DRIVE TRANSMISSION APPARATUS

Abstract: A drive transmission apparatus, such as a gearbox, having a reduced width is disclosed. The apparatus comprises: a straight input shaft (1); a group of large and small gears (2) rigidly mounted on and adapted to turn with the input shaft; a straight transmission shaft (4) installed near and parallel to the input shaft; a group of large and small gears (3) rotatably mounted on the transmission shaft, the sizes of the gears (3) being in opposite relationship with those of the gears (2) on the input shaft and being in mesh therewith; a gear (7) rigidly mounted on the transmission shaft; a back or reverse gear (23) rotatably mounted on the transmission shaft; partition rings (35) installed between each of the gears on the transmission shaft with no gaps between the partition rings and the gears; engagement grooves (10, 11, 25) formed in the internal surfaces of the gears on the transmission shaft, the engagement grooves being separated from each other by the partition rings; an axially extending speed change groove (8) formed in the surface of the transmission shaft; and an axially movable speed change claw (9) installed in the speed change groove; whereby the speed change claw, when it engages with an engagement groove (10 or 25) formed in the rotatable gears (3, 23) drives the transmission shaft and, when it engages with the engagement groove formed in the rigidly mounted gear (7), i.e. in the neutral position, does not drive the transmission shaft. A gear (34) rigidly mounted on an intermediate shaft (5) which is driven by the gear (7), is in permanent engagement with a gear (29) which drives at least one running shaft (20) through a direction clutch (31).

Description: The present invention relates to drive transmission apparatus and more specifically to a gear box for use in general vehicles and moving agricultural machines. In the conventional drive transmission gearboxes, a straight input shaft has a train of large and small gears fixed thereto which rotates with it. A linear transmission shaft is provided parallel to and near the input shaft and has a group of large and small gears rotatably mounted thereon, with the gear sizes being in opposite relation to the group of gears on the input shaft. These two groups of gears are engaged with each other. A speed change claw is provided between the transmission shaft and the gear train on the shaft to selectively bring a desired gear into engagement with the transmission shaft. There is a time when the speed change claw must be set to a neutral position in which no gears are engaged with the transmission shaft in order to cut off the transmission of engine power to drive axles. The conventional apparatus has a dedicated neutral position with no gear engaged and the neutral condition where no engine power is transmitted is achieved by setting the speed change claw in the dedicated no-gear neutral position. However, provision of the dedicated neutral position results in an increase in width of the apparatus. As an idea of eliminating the dedicated neutral position has not come to anybody's mind, the conventional apparatuses, without exception, have the dedicated no-gear neutral postiion and therefore have a large width. It is, however, possible to eliminate the dedicated no-gear neutral position by the following method. Object of the Invention The object of this invention is to reduce the width of the transmission apparatus by eliminating the dedicated neutral position where no gear is installed. Other associated advantages can also be achieved by this invention. Brief Description of the Invention In the attached drawings; Figure l is a developed cross-section on the line I-I of Figure 2, of a drive-transmitting gearbox of this invention; Figure 2 is a vertical cross section of the same embodiment as seen from the side; and Figure 3 is a partial enlarged cross section showing the transmission shaft and the gear in coupled condition. In this preferred embodiment the drive transmission apparatus, or gear box, provides five forward drives and one reverse drive, in addition to a neutral state, and also provides a directioned crawler drive. Denoted 18 is a transmission case which rotatably supports, from top to bottom, an input shaft 1, a transmission shaft 4, and idler or intermediate shaft 5, a direction clutch shaft 19 and a pair of right and left drive shafts 20. The straight input shaft l is rigidly mounted with a group of large and small gears 2 that rotates with the shaft. The external end of the input shaft l projecting from the