GB1570759A - Shift device for change-speed gearboxes in motor vehicles - Google Patents

Description

(54) SHIFT DEVICE FOR CHANGE-SPEED GEARBOXES IN MOTOR VEHICLES (71) We, ZAHNRADFABRIK FRIEDRICH SHAFEN AKTIENGESELLSCHAFT, of Friedrichshafen-on-the-Bodensee, Federal Republic of Germany, a Joint-Stock Company organised under the laws of the Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: Because of the larger clutches and greater flywheel moments of the driving parts in vehicles of higher power, particularly commercial vehicles, the shifting forces are so great that the unfavourable efficiency of usual shift devices with slide guides which are loaded by the shifting forces can no longer be accepted.

In one known shift device constituting the starting point of the invention (German Published Specification 1,455,674) both transverse and longitudinal guiding are provided by rolling-contact bearings whose rolling elements (balls) roll on relatively short axial tracks between an inner ring and an outer ring. In order to ensure that when the shift device is not under load the rolling elements will be held in a defined position in relation to their 'tracks, the tracks are arranged to cross at an angle.

Because of this construction the rollingcontact bearings cannot be serially produced or standard parts. Furthermore, during the shift movement the rolling elements undergo not only a rolling movement but also a sliding movement relative to the tracks, which, depending on the angle of the tracks to one another, may be disadvantageous to easy running.

The problem underlying the invention is that of providing a shift device which has good efficiency in the transmission of the shift forces, can be produced at low cost, and can be installed in a simple manner inside the change-speed gearbox.

To this end, the present invention consists in a mechanical shift device for a changespeed gearbox of a motor vehicle for engaging and disengaging positive clutches in said gearbox, which comprises a plurality of connecting rods mounted for longitudinal movement in the gearbox casing by means of spaced apart rolling-contact bearings and each having a shift fork fast therewith, guidance for the longitudinal movement of at least one of the connecting rods is effected by rollers mounted for rotation in said bearings and arranged so that at least one roller rolls on a longitudinal track on one side of the respective connecting rod and at least one roller rolls on a longitudinal track on the opposite side of the said connecting rod, while guidance transversely of said movement of said at least one connecting rod is effected by lateral guide edges provided on the or each roller associated with one longitudinal track.

The guiding of the connecting rod by means of rollers ensures particularly easy running and is insensitive to manufacturing inaccuracies and to deformation under force, since the shift forces are taken by the accurate rolling of the guide parts, while the rollers have rolling-contact mounting, so that good shifting efficiency is achieved, which is particularly important, for example, in synchronous gearboxes for higher powered vehicles.

The arrangement of the shift device permits an assembly in which the connecting rod and the fork can be joined fast to one another. Expensive screw or pin connections between fork and connecting rod are thus not required. This is made possible by the fact that some of the rollers can without difficulty be installed in the casing, for example by sliding-in axially from outside, even after the assembly comprising the connecting rod and fork has been inserted, if the bearing holes for mounting the rollers are at least as large as the largest diameter of the respective roller.

For more accurate guidance of the shift device and advantageous absorption or supporting of the shift forces the centre axes of the rollers may be aligned substantially at right angles to the plane which is common to the centre axis of the positive clutches to be operated and of the central connecting rod. Advantageously, two rollers provided with guide edges are associated with one longitudinal track of the connecting rod and at least one roller having no lateral guide edge is associated with the other, oppositely disposed longitudinal track. The connecting rod is thus supported by three or four rollers, and is guided laterally only by the rollers of one side.

The smooth cylindrical roller receives no lateral forces and has the advantage that it can be installed by sliding axially into its receiving mounting.

In this case it is of particular advantage for the connecting rod to be made of bright drawn flat material and for essential parts of the fork to be made (as is known per se) of simple rolled flat material, whereupon they are permanently joined together, for example by welding or riveting. Assembly is possible without difficulty, since the roller having no guide edge can be inserted after insertion of the connecting rod.

