Hydraulic drive for steering a wheel, method for diagnosis, wishbone with a hydraulic drive and hydraulic steering system

Abstract

The invention relates to a hydraulic drive for steering a wheel which is pivotably mounted on a wheel suspension about a pivot axis, comprising an electric motor (2), a hydraulic pump (4) which has two pressure connections and is driven by the electric motor, and a hydraulic pivot drive (6) which is or can be coupled to the pivot axis of the wheel and which has two working connections which are or can be connected hydraulically to the pressure connections and whose pressurization causes pivoting movements in opposite directions.

Description

The present invention relates to a hydraulic drive for steering a wheel, to a method for diagnosing a hydraulic drive, to a suspension arm having a hydraulic drive, and to a hydraulic steering system.BACKGROUND OF THE INVENTIONVehicles, i.e., passenger cars, utility vehicles, and mobile work machines, typically have one or more steerable wheels. In this case, a steering request of a driver of the vehicle detected by a steering wheel is usually converted into a steering movement of the steerable wheels by means of a mechanical transmission, which can include, for example, worm screws, spindles, gear racks and the like or else an electrical or hydraulic power assistance.Disclosure of the InventionAccording to the invention, a hydraulic drive for the steering of a wheel, a method for diagnosing a hydraulic drive, a suspension arm with a hydraulic drive and a hydraulic steering system with 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 use of the measure for steering a wheel which is mounted on a wheel suspension such that it can be pivoted about a pivot axis, a hydraulic drive or electro-hydraulic drive which has an electric motor, a hydraulic pump which has two pressure connections and is driven by the electric motor, and a hydraulic pivot drive. The hydraulic pivot drive is coupled or couplable to the pivot axis of the wheel and has two working connections which are hydraulically connected or can be connected to the pressure connections of the hydraulic pump and the pressurization of which brings about pivot movements (of the pivot axis) in opposite rotational directions (or directions). One advantage of the proposed solution lies in the scalability and adjustability by combination of different electric motors, hydraulic pumps and hydraulic pivot drive, so that, for example, the transmission ratio (between electric motor and pivot axis) can be selected optimally and a high efficiency can be achieved by pump output according to requirements. Furthermore, the electric motor and the hydraulic pump can be positioned relatively freely on the wheel suspension or on a vehicle frame.The hydraulic drive (or electrohydraulic drive, or hydraulic steering drive) is provided for steering a wheel of a vehicle, for example of a passenger car, of a commercial vehicle or of a mobile working machine.According to one embodiment, the hydraulic pump is a fixed displacement pump and the electric motor has an output shaft and is configured to effect a rotational movement of the output shaft in both rotational directions. This embodiment is expedient since it is easily controllable, is robust with respect to external influences during operation, e.g. vibrations during driving operation, and is cost-effective.According to one embodiment, a closed hydraulic system is formed, which comprises the hydraulic pump, the hydraulic pivot drive and the hydraulic connections. The hydraulic system contains or has, in particular, a hydraulic medium. According to this configuration, leakage is reduced. Furthermore, reservoirs or compensation tanks, filters or other elements for the hydraulic medium can be integrated in the system, which will not be discussed in more detail here.According to one embodiment, the hydraulic pivot drive has a rotary cylinder, wherein in particular an output axis of the rotary cylinder can be or is coupled to the pivot axis or is formed integrally with the pivot axis. A rotating cylinder has two oppositely directed pressure surfaces, wherein the rotating cylinder can be rotated about its pivot axis by mutual pressurization.The terms "hydraulic connection" or "hydraulically connected" are to be understood in the sense that a hydraulic line, a hydraulic passage, a hydraulic channel or the like is present, which enables a volume flow of hydraulic medium between the elements connected by the connection, wherein optionally a valve, a diaphragm or the like can be arranged in the connection, which influences or controls the flow of hydraulic medium through the connection.According to one embodiment, the hydraulic connections between the pressure connections and the working connections are formed by hydraulic lines and / or hydraulic channels. In particular, in this embodiment, no valves are provided in the hydraulic connections (i.e. in the