Title of Invention

A GEAR SHIFT DEVICE FOR A SYNCHROMESH TRANSMISSION SYSTEM

Abstract

A gear shift device for a synchromesh transmission system comprising a single shifter shaft for shifting the gears by shifter forks supported on the said shaft,said shifter shaft having three gear shiftactuation pins lying on the same plane;shifter forks held in their respective neutral positions by shifter sleeves,said shift6er forks having integral yokes and said actuation pins being positioned such that they lie in the center of their respective yoke's plane;ball catch profiles provided on thye shifter shaft,one of t6he ball cdatcvhes for the neutral and the other ball catches for the gears in the engaged position;a spring loade3d ball lying on the neutral ball catch profile.

Full Text

This invention relates to a gear shift device for a synchromesh transmission system. The device proposed herein uses a single central shifter/select shaft for shifting the gears by shifter forks supported on the shifter shaft and operated when the shifter shaft is actuated. The function of a gearbox is to alter the available torque and speed of the engine according to requirement and then pass it on to the other components of the drive train. The synchromesh gearbox has two sets of gears, which are in constant mesh. They are the drive gears on the input shaft, which get their drive from the output of the engine and the driven gears of the counter shaft that are driven by the input shaft gears. Although the two shaft assemblies are in constant mesh the appropriate speed ratio is selected by the driver by moving the shifter sleeve of the synchronizer unit and engaging it with the desired gear. The existing system has shifter shafts for gear selection ranging from 4 shafts to 2 shafts both inclusive of a guide shaft. The movement of the shifter shaft is in linear direction only. They move from mean position or neutral position towards the chosen gear. The internal shift mechanism has a shift select assembly that helps to select the desired plane and gear. This mechanism is driven by the external shift mechanism, which is actuated by the driver. Shifter shafts are machined with interlock and detent notches. In the existing system the major drawback is the number of components used which increases the manufacturing cost and time. It also increases the overall dimensions of the gear box housing due to the space required for mounting of the shifter and shift/select assembly. It again increases die assembly time. To cope with the above problem, this invention proposes to reduce the number of shifter shafts to a minimum, while performing the same functions of shifting and selecting the desired gear. The proposed device should also be such that it does not allow the shifting of two gears at the same time. The device should also be such mat it is able to lock the gear in the engaged position and not allow it to slip back to neutral. The gear shift device for a synchromesh transmission system, according to mis invention, comprises a single shifter shaft for shifting the gears by shifter forks supported on the said shaft, said shifter shaft having three gear shift actuation pins lying on the same plane; shifter forks held in their respective neutral positions by shifter sleeves, said shifter forks having integral yokes, and said actuation pins being positioned such that that they He in the centre of their respective yoke's plane: ball catch profiles provided on the shifter shall, one of the ball catches for the neutral and the other ball catches for the gears hi the engaged position, a spring loaded ball lying on the neutral ball catch profile. This invention will now be described with reference to the accompanying drawings which illustrate, by way of example, and not by way of limitation, one of various possible em b o dun en ts th ereo f, Fig. 1 illustrating the known internal gear shift mechanism of five speed synchro mesh transmission Fig 2 illustrating the single shaft called the central shaft/select shaft and gear shift actuation pins. Fig. 3 illustrating the shift mechanism engaged in first gear. Fig. 4 illustrating the shift mechanism engaged in second gear. Fig. 5 illustrating the shift mechanism engaged in third gear. Fig. 6 illustrating the shift mechanism engaged in fourth gear. Fig. 7 illustrating the shift mechanism engaged in fifth gear. Fig.l illustrates a gear shift mechanism in a typical 5 speed gear box with three shifter shafts SI, S2 and S3 and one gear shift guide shaft S4. Yokes Yl, Y2 and Y3 and forks Fl, F2 and F3 are fastened to the shifter shafts. The gear shift/select mechanism comprising the gear shift/select shaft GS and gear shift/select assembly GA is connected to the yokes Yl, Y2 and Y3 on one side and gear shaft control shaft GO'S on the other side. When the driver operates a gear, the gear control shaft rotates or moves axially. This actuates the gear shift/select shaft GS to select and shift the desired gear. When the gear shift/select shaft GS moves axially the plane is selected and when the gear shift/select shaft rotates at an angle, the desired gear is engaged. As the shifter shaft moves, a spring-loaded detent ball DB moves ont of its neutral detent notch DN and drops into the detent notch DN for the selected gear. The same procedure is repeated to engage the other gears. This invention therefore proposes a device which provides a single shift/select shaft, which will be able to shift as well as select all the gears in the synchromesh gear box, one at a time. With a view to attaining the aforesaid object, a single shaft called the central shift/select shaft CS is provided. The driver by using the known external shift mechanism actuates the central shifter shaft. The central shift/select shaft CS consists of 3 projections called the gear shift actuation pins PI, P2 and P3 which lie on the same