GB2466000A

GB2466000A - Shift fork with two part slider arm which prevents vibrations

Info

Publication number: GB2466000A
Application number: GB0822191A
Authority: GB
Inventors: Eckhard Kirchner
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2008-12-05
Filing date: 2008-12-05
Publication date: 2010-06-09
Also published as: RU2009145071A; GB0822191D0

Abstract

A shift fork for a vehicle gearbox comprises a slider body 5 having a guide surface for linearly displaceable contact with a rail member 3, a sleeve-engaging projection 6 and a slider arm 8 extending between the slider body 5 and an engagement contour 9 in the direction of displacement defined by the guide surface. The slider arm 8 comprises first and second elements or parts 10, 11 which are joined together by a rigid connection such as spot welding or gluing. Second part 11 of the arm 8 is fixed to the slider body 5 the first part 10 comprises the engagement contour 9. A plane of contact (24, fig 5) between the two elements 10, 11 extends in the direction of displacement. A method of assembling the shift fork with the gearbox comprises providing second part 11 with a projection 17 that engages with a slot 20 in the first part 10 so that parts 10, 11 are relatively moveable. A length of the parts 10, 11 is adjusted and a pin (19) inserted in any suitable pair of holes 18 after which the two parts 10, 11 may be connected by, for example, spot welding and the shift fork installed in the gearbox.

Description

Shift Fork and Assembly Method for a Vehicle Gearbox

Description

The present invention relates to a shift fork for a gearbox of a motor vehicle and to a method for assembling such a gearbox.

Conventionally, a vehicle gearbox has at least one shaft with one or more idle gearwheels which are locked to or unlocked from the shaft by axial displacement of a shift sleeve, and a shift fork is used for transmitting to the shift sleeve a movement of a shift lever which is located outside the gearbox and is operated by the driver of the vehicle.

When the sleeve is in a position in which it locks a gearwheel to the shaft, imperfections of the rotation of shaft and gearwheel are transmitted to the sleeve, and if the shift fork is in contact with the sleeve, vibrations of the shift sleeve are transmitted back to the shift lever. Vibrations of the shift lever cause noise to be emitted into the passenger compartment, and they are felt by the driver when handling the shift lever.

In order to attenuate the transmission of vibrations from the gearbox to the shift lever, DE 10 2004 053 893 Al suggests a shift fork comprising a linearly displaceable slider body, two fingers projecting from the slider body for engaging a shift sleeve, and an arm extending in the direction of displacement of the slider body, the arm carrying an engagement contour for engaging a shift finger connected to the shift lever. The arm and the slider body are moveable with respect to one another in the direction of displacement, and a spring is provided between the two, which is stressed by a relative movement of the arm and the slider body and defines a rest position of arm and slider body with respect to one another. If the slider body is excited to vibrate by the shift sleeve it engages, the spring is flexed, and only a small fraction of the vibration energy is transmitted to the arm and from there to the shift lever. However, this conventional shift fork has a problem in that the spring decreases the degree of control the driver has over the position of the shift fork. If the sleeve driven by the shift fork meets an obstacle it cannot pass, the shift lever will not be blocked, but the driver will only feel an increasing degree of resistance from the spring.

The object of the present invention is to provide a shift fork capable of preventing the transmission of vibrations from a gearbox to a shift lever in the motor vehicle and which at the same time allows the driver to control precisely the shifting movements within the gearbox.

This object is achieved by a shift fork comprising a slider body having a guide surface for linearly displaceable contact with a rail member, a sleeve-engaging projection and an arm extending between the slider body and an engagement contour in a direction of displacement defined by the guide surface, in which the arm comprises two elements, one of which is fixed to the slider body, the other of which comprises the engagement contour, a rigid connection is formed between the two elements, and a plane of contact between the two elements extends in the direction of displacement. The two-part construction of the slider arm allows to adjust its length precisely when installing it in the gearbox, so that when a sleeve of the gearbox driven by the sleeve-engaging projection of the shift fork is in a position in which it locks a gearwheel to its respective shaft, there is rio contact between the sleeve and the sleeve-engaging projection. While there is no contact, vibrations of the sleeve cannot be transmitted to the shift fork. The precision at which the displacement of the sleeve can be controlled depends on an amount of play between the sleeve and its engaging projection, i.e. on the distance the shift fork can be displaced before it comes into contact with the sleeve.

