Patent Description:
Conventionally, continuously variable transmissions such as HMT (Hydraulic Mechanical Transmission) have been known. For example, the transmission of <CIT> includes a first planetary gear mechanism, a second planetary gear mechanism, a first pump / motor, and a second pump / motor.

An input shaft of the transmission is connected to a sun gear of the first planetary gear mechanism via a FR switching mechanism. A ring gear of the first planetary gear mechanism is connected to a carrier of the second planetary gear mechanism via a clutch. A ring gear of the second planetary gear mechanism is connected to an output shaft. The first pump / motor is connected to a carrier of the first planetary gear mechanism. The second pump / motor is connected to the ring gear of the first planetary gear mechanism.

<CIT> and <CIT> disclose an electrically variable transmission with selective operation both in power-split variable speed ratio ranges and in fixed speed ratios, and having three planetary gears sets, two motor/generators and three or four clutches.

In the transmission of <CIT>, the ring gear of the first planetary gear mechanism is connected to the clutch. Besides, in a similar way <CIT> and <CIT> also comprise a clutch that selectively connects the ring gear with the sun gear. The ring gear have a larger outer diameter than other gears. Therefore, as the clutch becomes larger, the transmission becomes larger. Further, the ring gear of the first planetary gear mechanism and the ring gear of the second planetary gear mechanism each have an external tooth type output gear. Therefore, the transmission becomes even larger.

An object of the invention as claimed is to reduce a size of a continuously variable transmission by a variable device.

A transmission according to the invention as claimed in claim <NUM> includes an input shaft, an output shaft, a first planetary gear mechanism, a second planetary gear mechanism, and a first variable device. The first planetary gear mechanism includes a first carrier, a first planetary gear, a first sun gear, and a first ring gear. The first carrier is connected to the input shaft. The first planetary gear is rotatably carried by the first carrier. The first sun gear meshes with the first planetary gear. The first ring gear meshes with the first planetary gear. The second planetary gear mechanism includes a second sun gear, a second planetary gear, and a second ring gear. The second sun gear is connected to the first carrier. The second planetary gear meshes with the second sun gear. The second ring gear meshes with the second planetary gear. The second ring gear is connected to the first ring gear. The first variable device continuously changes a speed ratio of the output shaft to the input shaft. The first variable device is connected to the first ring gear and the second ring gear.

The transmission comprises further a second variable device that continuously changes the speed ratio, a shaft that directly connects the first sun gear and the second variable device, a high speed gear connected to the output shaft, a high speed clutch that switches engaging and disengaging between the high speed gear and the shaft, a low speed gear connected to the shaft, and a low speed clutch that switches engaging and disengaging between the output shaft and the low speed gear.

Preferred embodiments are described in dependent claims <NUM> to <NUM>.

A work vehicle according to the invention as claimed in claim <NUM> includes the transmission described above.

In the transmission according to the invention as claimed, the second ring gear is connected to the first ring gear. Therefore, a large clutch connected to the first ring gear is unnecessary. Further, it is not necessary to provide external tooth type gears on both the first ring gear and the second ring gear. Therefore, the transmission can be downsized.

<FIG> is a side view of the work vehicle <NUM> according to an embodiment of the present invention. As illustrated in <FIG>, the work vehicle <NUM> includes a vehicle body <NUM> and a work implement <NUM>.

The vehicle body <NUM> includes a front vehicle body 2a and a rear vehicle body 2b. The rear vehicle body 2b is connected to the front vehicle body 2a so as to be able to turn left and right. A hydraulic cylinder <NUM> is connected to the front vehicle body 2a and the rear vehicle body 2b. As the hydraulic cylinder <NUM> expands and contracts, the front vehicle body 2a turns left and right with respect to the rear vehicle body 2b.

