GB1559598A - Power unit for a motor cycle - Google Patents

Description

(54) POWER UNIT FOR A MOTOR CYCLE (71) We, HONDA GIKEN KOGYO KABU SHIKI, KAISHA a corporation of Japan, of 27-8, 6-chome, Jingumae, Shibuya-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement :- This invention relates to a power unit for a motorcycle.

According to the present invention there is provided a power unit for a motor-cycle, the power unit comprising: a power transmission case fast with an engine crankcase and supporting at its rear end a rear road wheel axle, the transmission case being constituted by an inboard half connected to the crank case and an outboard half separably connected to the inboard half, the rear axle being supported by the inboard half of the power transmission case; a driving power transmission mechanism connecting the rear axle and the crank shaft of the engine; a pedal shaft having an engine starting pedal connected at one end thereof, this shaft being supported by the outboard half of the power transmission case; an engine starting shaft adjacent the crank shaft on the same axis as the crank shaft and also supported by the outboard half of the power transmission case; a starting power transmission mechanism connecting the pedal shaft and the engine starting shaft; and a driving member and a driven member of an over-running clutch provided at the opposing ends of the starting shaft and the crank shaft, these members being engaged with each other at the time of coupling together the inboard and outboard halves of the power transmission case.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying draw ings, in which; Figure 1 is a general side view of a motorcycle; Figure 2 is a plan view of a power unit of the motor-cycle of Figure 1, taken along the line IT-TI in Figure 1 Figure 3 is a longitudinal cross-sectional view of the main part of the power unit; Figure 4 is a cross-sectional view taken along the line IV-IV in Figure ; Figure 5 is a cross-sectional view taken along the line V-V in Figure 4; Figure 6 is a cross-sectional view taken along the line VI-VI in Figure 3 but on a larger scale ; and Figure 7 is a cross-sectional view on a still larger scale showing a spiral spring for starting the engine of the power unit.

Referring to the drawings, a pair of supporting brackets S, S are fixedly provided at the lower centre part of a frame F of the motor-cycle where it is bent, one bracket being on one side and the other being on the other side of the frame. These brackets S, S support the front part of the power unit P by a supporting bolt B, such that the power unit is free to oscillate in the up and down direction. Between the part of the power unit P and the upper rear end part of the vehicle frame F, there is connected by means of bolts B, and B3 a shock absorber D of telescopic type that inclues a vehicle suspension spring C.

The power unit P mainly consists of the engine I which has a crank shaft 2 that extends transversely of the motor-cycle, and a power transmission case 4 fast with the rear of a crank case 3 of the engine I on one side of the motor-cycle and extending to the rear with respect to the forward running direction of the motor-cycle. The power transmission case 4 has an inboard half 4a which is integral with the crank case 3, and an outboard half 4b which is releasably connected to the inboard half 4a by a number of bolts 5,5,.....

A rear axle 7 is mounted in a freely rotatable manner in the side wall of the rear end of the inboard half 4a of the case 4 by means of a bearing 6. A hub 8 of a rear wheel Wr is splined to the outer end of the rear axle 7.

The inner end of the rear axle 7 is supported, so as to be freely insertable and withdrawable, when the two halves 4a and 4b of the case 4 are being coupled together or dismantled, in a bore in a boss 12 projecting from the inner surface of the outboard half 4b of the case 4.

A driving power transmission mechanism 9 provided consists of a centrifugal clutch 10 of an internally expanding type having an input member 10a fixed to an end portion of the crank shaft 2 and an output member 10b held on the same end portion of the shaft 2 in a freely rotatable manner; a primary speed reducing mechanism 9a capable of driving an intermediate power transmission shaft I 1 at a reduced speed from the output member 10b ; and a second speed reducing mechanism 9b capable of driving the rear axle 7 at a reduced speed from the intermediate power transmission shaft 11. The intermediate power transmission shaft 11 is supported at both ends thereof in bores in bosses 13 and 14 projecting from the inner surfaces of the transmission case halves 4a and 4b.

