inventive method for operating a hydrostatic vehicle steering system is explained in more detail below with reference to the accompanying drawings. Identical reference numerals refer to components that are identical or comparable in function. The drawings show: Fig. 1 shows a first embodiment of a hydrostatic vehicle steering system operated by means of the method according to the invention in a first operating mode, Fig. 2 shows the embodiment in Fig. 1 hydrostatic vehicle steering in a second operating mode, Fig. 3, one of the in Fig. 1The failsafe function of the hydrostatic vehicle steering system shown in Fig. 4, a second embodiment of a hydrostatic vehicle steering system operated by means of the method according to the invention in a first operating mode, Fig. 5, which is shown in Fig. 4 The hydrostatic vehicle steering system is shown in a second operating mode, and Fig. 6 shows one of the hydrostatic vehicle steering systems in a second operating mode. Fig. 4 The failsafe function is implemented in the hydrostatic vehicle steering system.

[0025] Figs. 1 to 3 Figure 1 shows a first embodiment of a hydrostatic vehicle steering system 10 operated by means of the method according to the invention in a vehicle designed as an agricultural tractor 12. Various operating states are shown, wherein the implementation of the method according to the invention is the responsibility of a microprocessor-controlled control unit 14, which is also part of the vehicle steering system 10.

[0026] The use in an agricultural tractor 12 is merely exemplary; it could just as easily be another vehicle from the agricultural, forestry or construction machinery sector.

[0027] As in Fig. 1As can be seen, the hydrostatic vehicle steering system 10 housed in the agricultural tractor 12 (not shown in detail) comprises an input shaft 18 rotatable by means of a steering handle 16, an output shaft 20 for rotary actuation of a steering metering valve 22, which is supplied with pressurized hydraulic fluid from a hydraulic source 24 and serves for the hydraulic control of a steering cylinder 28 that interacts with steerable vehicle wheels 26, a coupling device 30 for establishing a detachable rotary connection between the input and output shafts 18, 20, and an actuator 32 for applying a predefinable steering torque to the output shaft 20. The steering handle 16 is, for example, a conventional steering wheel 34.

[0028] The function of the steering metering valve 22, designed as an orbitrol 36, is limited to adjusting the hydraulic flow towards the steering cylinder 28, whereas the hydraulic pressure, and thus the hydraulic energy, is supplied by the hydraulic source 24, designed as a high-pressure hydraulic pump 38. The high-pressure hydraulic pump 38 is driven by a drive motor 40, in this case a diesel engine of the agricultural tractor 12.

[0029] According to the in Figs. 1 to 3 In the first embodiment of the vehicle steering system 10 shown, the clutch assembly 30 is hydraulically pressure-actuated, and in a pressureless state, it automatically assumes a closed clutch position under the action of a restoring spring force of a hydraulically controlled switching mechanism 42. This state corresponds to a Fig. 1The first operating mode of the clutch device 30, intended for manual steering operation, is shown, in which the input shaft 18 and output shaft 20 are rotationally fixed to each other, so that a rotation of the steering handle 16 and thus of the steering metering valve 22 is directly translated into a corresponding deflection of the steering cylinder 28. In addition, in Fig. 2 A second operating mode intended for autonomous steering operation is shown, in which the clutch device 30 is moved into an open clutch position at the instigation of the control unit 14 against the effect of the restoring spring force of the switching mechanism 42.

[0030] The actuator 32 is an electric geared motor 44 that can be controlled by the control unit 14.

[0031] The geared motor 44 incorporates a (not shown) slip clutch, which allows the operator to influence the vehicle steering 10 at any time in the first operating mode, regardless of the respective operating state of the actuator 32, by turning the steering handle 16 and thus the steering metering valve 22.

[0032] In the case of the first operating mode intended for manual steering operation according to Fig. 1 Steering inputs are made via the steering handle 16 on the operator side. Here, by means of the actuator 32, a corresponding steering torque is applied to the output shaft 20 and thus to the input shaft 18, which is in rotary connection with it via the coupling device 30, in a manner controlled by the control unit 14. "Feedback Assistance Mode"a haptically perceptible actuation or hand torque at the steering handle 16 in order to (i) indicate a driving direction correction to be made via the steering handle 16, (ii) provide feedback on steering torques acting on the steerable vehicle wheels 26 due to driving conditions, and / or (iii) generate steering resistance that depends on the steering angle and, if applicable, other parameters. On the other hand, it is also possible to perform a function carried out by the control unit 14. "Emergency Assistance Mode" In the event of a failure of the hydraulic supply to the hydrostatic vehicle steering system 10, in particular the hydraulic high-pressure pump 38, active power steering assistance is provided. The steering torque generated by the actuator 32 is detected by means of a torque sensor 46 assigned to the output shaft 20 and fed back to the control unit 14 to form a control loop.

