GB1558429A

GB1558429A - Stepless speed change systems

Info

Publication number: GB1558429A
Application number: GB11207/77A
Authority: GB
Original assignee: Kubota Corp
Current assignee: Kubota Corp
Priority date: 1976-04-10
Filing date: 1977-03-16
Publication date: 1980-01-03
Also published as: DE2714234A1; FR2347581A1; FR2347581B1; TR19860A; IT1078159B; NZ183624A; DE2714234B2; CA1078647A; PT66357B; DE2714234C3; PT66357A; AU2418277A

Description

(54) IMPROVEMENTS IN AND RELATING TO STEPLESS SPEED CHANGE SYSTEMS (71) We, KUBOTA LTD., a Japanese Company of No. 22, 2-chome, Funade-cho, Naniwa-ku, Osaka-shi, Osaka-fu, Japan, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: The present invention relates to power transmission systems employing planetary speed reduction means, and more particularly to stepless speed change systems incorporating means operatively associated with the reduction means and adapted to transmit the torque of an input shaft to an output shaft with stepless speed change.

Stepless speed change systems are used as power transmission systems for agricultural, civil engineering and construction tractors, motor vehicles, tillers, combine harvesters and various other industrial machines.

Systems heretofore known as stepless speed change systems include hydraulic systems comprising a hydraulic pump and a hydraulic motor and mechanical gear systems. Hydraulic systems adapted for the transmission of great torque are expensive and inefficient, require special high-precision machining techniques and are prone to troubles due to the presence of extraneous solids in the oil.

On the other hand, conventional mechanical stepless speed change systems have a low torque transmitting capacity, involve noticeable slippage leading to inaccurate torque transmission and have structural limitations resulting in difficulties in making the overall transmission compact and inexpensive. Accordignly, it is difficult to install the mechanical system in tractors and like vehicles within the limited space of the housing.

According to the present invention, there is provided a power transmission system comprising a power input means, a planetary speed reduction means and a power output means, and a stepless speed change system; said stepless speed change system comprising a power transmitting friction disc, first power transmitting means operatively connected to the input means and including a hollow gear mounted on a friction disc shaft having a friction disc mounted thereon and arranged to impart to said disc shaft a speed of rotattion in excess of that of the input, said disc shaft being biased axially toward the disc with respect to said hollow gear, second power transmitting means operatively connected to the planetary speed reduction means, and stepless speed change means provided between the first and second transmitting means and comprising said disc rotatable by the friction disc shaft and a roller incorporated into the second transmitting means and shiftable by means for operating the stepless change means diametrically of the disc in a direction intersecting the axis of rotation of the disc, the roller being in contact with an outer surface of the disc, whereby when the operating means is operated power from the input means is transmitted to the planetary speed reduction means to cause the output means to be halted or to be rotated in a forward or reverse direction by means of said stepless speed change system.

Preferably when the output means is subjected to a load part of the resulting counteracting torque is fed back to the input means through the stepless speed change means.

The invention further includes in a tractor transmission a main shaft having a plurality of power transmitting gears for receiving engine power by way of a clutch and a propelling power transmitting system and a PTO power transmitting system disposed on the opposite sides of the main shaft respectively to transmit the power with a desired speed change, the propelling power transmitting system including input means for receiving power from the main shaft, planetary speed reduction means, and power output means and in cluding a stepless speed change system comprising a power transmitting friction disc, first power transmitting means operatively connected to the input means and including a hollow gear mounted on a friction disc shaft having a friction disc mounted thereon and arranged to impart to said disc shaft a speed of rotation in excess of the input, said disc shaft being biassed axially towards the disc with respect to the hollow gear second power transmitting means operatively connected to the planetary speed reduction means, and stepless speed change means provided between the first and second transmitting means and comprising said disc rotated by the friction disc shaft and a roller incorporated into the second transmitting means and shiftable by means for operating the stepless speed change means diametrically of the disc in a direction intersecting the axis of rotation of the disc, the roller being in contact with an outer sur face of the disc, whereby when the operating means is operated power from the input means is transmitted to the planetary speed reduction means to cause the output means to be halted or to be rotated in a forward or reverse direc tion by means of said stepless speed change system. Preferably, when the output means is subjected to a load part of the resulting counteracting torque is fed back to the input means through the stepless speed change means.

