Hydraulic system for a transmission of a motor vehicle

Abstract

A hydraulic system for a transmission of a motor vehicle, the system having first and second pumps for conveying hydraulic fluid into primary and/or system-pressure circuits so that an intended pressure prevails in the circuits. The system further including liquid retention means preventing a flow of hydraulic fluid conveyed by the second pump from being conducted through the first pump when the first pump is not conveying and the second pump is conveying, and preventing a flow of hydraulic fluid conveyed by the first pump from being conducted through the second pump when the second pump is not conveying and the first pump is conveying. The system additionally including a sailing-mode lubricating valve for controlling, by an open-loop system, a flow rate of hydraulic fluid conveyed by the second pump into the primary and/or secondary system-pressure circuits such that the intended pressure is set in the system-pressure circuits.

Claims

1. A hydraulic system (4) for a transmission (3) of a motor vehicle (1), comprising: a primary system-pressure circuit (16); a secondary system-pressure circuit (18); a first pump (5) drivable by an engine (2) of the motor vehicle (1) and an electrically drivable second pump (20), the first pump (5) and the second pump (20) each being configured for conveying hydraulic fluid into the primary system-pressure circuit (16) and into the secondary system-pressure circuit (18) so that an intended pressure prevails in the primary system-pressure circuit (16) and in the secondary system-pressure circuit (18); a sailing-mode lubricating valve (22) configured for controlling, by an open-loop system, a flow rate of hydraulic fluid conveyed by the second pump (20) into the primary system-pressure circuit (16) and into the secondary system-pressure circuit (18) such that the intended pressure is set in the primary system-pressure circuit (16) and in the secondary system-pressure circuit (18); and liquid retention means (15, 26) configured for preventing a flow of hydraulic fluid conveyed by the second pump (20) from being conducted through the first pump (5) when the first pump (5) is not conveying and the second pump (20) is conveying, and for preventing a flow of hydraulic fluid conveyed by the first pump (5) from being conducted through the second pump (20) and the sailing-mode lubricating valve (22) when the second pump (20) is not conveying and the first pump (5) is conveying.

2. The hydraulic system (4) of claim 1, wherein the sailing-mode lubricating valve (22) comprises: a housing (30); a spring (24); a piston rod (23) axially preloaded with the aid of the spring (24); and at least two pistons (27 to 29), wherein the housing (30) and the piston rod (23) via the at least two pistons (27 to 29) form at least two recesses (25, 31), and wherein a first recess (25) and a second recess (31) of the at least two recesses are connected when a first pressure value is exceeded.

3. The hydraulic system (4) of claim 2, wherein a second piston (28) of the at least two pistons has a second hydraulically active surface (34) and a third piston (29) of the at least two pistons has a first hydraulically active surface (33), the first hydraulically active surface (33) being of a different size than and being positioned opposed to the second hydraulically active surface (34), wherein the piston rod (23) is axially preloaded by the spring (24) towards the smaller of the first and second hydraulically active surfaces (33, 34).

4. The hydraulic system (4) of claim 2, wherein the at least two recesses further comprises a third recess (32), the third recess (32) being connected to the first recess (25) and to the second recess (31) when a second pressure value is exceeded.

5. The hydraulic system (4) of claim 4, wherein a closed orifice (36) is connected to the third recess (32) and the second pump (20) is a pressure-controllable pump.

6. The hydraulic system (4) of claim 4, wherein an open orifice (36) is connected to the third recess (32) and the second pump (20) is a volumetric flow rate-controllable pump.

7. The hydraulic system (4) of claim 2, further comprising a system pressure regulator (37) which makes an adjustable output pressure (p.sub.a) available for the alternative support of an axial preload force of the spring (24) of the sailing-mode lubricating valve (22).

8. The hydraulic system (4) of claim 7, wherein the system pressure regulator (37) is connected to the primary system-pressure circuit (16) on an inlet side and to the sailing-mode lubricating valve (22) and to a system pressure valve (9) on an outlet side.

9. The hydraulic system (4) of claim 1, wherein the sailing-mode lubricating valve (22) comprises an orifice (35) at an outlet which is connected to the secondary system-pressure circuit (18).

10. The hydraulic system (4) of claim 9, further comprising a fourth liquid retention means (43) arranged between the orifice (35) and the secondary system-pressure circuit (18), the fourth liquid retention means (43) permitting a flow from the sailing-mode lubricating valve (22) to the secondary system-pressure circuit (18) and preventing a flow from the secondary system-pressure circuit (18) toward the sailing-mode lubricating valve (22).

