Speed change transmission system

In order to provide a speed change transmission system which can be obtained compactly, while obtaining output at steplessly varied speeds over a large speed change range only by carrying out a simple shifting operation, the speed change transmission system has a hydrostatic stepless transmission to which engine drive is inputted. A planetary transmission device (P) has a plurality of planetary transmission mechanisms, for combining output of the stepless transmission and engine drive not undergoing speed change action by the hydrostatic stepless transmission. A plurality of transmission shafts are provided with a plurality of speed range setting clutches switchable for converting the combined driving force from the planetary transmission device (P) to a driving force in a plurality speed ranges, and transmitting it to an output rotary member. The plurality of transmission shafts are juxtaposed and arranged in parallel.

TECHNICAL FIELD

The present invention relates to a speed change transmission system, and more particularly to a speed change transmission system having a hydrostatic stepless transmission to which engine drive is inputted, and a planetary transmission device having a plurality of planetary transmission mechanisms for combining output of the hydrostatic stepless transmission and the engine drive not undergoing change speed action by the hydrostatic stepless transmission, wherein a combined driving force from the planetary transmission device is stage-divided into a plurality of speed ranges, and each stage of speed range is put to stepless speed changing to be outputted from an output rotary member.

BACKGROUND ART

In the above change speed transmission system, the stepless transmission is shiftable to stage-divide a combined driving force of engine output and the output of the stepless transmission or a combined driving force of engine output and the output of an electric motor into a plurality of speed ranges, and to output a driving force resulting from each speed range subjected to stepless speed changing. When this is used in driving a travel device, change speed transmission is realized advantageously, such as smoothing traveling speed changes, and simplifying shifting operations.

As this type of change speed transmission system, what is described in Patent Document 1 has been developed previously. While embodiments in Patent Document 1 are described hereinafter in order to facilitate understanding of the present invention, this is not necessarily an acknowledgement that Patent Document 1 constitutes prior art providing a basis for determining novelty or obviousness of the present invention.

In Patent Document 1, three types of speed change transmission system are described. One of the three speed change transmission systems (what is illustrated in FIG. 2 of Patent Document 1) includes a stepless transmission, a planetary transmission device, a clutch device, a third planetary transmission mechanism, and a brake for acting on the third planetary transmission mechanism.

The stepless transmission has a hydraulic pump of the variable displacement type with a pump shaft interlocked to an engine output shaft through a main clutch, and a hydraulic motor driven by pressure oil from this hydraulic pump.

The planetary transmission device has a first planetary transmission mechanism and a second planetary transmission mechanism. Planet gears of the first planetary transmission mechanism and planet gears of the second planetary transmission mechanism are interlocked by engagement between interlocking gear portions provided on the respective planet gears. The planet gears of the first planetary transmission mechanism and the planet gears of the second planetary transmission mechanism are supported by a carrier common to the first planetary transmission mechanism and second planetary transmission mechanism.

The clutch device has a first clutch, a second clutch, a third clutch and a fourth clutch. The first clutch has an input side rotary member interlocked to a ring gear of the second planetary transmission mechanism through an interlocking mechanism. The second clutch has an input side rotary member interlocked to a sun gear of the second planetary transmission mechanism through a rotary shaft. The third clutch has an input side rotary member interlocked to a carrier of the planetary transmission device through an interlocking mechanism.

The interlocking mechanism interlocking the input side rotary member of the first clutch and the ring gear of the second planetary transmission mechanism has a clutch side transmission gear meshed with the input side rotary member of the first clutch, a planetary side transmission gear meshed with the ring gear of the second planetary transmission mechanism, and a rotary shaft connected to the clutch side transmission gear and planetary side transmission gear. The interlocking mechanism interlocking the input side rotary member of the third clutch and the carrier of the planetary transmission device has a clutch side transmission gear meshed with the input side rotary member of the third clutch, a planetary side transmission gear meshed with the carrier, and a rotary shaft connected to the clutch side transmission gear and planetary side transmission gear.

The sun gear of the third planetary transmission mechanism is interlocked to an output side rotary member of the first clutch and second clutch, and the input side rotary member of the third clutch. The carrier of the third planetary transmission mechanism is interlocked to an output side rotary member of the third clutch and fourth clutch.

The brake is switchable between an engaged state for exerting braking action on the ring gear of the third planetary transmission mechanism, and a disengaged state for canceling the braking action on the ring gear.

With the speed change transmission system illustrated in FIG. 2 of Cited Document 1, output of the stepless transmission and the driving force of the pump shaft of the stepless transmission (engine drive not undergoing change speed action by the stepless transmission) are combined by the planetary transmission device. By shifting the stepless transmission, and by properly switching the first to fourth clutches and the brake between engaged state and disengaged state in timed relationship with the shifting operation, the combined driving force outputted from the planetary transmission device is stage-divided into a first speed range to a fourth speed range, and each speed range is put through stepless speed changing to be outputted from a carrier shaft of the third planetary transmission mechanism.

Another one (what is illustrated in FIG. 12 of Patent Document 1) and the other (what is illustrated in FIG. 16 of Patent Document 1) of the three speed change transmission systems described in Patent Document 1 have a stepless transmission, a planetary transmission device, a clutch device and an auxiliary change speed device.

The stepless transmission and planetary transmission device have the same constructions as the stepless transmission and planetary transmission device of the speed change transmission system illustrated in FIG. 2 of Patent Document 1.

The clutch device has a first clutch and a second clutch. The first clutch has an input side rotary member interlocked to the ring gear of the second planetary transmission mechanism of the planetary transmission device through an interlocking mechanism. The interlocking mechanism has a planetary side transmission gear meshed with the ring gear of the second planetary transmission mechanism, a clutch side transmission gear meshed with a gear portion of the input side rotary member of the first clutch, and a rotary interlocking shaft connected to the planetary side transmission gear and clutch side transmission gear.

The auxiliary change speed device has a high-speed clutch and a low-speed clutch. In the auxiliary change speed device illustrated in FIG. 16 of Patent Document 1, the high-speed clutch and low-speed clutch are dog clutches.

With the speed change transmission systems illustrated in FIG. 12 and FIG. 16 of Cited Document 1, output of the stepless transmission and the driving force of the pump shaft of the stepless transmission (engine drive not undergoing change speed action by the stepless transmission) are combined by the planetary transmission device. By shifting the stepless transmission, and by properly switching the first clutch, second clutch, high-speed clutch and low-speed clutch between engaged state and disengaged state in timed relationship with the shifting operation, the combined driving force outputted from the planetary transmission device is stage-divided into a first speed range to a fourth speed range, and each speed range is put through stepless speed changing to be outputted from an output shaft of the auxiliary change speed device.

In the case of a speed change transmission system employing the above conventional technique, the first to fourth clutches, or the first and second clutches and the high-speed and low-speed clutches, provided for stage-dividing the combined driving force from the planetary transmission device into a plurality of speed ranges for transmission to the output rotary member are arranged in the fore and aft direction of a transmission case, and tend to be large in the fore and aft direction of the transmission case.

Another problem of the conventional speed change transmission system is power cutting accompanying a shifting operation. A conventional speed change structure that can inhibit the power cutting accompanying a shifting operation is described in Patent Document 2.

The speed change transmission system described in Patent Document 2 has a first transmission line and a second transmission line arranged in parallel between a transmission shaft located upstream with respect to transmission for receiving engine power (hereinafter called the upstream transmission shaft) and a transmission shaft located downstream with respect to transmission for transmitting power to a travel device (hereinafter called the upstream transmission shaft). A transmission clutch of the hydraulic multi-plate type is disposed downstream of the first and second transmission lines. Between the upstream transmission shaft and first transmission line is a first gear speed change mechanism having a plurality of speed positions, and the first transmission line includes a first friction clutch. Between the upstream transmission shaft and second transmission line is a second gear speed change mechanism having a plurality of speed positions, and the second transmission line includes a second friction clutch. Between the first transmission line and downstream transmission shaft is a first auxiliary gear speed change mechanism having a plurality of speed positions. Between the second transmission line and downstream transmission shaft is a second auxiliary gear speed change mechanism having a plurality of speed positions.

The first gear speed change mechanism has a shift member operable by a first actuator, and the second gear speed change mechanism has a shift member operable by a second actuator. The first auxiliary gear speed change mechanism has a shift member operable by a first auxiliary actuator, and the second gear speed change mechanism has a shift member operable by a second auxiliary actuator.

