Transmission gear shift system

Abstract: In a transmission for automobiles, the shift feeling is improved by smoothly transferring the operational load between a shift rod (78) and a reverse shift fork (50). This is accomplished by cam faces (a,b,c) formed on a reverse shift fork which shifts a reverse idle gear (41) between a neutral position and a reverse position, and cam faces (d,e) are formed on a drive cam (88) which moves integrally with a shift rod. When the drive cam is moved from a neutral position to the reverse position, one of the cam faces presses against another of the cam faces moving the reverse shift fork in a circular manner in an anticlockwise direction, and the reverse idle gear moves to the reverse position. When the drive cam member is moved from the reverse position to the neutral position, another of the cam faces presses against still another of the cam faces moving the reverse shift fork in a circular manner in a clockwise direction, and the reverse idle gear moves to the neutral position.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to gear shift systems for transmissions in which a reverse gear shift stage is established by moving a reverse idle gear from a neutral position to a reverse position by means of a reverse shift fork. Description of the Prior Art Fig. 14 shows a gear shift system for a manual transmission of the prior art. A reverse shift fork 02 whose middle part is pivotally supported by a fulcrum pin 01, has an L-shaped long hole 02a at one end and a U-shaped fork channel 02b at the other end. A drive pin 03 fixed on a shift piece (not illustrated), engages with the long hole 02a, and a reverse idle gear 04 which can move freely in the axial direction engages with the fork channel 02b. When the shift piece is in a neutral position, the drive pin 03 provided on the shift piece is positioned at the bend in the middle of the L-shaped long hole 02a of the reverse shift fork 02 (broken line). When the drive pin 03 moves from this state towards a reverse position, which is upwards in the figure, the reverse shift fork 02 whose long hole 02a is pushed by the drive pin 03, moves clockwise in a circular manner, and its fork channel 02b moves the reverse idle gear 04 downwards (as shown in the figure) to establish a reverse gear shift stage (solid line). On the other hand, when the drive pin 03 moves from the reverse position to the neutral position, the reverse shift fork 02 whose long hole 02a is pushed by the drive pin 03, moves anticlockwise in a circular manner, and its fork channel 02b moves the reverse idle gear 04 upwards (as shown in the figure) to release the established reverse gear shift stage. When the drive pin 03 moves from the neutral position towards a fifth speed position which is on the opposite side to the reverse position, the drive pin 03 slips inside the long hole 02a, the reverse shift fork 02 remains stopped at the position shown by the broken line, and the reverse idle gear 04 is maintained in the neutral position. In the above-described prior art device, since the drive pin 03 provided on the shift piece engages with the long hole 02a provided on the reverse shift fork 02 and the reverse shift fork 02 moves in a circular manner between the neutral position and the reverse position through movement of the drive pin 03, there is the problem that galling or non-smooth sliding is caused between the drive pin 03 and the long hole 02a, preventing smooth operation and thus degrading the shift feeling when establishing and releasing the reverse shift state. EP-A-0 249 581 discloses a transmission gear shift system in accordance with the preamble of claim 1. There, a catch appendage used as a drive cam has a pin shape. The engagement of this catch appendage with the recess or projections of the reverse shift fork will cause the reverse shift fork to be pivoted around a pin to move the reverse idle gear to the neutral position or to the reverse position. SUMMARY OF THE INVENTION The present invention has been carried out in view of the above-mentioned circumstances and it is an objective of the present invention to improve the shift feeling by carrying out smooth transfer of an operational load between a shift rod and a reverse shift fork. In order to achieve the above-mentioned objective according to claim 1, a transmission gear shift system comprising a transmission case , a reverse shift fork supported on the transmission case in a circularly movable manner by a fulcrum pin, wherein the reverse shift fork is moved in a circular manner in one direction by an axial movement of a shift rod from a neutral position to a reverse position, and a reverse idle gear is shifted from a neutral position to a reverse position by the reverse shift fork for establishing a reverse gear shift stage, wherein the reverse shift fork is moved in a circular manner in the other direction by an axial movement of the shift rod from the reverse position to the neutral position and the reverse idle gear is shifted from the reverse position to the neutral position by the reverse shift fork to release the established reverse gear shift stage, a drive cam integrally formed with the shift rod, the drive cam having a first drive cam face for reverse shift and a second drive cam face for neutral return; and the reverse shift fork having a third driven cam face for reverse shift and a fourth driven cam face for neutral return, wherein movement of the shift rod from the neutral position to the reverse position presses the first drive cam face for reverse shift of the drive cam against the third driven cam face for reverse shift of the reverse shift fork to move the reverse shift fork in a circular manner in the one direction, and movement of the shift rod from the reverse position to the neutral position presses the second drive cam face for neutral return of the drive cam against the