Abstract:
A shifting mechanism for a multi-speed manual overdrive (OD) transmission. A &#34;flipper&#34; reverses the action of the shift stick for the final stage shift fork to maintain progressive &#34;H&#34; or &#34;HH&#34; shift patterns yet engage a direct drive coupling as the next-to-last range and OD as the final engagement. The mechanism employs a quadrangular frame slidably received on two adjacent shift rails in a shift rail array. The frame has one side above the shift rail array notched to engage the shift stick end of an opposite side below the array. The flipper is pivotally mounted below the array with one end engaging a notch in the frame and the other end engaging the final stage shift fork so as to minimize bending stresses on the fork end and reaction loads of the sliding frame on the shift rails.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to manual gear shifting mechanisms for power transmissions such as multi-speed transmissions employed in automotive vehicles, and particularly relates to such transmissions having the final speed range as an overdrive. 
     In order to maintain the shift stick or lever pattern as a conventional progressive &#34;H&#34; type pattern for the forward speed ranges, it has been found necessary to reverse the internal shift fork movement for the final speed changes in order to provide for the overdrive speed range to be attained in the final position of the shift stick or lever. Heretofore, this reversing of the shift fork action within the transmission for the final speed change in an overdrive transmission has been accomplished by employing a pivoted lever or &#34;flipper&#34; between the shift stick and the shift fork to reverse the action of the shift stick on the movement of the shift fork to cause the shift fork to engage the direct drive ratio in the next to the final position, and the overdrive ratio engagement in the final position of the shift stick. 
     Known techniques for mounting a shift fork reversing flipper in a manually shiftable vehicle transmission have utilized an arrangement wherein the flipper was mounted above the shift rail array on the underside of the gear box cover. Typically, in such an arrangement the flipper or lever engages the final shift fork on one end of the lever and a slider block, mounted on another shift rail, engages the lever at the end opposite the lever pivot or fulcrum. This arrangement whereby the flipper engaged the slider and final shift fork on the opposite side of the shift rail array from the side of the rail array where the shift fork loads are applied has resulted in additive effects of the bending moments on the shift fork. This in turn has resulted in increases in the reaction loads on the shift fork hub where it is joined to its rail; and also has resulted in additive moments and reaction forces of the hub of the slider block which with respect to the rail upon which it is guided for movement. In some instances this increase in reaction to forces has caused binding of the block during shifting where the slider block has a narrow hub. 
     Referring to FIG. 7, a known arrangement of a shift fork reversing arrangement as employed for the final stage in an overdrive transmission is indicated generally at 10, wherein the transmission housing structure or cover 12 has a flipper or lever 14 pivotally mounted about the pin 16 attached to the housing 12 on the underside of the cover portion thereof. Plural shift rails, denoted 18,20,22, are slidably guided at their ends, respectively, for axial movement on the housing 12. The shift block 24 is shown as rigidly connected to rail 22 by screw 26 for movement therewith. Block 24 has lug 28 extending upwardly therefrom, which is notched to engage one end of lever 14. A portion of a shift yoke or fork 30 is illustrated for the final stage and as slidably received on rail 18, and has upwardly-extending lug 32 which is notched to engage the end of lever 14 on the opposite side of pin 16 from the lug 28. A shift block (not shown) connected to rail 22 is selectively engaged by a shift stick or lever (not shown); and, movement of shift block 24 in one direction along rail 22 results in movement of the yoke 30 in the opposite direction. 
     It will be seen by those familiar with automotive power transmissions that the bending moments on the shift yoke 30 are additive, resulting in increased reaction loads on the sliding surface of the yoke 30 on rail 18. This has resulted in increased wear of the parts and resilient deflection under load which can produce sloppiness on the shifting action. 
     In the prior art arrangement of an overdrive transmission shift mechanism employing a flipper as shown in FIG. 7, the Neutral positioning of yoke or fork 30 is provided by spring loaded ball detenting of rail 22. Thus the Neutral positioning of yoke 30 is subject to tolerance accumulations of the engagement of lever 14 with block 24, location and fit on pin 16, and engagement of lever 14 in the notch in lug 32 on yoke 30. This tolerance accumulation in the prior art has caused sloppiness of shift action and Neutral positioning of yoke 30. 
