WO2012089227A1

WO2012089227A1 - Method for operating a continuously variable transmission

Info

Publication number: WO2012089227A1
Application number: PCT/EP2010/007980
Authority: WO
Inventors: Wilhelmus Johannes Maria Van Wijk
Original assignee: Robert Bosch G.M.B.H.
Priority date: 2010-12-30
Filing date: 2010-12-30
Publication date: 2012-07-05
Also published as: KR20140015316A; KR101822219B1; CN103282693B; CN103282693A

Abstract

The invention relates to a control system in a continuously variable transmission (1) that comprises a variator unit (30), a planetary gearing (20) with a forward drive clutch (26) and a torque converter (10) with a lock-up clutch (16), which control system includes a lock-up switch valve (V1) for engaging or disengaging the lock-up clutch (16) and a clutch engagement valve (V2) for engaging or disengaging the forward drive clutch (26). In accordance with the invention the control system includes a single electromagnetic actuator (S6) that directly or indirectly operates both the said lock-up switch valve (V1) and the said clutch engagement valve (V2).

Description

METHOD FOR OPERATING A CONTINUOUSLY VARIABLE TRANSMISSION

The present invention relates to a method for operating a continuously variable transmission with a control system as defined in the preamble of the following claim 1 , in particular for use in a motor vehicle, as well as to the control system as such.

Such a control system and transmission are known, for example from the European patent publication EP 1 939 503 A. The known continuously variable transmission includes a variator unit with a primary or drive variable pulley and with a secondary or driven variable pulley, as well as an endless flexible transmission element or drive belt, which may be one of several known types, wrapped around and in frictional contact with the said pulleys. The transmission further includes an epicyclic or planetary gearing with at least two clutches for respectively engaging forward drive and reverse (drive), which gearing is also referred to as a DNR-set (Drive-Neutral- Reverse-set), and a torque converter for amplifying a drive torque, in particular during the initial acceleration of the motor vehicle from standstill. The known torque converter is provided with a lock-up clutch that is engaged, i.e. closed sometime after the said initial acceleration to improve the power transmission efficiency.

The transmission provides a speed ratio between the primary and secondary pulleys that may be controlled to an arbitrary value within a range of speed ratios covered by the transmission through an appropriate actuation of the said pulleys by means of the control system of the transmission. More in particular, each pulley comprises two sheaves where between the drive belt is held and whereof one sheave is arranged axially moveable along a respective pulley shaft, energised by the control system. To this end, the known control system includes two pressure cylinders, each associated with a respective one of the said moveable pulley sheaves. Further, the control system includes a primary valve for realising, in a controlled manner, a pressure level in the pressure cylinder associated with the primary pulley and a secondary valve for realising, in a controlled manner, a pressure level in the pressure cylinder associated with the secondary pulley. These cylinder pressures determine the clamping forces respectively exerted on the drive belt between the sheaves of each pulley and as a consequence the said speed ratio, as well as the torque that can be transmitted by the transmission.

The control system further includes a clutch engagement valve for realising the controlled gradual and, hence, smooth engagement, i.e. closing, of either one of the two clutches of the DNR-set and a lock-up shift valve for realising the engagement of the lock-up clutch of the torque converter. Also a pump is provided for supplying the control system with a flow of pressurised hydraulic fluid to a main line of the control system. A hydraulic pressure in the main line, i.e. the line pressure, is regulated by means of a line pressure valve of the control system. The clutch engagement valve, the lock-up shift valve and at least one of the primary and the secondary valve are arranged to -directiy or indirectly- draw fluid from said main line to a respective downstream line of the control system and to regulate a hydraulic pressure in the downstream line respectively associated with such respective valve.

All of said line pressure, clutch engagement, lock-up shift, primary and secondary valves are controllable by means of a respective electromagnetic actuator or solenoid. Typically, said solenoid effectively operates a pilot valve that generates a valve control or pilot pressure that acts on a respective one of said valves, to indirectly effect the control of such respective valve. However, it is also possible that the solenoid directly, i.e. mechanically, operates such respective valve.