hydraulic lines or hydraulic channels), so that the pressure connections and the working connections are connected directly, without interposed valves or the like. This embodiment is expedient since high efficiency is thus achieved without pressure losses via valve orifices or the like and volume flows of the hydraulic pump are converted directly into corresponding steering movements.According to one embodiment, the hydraulic drive also has a first sensor for measuring a wheel steering angle and / or second sensors for measuring the pressure of the hydraulic medium in the hydraulic connections and / or a third sensor for measuring the rotor position and / or a fourth sensor for measuring the current consumption of the electric motor. Such sensors may be used to determine the state of the drive and / or to control the hydraulic drive.In a method according to the invention for diagnosing a hydraulic drive according to the invention, measured values of at least one of the sensors are detected, and at least one variable is determined from the detected measured values of a first steering torque, which is determined from the measured values of the second sensors; a second steering torque, which is determined from the measured values of the third and / or of the fourth sensor; a derived wheel steering angle, which is determined from the measured values of the third sensor. The above-mentioned variables are particularly helpful for a state diagnosis of the hydraulic drive.According to one embodiment, the first and the second steering torque are determined and a steering torque deviation between the first and the second steering torque is determined. Alternatively or additionally, a wheel steering angle is detected by means of the first sensor, the derived wheel steering angle is determined and a wheel steering angle deviation between the wheel steering angle and the derived wheel steering angle is determined. Based on the steering torque deviation and / or the wheel steering angle deviation, errors of the hydraulic drive are detected and / or modified control parameters for the electric motor are determined, so that the steering torque deviation and / or the wheel steering angle deviation are compensated. Leakage, wear, friction or the like on the components of the hydraulic drive can be detected by the aforementioned deviations, possible malfunctions can thus be detected and / or compensated for at an early stage, and / or information about a necessary maintenance / repair is given to the user.A computing unit according to the invention, e.g. a control device of a mobile work machine, is configured, in particular by program technology, to carry out a method according to the invention for diagnosis.A suspension control arm according to the invention, on which a wheel is mounted so as to be pivotable about a pivot axis, has a transverse limb and a hydraulic drive according to the invention, wherein the hydraulic pivot drive is arranged at an end of the transverse limb, which is coupled or couplable to a bearing of the pivot axis, and is coupled or couplable to the pivot axis. The suspension arm has in particular one or two suspension arms which are mounted or can be pivoted in particular on a chassis of a vehicle. A suspension arm according to the invention is advantageous since there is no installation space requirement on the vehicle frame and the steering system can be easily adapted to different vehicle types.According to one embodiment, the electric motor and the hydraulic pump are arranged on the transverse limb. This configuration is very compact.According to another embodiment, the electric motor and the hydraulic pump are arranged on a carrier element of the suspension arm, so that the electric motor and the hydraulic pump are arranged in particular on or above or near a suspension arm pivot axis of the suspension arm. This embodiment has a small moving mass on the suspension arm.A hydraulic steering system according to the invention for steering two wheels, which are each mounted on a wheel suspension such that they can be pivoted about a pivot axis, has a first hydraulic drive according to the invention, which has a first electric motor, a first hydraulic pump and a first hydraulic pivot drive, a second hydraulic drive according to the invention, which has a second electric motor, a second hydraulic pump and a second hydraulic pivot drive, and a valve arrangement, which is hydraulically connected to the pressure connections of the first and second hydraulic pumps and to the working connections of the first and second hydraulic pivot drives. The valve arrangement has a first switching state in which volume flows are possible between the pressure connections of the first hydraulic pump and the working connections of the first hydraulic swivel drive and volume flows are possible between the pressure connections of the second hydraulic pump and the working connections of the second hydraulic swivel drive, and