MXPA99010212A - Clutch with rodi fork - Google Patents

Abstract

The present invention relates to a clutch for rotatably connecting a vehicle engine crankshaft with a transmission input shaft, the clutch comprising: a flywheel rotatably disposed on a rotation shaft; a transmission input shaft disposed on the transmission shaft; rotation and having a shackled portion; a clutch cover fixed to the flywheel; a pressure plate arranged between the clutch cover and the flywheel for axial movement between them and rotatably fixed to the cover; a clutch driven disc fixed rotatably to the arrow inlet through notches and disposed between the flywheel and the pressure plate for axial movement slidable therebetween; a clutch release sleeve slidably disposed on the input shaft, having a first end disposed between the pressure plate and the cover and having a second end disposed on one side of the cover opposite the pressure plate; of radially oriented levers, distributed around the axis of rotation and having ends arranged radially inwardly by linking a first end of the release sleeve and the levers extending between the release sleeve and the pressure plate, a spring disposed between the pressure plate and the cover, by polarizing the pressure plate towards the driven disc, a clutch release bearing connected to a second end of the release sleeve and disposed outside the clutch cover and the bearing also having a bonding surface; clutch disposed on the clutch cover and the release bearing, a clutch release arrow disposed in the clutch housing and pivotable about a second axis oriented at 90 ° with the axis of rotation, a clutch release fork fixed rotatably to the clutch release arrow for rotation with and having first and second arms extending adjacent to the release bearing, and a plurality of rollers with a roller rotatably disposed one way inward of each of the first and second arms of the clutch release fork and in engagement with the link surface release bearing, the rollers each including a pin pin with a first end received by a respective fork arm, the pin pin having a second end surrounded by a rotatably mounted tire, the tire having a bore its through and a bushing fixedly mounted therein, and a retainer disposed between the pin and the tire to prevent axial displacement of the tire from the second end of the spline pin.

Description

CLUTCH WITH ROLLER FORK Field of the Invention This invention relates to clutches for motor vehicles and, in particular, to clutches employing a release sleeve disposed between a release bearing and a sleeve end that links a clutch spring and / or clutch levers , and means for displacing the release bearings associated with such clutches. BACKGROUND OF THE INVENTION Clutches designed for use in heavy and medium duty applications commonly employ sleeves that travel over an input shaft of the transmission. The sleeve connects a release bearing with a clutch spring and / or clutch levers that provide a clutch engagement load against the pressure plate. The sleeve is arranged on the input shaft of the transmission and rotates with the spring, as well as the cover, the flywheel and the clutch pressure plate. A bushing in axial alignment with the bearing is press fit into the sleeve for unitary rotation with it and travels directly on the input shaft of the transmission. The relative rotation between the sleeve and the input shaft of the transmission occurs when the clutch is partially or fully released. An internal guide of the release bearing is connected to the sleeve for movement therewith. An external guide is prevented from turning, and is in connection with a clutch fork. Wear pads on the outer guide are linked by the ends of the fork arms. The clutch fork is pivotally mounted in a clutch housing that connects an engine block and a transmission case. The clutch fork is connected with a pedal controlled by the operator for selective axial displacement of the bearing and the sleeve and consequent uncoupling of the clutch. The pivotal movement of the clutch fork, in combination with the friction force between the fork arms and the wear pads, induces a "lift" force on the bearing that is transferred through the bearing to the sleeve and to the bushing in he. The lifting force is approximately equal to the coefficient of friction between the fork arms and the pads, multiplied by the normal force applied by the arms against the pads. The lifting force presses the sleeve of the sleeve against the input shaft during disengagements of the clutch, thereby accelerating the wear of the sleeve of the sleeve. OEMs currently require that the clutches be substantially maintenance-free for extended periods of mileage. In order to increase the