Thus, in accordance with the present in ventional a stepless speed change system of -the existing mechanical type is provided which is capable of transmitting great torque with accuracy and which is serviceable also as speed reduction means. The stepless speed change system of the invention is compact in its entirety and which consists generally of planetary speed change means with a minor modification made thereto but without necessitating any special machining technique.

Thus when the output shaft is loaded during the operation of the planetary speed reduc tion means, part of the torque resulting from the reaction of the internal gear of the means is fed back to the input shaft by way of stepless speed change means so as to preclude the reduction in the efficiency which other wise would take place.

The stepless speed change system in accord ance with the invention may be serviceable as a propelling power transmission system for tractors by fulfilling the speed requirements suitable for various working implements, ground conditions and agricultural working practice and also assuring ease of speed change and providing PTO function.

Following is a description by way of ex ample only and with reference to the acompanying drawings of methods of carrying the invention into effect.

In the drawings: Figure 1 is an overall side elevation in section showing a stepless speed change system according to this invention; Figure 2 is an enlarged view in section taken along the line 2 2 in Figure 1; Figure 3 is an enlarged view in section taken along the line 3-3 in Figure 1; Figure 4 is a view in section taken along the line 44 in Figure 3; Figure 5 is a sectional view showing a modification of the means shown in Figure 4; Figure 6 is an overall side elevation in section showing another embodiment of the stepless speed change system; Figure 7 is a side elevation in section showing a tractor transmission in which a stepless speed change system of this invention is employed as a tractor propelling system; and Figure 8 is a view in section taken along the line 10-10 in Figure 7.

With reference to Figure 1, an input shaft 1 carrier a sun gear 2 splined to its one end.

An output shaft 3 includes a bowl-shaped portion 4 and a shaft portion 5 axially in alignment with the input shaft 1.

The end of the input shaft 1 fits in the output shaft 3 in the form of a socketand-spigot joint, with a bearing member 6 such as a bush or needle bearing interposed therebetween. The input shaft 1 and the output shaft 3 are therefore rotatable relative to each other. A planetary gear 7 is freely rotatably mounted on a pin 8 and housed in the bowl portion 4 of the output shaft 3. A plurality of like planetary gears 7 are provided, each in meshing engagement with the sun gear 2.

An internal gear 9 concentric with and surrounding the input shaft 1 and output shaft 3 meshes with the planetary gears 7.

Thus, the planetary gears 7 are rotatable about their own axes and also revolvable in known manner.

A pair of reduction cases 10 and 11 are each in the form of a bowl and clamp the internal gear 9 therebetween. The cases 10 and 11 and the interial gear 9 are tightly held together by fasteners comprising bolts and nuts.

Housings 13, 14 and 15 surround and support the entire power transmission system.

The input shaft 1 is supported by a ball bearing 16 on the first housing 13 and has a spline portion 17 projecting outward from the first housing 13. The engine power can be transmitted to the input shaft 1 by a gear fitted to the spline portion 17 or by another shaft connected to the portion 17 with a coupling.

The pair of reduction cases 10 and 11 are supported by a ball bearing 20 on an annular wall 18 formed in the interior of the second housing 14 and by another ball bearing 21 on a cylindrical boss portion 19 of the third housing 15. The output shaft 3 is made rotatable relative to the bases 10 and 11 by thrust bear ings 22 and 23 and a bearing 24, such as a bush or needle bearing, which are provided therebetween. The outer end of the output shaft 3 is splined as at 25. The spline portion 25 projects outward from the cylindrical boss portion 19 of the third housing 15 and is fittable to a gear or coupling.

A cylindrical boss portion 26 is secured to one reduction case 10, for example by welding, and surrounds the input shaft 1 free of interference therewith. The boss portion 26 is supported substantially by the annular wall 18 with the bearing 20 interposed therebetween. The outer peripheral portion of the cylindrical boss portion 26 is toothed to provide a worm wheel 27. Alternatively, the worm wheel 27 may be an independent one which is mounted on the boss portion.

As shown in Figure 2, a worm shaft 28 is supported at its opposite ends by a pair of tapered-roller bearings 29 and 30 on the wall of the second housing 14. The worm shaft 28 has a worm 31 and a spline portion 32.

As illustrated in Figures 1 and 2, the worm 31 is in mesh with the worm wheel 27. The worm 31 and the wheel 27 constitutes second transmitting means. The worm shaft 28 is positioned substantially at right angles to the input shaft 1. A fork shaft 3 extends in parallel to the worm shaft 28 and is supported by the wall of the second housing 14. The fork shaft 33 is restrained from axial displacement by bearing holders 34 and 35 for the worm shaft 28. A roller 36 having a groove 36a in its outer periphery is mounted on the spline portion 32 of the worm shaft 28 and is slidable axially thereof.