The first actuator, first auxiliary actuator, second actuator and second auxiliary actuator are linked to a control device. The control device, based on a result of detection of a control position of the shift lever and a speed change mode selected by a setting switch, operates the first actuator to shift the first gear speed change mechanism, operates the second actuator to shift the second gear speed change mechanism, operates the first auxiliary actuator to shift the first auxiliary gear speed change mechanism, and operates the second auxiliary actuator to shift the second auxiliary gear speed change mechanism.

In a state where the shift lever is operated to one of a first speed position to an eighth speed position, the first gear speed change mechanism, first auxiliary gear speed change mechanism, second gear speed change mechanism and second auxiliary gear speed change mechanism are operated to a speed change state corresponding to the operated position of the shift lever. The power of the upstream transmission shaft is transmitted to the downstream transmission shaft through one of the first and second transmission lines.

When, for example, a second speed change mode is selected and the shift lever is operated from the first speed position to the fifth speed position, in the first half of speed change control accompanying this shifting operation, a double transmission state occurs in which power is transmitted to the downstream transmission shaft in a state where the shift member of the first gear speed change mechanism is in a first speed position, and simultaneously therewith and in addition thereto power is transmitted to the downstream transmission shaft in a state where the shift member of the second gear speed change mechanism is in a second speed position. In the second half of the speed change control, a double transmission state occurs in which power is transmitted to the downstream transmission shaft in a state where the shift member of the second gear speed change mechanism is in a second speed position, and simultaneously therewith and in addition thereto power is transmitted to the downstream transmission shaft in a state where the shift member of the first gear speed change mechanism is in a third speed position.

Even if torque variations arise in the double transmission states, the torque variations are absorbed by the transmission clutch in a half-transmission state slipping to some extent.

When speed changing is realized while inhibiting the power cutting by employing the above conventional technique, torque variations in the double transmission states are absorbed by slips of the friction clutches and transmission clutch. Then, when the double transmission states occur, it has been necessary to weaken operating forces that pressurize the friction clutches and transmission clutch to the half-transmission state, so that slips of the friction clutches and transmission clutch occur conveniently, thereby reliably avoiding damage to the transmission case and others. That is, a transmission loss in the double transmission states has tended to become large.

DISCLOSURE OF THE INVENTION

The object of this invention is to provide an improved speed change transmission system.

According to an embodiment of this invention, a speed change transmission system has a hydrostatic stepless speed change device for receiving engine drive; and a planetary transmission device having a plurality of planetary transmission mechanisms for combining output of the hydrostatic stepless speed change device and the engine drive not undergoing a speed change action by the hydrostatic stepless speed change device; a combined driving force from the planetary transmission device being stage-divided into a plurality of speed ranges, and subjected to stepless speed changing at each speed range for output from an output rotary member; the speed change transmission system comprising a first output gear interlocked to the planetary transmission device; a first input gear meshed with the first output gear; a first transmission shaft for supporting the first input gear; a first speed range setting clutch corresponding to the first transmission shaft, and having a first state for fixing the first input gear to the first transmission shaft, and a second state for allowing rotation of the first input gear relative to the first transmission shaft; a second output gear interlocked to the planetary transmission device; a second input gear meshed with the second output gear; a second transmission shaft for supporting the second input gear; and a second speed range setting clutch corresponding to the second transmission shaft, and having a first state for fixing the second input gear to the second transmission shaft, and a second state for allowing rotation of the second input gear relative to the second transmission shaft; wherein the first and second transmission shafts are juxtaposed and arranged in parallel for selectively transmitting drive to the output rotary member.

According to such construction, when the plurality of speed range setting clutches are switched appropriately in response to a shifting operation of the hydrostatic stepless transmission, the combined driving force from the planetary transmission device is stage-divided into a plurality of speed ranges, and is subjected to stepless speed changing in each speed range to be transmitted to the output rotary member. In order to carry out transmission from the planetary transmission device to the output rotary member through a transmission shaft corresponding to a speed range of this transmission, a plurality of transmission shafts including at least the first and second transmission shafts are provided. Since at least the first and second transmission shafts are juxtaposed and arranged in parallel, this part of the transmission system can be reduced to a size smaller than the conventional speed change transmission system in the fore and aft direction of the transmission case.

Therefore, output at steplessly varied speeds over a large speed change range can be obtained by carrying out a simple shifting operation consisting of shifting of the stepless transmission. Yet, the size in the fore and aft direction of the transmission case is made small and compact. The speed change transmission system obtained is easy to use, e.g. easy to mount in small vehicles also.

Preferably, the embodiment of this invention further comprises a third output gear interlocked the planetary transmission device; a third input gear supported on the first transmission shaft and meshed with the third output gear; a fourth output gear interlocked to the planetary transmission device; a fourth input gear supported on the second transmission shaft and meshed with the fourth output gear; wherein the first speed range setting clutch has a third state for fixing the third input gear to the first transmission shaft, and a fourth state for allowing rotation of the third input gear relative to the first transmission shaft; and the second speed range setting clutch has a third state for fixing the fourth input gear to the second transmission shaft, and a fourth state for allowing rotation of the fourth input gear relative to the second transmission shaft.

With this construction, a speed change transmission system can be provided which has at least four speed ranges by using two transmission shafts.

The above construction is applicable to a speed change transmission system having three or more transmission shafts.

Specifically, it is preferred that the embodiment of this invention comprises at least three transmission shafts including the first and second transmission shafts, having corresponding gear pairs and corresponding speed range setting clutches, and interlockable to the planetary transmission device through the gear pairs and the speed range setting clutches, wherein the at least three second transmission shafts are juxtaposed and arranged in parallel for selectively transmitting drive to the output rotary member.

In the embodiment of this invention, preferably, the planetary transmission device includes a pair of planetary transmission mechanisms having planet gears meshed with each other; and the first and second transmission shafts are juxtaposed over entire lengths thereof.

With this construction, since the first and second transmission shafts are juxtaposed over the entire lengths thereof, the length of the transmission from the planetary transmission device to the output rotary member can be reduced in the fore and aft direction of the transmission case, compared with these transmission shafts being arranged in parallel and staggered in the fore and aft direction of the transmission case.

In the embodiment of this invention, preferably, each of the first and second speed range setting clutches is a claw clutch.

With this construction, since the speed range setting clutches are claw clutches, the speed range setting clutches can be made lightweight and compact, compared with employing friction clutches as the speed range setting clutches.

In the embodiment of this invention, preferably, each of the claw clutches is hydraulically operable.

Being hydraulically operable enables a subtle operation.

In an embodiment of this invention, each of the first transmission shaft and the second transmission shaft has a friction clutch mounted thereon, thereby allowing a selective transmission of drive from one of the first transmission shaft and the second transmission shaft to the output rotary member.

With this construction, when switching between the first transmission shaft and the second range transmission shaft, for example, a double transmission state can be produced where the driving forces from these transmission shafts are simultaneously transmitted to the output rotary member. This can produce slips of the clutches to absorb torque variations.

According to an embodiment of this invention, a speed change transmission system has a hydrostatic stepless transmission for receiving engine drive; and a planetary transmission device having a plurality of planetary transmission mechanisms for combining output of the hydrostatic stepless transmission and the engine drive not undergoing a speed change action by the hydrostatic stepless transmission; a combined driving force from the planetary transmission device being stage-divided into a plurality of speed ranges, and subjected to stepless speed changing at each speed range for output from an output rotary member; the speed change transmission system comprising a first output gear interlocked to the planetary transmission device; a first input gear meshed with the first output gear; a first transmission shaft for supporting the first input gear; a first speed range setting clutch corresponding to the first transmission shaft, and having a first state for fixing the first input gear to the first transmission shaft, and a second state for allowing rotation of the first input gear relative to the first transmission shaft; a second output gear interlocked to the planetary transmission device; a second input gear meshed with the second output gear; a second transmission shaft for supporting the second input gear; and a second speed range setting clutch corresponding to the second transmission shaft, and having a first state for fixing the second input gear to the second transmission shaft, and a second state for allowing rotation of the second input gear relative to the second transmission shaft; wherein the first output gear and the first input gear have a gear ratio for forming a first speed range; and the second output gear and the second input gear have a gear ratio for forming a second speed range continuous with the first speed range and faster than the first speed range.

According to such construction, when the hydrostatic stepless transmission is shifted and the plurality of speed range setting clutches are switched appropriately in response to this shifting operation, the driving force outputted from the planetary transmission device is stage-divided into a plurality of speed ranges, and is subjected to stepless speed changing in each speed range to be transmitted to the output rotary member.