The present invention aims to further optimise the known control system transmission, in particular by reducing the cost price thereof, while maintaining its function. In accordance with the invention such aim may be realised by reducing the number of components of the control system in the manner described in claim 1 hereinafter.

In practice, the lock-up clutch is closed only after at least one of the clutches of the DNR-set has been closed to allow acceleration of the motor vehicle in the first place. According to the invention, the clutch engagement valve and the lock-up shift valve may favourably be controlled by a single solenoid, which solenoid thus directly or indirectly controls both the closing of one of the DNR-set clutches and the closing of the torque converter lock-up clutch. In dependence on an electric (control) current applied to the solenoid and/or the level of the pilot pressure generated thereby, first the DNR-set clutch is gradually closed and only then the torque converter lock-up clutch.

In a preferred embodiment, the clutch engagement valve and the lock-up shift valve are combined into one, i.e. into a single valve unit comprising a valve housing and a valve spool, which singe valve unit is controllable by said single solenoid. In an alternative preferred embodiment, the clutch engagement pressure that is set by the clutch engagement valve under the control of the said single solenoid also acts on, i.e. controls the lock-up shift valve, i.e. controls the closing of the lock-up clutch. In this latter solution the lock-up shift valve is activated, i.e. the lock-up clutch is arranged to close only above a threshold level of the clutch engagement pressure, whereas the respective DNR-set clutch is arranged to be completely engaged/closed at or even below such threshold level of the clutch engagement pressure. The invention will now be elucidated further along a drawing in which:

figure 1 is a schematic representation of the known continuously variable transmission,

figure 2 is a diagrammatic representation of the known control system as part of a schematically depicted continuously variable transmission that is actuated thereby,

figure 3 diagrammatically illustrates a first possible embodiment of the control system according to the invention, and

figure 4 diagrammatically illustrates a second possible embodiment of the control system according to the invention.

Figure 1 provides a schematic representation of a continuously variable transmission 2 that is, for example, provided between an engine 1 and the driven wheels 4 of a motor vehicle. The known transmission 2 comprises a torque converter 10 for amplifying a drive torque, in particular during the initial acceleration of the motor vehicle from standstill, a planetary gearing or DN (Drive-Neutral-Reverse)-set 20 for respectively engaging a forward or a reverse drive mode of the transmission 2 and a variator unit 30 for varying a speed ratio between the engine 1 and the driven wheels 4 of the motor vehicle to an arbitrary value within a range of speed ratios. Typically, also a final drive gear train with a differential gearing 3 is included in the transmission 2.

A crank shaft 5 of the engine 1 is coupled to an ingoing shaft 11 of the torque converter 10 that drives a pump wheel 13 thereof. A turbine wheel 14 of the torque converter 10 drives an outgoing shaft 12 thereof. The torque converter 10 is further provided with a stator 15 and a selectively engageable bridging or lock-up clutch 16 that can be closed to directly couple the ingoing shaft 11 to the outgoing shaft 12 after the initial acceleration of the motor vehicle. The construction, function and operation of the torque converter 10 are otherwise well-known in the art.