fourth driven cam face for neutral return of the reverse shift fork, to move the reverse shift fork in a circular manner in the other direction, characterized in that shift motions of the reverse shift fork between respective positions corresponding to the neutral position and the reverse position of the shift rod are continuously guided by the reverse shift fork and the drive cam engaging each other at two distinct contact portions. In accordance with the above-mentioned arrangement, since movement of the shift rod from the neutral position to the reverse position presses the drive cam face for reverse shift of the drive cam against the driven cam face for reverse shift of the reverse shift fork to move the reverse shift fork in a circular manner to the reverse position, and movement of the shift rod from the reverse position to the neutral position presses the drive cam face for neutral return of the drive cam against the driven cam face for neutral return of the reverse shift fork to move the reverse shift fork in a circular manner to the neutral position, the shift fork can be operated smoothly by the drive cam without causing galling, and thus the shift feeling when establishing and releasing a reverse gear shift stage, can be improved. Owing to such mutual engagement between the reverse shift fork and the drive cam at two portions, the reverse fork can be guided to desired positions providing the neutral and reverse positions of the reverse idle gear. Thus, the shifting operations between the neutral and reverse positions can be carried out smoothly, i.e. free of any galling or non-smooth sliding. Preferably, a fifth cam face for neutral hold which extends from the fourth driven cam face for neutral return is provided on the reverse shift fork, and when the shift rod moves from the neutral position to a forward position which is in the opposite direction to the reverse position in order to establish a forward gear shift stage, the second drive cam face for neutral return of the drive cam, moves along the fifth driven cam face for neutral hold of the reverse shift fork, while maintaining the reverse shift fork in the neutral position. In accordance with the above-mentioned arrangement, since the driven cam face for neutral hold which extends from the driven cam face for neutral return is provided on the reverse shift fork, when the shift rod moves from the neutral position to a forward position which is in the opposite direction to the reverse position, in order to establish a forward gear shift stage, the drive cam face for neutral return moves along the driven cam face for neutral hold while maintaining the reverse shift fork in the neutral position, and it is possible to prevent unnecessary circular movement of the reverse shift fork from the neutral position accompanying the movement of the shift rod to the forward position. Preferably , movement of the reverse idle gear in the direction away from a first end face of the transmission case is restricted by the second drive cam face for neutral return of the drive cam causing the reverse idle gear to be pushed against the end face when in neutral. In accordance with the above-mentioned arrangement, since movement of the reverse idle gear in the direction away from the end face of the transmission case is prevented by the drive cam face for neutral return of the drive cam causing the reverse idle gear to be pushed against the end face when in neutral, it is possible to effectively maintain the reverse idle gear in the neutral position without providing a special detent mechanism on the reverse shift fork, and thus this can contribute to a reduction in the number of parts. Preferably, movement of the reverse idle gear in the direction away from a second end face of the transmission case is restricted by the first drive cam face for reverse shift of the drive cam, causing the reverse idle gear to be pushed against the second end face when a reverse gear shift stage is established. In accordance with the above-mentioned arrangement, since movement of the reverse idle gear in the direction away from the end face of the transmission case, is prevented by the drive cam face for reverse shift of the drive cam, causing the reverse idle gear to be pushed against the end face when a reverse shift gear stage is established, it is possible to effectively maintain the reverse idle gear in the reverse position without providing a special detent mechanism on the reverse shift fork and thus this can contribute to a reduction in the number of parts. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a vertical cross-sectional view of a manual transmission for a vehicle. Fig. 2 is a diagram showing the change patterns of a change lever. Fig. 3 is a horizontal cross-sectional view of an essential part of the manual transmission for a vehicle. Fig. 4 is a magnified view of an essential part of Fig. 3 (third speed - fourth speed select position). Fig. 5 is a cross-sectional view at line 5 - 5 in Fig. 4. Fig. 6 is a view for explaining an action corresponding to Fig. 4 (fifth speed - reverse select position). Fig. 7 is a view for explaining an action corresponding to Fig. 4 (first speed - second speed select position). Fig. 8 is a view taken in the direction of an arrow 8 in Fig. 3. Fig. 9 is a cross-sectional view at line 9 -9 in Fig. 8. Fig. 10 is a magnified view of an essential part of Fig. 8 (neutral position). Fig. 11 is a view for explaining an action corresponding to Fig. 10 (reverse position). Fig. 12 is a view for explaining an action corresponding to Fig. 10 (fifth speed position). Fig. 13 is a view from line 13 - 13 in Fig. 10. Fig. 14 is a prior art gear shift mechanism. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in Fig. 1 a transmission case 11 for a manual transmission M for vehicle with five forward speeds and one reverse speed, comprises a case left half 12 and a case right half 13 which are separated on a dividing plane extending in the longitudinal direction of the vehicle, and a gear shift clutch C is housed in a clutch chamber 14 formed on the side surface of the case left half 12 on the side of the engine E. The right and left ends of a main shaft Sm connected to the engine E via the gear shift clutch C, are supported by means of ball bearings 16 and 15 on the case right half 13 and the case left half 12 respectively, and the right and left ends of a counter shaft Sc positioned in parallel to the main shaft Sm are supported by ball bearings 18 and roller bearings 17 on the case right half 13 and the case left half 12 respectively. A differential gear D which distributes the output from the counter shaft Sc to the right and left axles 19, 19 is supported by a pair of right and left ball bearings 21, 20 on the case right half 13 and the case left half 12 respectively. The gear shift clutch C housed inside the clutch chamber 14, comprises a clutch wheel 22 which is connected to the right end of the crankshaft of the engine E and a clutch disc 24, connected to the left end of the main shaft Sm via a damper 23. They are normally engaged by clamping the facings 27 of the clutch disc 24 between a pressure plate 26 and the clutch wheel 22 by means of the resilient force of a diaphragm spring 25 and the engagement is released during gear shifting by means of a release fork 28 pushing a release bearing 29 leftwards. On the main shaft Sm are secured a main first speed gear 31, a main second speed gear 32, a main third speed gear 33, a main fourth speed gear 34 and a main fifth speed gear 35, which are all supported in a relatively rotatable manner. On the counter shaft Sc, a counter first speed gear 36 and a counter second speed gear 37 which mesh with the main first speed gear 31 and main second speed gear 32, are supported in a relatively rotatable manner. A counter third speed gear 38, a counter fourth speed gear 39 and a counter fifth speed gear 40 are also secured with counter shaft Sc and mesh with the main third speed gear 33, main fourth speed gear 34 and main fifth speed gear 35 respectively. The right and left ends of a reverse idle shaft Sr are supported on the case right half 13 and the case left half 12, and a reverse idle gear 41 which is supported on the reverse idle shaft Sr, in a laterally slidable manner, can mesh with a main reverse gear 42 which is secured on the main shaft Sm as well as with a counter reverse gear 43 which is supported on the counter shaft Sc in a relatively rotatable manner. By moving a sleeve 45 of a first speed - second speed synchronous mechanism S1 leftwards by means of a first speed - second speed shift fork 44, the counter first speed gear 36 is connected to the counter shaft Sc to establish a first speed gear shift stage, and by moving the sleeve 45 of the first speed - second speed synchronous mechanism S1 rightwards by means of the first speed - second speed shift fork 44, the counter second speed gear 37 is connected to the counter shaft Sc to establish a second speed gear shift stage. By moving a sleeve 47 of a third speed - fourth speed synchronous mechanism S2 leftwards by means of a third speed - fourth speed shift fork 46 the main third speed gear 33 is connected to the main shaft Sm to establish a third speed gear shift stage, and by moving the sleeve 47 of the third speed - fourth speed synchronous mechanism S2 rightwards by means of the third speed - fourth speed shift fork 46, the main fourth speed gear 34 is connected to the main shaft Sm to establish a fourth speed gear shift stage. By moving a sleeve 49 of a fifth speed synchronous mechanism S3 leftwards by means of a fifth speed shift fork 48, the main fifth speed gear 35 is connected to the main shaft Sm to establish a fifth speed gear shift stage. When the sleeve 49 of the fifth speed synchronous mechanism S3 is moved rightwards by means of the fifth speed shift fork 48, a reverse shift fork 50 which supports the reverse idle gear 41 in a rotatable manner, moves leftwards in operative connection with the fifth speed shift fork 48, and the reverse idle gear 41 meshes with the main reverse gear 42 and the counter reverse gear 43 provided on the sleeve 45 of the first speed - second speed synchronous mechanism S1, to establish a reverse gear shift stage. The first speed - second speed synchronous mechanism S1, the third speed - fourth speed synchronous mechanism S2 and the fifth speed synchronous mechanism S3 are known and they carry out a synchronous action by means of the frictional force between a blocking ring and a synchro cone due to the lateral movement of the sleeves 45, 47 and 49. When the first to fifth gear shift stage or reverse gear shift stage is thus established, rotation of the counter shaft Sc is transmitted to the differential gear D via a final drive gear 51 and a final driven gear 52 thus driving the right and left axles 19, 19. The structure of a shifting system for establishing the first speed to fifth speed gear shift stages and the reverse gear shift stage is explained below by reference to Fig. 2 to Fig. 12. Fig. 2 shows an operational pattern of a shift lever L of the shifting system; P1 denotes a first speed - second speed select position, P2 denotes a third speed - fourth speed select position (neutral position), P3 denotes a fifth speed - reverse select position, , 1 ○ and 2 ○ which are located on either side of the first speed - second speed select position P1, denote a first speed position and a second speed position respectively, 3 ○ and 4 ○ which are located on either side of the third speed - fourth speed select position P2, denote a third speed position and a fourth speed position respectively, and 5 ○ and R which are located on either side of the fifth speed - reverse select position P3, denote a fifth speed position and