A connecting rod made of flat material in such an arrangement may have simple cutouts adapted to engage a shift finger for initiating the shift movements.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example one embodiment of shift device in accordance therewith: Figure 1 is a partial axial section of a motor vehicle change-speed gearbox, with synchronised shift clutches and a shift device according to the invention; Figure 2 is a section, at right angles to the axis, through the shift device of Figure 1 along the line A-B in Figure 1 (gears and gearbox shafts not shown), in order to show a shift fork and one of the rollers; Figure 3 is another section at right angles to the axis, through the shift device along the line C-D in Figure 1, in order to show another shift fork and another roller; Figure 4 shows an assembly consisting of a connecting rod and a shift fork permanently fastened thereto by riveting; and Figure 5 is an end view partly in section of Figure 4.

The change-speed gearbox, of which part is shown in Figure 1 is intended for motor vehicles of higher power, that is to say for commercial vehicles. Gear changing is effected manually by the driver, the shift movement being transmitted from a gear lever (not shown) to a shift shaft 10 in the gearbox by way of conventional transmission elements (not shown). The gearbox, which is here a synchronous gearbox having five forwards speeds and one reverse speed, contains three shift clutches 11,12 and 13, which are in the form of positive clutches and are each disposed in a double-acting arrangement on a gearbox shaft 14, in order to connect this shaft 14 selectively to one of the gears 15 to 20 rotatably mounted on it. These gears are in constant mesh with other gears of the change-speed gearbox.

In order to be able to bring the rotationally fixed and axially movable sliding coupling sleeves 21,22 and 23 of the shift clutches 11,12,13 selectively into engagement with the teeth of the gears 15 to 20, connecting rods 24, 25 and 26 guided for longitudinal movement are disposed in the gearbox casing, and on each of them respective shift forks 27,28 and 29 are permanently and rigidly fastened by riveting.

Each of the shift forks engages by means of sliding parts disposed on their ends in slots extending round the corresponding sliding sleeves 21,22 and 23.

The connecting rods 24,25 and 26 have identical rectangular cross-sectional surfaces and are disposed side by side in the casing in such a manner that the connecting rods lie with the longer sides of the rectangle parallel and adjoining one another, while the shorter sides of the rectangular crosssection lie flush in one plane. The connecting rods consist of bright drawn flat material and the parts of the fork fastened thereto by riveting consists of simple rolled flat material and can thus be produced inexpensively.

The longitudinal guidance and supporting of the shift forces of the connecting rods 24,25 and 26 are effected on rollers 30,31 and 32 which are mounted for free rotation in roller-contact bearings 42 and 43 in the casing and whose centre axes are aligned at right angles to the plane which is common to the centre axes of the positive clutches 11 to 13 which are to be operated and of the central connecting rod 25. On the shorter side of their rectangular crosssection the connecting rods 24,25 and 26 each have longitudinal tracks 33,34,35 and 36,37 and 38 respectively, which serve as running tracks for the rollers. On the longitudinal tracks 33,34, and 35, which are situated on the shorter sides of the connecting rods remote from the clutches, the rollers 30 and 31 engage, that is to say rollers having guide edges 41 for lateral guidance, which rollers are mounted with relatively wide spacing in the casing, while on the longitudinal tracks 36,37, and 38, which lie on the shorter sides of the connecting rods facing the clutches, a single, smooth cylindrical roller 32 (without a guide edge) engages, which forms a counter-guide for the rollers 30 and 31. In relation to the longitudinal direction of the connecting rods the rollers 32 lies between the oppositely disposed rollers 30 and 31.

In contrast to known slide guides, because of the counterforce acting outside the connecting rod (on the shift fork), the shift force, initiated by the shift shaft 10 with the aid of a shift finger 39, applies a load to the rollers which, however, in consequence of the rolling friction does not substantially hinder the shift movement. Because the distance between the rollers is long as possible, the forces on the rollers are relatively slight, while at the same time accurate guiding of the connecting rods is achieved.

For the initiation of the shift force by the shift fingers 39 each of the connecting rods 24 to 26 is provided with a respective cutout 40 in order to eliminate the drivers which would otherwise usually have to be installed.