The DNR-set 20 includes a central sun gear 21 that is coupled to the outgoing shaft 12 of the torque converter 10, a ring gear 25 and a number of sets of two planet gears 22, 23 each, the axes whereof carried by a rotatable planet carrier 24 that is coupled to a primary shaft 31 of the variator unit 30. Of each set of two, mutually meshing planet gears 22, 23, a first planet gear 22 is in meshing arrangement with the sun gear 21 and a second planet gear 23 is in meshing arrangement with the ring gear 25. The DNR-set 20 further includes two clutches 26, 27, whereof a first or forward drive clutch 26 can be closed to rotationally couple the sun gear 21 to the planet carrier 24, in which case the outgoing shaft 12 of the torque converter 10 is directly coupled to the primary shaft 31 of the variator unit 30. The second or reverse drive clutch 27 of the DNR-set 20 can be closed to rotationally fix the ring gear 25, in which case the primary shaft 31 of the variator unit 30 is driven by the outgoing shaft 12 of the torque converter 10 via the sun gear 21 , the planet gears 22, 23 and the planet carrier 24, however, in a rotationally opposite sense, i.e. in reverse. If both said clutches 26, 27 of the DNR-set 20 are open, the transmission 2 is said to be in neutral, i.e. no drive torque can then be transmitted thereby. The construction, function and operation of the DNR-set 20 are otherwise well-known in the art.

The variator unit 30 includes a hydraulically actuated primary variable pulley 33 on the primary shaft 31 , a hydraulically actuated secondary variable pulley 34 on a secondary shaft 32 and a drive belt 35 that is wrapped around and in frictional contact with both such pulleys 33, 34. The construction, function and operation of the variator unit 30 are otherwise well-known in the art.

The known transmission 2 is provided with an electro-hydraulic control system, which is schematically illustrated in figure 2, to control at least the opening, respectively closing of the lock-up clutch 16 of the torque converter 10 and the forward, respectively reverse drive clutches 26, 27 of the DNR-set 20. To this end, the control system is equipped with a pump 40 for providing a flow of pressurized hydraulic fluid and a lock-up switch valve V1 and a clutch engagement valve V2 that are both controlled electrically by means of a respective electromagnetic actuator or solenoid S1 and S2. In the present example of the control system, these respective solenoids S1 , S2 control the respective valves V1 , V2 indirectly by means of a respective pilot pressure p1 , p2, respectively generated by the said respective solenoids S1 , S2. It is, however, also possible that a respective solenoid S1 , S2 acts directly on a respective valve V1 , V2.

Typically, the complete control system is equipped with several further valves V3- V8 and solenoids S3-S5. For example in the figure 2 embodiment thereof, the control system further includes:

- a line pressure valve V3 and an associated solenoid S3 for controlling the pump pressure LP to a desired level via a respective pilot pressure p3,

- a primary pressure valve V4 and an associated solenoid S4 for controlling the primary actuation pressure PP of the primary pulley 33 to a desired level via a respective pilot pressure p4,

- a secondary pressure valve V5 and an associated solenoid S5 for controlling the secondary actuation pressure SP of the secondary pulley 34 to a desired level via a respective pilot pressure p5, - a solenoid feed pressure valve V6 for controlling a fixed solenoid feed pressure FP to supply the solenoids S1-S5 with pressurized hydraulic fluid to generate the respective pilot pressures p1-p5,

- an auxiliary pressure valve V7 for controlling a fixed auxiliary pressure AP to supply auxiliary devices of the transmission 2, such as a lubrication point 41 , the torque converter 10 and the said clutches 26, 27 of the DNR-set 20 with fluid and

- a manual valve V8 for manually connecting respectively the forward drive clutch 26 or the reverse drive clutch 27 of the DNR-set 20 to the auxiliary pressure AP, while disconnecting the respective other one of said DNR-set clutches 26; 27. In figure 2 the manual valve V8 is set to connect the forward drive clutch 26 to and to disconnect the reverse drive clutch 27 from the auxiliary pressure AP.

The iock-up switch valve V1 switches the connection of two hydraulic lines 17, 18 connected to the torque converter 10, to close the lock-up clutch 16 if the pressure level in the first line 17 is higher than the pressure level in the second line 18 or to open the lock-up clutch 16 if the pressure level in the second line 18 is higher than the pressure level in the first line 17. This latter situation is depicted in figure 2, wherein the required pressure drop between said lines 18, 17 is realized by the hydraulic restriction 42 provided there between. In the former situation, the required pressure drop between said lines 18 and 17 is realized by the auxiliary pressure valve V7. The switching of the lock- up switch valve V1 is controlled by its respective pilot pressure p1. For example, if the respective pilot pressure p1 is less than 2 bar, the lock-up switch valve V1 is in its position depicted in figure 2, whereas, if the said respective pilot pressure p1 exceeds 2 bar, the lock-up switch valve V1 switches the connection of the said two hydraulic lines 17, 18 to close the lock-up clutch 16.