At a time of a speed range switching shifting operation for switching from one to the other of an odd number speed range such as the first speed range and an even number speed range such as the second speed range (hereinafter called inter-range speed change), switching is made from one to the other of a state where the driving force from the planetary transmission device is transmitted to the output rotary member through the first transmission shaft and a state where it is transmitted to the output rotary member through the second transmission shaft. Therefore, when, with an increase in speed, a change is made from one speed range to a faster (or slower) speed range speed, the speed change transmission system provided can use a different transmission shaft.

The embodiment of this invention, preferably, further comprises a third output gear interlocked the planetary transmission device; a third input gear supported on the first transmission shaft and meshed with the third output gear; a fourth output gear interlocked to the planetary transmission device; a fourth input gear supported on the second transmission shaft and meshed with the fourth output gear; wherein the first speed range setting clutch has a third state for fixing the third input gear to the first transmission shaft, and a fourth state for allowing rotation of the third input gear relative to the first transmission shaft; the second speed range setting clutch has a third state for fixing the fourth input gear to the second transmission shaft, and a fourth state for allowing rotation of the fourth input gear relative to the second transmission shaft; the third output gear and the third input gear have a gear ratio for forming a third speed range continuous with the second speed range and faster than the second speed range; and the fourth output gear and the fourth input gear have a gear ratio for forming a fourth speed range continuous with the third speed range and faster than the third speed range.

This construction can provide four speed ranges.

The embodiment of this invention, preferably, further comprises a shift detecting device for detecting a shift position of the hydrostatic stepless transmission; and a control device for switching each of the speed range setting clutches based on detection information by the shift detecting device, such that, in response to the shift position of the hydrostatic stepless transmission, the combined driving force from the planetary transmission device is stage-divided into the plurality of speed ranges, and subjected to stepless speed changing at each speed range for output from the output rotary member; wherein the control device is constructed to switch the first and second speed range setting clutches such that a speed range switching operation goes through a switching stage where the first speed range setting clutch mounted on the first transmission shaft and the second speed range setting clutch mounted on the second transmission shaft are both engaged.

That is, a shifting operation goes through a switching stage where the first speed range setting clutch mounted on the first transmission shaft and the second speed range setting clutch mounted on the second transmission shaft are both engaged. Specifically, before one of an odd number transmission line with the first transmission shaft and an even number transmission line with the second transmission shaft which transmit the driving force from the planetary transmission device to the output rotary member is switched to a disengaged state, the other is switched to an engaged state, and after the other is switched to the engaged state, the one is switched to the disengaged state. Thus, speed is changed through a double transmission state to prevent a break in the transmission to the output rotary member.

Thus, torque variations are effectively absorbed by the double transmission state of the clutches.

In an embodiment of this invention, preferably, the first transmission shaft has a fifth output gear; the second transmission shaft has a sixth output gear; the output rotary member has a fifth input gear meshed with the fifth gear and the sixth gear; the number of rotations is reduced between the third output gear and the third input gear and between the fifth output gear and the said fifth input gear; and gear ratios of the respective gears are set such that the number of rotations is reduced between the fourth output gear and the fourth input gear, and in a gear ratio of the sixth output gear and the fifth input gear.

With this construction, in transmitting the driving force of the third output gear to the output rotary member deceleration is made in two places, i.e. between the third output gear and first transmission shaft and between the fifth output gear and output rotary member. Similarly, in transmitting the driving force of the fourth output gear to the output rotary member deceleration is made in two places, i.e. between the fourth output gear and second transmission shaft and between the sixth output gear and output rotary member. This realizes a reduced space between the transmission shafts, and deceleration may be carried out without enlarging the portion of the gear mechanisms which set the speed ranges.

In an embodiment of this invention, preferably, the gear ratios are set to increase the number of rotations between the first output gear and the first input gear; and increase the number of rotations between the second output gear and the second input gear.

With this construction, it is assumed that gear ratios are set such that, for example, the number of rotations is increased to twice between the first output gear and first input gear, and the number of rotations is decreased to one half each between the third output gear and third input gear and between the fifth output gear and fifth input gear. By transmitting the driving force through the first output gear and first input gear and through the fifth output gear and fifth input gear, the driving force can be transmitted with reduction ratio 1, i.e. in a state of no reduction. By transmitting the driving force through the third output gear and third input gear and through the fifth output gear and fifth input gear, the driving force can be transmitted with the number of rotations reduced to one fourth.

On the other hand, in Patent Document 1 noted hereinbefore, one of the planetary mechanisms having a ring gear brake (third planetary transmission mechanism) reduces a rotating speed to one fourth with the ring gear brake engaged, and transmits the rotating speed without change with the ring gear brake released. Therefore, the above embodiment can obtain desired reduction ratios without using a complicated planetary mechanism having a brake.

The embodiment of this invention is not limited to two transmission shafts having the speed range setting clutches, but may include three or more.

That is, one embodiment, preferably comprises at least three transmission shafts including the first and second transmission shafts, having corresponding gear pairs and corresponding speed range setting clutches, and interlockable to the planetary transmission device, wherein the at least three second transmission shafts are juxtaposed and arranged in parallel for selectively transmitting drive to the output rotary member.

As in the embodiment of this invention, claws clutches engageable by hydraulic pressurization are used as the speed range setting clutches when a double transmission state is produced, or friction clutches are used on the first transmission shaft and second transmission shaft when claws clutches are used as the speed range setting clutches, to absorb torque variations in the double transmission state by slipping of the clutches. Besides absorbing torque variations in the double transmission state by the clutches, the hydrostatic stepless transmission absorbs the torque variations effectively by slipping of pressure oil. Absorption of the torque variations in the double transmission state is carried out effectively even when a relatively strong operating force pressurizes each clutch to a half-transmission state at the time of the double transmission state.

Therefore, also when stepless speed changing is carried out in each speed range and also when an inter-range speed changing is carried out, a break in transmission to the output rotary member does not easily occur. Moreover, high transmission efficiency of the clutches operated to the half-transmission state is achieved at the time of inter-range speed changing. The speed change transmission system provided can enable a smooth shifting operation with little chance of power break or transmission loss.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of this invention will be described hereinafter with reference to the drawings.

FIG. 1is a line map of a traveling transmission system of a tractor equipped with a speed change transmission system A in a first embodiment of this invention. As shown in this figure, the traveling transmission system of the tractor includes a main clutch2which receives output from an output shaft1aof an engine1, a forward and backward changeover device10which receives output of the main clutch2through an input shaft11, the speed change transmission system A according to the first embodiment of this invention which has an input shaft22interlocked through a gear21to an output gear12of the forward and backward changeover device10, a rear wheel differential mechanism32which has an input gear31connected to a rear end of an output shaft30acting as an output rotary member of the speed change transmission system A to be rotatable together, a front wheel change speed device40which has an input shaft41connected a through a joint33to a forward end of the output shaft30to be rotatable together, and a front wheel differential mechanism35which receives output from an output shaft42of the front wheel change speed device40through a rotary transmission shaft34.

The forward and backward changeover device10, speed change transmission system A, rear wheel differential mechanism32and front wheel change speed device40are housed in the same transmission case36

As shown inFIG. 1, a power takeoff shaft37projecting rearward from the transmission case36serves to transmit a driving force to various types of working implements such as a rotary plow connected to the tractor. This power takeoff shaft37is interlocked with the input shaft11of the forward and backward changeover device10through an interlocking shaft38and a working clutch39.

As shown inFIG. 1, the forward and backward changeover device10includes, besides the input shaft11and output gear12, an input side rotary member13mounted on the input shaft11to be rotatable together, and a forward drive friction clutch14of the multi-plate type mounted between one end of the input side rotary member13and the output gear12. The forward and backward changeover device10further includes a transmission gear15located opposite the output gear12across the input side rotary member13and supported to be rotatable relative to the input shaft11, a backward drive friction clutch16of the multi-plate type mounted between the transmission gear15and the other end of the input side rotary member13, a reversing gear17meshed with the transmission gear15, and an interlocking shaft18for interlocking the reversing gear17to the output gear12.