[0033] The feedback assistance modes (i), (ii) or (iii) are assigned to respective steering assistance systems, the selection of which is made by the operator via a user interface 48 connected to the control unit 14, in this case a touch-sensitive display 50. The feedback assistance mode (iii) corresponds to a so-called parameter steering system, in which an increasing actuation resistance with the steering angle as well as its modification depending on the vehicle speed can be implemented.

[0034] If, however, the coupling device 30 is in the second operating mode reserved for carrying out autonomous steering operation according to Fig. 2The actuator 32 is controlled by the control unit 14 according to steering commands specified by an autonomous vehicle control system 52, for example, according to a track trajectory to be followed by the agricultural tractor 12. The separation of the rotary connection between the input and output shafts 18, 20 by opening the coupling device 30 ensures in such a case "Driving assistance mode", that the steering handle 16 does not move in a manner that is disruptive to the operator. Meanwhile, the steering handle 16 is fixed in such a way that free rotation of the input shaft 18 is inhibited in the second operating mode by means of a brake element 54 actuated by the control unit 14. The selection of the driving assistance mode is made by the operator via the user interface 48, which communicates with the control unit 14.

[0035] An actuating arrangement 56 serves to actuate the clutch device 30 or the switching mechanism 42 and thus to switch from the first to the second operating mode. This arrangement comprises a parallel connection of first and second hydraulic 3 / 2-way valves 58, 60, whose valve outlets 62, 64 are connected to each other. The two 3 / 2-way valves 58, 60 can be opened from a rest position A connecting the valve outlets 62, 64 to a hydraulic reservoir 66 (see Figure 1) to generate a hydraulic switching signal ctrl_h that controls the switching mechanism 42. This switching signal is triggered by a first and second release signal init_1, init_2 transmitted by the control unit 14. Fig. 1 ) to an operating position B connecting the valve outlets 62, 64 with the hydraulic source 24 or the hydraulic high-pressure pump 38 (see Fig. 2When both 3 / 2-way valves 58, 60 are in their operating position B, the delivery pressure p_feed generated by the hydraulic high-pressure pump 38 is present at the valve outlets 62, 64. This pressure is used to actuate the switching mechanism 42, so that the coupling device 30 is forced into its open coupling position.

[0036] If one of the two 3 / 2-way valves 58, 60 is in its rest position A, pressure build-up at the valve outlets 62, 64 is prevented due to the pressure relief connection with the hydraulic reservoir 66. This situation is in Fig. 3 shown, in which a failsafe function is implemented which, in the event of a failure of one of the two 3 / 2-way valves 58, 60 or faulty release signals init_1, init_2, ensures that the coupling device 30 remains in its closed coupling position.

[0037] As a result, the coupling device 30 is only moved into its open coupling position if both 3 / 2-way valves 58, 60 are simultaneously in their operating position B and the hydraulic switching signal ctrl_h applied to the valve outlets 62, 64 assumes a pressure value suitable for actuating the coupling device 30 or the switching mechanism 42, here that of the delivery pressure p_feed.

[0038] This creates an AND gate between the two trigger signals init_1, init_2, which largely prevents the rotary connection created between input and output shafts 18, 20 by means of the coupling device 30 from being unintentionally disconnected.

[0039] The actual actuation of the 3 / 2-way valves 58, 60 by the trigger signals init_1, init_2 transmitted by the control unit 14 is carried out electrically, in this case by using a respective associated solenoid 68, 70.

[0040] To ensure that the operator always retains control over the vehicle steering 10, the clutch device 30 switches from the second operating mode to the first operating mode in the event of manual steering input via the steering handle 16 and / or a pressure drop in the hydraulic source 24 or high-pressure hydraulic pump 38 supplying the steering metering valve 22. The latter corresponds to the emergency assist mode intended for a failure of the hydraulic supply to the vehicle steering 10. In this case, the switch to the first operating mode is carried out automatically by the control unit 14, which evaluates the signals from an angle sensor 72 to detect rotation occurring at the steering handle 16 or the input shaft 18 of the vehicle steering 10, and from a pressure sensor 74 to monitor the delivery pressure p_feed of the high-pressure hydraulic pump 38.

[0041] In Figs. 4 to 6A second embodiment of a hydrostatic vehicle steering system 10 operated by means of the method according to the invention is shown. This differs from the first embodiment only with regard to the design of the actuating arrangement 56. Thus, the clutch device 30 is electrically actuated in this case, wherein it is designed according to Fig. 4 In the unenergized state, the clutch automatically assumes the closed position under the action of a restoring spring force of an electrically controlled switching mechanism 76. Regarding the implementation of the various (assistance) modes, reference is therefore made to the description of the first embodiment.