life of the sleeve bushes, it is highly desirable to reduce the friction between the fork and the release bearing and thereby reduce the lifting force. The clutch forks are known, which employ rollers to link the release bearings of those clutches. However, such forks are used in combination with a clutch bearing that travels not on the input shaft of the transmission, but on a stationary calamus that extends from the transmission case and circumscribes, but does not touch the input shaft . Additionally, known roller forks are not appropriately configured to allow them to be replaced in existing clutch systems by having extremely limited space within the clutch housing. It is desired to provide a low friction clutch fork to release the bearing shell, which will reduce wear on the sleeve bush. It is further desired to provide such a combination of clutch fork and release bearing that fits in the space available for a combination of conventional fork and release bearing. SUMMARY OF THE INVENTION A clutch release mechanism includes a clutch release sleeve, a clutch release bearing and a clutch release fork. The clutch release bearing links a second end of the clutch release sleeve and has an internal guide rotatably fixed to the second end of the clutch release sleeve. The clutch release fork has rollers disposed on each of two arms for engagement with an outer guide of the clutch release bearing. A clutch includes a flywheel, an input shaft of the transmission, a clutch cover, a pressure plate, a clutch-driven disc, a clutch release sleeve, a plurality of radially oriented levers, a spring, a bearing release, a clutch housing, a clutch release arrow, a clutch release fork, and rollers. The flywheel is rotatably disposed on an axis of rotation. The input arrow of the transmission is disposed on the axis of rotation and has a frozen portion. The clutch cover is fixed to the steering wheel. The pressure plate is arranged between the clutch cover and the flywheel for axial movement therebetween, and is rotatably fixed to the cover. The clutch-driven disk is rotatably fixed to the input shaft through notches and is disposed between the flywheel and the pressure plate for "axial movement slidable therebetween." The clutch release sleeve is slidably disposed on the input shaft. and has a first end disposed between the pressure plate and the cover, and a second end disposed on a side of the cover opposite the pressure plate.The plurality of radially oriented levers are distributed around the axis of rotation. Radially inwardly disposed to engage a first end of the release sleeve Levers extend between the release sleeve and the pressure plate or spring The spring is disposed between the pressure plate and the cover and biases the pressure plate towards The driven disc The clutch release bearing is disposed at the second end of the sleeve ito release, outside the clutch cover. The clutch housing is disposed on the clutch cover and the release bearing. The clutch release arrow is rotatably disposed in the clutch housing and the release bearing. The clutch release arrow is rotatably disposed in the clutch housing and is capable of pivoting about a pivot axis oriented 90 'with the axis of rotation. The clutch release fork is fixed to the clutch release arrow for rotation with it and has first and second arms that extend adjacent to the release bearing. The rollers are rotatably disposed on each of the first and second arms of the clutch release fork, and are in engagement with the release bearing. The rollers each include a pin pin with a first end received by a respective fork arm. The spike pin has a second end surrounded by a tire rotatably mounted. The tire has a perforation through it with a cap fixedly mounted on it. A detent is provided to prevent axial displacement of the tire from the second end of the dowel pin. The clutch and clutch release mechanism of the invention employing a fork with rollers are highly effective in reducing friction between the fork and the release bearing and advantageously reduce the wear of the sleeve of the sleeve. The disclosed combination of fork and bearing is advantageously configured to fit within a clutch housing having an extremely limited amount of space. Brief Description of the Drawings Figure 1 is a rearward-facing end view of the clutch release bearing and the clutch fork. Figure 2 is a side view of the release bearing and the fork of Figure 1, shown in the direction of the arrows 2. Figure 3 is a sectional side view of a clutch assembly employing the release bearing and the fork of Figure 2 and shown in a disengaged position. Figure 4 is a sectional side view of the clutch assembly of Figure 3 in a released position.

