Electrohydraulic actuator

Abstract

The invention relates to an electrohydraulic actuator comprising a hydraulic piston-cylinder unit, a hydraulic pump hydraulically connected to a pressure chamber of the piston-cylinder unit, an electric motor for driving the hydraulic pump, and a pressure relief valve hydraulically connected to the pressure chamber of the piston-cylinder unit and designed to relieve the pressure chamber to a hydraulic tank when the pressure rises above a limit pressure. According to the invention, the electrohydraulic actuator further comprises a control unit electrically connected to the electric motor and configured to detect an increase in current in the electric motor due to a pressure increase in the pressure chamber and, in response, to automatically adjust the operation of the electric motor, in particular to stop it.

Description

[0001] The present invention relates to an electrohydraulic actuator according to the preamble of claim 1.

[0002] Electro-hydraulic actuators are known from the state of the art and typically comprise a number of components for controlling and detecting end positions of the actuator, such as sensors and solenoid valves.

[0003] Pneumatic actuators are used for certain applications, such as the automatic coupling of train carriages in passenger transport. In the case of passenger trains, this is possible because, in addition to the brake air line, there is an additional air line for the pneumatic coupling cylinders. However, in freight transport, the use of pneumatic coupling cylinders is not readily possible, as there is usually no additional air line, and using the brake air line for coupling is not permitted.

[0004] Against this background, the present invention is based on the object of providing an actuator which is suitable for use in automatic coupling devices in freight transport.

[0005] According to the invention, this object is achieved by a device having the features of claim 1. Advantageous embodiments of the invention emerge from the subclaims and the following description.

[0006] Accordingly, an electro-hydraulic actuator is proposed which comprises a hydraulic piston-cylinder unit, a hydraulic pump hydraulically connected to a pressure chamber of the piston-cylinder unit, an electric motor, and a pressure relief valve. The hydraulic pump is driven by the electric motor. The pressure relief valve is hydraulically connected to the pressure chamber of the piston-cylinder unit and is designed to relieve the pressure chamber to a hydraulic tank when the pressure in the pressure chamber rises above a limit pressure. The pressure relief valve therefore opens when a defined limit pressure in the pressure chamber is reached or exceeded, which is particularly the case when the actuator has reached an end position (i.e., when the piston-cylinder unit is fully extended or retracted).

[0007] According to the invention, the electrohydraulic actuator comprises a control unit electrically connected to the electric motor and configured to detect a current increase in the electric motor resulting from a pressure increase in the pressure chamber and, in response, to automatically adjust the operation of the electric motor. The control unit can be the motor driver of the electric motor or a separate control unit. The adjustment of the motor operation can occur when the motor current rises above a defined threshold and / or when a predetermined characteristic (e.g., a specific gradient) of the detected motor current is detected.

[0008] In particular, it is provided that the control unit stops the electric motor and thus the delivery of hydraulic fluid into the pressure chamber by the hydraulic pump when a certain pressure increase is registered via an increased motor current.

[0009] By detecting the motor current and controlling the electric motor based on this, the actuator can detect when it has reached its end position without the need for special sensors. When the actuator reaches an end position (e.g., the piston rod of the piston-cylinder unit is fully extended), the hydraulic pressure in the pressure chamber increases due to the continued delivery of the hydraulic pump until, at a certain limit pressure, the pressure relief valve opens and relieves the pressure chamber. The resulting current increase in the electric motor is detected by the control unit, and motor operation is adjusted accordingly (e.g., reducing the speed or stopping operation). This enables sensorless detection of the corresponding stop of the piston-cylinder unit.

[0010] By omitting end position sensors, the electro-hydraulic actuator according to the invention has a compact design, making it suitable for use in the automatic coupling / uncoupling of wagons in freight transport, where only limited installation space is available for the coupling device.

[0011] In one possible embodiment, the piston-cylinder unit is designed as a differential cylinder with two pressure chambers. This enables bidirectional operation of the piston-cylinder unit (extension and retraction) and thus of the actuator (e.g., opening / closing or coupling / uncoupling).

