WO2008132771A2

WO2008132771A2 - An improved control system for clutches and like torque transmission devices

Info

Publication number: WO2008132771A2
Application number: PCT/IT2008/000289
Authority: WO
Inventors: Leonardo Dalla Vecchia
Original assignee: Carraro S.P.A.
Priority date: 2007-04-27
Filing date: 2008-04-23
Publication date: 2008-11-06
Also published as: WO2008132771A3; ITPD20070157A1

Abstract

An improved control system for clutches and like torque transmission devices comprising an actuator (14) controlling the device which may be displaced between two respective positions of engagement and disengagement of the device and a resilient return member acting on the actuator in order to urge it towards one of these positions and oppose its displacement towards the other position, in which the resilient return member comprises separate first (20) and second (28) resilient means disposed in parallel, the second resilient means (28) acting on the actuator (14) only after a predetermined stroke of the actuator in order to show, by means of increased opposition to the displacement of the actuator (14), the achievement of a predetermined intermediate position of the actuator between the engagement and disengagement positions.

Description

AN IMPROVED CONTROL SYSTEM FOR CLUTCHES AND LIKE TORQUE TRANSMISSION DEVICES DESCRIPTION Technical field The present invention relates to an improved control system for clutches and like torque transmission devices of the type including the features described in the preamble of the main claim. Technological background

These conventional systems comprise a hydraulic actuator acting on a pack of clutch disks and counter-disks whose compression causes the engagement by friction of the transmission. The actuator is generally of the type with a cylinder and piston which jointly define a variable volume chamber for a pressurised control fluid. The introduction of pressurised fluid (generally oil) into the chamber causes the piston to be displaced in opposition to a resilient return member which, after an empty stroke (the so-called filling stage), firstly brings the disks and counter-disks into a stage where they are brought together (the so-called kissing stage) and then the clutch begins to close with a gradual increase of the torque transmitted.

The problem underlying devices of this type lies essentially in the fact that the point of transition from the filling stage to the kissing stage is not easy to determine. The two stages have completely contrasting control requirements from the point of view of the actuator, with the result that it is extremely important to detect the moment of transition from one stage to the other. Moreover, while, in the filling stage, it is desired to supply the chamber with the maximum input of pressurised oil in order to reduce the down times of the actuation, from the kissing stage onwards it is necessary to limit the flow and regulate the pressure of the control fluid to enable a gradual engagement of the clutch.

At present the moment of transition between the filling stage and the kissing stage is evaluated predominantly by estimation models which

"estimate" the position of the piston in the cylinder in order to assess how far there is to go to the kissing stage. The estimate is nevertheless imprecise and does not make it possible precisely to determine the transition from the filling stage to the transmission of torque, leading to a decrease in the performance of the clutch in terms of actuation or modulation time (comfort of use of the vehicle).

Description of the invention

The problem which the present invention seeks to resolve is that of developing an improved system which is structurally and functionally designed to remedy the drawbacks described with reference to the cited prior art.

This problem is resolved by the invention by means of a system according to the appended claims.

Brief description of the drawings The features and advantages of the invention are set out in further detail in the detailed description of an embodiment thereof, given purely by way of non-limiting example, with reference to the appended drawings, in which:

Fig. 1 is a diagrammatic view in partial section of a clutch and a related control system of the invention; Fig. 2 is a view on an enlarged scale of a detail of Fig. 1; Fig. 3 is a diagram showing the operation of the control system of Fig. 1 in comparison with the operation of a system of known type. Preferred embodiments of the invention In Fig. 1, a clutch assembly - known simply as a clutch hereafter - is shown overall by 1 and lies between two members 2, 3 which may be fixed in rotation by the clutch 1.

A system 4 of the invention provides for the operational control to engage and disengage the clutch 1. The clutch 1 comprises a pack 5 of disks 6 and counter-disks 7 comprised between a pressure plate 8 and an abutment plate 9. The disks 6 are fixed in rotation with the member 3 by means of a grooved-profile coupling 10. The counter-disks 7 are fixed in rotation with a bell 11 secured on the member 2 by means of a second grooved-profile coupling 12, The abutment plate 9 is also made rigid with the bell by means of the same coupling 12 and is retained by a resilient ring 13.

The pressure plate 8 is rigid and preferably integral with a piston 14 mounted in a leak-tight manner in a cylinder 15 with which it defines a chamber 16 for a pressurised actuator fluid. The piston 14 acts as an actuator for the operational control to engage the clutch 1. Its movement in the direction of compression of the pack 5 is opposed by a resilient return member including a first helical spring 20 keyed on a sleeve 21 between respective shoulders 23, 24. The sleeve 21 is formed by two parts 21a, 21b which may be axially displaced with respect to one another so that the sleeve 21 is axially contractile. The first part 21a abuts with the shoulder 23 on the piston 14 and may be axially displaced therewith. The second part is secured in an adjustable position on a threaded collar 25 of the member 2 where it may be secured by a pin 26.