plane. Refer Fig.2. The Central shift/select shaft CS guides the forks Fl, F2 and F3. The forks are not fastened to the shaft CS. They are held in their respective neutral position by the shifter sleeves SL1, SL2 and SL3. The forks Fl, F2 and F3 have integrated yokes. The gear shift actuation pins PI, P2 and P3 are positioned in such a way that they lie in the center of their respective yoke's plane. Only the 3rd /4th gear shift actuation pin P2 lies inside the yoke of the 3rd /4th fork F2 in the neutral position. Detent Notches DN are machined at three places on the central shift/select shaft. The central detent notch is for neutral and the other 2 detent notches are for gears in engaged position. A spring loaded detent ball DB is placed in the housing and lie on the central detent notch DN of the gear shift/select shaft CS in neutral position. Fig.3 illustrates the shift mechanism engaged in first gear position 01. When the driver desires to shift to the first gear Gl, the central shift/select shaft CS rotates 90 degrees with the gear shift actuation pin PI moving towards the yoke integrated with the first/second fork Fl. Once the actuation pin PI is inside the yoke Fl, the shaft CS moves in linear direction towards the Ist gear side 01. As it overcomes the detent mechanism DB and moves towards the 1st gear 01 it forces the fork Fl to move and engage the first gear Gl after synchronization. As the first gear Gl is engaged the detent ball drops into the detent notch DN on the central shift/select shaft for the engaged gear position. Thus the central shift/select shaft CS h locked in the desired gear. Fig. 4 illustrates the shift mechanism engaged in second gear G2 position. When the driver desires to shift to second gear position he moves from lrtgear Gl to 2Bi gear G2 in the same plane. The central shift/select shaft CS moves linearly in the opposite direction of the first gear Gl moving the fork Fl along with it The detent hail DB is lifted up and as the central shift/select shaft CS passes the neutral position the ball drops into the neutral detent notch. As the central shift/select shaft CS continues to move towards the second gear G2 position the detent ball DB is lifted again. Once the shifter sleeve SL1 has engaged with the 2nd gear, the detent ball DB drops into the engaged gear position detent notch DN. Thus the central shift/select shaft CS is locked in the desired gear. Fig.5 shows the shift mechanism engaged in 3rd gear G3 position. The driver moves towards neutral from 2nd gear G2 position by moving central shift/select shaft CS linearly towards the centre. Then shaft CS is rotated by 90 degrees to its original position as shown in Fig.2. The gear shift actuation pin P2 positions itself in the center of the 3rf/4* yoke, which is integrated to the 3rd14th fork F2. Since the detent notch DN is machined for 360 degrees, the detent ball sits in the particular groove without any movement when the shaft CS is rotated. Then the same procedure is followed by the internal shift mechanism as it had done for the first gear. Fig. 6 shows the shift mechanism engaged in the 4th gear G4 position. The procedure followed is the same as that in engaging the 2nd gear G2. Fig.7 shows the shift mechanism engaged in the 5th gear 05 position. When the driver desires to shift to the fifth gear G5 he rotates the shaft CS by 90 degrees from the original neutral position in the direction opposite to that followed for engaging first gear Gi. The gear shift actuation pin P3 moves towards the integrated yoke of the 5* fork F3. Once the actuation pin P3 is in the centre of the integrated yoke of fifth fork F3, the shaft CS is moved in linear direction towards the 5th gear G5 side. As it overcomes the detent direction towards the 5* gear G5, it forces the fork F3 to move and engage the gear after synchronization. As the gear is engaged the detent ball DB drops into the detent notch DN on the central shift/select shaft in the engaged gear position. Thus the shaft CS is locked in the 5th gear G5 position. Even though the invention relates to a 5 speed gearbox, the above mentioned description is applicable to 4 and 6 speed gearbox also. The known system uses 3 shifter shafts and 1 gear shift guide shaft in a 5 speed synchromesh transmission resulting in higher manufacturing cost and process and increasing the assembly time. On the other hand, the present invention uses a single central shift/select shaft thus eliminates the 3 shifter shafts, the guide shaft and the entire shift/select assembly. Compared to the earlier system the present invention is more user friendly and is of lighter weight. We Claim: 1 A gear shift device for a synchromesh transmission system comprising a single shifter shaft for shifting the gears by shifter forks supported on the said shaft, said shifter shaft having three gear shift actuation pins lying on the same plane; shifter forks held in their respective neutral positions by shifter sleeves, said shifter forks having integral yokes, and said actuation pins being positioned such that that they lie in the centre of their respective yoke's plane, ball catch profiles provided on the shifter shaft, one of the ball catches for the neutral and the other ball catches for the gears in the engaged position; a spring loaded ball lying on the neutral bail catch profile. 2. A gear shift device for a synchro mesh transmission system substantially as herein described and illustrated with reference to the accompanying drawings

Documents:

584-che-2004-abstract.pdf

584-che-2004-claims duplicate.pdf

584-che-2004-claims original.pdf

584-che-2004-correspondnece-others.pdf

584-che-2004-correspondnece-po.pdf

584-che-2004-description(complete) duplicate.pdf

584-che-2004-description(complete) original.pdf

584-che-2004-drawings.pdf

584-che-2004-form 1.pdf

584-che-2004-form 19.pdf

584-che-2004-form 26.pdf