Hydraulic system with dry sump

Abstract

The invention relates to a hydraulic supply system (100), in particular for a drive machine (115) of a motor vehicle, wherein the supply system (100) comprises the following elements: 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); and a bilge pump (130) which is designed to deliver the hydraulic medium (110) from the sump (150) into the storage container (125). In the process, the pump capacity of the bilge pump (130) exceeds the volume flow of medium (110) flowing through the supply line (135) so that the bilge pump (130) can deliver a mixture of hydraulic medium (110) and air. The storage container (125) is designed as a pressure vessel, the internal pressure of which can exceed the ambient pressure, and the bilge pump (130) is designed to separate air from the delivered hydraulic medium (110) such that a substantially air-free hydraulic medium (110) is delivered into the storage container (125).

Description

[0001] ZF Friedrichshafen AG File 304273 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 for this flow rate, the bilge pump may draw air into the hopper. 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 hopper can be challenging.

[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 304273 Friedrichshafen 2024-08-29

[0008] A hydraulic supply system, particularly for a motor vehicle's drive unit, comprises a reservoir for hydraulic fluid; a supply line for delivering hydraulic fluid from the reservoir to a cooling or lubrication point, with hydraulic fluid exiting the cooling or lubrication point being collected in a sump; and a bilge pump configured to pump hydraulic fluid from the sump into the reservoir. The pumping capacity of the bilge pump exceeds the volume flow of fluid through the supply line, enabling the bilge pump to pump a mixture of hydraulic fluid and air.The reservoir is designed as a pressure vessel whose internal pressure can exceed ambient pressure; the bilge pump is designed to remove air from the pumped hydraulic medium, so that essentially air-free hydraulic medium is pumped into the reservoir.

[0009] 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.

[0010] Due to the high flow rate of the bilge pump, the reservoir can be pressurized pneumatically, allowing hydraulic fluid to be drawn from it without the use of a pressure pump. By separating air from the pumped hydraulic fluid, the pressure in the reservoir can be more easily maintained within predetermined limits. For example, the operating pressure of the reservoir can be approximately 2 bar. If there is too much hydraulic fluid in the reservoir, the bilge pump can be driven to a higher flow rate. The reservoir can then hold more hydraulic fluid, which may cause its internal pressure to rise. A certain amount of air can be held in the reservoir, which can be compressed, thus moderating the pressure increase.The gaseous component of the fluid in the reservoir can create a kind of pressure accumulator, so that the pressure in the reservoir only decreases slowly when more hydraulic medium 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.

[0011] 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.

[0012] It is particularly advantageous for the bilge pump to include a side-channel pump. The side-channel pump combines features of a positive displacement pump with those of a centrifugal pump and is especially suitable for pumping mixtures of liquid and gaseous media. At least temporarily, the side-channel pump can pump only gaseous media and thus operate as a vacuum pump. During pumping, the liquid and gaseous phases of the pumped medium are separated by centrifugal force and exit the side-channel pump through separate outlets. The side-channel pump has a high suction capacity and can achieve a high pressure coefficient. A relatively low drive speed is therefore possible, for example, in the range of approximately 1450 rpm. 1The slow rotational speed allows for better control of mechanical stresses, partial load behavior, and noise generation. Furthermore, the tendency to cavitate is reduced. Consequently, the service life of the bilge pump can be extended.

[0013] It is preferred that air separated from the hydraulic supply system by the bilge pump is released. The air can, for example, be released into the environment.

[0014] The bilge pump can be driven by an external source, for example, the vehicle's engine. If the flow rate discharged through the supply line is low, the power required from the external source can also be low. Preferably, the bilge pump is driven partially or entirely by an electric motor. The drive power or speed of the electric motor can be easily controlled, allowing the system (ZF Friedrichshafen AG File 304273 Friedrichshafen 2024-08-29) to be flexibly controlled, for example, with regard to different flow rates of medium supplied by the supply line or with regard to the fill level of medium in the sump or storage tank.

[0015] Preferably, a charging valve is provided for draining hydraulic medium from the reservoir to a suction side of the bilge pump. The charging valve is preferably a spring-loaded flow element that opens when a predetermined pressure difference between its inlet and outlet sides is exceeded.