In order to keep the length adjustment of the arm simple, a first one of the two elements should comprise a guide rail for guiding a relative movement of the two elements in the direction of displacement of the sleeve. The guide rail may comprise a straight edge or a groove formed in said first element, or a slot formed in said first element and engaged by a pin of the second element.

In order to prevent a relative rotation of the two elements, the pin preferably is elongate in the direction of displacement.

The rigid connection between the two elements preferably comprises a glue layer and/or a weld, in particular a spot-weld.

According to a particularly preferred embodiment, the shift fork comprises a plurality of hole pairs, one hole of each pair being formed in the first element and the other in the second element, the hole pairs overlapping to different degrees, and the rigid connection comprises a pin engaged in the best-overlapping hole pair.

When adjusting the shift fork to the gearbox, before formation of the rigid connection, the two elements are freely displaceable with respect to one another. They can be placed in the gearbox at their intended mounting location for length adjustment, and they can be fixed to one another at a thus determined ideal length of the arm by inserting the pin in the one hole pair where it fits, i.e. in the best-overlapping hole pair. When this has been done, the arm can be extracted again from the gearbox, and its two elements can be disassembled again for placing glue on their plane of contact, and they can be reassembled with exactly the same length due to the pin.

Alternatively, the two elements can immediately be welded in the position defined by the pin, without prior disassembling.

The holes of incompletely overlapping hole pairs are preferably offset with respect to one another in the direction of displacement. In order to ensure a desired precision of the length adjustment, the offset of each hole pair should be either a fundamental offset corresponding to this desired precision or an integer multiple thereof.

In order to facilitate finding the best-overlapping hole pair it is preferred that the offset of the incompletely overlapping hole pairs increases with their distance from the best-overlapping one or the pin inserted in it. This will be achieved e.g. by placing the holes of the first element and those of the second element at slightly different pitches in the direction of displacement.

A further object of the invention is to provide a method for the assembly of a gearbox allowing precise control of the shifting movement without transmitting vibrations from the gearbox to the outside.

This object is achieved by the steps of providing a gearbox in which a slider body is displaceably guided, a sleeve-engaging projection of the slider body engages a shifter sleeve, arid a shifter finger is unconnected to the slider body, providing first and second elements of a shift fork arm for interconnecting the slider body and the shifter finger, one of which elements is adapted to be fixed to the slider body, and the other of which comprises a contour for engaging the shift finger, a plane of contact between the two elements extending in the direction of displacement when the first element is fixed to the slider body; adapting the length of the shift fork arm to the distance between the slider body and the shift finger; and installing the shift arm.

The adapting step may comprise placing one of the elements at the slider body, bringing the engagement contour of the other element into engagement.with the shift finger and locking the two elements in their relative position.

The locking step may comprise introducing a pin in overlapping holes of the two elements and/or of pressing the elements together and welding them.

In an alternative embodiment of the method, the adapting step may comprise measuring the distance between the slider body and the shift finger, selecting a pair of holes of the two elements associated to the measured distance, introducing a pin in said pair of holes and fixing the two elements to one another.

In either embodiment of the method, after the members of the shift fork are attached to each other by gluing or welding, the pin used to position the two members relative to each other may be again removed from the fork. I.e. the pin can be regarded as associated to the assembly device and not intrinsically to the shift fork.

Further features and advantages of the invention will become apparent from the subsequent description of embodiments thereof referring to the appended drawings.

Fig. 1 is a schematic perspective view of a shift fork according to the present invention; Fig. 2 is a plan view of the arm of the shift fork of Fig. 1; Fig. 3 is a plan view analogous to Fig. 2, of an arm according to a second embodiment of the invention; Fig. 4 is a plan view of an arm according to a third embodiment of the invention; Fig. 5 is a cross section of the arm of Fig. 4 along plane V-V of Fig. 4; Fig. 6 is a cross section, analogous to Fig. 5, of an arm according to a fourth embodiment; Fig. 7 is a cross sectionof an arm according to a fifth embodiment; and Fig. 8 is a plan view of an arm according to a sixth embodiment.

