Hydraulic system for a dual-clutch transmission

Abstract

Hydraulic system (1) for a dual-clutch transmission with a first pump (4) which is connected via an output of the first pump (4) to an actuating fluid line (6) of a dual clutch, with a second pump (12) which is connected via an output of the second pump (12) to an actuating line (11) to at least one gear actuator (GS-A, GS-B, GS-C) and a cooling and lubrication line (16), wherein a heat exchanger (15) is provided, wherein an output of the heat exchanger (15) is connected to the cooling and lubrication line (16), wherein a pressure relief valve (14) is arranged to protect the heat exchanger (15) from excessive pressure between the heat exchanger (15) and the output of the second pump (12), characterized in that the second pump (12) is implemented as an electric pump and the output of the second pump (12) is directly connected to an inlet of the pressure relief valve (14),wherein an outlet of the pressure relief valve (14) is directly connected to an inlet of the heat exchanger (15).

Description

[0001] The invention relates to a hydraulic system for a dual-clutch transmission according to the type defined in the preamble of claim 1.

[0002] A hydraulic system for a dual-clutch transmission is described in DE 10 2018 214 427 A1. The hydraulic system for a dual-clutch transmission is divided into two subsystems connected by a check valve, each with its own pump. The first subsystem, which is supplied with pressure by an electric pump, serves to actuate the dual clutch. The second subsystem comprises the cooling, lubrication, and gear selectors within the dual-clutch transmission. It is supplied with pressure by its own pump, which can be mechanically and / or electrically driven.

[0003] Despite this division into two separate areas or subsystems, it remains critical that the gear adjusters, on the one hand, and the cooling and lubrication systems, on the other, have very different oil pressure and flow requirements. The gear adjusters require medium pressures with a medium flow rate for adjustment, and high pressures with a very low flow rate for synchronization. Cooling and lubrication typically operate at ideally low pressures and low to very high oil flows.

[0004] Particularly when the size of the oil pump, which can be electrically driven, is continually reduced as part of energy consumption optimization, it becomes virtually impossible to adequately supply the gear selectors while simultaneously maintaining maximum oil demand for cooling and lubrication, and this must be prioritized. Furthermore, the high pressures that occur, for example, during gear selector synchronization, but possibly also during gear adjustment, can be critical for the components in the cooling and lubrication circuit.

[0005] The generic DE 103 16 215 A1 and WO 2010 / 083 862 A1 also show hydraulic systems with two pumps and corresponding subsystems. Both hydraulic systems are highly complex.

[0006] Furthermore, DE 10 2018 130 528 A1 and DE 10 2016 218 118 A1 each show hydraulic systems with a reversing pump.

[0007] The object of the present invention is therefore to provide an improved hydraulic system which provides an optimized structure, particularly with regard to the disadvantages mentioned above.

[0008] According to the invention, this object is achieved by a hydraulic system having the features in claim 1, and in particular in the characterizing part of claim 1. Advantageous embodiments and further developments of the hydraulic system according to the invention emerge from the dependent claims.

[0009] The design of the hydraulic system is essentially based on the structure known in principle from the prior art, with a first pump supplying the dual clutches and a second pump supplying the gear selector as well as cooling and lubrication. A heat exchanger is arranged downstream of the second pump, i.e. indirectly connected to its outlet, to cool the oil used for cooling before it is pumped again to the components to be cooled and lubricated. To protect the heat exchanger and the downstream components from excessive pressure, a pressure relief valve is arranged between the heat exchanger and the outlet of the second pump supplying this second area with pressure. This pressure relief valve prevents flow to the heat exchanger and the downstream components if the pressure upstream of the heat exchanger becomes too high.In parallel, the gear adjusters are connected to the pump output via at least one control line. This allows both the gear adjusters to be supplied with oil at the required flow rate and pressure level, which can be further adjusted downstream of the pump via a pressure control system, and the cooling and lubrication circuit. The pressure relief valve according to the invention between the pump and the heat exchanger reliably protects this system from excessive pressure.

[0010] According to the invention, the second pump is implemented as an electric pump, and the output of the second pump is directly connected to an inlet of the pressure relief valve. And, according to the invention, an output of the pressure relief valve is directly connected to an inlet of the heat exchanger.

