SE539703C2

SE539703C2 - Automatically adjusting pneumatic clutch actuator

Info

Publication number: SE539703C2
Application number: SE1551171A
Authority: SE
Inventors: Tore Ljøsne Knut; Vestgård Bård
Original assignee: Kongsberg Automotive As
Priority date: 2015-09-14
Filing date: 2015-09-14
Publication date: 2017-11-07
Also published as: SE1551171A1; DE112016004153T5; WO2017046123A1

Abstract

P11130SE00 Abstract A pneumatic clutch actuator is formed as a concentric clutch actuator (201) able to beactuated by an increase in the initial Volume of ﬂuid inside it Wherein it comprises means forautomatic clutch Wear adjustment Which compensate for Wear in a clutch and is adapted toensure that When the actuator is not actuated the ﬂuid Volume inside it always remains substantially the same. Figure 2b)

Description

Automatically adjusting pneumatic clutch actuator Background of the Invention Clutches are used to disconnect the ﬂywheel of an engine from the transmission input shaft ofa gearbox connected to it. Clutches comprise a clutch disc attached to the transmission inputshaft by splines so that it rotates with the transmission input shaft and can slide axially withrespect to the drive shaft between engaged and disengaged positions. The clutch disc hasfriction surfaces which are pressed by a pressure plate against the face of the ﬂywheel. Theforce which presses the pressure plate against the clutch disk when the clutch is engagednorrnally is provided by a diaphragm spring. The diaphragm spring is pivotably mounted tothe clutch cover and is arranged so that when the clutch is being disengaged an axial forceprovided via a thrust bearing to the centre of the diaphragm spring moves the pressure plateaway from the clutch disc, thereby reducing the pressure holding the clutch disc against theﬂywheel and reducing the amount of rotational force which the ﬂywheel can transmit to theclutch plate and the gearbox. A suff1ciently large deﬂection of the diaphragm spring willreduce all the force oppressing the clutch plate against the ﬂywheel and will prevent the rotational movement of the ﬂywheel from being transmitted to the gearbox.

The axial force in the centre of the diaphragm spring is provided by mechanical, hydraulic orpneumatic clutch actuators. Movement of the centre of the diaphragm spring towards theﬂywheel causes the outer circumference of the diaphragm spring to pivot away from theﬂywheel. As the clutch friction surfaces wear and become thinner the centre of the diaphragmspring moves further away from the ﬂywheel. Mechanical and hydraulic clutch actuators are provided with means to automatically compensate for the wear of the clutch friction surfaces.

Pneumatic clutch actuators comprise an actuator piston which is movable axially bycompressed air along a cylinder arranged around the transmission input shaft when the clutchis actuated to disengage the drive from the engine to the gearbox. The piston is maintained incontact with the diaphragm spring by a clutch preload spring inside the cylinder which acts inthe axial direction. A problem which occurs with such pneumatic systems is that as thefriction surfaces of clutch plates wear and become thinner the position of the piston when theclutch is engaged moves away from the ﬂywheel, thereby decreasing the volume of dead air in the cylinder. This causes changes in the operating characteristics of the clutch as it wears. l Brief Description of the InVention The present invention is intended to overcome the disadvantages of prior art pneumatic clutch actuators.

The present inVention provides a pneumatic clutch actuator Which can automatically compensate for Wear of the friction surfaces of a clutch.

Brief Description of the DraWing Figure la) shows schematically a cross-section through a prior art pneumatic clutch actuator With the clutch engaged.

Figure lb) shoWs schematically a cross-section through the prior art pneumatic clutch actuator With the clutch engaged When the clutch friction surfaces are Wom.

Figure 2a) shoWs schematically a cross-section through an embodiment according to the inVention of a pneumatic clutch actuator With the clutch engaged.

Figure 2b) shoWs schematically a cross-section through an embodiment according to the inVention of a pneumatic clutch actuator With the clutch disengaged.

Figure 2c) shoWs schematically a cross-section through an embodiment according to theinVention of a pneumatic clutch actuator With the clutch engaged When the clutch friction surfaces are Wom.