Fig. 1 is a perspective view of part of a motor vehicle gearbox. A shift rod 1 isconnected to a shift lever, not shown, mounted in the passenger compartment of the motor vehicle. The shift lever has two degrees of freedom. By operating the shift lever, a driver can rotate shift rod 1 and displace it in its axial direction, as indicated by arrows. A shift finger 2 is splined to shift rod 1.

A guiding rod 3 extends perpendicular to shift rod 1 and in parallel to a shaft, not shown, of the gearbox. On guiding rod 3, a shift fork 4 is mounted displaceably in the longitudinal direction of guiding rod 3. Shift fork 4 comprises a slider body 5 of substantially tubular shape having a central bore through which extends guiding rod 3, a sleeve-engaging projection 6, a circular cutout 7 of which is to engage a shift sleeve, not shown, in a manner familiar to the man of the art. By displacing the shift sleeve along a shaft carrying it, an idle gearwheel carried by said same shaft is locked to or unlocked from the shaft. Depending on the type of gearbox, a conventional synchronizer may be provided between the sleeve and the gearwheel which establishes a friction contact between the sleeve and the gearwheel and allows the sleeve to lockingly engage the gearwheel only after its rotation is synchronized to that of the shaft, or other means for synchronizing the rotation of gearwheel and shaft may be provided.

An arm 8 extends from slider body 5 substantially parallel to guiding rod 3 and carries at its free end a cutout 9 for engagement by shift finger 2.

By an axial displacement of shift rod 1, shift finger 2 is brought into or out of engagement with cutout 9. Other shift fingers, not shown, may be provided on shift rod 1 so that each of these shift fingers has a different axial position of the shift rod 1 associated to it, in which said shift finger engages a cutout of an associated shift fork.

The shift arm 8 is formed of two elements 10, 11, which may be formed by die-cutting from sheet material. Each of the two elements 10, 11 comprises two mutually offset planar sections, larger ones 12, 13 fixed to each other in a side by side relationship, and smaller sections 14, 15 which in case of element 10 has the cutout 9 formed in it, or, in case of element 11, is fixed in a reproducibly predetermined position to slider body 5. In section 12 a slot 16 extends in the direction of guiding rod 3. A web 17 connected to element 11 engages slot 16 with several millimetres play in the longitudinal direction and minimal play in the transversal direction.

In a row parallel to slot 16, a plurality of holes 18 of identical diameter are formed in element 10 and element 11. All holes 18 are placed at a regular -9-.

pitch, the pitch of the holes 18 in element 10 being slightly different from that of the holes 18 in element 11. Preferably pitches dlO, dli of the bores in element and element 11 are related by dlO=dll*(n_1)/n (1) or dlO=n/ (n-i) *dll (2) wherein the number of holes 18 in each element 10, 11 is at least n.

Fig. 2 is a plan view of the two elements 10, 11 forming arm 8. In this plan view, a pair, denoted 18', of holes 18 of the two elements 10, 11 is in perfect overlap. If element 10 was displaced to the left by a distance IdlO-dill, the pair of holes irrunediately to the left of hole pair 18' would overlap perfectly. If the two elements 10, 11 are displaced with respect to one another, there are positions where two holes 18 overlap perfectly at pitch of dll/n in case of eq. (1) or dlO/n in case of eq. (2) With the shift fork 4 of Fig. 1, 2, the gearbox can be assembled as follows: Initially shafts and meshing gearwheels on these shafts, shift sleeves associated to idle gearwheels, shift rod or rods 1 and slider bodies 5 are assembled in a conventional manner which need not be described in detail here. A shift sleeve which is to be controlled by a given slider body 5 is placed in a position where it locks a gearwheel associated to it to its shaft, and slider body 5 is placed at a location on guiding rod 3 where its engagement projection 6 engages a groove of said shift sleeve without touching it. The shift lever in the passenger compartment of the vehicle is brought into a position associated to the gear of said particular gearwheel, causing shift finger 2 to assume a specific position. Arm 8 is then placed with its element L 10 - 11 at a predetermined mounting position of slider body 5 and with the cutout 9 of its element 10 engaging shift finger 2. The length of the arm 8 is adjusted by displacing elements 10, 11 with respect to each other such that there is no direct contact between shift finger 2 and the sidewalls of cutout 9. Then the two elements 10, 11 are locked to each other by introducing a tightly fitting cylindrical pin 19 (see e.g. Fig. 5) in the best-overlapping pair 18' of holes 18. The arm 8 is now removed from the gearbox. The elements 10, 11 are spot welded to each other in the position defined by said pin 19. By carrying out the spot welding outside the gearbox it is assured that no debris is formed in the gearbox which might later cause damages. Exemplary locations of spot welds are denoted 25 in Fig. 2.