a reverse position respectively. The arrow SE in the figure illustrates the directions of the select operation of the shift lever L and the arrow SI in the figure illustrates the directions of the shift operation of the shift lever L. As shown in Fig. 3 to Fig. 5, a dish-shaped indentation 13a is formed on the upper part of the case right half 13 of the transmission case 11, and by connecting a cover member 57 by means of six bolts 56 to cover the opening of the indentation 13a, a breather chamber 58 is formed between the cover member 57 and the indentation 13a. A shift select shaft 59 is supported in a rotatably and longitudinally movable manner in a guide hole 57a formed in the center of the cover member 57 and a guide hole 13b formed inside the case right half 13. A notch 59a is formed on the upper end of the shift select shaft 59 which extends externally from the cover member 57 via a sealing member 60, and a select lever 61 engages with the notch 59a. The select lever 61 swings vertically in operative connection with the select operation (operation in the direction of the arrow SE in Fig. 2) of the shift lever L and can move the shift select shaft 59 between the third speed - fourth speed select position shown in Fig. 4, the fifth speed - reverse select position (see Fig. 6), which is upwards relative to the third speed - fourth speed select position, and the first speed - second speed select position (Fig. 7), which is downwards relative to the third speed - fourth speed select position. A shift lever 62 is fixed beneath the notch 59a of the shift select shaft 59, and the shift lever 62 rotates in lateral directions in operative connection with the shift operation (operation in the direction of the arrow SI in Fig. 2) of the shift lever L. When the shift lever L is in the first speed - second speed select position P1, the third speed - fourth speed select position P2 or the fifth speed - reverse select position P3, the shift select shaft 59 is in the neutral position; when the shift lever L is operated to move to the first speed position 1 ○, the third speed position 3 ○ or the fifth speed position 5 ○, the shift select shaft 59 rotates leftwards from the neutral position, and when the shift lever L is operated to move to the second speed position 2 ○, the fourth speed position 4 ○ or the reverse position R, the shift select shaft 59 rotates rightwards from the neutral position. The shift select shaft 59 can be stopped at nodal points in the three rotational positions by means of a detent mechanism 63 (Fig. 8). A shift arm 64 is fixed by a fixing pin 65 on the shift select shaft 59 which extends inside the case right half 13, and an interlock plate 66 is also supported on the shaft 59 in a relatively rotatable manner such that the shift arm 64 is vertically sandwiched by the plate 64. The interlock plate 66 comprises a pair of upper and lower lock claws 66a, 66b, and the pair of lock claws 66a, 66b face the top and bottom respectively of a drive part 64a formed at the forward end of the shift arm 64. The interlock plate 66 comprises a guide channel 66c which extends in a direction perpendicular to the shift select shaft 59 and a rotation stopping pin 67 fixed on the case right half 13 engages with the guide channel 66c. Therefore, when the shift select shaft 59 moves vertically, the shift arm 64 and the interlock plate 66 ascend and descend together, but when the shift select shaft 59 rotates, the shift arm 64 rotates together with the shift select shaft 59, but rotation of the interlock plate 66 is restricted by engagement of the guide channel 66c with the rotation stopping pin 67. The shift select shaft 59 has a lower half with a smaller diameter beneath a step-shaped first stopper surface 59b which is formed almost at its center in the longitudinal direction, and the upper surface of the inner circumference of a first spring seat 68 which fits in a slidable manner on the lower half of the shift select shaft 59 having the smaller diameter, engages with the first stopper surface 59b from the lower side, whereas the upper surface of the outer circumference of the first spring seat 68 is in contact with a first support surface 57b which is a lower surface of the cover member 57. With regard to a disc-shaped second spring seat 69 which is placed beneath the first spring seat 68 and fits in a slidable manner on the shift select shaft 59, the lower surface of the inner circumference thereof engages with a second stopper surface 66d which is formed on the upper surface of the interlock plate 66. A roughly cross-shaped opening 13c is formed on the bottom wall of the indentation 13a of the case right half 13, and the lower surface of the outer circumference of the second spring seat 69 is supported by four step-shaped second supporting surfaces 13d which are formed on the edge of the opening 13c. The upper and lower ends of a select spring 70 are supported between the lower surface of the first spring seat 68 and the upper surface of the second spring seat 69. Thus, when the shift select shaft 59 is in the three speed - fourth speed select position shown in Fig. 4, the upper surface of the inner circumference of the first spring seat 68 and the lower surface of the inner circumference of the second spring seat 69 which are supported in a slidable manner on the shift select shaft 59 and are forced by the select spring 70 in a direction such that they move apart from each other, are resiliently in contact with both the first stopper surface 59b of the shift select shaft 59 and with the second stopper surface 66d formed on the upper surface of the interlock plate 66, and the upper surface of the outer circumference of the first spring seat 68 and the lower surface of the outer circumference of the second spring seat 69 are supported by being in contact with the first support surface 57b of the cover member 57 and