GB2154694A - Clutch/brake combination in a power transmission for motor vehicles - Google Patents

Abstract

A transmission system for a motor vehicle such as a tractor for mowing or soil working includes a hydraulic clutch 68 and shaft brake 69 on a clutch shaft 62. The clutch 68 is actuated by a hydraulic actuating circuit communicated with the clutch 68 by a conduit 85 within the clutch shaft 62 which is connected by a rotary joint 89 on the clutch shaft 62. The shaft brake 69 is connected with the hydraulic actuating circuit such that engagement of the clutch 68 releases the brake 69 which is normally biased in the engaged position by a spring 99 acting on a brake piston 96. The overall length of the system is reduced by mounting the rotary joint 89 and shaft brake 69 inside the transmission case 28 within a sleeve 86 which forms the casing of the brake. The sleeve 86 also supports the bearing 88 between the brake and the clutch to be mounted adjacent the clutch 68 thus strengthening the clutch mounting. A change speed gearing arrangement is described (Fig. 3 (not shown)) wherein the engine drives all four wheels via a rotor (43) of a hydrostatic transmission (42,43) and two power take off shafts (37,38) from the pump (42) of the hydrostatic transmission, the clutch/brake combination controlling the engagement of either or both of the power take off shafts. In Figs. 1 and 2 (not shown) a front engined tractor is shown with the gearing at the rear and one power take off shaft driving a centrally mounted mower and the other protruding at the rear of the tractor. <IMAGE>

Description

SPECIFICATION Power transmission for motor vehicles This invention relates to transmission systems for motor vehicles performing for example mowing, reaping, earth moving operations and the like.

More particularly, the present invention relates to transmission systems for motor vehicles wherein a fluid-operated clutch includes brake means on one end of a clutch shaft for braking the shaft when the clutch is disengaged.

Because a fluid path for supplying and draining clutch-operating fluid cannot be formed by a conduit directly connected to a rotating clutch it is thus formed in the transmission shaft. Because such a fluid path is rotated with the clutch shaft, it is necessary to provide a rotary joint in the fluid conduit line as an interface between the clutch and a control valve.

In the prior art, such a rotary joint, as shown in, for example, U.S. Patent Nos.

2,843,213 and 3,831,690, one end of the clutch shaft, having a fluid-operated clutch thereon, is formed at the outer surface thereof with an annular groove or grooves, the clutch shaft is located in a transmission case so that the end projects outwardly from the case, and a sealed housing or cover is placed over that end of the shaft and fastened to the outer surface of the transmission case so as to enclose and seal the annular groove and connect the fluid path in the cover to the annular groove so that the groove acts as a rotary joint for connecting the rotary fluid path and a stationary fluid path.

Such a construction will require an extra length of clutch shaft projecting out of the transmission case even when the clutch is mounted within the case at a position which is relatively remote from the inner wall surface of the transmission case. Such a lengthened shaft will not only result in an increase in manufacturing cost but also a considerable drop in fluid pressure due to the resistance to fluid-flow in the lengthened fluid path in the shaft. Further, it is preferable not to support a clutch at a point relatively remote from the clutch housing due to the weight of the assembly.

Although the input to a transmission shaft, which is selectively interrupted by a fluidoperated clutch mounted on the shaft, ought to be stopped in the disengaged state of the clutch, frictional elements on the driving side of the clutch may cause a rotation of the frictional elements on the driven side of the clutch due to drag of the oil within the clutch causing a rotation of the clutch shaft. This may cause an unexpected movement of the vehicle when such a clutch is disposed in the transmission path for driving the vehicle and may cause an unexpected drive of auxiliary equipment when such a clutch is disposed in the transmission path for driving such auxiliary equipment. An unexpected movement or drive of this kind may be dangerous.It has thus alrerady been proposed, as shown in, for example, U.S.4,148,382, to provide at one end of a clutch shaft, supporting a fluidoperated clutch, a brake which brakes the shaft in the disengaged state of the clutch.

Such a brake prevents an unexpected rotation of the clutch shaft in the disengaged state of the fluid-operated clutch.

Thus U.S. Patent No.4,148,382 discloses a transmission system, including a hydraulic clutch and a shaft brake biased to the engaged position, mounted on a clutch shaft, the clutch and clutch shaft being mounted in a transmission case, the clutch being hydraulically connected, through a conduit within the clutch shaft and a rotary joint on the clutch shaft, to a hydraulic actuating circuit.

Furthermore, in the case where a mechanically operated clutch or change speed mechanism, operated by shifting a shiftable clutch member or change speed gear, is provided downstream of a fluid-operated clutch means, such a brake acts to arrest the inertial rotation of the shaft quickly by braking the shaft when the fluid-operated clutch has been disengaged prior to shifting the shiftable clutch member, or change speed gear, so as to stop rotation of the rotatable members of the clutch or change speed mechanism, including the shiftable member or gear.

On the other hand,, a brake of the type referred to above increases the length of the transmission case in which the brake is mounted, on one end of the clutch shaft. In the case where such a brake is provided at one end of the clutch shaft, having a rotary joint in a fluid path, as described before, made by placing a fixed sealed housing or cover on that end of the clutch shaft projected outwardly from the transmission case, a large structure results on the outer surface of the transmission case. Such a large structure restricts the arrangement of the other mechanisms in the vehicle as well as causing difficulties in assembling same in the vehicle.