transmission case l8 is rigidly mounted with an input pulley 2l through a shock absorbing spring 22. The input pulley 2l is connected to a drive pulley installed on the engine side through a belt running between the pulleys. The straight transmission shaft 4 parallel to the input shaft l has on its periphery two axially extending transmission grooves 8, 8 spaced l80° apart, shaped like a key slot, in which is installed a speed change claw arm l3 with a speed change claw 9 formed at its end. The transmission shaft 4 has rotatably supported thereon a group of large and small gears 3 whose sizes are in opposite relation to those of the gears 2 on the input shaft l. The transmission gears 2 and the transmission gears 3 are in mesh at all times. At the side of the transmission gear train 3 is situat ed a gear 7 which is rigidly secured to the transmission shaft 4 by a key 7A. A back or reverse gear 23 is rotatably mounted on transmission shaft 4 at the side of gear 7. It is noted here that a dedicated neutral position where no gear is installed is not provided. The gear 7 is in mesh with a gear 6 rigidly secured to an idler shaft 5 parallel to the transmission shaft 4. The back gear 23 is always engaged with a back idle gear 24 rotatably mounted on the idler shaft 5. The back idle gear 24 is engaged with a gear 2A rigidly mounted on the input shaft l, as can be appreciated from Figure 1. The gears of the transmission gear train 3, the gear 7 and the back gear 23 are separated from each other by partition rings 35. Sleeved over one end of the transmission shaft 4 is a speed change operation boss l2 that can be moved axially by a speed change shifter 27. The base portions of the speed change claw arm l3 which are formed of resilient material such as leaf spring are pivotably supported at l4 on the speed change operation boss l2. The speed change claw 9 is triangular in shape and brought into selective engagement with one of the engagement grooves l0, ll, 25 formed in the internal surface of the transmission gear train 3, gear 7 and back gear 23. At the end of the transmission shaft 4 where the speed change operation boss l2 is mounted, a plurality of circular engagement cam grooves l5 is formed. A clip ball (not shown) installed in the speed change operation boss l2 engages with one of the cam grooves l5. The speed change operation boss l2 is fitted with adjuster screws 16 which, when screwed in toward the center of the axis against the base portion of the speed change claw arm l3, causes the speed change claws 9 to project outward thus making it possible to adjust the outward pressing force of the speed change claws. Denoted 26 is a case housing the speed change operation boss l2; and 28 is an output pulley rigidly mounted at the other end of the transmission shaft 4 to derive a driving power. Denoted l9 is a direction clutch shaft which has a center gear 29 rotatably mounted at its center and in mesh with a gear 34 of the idler shaft 5. The direction clutch shaft also has axially slidable side gears 30 on each side of the center gear 29. The center gear 29 and the side gears 30 form a direction clutch 31 operated by a mechanism 31A (Figure 2). On the outside of the side gears 30 are provided brake teeth (reference numeral not assigned) that engage with brake teeth 32 formed integral with the transmission case l8. The brake teeth, when the side gears 30 are moved outwardly, come into mesh with the brake teeth 32, applying brake on the direction clutch shaft l9. The side gears 30 are engaged with running gears 33 on a pair of running shafts 20 to drive a sprocket shaft such as a crawler. Action and Operation An engine drives the input pulley 2l through a drive pully, rotating the input shaft l through the shock absorbing spring 22. As the input shaft l turns, the transmission gears 2 rigidly on the input shaft l also turn, causing the transmission gears 3 in mesh with the transmission gears 2 to rotate. However, since the transmission gears 3 are rotatably or loosely mounted on the transmission shaft 4, the transmission shaft 4 is not driven. Now, the shifter 27 is operated to move the speed change operation boss l2 along the shaft to cause the speed change claw 9 to engage with an appropriate one of the five engagement grooves l0 of the transmission gears 3. This transmits the rotation of the selected transmission gear 3 with which the speed change claws engage to the transmission shaft 4 through the claws 9, thus driving the transmission shaft 4 at the selected speed (or rotation ratio). Because the transmission shaft 4 and the gear 