Detailed Description of the InVention Figures la) and lb) shoW schematically a simplif1ed cross-section through a prior artpneumatic clutch actuator 1, a clutch 3 and a flyWheel 5 Where parts Which are not necessaryto explain its function (such as seals, fastener and the like) are omitted. Clutch lconVentionally comprises a clutch disc 7 attached to a transmission input shaft 9 by splines (not shoWn) so that it rotates With the transmission input shaft and can slide axially With 2 respect to the transmission input shaft. The clutch disc has friction surfaces 11 which arepressed by a pressure plate 13 against the face 15 of the ﬂywheel 5. The force which pressesthe pressure plate against the clutch disk is provided by a diaphragm spring 17. Thediaphragm spring is pivotably mounted to a clutch cover 19 and is arranged so that an axialforce provided via a thrust bearing 21 to the centre of the diaphragm spring will move the pressure plate away from the clutch disc.

The pneumatic clutch actuator comprises an actuator piston 23 which is moved axially alonga cylinder 25 arranged around the transmission input shaft by compressed air via an air port27 when the clutch is actuated to disengage the drive from the engine to the gearbox. Thepiston is maintained in contact with the diaphragm spring by a clutch preload spring 29 acting in the axial direction which presses against the rear wall 31 of the cylinder.

Figure lb) shows the clutch when the clutch disc friction surfaces ll have wom, leading tothe piston in its resting position (i-e- its position when the clutch is engaged) moving furtheraway from the clutch than its original resting position shown by dashed lines. This reduces thevolume of ﬂuid in the cylinder which leads to changes in the operating characteristics of the actuator.

Figures 2a), 2b) and 2c) show schematically a cross-section through an embodiment of apneumatic clutch actuator 201 according to the present invention, a clutch 203 and a ﬂywheel205 where parts which are not necessary to explain its function (such as seals, fastener and thelike) are omitted. Clutch 201 conventionally comprises a clutch disc 207 attached to atransmission input shaft 209 by splines (not shown) so that it rotates with the transmissioninput shaft and can slide axially with respect to the transmission input shaft. The clutch dischas friction surfaces 211 which are pressed by a pressure plate 213 against the face 215 of theﬂywheel 205. The force which presses the pressure plate against the clutch disk is providedby a diaphragm spring 217. The diaphragm spring is pivotably mounted to a clutch cover 219and is arranged so that an axial force provided via a thrust bearing 221 to the centre of the diaphragm spring will move the pressure plate away from the clutch disc.

The pneumatic clutch actuator comprises an actuator main piston 223 which is moved axiallyalong a cylinder 225 arranged around the transmission input shaft by compressed air entering the cylinder via an air port 227 when the clutch is actuated to disengage the drive from the 3 engine to the gearbox. The main piston is maintained in contact with the diaphragm spring bya clutch preload spring means 229 such a spring or set of springs which presses against therear wall 231 of the cylinder and which acts in the axial direction on an axially movableadjustment piston 233 which can transmit a force which presses the main piston towards thediaphragm spring. The main piston and adjustment pistons are axially slidable on anadjustment sleeve 235 axially displaceable along a central sleeve 237 mounted around thetransmission input shaft. Preferably the mutually facing surfaces of the adjustment piston andmain piston are in contact with each other when the actuator is not actuated (i.e. clutch isengaged and there is a drive path between the ﬂywheel and transmission) so that the volume of air between them is zero or as close to zero as practical.

Central sleeve 237 is fixed in the longitudinal direction with respect to transmission inputshaft (for example by being attached to the cylinder rear wall 231) but the transmission input shaft can rotate freely inside it.

Adjustment piston 233 is provided with a circumferential groove 239 which is in ﬂuidcommunication with the air port 227. When pressurized air is introduced into the groove 239from air port 227 it will adjustment piston 233 to slide away from the main piston 223 onadjustment sleeve 235 and a gap 261 to open up between the gap-facing surface 263 of main piston 223 faces the gap-facing surface 265of adjustment piston 233.

Adjustment sleeve is preloaded towards the main piston by an adjustment sleeve preloadspring means 241 such a spring or set of springs which acts on a radially projecting ﬂange 242 at, or near, the end of the adjustment sleeve which is closest to the cylinder end wall 231.

The exact position on the central sleeve of the main piston, the adjustment piston and theadjustment sleeve when the clutch is engaged is deterrnined by the level of wear of thefriction surfaces of clutch disc and the equilibrium of the forces generated by the clutchpreload spring means and adjustment sleeve preload spring means which act to move thesecomponents towards the clutch, and the force in the diaphragm spring which act to move them away from the clutch.

Adjustment sleeve 235 is releaseably lockable into position on central sleeve 237 by uni- directional locking means 243 which causes the adjustment sleeve to be locked onto the 4 central sleeve when the adjustment piston moves away from the clutch on the adjustmentsleeve. The locking means causes the adjustment sleeve to become unlocked from the centralsleeve when the adjustment piston moves towards the clutch on the adjustment sleeve, as will be described in more detail below.

