FORM2
THE PATENTS ACT, 1970
(39 of 1970)
and Patent Rules 2003
PROVISIONAL SPECIFICATION
(See section 10; rule 13)
1. Title - SPEED CHANGE MECHANISM (Gear-box)
2. Applicant - MAHINDRA & MAHINDRA LTD
1, GATEWAY BUILDING, APOLLO BUNDER, MUMBAI -400001. AN INDIAN COMPANY.
The following specification particularly describes the nature of this invention and the manner in which it is to be performed.
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Field of Invention
The present invention relates to speed change mechanism (gear-box) generally used in automobiles, earthmoving and off-road vehicles. More particularly the invention relates to a gear-box incorporated in off-set power transmission system. The gear-box of the present invention comprises main (input), intermediate and output shaft, gear pairs, shifting couplings, shifting linkages, bearings and housing, wherein said shafts, gear pairs, shifting couplings and shifting linkages are so configured that additional torque and speeds can be achieved through conventional gear-box.
Background of the Invention
In automobile vehicles running on road or off-road and earthmoving vehicles, a speed change mechanism (Gear-box) is provided in-between engine and final drive (differential) to avail torque and speeds suitable for various operations and applications. Therefore the speed changing device is continually subjected to demand for more power transmission and therefore more number of speeds. Conventionally Gear-box is provided with 3, 4 and 5 to N number of speeds. In order to transmit more power with increased number of speeds, it is necessary to increase the centre distance between the shafts, thus necessitating the use of larger housing which takes up more space in the overall vehicle design, and large and more number of gears. Increasing centre distance also involves increased load on the bearing, so that bearing design may become the limiting problem in the gearbox design. Further, with more number of gears and their large size, the pitch line speed will increase, which increases noise in operation, and this noise is a serious problem in gearbox design. Finally, above design changes in conventional gearbox ultimately increase fore and aft length of overall vehicle design. The increased fore and aft length increases distance between front and rear wheels of the vehicle. This impairs the small turning performance
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of the vehicle. Plus every additional speed requirement in conventional gearbox involves huge development time and cost.
More importantly in case of vehicle like tractor, a separate creeper mechanism is provided in conventional transmission system to provide a much lower speed option as compared to the conventional speeds. A creeper mechanism is nothing but a separate 2-speed gear-box, which needs to be provided in the conventional transmission system, but which again has similar problems with automotive speed change mechanism as mentioned above.
US patents US 5,178,039 by Shirley et. al. dated Jan 12 1993, US 4,862,765 by Schaeter et. al. dated Sep 5 1989, US 4,706,519 by Beln dated Nov 17 1987 and US 4,373,409 by Benedek et. al. disclose transmission system especially with creeper speeds in a vehicle like tractor. Here also a separate 2-speed gear-box is provided in power transmission system, which has above mentioned constrains / problems of wheel base and cost impact.
European patent EP 0 217 639 B1 by Uchiyama et al. dated Sep 25 1986 discloses power transmission system of a part-time four-wheel drive motor vehicle having a sub-transmission for providing a high speed range and a low speed range. In this power transmission system, an additional ultra low speed is achieved with the combination of low, first and four-wheel drive speed gear through common gear shifter that of main speed transmission. Here an ultra low gear shifting system is combination of mechanical, electrical and pneumatic operation of shifting mechanism.
This is combination of main, sub and four-wheel drive transmission system, which further complicates the shifting system. Also it leads to increase in cost, poor maintainability and serviceability, because of the combined operation of mechanical, electrical and pneumatic shifting mechanisms.
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Need of the Invention
Therefore, need exists for a speed change mechanism (gear-box), which will transmit an additional torque and thereby provide an additional speed, may be creeper speed through conventional speed change arrangement of an off-set
power transmission system. Thus eliminating problems associated with fore and aft length of transmission system and need of separate or entire development of a new transmission system.
Objects and Advantages of the present Invention
A primary objective of the present invention is to propose a speed change mechanism, which will transmit an additional torque and thereby provide an additional speed through conventional speed change configuration of an off-set power transmission system.
Another object of this invention is to propose creeper speeds through existing speed change configuration of a tractor, thereby eliminating need of an additional creeper mechanism (separate 2-speed gear-box) and problems associated with the same.