a second switching state in which volume flows are possible between the pressure connections of the second hydraulic pump and the working connections of the first and the second hydraulic swivel drive. Furthermore, the valve arrangement has one or more of: a third switching state in which volumetric flows between the pressure connections of the first hydraulic pump and the working connections of the first and second hydraulic swivel drive are possible, a fourth switching state in which volumetric flows between the pressure connections of the first hydraulic pump and the working connections of the second hydraulic swivel drive are possible, and a fifth switching state in which volumetric flows between the pressure connections of the second hydraulic pump and the working connections of the first hydraulic swivel drive are possible. The steering system allows continued operation when a malfunction occurs at one of the electric motors or one of the hydraulic pumps.According to one configuration, the hydraulic steering system has an electronic controller which is configured to control the valve arrangement. The electronic controller is further configured to switch the valve arrangement into the second switching state in response to a malfunction of the first electric motor and / or of the first hydraulic pump, and to switch the valve arrangement into the third switching state in response to a malfunction of the second electric motor and / or of the second hydraulic pump. If there is no malfunction, the valve arrangement can remain in the first switching state. The first switching state can optionally be a switching state in which valves of the valve arrangement are prestressed, such that no control currents or control signals of the electronic controller are necessary in order to assume the first switching state.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 drawing on the basis of exemplary embodiments and is described in detail below with reference to the drawing.DESCRIPTION OF THE FIGURESFIG. 1 shows a hydraulic drive for a steering system of a wheel according to one specific embodiment of the present invention. FIG. 2 shows a method for diagnosing a hydraulic drive according to an embodiment of the invention. FIGS. 3A, 3B show suspension arms, each having a hydraulic drive arranged thereon, according to an embodiment of the invention. FIG. 4 shows a hydraulically driven steering system for two wheels according to an embodiment of the invention.Detailed Description of the DrawingsFIG. 1 shows a hydraulic drive for a steering system of a wheel (of a vehicle) according to one specific embodiment of the present invention.The hydraulic drive comprises an electric motor 2, a hydraulic pump 4 and a hydraulic swivel drive 6. the electric motor 2 is coupled, for example by means of a drive shaft, to the hydraulic pump 4 in order to drive the latter. The electric motor 2 is configured or controllable to selectively drive a rotation or rotation of the drive shaft in each of the two rotational directions.The hydraulic pump 2 is in particular a constant pump, i.e. it has a constant delivery volume or volume of hydraulic medium delivered per revolution. The hydraulic pump 2 has two pressure outputs or pressure connections and is designed such that it can convey hydraulic medium in both directions between the pressure outputs. In the embodiment shown, the conveying direction corresponds to the direction of rotation of the hydraulic pump, i.e. the direction of rotation of the electric motor. Hydraulic connections are provided, so that the pressure connections are hydraulically connected to working connections of the hydraulic swivel drive 6, e.g. by means of hydraulic connections 8, 9, wherein it can be provided that valves are provided in the hydraulic connections or a valve arrangement is provided (as in FIG. 4 for example) in order to control volume flows between the pressure connections and the working connections. The hydraulic lines 8, 9 are in particular hydraulic lines (e.g. hydraulic hoses or hydraulic pipes) or hydraulic channels.The hydraulic swivel drive 6 has an output axis, the rotation of which is driven in different directions or directions of rotation depending on the pressurization at the working connections. That is, a volume flow of hydraulic medium into a first of the working connections (and a corresponding volume flow from the other, second, of the working connections) causes a rotation of the output axis in a first direction and a volume flow of hydraulic medium into the second of the working connections (and a corresponding volume flow from the other, first, of the working connections) causes a rotation of the output axis in a second direction, which is opposite the first. The hydraulic swivel drive 6 is designed in particular as a rotating cylinder. A rotary cylinder has, for example, two chambers which are hydraulically connected to one of the pressure connections in each case, a piston