According to the present invention a transmission system has a hydraulic clutch wherein the rotary joint is located within a sleeve formed by an inwardly projecting portion of the wall of the transmission case, the shaft brake is carried by the sleeve and the rotary joint is connected to the hydraulic actuating circuit through the sleeve wall.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic side view, partially cut away, of a vehicle in which an embodiment of the present invention is employed; Figure 2 is a schematic plan view showing the arrangement of various components of the vehicle shown in Fig. 1; Figure 3 is a side elevation of the hydrostatic transmission and transmission in a transmission case employed in the vehicle shown in Fig. 1, showing the transmission in the transmission case in section and partially developed form; Figure 4 is a partial sectional front view taken along the line IV-IV of Fig. 3, showing the arrangement of transmission shafts and some of the gear trains in the transmission case shown in Fig. 3; Figure 5 is a partial cross-sectional plan view, taken along the line V-V of Fig. 3;; Figure 6 is a cross-sectional plan view taken along the line VI-VI of Fig. 3; Figure 7 is an enlarged sectional side view of a part of the transmission in the transmits sion case shown in Fig. 3; Figure 8 is a partial sectional rear view, taken along the line VIII-VIII of Fig. 3; Figure 9a and Figure 9b are sectional side views of a part of Fig. 7 showing other states of the PTO-exchanging clutch shown in Fig.

7; Figure 10 is a diagram showing the fluid circuit of the hydraulic system for the hydrostatic transmission and PTO system shown in Fig. 3; Figure 11 is a schematic graph illustrating the operation of the hydraulic system shown in Fig. 10; Figure 12 is a partial side elevation, of the transmission case shown in Figs. 3 and 4 seen along arrows XII-XII of Fig. 4; Figure 13 is a partial cross-sectional plan view, taken along the line XII-XII of Fig. 3; and Figure 14 is a partial sectional front view, taken along the line XIV-XIV of Fig. 3.

Fig. 1 shows schematically the whole of the motor vehicle in which an embodiment of the power transmission system according to the present invention is employed, and Fig. 2 shows schematically the arrangement of various components in such a vehicle.

The vehicle shown is a relatively small tractor equipped with a mid-mounted mower M between a pair of front wheels 21 and a pair of rear wheels 22. An engine 23 is mounted on the front of the vehicle. A transmission system, to which power is fed by the engine 23 through transmission shaft 24, having at their ends flexible joints 25 and 26, is arranged at the rear of the vehicle, between the left and right rear wheels 22. This transmission system comprises a hydrostatic transmission 27 disposed on a front end of the transmission system, and a transmission in a transmission case 28 disposed at the rear of the transmission system. Power is transmitted from a transmission shaft 24 to the hydrostatic transmission 27 and then from the hydrostatic transmission 27 into the transmission case 28. A seat 29 is located on top of the rear end of the vehicle frame.As is conventional, the vehicle is steered by an operator on the seat 29 by means of a steering wheel 30.

The vehicle shown is moved by driving rear wheels 22 and, when required, front wheels 21. For driving the rear wheels 22, left and right axle housing 32, supporting the left and right rear drive shafts 31, are fixedly secured to the transmission case 28 so that power is transmitted from the inside of transmission case 28 directly to the left and right shafts 31. In order to drive the front wheels 21, a transmission shaft 33 transmits power from a lower portion of the inside of transmission case 28 into a front axle case 34 disposed between left and right front wheels 21. This shaft 33 is selected by means of a front wheel-driving clutch which is arranged in the transmission case 28, as will be described later, and comprises universal joints 35 and 36 at both ends.

There are two PTO (power take-off) shafts, for driving auxiliary machinery attached to the vehicle for various purposes, namely a front PTO shaft 37, which extends forwardly at a low level from the inside of transmission case 28, and a rear PTO shaft 38 which extends rearwardly at an intermediate level from the inside of the transmission case 28. The front PTO shaft 37 shown is fashioned such that it transmits power to a gear box M1 for driving the mower M through a transmission shaft 39 having universal joints at both ends. On the top of transmission case 28 there is located a hydraulic lift mechanism which comprises left and right lift arms 40, shown in Fig. 1.The rear PTO shaft 38 is used for driving auxilliary machinery, such as a mower, rotary tiller etc., which are selectively connected to the rear end of the vehicle by means of a link mechanism not shown in the drawings so as to be drawn by the vehicle and are selectively lifted and lowered by the hydraulic lift mechanism referred to above.

As shown in Fig. 3, the hydrostatic transmission 27 comprises a hydraulic variable displacement pump 42 and a fixed displacement motor 43 which are arranged in parallel by placing the pump 42 above the motor 43. The front end pump shaft 44 of the hydraulic pump 42 is connected to the transmission shaft 24 shown in Fig. 1 and is projected rearwardly into the transmission case 28 for use as an input shaft for the PTOline in the case 28. The motor shaft 45 of the hydraulic motor 43, which is driven by the hydraulic pump 42 at variable speed with a selective reverse direction of rotation, is projected rearwardly into the transmission case 28 for use as an input shaft for vehicle motive power in the case 28.

