Shift control mechanism for a transmission

Abstract: A neutral-reverse shift control actuator is provided in a countershaft transmission. The actuator is comprised of a spring member (114) and utilises one of the forward ratio synchronisers (66). During a neutral-reverse shift manoeuvre, the spring member is effective to enforce engagement of the cone clutch (74,76) of the forward synchroniser which, through a connection with a stationary output shaft (40), will retard rotation of the input shaft.

Description: This invention relates to shift control mechanisms for transmissions, and more particularly, to neutral-reverse controls for countershaft transmissions. Countershaft type transmissions have incorporated a neutral-reverse brake mechanism in the transmission by placing a cone on a stationary housing. The cone is engaged by a synchroniser cone clutch which is operated by the synchroniser sleeve of one of the forward ratio (i.e., fifth gear) synchroniser mechanisms. The engagement between the cone surfaces will bring the shaft, generally the input shaft, associated with the synchroniser sleeve to a halt, such that the reverse idler gear can be meshed with a pair of reverse ratio gears. One such system is described in US-A-4,598,599. This and similar systems, require that an additional cone clutch, blocker ring and stationary cone be provided in the transmission to accomplish the braking action desired during a neutral to reverse shift. These components add to the cost and complexity of the transmission. GB-A-2213884 describes a mechanism in accordance with the preamble of claim 1. A shift control mechanism in accordance with the present invention is characterised over GB-A-2213884 by the features specified in claim 1. A neutral-reverse brake or actuator which uses a forward synchroniser mechanism is provided by the present invention. A spring means is disposed in operative relation with the cone clutch of the forward synchroniser mechanism, such that during a neutral-reverse shift, the spring means is operated on by the synchroniser sleeve to actuate the cone clutch to engage the complementary cone on a forward ratio gear, such as fifth gear. This alleviates the need to assemble additional synchroniser components that are required by the prior art. In a preferred embodiment, a spring having a plurality of axially extending arms, each having an actuating section, is assembled in the synchroniser clutch sleeve of the fifth ratio synchroniser. When the transmission control is manipulated for the reverse engagement, the clutch sleeve is moved axially in a direction opposite to the fifth gear selection. The actuator sections on the spring arms are engaged with and operated by the clutch sleeve to enforce the arms to extend axially, whereby the fifth synchroniser cone clutch is engaged with the fifth ratio gear on the input shaft. This causes a braking or retarding effect at the input shaft in bringing it to a halt. Upon or near completion of the reverse engagement, the actuating sections of the spring arms are disengaged by the clutch sleeve thereby releasing the axial spring force in the fifth synchroniser cone clutch. It is an object of this invention to provide an improved neutral-reverse shift using a forward synchroniser to control the speed of the input and output shafts during a reverse shift. The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a cross-sectional elevational view of a countershaft type transmission incorporating the present invention; Figure 2 is a view taken along line 2--2 of Figure 1; Figure 3 is an enlarged view of a portion of the fifth ratio synchroniser and reverse actuator shown in Figures 1 and 2; and Figure 4 is a view taken along line 4--4 of Figure 1. A power transmission 10 having a housing 12, a front end cover 14, a rear cover 16 and a differential assembly 18 is seen in Figure 1. The transmission 10 has an input shaft 20 rotatably supported in the housing 12 by a wall 22 and in the front cover 14. The input shaft 20 is rotatably supported on conventional bearings 24 and 26. The input shaft 20 has rotatably secured thereto a cluster gear 28 which includes a reverse input gear 30, a first ratio input gear 32 and a second ratio input gear 34. The gears 32 and 34 mesh with a first ratio output gear 36 and a second ratio output gear 38, respectively, which are rotatably mounted on a transmission countershaft or output shaft 40 which is rotatably mounted in the end cover 14 by a bearing 42 and in the wall 22 by a bearing 44. The gears 36 and 38 are operably connected with a 1-2 synchroniser assembly 46 which is selectively manipulable to control the first ratio by rightward movement of a clutch sleeve 48. Leftward movement of the clutch sleeve 48 will control engagement of the second ratio. As is well known, synchroniser assemblies, such as 46, are operable to connect the gear member with the shaft on which they are rotatably supported. The construction and operation of synchronisers, such as 46, is well known and it is not considered that a more complete description would be necessary in that persons of ordinary skill in the art will readily recognise these mechanisms and their operation. The input shaft 20 has rotatably supported thereon a third ratio input gear 50 and a fourth ratio input gear 52 which are controlled by a conventional 3-4 synchroniser assembly 54. The synchroniser assembly 54 has a clutch sleeve 56 which when moved rightwardly will cause the third ratio gear 50 to be engaged with the input shaft 20 and leftward movement of the sleeve 56 will cause the gear 52 to be engaged with the input shaft 20. The gears 50 and 52 mesh with