Hydraulic system with dry sump

Abstract

A hydraulic supply system (100), in particular for a drive machine (115) of a motor vehicle, comprises a storage container (125) for a hydraulic medium (110); a supply line (135) for providing the hydraulic medium (110) from the storage container (125) to a cooling or lubricating point (105), the hydraulic medium (110) which emerges from the cooling or lubricating point (105) being collected in a sump (150); a bilge pump (130) which is designed to deliver the hydraulic medium (110) from the sump (150) into the storage container (125); and an electric motor (145) for driving the bilge pump (130). Furthermore, a compressed air motor (140) is provided for driving the bilge pump (130), the compressed air motor (140) being supplied with air from the storage container (125). A pressure pump (205) for providing a volume flow of the medium (110) to a parking lock (215) is coupled to the bilge pump (130) by means of an overrunning clutch (210).

Description

[0001] ZF Friedrichshafen AG File 304254 Friedrichshafen 2024-08-29

[0002] Hydraulic system with dry sump

[0003] The present invention relates to a hydraulic system with a dry sump, in particular for a drive motor of a motor vehicle.

[0004] A motor vehicle's engine is lubricated and cooled by means of a hydraulic fluid. This fluid is pumped to the cooling and lubrication points by a pressure pump. Fluid escaping from these points collects in a sump. In a dry sump system, a bilge pump transfers the fluid from the sump to a reservoir, from where the pressure pump can be supplied with fluid.

[0005] DE 10 2016 211 226 B3 proposes such a supply system for a motor vehicle's drive unit. In this system, the bilge pump and the pressure pump are driven on a common shaft by an electric motor.

[0006] To ensure a sufficient supply of fluid from the dry sump at all times, the bilge pump is typically designed for a higher flow rate than the pressure pump. Due to the rigid coupling between the bilge and pressure pumps, the bilge pump can continuously deliver a higher flow rate than the pressure pump. If there is insufficient fluid in the sump to meet this flow rate, the bilge pumps may draw air into the reservoir. Controlling the system to simultaneously ensure an adequate supply of fluid to a cooling or lubrication point and maintain a predetermined fill level in the sump or reservoir can be challenging. Another potential problem arises when operating a vehicle's parking lock. The parking lock may require high pressure for a short period of operation.

[0007] One object of the present invention is to provide an improved hydraulic supply system, particularly for the drive motor of a motor vehicle. The invention achieves this object by means of the subject matter of the independent claims. Dependent claims describe preferred embodiments. ZF Friedrichshafen AG File 304254 Friedrichshafen 2024-08-29

[0008] According to a first aspect of the present invention, a hydraulic supply system, particularly for a motor vehicle's drive engine, comprises a reservoir for hydraulic medium; a supply line for delivering hydraulic medium from the reservoir to a cooling or lubrication point, wherein hydraulic medium exiting the cooling or lubrication point is collected in a sump; a bilge pump configured to pump hydraulic medium from the sump into the reservoir; and an electric motor for driving the bilge pump. Furthermore, a pneumatic motor is provided for driving the bilge pump, wherein the pneumatic motor is supplied with air from the reservoir.Furthermore, a pressure pump is provided to supply a volume flow of the medium to a parking lock; wherein the pressure pump is coupled to the bilge pump by means of an overrunning clutch, so that in a first direction of rotation the electric motor drives only the bilge pump and in a second direction of rotation the pressure pump.

[0009] The overrunning clutch, also known as a freewheel or free-running clutch, transmits torque only in one predetermined direction of rotation; in the opposite direction, it allows free rotation in both directions. When the electric motor rotates in the first direction, the bilge pump is driven, a certain pressure builds up in the reservoir, and fluid at this pressure is supplied through the supply line. When the electric motor rotates in the second direction, the pressure pump is driven, which can supply fluid at a pressure sufficient to engage the parking brake.

