FIELD OF THE INVENTION
This invention relates to a transmission system applicable to vehicles.
BACKGROUND TO THE INVENTION
A wide range of vehicles are available for transport of goods. Among these are three and four wheel vehicles which may be compact and of quite small size, possibly being adapted to carry only one person who drives the vehicle to pick up and drop off goods as required. Such vehicles may be termed "goods carriers".
The demand for compactness arises from the conditions in which the vehicle will be used. It is quite possible that the vehicle will need to operate in narrow streets in crowded areas and compactness is essential to effective goods distribution using such vehicles. The demand for compactness also calls for a transmission system that is simple and compact in configuration. Furthermore, the cost of the transmission must be maintained as low as possible.
Compactness and cost of a transmission may be impacted by the arrangements made for inclusion of a reverse gear. Previously, an attempt has been made to provide access to a reverse gear - in vehicles for off the road use - through provision of primary and auxiliary transmissions, the primary transmission possibly taking the form of a motorcycle transmission which is not provided with a reverse gear. Such a system is disclosed in US Patent No. 4,620,453, assigned to Yamaha, which describes the practice to employ auxiliary transmissions having their input shafts driven by the primary transmission output shaft and which include either plural speed ratios and/or a reversing gear. US 4,620,453 provides a primary transmission having a first housing accommodating an input shaft, an output shaft and first shifting means for controlling the rotational relationship between the input shaft and the output shaft. The first shifting means comprises a first shifting drum that is supported for rotation about a first axis and means responsive to the rotation of the first shifting drum for changing the rotational relationship between the input and output shafts. The auxiliary transmission has a second housing accommodating an input shaft that is driven by the primary transmission output shaft and an output

shaft. Second shifting means are provided for controlling the rotational relationship between the input and output shafts of the auxiliary transmission and this shifting means comprises a second shifting drum supported for rotation about a second axis and means responsive to rotation of the second shifting drum for changing rotational relationship of input and output shafts of the auxiliary transmission. This is a complex arrangement with multiple components in terms of shifting drums and shift levers and it may not be suitable for applications which require simpler and lower cost systems. The off the road application to which this transmission system is addressed is also contrastable with the goods distribution application which has a greater requirement for cost reduction and compactness.
It is an object of the present invention to provide a transmission system accommodating a reverse gear which is more readily applicable, than currently available transmission systems, to small vehicles such as goods carriers.
SUMMARY OF THE INVENTION
With this object in view, the present invention provides a transmission system with reverse gear comprising:
a housing;
an Input shaft provided with an input reverse gear; and
an output shaft provided with an output reverse gear;
wherein the input and output shafts are located within the housing and a dog clutch assembly, also accommodated within the housing, is used for reverse gear selection by causing driving engagement of the input reverse gear to the output shaft when an operator of the transmission selects reverse gear.
The input and output shafts, as well as the dog clutch assembly, are accommodated within the same housing greatly assisting the objective of compactness and lower costs important to applications such as goods distribution. Plural housings are not required and this may facilitate servicing.

The dog clutch assembly couples the input and output shafts together, when required, by interference rather than friction. The clutch provided for reverse gear may equally be defined as a dog clutch selector. A dog clutch selector is a sliding mechanism which is splined to the output shaft. Teeth on the hub of the dog clutch fit into splines within the output shaft forcing it to rotate with that shaft. When reverse gear is selected by an operator of the vehicle, including the above transmission system, an actuator - typically a fork selector provided for reverse - pushes the dog clutch such that the input reverse gear is drivingly engaged to the output shaft reversing direction of rotation of the output shaft and accordingly implementing reverse of the vehicle. This differs from conventional practice where reverse gear is implemented not through a constant mesh system but rather through an idler gear which slides between reverse input and output gears when reverse gear is selected. The idler gear teeth mesh with both input and output reverse gears such that the direction of rotation of the output shaft is reversed. In this case the idler is in constant mesh with the reverse input and reversed output gears.
A further advantage arising from use of the dog clutch selector is that the stroke length required for engagement of reverse gear is substantially less than the stroke length required for the reverse idler of a reverse idler type transmission, typically used in cars, to engage or disengage reverse input and output gears to implement reverse. Preferably, stroke length is less than half that required for a reverse idler type transmission and more preferably, less than a third that required for a reverse idler type transmission to implement reverse gear. The reduction in required stroke length greatly assists achievement of the object of transmission system compactness.
A still further advantage may be obtained by avoidance of the chamfering of reverse gear teeth ends as commonly used in car type reverse systems. While this may cause some level of harshness on movement into reverse gear, reverse is not implemented as frequently as a fonward gear; so the harshness level (if encountered) will be acceptable functionally.
The transmission system is advantageously configured so as to avoid unintentional selection of reverse gear by an operator of a vehicle incorporating it. Unintentional