with the second support surfaces 13d of the indentation 13a respectively, and the shift select shaft 59 thus stops in a stable manner at the third speed - fourth speed select position. When the shift select shaft 59 moves upwards from the above-mentioned state to the fifth speed - reverse select position (Fig. 6), since the second spring seat 69 which is pressed by the second stopper surface 66d of the interlock plate 66 which is integral with the shift select shaft 59, ascends while leaving the first spring seat 68 which is latched onto the first support surface 57b of the cover member 57 at its original position, the select spring 70 is compressed, generating a force to return the shift select shaft 59 to the third speed - fourth speed select position. On the other hand, when the shift select shaft 59 moves downwards from the third speed - fourth speed position to the first speed - second speed select position (Fig. 7), since the first spring seat 68 which is pressed by the first stopper surface 59b of the shift select shaft 59, descends while leaving the second spring seat 69 which is latched onto the second support surfaces 13d of the opening 13c, at its original position, the select spring 70 is compressed, generating a force to return the shift select shaft 59 to the third speed - fourth speed select position. As hereinbefore described, since the shift select shaft 59 can be centered by forcing it to the third speed - fourth speed select position, which is the neutral position, by means of just one select spring 70, in comparison with the case in which the shift select shaft 59 is forced upwards and downwards by means of two springs, the number of parts and the cost can be reduced. Moreover, when two springs are supported on the shift select shaft 59, the length of the shift select shaft 59 inevitably increases, but by using only one spring it is possible to reduce the overall length of the shift select shaft 59. The internal space of the breather chamber 58 which is defined by the indentation 13a of the case right half 13 and the cover member 57 is connected to the internal space of the transmission case 11 via four through holes 71 which are formed between the inner circumference of the opening 13c and the outer circumference of the second spring seat 69 and is connected to the outside of the transmission case 11 via a breather tube 73 provided on the forward end of a breather pipe 72, which is integral with the cover member 57. A subassembly A is formed by assembling the shift select shaft 59, the first spring seat 68, the second spring seat 69, the select spring 70, the shift arm 64, the fixing pin 65 and the interlock plate 66 beforehand, onto the cover member 57, and by inserting this subassembly A into the opening 13c through the indentation 13a of the case right half 13 during assembly. Thus, the assembly operation can be outstandingly enhanced. Since the breather chamber 58 is defined by the indentation 13a of the case right half 13 and the cover member 57, and the first spring seat 68, the second spring seat 69 and the select spring 70 are housed inside the breather chamber 58, a single space functions as both the space forming the breather chamber 58 and the space for housing the first spring seat 68, the second spring seat 69 and the select spring 70, and it is possible to avoid an increase in the size of the transmission case 11 and the number of parts. Moreover, since the breather chamber 58 is connected to the internal space of the transmission case 11 via the four through holes 71 which are formed between the inner circumference of the opening 13c and the outer circumference of the second spring seat 69, and the shift arm 64 and the interlock plate 66 are positioned so as to adjoin each other beneath the through holes 71, oil can be effectively prevented from entering the breather chamber 58 due to the labyrinth effect. As shown in Fig. 4 and Fig. 8, the two ends of a first speed - second speed shift rod 76 comprising the first speed - second speed shift fork 44, the two ends of a third speed - fourth speed shift rod 77 comprising the third speed - fourth speed shift fork 46 and the two ends of a fifth speed - reverse shift rod 78 comprising the fifth speed shift fork 48 are supported in a slidable manner on the case left half 12 and the case right half 13 respectively. A first speed - second speed shift piece 79, a third speed - fourth speed shift piece 80 and a fifth speed - reverse shift piece 81 are fixed on the first speed - second speed shift rod 76, the third speed - fourth speed shift rod 77 and the fifth speed - reverse shift rod 78 respectively, and notches 79a, 80a, 81a formed at the forward ends of the three shift pieces 79, 80, 81 respectively are aligned vertically so that they can selectively engage with the drive part 64a provided at the forward end of the shift arm 64. Thus, when the shift select shaft 59 is in the third speed - fourth speed select position as shown in Fig. 4, since the drive part 64a of the shift arm 64 engages with the notch 80a of the third speed - fourth speed shift piece 80, the third speed - fourth speed shift rod 77 can be driven together with the third speed - fourth speed shift piece 80 from the neutral position to the third speed position or the fourth speed position by a circular movement of the shift select shaft 59. At this stage, the locking claw 66b on the lower side of the interlock plate 66 engages with the notch 79a of the first speed - second speed shift piece 79, and the locking claw 66a on the upper side of the interlock plate 66 engages with the notch 81a of the fifth speed - reverse shift piece 81, and thus malfunctions of the first speed - second speed shift piece 79 and the fifth speed -reverse shift piece 81 can be prevented. As shown in Fig. 7, when the shift select shaft 59 is moved to the first speed - second speed select position