[0010] The pressure pump is preferably configured to pressurize the medium to a higher pressure than that present in the reservoir. For example, hydraulic medium can be supplied in the reservoir at a pressure of approximately 2-3 bar, while the parking lock requires a hydraulic pressure of 5-6 bar for insertion. However, the pressure pump only needs to supply a small flow rate and can therefore be dimensioned accordingly. In a preferred embodiment, the pressure pump is implemented as a gerotor. ZF Friedrichshafen AG File 304254 Friedrichshafen 2024-08-29

[0011] Engaging the parking lock typically requires only a short time, and it may be sufficient to run the electric motor in the second direction of rotation for a predetermined duration. For example, activating the parking lock might take approximately 100 ms, and the electric motor can run in the second direction for about this time. The electric motor can be switched back to the first direction of rotation as soon as the parking lock is engaged. While rotating in the second direction, the bilge pump may be inactive, so no fluid is pumped into the reservoir. The cooling and lubrication points can be supplied with fluid from the residual pressure in the reservoir.

[0012] The parking lock can be self-retaining, for example, by means of a mechanical retaining element. To deploy the parking lock, the retaining element can be actuated, and the parking lock can be pushed back into an inactive position by means of an elastic element.

[0013] The hydraulic medium can be, in particular, oil. The drive unit can be an internal combustion engine or an electric motor. A hybrid drive system with an electric motor and an internal combustion engine can also be powered by the hydraulic system. Optionally, a gearbox connected to the drive unit can also be powered by the hydraulic system.

[0014] Preferably, the delivery rate of the bilge pump exceeds the volume flow rate of medium through the supply line. This allows the bilge pump to pump a mixture of hydraulic fluid and air. The reservoir is further preferably designed as a pressure vessel whose internal pressure can exceed ambient pressure. For example, the reservoir can have an internal pressure of approximately 2-3 bar; pressure resistance can be guaranteed up to a higher value.

[0015] Due to the high flow rate of the bilge pump, the reservoir can be pressurized, allowing hydraulic fluid to be drawn directly from it for cooling and lubrication points. ZF Friedrichshafen AG File 304254 Friedrichshafen 2024-08-29

[0016] Furthermore, it is advantageous that air, which is pumped into the reservoir by the bilge pump in many operating states of the hydraulic system, can be used to build up pressure. The gaseous component in the reservoir can act as a kind of pressure accumulator, so that the pressure in the reservoir drops only slowly when more hydraulic fluid is discharged than supplied. This allows the hydraulic system to better bridge periods of reduced inflow or increased outflow without significantly reducing the volume of fluid supplied.

[0017] By using air from the reservoir to drive the bilge pump, losses caused by excessive air transfer from the sump to the reservoir can be reduced. Furthermore, by controlling the air flow to the pneumatic motor, the pressure in the reservoir can be easily regulated to a predetermined value.

[0018] The hydraulic system can be manufactured and operated economically. A drive motor, particularly a motor vehicle, powered by the hydraulic system can be maintained with improved operational reliability.

[0019] The pneumatic motor is typically rigidly coupled to the bilge pump. In another embodiment, the electric motor can be coupled to the bilge pump via an additional overrunning clutch. In this configuration, the electric motor is positioned between two overrunning clutches, one leading to the bilge pump and the other to the pressure pump. The overrunning clutches lock in different directions of rotation of the electric motor. Thus, in the second direction of rotation, the electric motor can be disengaged from the bilge pump, preventing it from pumping fluid from the reservoir into the sump. This allows for better pressure maintenance in the reservoir, ensuring an uninterrupted flow of fluid to the cooling and lubrication points.

[0020] A hydraulic fluid separator is preferably provided for air from the reservoir. The pneumatic motor can be configured to tolerate a certain amount of hydraulic fluid in the supplied air. The separator ensures that this amount is not exceeded. This prevents the pneumatic motor from being supplied with incompressible hydraulic fluid instead of compressible air.

[0021] In a simple embodiment, the separator can be integrated into the storage tank. For example, a mixture of hydraulic fluid and air can be introduced into an upper section of the storage tank, while hydraulic fluid for the supply line is drawn from a lower section. The shape and vertical extent of the storage tank can be chosen such that the gaseous and liquid phases separate. A foam can form in a central section of the storage tank, where segregation occurs due to the effects of gravity and / or the surface tension of the hydraulic fluid.

