GB2338273A

GB2338273A - Plastics gearbox fork having a tubular metal insert

Info

Publication number: GB2338273A
Application number: GB9913308A
Authority: GB
Inventors: Dominique Benoit; Eric Prique; Stephane Kippelen
Original assignee: MGI Coutier SA
Current assignee: Akwel SA
Priority date: 1998-06-12
Filing date: 1999-06-09
Publication date: 1999-12-15
Anticipated expiration: 2019-06-09
Also published as: ITMI991300A1; ITMI991300A0; GB2338273B; GB9913308D0; FR2779794A1; FR2779794B1; DE19926785A1

Abstract

A plastics gearbox fork comprises a tubular metal insert 5 on which a body 1 of plastics material is moulded. The body 1 has a sleeve 2 carrying two arms 3, 4, for controlling sliding of the fork, which are connected by ribs and cruciform members. A metal shaft 6, carrying a crosshead 7 for gear selection, is received in the insert 5 and fixed thereto by a pin 9 which extends through a lengthened portion 21 of sleeve 2 and insert 5. Alternatively only the insert 5 has a lengthened portion 21 for receiving the pin 9. The insert 5 has a coupling bead (52, fig 3), eg produced by swaging, to promote coupling of the insert 5 with the body 1. In another embodiment the body 1 carries the crosshead 7 (see fig 4) so that the sliding action of the fork is directly controlled on shaft 6.

Description

1 GEARBOX FORK 2338273 The present invention relates to a gearbox fork

comprising a body carried by a shaft and having two arms for controlling the sliding component, and an operating crosshead with which the gear selection finger cooperates.

There are various types of gearbox fork for driving the sliding component. Those forks are either unitary with a shaft and the whole slides in bearings, or the fork slides on a fixed shaft. In both cases, a component known as a "crosshead" is provided in which the gear selection finger associated with the gear lever engages in order to slide and manoeuvre the fork for changing the speed ratios.

For example, the document JP-59218522 discloses a gearbox fork produced from plastics material. The fork comprises a body having two arms terminated by grippers for cooperating with the sliding component. The body and the two arms are produced from a plastics material and the two arms are reinforced by a U-shaped metal insert on which the fork is moulded.

However. the known device has the disadvantage of not exploiting the advantages of the plastics material because the two arms and more generally the fork, which comprise a metal insert, are heavy. Furthermore, nothing is stated in connection with this fork in respect of the type of movement it performs, either a sliding movement on a fixed shaft or a sliding movement by way of a shaft unitary with the fork.

In both cases, the connection or the contact between the shaft and the body of the fork is a source of difficulty in this known technique because the plastics material does not permit the production of a moulded component with sufficient 2 precision. Such precision can be obtained only by machining, but that increases the cost of the product considerably.

The object of the present invention is to overcome those disadvantages and proposes to develop a gearbox fork of plastics material which can be manufactured by moulding and which can be used as such without requiring any machining after moulding.

To that end, the invention relates to a fork of the type defined above, characterised in that the body comprises a sleeve carrying the two arms of the fork, a tubular metal insert on which the body of plastics material is moulded, and a metal shaft received by the body by way of the tubular insert.

The fork according to the invention offers the advantage of a very light weight associated with a rigidity consistent with the function of a fork. The light weight is obtained by a considerable reduction in the amount of plastics material used and by the omission of the metal insert from the two arms of the fork, which, apart from reducing the weight, also permits a reduction in the amount of plastics material to be injected.

The metal insert is produced exactly to size and there is no moulding deformation in the region of the junction between the insert and the shaft of the fork because the precision is ensured by the precision of the tubular insert. The fork so produced can be used in the state in which it leaves the mould without requiring additional machining.

