Hydraulic steering system for a mobile work machine

Abstract

The invention relates to a hydraulic steering device (1) for a mobile working machine, wherein the steering device (1) has a hydraulic pump (3) driven by a drive motor (2) which supplies a steering control valve (12) with pressure medium, wherein the steering control valve (12) can be actuated depending on the actuation of a steering encoder (25) and controls a steering actuator (15).An electronic control unit (60) controlling the drive motor (2) is provided, which is connected to a steering sensor device (61) that detects the actuation of the steering encoder (25) and to a steering actuator sensor device (70a; 70b) that detects at least the straight-ahead driving position of the steering actuator (15), wherein the electronic control unit (60) is configured to control the drive motor (2) of the hydraulic pump (3) on the basis of the signals from the steering sensor device (61) and the steering actuator sensor device (70a; 70b) such that when steering begins, whereby the steering encoder (25) is actuated, the drive motor (2) of the hydraulic pump (3) is switched on, and the drive motor (2) of the hydraulic pump (3) is only switched off again when at the same time the steering encoder (25) is in a neutral position and the steering actuator (15) is in the straight-ahead driving position.

Description

[0001] The invention relates to a hydraulic steering device for a mobile work machine, wherein the steering device has a hydraulic pump driven by a drive motor, which supplies a steering control valve with pressure medium, wherein the steering control valve can be actuated in dependence on the actuation of a steering sensor and controls a steering actuator.

[0002] In such hydraulic steering systems for mobile work machines, such as industrial trucks, the hydraulic pump supplies pressure fluid to the steering control valve and thus to the steering actuator controlled by the steering control valve. The steering actuator is formed, for example, by a hydraulic steering cylinder, which uses steering kinematics to control the steering angle of the steered wheel(s).

[0003] With such hydraulic steering systems for mobile work machines, it must be ensured that a sufficient pressure medium volume flow provided by the hydraulic pump is always available at the appropriate pressure so that any steering movements requested by the operator of the work machine by actuating the steering sensor can be carried out at any time.

[0004] For this purpose, it is known to permanently drive the drive motor of the hydraulic pump, which supplies the steering control valve and the steering actuator with pressure medium, at least at a minimum speed as soon as the working machine is moving in order to constantly ensure a sufficient supply to the hydraulic steering device. However, this results in the following disadvantages:

[0005] Due to the continuous operation of the hydraulic manifold at a minimum speed, a large portion of the energy is converted into heat as losses, since a significantly smaller amount of pressure fluid is often required for a steering movement than is delivered by the hydraulic pump at the minimum speed. Furthermore, unnecessary energy consumption occurs because the hydraulic pump delivers pressure fluid even when the steering mechanism is not actuated.

[0006] The operation of the hydraulic pump even when the steering system is not actuated leads to undesirable noise development from the pump unit consisting of the hydraulic pump and the drive motor, even though no hydraulic energy is required to supply the hydraulic steering system.

[0007] Operating the hydraulic pump even when the steering system is not actuated leads to additional wear on the hydraulic pump during the unnecessary pump running time.

[0008] The present invention is based on the object of providing a hydraulic steering device of the type mentioned at the outset which is improved with regard to the disadvantages mentioned.

[0009] This object is achieved according to the invention in that an electronic control device which controls the drive motor is provided and which is connected to a steering sensor device which detects the actuation of the steering sensor and to a steering actuator sensor device which detects at least the straight-ahead driving position of the steering actuator, wherein the electronic control device is designed to control the drive motor of the hydraulic pump based on the signals from the steering sensor device and the steering actuator sensor device in such a way that when steering begins, wherein the steering sensor is actuated, the drive motor of the hydraulic pump is switched on, and the drive motor of the hydraulic pump is only switched off again when the steering sensor is in a neutral position and the steering actuator is in the straight-ahead driving position at the same time.

