Hydraulic system for a transmission of a motor vehicle

Abstract

Hydraulic system (4) for a transmission (3) of a motor vehicle (1), comprising a first pump (5) driven by an engine (2) of the motor vehicle (1); an electrically driven second pump (20), wherein the first pump (5) and the second pump (20) are each designed solely to pump hydraulic fluid into a primary system pressure circuit (16) and a secondary system pressure circuit (18) of the hydraulic system (4), so that a predetermined pressure prevails in the primary system pressure circuit (16) and the secondary system pressure circuit (18), wherein the hydraulic system (4) has retaining means (15, 26) which, when the first pump (5) is not delivering and the second pump (20) is delivering, are designed to prevent a volume flow of hydraulic fluid delivered by the second pump (20) from being passed through the first pump (5), or when the second pump (20) is not delivering and the first pump (5) is delivering, are designed to prevent a volume flow of hydraulic fluid delivered by the first pump (5) from being passed through the second pump (20), and wherein the hydraulic system (4) has a sail lubrication valve (22) which is designed to control a volume flow of hydraulic fluid delivered by the second pump (20) into the primary system pressure circuit (16) and into the secondary system pressure circuit (18) in such a way that a predetermined pressure is established in the primary system pressure circuit (16) and in the secondary system pressure circuit (18), wherein the sail lubrication valve (22) has a housing (30) and a piston rod (23) axially prestressed by a spring (24) with at least two pistons (27 to 29), wherein the housing (30) and the piston rod (23) with their pistons (27 to 29) form at least two pockets (25, 31) between them, and wherein when a first pressure value is exceeded, a first pocket (25) and a second pocket (31) are connected to one another; and a system pressure regulator (37) which has an adjustable output pressure (p a ) for optionally supporting an axial preload force of the spring (24) of the sail lubrication valve (22).

Description

[0001] The invention relates to a hydraulic system for a transmission, in particular an automatic transmission, of a motor vehicle. The hydraulic system comprises a dual pump system with a first pump driven by an internal combustion engine and an electrically driven second pump.

[0002] Dual pump systems of the aforementioned type are known and are used particularly in automatic transmissions of motor vehicles and transmissions of hybrid vehicles. The first and second pumps are used in combination to pump hydraulic oil within the transmission at specified pressures, e.g., into a primary system pressure circuit and a secondary system pressure circuit. The first pump is typically a vane pump, which can be driven by the internal combustion engine of the motor vehicle.

[0003] A vane pump typically comprises a stator within which a rotor, mounted eccentrically relative to the stator and driven by the internal combustion engine, rotates. The rotor comprises several circumferentially distributed radial slots in which vanes are arranged for radial displacement. As the rotor rotates, the resulting centrifugal forces push the vanes radially outward and into contact with an inner wall of the stator, enabling the suction or displacement of fluid. Vane pumps are preferred due to their relatively high efficiency.

[0004] The second pump can be either a variable-flow or a constant-flow pump, e.g., a vane pump. The second pump makes it possible to maintain a specified hydraulic pressure when the combustion engine is at a standstill and the first pump is not driven, for example, in a so-called "start-stop" mode or in a so-called "sailing" mode. Furthermore, the second pump can support the first pump at certain operating points, allowing the first pump to be downsized and / or operated more efficiently.

[0005] With known solutions, according to which the primary and secondary system pressure circuits are supplied with oil via the second pump, the problem can arise that the primary system pressure can only be adjusted via a pressure-controlled second pump with a high pressure control tolerance, which can have a negative impact on clutch pressure control. A reduction in the pressure control tolerance can be associated with correspondingly increased effort - such as with a pressure sensor - and thus rising costs. Furthermore, it can happen that supply to the secondary system pressure circuit can only be guaranteed if the first pump in the form of a vane pump is absolutely leak-tight. If this is not done sufficiently, the oil pumped for the secondary system pressure circuit can escape via the vane pump into the transmission sump. One possible consequence is that the transmission lubrication is insufficient, which can lead to permanent damage to the transmission.

