Gear shift actuator for an internal combustion engine

FIELD OF THE INVENTION

The present invention relates to a transmission system for an engine and more particularly to an automatic gear shift actuator mechanism for a four stroke single cylinder internal combustion engine.

BACKGROUND OF THE INVENTION

A conventional two wheeled vehicle is powered by an internal combustion engine (hereinafter "engine") generally disposed at a lower half of the vehicle. This engine converts chemical energy into mechanical energy by combustion of air-fuel mixture within a combustion chamber of the engine. The engine, among other components, has a cylinder block comprising a cylinder head atop the cylinder block and receiving a reciprocating piston from the bottom. On combustion of the air-fuel mixture, the piston transfers the energy generated during combustion to a crankshaft through a connecting rod thereby driving the crankshaft. In this way, the reciprocatory motion of the piston is converted to rotatory motion of the crankshaft. The crankshaft is housed inside a crankcase beneath the cylinder block.

In order to set the vehicle into motion, the power supplied to the crankshaft of the internal combustion engine is carried to a wheel of the vehicle, in a controllable way, through a transmission system. The transmission system for the engine of a two wheeled vehicle such as a motorcycle generally comprises of a clutch, a gearbox containing gear train and a drive mechanism connecting the gear box to the wheel. The gear train has multiple gear ratios with the ability to switch between them as the speed of the vehicle varies. When an operator of the motorcycle acts on a clutch lever proximate to the handle bar of the motorcycle, the clutch temporarily disconnects (i.e. disengages) the gearbox from the engine crankshaft before a gear shift operation.

As illustrated in Figure 1, ordinarily the gear shifting operation in the motorcycle wherein the gears are shifted from one stage to another is entirely operated by a gear shift lever 17 manually operated by an operator of the motorcycle and customarily located in a lateral direction of the motorcycle. The gear shift lever 17 turnably supports plurality of gears on parallel shafts in a gear box 12 enabling selecting one of the several gear ratios through a shift fork 11. The gears are in constant mesh and free running when in neutral. The gear shift lever 17 drives the gear shift arm 13 connected to a star index 16 through a pawl 15. The gear shift arm 13 is further supported by a spring 14. After the clutch (not shown) is disengaged, the gear shift lever 17 eventually drives the shift drum 10 through the star index 16 thereby effecting a gear shift and locks free running gears to their shaft by shift fork 11.
This manual gear shifting requires continuous attention by the operator on the speed of the motorcycle and engine r.p.m. Further in heavy traffic, it becomes cumbersome for the operator to shift the gear shift lever at short time intervals to extract the required torque for pulling the motorcycle. Manual gear shifting thus leads to operator uneasiness and pain in the operator's feet thus jeopardising the stability of the motorcycle.

Likewise, in another type of two wheeled vehicles such as a scooter type motorcycle usually devoid of a clutch lever and a foot operated gear shift lever, the power of the engine is transmitted to the rear wheel through a continuously variable transmission system and using a belt drive to transmit the power. However the disadvantage of such a transmission system lies in significant transmission losses and low fuel efficiency in the scooter type motorcycle.

Furthermore, semi-automatic and automatic transmission systems are known in the art for ease of operation of gearshift and clutch actuation. In an automatic transmission system, major system modifications are required for adopting the electric source into the vehicle, most notably crankcase alterations. Hence, for same engine design and capacity, a totally new engine crankcase construction is required. This in effect increases variation and complicates overall design standardisation of concerned components to accommodate the electric source. Hence there is a scope for design change that can accommodate automatic transmission in an engine without any major variation in engine assembly configuration in terms of size and weight and without jeopardising the functionality of the engine.

Therefore the challenge is to design an automatic transmission system for an internal combustion engine accommodating an electrically operated gear shift actuator with minimum engine assembly design alterations and capable to be accommodated with any two wheeled vehicle including a motorcycle or a scooter type motorcycle and irrespective of the engine type, horizontal or vertical. The present invention is directed to overcoming one or more problems as set forth above.

SUMMARY OF THE INVENTION

It is hence an object of the present invention to disclose a transmission system for an internal combustion engine comprising of an automatic gear shift actuation system with appropriate embodiments for selecting available gear ratios for transmission of power, thereby removing the need for manual gear shifting. To this end, an embodiment of the present invention discloses an electrically operated gear shift actuator system for an internal combustion engine for actuating the operation of change of gear ratio comprising of a gear shift motor, a reduction gear box connected to the said gear shift motor for reducing the power received from the said gear shift motor, a power transmission mechanism for transmitting rotational driving force of the said gear shift motor to a shift drum, a shift control unit and a shift position detector for detecting the gear ratio wherein the shift drum, turnably supported by a crankcase, is driven by the said gear shift actuator system to select the desired gear ratio.

