GB2118646A - Shift bracket assemblies for manual change-speed mechanisms - Google Patents

Abstract

A shift bracket assembly (30) for a manually operated change-speed mechanism is secured to an axially movable shift rail (14). The bracket comprises a transverse plunger (80) which is slidable within a bore (78) in the bracket (72). The plunger (80) has a cam surface (82) for continuous coaction with a spring-loaded poppet ball (96), in all operative positions of the plunger, to bias the plunger in the direction towards a shift finger. The assembly provides a lighter and more desirable spring force on a gearchange lever, and comprises fewer parts, than a known assembly. <IMAGE>

Description

SPECIFICATION Shift bracket assemblies for manual changespeed mechanisms This invention relates to shift bracket assemblies for use on shift rails of manually operated change-speed mechanisms.

Shift bracket assemblies are known in which spring loaded plungers are employed to assist in the movement of gearchange levers, and to provide or enhance physical sensing of lever position.

Prior art shift bracket assemblies have incorporated direct or "in-line" spring-loaded plungers, in combination with angularly off-set spring and poppet ball detent systems. The latter spring and poppet ball systems have been employed only as ball catches to retain the plungers in their most outwardly or extreme positions. While for left-hand drive vehicles, the known shift bracket assembly has been and is yet satisfactory in the operation of the lowest ratio gears of heavy duty truck transmissions, the inline forces associated therewith have been unsatisfactory when shifting among the top end or highest ratio gears, the latter being more frequently utilized in operation of the highway.

It is conventional for shift levers to have shift fingers which engage axially movable rails for effecting gear changes. There exists a strong preference for lighter shift lever control forces in left-hand drive vehicles during shifts involving the highest ratio gears. This is because it is generally easier for a driver to pull a shift lever transversely toward his right knee (viz. toward the first and reverse shift rail in most trucks) than to push the lever away (viz. toward the highest ratio shift rail) under an identical spring force. Thus, in highway operation when changing gear in, for example, hilly areas, a lighter spring return force is desirable in association with the frequently utilized highest ratio shift rail.Of course, the opposite situation arises in right-hand drive vehicles, where it would be desirable for the lighter spring return forces to occur during changes between the lower gears.

The most commonly utilized prior art shift bracket assembly requires two separate spring systems in its normal operation, and is thus complex and expensive to manufacture.

According to the present invention there is provided a shift bracket assembly for use in a manual change-speed mechanism comprising an axially movable shift rail and a manually operable shift finger, the shift bracket assembly comprising a shift bracket which is adapted to be secured to the shift rail and is provided with engagement means for engagement with the shift finger whereby operation of the shift finger causes axial displacement of the shift rail, the shift bracket assembly further comprising a plunger which is slidable in a transverse bore in the shift bracket, one end of the plunger being presented for engagement by the shift finger as the shift finger is moved into engagement with the engagement means, the plunger and the bore cooperating with each other to limit movement of the plunger in the direction towards the shift finger, the plunger being provided with a cam surface which is inclined with respect to the axis of the plunger, pressure means being provided for engaging the cam surface to bias the plunger in the direction towards the shift finger in all operative positions of the plunger.

A shift bracket assembly in accordance with the present invention provides a more satisfactory, simpler and less costly alternative for shift bracket assemblies than those traditionally utilized in shifting among the highest ratio gears of heavy truck transmissions. Thus, while similar shift bracket assemblies have often been employed on both the lowest and highest gear ratio shift rails, the highest ratio bracket (in left-hand drive vehicles) may now be simply modified to effect lower and more desirable spring return forces. An assembly in accordance with the present invention requires only one of the two previously utilized spring systems, and can be easily retrofitted on existing vehicles utilizing multiple spring systems wherein the spring return forces are of the direct or in-line type.

In a preferred embodiment the shift bracket assembly is fixed to an axially movable shift rail for movement therewith, the bracket including a transversely aligned and stepped bore. The bore contains a slidably and matingly stepped plunger, wherein the plunger includes a cam surface disposed for coaction with a spring loaded poppet ball. The invention provides for the elimination of all in-line or direct spring forces against the plunger, as the poppet ball maintains continuous contact with the cam surface in all operative positions of the plunger.

For a better understanding of the present invention and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a plan view in section of a heavy duty transmission; Figure 2 is a view taken along the line 2-2 of Figure 1; Figure 3 is a sectional view of a prior art shift bracket assembly; and Figure 4 is a cross sectional view of a shift bracket assembly in accordance with the present invention.

