DE102011016571A1 - Hydraulic system for continuously variable transmission for motor vehicle, has load subjected with pressure by operating pressure connection and operating pressure region, where controlled leakage from region is discharged by leakage valve - Google Patents

Abstract

The system (1) has a pressure reducing valve (10) e.g. 3/3 directional valve, designed as a slide valve with a positive overlap. The pressure reducing valve includes an operating pressure connection, which is connected with a tank connection or a system pressure connection by the pressure reducing valve. A load (18) e.g. adjusting cylinder, is subjected with operating pressure by the operating pressure connection and an operating pressure region. Controlled leakage from the operating pressure region is discharged by an actively actuated leakage valve (30) i.e. 2/2 directional valve. An independent claim is also included for a method for operating a hydraulic system.

Description

The invention relates to a hydraulic system with a tank, designed as a positive overlap valve pressure reducing valve having a tank port, a system pressure port and a working pressure port, which is connectable by the pressure reducing valve to the system pressure port or the tank port, and with a consumer, via the Working pressure port of the pressure reducing valve and a working pressure range is acted upon by a working pressure. The invention further relates to a method for operating such a hydraulic system.

From the international release WO 2007/003151 A1 Pressure reducing valves are known which connect the working pressure either with the tank pressure or with the system pressure or occupy intermediate positions in order to steplessly modulate the working pressure.

The object of the invention is to improve the response of a pressure reducing valve in a hydraulic system according to the preamble of claim 1 in critical situations.

The object is in a hydraulic system with a tank, designed as a positive overlap valve pressure reducing valve having a tank port, a system pressure port and a working pressure port that is connectable through the pressure reducing valve to the system pressure port or the tank port, and with a consumer who over the working pressure port of the pressure reducing valve and a working pressure range is acted upon by a working pressure, achieved by an actively actuated leakage valve through which a regulated leakage can be discharged from the working pressure range to improve the response of the pressure reducing valve. Leakage is the term used to refer to a volume flow that is deliberately released from the working pressure range, for example into the tank in order to lower the working pressure in a targeted manner or to improve controllability. This can be particularly advantageously avoided that the pressure reducing valve in certain operating conditions in overlap between a system pressure edge and a tank control edge or even completely moves to the tank control edge. As a result, slide change paths can be avoided, which reduce the dynamics of the hydraulic system and could lead to pressure jumps when driving over the control edge in certain driving situations. Through the leakage valve, the response time or dynamics of the pressure reducing valve can be increased in certain driving situations and in a restart of the engine in a start-stop operation by means of regulated leakage. The controlled leakage has the consequence that the valve slide, which is also referred to as a valve piston, does not have to move from the overlap between the system pressure edge and the tank control edge in order to realize a pressure increase at the load. The pressure reducing valve is preferably designed as a 3/2-way valve with positive coverage or as a 3/3-way valve. The tank connection communicates with a tank containing a working medium, such as hydraulic oil, which is subjected to a tank pressure, preferably ambient pressure. At least one consumer is connected to the working pressure connection. The consumer is, for example, a hydraulic cylinder, in particular an adjusting cylinder for a CVT transmission, a gear adjusting cylinder for an automated manual transmission or for a dual-clutch transmission or a clutch cylinder. In a positive overlap zone, the valve spool can move away without changing the working pressure. The positive overlap is needed to prevent working fluid from constantly flowing through the pressure reducing valve during operation. If the working fluid is relatively cold, the positive coverage, for example, due to viscous friction of the valve spool, may adversely affect the responsiveness of the pressure reducing valve. Furthermore, the response of the pressure reducing valve in certain operating conditions may be too slow, as in a vehicle in start-stop operation. In this case, for example, a clutch can be acted upon very quickly. In such critical situations, the valve spool of the pressure reducing valve according to an essential aspect of the invention is maintained by the regulated leakage at or near the control edge. This significantly improves the response in critical situations.

A preferred embodiment of the hydraulic system is characterized in that the leakage valve is directly controlled or actuated. The leakage valve is preferably actuated electromagnetically via a control unit, in particular an engine control unit or a transmission control unit.

A further preferred embodiment of the hydraulic system is characterized in that the leakage valve is designed as a 2/2-way valve with an open and a closed position as a basic position. In the open position, the working pressure range is preferably connected to the tank to discharge the regulated leakage into the tank. In the closed position, the connection to the tank is interrupted. By a biasing force, which is applied for example by a spring, the leakage valve is preferably in his Pre-biased closed position, which is therefore referred to as the basic position.