WHAT WE CLMM IS : - 1. A mechanical shift device for a change-speed gearbox of a motor vehicle for engaging and disengaging positive clutches in said gearbox, which comprises a plurality of connecting rods mounted for longitudinal movement in the gearbox casing by means of spaced apart rollingcontact bearings and each having a shift fork fast therewith, guidance for the longitudinal movement of at least one of the connecting rods is effected by rollers mounted for rotation in said bearings and arranged so that at least one roller rolls on a longitudinal track on one side of the respective connecting rod and at least one roller rolls on a longitudinal track on the opposite side of the said connecting rod, while guidance transversely of said movement of said at least one connecting rod is effected by lateral guide edges provided on the or each roller associated with one longitudinal track.

2. A shift device as claimed in claim 1, wherein the centre axes of the rollers are aligned substantially at right angles to the plane which is common to the centre axis of the positive clutches to be operated.

3. A shift device as claimed in claim 1 or 2, wherein two rollers provided with guide edges are associated with one longitudinal track of the connecting rod, and at least one roller having no lateral guide edge is associated with the other, oppositely disposed longitudinal track.

4. A shift device as claimed in any one of the preceding claims, wherein the connecting rods of rectangular cross-section, characterised in that the connecting rods consist of bright drawn flat material and essential parts of the fork consist of simple rolled flat material.

5. A shift device as claimed in claim 3, wherein the forks are permanently joined to the respective connecting rods.

6. A shift device as claimed in claim 4, wherein the connecting rods have cutouts adapted to engage a shift finger for initiating the shift movements.

7. A shift device for a motor vehicle change-speed gearbox, substantially as herein described with reference to and as shown in the accompanying drawings.

8. A change speed gearbox for a motor vehicle, substantially as herein described with reference to and as shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. on the longitudinal tracks 36,37, and 38, which lie on the shorter sides of the connecting rods facing the clutches, a single, smooth cylindrical roller 32 (without a guide edge) engages, which forms a counter-guide for the rollers 30 and 31. In relation to the longitudinal direction of the connecting rods the rollers 32 lies between the oppositely disposed rollers 30 and 31. In contrast to known slide guides, because of the counterforce acting outside the connecting rod (on the shift fork), the shift force, initiated by the shift shaft 10 with the aid of a shift finger 39, applies a load to the rollers which, however, in consequence of the rolling friction does not substantially hinder the shift movement. Because the distance between the rollers is long as possible, the forces on the rollers are relatively slight, while at the same time accurate guiding of the connecting rods is achieved. For the initiation of the shift force by the shift fingers 39 each of the connecting rods 24 to 26 is provided with a respective cutout 40 in order to eliminate the drivers which would otherwise usually have to be installed. WHAT WE CLMM IS : -

1. A mechanical shift device for a change-speed gearbox of a motor vehicle for engaging and disengaging positive clutches in said gearbox, which comprises a plurality of connecting rods mounted for longitudinal movement in the gearbox casing by means of spaced apart rollingcontact bearings and each having a shift fork fast therewith, guidance for the longitudinal movement of at least one of the connecting rods is effected by rollers mounted for rotation in said bearings and arranged so that at least one roller rolls on a longitudinal track on one side of the respective connecting rod and at least one roller rolls on a longitudinal track on the opposite side of the said connecting rod, while guidance transversely of said movement of said at least one connecting rod is effected by lateral guide edges provided on the or each roller associated with one longitudinal track.

2. A shift device as claimed in claim 1, wherein the centre axes of the rollers are aligned substantially at right angles to the plane which is common to the centre axis of the positive clutches to be operated.

3. A shift device as claimed in claim 1 or 2, wherein two rollers provided with guide edges are associated with one longitudinal track of the connecting rod, and at least one roller having no lateral guide edge is associated with the other, oppositely disposed longitudinal track.

4. A shift device as claimed in any one of the preceding claims, wherein the connecting rods of rectangular cross-section, characterised in that the connecting rods consist of bright drawn flat material and essential parts of the fork consist of simple rolled flat material.

5. A shift device as claimed in claim 3, wherein the forks are permanently joined to the respective connecting rods.

6. A shift device as claimed in claim 4, wherein the connecting rods have cutouts adapted to engage a shift finger for initiating the shift movements.

7. A shift device for a motor vehicle change-speed gearbox, substantially as herein described with reference to and as shown in the accompanying drawings.

8. A change speed gearbox for a motor vehicle, substantially as herein described with reference to and as shown in the accompanying drawings.