[0010] In the steering system according to the invention, the control device thus switches on the drive motor of the hydraulic pump when the operator initiates a corresponding steering movement and thus initiates steering by actuating the steering sensor detected by the steering sensor device. After the drive motor is switched on, the hydraulic pump delivers a pressure fluid volume flow to supply the steering system. The drive motor of the hydraulic pump is left switched on by the control device and is only switched off again when the steering sensor is in a neutral position and the steering actuator is in the straight-ahead position detected by the steering actuator sensor device.A steering sensor in the neutral position and a steering actuator in the straight-ahead position can be detected by the control device as the end of the operator's steering movement request and thus as the end of a steering movement, which leads to the shutdown of the drive motor of the hydraulic pump. With the inventive control of the drive motor of the hydraulic pump, the control device thus considers the operator's steering movement request and thus the steering movement as not completed as long as the steering actuator has not returned to its straight-ahead position, whereby the drive motor of the hydraulic pump remains switched on and continues to run even when the steering sensor actuated from the neutral position is no longer actuated and thus the steering sensor sensor device no longer detects any movement of the steering sensor.

[0011] In mobile work machines, such as industrial trucks, there are many operating conditions, such as driving in long curves, in which the steering sensor detects a rotational movement of the steering sensor but cannot detect that the operator's steering movement has actually been completed. If the hydraulic pump drive motor were to be switched off in such an operating condition, in which the steering sensor actuated from the neutral position is no longer actuated, the switching off of the hydraulic pump drive motor would lead to a sudden increase in the operating force on the steering sensor, resulting in a loss of comfort for the operator and suggesting to the operator that the steering system is defective.With the control of the drive motor of the hydraulic pump according to the invention, the drive motor remains switched on in such an operating state, wherein the steering sensor actuated from the neutral position is no longer actuated, so that with the control of the drive motor of the hydraulic pump according to the invention by the control device, energy savings can be achieved because the hydraulic pump only runs when steering is taking place, whereby a hard point in the steering due to a sudden increase in operating force and the associated loss of comfort for the operator is avoided.

[0012] According to an advantageous embodiment of the invention, the steering sensor device detects the rotational position and / or a rotational speed of the steering sensor. Preferably, the steering sensor device detects a rotational speed of the steering sensor and the change in the absolute position of the steering sensor.

[0013] According to an advantageous embodiment of the invention, the electronic control device is designed to control the speed of the drive motor as a function of the rotational speed of the steering sensor. This leads to the advantage that the drive motor's speed can be controlled in such a way that the hydraulic pump delivers the required volume flow of the steering device as needed.

[0014] According to an advantageous embodiment of the invention, the steering sensor is connected to the steering control valve via a steering column for actuating the latter, with the steering sensor sensor device being designed as a steering column sensor. A steering column sensor can easily detect the actuation and thus the rotational position and / or rotational speed of the steering sensor.

[0015] According to an advantageous embodiment of the invention, the drive motor is designed as an electric motor. A drive motor designed as an electric motor can be easily controlled by the control device and thus switched on and off.

[0016] According to an advantageous embodiment of the invention, a pressure fluid accumulator is connected to a delivery line of the hydraulic pump. With such a pressure fluid accumulator connected to the delivery line of the hydraulic pump, the time until the hydraulic pump must start running when the drive motor is switched on can be extended, thus ensuring a constant supply of pressure fluid to the steering system. A further advantage of such a pressure fluid accumulator is that, with an appropriate design of the pressure fluid accumulator, the hydraulic pump does not have to start up for very small steering movements, for example, steering corrections in the straight-ahead position.

[0017] The invention further relates to a mobile work machine, in particular an industrial truck, with a hydraulic steering device according to the invention as described above.

[0018] According to an advantageous embodiment of the invention, the work machine has a battery-electric drive system. In a work machine with a battery-electric drive system, the energy savings achieved by switching the drive motor of the hydraulic pump of the steering device on and off according to the invention can extend the operating time of the work machine with one battery charge of a traction battery of the battery-electric drive system.

[0019] According to an advantageous embodiment of the invention, the hydraulic pump additionally supplies a working hydraulic system of the drive machine with pressure fluid, with a priority valve being provided for preferentially supplying the steering system with pressure fluid. If the hydraulic pump supplies the steering system and the working hydraulic system with pressure fluid, the hydraulic pump has a larger delivery volume than a hydraulic pump that only supplies the steering system. Thus, significant energy savings can be achieved by switching the drive motor of the hydraulic pump that supplies the steering system and the working hydraulic system with pressure fluid.

[0020] The invention has a number of advantages.

