Power Transmission System for Vehicles

1. Field of the Invention

This invention relates to a power transmission system for vehicles, mainly for motorcycles.

2. Description of the Prior Art

In general, a power transmission system for vehicles experiences vibration when it receives an excessively large back load due to sudden deceleration of the vehicle. For minimizing such vibration, there has been proposed a power transmission system which is provided with a damper formed of an elastic material such as rubber. However, in this known power transmission system, it is necessary to make the capacity of the elastic element sufficiently high. This causes an increase in the dimensions not only of the damper but also of the power transmission system as a whole. Moreover, the above-mentioned damper responds to load both in the forward and reverse directions, so that it causes an increase in vibration of the power transmission system when the load is varied.

An object of the present invention is to provide a power transmission which eliminates the abovementioned drawbacks encountered in the conventional power transmission systems for vehicles.

A further object of this invention is to provide a comparatively small-sized power transmission system for vehicles, capable of effectively absorbing vibration, which permits, when a forward load is applied to the engine, the transmission of power from the engine to a driving wheel without causing any decrease in the power level and which, when a back load is applied to the engine, prevents the level of the back load from being increased to a value in excess of a predetermined value, so that an excessively large back load is not applied to the engine.

To this end, the present invention provides a power transmission system for vehicles, comprising a driving member connected to the crankshaft of the engine, and a driven member connected to a driving wheel, the driving and driven members being connected to each other via a one-way clutch and a friction clutch which are disposed parallel to each other, the one-way clutch being adapted to be connected when a forward load is applied to the engine and disconnected when a back load is applied to the engine, the friction clutch being operable to slip when it receives a torque greater than a predetermined value.

The above and other objects as well as advantageous features of the invention will become apparant from the following detailed description of a preferred embodiment of the invention taken in conjunction with the accompanying drawings.

FIG. 1 is a developed plan view of a power transmission system for motorcycles embodying the present invention; and

FIG. 2 is an enlarged longitudinal sectional view of an essential portion of the same.

A power transmission system according to the present invention which is applied to a motorcycle will be described with reference to the accompanying drawings.

Referring to FIG. 1, an engine, generally designated at E and a speed change gear, generally designated at M, are coupled in such a manner that a crankshaft 1 of the engine and a main shaft 2 and a countershaft 3 of the speed change gear are supported in a common casing 4.

An intermediate shaft 5 is disposed between and parallel to the crankshaft 1 and the main shaft 2. A one-way clutch C.sub.1 and a friction clutch C.sub.2 are mounted parallel to each other on the intermediate shaft 5. An input gear 7 which is common to the clutches C.sub.1, C.sub.2 is also mounted on the intermediate shaft 5, which gear 7 is in mesh with an output gear 6 formed on the outer circumferential surface of a crank web of the crankshaft 1.

A gear 8 is fixedly mounted on an output end of the intermediate shaft 5, and is in mesh with an input gear 9 of a conventional manual clutch C.sub.3 mounted on an input end of the main shaft 2.

A conventional change gear mechanism 10 operatively connects the main shaft 2 and the countershaft 3. A sprocket 11 is fixedly mounted on an output end of the main shaft 2, and is adapted to drive a driving wheel, i.e. a rear wheel of a motor-cycle via a chain (not shown).

The construction of the one-way clutch C.sub.1 and friction clutch C.sub.2 referred to above will be described in detail with reference to FIG. 2.

The one-way clutch C.sub.1 comprises an inner clutch member 12 spline-fitted around the intermediate shaft 5, an outer clutch member 13 formed on the inner circumferential surface of a boss 7a of the input gear 7 and surrounding the inner clutch member 12, and a sprag 14 inserted between the inner and outer clutch members 12, 13. The boss 7a is rotatably supported on the inner clutch member 12 and on an outer clutch boss 17b, which will be described later, of the clutch C.sub.2 via bearings 15, 15'. When the one-way clutch C.sub.1 receives a forward load during operation of the engine, the inner and outer clutch members 12, 13 are connected to each other by the locking action of the sprag 14. When the one-way clutch C.sub.1 receives a back load, the inner and outer clutch members 12, 13 are disconnected from each other by the sprag 14.

