GB2200971A - Drive transfer mechanisms - Google Patents

Abstract

A drive transfer assembly for transferring drive from a crankshaft gear to a camshaft gear of a vehicle engine comprises an idler gear wheel 6 mounted freely for rotation on a cylindrical shaft member 4 carried by a fixed mounting plate 1, the mounting plate 1, shaft member 4 and idler gear wheel 6 each including internal passageways 3, 5, 9 which co-operate to place the bearing surface of the shaft member 4 and the teeth of the idler gear wheel 6 in communication with a source of lubricant under pressure. Preferably the idler gear wheel includes one or more additional passageways 10 for conveying lubricant to the gear wheel face remote from the mounting plate. <IMAGE>

Description

DRIVE TRANSFER MECHANISMS This invention relates to drive transfer mechanisms for transferring drive between a crankshaft and a camshaft of a reciprocating piston engine and more especially to gear assemblies by which such drive can be transferred. The invention also relates to idler gears for transferring drive from one gear wheel to another gear wheel.

In reciprocating piston engines working on a multi-stroke cycle, each spring biased valve through which combustible and combusted mixtures respectively enter and leave the working cylinders of the engine must open once every one or more revolutions of the crankshaft. In a four-stroke engine, for example, each valve must open once every two revolutions of the crankshaft. The opening and closing of these valves is normally effected by cams carried by a camshaft driven at one half of the rotational speed of the crankshaft through a timing chain, or less frequently an idler gear, meshing with gear wheels carried by the crankshaft and camshaft.

Conventionally, timing chains are more widely used because of their inherent simplicity and accessibility for lubrication. For vehicles subjected to higher than average mileages, for example taxi cabs, the excessive wear engendered can lead to chain breakage with consequent loss of drive and inherent possibility of damage to adjacent engine parts by the flailing ends of the chain.

Idler gears have been used previously but have achieved limited success because of an inability effectively to lubricate bearing surfaces with resulting noise and wear problems.

The present invention sets out to provide an idler transfer gear for transferring drive from a crankshaft gear to a camshaft gear which does not suffer from, or at least alleviates, the disadvantages referred to in the preceding paragraph. The invention further sets out to provide a kit of parts by which a timing chain of a vehicle, e.g. a taxi cab, can be replaced by an idler gear wheel which does not suffer from, or at least alleviates, such disadvantages.

According to the present invention in one aspect, there is provided a drive transfer assembly for transferring drive from a crankshaft gear to a camshaft gear of a vehicle engine, the assembly comprising an idler gear wheel mounted freely for rotation on a cylindrical shaft member carried by a fixed mounting plate, the mounting plate, shaft member and idler gear wheel each including internal passageways which co-operate to place the bearing surface of the shaft member and the teeth of the idler gear wheel in communication with a source of lubricant under pressure.

Preferably the idler gear wheel includes one or more additional passageways for conveying lubricant to the gear wheel face remote from the mounting plate.

In one arrangement, the internal passageway formed in the shaft member enters the shaft member along a line generally parallel to or coincident with the longitudinal axis of the shaft member and leaves the shaft member through a generally radial passageway. The or each lubricant feed passageway formed in the idler gear wheel preferably extends along a line generally radially of the idler gear wheel and terminates at a location intermediate adjacent gear teeth of the gear wheel.

In another aspect, the invention provides an assembly of an idler gear wheel and a shaft member on which the idler gear wheel is mounted freely for rotation, the shaft member being carried. by a mounting plate, the mounting plate, shaft member and idler gear wheel-of the assembly being formed with lubricant feed passageways by which the bearing surface of the shaft member and the teeth of the idler gear wheel can be placed in communication with a source of lubricant 10 under pressure.

In a further aspect, the invention provides a kit of parts for replacing a timing chain for transferring drive between a crankshaft and a camshaft of a vehicle engine with an idler gear wheel, the kit comprising a mounting plate attachable to fixed structure of the engine housing which carries a cylindrical shaft member which defines a bearing surface for the idler gear wheel, the mounting plate, shaft member and idler gear wheel being formed with communicating passageways for placing the bearing surface of the shaft member and the teeth of the idler gear wheel in communication with a source of lubricant under pressure.

The invention will now be described by way of example only with reference to the accompanying diagrammatic drawings in which: Figures 1 and 2 are respectively plan and side elevational views of a mounting plate and shaft member used in accordance with the invention; Figure 3 is an end elevational view of a drive transfer mechanism in accordance with the invention; and Figure 4 is a side view of the mechanism illustrated in Figure 3.

