GB2471022A

GB2471022A - Engine arrangement for a motorcycle in which the starter motor is hidden by the gearbox

Info

Publication number: GB2471022A
Application number: GB1009795A
Authority: GB
Inventors: Stephen Ronald Mcfarlane
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-06-12
Filing date: 2010-06-11
Publication date: 2010-12-15
Anticipated expiration: 2030-06-11
Also published as: GB0910152D0; GB201009795D0; GB2471022B

Abstract

A starter motor arrangement is disclosed comprising an engine casing 2 and gearbox casing 24 supported by at least one engine plate 26, a first transmission between the engine and gearbox and a transmission casing 22, a starter motor 100 directly or indirectly attached to the engine plate 26, a chain 104 for supplying power from the starter motor 100 and a transfer shaft driven by the chain of the first transmission. Part of the transfer shaft 108 is internal of the transmission casing 22 and part of the transfer shaft 108 is external of the transmission casing 22. A second geared transmission within the transmission casing 22 transmits power from the driven transfer shaft 108 to an end of a crank shaft 4 within transmission casing 22. The arrangement provides a means of providing a starter motor on a large motorcycle engine, in excess of 600cc, such that the starter motor may be hidden underneath the gearbox casing and is not conspicuous, maintaining the `classic' look of the motorcycle engine.

Description

Starter motor arranciement This invention relates to a starter motor arrangement for motorcycles and the like.

While modern motorcycles with larger engines usually have electrically powered starter motors, that has not always been the case. So-called classic motorcycles, for example those of the 1950's and 60's, were generally not fitted with electric starter motors. These classic motorcycles can have engine capacities of 600cc or more which makes them difficult to start using the conventional kick-start mechanism.

Although starter motors are known on motorcycles and other engined vehicles, it is a difficult task provide an arrangement which will fit an existing engine and does not spoil the classic look of the motorcycle or vehicle. The inventor has developed a reliable and easy to fit starter motor arrangement which will fit most classic motorcycles and yet is discreet so that the classic look of the motorcycle is maintained.

According to a first aspect of the invention there is provided a starter motor arrangement suitable for an engine having a crank shaft rotatable about an engine axis, an engine casing, a gearbox having an input rotatable about a gearbox input axis, a gearbox casing, and a transmission between the engine and gearbox casings for transmitting torque between the engine and gearbox axes, said transmission having a transmission casing, and the engine and gearbox casings being supported by at least one engine plate, the arrangement including: a starter motor mountable directly or indirectly to the engine plate; a first chain type transmission for supplying power from the starter motor; a transfer shaft for being driven in use by the chain of the first transmission, the transfer shaft including a first portion in use external to the transmission casing and a second portion disposed in use within the transmission casing, and; a second geared transmission within the transmission casing for transmitting power from the driven transfer shaft to an end of the crank shaft disposed within the transmission casing.

In a refinement one or both the first and second transmissions are speed reducing transmissions.

In an embodiment the transfer shaft is disposed between the engine and gearbox axes.

In an embodiment, the second geared transmission includes any one or more of: a first gear forming part of or connected to the second portion of the shaft driveable by the first transmission; a second gear having more teeth than the first gear, and driveable by the first gear; a third gear coaxial with the second gear and driveable by the second gear; and a fourth gear having more teeth than the third gear, mountable to the crankshaft of the engine and driveable by the third gear.

In an embodiment, the geared starter motor transmission includes a freewheel so that torque can be transmitted to the crank shaft from the starter motor but not from the crank to the starter motor when the engine is running.

Preferably the freewheel is positioned to allow the fourth, or fourth and third gears only to be driven by the engine.

Preferably the freewheel is in the form of a sprag clutch.

In an embodiment, the gears are mounted to a gear support, in turn mounted, via an attachment or attachments, to the engine casing, said attachment(s) passing through the transmission casing. Thus torque exerted on the transmission gears is reacted by the engine casing and not substantially the transmission casing.

In an embodiment, the first transmission is supported on a first transmission support, which in turn is mounted to the engine plate(s). Thus torque exerted on the chain type transmission is reacted by the engine plate(s) and not the transmission casing or gearbox casing.

According to a second aspect the invention comprises a vehicle including an engine having a starter motor arrangement according to the first aspect.