[0021] Since in the steering device according to the invention the drive motor and thus the hydraulic pump can be switched off as long as the operator of the work machine does not wish to carry out a steering movement, and only needs to be switched on and operated when a steering movement is to be carried out and a pressure medium volume flow is required for steering, a low energy consumption of the steering device is achieved.

[0022] In addition, in the steering device according to the invention, reduced operating times of the hydraulic pump are achieved by switching off the drive motor and thus the hydraulic pump, whereby reduced heating of the pressure medium of the hydraulic system can be achieved, the noise development of the pump unit consisting of the hydraulic pump and the drive motor can be reduced and the wear of the hydraulic pump can be reduced and thus the service life of the hydraulic pump in relation to the operating time of the work machine can be increased.

[0023] Further advantages and details of the invention are explained in more detail with reference to the embodiment shown in the schematic figure.

[0024] The figure shows a circuit diagram of a hydraulic steering device 1 according to the invention for a mobile work machine. The mobile work machine is designed, in particular, as an industrial truck. In particular, the mobile work machine is designed as a battery-powered work machine, for example, as a battery-powered industrial truck.

[0025] The hydraulic steering device 1 has a hydraulic pump 3 driven by a drive motor 2. The hydraulic pump 3 is operated in an open circuit and draws pressure fluid from a reservoir 5 on a suction side via a suction line 4 and conveys the pressure fluid into a delivery line 6, which is connected to a delivery side of the hydraulic pump 3.

[0026] In the illustrated embodiment, the drive motor 2 is designed as an electric motor. The hydraulic pump 3 is designed as a fixed-displacement pump in the illustrated embodiments.

[0027] The hydraulic pump 3 serves to supply the hydraulic steering device 1 with pressure medium.

[0028] In the illustrated embodiment, the hydraulic pump 3 also serves to supply a working hydraulic system 10 of the mobile work machine with pressure fluid. In a work machine designed as an industrial truck, the working hydraulic system 10 comprises several hydraulic consumers, for example, a lifting drive for a load-handling device, a tilt drive for a mast, and, in corresponding variants, one or more additional consumers, for example, a sideshift device for the load-handling device.

[0029] A priority valve 11 is arranged in the delivery line 6 for the preferential supply of the steering device 1. The priority valve 11 is connected on the inlet side to the delivery line 6 of the hydraulic pump 3 at a port P. On the outlet side, a supply line 13 of the steering device 1, which is primarily supplied with pressure medium, is connected to the priority valve 11 at a port CF and leads to a port P of a steering control valve 12 of the steering device 1. On the outlet side, a supply line 14 leading to the working hydraulics 10 is also connected to the priority valve 11 at a port EF.

[0030] The priority valve 11 has a first control position 11a, in which the delivery line 6 is connected to the supply line 13 and the connection between the delivery line 6 and the supply line 14 is blocked. The priority valve 11 has a second control position 11b, in which the delivery line 6 is connected to the supply line 14 and the connection between the delivery line 6 and the supply line 13 is blocked. In an intermediate position 11c, the delivery line 6 is connected to the supply line 13 and the supply line 14.

[0031] The priority valve 11 is actuated by the pressure present in the supply line 13 in the direction of the second control position 11b. For this purpose, a control line 23 is connected to a control pressure surface of the priority valve 11 acting in the direction of the second control position 11b, which is connected to the supply line 13. A throttle device, for example, an orifice plate, is arranged in the control line 23.

[0032] The priority valve 11 is actuated in the direction of the first control position 11a by a spring device 20 and the pressure present in a load pressure signaling line 21 of the steering system 1. For this purpose, the load pressure signaling line 21 is connected to a control pressure surface of the priority valve 11 acting in the direction of the first control position 11a. A throttle device, for example, an orifice plate, is arranged in the load pressure signaling line 21.

[0033] The load pressure signaling line 21 is further connected to the supply line 13 via a control line 22. The control line 22 is connected to the load pressure signaling line 21 between the throttle device and the control pressure surface. A further throttle device, for example, an orifice plate, is arranged in the control line 22.

[0034] In the illustrated embodiment, the steering control valve 12 is designed as a steering orbitrol. The steering control valve 11 is manually operated in the illustrated embodiment and is connected to a steering sensor 25, for example, a steering wheel operated by an operator of the work machine.

[0035] The steering control valve 12 controls a steering actuator 15.