11. A transmission (3) for a motor vehicle (1), comprising the hydraulic system (4) of claim 1.

12. The hydraulic system (4) of claim 1, further comprising a system pressure valve (9) configured for controlling, by an open-loop system, a flow rate of hydraulic fluid conveyed by the first pump (5) into the primary system-pressure circuit (16) and into the secondary system-pressure circuit (18) such that the intended pressure is set in the primary system-pressure circuit (16) and in the secondary system-pressure circuit (18).

13. The hydraulic system (4) of claim 12, wherein the liquid retention means (15, 26) is configured for preventing the flow of hydraulic fluid conveyed by the second pump (20) from being conducted through the first pump (5) and the system pressure valve (9) when the first pump (5) is not conveying and the second pump (20) is conveying.

14. A hydraulic system (4) for a transmission (3) of a motor vehicle (1), comprising: a primary system-pressure circuit (16); a secondary system-pressure circuit (18); a first pump (5) drivable by an engine (2) of the motor vehicle (1) and an electrically drivable second pump (20), the first pump (5) and the second pump (20) each being configured for conveying hydraulic fluid into the primary system-pressure circuit (16) and into the secondary system-pressure circuit (18) so that an intended pressure prevails in the primary system-pressure circuit (16) and in the secondary system-pressure circuit (18); liquid retention means (15, 26) configured for preventing a flow of hydraulic fluid conveyed by the second pump (20) from being conducted through the first pump (5) when the first pump (5) is not conveying and the second pump (20) is conveying, and for preventing a flow of hydraulic fluid conveyed by the first pump (5) from being conducted through the second pump (20) when the second pump (20) is not conveying and the first pump (5) is conveying; a sailing-mode lubricating valve (22) configured for controlling, by an open-loop system, a flow rate of hydraulic fluid conveyed by the second pump (20) into the primary system-pressure circuit (16) and into the secondary system-pressure circuit (18) such that the intended pressure is set in the primary system-pressure circuit (16) and in the secondary system-pressure circuit (18), the sailing-mode lubricating valve (22) comprising an orifice (35) at an outlet which is connected to the secondary system-pressure circuit (18); and a further liquid retention means (43) arranged between the orifice (35) and the secondary system-pressure circuit (18), the further liquid retention means (43) permitting a flow from the sailing-mode lubricating valve (22) to the secondary system-pressure circuit (18) and preventing a flow from the secondary system-pressure circuit (18) toward the sailing-mode lubricating valve (22).

15. A hydraulic system (4) for a transmission (3) of a motor vehicle (1), comprising: a primary system-pressure circuit (16); a secondary system-pressure circuit (18); a first pump (5) drivable by an engine (2) of the motor vehicle (1) and an electrically drivable second pump (20), the first pump (5) and the second pump (20) each being configured for conveying hydraulic fluid into the primary system-pressure circuit (16) and into the secondary system-pressure circuit (18) so that an intended pressure prevails in the primary system-pressure circuit (16) and in the secondary system-pressure circuit (18); liquid retention means (15, 26) configured for preventing a flow of hydraulic fluid conveyed by the second pump (20) from being conducted through the first pump (5) when the first pump (5) is not conveying and the second pump (20) is conveying, and for preventing a flow of hydraulic fluid conveyed by the first pump (5) from being conducted through the second pump (20) when the second pump (20) is not conveying and the first pump (5) is conveying; a sailing-mode lubricating valve (22) configured for controlling, by an open-loop system, a flow rate of hydraulic fluid conveyed by the second pump (20) into the primary system-pressure circuit (16) and into the secondary system-pressure circuit (18) such that the intended pressure is set in the primary system-pressure circuit (16) and in the secondary system-pressure circuit (18); and a system pressure regulator (37), wherein the sailing-mode lubricating valve (22) comprises a housing (30), a spring (24), at least two pistons (27 to 29), and a piston rod (23) axially preloaded with the aid of the spring (24), the housing (30) and the piston rod (23) via the at least two pistons (27 to 29) forming at least a first recess (25) and a second recess (31), the first and second recesses (25, 31) being connectable when a first pressure value is exceeded, and wherein the system pressure regulator (37) makes an adjustable output pressure (p.sub.a) available for the alternative support of an axial preload force of the spring (24) of the sailing-mode lubricating valve (22).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are explained in greater detail in the following with reference to the schematic drawing. In the drawings, the following is shown:

(2) FIG. 1 shows a vehicle including an automatic transmission which includes an exemplary embodiment of a hydraulic system according to the invention, and

(3) FIG. 2 shows a hydraulic diagram of one part of a hydraulic system for use in the automatic transmission according to FIG. 1.