As shown in Figs. 3 and 4, in the transmission case 28 there are forwardly and backwardly extending motor shaft 45, intermediate shaft 46 and change speed 7 which are arranged on top of one another approximately laterally central in the transmission case 28. These shafts 45, 46, 47 transmit motive power for the vehicle from the hydraulic motor 43. To the front of the transmission case 28 is fixedly secured a frame plate 48, to which is fixedly secured, at the front of its lower portion, a clutch case 49 for the front wheel-driving clutch. The intermediate shaft 46 is rotatably supported by the frame plate 48 and a supporting wall projected from an inner wall of the case 28, whereas change speed shaft 47 is rotatably supported by the clutch case 49 and the supporting wall referred to above.These shafts 46 and 47 are disposed at the front of the inside of transmission case 28. An output shaft 50 for front wheel-driving power is rotatably supported by the clutch case 49 and frame plate 48 and is projected forwardly from the transmission case 28. This output shaft 50 is connected to the transmission shaft 33 shown in Figs. 1 and 2.

The motor shaft 45 and intermediate shaft 46 are operatively connected with each other by meshing gears 51 and 52 fixedly mounted on these shafts. Between intermediate shaft 46 and change speed shaft 47 is disposed change speed gearing 53 through which change speed shaft 47 is driven according to selectable gear ratios. The rear end of the change speed shaft is formed with an integral bevel gear 54 which is meshed with input bevel gear 56 of a differential gearing 55, shown in detail in Fig. 5.As shown in Fig. 5, the left and right rear wheel shafts 31 are arranged coaxially with left and right output shafts 57 of the differential gearing 55, and each of the output shafts 57 is operatively connected to each of the rear wheel shafts 31 through a disc brake 58 and speed-reduction planetary gearing 59 which are disposed within each of the axle housings 32 at the base end portion of the housing. A front wheel-driving clutch 60 for connecting the output shaft 50 to the change speed shaft 47 is arranged, as shown in Fig. 4, in the clutch case 49.

As shown in Figs. 3 and 4, there are provided in the transmission case 28 forwardly and backwardly extending transmission shafts for the PTO-line shafts 61 and 62 and intermediate shaft 63, each of which is reltively long. These shafts are positioned in the upper portion of the case 28, with transmission shaft 61 disposed coaxially with the pump shaft 44. The clutch shaft 62 and intermediate shaft 63 are disposed below the transmission shaft 61 such that these shafts 62 and 63 are separated from each other across the case 28. The front PTO shaft 37 is rotatably supported by the frame plate 48 and the supporting wall projecting from an inner wall of the transmission case 28 and is arranged in a lower portion of the case 28 such that this shaft 37 is disposed across from the output shaft 50, with the change speed shaft 47 in between.The rear PTO shaft 38 is rotatably supported by a supporting wall projected from an inner wall of the transmission case 28 and a cover plate 64 on the rear of the case 28, and is arranged at an intermediate level in the transmission case 28 such that it is disposed between and below the shafts 62 and 63, extending backwardly from the transmission case 28.

As shown in Fig. 3, the transmission shaft 61 is fixedly connected to the motor shaft 44 by means of a coupling 65. A gear 66, meshed with gear 67 mounted on the transmission shaft 61, is rotatably mounted on the clutch shaft 62. On the clutch shaft 62 is mounted a fluid-operated clutch 68 which, when operated, connects gear 66 to transmission shaft 62 so as to drivably connect the two transmission shafts 61 and 62. To this fluid-operated clutch 68 is annexed a brake 69 for braking the transmission shaft 62 in the non-operated state of clutch 68, as will be detailed later. In front of the fluid-operated clutch 68, a pair of spaced gears 70 and 71 are rotatably mounted on clutch 68, a pair of spaced gears 70 and 71 are rotatably mounted on clutch shaft 62. Between these gears 70 and 71 is a PTO selecting clutch 72 for selectively connecting gears 70 and 71 to the clutch shaft 62.As shown in Figs. 4 and 6, an idler shaft 73, which is rotatably supported by the transmission case 28 through a pair of bearings is arranged in the case 28 at an intermediate level between the clutch shaft 62 and the front PTO shaft 37. Of the gears 70 and 71 on the shaft 62, gear 70, having a larger diameter, is operatively connected to the front PTO shaft 37 through an intermediate gear 74 which is fixedly mounted on the idler shaft 73 and meshes with the gear 70 and gear 75 fixedly mounted on the front PTO shaft 37. Another gear 71 on the shaft 62 is meshed with a gear 76 which is fixedly mounted on the intermediate shaft 63. As shown in Fig. 3, the rear PTO change speed gearing 77 is disposed between the intermediate shaft 63 and the rear PTO shaft 38. The intermediate shaft 63 drives the rear PTO shaft 38 through change speed gearing 77 with a step variable speed of rotation.

Fig. 7 shows in detail the PTO clutch mechanism which comprises a fluid-operated clutch 68, shaft brake 69 and PTO selecting clutch 72. The fluid-operated clutch 68 comprises a clutch case 80 which is fixedly mounted on the transmission shaft 62 by using a key 79 shown in Fig. 3. This clutch 68 is of the multi-disc type in which two sets of frictional elements 81 and 82 are slidably but non-rotatably supported by the gear 66 and clutch case 80, respectively. In the clutch case 80 is arranged a piston 84 which is biased by return spring 83 to move away from frictional elements 81 and 82. As is conventional, the clutch 68 is operated by a supply of fluid under pressure through a fluid path 85 formed in the transmission shaft 62 so as to advance the piston 84 to cause a frictional engagement between the two sets of frictional elements 81 and 82.