Alternatively, after removal of the arm 8 from the gearbox the two elements 10, 11 are taken apart again, glue is spread on one or both of the facing sides of the elements 10, 11, and they are reassembled in exactly the same position they previously had using the pin 19 in matching holes 18' as a reference. The length of the arm 8 is now fixed to the previously adjusted value, and the arm 8 is installed in the gearbox for good.

The pin 19 may be left in the two holes 18', or it may be removed after the adhesive or weld based connection between elements 10, 11 is settled. In the latter case, pin 19 may eventually be re-used in the assembly of another shift fork. Therefore, the pin 19 can be regarded as part of the machinery used for assembling the gearbox, and not as a component of the shift fork.

Fig. 3 is a plan view of a length-adjustable arm 8 according to a second embodiment. In this -11 -embodiment, web 17 is replaced by two spaced-apart pins 20, which, just like web 17, serve the purpose of admitting a relative displacement of the two elements 10, 11 only in the longitudinal direction of the slot 16.

The holes 18 are arranged in a staggered configuration in two lines parallel to slot 16. By arranging the holes 18 in two (or even more lines), the distance between directly adjacent holes 18 can be made larger than their pitch dlO or dli in the direction of displacement, improving the rigidity of arm 8, or the diameter of the holes 18 can be increased.

Fig. 4 is a plan view of arm 8 according to a third embodiment, and Fig. 5 is a cross section of this arm 8 in the plane denoted V-V in Fig. 4. In this embodiment, the slot 16 is missing, and, instead, a web 21 extending in the direction of guiding rod 3 is formed at a longitudinal edge of section 13 of element 11.

Element 10 is thus displaceably guided in contact with facing sides of section 13 and web 21. Reference numeral 24 denotes a plane of contact between the two elements 10, 11, where a glue layer can be applied for rigidly connecting them after length adjustment.

A bent web similar to web 21 of Fig. 5 may be provided not for guiding a relative displacement of elements 10, 11, but merely for rigidification. This is shown in the embodiments of Fig. 6 and 7. In Fig. 6, element 11 has two webs 22, 23 formed at its upper and lower edges, and element 10 is received in the groove between the two webs 22, 23 since there is no direct contact between element 10 and the webs 22, 23, element is guided in its longitudinal direction by pins 20 engaging slot 16, as shown with respect to Fig. 3.

-12 -Alternatively each element 10, 11 has a rigidifying web 22, 23 formed at one of its edges, as shown in Fig. 7.

When installing the arm B in the gearbox for length adjustment, not its sections 12, 13 may be accessible along their entire length for introducing locking pin 19, because other components of the gearbox are in the way. In such a case it is preferable to concentrate the holes 18 in a region which is accessible, e.g. in case of Fig. 8, in a region close to section 15 of element 11. Here, too, the holes 18 are arranged in a staggered configuration for stability purposes. As in the other embodiments, mismatch between overlapping hole is pairs 18 of the two elements 10, 11 increases with the distance from best-overlapping hole pair 18' . The difference is in that in Fig. 8 the distance is perpendicular to the direction of displacement instead of parallel, as in the embodiments of Figs.1 to 4.

The length of slot 16 is reduced to a small fraction of the length of the sections 12, 13.

Transversal play between the slot 16 and the web 17 engaging it may allow the elements 10, 11 to rotate slightly with respect to one another, as long as locking pin 19 is not installed. This rotation can be admitted since it does not substantially decrease the precision of adjustment. Once locking pin 19 is set in hole pair 18', the rotation is blocked.