[0036] The steering control valve 12 is connected to the supply line 13, to a first pressure medium line 16a leading to the steering actuator 15, to a second pressure medium line 16b leading to the steering actuator 15, and to a tank line 17 leading to the tank 5. The tank line 17 is connected to a tank connection T of the steering control valve 12.

[0037] In the illustrated embodiment, the steering actuator 15 is designed as a double-acting hydraulic steering cylinder 30, which is configured as a double-acting cylinder. The steering cylinder 30 has a first control pressure chamber 30a and a second control pressure chamber 30b. The first control pressure chamber 30a is connected to the steering control valve 12 via the first pressure medium line 16a, and the second control pressure chamber 30b is connected via the second pressure medium line 16b.

[0038] Furthermore, the steering control valve 12 is connected to the load pressure signaling line 21.

[0039] The load pressure of the steering device 1 present in the load pressure signaling line 21, which is reported in the load pressure signaling line 21, is tapped in the steering control valve 12.

[0040] In the illustrated neutral position, which corresponds to a straight-ahead driving position of the steering sensor 25, in which the steering control valve 12 is not actuated by the steering sensor 25 and the supply line 13 and the pressure medium lines 16a, 16b are shut off, the steering control valve 12 connects the load pressure signaling line 21 to the reservoir line 17.

[0041] When the steering control valve 12 is actuated by the steering sensor 25 in a first direction of rotation in response to a corresponding steering request, the steering control valve 12 controls a hydraulic control path from the supply line 13 to the pressure medium line 16a and from the pressure medium line 16b to the reservoir line 17. The load pressure signal line 21 is connected to the pressure medium line 16a for tapping the load pressure in the steering control valve 12. When the steering control valve 12 is actuated by the steering sensor 25 in an opposite second direction of rotation in response to a corresponding steering request, the steering control valve 12 controls a hydraulic control path from the supply line 13 to the pressure medium line 16b and from the pressure medium line 16b to the reservoir line 17. The load pressure signal line 21 is connected to the pressure medium line 16b for tapping the load pressure in the steering control valve 12.

[0042] In a valve housing 40 of the steering control valve 12, pressure relief valves 41a, 41b and suction valves 42a, 42b assigned to the pressure medium lines 16a, 16b are arranged to protect the steering system 1. The pressure relief valves 41a, 41b are connected to the reservoir line 17 on the output side, and the suction valves 42a, 42b are connected to the inlet side. Furthermore, in the illustrated embodiment, a pressure relief valve 43 is arranged in the valve housing 40, which is connected to the load pressure signaling line 21 on the inlet side and to the reservoir line 17 on the outlet side.

[0043] A piston rod 30c of the steering actuator 15 designed as a steering cylinder 30 is connected to a first steered wheel 51a by means of a steering kinematics 50a and to a second steered wheel 51b by means of a steering kinematics 50b.

[0044] An electronic control device 60 is provided to control the drive motor 2 of the hydraulic pump 3.

[0045] The electronic control device 60 is connected to a steering sensor device 61 which detects the actuation of the steering sensor 25.

[0046] The steering sensor device 61 can be designed, for example, as a steering column sensor that detects the rotational position and / or rotational speed of a steering column 62, which connects the steering sensor 25 to the steering control valve 12 for actuation thereof. The steering column sensor preferably detects a rotational speed of the steering column 62 and the change in the absolute position of the steering sensor 25.

[0047] The electronic control device 60 is further connected to a steering actuator sensor device 70a or 70b that detects the straight-ahead driving position of the steering actuator 15. In the illustrated embodiment, two alternative embodiments of a steering actuator sensor device 70a or 70b are shown, wherein the steering actuator sensor device 70a is coupled to the steering kinematics 50a or 50b, and the steering actuator sensor device 70b is coupled to the piston rod 30c of the steering actuator 15, which is designed as a steering cylinder 30.

[0048] The steering actuator sensor device 70a or 70b detects in particular the straight-ahead driving position of the steering actuator 15 and the deflection of the steering actuator 15 to the straight-ahead driving position.

[0049] The electronic control device 60 is designed to control the drive motor 2 of the hydraulic pump 3 based on the signals of the steering sensor device 61 and the steering actuator sensor device 70a, 70b in such a way that when steering begins, wherein the steering sensor 25 is actuated, the drive motor 2 of the hydraulic pump 3 is switched on, and the drive motor 2 of the hydraulic pump 3 is only switched off again when the steering sensor 25 is in the neutral position and the steering actuator 15 is in the straight-ahead position at the same time.

