GB2142393A

GB2142393A - Gear shift mechanism

Info

Publication number: GB2142393A
Application number: GB08413359A
Authority: GB
Inventors: Gunther Villwock; Dieter Schneider; Sabina Tenbusch; Manfred Heiber
Original assignee: IFA GETRIEBEWERKE BRANDENBURG
Current assignee: IFA GETRIEBEWERKE BRANDENBURG
Priority date: 1983-06-30
Filing date: 1984-05-24
Publication date: 1985-01-16
Also published as: FR2548406B1; GB8413359D0; SE8403106D0; HU189411B; DD216771A1; HUT35801A; DE3416048A1; SE8403106L; FR2548406A1

Abstract

A gear shift mechanism includes a rotatable and axially displaceable gear selecting sleeve (5) provided with a circumferential groove (4), and a selector fork (3) provided at the free end of each of its arms with a pin (2) journalling a slide member (1) slidably engaged in the groove (4). Movement of the fork effects axial displacement of the sleeve by way of the slide members. A sliding friction contact so arises that a physical-chemical process, based on a certain material composition of the slide members (1) and on arising heating, leads to formation of a metallic protective film to inhibit frictional wear, the slide members being of an aluminium-silicon alloy with various additions. <IMAGE>

Description

SPECIFICATION Gear shift mechanism The present invention relates to a gear shift mechanism including a gear selecting sleeve operable by a fork.

Siide rings for gear selector forks are used in gear shift mechanisms, especially commercial vehicle transmissions, in which a gear selecting sleeve must be axially displaced for the purpose of a gear change operation, the slide ring sliding in a groove at the external circumference of the sleeve. For the reduction of the sliding friction wear at the friction couple of the slide ring and sleeve, known slide rings are produced from different materials, for example brass, bronze, heat-treated steels or non-metallic material, or have a steel body which is coated. Also known are compact slide ring assemblies, for example of cast construction, which consists of a cylindrical pin part and a prismatic part and a pin, and slide ring assemblies which consist of a pin fixedly arranged in the fork and a slide ring pivotably disposed thereon.

The associated sleeves consist of heattreated steel.

These arrangements have the disadvantages of a high rate of wear at the sliding surfaces leading to early failure, increased production due to additional thermal treatment in the case of ferric materials, and high material costs for coating.

According to the present invention there is provided a gear shift mechanism including a rotatable and axially displaceable gear selecting sleeve provided around its circumference with a groove, and a fork which is provided at the free end of each arm thereof with an axle rotationally journalling a respective slide member slidably engaged in the groove of the sleeve to permit rotation of the sleeve relative to the fork and which is movable to effect axial displacement of the sleeve by way of the slide members, the slide members and sleeve being made of such materials that sliding friction and consequent heat arising at relatively moving mutually contacting surfaces thereof during use of the mechanism cause formation of a wear-resisting metallic film.

A mechanism embodying the invention may have the advantages that the mechanism has an extended life due to a low rate of wear, that relatively low material and production costs are involved, that additional coatings are not necessary, and that a good thermal conduction is provided. In use of the mechanism, a sliding friction contact is realised in the form that recognitions, for example from the field of the synchronisation of change speed gears, are so transferred and come into application that a completely different effect arises here through analogous material composition in spite of different set objectives in the respective cases of application.Expediently, each slide member is composed of an aluminium alloy with main alloy components of silicon (11 to 23%), copper (1 to 3.5%), nickel (0.8 to 2.7%), magnesium (up to 1.5%), manganese (0.8 to 2.7%) and titanium (up to 0.2%).

The Brinell hardness of the alloy preferably does not exceed substantially 1 30. This alloy has adequate compression strength even at high temperatures. During the friction process, the slide members are loaded predominantly in compression. The sleeve can be made of heat-treated steel so that a physicalchemical process of the selective transfer takes place during the contact of these materials due to the arising heating, as a result of which process there is formed a metallic protective film which almost completely prevents a frictional wear of the contact surfaces.

The sliding friction contact thus contributes, due to the low wear, to an increase in the life so that good material economy is possible. In addition, arising heat is conducted away rapidly.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawing, in which: Figure 1 is a sectional view of a slide member of a gear shift mechanism embodying the invention; and Figure 2 is a partly sectioned end view of part of the mechanism.

Referring now to the drawing, there is shown part of a gear shift mechanism which includes a gear selecting sleeve 5, for example a dog sleeve, which is rotatable and axially displaceable, the sleeve being provided around its circumference with a groove 4.

Axial displacement of the sleeve, for example to effect intercoupling of a gear with a main shaft in a gear transmission, especially a commercial vehicle transmission, is effected by a selector fork 3, which is provided at the free end of each of its arms with a fixed axle in the form of a cylindrical pin 2. Rotatably mounted on each pin 2 is a slide member 1, namely a block or a ring, which is slidably engaged in the groove 4 to permit rotation of the sleeve relative to the fork. The sleeve 5 is made of heat-treated steel, and each member 1 of an aluminium alloy which comprises 11 to 23% of silicon, 1 to 3.5% of copper, 0.8 to 2.7% of nickel, up to 1.5% of magnesium, up to 0.5% of manganese and up to 0.2% of titanium and has a maximum Brinell hardness of substantially 1 30. On displacement of the fork 3 to axially displace the sleeve 5, the members 1 are loaded in compression. The slidng friction and heat arising at the mutually contacting and relatively moving surfaces of the sleeve and slide members caused formation of a protective metallic film inhibiting wear at these surfaces.

Claims

1. A gear shift mechanism including a rotatable and axially displaceable gear selecting sleeve provided around its circumference with a groove, and a fork which is provided at the free end of each arm thereof with an axle rotationally journalling a respective slide member slidably engaged in the groove of the sleeve to permit rotation of the sleeve relative to the fork and which is movable to effect axial displacement of the sleeve by way of the slide members, the slide members and sleeve being made of such materials that sliding friction and consequent heat arising at relatively moving mutually contacting surfaces thereof during use of the mechanism cause formation of a wear-resisting metallic film.

2. A mechanism as claimed in claim 1, wherein the material of each of the slide members is an aluminium alloy comprising 11 to 23% of silicon, 1 to 3.5% of copper, 0.8 to 2.7% of nickel, up to 1.5% of magnesium, up to 0.5% of manganese and up to 0.2 of titanium and has a maximum Brinell hardness of substantially 1 30.

3. A mechanism as claimed in either claim 1 or claim 2, wherein the material of the sleeve is heat-treated steel.

4. A gear shift mechanism substantially as hereinbefore described with reference to the accompanying drawing.