A shift fork 37 slidably mounted on the fork shaft 3 has a bifurcated portion 38 engaging in the peripheral groove 36a of the roller 36. A lever support 39 supported by the third housing 15 is turnable about its own axis and is fixedly provided with a handle lever 40 outside the housing 15. Within the housing, a fork lever 41 is secured to the lever support 39. The fork lever 41 extends toward the shift fork 37 and has a bifurcated portion 41 engaging a pin portion 37a on the shift fork 37 as seen in Figures 1 and 2.

Figure 1 shows means 42 for setting the output shaft 3 in its zero rotation position.

The setting means 42 comprises a ball 43 and a spring 44 for biasing the ball 43, such that the spring 44 forces the ball 43 into a recess 41b in the work lever 41, whereby the output shaft 3 is settable for zero rotation.

With reference to Figures 3 and 4, a coupling gear 45 in the illustrated embodiment is integral with a tubular shaft 46 splined in its inner surface. The tubular shaft 46 extends in parallel to the input shaft 1 on one side thereof and is rotatably supported by a pair of tapered-roller bearings 47 and 48 on the first and second housings 13 and 14. As shown in Figures 1 and 3, a gear 49 is splined to the input shaft 1 and meshes with the coupling gear 45. Thus, the gears 49 and 45 provide first transmitting means to deliver the torque from the input shaft 1 to the tubular shaft 46 with an increased speed. Stated conversely, the gear 49 serves as a reduction gear relative to the gear 45 for the torque feedback operation to be described later. A disk shaft 50 is inserted in and splined to the tubular shaft 46 and is provided with a disk 51 at its one end as shown in Figure 4. The disk shaft 50 has pressing means for pressing the disk 51 against the roller 36 as shown in Figure 4. The pressing means 52 in Figure 4 consists substantially of a closure 53 closing the tubular shaft 46 and a coiled spring 55 accommodated in a cavity 54 in the disk shaft 50. By virtue of the force of the pressing means 52, the outer peripheral surface of the roller 36 is always held in contact with an end surface 51a of the disk 51.

Figure 5 shows hydraulic means serviceable as the disk pressing means 52. The interior of the first housing 13 in Figure 5 serves as an oil-containing cylinder chamber 56. A piston 58 fits in the cylinder chamber 56, with O-rings 57 ensuring oiltight contact between the piston 58 and the inner surface defining the chamber 56. The piston 58 is slidable axially of the disk shaft 50 and is mounted on the outer end of the disk shaft 50 by means of a thrust bearing 59. The first housing 13 is provided with a plunger chamber 61 with a passage 60 extending between the plunger chamber 61 and the cylinder chamber 56. The plunger chamber 61 has a detachable cover 62. A plunger 64 having a spring seat 63 at its one end is slidably inserted into the passage 60 and biased toward the piston 58 by a coiled spring 55 provided between the cover 62 and the spring seat 63. With the hydraulic pressing means shown in Figure 5, the force of the spring 55 acts on the plunger 64, which in turn causes the hydraulic piston 58 to exert a pressing force on the disk shaft 50. Because there is no slippage between the roller 36 and the disk 51, the power can be transmitted from each other as well be described later. Thus, without employing a hydraulic pump, constant pressure valve. etc. the hydraulic pressing means can be provided by merely adding plunger 64 and piston 58 to the pressing means of Figure 4. The cover 62 which is detachable permits the replacement of the spring 55, so that the pressing force of the disk 51 acting on the roller 36 is suitably adjustable.

If the internal gear 9 in the planetary gear speed reduction means included in the embodiment of Figures 1 to 4 and comprising the sun gear 2, planetary gears 7 and internal gear 9 is fixed, the speed of rotation, N1, of the input shaft 1 will be delivered to the output shaft 3 at a reduced speed of Z Nlx Z1 +Z2 where Z1 is the number of teeth of the sun gear 2 and Z2 is the number of teeth of the internal gear 9.

If then the internal gear 9 is driven at a rotational speed of Z Nlx Z1+Z2 in the reverse direction to the direction of rotation of the input shaft 1, namely of the output shaft 3, the rotational speed of the output shaft 3 will be zero. Further if the internal gear is driven at a rotational speed exceeding Z N1x Z,+Z2 the output shaft 3 will rotate reversely relative to the input shaft 1.