[0012] In another possible embodiment, both pressure chambers are hydraulically connected to the hydraulic pump, i.e., only a single hydraulic pump is used to operate the piston-cylinder unit. The hydraulic pump is therefore designed as a bidirectional hydraulic pump, by means of which a fluid flow can be generated in both directions to selectively pressurize one of the two pressure chambers. This allows the piston-cylinder unit or the actuator to be operated in both directions without a switching valve, resulting in an even more compact design of the electrohydraulic actuator according to the invention.

[0013] In another possible embodiment, the electric motor is designed as a reversible electric motor. The delivery direction of the hydraulic pump can thus be changed by switching the direction of rotation of the electric motor. Thus, simply by controlling the electric motor accordingly, one of the two pressure chambers can be pressurized, thus allowing the actuator to operate in the corresponding direction.

[0014] In principle, the hydraulic pump could have a variable displacement and be designed, for example, as an axial piston pump with a swivel plate. By changing the displacement accordingly (e.g., controlling the swivel angle), the retraction and extension speed of the piston-cylinder unit could be controlled or regulated. For a simple and compact design, however, it is preferred for the hydraulic pump to have a constant displacement. The retraction and extension speed of the piston-cylinder unit could be controlled or regulated, for example, via a corresponding control of the electric motor.

[0015] In a further possible embodiment, it is provided that each of the pressure chambers is hydraulically connected to its own pressure relief valve, wherein the pressure relief valves are designed to relieve the associated pressure chamber to a hydraulic tank in the event of a pressure increase in the respective pressure chamber above a limit pressure.

[0016] The pressure relief valve connected to a specific pressure chamber opens when a defined limit pressure is reached or exceeded in the corresponding pressure chamber, which is particularly the case when the actuator has reached one of the two end positions (i.e. when the piston-cylinder unit is fully extended or retracted).

[0017] In a differential cylinder design with two pressure chambers and two pressure relief valves, the motor current is detected and motor operation is adjusted accordingly for each pressure chamber. This enables sensorless detection of both end stops (fully extended / retracted) of the piston-cylinder unit.

[0018] In general terms, the piston-cylinder unit can have a piston rod that only protrudes from the cylinder housing on one side of the piston, or one that protrudes from the cylinder housing on both sides of the piston. In the latter case, the pressure relief valves and corresponding limit pressures of the two pressure chambers can be identical. In the former case (piston rod only connected to the piston on one side), one of the pressure chambers is an annular space (side of the piston rod) with a smaller maximum volume than the opposite piston chamber. Accordingly, it can be provided that the pressure relief valve connected to the annular space relieves at a different limit pressure than the pressure relief valve connected to the piston chamber. Alternatively or additionally, the control unit can adapt the motor operation at a different limit current depending on the operating direction. Alternatively, the limit pressures and / orLimit currents for both pressure chambers must be identical.

[0019] In a further possible embodiment, a first pressure chamber of the piston-cylinder unit is connected in parallel to a first pressure relief valve with a switchable relief valve, which, when actuated, relieves the first pressure chamber to a hydraulic tank. The pressure relief valve relieves pressure when a limit pressure in the associated pressure chamber is reached or exceeded, while the relief valve can, for example, relieve the first pressure chamber when a certain pressure prevails in the second pressure chamber. This can be the case, for example, when the second pressure chamber is pressurized, whereby the volume of the first pressure chamber reduces. The hydraulic fluid displaced from the first pressure chamber can then be discharged to the hydraulic tank via the open relief valve. In the simplest case, the relief valve can comprise or represent a pilot-operated check valve.

[0020] In a further possible embodiment, the relief valve is hydraulically switchable and has a control input hydraulically connected to a hydraulic line connecting the hydraulic pump to a second pressure chamber of the piston-cylinder unit (i.e., the pressure chamber not connected to the relief valve considered here). The relief valve is configured to relieve the first pressure chamber to the hydraulic tank when a limit pressure in the hydraulic line is exceeded. Thus, if the second pressure chamber is pressurized, this results in a higher pressure in the corresponding hydraulic line and the control line connected to the relief valve, causing the relief valve to open.