The forward and backward changeover device10is placed in a forward drive state when an operating hydraulic pressure is supplied to a forward drive piston, of the forward drive piston and a backward drive piston provided inside the input side rotary member13, whereby the forward drive piston pressurizes the forward drive friction clutch14into an engaged state, and is placed in a backward drive state when the operating hydraulic pressure is supplied to the backward drive piston whereby the backward drive piston pressurizes the backward drive friction clutch16into an engaged state.

When the forward and backward changeover device10is in the forward drive state, the driving force of the input shaft11is converted into a forward driving force through the input side rotary member13, forward drive friction clutch14and output gear12to be outputted from the output gear12to a stepless transmission20and a planetary transmission device P. When the forward and backward changeover device10is in the backward drive state, the driving force of the input shaft11is converted into a backward driving force through the input side rotary member13, backward drive friction clutch16, transmission gear15, reversing gear17and transmission shaft18, which is transmitted to the output gear12and outputted from the output gear12to the stepless transmission20and planetary transmission device P.

As shown inFIG. 1, the speed change transmission system A in the first embodiment of this invention includes, besides the input shaft22and output shaft30, the stepless transmission20, the planetary transmission device P having a sun gear shaft61interlocked to a motor shaft23of the stepless transmission20through a gear50and a gear51, and a speed range setter90having a first input gear91meshed with a first output gear81of the planetary transmission device P.

As shown inFIG. 1, the stepless transmission20includes a hydraulic pump24of the axial plunger type and variable displacement type having the input shaft22as a pump shaft (the input shaft being hereinafter called the pump shaft22), and a hydraulic motor25of the axial plunger type driven by pressure oil from the hydraulic pump24. The hydraulic motor25has the motor shaft23.

That is, the stepless transmission20is a hydrostatic stepless transmission switchable to a forward rotational transmission state, a neutral state, and a reverse rotational transmission state by changing a swash plate angle of the hydraulic pump24. The stepless transmission20, with the swash plate angle of the hydraulic pump24changed in the forward rotational transmission state, converts the engine drive force transmitted to the pump shaft22through the forward and backward changeover device10into a driving force in a direction of forward rotation, and changes its speed steplessly for output from the motor shaft23. The stepless transmission20, with the swash plate angle of the hydraulic pump24changed in the reverse rotational transmission state, converts the engine drive force transmitted to the pump shaft22through the forward and backward changeover device10into a driving force in a direction of reverse rotation, and changes its speed steplessly for output from the motor shaft23. The stepless transmission20, in the neutral state, stops output from the motor shaft23.

FIG. 2shows a sectional structure of the planetary transmission device P. As shown in this figure andFIG. 1, the planetary transmission device P includes a planetary transmission mechanism60located upstream in the direction of transmission (hereinafter abbreviated as the upstream planetary mechanism60), and a planetary transmission mechanism70located downstream (hereinafter abbreviated as the downstream planetary mechanism), for transmitting the driving forces inputted from the stepless transmission20and forward and backward changeover device10toward the speed range setter90.

The upstream planetary mechanism60a sun gear62provided at one end of the sun gear shaft61to be rotatable together, three planet gears63located peripherally of the sun gear62, distributed circumferentially of the sun gear62and meshed with the sun gear62, a carrier64for freely rotatably supporting the three planet gears63, and a ring gear65meshed with the three planet gears63. The sun gear62and sun gear shaft61are formed integrally.

The downstream planetary mechanism70includes a sun gear72located downstream, in the direction of transmission, of the sun gear62of the upstream planetary mechanism60to be rotatable about the same axis as the sun gear62, three planet gears73located peripherally of the sun gear72, distributed circumferentially of the sun gear72and meshed with the sun gear72, the carrier64for freely rotatably supporting the three planet gears73, and a ring gear75meshed with the three planet gears73.

FIG. 3is an arrangement plan of planet gears63of the upstream planetary mechanism60and the planet gears73of the downstream planetary mechanism70. As shown in this figure andFIG. 2, the three planet gears63of the upstream planetary mechanism60and the three planet gears73of the downstream planetary mechanism70are arranged such that one planet gear63of the upstream planetary mechanism60and one planet gear73of the downstream planetary mechanism70form one gear pair close together circumferentially of the sun gears62and72, that another planet gear63of the upstream planetary mechanism60and another planet gear73of the downstream planetary mechanism70form one gear pair close together circumferentially of the sun gears62and72, and that the remaining one planet gear63of the upstream planetary mechanism60and the remaining one planet gear73of the downstream planetary mechanism70form one gear pair close together circumferentially of the sun gears62and72. The planet gear63of the upstream planetary mechanism60and the planet gear73of the downstream planetary mechanism70in each gear pair are meshed with and interlocked to each other at ends opposite from the ends of the planet gears63and73meshed with the sun gears62and72.

In two adjacent gear pairs, the tooth tips of the planet gears63and73of one gear pair are located between the tooth tips of the planet gears63and73of the other gear pair. However, in two adjacent gear pairs, the planet gears63and73of one gear pair are not interlocked to the planet gears63and73of the other gear pair. By employing the arrangement where the tooth tips are located between the tooth tips of the planet gears63and73, the planetary transmission device P can be compact with a small outside diameter, with the sun gears62and72and ring gears65and75having reduced diameters, while allowing the planetary transmission device P to have necessary gear ratios.

As shown inFIG. 3, the planet gears63of the upstream planetary mechanism60are rotatably supported by support shafts64aof the carrier64, while the planet gears73of the downstream planetary mechanism70are rotatably supported by support shafts64bof the carrier64. That is, the carrier64is common to the upstream planetary mechanism60and downstream planetary mechanism70. Specifically, the carrier64supports the planet gears63and73so that each planet gear63of the upstream planetary mechanism60revolves around the sun gear62while rotating in mesh with the planet gear73forming a gear pair therewith of the downstream planetary mechanism70, and that each planet gear73of the downstream planetary mechanism70revolves around the sun gear72while rotating in mesh with the planet gear63forming a gear pair therewith of the upstream planetary mechanism60.

The ring gear65of the upstream planetary mechanism60is interlocked to the output gear12through an interlocking member66continuous from the ring gear65to be rotatable together, and through a transmission gear67connected by spline engagement to an end of the interlocking member66to be rotatable together, and engageable with the output gear12of the forward and backward changeover device10. The ring gear65and interlocking member66are formed integrally. The sun gear62of the upstream planetary mechanism60is interlocked to the motor shaft23of the stepless transmission20through the sun gear shaft61, gear51and gear50.

The planetary transmission device P includes, besides the first output gear81, a second output gear82, a third output gear83and a fourth output gear84arranged in the fore and aft direction in the transmission case and rearward of the first output gear81.

The first output gear81is interlocked to the ring gear75of the downstream planetary mechanism70to be rotatable together, through an interlocking member76having one end thereof connected by spline engagement to the first output gear81to be rotatable together. The interlocking member76and ring gear75are formed integrally.

A rotary support shaft85supporting the second output gear82and fourth output gear84to be rotatable together, and a sun gear shaft71supporting the sun gear72of the downstream planetary mechanism70to be rotatable together, are connected to be rotatable together by spline engagement. Thus, the second output gear82and fourth output gear84are rotatable together, and are interlocked to the sun gear72of the downstream planetary mechanism70to be rotatable together.

The third output gear83is connected to be rotatable together by spline engagement to the other end of a rotary shaft86having one end thereof connected to the carrier64to be rotatable together by spline engagement. Thus, the third output gear83is connected to the carrier64to be rotatable together through the rotary shaft86.

That is, in the planetary transmission device P, output from the motor shaft23of the stepless transmission20having received engine drive is inputted to the sun gear62of the upstream planetary mechanism60through the gear50, gear51and sun gear shaft61. The driving force of the output gear12of the forward and backward changeover device10is inputted as engine drive not undergoing the speed change action of the stepless transmission20, to the ring gear65of the upstream planetary mechanism60through the gear67and interlocking member66. The output of the stepless transmission20and the engine drive not undergoing the speed change action of the stepless transmission20are combined by the upstream planetary mechanism60and downstream planetary mechanism70. The combined driving force is outputted from the first second, third and fourth output gears81,82,83and84to the speed range setter90.

FIG. 2shows a sectional structure of the speed range setter90. As shown in this figure andFIG. 1, the speed range setter90includes, besides the first input gear91, a second input gear92, a third input gear93and a fourth input gear94meshed with the second output gear82, third output gear83and fourth output gear84, respectively, an odd number range transmission shaft95(first transmission shaft) as acting a transmission shaft for relatively rotatably supporting the first input gear91and third input gear93, and an even number range transmission shaft96(second transmission shaft) acting as a transmission shaft for relatively rotatably supporting the second input gear92and fourth input gear94.