The friction clutch C.sub.2 comprises an inner clutch member 16 formed on the outer circumferential surface of the boss 7a of the input gear 7, an outer clutch member 17 surrounding the inner clutch member 16, a plurality of driving friction plates 18 slidably spline-fitted on the inner circumferential surface of the inner clutch member 16, and a plurality of driven friction plates 19 interlaced with the driving friction plates 18 and slidably fitted in the outer circumferential surface of the outer clutch member 17. A side wall 17a of the outer clutch member 17 is opposed to a side surface of the input gear 7 with the driving and driven friction plates 18, 19 held therebetween. The side wall 17a receives on its rear surface a resilient force from a belleville spring 20 to press the friction plates 18, 19 against each other. Accordingly, a frictional binding force, or a slip torque, of the friction plates 18, 19 is determined by a set load of the belleville spring 20 acting against the side wall 17a.

The outer clutch member 17 has a boss 17b in the central portion of the side wall 17a thereof. The boss 17b is slidably spline-fitted on the intermediate shaft 5 so as not to prevent the side wall 17a from pressing against the friction plates 18, 19.

In the embodiment shown in FIG. 1 of the drawings, a drive shaft 21 for an engine-cooling water supply pump P is disposed in a space between the intermediate shaft 5 and the main shaft 2. The drive shaft 21 is driven by the intermediate shaft 5 via gears 22, 23 which are in mesh with each other. In this arrangement, a light load from the pump P constantly acts on the intermediate shaft 5 so that vibrations of the intermediate shaft 5 can be effectively prevented.

The operation of this embodiment will be described hereafter.

When a forward load is applied to the engine E, an output torque from the crankshaft 1 is transmitted to the input gear 7 via the output gear 6 and thence to the one-way clutch C.sub.1 and friction clutch C.sub.2. Since the one-way clutch C.sub.1 is in a connected state when a forward load is applied to the engine E, the torque distributed to the clutch C.sub.1 is transmitted to the intermediate shaft 5 via the outer clutch member 13, sprag 14 and inner clutch member 12. On the other hand, the torque distributed to the friction clutch C.sub.2 is also transmitted to the intermediate shaft 5 via the inner clutch member 16, drive friction plates 18, driven friction plates 19 and outer clutch member 17. Even when the output torque from the crankshaft 1 exceeds the predetermined slip torque for the friction clutch C.sub.2, the entire excess torque is transmitted to the intermediate shaft 5 by the one-way clutch C.sub.1, so that no slip occurs in the friction clutch C.sub.2. Accordingly, the output torque from the crankshaft 1 is transmitted to the intermediate shaft 5 efficiently. The torque is then transmitted to the driving sprocket 11 via the gears 8, 9, manual clutch C.sub.3 and speed change gear M to drive the rear wheel (not shown).

When a back load is applied to the engine E, or, for example, when the vehicle is shifted from a high-speed running condition to a decelerated running condition, a drive torque applied from the road surface to the rear wheel is transmitted to the crankshaft 1 in reverse through the above-mentioned power conduction path. In this case, the intermediate shaft 5 acts as the driving side with respect to the input gear 7, so that the one-way clutch C.sub.1 is in a disconnected state. Consequently, the driving torque from the rear wheel is transmitted from the intermediate shaft 5 to the input gear 9 via the friction clutch C.sub.2 only. When the reverse driving torque exceeds the predetermined slip torque for the friction clutch C.sub.2, a slip occurs between the friction plates 18 and 19. Thus, back load transmitted to the engine E can be kept to a value less than a predetermined level.

In the above embodiment of the present invention, the input gear 7 constitutes a driving member, and the intermediate shaft 5 a driven member.

According to the present invention, as described above, a driving member and a driven member provided in a power conduction path extending from a crankshaft in an engine to the driving wheel are connected together via a one-way clutch and the friction clutch which are disposed parallel to each other. The one-way clutch is constructed in such a manner that it is in connected state when a forward load is applied to the engine and disconnected when a back load is applied to the engine. The friction clutch is so constructed that slip occurs therein when it receives a torque exceeding a predetermined level. Accordingly, power from the engine is normally transmitted to the driving wheel via the one-way clutch and the friction clutch without causing any substantial power loss, so that a high transmission efficiency can be obtained. The one-way clutch and the friction clutch cooperate to share the load so that the usable lives thereof can be increased and the capacities of these clutches can be reduced to minimize the dimensions of the power transmission system as a whole. When an excessively large back load is applied to the engine, it can be limited to a value less than a predetermined level due to the slipping operation of the friction clutch to effectively decrease the resulting vibration of the power transmission system, thus providing a comfortable ride.

The present invention is not, of course, limited to the above-described embodiment; it may be modified in various ways within the scope of the appended claims.