[0022] In a preferred embodiment, the separator comprises a centrifugal separator, which can also be called a cyclone, cyclone filter, or cyclone separator. An inflowing mixture of air and hydraulic medium is set into rotational motion by its own flow velocity through a suitably designed stationary separator. Liquid medium has a higher density than gaseous medium and is forced radially outwards within the separator, so that the gaseous component remains radially inside.

[0023] In another embodiment, a centrifuge can also be used, in which a rotational movement of a container acts on the incoming mixture. The centrifuge can be driven by a drive motor of the bilge pump or by another drive. Alternatively, an air-permeable and pressure-resistant membrane can act as a separator. Another possibility for implementing the separator is a poppet valve, which can optionally be actuated by a float. If the level of hydraulic medium in a container of the separator rises, the float can be driven upwards and close the poppet valve. The same effect can occur if a foam consisting of air and hydraulic medium loses density because the air-to-medium ratio decreases. ZF Friedrichshafen AG File 304254 Friedrichshafen 2024-08-29Closing the seat valve prevents larger quantities of the hydraulic fluid from entering the supply line. This may, under certain circumstances, cause a temporary increase in pressure in the reservoir.

[0024] The compressed air motor can be a vane motor. Alternatively, a piston motor or another positive displacement motor that can be driven by a gaseous medium can be used. A fluid motor can also be used, but is less preferred due to the expected fluctuating flow conditions.

[0025] The pneumatic motor is preferably tolerant of operation in which the pump shaft rotates faster than the pneumatic motor would rotate due to the airflow passing through it. Optionally, a bypass valve can be provided for this case, allowing airflow from the outlet to the inlet of the pneumatic motor when the outlet pressure exceeds the inlet pressure. Alternatively, a mechanical freewheel between the pneumatic motor and the pump shaft can ensure that the rotational speed of the pneumatic motor does not exceed what can be achieved by the airflow.

[0026] In another embodiment, a second bilge pump is provided, which draws fluid from a different point in the sump. The drives of the bilge pumps are rigidly coupled to each other. Such a design can be particularly useful if the sump can be tilted so that the hydraulic fluid can collect at different points. This can be the case, for example, on board a motor vehicle. The delivery capacity of each bilge pump can be at least as high as the volume flow through the supply line; however, a bilge pump is usually dimensioned for a larger volume flow, for example, approximately 120% or more of the volume flow through the supply line. In this example, the combined delivery capacity of both bilge pumps can be approximately 240% of the discharged volume flow, so a large quantity of air must be expected to be pumped. ZF Friedrichshafen AG File 304254 Friedrichshafen 2024-08-29

[0027] To prevent the reservoir from emptying when the system is shut down (i.e., when the bilge pump is not running), a drain valve can be installed between the reservoir and the supply line. This ensures that hydraulic fluid is immediately available through the supply line when the hydraulic system is started. The drain valve can, for example, include a siphon. The siphon can have a predetermined volume that is available at the supply line when the system starts, before new fluid is pumped from the sump into the reservoir. In another embodiment, a space-saving pre-tensioned poppet valve can be used as a drain valve.The seat valve can be pre-tensioned with an elastic element so that it only opens when there is a predetermined pressure difference between the inlet side facing the storage tank and the outlet side facing the supply line.

[0028] In yet another embodiment, a control valve is provided to regulate the flow rate of medium from the storage tank to the supply line. The control valve can also function as a dry-run prevention valve by closing when the system is switched off. The flow rate of medium through the supply line or the pressure of the medium in the supply line can be appropriately controlled during system operation.

[0029] In another embodiment, a nebulizer nozzle is provided for supplying a mist of air and hydraulic fluid. The nebulizer nozzle can be supplied with air from the reservoir. If an air separator is provided, the nebulizer nozzle can be supplied with air from which the hydraulic medium has already been largely separated. This allows the fact that the separated air always contains a residual amount of hydraulic medium, which can be used, in particular, for cooling or lubricating a low-stress area, to be utilized.