According to a third aspect the invention comprises a method of fitting a starter motor to an engine which engine includes separable engine, gearbox and transmission casings, at least the engine and gearbox casings being supported on at least one engine plate, the method including the steps of: fitting a starter motor underneath the gearbox casing; fitting a chain drive from the starter motor to a transfer shaft; and fitting gears within the transmission casing for transmitting power from the driven transfer shaft to a crank shaft of the engine.

In the method above, the chain drive may be supported on chain drive supports which themselves may be substantially directly supported on the engine plate(s) and the gears may be supported by supports which themselves may be supported substantially directly by the engine casing.

The invention extends to any novel feature described herein, or any novel combination of features described herein.

Although the invention can be put into effect in numerous ways, one embodiment only is described below with reference to Figure 1 which shows a part sectional plan view representing schematically a starter motor arrangement.

Referring to Figure 1, there is shown an engine 1 having an engine casing 2 and an exposed portion of a crankshaft 4. The crankshaft 4 includes an output sprocket 6 which transmits engine power to a gearbox sprocket 10 via a chain drive 8. The chain drive 8 is prevented from being over stressed by a so-called cush drive 12 which is a sprung-loaded mechanism acting as an engine shock absorber for smoothing power pulses from the engine crank shaft 4. A clutch arrangement 14 allows power from the engine to be selectively transmitted to a gear box 18 via shaft 16. The gearbox 18 has an output sprocket 20 which is co-axial with the shaft 16. The sprockets 6 and 10, as well as the clutch 14 are housed in a transmission casing 22 so that they can be kept lubricated with oil. The engine casing 2 and the casing 24 of the gearbox 18 are mounted to engine plate members 26.

The above-mentioned features are generally conventional in older motorcycles.

These older motorcycles do not generally have an electric starter motor arrangement and the following description sets out one arrangement for fitting a starter motor to the known configuration mentioned above.

Also shown in Figure 1 is an electric starter motor 100 which is connected to a battery via a starter switch, in a known manner. The starter motor 100 has an output sprocket 102 for driving a chain 104. The chain 104 drives a receiving sprocket 106 mounted to a transfer shaft 108. The starter motor is mounted underneath the gearbox 18 so that it is not visible when looking at the top of the gearbox 18. The sprockets 102 and 106 are mounted to two support plates 110 which are in turn mounted to the engine plate 26 via one or more fastenings 112.

The relative sizes of the sprockets 102 and 106 produce a reduction in the rotational speed of the starter motor 100 of approximately one-half. Transfer shaft 108 has a portion external to the transmission casing 22 and a further portion which extends into the casing 22, through a clearance hole 109, terminating in a spur gear 114. The clearance hole 109 needs to be drilled in the casing 22 but it is the only additional hole that needs to be drilled when fitting the starter motor arrangement. The transfer shaft 108 is supported within the casing 22 by means of a pair of support plates 116. The support plates are rigidly connected together and are bolted to the engine casing using one or more bolts 118. The spur gear 114 drives a larger gear 120. Gear 120 is co-axially mounted with a freewheel arrangement 122 and a further gear 124 mounted radially outwardly of the freewheel 122.

In use gear 120 is driven and in turn drives the freewheel 122. Gear 124 is driven also by the gear 120. Gear 124 drives yet another gear 126 which in turn is bolted to the output sprocket 6 of the engine. I this case the freewheel 122 is a sprag type clutch.

In use when the starter motor 100 is rotated the resulting power is transmitted through sprocket 102, through chain 104, through sprocket 106, through transfer shaft 108, through spur gear 114, through gear 120, axially to freewheel 122, radially outwardly through gear 124, through gear 126, through sprocket 6, through the cush drive mechanism 12, and into the crank shaft 4 to turn the engine for starting. Once started, in this instance, gear 126 rotates with the sprocket 6 and turns gear 124. The freewheel 122 allows rotation of the gear 124 without the transmission of substantive torque to the remainder of the starting transmission. It will be noted that the freewheel mechanism 122 could be mounted to the gear 126 sO that gear 124 need not be rotated with the engine.

The relative number of teeth of gears, 114, 120, 124, and 126 are such that they give approximately a 12:1 reduction ratio. This ratio, together with the reduction in rotational speed resulting from the sizes of the sprockets 102 and 106 means that the overall rotational speed reduction ratio from the starter motor to the crankshaft is around 24:1. However, reduction ratios in the region of 20:1 to 30:1 would be satisfactory.

