GB2038430A - Stepless Change-speed Mechanism - Google Patents

Abstract

A stepless change-speed mechanism comprises a rotary driven member 16 frictionally engaged with a plurality of rotary driving members 14a, 14b, 14c. The transmission ratio of the mechanism is changed by displacing the driven member 16 relative to the driving members in the axial direction of the driven member. Each of the driving members is rotated by a respective bevel wheel 12a, 12b, 12c meshed with a bevel wheel (not shown) on an input shaft coaxial with the shaft 15 of the member 16. Ball- cam mechanisms 20 between the members 14a, 14b, 14c and their bevel wheels generate a load- responsive pressure between the frictionally engaging members. The provision of a plurality of the rotary driving members in frictional engagement with a single common driven member ensures smooth and reliable transmission of the drive. <IMAGE>

Description

SPECIFICATION Stepless Change-speed Mechanism This invention relates to a change-speed mechanism adapted to produce a stepless or infinitely variable output speed by displacement of a rotary driven member relative to rotary driving means in frictional engagement with the driven member.

In conventional stepless change-speed mechanisms of this type, a single driving member is arranged in frictional engagement with a driven member. With such a conventional mechanism, reliable transmission cannot be achieved unless the driving and driven members are urged together under considerable force, because both members are in frictional engagement with each other at a single point of contact. In practice use of such a strong force has the drawback of causing heavy abrasion of both members.

Furthermore, a strong force is exerted on a single point of contact with a view to attaining sufficient driving power cause the difficulty that heavy unbalanced bending loads are applied to the shaft of the driven member in one direction, resulting ultimately in failure to attain smooth transmission of the drive.

An object of the present invention is to provide a stepless change-speed mechanism which eliminates or reduces the abovementioned difficulties experienced with convention constructions and reliable and smoothly transmits sufficient driving power. Another object is to provide a more simple stepless change-speed mechanism of the type described above.

The invention consists in a stepless changespeed mechanism comprising a driving bevel gear, a plurality of driven bevel gears meshing with the driving bevel gear and having axes of rotation which intersect at a point, rotary driving members associated respectively with the driven bevel gears so as to be rotatable therewith an axially movable relative thereto, said rotary driving members having friction transmission surfaces, an output shaft mounted coaxially with the driving bevel gear, a rotary driven member rotatable with the output shaft and having a peripheral friction surface in driving engagement with the friction transmission surfaces of the rotary driving members, the position of engagement of sound surfaces being variable, and means for urging the rotary driving members against the rotary driven member.

By providing a plurality of rotary driving members in power transmitting engagement with the rotary driven member, the driving force apportioned to and borne by each point of transmission engagement is aileviated, thereby to reduce abrasion and consequently transmission power loss in the stepless change-speed mechanism.

At the same time, the transmission of power at a plurality of separate engagement points about the driven member contributes to better balancing of the transmission, that is, the alleviation of the heavy unbalanced bending loads which are applied to the shaft of the driven member in one direction in the conventional structure, where only a single engagement point is utilized. Hence smooth transmission is achieved.

As the division of the driving force into such a plurality of transmission branches is achieved by providing a corresponding number of driven bevel gears meshing with a common driving bevel gear, the structure is quite simple and compact.

In order to assume the frictional coupling between the driving members and the driven member, the urging means may comprise cam mechanisms adapted to urge the driving members against the driven member, as the driven bevel gears are rotated with a force proportional to the driving torque.

In order that the present invention may be more readily understood, reference will now be made to the accompanying drawings which show, by way of example, two embodiments of the invention as incorporated in a tractor, and in which Figure 1 is a vertical longitudinal section through the transmission of the tractor and illustrates the first embodiment, some of the irrelevant parts of the transmission being omitted for clarity, Figure 2 is an enlarged cross sectional view illustrating the essential elements of the invention, Figure 3 is a section along the line Ill-Ill of Figure 2, Figure 4 is a view similar to Figure 3 illustrating the second embodiment.

In the tractor transmission shown in Figure 1 of the accompanying drawings, the drive from an engine E is coupled to a main shaft 2 of the transmission, via a main clutch 1, and is then transmitted, via a main change-speed mechanism 3 and a planetary reduction gear mechanism 4, to a sleeve shaft 5. It is to be assumed that the drive is thereafter transmitted from the sleeve shaft 5, as is normal, via an auxiliary change-speed mechanism (not illustrated) to a sleeve transmission shaft 6. From the latter, the drive is transmitted, on the one hand, to a rear axle (not illustrated) via a differential mechanism and, on the other hand, to the front axle (not illustrated) via a propeller shaft 8 journalled in the lowermost portion of the transmission case 7.

It is further to be assumed that the main shaft 2 extends to the rear of the transmission case 7, where the drive is transmitted from the rear end thereof, via another change-speed mechanism, to a power-take-off shaft, as is also normal.

9 is a hydraulic pump for driving a lift-armdriving cylinder (not illustrated) gear oil in the transmission case 7 serving as the hydraulic medium.