[0006] The document DE 10 2005 013 137 A1 relates to a method and a device for controlling an oil supply for an automatic transmission and a starting element.

[0007] It is the object of the present invention to provide a hydraulic system of the type mentioned above which does not require the first pump to be tight and which enables the second pump to be controlled with low pressure tolerances.

[0008] The object is achieved by the subject matter of the independent patent claims. Advantageous embodiments are the subject matter of the dependent claims, the following description, and the figures.

[0009] The hydraulic system according to the invention for a transmission of a motor vehicle comprises a first pump driven by an engine of the motor vehicle and an electrically driven second pump. The first pump and the second pump are each configured solely to pump hydraulic fluid into a primary system pressure circuit and a secondary system pressure circuit of the hydraulic system, so that a predetermined pressure prevails in the primary system pressure circuit and the secondary system pressure circuit.The hydraulic system further comprises retention means which, when the first pump is not delivering and the second pump is delivering, are configured to prevent a volume flow of hydraulic fluid delivered by the second pump from being directed through the first pump, or - conversely - when the second pump is not delivering and the first pump is delivering, are configured to prevent a volume flow of hydraulic fluid delivered by the first pump from being directed through the second pump. Furthermore, the hydraulic system comprises a sail lubrication valve which is configured to control a volume flow of hydraulic fluid delivered by the second pump into the primary system pressure circuit and into the secondary system pressure circuit in such a way that a predetermined pressure is established in the primary system pressure circuit and in the secondary system pressure circuit.

[0010] The first pump can be driven, in particular, by an internal combustion engine of the vehicle, whereas the second pump can be electrically driven. Both pumps can be connected to both the first system pressure circuit and the second system pressure circuit, so that hydraulic fluid, in particular oil, can be pumped from the first pump and / or the second pump into the primary system pressure circuit and / or the secondary system pressure circuit in such a way that a specified pressure is established in the respective system pressure circuit.

[0011] The first pump can be a single pump. However, in the context of the present invention, the "first pump" also refers to a pump system with two pumps, which together are configured to pump hydraulic fluid into the primary system pressure circuit and the secondary system pressure circuit of the hydraulic system, so that a predetermined pressure prevails in the primary system pressure circuit and the secondary system pressure circuit. The first pump can, for example, be connected to the primary and secondary system pressure circuits via a system pressure valve, wherein the system pressure valve can establish and close a connection between the first pump and the primary system pressure circuit and / or the secondary system pressure circuit depending on the pressure.In particular, it can be provided that the system pressure valve establishes the connection between the first pump and the primary system pressure circuit when a first pressure value is exceeded and also establishes the connection to the secondary system pressure circuit when a higher second pressure value is exceeded.

[0012] The second pump can be connected to the primary and secondary system pressure circuits via the sail lubrication valve, whereby the sail lubrication valve can establish and close a connection between the second pump and the primary system pressure circuit and / or the secondary system pressure circuit depending on the pressure. In particular, it can be provided that the sail lubrication valve establishes the connection between the second pump and the primary system pressure circuit when a first pressure value is exceeded and also establishes the connection to the secondary system pressure circuit when a higher second pressure value is exceeded.

[0013] The second pump, the primary system pressure circuit, and the secondary system pressure circuit can, in particular, be connected to separate ports of the sail lubrication valve. The sail lubrication valve can have a piston rod and a housing, wherein the piston rod comprises a plurality of spaced-apart pistons along its longitudinal axis. The piston rod with its pistons and the housing can form a plurality of pockets between them, which are designed as radially directed depressions in the housing. The hydraulic fluid delivered by the second pump can flow into the pockets. Depending on the position of the piston rod, two or more ports of the sail lubrication valve can be connected to one another via the pockets.In this way, for example, a hydraulic connection can be established between the second pump and the primary system pressure circuit and / or the secondary system pressure circuit, and a specified pressure can be set within the corresponding system pressure circuit. To enable these connections to be established in a pressure-dependent manner, the piston rod can be preloaded by a spring, particularly in its longitudinal direction.