[0021] Alternatively, the relief valve could be electrically connected to the control unit and be electrically controlled by it.

[0022] In another possible embodiment, the first pressure chamber is connected to the hydraulic pump via a check valve, which blocks any backflow of hydraulic fluid from the first pressure chamber to the hydraulic pump. This allows the piston-cylinder unit to be held in a specific position against load (for example, in an end position in which the first pressure chamber has a maximum volume) without having to operate the hydraulic pump or electric motor. It can be provided that only one of the pressure chambers is connected to the hydraulic pump via such a check valve. The position to be held can correspond to a maximum extension position of the piston-cylinder unit.

[0023] In another possible embodiment, the retraction and extension of the piston-cylinder unit can be controlled solely by the electric motor, i.e., in particular, without a switching valve. This results in a particularly simple and compact design of the electrohydraulic actuator according to the invention. The retraction and extension of the actuator is controlled solely by the electric motor. Furthermore, since the motor current is detected, no sensors are required.

[0024] The invention further relates to a vehicle with at least one electrohydraulic actuator according to the invention. This obviously results in the same properties and advantages as the electrohydraulic actuator according to the invention, which is why a repetitive description is omitted. The vehicle can be a rail vehicle, in particular a freight train. The electrohydraulic actuator can be used in particular for coupling two wagons. However, the compact actuator according to the invention can also be used in any other applications and is therefore not limited to coupling train wagons.

[0025] In one possible embodiment, the vehicle is a rail vehicle, in particular a freight train, with at least two wagons, wherein the wagons can be coupled to one another detachably and automatically by means of a coupling device (i.e. not manually as has frequently been the case hitherto), and the coupling device comprises an electro-hydraulic actuator according to the invention, by means of which the coupling can be opened and closed. The electro-hydraulic actuator can comprise a differential cylinder with a relief valve and a check valve for the hydraulic pump, as described above, wherein the position of the piston-cylinder unit which can be maintained against load preferably corresponds to a closed clutch. This prevents unintentional opening of the clutch, and the clutch can only be opened by corresponding actuation of the electric motor in the unlocking direction.

[0026] Further features, details and advantages of the invention will become apparent from the embodiment explained below with reference to the single figure.

[0027] The Figure 1 shows a hydraulic diagram of the electro-hydraulic actuator 10 according to the invention (hereinafter also referred to as "EHA") according to a preferred embodiment.

[0028] The EHA 10 comprises a piston-cylinder unit 12 with a piston 13 that can be moved within a cylinder housing and a piston rod, which in this embodiment is connected to the piston 13 on one side and extends out of the cylinder housing on one side. In this embodiment, the piston-cylinder unit 12 is designed as a differential cylinder with a first pressure chamber 21 (piston chamber) and a second pressure chamber 22 (annular chamber), resulting in a particularly compact design.

[0029] An example of the use of the EHA 10 according to the invention is the coupling of two wagons of a freight train. For this purpose, the end of the piston rod 14 can be connected to a corresponding coupling device (not shown). In this embodiment, a fully extended piston rod 14 can correspond to a locked or coupled state, and a fully retracted piston rod 14 can correspond to an unlocked or uncoupled state.

[0030] The two pressure chambers 21, 22 of the piston-cylinder unit 12 are connected to a single hydraulic pump 16, which in this embodiment is designed as a bidirectional pump and is thus configured to pump hydraulic fluid into the first or second pressure chamber 21, 22. The hydraulic pump 16 is driven by an electric motor 18 whose direction of rotation is reversible. Depending on the direction of rotation of the electric motor 18, the hydraulic pump 16 selectively supplies hydraulic pressure to the first or second pressure chamber 21, 22, thus either retracting or extending the piston rod 14. This configuration allows the retraction and extension of the piston rod 14 to be controlled without a switching valve, resulting in a particularly simple and compact design of the EHA 10.