The apparatus illustrated in the drawings includes a mounting plate 1 including four countersunk holes 2 for receiving threaded bolts by which the mounting plate can be secured rigidly to a fixed structure of the engine housing. The mounting plate 1 is formed with an internal lubricant feed passageway 3 in communication with a source of lubricant e.g. oil under pressure. The mounting plate 1 carries a cylindrical shaft member 4 formed with an internal lubricant feed passageway 5 which communicates at one end with the lubricant feed passageway 3 formed in the mounting plate 1 and at its other end with the shaft circumference. The shaft member 4 is preferably induction hardened and may be formed integrally with the mounting plate 1 (e.g. by a turning procedure) or may be secured thereto by any conventional means.The internal passageway 5 enters the shaft member in a direction generally concentric with the longitudinal axis of the shaft member and leaves in a direction generally radially of the shaft member.

As will be seen from Figure 3 and II, the shaft member 4 provides a bearing surface for an idler gear wheel 6. The idler gear is retained on the circumference of the shaft member by means of an endplate 7 detachably connected to the shaft member through threaded bolts 8. The idler gear wheel is formed with one or more radially extending lubricant feed passageways 9 for transferring lubricant from the bearing surface of the shaft member to the teeth of the gear wheel. Preferably the or each passageway 9 terminates at a location intermediate adjacent teeth.

The idler gear wheel is formed with one or more additional inclined lubricant feed passageways 10, for conducting lubricant to the rear face of the idler gear wheel 6.

The idler gear wheel is employed to transfer drive from a crankshaft gear wheel 12 to a camshaft gear wheel 13, the latter being formed with recesses 14 in its rear face. For timing purposes, key ways are formed within the camshaft gear 13 and the crankshaft gear 12.

In one particular arrangement, the camshaft gear wheel 13 has an outer diameter of 5.25", an internal bore of 0.875", a key way of 0.25" and carries 40 o teeth cut to a 2Q helix. The idler gear wheel 6 also has an outer diameter of 5.25", an internal bore of o 1.25" and carries 40 teeth cut to a 20 helix. The outer diameter of the bush 11 of the idler gear is 1.25"; preferably the bush is of bronze or white metal or coated with white metal. The crankshaft gear wheel 12 has an outer- diameter of 2.75", an internal bore of 1.25", an 0.25" key way and carries 20 teeth cut to a o 20 helix. It is to be understood that these dimensions are merely exemplary of one particular assembly in accordance with the invention.

The invention has especial application as a conversion -kit for replacing timing chains used in reciprocating piston engines with idler gear wheels for- transfering drive between the crankshaft and camshaft of the engine. In such engines, and in particular those used to power high mileage vehicles such as taxi cabs, the conversion essentially entails removing the existing timing chain, securing the backing plate 1 to a suitable engine structure with the lubricant passageway 3 in communication with an oilline of the engine, and locating the idler gear wheel 6 on the shaft member 4 such that its teeth mesh with and transfer drive between the crankshaft 12 and 15 camshaft 13.

It will be appreciated that the foregoing is exemplary of one embodiment of the invention and that various modifications may be made thereto without departing from the true scope of the invention.

Claims (7)

1 A drive transfer assembly for transferring drive from a crankshaft gear to a camshaft gear of a vehicle engine, the assembly comprising an idler gear wheel mounted freely for rotation on a cylindrical shaft member carried by a fixed mounting plate, the mounting plate, shaft member and idler gear wheel each including internal passageways which co-operate to place the bearing surface of the shaft member and the teeth of the idler gear wheel in communication with a source of lubricant under pressure.

2 An assembly as claimed in claim 1 wherein the idler gear wheel includes one or more additional passageways for conveying lubricant to the gear wheel face remote from the mounting plate.

3 An assembly as claimed in claim 1 or claim 2 wherein the internal passageway formed in the shaft member enters the shaft member along a line generally parallel to or coincident with the longitudinal axis of the shaft member and leaves the shaft member through a generally radial passageway.

4 An assembly as claimed in claim 2 or claim 3 wherein the or each lubricant feed passageway formed in the idler gear wheel extends along a line generally radially of the idler gear wheel and terminates at a location intermediate adjacent gear teeth of the gear wheel.

5 An assembly of an idler gear wheel and a shaft member on which the idler gear wheel is mounted freely for rotation, the shaft member being carried by a mounting plate, the mounting plate, shaft member and idler gear wheel of the assembly being formed with lubricant feed passageways by which the bearing surface of the shaft member and the teeth of the idler gear wheel can be placed in communication with a source of lubricant under pressure.

6 A kit of parts for replacing a timing chain for transferring drive between a crankshaft and a camshaft of a vehicle engine with an idler gear wheel, the kit comprising a mounting plate attachable to fixed structure of the engine housing which carries a cylindrical shaft member which defines a bearing surface for the idler gear wheel, the mounting plate, shaft member and idler gear wheel being formed with communicating passageways for placing the bearing surface of the shaft member and the teeth of the idler gear wheel in communication with a source of lubricant under pressure.

7 A drive transfer assembly substantially as herein described with reference to the accompanying drawings.