FIG. 4is an arrangement plan in cross section of the speed change transmission system A. As shown in this figure andFIG. 2, the odd number range transmission shaft95and even number range transmission shaft96are, throughout their lengths, juxtaposed vertically in the transmission case36, and arranged parallel to each other. This realizes a reduced size of the speed range setter90in the fore and aft direction of the transmission case.

The odd number range transmission shaft95has a first clutch101mounted on a transmission tube portion91aof the first input gear91and the odd number range transmission shaft95, a third clutch103mounted on a transmission tube portion93aof the third input gear93and the odd number range transmission shaft95, and an odd number range transmission clutch107mounted on an end region remote from the end region on which the first input gear91is located of the odd number range transmission shaft95.

The even number range transmission shaft96has a second clutch102mounted on one side portion of the second input gear92and the even number range transmission shaft96, a fourth clutch104mounted on one side portion of the fourth input gear94and the even number range transmission shaft96, and an even number range transmission clutch108mounted on an end region remote from the end region on which the second input gear92is located of the even number range transmission shaft96.

FIG. 2shows sectional structures of the first clutch101, second clutch102, third clutch103and fourth clutch104. As shown in this figure, the first clutch101, second clutch102, third clutch103and fourth clutch104are claw clutches having shift gears105,106supported by the odd number range transmission shaft95or even number range transmission shaft96to be rotatable therewith and slidable through holders105a,106a, and gears101a,102a,103aand104aformed on the transmission tube portions91aand93aor side portions of the corresponding of input gears91,92,93and94.

Specifically, the first clutch101, second clutch102, third clutch103and fourth clutch104are engageable when hydraulic pistons111,112interlocked to the shift gears105,106through shifters and provided outside the transmission case36are operated to slide the shift gears105,106relative to the holders105aand106aand mesh with the holders105aand106aand the gears101a,102a,103aand104a, thereby transmitting the driving force of input gears91,92,93and94to the odd number range transmission shaft95and even number range transmission shaft96through the shift gears105,106and holders105aand106a, and rotating the input gears91and93with the odd number range transmission shaft95, or the input gears92and94with the even number range transmission shaft96.

The first clutch101, second clutch102, third clutch103and fourth clutch104are disengaged when the shift gears105,106are slid relative to the holders105aand106aand separated from the gears101a,102a,103aand104a, thereby allowing relative rotation between the input gears91and93and odd number range transmission shaft95or the input gears92and94and even number range transmission shaft96.

FIG. 2shows sectional structures of the odd number range transmission clutch107and even number range transmission clutch108. As shown in this figure, the odd number range transmission clutch107and even number range transmission clutch108are friction clutches having input side rotary members107aand108amounted on the odd number range transmission shaft95and even number range transmission shaft96to be rotatable together, output gears107b(fifth output gear) and108b(sixth output gear) mounted in the odd number range transmission shaft95and even number range transmission shaft96to be rotatable relative thereto, and friction clutch bodies107cand108cof the multi-plate type mounted between sides of the output gears107band108band the input side rotary members107aand108a.

The output gear107bof the odd number range transmission clutch107is interlocked to the output shaft30through a transmission gear109(fifth input gear) meshed with the output gear107band mounted on the output shaft30to be rotatable together. The output gear108bof the even number range transmission clutch108is meshed with the transmission gear109, and interlocked to the output shaft30through this transmission gear109.

Specifically, the odd number range transmission clutch107and even number range transmission clutch108are engaged when control hydraulic pressure is supplied from control oil lines116,117to hydraulic pistons114,115slidably mounted inside the input side rotary members107aand108a, and the hydraulic pistons114,115pressurize the friction clutch bodies107cand108cto a state of engagement, whereby the input side rotary members107aand108aand output gears107band108bare interlocked to be rotatable together by the friction clutch bodies107cand108c. The odd number range transmission clutch107and even number range transmission clutch108are disengaged when the control hydraulic pressure is discharged from the hydraulic pistons114,115, and the pressurization by the hydraulic pistons114,115of the friction clutch bodies107cand108cis canceled to place the friction clutch bodies107cand108cin an disengaged state, thereby allowing relative rotation of the input side rotary members107aand108aand the output gears107band108b.

Thus, the odd number range transmission clutch107, when engaged, transmits the driving force of the odd number range transmission shaft95to the output gear107bto establish transmission from the odd number range transmission shaft95to the output shaft30, and when disengaged, breaks the transmission from the odd number range transmission shaft95to the output shaft30.

The even number range transmission clutch108, when engaged, transmits the driving force of the even number range transmission shaft96to the output gear108bto establish transmission from the even number range transmission shaft96to the output shaft30, and when disengaged, breaks the transmission from the even number range transmission shaft96to the output shaft30.

FIG. 5is an explanatory view of operative states of the speed range setter90. The sign “ON” shown inFIG. 5indicates engaged states of the first, second, third and fourth clutches101,102,103,104, odd number range transmission clutch107and even number range transmission clutch108. The sign “−” shown inFIG. 5indicates disengaged states of the first, second, third and fourth clutches101,102,103,104, odd number range transmission clutch107and even number range transmission clutch108.

As shown in this figure, the speed range setter90sets the speed change transmission system A to a first speed range when the first clutch101is engaged and the second, third and fourth clutches102,103,104are disengaged. Then, the speed change transmission system A changes, through the first output gear81and first input gear91, the speed of a combined driving force outputted by the planetary transmission device P from the first output gear81, and transmits it to the odd number range transmission shaft95through the first clutch101. At this time, as the odd number range transmission clutch107is engaged, the speed change transmission system A transmits the driving force of the odd number range transmission shaft95to the output shaft30through the odd number range transmission clutch107and transmission gear109.

The speed range setter90sets the speed change transmission system A to a second speed range when the second clutch102is engaged and the first, third and fourth clutches101,103,104are disengaged. Then, the speed change transmission system A changes, through the second output gear82and second input gear92, the speed of a combined driving force outputted by the planetary transmission device P from the second output gear82, and transmits it to the even number range transmission shaft96through the second clutch102. At this time, as the even number range transmission clutch108is engaged, the speed change transmission system A transmits the driving force of the even number range transmission shaft96to the output shaft30through the even number range transmission clutch108and transmission gear109.

The speed range setter90sets the speed change transmission system A to a third speed range when the third clutch103is engaged and the first, second and fourth clutches101,102,104are disengaged. Then, the speed change transmission system A changes, through the third output gear83and third input gear93, the speed of a combined driving force outputted by the planetary transmission device P from the third output gear83, and transmits it to the odd number range transmission shaft95through the third clutch103. At this time, as the odd number range transmission clutch107is engaged, the speed change transmission system A transmits the driving force of the odd number range transmission shaft95to the output shaft30through the odd number range transmission clutch107and transmission gear109.

The speed range setter90sets the speed change transmission system A to a fourth speed range when the fourth clutch104is engaged and the first, second and third clutches101,102,103are disengaged. Then, the speed change transmission system A changes, through the fourth output gear84and fourth input gear94, the speed of a combined driving force outputted by the planetary transmission device P from the fourth output gear84, and transmits it to the even number range transmission shaft96through the fourth clutch104. At this time, as the even number range transmission clutch108is engaged, the speed change transmission system A transmits the driving force of the even number range transmission shaft96to the output shaft30through the even number range transmission clutch108and transmission gear109.

FIG. 8is a block diagram of an operating system provided for the tractor for operating the traveling transmission system. As shown in this figure, this operating system includes a shift lever120, a shift detecting device121, an engine output sensor122, a stepless transmission output sensor123, a vehicle speed sensor124, a forward and backward drive lever125, a forward and backward drive detecting device126, a speed change detecting device127, and a control device128linked with the detecting devices121,126,127and sensors122,123,124.

The control device128is linked with an operating device (not shown) of an actuator (not shown) for changing the swash plate angle of the hydraulic pump24of the stepless transmission20. The control device128is linked with control valves (not shown) for operating the hydraulic pistons111,112,114,115of the first clutch101, second clutch102, third clutch103, fourth clutch104, odd number range transmission clutch107and even number range transmission clutch108. The control device128is linked with an actuator (not shown) for switching the forward drive friction clutch14and backward drive friction clutch16.