[0014] The retention means may, in particular, be a check valve, which is preferably arranged in a connecting line between a pressure outlet of the system pressure valve and a node at which the second pump can pump hydraulic fluid into the primary system pressure circuit, such that, although hydraulic fluid can be pumped into the primary system pressure circuit by the first and second pumps, the second pump cannot pump hydraulic fluid into the connecting line and thus through the first pump via the system pressure valve. The check valve can be designed, for example, as a plate valve or a ball seat valve.

[0015] According to the invention, the sail lubrication valve has a housing and a piston rod which is axially preloaded by a spring and has at least two pistons, wherein the housing and the piston rod with their pistons form at least two pockets between them, and wherein a first pocket and a second pocket are connected to one another when a first pressure value is exceeded. The pockets can in particular be arranged next to one another in the longitudinal direction of the piston rod and extend radially between the piston rod and the housing. The first pocket can in particular be connected to the second pump on the inlet side and to the primary system pressure circuit on the outlet side. The second pocket can in particular be connected to the second system pressure circuit on the outlet side.The spring can preload the piston rod within the housing such that the first and second pockets are initially not connected to one another and the second pump delivers hydraulic fluid to the primary system pressure circuit and sets a predetermined pressure within the primary system pressure circuit, but not to the secondary system pressure circuit. As the pressure within the first pocket increases, the piston rod is moved axially against a preload force of the spring. If the pressure within the first pocket exceeds the first pressure value, the piston rod is sufficiently displaced axially against the preload force of the spring that the first pocket and the second pocket are now connected to one another.The second pump is now connected to the primary system pressure circuit via the first pocket and to the secondary system pressure circuit via the first and second pockets and can pump hydraulic fluid into both system pressure circuits and set the required pressures in both system pressure circuits.

[0016] The two pistons can have opposing hydraulically active surfaces of different sizes, with the piston rod being axially preloaded by the spring in the direction of the smaller hydraulically active surface. The hydraulically active surfaces can in particular be opposing, annular end faces of the pistons which have different diameters. Because the larger hydraulically active surface is arranged on the side of the spring, the pressure of the second pump can generate a pressure force which counteracts the preload force of the spring. In this way, pressure regulation within the sail lubrication valve can be achieved through a force balance on the piston rod.

[0017] According to a further embodiment, it is provided that the housing and the piston rod with their pistons form at least three pockets between them, wherein when a first pressure value is exceeded, the first pocket and the second pocket are connected to one another and when a second pressure value is exceeded, a third pocket is connected to the first pocket and the second pocket.

[0018] The three pockets can in particular be arranged next to one another in the longitudinal direction of the piston rod and extend radially between the piston rod and the housing, wherein the first pocket is preferably located between the second pocket and the third pocket and the second pocket faces the spring. The first pocket can in particular be connected to the second pump on the inlet side and to the primary system pressure circuit on the outlet side. The second pocket can in particular be connected to the second system pressure circuit on the outlet side. The spring can preload the piston rod within the housing in such a way that the first and second pockets are initially not connected to one another and the second pump pumps hydraulic fluid into the primary system pressure circuit and sets a predetermined pressure within the primary system pressure circuit, but does not pump fluid into the secondary system pressure circuit.

[0019] As the pressure within the first pocket increases, the piston rod is moved axially against a spring preload. If the pressure within the first pocket exceeds the first pressure value, the piston rod is displaced axially sufficiently against the spring preload that the first pocket and the second pocket are now connected. The second pump is now connected to the primary system pressure circuit via the first pocket and to the secondary system pressure circuit via the first and second pockets. It can pump hydraulic fluid into both system pressure circuits and set the specified pressures in both system pressure circuits.