[0030] In yet another embodiment, a further pressure sink can be supplied with air. This further pressure sink can comprise any device. ZF Friedrichshafen AG File 304254 Friedrichshafen 2024-08-29

[0031] On board a motor vehicle, the pressure sink may, for example, include another compressed air motor or a pneumatic actuator.

[0032] A control device for regulating the flow rate of the medium through the supply line is preferably provided. The control device can operate the electric motor for driving the bilge pump and / or a control valve for the flow rate through the supply line. The control device can operate based on sensor values ​​that can be provided by the system. In one embodiment, a temperature sensor and / or a pressure sensor are provided on the storage tank. Additional temperature or pressure sensors can be provided at other locations, for example, on the supply line or at a lubrication or cooling point.

[0033] The hydraulic supply system can further include a hydraulic valve for controlling the flow of hydraulic fluid from the supply line to different lubrication or cooling points. For example, a first point can be provided that receives fluid from the supply line when the valve is not actuated and not when the valve is actuated. Conversely, a second point can be provided that receives fluid only when the valve is actuated and not when it is not. Naturally, multiple first and / or multiple second points can also be provided.

[0034] According to yet another aspect of the present invention, a drive axle for a motor vehicle comprises a hydraulic supply system as described herein. The drive axle is designed to propel a motor vehicle and may include an electric drive motor and / or a transmission. Optionally, an input shaft for an internal combustion engine is also provided. A drive axle with an electric drive motor may also be called an electric drive axle.

[0035] According to yet another aspect of the invention, a motor vehicle comprises a drive axle as described herein. The motor vehicle can, in particular, comprise a motorcycle or a passenger car; other possible motor vehicles include a construction machine, an agricultural machine, a truck, or a bus.

[0036] The invention will now be described in more detail with reference to the attached figures, in which:

[0037] Figure 1 shows a hydraulic supply system in a first embodiment; and

[0038] Figure 2 shows a hydraulic supply system in a second embodiment.

[0039] Figure 1 shows a hydraulic supply system 100 in an exemplary first embodiment. The supply system 100 is configured to supply a number of lubrication or cooling points 105 with a hydraulic medium 110, which typically comprises oil. The points 105 are preferably located by a drive motor 115 for a motor vehicle 120.

[0040] The supply system 100 comprises a storage tank 125 for medium 110, a bilge pump 130, a supply line 135, and a compressed air motor 140. For illustrative purposes only, two bilge pumps 130 are shown connected in parallel, capable of drawing from different suction points. Instead of two bilge pumps 130, a double-stroke vane pump or a suitably designed internal gear pump with two suction lines can also be used. More than two bilge pumps 130 or a corresponding multi-acting bilge pump 130 can also be provided.

[0041] A bilge pump 130 can be driven by a pneumatic motor 140 and an electric motor 145. The pneumatic motor 140 is preferably designed as a vane motor; other embodiments are also possible. A bilge pump 130 pumps medium 110 from a sump 150 into the reservoir 125. The pumping capacity of a bilge pump 130 is sufficient to pump a mixture of medium 110 and a gaseous medium, usually air, from the sump 150 during normal operation of the supply system 100 or the drive motor 115. The two bilge pumps 130 can draw in fluid from different points in the sump 150, which may or may not contain medium 110 depending on the operating conditions of the drive motor 115. Optional filters 155 are preferably assigned individually to the bilge pumps 130.

[0042] The storage container 125 is pressure-resistant up to a predetermined pressure, for example, approximately 2-3 bar. An air separator 160 is preferably mounted in or on the storage container 125, separating a mixture of medium 110 and air. In one embodiment, the air separator 160 is designed as a centrifugal separator; other embodiments are also possible. Outgoing air is directed to an air distributor 165, which in a simple embodiment can be formed by a single pipe. If required, an atomizer nozzle 170 can be supplied with air. The air is usually not completely free of medium 110, and the atomizer nozzle 170 can be used to cool or lubricate a component that does not require a flow rate of medium 110.