Figure 5 is a sectional side view of the release bearing of Figure 1. Figure 6 is a side view of a roller used with the fork of Figures 1-4. Figure 7 is a sectional view of a roller used with the fork of Figure 8 in the direction of the arrows 7 in Figure 8. Figure 8 is a rearward-facing end view of a clutch release bearing and a clutch fork. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 shows a clutch housing 10 pivotally supporting a clutch fork 12. Clutch fork 12 is used to selectively disengage clutch assembly 14, as best shown in FIGS. 4, by displacement of the clutch release bearing 15. A clutch link 16 disposed between a vehicle operator and the clutch fork 12 includes an operating lever 17 disposed outside the clutch housing 10. The clutch assembly 14 includes a clutch cover 18 fixed to a flywheel 20. The flywheel 20 is in turn fixed to a motor crankshaft (not shown) for rotation about an axis of rotation 22. An input arrow of the transmission 24, muted in a first end, extends from a transmission case (not shown) along the axis 22. A driven disc 26 is slidably disposed on the portion fired from the input arrow 24 for rotation with it. A pressure plate 28 compresses the driven disc 26 between itself and the flywheel 20. Six clutch engagement levers 30 are circumferentially distributed about the axis 22, and extend radially from a first end of a release sleeve 32. One end radially external of each lever 30 links the cover 18 directly or indirectly through an adjustment mechanism. An internal guide 36 of the release bearing 15 is linked to the release sleeve 32 for axial movement therewith. An elastic ring helps retain the inner guide 36 on the sleeve 32. An inlet arrow sleeve 37 is press fit into the sleeve 32 in axial alignment with the bearing 15. An outer guide 38, rotatably fixed to a bearing housing 39, is prevented from rotating relative to the clutch housing 10. Angle springs 40, which develop the clutch engagement loads, are disposed between the clutch cover 18 and the first end of the sleeve 32. Both the sleeve 32 and the cover 18 has corresponding spring engaging characteristics 42 and 44, respectively. The clutch fork 12 straddles the bearing 15 and is fixed to two coaxial fork arrows 46 for pivoting about the pivot shaft 48. The operating lever 17 is fixed to one of the fork arrows 46. A cross member 50 of the fork 12 connects two opposite arms 52 adjacent to the bearing 15. Each of the arms 52 has rollers 54 arranged on pins 55 extending inwardly from near the ends of the arms 52. The rollers 54 link wear pads 56 on a front side of the bearing 15. A roller 54 is shown in greater detail in Figure 6. A spigot pin 58 has a first end received by one of the arms 52. A second end of the pin 58 supports the needle roller 60 retained by a cup 62. An outer housing 64 houses the cup 62 and serves as a roller surface. A retaining ring 66 disposed in a groove in the pin 58 helps retain the housing 64 and the cup 62. All elements of the roller 54 illustrated are formed of steel. Alternate roller designs include the use of ball bearing elements in place of needle rollers, or a Teflon-coated bushing that travels directly over the dowel pin. With reference to figures 7 and 8, it is shown an alternative roller configuration. A roller 70 has a pin pin 72. The pin pin 72 has a first end 74 which is received by and fixed within a bore through it 75 on the inward side of the respective fork arm 52. The pin 72 and the perforation 75 are dimensioned to provide a snap fit between them. The pin pin 72 also has a second end 76. The second end 76 is surrounded by a rotatably mounted tire 78. The tire 78 provides a roller surface that contacts wear pads 56. The tire 78 has a bore to its through 80. Mounted fixedly in the transverse bore 80 are two bushes 82. The bushes 82 in the illustrated embodiment are depressed within the transverse bore 80 of the tire 78 and are sized to provide an interference fit. The bushings 82 define an annular groove 83 therebetween. The pin pin 72 also has an annular groove 84 aligned with the groove 83. The pin 72 is formed, in one embodiment, selecting an unhardened needle roller of the desired pin diameter. The slit 84 is cut in the pin 72. The pin 72 is then hardened and polished. Arranged within the annular grooves 83 and 84 is a retaining ring 86. The retaining ring 86 is divided to allow it to expand radially elastically to fit over the pin 72 and to contract to return to the groove 84. Via the bushings 82, the retaining ring 86 restricts the axial displacement of the tire 78 on the pin 72. A contact surface 88 of the tire 78 is slightly crowned, having an apex at its mid-point 90. The crowning of the tire 78 allows the tire to compensate for deflections and misalignment without excessive edge loading of the tire 78 and the bushes 82. In one embodiment, a crown having a radius of 3,000 mm is placed on a tire approximately 12 mm wide and having a diameter of approximately 19 mm. The retaining ring 86 shown is carried by the tire 78 in the groove 84, between the bushings 82, before assembly on the pin 72. In a free or undistorted condition, the ring 86 has an internal diameter smaller than an outer diameter of the pin 72 and has an outer diameter greater than an inner diameter of the bushes 82. The slot between the bushes 82 has a radial depth that at least equals a wire diameter of the ring 86. The depth of the slot 83 allows the ring 86 disposed fully within the slit 83. The tire 78 assembled on the pin 72 