As shown in Fig. 7, the rear wall of transmission case 28 is formed with an integral sleeve 86 which projects into the case 28 from the rear wall of the case 28 and encloses the rear end of the clutch shaft 62. This sleeve 86 is open at both ends. The innermost end portion of the sleeve 86 is formed, on its inner surface, with an annular step, and the clutch shaft 62, which is supported at its front end by the frame plate 48 through a ball race 87, is supported at the rear end by a ball race 88, which is mounted in the innermost end of the sleeve 86 by using the annular step referred to above. The innermost end of the sleeve 86 is slightly spaced from the rear end of the clutch case 80, and the ball race 88 is sandwiched between a collar 80a, formed integrally with the clutch case 80, and the sleeve 86.The bearing 88 for supporting the rear end of the clutch shaft 62 is supported by the innermost end of the sleeve 86 so as to dispose the bearing 88 at a position as near as possible to the fluid-operated clutch 68 which is relatively heavy. The clutch shaft 62 is thus firmly supported. The collar 80a reduces the number of parts of the transmission system by omitting a separate collar and also makes it possible to enlarge the length of the key 79 shown in Fig. 3.

The fluid path 85 in the clutch shaft 62 constitutes the end of the fluid conduit line for supply and draining the clutch-operating fluid for the fluid-operated clutch 68 and is moved to rotate together with the shaft 62. To connect the rotating fluid path 85 to a stationary fluid path, an annular groove 89, communicated to the path 85, is formed on the outer peripheral surface of the clutch shaft 62 at a position near to the inner end of sleeve 86.

The sleeve 86 has a reduced inner diameter near the groove 89 and seals it by means of the inner peripheral surface of the sleeve 86 so as to form an annular fluid chamber 90. To this fluid chamber 90 is communicated a fluid path 91 which is formed in the sleeve 86.

The latter fluid path 91 is connected to a control valve for the fluid-operated clutch 68, as will be detailed later, so that a rotary joint in the fluid conduit line for the clutch 68 is formed by the annular fluid chamber 90. A pair of O-rings 92 are disposed between the clutch shaft 62 and the sleeve 86 preventing leakage of fluid from the chamber 90 along the shaft 62.

As also shown in Fig. 7, the clutch shaft 62 has a length taking up approximately half the sleeve 86. The brake 69 is fashioned as a frictional brake by employing the sleeve 86 as its brake case such that it comprises a plurality of frictional plate members 93, which are slidably but non-rotatably supported at their inner peripheral ends by the clutch shaft 62, and a plurality of other frictional plate members 94, which are slidably but non-rotatably supported at their outer peripheral ends by the sleeve 86. In front of the series of frictional plate members 93 and 94, the inner peripheral surface of sleeve 86 is formed with an annular reaction area 95. Behind the series of frictional plate members 93 and 94, a brake piston 96 is provided in the cylinder 86 facing the plate members 93 and 94.The opening of the sleeve 86 is closed by a cover 98 which is fixedly secured to the wall of the transmission case 28 by means of fastening bolts (not shown). It is to be understood that references to a plurality of plate members do not exclude the use of single plates similarly located on the shaft 62 and sleeve 86 respectively. The piston 96 may retreat to a position where it engages the cover 98. The rear of the piston 96 has a hollow cylindrical shape, within this are arranged a pair of compression coil springs 99 which bear, at their base ends, on the cover 98 and bear, at their front ends, on the piston 96. Springs 99 thus force the series of frictional plate members 93 and 94, through piston 96, to move toward the reaction area 95 so as to cause a frictional engagement of the plate members 93 and 94 between the area 95 and the piston 96, resulting in a braking action.To release the brake 69 an annular fluid chamber 100 is formed within the sleeve 86 such that it faces an annular step on the outer peripheral surface of the piston 96. This fluid chamber 100 is communicated to the fluid path 91 in the sleeve 86 so that in the operated state of the clutch 68, to which fluid is supplied under pressure via fluid path 91, the piston 96 is retreated against the biasing springs 99 by the same fluid pressure, thus releasing the brake 69. As shown in Figs. 3, 7 and 8, another sleeve 101, which projects into the transmission case 28 and supports a rear portion of the transmission shaft 61 is integrally formed with the sleeve 86, within the rear wall of the case 28. As can be understood from the arrangement of threaded bores 97 shown in Fig. 8, the cover 98 is large enough to close the openings of both the sleeves 86 and 101 simultaneously.

The PTO selecting clutch 72 will be explained by referring to Figs. 7 and 9. On the transmission shaft 62 is non-rotatably mounted a splined collar 102 between the pair of gears 70 and 71. The boss of each of the gears 70 and 71 has an extension abutting the collar 1 02. Such extensions of the bosses and the splined collar are formed with axially aligned teeth 70a, 71a and 102a.

Between gears 70 and 71 is disposed a selection sleeve 103 which is axially shiftable over the boss extensions of gears 70 and 71 and splined collar 102. This selection sleeve 103 is formed on its inner peripheral surface with teeth which may mesh with the teeth 70a, 71a and 102a. The axial length of the selection sleeve 103 is predetermined so that the sleeve 103 may be placed as shown in Fig. 7, where the teeth of the sleeve 103 are meshed with all of the teeth 70a, 71 a and 102a. In Fig. 9a the teeth of the sleeve 103 are meshed with teeth 70a and 102a, and in Fig. 9b the teeth of the sleeve 103 are meshed with teeth 71 a and 102a. Accordingly, both of the gears 70 and 71 are connected to the clutch shaft 62 by the sleeve 103 in Fig. 7 so that power is transmitted from the clutch shaft 62 to both of the PTO shafts 37 and 38.Only the gear 70 is connected to the shaft 62 in Fig. 9a, so that power is transmitted from the shaft 62 only to the front PTO shaft 37, whereas only gear 71 is connected to the shaft 62 by the sleeve 103 in Fig. 9b, so that power is transmitted from the shaft 62 only to the rear PTO shaft 38.