The clutch engagement valve V2 controls a variable clutch engagement pressure

CP in the hydraulic line 43 in dependence on its respective pilot pressure p2, which clutch engagement pressure CP is applied to either the forward drive clutch 26 or the reverse drive clutch 27 (or neither) in dependence on the (manual) setting of the manual valve V8 for engaging such respective clutch 26, 27. For example, in dependence on the respective pilot pressure p2 gradually increasing to 5 bar, the clutch engagement valve V2 gradually controls the clutch engagement pressure CP from atmospheric pressure, at which pressure the respective clutch 26; 27 is fully open, via a partially closed or slipping clutch 26; 27, to the auxiliary pressure level AP set by the auxiliary pressure valve V8, at which auxiliary pressure level AP the respective clutch 26; 27 is fully closed/engaged. In a first embodiment of the invention, the above known control system is simplified, favorably reducing the cost and complexity thereof, by controlling both the clutch engagement valve V2 and the lock-up shift valve V1 by means of single solenoid S6, as is schematically illustrated in figure 3.

In practice, the lock-up clutch 16 of the torque converter 10 is, or at least can be closed only after one of the said clutches 26, 27 of the DNR-set 20 has been fully engaged, i.e. has been closed to allow the acceleration of the motor vehicle in the first place. According to the invention, the said single solenoid S6 can thus be arranged to first activate, e.g. control, the clutch engagement valve V2 and thereafter to activate, e.g. switch, the lock-up switch valve V1 both in dependence on the level of the control current supplied to the solenoid and/or the level of a respective pilot pressure p6 generated thereby. For example, if the solenoid S6 can set the respective pilot pressure p6 between atmospheric pressure and 5 bar, the first 3 bar of that pilot pressure p6 range can be used to control the clutch engagement valve V2 to gradually increase the clutch engagement pressure CP from atmospheric pressure to the auxiliary pressure level AP (by means of the clutch engagement valve V2), whereas the lock-up clutch is closed only at a level of 4 bar of the respective pilot pressure p6 (at which pilot pressure level lock-up switch valve V1 switches the connection of said two hydraulic lines 17, 18). Obviously, such desired behavior of the said valves V1 , V2 can be realized in a well-known manner by appropriately designing the valves V1 , V2 in particular in terms of the surface area of a valve spool whereon the pilot pressure acts and/or the counteracting force on the said valve spool, as exerted by a spring incorporated in the valve.

In a second embodiment of the invention, the above known control system is simplified, favorably reducing the cost and complexity thereof, by controlling the lock-up shift valve V1 in dependence of the clutch engagement pressure CP, as is schematically illustrated in figure 4.