[0016] If the level of hydraulic fluid on the suction side of the bilge pump is too high, the pump can be operated at increased power to remove the maximum volume of fluid from the intake area. In this case, the charging valve can open and return hydraulic fluid to the suction side of the bilge pump. Opening the charging valve reduces the flow towards the cooling or lubrication points, resulting in more hydraulic fluid being drawn in than is delivered to these points.

[0017] The supply system can include an air separator to equalize pneumatic pressure in the reservoir. The air separator can release air from the reservoir, ensuring that a predetermined maximum pressure is not exceeded. Simultaneously, the air separator can retain fluid medium in the reservoir, preventing fluid loss. The air separator can be implemented in various ways. It should be noted that several different techniques can also be used in parallel or in series to separate air and hydraulic medium.

[0018] The air separator can, for example, comprise an air-permeable and fluid-impermeable membrane. The membrane can be pressure-resistant up to the maximum pressure prevailing in the reservoir and, for example, made of PTFE. The membrane can be mounted on a support structure, which can be, for example, slotted, griddled, or honeycomb-shaped, and divides the membrane into smaller sections that can better withstand the pressure difference between the upper and lower surfaces. Multiple membranes can also be used sequentially. The membranes can be progressively finer, so that increasingly smaller droplets are captured within them. Retained hydraulic fluid can drain off a membrane and, for example, be returned to the reservoir.

[0019] Another way to implement an air separator is with a poppet valve, which can be actuated, for example, by a float. If the level of hydraulic fluid in a reservoir of the air separator rises, the float can be driven upwards and close the poppet valve. Closing the poppet valve prevents larger quantities of hydraulic fluid from entering the supply line.

[0020] The poppet valve can also be spring-loaded, so that it opens at a predetermined pressure differential between its inlet and outlet sides. Furthermore, two antiparallel, pre-loaded poppet valves can be provided to compensate for not only overpressure but also underpressure in the reservoir. Active pressure control is also optionally available, for example, via a processing unit to control the supply system.

[0021] 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. The combined delivery capacity of both bilge pumps in this example 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 304273 Friedrichshafen 2024-08-29

[0022] The described hydraulic system can operate without a pressure pump to draw fluid from the reservoir. 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 is started, 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 the 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.

[0023] 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.

[0024] In another embodiment, a nebulizer nozzle is provided for supplying a mist of air and hydraulic fluid from the reservoir. The nebulizer nozzle can be supplied with air or a mixture of air and fluid 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 may contain a residual amount of hydraulic medium, which can be used for cooling or lubricating a low-stress area, to be utilized. ZF Friedrichshafen AG File 304273 Friedrichshafen 2024-08-29

[0025] In yet another embodiment, a further pressure sink can be supplied with air. This further pressure sink can comprise any device. On board a motor vehicle, for example, the pressure sink can comprise another compressed air motor or a pneumatic actuator.

[0026] A control device for regulating the flow rate of the medium through the supply line is preferably provided. The control device can operate an additional drive motor for 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.

[0027] The hydraulic supply system can further include a switching 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 is supplied with hydraulic fluid only in one position of the switching valve, and a second point that is supplied in both positions. In another embodiment, only the first point can be supplied with fluid from the supply line when the valve is not actuated, and only the second point when the valve is actuated. Other distribution strategies are also possible. Naturally, multiple first and / or multiple second points can also be provided.

[0028] According to yet another aspect of the present invention, a drive axle for a motor vehicle comprises a hydraulic supply system 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. ZF Friedrichshafen AG File 304273 Friedrichshafen 2024-08-29

[0029] According to yet another aspect of the invention, a motor vehicle comprises a drive axle as described herein. The motor vehicle may in particular be a motorcycle or a passenger car; other possible motor vehicles include a construction machine, an agricultural machine, a truck, or a bus.

[0030] The invention will now be described in more detail with reference to the attached figures, in which:

[0031] Figure 1 shows a hydraulic supply system in a first embodiment; and

[0032] Figure 2 shows a hydraulic supply system in a second embodiment.

[0033] 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.