Fig. 10 is a hydraulic circuit diagram which illustrates the circuit for actuating the fluidoperated clutch 68 and shaft brake 69, associated with the clutch, employed in the PTO transmission according to the present invention, together with the hydraulic system for the hydrostatic transmission 27 employed in the transmission for driving the vehicle.

In the hydraulic circuit shown in Fig. 10, the hydraulic pump 42 and hydraulic motor 43 of the hydrostatic transmission 27 are connected with each other in a conventional fashion by a pair of fluid pressure-supplying and draining circuits 105 and 106 so that a closed circuit is formed. For supplementing fluid or oil from an oil tank 107, which is formed in a lower portion of transmission case 28, a charge pump 108 is provided which is driven by the engine 23 via the hydraulic pump 42. The oil charge circuit 109, including the charge pump 108, is connected to the pair of circuits 105 and 106 via a pair of check valves 110 and 111 which permit the flow of oil only toward the circuits 105 and 106.To control the pressure of the oil supplied to the closed circuit 105, 106, a first relief valve 11 3 is provided which is connected to charge circuit 109 via a check valve 11 2 permitting a flow of oil only from the circuit 109.

The hydraulic system for the PTO system is designed such that a supply of clutch-operating fluid to the fluid-operated clutch 68 is made by the charge pump 108 of the hydrostatic transmission 27. To this end, a fluid supply circuit 114 for the clutch 68 is branched from the circuit connecting the check valve 11 2 and the first relief valve 11 3.

In this fluid supply circuit 114 is incorporated a control valve 11 5 for controlling the supply and drainage of fluid for the clutch 68. This control valve 11 5 has an operating position I, wherein fluid is supplied to the clutch 68, and a neutral position N wherein fluid is drained from the clutch 68 to the tank 107. The fluid chamber 100 for the brake 69 is connected to the fluid supply circuit 11 4 at the clutch port side of the control valve 11 5 by means of a connecting circuit 11 6.

It is designed that oil drained through the first relief valve 11 3 is used as lubricating oil for parts to be lubricated 115, such as the frictional elements of the clutch 68, frictional plate members of the brake 69, bearings on the clutch shaft 62 and the like. To this end, a second relief valve 11 7 is incorporated in the drain circuit 11 6 of the first relief valve 11 3 to establish the pressure of the lubricating oil. A lubricant supply circuit 11 8 which is communicated to the parts to be lubricated 11 5 is branched from a point before the second relief valve 11 7 in the drain circuit 116.

To establish the fluid pressure applied to the fluid-operated clutch 68, use is made of a relief valve of the type which modulates fluid pressure applied to the clutch 68 so as to increase such pressure gradually to a predetermined value. A third relief valve 1 20 of such a pressure-modulating type is incorporated in a circuit 11 9 which is branched from the fluid supply circuit 114 at the outlet side of control valve 11 5 and is connected to the second relief valve 11 7. The third relief valve 1 20 is fashioned such that the base end of a spring 102a, for establishing fluid pressure, is received by a control piston 1 20b which may advance to a predetermined position and to which fluid pressure at the inlet side of the valve 1 20 is applied through a throttled fluid path. In the pressure-modulating system shown, a throttle valve 1 22 including first and second orifices 1 22a and 1 22b is incorporated in a ciucuit 1 2 for applying fluid pressure to the control piston 120b. The first orifice 1 22a restricts the flow of fluid more than the second orifice 122b.Throttle valve 1 22 has a first position A where the first orifice 1 22a is inserted in the circuit 121 and a second position B where the second orifice 1 22b is inserted in the circuit 121, the valve being biased by a spring 1 23 toward the first position A. A pilot circuit 1 24 applies fluid pressure on the outlet side of throttle valve 1 22 to the valve to displace it to the second position B so that, when the fluid pressure on the outlet side of throttle valve 1 22 has been increased to a predetermined value, enough to overcome the biasing force of the spring 123, the valve 1 22 is displaced to the second position B. To release the fluid pressure applied to the control piston 1 20b quickly when the control valve 11 5 is displaced from the operating position I to the neutral position N,, a check valve 225 is provided which is connected in parallel with the throttle valve 1 22.

Owing to the provision of a pressure-modulating system, including the third relief valve 1 20 set forth above, when the control valve 11 5 is displaced from the neutral position N to the operating position 1, fluid pressure applied to the fluid-operated clutch 68 is then increased in a manner shown in Fig. 11. This illustrates the fluid pressure P applied to the clutch 68 with time t. At the point at which the control valve 11 5 is displaced to the operating position I, fluid pressure P is quickly enlarged to a low initial pressure P,, such as 2 kg/cm2, which corresponds to the biasing force of the pressure-establishing spring 1 20a at the most retreated position of the control piston 120b.Due to a gradual supply of fluid to the control piston 1 20b through the first orifice 1 22a of the throttle valve 122, the control piston 120b is then gradually advanced so as to enlarge the biasing force of the spring 120a gradually. Consequently, the fluid pressure P is gradually increased along a line C1 shown in Fig. 11. Enlargement of the fluid pressure P along the line C, continues until the pressure P has been reached a value corresponding to the biasing force of the spring 123 resulting in displacement of the throttle valve 1 22 to the second position B.