[0031] The first pressure chamber 21 is connected to a hydraulic tank 40 via a pressure relief valve 23. The pressure relief valve 23 is designed to relieve the first pressure chamber 21 toward the hydraulic tank 40 when a certain limit pressure is reached or exceeded in the first pressure chamber 21. The limit pressure is selected such that it is reached when the piston-cylinder unit 12 is in a fully extended position and the pressure in the first pressure chamber 21 increases with continued delivery of hydraulic fluid into the latter.

[0032] The second pressure chamber 22 is also connected to the hydraulic tank 40 via a corresponding pressure relief valve 24. This opens when the hydraulic pressure in the second pressure chamber 22 reaches or exceeds a certain limit pressure upon reaching the fully retracted position of the piston-cylinder unit 12.

[0033] According to the invention, the EHA 10 comprises a control unit 19, which detects the motor current in the electric motor 18. Reaching the end stop positions of the piston-cylinder unit 12 (fully retracted / extended) is accompanied by an increase in the motor current in the electric motor 18, which is detected by the control unit 19. The control unit 19 is configured such that, upon detecting a corresponding increase in the motor current, it stops the electric motor so that no further hydraulic fluid is pumped into the corresponding pressure chamber 21, 22. This makes it possible to detect when the front or rear stop of the piston-cylinder unit 12 has been reached without the use of sensors.

[0034] The side of the hydraulic pump 16 assigned to the first pressure chamber 21 is connected to the hydraulic tank 40 via a check valve 28, through which hydraulic fluid is pumped from the tank 40 to retract the piston rod 14 (pressurizing the second pressure chamber 22). The side of the hydraulic pump 16 assigned to the second pressure chamber 22 is connected to the hydraulic tank 40 via another, reversely connected check valve 29, through which hydraulic fluid is pumped from the tank 40 to extend the piston rod 14 (pressurizing the first pressure chamber 21).

[0035] In the illustrated embodiment, the first pressure chamber 21 is connected to the hydraulic pump via a first hydraulic line 31. Located in the first hydraulic line 31 is a check valve 27, which is configured to block a backflow of hydraulic fluid from the first pressure chamber 21 to the hydraulic pump 16. The second pressure chamber 22 is directly connected to the hydraulic pump 16 via a second hydraulic line 32.

[0036] The first pressure chamber 21 is connected to the hydraulic tank 40 in parallel with the pressure relief valve 23 via a hydraulically actuated relief valve 26. In this embodiment, the relief valve 26 is designed as a releasable check valve and has a control input connected to the second hydraulic line 32 via a control line 33. The relief valve 26 is thus switched via the pressure in the second hydraulic line 32.

[0037] When the piston-cylinder unit 12 is extended, the hydraulic pump 16 pumps hydraulic fluid from the tank 40 via the open check valve 28, as well as returning hydraulic fluid, which is forced from the second pressure chamber 22, into the first pressure chamber 21. Once the front stop is reached (piston rod 14 fully extended), the pressure relief valve 23 connected to the first pressure chamber 21 opens. The resulting increase in motor current is detected by the control unit 19, thus achieving sensorless detection of the front stop. With the help of the check valve 27 in the first hydraulic line 31, the piston-cylinder unit 12 can be held in the front or extended position against a load without having to operate the hydraulic pump 16 or the electric motor 18.

[0038] When the piston-cylinder unit 12 is retracted, the direction of rotation of the electric motor 18 and thus the delivery direction of the hydraulic pump 16 are reversed. As a result, hydraulic fluid now flows from the tank 40 via the now opened check valve 29 and the hydraulic pump 16 into the second pressure chamber 22. To release the hydraulic blockage in the first pressure chamber 21, the relief valve 26 is opened by the pressure in the second hydraulic line 32 (and thus the pressure in the second pressure chamber 22), and the hydraulic fluid can flow from the first pressure chamber 21 into the tank 40. As before, reaching the rear stop (piston rod 14 fully retracted) is detected by opening the pressure relief valve 24 connected to the second pressure chamber 22 and a corresponding increase in the motor current.