Figure 1 is a top plan view of a heavy duty truck transmission 10, showing shift control apparatus 12.

The shift control apparatus 12 includes shift rails 14, 1 16, 17, and 1 8 for seven forward speeds and one reverse speed; the shift rail 14 represents the highest gears, sixth and seventh, the shift rail 1 6 represents the next highest gears, fourth and fifth, the shift rail 1 7 represents lower gears, second and third, and the shift rail 1 8 represents the lowest ratio gears, first and reverse. Each of the shift rails carries a shift fork for axial movement in the transmission. Figure 2 shows one such shift fork 20 mounted on the shift rail 17, which controls shifting of second and third gears. The other shift forks are omitted from Figure 2 for clarity.Each shift fork, e.g. 20, is fixed to its respective shift rail, e.g. 1 7, and includes a pair of lugs 22 and 24 (Figure 1) which define a channel or slot 26 for receiving a shift finger (not shown), as in conventional practice. For convenience, the lugs 22 and 24 and the slots 26 are given suffixes A, B, C, and D to indicate their correspondence and association with the respective shift rails 14,16,17 and 18.

Shift bracket assemblies 28 and 30 (Figure 2) are fixed to the outer shift rails 18 and 14, i.e. the lowest and highest ratio rails, respectively. These shift bracket assemblies are shown in greater detail in Figures 3 and 4. Figure 3 shows an existing or prior art shift bracket assembly 28, suitable for use with the lowest ratio rail. This assembly is first described, both to provide background and to make clear the distinction between the old and the new. The prior art bracket, which has also commonly but unsatisfactorily been employed-with the highest ratio rails, includes a housing 32 which includes a bore 34 in which the shift rail 1 8 is received and secured by a threaded screw 36 (Figure 2). A second bore 38, which slidably contains a plunger 40, extends in a plane perpendicular to the bore 34.The bore 38 and the plunger 40 are stepped, so as to limit movement of the plunger 40 in one direction only. Thus, shoulders 42 and 44 of the bore 38 and plunger 40, respectively, abut one against the other to provide a mechanical stop or limit for the plunger movement. The plunger 40 is thus force lockingiy retained within the bore 38 against the pressure of an in-line spring 46 which bears between a reaction pin 50 and the rear end 52 of the plunger 40. The plunger 40 has an annular groove 54 against which a poppet ball 56 is urged to retain the plunger in its extended position as shown. The groove is arcuate, having a radius equal to that of the ball, whereby the ball secures the plunger in a manner such that the plunger does not rotate.For this purpose, the housing 32 contains a third bore 58 connecting the two previously mentioned bores 34 and 38, the bore 58 containing a second spring 60 interposed between the poppet ball 56 and the shaft 1 8.

The operation of the shift bracket assembly may now be described as follows. As a truck driver changes down from second or third gear to first gear. the shift finger of his shift lever will bear against the end 53 of plunger 40, as the finger is moved out of the channel or slot 26C (Figure 1) towards the slot 26D. The plunger 40 and the associated spring 46 will provide the driver with a "feel" of the position of the shift finger as movement of the finger into operative engagement with the shift rail 1 8 is effected. It will be noted that the spring return forces herein explained are provided for and "felt" only in the neutral mode of the transmission, thus only along the transversely extending neutral shift axis 8-8.

Thus, once the slot 26D is engaged and the operator moves the axially movable rail 1 8 into first or reverse positions, the spring forces will no longer be felt.

Upon movement in the opposite direction, i.e.

when the operator moves the lever along the neutral shift axis 8-8 from the rail 1 8 to the shift rail 17 for engagement of second or third gear positions, the spring 46 will assist in urging the gear shift lever over to the next adjacent shift rail.

It may be noted that prior art shift brackets 28 of the type herein described occasionally have very high in-line or direct return forces which tend to urge the shift lever objectionably beyond the next adjacent lower shift rail, notwithstanding that the truck driver may be exerting a pull on the lever to compensate for an undesirably high force. Thus the present invention may also be suitable for application to the lowest or first and reverse, shift rails where the noted problem is particularly severe, or as otherwise preferred.