[0020] As the pressure within the first pocket and the second pocket increases, the piston rod can be moved further axially against the preload force of the spring. If the pressure within the first pocket and the second pocket exceeds the second pressure value, the piston rod is displaced axially sufficiently against the preload force of the spring that the first pocket is now connected to the second and third pockets. In this way, for example, the second pump can be connected to the primary system pressure circuit, the secondary system pressure circuit and a preferably pressureless reservoir for hydraulic fluid. In this way, unintended high pressures within the primary and secondary system pressure circuits can be avoided.

[0021] According to a further embodiment, a closed orifice is connected to the third pocket, and the second pump is a pressure-regulatable pump. According to this embodiment, system pressure control, i.e., control of the pressure within the primary and secondary system pressure circuits, can be achieved via a pump regulator, i.e., the pressure-regulated pump can adjust a delivery rate to achieve a predetermined pressure level based on characteristic control variables. The orifice is preferably arranged in a return line that connects the third pocket of the sail lubrication valve to the pressureless reservoir for hydraulic fluid, in particular a pressureless oil sump. The closed orifice prevents pressure limitation against the reservoir.Limitation of the pressure within the primary and secondary system pressure circuits can be ensured by the pump controller, in particular by reducing the speed of the pump.

[0022] Alternatively, it can be provided that an open orifice is connected to the third pocket, and that the second pump is a volume flow-adjustable pump. According to this embodiment, system pressure can be regulated via the sail lubrication valve with conventional pressure tolerances. The volume flow-adjustable pump can, in particular, be a pump that can be operated at a constant speed. Also according to this alternative, the orifice is preferably arranged in the return line that connects the third pocket of the sail lubrication valve to the unpressurized reservoir for hydraulic fluid, in particular the unpressurized oil sump. The sail lubrication valve can be used to adjust the proportions of the volume flow of hydraulic fluid pumped by the second pump into the sail lubrication valve, which are to be pumped into the primary and secondary system pressure circuits or returned to the reservoir via the open orifice.In this way, it is possible to limit the pressure within the primary and secondary system pressure circuits.

[0023] According to the invention, the hydraulic system comprises a system pressure regulator that provides an adjustable output pressure for selectively supporting an axial preload force of the spring of the sail lubrication valve. The system pressure regulator can, for example, comprise a variably adjustable, electric pressure control valve, to which, for example, the pressure prevailing in the primary system pressure circuit can be applied on the inlet side. The output pressure of the system pressure regulator can, in particular, be variably adjustable, e.g., by means of a variable solenoid coil.

[0024] In the context of this embodiment, "optional" means that the output pressure can also be set to the value "zero". In this case, the axial preload force of the spring is not supported. In particular, if the second pocket connected to the secondary system pressure circuit is arranged closer to the compression spring than the first pocket connected to the second pump and the primary system pressure circuit, this makes it possible for the pressure within the first pocket to only have to exceed the first pressure value in order for the first pocket to be connected to the second pocket and thus for hydraulic fluid to be pumped into the secondary system pressure circuit.

[0025] If a particularly high pressure is required and intended in the primary system pressure circuit, e.g. if clutch filling at a higher pressure is necessary when exiting sailing mode with the combustion engine switched off or in start-stop mode, the output pressure of the system pressure regulator can be set sufficiently high that a connection between the first pocket and the second pocket is prevented or severed. In this way, the delivery of hydraulic fluid by means of the second pump into the secondary system pressure circuit can be prevented or stopped. A corresponding volume can then be used to fill, for example, a sailing exit clutch, which is pressurized by the primary system pressure circuit.

[0026] The system pressure regulator can advantageously be connected on the inlet side to the primary system pressure circuit and on the outlet side to both the sail lubrication valve and a system pressure valve. As described above, the output pressure can support both a preload force of the spring of the sail lubrication valve and a corresponding preload force of a spring of the system pressure valve in order to control the delivery of hydraulic fluid by the first pump into the primary and secondary system pressure circuits.

[0027] The sail lubrication valve may further include an orifice at an outlet connected to the secondary system pressure circuit. The orifice is open and contributes to limiting the volume flow of hydraulic fluid pumped into the secondary system pressure circuit by the second pump.