[0043] Compressed air can be directed from the air distributor 165 to the pneumatic motor 140 to drive it. An optional pressure relief valve 175 can release air from the reservoir 125 to the pneumatic motor 140 as needed.

[0044] Medium 110 exiting the storage tank 125 can be directed into the supply line 135 via a throttle 180. A dry-run protection device 185 prevents the storage tank 125 from emptying due to gravity when the bilge pump 130 is not running. In this case, the dry-run protection device 185 is formed by a siphon; other embodiments are also possible.

[0045] The medium 110 can then be passed through a heat exchanger 190 to cool it to a predetermined temperature. An optional filter 195 ensures that no foreign matter reaches the cooling or lubrication points 105. ZF Friedrichshafen AG File 304254 Friedrichshafen 2024-08-29

[0046] Figure 2 shows a hydraulic supply system 100 in a second embodiment, which is based on the embodiment in Figure 1. For illustrative purposes, only a single bilge pump 130 with two different suction points is used here.

[0047] A drive shaft of the bilge pump 130 is rigidly coupled to an output shaft of the compressed air motor 140. An output shaft of the electric motor 145 can also be rigidly coupled to the drive shaft of the bilge pump 130. A pressure pump 205 is coupled to the output shaft of the electric motor 145 by means of an overrunning clutch 210.

[0048] In normal operation of the supply system, which can correspond to normal operation of the drive motor 115, the electric motor 145 rotates in a first direction of rotation, thereby driving the drive shaft of the bilge pump 130. The pressure pump 205, on the other hand, is disconnected from the output shaft via the freewheel 210 and is not driven.

[0049] A parking lock 215 can be engaged by means of hydraulic pressure from the pressure pump 205. For this purpose, the electric motor 145 can be temporarily driven in a second direction of rotation. In this second direction of rotation, the overrunning clutch 210 engages, and the electric motor 145 drives the pressure pump 205. This pump draws medium 110 from the reservoir 125 via an optional check valve 220 and supplies it to a hydraulic actuator 225 for the parking lock 215. The actuator 225 can be actuated against the restoring force of an elastic element. A holding element 230 can hold the parking lock 215 in the engaged position.

[0050] While the electric motor 145 rotates in the second direction, the bilge pump 130 preferably does not pump any fluid from the sump 150 into the reservoir 125. Depending on the design of the bilge pump 130, however, fluid can be pumped from the reservoir 125 into the sump in the second direction of rotation. Advantageously, a line of the bilge pump 130 opens into the reservoir in an upper section, so that the bilge pump draws back air or, at most, a mixture of medium 110 and air into the sump 150. To counteract a pressure loss in the reservoir 125, an additional overrunning clutch 210 can be provided, which decouples the electric motor 145 from the bilge pump 130 in the second direction of rotation. The pneumatic motor 140 can remain rigidly coupled to the bilge pump 130. This prevents the bilge pump 130 from being driven in the second direction of rotation of the electric motor 145, causing it to stop.

[0051] Once the actuator 225 has reached its end position, the parking lock 215 is fully engaged, or a predetermined time has elapsed that is typically sufficient for this process, the electric motor 145 can be steered back into its first direction of rotation. The parking lock 215 can remain engaged for virtually any length of time while the supply system 100 continues to operate.

[0052] To deploy the parking lock 215, the holding element 230 can be activated to unlock the parking lock 215. For this purpose, the holding element 230 can include an electrically or magnetically actuated actuator. The parking lock 215 can be pushed back into the deployed position by the elastic element. Medium 110, which is contained in a working chamber of the actuator 225, can be drained into the sump 150 through a throttle 235. The electric motor 145 should not be running in the second direction of rotation when deploying the parking lock 215.