If the fork is unitary with the shaft, it is advantageous to render the fork unitary with the shaft by means of a pin extending through the tubular insert and, in an especially 3 1 advantageous manner, the tubular metal insert extends beyond the body of plastics material so that the connecting means, such as a pin connecting the shaft and the body of the fork, extends through only the tubular insert without extending through the plastics material of the fork body. Any incipient fracture in the plastics material is thus avoided since the connection is produced only in the region of that portion of the tubular insert which is outside the plastics material.

In some cases it is possible, by complicating the injection mould, to make recesses in the form of cylindrical holes in the plastics material as far as the insert. Thus, counter- drill ing is effected only on the shaft and the insert without causing incipient fracture in the region of the plastics material and also without causing premature wear on the drilling tool owing to the fibres contained in the plastics material.

In order to promote the connection between the body of the fork of plastics material and the metal insert, it is advantageous to provide the insert with a raised coupling bead and, in particular, to produce the bead by swaging. It is also possible to provide the surface of the tubular insert with other coupling means, such as bumpy and rough areas promoting coupling.

In an especially advantageous manner, the body and the arms are in one piece f ormed by a f ront f ace and a rear f ace, in the direction of the shaft, which are connected by ribs and cruciform members.

That embodiment of the body and the arms results in a rigid but nevertheless very light fork having a reduced volume of plastics material.

1 4 When the fork body is unitary with the shaft, the shaft carries the crosshead which drives it.

When the fork slides on a fixed shaft, the fork is driven by a crosshead integrated in the fork.

The present invention will be described hereinafter in more detail with reference to the appended drawings in which:

- Figure 1 is a partially sectional diagrammatic view of a first embodiment of a fork carried by a mobile shaft, Figure 2 is a perspective view of a fork according to Figure Figure 3 is a perspective view of a tubular insert for a fork according to Figures 1 and 2, - Figure 4 is a perspective view of another embodiment of a fork that is to slide on a fixed shaft, - Figure 5 is a side view of the fork of Figure 4.

According to Figure 1, the invention relates to a gearbox fork that is to drive a sliding gearwheel (not shown). The fork is composed of a body 1 carried by a shaft 6 and having arms 3, 4 and a crosshead 7.

According to the embodiment of Figures 1, 2, 3, the fork is unitary with the shaft 6, that is to say, the shaft 6 is mobile for sliding in end bearings which are unitary with the casing of the gearbox, such as, for example, the bearing 8 represented diagrammatically on the left. There is a bearing of the same type at the other end.

The body 1, which is produced from plastics material, comprises a tubular metal insert 5 by means of which the body 1 is engaged on the shaft 6.

In the region of the insert 5, the body 1 is in the form of a sleeve 2 of plastics material carrying the arms 3, 4. The sleeve 2 continues in this example in a portion 21 covering the tubular insert 5 of which the length L is greater than the width 1 of the fork. It is, however, also possible to stop the sleeve 2 at the width 1 and, when the fork body is injected, to leave the corresponding portion 51 of the tubular insert 5 not covered by the plastics material.

Each arm 3, 4 comprises, at its end, on the inside, a shoe 31, 41 which cooperates with the sliding component.

According to Figure 1, the fork is connected to the metal shaft 6 by a pin 9 extending not only through the insert 5 but also through the portion 21 of the sleeve 2 of plastics material.

Although the value of extending the sleeve 2 into the region 21 resides in the fact that sealing at the injection mould is thus facilitated, it may be advantageous, in order to avoid incipient fracture, not to extend the sleeve 2 into the region 21 and to stop it in line with the arms 3, 4 so that the pin 9 is placed only in the exposed portion of the tubular insert 5.

Figures 2 and 3 show the form of the fork more accurately. The parts identical to those of Figure 1 bear the same references.

Figure 2 shows the very special form of the fork body 1 which is constituted by two end faces 101, 102, one being flat and the other having a step 103. The end faces are connected by cylindrical 104 and flat 105, 106 ribs; there are also ribs in the form of cruciform members 107 stiffening the assembly with 6 1 a very small volume of material. The faces 101, 102 comprise, for example, a passage 108 enabling a shaft to extend through.