A further preferred embodiment of the hydraulic system is characterized in that the leakage valve is actuated or actuated via a proportional valve designed as a pressure regulator. The proportional valve is preferably actuated electromagnetically and advantageously has a plurality of functional areas. In a functional area, for example, a cooling oil valve is activated. In another functional area, for example, a safety valve is activated. Particularly advantageously, the leakage valve according to the invention is activated in a further functional area. The various functional areas are pressure-dependent or current-dependent. Preferably, a lower current range or pressure range of the proportional valve is used to discharge the regulated leakage via the leakage valve in the tank. In a medium current range or pressure range of the proportional valve, cooling via the cooling oil valve is switched on / off. In an upper current range or pressure range, the safety valve is opened to relieve the working pressure range for safety reasons in the tank.

A further preferred embodiment of the hydraulic system is characterized in that the leakage valve is designed as a 2/3-way valve with two closed positions and an open position as the center position. In the two closed positions, the connection between the working pressure range and the tank is interrupted. In the open position, a controlled leakage from the working pressure range is discharged into the tank.

A further preferred embodiment of the hydraulic system is characterized in that the leakage valve comprises a valve spool, which is acted upon at a first end with a pilot pressure. About the pilot pressure, the leakage valve can be actively actuated, for example via a control unit, in particular an engine control unit or a transmission control unit. The valve spool is preferably acted upon at its second end with a spring force by which the valve spool is biased to its normal position. The basic position of the valve spool preferably corresponds to one of the closed positions.

A further preferred exemplary embodiment of the hydraulic system is characterized in that the valve slide has a first piston web, which releases or closes a working pressure port, and a second piston web, which releases or closes a tank port. The first piston web is preferably arranged at the first end of the valve spool. The second piston web is preferably acted upon at its free end with a spring force.

A further preferred embodiment of the hydraulic system is characterized in that the valve slide between the two piston webs has a connection region which connects the working pressure port in response to a valve spool movement with the tank port or not. Through the connection area of the valve spool, leakage from the working pressure range can be discharged into the tank via the working pressure connection and the tank connection.

Another preferred embodiment of the hydraulic system is characterized in that a hydraulic resistance between the working pressure range and the tank is connected. The hydraulic resistance may be upstream or downstream of the leakage valve in the direction of a leakage flow. The hydraulic resistance may include a throttle and / or a diaphragm. The size of the hydraulic resistor can be used to set the leakage quantity.

In a method for operating a hydraulic system described above, the above-mentioned object is alternatively or additionally achieved by activating or deactivating leakage from the working pressure range by active actuation of the leakage valve in order to improve the response of the pressure reducing valve.

Further advantages, features and details of the invention will become apparent from the following description in which, with reference to the drawings, various embodiments are described in detail. Show it:

1 an inventive hydraulic system for a CVT transmission in the form of a hydraulic circuit diagram;

2 an embodiment of a leakage valve for a hydraulic system, as in 1 is shown in longitudinal section and

3 a further embodiment of a hydraulic system in the form of a hydraulic circuit diagram.

In 1 is a hydraulic system 1 with a tank coming out with the help of a hydraulic pump 4 over a filter 5 Hydraulic medium is sucked. The hydraulic medium is, for example, hydraulic oil. The Tank 2 is symbolically indicated at various points of the hydraulic circuit diagram. The hydraulic pump 4 is drivingly coupled to an internal combustion engine in a motor vehicle or is powered by an electric motor. Thus, the hydraulic pump becomes 4 permanently driven when the internal combustion engine is running or in operation.

The pump 4 conveys hydraulic medium into a system pressure range 8th , which is subjected to a system pressure. To the system pressure area 8th is a pressure reducing valve 10 connected, which is designed as a proportional valve and hydraulically actuated. The pressure reducing valve 10 is designed as a 3/2-way valve with a positive overlap.

One tank connection of the pressure reducing valve 10 stands with the tank 2 in connection. One working pressure connection of the pressure reducing valve 10 stands with a working pressure range 15 in connection. A safety valve 16 is between the pressure reducing valve 10 and the working pressure range 15 connected. The safety valve 16 is designed as a 3/2-way valve and hydraulically controlled.

About the working pressure range 15 becomes a consumer 18 subjected to a working pressure. At the consumer 18 it is a hydraulic cylinder, in particular an adjusting cylinder of a continuously variable conical-pulley belt transmission, which is also referred to as CVT transmission. The consumer may also be a gear actuator in a transmission or a clutch cylinder.

To the system pressure area 8th is also a pilot pressure valve 20 connected, which serves to regulate the system pressure to a constant pilot pressure. The pilot pressure valve 20 are two proportional valves 21 . 22 downstream. Between the proportional valves 21 . 22 and the pilot pressure valve 20 each is a hydraulic resistance 23 . 24 connected.