As shown inFIG. 8, the shift lever120is rockable through an operating range from neutral position N to maximum speed position max. The portion of the operating range from neutral position N to a middle position M serves as a low-speed range L. The portion of the operating range from the middle position M to the maximum speed position max serves as a high-speed range H.

The shift detecting device121is formed of a rotary potentiometer interlocked to the shift lever120. This shift detecting device121detects an operating position of the shift lever120, and outputs this detection result to the control device128.

The engine output sensor122, stepless transmission output sensor123and vehicle speed sensor124are formed of rotary sensors. The engine output sensor122detects an output speed of the engine1, and outputs this detection result to the control device128. The stepless transmission output sensor123detects an output speed of the motor shaft23of the stepless transmission20, and outputs this detection result to the control device128. The vehicle speed sensor124detects a rotating speed of the output shaft30as vehicle speed, and outputs this detection result to the control device128. The speed change detecting device127detects a speed change state of the stepless transmission20, and feeds this detection result back to the control device128.

The forward and backward drive lever125is rockable to switch to a neutral position N, a forward position F and a reverse position R. The forward and backward drive detecting device126is formed of a rotary potentiometer interlocked to the forward and backward drive lever125. The forward and backward drive detecting device126detects an operating position of the forward and backward drive lever125, and outputs this detection result to the control device128.

The control device128is constructed using a microcomputer. This control device128controls the first, second, third and fourth clutches101,102,103,104, odd number range transmission clutch107and even number range transmission clutch108, based on detection information by the shift detecting device121, speed change detecting device127, engine output sensor122, stepless transmission output sensor123and vehicle speed sensor124, to place the speed change transmission system A in a speed range as an operating state corresponding to an operating position of the shift lever120to drive the output shaft30at a rotating speed corresponding to the operating position of the shift lever120. The control device128controls the forward drive friction clutch14and backward drive friction clutch16, based on detection information by forward and backward drive detecting device126, to place the forward and backward changeover device10in an operating state corresponding to the operating position of the forward and backward drive lever125.

Thus, by operating the shift lever120and forward and backward drive lever125, the tractor is caused to travel at a speed corresponding to an operating position of the shift lever120and an output speed of the engine1in a forward or backward direction corresponding to an operating position of the forward and backward drive lever125.

FIG. 6is an explanatory view showing a relationship between speed change states of the stepless transmission20, output speeds of the output shaft30of the speed change transmission system A, and speed ranges set by the speed range setter90of the speed change transmission system A. The vertical axis shown inFIG. 6represents the number of rotations of the output shaft30(hereinafter called output speed). The horizontal axis shown inFIG. 6represents the speed change states of the stepless transmission20. The sign “−MAX” on this horizontal axis indicates top speed in a reverse rotational transmission state of the stepless transmission20. “0” on the horizontal axis indicates neutral state of the stepless transmission20. The sign “+MAX” on the horizontal axis indicates top speed in a forward rotational transmission state of the stepless transmission20.

As shown in this figure,FIG. 5andFIG. 8, when the shift lever120is operated from neutral position N to a middle position Lm in the low-speed range L (hereinafter called low-speed middle position Lm), the control device128engages the first clutch101, and disengages the second, third and fourth clutches102,103,104, thereby placing the speed change transmission system A in the first speed range. At this time, the control device128engages the odd number range transmission clutch107, and disengages the even number range transmission clutch108. As a result, the speed change transmission system A transmits the driving force of the first output gear81of the planetary transmission device P to the odd number range transmission shaft95through the first input gear91and first clutch101, and transmits the driving force of the odd number range transmission shaft95to the output shaft30through the odd number range transmission clutch107and transmission gear109. As the shift lever120is operated from neutral position N toward low-speed middle position Lm, the control device128shifts the stepless transmission20from “−MAX” toward “+MAX”, thereby steplessly accelerating the output speed from “0”. When the shift lever120reaches the low-speed middle position Lm, the control device128operates the stepless transmission20to “+MAX”, thereby setting the output speed to “V1.”

When the shift lever120is operated from the low-speed middle position Lm in the low-speed range L to the middle position M, the control device128engages the second clutch102, and disengages the first, third and fourth clutches101,103,104, thereby placing the speed change transmission system A in the second speed range. At this time, the control device128engages the even number range transmission clutch108, and disengages the odd number range transmission clutch107. As a result, the speed change transmission system A transmits the driving force of the second output gear82of the planetary transmission device P to the even number range transmission shaft96through the second input gear92and second clutch102, and transmits the driving force of the even number range transmission shaft96to the output shaft30through the even number range transmission clutch108and transmission gear109. As the shift lever120is operated from the low-speed middle position Lm toward the middle position M, the control device128shifts the stepless transmission20from “+MAX” toward “−MAX”, thereby steplessly accelerating the output speed from “V1”. When the shift lever120reaches the middle position M, the control device128operates the stepless transmission20to “−MAX”, thereby setting the output speed to “V2.”

When the shift lever120is operated from neutral position N to a middle position Hm in the high-speed range H (hereinafter called high-speed middle position Hm), the control device128engages the third clutch103, and disengages the first, second and fourth clutches101,102,104, thereby placing the speed change transmission system A in the third speed range. At this time, the control device128engages the odd number range transmission clutch107, and disengages the even number range transmission clutch108. As a result, the speed change transmission system A transmits the driving force of the third output gear83of the planetary transmission device P to the odd number range transmission shaft95through the third input gear93and third clutch101, and transmits the driving force of the odd number range transmission shaft95to the output shaft30through the odd number range transmission clutch107and transmission gear109. As the shift lever120is operated from the middle position M toward the high-speed middle position Hm, the control device128shifts the stepless transmission20from “−MAX” toward “+MAX”, thereby steplessly accelerating the output speed from “V2”. When the shift lever120reaches the high-speed middle position Hm, the control device128operates the stepless transmission20to “+MAX”, thereby setting the output speed to “V3.”

When the shift lever120is operated from the high-speed middle position Hm in the high-speed range L to the maximum speed position max, the control device128engages the fourth clutch104, and disengages the first, second and third clutches101,102,103, thereby placing the speed change transmission system A in the fourth speed range. At this time, the control device128engages the even number range transmission clutch108, and disengages the odd number range transmission clutch107. As a result, the speed change transmission system A transmits the driving force of the fourth output gear84of the planetary transmission device P to the even number range transmission shaft96through the fourth input gear94and fourth clutch104, and transmits the driving force of the even number range transmission shaft96to the output shaft30through the even number range transmission clutch108and transmission gear109. As the shift lever120is operated from the high-speed middle position Hm toward the maximum speed position max, the control device128shifts the stepless transmission20from “+MAX” toward “−MAX”, thereby steplessly accelerating the output speed from “V3”. When the shift lever120reaches the maximum speed position max, the control device128operates the stepless transmission20to “−MAX”, thereby setting the output speed to “V4.”

When the forward and backward drive lever125is operated to the forward position F, the control device128engages the forward drive friction clutch14, and disengages the backward drive friction clutch16, thereby placing the forward and backward changeover device10in the forward drive state. Then, the forward and backward changeover device10transmits the driving force inputted from the engine1, as forward driving force, from the output gear12to the stepless transmission20and planetary transmission device P. The speed change transmission system A transmits the forward driving force to the front wheel differential mechanism35and rear wheel differential mechanism32, whereby the tractor travels forward.

When the forward and backward drive lever125is operated to the reverse position R, the control device128engages the backward drive friction clutch16, and disengages the forward drive friction clutch14, thereby placing the forward and backward changeover device10in the backward drive state. Then, the forward and backward changeover device10transmits the driving force inputted from the engine1, as backward driving force, from the output gear12to the stepless transmission20and planetary transmission device P. The speed change transmission system A transmits the backward driving force to the front wheel differential mechanism35and rear wheel differential mechanism32, whereby the tractor travels backward.

When the forward and backward drive lever125is operated to neutral position N, the control device128disengages the forward drive friction clutch14and backward drive friction clutch16, thereby placing the forward and backward changeover device10in neutral state. Then, the forward and backward changeover device10transmits no drive to the stepless transmission20or planetary transmission device P. The speed change transmission system A cuts transmission to the front wheel differential mechanism35and rear wheel differential mechanism32, thereby stopping the tractor.

FIG. 7is an explanatory view showing operating states of the first, second, third and fourth clutches101,102,103,104set by the control device128at the time of switching the speed ranges of the speed change transmission system A. The sign “inc” shown inFIG. 7indicates that the output speed of the output shaft30increases for switching of the speed ranges. The sign “dec” shown inFIG. 7indicates that the output speed of the output shaft30decreases for switching of the speed ranges.