aligning the tire 78 and the pin 72, and then pressing against the tire 78. A. The guide bevel on the pin 72 expands the ring 86 so that the ring 86 is fully disposed within the slit 83. When the slits 83 and 84 are aligned, the ring 86 returns to the slit 84 to retain the tire 78 on the pin 72. Alternatively, the retaining ring 84 can be carried by the pin 72 before the tire 78 is assembled on the spigot pin 72. However, the slit 84 would have to be deep enough to accommodate the full diameter in wire cross-section or the section thickness of the ring 86. The ring 86 would have an inner diameter smaller than an outer diameter of the pin 72 and an outer diameter greater than an internal diameter of the bushes 82. The slit 83 would have to be shallower that the slit 84, limiting the radial expansion outwardly of the ring 86. When the tire 78 is pushed over the pin 72, the ring 86 would collapse towards the slit. at 84, and would expand toward the slit 83 when the slits 83 and 84 are aligned to retain the tire 78 on the pin 72. The tire 78 can still be alternately assembled to the pin 72 in the following manner. The retaining ring 86 is expanded to slide on the pin 72 and in alignment with the slot 84. The ring 86 is allowed to return to the slit 84 and retain it. The slit 84 has a depth approximately equal to half the wire diameter or thickness of the ring 86. A first bushing 82 is pressed towards the tire 78. The first bushing 82 is depressed to a predetermined depth within the tire 78 such that its edge outer end is disposed slightly below a first side of the tire 78. The assembled tire 78 and the first bushing 82 are slid over the second end 76 of the pin 72 on a first side of the retaining ring 86. The inner end edge of the first the bushing 82 is near the middle part of the perforation 80. The second bushing is slid over the first end 74 of the pin 72 on a second side of the retaining ring 86. The tire 78 is axially constrained and the second bushing 82 is depressed towards the perforation 80 at a predetermined depth such that the inner end edge of the second bushing 82 is at a predetermined distance a of the inner end edge of the first bushing 82 and the end outer edge of the second bushing 82 is disposed below the second side of the tire 78. Placing the first bushing in a predetermined axial location within the tire, such as having the inner end edge of the first bushing at a predetermined distance from the second side of the tire 78, advantageously prevents a thrust load from developing which polarizes the tire 78 outwards towards the arms 52, between the ring 86 and the first bushing 82. Bushes 82 are not designed to withstand thrust loads and can be damaged if they bear considerable thrust loads. The predetermined location of the bushing 82 within the tire 78 is selected to ensure contact between the second side of the tire 78 and the corresponding arm 52 of the fork 12 when the tire 72 is depressed towards the arm 52. The assembled roller 70 has the second end 76 of the pin 72 axially offset from or slightly recessed below the first side or outer side of the tire 78. The placement relationship described above between the tire 78 and the retaining ring 86 and the fork arm 52 requires the pin 72 to be inserted. at a predetermined depth within the perforation 75. This is achieved by using a special press tool 92, best shown in Figure 7, on the ram (not shown) that pressed the rollers 70 toward the arms 52. The tool 92 is shaped of cup at its end. The tool 92 has a blind bore 94 of an internal diameter sized to radially rid the tire 78. The bore 94 has a depth less than an axial length of the tire 78. A male 96 in the lower portion 98 of the bore 94 extends toward up from the bottom 98 in an amount just slightly greater than the axial displacement between the second end 76 of the pin 72 and the side of the tire 78. The diameter of the core 96 is smaller than an outer diameter of the pin 72. To install the roller 70 on the arm 52, the tool 92 is slid over the tire 78, as shown in Fig. 7. The male 96 links the second end 76. The tool 92 is forced towards the fork arm 52, depressing the pin 72 toward the perforation 95. The tire 78 links the fork arm 52. After seating the tire 78 against the fork arm 52, the continuous ram force produces a slight The displacement magnitude of the tool 92 and the pin 72 relative to the wheel 78. This small amount of displacement is the result of the slight amount of axial displacement in the tool in excess of the pin-to-tire displacement of the roll 70. slight magnitude of excess displacement helps to ensure that the tool 92 acts against the pin 72, and not against the tire 78 when it forces the pin 72 towards the perforation 75. An advantage of the roller 70 is that it does not require initial lubrication or maintenance . The bushes 82 have a large contact area with the pin 72 in comparison with needle rollers 60, thereby eliminating any hardening of the pin 72. The roller 70 is extremely robust in environments of low angular displacement, vibratory, due to its resistance to hardening. It is evident that those skilled in the art that the retaining ring 86 can be of various cross sections and can be a wire ring or an elastic ring. The retention of the tire 78 can be achieved by having an integral flange collar with the spigot pin 72 and the sockets 82 juxtaposed. The retention of the tire 78 on the spigot pin 72 can also be achieved by having an end head on the spigot pin 72, allowing the use of a single bushing.