[0011] The “direct” connection of two components means that there is a connecting fluid line between the two connected components, but no further component such as a valve.

[0012] This design creates the conditions for ideal system behavior by decoupling the heat exchanger or cooler from the pressure of the second pump and thus protecting it from damage caused by excessive pressure. The pressure relief valve greatly reduces the oil flow to the cooling and lubrication system in the event of excessive pressure, so that the oil supplied by the second pump in this situation can be used primarily or even entirely for adjustment and / or synchronization in the gear actuators. Decoupling the cooling and lubrication system, which is designed for low to medium pressures, thus makes it possible to provide high pressures for gear adjustment, limited only by the pump output of the second pump, with a low oil requirement, thus enabling optimal prioritization.This situation-dependent prioritization of the gear selector or the cooling and lubrication system, in turn, enables the use of a reduced pump output for the second pump, making it more energy-efficient. In particular, the second pump can be implemented as an electric pump.

[0013] Since in a hydraulic system all components are in principle indirectly connected to one another in some way via the hydraulic oil, it should be noted here that a connection, for example between the output of the second pump and the pressure relief valve or the pressure relief valve or its output and the input of the heat exchanger, is always to be understood as a direct connection, i.e. as a direct connection without any further intermediate components, as long as such are not expressly mentioned.

[0014] According to a very advantageous development of the hydraulic system according to the invention, a control input of the pressure relief valve is connected to the inlet of the heat exchanger. The control pressure for the pressure relief valve is therefore the pressure directly present at the inlet of the heat exchanger, thus ensuring that the heat exchanger is protected from excessive pressures in all cases.

[0015] According to an exceptionally advantageous development, a cooling and lubrication valve with an overpressure function can also be provided, the inlet of which is connected to the cooling and lubrication line and the outlet of which is connected to a component or group of components to be cooled and / or lubricated. A control inlet of the cooling and lubrication valve with overpressure function is connected to the cooling and lubrication line. At least one cooling and lubrication valve with overpressure function can therefore be arranged downstream of the heat exchanger. According to an advantageous development, this can, for example, be the valve via which the cooling and lubrication area of ​​the dual clutch is connected. This cooling and lubrication valve with overpressure function is connected to the heat exchanger via the cooling and lubrication line and, at its control inlet, to the same cooling and lubrication line.If the pressure in the cooling and lubrication line, which feeds various components, for example the dual clutch, a gear set and an electric machine, becomes too high, then oil can be released into the lubrication area of ​​the dual clutch via at least one cooling and lubrication valve with overpressure function in order to limit the pressure in the cooling and lubrication line as required.

[0016] According to an advantageous development of the hydraulic system according to the invention, the first pump can be electrically operated, while the second pump can be mechanically or electrically operated, and, as already mentioned above, it is advantageously also electrically operated. Preferably, both pumps can be designed as electric pumps with an operating voltage of 12V, so that they can be easily operated in the on-board electrical system of a conventional vehicle, in particular a passenger car. Especially with such pumps, it is important to ensure, through the design according to the invention, that the gear selector, as well as the cooling and lubrication, are prioritized and, when required, are not operated simultaneously.

[0017] According to a very advantageous development of the hydraulic system according to the invention, it can now be provided in particular that the cooling and lubrication line is connected to the inlet of at least one cooling and lubrication valve for one or more components or component groups to be cooled and / or lubricated. A control inlet of this at least one cooling and lubrication valve is then connected to the at least one control line. This connection of the control inlet of the cooling and lubrication valve enables pressure control via the pilot pressure from the control line, i.e. the supply line for actuating the gear selector. This has the decisive advantage that a cooling and lubrication valve constructed and used in this way can be designed and implemented without external actuators and yet still enables reliable control and regulation in the desired manner.The complex, expensive, and disadvantageous electromagnetically controlled valve, which is common in this area in the state of the art, can therefore be dispensed with. This can be used for various components or component groups that are supplied via the cooling and lubrication line and a cooling and lubrication valve. Overall, this significantly reduces the effort required for the electromagnetic actuators for the valves.