selection of reverse gear is a safety hazard and highly likely, in addition, to cause damage to the transmission system. To this end, the transmission system includes a safety means to prevent the operator from unintentionally actuating the reverse gear whenever a forward gear state has been selected. In addition, the safety means prevents selection of reverse gear through the same operator motion as required for any of the forward gears. The operator must select reverse gear through a different motion and/or actuation of a reverse actuation safety means confirming that reverse gear is to be selected. The safety means may comprise a lock - whether mechanical, electrical or electro-mechanical - required to be disengaged when reverse gear is selected, the lock being disengaged when the operator presses a button or switch allowing a gear lever for gear selection to be moved into the reverse gear position. The configuration of the transmission system to avoid unintentional selection of reverse gear forms a further aspect of the present invention.
The transmission system includes forward input and output gears which may be implemented in accordance with a constant mesh or drum shift system. Any number of forward gears or transmission ratios may be selected though 4- and 5- speed systems would typically be preferred. A drum shift system, as commonly implemented in motorcycle transmissions, is preferred. In a drum shift system, gear is shifted in accordance with rotation or indexing of a shift drum in response to gear selection by an operator using an actuator such as a gear lever. Such transmissions are typically lightweight, compact and low cost and are preferred. Drum shift transmissions may, if desired, be implemented in accordance with the disclosures of the Applicant's co-pending Indian Provisional Patent Application Nos. 2281/CHE/2007 and 2282/CHE/2007 filed 10 October 2007 and the contents of which are hereby incorporated herein by reference.
If transmission systems of drum type are selected, the reverse actuation safety means may prevent rotation or indexing of the drum shift towards the reverse gear position. Absent such a safety means, movement into reverse - particularly when a series type gear lever or shift is used - could readily occur. A lock may be used to achieve this by positive stopping of rotation or indexing of the drum shift towards the reverse gear position. For example, the lock may comprise a plunger or pin - such a> a spring loaded pin or plunger - which may engage with a cam groove of the

drum, preventing rotation of the drum until released by the operator. For example, the gear lever may be moved with a specific motion which releases the lock or pin. This may require a lifting motion of a sleeve mounted on the gear lever which releases the lock and allows reverse gear to be selected when safe to do so.
The transmission system of the present invention is applicable to a variety of vehicles and is especially well adapted to 3 and 4 wheel vehicles used as goods carriers.
BRIEF DESCRIPTION OF THE DRAWINGS
The transmission system of the present invention may be more fully understood from the following description of a preferred embodiment thereof made with reference to the accompanying drawings in which:
Figure 1 is a side sectional view of a transmission system in accordance with one embodiment of the present invention;
Figure 2 is a top sectional view of the transmission system; and
Figure 3 is a schematic of a gear lever for gear selection using the transmission system of Figures 1 and 2.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
Referring first to Figures 1 and 2, there is shown a transmission system for a three wheeled goods carrier (not shown). The transmission system is a 4 - speed transmission of drum type (as typically used in motorcycles) in which gear or transmission ratio selection occurring as a function of rotation or indexing of the drum shifter 13 in response to movement of a gear lever 30 by the operator of the goods carrier. The transmission system has a housing 10, an input shaft 11 and an output shaft 12. Input shaft 11 carries an input reverse gear 51. Further detail of the gear lever 30, which is of series type, is shown in Figure 3.