It will also be noted that the gear transmission is completely within the transmission casing 22, and only the chain 104 and sprockets 102, 106 are mounted outside the casing, so the arrangement is not fully visible when fitted to the existing motorcycle engine. However, in use a further cover 128 will be used to cover the chain 104 and sprocket 106 that would otherwise be partially visible when looking down at the gearbox 18. The starter motor itself is not generally visible because it is mounted underneath the gearbox 18.

Although only one embodiment of the invention has been described, it will be apparent that other modifications, variations and improvements will be apparent to the skilled addressee. For example, although motorcycles have been described, the starter motor arrangement could be used on other vehicles such as three wheel vehicles which use an older motorcycle type engine.

The existing components may not be arranged as described, or could be replaced with alternatives or other components. For example the cush drive 12 could be replaced with an alternator, the chain drive 8 could be replaced by a belt drive.

Although for simplicity, the gears shown have the centres of rotation which are on one plane, in practice, to save space the centres of rotation of the gears shown will be in different planes.

In a modification, gear 126 can be located on the distal end of the crank shaft 4. Although a chain drive 8 has been described, belt drives could be modified into electric start also.

A kit of parts could be prepared for conversion to electric start by an individual.

Claims

Claims 1. A starter motor arrangement suitable for an engine having a crank shaft rotatable about an engine axis, an engine casing, a gearbox having an input rotatable about a gearbox input axis, a gearbox casing, and a transmission between the engine and gearbox casings for transmitting torque between the engine and gearbox axes, said transmission having a transmission casing, and the engine and gearbox casings being supported by at least one engine plate, the arrangement including: a starter motor mountable directly or indirectly to the engine plate; a first chain type transmission for supplying power from the starter motor; a transfer shaft for being driven in use by the chain of the first transmission, the transfer shaft including a first portion in use external to the transmission casing and a second portion disposed in use within the transmission casing, and; a second geared transmission within the transmission casing for transmitting power from the driven transfer shaft to an end of the crank shaft disposed within the transmission casing.
2. A starter motor arrangement as claimed in claim 1, wherein one or both the first and second transmissions are speed reducing transmissions.
3. A starter motor as claimed in claim 1 or 2, wherein the transfer shaft is disposed between the engine and gearbox axes.
4. A starter motor as claimed in claim 1, 2 or 3, wherein the second geared transmission includes any one or more of: a first gear forming part of or connected to the second portion of the shaft driveable by the first transmission; a second gear having more teeth than the first gear, and driveable by the first gear; a third gear coaxial with the second gear and driveable by the second gear; and a fourth gear having more teeth than the third gear, mountable to the crankshaft of the engine and driveable by the third gear.
5. A starter motor arrangement as claimed in any one of the preceding claims, wherein the geared starter motor transmission includes a freewheel so that torque can be transmitted to the crank shaft from the starter motor but not from the crank to the starter motor when the engine is running.
6. A starter motor arrangement as claimed in claim 5, wherein the freewheel is positioned to allow the fourth, or fourth and third gears only to be driven by the engine.
7. A starter motor arrangement as claimed in claim 5 or 6, wherein the freewheel is in the form of a sprag clutch.
8. A starter motor arrangement as claimed in any one of the preceding claims, wherein the gears are mounted to a gear support, in turn mounted, via an attachment or attachments, to the engine casing, said attachment(s) passing through the transmission casing.
9. A starter motor arrangement as claimed in claim 8, wherein the first transmission is supported on a first transmission support, which in turn is mounted to the engine plate(s).
10. A vehicle including an engine having a starter motor arrangement according to claims 1 to 9.
11. A method of fitting a starter motor to an engine which engine includes separable engine, gearbox and transmission casings, at least the engine and gearbox casings being supported on at least one engine plate, the method including the steps of: fitting a starter motor underneath the gearbox casing; fitting a chain drive from the starter motor to a transfer shaft; and fitting gears within the transmission casing for transmitting power from the driven transfer shaft to a crank shaft of the engine.
12. A method as claimed in claim 11, wherein the chain drive may be supported on chain drive supports which themselves may be substantially directly supported on the engine plate(s) and the gears may be supported by supports which themselves may be supported substantially directly by the engine casing.
13. A kit of parts suitable for assembly into the start motor arrangement of claims 1 to 9 or for carrying out the method of claim 11 or 12.
14. A starter motor arrangement, vehicle or method substantially as disclosed herein with reference to the drawing.