DETAILED DESCRIPTION

(4) Reference will now be made to embodiments of the invention, one or more examples of which are shown in the drawings. Each embodiment is provided by way of explanation of the invention, and not as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be combined with another embodiment to yield still another embodiment. It is intended that the present invention include these and other modifications and variations to the embodiments described herein.

(5) FIG. 1 shows a motor vehicle 1, specifically a passenger car in the example shown. The motor vehicle 1 includes an internal combustion engine 2 which drives the motor vehicle 1 via an automatic transmission 3 which includes a hydraulic system 4.

(6) FIG. 2 shows one part of a circuit diagram of the hydraulic system 4 according to FIG. 1. The hydraulic system 4 includes a first pump 5, specifically a pump system in the example shown, including a primary pump 6 and a secondary pump 7, which is drivable 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 includes a piston rod 11 which is accommodated so as to be axially displaceable within the system pressure valve 9 and is axially preloaded by a spring 12. In the switching position of the system pressure valve 9 shown in FIG. 2, the primary pump 6, provided it is driven by the internal combustion engine 2, can suction hydraulic fluid in the form of oil out of a reservoir for hydraulic fluid in the form of an oil sump 13 and convey the hydraulic fluid via a first recess 14 within the system pressure valve 9 and a first check valve 15 into a primary system-pressure circuit 16 (not represented in further detail), and so an intended pressure is set in the primary system-pressure circuit 16. The secondary pump 7, provided it is driven by the internal combustion engine 2, can suction oil out of the oil sump 13, in the switching position of the system pressure valve 9 shown in FIG. 2, and convey the oil via a second recess 17 within the system pressure valve 9 into a first branch (not represented in further detail) of the secondary system-pressure circuit 18, and so an intended pressure is set in the secondary system-pressure circuit 18. A second check valve 19 prevents oil conveyed by the primary pump 6 from reaching the secondary pump 7 via the second recess 17. All the check valves represented in FIG. 2 are plate valves.

(7) If the internal combustion engine 2 is not driving the primary pump 6 and the secondary pump 7, the oil supply of the primary system-pressure circuit 16 and of the secondary system-pressure circuit 18 can be taken over by a second pump 20, specifically an electrically drivable additional oil pump in this case. The second pump 20 is connected to a first inlet 21 of a sailing-mode lubricating valve 22. The sailing-mode lubricating valve 22 includes a piston rod 23 which is accommodated so as to be axially displaceable within the sailing-mode lubricating valve 22 and is axially preloaded with a preload force by a spring 24. In the switching position of the sailing-mode lubricating valve 22 shown in FIG. 2, the second pump 20, provided it is electrically driven, can suction hydraulic fluid in the form of oil out of the oil sump 13 and convey the oil via a first recess 25 within the sailing-mode lubricating valve 22 and via a third check valve 26 into the primary system-pressure circuit 16, and so an intended pressure is set in the primary system-pressure circuit 16 even when the primary pump 6 does not convey oil into the primary system-pressure circuit 16.

(8) The piston rod 23 includes a first piston 27 which is represented at the top in FIG. 2, a second piston 28 which is represented in the center in FIG. 2, and a pot-shaped third piston 29 which is represented at the bottom in FIG. 2 and within which the spring 24 is guided. The piston rod 23 is axially displaceably accommodated within a housing 30 of the sailing-mode lubricating valve 22, wherein the housing 30 is indicated in FIG. 2 simply by a line. In the switching position of the sailing-mode lubricating valve 22 shown in FIG. 2, the first recess 25 is delimited by the piston rod 23 via its second piston 28 and its third piston 29 as well as an inner wall of the housing 30. In a similar way, in the switching position of the sailing-mode lubricating valve 22 shown in FIG. 2, a second recess 32 is delimited by the piston rod 23 via its first piston 27 and its second piston 28 as well as the inner wall of the housing 30. Furthermore, in a similar way, in the switching position of the sailing-mode lubricating valve 22 shown in FIG. 2, a third recess 31 is delimited by the piston rod 23 via its third piston 29 as well as the inner wall of the housing 30.