As shown in this figure, when switching the speed ranges of the speed change transmission system A, the control device128operates the clutches101,102,103,104,107,108to create a double transmission state where both the odd number range transmission shaft95and even number range transmission shaft96temporarily become a driving state, and power is transmitted from planetary transmission device P to the output shaft30through the odd number transmission line having the odd number range transmission shaft95and the even number transmission line having the even number range transmission shaft96.

Specifically, when switching the speed change transmission system A from the first speed range to the second speed range, the control device128engages the second clutch102before disengaging the first clutch101, and disengages the first clutch101after the second clutch102is switched to the engaged state. At this time, the control device128engages the even number range transmission clutch108before disengaging the odd number range transmission clutch107, and disengages the odd number range transmission clutch107after the even number range transmission clutch108is switched to the engaged state.

When switching the speed change transmission system A from the second speed range to the third speed range, the control device128engages the third clutch103before disengaging the second clutch102, and disengages the second clutch102after the third clutch103is switched to the engaged state. At this time, the control device128engages the odd number range transmission clutch107before disengaging the even number range transmission clutch108, and disengages the even number range transmission clutch108after the odd number range transmission clutch107is switched to the engaged state.

When switching the speed change transmission system A from the third speed range to the fourth speed range, the control device128engages the fourth clutch104before disengaging the third clutch103, and disengages the third clutch103after the fourth clutch104is switched to the engaged state. At this time, the control device128engages the even number range transmission clutch108before disengaging the odd number range transmission clutch107, and disengages the odd number range transmission clutch107after the even number range transmission clutch108is switched to the engaged state.

When switching the speed change transmission system A from the fourth speed range to the third speed range, the control device128engages the third clutch103before disengaging the fourth clutch104, and disengages the fourth clutch104after the third clutch103is switched to the engaged state. At this time, the control device128engages the odd number range transmission clutch107before disengaging the even number range transmission clutch108, and disengages the even number range transmission clutch108after the odd number range transmission clutch107is switched to the engaged state.

When switching the speed change transmission system A from the third speed range to the second speed range, the control device128engages the second clutch102before disengaging the third clutch103, and disengages the third clutch103after the second clutch102is switched to the engaged state. At this time, the control device128engages the even number range transmission clutch108before disengaging the odd number range transmission clutch107, and disengages the odd number range transmission clutch107after the even number range transmission clutch108is switched to the engaged state.

When switching the speed change transmission system A from the second speed range to the first speed range, the control device128engages the first clutch101before disengaging the second clutch102, and disengages the second clutch102after the first clutch101is switched to the engaged state. At this time, the control device128engages the odd number range transmission clutch107before disengaging the even number range transmission clutch108, and disengages the even number range transmission clutch108after the odd number range transmission clutch107is switched to the engaged state.

When creating the double transmission state where both the odd number range transmission shaft95and even number range transmission shaft96are in the driving state, the control device128operates the odd number range transmission clutch107and even number range transmission clutch108to a half-transmission state. That is, even if variations in torque occur in the double transmission state, the stepless transmission20absorbs the variation in torque by slipping of its hydraulic oil. In addition, the control device128causes the odd number range transmission clutch107and even number range transmission clutch108to produce slipping for absorbing the variations in torque.

As shown inFIG. 1, the front wheel change speed device40includes, besides the input shaft41and output shaft42, a standard gear transmission mechanism45with a standard transmission clutch44, and an accelerating gear transmission mechanism47with an accelerating transmission clutch46, which are arranged on the input shaft41and output shaft42.

When the standard transmission clutch44is engaged and the accelerating transmission clutch46is disengaged, the front wheel change speed device40assumes a standard transmission state for transmitting the driving force of the input shaft41to the output shaft42through the standard gear transmission mechanism45. Then, the front wheel change speed device40drives the right and left front wheels such that an average peripheral velocity of the right and left front wheels and an average peripheral velocity of the right and left rear wheels are the same.

When the standard transmission clutch44is disengaged and the accelerating transmission clutch46is engaged, the front wheel change speed device40assumes a standard transmission state for transmitting the driving force of the input shaft41to the output shaft42through the accelerating gear transmission mechanism47. Then, the front wheel change speed device40drives the right and left front wheels such that an average peripheral velocity of the right and left front wheels is approximately twice as fast as an average peripheral velocity of the right and left rear wheels.

FIG. 9is a line map of a traveling transmission system of a tractor equipped with a speed change transmission system A in a second embodiment of this invention.

In the traveling transmission system of the tractor equipped with the speed change transmission system A in the second embodiment of this invention, output from output shaft30acting as output rotary member of the speed change transmission system A to a rear wheel differential mechanism32and a front wheel change speed device40through a forward and backward changeover device10.

As shown inFIGS. 9,10and11, the forward and backward changeover device10includes an input side rotary member13mounted on the output shaft30to be rotatable together, output gears19aand19blocated at the front and rear of this input side rotary member13, a forward drive friction clutch14mounted between one end of the input side rotary member13and the front output gear19a, a backward drive friction clutch16mounted between the other end of the input side rotary member13and the rear output gear19b, and a reversing gear17meshed with the rear output gear19b

The front output gear19ais interlocked to an input gear31of the rear wheel differential mechanism32an input shaft41of the front wheel change speed device40through a transmission gear130and a transmission shaft131. The reversing gear17is interlocked to the input gear31of the rear wheel differential mechanism32and the input shaft41of the front wheel change speed device40through a transmission gear132and the transmission shaft131.

When the speed change transmission system A in the second embodiment and the speed change transmission system A in the first embodiment are compared, the same construction is provided in which the planetary transmission device P combines the output of the stepless transmission20to which engine drive is inputted, and the engine drive force not undergoing the speed change action by the stepless transmission20, and the combined driving force from the planetary transmission device P is converted into the four stage speed ranges by switching of the first, second, third and fourth clutches101,102,103,104, which are transmitted by the two transmission shafts, i.e. the odd number range transmission shaft95and even number range transmission shaft96, to the output shaft30acting as the output rotary member. Different constructions are provided in respect of the planetary transmission device P. This difference will be described.

As shown inFIGS. 9 and 10, the planetary transmission device P of the speed change transmission system A in the second embodiment includes a first planetary transmission mechanism140, a second planetary transmission mechanism150and a third planetary transmission mechanism160.

As shown inFIG. 10, the first planetary transmission mechanism140, second planetary transmission mechanism150and third planetary transmission mechanism160have one sun gear141,151,161, a plurality of planet gears142,152,162, a ring gear143,153,163and a carrier144,154,164.

The sun gear141of the first planetary transmission mechanism140is interlocked to a motor shaft23of the stepless transmission20through a sun gear shaft145, a gear170and a gear171. The carrier144of the first planetary transmission mechanism140, the ring gear153of the second planetary transmission mechanism150and the carrier164of the third planetary transmission mechanism160are interlocked to be rotatable together. The ring gear143of the first planetary transmission mechanism140and the carrier154of the second planetary transmission mechanism150are interlocked to be rotatable together, and are interlocked to a pump shaft22of the stepless transmission20to be rotatable together through an interlocking shaft172. The sun gear151of the second planetary transmission mechanism150and the sun gear161of the third planetary transmission mechanism160are interlocked to be rotatable together.

The planetary transmission device P has a first output gear81interlocked to the carrier144of the first planetary transmission mechanism140to be rotatable together, has a second output gear82and a fourth output gear84interlocked to the sun gears151,161of the second and third planetary transmission mechanisms150,160to be rotatable together, and has a third output gear83interlocked to the ring gear163of the third planetary transmission mechanism160to be rotatable together.

The planetary transmission device P inputs output from the motor shaft23of the stepless transmission20to the sun gear141of the first planetary transmission mechanism140, inputs the driving force of the pump shaft22of the stepless transmission20as engine drive not undergoing the speed change action by the stepless transmission20to the ring gear143of the first planetary transmission mechanism140and the carrier154of the second planetary transmission mechanism150, and combines the inputted driving force of the stepless transmission20and driving force of the engine1through the first planet gear mechanism140, second planetary transmission mechanism150and third planetary transmission mechanism160. The combined driving force is transmitted from the first output gear81to the first input gear91of the odd number range transmission shaft95, transmitted from the second output gear82to the second input gear92of the even number range transmission shaft96, transmitted from the third output gear83to the third input gear93of the odd number range transmission shaft95, and transmitted from the fourth output gear84to the fourth input gear94of the even number range transmission shaft96.