Conversely, if the internal gear 9 is driven at a rotational speed a in the same direction as the input shaft 1, the output shaft 3 wilt have a rotational speed of Z1 Z2 (N1 X + x Z1 + Z2 Zi+Z, To rotate the internal gear 9, the worm 31 on the worm shaft 28 meshes with the worm wheel 27 on the cylindrical boss portion 26 substantially integral with the internal gear 9 as seen in Figures 1 and 2. The roller 36 splined to the worm shaft 28 and slidable axially thereof is kept in contact with the end face 51a of the disk 51 which is urged by the pressing means 52 and which is rotatable with the coupling gear 45. The gear 45 in turn meshes with the reduction gear 49 on the input shaft 1. Thus, the disk 51 is rotatable about its axis by way of the gears 45 and 49.

Now during operation of the system, the handle lever 40 is manipulated to cause the fork lever 41 to slidingly move the shift fork 37 along the fork shaft 33, which in turn slides the roller 36 on the worm shaft 28.

When the roller 36 is thus positioned at the centre of rotation, 0, of the disc 51 (see Figure 2), the rotational speed of the roller 36 will be zero, with the result that the internal gear 9 is held stationary, permitting the output shaft 3 to rotate at a reduced speed of Z1 Nlx Z1 +Z2 As the roller 36 moves away from the centre of rotation of the disk 51 by a distance a, the roller 36 rotates at an increased speed of a N,x- b where N2 is the rotational speed of the disk 51 and b is the radius of the roller, see Figure 2. The direction of rotation of the roller 36, when the roller is positioned on one of the left and right sides of the centre O of rotation of the disk 51 in Figure 2, is reversible when the roller is then shifted to the other side. Stated more specifically, the internal gear 9 is held stationary or driven in the same direction as or reverse direction to the output shaft 3, depending on where the roller 36 on the worm shaft 28 is positioned relative to the disk 51. Moreover, the internal gear 9 is rotatable with stepless variation in speed as the amount of movement of the roller 36 is altered. As a result, the output shaft 3 is rotatable in the positive or reverse direction with stepless speed change or can be held stationary.

On the other hand, when the output shaft 3 is subjected to a load, the internal gear 9 will have torque acting in the reverse direction to the input shaft 1 due to the resulting counterforce or reaction. By way of the worm wheel 27 and worm 31, the torque rotates the worm shaft 28, namely the roller 36 on the worm shaft 28. To compensate for a reduction in the speed of the output shaft 3, the roller 36 gives the torque to the disk 51 in frictional contact therewith. The torque is returned to the input shaft 1 via the disk shaft 50, tubular shaft 46 and gears 45 and 49 which are operatively related to serve as feedback means. In this way, part of the torque due to the reaction of the internal gear 9 is fed back to the input shaft 1, affording the corresponding increment to the torque of the output shaft 3 and thereby preventing a reduction in the efficiency.

Although the torque transmission between the disk 51 and the roller 36 is effected only by frictional force, the pressing means 52 employing the coiled spring 55 achieves satisfactory torque transmission without permitting slippage between the disk 51 and the roller 36, if the speed increase ratio between the worm 31 and the worm wheel 27 is set at a value of at least 10.

When the pressing means shown in Figure 5 is employed for this purpose in which the force of the coiled spring 55 acts on the plunger 64 which in turn hydraulically presses the piston 58, a more effective pressing force is applicable to the disk 51.

Figure 6 shows an improved embodiment of this invention which is basically shown in Figure 1. Accordingly, like parts are referred to by like reference numerals throughout these figures, and differences alone will be described in detail.