Another object of the present invention is to provide a transmission system comprising of an automatic gear shift actuator aimed at providing stress free and less toilsome ride to an operator of the vehicle. It is yet another object of the present invention to provide a transmission system for an internal combustion engine for automatic gear shift actuation and capable to be accommodated with different types of two wheeled vehicles.

The foregoing objectives and summary provide only a brief introduction to the present subject matter. To fully appreciate these and other objects of the present subject matter as well as the subject matter itself, all of which will become apparent to those skilled in the art, the ensuing detailed description of the invention and the claims should be read in conjunction with the accompanying drawings. However, it should be understood that the detailed description while indicating preferred embodiment(s) of the invention, is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features, aspects, and advantages of the subject matter will be better understood with regard to the following description, appended claims and accompanying drawings where:

Figure 1 depicts rear and perspective view of a typical manual gear shift actuation system in the transmission system of an internal combustion engine.

Figure 2 shows a perspective view of a first embodiment of a gear shift actuation . system comprising a rack and pinion system according to the present invention.

Figure 3 shows an exploded view of the first embodiment of the gear shift actuation system according to the present invention in a state where the clutch cover has been removed.

Figure 4 shows an exploded view illustrating the first embodiment of the gear shift actuation system according to the present invention along with the clutch cover.

Figure 5 depicts a second embodiment of the gear shift actuation system comprising a torsion bar according to the present invention.

Figure 6 depicts an assembly view of the second embodiment of the gear shift actuation system according to the present invention.

Figure 7 shows a partial sectional view of the second embodiment of the gear shift actuation system according to the present invention.

Figure 8 shows an exploded view of a third embodiment of the gear shift actuation system comprising a gearing system according to the present invention in a state where the clutch cover has been removed.

Figure 9 shows front view of the third embodiment of the gear shift actuation system according to the present invention.

Figure 10 shows rear exploded view of the third embodiment of the gear shift actuation system according to the present invention along with the clutch cover.

DETAILED DESCRIPTION OF THE INVENTION

The subject matter described herein relates to an electrically operated gear shift actuator system for an internal combustion engine for automatic actuation of the gear shifting operation for transmission of power generated by the engine.

Various other features and embodiments of the gear shift actuation system according to the present invention here will be discernible from the following further description thereof, set out hereunder. In the ensuing exemplary embodiments, the engine is a four stroke single cylinder internal combustion engine. However it is contemplated that the disclosure in the present invention may be applied to any engine capable of accommodating the present subject matter without defeating the spirit of the invention. Further "front" and "rear", and "left" and "right" referred to in the ensuing description for the illustrated embodiments refer to front and rear, and left and right directions as seen from the rear of the engine and looking forward. Furthermore, a "longitudinal" axis refers to a front to rear axis relative to the engine, while a "lateral" axis refers generally to a side to side, or left to right axis relative to the engine.

The present invention is now described in detail in connection with the rendered drawings. The detailed explanation of the constitution of parts other than the invention which constitutes an essential part has been omitted at suitable places.

The gear shift actuator system for an internal combustion engine according to the present invention for actuating the operation of change of gear ratio includes a gear shift motor, a reduction gear box, a power transmission mechanism, a shift control unit and a shift position detector.

Figures 2-4 illustrate a first embodiment of the present invention wherein the gear shift actuator system is positioned laterally to the engine towards the clutch side. The engine contains a cylinder head 21 and a cylinder block 22 incorporating a piston (not shown). It is started by a starter lever placed on the starter shaft 209 or by a starter motor 23. The gear shift motor 201 is mounted to an external surface of a clutch cover 25 and sealed against ingress of oil. The reduction gear box 202 is connected to the said gear shift motor 201 for reducing the power received from the said gear shift motor 201. The power transmission mechanism transmits rotational driving force of the said gear shift motor 201 to a shift drum 210 through a rack and pinion approach wherein the shift drum 210, turnably supported by a crankcase 24, is driven by the said gear shift motor 201 to select the desired gear ratio. The gear shift motor 201 is capable of rotating in both normal and reverse directions and is electrically connected to the shift control unit (not shown). The shift control unit may be programmed to control the direction of rotation of the gear shift motor 201 as well as the time duration of its operation.