The rollers 54, 70 and the release bearing 15 are designed as paired assemblies so that the axial position of the sleeve 32 varies as a function of the rotational position of the lever 17 exactly as the position of the sleeve 32 would vary with the position of the sleeve. lever 17 in a system without rollers. This allows the roller yoke 12 to be installed in a system not explicitly designed for compatibility with a roller yoke. The arms 52 of the fork 12 have been widened to make them more resistant to the torsional force introduced by the cantilever rollers 54, 70. The invention operates in the following manner. Figure 3 shows the clutch 14 in a linked condition. The position of the clutch fork 12 and the lever 17 is controlled by the position of the release bearing 15, which in turn is controlled by the displacement limits of the levers 30 against the pressure plate 28, in response to the force of the springs 40. When the clutch is released by the operator via the link 16, the operating lever 17 rotates the clutch fork 12 to the position shown in figure 4, axially displacing the release bearing 15 back against the force of the springs 40 to discharge the pressure plate 28. The discharge of the pressure plate 28 unlocks the driven disc 26, allowing relative rotation between the driven disc 26 and the pressure plate 28 and the flywheel 20.

As the yoke 12 is pivoted to the disengaged position, the rollers 54, 70 move in a first direction along wear pads 56. When the clutch is re-engaged by the operator, the rollers 54, 70 move in a second direction, opposite the first direction, along wear pads 56. Rollers 54, 70 prevent undesired wear of sleeve 37 by substantially eliminating all frictional drag of fork 12 against pads 56. It should be noted that many forms of alternative embodiments are readily apparent to those skilled in the art of clutches. For example, a diaphragm spring may be used in place of the angle springs 40. Still alternatively, a diaphragm spring may be used in place of both the diaphragm spring 40 and the levers 30. In such embodiment, fingers that extend radially inward of the diaphragm spring would serve as levers. The displacement of the ends disposed radially inward of the levers causes the pressure plate to be selectively discharged by diverting a radially external annular portion of the spring. The radially outer annular portion of the spring is disposed directly between the pressure plate 28 and the cover 18, instead of indirectly, as shown in the preferred embodiment, the spring 40 having an end acting on the cover 18 and a second end acting on the sleeve 32, which acts on the lever 30, which acts on the pressure plate 28. However, in both embodiments, the displacement of the sleeve results in the deflection of the spring or of the springs In light of these and other possible variations of the invention, the scope of the invention is defined by the appended claims and is not limited to the preferred embodiment disclosed.

Claims (21)

1. CLAIMS 1. A clutch for rotatingly connecting a vehicle engine crankshaft to a transmission input shaft, the clutch comprising: a flywheel rotatably disposed on an axis of rotation; a transmission input arrow disposed on the axis of rotation and having a chirped portion; a clutch cover fixed to the steering wheel; a pressure plate arranged between the clutch cover and the flywheel for axial movement between them and rotatably fixed to the cover; a clutch driven disc fixed rotatably to the inlet arrow through notches and disposed between the flywheel and the pressure plate for axial movement slidable therebetween; a clutch release sleeve slidably disposed on the entry shaft, having a first end disposed between the pressure plate and the cover and having a second end disposed on a side of the cover opposite the pressure plate; a plurality of radially oriented levers, distributed around the axis of rotation and having radially inwardly disposed ends linking a first end of the release sleeve and the levers extending between the release sleeve and the pressure plate; a spring disposed between the pressure plate and the cover, polarizing the pressure plate towards the driven disc; a clutch release bearing connected to a second end of the release sleeve and disposed outside the clutch cover and the bearing also having a bonding surface; a clutch housing disposed on the clutch cover and the release bearing; a clutch release arrow disposed in the clutch housing and pivotable about a second axis oriented 90 ° with the axis of rotation; a clutch release fork rotatably fixed to the clutch release arrow for rotation therewith and having first and second arms extending adjacent to the release bearing; and a plurality of rollers with a roller rotatably disposed on one side inward of each of the first and second arms of the clutch release fork and in engagement with the bonding surface release bearing, the rollers each including a pin pin with a first end received by a respective fork arm, the pin pin having a second end surrounded by a rotatably mounted tire, the tire having a bore therethrough and a bushing fixedly mounted therein, and a retainer disposed between the pin and the tire to prevent axial displacement of the tire from the second end of the pin.
2. 2. A clutch as defined in claim 1, wherein the bushing has an interference interference fit with the tire.