having two opposing (equally sized) pressure surfaces which delimit the volumes of the chambers being arranged between the chambers. An axis of rotation extends in FIG. 1 perpendicular to the plane of the drawing.The output axle of the hydraulic swivel drive 6 is connected or connectable in particular to a swivel axis of the wheel which is to be steered, so that a rotation or a swivel (steering) of the wheel about the swivel axis is effected. In particular, the output axis can be directly connected to the pivot axis or integrated therewith, so that they are aligned. The connection or coupling can also be implemented by means of toothings on the output axis and the pivot axis.Overall, the arrangement shown forms a closed hydraulic circuit which is filled with hydraulic medium (i.e. hydraulic fluid, e.g. a hydraulic oil). In addition, compensation containers and / or storage containers and / or dirt filters can be provided for the system (not shown).The electric motor can be controlled by a control device 16 (electronic control or computing unit). In this case, by means of suitable control signals (e.g. electrical voltages and / or electrical currents), the direction of rotation of the electric motor (and thus of the pivot drive or of the wheel) can be controlled and the rotational speed can be controlled. For example, the controller 16 receives steering signals from a steering device (steering wheel or joystick) that detects operator inputs.In FIG. 1, various sensors are also shown, which may be provided. A first sensor 12 (wheel steering angle sensor) for measuring a wheel steering angle, second sensors 10, 11 (pressure sensors) for measuring the pressures of the hydraulic medium in the hydraulic connections, e.g. in the hydraulic lines 8, 9, a third sensor 14 (rotor position sensor) for measuring the rotor position of the electric motor 2 and a fourth sensor 15 (current sensor) for measuring the current consumption of the electric motor 2 are shown here. Depending on the configuration, no sensor can be provided, at least one of the sensors mentioned can be provided or all of the sensors mentioned can be provided. Alternatively or additionally, at least one sensor different from the sensors mentioned can also be provided.The sensors can be configured to transmit respective measured values to the control device 16, which can use these for control purposes. In addition, the control unit 16 can be configured to carry out a method for diagnosing the hydraulic drive (for example as shown in FIG. 2 ) on the basis of the measurement values.FIG. 2 shows a method for diagnosing a hydraulic drive, which has a first sensor for measuring a wheel steering angle and / or second sensors for measuring the pressures of the hydraulic medium in the hydraulic connections and / or a third sensor for measuring the rotor position and / or a fourth sensor for measuring the current consumption of the electric motor, as shown in FIG. 1. The method for diagnosis can be implemented, for example, by a control unit of the hydraulic drive, in particular by the control unit 16.In step 110, measured values of the first and / or the second and / or the third and / or the fourth sensor or sensors are detected. These are transmitted, for example, via sensor lines from the sensor or sensors to the control device. From the measured values, direct and / or indirect statements can be made about the state of the hydraulic drive and / or of the wheel steered by them. The measured values of the first sensor (wheel steering angle sensor) allow, for example, a direct statement about the current steering angle of the wheel steered by the hydraulic drive. Likewise, for example, the measured values of the third sensor (rotor position sensor), depending on the configuration, can allow direct information about how many revolutions the electric motor has carried out with respect to a reference time (for example switching on), wherein the value of the number of revolutions is signed, corresponding to the two rotational directions. Alternatively, if the third sensor measures only a current angle of the rotor position, an indirect determination of the number of revolutions could be carried out by integration or summation over the current angle of the rotor position.In step 120, one or more variables are determined or calculated from the acquired measured values. For example, a first steering torque can be calculated from the measured values of the second sensors (pressure sensors). For this purpose, for example, the pressure difference between the two second sensors and the geometric relationships known from the design of the pivot drive (size of the pressure surfaces, lever between toothed rack and toothed wheel, etc.) are used. A proportionality constant can be derived from the geometric ratios, for example, which is multiplied by the pressure difference. Similarly, a second steering torque may be determined from the measurements of the third and / or