Figure 2 shows that, in order to reduce the weight and to save material, the grippers 31, 41 are hollow, as shown, for example, by the cavity 32. Thus, the walls of the various elements constituting the fork have substantially the same thickness.

Figure 3 shows an example of a tubular insert 5 having a bead 52 produced, for example, by swaging, in order to promote the coupling of the tubular insert 5 to the fork body, that is to say, especially the sleeve 2.

Figures 4 and 5 show a variant of the fork. This fork is intended to slide on a fixed shaft (not shown) and to that end it carries directly the crosshead which drives it.

For the description of this fork, references similar to those of the previous embodiment have been used to designate identical or similar elements, those references being completed by the suffix A; their description will not be repeated in its entirety.

The fork is composed of a body 1A comprising a sleeve 2A carrying two arms 3A, 4A which are each provided with a shoe 31A, 41A for cooperating with the sliding component. An overmoulded metal insert SA is arranged inside the sleeve 2A.

The sleeve 2A carries a crosshead 7A which enables the fork to be controlled.

The fork is produced in the same manner as that of the previous Figures, with two end faces 101A, 102A connected by 7 connecting and stiffening ribs and cruciform members 105A, which do not have separate references.

The crosshead 7A is preferably constituted by an insert of metal or engineering plastics, that is to say, a plastics material stronger than the plastics material used for the body 1A.

The insert 7A, like the tubular insert SA, is placed in the mould, and then the plastics material is injected over and around the inserts.

8

Claims

1. Gearbox fork comprising a body carried by a shaft and having two arms for controlling the sliding component, and an operating crosshead with which the gear selection finger cooperates, characterised in that the body comprises a sleeve carrying the two arms of the fork, a tubular metal insert on which the body of plastics material is moulded, and a metal shaft received by the body by way of the tubular insert.

2. Fork according to claim 1, characterised in that the body is connected to the shaft by a pin extending through the tubular insert and the shaft.

3. Fork according to claim 1, characterised in that the tubular insert comprises a coupling bead.

4. Fork according to claim 3, characterised in that the bead of the insert is produced by swaging.

5. Fork according to claim 1, characterised in that the body and the arms are in one piece formed by a front face and a rear face, in the direction of the shaft, which are connected by ribs and cruciform members.

6. Fork according to claim 1, characterised in that the shaft carries a crosshead.

7. Fork according to claim 1, characterised in that the body carries a crosshead.

8. Fork according to claim 1, characterised in that the tubular insert extends, on at least one side, beyond the body of plastics material, and the pin connecting the tubular 9 1 insert to the metal shaft extends through the tubular insert outside the plastics material.

9. A gearbox fork substantially as hereinbefore described with reference to or as shown in Figures 1 to 3) and 4 to 5.

9. A gearbox fork substantially as hereinbefore described with reference to or as shown in Figures 1 to 3 and 4 to 5.

Amendments to the claims have been filed as follows to CLAIMS:

1 Gearbox shift fork comprising a member carried by a shaft and having two arTns for controlling a sliding component of a gearbox, and an operating crosshead with which a gear selection fmger of a gearbox co- operates in use, characterised in that the member comprises a tubular metal insert on which is moulded a body of plastics material comprising a sleeve carrying the two arms of the fork, the shaft being received in the body by way of the tubular insert.

2. Fork according to claim 1, characterised in that the body is connected to the shaft by a pin 1 extending through the tubular insert and the shaft.

i 5. Fork according to claim 1, characterised in that the body and the arms are in one piece formed by a front face and a rear face, in the direction of the shaft, which are connected by ribs and cruciform members.

6. Fork according to claim 1, characterised in that the shaft carries the crosshead.

0 7. Fork according to claim 1, characterised in that the body carries the crosshead.

8. Fork according to claim 1, characterised in that the tubular insert extends, on at least one side. beyond the body of plastics material, and the pin connecting the tubular insert to the shaft extends through the tubular insert outside the plastics material.