From the point t1, where the throttle valve 122 is displaced to the second position B, fluid is supplied to the control piston 1 20b through the second orifice 122b, providing a smaller restriction to the flow of fluid, so that the control piston 120b is advanced relatively rapidly. Consequently, the fluid pressure P is enlarged relatively rapidly along a line C2 having the relatively steep gradient shown in Fig. 11. The biasing force of the spring 1 23 for placing the throttle valve 1 22 in the first position A is predetermined so that the fluid pressure P1 obtained at time t, is, for example, 5 kg/cm2 at the initial engagement between the frictional elements of the fluidoperated clutch 68 and the initial transmission of torque.

Accordingly, the fluid-operated clutch 68 is brought into its operated state without any shock owing to the gradual increase in fluid pressure P along the lines C1 and C2 shown in Fig. 11 which is, nevertheless, a relatively short period of time owing to the rapid increase in pressure along line C2. The maximum relief pressure of the third relief valve 120, namely a fluid pressure which corresponds to the biasing force of spring 120a at the most advanced position of the control piston 120b, is a pressure P2, for example 1 8 kg/cm2, as shown in Fig. 11, whereas the first relief valve 11 3 is biased such that it operates at a pressure Pa as shown in Fig.

11, for example 1 3 kg/cm2, which is lower than the maximum relief pressure P2 of the third relief valve 120. It is thus seen that, after the pressure established by the third relief valve 120 has reached the relief pressure Pa of the first relief valve 113, fluid pressure Pa determined by the first relief valve 11 3 is applied to the fluid-operated clutch 68.

In other words, fluid pressure applied to the clutch 68 in its normal operated state settles to a value Pa (relief pressure of the first relief valve 113) which is lower than the maximum value P2 obtainable due to the third relief valve 1 20 at time t2. Consequently, the fluid pressure P might be increased further along the line C2 if the pressure-modulating system were fashioned such that fluid pressure applied to the clutch 68 were determined only by the third relief valve 1 20.

The third relief valve 1 20 passes little oil in the period in which the fluid pressure is gradually enlarged. The first relief valve 113, which is connected in parallel with the third relief valve 120, does not operate during the period in which the fluid pressure established by the third relief valve 1 20 is lower than the relief pressure of the first relief valve. Accordingly, if the first relief valve 11 3 were biased such that it operated at a pressure equal to or larger than the maximum relief pressure P2 of the third relief valve 120, then little oil would be supplied to the lubricant supply circuit 118 until time t2 where fluid pressure P, increased gradually by the third relief valve 120, would reach its maximum value P2.Conversely, the first relief valve 11 3 will operate so as to supply lubricant to the circuit 118 from time ta, where the fluid pressure established by the third relief valve 1 20 reaches the relief pressure Pa of the first relief valve 11 3 so that the period in which the supply of lubricant oil to the parts to be lubricated 11 5 is interrupted, is made relatively short.

As can be seen from Fig. 4, the clutch shaft 62 is offset across the transmission case 28.

A valve housing 125, which is connected integrally with the inner surface of rear wall of the case 28 as well as with the inner surface of one of the side walls of the case nearer to the shaft 62, is projected into the transmission case 28 and connected integrally with the sleeve 86. As shown in Fig. 12, this valve housing 1 25 includes fluid paths which have been formed in the molding of the transmission case 28.These fluid paths are shaped to open on one side of the case 28, such openings being closed by a cover 202, shown in Fig. 8, which is secured to a side wall of transmission case 28 by means of fastening bolts 201 in threaded bores 1 26. The fluid paths include first and second fluid paths 1 27 and 1 28 which correspond respectively to portions of the fluid supply circuit 114 at the inlet and outlet sides of control valve 11 5 shown in Fig. 1 0, a third fluid path 1 29 corresponds to the lubricant supply circuit 11 8 shown in Fig. 10, and a fourth fluid path 130, which is communicated to the inside of the transmission case 28, includes an oil tank.

The second fluid path 1 28 is communicated to the fluid path 91 in the sleeve 86 shown in Figs. 7 and 8, whereas the third path is communicated, via a fluid path 1 32 formed in the sleeve 86 as shown in Fig. 8, to a space 1 32 shown in Fig. 7 within which the springs 99 are disposed.

As shown in Fig. 12, the control valve 11 5 comprises a spool which is slidably located within the valve housing 1 25 in a longitudinal direction. A shifter 1 33 for displacing the spool is attached within the housing 125 to a control shaft 1 34 which is rotatably supported by the valve housing 1 25. The control valve 11 5 can be displaced to a position corresponding to the operating position I shown in Fig. 10, in which first and second fluid paths 1 27 and 1 28 in the housing 1 25 are communicated with each other, and to another position, corresponding to the neutral position N, shown in Fig. 10, in which second and fourth fluid paths 1 28 and 1 30 in the housing 1 25 are communicated with each other. As can be understood from Fig. 13, the sleeve 86 and valve housing 1 25 are arranged at a corner of the upper portion of transmission case 28 in a compact fashion. Because the sleeve 86 and valve housing 1 25 are connected integrally with each other the fluid path between the control valve 115, the clutch 68 and the brake 69 may be formed without additional piping.

As shown in Fig. 7, the fluid path 85 in the clutch shaft 62 is bored out from the rear end and plugged by a threaded plug 1 35. In the clutch shaft 62 is another fluid path 1 36 which is communicated, through a central bore 1 37 in the piston 96, to the space 1 32 to which lubricant oil is supplied. This fluid path 1 36 is communicated to the parts 11 5 on the shaft 62 which are to be lubricated, as shown in Fig. 10.