The gear shift motor 201 has an output shaft over which a drive gear 203 is mounted. A cone clutch arrangement may be adapted to protect the mechanism from end stops and dog outs. The drive gear 203 is mated with a pinion 205 supported interior to the clutch cover 25. The pinion 205 engages with a driving rack 204 that is slidably supported on the crankcase interior through a pawl 206 present at an anterior portion of the rack 204. The pawl and the rack have a joint between them. The pawl 206 contains partial projections which rotate the shift drum 210 through a star index 207. A stopper 208 is provided to keep the shift drum 210 in the selected gear ratio so that it does not shift automatically. The rack and pinion assembly incorporates a centering spring 214 to ensure return to neutral position. The rack and pinion arrangement during assembly is hidden by a clutch 212 mounted on a countershaft 213 and anterior to the star index 207.

The working of the gear shift actuator system according to the first embodiment is now explained. The shift control unit is programmed to drive the gear shift motor 201 according to the riding conditions (e.g. engine r.p.m or throttle position). The gear shift actuation takes place only after the clutch has been disengaged. The reduction gear box 202 reduces the output of the gear shift motor 201 so as to optimally rotate the drive gear 203. The drive gear in turn rotates the pinion 205 which then slides the rack 204. The resultant force pushes the pawl 206 which turns the star index 207 by a certain degree, the rotation being enough to change the gear ratio. According to an embodiment of the present invention, the star index is to be turned by 72 degrees for effectuating a gear shift resulting into a gear change. The star index is then kept in this position by the stopper 208. The shift position detector detects the current gear ratio and provides input to the shift control unit. The rotation of the gear shift motor 201 can be reversed for a reverse operation. Thus the shift drum 210 will rotate in the same direction as that of the gear shift motor 201. As the shift drum rotates, the gear shift has been actuated and the shift fork (not shown) locks free running gears to their shaft thereby effecting a gear shift.

The gear shift motor 201 and the reduction gear box 202 are supported and secured on an external surface of the clutch cover 25 in a housing 211 in a lateral direction i.e. parallel to crankshaft axis and lateral to the rack axis. The drive gear 203 is interior to the clutch cover 25. A perspective view of the first embodiment along with the clutch cover 25 is shown in Figure 4.

Figures 5-7 illustrate a second embodiment of the gear shift actuator system described in the present invention. The power transmission mechanism transmits rotational driving force of a gear shift motor 201 to a shift drum 210 through a torsion bar 302. In this embodiment, the gear shift motor 201 is supported external to the crankcase 24 and is connected to a reduction gear box 202 through a worm wheel gear set 301. The worm wheel gear set 301 is turned by the gear shift motor 201 and transfers the torque to the gear box 202 through 90 degrees. The shift drum 210 is modified to accommodate the torsion bar 302 so that the gear shift motor 201 directly drives the shift drum 210. The torsion bar 302 acts to cushion the system against high impacts of the automated shifts. A shift control unit to control and run the motor in both directions and a shift position detector to detect the gear position are included as already mentioned in the first embodiment.

The gear shift motor 201 and the torsion bar mechanism described in the second embodiment are present on the left side of the engine i.e. on the crankcase side. Anterior to the crankcase 24, a cylinder block 22 and a cylinder head 21 pertaining to the engine are present.

Figures 8-10 illustrate a third embodiment of the gear shift actuation system wherein the power transmission from the gear shift motor to the shift drum is carried through the use of gearing system comprising a set of gears internal to a clutch cover and supported on crankcase. The gear shift motor 201 and reduction gear box 202 are positioned into a housing 211 external to the clutch cover 25 and laterally on the right side of the engine thus being on the same side as that of starter lever 209. The drive gear 23 of the gear shift motor 201 drives an idler gear big 401 in contact with idler gear small 402 on the crank facing side. A free play mechanism is provided in this embodiment by splitting the idler gear into idler gear big 401 having a slot 406 and idler gear small 402. Idler gear big 401 is driven by the gear shift motor 201. Idler gear small 402 is driven by idler gear big 401 through a pin which is mounted on idler gear small 402 and is inserted into the slot 406.

The idler gear small 402 further drives a driven gear 403 which is meshed with the idler gear small 402. The star index 207 is located anterior to the driven gear 403 and is connected to the shift drum 210 through pins. Thus the driven gear 403 is sandwiched between the shift drum 210 and star index 207. A shift control unit to control and run the motor in both directions and a shift position detector 407 to detect the gear position are included as already mentioned in the first embodiment. The shift position detector 407 is present on the other side of the clutch cover 25 and is connected with the shift drum.