The work implement <NUM> is used for work such as excavation. The work implement <NUM> is attached to the front vehicle body 2a. The work implement <NUM> includes a boom <NUM>, a bucket <NUM>, and hydraulic cylinders <NUM> and <NUM>. The boom <NUM> and the bucket <NUM> operate as the hydraulic cylinders <NUM> and <NUM> expand and contract.

The work vehicle <NUM> includes an engine <NUM>, a transmission <NUM>, and a traveling device <NUM>. The engine <NUM> is an internal combustion engine such as a diesel engine. The transmission <NUM> is connected to the engine <NUM>. The transmission <NUM> is configured to change the gear ratio continuously.

The traveling device <NUM> travels the work vehicle <NUM>. The traveling device <NUM> includes front wheels <NUM> and rear wheels <NUM>. The front wheels <NUM> is provided on the front vehicle body 2a. The rear wheels <NUM> is provided on the rear vehicle body 2b. The front wheels <NUM> and the rear wheels <NUM> are connected to the transmission <NUM> via an axle (not illustrated).

The work vehicle <NUM> includes a hydraulic pump (not illustrated). The hydraulic pump is connected to the engine <NUM>. The hydraulic pump is driven by the engine <NUM> and discharges hydraulic fluid. The hydraulic fluid discharged from the hydraulic pump is supplied to the hydraulic cylinders <NUM> to <NUM> described above.

The work vehicle <NUM> includes a controller <NUM>. The controller <NUM> includes, for example, a processor and a memory. The controller <NUM> controls the engine <NUM> and the transmission <NUM>.

<FIG> is a skeleton diagram showing the configuration of the transmission <NUM>. As illustrated in <FIG>, the transmission <NUM> includes an input shaft <NUM>, an output shaft <NUM>, a first planetary gear mechanism <NUM>, a second planetary gear mechanism <NUM>, a third planetary gear mechanism <NUM>, a first variable device <NUM>, and a second variable device <NUM>. The input shaft <NUM> is connected to the engine <NUM>. The output shaft <NUM> is connected to the traveling device <NUM>. The first planetary gear mechanism <NUM>, the second planetary gear mechanism <NUM>, and the third planetary gear mechanism <NUM> are arranged coaxially. The input shaft <NUM> and the output shaft <NUM> are arranged eccentrically from a central axis C1 of the first planetary gear mechanism <NUM>, the second planetary gear mechanism <NUM>, and the third planetary gear mechanism <NUM>.

The first planetary gear mechanism <NUM> includes a first carrier <NUM>, a plurality of first planetary gears <NUM>, a first sun gear <NUM>, and a first ring gear <NUM>. The first carrier <NUM> is connected to the input shaft <NUM>. An input gear <NUM> is connected to the input shaft <NUM>. The first carrier <NUM> includes an external tooth type gear <NUM>. The gear <NUM> of the first carrier <NUM> meshes with the input gear <NUM>. The first planetary gears <NUM> are connected to the first carrier <NUM>. The first planetary gears <NUM> are rotatable around the central axis C1 together with the first carrier <NUM>. The first sun gear <NUM> meshes with the first planetary gears <NUM> and is connected to the first planetary gears <NUM>. The first ring gear <NUM> meshes with the first planetary gears <NUM> and is connected to the first planetary gears <NUM>.

The second planetary gear mechanism <NUM> includes a second sun gear <NUM>, a plurality of second planetary gears <NUM>, a second carrier <NUM>, and a second ring gear <NUM>. The second sun gear <NUM> is connected to the first carrier <NUM>. The second sun gear <NUM> is rotatable around the central axis C1 together with the first carrier <NUM>. The second planetary gears <NUM> mesh with the second sun gear <NUM> and are connected to the second sun gear <NUM>. The second carrier <NUM> is connected to the second planetary gears <NUM>. The second carrier <NUM> is rotatable around the central axis C1 together with the second planetary gears <NUM>. The second ring gear <NUM> meshes with the second planetary gears <NUM> and is connected to the second planetary gears <NUM>.