[0018] As already mentioned several times, the second pump can be electrically driven. According to an exceptionally advantageous development of the hydraulic system according to the invention, it can be designed as an electrically driven pump that can be operated in both directions. The second pump can therefore be implemented as a forward and reverse pump. In one direction of rotation—for example, forward—it supplies the gear selector system as well as the cooling and lubrication system in the manner described. Its output, directed toward the cooling and lubrication system, is connected via the pressure relief valve to the heat exchanger and, in parallel, to the control line.

[0019] Rotating the second pump in reverse can now be used for other purposes. According to an extremely advantageous development of this variant of the hydraulic system according to the invention, the output of the second pump is connected to a parking lock system in addition to the control line and the cooling and lubrication line, and the inlet of the second pump is likewise connected. If this pump is operated forward, one side of the parking lock system is pressurized and, for example, a parking lock is released. If, on the other hand, it is operated in reverse, so that no operation of the gear selector and no cooling or lubrication is possible, then the actual inlet of the second pump, which acts as an output in this direction of rotation, can be connected to the other side of the parking lock system and lock the dual clutch transmission accordingly.According to an extremely advantageous further development of this idea, it is provided that the input of the second pump is connected to a device for engaging the parking lock and the output is connected accordingly to a device for disengaging the parking lock.

[0020] A further very advantageous embodiment of the hydraulic system according to the invention can also provide that the actuating fluid line of the dual clutch is designed on the pressure side to be independent and fluidically separated from the areas pressurized by the second pump. The first subsystem supplied with pressure by the first pump, i.e. the dual clutch, and the second subsystem supplied with pressure by the second pump, i.e. the gear selector and the cooling or lubrication system, are thus designed to be completely hydraulically separated from one another on the pressure side. Unlike in the generic prior art, where a connection is realized via a check valve, the structure in this variant of the invention is completely separate. The two systems are connected to one another exclusively via the oil sump and thus via the oil, which is typically present there at a pressure level of the ambient pressure.The complete separation on the pressure side makes it easier to control the respective pressures and oil quantities.

[0021] Further advantageous embodiments of the hydraulic system according to the invention also emerge from the exemplary embodiment which is illustrated in more detail below with reference to the figure.

[0022] The only attached figure shows an exemplary embodiment of a hydraulic system according to the invention.

[0023] The illustration in the only attached figure shows a possible embodiment of a hydraulic system 1. This is the hydraulic system 1 for a dual-clutch transmission (not shown). It essentially consists of two subsystems, a first subsystem 2 and a second subsystem 3. The first subsystem 2, which is shown on the left in the figure, comprises a first pump 4, which draws oil from, for example, a common oil sump 5 and delivers it into an actuating fluid line 6 of a dual clutch, from which the clutches K1, K2 and a separating clutch K0 are controlled via corresponding valves 7.

[0024] In the embodiment shown here, the actuating fluid line 6 is also connected to the oil sump 5 via an optional valve 8. This can be omitted if the working pressure is controlled accordingly via the first pump 4, which is easily possible, for example, with an electrically driven pump. However, the valve 8 can also be designed as an electrically controlled working pressure valve that is electromagnetically controlled, as indicated in the illustration in the figure. Another possibility would be to design the valve 8 so that it is a fixed pressure relief valve or an external pressure-controlled working pressure valve.

[0025] Otherwise, the first subsystem 2 of the hydraulic system 1 for the dual-clutch transmission largely corresponds to the structure known from the prior art, so this need not be discussed further. Completely separate from this first subsystem 2 in terms of fluid pressure, on the right-hand side of the illustration, is the second subsystem 3, which is designed, among other things, to supply gear selectors GS-A, GS-B, GS-C, etc. A pressure distributor 10 for the gear selectors GS-A, GS-B, GS-C, etc. is connected to a second pump 12 via a control line 11 via an intermediate pressure control 9. This second pump 12 is connected on the inlet side to the oil sump 5 via a check valve 13 and, at its outlet, to the control line 11 on the one hand, and directly, i.e., without any further intermediate components, to the inlet of a pressure relief valve 14, which is arranged upstream of a heat exchanger 15 that serves as a cooler.The pressure relief valve 14 is connected to the inlet of the heat exchanger 15 via a control input. The outlet of the heat exchanger 15 is connected to a cooling and lubrication line 16, via which corresponding components or component groups 17, 18, 19—here, for example, a gear set, the dual clutch, and an electric drive motor—are cooled or lubricated. Cooling and lubrication valves 20, 21, 22 are arranged between the respective components 17, 18, 19 and the cooling and lubrication line 16.