3. 3. A clutch as defined in claim 2, wherein the bushing is press fit into the tire. A clutch as defined in claim 1, wherein the pin pin has a first annular groove and the sleeve has a second annular groove, the first annular groove and the retaining ring disposed in both grooves for axially retaining the tire in the spike pin A clutch as defined in claim 1, wherein there are two fixed bushes within the tire defining a first annular groove and the pin pin has a second annular groove aligned with the first annular groove and the retainer is disposed in the grooves first and second row, thereby retaining the tire on the pin. 6. A clutch as defined in claim 1, wherein the retainer retains the tire on the dowel pin via the bushing. A clutch as defined in claim 1, wherein the release bearing and the roller are configured as a set to provide a predetermined relationship between a rotation angle of the clutch release shaft and an axial position of the release sleeve. of clutch. A clutch as defined in claim 5, wherein: a first bushing of the bushes is disposed remote from the fork arm; the first of the bushes has an inner end near the retainer; a first side of the tire is arranged close to the fork arm; and the inner end edge of the first bushing is spaced from the detent when the first side of the tire is in engagement with the fork arm. 9. A clutch release mechanism, comprising: a clutch release sleeve having a lever engaging feature at a first end; a clutch release bearing that connects a second end of the sleeve and having an internal guide rotatably fixed to the second end of the clutch release sleeve; and a clutch release fork having rollers disposed on each of the two arms for attachment to the clutch release bearing, the rollers each including a dowel pin with a first end received by a respective fork arm, the spike pin having a second end surrounded by a rotatably mounted tire, the tire having a perforation therethrough and a bushing fixedly mounted therein, and a retainer disposed between the tire and the pin to prevent axial displacement of the second tire end of the dowel pin. 10. A heavy clutch release mechanism, as defined in claim 9, wherein the rollers are mounted on one side inwardly of the arms. A clutch release mechanism, as defined in claim 9, wherein the release bearing and the roller are configured as an assembly to provide a predetermined relationship between a rotation angle of the clutch release arrow and a position of the clutch release sleeve. 12. A clutch release mechanism, as defined in claim 9, wherein the tire has a crown. 13. A clutch release mechanism, as defined in claim 9, wherein the bushing has an interference interference fit with the tire. 14. A clutch release mechanism, as defined in claim 13, wherein the bushing is snapped into the tire. A clutch release mechanism, as defined in claim 9, wherein the tire has a first annular groove and the pin pin has a second annular groove aligned with the first annular groove and a retaining ring is disposed in the first and second grooves aligned to axially restrict the tire in the dowel pin. 16. A clutch release mechanism, as defined in claim 9, wherein there are two fixed bushes within the tire defining a first annular groove and the pin pin has a second annular groove aligned with the first annular groove and retainer it is arranged in the first and second aligned slits. 17. A clutch release mechanism, as defined in claim 9, wherein the retainer retains the tire on the dowel pin via the bushing. 18. A clutch release mechanism, as defined in. claim 16, wherein a first bushing of the bushes is disposed remote from the fork arm; the first of the bushes has an inner end near the retainer; a first side of the tire is arranged close to the fork arm; and the inner end edge of the first bushing is spaced from the detent when the first side of the tire is in engagement with the fork arm. 19. A clutch release fork for engagement with a clutch release bearing, comprising: a cross member; two opposite arms connected to each other by means of the crossed member; a roller disposed on each arm for attachment to a clutch bearing, the roller comprising: a pin having first and second ends, the first end being received on a respective fork arm; a tire with a perforation therethrough that surrounds the second end of the spike pin, the tire being rotatably mounted on the second end of the spike pin; a bushing fixedly mounted in the bore through the tire; and a retainer configured to prevent axial displacement of the tire from the pin. 20. A clutch release fork for engagement with a clutch release bearing, as defined in claim 19, wherein the second end of the dowel pin has a first annular groove, and the tire has two ferrules defining a second. annular groove aligned with the first annular groove, and the retainer is a retaining ring on the dowel pin. 21. A clutch release fork for engagement with a clutch release bearing, as defined in claim 20, wherein: a first bushing of the bushes is disposed remote from the fork arm; the first of the bushes has an inner end near the retainer; a first side of the tire is arranged close to the fork arm; and the inner end edge of the first bushing is spaced from the detent when the first side of the tire is in engagement with the fork arm.