Tractor Transmission Structure

1. Field of the Invention

The present invention relates to tractor transmissions, and in particular to a transmission structure including first and a second gear transmissions operatively connected to each other in series, each gear transmission providing two speeds. Of the four speeds available from the combination of the two gear transmissions, only three are utilized. That is to say, one of the two intermediate speeds is not utilized since one gear transmission in a high speed position is almost equal to the other in a low speed position.

2. Description of the Prior Art

The first and second gear transmissions operatively connected to each other in series, each providing two speeds, namely a high speed and a low speed, as described above are normally operated by two hand levers, which makes the operation complicated and troublesome. Furthermore, although a total of four speeds are available from the combination of the two gear transmissions each providing two, high and low, speeds, one of these speeds is substantially redundant and makes the corresponding portion of the operation wasteful. Therefore, an improved construction has been desired in order to realize a rational operation in a simple way.

The object of the present invention is to provide a rationally constructed change-speed structure to facilitate speed-changing operations.

A tractor transmission according to the present invention comprises first and second gear transmissions including change-speed operator portions respectively, a change-speed lever operatively connected to the change-speed operator portions through interlocking link means, and guide means defining a substantially U-shaped opening for guiding the change-speed lever, the substantially U-shaped opening extending longitudinally of a tractor body, the change-speed lever being adapted to selectively assume positions at extreme ends of right and left arms of the substantially U-shaped opening and at a portion of the opening interconnecting the right and left arms to selectively provide a first speed state in which the first and second gear transmissions are in low speed positions, a second speed state in which the first gear transmission is in a high speed position and the second gear transmission is in the low speed position, and a third speed state in which the first and second gear transmission are in the high speed positions.

Thus, the invention provides two gear transmissions which are operable by shifting a single change-speed lever only. Moreover, the lever operations to switch change-speed positions of the gear transmission which require a relatively large operational force are now effected in longitudinal directions of the tractor body and at a relatively short stroke. On the whole, therefore, the change-speed operation is simplified and expedited in respect of both the amount of operation and the force of operation, thereby realizing an easy changing of traveling speed.

Other objects and advantages of the present invention will become apparent from the following description.

In the drawings illustrating a tractor transmission structure according to the present invention,

FIG. 1 is a side elevation of an agricultural tractor,

FIG. 2 is a diagram showing a transmission system,

FIG. 3 is a sectional view of gear transmissions,

FIG. 4 is a side view of an interlocking mechanism,

FIG. 5 is a plan view showing how a change-speed lever is mounted, and

FIG. 6 is a plan view showing a lever guide.

Referring to FIG. 1, an agricultural tractor is shown comprising a self-propelled wheeled vehicle having a prime mover section 1 at the front and a driver's section 2 rearwardly of the prime mover section 1. The vehicle is equipped with a lift arm 3 to which a working implement such as a rotary cultivator is attached to be vertically movable relative to the vehicle body, and a power takeoff shaft to drive the attached working implement. Thus the tractor shown is adapted to carry one of varied agricultural implements at the rear which is vertically moved and driven according to the driver's operations.

Referring to FIG. 2 showing a drive system for the tractor's traveling at varied speeds, power of an engine 5 is transmitted to a main clutch 6 and then through a gear type main change-speed mechanism 7 and a gear type auxiliary change-speed mechanism 8 to a differential mechanism 9 for driving rear wheels 10. The rear wheels 10 are driven backward and forward and at varied speeds by operating the main clutch 6 and the main and auxiliary change-speed mechanisms 7 and 8.

The auxiliary change-speed mechanism 8 is constructed as follows:

As shown in FIGS. 2 and 3, an input shaft 12 operatively connected to an output shaft 11 of the main change-speed mechanism 7 carries a first output gear 13 and a second output gear 14 having different diameters, the two gears 13 and 14 being rotatable and not slidable relative to the input shaft 12. The input shaft 12 also carries a change-speed gear 15 which is mounted thereon through a spacer 15a slidably relative to the input shaft 12 and rotatably together with the input shaft 12. When the change-speed gear 15 meshes with the first output gear 13, the first output gear 13 is operatively connected to the input shaft 12 through the change-speed gear 15 to provide a high speed. When the change-speed gear 15 meshes with the second output gear 14, the second output gear 14 is operatively connected to the input shaft 12 through the change-speed gear 15 to provide a low speed. Therefore, two speeds, high and low, are obtained by switching the change-speed gear 15 between a position to mesh with the first output gear 13 and a position to mesh with the second output gear 14. This construction constitutes a first gear transmission M1. There is provided a further input shaft 16 carrying a first input gear 17, a second input gear 18 and a transmission gear 19, the three gears 17, 18 and 19 being rotatable together with the input shaft 16 and not slidable thereon. An output shaft 21 carries a change-speed gear 20 rotatable together with the output shaft 21 and slidable thereon. When the change-speed gear 20 meshes with the transmission gear 19, the output shaft 21 is operatively connected to the input shaft 16 through the two gears 19 and 20 to provide a high speed. When the change-speed gear 20 meshes with the first input gear 17, the input shaft 16 and the output shaft 21 are operatively connected to each other through the two gears 17 and 20 to provide a low speed. Therefore, two speeds, high and low, are obtained by switching the change-speed gear 20 between a position to mesh with the transmission gear 19 and a position to mesh with the first input gear 17. This construction constitutes a second gear transmission M2. The first gear transmission M1 and the second gear transmission M2 are operatively connected in series, the two output gears 13 and 14 of the first gear transmission M1 being in mesh with the two input gears 17 and 18 of the second gear transmission M2, respectively.