fourth sensors (from which a torque of the electric motor may be determined). Furthermore, a wheel steering angle can be determined from the measured values of the third sensor, wherein the number of revolutions of the electric motor and the known transmission ratio of the hydraulic drive are used.The above-mentioned variables can also be used, for example, for controlling the hydraulic drive, for example, in order to set the wheel steering angle to a desired angle.In step 120, various of the measured and / or determined values are compared in order to identify faults or malfunctions of the hydraulic drive, e.g. leakage and / or wear, on the basis of deviations (or differences). For example, (at least) a steering torque deviation (steering torque difference) between the first steering torque (which is based on the pressure difference) and the second steering torque (which is based on the torque of the electric motor) is determined. It is also possible to determine (at least) a wheel steering angle deviation (wheel steering angle difference) between the measured values of the wheel steering angle (first sensor) and the derived wheel steering angle (which is based on the rotor position of the electric motor).In step 130, a malfunction of the hydraulic drive is detected on the basis of the (at least one) steering torque deviation and / or the (at least one) wheel steering angle deviation. For example, a malfunction can be detected if the deviations are above a predefined tolerance. If, for example, the first and the third sensor are present, a progression of wear, internal leakage or another disturbance can be deduced on the basis of a deviation from the expected rotational angles.Alternatively or additionally to step 130, in step 140, (at least) changed control parameters for the electric motor can be determined when a steering torque deviation and / or (at least) a wheel steering angle deviation is present, so that the steering torque deviation and / or the wheel steering angle deviation are compensated. For example, with increasing leakage, the case may occur that the first steering torque is smaller than the second steering torque, wherein the electric motor can then be controlled with a higher electric current in order to increase its power, so that the first steering torque reaches an ultimately desired value. In order to determine the changed control parameters, an appropriate learning method, for example, a machine learning (artificial intelligence) method may be used.Generally, the steps are performed continuously or repeatedly such that multiple steering torque deviations and / or wheel steering angle deviations are determined for different times.FIGS. 3A, 3B show transverse control arms which each have a hydraulic drive (or steering drive) arranged thereon with a hydraulic pivot drive 6. Shown is a respective wheel 20 which is steered by a hydraulic drive according to the invention, as shown for example in FIG. 1. The steering movement or pivoting movement of the wheel 20 effected by the hydraulic pivot drive 6 of the hydraulic drive is indicated in each case by a double arrow. Thus, a top view of the system is shown with the vehicle on the ground assumed, to which the wheel is attached.Furthermore, a respective transverse link (or delta link) is shown, which is intended to absorb transverse forces acting on the wheel. For this purpose, the suspension arm is connected on the one hand to a bearing for the wheel, in particular for the pivot axis, and on the other hand (here at two points) to a chassis of the vehicle (not shown in detail). For this purpose, the suspension arm has, for example, two (transverse) legs or struts which converge at the bearing for the wheel. The suspension arm can pivot at the point of attachment to the chassis about the axis shown as a dashed line, referred to as suspension arm pivot axis 26, (out and into the plane of the drawing) in order to enable a spring movement.In both figures, the hydraulic pivot drive 6 is arranged on a leg of the suspension arm in such a way that its output axis coincides with the pivot axis of the wheel or is coupled to the latter at least via a rotary connection, for example toothings.In FIG. 3A, the electric motor 2 and the hydraulic pump 4 of the hydraulic drive are both arranged on a (transverse) limb 22 of the suspension arm. According to this embodiment, the hydraulic drive can be designed very compactly, for example in a single housing.In FIG. 3B, the electric motor 2 and the hydraulic pump 4 of the hydraulic drive are both arranged on a longitudinal arm of the suspension arm or on a carrier element of the suspension arm (e.g. on the chassis of the vehicle) in such a way that they are situated very close to or on or above the suspension arm pivot axis 26 about which the suspension arm pivots relative to the chassis, or in other words in such a way that they are situated as close as possible to the suspension arm pivot axis, taking into