which is beneath the third speed - fourth speed select position, since the drive part 64a of the shift arm 64 engages with the notch 79a of the first speed - second speed shift piece 79, the first speed - second speed shift rod 76 can be driven together with the first speed - second speed piece 79 from the neutral position to the first speed position or the second speed position by a circular movement of the shift select shaft 59. At this stage, the locking claw 66a on the upper side of the interlock plate 66 engages with the notch 81a of the fifth speed - reverse shift piece 81 and the notch 80a of the third speed - fourth speed shift piece 80, and thus malfunctions of the fifth speed - reverse shift piece 81 and the third speed - fourth speed shift piece 80 can be prevented. As shown in Fig. 6, when the shift select shaft 59 is moved to the fifth speed - reverse select position which is above the third speed - fourth speed select position, since the drive part 64a of the shift arm 64 engages with the notch 81a of the fifth speed - reverse shift piece 81, the fifth speed - reverse shift rod 78 can be driven together with the fifth speed - reverse shift piece 81 from the neutral position to the fifth speed position or the reverse position by a circular movement of the shift select shaft 59. At this stage, the locking claw 66b on the lower side of the interlock plate 66 engages with the notch 79a of the first speed - second speed shift piece 79 and the notch 80a of the third speed - fourth speed shift piece 80, and thus malfunctions of the first speed - second speed shift piece 79 and the third speed - fourth speed shift piece 80 can be prevented. As shown in Fig. 8, a detent mechanism 82 is provided in order to stop the first speed - second speed shift rod 76 at nodal points so as to correspond to the first speed - second speed select position, the first speed position and the second speed position. Moreover, a detent mechanism 83 is provided in order to stop the third speed - fourth speed shift rod 77 at nodal points so as to correspond to the third speed - fourth speed select position, the third speed position and the fourth speed position. As shown in Fig. 8 to Fig. 10, a bracket 85 is fixed to the inner surface of the case right half 13 by means of two bolts 86, 86, and the reverse shift fork 50 is supported in a swingable manner on the bracket 85 via a fulcrum pin 87. A notch 50a which is interposed between the two side surfaces of the reverse idle gear 41 is formed at one end of the reverse shift fork 50 and a driven cam face a for reverse shift, a driven cam face b for neutral return and a driven cam face c for neutral hold are formed continuously at the other end, relative to the fulcrum pin 87, of the reverse shift fork 50. A drive cam face d for reverse shift which can come into contact with the driven cam face a for reverse shift and a drive cam face e for neutral return which can come into contact with the driven cam face b for neutral return and the driven cam face c for neutral hold, are formed continuously at the forward end of the drive cam 88, which is formed integrally with the fifth speed - reverse shift piece 81. A detent mechanism 84 for stopping the fifth speed - reverse shift rod 78 at nodal points to correspond to the fifth speed - reverse select position, the fifth speed position and the reverse position is provided at the forward end of an arm 85a which extends integrally from the bracket 85 supporting the reverse shift fork 50. As shown in Fig. 9, the detent mechanism 84 comprises a detent ball 84b which is urged by a detent spring 84a, and this detent ball 84b can selectively engage with three indentations 81b to 81d (Fig. 10 to Fig. 12) which are formed on the fifth speed - reverse shift piece 81. Thus, when the fifth speed - reverse shift piece 81 is at the neutral position as shown in Fig. 10, the drive cam face d for reverse shift and the drive cam face e for neutral return of the drive cam 88 of the fifth speed - reverse shift piece 81 are in contact with the driven cam face a for reverse shift and the driven cam face c for neutral hold of the reverse shift fork 50 respectively, and the reverse idle gear 41 is at the neutral position which is at the right end on the reverse idle shaft Sr and is in contact with the end face 13i of the case right half 13. Therefore, even if the reverse idle gear 41 attempts to move leftwards so as to move away from the end face 13i of the case right half 13, the leftward movement of the reverse idle gear 41 is prevented by the contact between the drive cam face e for neutral return of the drive cam 88 and the driven cam face c for neutral hold of the reverse shift fork 50. As shown in Fig. 12, when the fifth speed - reverse shift rod 78 moves leftwards from the neutral position to the fifth speed position in order to establish a fifth speed gear shift stage, the main fifth speed gear 35 is linked to the main shaft Sm by the fifth speed shift fork 48, which is provided on the fifth speed - reverse shift rod 78, to establish the fifth speed gear shift stage (Fig. 1). At this stage, the drive cam face e for neutral return of the drive cam 88 which operates integrally with the fifth speed - reverse shift rod 78 moves to slide along the driven cam face c for neutral hold of the reverse shift fork 50, and the reverse shift fork 50 remains stopped at the neutral position. In this case also, even if the reverse idle gear 41 attempts to move leftwards so as to move away from the end face 13i of the case right half 13, the leftward movement of the reverse idle gear 41 is prevented by the contact between the drive cam face e for neutral return of the drive cam 88 and the driven cam face c for neutral hold of the reverse shift fork 50. When the fifth speed - reverse shift rod 78 moves rightwards from the fifth position (Fig. 11) to the neutral position (Fig. 