Drum shifter 13 is provided with three cam grooves 20, 21 and 22 on its peripheral surface. Cam groove 20 is provided for shifting gears to 1*' and 2"*^ gear positions. Cam groove 21 is provided for shifting gears to 3'^'^ and 4"^ gear positions. Cam groove 22 is provided for reverse gear operation.
Reverse gear is selected using a dog clutch assembly or selector. The construction of the reverse gear assembly can be explained as follows. An input reverse gear 51 is integrally provided on input shaft 11, the said input reverse gear 51 being in constant mesh with idler gear (not shown). The said idler gear may be mounted freely on a shaft (not shown). This idler gear is in constant mesh with reverse output gear 52. Reverse output gear 52 is freely mounted on output shaft 12 through bearing 53 and bush 54. The said output reverse gear is provided with (may be machined) plurality of elliptical (say six numbers) holes 62. A reverse hub or hub gear 55 is rigidly mounted on the output shaft 12, through splines 56 provided on its inner periphery. The said reverse hub gear 55 is provided with outer splines 57 which are slidably in contact with reverse sleeve 58. The reverse sleeve 58 is provided with plurality (say three numbers) of dog teeth 59 and the reverse sleeve 58 is free to slide over the splines 57. The said sleeve 58 is provided with a circular disc like structure 60 on its outer periphery. The said disc like structure 60 is engaged with a substantially 'U' shaped structure of shifter fork 61, provided for gear engaging and disengaging purpose. When the operator or rider operates shifter fork 61, this leads movement of the sleeve 58 by means of disc 60. Due to this movement, the dog teeth 59 on the sleeve engages in corresponding elliptical holes 62 provided on reverse output gear 52. As reverse output gear is engaged, the power is transmitted from output gear 52 to reverse sleeve 58 from where the power is transmitted to reverse hub 55 and finally to output shaft 12. The direction of rotation of output shaft 12 Is opposite in reverse gear with respect to output from the forward gears. Thus in this way the transmission of power in reverse gear is achieved. The stroke of shifting the reverse sleeve 58 is very less as compared to other shifting of forward gears thus it benefits in achieving the compactness of the transmission system. Due to this short stroke, there arises need for providing a lock to prevent engaging of reverse gear accidentally.
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To prevent the accidental engagement, additional cam groove 23 is provided on the peripheral surface of drum shifter 13. This additional cam groove 23 may accommodate a reverse actuation safety means taking the form of a lock mechanism preventing rotation of drum shifter 13 towards the reverse gear position unless disengaged by the operator of the goods carrier. The neutral position in grooves 20, 21, 22, 23 is shown by circles 24, 25, 26, 27 respectively. The groove 23 ends at its neutral position 27.
The lock mechanism 40 for the reverse gear consists of plunger 14, coil spring 15, bush 16, cover 17, connection means 18 and steel wire 19. Plunger 14 includes a pin like structure which is engaged with cam groove 23 preventing rotation of drum shifter 13 towards reverse gear unless first disengaged from cam groove 23 by a positive action of the operator of the goods carrier. Coil spring 15 biases the plunger 14 towards this engaged "safe" position. The lock mechanism 40 therefore provides a positive stopper which enhances the safety of the transmission and goods carrier.
Figure 3 shows the gear lever or shifter 30 which is located in the cockpit of the vehicle. It consists of gear lever or shifter 30, of series type and a sleeve 31 for connection with wire 19, preferably made of steel. Wire 19 is connected to the transmission housing 10 and the drum shifter 13 through linkages which enable gear selection at the option of the operator of the goods carrier. Conventional forms of linkage, understood by those skilled in the transmission system art, may be employed.
The general working is explained as follows, when the operator drives the vehicle in any of the forward gears and intends to down shift gear and come to neutral position, the operator may unintentionally shift gear to the reverse position and damage to the transmission and engine, with accompanying safety hazards, may occur. However, the lock mechanism 40 prevents this because, when a forward gear is selected, plunger 14 is engaged in cam groove 23. The cam groove 23 ends at neutral position 27 so that when the operator tries to index or rotate the drum shifter 13, the engagement of plunger 14 with cam groove 23 will positively stop the drum shifter 13 from indexing and thus the reverse gear will not be selected accidentally.