account the structure of the suspension arm and / or of the carrier element. The hydraulic connections, for example the hydraulic lines 8, 9, run along a (transverse) limb 24 of the suspension arm. Accordingly, the mass (moved up and down with the wheel) of the suspension arm (with hydraulic drive) can be kept small, since there essentially only the hydraulic swivel drive 6 and the hydraulic lines 8, 9 are attached.FIG. 4 shows a hydraulically driven steering system for two wheels of a vehicle according to an embodiment of the invention. The steering system is designed redundantly. The two wheels are in particular jointly steered wheels.The steering system comprises two hydraulic drives according to the invention (as shown for example in FIGS. 1, 2, 3A, 3B ), wherein a first hydraulic drive is provided for a first wheel and a second hydraulic drive is provided for a second wheel. The first hydraulic drive has a first electric motor 2A, a first hydraulic pump 4A (which is in particular a fixed displacement pump) and a first pivot drive 6A. The second hydraulic drive has a second electric motor 2B, a second hydraulic pump 4B (which is in particular a fixed displacement pump) and a second pivot drive 6B.Additionally, a valve assembly 30 is provided with one or more valves (not shown) disposed in and between the hydraulic connections 8A, 9A, 8B, 9B between the hydraulic pumps 4A, 4B and the swing drives 6A, 6B. For example, the valve assembly 30 includes ports hydraulically connected to the pressure ports of the first hydraulic pump 4A, ports hydraulically connected to the working ports of the first swing hydraulic drive 6A, ports hydraulically connected to the pressure ports of the second hydraulic pump 4B, and ports hydraulically connected to the working ports of the second swing hydraulic drive 6B.The valve arrangement 30 has different switching states in which volume flows of hydraulic medium between the hydraulic pumps 4A, 4B and the hydraulic pivot drives 6A, 6B are enabled or disabled in different ways. The switching states are achieved by respective actuation of the one or more valves of the valve arrangement 30.In a first switching state, volumetric flows are possible between the pressure connections of the first hydraulic pump 4A and the working connections of the first hydraulic swivel drive 6A, and volumetric flows are possible between the pressure connections of the second hydraulic pump 4B and the working connections of the second hydraulic swivel drive 6B. Other volume flows between the connections are prevented, i.e. volume flows between the pressure connections of the first hydraulic pump 4A and the working connections of the second hydraulic swivel drive 6B, volume flows between the pressure connections of the second hydraulic pump 4B and the working connections of the first hydraulic swivel drive 6A, and volume flows between the pressure connections of the two hydraulic pumps and volume flows between the working connections of the two hydraulic swivel drives are prevented. In the first switching state, the two hydraulic drives are thus operated independently of one another, i.e. the two wheels can be controlled independently of one another, for example with a different steering angle. The first switching state can be regarded as a normal state accordingly. Valves of the valve arrangement can be prestressed, for example, in positions such that the first switching state is achieved.In a second switching state, volume flows are possible between the pressure connections of the second hydraulic pump 4B and the working connections of the first and second hydraulic swivel drive 6A, 6B, i.e. volume flows are possible between the pressure connections of the second hydraulic pump 4B and the working connections of the first hydraulic swivel drive 6A and volume flows are possible between the pressure connections of the second hydraulic pump 4B and the working connections of the second hydraulic swivel drive 6B. In the second switching state, the first hydraulic pump 4A is hydraulically separated from the rest of the system, i.e. volume flows between the pressure connections of the first hydraulic pump 4A and the working connections of the first and second hydraulic swivel drive 6A, 6B and volume flows between the pressure connections of the first and second hydraulic pumps 4A, 4B are prevented. In the second switching state, the two hydraulic pivot drives 6A, 6B are accordingly supplied with hydraulic medium by the second hydraulic pump 4B. This is useful for maintaining the steering of the first wheel when a malfunction occurs in the first electric motor 2A or the first hydraulic pump 4A. The second switching state can accordingly be regarded as a first redundancy state. The pressure connections of the second hydraulic pump 4B are connected by the valve arrangement 30 in the second switching state in particular to the working connections of the first and the second hydraulic swivel drive 6A, 6B in