In practice, the lock-up clutch 16 of the torque converter 10 is, or at least can be closed only after one of the said clutches 26, 27 of the DNR-set 20 has been fully engaged, i.e. has been closed to allow the acceleration of the motor vehicle in the first place. According to the invention, the lock-up shift valve V1 can thus be arranged to be activated, i.e. switched in dependence on the clutch engagement pressure CP. In particular the lock-up shift valve V1 is arranged to switch after the clutch engagement pressure CP reaches or exceeds a certain threshold value, which threshold value has been chosen such that and the forward, respectively the reverse drive clutches 26, 27 of the DNR-set 20 is fully closed/engaged. For example, if the solenoid S6 can set the respective pilot pressure p6 between atmospheric pressure and 5 bar that pilot pressure p6 range can be used to control the clutch engagement valve V2 to gradually increase the clutch engagement pressure CP from atmospheric pressure to the auxiliary pressure level AP (by means of the clutch engagement valve V2). However, the clutches 26, 27 of the DNR-set 20 have in this been designed to fully close not at or close to the auxiliary pressure level AP, but already at several bar below this level AP, i.e. at a pilot pressure p6 of several tens or even a couple of bar below said maximum of 5 bar. As the pilot pressure p6 and the clutch engagement pressure CP are raised even further the clutches 26, 27 of the DNR-set 20 of course remain firmly closed and lock-up switch valve V1 will finally be activated at such high clutch engagement pressure CP and switch the connection of said two hydraulic lines 17, 18. The switch valve V1 thus being arranged to switch at a clutch engagement pressure CP that eexceeds the said threshold value at which the clutches 26, 27 of the DNR-set 20 are already fully closed. Obviously, such desired behavior of the said valves V1 , V2 can again be realized in a well-known manner by appropriately designing the valves V1 , V2 in particular in terms of the surface area of a valve spool whereon the pilot pressure acts and/or the counteracting force on the said valve spool, as exerted by a spring incorporated in the valve.

Claims

1. Method for operating a continuously variable transmission (1) comprising a variator unit (30), a planetary gearing (20) with a forward drive clutch (26), a torque converter (10) with a lock-up clutch (16) and a control system with a lock-up switch valve (V1) for engaging or disengaging the lock-up clutch (16), a clutch engagement valve (V2) for engaging or disengaging the forward drive clutch (26) and with an electromagnetic actuator (S6) for setting a pilot pressure (p6) level in dependence on an input signal, such as an electric current or a voltage, supplied to it, characterised in that in dependence on the input signal, firstly the forward drive clutch (26) is gradually engaged and then the lock-up clutch (16) is engaged by the control system or firstly the lock-up clutch (16) is disengaged and then the forward drive clutch (26) is gradually disengaged by the control system.

2. Control system in a continuously variable transmission (1 ) comprising a variator unit (30), a planetary gearing (20) with a forward drive clutch (26) and a torque converter (10) with a lock-up clutch (16), which control system includes a lock-up switch valve (V1) for engaging or disengaging the lock-up clutch (16) and a clutch engagement valve (V2) for engaging or disengaging the forward drive clutch (26), characterised in that, the control system includes a single electromagnetic actuator (S6) that directly or indirectly operates both the said lock-up switch valve (V1) and the said clutch engagement valve (V2).

3. Control system according to claim 2, characterized in that, the said lock-up switch valve (V1) and the said clutch engagement valve (V2) are integrated in a single valve unit comprising with a single valve housing containing a single valve spool.

4. Control system according to claim 3, characterized in that, the said single electromagnetic actuator (S6) acts directly on the valve spool of the said singe valve.

5. Control system according to claim 2, characterized in that, a clutch engagement pressure (CP) that is set by the clutch engagement valve (V2) under the , as operated by the said single electromagnetic actuator (S6), is fed to and effects the operation the said lock-up switch valve (V1).

6. Control system according to claim 2, 3 or 5, characterized in that, the said single electromagnetic actuator (S6) acts on a pilot pressure valve that generates a pilot pressure (p6) that is fed to and effects the operation of either one or both of the said lock-up switch valve (V1) and the said clutch engagement valve (V2).

7. Control system according to any one of the preceding claims, characterized in that, the control system is arranged to engage the lock-up clutch (16) by means of the lockup switch valve (V1 ), directly or indirectly operated by the said single electromagnetic actuator (S6), only after the forward drive clutch (26) has been fully engaged by clutch engagement valve (V2), likewise directly or indirectly operated by the said single

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8. Control system according to any one of the preceding claims, characterized in that, in dependence on an electric current supplied to the said single electromagnetic actuator (S6), the lock-up switch valve (V1) is switched when the clutch engagement valve (V2) is fully opened.