[0028] In a further embodiment of the invention, a fourth retaining means is arranged between said orifice and the secondary system pressure circuit. This means allows flow from the sail lubrication valve to the secondary system pressure circuit, but is closed off from flow from the secondary system pressure circuit to the sail lubrication valve. This prevents the output pressure of the system pressure regulator from increasing in the event of a pressure increase in the secondary system pressure circuit due to a leak through the sail lubrication valve, which would lead to an undesirable influence on the control behavior of the system pressure valve.

[0029] The automatic transmission according to the invention comprises a hydraulic system according to the invention as described above. Regarding effects and advantageous embodiments, reference is made to the above explanations in connection with the hydraulic system according to the invention to avoid repetition.

[0030] In the following, embodiments of the invention are explained in more detail with reference to the schematic drawing. Fig. 1 a vehicle with an automatic transmission, which comprises an embodiment of a hydraulic system according to the invention, and Fig. 2 a hydraulic circuit diagram of a part of a hydraulic system for use in the automatic transmission according to Fig. 1.

[0031] Fig. 1 shows a motor vehicle 1, in the example shown a passenger car. The motor vehicle 1 comprises an internal combustion engine 2, which drives the motor vehicle 1 via an automatic transmission 3, which has a hydraulic system 4.

[0032] Fig. 2 shows a part of a circuit diagram of the hydraulic system 4 according to Fig. 1. The hydraulic system 4 comprises a first pump 5, in the example shown a pump system, with a primary pump 6 and a secondary pump 7, which is driven by the internal combustion engine 2 of the motor vehicle 1 ( Fig. 1). The primary pump 6 is connected to a first inlet 8 of a system pressure valve 9 and the secondary pump 7 is connected to a second inlet 10 of the system pressure valve 9. The system pressure valve 9 has a piston rod 11 which is axially displaceably received within the system pressure valve 9 and is axially preloaded by a spring 12. In the Fig. 2, the primary pump 6, if driven by the internal combustion engine 2, can suck hydraulic fluid in the form of oil from a reservoir for hydraulic fluid in the form of an oil sump 13 and convey it via a first pocket 14 within the system pressure valve 9 and a first check valve 15 into a primary system pressure circuit 16 (not shown in detail), so that a predetermined pressure is established in the primary system pressure circuit 16. The secondary pump 7, if driven by the internal combustion engine 2, can, in the position determined by Fig. 2, the system pressure valve 9 sucks oil from the oil sump 13 and delivers it via a second pocket 17 within the system pressure valve 9 into a first branch of the secondary system pressure circuit 18 (not shown in detail), so that a specified pressure is established in the secondary system pressure circuit 18. A second check valve 19 prevents oil delivered by the primary pump 6 from reaching the secondary pump 7 via the second pocket 17. All Fig. 2 The check valves shown are designed as plate valves.

[0033] If the internal combustion engine 2 does not drive the primary pump 6 and the secondary pump 7, the oil supply to the primary system pressure circuit 16 and the secondary system pressure circuit 18 can be taken over by a second pump 20, in this case an electrically driven auxiliary oil pump. The second pump 20 is connected to a first inlet 21 of a sail lubrication valve 22. The sail lubrication valve 22 has a piston rod 23, which is axially displaceably received within the sail lubrication valve 22 and is axially preloaded by a spring 24 with a preload force. In the Fig. 2, the second pump 20, if it is electrically driven, can suck hydraulic fluid in the form of oil from the oil sump 13 and deliver it via a first pocket 25 within the sail lubrication valve 22 and a third check valve 26 into the primary system pressure circuit 16, so that a specified pressure is established in the primary system pressure circuit 16 even when the primary pump 6 is not delivering into the primary system pressure circuit 16.