Adjustment sleeve 235 has a first cylindrical portion 245, which portion is closest to theclutch, and is of length l, where length l is greater than the thickness t of the main piston. Ithas a small outside diameter d which corresponds to, or is smaller than, the diameter of thecentral axial hole 247 in main piston 223 in order to allow main piston 223 to slide freely along this portion of adjustment sleeve 235.

Adjustment sleeve 235 has a second cylindrical portion 249, which portion is adjacent to thefirst cylindrical portion, and is of length L, where length L which is greater than the thicknessT of the adjustment piston. It has an outside diameter D which is larger than the outsidediameter d of the first cylindrical portion and which corresponds to or is smaller than thediameter of the central axial hole 25l in adjustment piston 233 in order to allow adjustmentpiston 233 to slide freely along this portion of adjustment sleeve 235. The face 253 of theincreased diameter of the second cylindrical portion of the adjustment sleeve acts as a stop forsliding movement of the main piston on the adjustment sleeve towards the rear wall - anyfurther movement of the main piston towards the rear wall can only take place if the adjustment sleeve slides with it axially on the central sleeve.

Unidirectional locking means are illustrated schematically by a number of preferably steelballs 255 which surrounds the adjustment sleeve and which are axially biased by biasingmeans such as springs 257 towards a corresponding circular, wedge-profiled groove in theadjustment piston. Movement of the wedge-profiled groove towards the steel balls causes theballs to exert a force towards the central sleeve which causes the adjustrnent sleeve to grip onthe central sleeve, thereby preventing longitudinal movement of the adjustment sleeve alongthe central sleeve in the direction of the cylinder end wall. Movement of the adjustment sleevein the opposite direction is not prevented by the unidirectional locking means. Other forms of unidirectional locking devices are also conceivable.

In the engaged position of the clutch as shown in figure 2a) the system is in equilibrium with the main piston in contact with the release bearing which is in contact with the diaphragm 5 spring. The clutch preload spring means pushes the adjustment piston against the main pistonand the adjustment sleeve preload spring means 241 pushes the adjustment sleeve towards theclutch and main piston so that the face 253 of the second cylindrical portion of the adjustment sleeve is in contact with the main piston.

Figure 2b) show the system when the clutch has been disengaged by providing pressurized airthrough air port 227. The incoming air ﬁrst causes the adjustment piston to move away fromthe clutch against the force of the clutch preload spring means 229 so that a gap 261 formsbetween the gap-facing surfaces, 263, 265 of the main piston and the adjustment piston. Themovement of the adjustment piston continues until the sloping surface of the wedge-profiledgroove rolls onto and presses onto the steel balls with sufficient force to lock the adjustmentsleeve onto the central sleeve. This prevents further movement of the adjustment piston andadjustment sleeve. Additional incoming air forces the main piston towards the thrust bearing and finally leads to the disengagement of the clutch.

The clutch is re-engaged by releasing air from the gap. When the air is released from the gapthe diaphragm spring pushes the main piston away from the clutch until it stops against theface 253 of the increased diameter of the second cylindrical portion of the still lockedadjustment sleeve. The forces generated by the clutch preload spring means cause theadjustment piston to move towards the clutch, releasing the locking means and allowing theadjustment piston and adjustment sleeve to retum to the equilibrium position which correspond by the wear of the clutch(shown by dashed lines).

Figure 2c) shows the same system when the clutch friction surface 211 have wom and theclutch is engaged. The components of the pneumatic actuator have automatically taken uppositions which compensate for the wear and ensure that the adjustment piston and mainpiston are in contact with each other. The wear of the friction surfaces causes the centre of thediaphragm spring to be pivoted away from the clutch. The displacement of the centre of thediaphragm spring caused by this pivotal movement is transmitted via the trust bearing to themain piston. This means that the position of the main piston when the clutch is engaged willmove away from the clutch. The contact between the face of the second cylindrical portion ofthe adjustment sleeve and the main piston ensures that the adjustment sleeve moves the samedistance away from the clutch as the main piston does (as the adjustment sleeve preload spring means ensure that the face of the second cylindrical portion of the adjustment sleeve 6 remains in contact with the main piston). This allows the adjustment piston to also move thesame distance from the clutch, thereby preserving the original distance between thecomponents -this allows for compensation of the wear while at the same time ensuring thatthe adjustment piston and main piston are in contact when the clutch is engaged, thus leavingthe same zero or practically zero volume between the two pistons as the start point for every operation of the actuator, regardless of clutch wear and position of thrust bearing.