The second embodiment includes planetary gear speed reduction means covered with cases 10 and 11. The case 10 is toothed in its outer surface to provide a bevel gear 65. A drive pinion shaft 67 supported by a pair of ball bearings 66 carries a pinion 68 meshing with the bevel gear 65. The drive pinion shaft 67, corresponding to the worm shaft 28 in Figure 1, carries a slidable roller 69 splined thereto. Means comprising a shift fork 70 a screw rod 71 and a handle lever 72 is provided to slidingly shift the roller 69 on the drive pinion shaft 67 axially thereof. The screw rod 71 extends in parallel to the drive pinion shaft 67 and is rotatably supported by the housing of the system. The shift fork 70 has a boss portion 70a which is screwed on the screw rod 71. The handle lever 72 is disposed outside the housing. The shift fork 70 has a bifurcated portion engaging in a peripheral groove 69a in the slidable roller 69. When the handle lever 72 is turned in the positive or reverse direction about the axis of the screw rod 71, the shift fork 70 is moved on the screw rod 71 in screwthreaded engagement therewith, with the result that the fork 70 in engagement with the slidable roller 69 reciprocally moves the roller 69 on the drive pinion shaft 67 as shown in Figure 6. Thus, the slidable roller 69 in contact with the end face 51a of a disk 51 is shiftable toward or away from the center of rotation of the disk 51 on either side of the centre. The means for pressing the disk 51 against the slidable roller 69 shown in Figure 6 is similar to the one shown in Figure 5 wherein the force of the coiled spring 55 is delivered to the plunger 64, which further hydraulically acts on the piston 58. In both Figures 5 and 6, like parts are referred to by like reference numerals. The pressing means of Figure 6 differs from that of Figure 5 in that whereas the plunger 64 is axially in alignment with the disk shaft 50 in Figure 5, the plunger 64 of Figure 6 is positioned at a right angle with the disk shaft 50. However, there is no difference between the two in operation. In Figure 6, a cap 37 is detachably fixed to the housing by unillustrated bolts or the like to provide a plunger chamber. Further with reference to Figure 6, a coupling gear 45 is in mesh with a reduction gear 49 on the input shaft 1.

With the embodiment shown in Figure 6, like the first embodiment shown in Figures 1 to 4, the internal gear 9 can be brought to a halt or is rotatable in the same direction as or reverse direction to the input shaft 1 with stepless variation in speed, depending on where the slidable roller 36 is positioned relative to the disk 51, during the torque transmission from the input shaft 1 to the output shaft 3 via the planetary gear speed change means.

Similarly, therefore, the output shaft 3 is rotatable in the positive or reverse direction with stepless speed variation or can be halted.

However, as compared with the construction of Figures 1 and 2, the construction of Figure 6 is more advantageous. In the case of the former, when part of the torque resulting from the reaction of the internal gear 9 is delivered by way of the worm wheel 27 and worm 31 to the stepless speed change means comprising the roller 36 and the disk 51 and is further fed back to the input shaft 1 via the gears 45 and 49, the feedback operation involves difficulty or inaccuracy due to the automatic locking action between the worm 31 and the worm wheel 27, failing to give an augmented torque at reduced speeds. The construction of Figure 6 is free of this drawback, since the meshing engagement between the bevel gear 65 and the pinion 68 does not involve any automatic locking action. In addition, the screw-thread mechanism shown in Figure 6 for shifting the roller 69 renders the handle lever smoothly turnable with a reduced force.

Although the bevel gear 65 is integral with the case 10 in Figure 6, an independent bevel gear is alternatively usable, in which case the gear 65, cases 10, 11 and internal gear 9 may be fastened together by bolts 12. Nevertheless, the gear 65 formed integrally with the case 10 as illustrated is advantageous in that the structure can be made compact with a reduced number of parts.

According to the present invention described, a stepless speed change system can be provided which is compact in its entirety and capable of transmitting great torque with high efficiency, merely by modifying part of planetary gear speed reduction means. The stepless speed change means is provided between the first transmitting means and second transmitting means coupled to the planetary speed reduction means, permitting the torque from the input shaft to be transmitted to the disk shaft with an increased speed for stepless speed change by the co-operation of the disk and the roller. The stepless speed change means does not involve any slippage which otherwise would produce a noticeable influence on efficiency. Reduced efficiency can be avoided even when the output shaft is loaded, because part of the torque due to the reaction of the internal gear is fed back to the input shaft via the stepless speed change means.

Figures 7 and 8 show a preferred embodiment of the stepless speed change system of this invention as incorporated into a tractor propelling transmission system.The application of this invention to tractors results in various advantages as will be apparent from the embodiment which will be described below for illustrative purposes. Similarly, the present invention is useful in tillers, combine harvesters, motor vehicles and other industrial machines.

Figures 7 and 8 show an engine 83, an engine clutch 84 and a main shaft 89 carrying four power transmitting gears 85, 86.

87 and 88. The engagement or disengagement of the clutch 84 effects or interrupts the transmission of the engine power to the main shaft 89.

