GB2031076A - Synchromesh transmission - Google Patents

Abstract

A synchromesh transmission of the type having a forward-reverse input section (18), an intermediate 4-speed constant mesh transmission (20), and a high-low output section (22). The 4-speed intermediate section has four driven gears (54, 56, 78, 80) mounted on a main shaft (24) for rotation therewith and respectively in constant mesh with four drive gears (50, 52, 70, 72) each of which can be selectively coupled to a countershaft (28) by synchronized collar-shift mechanisms (58, 68). The total shift effort required to engage the ratio of the intermediate change gear mechanisms is minimised by arranging at least three (50, 52, 70) of the drive gears to be of substantially smaller diameter than the corresponding driven gear. <IMAGE>

Description

SPECIFICATION Synchromesh transmission The present invention relates to transmissions and in particular to transmissions which provide a plurality of speeds and a forward and reverse function and include synchronizers operated by shift collars.

It is an object of the invention to provide an improved form of transmission of the type referred to above in which the total effort required to operate the shift collars is minimised.

According to the present invention there is provided a transmission having coaxial input and main shafts and coaxial counter and output shafts, a forward-reverse gear mechanism disposed about the input shaft and operable to drive an input gear coupled to the countershaft in either a forward or reverse direction, a high-low range gear mechanism selectively positionable to be in either a high range position or a low range position, and an intermediate change gear mechanism comprising four drive gears selectively engagable with the countershaft, four driven gears mounted upon the main shaft for rotation therewith and in constant mesh with said drive gears, at least three of the drive gears being of substantially smaller diameter than the corresponding driven gear, and synchronized collar-shift mechanisms on said countershaft whereby each drive gear can be selectively coupled to said countershaft by a synchronized collar shift mechanism thus minimizing the total shift effort required to engage the ratios of the intermediate change gear mechanism.

In a transmission in accordance with the present invention the total shift effort required to engage the ratios of the intermediate change gear mechanism is minimised since the collar-shift mechanisms associated with at least three of the four ratios provided by the intermediate change gear mechanism operate on the smaller diameter and thus faster rotating gear of each drive/driven constant mesh pair.

One embodiment of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawing of a transmission embodying the invention.

The transmission is disposed within a housing indicated by the broken line 10. An input shaft 1 2 is connected by a conventional clutch 14 to the output shaft 16 of an engine.

The input shaft is in turn coupled to a forward-reverse gear mechanism indicated generally at 1 8. The tranmission is also provided with a 4-speed intermediate change gear mechanism indicated generally at 20 and a 2speed or high-low range output mechanism indicated generally at 22. A main shaft 24 extends rearwardly from the input shaft 1 2.

both the input shaft 1 2 and main shaft 24 are hollow and a power takeoff shaft 26 extends through these shafts and through the rear wall of the transmission housing 1 0. A counter shaft 28 and an output shaft 30 are parallel to the main shaft and are coaxial to each other.

The forward-reverse mechanism 1 8 includes forward and reverse drive gears 32, 34, respectively, journaled about the input shaft 12, a forward input gear 36 in driven engagement with gear 32, input gear 36 being coupled to the counter shaft 28 for rotation therewith, and a one piece idler gear set 37 including portion 38 which is rotatable with the shaft portion 40, and a further reverse idler gear portion 42 in driving engagement with the input gear 36. (It should be noted at this point that for reasons of clarity the gear set 37 is not shown in its correct position in the drawing.) A shift gear 44 is carried by the input shaft 1 2 for rotation therewith, the shift gear being disposed between rotatable gears 32, 34. The gears 32, 34 have splined sections 32s, 34s, respectively disposed adjacent the shift gear.

A shift-collar 46 is disposed about the shift gear 44 and splines 32s and 34s. By moving the shift collar to the right as shown in the drawing the shift gear 44 becomes engaged with the forward drive gear 32 thereby causing the input gear 36 to be driven in a forward direction. If the shift collar were shifted to the left, it would pass through a neutral position to a reverse position wherein it would couple the shift gear 44 with the reverse gear 34 through idler gear set 37 thereby causing the input gear 36 to rotate in a reverse direction. The shift collar 46 is caused to be moved from its forward position to its reverse position by a shift fork 48, the shift fork in turn being coupled to a shift rail and other control linkage which are not a feature of the present invention.

The input gear 36 is secured to the forward end of the counter shaft 28 and rotation of the gear 36 will cause the counter shaft to rotate. In accordance with the present invention first and second drive gears 50, 52 are rotatably journaled about the counter shaft 28, the drive gears 50, 52 being in mesh with driven first and second gears 54, 56, respectively. The driven gears 54 and 56 are in turn mounted on the main shaft 24 for rotation therewith. A synchronizing mechanism indicated generally at 58 is disposed between the first and second drive gears, the synchronizing mechanism including a synchronizer collar 60 mounted upon a hub 62 which is in turned coupled to the counter shaft 28.