Instead of preliminarily placing the arm 8 in the gearbox for length adjustment, it is conceivable to place a shift finger 2 and a slider body 5 in positions associated to a gear controlled by that slider body 5, and measure a distance between the shift finger 2 and the slider body 5 using an appropriately shaped caliper. A -13 -distance measured by the caliper can then be set at an arm 8 by placing a locking pin 19 in a hole pair 18 associated to the measured length, forming a rigid connection between the elements 10, 11 by welding or gluing, and installing the thus length-adjusted arm 8.

List of reference signs 1 shift rod 2 shift finger 3 guiding rod 4 shift fork slider body 6 sleeve-engaging projection 7 cutout 8 arm 9 cutout element 11 element 12 large section 13 large section 14 small section small section 16 slot 17 web 18 hole 19 pin pin 21 web 22 web 23 web 24 plane of contact, glue layer, spot weld

Claims

Claims 1. A shift fork for a vehicle gearbox comprising a slider body (5) having a guide surface for linearly displaceable contact with a rail member (3), a sleeve-engaging projection (6) and an arm (8) extending between the slider body (5) and an engagement contour (9) in the direction of displacement defined by the guide surface, characterized in that the arm (8) comprises two elements (10, 11), one (11) of which is fixed to the slider body (5), the other (10) of which comprises the engagement contour (9), that a rigid connection is formed between the two elements (10, 11) and that a plane of contact (24) between the two elements extends in the direction of displacement.
2. The shift fork of claim 1, in which a first one (10; 11) of the two elements (comprises a guide rail (16; 21) for guiding a relative movement of the two elements (10, 11) in the direction of displacement.
3. The shift fork of claim 2, wherein the guide rail comprises a straight edge (21) or a groove formed in said first element.
4. The shift fork of claim 2, wherein the guide rail is a slot (16) formed in said first element (10) and engaged by a projection (17; 20) of the second element (11)
5. The shift fork of claim 4, in which said projection (16) is elongate in the direction of displacement.
6. The shift fork of any of the preceding claims, in which the rigid connection comprises a glue layer and/or a weld between the two elements (10, 11)
7. The shift fork of any of the preceding claims, comprising a plurality of hole pairs (18), one hole of each pair being formed in the first element (10) and the other in the second element (11), the hole pairs (18) overlapping to different degrees, and wherein the rigid connection comprises a pin (19) engaged in the best-overlapping hole pair (18')
8. The shift fork of claim 7, wherein the pairs of incompletely overlapping hole pairs (18) are offset with respect to one another in the direction of displacement.
9. The shift fork of claim 8, wherein the offset of each hole pair is a fundamental offset or an integer multiple thereof.
10. The shift fork of claim 8 or 9, wherein the offset of the incompletely overlapping hole pairs (18) increases with their distance from the pin (19)
11. A method of assembling a gearbox, comprising the steps of providing a gearbox in which a slider body (5) is displaceably guided and a sleeve-engaging projection (6) of the slider body (5) engages a shifter sleeve, and a shifter finger (2) is unconnected to the slider body (5); providing first and second elements (10, 11) of a shift fork arm (8), one (11) of which elements is adapted to be fixed to the slider body (5), and the other (10) of which comprises an engagement contour (9) for engaging the shift finger (2), a plane of contact between the two elements (10, 11) extending in the direction of displacement when the first element (11) is fixed to the slider body (5); adapting the length of the shift fork arm (8) to the distance between the slider body (5) and the shift finger (2); and installing the shift arm (8).
12. The method of claim 11, wherein the adapting step comprises placing one (11) of the elements at the slider body (5), bringing the engagement contour (9) of the other element. (10) into engagement with the shift finger (2) and locking the two elements (10, 11) in their relative position.
13. The method of claim 12, wherein the locking step comprises introducing a pin (19) in overlapping holes (18') of the two elements (10, 11)
14. The method of claim 12, wherein the locking step comprises pressing the elements (10, 11) together and welding them.
15. The method of claim 11, wherein the adapting step comprises measuring the distance between the slider body (5) and the shift finger (2), selecting a pair of holes (18) of the two elements (10, 11) associated to the measured distance, introducing a pin (19) in said pair of holes and fixing the two elements (10, 11) to one another.