The second ring gear <NUM> is connected to the first ring gear <NUM>. The first ring gear <NUM> and the second ring gear <NUM> are integrally formed. Specifically, the transmission <NUM> includes a ring member <NUM>. The ring member <NUM> is a component including the first ring gear <NUM> and the second ring gear <NUM> that are integrated. An outer peripheral surface of the ring member <NUM> includes an external tooth type gear <NUM>. The gear <NUM> of the ring member <NUM> is connected to the first variable device <NUM>.

The first variable device <NUM> is a hydraulic pump / motor. The displacement of the first variable device <NUM> is controlled by the controller <NUM>. The controller <NUM> controls the rotation speed of the first variable device <NUM>. As a result, the first variable device <NUM> continuously changes the speed ratio of the output shaft <NUM> to the input shaft <NUM>. A gear <NUM> is connected to the rotation shaft of the first variable device <NUM>. The gear <NUM> of the first variable device <NUM> meshes with the gear <NUM> of the ring member <NUM>.

The third planetary gear mechanism <NUM> includes a third carrier <NUM>, a plurality of third planetary gears <NUM>, a third sun gear <NUM>, and a third ring gear <NUM>. The third carrier <NUM> is connected to the second carrier <NUM>. The third carrier <NUM> is rotatable around the central axis C1 together with the second carrier <NUM>. The third carrier <NUM> may be integrated with the second carrier <NUM>. Alternatively, the third carrier <NUM> may be provided separately from the second carrier <NUM>. The third planetary gears <NUM> are connected to the third carrier <NUM>. The third planetary gears <NUM> are rotatable around the central axis C1 together with the third carrier <NUM>.

The third sun gear <NUM> meshes with the third planetary gears <NUM> and is connected to the third planetary gears <NUM>. The third ring gear <NUM> meshes with the third planetary gears <NUM> and is connected to the third planetary gears <NUM>. The third ring gear <NUM> is non-rotatable. The third ring gear <NUM> is fixed to, for example, the housing of the transmission <NUM>. The third planetary gear mechanism <NUM> speeds up and outputs the rotation from the second planetary gear mechanism <NUM>.

The second variable device <NUM> is a hydraulic pump / motor. The second variable device <NUM> is connected to the first variable device <NUM> by a hydraulic circuit (not illustrated). When the first variable device <NUM> functions as a pump and discharges the hydraulic fluid, the second variable device <NUM> functions as a motor and is driven by the hydraulic fluid from the first variable device <NUM>. Conversely, when the second variable device <NUM> functions as a pump and discharges the hydraulic fluid, the first variable device <NUM> functions as a motor and is driven by the hydraulic fluid from the second variable device <NUM>.

The displacement of the second variable device <NUM> is controlled by the controller <NUM>. The controller <NUM> controls the rotation speed of the second variable device <NUM>. As a result, the second variable device <NUM> continuously changes the speed ratio. The second variable device <NUM> is arranged coaxially with the second planetary gear mechanism <NUM>. In an extending direction of the central axis C1, the second planetary gear mechanism <NUM> and the third planetary gear mechanism <NUM> are arranged between the second variable device <NUM> and the first planetary gear mechanism <NUM>.

A shaft <NUM> is connected to the rotating shaft of the second variable device <NUM>. The shaft <NUM> is connected to the first sun gear <NUM>. The shaft <NUM> directly connects the first sun gear <NUM> and the second variable device <NUM>. The shaft <NUM> is arranged coaxially with the first to third planetary gear mechanisms <NUM> to <NUM>. The shaft <NUM> passes through an opening of the second sun gear <NUM> and an opening of the third sun gear <NUM>.