     It has thus been desired to provide for conventional H type shift pattern in a multi-speed transmission having an overdrive final shift position, and to provide for long life of the shifting mechanism and precision shift action. 
     SUMMARY OF THE INVENTION 
     The present invention provides a novel shift rail fork arrangement for a six speed transmission utilizing a quadrilateral frame slidably mounted on the shift rails to engage a pivoted lever for reversing the direction of the shift lever throw to maintain the conventional progressive &#34;H&#34; type pattern for shifting where the transmission has the final range as an overdrive. The quadrilateral shift frame reduces the bending moments on the shift fork and the reaction forces on the frame with respect to the rails upon which it is guided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic of the transmission shaft and gear arrangement; 
     FIG. 2 is a detailed view of the shift fork arrangement; 
     FIG. 3 is a diagram of the shifting pattern of the shift lever; 
     FIG. 4 is a cross-section of a transmission employing the present invention; 
     FIG. 5 is an exonometric view of the shift rail mechanism of a transmission employing the present invention; 
     FIG. 6 is a cross-section taken along section-indicated lines 6--6 of FIG. 5; and, 
     FIG. 7 is a view similar to FIG. 6, illustrating the prior art. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 1, 2, and 3, the power flow of a transmission embodying the present invention is indicated generally schematically at 100. 
     Referring to FIG. 1, a typical power flow schematic is shown for a typical six-speed vehicle power transmission wherein the engine is denoted by the reference character E and the clutch denoted generally by the reference character C, with the clutch driver plate indicated by reference numeral 102 and the driven plate by reference numeral 104. The transmission input shaft 106 is connected to drive input gear 108, which meshes with countershaft driven gear 110, which drives countershaft 12 journalled at its ends on the casing as denoted by reference numerals 114,116. 
     Countershaft 112 has rigidly attached thereto in driving engagement the first speed countergear 118 which is meshed with a first speed main shaft driven gear 120, which is journalled thereon by needle bearings and is freely rotatable about main output shaft 124 which is disposed axially coincident with the input shaft 106 with its forward end journalled in the end of the input shaft. First speed driven gear 120 is engaged with output shaft 124 by movement of the dog clutch member 122 in an aftward direction to provide engagement between the hub of gear 120 and shaft 124 by movement of the shift fork 126, which has the ends thereof received over the dog clutch 122. 
     Referring to FIGS. 1, 2, and 3, movement of shift fork 126 is effected by movement of a shift stick or lever 128, which is pivoted on a shift tower 130 which forms a part of a shift rail deck assembly indicated generally at 132. Movement of the shift stick 128 to the position shown as the number one speed position in FIG. 3 results in movement of the shift fork 126 and dog clutch 122 to engage the first speed driven gear 120 with the output shaft 124. 
     Countershaft 112 has drivingly mounted thereon a second speed countergear 134, which is meshed with a second speed main shaft gear 136, which is journalled on needle bearings to rotate about main shaft 124 and is drivingly connected to the main output shaft 124 by forward movement of dog clutch 122. Forward movement of clutch 122 is effected by shift fork 126 in response to movement of lever 128 to the second speed position shown in FIG. 3. 
     A third speed countergear 138 is drivingly attached to countershaft 112 and is meshed with a third speed main shaft gear 140 journalled on needle bearings for free rotation about output shaft 124. A third and fourth speed dog clutch 142 is operative upon aftward movement by shift fork 144 to engage the hub of gear 140 to drive output shaft 124. Shift fork 144 is moved to the aft position by movement of the shift stick 128 to the third speed position shown in FIG. 3. 