[0034] The piston rod 23 has a Fig. 2 first piston 27 shown above, one in Fig. 2 centrally shown second piston 28 and one in Fig. 2 below, a pot-shaped third piston 29, within which the spring 24 is guided. The piston rod 23 is accommodated axially displaceably within a housing 30 of the sail lubrication valve 22, wherein the housing 30 is Fig. 2 is only indicated by a line. In the Fig. 2, the first pocket 25 is limited by the piston rod 23 with its second piston 28 and its third piston 29 as well as an inner wall of the housing 30. Similarly, in the position shown by Fig. 2, a second pocket 32 is defined by the piston rod 23 with its second piston 27 and its third piston 28 as well as the inner wall of the housing 30. Furthermore, in a similar manner in the position shown by Fig. 2, a third pocket 31 is delimited by the piston rod 23 with its second piston 29 and the inner wall of the housing 30.

[0035] The spring 24 tensions - as if by Fig. 2, the piston rod 23 is advanced axially such that the three pockets 25, 31, and 32 are not connected to one another. Thus, oil initially drawn from the oil sump 13 by the second pump 20 is only pumped into the primary system pressure circuit 16 via the pocket 25 and the third check valve 26. The third check valve 26 prevents oil pumped into the primary pressure circuit 16 by the primary pump 6 from being pumped through the second pump 20 via the sail lubrication valve 22.

[0036] As the pressure within the primary pressure circuit 16 and within the first pocket 25 increases, a force equilibrium is established on the piston rod 23, with the piston rod 23 being axially displaced against the preload force of the spring 24. This is made possible by the fact that the third piston 29 forms a larger hydraulically active first annular surface 33 than an opposite hydraulically active second annular surface 34 of the second piston 28. If the pressure within the first pocket 25 exceeds a first limit value p1, the piston rod 23 with its third piston 29 is displaced so far against the preload force of the spring 24 and in the direction of the spring 24 that the first pocket 25 is connected to the third pocket 31. The third pocket 31 is connected to a second branch of the secondary system pressure circuit 18 via a first orifice 35 for volume flow limitation.Thus, oil pumped from the oil sump 13 by the second pump 20 can be pumped via the first pocket 25 and the second pocket into the secondary system pressure circuit 18 in a pressure-dependent manner, and a predetermined pressure can be set in the secondary system pressure circuit 18.

[0037] If the pressure in the first pocket 25 and in the third pocket 31, which are now connected to each other, rises above a second limit value p2, which is higher than the first limit value p1, the piston rod 23 with its second piston 28 and its third piston 29 is displaced so far against the preload force of the spring 24 and in the direction of the spring 24 that the first pocket 25 is connected to the third pocket 31 and to the second pocket 32. The second pocket 32 is connected to the oil sump 13 via a second orifice 36.

[0038] A pressure-controlled pump can be used as the second pump 20, which adjusts a flow rate based on characteristic control variables to achieve a specified pressure level. In this case, the second orifice 36 is closed, so that when pockets 25, 31, and 32 are connected to one another, in the event of an overpressure, the pressure-controlled second pump 20 limits the pressure within pockets 25, 31, and 32, as well as within the primary system pressure circuit 16 and the secondary system pressure circuit 18, particularly by reducing the speed of the second pump 20.

[0039] Alternatively, a volumetric flow-controlled pump can be used as the second pump 20. In this case, the second orifice 36 is open, allowing pressure limitation against the oil sump 13 by venting excess oil volume and limiting the pressure within the primary system pressure circuit 16 and the secondary system pressure circuit 18. The volumetric flow-controlled pump can, for example, be a constant-speed pump, with the volumetric flow delivered into the primary system pressure circuit 16 and the secondary system pressure circuit 18 being adjusted via the sail lubrication valve 22 with conventional pressure tolerances.

[0040] The hydraulic system 2 further comprises a system pressure regulator 37, which has an adjustable output pressure p ato selectively support the axial preload force of both the spring 24 of the sail lubrication valve 22 and the spring 12 of the system pressure valve 9. For this purpose, the system pressure regulator 37 is connected on the inlet side to the primary system pressure circuit 16 and on the outlet side via a line 44 to both the sail lubrication valve 22 and a system pressure valve 9.