When the driver intentionally selects reverse gear, sleeve 31 must be lifted to move gear shifter lever 30 Into the reverse position, so that the steel wire 19 connected to plunger 14 will lift it upwards against the bias of coil spring 15. This will disengage plunger 14 from cam groove 23 and indexing of the drum shifter 13 into the reverse position will occur. Thus shifting of reverse gear is possible only when the plunger 14 is disengaged from cam groove 23. The driver may be provided with some indication that reverse gear has been engaged by a light or sound alarm. The gear lever 30 may also show that reverse gear has been selected by other indicia. When the operator of the goods vehicle once again shifts gear to neutral or any of the fonward gears, a downward movement of gear lever 30 will accomplish this, such downward movement causing the coil spring 15 to again engage plunger 14 with cam groove 23. Any indicia indicating reverse gear selection may then be ceased.
Modifications and variations to the transmission system of the present invention may be apparent to skilled readers of this disclosure. Such modifications and variations are deemed to be within the scope of the present disclosure. For example, the transmission system may have 5 gears or transmission ratios and would work in the same manner as described above. Applicability of the transmission system to vehicles other than goods carriers may also be contemplated.

WE CLAIM :
1. A transmission system with reverse gear comprising:
a housing;
an input shaft provided with an input reverse gear; and
an output shaft provided with an output reverse gear;
wherein the input and output shafts are located within the housing and a dog
clutch assembly, also accommodated within the housing, is used for reverse
gear selection by causing driving engagement of the input reverse gear to the
output shaft when an operator of the transmission system selects reverse
gear.
2. The transmission system of claim 1 wherein the input shaft and output shaft, as well as the dog clutch assembly, are accommodated within the same housing.
3. The transmission system of claim 1 or claim 2 wherein the dog clutch assembly is a dog clutch selector splined to the output shaft forcing a dog clutch to rotate with the output shaft and, when reverse gear is selected, an actuator pushes the dog clutch such that the input reverse gear is drivingly engaged to the output shaft reversing direction of rotation of the output shaft and implementing reverse.
4. The transmission system of any one of the preceding claims wherein the actuator is a fork selector.
5. The transmission system of any one of the preceding claims wherein input and output reverse gears are not chamfered.
6. The transmission system of any one of the preceding claims including safety means to prevent an operator unintentionally actuating the reverse gear when a forward gear state has been selected.
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7. The transmission system of claim 6 wherein the safety means prevents selection of reverse gear through the same operator motion as required for any of the forward gears.
8. The transmission system of claim 6 or 7 wherein selection of reverse gear requires actuation of a reverse actuation safety means confirming that reverse gear is to be selected.
9. The transmission system of any one of claims 6 to 8 wherein the safety means is a lock required to be disengaged when reverse gear is selected.
10. The transmission system of any one of the preceding claims including forward input and output gears which are implemented in accordance with a constant mesh or drum shift system.
11. The transmission system of claim 10 wherein the transmission is a drum shift system.
12. The transmission system of claim 10 or 11 is a 4- or 5- speed system.
13. The transmission system of claim 11 or 12, as dependent from claim 8, wherein the reverse actuation safety means prevents rotation or indexing of the drum shift towards the reverse gear position.
14. The transmission system of claim 13 wherein the reverse actuation safety means is a lock for positive stopping of rotation or indexing of the drum shift towards the reverse gear position.
15. The transmission system of claim 14 wherein the lock comprises a plunger or pin engaging with a cam groove of the drum shift preventing rotation of the drum until released by the operator.
16. The transmission system of claim 15 wherein the pin is a spring loaded plunger or pin.
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17. The transmission system of claim 15 or 16 wherein the plunger or pin is
released by moving a gear lever in a specific motion.
18. The transmission system of claim 17 wherein a sleeve is mounted on the gear lever and a lifting motion of the sleeve releases the lock.
19. A vehicle comprising a transmission system as claimed in any one of the preceding claims.
20. The vehicle of claim 19 being a 3 or 4 wheel vehicle such as a goods carrier.

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