In Fig. 3, the charge pump 108 is arranged on the rear of transmission case 28 and is integral with hydraulic pump 1 38 for the hydraulic lift mechanism, which has lift arms 40 shown in Fig. 1. The pump shaft 1 39 of this charge pump 108 is located within another sleeve 101 and driven by the transmission shaft 61 by means of a coupling 140.

As shown in Fig. 3, the rear PTO change speed gearing 77 comprises two gears 142 and 143 fixedly mounted on the intermediate shaft 63 and two gears 144 and 145 rotatably mounted on the rear PTO shaft 38. Gears 142 and 1 43 are constantly meshed with gears 144 and 145, respectively. Between gears 1 44 and 145 is slidably but non-rotatably mounted a selection sleeve 146 on the rear PTO shaft 38 for connecting one of the gears 144,145 to the shaft 38. The gearing 77 is thus fashioned as two-speed ratio gearing. The selection sleeve 146 is moved by a shift mechanism 146 shown in Fig. 8 which is supported by the transmission case 28 and extends through a side wall of the case 28.

The shift mechanism 148 for moving the selection sleeve 103 of the PTO selecting clutch 72 is supported by the transmission case 28 and extends through a side wall of the case 28, as shown in Fig. 4.

As shown in Fig. 3, the change speed gearing 53 for two-stage speed variation of the vehicle comprises the gear 52, another gear 149, fixedly mounted on the intermediate shaft 46, and two gears 150 and 151 rotatably mounted on the change speed shaft 47. Gears 52 and 149 are constantly meshed with gears 1 50 and 151, respectively. Between the gears 150 and 151 is slidably but non-rotatably mounted a selection sleeve 1 52 on the change speed shaft 47 for connecting one of the gears 150 and 151 selectively to the shaft 47. The gearing 53 is thus twospeed gearing. The selection sleeve 1 52 is moved by a shift mechanism 1 53 which is supported by the transmission case 28 and extends through a side wall of the case 28.

As shown in Fig. 5, a clutch 1 54 for locking the differential 55 is annexed to the gearing 55. Thus clutch 1 54 comprises a pin 1 57 which is attached to a selection sleeve 1 58 slidably mounted on a hub portion of a differential casing 1 55. When the sleeve 1 58 is slid toward the left as seen in Fig. 5, pin 1 57 is projected into the differential casing 1 55 so as to connect one of the driven pinions 1 56 non-rotatably to the casing 1 55.

As also shown in Fig. 5, each of the left and right disc brakes 58 comprises a pressure plate 159, which pushes the frictional elements together, i.e. supported non-rotatably by the output shaft 57 and transmission case 28, against a reaction area on the case 28, so as to cause an engagement between the frictional elements.In the brake 58 shown, a series of balls 1 60 which are inserted in cam grooves formed on the pressure plate 159, so as to displace the plate 1 59 toward the frictional elements when the plate 1 59 is rotated, are also fitted in complementary grooves formed on the inner surface of the boss of the internal gear 1 61 of the planetary gearing 59, so that the balls 1 60 bear on the internal gear 1 61. Sun gear 1 62 of the planetary gearing 59 is formed integrally with output shaft 57, and planetary gears 1 63 are supported by a carrier 1 64 fixedly mounted on the rear wheel drive shaft 31.

As shown in Fig. 3, the front wheel-driving clutch 60 comprises a gear 1 65 fixedly mounted on the change speed shaft 47 and another gear 166 rotatably mounted on the output shaft 50. These gears 1 65 and 1 66 are meshed with each other. For actuating the clutch 60, a shiftable clutch sleeve 167, for connecting a gear 1 66 to the shaft 50, is mounted on the shaft 50. This clutch sleeve 167 is moved by a shift mechanism 1 68 shown in Fig. 14 which is supported by the clutch case 49.

The frame plate 48 is fixedly secured to the front of the transmission case 28 by means of bolts 169 shown in Fig. 12 which are fitted into threaded bores 1 71 of the case 28 shown in Fig. 4 through bores 1 70 in the plate 48 shown in Fig. 14. As shown in Fig.

14, the frame plate 48 is formed with threaded bores 1 72 for fastening the hydrostatic transmission 27.

The cover plate 64 shown in Figs. 3 and 12 is secured to the rear of the transmission case 28 by means of bolts 1 73 which are in threaded bores 1 74 in the rear wall of the case 28 shown in Fig. 8. Axle housings 32 shown in Fig. 5 are secured to the transmission case 28 by means of bolts 175, only one of which is shown in Fig. 5. These bolts 1 75 are fitted in threaded bores 1 76 shown in Fig.

1 2 which are formed in the left and right walls of the transmission case 28.

An oil filter 177, shown in Fig. 10, which is provided within the oil tank 107, at the end of the charge circuit 109, is also located in a lower portion of transmission case 28 and constitutes a part of the case 28, as shown in Fig. 3.

As mentioned the working vehicle shown is used for various purposes such as reaping and earth-moving. In such uses, the vehicle travels at a speed controlled by the hydrostatic transmission 27 and change speed gearing 53, it also having a selective reverse direction.