The main shaft 89 is rotatably supported by bearings 91 on a transmission case 90. A propelling power transmitting system and a PTO transmitting system are disposed on the upper and lower sides of the main shaft 89 respectively in parallel to the shaft 89.

The PTO power transmitting system comprises a speed change shaft 92 supported by the transmission case 90 and four speed change gears 93, 94, 95 and 96 mounted side by side on the shaft 92. The change gears 94 and 95 are selectively meshable with the gears 86 and 87 on the main shaft 89. As shown in Figure 9, the speed change shaft 92 extends and is connected by a coupling 97 to a transmitting shaft 98 such as a PTO shaft or an intermediate shaft for power transmission to the PTO shaft.

With reference to Figures 7 and 8, a PTO speed change lever 99 is supported on a frame 101 by a ball joint 102, a flexible seal 103.

etc. The frame 101 is detachably mounted on an intermediate case 100 which is installed on the transmission case 90. The lower end of the speed change lever 99 is engageable with and disengageable from intermediate shift members 105 on shifts shafts 104. The shift members 105 extend downward as seen in Figure 8 and are connected to shift forks 106 in engagement with the speed change gears 94 and 95 respectively. The lever 99, when manipulated, causes these speed change gears to mesh selectively with the power transmitting gears.

The propelling power transmitting system comprises the speed change means described in detail with reference to Figures 1 to 5.

Figure 7 shows an input shaft 107 having a transmitting gear 108 meshing at all times with the gear 85 on the main shaft 89 so as to be positively driven by the nower delivered from the gear 85. A gear 109, serviceable for feedback, is splined to an intermediate portion of the input shaft 107, which is provided also with a sun gear 110 at its shaft end. As will be apparent from Figure 7, the input shaft 107 extends in parallel to the main shaft 89 and is supported at its front end by a bearing 111 on the wall of the transmission case 90. An output shaft 112 extends rearward in alignment with the input shaft 107, Provided between the input shaft 107 and the output shaft 112 is planetary speed reduction means comprising the sun gear 110, planetary gears 113 and an internal gear 114 which are housed in cases 115 and 116. The front and rear portions of these cases are supported by bearings 117 and 118 on the wall of the transmission case 90.

The case 115 has a cylindrical boss portion fixedly carrying a worm wheel 119. As seen in Figure 8, the intermediate case 100 is integrally formed with a pair of opposite walls 120 supporting a worm shaft 121 by means of a pair of bearings 122. If the input shaft 107 extends longitudinally of the tractor body, the worm shaft 121 extends transversely thereof and is positioned above the input shaft 107. The worm shaft 121 is formed with a worm 123 meshing with the worm wheel 119. As will be apparent from Figure 8, the worm shaft 121 has a splined portion carrying a slidable roller 124 formed with a peripheral groove. Disposed above and in parallel to the worm shaft 121 is a fork shaft 125 secured to the walls 120 of the intermediate case 100. A shift fork 126 slidbly mounted on the fork shaft 125 has a bifurcated portion engaging in the groove of the slidable roller 124.

A lever support 127 turnable about its vertical axis is supported by the frame 101 on the intermediate case 100 and fixedly provided with a fork lever 128 which engages a portion of the shift fork 126 as sheen in Figure 7. Secured to the lever support 127 projecting from the frame 101 is a lever 129 in engagement with a handle lever 130 turnable about a lateral pin. The lever 129 and the handle lever 130 may be integral with each other, insofar as the manipulating force on the handle lever 130 can be delivered to the slidable roller 124.

With vided with a bevel pinion 145 meshing with a bevel gear 147 of differential means 146.

With the embodiment of Figures 7 and 8, the transmission of the torque of the engine is effected or interrupted by the engagement or disengagement of the clutch 84. The torque drives the input shaft 107 by way of the gears 85 and 108.

Since the input shaft 107 fixedly carries the gear 109 meshing with the gear 138, the input shaft 107 drives both the gears 109 and 138.

Further because the gear 138 is rotatable with the disk shaft 133 which is pressed on by the pressing means, the disk 134 rotates about its axis in contact with the slidable roller 124. Accordingly, when the handle lever 130 is manipulated, causing the slidable roller 124 on the worm shaft 121 to move diameuically of the disk 134 in a direction intersecting the centre of rotation of the disk, the internal gear 114 is rotated in the same direction as or reverse direction to the direction of rotation of the output shaft 112 or is stopped with stepless speed change as is the case with the embodiment of Figures 1 to 5.