The first output gear81and first input gear91are interlocked in a transmission ratio in which the number of rotations of the first input gear91is twice the number of rotations of the first output gear81. The second output gear82and second input gear92are interlocked in a transmission ratio in which the number of rotations of the second input gear92is twice the number of rotations of the second output gear82. The third output gear83and third input gear93are interlocked in a transmission ratio in which the number of rotations of the third input gear93is one half of the number of rotations of the third output gear83. The fourth output gear84and fourth input gear94are interlocked in a transmission ratio in which the number of rotations of the fourth input gear94is one half of the number of rotations of the fourth output gear84. An output gear107bof the odd number range transmission clutch107and a driven gear173of the output shaft30are interlocked in a transmission ratio in which the number of rotations of the output shaft30is one half of the number of rotations of the output gear107b. An output gear108bof the even number range transmission clutch108and a driven gear174of the output shaft30are interlocked in a transmission ratio in which the number of rotations of the output shaft30is one half of the number of rotations of the output gear108b.

Thus, in transmitting the driving force of the third output gear83to the output shaft30with deceleration to one fourth of the number of rotations, deceleration is made in two places, i.e. between the third output gear83and odd number range transmission shaft95and between the output gear107band output shaft30. In transmitting the driving force of the fourth output gear84to the output shaft30with deceleration to one fourth of the number of rotations, deceleration is made in two places, i.e. between the fourth output gear84and even number range transmission shaft96and between the output gear108band output shaft30. Then, one fourth deceleration can be achieved while maintaining the size of the speed range setter90small.

FIG. 12is a line map of a traveling transmission system of a tractor equipped with a speed change transmission system A in a third embodiment of this invention.

In the traveling transmission system of the tractor equipped with the speed change transmission system A in the third embodiment of this invention, output from output shaft30acting as output rotary member of the speed change transmission system A to a rear wheel differential mechanism32and a front wheel change speed device40through a forward and backward changeover device10.

As shown inFIGS. 12,13and14, the forward and backward changeover device10in the traveling transmission system equipped with the speed change transmission system A in the third embodiment has the same construction as the forward and backward changeover device10in the traveling transmission system equipped with the speed change transmission system A in the second embodiment.

When the speed change transmission system A in the third embodiment and the speed change transmission system A in the first embodiment are compared, the same construction is provided in which the planetary transmission device P combines the output of the stepless transmission20to which engine drive is inputted, and the engine drive force not undergoing the speed change action by the stepless transmission20, and the combined driving force from the planetary transmission device P is converted into the four-stage speed ranges by switching of the first, second, third and fourth clutches101,102,103,104, which are transmitted by the two transmission shafts, i.e. the odd number range transmission shaft95and even number range transmission shaft96, to the output shaft30acting as the output rotary member. Different constructions are provided in respect of the planetary transmission device P and speed range setter90.

As shown inFIGS. 12 and 13, the planetary transmission device P of the speed change transmission system A in the third embodiment has the same construction as the planetary transmission device P of the speed change transmission system A in the second embodiment.

As shown inFIGS. 12 and 13, the speed range setter90of the speed change transmission system A in the third embodiment, and the speed range setter90of the speed change transmission system A in the first embodiment, are the same in that the odd number range transmission shaft95and even number range transmission shaft96are arranged in juxtaposition and in parallel.

The speed range setter90of the speed change transmission system A in the third embodiment, and the speed range setter90of the speed change transmission system A in the first embodiment, are the same in construction in that the odd number range transmission shaft95has, freely rotatably mounted thereon, a first input gear91meshed with the first output gear81of the planetary transmission device P and a third input gear93meshed with the third output gear83of the planetary transmission device P, that the even number range transmission shaft96, has, freely rotatably mounted thereon, a third input gear93meshed with the second output gear83of the planetary transmission device P and a fourth input gear94meshed with the fourth output gear84of the planetary transmission device P, that the first clutch101transmits the driving force of the first input gear91to the odd number range transmission shaft95, that the second clutch102transmits the driving force of the second input gear92to the even number range transmission shaft96, that the third clutch103transmits the driving force of the third input gear93to the odd number range transmission shaft95, and that the fourth clutch104transmits the driving force of the fourth input gear94to the even number range transmission shaft96.

The speed range setter90of the speed change transmission system A in the third embodiment transmits the driving force of the odd number range transmission shaft95to the output shaft30through an output gear95amounted on a rear end portion of the odd number range transmission shaft95to be rotatable together, and an input gear30amounted on a forward end region of the output shaft30to be rotatable together and meshed with the output gear95a. The driving force of the even number range transmission shaft96is transmitted to the output shaft30through an output gear96amounted on a rear end region of the even number range transmission shaft96to be rotatable together, and the input gear30ameshed with this output gear96a.

The output gear95aof the odd number range transmission shaft95and the output gear96aof the even number range transmission shaft96are meshed with the same input gear30afor transmission to the output shaft30. This transmission structure allows the size in the fore and aft direction of the speed range setter90to be small.

In the speed range setter90of the speed change transmission system A in the third embodiment, the first clutch101, second clutch102, third clutch103and fourth clutch104are claw clutches with hydraulic pistons101b,102b,103band104brotatable with and slidable relative to the odd number range transmission shaft95or even number range transmission shaft96.

That is, the hydraulic pistons101b,102b,103band104bare interlocked by engagement of opposite clutch projections.

When both the clutch of the odd number range transmission shaft95(first clutch101or third clutch103) and the clutch of the even number range transmission shaft96(second clutch102or fourth clutch104) are engaged to provide a double transmission state, the speed range setter90in the third embodiment absorbs torque variations in the double transmission state. Thus, the speed range setter90in the third embodiment dispenses with the odd number range transmission clutch107and even number range transmission clutch108employed in the speed range setter90of the first embodiment and second embodiment, thereby achieving an increase in transmission efficiency and compactness of the speed range setter90.

FIG. 15is a line map of a traveling transmission system of a tractor equipped with a speed change transmission system A in a fourth embodiment of this invention. When the speed change transmission system A in the fourth embodiment and the speed change transmission system A in the first embodiment are compared, the same construction is provided in respect of the planetary transmission device P and speed range setter90. The speed change transmission system A in the fourth embodiment and the speed change transmission system A in the first embodiment are different in the construction for inputting a driving force for stepless speed changing. This difference will be described next.

The speed change transmission system A in the fourth embodiment has an electric motor180. The planetary transmission device P inputs output from an output shaft180aof the electric motor180to the sun gear62of the upstream planetary mechanism60through a transmission gear181, a transmission gear182and a sun gear shaft61. The planetary transmission device P inputs output from an output shaft1aof engine1to the ring gear65of the upstream planetary mechanism60through the main clutch2, forward and backward changeover device10and gear67. The planetary transmission device P receives and combines the driving force of engine1and the driving force of electric motor180, transmits this combined driving force from the first output gear81and third output gear83to the odd number range transmission shaft95of the speed range setter90, and transmits from the second output gear82and fourth output gear84to the even number range transmission shaft96of the speed range setter90.

The electric motor180changes the number of drive rotations steplessly in response to a shifting operation by a driver183. With this speed change operation of the electric motor180, the first, second, third and fourth clutches101,102,103,104, odd number range transmission clutch107and even number range transmission clutch108are switched to drive the output shaft30as divided into the four stages of the first speed range to the fourth speed range, and subjected to stepless speed changing in each speed range, as in the speed change transmission system A in the first embodiment

Other Embodiment

Each embodiment described above may be modified such that the odd number range transmission shaft95is divided into a transmission shaft having the first clutch101and interlocked to the output shaft30, and a transmission shaft having the third clutch103and interlocked to the output shaft30, that the even number range transmission shaft96is divided into a transmission shaft having the second clutch102and interlocked to the output shaft30, and a transmission shaft having the fourth clutch104and interlocked to the output shaft30, and that the transmission shafts are juxtaposed and arranged in parallel. A construction may be employed which includes one transmission shaft with the first clutch101and second clutch102, and one transmission shaft with the third clutch103and fourth clutch104, the two transmission shafts being juxtaposed and arranged in parallel. Either case can fulfill the object of this invention.

INDUSTRIAL UTILITY

The speed change power transmission system according to this invention can be used as a speed change transmission system included in a drive system of a working vehicle such as a tractor.