such a way that a swivel movement of the two wheels in the same direction is effected.In a third switching state, volume flows are possible between the pressure connections of the first hydraulic pump 4A and the working connections of the first and second hydraulic swivel drive 6A, 6B, i.e. volume flows are possible between the pressure connections of the first hydraulic pump 4A and the working connections of the first hydraulic swivel drive 6A and volume flows between the pressure connections of the first hydraulic pump 4A and the working connections of the second hydraulic swivel drive 6B. The second hydraulic pump 4B is hydraulically separated from the remaining system in the third switching state, i.e. volume flows between the pressure connections of the second hydraulic pump 4B and the working connections of the first and the second hydraulic swivel drive 6A, 6B and volume flows between the pressure connections of the first and the second hydraulic pump 4A, 4B are prevented. In the third switching state, the two hydraulic pivot drives 6A, 6B are accordingly supplied with hydraulic medium by the first hydraulic pump 4A. This is useful for maintaining the steering of the second wheel when a malfunction occurs in the second electric motor 2B or the second hydraulic pump 4B. The third switching state can accordingly be regarded as a second redundancy state. The pressure connections of the first hydraulic pump 4A are connected by the valve arrangement 30 in the third switching state in particular to the working connections of the first and second hydraulic swivel drive 6A, 6B in such a way that a swivel movement of the two wheels in the same direction is effected.Further types of interconnection are conceivable, for example, that the hydraulic pump 2A acts only on the pivot drive 6B or that the hydraulic pump 2B acts only on the pivot drive 6A.The control of the valve arrangement 30 can be effected by a control device 16 which is configured to generate control signals corresponding to the switching states of the valve arrangement 30, so that the valve arrangement is thus switched into the respective switching state. The controller can, for example, evaluate measured values from sensors, as shown in FIG. 1, for example by means of a method for diagnosis described in connection with FIG. 2, in order to detect a malfunction of one of the electric motors 2A, 2B and / or of one of the hydraulic pumps 4A, 4B.

Claims

Hydraulic drive for steering a wheel, which is mounted on a wheel suspension such that it can be pivoted about a pivot axis, having an electric motor (2); a hydraulic pump (4) which has two pressure connections and is driven by the electric motor; and a hydraulic pivot drive (6) which is coupled or can be coupled to the pivot axis of the wheel and which has two working connections which are hydraulically connected or can be connected to the pressure connections and the pressurization of which brings about pivoting movements in opposite rotational directions about the pivot axis of the wheel.Hydraulic drive according to Claim 1, wherein the hydraulic pump (4) is a fixed displacement pump and the electric motor (2) has an output shaft and is configured to bring about a rotational movement of the output shaft in both rotational directions.Hydraulic drive according to claim 1 or 2, wherein a closed hydraulic system is formed, which comprises the hydraulic pump (4), the hydraulic pivot drive (6) and the hydraulic connections; and in particular further comprising a hydraulic medium.Hydraulic drive according to one of the preceding claims, further comprising a compensating container for hydraulic medium and / or a storage container for hydraulic medium and / or a dirt filter for hydraulic medium; wherein, with reference back to claim 3, the compensating container and / or the storage container and / or the dirt filter are part of the closed hydraulic system.Hydraulic drive according to one of the preceding claims, wherein the hydraulic pivot drive (6) has a rotary cylinder; wherein in particular an output axis of the rotary cylinder is couplable or coupled to the pivot axis of the wheel or is integrally formed with the pivot axis of the wheel.Hydraulic drive according to one of the preceding claims, wherein the hydraulic connections between the pressure connections and the working connections are formed by hydraulic lines (8, 9) and / or hydraulic channels.Hydraulic drive according to one of the preceding claims, further comprising a first sensor (12) for measuring a wheel steering angle and / or second sensors (10, 11) for measuring the pressures of the hydraulic medium in the hydraulic connections and / or a third sensor (14) for measuring the rotor position and / or a fourth sensor (15) for measuring the current consumption of the electric motor (2).Method for diagnosing a hydraulic drive according to Claim 7, wherein, measured values of at least one of the sensors are detected (110); wherein at