[0050] At the start of steering, the operator deflects the steering sensor 25 from the neutral position, which corresponds to the straight-ahead driving position. The steering sensor device 61 detects a rotational speed at the steering column 62 and the change in the absolute position of the steering sensor 25 and reports this to the control device 60. The control device 60 switches on the drive motor 2 and controls the drive motor 2 as needed by means of a speed control, so that the hydraulic pump 3 provides the steering device 1 with the required power requested by the actuation of the steering sensor 25. Actuation of the steering sensor 25 actuates the steering control valve 12 and the steering actuator 15 accordingly. The steering actuator sensor device 70a or 70b on the steering actuator 15 detects the deflection to the straight-ahead driving position of the steering actuator 15 and reports this to the control device 60.As long as the steering actuator 15 has not returned to its straight-ahead position, the steering movement is considered incomplete and the drive motor 2 remains switched on, even if the steering sensor device 61 no longer detects any movement of the steering sensor 25. As soon as the steering actuator 15 has returned to the straight-ahead position with the steering sensor 25 in the neutral position, which is detected by the steering sensor device 61 and reported to the control device 60, the control device 60 switches off the drive motor 2.

[0051] The invention is not limited to the illustrated embodiment.

[0052] Instead of a steering actuator 15 designed as a steering cylinder 30, the steering actuator 15 can be designed as a hydraulic motor.

[0053] Alternatively, the hydraulic pump 3 can only supply the steering device 1 with pressure medium, whereby the priority valve 11 can be omitted.

[0054] A pressure fluid accumulator can be connected to the delivery line 6 of the hydraulic pump 3.

Claims

[1] Hydraulic steering device (1) for a mobile work machine, wherein the steering device (1) has a hydraulic pump (3) driven by a drive motor (2) which supplies a steering control valve (12) with pressure medium, wherein the steering control valve (12) is operable in dependence on the actuation of a steering transmitter (25) and controls a steering actuator (15), characterized bythat an electronic control device (60) is provided which controls the drive motor (2), which is connected to a steering sensor device (61) which detects the actuation of the steering sensor (25) and to a steering actuator sensor device (70a; 70b) which detects at least the straight-ahead driving position of the steering actuator (15), wherein the electronic control device (60) is designed to control the drive motor (2) of the hydraulic pump (3) on the basis of the signals from the steering sensor device (61) and the steering actuator sensor device (70a; 70b) in such a way that when steering begins, wherein the steering sensor (25) is actuated, the drive motor (2) of the hydraulic pump (3) is switched on, and the drive motor (2) of the hydraulic pump (3) is only switched off again when the steering sensor (25) is in a neutral position and the steering actuator (15) is in the straight-ahead driving position at the same time. [2] Hydraulic steering device (1) according to claim 1, characterized bythat the steering sensor device (61) detects the rotational position and / or a rotational speed of the steering sensor (25). [3] Hydraulic steering device (1) according to claim 1 or 2, characterized by that the electronic control device (60) is designed to control the speed of the drive motor (2) as a function of the rotational speed of the steering sensor (25). [4] Hydraulic steering device (1) according to one of claims 1 to 3, characterized by that the steering sensor (25) is connected to the steering control valve (12) by means of a steering column (62) for the purpose of actuating the latter, the steering sensor sensor device (61) being designed as a steering column sensor. [5] Hydraulic steering device (1) according to one of claims 1 to 4, characterized by that the drive motor (2) is designed as an electric motor. [6] Hydraulic steering device (1) according to one of claims 1 to 5, characterized bythat a pressure medium accumulator is connected to a delivery line (6) of the hydraulic pump (3). [7] Mobile working machine, in particular industrial truck, with a hydraulic steering device (1) according to one of the preceding claims. [8] Mobile work machine according to claim 7, characterized by that the work machine has a battery-electric drive system. [9] Mobile work machine according to claim 7 or 8, characterized by that the hydraulic pump (3) additionally supplies a working hydraulic system (10) of the drive machine with pressure medium, wherein a priority valve (11) is provided for the preferential supply of the steering device (1) with pressure medium.

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