The physical operation of the plunger 40 (Figure 3) may now be more fully described as follows. As the operator moves the shift lever to engage the shift rail 18, the plunger 40 is depressed against the bias of the spring 46, and this causes the poppet ball 56 to be urged downwardly against the spring 60. it will be noted that once the poppet ball 56 is out of the groove 54, it ceases to urge the plunger in an outwards direction. Thus, once the ball 56 is beyond the edge 62 of the groove 54, the spring 60 and the ball 56 are ineffective to apply any force to extend the plunger 40. This particular aspect of the prior art bracket 28 provides a distinctive limitation of the prior art, as will become more fully appreciated upon description of the bracket 30 of the present invention.

Referring now to Figure 4, the bracket 30 in accordance with the present invention is depicted, which includes a housing 72, having bores 74 and 78 which are analogous to the bores 34 and 38 of the prior art bracket 28 of Figure 3. Similarly, a threaded nut 66 (Figure 2) holds the bracket 30 in place on its shift rail 14. Moreover a stepped plunger 80 and a correspondingly stepped bore 78 having shoulders 102 and 103, respectively, are provided for limiting movement of the plunger against the spring forces imposed thereon. An end 93 of the plunger 80 is presented for engagement with a shift finger. The similarities, however, end at this point. The stepped plunger 80 has a cam surface 82 instead of the groove 54 of the prior art plunger 40. The cam surface 82 slopes towards the shift finger lugs 22, 23 in a manner such that the plunger 80 is urged into the slot or channel 26A by the action of a spring 100 and a poppet ball 96. Preferably, the cam surface 82 is inclined at an angle in the range of 25 to 35 degrees from the longitudinal axis 94-94 of the plunger 80, as shown in Figure 4. The spring 100 urges the poppet ball 96 against the cam surface 82 of the plunger 80 in all operative positions of the plunger within the bore 78. As will be appreciated, the spring 100 and poppet ball 96 are also angularly disposed toward the shift finger engaging lugs 22, 24 to provide a force in a direction for urging the plunger against its rightward limit. In this manner, the spring 46 and retaining pin 50 of the prior art bracket 28 are neither required nor desirable. The direct or in-line forces created by the latter spring 46 are avoided, and lighter control forces may be achieved, via the use of standard parts. Thus, the bracket of the present invention provides an easily retrofitted, relatively simple alternative bracket assembly which employs a ligher spring return force for the highest ratio shift rail of the transmission.

Claims (8)

1. A shift bracket assembly for use in a manual change-speed mechanism comprising an axially movable shift rail and a manually operable shift finger, the shift bracket assembly comprising a shift bracket which is adapted to be secured to the shift rail and is provided with engagement means for engagement with the shift finger whereby operation of the shift finger causes axial displacement of the shift rail, the shift bracket assembly further comprising a plunger which is siidable in a transverse bore in the shift bracket, one end of the plunger being presented for engagement by the shift finger as the shift finger is moved into engagement with the engagement means, the plunger and the bore cooperating with each other to limit movement of the plunger in the direction towards the shift finger, the plunger being provided with a cam surface which is inclined with respect to the axis of the plunger, pressure means being provided for engaging the cam surface to bias the plunger in the direction towards the shift finger in all operative positions of the plunger.

2. A shift bracket assembly as claimed in claim 1, in which the pressure means comprises a spring loaded poppet ball, the spring, in use, bearing against the shift rail, and the ball being in contact with the cam surface and being disposed between the spring and the cam surface.

3. A shift bracket assembly as claimed in claim 2, in which the spring exerts on the poppet ball a force in a direction which is inclined to the axis of the plunger, whereby the force urges the plunger in the direction towards the shift finger.

4. A shift bracket assembly as claimed in any one of claims 1 to 3, in which the cam surface is inclined to the axis of the plunger at an angle which is not less than 250 and not more than 350, whereby the pressure means engages the cam surface to urge said plunger in the direction towards the shift finger.

5. A shift bracket assembly as claimed in any one of the preceding claims, in which the shoulder is provided at one end region of the plunger, and a corresponding shoulder is provided within the bore, whereby contact between the shoulders limits movement of the plunger in the direction towards the shift finger.

6. A shift bracket assembly as claimed in any one of the preceding claims, in which the engagement means comprises a pair of lugs fixed to the bracket and defining a channel for operatively receiving the shift finger.

7. A shift bracket assembly substantially as described herein with reference to, and as shown in, the accompanying drawings.

8. A manual change-speed mechanism including a shift bracket assembly in accordance with any one of the preceding claims.