[0042] By way of example, the actuating arrangement 56 comprises a series connection of first and second electrical normally closed contacts 78, 80. These can be moved to a closed position to generate an electrical switching signal ctrl_e that controls the switching mechanism 76, upon instigation of a first and second release signal init_1, init_2 transmitted by the control unit 14. The electrical normally closed contacts 78, 80, which are designed here as components of associated relays 82, 84, are characterized in that, in the unactuated state, they automatically assume an open position under the influence of a restoring spring force. This also allows, in the case of the second embodiment, a Fig. 6 The illustrated failsafe function is implemented, which ensures that in the event of a failure of one of the two relays 82, 84 or faulty trigger signals init_1, init_2, the coupling device 30 remains in its closed coupling position.

[0043] According to Fig. 5 The clutch device 30 is only moved into its open clutch position if both closing contacts 78, 80 simultaneously assume their closed position and the electrical switching signal ctrl_e applied on the output side assumes a voltage value +Vss (corresponding to the on-board voltage of the agricultural tractor 12) suitable for actuating the clutch device 30 or the switching mechanism 76.

[0044] The AND gate formed in this way between the two trigger signals init_1, init_2 largely prevents the rotary connection established between input and output shafts 18, 20 by means of the coupling device 30 from being unintentionally separated.

Claims

1. Method for operating a hydrostatic vehicle steering system that comprises an input shaft (18), which can be rotationally operated by means of a steering handle (16); an output shaft (20) for rotary operation of a steering dosing valve (22), which is used for hydraulic actuation of a steering cylinder (28) interacting with steerable vehicle wheels (26); a clutch device (30) for establishing a releasable rotary connection between the input shaft (18) and the output shaft (20); and an actuating drive (32) for applying a predefinable steering torque to the output shaft (20), wherein the clutch device (30) automatically assumes a closed clutch position under the effect of a restoring spring force in a first operating mode intended for manual steering operation and is brought into an open clutch position counter to the effect of the restoring spring force at the prompting of a control unit (14) in a second operating mode intended for autonomous steering operation, characterized in that the clutch device (30) is brought into the open clutch position, at the prompting of a switchover signal that can be generated by means of an operating arrangement (56), only when first and second trigger signals transmitted by the control unit (14) are present at the operating arrangement (56) at the same time.

2. Method according to Claim 1, characterized in that, in the first operating mode, the actuating drive (32) is actuated by the control unit (14) in the sense of haptically perceivable steering feedback and / or a reduction in steering operation forces to be applied by the operator.

3. Method according to Claim 1 or 2, characterized in that, in the second operating mode, the actuating drive (32) is actuated by the control unit (14) according to steering commands predefined by an autonomous vehicle controller (52).

4. Method according to at least one of the preceding claims, characterized in that, in the second operating mode, a free rotation of the input shaft (18) is inhibited by means of a brake element (54) that is passive or can be operated by the control unit (14).

5. Method according to at least one of the preceding claims, characterized in that the actuating drive (32) is an electric gear motor (44) that can be actuated by the control unit (14).

6. Method according to at least one of the preceding claims, characterized in that the clutch device (30) is switched over into the first operating mode from the second operating mode in the event of a manual steering operation exerted via the steering handle (16) and / or a pressure drop of a hydraulic source (24) provided for feeding the steering dosing valve (22) with pressurized hydraulic fluid.

7. Method according to at least one of the preceding claims, characterized in that the clutch device (30) is electrically operated, wherein it automatically assumes the closed clutch position under the effect of a restoring spring force of an electrically controllable switchover mechanism (76) when in the non-energized state.

8. Method according to Claim 7, characterized in that the operating arrangement (56) comprises a series circuit of first and second electrical normally open contacts (78, 80), which are brought into a closed position at the prompting of the first and second trigger signals to generate an electrical switchover signal actuating the switchover mechanism (76).

9. Method according to at least one of the preceding claims, characterized in that the clutch device (30) is designed to be operated by hydraulic pressure, wherein it automatically assumes the closed clutch position under the effect of a restoring spring force of a hydraulically controllable switchover mechanism (42) when in the depressurized state.

10. Method according to Claim 9, characterized in that the operating arrangement (56) comprises a parallel circuit of first and second hydraulic 3 / 2-way valves (58, 60), the valve outlets (62, 64) of which are connected to one another, wherein these are transferred from a rest position connecting the valve outlets (62, 64) to a hydraulic reservoir (66) into an operating position connecting the valve outlets (62, 64) to a hydraulic source (24) at the prompting of the first and second trigger signals in order to generate a hydraulic switchover signal actuating the switchover mechanism (42) .