     A fourth speed countershaft gear 146 is drivingly mounted on countershaft 112 and meshes with main shaft driven gear 148, which is journalled on needle bearings for free rotation about shaft 124, but is drivingly engaged with shaft 124 by forward movement of dog clutch 142 to engage the hub of gear 148. The forward movement of dog clutch 142 is effected by movement of shift fork 144 in response to positioning of shift stick 128 to the fourth speed position shown in FIG. 3. 
     A fifth speed is effected by forward movement of a third dog clutch 150 to engage the hub of input gear 108 to lock output shaft 124 to input shaft 106 for direct drive. The forward movement of dog clutch 150 is effected by forward movement of shift fork 152, which engages the dog clutch 150. Forward movement of fork 152 is effected by movement of shift stick 128 to the fifth speed position shown in FIG. 3, and is accomplished by a mechanism contained within shift rail deck assembly 132 in a manner which will hereinafter be described in greater detail. 
     The countershaft 112 has an overdrive countergear 154 drivingly attached thereto which meshes continuously with main shaft overdrive gear 156, which is journalled on needle bearings for free rotation about shaft 124 and is drivingly engaged therewith by aftward movement of dog clutch 150 to engage the hub of gear 124. Aftward movement of dog clutch 150 is effected by movement of shift fork 152 in response to movement of shift stick 128 to the overdrive position shown in FIG. 3, and is effected by a mechanism contained within shift rail deck assembly 132. 
     Countershaft 112 has drivingly attached thereto reverse countergear 156, which continuously meshes with a reverse idler gear 158 mounted on idler shaft 160, which is journalled on the casing or housing for rotation as denoted by reference numerals 162,164. Reverse idler 158 continually meshes with a reverse mainshaft gear 166, which is journalled on needle bearings for free rotation about output shaft 124. A fourth dog clutch 168 is provided and is operably moved by a shift fork 170 engaged therewith and upon aftward movement thereof, dog clutch 168 is moved in an aft direction to engage the hub of reverse output gear 166 to drive output shaft 124 in a reverse direction. Aftward movement of shift fork 170 is effected by movement of shift stick 128 to the reverse position as indicated in FIG. 3. 
     Referring to FIG. 4, the invention is shown embodied in a synchronized six forward speed range overdrive transmission; however, it will be understood that the invention may be employed in non-synchronized transmission of the type illustrated in U.S. Pat. Nos. 4,567,785 and 4,485,686, incorporated herein by reference. 
     Referring to FIGS. 4, 5, and 6, the details of the shift rail subassembly 132 are shown wherein the transmission case or housing structure 172 has mounted therein in longitudinally freesliding arrangement four spaced parallel shift rails 174,176,178,180 preferably in a planar array, as illustrated in FIG. 5. The forward position of the shift rails is indicated in dashed outline in FIG. 5 and the aft position is indicated in solid outline. The outer shift rail 180 has shift fork 152 secured thereto by pin or screw 182 for axial movement therewith. The ends 184,186 engage the dog clutch 150 on the main shaft 124 for movement thereof as described above with regard to the power flow diagram in FIG. 1. 
     Referring particularly to FIG. 4, shift fork 144 is pinned to shift rail 178 by a pin or screw 188; and, shift fork 126 is pinned to shift rail 176 by pin or screw 190. Reverse shift fork 170 is pinned to shift rail 174 by a pin or screw 192. 
     Referring particularly to FIGS. 5 and 6, a bar or strap 194 is anchored to the housing 172 by suitable fasteners (not shown in FIG. 5) received through apertures 196,198 provided therein and bar 194 is disposed transversely with respect to the transmission mainshaft axis. Bar 194 has an extension or projection 200 extending centrally therefrom on the undersurface thereof in an axial direction with respect to the transmission mainshaft and has a pin 202 secured therein. A lever or flipper 206 which has an aperture 208 provided therein is journalled over the pin 202 for pivotal movement thereon; and, flipper 206 is retained by the head 204 of the pin. The right hand end 210 of lever 206 is engaged in a notch 212 formed in an inboard side of shift fork 152. 