[0041] The outlet pressure p a of the system pressure regulator 37 can act on a hydraulically active first circular surface 38 of the third piston 29, opposite the first annular surface 33 of the cup-shaped third piston 29. Similarly, the output pressure p aof the system pressure regulator 37 also act on a hydraulically effective second circular surface 39 of a cup-shaped piston 40 of the system pressure valve 9. The system pressure regulator 37 comprises a variably adjustable, electric pressure control valve 41, to whose inlet the primary system pressure circuit 16 is connected. The output pressure p a of the system pressure regulator 37 can be variably adjusted by means of a variable solenoid coil 42. The output pressure p a is maximum when no current is applied to the variable solenoid coil 42. The output pressure p a is minimal when the maximum current is applied to the variable solenoid coil 42. In this way, the output pressure p a variably adjusted. Thus, a control pressure acting in the direction of the preload force of the spring 24 or 12 and the opening pressure of the sail lubrication valve 22 with respect to the secondary system pressure circuit 18 can also be variably adjusted.

[0042] The outlet pressure p a can also be set to the value "zero". In this case, the axial preload force, in particular of the spring 24 of the sail lubrication valve 22, is not supported. In this way, it is possible that the pressure within the first pocket 25 only has to exceed the first pressure value p1 so that the first pocket 25 can be connected to the second pocket 31 and thus oil can also be pumped into the secondary system pressure circuit 18. If a particularly high pressure is required and provided in the primary system pressure circuit 16, e.g., if a clutch filling at a higher pressure is required when exiting a sailing mode with the combustion engine switched off or in a start-stop mode, the output pressure p aof the system pressure regulator 37 can be set sufficiently high to prevent or interrupt a connection between the first pocket 25 and the second pocket 31. In this way, the delivery of hydraulic fluid by the second pump into the secondary system pressure circuit 18 can be prevented or shut off. A corresponding volume can then be used to fill, for example, a sail exit coupling, which is pressurized by the primary system pressure circuit 16.

[0043] The Fig.The hydraulic system 4 shown in Figure 2 further enables the second pump 20 to support the first pump system 5 with regard to the oil supply to the primary system pressure circuit 16 and the secondary system pressure circuit 18, particularly in driving situations with insufficient supply. This functionality can also be used to reduce the delivery volume of the first pump system to a minimum. This allows the energy consumed outside of dynamic gearshifts to be reduced, thus enabling fuel consumption savings.

[0044] Optionally, a fourth check valve 43 can be arranged between the first orifice 35 and the secondary system pressure circuit 18. This check valve allows flow from the sail lubrication valve 22 to the secondary system pressure circuit 18 and closes off flow in the opposite direction. This prevents an increase in pressure in the secondary system pressure circuit 18 from passing through the sail lubrication valve 22 to the outlet pressure p a of the system pressure regulator 37. This would be possible due to leakage from the third pocket 31 to the first pocket 25 and due to leakage through the space in which the spring 24 is arranged. An influence on the output pressure p a would ultimately have adverse effects on the function of the system pressure valve.

[0045] As a further option, a hydraulic capacity can be connected to the line 44 as a damping device 45, which absorbs oscillations of the output pressure pa could dampen any such impacts if they were to occur. The damping device 45 comprises a damping cylinder 46 and a third aperture 47. Reference symbol 1 motor vehicle 2 internal combustion engine 3 automatic transmissions 4 Hydraulic system 5 Pump system 6 Primary pump 7 Secondary pump 8 first entrance 9 System pressure valve 10 second entrance 11 Piston rod 12 springs 13 Oil sump 14 first pocket of the system pressure valve 15 Check valve 16 primary system pressure circuit 17 second pocket of the system pressure valve 18 secondary system pressure circuit 19 second check valve 20 second pump 21 first entrance 22 Sail lubrication valve 23 Piston rod 24 springs 25 first bag 26 third check valve 27 first piston 28 second piston 29 third piston 30 housings 31 third pocket 32 second pocket 33 first ring surface 34 second ring surface 35 first aperture 36 second aperture 37 System pressure regulator 38 first circular area 39 second circular area 40 pistons 41 Pressure control valve 42 Solenoid coil 43 fourth check valve 44 Line 45 Damping device 46 damping cylinders 47 third aperture p a Outlet pressure