Now, on receiving suitable input, the gear shift motor 201 drives the drive gear 203 which further drives the idler gear big 401. The idler gear big 401 rotates idler gear small 402. The idler gear small 402 rotates the driven gear 403 which further turns the shift drum 210 through the star index 207. The extent of rotation of the star index 207 determines the extent of the gear shift. A stopper 404 is provided below the star index 207 to keep the star index in the chosen position i.e. in the selected gear ratio. The stopper 404 is held interior to the clutch cover 25 through a loaded spring 405.

The gear shift motor in all the aforementioned embodiments may be of 12 V DC rating with 1:32 ratio reduction gear box and its specifications may be varied according to the requirements.

It will be appreciated that the present subject matter and its equivalent thereof offers many advantages, including those which have been described henceforth. The present invention improves operability of the vehicle by removing the need for a gear shift lever thereby increasing the comfort and ease of the operator of the vehicle. Further the automatic transmission system comprising the gear shift actuation system can be accommodated in any engine, horizontal or vertical, and with any two wheeled vehicle containing such an engine. Preferably the present invention works best with a horizontal type engine. Furthermore, the present invention works best with an automatic clutch actuator for disengagement and engagement of clutch before a gear shift operation.

The present invention is thus described. The foregoing description of the invention including the embodiments thereof has been presented for the purpose of illustration and description. It is not intended to be exhaustive nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the disclosed embodiments may be modified in light of the above description. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore the forgoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the appended claims.

We claim:

1. An electrically operated gear shift actuator system for an internal combustion engine for actuating the operation of change of gear ratio comprising of a gear shift motor mounted to an external surface of a clutch cover and sealed against ingress of oil, a reduction gear box connected to the said gear shift motor for reducing the power received from the said gear shift motor, a power transmission mechanism for transmitting rotational driving force of the said gear shift motor to a shift drum, a shift control unit and a shift position detector for detecting the gear ratio wherein the shift drum, turnably supported by a crankcase, is driven by the said gear shift actuator system to select the desired gear ratio.

2. The gear shift actuator system as claimed in claim 1 wherein the said power transmission mechanism comprises a rack and pinion assembly for driving the said shift drum through a pawl and pin arrangement, the said rack and pinion assembly incorporating a cantering spring for ensuring return to neutral position.

3. An electrically operated gear shift actuator system for an internal combustion engine for actuating the operation of change of gear ratio comprising of a gear shift motor mounted to an external surface of a crankcase and sealed against ingress of oil, a reduction gear box connected to the said gear shift motor through a worm gear set, a power transmission mechanism for transmitting rotational driving force of the said gear shift motor, a shift control unit and a shift position detector for detecting the gear ratio wherein a shift drum, turnably supported by the crankcase, is driven by the said gear shift actuator system to select the desired gear ratio; and wherein the said power transmission mechanism includes a torsion bar connected to the said shift drum and driven by the said gear shift motor, the said torsion bar cushioning the system against high impact caused during the gear shift operation.

4. An electrically operated gear shift actuator system for an internal combustion engine for actuating the operation of change of gear ratio comprising of a gear shift motor mounted to an external surface of a clutch cover and sealed against ingress of oil, a reduction gear box connected to the said gear shift motor, a set of gears including an idler gear big, idler gear small and a driven gear supported interior to a clutch cover for transmitting rotational driving force of the said gear shift motor, a shift control unit and a shift position detector for detecting the gear ratio wherein a shift drum, turnably supported by the crankcase, is driven by the said gear shift actuator system to select the desired gear ratio.

5. The gear shift actuator system as claimed in claim 4 wherein the said set of gears includes a gear directly mounted on the said shift drum and indirectly rotated by the said gear shift motor.

6. The gear shift actuator system as claimed in any of the preceding claims wherein the said gear shift motor may be supported on the crankcase or the clutch cover, either horizontally or vertically or through a predetermined angle.

7. The gear shift actuator system as claimed in any of the preceding claims wherein the motor may be of 12 V DC rating with 1:32 ratio reduction gear box.

8. An internal combustion engine of any type including a horizontal internal combustion engine comprising a gear shift actuator system as claimed in any of the preceding claims.

9. A gear shift actuator system for an internal combustion engine substantially as herein described and illustrated with reference to the accompanying drawings.