Referring now to Figures 2 and 3, where the main change-speed mechanism is shown in more detail, the drive is transmitted from the main shaft 2 to an input shaft 11 and then, via a drive gear 13, to three driven bevel gears 1 2a, 1 2b, 1 2c disposed in such a manner that the axes thereof intersect at a point. Associated respectively with these driven bevel gears 1 2a, 1 2b, 1 2c are rotary driving members 1 4a, 1 4b, 1 4c which are freely rotatable and axial slidable relative to the bevel gears. The rotary driving members have front surfaces F adapted for frictional transmission engagement. With the space defined by the three rotary driving members 1 4a, 1 4b, 1 4c which are arranged generally in gate form, there is journalled an output shaft 15 which is coaxial with the driving bevel gear 13 and is arranged as an extension of the axis thereof.A rotary driven member 1 6 is splined onto the output shaft 1 5 and has a peripheral friction surface transmission engagement with the friction surfaces F of the rotary driving members 1 4a, 1 4b, 1 4c. The position of engagement of the peripheral friction surface of the driven member with the friction surfaces F is variable in the radial directions of the driving members.

Referring particularly to the driving member 1 4a, as an example, it will be seen that, in the surface thereof opposite to the frictional transmission surface F and in the opposing surface of the driven bevel gear 1 2a, there are disposed pairs of scooped alignable depressions 1 7 and 18, respectively, preferably three or more pairs of such depressions. A bail 1 9 is assembled in the cavity formed by each pair of aligned depressions 17, 1 8. The depression 1 7 in the surface of the driving member 14a is conical in shape. This assembly constitutes urging means which is constructed as a ball-cam mechanism 20 and which urges the driving member 1 4a forcibly against the driven member 16, as the driven bevel gear 1 2a is rotated.As a result of the camming action, the force urging the driving member 1 4a against the driven member 16, which is set in a desired adjusted position, is proportional to the driving torque of the rotary driving member 1 4a, thereby producing a stronger compression force at a higher torque and achieving reliable transmission of the drive from the engine.

Whilst the ball-cam mechanism 20 has been described solely with reference to the driving member 14a and its associated driven bevel gear 1 2a, it will be appreciated that identical ball-cam mechanisms 20 are similarly provided on the other pairs of driving members 1 4b, 1 4c and driven bevel gears 1 2b, 1 2c. With this construction, it is possible to transmit the drive from the driven bevel gears 1 2a, 1 2b, 1 2c to the output shaft 1 5 under stepless speed-changing conditions, utilizing the peripheral speed differences at different selected radial positions on the rotary driving members 1 4a, 1 4b, 1 4c. As will be apparent, each depression 1 7 may also be of elongated shape in the circumferential direction, besides the conical shape already mentioned, resulting in substantially the same effect.

In Figures 2 and 3, 21 are compression springs for respectively urging the rotary driving members 1 4a, 1 4b, 1 4c continuously into contact with the rotary driven member 16.

Figure 4 shows the three pairs of driven bevel gears and driving members 1 2a, 1 4a, etc.

disposed in a modified arrangement. More particularly, in this embodiment, the axes of rotation of three pairs of bevel gears and driving members are spaced from one another at angles greater than a right angle so that the driving members 1 4a, 1 4b, 1 4c serve fixedly to position or securely set the driven member 16 and also to restrain fluctuating movements of the axis thereof as it is rotated.

Whilst particular embodiments have been described it will be appreciated that modifications can be made without departing from the scope of the invention as defined by the appended claims.

For example, the cam mechanism 20 is not limited to a ball-cam mechanism but may alternatively be of various other types of construction. For instance, it may comprise lug portions integral with either the driven bevel gear 1 2a, 1 2b, 1 2c of the driving members 1 4a, 1 4b, 1 4c adapted to fit into associated depressions of the other element thereby producing a camming action similar to that described above.

Moreover, this invention is not limited to the main change-speed mechanism of a tractor and is also applicable to other change-speed mechanisms, such as, auxiliary change-speed mechanisms.

Claims (8)

Claims

1. A stepless change-speed mechanism comprising a driving bevel gear, a plurality of driven bevel gears meshing with the driving bevel gear and having axes of rotation which intersect at a point, rotary driving members associated respectively with the driven bevel gears so as to be rotatable therewith and axially movable relative thereto, said rotary driving members having friction transmission surfaces, an output shaft mounted coaxially with the driving bevel gear, a rotary driven member rotatable with the output shaft and having a peripheral friction surface in driving engagement with the friction transmission surfaces of the rotary driving members, the position of engagement of said surfaces being variable, and means for urging the rotary driving members against the rotary driven member.

2. A mechanism as claimed in claim 1, including three pairs of driven bevel gears and associated rotary driving members arranged generally in gate form about the rotary driven member.

3. A mechanism as claimed in claim 1 or 2, wherein said urging means comprises cam mechanisms interposed respectively between the rotary driving members and their associated driven bevel gears, said cam mechanisms as the driven bevel gears are rotated, being adapted to urge, the rotary driving members along their respective axes and against the rotary driven member.

4. A mechanism as claimed in claim 3, wherein the cam mechanisms comprise ball-cams.

5. A mechanism as claimed in claim 1, or claims 3, 4 or 5 as appendant to claim 2, wherein the pairs of driven bevel gears and rotary driving members are arranged with their axes at obtuse angles with respect to one another.

6. A mechanism as claimed in any one of the preceding claims, which is incorporated in a tractor as a main change-speed mechanism therefor.

7. A stepless change-speed mechanism constructed and adapted to operate substantially as hereinbefore described with reference to Figures 1, 2 and 3 of the accompanying drawings

8. A stepless change-speed mechanism as claimed in claim 7 and modified substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.