[0034] The supply system 100 comprises a storage tank 125 for medium 110, a bilge pump 130, and a supply line 135. By way of example, two bilge pumps 130 are provided in parallel, capable of drawing from different suction points. One bilge pump 130 is preferably designed as a phase-separating pump, separating a gaseous phase from a liquid phase of the medium 110 being pumped. The bilge pump 130 can have separate connections for the pumped air and the pumped liquid.

[0035] A bilge pump 130 particularly preferably comprises a side-channel pump. In a side-channel pump 130, power is transferred from a star-shaped impeller (e.g., star wheel) rotating concentrically in the housing to the medium 110 in a side channel arranged next to the impeller. The star wheel with straight radial ZF Friedrichshafen AG File 304273 Friedrichshafen 2024-08-29

[0036] The impeller, lacking sidewalls, is of very simple construction and is enclosed externally and on both sides by the housing walls with narrow gaps. The housing has a side channel on one or both sides, extending almost around its entire circumference, but interrupted at one point, namely between an inlet and an outlet slot. Liquid medium 110 is conveyed through a radially outer port, and gaseous medium 110 through a radially inner port. Conveyed liquid medium 110 is directed into the storage tank 125. Conveyed gaseous medium 110 can be released into the environment.

[0037] In the illustrated supply system 100, the cooling or lubrication points 105 are divided into two groups, and a switching valve 140 is provided to control the flow of medium 110 to the points 105. The switching valve 210 can be actuated electrically or pressure-controlled. In a first position of the switching valve 210, only the cooling or lubrication points 195 shown in a lower row are supplied with medium 110, as shown in Figure 2. When the switching valve 210 is actuated, it assumes a second position in which the cooling or lubrication points 195 shown in an upper row are also supplied with medium 110.

[0038] A bilge pump 130 can be driven by a drive motor 145, preferably an electric motor, although other types of drive motors 145 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. ZF Friedrichshafen AG File 304273 Friedrichshafen 2024-08-29

[0039] The reservoir 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 reservoir 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. An optional charge valve 175 can release air from the reservoir 125 as needed, for example, towards one of the bilge pumps 130.Air released from the reservoir 125 can be directed to a suction side of a bilge pump 130, thereby relieving the bilge pump 130 in the manner of a suction charging.

[0040] Medium 110 exiting the storage tank 125 can, for example, be directed into the supply line 135 via a throttle 180. A dry-run protection device 185 can prevent 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.

[0041] 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.

[0042] Figure 2 shows a hydraulic supply system 100 in an exemplary second embodiment, which is based on the embodiment of Figure 1. For improved clarity, only those elements of the supply system 100 that are mentioned in the following text are provided with reference numerals; for all other elements shown, the reference numerals of Figure 1 and the associated descriptions apply. ZF Friedrichshafen AG File 304273 Friedrichshafen 2024-08-29

[0043] In the illustrated embodiment, a control unit 205 is provided, which preferably operates electronically, in particular on the basis of a microcomputer or microcontroller. The control unit comprises at least one input 210 and at least one output 215. Signals at the inputs 210 and the outputs 215 are preferably electrical.

[0044] The control unit 205 is configured to control the drive power or speed of the additional drive motor 145. A speed signal from the additional drive motor 145 can be fed to the control unit 205 for feedback purposes. Furthermore, the control unit 205 can control the controllable valve 205 to regulate the flow rate of the medium 110 to the cooling or lubrication points 105.

[0045] The control unit 205 can control the additional drive motor 145 such that a predetermined pressure is established in the reservoir 125. Additionally, the control unit can ensure that a predetermined level of medium in the sump 150 is not exceeded. Optionally, the air separator 160 can be actively controlled to release air from the reservoir 125. A controllable or switchable valve can also be provided instead of the air separator 160.

[0046] Controls can be implemented based on sensor values ​​acquired by sensors on the supply system 100. In particular, a temperature sensor 220 and / or a pressure sensor 225 can be provided on the storage tank 125.