[0039] The electrohydraulic actuator 10 according to the invention is characterized by a minimum of components. Apart from the electric motor 18, no other electrical elements such as solenoid valves or sensors are used. List of reference symbols:

[0040] 10 Electro-hydraulic actuator 12 Piston-cylinder unit 13 Piston 14 Piston rod 16 Hydraulic pump 18 Electric motor 19 Control unit 21 First pressure chamber 22 Second pressure chamber 23 First pressure relief valve 24 Second pressure relief valve 26 Relief valve 27 Check valve 28 Check valve 29 Check valve 31 First hydraulic line 32 Second hydraulic line 33 Control line 40 Hydraulic tank

Claims

1. Electro-hydraulic actuator (10) comprising a hydraulic piston-cylinder unit (12), a hydraulic pump (16) hydraulically connected to a pressure chamber (21, 22) of the piston-cylinder unit (12), an electric motor (18) for driving the hydraulic pump (16), and a pressure relief valve (23, 24) hydraulically connected to the pressure chamber (21, 22) of the piston-cylinder unit (12) and designed to relieve the pressure chamber (21, 22) to a hydraulic tank (40) in the event of a pressure increase in the pressure chamber (21, 22) above a limit pressure, characterized by a control unit (19) which is electrically connected to the electric motor (18) and is configured to detect a current increase in the electric motor (18) due to a pressure increase in the pressure chamber (21, 22) and, in response thereto, to automatically adapt, in particular to stop, an operation of the electric motor (18).

2. Electrohydraulic actuator (10) according to claim 1, wherein the piston-cylinder unit (12) is designed as a differential cylinder with two pressure chambers (21, 22).

3. Electro-hydraulic actuator (10) according to the preceding claim, wherein both pressure chambers (21, 22) are hydraulically connected to the hydraulic pump (16) and the hydraulic pump (16) is designed as a bidirectional hydraulic pump by means of which a fluid flow can be generated in both directions.

4. Electro-hydraulic actuator (10) according to the preceding claim, wherein the electric motor (18) is designed as a reversible electric motor and the hydraulic pump (16) preferably has a constant displacement volume.

5. Electro-hydraulic actuator (10) according to one of claims 2 to 4, wherein each of the pressure chambers (21, 22) is hydraulically connected to a pressure relief valve (23, 24), wherein the pressure relief valves (23, 24) are designed to relieve the respective pressure chamber (21, 22) to a hydraulic tank (40) in the event of a pressure increase in the respective pressure chamber (21, 22) above a limit pressure.

6. Electro-hydraulic actuator (10) according to one of claims 2 to 5, wherein a first pressure chamber (21) of the piston-cylinder unit (12) is connected in parallel to a first pressure relief valve (23) to a switchable relief valve (26) which, when actuated, relieves the first pressure chamber (21) to a hydraulic tank (40), wherein the relief valve (26) preferably comprises a pilot-operated check valve.

7. Electro-hydraulic actuator (10) according to the preceding claim, wherein the relief valve (26) is hydraulically switchable and has a control input which is hydraulically connected to a hydraulic line (32) connecting the hydraulic pump (16) to a second pressure chamber (22) of the piston-cylinder unit (12), wherein the relief valve (26) is configured to relieve the first pressure chamber (21) to the hydraulic tank (40) when a limit pressure in the hydraulic line (32) is exceeded.

8. Electro-hydraulic actuator (10) according to claim 6 or 7, wherein the first pressure chamber (21) is connected to the hydraulic pump (16) via a check valve (27) which blocks a backflow of hydraulic fluid from the first pressure chamber (21) to the hydraulic pump (16).

9. Electrohydraulic actuator (10) according to one of the preceding claims, which is further developed at least by the features of claim 4, wherein the retraction and extension of the piston-cylinder unit (12) can be controlled only via the electric motor (18).

10. Vehicle, in particular a rail vehicle, with an electro-hydraulic actuator (10) according to one of the preceding claims.

11. Vehicle according to the preceding claim, wherein the vehicle is a rail vehicle, in particular a freight train, with at least two wagons, wherein the wagons can be releasably coupled to one another by means of a coupling device and the coupling device comprises an electro-hydraulic actuator (10) according to one of claims 1 to 10, by means of which the coupling can be opened and closed.

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