On the other hand, when the output shaft 112 is subjected to a load, part of the resulting reaction of the internal gear 114 is fed back to the input shaft 107 by way of the worm wheel 119, worm 123, slidable roller 124, disk 134 and gears 138, 109. Thus, the handle lever 130, when operated, slides the roller 124 on the worm shaft 121 to shift the roller relative to the disk 134 in sliding contact therewith, thereby giving a forward, zero or rearward speed steplessly, while permitting a live PTO operation without the necessity of disengaging the clutch 84. In other words, the speed change shaft 92 continues to rotate free of any change despite changes in the travelling speed whether forward, zero or rearward.

The torque of the output shaft 112, which is rotatable in a positive or reverse direction or stoppable with stepless speed change, is delivered through the drive pinion shaft 143 of the secondary speed change means, differential means 146 and, preferably via final speed reduction means to drive unillustrated drive wheels. With the embodiment of Figures 7 and 8, the speed change lever 99, when operated, of course gives varying speeds for the PTO system.

The advantages and features of this invention will be fully apparent from the foregoing detailed description given for illustrative purposes only. It is therefore to be understood that various modifications and alternations are included within the scope of the invention.

For example, the planetary gears, sun gear and internal gear of the planetary gear speed reduction means are all replaceable by rollers to provide a planetary speed reduction mechanism. In place of the worm and worm wheel, the second transmitting means may alternatively comprise spur gears or the like.

WHAT WE CLAIM IS: 1. A power transmission system comprising a power input means, a planetary speed reduction means and a power output means and a stepless speed change system; said stepless speed change system comprising a power transmitting friction disc, first power transmitting means operatively connected to the input means and including a hollow gear mounted on a friction disc shaft having a friction disc mounted thereon and arranged to impart to said disc shaft a speed of rotation in excess of that of the input, said disc shaft being biased axially toward the disc with respect to said hollow gear, second power transmitting means operatively connected to the planetary speed reduction means, and stepless speed change means provided between the first and second transmitting means and comprising said disc rotated by the friction disc shaft and a roller incorporated into the second transmitting means and shiftable, by means for operating the stepless speed change means, diametrically of the disc in a direction intersecting the axis of rotation of the disc, the roller being in contact with an outer surface of the disc, whereby when the operating means is operated, power from the input means is transmitted to the planetary speed reduction means to cause the output means to be halted or to be rotated in a forward or reverse direction by means of said stepless speed change system.

2. A stepless speed change system as defined in claim 1 wherein the output means is subjected to a load part of the resulting counteracting torque is fed back to the input means through the stepless speed change means.

3. A stepless speed change system as defined in claim 1 or claim 2 wherein the second transmitting means comprises a worm wheel and a worm shaft having a worm meshing with the worm wheel, the roller being mounted on the worm shaft rotatably therewith and shiftably axially thereof.

4. A stepless speed change system as defined in Claim 3, wherein the disc is biased against the roller by hydraulic pressure.

5. A stepless speed change system as defined in Claim 1 or 2 wherein the second transmitting means comprises a bevel gear formed directly on or secured to a reduction case for the speed reduction means and a bevel pinion shaft having a bevel pinion meshing with the bevel gear, the roller being mounted on the bevel pinion shaft rotatably therewith and shiftably axially thereof.

6. A stepless speed change system as defined in claim 5, wherein the disc is pressed against the roller by hydraulic pressure.