[0026] By way of example and optionally, the cooling and lubrication valve 22 is shown as an electromagnetically controlled valve. The cooling and lubrication valve 20 for supplying component 17, for example the wheelset, is designed as an external pressure-controlled valve. Its control input is connected via the control line designated 23 to the control line 11, specifically downstream of the pressure control 9. The control of the cooling or lubrication of the wheelset as a component or component group 17 is therefore dependent on the pressure in the control line 11. Particularly advantageously, the control of the cooling or lubrication of the wheelset as a component or component group 17 is dependent on a pressure downstream of the pressure control 9.This eliminates the need for electromagnetic control, as provided purely for example in the cooling and lubrication valve 22 for component 19, for example, an electric drive motor. This is advantageous in terms of the required installation space, the control effort, and the costs.

[0027] The cooling and lubrication valve 21 for supplying component 18, i.e., the dual clutch, with oil for cooling or lubrication is designed as a cooling and lubrication valve with an overpressure function, which is connected via its control inlet to the cooling and lubrication line 16. If the pressure level in this cooling and lubrication line 16 is above a preset pressure of the cooling and lubrication valve with an overpressure function 21, then oil is drained towards component 18, i.e., for cooling or lubricating the dual clutch. In addition to connecting the control inlet of the cooling and lubrication valve with an overpressure function 21, a spring shown in the figure acts in the same direction, i.e., in the "valve open" direction. An electromagnetic actuator then acts in the opposite direction, i.e., in the "valve close" direction. The cooling and lubrication valve with an overpressure function 21 is open when de-energized.The higher the current in the electromagnetic actuator of the cooling and lubrication valve with overpressure function 21, the greater the closing force becomes. This allows, on the one hand, the release of excess pressure into the area of ​​component 18, and, on the other hand, the electromagnetic actuator of this cooling and lubrication valve with overpressure function 21 can be used to control the valve as needed, with the pressure at the control input acting merely as a kind of "offset."

[0028] In practical operation, the lubrication and cooling of component 17, i.e. the gear set, and component 19, i.e. the electric drive motor, take priority over the cooling of the dual clutch. In the second subsystem 3, there are essentially two manipulated variables for this purpose. Firstly, the speed of the second pump 12 and, secondly, the pressure threshold, which is specified by the cooling and lubrication valve with overpressure function 21. If there is a high oil demand in the area of ​​component 17 or 19, the speed of the second pump 12 can be increased accordingly, and by increasing the current supplied to the actuator of the cooling and lubrication valve with overpressure function 21, the pressure in the cooling and lubrication line 16 can be increased.Furthermore, cooling of the dual clutch is also possible if necessary because, due to pressure losses in components 17 and 19 or due to the active closure of their associated cooling and lubrication valves 20, 22, the pressure upstream of the cooling and lubrication valve with overpressure function 21 increases due to the higher pump speed in the cooling and lubrication line 16, which in turn cools component 18, i.e. the dual clutch, accordingly. However, its priority is lower than that of components 17, 19. Overall, this leads to energy optimization, so that the second pump 12 can be operated with a very adapted operation, thus causing only very small excess oil and thus low line losses.