On the side wall at the centre part of the outboard half 4b of the case 4 there is fitted a pedal shaft 17 which can be subjected to swing motions in the directions of arrows a and b (Figure 5) by pressing down the engine starting pedal 15 against the restoring action of a return coil spring 16. The inner end of the pedal shaft 17 is supported so as to be freely insertable and withdrawable into and from a bore in a boss 18 of the inboard half 4a of the case 4 when the halves 4a and 4b of the case 4 are being connected together or dismantled.

A driving clutch member 19 of a one-way clutch mechanism is splined in a freely slidable manner on an intermediate portion of the pedal shaft 17 to one side of a driven clutch member 20 of this clutch mechanism, which member 20 is fast with a driving sprocket 21 of a relatively large diameter and is mounted on the pedal shaft 17 in a freely rotatable manner. The driving clutch member 19 is urged in the clutch-engaging direction, i. e., in the direction towards the driven clutch member 20, by a clutch spring 22. The driving clutch member 19 has, as an integral part thereof, an actuating arm 23 which projects radially of the member 19 and is engaged with a plate-like control lever 24. The control lever 24 is carried by the inner wall of the outboard half 4b of the case 4 by a pivot shaft 25 in a freely oscillatable manner. A stop pin 27 fixedly secured to the outboard half 4b of the case 4 is engaged in an elongated aperture 26 of arcuate shape which is formed in one part of the control lever 24. At an extremity of the control lever 24 remote from the pivot shaft 25 there are formed (as shown best in Figure 5) a first stop surface 28 which is capable of contacting a side surface of the actuating arm 23 to restrict return movement of the pedal shaft 17 under the action of the return spring 16 ; a cam surface 31 which is inclined to the stop surface 28, and hence is also incline to the driving sprocket 21, for controlling movement of the actuating arm 23 against the action of the clutch spring 22; a second stop surface 29 which is capable of contacting a first projection 32 provided on the side surface of the driving sprocket 21 so as to determine the starting point of rotation of the driving sprocket 21 in the direction of the arrow a ; and a third stop surface 30 which is capable of contacting a second projection 33 (Figure 4) provided on the side surface of the driving sprocket 21 so as to determine the terminating point of rotation of the driving sprocket 21 in the direction of the arrow a. Further, a buffer cylinder 35 which is filled with an elastic buffer material 34 such as rubber is fixedly provided on the control lever 24. At an open end of this buffer cylinder 35 there is fitted, in a freely slidable manner, a cup-shaped member 37 which covers the free surface of the buffer material 34 and faces a contact surface 36 of the outboard half 4b of the case 4.

On the outboard half 4b of the case 4 there is integrally formed a supporting boss 38 on the same axial line as that of the crank shaft 2.

An engine starting shaft 41 is fitted onto this supporting boss 38 in a freely rotatable manner. A hook-shaped inner end 40a of a spiral spring 40 (Figure 7) is engaged in a groove 41a at one side of the engine starting shaft 41.

A hook-shaped outer end 40b of this spring 40 is engaged with an engaging pawl 39 on the inner wall of the outboard half 4b of the case 4. The spiral spring 40 is so designed that at least a single windmg (in the power unit illustrated it is wound twice) at the inner end of the spring is formed as a tightly-wound part 40c that tightly enbraces the engine starting shaft 41 by its own embracing force.

The remainder of the spring has tension in the expanding direction of the spring so that spring force is accumulated when the spring is wound around the engine starting shaft 41.

In consequence, at the time of releasing the accumulated spring force from the spiral spring 40 and because of inertial effects, rotation of the engine starting shaft 41 results in reverse rotational force on this spiral spring 40. However, the tightly-wound part 40c of the spiral spring 40, which tightly squeezes the starting shaft 41, absorbs this reverse rotational force, so that the risk of the spring breaking, or of the spring end 40a separating from the groove 41a in the engine starting shaft 41, is minimised.

On the engine starting shaft 41 there is integrally formed a driven sprocket 42 having a smaller diameter than that of the driving sprocket 21. A power transmission chain 43 runs around the driving and driven sprockets 21 and 42. In this manner, the driving sprocket 21, the driven sprocket 42, and the power transmission chain 43 constitute a starting power transmission mechanism 44.