The above description of the present disclosure is provided for the purpose of illustration, andit would be understood by those skilled in the art that various changes and modifications maybe made without changing the concept and essential features of the present disclo sure. Thus, it is clear that the above-described embodiments are illustrative in all aspects and do not limit the present disclosure.

The scope of the present disclosure is defined by the following claims rather than by thedetailed description of the embodiment. It shall be understood that all modif1cations andembodiments conceived from the meaning and scope of the claims and their equivalents are included in the scope of the present disclosure.

Claims

1. Pneumatic concentric clutch actuator (201) comprising a central sleeve (237), a main piston(223) arranged coaxial With, and adjacent to, an adjustment piston (233) on said central sleeve(237), wherein the main piston (223) has a piston surface (263) and the adjustment piston(233) has a piston surface (265) which faces towards the piston surface (263) of the mainpiston (223), and said actuator (201) is able to be actuated by an increase in the initial volumeof ﬂuid between said piston surfaces (263, 265), wherein it comprises means for automaticclutch wear adjustment which compensates for wear in a clutch and is adapted to ensure thatwhen the actuator is not actuated said initial volume of ﬂuid always remains substantially thesame even as a clutch wears, characterised in that the main piston (223) is axially movable along said central sleeve (237), the adjustment piston(233) is axially movable along said central sleeve (237) and transmits a preload force from aclutch preload spring (229) onto said main piston (223), an air port (227) is in ﬂuidconnection with said main piston (223) and said adjustment piston (233) and is adapted tosupply ﬂuid to the piston surfaces (263, 265) when the actuator (201) is actuated in order tomove said piston surfaces (263, 265) apart; wherein the means for automatic clutch wear adjustment comprises an coaxially arrangedadjustment sleeve (235) axially movable along said central sleeve (235) under the influence ofa preload spring (241) towards said adjustment piston (233) for adjusting the position of saidadjustment piston (233), unidirectional locking means (243) for releaseably locking saidadjustment sleeve (235) onto said central sleeve (237) when said adjustment piston (233)moves away from said main piston (223) under the influence of ﬂuid supplied to said pistonsurfaces (263, 265); and said adjustment sleeve has a diameter (D) which can prevent movement of the main piston(223), said diameter being arranged such that when said ﬂuid is being released from saidpiston surfaces(263, 265) if said diameter and said main piston (223) come into contact thensaid main piston movement is prevented thereby allowing said adjustment sleeve lockingmeans (243) to be unlocked by said adjustment piston (233) in order to allow said adjustmentpiston (233) and said adjustment sleeve (233) to move along said central sleeve (237) towardssaid preload spring (241) when the force exerted on them by the main piston (223) is greaterthan the force exerted on them by the clutch preload spring (229) and adjustment sleevepreload spring (241).

2. Pneumatic clutch actuator according to claiml characterised in that adjustment sleeve (235)has a first cylindrical portion (245), Which portion is closest to a clutch, having an outsidediameter d Which corresponds to or is less than the diameter of a central axial hole (247) inmain piston (223) in order to alloW main piston (223) to slide freely along this portion ofadjustment sleeve (235), Which first cylindrical portion (245) is of length lWhich is greaterthan the thickness t of the main piston (223); and, that adjustment sleeve (235) has a second cylindrical portion (249), Which portion (249)isadjacent to the first cylindrical portion (245), Which second cylindrical portion (249) has anoutside diameter D Which is larger than the outside diameter d of the first cylindrical portion(245) and Which corresponds to or is larger than the diameter of a central axial hole (25 l) inadjustment piston (233) in order to alloW adjustment piston (233) to slide freely along thisportion of adjustment sleeve (235), Which second cylindrical portion is of length L Which is greater than the thickness T of the adjustment piston (233).

3. Pneumatic clutch actuator according to any of claims l or 2 characterised in that saidunidirectional locking means (243) comprises a plurality of balls biased towards a Wedge- shaped circular groove in said adjustment sleeve (235).

4. Pneumatic clutch actuator according to any of claims l to 3 characterised in that saidadjustment sleeve preload spring (24l) acts on a radially projecting ﬂange (242) at, or near, the end of the adjustment sleeve (235) Which is furthest from the main piston (233).

5. Pneumatic clutch actuator according to any of the previous claims characterised in that inthe mutually facing surfaces (263, 265) of the adjustment piston (233) and main piston (223) are in contact With each other When the actuator(20l) is not actuated.