10) in order to release an established fifth gear shift stage, since the drive cam face e for neutral return of the drive cam 88 moves to slide along the driven cam face c for neutral hold of the reverse shift fork 50, the reverse shift fork 50 remains stopped at the neutral position. As shown in Fig. 11, when the fifth speed - reverse shift rod 78 moves rightwards from the neutral position to the reverse position in order to establish a reverse gear shift stage, the fifth speed shift fork 48 provided on the fifth speed - reverse shift rod 78 slips rightwards (Fig. 1). At the same time, the drive cam face d for reverse shift of the drive cam 88 which operates integrally with the fifth speed - reverse shift rod 78 presses against the driven cam face a for reverse shift of the reverse shift fork 50, swinging the reverse shift fork 50 anticlockwise. As a result, the reverse shift fork 50 slides the reverse idle gear 41 leftwards along the reverse idle shaft Sr, and the reverse idle gear 41 meshes with the main reverse gear 42 and the counter reverse gear 43 to establish a reverse gear shift stage. In this state, the left end face of the reverse idle gear 41 is in contact with the end face 12b of the case left half 12, and even if the reverse idle gear 41 attempts to move rightwards therefrom, the rightward movement of the reverse idle gear 41 is prevented by the contact between the drive cam face d for reverse shift of the drive cam 88 and the driven cam face a for reverse shift of the reverse shift fork 50. When the fifth speed - reverse shift rod 78 moves leftwards from the reverse position (Fig. 12) to the neutral position (Fig. 10) in order to release an established reverse gear shift stage, the drive cam face e for neutral return of the drive cam 88 presses against the driven cam face b for neutral return of the reverse shift fork 50, swinging the reverse shift fork 50 clockwise. As a result, the reverse shift fork 50 slides the reverse idle gear 41 rightwards along the reverse idle shaft Sr, and the reverse idle gear 41 moves away from the main reverse gear 42 and the counter reverse gear 43 to release the established reverse gear shift stage. As is clear from Fig. 10 and Fig. 13, with regard to the reverse idle shaft Sr, its left end is held by being fitted in a shaft support hole 12a which is formed in the case left half 12 and its right end is held by being fitted in a shaft support hole 13e which is formed in the case right half 13. The inner wall surface of the shaft support hole 13e of the case right half 13 is not closed in the circumferential direction, and a portion thereof opens in the direction facing the main shaft Sm via a notch. That is to say, a shaft support surface 13f of the shaft support hole 13e which supports the reverse idle shaft Sr comprises a major arc having an angle of about 250°, and a portion of the outer circumference of the reverse idle shaft Sr is exposed to the internal space of the case right half 13 through an opening 13g comprising a minor arc having an angle of about 110°. Thus, even when a portion of the inner wall surface of the shaft support hole 13e is lacking, if the shaft support surface 13f of the shaft support hole 13e has a central angle of 180° or more, there is no possibility of the reverse idle shaft Sr dropping from the shaft support hole 13e. As shown by the broken line in Fig. 8, if the shaft support hole 13e is made in the form of a closed pocket, since an inner wall surface 13h of the case right half 13 projects into the inside of the transmission case 11, there is a possibility of the inner wall surface 13h interfering with a gear provided on the main shaft Sm, and if the distance between the reverse idle shaft Sr and the main shaft Sm is increased in order to avoid the interference, there is the problem that the size of the transmission case 11 increases. However, by cutting a portion of the shaft support hole 13e for the reverse idle shaft Sr as in the present embodiment, the size of the transmission case 11 can be reduced by allowing the reverse idle shaft Sr to approach the main shaft Sm as closely as possible without providing a special member for supporting the reverse idle shaft Sr or carrying out special processing. Although a manual transmission M is illustrated in the embodiment, the present invention can be applied to an automatic transmission in which the shift/select operation is carried out by an actuator. In accordance with the invention, since movement of the shift rod from the neutral position to the reverse position presses the drive cam face for reverse shift of the drive cam against the driven cam face for reverse shift of the reverse shift fork to move the reverse shift fork in a circular manner to the reverse position, and movement of the shift rod from the reverse position to the neutral position presses the drive cam face for neutral return of the drive cam against the driven cam face for neutral return of the reverse shift fork to move the reverse shift fork in a circular manner to the neutral position, the shift fork can be operated smoothly by the drive cam without causing galling, and thus the shift feeling when establishing and releasing a reverse gear shift stage can be improved. Further, in accordance with the invention, since the driven cam face for neutral hold which extends from the driven cam face for neutral return, is provided on the reverse shift fork, when the shift rod moves from the neutral position to a forward position which is in the opposite direction to the reverse position, in order to establish a forward gear shift stage, the drive cam face for neutral return moves along the driven cam face for neutral hold while maintaining the reverse shift fork in the neutral position. Thus, it is possible to prevent unnecessary circular movement of the reverse shift fork from the neutral position accompanying the movement