Another object of this invention is to propose a common gear shifting system for an additional creeper speed in line with main or sub-transmission system of a vehicle. Therefore 1st / LOW, 2nd / HIGH, 3rd / MEDIUM and 4th / CREEPER speed can be operated through common shifting system of main or sub-transmission system.
A still further object of this invention is to provide an additional speed, may be creeper speed in conventional speed change mechanism without increasing fore and aft length of the transmission system, thereby eliminating need of new development of transmission system and problems associated with the same.
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Further objects and advantages of the present invention will become apparent from consideration of the figures and detailed description of preferred embodiments.
Brief Description of the Drawings
Figure 1 is a schematic view of gearing and shifter block arrangement in
conventional 3-speed change mechanism in an off-set power transmission
system.
Figure 2 is a schematic view of gearing and shifter block arrangement in neutral
condition, for an additional torque and speed in conventional 3 speed change
mechanism in one embodiment of this invention.
Figure 3a, 3b, 3c and 3d are schematic views of gearing and its shifter block
arrangement in the first, second, third and additional fourth speed as per the first
embodiment of this invention shown in figure 2.
Figure 4 is a schematic view of a power transmission system in second
embodiment of this invention for creeper speeds in a vehicle like tractor.
Figure 5 is a schematic view of gearing mechanism for an additional speed in
conventional 3 speed change mechanism in another embodiment of this
invention in combination with reverse drive.
Figure 6 is a schematic view of a gear shifting pattern for conventional 3 speed
change mechanism as illustrated in figure 1.
Figure 7 is a schematic view of a gear shifting pattern for the first and second
embodiment of this invention shown in figure 2 and 4.
Figure 8 is a schematic view of a gear shifting pattern for another embodiment of
this invention shown in figure 5.
Detailed Description of the Preferred Embodiments
Referring to figure 1, which is the schematic view of gearing arrangement in conventional 3 speed change mechanism (1) in off-set power transmission
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system. The arrangement consists of six constant mesh gears (G1 to G6), two shafts S1 and S2 namely input shaft and output shaft, two gear engagement couplings C1 and C2 and respective coupling shifting linkages namely forks, rails, shifter blocks (B1 and B2), etc. Gears G1, G3 and G6 are rigidly mounted on main shafts S1 and counter shaft S2 respectively through splines, while the remaining gears G2, G4 and G5 are mounted on the same shafts through bearings. In this arrangement when couplings C1 and C2 engage with respective gear pairs G1 and G2 or G3 and G4 or G5 and G6, three different speeds are available at output shaft S2. The shifter block arrangement and gear shifting pattern with this conventional three speed gearing arrangement is as shown in figure 1A and 6.
Speed change mechanism (Gear-box) for off-set power transmission system according to the present invention is explained with reference to figure 2, which is a schematic view of gearing arrangement in neutral condition. The gear-box configuration in this arrangement (2) is similar to conventional system (1) as described in figure 1, whereas gears (G1 to G6), input and output shaft (S1 and S2), engagement couplings (C1 and C2), shifter blocks (B1 and B2) and gear shifting linkages are so configured that an additional speed is achieved over conventional gear-box design (1). The gear-box arrangement (2) consist of gears G1 and G4, compound gears G2 and G3, input, intermediate and output shaft S1, S2 and S3, engagement couplings C1 and C2, shifter blocks B1 and B3 and gear shifting linkages. Gears G1, G3 and Gear G4 are freely mounted on input shaft S1 and output shaft S3 respectively through bearings, while gear G2 is fixedly mounted on shaft S2 having its free end supported in output shaft S3. Gear G2 and G3 are compound gears, wherein gear A and B of different pitch are connected to each other and rotating with the same speed. Gear engagement coupling C1 and C2 are fixedly mounted on input and output shaft S1 and S3 respectively.
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Neutral condition of this gear-box (4) is shown in figure 2, wherein the coupling C1 is in neutral i.e. center position of gear G1 and Gear A of compound gear G3, while the coupling C2 is in engagement with gear B of compound gear G2. In this situation no power is transmitted through gears G1, G2, G3 and G4 and therefore the output shaft S3 will be in stationary condition as coupling C1 is also in neutral condition.