The transmission <NUM> includes a low speed gear <NUM>, a high speed gear <NUM>, a medium speed gear <NUM>, a low speed clutch <NUM>, a high speed clutch <NUM>, and a medium speed clutch <NUM>. The low speed gear <NUM>, the high speed gear <NUM>, and the medium speed gear <NUM> are arranged coaxially with the first to third planetary gear mechanisms <NUM> to <NUM>. The low speed gear <NUM> is connected to the shaft <NUM>. The low speed gear <NUM> is rotatable around the central axis C1 together with the shaft <NUM>. The low speed gear <NUM> is connected to the output shaft <NUM> via the low speed clutch <NUM>.

The high speed gear <NUM> is connected to the shaft <NUM> via the high speed clutch <NUM>. When the high speed clutch <NUM> is in an engaged state, the high speed gear <NUM> is rotatable together with the shaft <NUM>. The high speed gear <NUM> is connected to the output shaft <NUM>. The medium speed gear <NUM> is connected to the third sun gear <NUM>. The medium speed gear <NUM> is integrally formed with the third sun gear <NUM>. However, the medium speed gear <NUM> may be provided separately from the third sun gear <NUM>. The medium speed gear <NUM> is rotatable around the central axis C1 together with the third sun gear <NUM>.

The low speed gear <NUM>, the high speed gear <NUM>, and the medium speed gear <NUM> are arranged between the third planetary gear mechanism <NUM> and the second variable device <NUM> in the extending direction of the central axis C1. The low speed clutch <NUM>, the high speed clutch <NUM>, and the medium speed clutch <NUM> are arranged between the third planetary gear mechanism <NUM> and the second variable device <NUM> in the extending direction of the central axis C1. The low speed clutch <NUM>, the high speed clutch <NUM>, and the medium speed clutch <NUM> are, for example, hydraulic clutches. The low speed clutch <NUM>, the high speed clutch <NUM>, and the medium speed clutch <NUM> are controlled by the controller <NUM>.

The low speed clutch <NUM> switches engaging and disengaging between the output shaft <NUM> and the shaft <NUM>. When the low speed clutch <NUM> is in an engaged state, the rotation of the shaft <NUM> is transmitted to the output shaft <NUM> via the low speed gear <NUM>. The high speed clutch <NUM> switches engaging and disengaging between the output shaft <NUM> and the shaft <NUM>. When the high speed clutch <NUM> is in the engaged state, the rotation of the shaft <NUM> is transmitted to the output shaft <NUM>. The medium speed clutch <NUM> switches engaging and disengaging between the output shaft <NUM> and the third sun gear <NUM>. When the medium speed clutch <NUM> is in the engaged state, the rotation of the third sun gear <NUM> is transmitted to the output shaft <NUM> via the medium speed gear <NUM>.

In <FIG>, a part of the configuration between the clutches <NUM> to <NUM> and the output shaft <NUM> is omitted. Another clutch or gear may be arranged between the clutches <NUM> to <NUM> and the output shaft <NUM>. For example, a forward gear and a reverse gear may be arranged between the clutches <NUM> to <NUM> and the output shaft <NUM>.

<FIG> is an operating characteristic diagram of the transmission <NUM>. <FIG> shows the rotation speeds of the first and second variable devices <NUM> and <NUM> with respect to the vehicle speed. In <FIG>, the broken line indicates the rotation speed of the first variable device <NUM>. The solid line shows the rotation speed of the second variable device <NUM>. <FIG> shows the displacements of the first and second variable devices <NUM> and <NUM> with respect to the vehicle speed. In <FIG>, the broken line indicates the displacement of the first variable device <NUM>. The solid line shows the displacement of the second variable device <NUM>.

<FIG> shows the states of the clutches <NUM> to <NUM> for each vehicle speed range. The vehicle speed range includes a low speed range, a medium speed range, and a high speed range. The low speed range is a range in which the vehicle speed is <NUM> or more and less than V1. The medium speed range is a range in which the vehicle speed is V1 or more and less than V2. The high speed range is a range in which the vehicle speed is V2 or more and less than V3. In <FIG>, "ON" indicates that the clutches <NUM> to <NUM> are in the engaged state. "OFF" indicates that the clutches <NUM> to <NUM> are in the disengaged state.