(9) As shown in FIG. 2, the spring 24 axially preloads the piston rod 23 in such a way that the three recesses 25, 31 and 32 are not connected to each other. Therefore, oil suctioned out of the oil sump 13 by the second pump 20 is initially conveyed only via the second recess 25 and the third check valve 26 into the primary system-pressure circuit 16. The third check valve 26 prevents oil which has been conveyed into the primary pressure circuit 16 with the aid of the primary pump 6 from being conveyed through the second pump 20 via the sailing-mode lubricating valve 22.

(10) As the pressure within the primary pressure circuit 16 and within the first recess 25 increases, an equilibrium of forces sets in at the piston rod 23, wherein the piston rod 23 is axially displaced against the preload force of the spring 24. This is made possible due to the fact that the third piston 29 forms a larger hydraulically active first annular surface 33 than an opposed, hydraulically active second annular surface 34 of the second piston 28. If the pressure within the first recess 25 exceeds a first limiting value p1, the piston rod 23 via its third piston 29 is displaced against the preload force of the spring 24 and in the direction of the spring 24 to such an extent that the first recess 25 is connected to the third recess 31. The third recess 31 is connected via a first orifice 35 for flow-rate limitation to a second branch of the secondary system-pressure circuit 18. Therefore, oil conveyed from the oil sump 13 by the second pump 20 can be conveyed via the first recess 25 and the third recess 31, in a pressure-dependent manner, into the secondary system-pressure circuit 18 and an intended pressure can be set in the secondary system-pressure circuit 18.

(11) If the pressure in the first recess 25 and in the third recess 31, which are now connected to each other, increases above a second limit value p2 which is higher than the first limit value p1, the piston rod 23, via its second piston 28 and its third piston 29, is displaced against the preload force of the spring 24 and in the direction of the spring 24 to such an extent that the first recess 25 is connected to the third recess 31 and to the second recess 32. The second recess 32 is connected to the oil sump 13 via a second orifice 36.

(12) A pressure-controlled pump is usable as the second pump 20, which adapts a delivery rate on the basis of characteristic control parameters in order to achieve an intended pressure level. The second orifice 36 is closed in this case, and so, when recesses 25, 31 and 32 are connected to each other, in the event of an overpressure, the pressure-controlled second pump 20 limits the pressure within the recesses 25, 31 and 32 and within the primary system-pressure circuit 16 and the secondary system-pressure circuit 18, in particular by reducing the rotational speed of the second pump 20.

(13) Alternatively, a volumetric flow rate-controllable pump is usable as the second pump 20. The second orifice 36 is open in this case, and so a pressure limitation with respect to the oil sump 13 can take place, in that excess oil volume is vented and the pressure within the primary system-pressure circuit 16 and the secondary system-pressure circuit 18 is limited. The volumetric flow rate-controllable pump can be, for example, a pump having a constant rotational speed, wherein the flow conveyed in the primary system-pressure circuit 16 and the secondary system-pressure circuit 18 is adjusted with conventional pressure tolerances via the sailing-mode lubricating valve 22.

(14) The hydraulic system 4 further includes a system pressure regulator 37 which makes an adjustable output pressure p.sub.a available for the alternative support of the axial preload force of the spring 24 of the sailing-mode lubricating valve 22 as well as of the spring 12 of the system pressure valve 9. For this purpose, the system pressure regulator 37 is connected to the primary system-pressure circuit 16 on the inlet side and to the sailing-mode lubricating valve 22 and to a system pressure valve 9 on the outlet side, via a line 44.

(15) The output pressure p.sub.a of the system pressure regulator 37 can act on a hydraulically active, first circular surface 38 of the third piston 29, which is arranged opposite the first annular surface 33 of the pot-shaped third piston 29. In a similar way, the output pressure p.sub.a of the system pressure regulator 37 can also act on a hydraulically active, second circular surface 39 of a pot-shaped piston 40 of the system pressure valve 9. The system pressure regulator 37 includes a variably adjustable, electric pressure control valve 41, to the inlet of which the primary system-pressure circuit 16 is connected. The output pressure p.sub.a of the system pressure regulator 37 is variably adjustable with the aid of a variable solenoid 42. The output pressure p.sub.a is maximal when no current is applied at the variable solenoid 42. The output pressure p.sub.a is minimal when the maximum current is applied at the variable solenoid 42. In this way, the output pressure p.sub.a is variably adjustable. Therefore, a control pressure also acting in the direction of the preload force of the spring 24 or 12, and the opening pressure of the sailing-mode lubricating valve 22 with respect to the secondary system-pressure circuit 18 is variably adjustable.