respective ratio output gears 58 and 60 which are rotatably secured to the output shaft 40. Also rotatably supported on the input shaft 20 is a fifth ratio input gear 62. This gear 62 meshes with a fifth ratio output gear 64 which is rotatably secured with the output shaft 40. The fifth ratio input gear 62 is selectively connectable with the input shaft 20 by a synchroniser assembly 66. The fifth ratio synchroniser assembly 66, as best seen in Figures 2 and 3, includes a hub 68 rotatably connected with the input shaft 20. A synchroniser clutch sleeve or collar 70 is slidably disposed on the hub 68 and drivingly connected therewith through a spline connection 72. The clutch sleeve 70 has a conventional blocker or key assembly, not shown, which is adapted to engage a cone clutch 74 which is rotatably supported on a cone surface or section 76 of the fifth ratio input gear 62. The clutch sleeve 70, as is well known, when shifted rightwardly from the position shown in Figure 2, will force the cone clutch 74 to engage the cone surface 76 thereby causing the fifth ratio input gear 62 to synchronise with the speed of the input shaft 20. When the speed is synchronised, the cone clutch 74 will cease to rotate relative to the cone surface 76 such that the clutch sleeve 70 can complete its rightward movement to provide an engagement between the sleeve 70 and a toothed element 78 which is secured to the fifth ratio input gear 62. This is a conventional operation of a synchroniser assembly and countershaft gear. The input shaft 20 has associated therewith a friction clutch (not shown) which is operable to connect the input shaft 20 with an engine (not shown). The friction clutch is controlled through a clutch lever or actuator 80. The actuator 80 is controlled by the vehicle operator to permit connection and disconnection between the input shaft 20 and the engine (not shown). Generally, when the ratio change is to be made in the transmission, the actuator 80 is manipulated such that the engine is disconnected and the input shaft 20 is free to accelerate or decelerate depending upon the direction of the ratio interchange. The acceleration and deceleration of the input shaft 20 is controlled, as is well known, by the cone clutch sections of the various synchronisers. As best seen in Figures 2, 3 and 4, a reverse actuator mechanism is provided which will control the manipulation of a reverse idler gear 82 into mesh with the reverse input gear 30 and a reverse output gear 84 which is secured to the output shaft 40 through the 1-2 synchroniser 46. The gear 82 is slidably disposed on idler shaft 86 which is rotatably supported in the housing 12 and the end cover 14. The gear 82 is manipulated axially on the shaft 86 by a reverse fork or control lever 88. The lever 88 is pivotally supported on a two-way bracket 90 through a pin 92. The lever 88 has connected therewith an overcentre spring 94 which provides the operator with some amount of shift feel and will also assist in ensuring the completion of the neutral to reverse shift as the spring travels overcentre. These devices are well known and have been utilised in a number of transmissions. The lever 88 has operatively associated therewith a link or rod 96 which is secured to a 5/R shift actuator 98. The actuator 98 is controlled by a manually actuated lever or paddle 100. The paddle 100 is movable between a plurality of actuators for the control of the 1-2 shift, the 3-4 shift and the fifth reverse shift. These actuators and their assemblies and operation is well known. One such system is shown in US Patent No. 5,036,721, and another is shown in US Patent No. 5,101,680. One wishing more information on the operation of such shift controls is directed to either of these US patents. The actuator 98 is also secured to a shift rod 102 which has secured thereto a shift fork 104. The shift fork is, as best seen in Figures 1 and 3, engaged in a slot 105 formed in the clutch sleeve 70. As the actuator shift rod 102 is moved longitudinally or axially in bearing supports formed in the housing 12 and end cover 14 the fork 104 will manipulate the collar 70 in the same direction as the rod 102. If the rod 102 is moved rightward, the shift fork 104 will move the collar 70 rightward, thereby completing a fifth ratio engagement. The sleeve or collar 70 has a plurality of cams 106 having a pair of side cam ramps 108 and 110 and a central detent portion 112. An actuator spring 114 is mounted on the hub 68. The actuator spring 114, as best seen in Figure 4, has an annular portion 116 which is disposed in abutment with a washer 118 secured on the input shaft 20. The spring 114 also has a plurality of axially extending arms 120 which are disposed in complementary slots 122 formed in the hub 68. The spring arms 120, as best seen in Figures 2 and 3, have a central hump or detent surface 124 which is engageable by the cam 106 formed on the collar 70. Each spring arm 120 has an operating end 126 which abuts the cone clutch 74. In the neutral position of the collar 70 shown in Figure 2, the detent surface 124 is extended radially outward thereby relieving any load which the end 126 might transfer to the cone clutch 74. In this position, the cone clutch 74 is free to rotate relative to the gear 62. During the selection of fifth gear, the spring arms 120 are not energised by the cam 106. However, on a neutral to reverse manipulation, the cam ramp 108 will cause the spring arms 120 and the surface 124 to move radially inward. Since the annular portion 116 is prevented from moving axially by the washer 118, the arms 120 will extend axially or longitudinally toward the cone clutch 