The hydraulic resistance 23 . 24 may include an orifice or throttle and serves to supply the proportional valves 21 . 22 to throttle. The proportional valves 21 . 22 are controlled by electromagnets with the aid of a control unit. The proportional valve 21 is via a pilot control line 25 in control with a leakage valve 30 in connection. The proportional valve 22 is via a pilot control line 26 in terms of control with the pressure reducing valve 10 in connection.

In the pilot control line 25 are three branches 27 . 28 . 29 intended. At the junction 27 branches a control line to the proportional valve 21 from. At the junction 28 branches a control line 31 to a cooling oil valve 32 from. The cooling oil valve 32 serves to supply a clutch with cooling oil. The connecting pipes of the cooling oil valve 32 are shown cut off for simplicity.

At the junction 29 branches a control line 33 to the safety valve 16 from. The safety valve 16 serves to the working pressure in the working pressure range 15 in dangerous situations in the tank 2 to relieve.

Via the proportional valve 21 be particularly advantageous, the three valves 32 . 16 and 30 driven. The control of the valves 32 . 16 . 30 is preferably carried out in different pressure ranges, which have a different strong current flow of the proportional valve 21 can be represented. The energization of the proportional valve 21 via the control unit. About the control unit, the valves 32 . 16 . 30 For example, on the basis of maps stored in the control unit driving situation depending actively activated or switched.

The leakage valve 30 is on his in 1 right side via the pilot pressure line 25 hydraulically through the proportional valve 21 driven. On his in 1 left side is the leakage valve 1 acted upon by a spring, which is the leakage valve 30 in his in 1 illustrated basic position pretensions. In the basic position, there is a connection between the working pressure range 15 and the tank 2 interrupted. A hydraulic resistance 35 , for example in the form of an aperture and / or a throttle, is between the tank 2 and the leakage valve 30 connected.

The leakage valve 30 In addition to its illustrated basic position still includes an open position as a middle position, in which the working pressure range 15 over the hydraulic resistance 35 in the tank 2 is relieved to allow a regulated leakage. In addition, the leakage valve includes 30 a second closed position in which the connection between the working pressure range and the tank 2 is interrupted.

About the leakage valve 30 can be generated in a simple manner, a driving situation-dependent leakage. For this purpose, advantageously, a lower current range, for example up to 300 mA, of the proportional valve 21 be used. The main advantage is that the leakage can be switched off in flow-critical driving situations or in situations where no specific control behavior is desired.

In 2 is a leakage valve 40 shown in longitudinal section, the one embodiment of the leakage valve 30 out 1 equivalent. The leakage valve 40 is as a slide valve with a valve slide 42 shown, which is accommodated to be moved back and forth in a valve bore. An end 44 , in 2 the left end, the valve spool 42 is in his illustrated basic position to a stop. At one end 45 , in 2 the left end, is the valve spool 42 by a spring 47 applied. By a biasing force of the spring 47 becomes the valve spool 42 biased into his illustrated basic position. The feather 47 is in a spring room 48 arranged.

The leakage valve 40 has four connections 51 . 52 . 53 . 54 , About the connection 51 is the left end 44 of the valve spool 42 controlled by a pilot pressure, preferably with the pilot pressure, which in the in 1 illustrated hydraulic system 1 via the pilot control line 25 from the proportional valve 21 provided. The connection 52 stands with the interposition of a hydraulic resistor 56 , which comprises a throttle and / or a diaphragm, with the working pressure range ( 15 in 1 ) in connection. The connections 53 and 54 are to one or the tank 2 connected.

On the valve spool 42 are two piston webs 61 . 62 formed by a connection area 64 connected to each other. In the connection area 64 has the valve spool 42 a smaller outer diameter than in the region of the piston webs 61 . 62 , This will create a flow connection between the ports 52 and 53 allows to represent a regulated leakage from the working pressure range into the tank.

In the illustrated basic position of the leakage valve 40 is the connection between the connections 52 and 53 interrupted. When the valve spool 42 in 2 from his illustrated basic position to the right, so the spring 47 to, is moved, then the connection between the terminals 52 and 53 from the piston land 62 enabled to allow the regulated leakage from the working pressure range in the tank. This can be done in 1 upstream pressure reducing valve 10 be held at the system pressure control edge and thereby react more dynamically. When the valve spool 42 by further increasing the pilot pressure at the end 44 continue to the right, so continue on the spring 47 to, is moved, then the connection between the terminals 52 and 53 through the piston ridge 61 interrupted.