[0029] As a further optional feature of the hydraulic system 1, a parking lock system 25 is shown in the figure. The parking lock system 25 serves to engage and disengage a parking lock, for example a parking pawl, in the transmission. It comprises a device 26 for disengaging the parking lock on the one hand and a device 27 for engaging the parking lock on the other. The electric pump 12 can be operated in both directions, i.e., it can rotate both forwards and reverse. If it rotates forwards, it pumps the oil for the second subsystem 3 in order to operate the gear selectors GS-A, GS-B, GS-C, ... and to cool or lubricate the components or component groups 17, 18, 19 in the manner described above. The output of the pump 12 is simultaneously connected to the parking lock system 25, and here in particular to the device 26 for disengaging the parking lock.If pressure is applied to device 26, a piston, for example, which is preloaded against the force of a spring in the direction of the locked state can be disengaged by this pressure. To enable targeted engagement of the parking lock and to prevent accidental engagement of the parking lock, for example in the event of a pressure drop in the second subsystem 3 due to an error or an intentional pressure reduction which is not intended to engage the parking lock, the piston can be locked via a small additional piston. This additional piston would then form device 27 or constitute a part of it. If the parking lock is now to be deliberately engaged, then pump 12 is actuated in the other direction, since neither cooling, lubrication nor gear shifting is necessary in this state.Using the residual oil present in the second subsystem 3 and blocked from the oil sump 5 by the aforementioned check valve 13, oil is then pumped into the device 27 for engaging the parking lock of the parking lock system 25. The small piston can, for example, be actuated against the force of a spring to release the locking of the large piston of the device 26, so that the large piston, which is no longer pressurized, engages the parking lock pawl of the parking lock system 25 through the force of its spring. If this pawl is to be disengaged again, the pump 12 is rotated in the other direction again to supply the second subsystem 3 with pressure. The small piston of the device 27 is now depressurized and is preloaded into its locking position by a spring.The large piston of device 26 is pressurized, thereby releasing the locking state by moving the parking lock pawl from its locked position. In its final position, it is locked by the spring load of the small piston of device 27.

Claims

[1] Hydraulic system (1) for a dual-clutch transmission, comprising a first pump (4) which is connected via an outlet of the first pump (4) to an actuating fluid line (6) of a dual clutch, comprising a second pump (12) which is connected via an outlet of the second pump (12) to a control line (11) to at least one gear selector (GS-A, GS-B, GS-C) and to a cooling and lubricating line (16), wherein a heat exchanger (15) is provided, wherein an outlet of the heat exchanger (15) is connected to the cooling and lubricating line (16), wherein a pressure relief valve (14) is arranged between the heat exchanger (15) and the outlet of the second pump (12) to protect the heat exchanger (15) from excessive pressure, characterized bythat the second pump (12) is realized as an electric pump and the output of the second pump (12) is directly connected to an inlet of the pressure relief valve (14), wherein an output of the pressure relief valve (14) is directly connected to an inlet of the heat exchanger (15). [2] Hydraulic system (1) according to claim 1, characterized by that a control input of the pressure relief valve (14) is connected to the input of the heat exchanger (15). [3] Hydraulic system (1) according to claim 1 or 2, characterized by that a cooling and lubricating valve with overpressure function (21) is provided, the inlet of which is connected to the cooling and lubricating line (16) and the outlet of which is connected to a component (18) or component group to be cooled and / or lubricated, wherein a control inlet of the cooling and lubricating valve with overpressure function (21) is connected to the cooling and lubricating line (16). [4] Hydraulic system (1) according to claim 3, characterized by that the outlet of the cooling and lubrication valve with overpressure function (21) is connected to a line for cooling and / or lubricating the double clutch. [5] Hydraulic system (1) according to one of claims 1 to 4, characterized by that the first pump (4) is electrically driven. [6] Hydraulic system (1) according to one of claims 1 to 5, characterized by that the cooling and lubricating line (16) is connected to an inlet of at least one cooling and lubricating valve (20) for a component (17) or component group to be cooled and / or lubricated, wherein a control inlet of the cooling and lubricating valve (20) is connected to the at least one control line (11). [7] Hydraulic system (1) according to one of claims 1 to 6, characterized by that the second pump (12) can be operated in both directions. [8] Hydraulic system (1) according to claim 7, characterized bythat the output of the second pump (12), which is connected to the control line (11) and indirectly to the cooling and lubrication line (16), is further connected to a parking lock system (25), and wherein an inlet of the second pump (12), which is connected to an oil sump (5) via a check valve (13), is connected to the parking lock system (25). [9] Hydraulic system (1) according to claim 8, characterized by that the parking lock system (25) comprises a device (27) for engaging a parking lock and a device (26) for disengaging a parking lock, wherein the input of the second pump (12) is connected to the device (27) for engaging the parking lock and the output of the second pump (12) is connected to the device (26) for disengaging the parking lock. [10] Hydraulic system (1) according to one of claims 1 to 9, characterized bythat the actuating fluid line (6) of the double clutch is designed on the pressure side to be independent and fluidically separated from the areas pressurized by the second pump (12).

Images