A housing 27 is provided in the second part 21b and houses a second spring 28 of the resilient control member disposed in parallel with the helical spring 2Oe, the second spring 28 being retained in the housing 27 by a ring 29 secured by means of a resilient ring 30 which renders it preloaded.

A cylindrical tang 31 of the first part 21a is adapted to penetrate into the housing 27, pressing on the ring 29 so as to compress the second spring 28 during the stroke of the piston. By adjusting the position of the second part 21b on the collar 25, it is possible to regulate the position of action of the second spring in order to cause it to intervene in the resilient return of the piston immediately prior to the kissing stage. The spring 28 is preferably an undulated spring formed by a ring circumferentially bearing a plurality of adjacent undulations and has a small axial thickness. A cup, helical or other type of spring may similarly be used.

The relative positioning between the two parts 21a, 21b of the sleeve is chosen such that the cylindrical tang 31 comes into contact with the spring 28 only after the stage of filling of the chamber 16 with pressurised oil has been completed and the pack of disks and counter-disks 5 is close to the kissing stage.

With reference to the graph of Fig. 3, where time is given on the abscissa and pressure in the chamber 16 on the ordinate, it will be seen that in the curve A which represents the behaviour of the hydraulic pressure over time, only the helical spring 20 opposes the movement of the piston during the filling stage of the chamber 16. The operational pressure in the chamber 16 and in the hydraulic control circuit of the piston 14 increases substantially in a linear manner, with the compression of the spring 20 remaining relatively low. When the displacement of the piston 14 is such that the filling stage of the chamber 16 has been completed and the kissing stage is beginning, the piston 14 comes into contact with the second spring 28 by means of the cylindrical tang 30 of the first part 21a of the sleeve 21 causing a sudden, albeit modest, pressure increase. By detecting this event by means of a pressure sensor (not shown), it is thus possible to meter the pressure increase by means of a simple closed-loop electronic control enabling complete control and metering of the torque transmitted by the friction clutch.

However, in curve B, which is the same graph for a conventional actuation, there is no clear and immediate evidence of the beginning of the kissing stage, thus making it necessary to carry out a check to estimate the piston which is less reliable and more complex.

The invention thus resolves the problem as stated and achieves a number of advantages including: - increasing the kissing pressure which enables the proportional control valve of the actuation pressure of the piston to work in a better and more controllable range (better performance of the electronic control which governs the proportional valve), enabling a better control of the torque transmitted by the clutch as a result of the closure of the pressure control ring by means of the pressure sensor (improved driveability of the vehicle in manoeuvres where an "inching" torque control is required, i.e. when the driver has to close gradually and slowly up to an obstacle by controlled slipping of the clutch ("slipping" stage in the graphs), - together with a revolution sensor of the output shaft of the gear change, enabling the electronic control to carry out a speed and therefore also an acceleration control which makes it possible to apply the acceleration to the vehicle which Is considered most comfortable for starting, reversals of direction and gear changes, - as a result of the second spring stage together with pressure sensor, eliminating the stage of electronic calibration of the clutch, thereby reducing the vehicle set-up times for the calibration of the estimation system, increasing safety as the electronics combined with the pressure and output revolution sensor may monitor the operation of the clutch in real time and thus intervene if the control parameters are not appropriate, drastically reducing the hydraulic components involved in the clutch control which is delegated to the electronic system.

Claims

1. An improved control system for clutches and like torque transmission devices comprising an actuator (14) controlling the device which may be displaced between two respective positions of engagement and disengagement of the device and a resilient return member acting on the actuator in order to urge it towards one of these positions and oppose its displacement towards the other position, characterized in that the resilient control member comprises separate first (20) and second (28) resilient means disposed in parallel, the second resilient means (28) acting on the actuator (14) only after a predetermined stroke of the actuator between the two positions in order to show, by means of increased opposition to the displacement of the actuator, the achievement of a predetermined intermediate position of the actuator between these engagement and disengagement positions.

2. A control system according to claim 1, wherein the second resilient means (28) comprise an annular spring.

3. A control system according to claim 2, wherein the annular spring is of the type with undulations.

4. A control system according to claim 2, wherein the intervention position of the annular spring is adjustable.

5. A control system according to one or more of the preceding claims, wherein the control actuator of the device comprises a piston (14) acting on a sleeve (21) defining two shoulders (23, 24) between which the first resilient means (20) are disposed, the sleeve (21) comprising a portion acting on the second resilient means (28) after a predetermined stroke.

6. A torque transmission device such as a clutch or the like including a pack (5) of disks (6) and counter-disks (7), a pressure plate (8) acting on the pack (5) for the compression or release thereof and a control actuator (14) for the pressure plate (8), characterized in that it comprises a control system according to one or more of the preceding claims.