At an intermediate position between the driving sprocket 21 and the driven sprocket 42, a supporting plate 63 is fixedly secured to the inner wall of the outboard half 4b of the case 4 by screws 64 so that substantially half of the peripheral surface of the intermediat. : portion of the engine starting shaft 41 is supported by a fork portion 63a of the plate 63 whereby the engine starting shaft 41 can be prevented from inclination or off-centering due to the tension imparted thereto by the power transmission chain 43, and, at the same time, its movement in the axial direction can be restricted. Moreover, as this supporting plate 63 crosses over the open surface of the housing 6S accommodating therein the spiral spring 40, it also has a function to suppress protrusion of the spiral spring 40.

At an intermediate position between the pedal shaft 17 and the engine starting shaft 41 there is fixedly provided on a pivot shaft 47 a ratchet pawl 48 which is urged by a coil spring 49 into engagement with the teeth of the driving sprocket 21. The pivot shaft 47 is rotatably supported in bores in bosses 45 and 46 of the inboard and outboard halves 4a and 4b of the case 4. The ratchet pawl 48 constitutes an intermittent forwarding mechanism 50 which permits the driving sprocket 21 to rotate in the direction of the arrow a in Figure 4 but prevents it from rotating in the direction of the arrow b. Furthermore, a release lever 51 is fixedly provided on the pivot shaft 47. An inner lever arm 53a of a bell crank lever 53 which is pivotally supported at 52 on the inboard half 4a of the case 4 is engaged with the lever 51. An outer lever arm 53b of the bell crank lever 53 is connected at a position mid-way along a brake wire 57 connected between a brake operating lever 54 provided on the handle bars H of the motor-cycle and an actuating lever 56 of a brake mechanism 55 of the internal expanding type incorporated in the hub of the rear wheel Wrz The pivot shaft 47 is fitted at one end thereof into a bore in the boss 46 of the outboard half 4b of the case 4 and is fitted, at the other end thereof, into a bore in the boss 45 of the inboard half 4a of the case 4 when these halves 4a and 4b are coupled together and, at the same time, the release lever 51 and the inner lever arm 53a of the bell crank lever 53 are mutually engaged.

A ratchet wheel 58 is integrally formed at the centrifugal clutch 10 end of the engine starting shaft 41, and a plurality of ratchet pawls 60,60,.. biased inwardly by springs 59,59,... are supported on the input member 10a of the centrifugal clutch 10 by pivot shafts 61,61,... in a freely oscillatable manner subject to the action of the springs 59,59,... These ratchet pawls 60,60,... and the ratchet wheel 58 are engaged with each other at the time of coupling together the inboard and outboard halves 4a and 4b of the case 4 and constitute an over-running clutch 62 for starting.

In the following, the functions and operations of the power unit just described will be explained.

In order to start the engine I the engine starting pedal 15 is first repeatedly pressed thereby to impart to the pedal shaft 17 a plurality of swing motions. The repeated movements of the pedal 17 in the direction of the arrow a have each the result first that the actuating arm 23 of the driving clutch member 19 shifts to a lower position along the cam surface 31 on the control lever 24, and, along with this shifting of the actuating arm 23, the driving clutch member 19 is forwarded by the spring force of the clutch spring 22 to be engaged with the driven clutch member 20, whereby further swing motion of the pedal shaft 17 in the direction of the arrow a is transmitted to the driving sprocket 21 through both driving and driven clutch members 19 and 20, and further to the power transmitting chain 43 and the driven sprocket 42. As the result of this transmission of rotational force, the engine starting shaft 41 is rotated and the spiral spring 40 is wound around this engine starting shaft 41, whereby driving force is accumulated in it.

It is to be noted that on each return swing motion of the pedal shaft 17 in the direction of the arrow b due to the restoring force of the return spring 16, since the actuating arm 23 is shifted to a higher position along the cam surface 31, the driving clutch member 19 retracts against the spring force of the clutch spring 22, whereby the engagement between the driving clutch member 19 and the driven clutch member 20 is released, and the rotation of the pedal shaft 17 in the rotational di- rection b is not transmitted to the driving sprocket 21. During this period, the ratchet pawl 48 of the intermittent forwarding mechanism 50 is engaged in the valley between adjacent peripheraI teeth of the driving sprocket 21 so as to prevent the driving sproc21 from rotating in the reverse direction due to the spring force accumulated in the spiral spring 40.