In 3 is a hydraulic system 71 with a tank 72 , a pump 74 and a filter 75 shown. With the help of the pump designed as a hydraulic pump 74 , which is mechanically driven by an internal combustion engine or electrically by an electric motor, becomes hydraulic medium from the tank 2 over the filter 75 sucked and in a system pressure range 78 promoted. A pressure reducing valve 80 that the pressure reducing valve 10 in 1 equals, is between the system pressure range 78 and a working pressure range 85 with a consumer 82 connected.

At the consumer 82 It is a hydraulic cylinder for clutch control for various transmission applications in motor vehicles. The transmission is, for example, a CVT transmission, a DL transmission or a step machine. Via a leakage valve 90 and over a hydraulic resistance 95 can easily regulate leakage from the working pressure range 85 in the tank 72 be dissipated.

The leakage valve 90 is designed as a 2/2-way valve with an open position and a closed position. The illustrated closed position corresponds to the basic position of the leakage valve 90 , In the basic position is the connection between the working pressure range 85 and the tank 72 interrupted.

The leakage valve 90 , is, as well as the pressure reducing valve 80 and, unlike the previous embodiments, directly controlled. The direct control is done for example by an electromagnet. About the electromagnet, the valves 80 and 90 directly controlled by a control unit. In the control unit, for example, maps are stored, which is a driving situation-dependent connection / disconnection of the leakage via the leakage valve 90 enable.

LIST OF REFERENCE NUMBERS

1

hydraulic system

2

tank

4

hydraulic pump

5

filter

8th

System pressure range

10

Pressure reducing valve

15

Working pressure range

16

safety valve

18

consumer

20

Pilot pressure valve

21

proportional valve

22

proportional valve

23

hydraulic resistance

24

hydraulic resistance

25

pilot line

26

pilot line

27

diversion

28

diversion

29

diversion

30

leakage valve

31

control line

32

Cooling oil valve

33

control line

35

hydraulic resistance

40

leakage valve

42

valve slide

44

The End

45

The End

47

feather

48

spring chamber

51

connection

52

connection

53

connection

54

connection

56

hydraulic resistance

61

piston land

62

piston land

64

connecting area

71

hydraulic system

72

tank

74

pump

75

filter

78

System pressure range

80

Pressure reducing valve

82

consumer

85

Working pressure range

90

leakage valve

95

hydraulic resistance

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2007/003151 A1 [0002]

Claims (10)

Hydraulic system with a tank ( 2 ; 72 ), designed as a slide valve with positive overlap pressure reducing valve ( 10 ; 80 ), which has a tank connection, a system pressure connection and a working pressure connection, which is passed through the pressure-reducing valve ( 10 ; 80 ) is connectable to the system pressure port or tank port, and to a consumer ( 18 ; 82 ), which via the working pressure connection of the pressure reducing valve ( 10 ; 80 ) and a working pressure range is acted upon by a working pressure, characterized by an actively actuated leakage valve ( 30 ; 40 ; 90 ), via which a regulated leakage from the working pressure range ( 15 ; 85 ) can be dissipated to the response of the pressure reducing valve ( 10 ; 80 ) to improve. Hydraulic system according to claim 1, characterized in that the leakage valve ( 90 ) is directly controlled or actuated. Hydraulic system according to one of the preceding claims, characterized in that the leakage valve ( 90 ) is designed as a 2/2-way valve with an open and a closed position as a basic position. Hydraulic system according to claim 1, characterized in that the leakage valve ( 30 ; 40 ) via a designed as a pressure regulator proportional valve ( 21 ) is activated or actuated. Hydraulic system according to claim 4, characterized in that the leakage valve ( 30 ; 40 ) is designed as a 2/3-way valve with two closed positions and an open position as a middle position. Hydraulic system according to claim 4 or 5, characterized in that the leakage valve ( 30 ; 40 ) a valve spool ( 42 ), which at a first end ( 44 ) is subjected to a pilot pressure. Hydraulic system according to claim 6, characterized in that the valve slide ( 42 ) a first piston land ( 61 ), which releases or closes a working pressure connection, and a second piston web ( 62 ), which releases or closes a tank connection. Hydraulic system according to claim 7, characterized in that the valve slide ( 42 ) between the two piston webs ( 61 . 62 ) a connection area ( 64 ), which connects the working pressure port in response to a valve spool movement with the tank port. Hydraulic system according to one of the preceding connections, characterized in that a hydraulic resistance ( 35 ; 53 ; 95 ) between the working pressure range ( 15 ; 85 ) and the tank ( 2 ; 72 ) is switched. Method for operating a hydraulic system ( 1 ; 41 ) according to one of the preceding claims, characterized in that by active actuation of the leakage valve ( 30 ; 40 ; 90 ) a leakage from the working pressure range ( 15 ; 85 ) is switched on or switched off in order to reduce the response of the pressure reducing valve ( 10 ; 80 ) to improve.

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