7. A stepless speed change system as defined in Claim 6 wherein the operating means

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. vided with a bevel pinion 145 meshing with a bevel gear 147 of differential means 146. With the embodiment of Figures 7 and 8, the transmission of the torque of the engine is effected or interrupted by the engagement or disengagement of the clutch 84. The torque drives the input shaft 107 by way of the gears 85 and 108. Since the input shaft 107 fixedly carries the gear 109 meshing with the gear 138, the input shaft 107 drives both the gears 109 and 138. Further because the gear 138 is rotatable with the disk shaft 133 which is pressed on by the pressing means, the disk 134 rotates about its axis in contact with the slidable roller 124. Accordingly, when the handle lever 130 is manipulated, causing the slidable roller 124 on the worm shaft 121 to move diameuically of the disk 134 in a direction intersecting the centre of rotation of the disk, the internal gear 114 is rotated in the same direction as or reverse direction to the direction of rotation of the output shaft 112 or is stopped with stepless speed change as is the case with the embodiment of Figures 1 to 5. On the other hand, when the output shaft 112 is subjected to a load, part of the resulting reaction of the internal gear 114 is fed back to the input shaft 107 by way of the worm wheel 119, worm 123, slidable roller 124, disk 134 and gears 138, 109. Thus, the handle lever 130, when operated, slides the roller 124 on the worm shaft 121 to shift the roller relative to the disk 134 in sliding contact therewith, thereby giving a forward, zero or rearward speed steplessly, while permitting a live PTO operation without the necessity of disengaging the clutch 84. In other words, the speed change shaft 92 continues to rotate free of any change despite changes in the travelling speed whether forward, zero or rearward. The torque of the output shaft 112, which is rotatable in a positive or reverse direction or stoppable with stepless speed change, is delivered through the drive pinion shaft 143 of the secondary speed change means, differential means 146 and, preferably via final speed reduction means to drive unillustrated drive wheels. With the embodiment of Figures 7 and 8, the speed change lever 99, when operated, of course gives varying speeds for the PTO system. The advantages and features of this invention will be fully apparent from the foregoing detailed description given for illustrative purposes only. It is therefore to be understood that various modifications and alternations are included within the scope of the invention. For example, the planetary gears, sun gear and internal gear of the planetary gear speed reduction means are all replaceable by rollers to provide a planetary speed reduction mechanism. In place of the worm and worm wheel, the second transmitting means may alternatively comprise spur gears or the like. WHAT WE CLAIM IS:

1. A power transmission system comprising a power input means, a planetary speed reduction means and a power output means and a stepless speed change system; said stepless speed change system comprising a power transmitting friction disc, first power transmitting means operatively connected to the input means and including a hollow gear mounted on a friction disc shaft having a friction disc mounted thereon and arranged to impart to said disc shaft a speed of rotation in excess of that of the input, said disc shaft being biased axially toward the disc with respect to said hollow gear, second power transmitting means operatively connected to the planetary speed reduction means, and stepless speed change means provided between the first and second transmitting means and comprising said disc rotated by the friction disc shaft and a roller incorporated into the second transmitting means and shiftable, by means for operating the stepless speed change means, diametrically of the disc in a direction intersecting the axis of rotation of the disc, the roller being in contact with an outer surface of the disc, whereby when the operating means is operated, power from the input means is transmitted to the planetary speed reduction means to cause the output means to be halted or to be rotated in a forward or reverse direction by means of said stepless speed change system.

for shifting the roller on the bevel pinion shaft is screw-thread shifting means including at least a shift fork engaging the roller and a screw rod having the shift fork in screwthread engagement therewith.

8. In a tractor transmission including a main shaft having a plurality of power transmitting gears for receiving engine power by way of a clutch and a propelling power transmitting system and a PTO power transmitting system disposed on the opposite sides of the main shaft respectively to transmit the power with a desired speed change, the propelling power transmitting system including input means for receiving power from the main shaft, planetary speed reduction means, and power output means and including a stepless speed change system comprising a power transmitting friction disc, first power transmitting means operatively connected to the input means and including a hollow gear mounted on a friction disc shaft having a friction disc mounted thereon and arranged to impart to said disc shaft a speed of rotation in excess of that of the input, said disc shaft being biassed axially toward the disc with respect to the hollow gear, second power transmitting means operatively connected to the planetary speed reduction means, and stepless speed change means provided between the first and second transmitting means and comprising said disc rotated by the friction disc shaft and a roller incorporated into the second transmitting means and shifable, by means for operating the stepless speed change means, diametrically of the disc in a direction intersecting the axis of rotation of the disc, the roller being in contact with an outer surface of the disc, whereby when the operating means is operated power from the input means is transmitted to the planetary speed reduction means to cause the output means to be halted or to be rotated in a forward or reverse direction by means of said stepless speed change system.

9. A stepless speed change system as defined in Claim 8, wherein when the output means is subjected to a load part of the resulting counteracting torque is fed back to the input means through the stepless speed change means.

10. A stepless speed change system as defined in Claim 8 or 9, wherein the second transmitting means comprising a worm wheel and a worm shaft having a worm meshing with the worm wheel, the roller being mounted on the worm shaft rotatably therewith and shiftably axially thereof

11. A stepless speed change system as defined in claim 10 wherein the disc is pressed against the roller by hydraulic pressure.

12. A power transmission system substantially as herein described with reference to and as illustrated in Figures 1 to 8 of the accompanying drawings.