of the shift rod to the forward position. Also, in accordance with the invention, since movement of the reverse idle gear in the direction away from the end face of the transmission case is prevented by the drive cam face for neutral return of the drive cam, causing the reverse idle gear to be pushed against the end face when in neutral, it is possible to effectively maintain the reverse idle gear in the neutral position without providing a special detent mechanism on the reverse shift fork and thus this can contribute to a reduction in the number of parts. Still further, in accordance with the invention, since movement of the reverse idle gear in the direction away from the end face of the transmission case is prevented by the drive cam face for reverse shift of the drive cam causing the reverse idle gear to be pushed against the end face when a reverse shift gear stage is established, it is possible to effectively maintain the reverse idle gear in the reverse position without providing a special detent mechanism on the reverse shift fork and thus this can contribute to a reduction in the number of parts. The present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are, therefore, to be embraced therein. In a transmission for automobiles, the shift feeling is improved by smoothly transferring the operational load between a shift rod and a reverse shift fork. This is accomplished by cam faces formed on a reverse shift fork which shifts a reverse idle gear between a neutral position and a reverse position, and cam faces are formed on a drive cam which moves integrally with a shift rod. When the drive cam is moved from a neutral position to the reverse position, one of the cam faces presses against another of the cam faces moving the reverse shift fork in a circular manner in an anticlockwise direction, and the reverse idle gear moves to the reverse position. When the drive cam member is moved from the reverse position to the neutral position, another of the cam faces presses against still another of the cam faces moving the reverse shift fork in a circular manner in a clockwise direction, and the reverse idle gear moves to the neutral position.

Claims: A transmission gear shift system comprising a transmission case (11), a reverse shift fork (50) supported on the transmission case (11) in a circularly movable manner by a fulcrum pin (87), wherein the reverse shift fork (50) is moved in a circular manner in one direction by an axial movement of a shift rod (78) from a neutral position to a reverse position, and a reverse idle gear (41) is shifted from a neutral position to a reverse position by the reverse shift fork (50) for establishing a reverse gear shift stage, wherein the reverse shift fork (50) is moved in a circular manner in the other direction by an axial movement of the shift rod (78) from the reverse position to the neutral position and the reverse idle gear (41) is shifted from the reverse position to the neutral position by the reverse shift fork (50) to release the established reverse gear shift stage, a drive cam (88) integrally formed with the shift rod (78), the drive cam (88) having a first drive cam face (d) for reverse shift and a second drive cam face (e) for neutral return; and the reverse shift fork (50) having a third driven cam face (a) for reverse shift and a fourth driven cam face (b) for neutral return, wherein movement of the shift rod (78) from the neutral position to the reverse position presses the first drive cam face (d) for reverse shift of the drive cam (88) against the third driven cam face (a) for reverse shift of the reverse shift fork (50) to move the reverse shift fork (50) in a circular manner in the one direction, and movement of the shift rod (78) from the reverse position to the neutral position presses the second drive cam face (e) for neutral return of the drive cam (88) against the fourth driven cam face (b) for neutral return of the reverse shift fork (50), to move the reverse shift fork (50) in a circular manner in the other direction characterized in that shift motions of the reverse shift fork (50) between respective positions corresponding to the neutral position and the reverse position of the shift rod (78) are continuously guided by the reverse shift fork (50) and the drive cam (88) engaging each other at two distinct contact portions. A transmission gear shift system according to Claim 1, wherein a fifth driven cam face (c) for neutral hold extends from the fourth driven cam face (b) for neutral return, and when the shift rod (78) moves from the neutral position to a forward position which is in the opposite direction to the reverse position in order to establish a forward gear shift stage, the second drive cam face (e) for neutral return of the drive cam (88) moves along the fifth driven cam face (c) for neutral hold of the reverse shift fork (50) while maintaining the reverse shift fork (50) in the neutral position. A transmission gear shift system according to Claim 1, wherein movement of the reverse idle gear (41) in the direction away from a first end face (13i) of the transmission case (11) is restricted by the second drive cam face (e) for neutral return of the drive cam (88) causing the reverse idle gear (41) to be pushed against the first end face (13i) when in neutral. A transmission gear shift system according to Claim 1, wherein movement of the reverse idle gear (41) in the direction away from a second end face (12b) of the transmission case (11) is restricted by the first drive cam face (d) for reverse shift of the drive cam (88) causing the reverse idle gear (41) to be pushed against the second end face (12b) when a reverse gear shift stage is established.

Inventors: EDURE YOSHINOBU, KOYAMA SHIGERU, EDURE, YOSHINOBU, KOYAMA, SHIGERU
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 2000
Main classification: F16H63
IPC codes: F16H63