Claims

[1] Hydraulic system (4) for a transmission (3) of a motor vehicle (1), comprising a first pump (5) driven by an engine (2) of the motor vehicle (1); an electrically driven second pump (20), wherein the first pump (5) and the second pump (20) are each designed solely to pump hydraulic fluid into a primary system pressure circuit (16) and a secondary system pressure circuit (18) of the hydraulic system (4), so that a predetermined pressure prevails in the primary system pressure circuit (16) and the secondary system pressure circuit (18), wherein the hydraulic system (4) has retaining means (15, 26) which, when the first pump (5) is not delivering and the second pump (20) is delivering, are designed to prevent a volume flow of hydraulic fluid delivered by the second pump (20) from being passed through the first pump (5), or when the second pump (20) is not delivering and the first pump (5) is delivering, are designed to prevent a volume flow of hydraulic fluid delivered by the first pump (5) from being passed through the second pump (20), and wherein the hydraulic system (4) has a sail lubrication valve (22) which is designed to control a volume flow of hydraulic fluid delivered by the second pump (20) into the primary system pressure circuit (16) and into the secondary system pressure circuit (18) in such a way that a predetermined pressure is established in the primary system pressure circuit (16) and in the secondary system pressure circuit (18), wherein the sail lubrication valve (22) has a housing (30) and a piston rod (23) axially prestressed by a spring (24) with at least two pistons (27 to 29), wherein the housing (30) and the piston rod (23) with their pistons (27 to 29) form at least two pockets (25, 31) between them, and wherein when a first pressure value is exceeded, a first pocket (25) and a second pocket (31) are connected to one another; and a system pressure regulator (37) which has an adjustable output pressure (p a ) for optionally supporting an axial preload force of the spring (24) of the sail lubrication valve (22). [2] Hydraulic system (4) according to claim 1, characterized by that the two pistons (28, 29) have different sized, opposing hydraulically active surfaces (33, 34), wherein the piston rod (23) is prestressed axially in the direction of the smaller hydraulically active surface (34) by means of the spring (24). [3] Hydraulic system (4) according to claim 2, characterized bythat the housing (30) and the piston rod (23) with their pistons (27 to 29) form at least three pockets (25, 31, 32) between them, wherein when a first pressure value is exceeded the first pocket (25) and the second pocket (31) are connected to one another and when a second pressure value is exceeded a third pocket (32) is connected to the first pocket (25) and the second pocket (31). [4] Hydraulic system (4) according to one of claims 1 to 3, characterized by that a closed aperture (36) is connected to the third pocket (32), and that the second pump (20) is a pressure-adjustable pump. [5] Hydraulic system (4) according to one of claims 1 to 3, characterized by that an open aperture (36) is connected to the third pocket (32), and that the second pump (20) is a volume flow controllable pump. [6] Hydraulic system (4) according to claim 1, characterized bythat the system pressure regulator (37) is connected on the inlet side to the primary system pressure circuit (16) and on the outlet side to both the sail lubrication valve (22) and a system pressure valve (9). [7] Hydraulic system (4) according to one of the preceding claims, characterized by that the sail lubrication valve (22) has an orifice (35) at an outlet which is connected to the secondary system pressure circuit (18). [8] Hydraulic system (4) according to claim 7, characterized by that a fourth retaining means (43) is arranged between the orifice (35) and the secondary system pressure circuit (18), which fourth retaining means (43) allows a flow from the sail lubrication valve (22) to the secondary system pressure circuit (18), but is closed against a flow from the secondary system pressure circuit (18) to the sail lubrication valve (22). [9] Transmission (3) for a motor vehicle (1) comprising a hydraulic system (4) according to one of the preceding claims.

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