By the repetition of these operations, the driving sprocket 21 is rotated in the direction of the arrow a through a certain definite rotational angle, determined by the second projection 33 provided at one side surface of the driving sprocket 21 contacting the third stop surface 30 of the control lever 24. At this stage the spiral spring 40 is placed in a state of having an adequate and satisfactory spring force accumulation, and pressing the engine starting pedal 15 can be ceased.

Next the brake operating lever 54 is operated to pull the brake wire 57, that is, to move this wire to the left in Figure 4. The bell crank lever 53 is rotated in the clockwise direction in Figure 4 to cause the release lever 51 to pivot anti-clockwise to disengage the ratchet pawl 48 from the teeth of the driving sprocket 21 to free the driving sprocket 21.

Thereby the spiral spring 40 is permitted to release its accumulated force at once so that a powerful rotational torque is applied to the crank shaft 2 through the starting shaft 41 and the over-running clutch 62, whereby the engine I is subjected to a cranking action for starting.

After the engine has started and when the rotational speed of the crank shaft 2 surpasses the rotational speed of the starting shaft 41 imparted by the accumulated force of the spiral spring 40, the ratchet pawls 60,60.... of the over-running clutch 62 slide on the ratchet wheel 58, and, by the time the crank shaft 2 attains its normal idling speed the ratchet pawls 60,60,... have swung outwardly against the set load of the springs 59, 59,....... due to centrifugal action, sufficiently far for the ratchet pawls to be com- pletely separated from the ratchet wheel 58.

On account of this, there is no possibility that, in the ordinary operating conditions of the engine 1, the ratchet pawls 60,60... contact the ratchet wheel 58 to generate noise.

With exertion of this accumulated force from the spiral spring 40, the driving sprocket 21 is subjected to reverse rotation, i. e., it is given a rotation in the direction of the arrow b. When the first projection 32 integrally formed on one side surface of the driving sprocket 21 contacts the second stop surface 29 of the control lever 24, the rotation of the driving sprocket 21 is stopped, whereby a residual spring force can be retained in the spiral spring 40. At this time, also, the control lever 24 receives a part of the accumulated energy in the spiral spring 40 and inertia force of the driving sprocket 21, etc., as impact force which causes the control lever 23 to pivot upwardly, as shown in Figure 4, about the pivot shaft 25. As a result the buffer material 34 is compressed in the buffer cylinder 35 which moves with the control plate 24 because this movement causes the cup-shaped member 37 to abut the contact surface 36 of the outboard half 4b of the case 4. Thus the impact force just mentioned can be tolerated, and each component is protected from damage due to the impact force.

At the time of starting the engine !, the brake mechanism 55 is brought to an actuated condition by the actuation of the brake wire 57 which initiated engine starting, thus al- though the rotational speed of the crank shaft 2 is abruptly increased so that the centrifugal clutch 10 is engaged, even if an output from the crank shaft reaches the rear axle 7 through the driving power transmission mechanism 9, unexpected forward running of the motor-cycle can be prevented. In order to allow the motor-cycle to run forward the brake mechanism 55 is, needless to say, re ! eased.

As described in the foregoing, the power unit is so constructed that the power transmission case 4 is divided into two portions, the inboard half 4a which is directly connected to the crank case 3 of the engine I and the outboard half 4b which is separably joined with the inboard half 4a ; the driving power transmission mechanism 9 to drive the rear axle 7 is disposed in the inboard half 4a ; and the starting power transmission mechanism 44 to start the engine I is disposed in the outboard half 4b. Hence both driving and starting power transmission mechanisms 9 and 44 can be individually assembled and disassembled within the respectively corresponding inboard and outboard halves 4a and 4b of the case 4, and the assembly and main tenancc of the power unit P can be carried out easily and efficiently. On the other hand, since the driving member and the driven member of the over-running clutch 61 for starting, which are mutually engaged at the time of coupling together the inboard and outboard halves 4a and 4b of the case, are provided respectively at the opposing end portions of the starting shaft 41 of the starting power transmission mechanism 44 and the crank shaft 2 of the engine 1, the over-running clutch 62 for starting can also serve as a joint for engaging and disengaging between the driving member and the driven member along with coupling and separation of the inboard and outboard halves 4a and 4b of the case 4.