[0053] ZF Friedrichshafen AG File 304254 Friedrichshafen 2024-08-29

[0054] Reference mark

[0055] 100 hydraulic supply system

[0056] 105 Cooling or lubrication point

[0057] 110 Medium

[0058] 115 Drive machine

[0059] 120 motor vehicles

[0060] 125 storage containers

[0061] 130 bilge pump

[0062] 135 Supply line

[0063] 140 compressed air motor

[0064] 145 electric motor

[0065] 150 swamp

[0066] 155 filters

[0067] 160 air separators

[0068] 165 air distributors

[0069] 170 Nebulizer nozzle

[0070] 175 Pressure relief valve

[0071] 180 Throttle

[0072] 185 Idle fuse

[0073] 190 heat exchangers

[0074] 195 filters

[0075] 205 Pressure pump

[0076] 210 Overhaul pump, freewheel

[0077] 215 Parking restrictions

[0078] 220 Check valve

[0079] 225 Actuator

[0080] 230 retaining element

[0081] 235 throttle

Claims

ZF Friedrichshafen AG File 304254 Friedrichshafen 2024-08-29 Patent claims 1. Hydraulic supply system (100), in particular for a drive motor (115) of a motor vehicle, wherein the supply system (100) comprises the following elements: - a reservoir (125) for hydraulic medium (110); - a supply line (135) for providing hydraulic medium (110) from the reservoir (125) to a cooling or lubrication point (105), wherein hydraulic medium exiting from the cooling or lubrication point (105) (110) is collected in a swamp (150); - a bilge pump (130) designed to pump hydraulic medium (110) from the sump (150) into the reservoir (125); - an electric motor (145) to drive the bilge pump (130); - a compressed air motor (140) for driving the bilge pump (130), wherein the compressed air motor (140) is supplied with air from the reservoir (125); - a pressure pump (205) to provide a volume flow of the medium (110) to a parking lock (215); - wherein the pressure pump (205) is coupled to the bilge pump (130) by means of an overrunning clutch (210), - so that in a first direction of rotation the electric motor (145) drives only the bilge pump (130) and in a second direction of rotation the pressure pump (205).

2. Supply system (100) according to claim 1, wherein the pressure pump (205) is configured to pressurize the medium (110) to a higher pressure than that prevailing in the storage container (125).

3. Supply system (100) according to claim 1 or 2, wherein the electric motor (145) is controlled in the second direction of rotation only for a predetermined duration upon a request to engage the parking lock (215).

4. Supply system (100) according to one of the preceding claims, wherein the electric motor (145) is coupled to the bilge pump (130) by means of a further overrunning clutch (210). ZF Friedrichshafen AG File 304254 Friedrichshafen 2024-08-29 5. Supply system (100) according to one of the preceding claims, further comprising a separator for hydraulic medium (110) from the air from the storage tank (125).

6. Supply system (100) according to one of the preceding claims, wherein the compressed air motor (140) comprises a vane motor.

7. Supply system (100) according to one of the preceding claims, wherein a further bilge pump (130) is provided which draws from another location in the sump (150), wherein the drives of the bilge pumps (130) are rigidly coupled to each other.

8. Supply system (100) according to one of the preceding claims, wherein an idle prevention device (180) is provided between the storage container (125) and the supply line (135).

9. Supply system (100) according to one of the preceding claims, further comprising a control valve for controlling a volume flow of medium (110) from the storage tank (125) to the supply line (135).

10. Supply system (100) according to one of the preceding claims, further comprising a nebulizer nozzle (170) for providing a mist of air and hydraulic fluid.

11. Supply system (100) according to one of the preceding claims, further comprising a control device for controlling a volume flow of the medium (110) through the supply line (135).

12. Supply system (100) according to one of the preceding claims, further comprising a hydraulic valve for controlling hydraulic medium (110) from the supply line (135) to different lubrication or cooling points. ZF Friedrichshafen AG File 304254 Friedrichshafen 2024-08-29 13. Drive axle for a motor vehicle, comprising a supply system (100) according to any of the preceding claims.

14. Motor vehicle (120) comprising a drive axle according to claim 13.

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