<FIG> shows the relative speeds of the clutches <NUM> to <NUM> with respect to the vehicle speed. In <FIG>, "Low" indicates the relative speed of the low speed clutch <NUM>. "Mid" indicates the relative speed of the medium speed clutch <NUM>. "High" indicates the relative speed of the high speed clutch <NUM>.

The controller <NUM> controls the displacements of the first and second variable devices <NUM> and <NUM> and the states of the clutches <NUM> to <NUM> according to the vehicle speed. As illustrated in <FIG>, when the vehicle speed is <NUM>, the relative speed of the low speed clutch <NUM> is <NUM>. As illustrated in <FIG>, the controller <NUM> sets the low speed clutch <NUM> in the engaged state when the vehicle speed is <NUM>. Further, the controller <NUM> sets the medium speed clutch <NUM> and the high speed clutch <NUM> in the disengaged state. As a result, the driving force input from the engine <NUM> to the input shaft <NUM> is transmitted to the output shaft <NUM> via the first carrier <NUM>, the first planetary gears <NUM>, the first sun gear <NUM>, the shaft <NUM>, and the low speed gear <NUM>.

The controller <NUM> maintains the low speed clutch <NUM> in the engaged state when the vehicle speed is within the low speed range. As illustrated in <FIG>, the controller <NUM> controls the displacements of the first and second variable devices <NUM> and <NUM> according to the vehicle speed. As a result, as illustrated in <FIG>, when the vehicle speed is within the low speed range, the rotation speed of the first variable device <NUM> decreases and the rotation speed of the second variable device <NUM> increases as the vehicle speed increases.

As illustrated in <FIG>, when the vehicle speed is V1, the relative speed of the medium speed clutch <NUM> is <NUM>. As illustrated in <FIG>, when the vehicle speed reaches V1, the controller <NUM> sets the medium speed clutch <NUM> in the engaged state. Further, the controller <NUM> sets the low speed clutch <NUM> and the high speed clutch <NUM> in the disengaged state. As a result, the driving force input from the engine <NUM> to the input shaft <NUM> is transmitted to the output shaft <NUM> via the first carrier <NUM>, the second sun gear <NUM>, the second carrier <NUM>, the third carrier <NUM>, the third planetary gears <NUM>, the third sun gear <NUM>, and the medium speed gear <NUM>.

The controller <NUM> maintains the medium speed clutch <NUM> in the engaged state when the vehicle speed is within the medium speed range. As illustrated in <FIG>, the controller <NUM> controls the displacements of the first and second variable devices <NUM> and <NUM> according to the vehicle speed. As a result, as illustrated in <FIG>, when the vehicle speed is within the medium speed range, the rotation speed of the first variable device <NUM> increases and the rotation speed of the second variable device <NUM> decreases as the vehicle speed increases.

As illustrated in <FIG>, when the vehicle speed is V2, the relative speed of the high speed clutch <NUM> is <NUM>. As illustrated in <FIG>, the controller <NUM> sets the high speed clutch <NUM> in the engaged state when the vehicle speed is V2. Further, the controller <NUM> sets the low speed clutch <NUM> and the medium speed clutch <NUM> in the disengaged state. As a result, the driving force input from the engine <NUM> to the input shaft <NUM> is transmitted to the output shaft <NUM> via the first carrier <NUM>, the first planetary gears <NUM>, the first sun gear <NUM>, the shaft <NUM>, and the high speed gear <NUM>.

The controller <NUM> maintains the high speed clutch <NUM> in the engaged state when the vehicle speed is within the high speed range. As illustrated in <FIG>, the controller <NUM> controls the displacements of the first and second variable devices <NUM> and <NUM> according to the vehicle speed. As a result, as illustrated in <FIG>, when the vehicle speed is within the high speed range, the rotation speed of the first variable device <NUM> decreases and the rotation speed of the second variable device <NUM> increases as the vehicle speed increases.