Hence the overall construction of the power unit becomes simple. Further, since the driving power transmission mechanism 9 in the inboard half 4a of the case 4 is disposed adjacent the crank shaft 2 and the rear wheel Nu,., stress applied to the bearings in the driving power transmission mechanism 9 is minimise with the consequence that the motor-cyc! e can be driven smoothly, and durability of the power unit is high.

Also, as the inner end of the rear axle 7 fitted to the inboard half 4a of the case 4 is supported by the outboard half 4b thereof in a freely insertable and withdrawable manner, and since the inner end of the pedal shaft 17 having the engine starting pedat) 5 at its outer end and fitted to the outboard half 4b of the case 4 is supported by the inboard half 4a thereof in a freely insertable and withdrawable manner, the rear axle 7 and the pedal shaft 17 which are subjected to a particularly large bending load are supported at two points with the consequence that their durability is further improved, and, at the same time, such double-point supporting structures do not in any way hinder the coupling together and separation of the inboard and outboard halves 4a and 4b of the case 4.

Further, as the power unit is so constructed that the spiral spring 40 is wound around the engine starting shaft 41 by the oscillating movement of the pedal shaft 17 to accumulate spring force therein, with the accumulated force of which the engine starting shaft 41 is rapidly rotated to crank the engine I, the motor-cycle engine can be started easily and definitely even by females without requiring them to exert large operating energy. In addition, no expensive component parts such as an electric starting motor are utilised in the power unit, so that the starting device can be provided at a low price.

Moreover, the device is provided with thecontrol lever 24 which is capable of restricting the winding or unwinding of the spiral spring 40 to a definite extent by regulating the range of rotation of the driving sprocket 21 which is interlocked with the starting shaft 41. As a result, the spring 40 can not be excessively wound up. At the same time, a reserved tension can usually be held in the spiral spring 40, which contributes to a reduction in the number of pressing operations usually required of the engine starting pedal for accumulating force in the spiral spring 40.

In addition, since the control plate 24 is supported on the power transmission case 4 through the buffer material 34 so as to absorb shock or impact occuring at the time of limiting the extent of unwinding of the spiral spring 40, breakage of the spring and separation of its hook-shaped ends from their fixing points as already mentioned in the foregoing can be successfully prevented, hence the durability of the device becomes very high.

Furthermore, since the buffer member 34 is subjected to limitation in its compressive deformation in a chamber defined by the buffer cylinder 35 and the cup-shaped member 37 slidably engaged with the cy- linder, it can withstand a high compressive force and can exhibit a very effective and favourable buffer effect to the spiral spring 40 over a long period of time.

Moreover, as the over-running clutch 62 for starting is constituted by the ratchet wheel 58 (provided on the starting shaft 41 connected to the force accumulating source constituted by the spiral spring 40) and the ratchet pawls 60,60... (provided on the side of the crank shaft 2) and as the ratchet pawls 60,60, ... are separated from engagement with the ratchet wheel 58 by centrifugal force when the rotational speed of the crank shaft 2 exceeds a predetermined value, the engine I does not create any frictional resistance by the sliding action of the over-running clutch 62 at the time of the force accunulating operation, so that the operation can be performed lightly, and yet after starting of the engine, a completely disengaged state of the over-running clutch 62 can be attained, whereby the transmission of the reverse load from the crank shaft 2 to the engine starting shaft 41 can be prevented without failure and without any accompanying noise. Also, since the afore-mentioned ratchet pawls 60, 60,... do not bring about any problem in their engagement with the ratchet wheel 58, even if the ratchet wheel 58 performs a slightly eccentric motion, no inconvenience whatsoever is encountered even when there is an error to a slight extent in the c-axial positioning of the crank shaft 2 and the engine starting shaft 41, hence great advantages are afforded in the manufacture of the device owing to broadening of the permissible range of allowance in the machining errors and the assembling errors as well. Further, since the input member 10a of the clutch for power tranmission which is usually provided on the crank shaft 2 is also used for the fitting base plate of the above-mentioned ratchet pawls 60,60,..., the construction of the device can be made simple.