When required, the front wheels 21 are also driven by engaging the front-wheel driving clutch 60. By using the PTO selecting clutch 72, either the front PTO shaft 37 or rear PTO shaft 38 or both of them may be driven so as to drive any piece of auxiliary machinery, such as a rotary tiller or mower connected to and drawn by the vehicle. Working implements drawn by the vehicle may be driven at a relatively high speed or a low speed by using the rear PTO change speed gearing 77.

Before the mechanically operated PTO-exchanging clutch 72 or rear PTO change speed gearing 77 is selected the fluid-operated clutch 68 is disengaged by operating the control valve 11 5. At that time, the brake 69 is automatically operated so as to brake the clutch shaft 62 so that inertial rotation of such shaft is terminated quickly. The springs 99 for actuating the brake 69 are predetermined to have a relatively small biasing force so that they do not prevent a shifting operation of the selection sleeve 103 or 146.That is, it is predetermined that the clutch shaft 62 is braked with a relatively small braking force, enough to permit some rotation of the shaft 62 when the teeth of the selection sleeve 103 or 106 are not in the correct angular positions for engagement with the teeth to be meshed, so that when the sleeve is shifted the correct angular positions of the teeth are obtained rapidly by some rotation of the shaft and selection sleeve for engagement. The brake 69 also acts in the non-operated state of the fluid-operated clutch 68 to prevent an unexpected transmission of power from the transmission shaft 61 to the clutch shaft 62 which might be caused by the drag of the lubricating oil within the clutch 68.

As can be understood from Figs. 3 and 7, the clutch shaft 62, supporting the fluidoperated clutch 68, is reduced in length considerably in comparsion with the conventional transmission, having a rotary joint in the fluid conduit line on the outside of transmission case, owing to the annular fluid chamber 90, constituting the rotary joint, being formed within the sleeve 86 which projects into the transmission case 28. Because the ball race 68, which receives the clutch shaft 62 at one end of the shaft, is supported by the innermost end portion of the sleeve 86, the clutch shaft 62 supporting the fluid-operated clutch 68, having a relatively large weight, is supported in a rigid manner.The brake 69 which is constructed by using the sleeve 86 projecting into the transmission case 28 as a brake case also does not require a structure which projects outwardly from an outer surface of the case 28.

Because the annular fluid chamber 90 constituting the rotary joint in the fluid conduit line is located as near as possible to the fluidoperated clutch 68, a drop in fluid pressure in the fluid-supplying and -draining path 85 within the clutch shaft 62 is largely avoided.

A drop in fluid pressure between the control valve 11 5 and the annular fluid chamber 90 is also avoided because the control valve 11 5 is disposed within a valve housing 1 25 which projects inwardly from the inner wall of the transmission case and is connected integrally with the sleeve 86 which includes therein the annular fluid chamber. The sleeve 86 and valve housing 1 25 eliminate the need for piping between the control valve 11 5 and the annular fluid chamber 90. Both sleeve and housing are arranged at a corner of the inside of transmission case 28 in a compact fashion.

Although such embodiment relates to a power transmission of PTO (power take-off) system for driving working implements in a working vehicle, the present invention may, of course, be embodied as a power transmission of vehicle-travelling or -driving system. Further, although the embodiment shown in the drawings relates to a power transmission in which only one fluid-operated clutch is provided on a transmission shaft, the present invention may also be embodied as a transmission having two or more fluid-operated clutches on a transmission shaft.

Claims (9)

1. A transmission system, including a hydraulic clutch and a shaft brake biased to the engaged position, mounted on a clutch shaft, the clutch and clutch shaft being mounted in a transmission case, the clutch being hydraulically connected, through a conduit within the clutch shaft and a rotary joint on the clutch shaft, to a hydraulic actuating circuit, wherein the rotary joint is located within a sleeve formed by an inwardly projecting portion of the wall of the transmission case, the shaft brake is carried by the sleeve and the rotary joint is connected to the hydraulic actuating circuit through the sleeve wall.

2. A transmission system as claimed in claim 1, wherein the clutch shaft is supported, on the brake side of the clutch, by a bearing mounted on the end of the sleeve nearest the clutch.

3. A transmission system as claimed in claim 2, wherein the bearing abuts a collar surrounding the clutch shaft and adjacent the outer case of the clutch.

4. A transmission system as claimed in claim 3, wherein the sleeve is integral with the wall of the transmission case and forms a recess in the outer face of the wall of the transmission case which is covered by a plate fixedly secured to the wall.

5. A transmission system as claimed in claim 4, wherein the brake is biased by means of a spring which bears against the inside of the plate at one end, and against one side of a brake piston at the other end, the fluid pressure in the clutch is applied to the piston to move the piston, against the force of the spring, to release the brake when the clutch is being engaged.

6. A transmission system as claimed in claim 5, wherein the brake comprises a set of annular friction plates, axially slidable and non-rotatably mounted on the clutch shaft, interleased with a set of annular friction plates, axially slidable and non-rotatably mounted on the inner surface of the sleeve, the brake piston has an annular end face to act on the plates.

7. A transmission system as claimed in any of preceding claims, wherein the hydraulic circuit includes a control valve movable in a valve housing, the valve housing being integral with the sleeve and the wall of the transmission case, the hydraulic connection between the rotary joint and the control valve being formed within the valve housing and sleeve.

8. A transmission system as claimed in claim 7, wherein the clutch shaft is laterally offset from the centre of the transmission case and the valve housing is located against a wall toward which the clutch shaft is offset and a perpendicular wall thereto.

9. A transmission system substantially as described with reference to the accompanying drawings.