     A slider frame 214 has spaced parallel bores 216,218 formed through opposite sides thereof with bore 216 received in loosely fitting or clearance arrangement over shift rail 174 and bore 218 closely interfitted in closely sliding engagement over shift rail 176 for accurately locating and positioning the frame 214 for sliding fore and aft movement along the rails 174,176. 
     The inboard side of frame 214 extending generally parallel to the transmission mainshaft is disposed above the shift rail array as denoted by reference numeral 220 in FIGS. 5 and 6. The opposite outboard side of the frame, denoted by reference numeral 222, is disposed on the opposite side or underneath the shift rail array. Side 222 of frame 214 has a notch 224 formed therein, which is engaged by the end 226 of lever 206 on the opposite side of pin 202 from end 210 of lever 206. 
     The inboard side 220 of frame 214 has a notch 228 formed on the inner surface thereof, and which is adapted for selective engagement for shift stick 128. It will be understood that upon movement of the shift stick to the fifth speed position in FIG. 3 that the stick engages notch 228 to move the frame 214 in an aft direction with respect to the transmission mainshaft, which causes flipper 206 to move shift fork 152 and its lugs 184,186 to the forward position shown in dashed outline in FIG. 5. Shift stick 128 is shown as engaging notch 228 in dashed outline in FIG. 6. 
     Shift rail 178 has a shifting hub 230 received thereover and pinned thereto by pin or screw 232. Hub 230 has a vertically-extending lug 234 provided thereon, and which has formed therein a notch 236 adapted for being engaged by the shift stick to effect fore and aft movement of shift rail 178 and shift fork 144. 
     Shift rail 176 has a shifting hub 235 received thereover and secured thereon by a pin 237, and has an upwardly-extending lug or projection 238 which is spaced adjacent lug 234 and which has a notch 240 provided therein, and which is adapted for being selectively engaged by shift stick 128. 
     Shift rail 174 has a shifting hub 242 received thereon and disposed intermediate the opposite transverse sides of frame 214 and secured to the rail 174 by pin or screw 244 for movement longitudinally fore and aft therewith. Hub 242 has an upwardly-extending projection 246 provided thereon, which has a notch 248 provided therein and which is adapted for engagement by shift stick 128. Movement of hub 234 by engagement of shift stick 128 with the notch 240 effects fore and aft movement of the shift rail 176 and causes movement of the shift fork 126 between the first and second speed positions. Movement of the hub 242 by engagement of shift stick 128 with notch 248 causes fore and aft movement of shift rail 174 and effects movement of shift fork 170 for engagement of the reverse gear 166 with output shaft 124. 
     Shift stick 128 is shown in solid outline in FIG. 6 as engaged with notch 248 in the shift hub projection 246. 
     It will be understood that each of the rails 174,176,178,180 is Neutral positioned by a recess formed in the rail which is engaged by a spring loaded ball shown typically at 250 in FIG. 4. Thus the final stage shift fork 152, being pinned to rail 180, is directly Neutral positioned with rail 180. This feature of the invention overcomes the aforesaid disadvantage of the Neutral positioning of the prior art as described above with respect to FIG. 7. 
     The present invention thus provides an improved shifting mechanism for a multi-speed manual shift power transmission and maintains a progressive H or HH shift stick pattern where the transmission has an overdrive as the final stage. The shift stick selectively engages a slider frame slidably received over adjacent shift rails. The stick engages the frame on one side of the rail array, and the frame engages a flipper or lever mounted on the opposite side of the rail array. The end of the flipper or lever opposite the fulcrum thereof from the frame is engaged with the shift fork for the penultimate and final drive stages. Thus, the shift from the penultimate-to-final stage is reversed to accommodate direct drive for penultimate range and overdrive for the final stage. 
     The reaction loads on the shift rails are reduced because the flipper arrangement of the present invention applies moments to the shift fork which are subtracted from those applied by the dog clutch. The reduced rail reaction loads results in less friction and more positive movement of the shifting mechanism. 
     Although the present invention thus has hereinabove been described with respect to the illustrated embodiments, it will be understood to those skilled in the art that the invention is capable of modification and variation within the purview of the following claims.