Disposed to either side of the hub 62 are synchro rings 64. By shifting the collar 60 from the neutral position illustrated in the drawing to the right, short spline 50s on the drive gear 50 will become engaged after the gear has been brought up to speed in a known manner. In a similar manner, movement of the collar 60 to the left will cause short spline 52s to become engaged. The synchronizing collar 60 is caused to be shifted by a fork 66 which is in turn connected to a shift mechanism not illustrated.

It should be observed at this point that the gears 50. 52 are of much smaller diameter than the driven gears 54, 56. Shift effort is reduced by placing the synchronizer mechanism 58 between the faster rotating gears 50, 52 rather than between the slower gears 54, 56.

A second synchronizing mechanism 68 is disposed between the third drive gear 70 and the fourth drive gear 72. The third drive gear 70 is journaled for rotation about the output shaft 30, and the fourth drive gear 72 is journaled for rotation about the counter shaft 28. A hub 74 is coupled to the counter shaft 28 for rotation therewith, and the hub 74 can in turn be coupled with either the third or the fourth drive gear by shifting the synchronizer collar 76 to the right or to the left from the neutral position illustrated. The third and fourth drive gears 70, 72 are in turn disposed in driving relationship with the third and fourth driven gears 78 and 80, the third and fourth driven gears being fixed on the main shaft 24.

The high-low range gear mechanism 22 includes an output gear 82 which is splined to the output shaft 30 for sliding movement thereon. The output gear is provided with a coupler section 84 on one side which is adapted to mate with a corresponding coupler 86 on the third drive gear 70 when the output gear is shifted to its left hand position by fork 88 as shown in the drawing. When the output gear 82 is shifted to the right, the teeth on the gear 82 will become engaged with corresponding teeth on gear 90 which is integral with the main shaft 24 for rotation therewith.

The transmission illustrated may be utilized to drive the rear wheels of a tractor or both front and rear wheels. When driving front wheels a further gear 92 is provided which is mounted on a forwardly extending output shaft 94.

In operation when the output gear 82 is in its left hand position the transmission will be disposed in its high range and shifts can be made into fifth, sixth, seventh, and eigth gears. When the output gear is in its right hand position the transmission will be in its low range and shifts can be made into first, second, third and fourth gears. Shifts between gears in either the high or low range are all synchronized. Thus the synchronizers 58, 68, will synchronize the shifting when shifting into gears one to four and five to eight. First gear is obtained by shifting the fork 66 to the right which will cause the hub 62 to be coupled with the first drive gear 50 after the rotational speed of the drive gear and hub have been matched. In the meantime, the synchronizer sleeve 76 is maintained in its neutral position.

A shift into second gear is obtained merely by shifting the fork 66 to the left hand position.

If it is desired to shift from second into third, the fork 66 will be moved into its neutral position and fork 96 will be shifted to the right to cause third drive gear 70 to become engaged with its hub 74. Finally, fourth gear is obtained by shifting the fork 96 to the left hand position.

In the preferred embodiment the drive gears have fewer teeth than the driven gears with the exception of fourth gear. However, the drive and driven gears in fourth have almost the same number of teeth. Thus, in the preferred embodiment, gear 50 has 1 7 teeth while driven gear 54 has 46 teeth. Drive gear 52 has 21 teeth while driven gear has 41 teeth. Drive gear 70 has 27 teeth while driven gear 78 has 36 teeth. Finally, drive gear 72 has 32 teeth while driven gear 80 has 30 teeth.

It has been determined that the shifting effort with a synchronizer is minimized by working with the fastest rotating or smallest diameter gears, it can be seen that the shifting effort into first, second, and third gears is minimized by disposing the synchronizers in the position illustrated in the drawing. If the synchronizer 68 were disposed on the main shaft 24, there would be a slightly less shifting effort into fourth gear. However, with the synchronizer in the last position, there would be a substantially greater shifting effort in third gear. Therefore, by disposing the synchronizer 68 on the countershaft, the total shifting effort has been minimized.

Claims (1)

1. A transmission having coaxial input and main shafts and coaxial counter and output shafts, a forward-reverse gear mechanism disposed about the input shaft and operable to drive an input gear coupled to the countershaft in either a forward or reverse direction, a high-low range gear mechanism selectively positionable to be in either a high range position or a low range position, and an intermediate change gear mechanism comprising four drive gears selectively engagable with the countershaft, four driven gears mounted upon the main shaft for rotation therewith and in constant mesh with said drive gears, at least three of the drive gears being of substantially smaller diameter than the corresponding driven gear, and synchronized collar-shift mechanisms on said countershaft whereby each drive gear can be selectively coupled to said countershaft by a synchronized collar shift mechanism thus minimizing the total shift effort required to engage the ratio of the intermediate change gear mechanism.