In the transmission <NUM> according to the present embodiment described above, the second ring gear <NUM> is connected to the first ring gear <NUM>. Therefore, a large clutch connected to the first ring gear <NUM> or the second ring gear <NUM> is unnecessary. Further, the number of external tooth type gears provided in the first ring gear <NUM> and the second ring gear <NUM> can be reduced. Thereby, the transmission <NUM> can be downsized.

As illustrated in <FIG>, the rotation directions of the first and second variable devices <NUM> and <NUM> are the same over the entire speed range. Therefore, a pump having a simple structure can be adopted as the first and second variable devices <NUM> and <NUM>. Thereby, the transmission <NUM> can be downsized.

The input shaft <NUM> is connected to the first carrier <NUM> of the first planetary gear mechanism <NUM>. The first ring gear <NUM> of the first planetary gear mechanism <NUM> is connected to the first variable device <NUM> via the external tooth type gear <NUM>. Further, the first sun gear <NUM> of the first planetary gear mechanism <NUM> is directly connected to the second variable device <NUM>. Thereby, the mechanism for input division of the transmission <NUM> suitable for the used rotation range of the first and second variable devices <NUM> and <NUM> can be simply and compactly configured.

The second carrier <NUM> of the second planetary gear mechanism <NUM> is connected to the third carrier <NUM> of the third planetary gear mechanism <NUM>. The third sun gear <NUM> of the third planetary gear mechanism <NUM> is integrated with the medium speed gear <NUM>. Further, the third planetary gear mechanism <NUM> is arranged coaxially with the first planetary gear mechanism <NUM> and the second planetary gear mechanism <NUM>. Thereby, the transmission <NUM> can be downsized.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and the following modifications can be made. The work vehicle <NUM> is not limited to the wheel loader, and may be another vehicle such as a bulldozer or a hydraulic excavator.

The arrangement of the first variable device <NUM> and / or the second variable device <NUM> may be changed. The first variable device <NUM> and / or the second variable device <NUM> is not limited to the hydraulic pump / motor, and may be another device such as an electric generator / motor.

The arrangement of the low speed clutch <NUM> and / or the medium speed clutch <NUM> and / or the high speed clutch <NUM> may be changed.

Claim 1:
A transmission (<NUM>) comprising:
an input shaft (<NUM>);
an output shaft (<NUM>);
a first planetary gear mechanism (<NUM>) including a first carrier (<NUM>) connected to the input shaft (<NUM>), a first planetary gear (<NUM>) rotatably carried by the first carrier, a first sun gear (<NUM>) meshed with the first planetary gear (<NUM>), and a ring gear (<NUM>) meshed with the first planetary gear (<NUM>);
a second planetary gear mechanism (<NUM>) including a second sun gear (<NUM>) connected to the first carrier (<NUM>), a second planetary gear (<NUM>) meshed with the second sun gear (<NUM>), and a second ring gear (<NUM>) meshed with the second planetary gear (<NUM>) and connected to the first ring gear (<NUM>); and
a first variable device (<NUM>) connected to the first ring gear (<NUM>) and the second ring gear (<NUM>) to continuously change a speed ratio of the output shaft (<NUM>) to the input shaft (<NUM>);
a second variable device (<NUM>) that continuously changes the speed ratio; and
a shaft (<NUM>) that directly connects the first sun gear (<NUM>) and the second variable device (<NUM>);
characterized by
a high speed gear (<NUM>) connected to the output shaft (<NUM>);
a high speed clutch (<NUM>) that switches engaging and disengaging between the high speed gear (<NUM>) and the shaft (<NUM>);
a low speed gear (<NUM>) connected to the shaft (<NUM>); and
a low speed clutch (<NUM>) that switches engaging and disengaging between the output shaft (<NUM>) and the low speed gear (<NUM>).