(16) The output pressure p.sub.a can also be adjusted to the value zero. In this case, the axial preload force, in particular of the spring 24 of the sailing-mode lubricating valve 22, is not supported. In this way, it is made possible that the pressure within the first recess 25 must only exceed the first pressure value p1 in order for the first recess 25 to be connected to the third recess 31 and, therefore, for oil to also be conveyed into the secondary system-pressure circuit 18. If a particularly high pressure is required and provided in the primary system-pressure circuit 16, for example, when a clutch fill with higher pressure is required when exiting a sailing mode with a shut-off internal combustion engine or in a start-stop mode, the output pressure p.sub.a of the system pressure regulator 37 can be set sufficiently high for preventing or disconnecting a connection between the first recess 25 and the third recess 31. In this way, a delivery of hydraulic fluid with the aid of the second pump into the secondary system-pressure circuit 18 can be prevented or stopped. An appropriate volume can then be utilized for filling, for example, a sailing mode-exit clutch, to which pressure is applied with the aid of the primary system-pressure circuit 16.

(17) The hydraulic system 4 shown in FIG. 2 further makes it possible for the second pump 20 to support the first pump system 5 with respect to the oil supply of the primary system-pressure circuit 16 and the secondary system-pressure circuit 18, in particular in driving situations with undersupply. This functionality can also be utilized for reducing the displacement volume of the first pump system to a minimum. Therefore, energy utilized beyond dynamic switching operations can be reduced, which makes it possible to reduce fuel consumption.

(18) Optionally, a fourth check valve 43 can be arranged between the first orifice 35 and the secondary system-pressure circuit 18, which permits a flow from the sailing-mode lubricating valve 22 to the secondary system-pressure circuit 18 and closes against a through-flow in the opposite direction. As a result, the situation is prevented in which an increase of the pressure in the secondary system-pressure circuit 18 affects the output pressure p.sub.a of the system pressure regulator 37 through the sailing-mode lubricating valve 22. This would be possible due to a leakage from the third recess 31 to the first recess 25 and due to a leakage through the chamber in which the spring 24 is arranged. An influencing of the output pressure p.sub.a would ultimately negatively affect the function of the system pressure valve.

(19) As a further option, a hydraulic capacitance, as a damper unit 45, is connectable to the line 44, which could dampen fluctuations in the output pressure p.sub.a if such fluctuations would occur. The damper unit 45 includes a damping cylinder 46 and a third orifice 47 in this case.

(20) Modifications and variations can be made to the embodiments illustrated or described herein without departing from the scope and spirit of the invention as set forth in the appended claims.

REFERENCE CHARACTERS

(21) 1 motor vehicle

(22) 2 internal combustion engine

(23) 3 automatic transmission

(24) 4 hydraulic system

(25) 5 pump system

(26) 6 primary pump

(27) 7 secondary pump

(28) 8 first inlet

(29) 9 system pressure valve

(30) 10 second inlet

(31) 11 piston rod

(32) 12 spring

(33) 13 oil sump

(34) 14 first recess of the system pressure valve

(35) 15 check valve

(36) 16 primary system-pressure circuit

(37) 17 second recess of the system pressure valve

(38) 18 secondary system-pressure circuit

(39) 19 second check valve

(40) 20 second pump

(41) 21 first inlet

(42) 22 sailing-mode lubricating valve

(43) 23 piston rod

(44) 24 spring

(45) 25 first recess

(46) 26 third check valve

(47) 27 first piston

(48) 28 second piston

(49) 29 third piston

(50) 30 housing

(51) 31 third recess

(52) 32 second recess

(53) 33 first annular surface

(54) 34 second annular surface

(55) 35 first orifice

(56) 36 second orifice

(57) 37 system pressure regulator

(58) 38 first circular surface

(59) 39 second circular surface

(60) 40 piston

(61) 41 pressure control valve

(62) 42 solenoid

(63) 43 fourth check valve

(64) 44 line

(65) 45 damper unit

(66) 46 damping cylinder

(67) 47 third orifice

(68) p.sub.a output pressure