1st / LOW speed of this gear-box (2) is shown in figure 3A, wherein , the coupling C1 is shifted to engage gear G1 by means of shifter block B1 and gear shifting linkages, while the coupling C2 is in engagement with gear B of compound gear G2. In this situation power is transmitted from input shaft S1 to output shaft S3 through coupling C1, gear G1, G2 and coupling C2.
2nd / HIGH speed of this gear-box (2) is shown in figure 3B, wherein the coupling C1 is shifted to engage gear A of compound gear G3 by means of shifter block B1 and gear shifting linkages, while the coupling C2 is in the same position, that is in engagement with gear B of compound gear G2. In this situation power is transmitted from input shaft S1 to output shaft S3 through coupling C1, gear A of compound gear G3, gear B of compound gear G2 and coupling C2.
3rd / MEDIUM speed of this gear-box (2) is shown in figure 3C, wherein the coupling C1 remains in the same position that is in engagement with gear A of compound gear G3, while the coupling C2 is shifted towards gear G4 by means of shifter block B3 and shifting linkages. In this condition power is transmitted from input shaft S1 to output shaft S3 through coupling C1, gear A of compound gear G3, gear G4 and coupling C2.
Now in addition to above 3 speeds namely 1st / Low, 2nd / Hi, and 3rd / Medium, the 4th speed may be creeper speed that can be achieved in case of vehicles like tractor. This 4th speed can be achieved by shifting coupling C1 to engage gear G1, while the coupling C2 remains in engagement with gear G4 as shown in
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figure 3D. In this condition an additional 4th speed is transmitted from input shaft S1 to output shaft S3 while passing through coupling C1, gear G1, compound gear G2, compound gear G3, gear G4 and coupling C2. In this way a triple (three times) speed reduction is obtained. Hence speed available at output shaft S3 is even lower than that of 1st / low speed as shown in figure 3A.
The shifting system for engaging couplings C1 and C2 comprises of forks, rails, shifter blocks B1 and B3, cam link and shifting lever. The position of shifter blocks B1 and B3 for the above four speeds are shown along with the respective schematic gearing arrangements.
Most importantly, in tractor applications creeper speeds are required for operations requiring exceptional low speeds. These creeper speeds can be achieved through the second embodiment of this invention as shown in figure 4. In this arrangement four speeds are achieved through main speed change transmissions (3), which are transmitted to the input shaft S1 of auxiliary speed change transmission (4). Therefore when the auxiliary speed change transmission (4) is as per the first embodiment of the invention as shown in figure 2, additional four speeds than conventional system could be available at the output shaft S3. Hence otherwise need of an additional creeper mechanism (a separate 2 speed gear-box) as a part of conventional transmission system and problems associated with the same can be eliminated.
Since the entire gear shifting of an auxiliary speed change mechanism (4) can be accomplished by a single gear shifting lever, therefore no separate shifting system is required for achieving creeper speeds. Also requirement of a separate interlocking arrangement between auxiliary speeds and creeper speed is eliminated due to the common shifting lever.
Figure 5 depicts gearing arrangement when reverse drive is integrated as another embodiment of the present invention. It consists of additional gear R1,
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integral with engagement coupling C1 and a compound gear R2. Gear R1 meshes with gear A of compound gear R2 and gear B of compound gear R2 meshes with gear B of compound gear G2. In this case power is transmitted from input shaft S1 through coupling C1, gear R1, gear R2A, gear R2B, gear G2B and finally output shaft S3 through coupling C2. In this arrangement neutral position that of figure 2 is replaced by reverse position. Therefore additional four reverse speeds that of main speed change transmission system (3) can be achieved. Here also like creeper mechanism, need of a separate shifting system and problem associated with forward / reverse shuttle can be eliminated.
While the above description contains much specificity, these should not be construed as limitation in the scope of the invention, but rather as an exemplification of the preferred embodiments thereof. Many other variations are possible depending upon various embodiments of the present invention.

Date: Feb 28th ,2007

Mr. GAUTAM V NAGWEKAR
(Chief Operating Officer )