least one variable is determined (120) from the detected measured values of: a first steering torque which is determined from the measured values of the second sensors (10, 11), a second steering torque which is determined from the measured values of the third and / or of the fourth sensor (14, 15), a derived wheel steering angle which is determined from the measured values of the third sensor (14), a transmission ratio of the steering drive which is determined from the measured values of the first and of the third sensor.Method according to Claim 8, wherein the first and the second steering torque are determined and a steering torque deviation between the first and the second steering torque is determined, and / or wherein a wheel steering angle is detected by means of the first sensor (12), the derived wheel steering angle is determined and a wheel steering angle deviation between the wheel steering angle and the derived wheel steering angle is determined; wherein errors of the hydraulic drive are detected (130) on the basis of the steering torque deviation and / or the wheel steering angle deviation and / or deviations of the transmission ratio of the steering drive, and / or modified control parameters for the electric motor (2) are determined (140), such that the steering torque deviation and / or the wheel steering angle deviation is compensated.The hydraulic drive arithmetic unit (16) according to claim 7, comprising a processor configured to perform the method according to any one of claims 8 or 9.Suspension arm with a hydraulic drive, on which a wheel (20) is mounted so as to be pivotable about a pivot axis, having a transverse arm (22, 24) and a hydraulic drive according to one of Claims 1 to 7; wherein the hydraulic pivot drive (6) is arranged at an end of the transverse arm (22, 24) which is coupled or couplable to a bearing of the pivot axis and is coupled or couplable to the pivot axis.Suspension arm according to Claim 11, wherein the electric motor (2) and the hydraulic pump (4) are arranged on the transverse limb (22).Suspension arm according to Claim 11, wherein the electric motor (2) and the hydraulic pump (4) are arranged on a carrier element of the suspension arm; wherein in particular the electric motor (2) and the hydraulic pump (4) are arranged as close as possible and / or on or above a suspension arm pivot axis (26).Hydraulic steering system for steering two wheels, each of which is mounted on a wheel suspension such that it can be pivoted about a pivot axis, having a first hydraulic drive according to one of Claims 1 to 7, which has a first electric motor (2A), a first hydraulic pump (4A) and a first hydraulic pivot drive (6A); a second hydraulic drive according to one of Claims 1 to 7, which has a second electric motor (2B), a second hydraulic pump (4B) and a second hydraulic pivot drive (6B); and a valve arrangement (30), which is hydraulically connected to the pressure connections of the first and the second hydraulic pump (4A, 4B) and to the working connections of the first and the second hydraulic pivot drive (6A, 6B); wherein the valve arrangement has: a first switching state in which volumetric flows between the pressure connections of the first hydraulic pump (4A) and the working connections of the first hydraulic swivel drive (6A) and volumetric flows between the pressure connections of the second hydraulic pump (4B) and the working connections of the second hydraulic swivel drive (6B) are possible, and a second switching state in which volumetric flows between the pressure connections of the second hydraulic pump (4B) and the working connections of the first and the second hydraulic swivel drive (6A), (6B) are possible; and wherein the valve arrangement has one or more of: a third switching state in which volumetric flows are possible between the pressure connections of the first hydraulic pump (4A) and the working connections of the first and the second hydraulic swivel drive (6A), (6B), a fourth switching state in which volumetric flows are possible between the pressure connections of the first hydraulic pump (4A) and the working connections of the second hydraulic swivel drive (6B), and a fifth switching state in which volumetric flows are possible between the pressure connections of the second hydraulic pump (4B) and the working connections of the first hydraulic swivel drive (6A).Hydraulic steering system according to claim 14, further comprising an electronic controller (16) configured to control the valve arrangement (30); wherein the electronic controller (16) is further configured to switch the valve arrangement to the second switching state in response to a malfunction of the first electric motor (2A) and / or the first hydraulic pump (4A), and to switch the valve arrangement to the third switching state in response to a malfunction of the second electric motor (2B) and / or the second hydraulic pump (4B).

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