74. This movement of the cone clutch 74 will continue until the collar 70 reaches the position shown in Figure 3, wherein the detent surface 124 is disposed adjacent the detent 112. At this position, the cone clutch 74 has been fully engaged with the cone surface 76 thereby causing the ratio gear 62 to synchronise with the input shaft 20. The ratio gear 62 is meshed with the ratio gear 64. Since the gear 64 rotates with the output shaft 40, and since during a neutral to reverse shift the output shaft 40 is stationary, the ratio gear 64 will be stationary. With the ratio gear 64 stationary, the ratio gear 62 will also be stationary and due to the high inertia of the vehicle, cannot be rotated by engagement of the cone clutch 74. Since the lower inertia component within the system will be the input shaft and its related gearing, the input shaft 20 will be brought into speed synchronisation with the output shaft 40, which at this point, is zero. Thus, the input shaft 20 and output shaft 40 will both be at zero speed as will the gears 84 and 30. This will permit the reverse idler gear 82 to be meshed with these gears without the buzz associated with transmissions not utilising a braking apparatus or mechanism during a reverse shift manoeuvre. Upon completion of the reverse shift, the collar 70 will be moved leftward past the position shown in Figure 3, such that the detent surface 124 will be permitted to expand radially outward along the ramp 110, thereby relieving engagement pressure on the cone clutch 74, such that the fifth ratio gear 62 will be free to rotate relative to the input shaft 20. The rod 96 is disposed in an L-shaped slot 130 formed in the lever 88. This L-shaped slot 130 permits the rod 96 to move freely during rightward movement of the shift rod 102, such that the shift fork 88 will be free from forces during a fifth ratio engagement manoeuvre. During a reverse manoeuvre, however, the L-shaped slot 130 cooperates with the rod 96 to enforce pivoting of the shift fork 88 about the pin 92 without binding on the rod 96. Such structures are commonly used in manual transmissions of the type disclosed herein. The output shaft 40 also has disposed rotatably therewith an output gear 132 which meshes with a differential input gear 134. As is well known, the differential input gear will drive the carrier of a differential disposed in the assembly 18 to enforce rotation of a pair of drive shafts 136 and 138, which in turn are connected to drive the wheels of a vehicle (not shown). It should be appreciated from the foregoing description that a simple mechanism has been provided to enforce the synchronisation of the input and output shafts of a countershaft transmission during a neutral-reverse shift manoeuvre. The use of the fifth ratio synchroniser to provide this speed synchronisation eliminates the need for additional cone clutches being installed within the transmission thereby reducing the assembly time and cost. The spring member 114 is a simple stamped construction which can be readily manufactured without significant cost. The hub 68 of the synchroniser 66 has the slots 122 formed therein at the point of manufacture during the cutting of the spline teeth. Thus, there is not significant cost associated with the introduction of the spring 114 and its accompanying components.

Claims: A shift control mechanism in a transmission (10) for retarding rotation of an input shaft (20) during a shift manoeuvre from neutral to reverse comprising a synchroniser means (66) for connecting a forward ratio gear means (62,64) in torque transmitting relation between the input shaft and another shaft (40), the synchroniser means including a selectively operable friction clutch means (74,76) and a shift collar (70) operable upon movement in a first direction to operate the synchroniser means to establish the forward ratio and movable in a second direction during a neutral to reverse shift, the shift collar having an actuating surface (106); and spring means (114) disposed between the shift collar and the friction clutch means and cooperating with the shift collar for engaging the friction clutch means with the forward ratio gear means to retard the input shaft during a portion of the neutral to reverse shift and for releasing the friction clutch means upon completion of neutral to reverse shift; characterised in that the spring means (114) comprises a detent surface (124) on arm means (120) which directly engage the actuating surface (106) on the shift collar (70). A shift control mechanism as claimed in claim 1, wherein the friction clutch means comprises a cone clutch means (74) and a cone surface (76) on a gear member (62) of the forward ratio gear means (62,64); and wherein the arm means (120) of the spring means (114) abuts the cone clutch means and cooperating with the actuating surface (106) on the shift collar (70) for enforcing engagement of the cone clutch means with the cone surface to retard the input shaft (20) during a portion of the neutral to reverse shift and the actuating surface releasing the spring means to permit disengaging of the cone clutch means upon completion of neutral to reverse shift. A shift mechanism as claimed in claim 1 or claim 2, wherein the arm means (120) includes an operating portion (126), the arm means being responsive during movement of the shift collar (70) in the second direction to extend the operating portion (126) for enforcing the engagement of the friction clutch means (74,76).

Inventors: REYES CARLOS CRUZ, REYES, CARLOS CRUZ
Applicants: SATURN CORP, SATURN CORPORATION
Application year: 1995
Main classification: F16H63
IPC codes: F16H63, F16D23, F16H3