Claims (9)

1. WHAT WE CLAIM IS :- 1. A power unit for a motor-cycle, the power unit comprising : a power transmission case fast with an engine crank case and supporting at its rear end a rear road wheel axle, the transmission case being constituted by an inboard half connected to the crank case and an outboard half separably connected to the inboard half, the rear axle being supported by the inboard half of the power transmission case; a driving power transmission mechanism connecting the rear axle and the crank shaft of the engine ; a pedal shaft having an engine starting pedal connected at one end thereof, this shaft being supported by the outboard half of the power transmission an engine starting shaft adjacent the crank shaft on the same axis as the crank shaft and also supported by the outboard half of the power transmission ; a starting power transmission mechanism connecting the pedal shaft and the engine starting shaft; and a driving member and a driven member of an over-running clutch provided at the opposing ends of the starting shaft and the crank shaft, these members being engaged with each other at the time of coupling together the inboard and outboard halves of the power transmission case.
2. 2. A power unit as claimed in claim 1, in which the inner end of the rear axle is supported by the outboard half of the power transmission case in a freely insertable and withdrawable manner; and in which the inner end of the pedal shaft is supported by the inboard half of the power transmission case.
3. 3. A power unit as claimed in claim 1 or 2, in which the starting power transmission mechanism comprises a driving sprocket rotationally fast via a one-way clutch mechanism with the pedal shaft, a driven sprocket integrally formed on the outer periphery of the starting shaft, and a chain extending around this driving sprocket and this driven sprocket.
4. 4. A power unit as claimed in claim 3 and further comprising a spiral spring connected to be wound up by rotation of the pedal shaft in one direction; a releasable intermittent forwarding mechanism which in operative condition permits rotation of the pedal shaft to wind-up the spiral spring but prevents rotation of said driving sprocket under the action of the spiral spring, and which upon release permits the spiral spring to be effective in the sense to rotate the driving sprocket for engine cranking; a control lever for controlling the extent of winding-up of the spiral spring, and unwinding thereof upon release by the intermittent forwarding mechanism, by contacting projections provided on one side of the driving sprocket; and a buffer member associated with the control lever for absorbing impact when the control lever serves to restrict unwinding of the spiral spring upon its release from the wound state.
5. 5. A power unit as claimed in claim 4, wherein the buffer member is accomodated within a burffer cylinder fixedly provided on the control lever; a cup-shaped member for contacting the power transmission case, or a fixed part connected to the power transmission case, when the control plate is moved by the driving sprocket at the time of absorbing said impact, being mounted on an open end of the buffer cylinder.
6. 6. A power unit as claimed in claim 4 or 5, wherein the intermittent forwarding mechanism includes a ratchet pawl fixedly secured to a pivot supported in a freely rotatable manner by bosses of the inner and outer halves of the power transmission case, and a spring urging this ratchet pawl into engagement with the teeth of the driving sprocket of the starting power transmission mechanism.
7. 7. A power unit as claimed in any one of the preceding claims, wherein the overrunning clutch comprising a ratchet wheel provided on the starting shaft and ratchet pawls which are pivoted for swinging in the radial direction on an input member of a clutch for connecting and disconnecting the driving power which is provided on the crank shaft, so that, when the rotational speed of the crank shaft is at or above a predetermined value these ratchet pawls are disengaged from this ratchet wheel due to centrifugal force.
8. 8. A power unit as claimed in claim 7, wherein the clutch for connecting and disconnecting the driving power is a centrifugal clutch of an internally expanding type.
9. 9. A power unit for a motor-cycle, substantially as hereinbefore described with reference to the accompanying drawings.