7 are always turning as one, the gear 6 in mesh with the gear 7 is rotated driving the idler shaft 5. When one wants to shift the gear to the neutral position, one has only to engage the speed change claws 9 with the engagement groove ll formed in the internal surface of the gear 7. That is, when the speed change claws are brought out of engagement with the groove l0 of the transmission gears 3 or the groove 25 of the back gear 23, the transmission shaft 4 is released from the forward or backward driving force. In other words, the gear is in the neutral position. This is the main point of the invention. The speed change claw 9, when driven axially, crosses the partition rings 35 coming into engagement with the adjacent engagement groove l0 or 25 of the transmission gears 3 and the back gear 23. The speed change claw 9 is held in its position and restricted of axial movement by the clip ball engaging with the engagement cam groove l5. As to the direction clutch 3l, when one of the side gears 30 is moved away from the center gear 29 and disengages from it and the other side gear 30 is brought into engagement with the center gear 29, the direction gradually changes. When a quick turn is to be made, the first side gear 30 is further moved outwardly to come into engagement with the brake teeth 32, stopping the rotation of one of the running shafts 20 (to prevent idle rotation). Effect of the Invention The conventional transmission apparatus has a dedicated neutral position where no gear is installed to accommodate the speed change claw in order to shift the gear into neutral. With this invention, however, since the engagement groove ll of the gear 7 mounted on the transmission shaft 4 is used as a neutral position, it is not necessary to provide a dedicated neutral position on the transmission shaft 4. This reduces the width of the transmission apparatus, making it more compact.

Claims: 1. A drive transmission apparatus comprising: a straight input shaft (1); a group of large and small gears (2) rigidly mounted on the input shaft and adapted to turn with the shaft; a straight transmission shaft (4) installed near and parallel to the input shaft; a group of large and small gears (3) rotatably mounted on the transmission shaft, the sizes of the gears on the transmission shaft being in opposite relationship with those of the gears on the input shaft; a gear (7) rigidly mounted on the transmission shaft; engagement grooves (10, 11) formed in the internal surface of each of the gears (3, 7) mounted on the transmission shaft; an axially extending speed-change groove (8) formed in the surface of the transmission shaft; and an axially movable speed change claw (9) installed in the groove; whereby the claw, when it engages with one of said engagement grooves in the rotatably mounted gears (3) drives the transmission shaft, and when it engages with the engagement groove in the rigidly mounted gear (7), i.e. in the neutral state, does not drive the transmission shaft. 2. An apparatus as claimed in Claim 1, wherein a reverse gear (23) is rotatably mounted on said transmission shaft (4) and is formed in its internal surface with an engagement groove (25) for engagement by said change-speed claw (9). 3. An apparatus as claimed in Claim 2, wherein said reverse gear (23) is engaged by an idler gear (24) which is driven by a gear (2A) rigidly mounted on said input shaft (1). 4. An apparatus as claimed in any preceding Claim, wherein partition rings (35) are installed between each of the gears on the transmission shaft (4) to define said grooves, no gaps being provided between the rings and the gears. 5. An apparatus as claimed in any preceding Claim, wherein an intermediate shaft (5) is positioned close to and parallel with said input shaft (1) and said transmission shaft (4), said intermediate shaft being driven by a gear (6) fixed ther eon and in engagement with the gear (7) rigidly mounted on said transmission shaft, to provide a low-speed power output. 6. An apparatus as claimed in Claims 2 and 5 or 3 and 5, wherein said idler gear (24) is rotatably mounted on said intermediate shaft (5). 7. An apparatus as claimed in Claim 6, wherein a gear (34) is rigidly mounted on a said intermediate shaft (5) and is in permanent engagement with a gear (29) which drives at least one running shaft (20) through a direction clutch (31). 8. The features herein described, or their equivalents, in any patentably novel selection.

Inventors: FUJITA, YASUSHI
Applicants: ISEKI & CO., LTD.
Application year: 1987
Main classification: F16H3
IPC codes: F16H3, F16H63