Referring to FIGS. 4 and 5, a change-speed lever 22 comprises a base portion 22a pivotably attached to a support rod 24 provided in a transmission case 23 and extending transversely of the tractor body, and a grip carrying portion 22b connected to the base portion 22a flexibly about an axis 25 extending longitudinally of the tractor body and urged towards a stretch position by a spring 26. A lever guide 27 is provided which defines a substantially U-shaped opening 28 extending longitudinally of the tractor body, as shown in FIG. 6. The opening 28 receives the grip carrying portion 22b of the change-speed lever 22, whereby the lever 22 is shiftable along the opening 28.

As best shown in FIG. 4, the change-speed lever 22 is operatively connected to the first and second gear transmissions M1 and M2 through an interlocking link mechanism. A rotatable operator portion 29 is operatively connected to a shift fork (not shown) for the first gear transmission M1. An oscillatable arm 30 is rigidly attached to this rotatable operator portion 29. The base portion 22a of the change-speed lever 22 includes a boss for mounting on the support rod 24, and from this boss extends an oscillatable arm 31 rigidly attached to the boss. The two arms 30 and 31 are interlocked by a push-pull member 32. A further rotatable operator portion 33 is operatively connected to a shift fork (not shown) for the second gear transmission M2. An oscillatable arm 34 is rigidly attached to this rotatable operator portion 33. An oscillatable member 35 is mounted on the support rod 24 rotatably relative to the support rod 24 and including a first arm portion 35a which is interlocked with the arm 34 by a push-pull member 36. The grip carrying portion 22b of the change-speed lever 22 has a pin 37 projecting therefrom to engage with and disengage from a hole defined in a second arm portion 35b of the oscillatable member 35 thereby to switch, with flexion of the change-speed lever 22, between an interlocking position in which the change-speed lever 22 and the oscillatable member 35 are oscillatable in a unitary manner and a non-interlocking position in which the change-speed lever 22 and the oscillatable member 35 are oscillatable relative to each other.

The shifting operation of the change-speed lever causes the two rotatable operator portions 29 and 33 to be operated by way of the described interlocking link mechanism, and this is particularly described hereinafter. Both the operator portions 29 and 33 are operated when the change-speed lever 22 is shifted along the lefthand arm 28a of the U-shaped guide opening 28. When the change-speed lever 22 is shifted within a portion 28c of the opening interconnecting the right and left arms 28a and 28b, respectively only the operator portion 29 of the first gear transmission M1 is moved into and out of operative connection with the change-speed lever 22. When the change-speed lever 22 is shifted along the righthand arm 28b of the U-shaped opening 28, only the operator portion 29 of the first gear transmission M1 is operated. When the change-speed lever 22 assumes a third position H at an extreme end of the lefthand arm 28a as shown in FIG. 6, the two operator portions 29 and 33 cause the first and second gear transmissions M1 and M2 to provide the high speed, respectively. When the lever 22 assumes a first position L at the interconnecting opening portion 28c, the two transmissions M1 and M2 both provide the low speed. When the lever 22 assumes a second position M at an extreme end of the righthand arm 28b of the U-shaped opening 28, the second gear transmission M2 provides the low speed and the first gear transmission M1 provides the high speed.

In summary, a total of three speeds are obtained by shifting the change-speed lever 22 along the U-shaped guide opening 28. By shifting the lever 22 to the first position L, a first speed state is obtained in which both gear transmissions M1 and M2 provide the low speed, respectively. By shifting the lever 22 to the second position M, a second speed state is obtained in which the first gear transmission M1 provides the high speed and the second gear transmission M2 provides the low speed. By shifting the lever 22 to the third position H, a third speed state is obtained in which both gear transmissions M1 and M2 provide the high speed, respectively.

It should be understood that, in determining the first to third positions of the change-speed lever 22 to selectively obtain the first to third speed states, the first to third positions in the substantially U-shaped opening may be arranged in a different order than that described above, by changing the change-speed mechanisms of the first and second gear transmissions M1 and M2 or the construction of the interlocking link mechanism. In short, it is in accordance with the present invention if the selective shifting of the change-speed lever 22 to the first to third positions results in the selective provision of the first to third speed states.

The described transmission structure of the present invention is applicable to varied working vehicles such as those for transportation and construction purposes.