[0047] Additionally, a further temperature sensor 230 can be provided in the area of ​​a supply to the cooling or lubrication points 105. The control unit 205 can control the switching valve 210 depending on the temperature of the supplied medium 110. The temperature of the supplied medium can also be taken into account for controlling the additional drive motor 145 and / or the controllable valve 205. Conversely, the switching valve 210 can also be controlled depending on a pressure or a temperature at the reservoir 125. ZF Friedrichshafen AG File 304273 Friedrichshafen 2024-08-29

[0048] Preferably, a controllable valve 235 is used instead of the throttle 180 to control the flow rate of medium 110 exiting the reservoir 125. The valve 205 can be actuated by the processing unit 205 to provide an appropriate flow rate to the lubrication points 105. Furthermore, the processing unit 205 can completely shut off the flow rate when the supply system 100 is switched off and the bilge pump 130 is not running. The separate idle prevention device 185 can then be omitted. The processing unit 205 cannot actuate the valve 235 when the supply system 100 is not in operation, for example, when a nearby vehicle is parked. The controllable valve 235 can be configured to shut off the flow rate when it is not actuated.

[0049] ZF Friedrichshafen AG File 304273 Friedrichshafen 2024-08-29

[0050] Reference mark

[0051] 100 hydraulic supply system

[0052] 105 Cooling or lubrication point

[0053] 110 Medium

[0054] 115 Drive machine

[0055] 120 motor vehicles

[0056] 125 storage containers

[0057] 130 bilge pump

[0058] 135 Supply line

[0059] 140 switching valve

[0060] 145 Drive motor

[0061] 150 swamp

[0062] 155 filters

[0063] 160 air separators

[0064] 165 air distributors

[0065] 170 Nebulizer nozzle

[0066] 175 Charging valve

[0067] 180 throttle

[0068] 185 Idle fuse

[0069] 190 heat exchangers

[0070] 195 filters

[0071] 205 Processing facility

[0072] 210 Entrance

[0073] 215 Exit

[0074] 220 temp temperature sensor

[0075] 225 Pressure sensor

[0076] 230 temp temperature sensor

[0077] 235 controllable valve

Claims

ZF Friedrichshafen AG File 304273 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); - wherein the delivery capacity of the bilge pump (130) exceeds the volume flow of medium (110) flowing through the supply line (135), so that the bilge pump (130) can pump a mixture of hydraulic medium (110) and air; - wherein the storage container (125) is designed as a pressure vessel whose internal pressure can exceed an ambient pressure; - wherein the bilge pump (130) is designed to remove air from the pumped hydraulic medium (110) so that essentially air-free hydraulic medium (110) is pumped into the reservoir (125).

2. Supply system (100) according to claim 1, wherein the bilge pump (130) comprises a side channel pump (130).

3. Supply system (100) according to claim 1 or 2, wherein the air separated from the bilge pump is released from the hydraulic supply system (100).

4. Supply system (100) according to one of the preceding claims, wherein the bilge pump (130) is driven by an electric motor (145). ZF Friedrichshafen AG File 304273 Friedrichshafen 2024-08-29 5. Supply system (100) according to one of the preceding claims, further comprising a charging valve (175) for draining hydraulic medium (110) from the reservoir (125) to a suction side of the bilge pump (130).

6. Supply system (100) according to one of the preceding claims, further comprising an air separator (160) for equalizing a pneumatic pressure in the storage container (125).

7. Supply system (100) according to claim 6, wherein the air separator (160) comprises an air-permeable and fluid-impermeable membrane.

8. Supply system (100) according to claim 6 or 7, wherein the air separator (160) comprises a seat valve.

9. 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.

10. Supply system (100) according to one of the preceding claims, wherein an idle prevention device (185) is provided between the storage container (125) and the supply line (135).

11. Supply system (100) according to one of the preceding claims, further comprising a control valve (205) for controlling a volume flow of medium (110) from the storage container (125) to the supply line (135).

12. 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 from the reservoir (125). ZF Friedrichshafen AG File 304273 Friedrichshafen 2024-08-29 13. Supply system (100) according to one of the preceding claims, further comprising a control device (305) for controlling a volume flow of the medium (110) through the supply line (135).

14. Supply system (100) according to one of the preceding claims, further comprising a switching valve (210) for controlling hydraulic medium (110) from the supply line (135) to different lubrication or cooling points.

15. Drive axle for a motor vehicle, comprising a supply system (100) according to any of the preceding claims.

16. Motor vehicle (120) comprising a drive axle according to claim 15.

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