Patent Description:
Conventionally, in a tractor for the agricultural work, which is an example of a traveling vehicle, a so-called hybrid type that improves drive efficiency by using both power of an engine and power of an electric motor has been known (see Patent Documents <NUM> and <NUM>, for example). In the tractor of Patent Document <NUM>, such a configuration is adopted that left and right rear wheels and front and rear four wheels are driven by rotation power of an electric motor. In a case of insufficient torque of the electric motor, the rotation power of the engine is supplemented. In the tractor of Patent Document <NUM>, such a configuration is adopted that left and right front wheels are driven by the rotation power of the electric motor in the case of the four-wheel drive mode.

Further, document <CIT> describes a transmission arrangement for the controllable distribution of a drive torque from an input element to two output elements, the transmission arrangement being assigned to a secondary axle of a drive train of a temporarily four-wheel-drive motor vehicle. In details, said document discloses a vehicle in which an internal combustion engine, a main drive wheel, and a pair of sub drive wheels are supported on a machine body, and the internal combustion engine drives the main drive wheel through a transmission mechanism, the vehicle comprising: an electric motor and a planetary gear mechanism that are provided inside an axle case that supports the pair of sub drive wheels, wherein in three elements of the planetary gear mechanism, a first element is interlockingly connected to the electric motor, a second element is interlockingly connected to the pair of sub drive wheels, and a third element is drivingly connected to an output side of the traveling transmission mechanism.

Document <CIT> describes an electrical drive arrangement for driving a motor vehicle.

However, in the conventional configuration, since the left and right front wheels, the left and right rear wheels, or the front and rear four wheels are driven by the electric motor alone in some cases, a large-sized electric motor having a sufficient output is required for various works and traveling. For this reason, there were problems that it is difficult to downsize the electric motor, a manufacturing cost increases, and mountability on a traveling vehicle is poor.

The present invention has a technical object to provide a traveling vehicle which is improved in view of the aforementioned circumstances.

The present invention is a traveling vehicle configured such that an internal combustion engine, a main drive wheel, and a pair of sub drive wheels are supported on a traveling machine body, and the internal combustion engine drives the main drive wheel through a traveling transmission mechanism, in which an electric motor and a planetary gear mechanism are provided inside an axle case which supports the pair of sub drive wheels, in three elements of the planetary gear mechanism, a first element is interlockingly connected to the electric motor, a second element is interlockingly connected to the sub drive wheel, and a third element is interlockingly connected to an output side of the traveling transmission mechanism.

In the traveling vehicle of the present invention, the axle case is supported on the traveling machine body so as to be swingable around a center pin disposed at an intermediate part in a vehicle width direction, the pair of sub drive wheels is attached so as to be movable up and down, and each of a pair of electric motors, included in the electric motor, and each of a pair of planetary gear mechanisms, included in the planetary gear mechanism, are accommodated in the axle case by being distributed to both left and right sides with the center pin interposed therebetween.

In the traveling vehicle of the present invention, a through hole communicating from an inside to an outside of the axle case may be formed inside the center pin, and a wiring cable for each of the electric motors may be drawn out to the outside of the axle case via the through hole.

In the traveling vehicle of the present invention, oil may be stored in the axle case, and the axle case may be connected to an oil cooler mounted on the traveling machine body so that the stored oil can flow freely via the through hole of the center pin.

In the traveling vehicle of the present invention, it may be so configured that a power take-out portion for the pair of sub drive wheels is provided on an output side of the traveling transmission mechanism, and the power take-out portion includes a switching mechanism for switching a drive form of the main drive wheel and the pair of sub drive wheels among drive forms which drive only the pair of sub drive wheels, drive all-wheel, and drive only the main drive wheel, and when the switching mechanism is switched to the driving state which drives only the pair of sub drive wheels, power transmission from the traveling transmission mechanism to the third element of the planetary gear mechanism is disconnected in a braking state, and the pair of sub drive wheels is rotated and driven by drive of the electric motor.

In the traveling vehicle of the present invention, the pair of sub drive wheels may be configured to be steerable by an operation of an operator, and a control device of the electric motor may be configured to differentially cause the pair of sub drive wheels to be driven on the basis of a steering signal of the control device.

According to the present invention, when the pair of sub drive wheels are rotated and driven, a part of the power of the internal combustion engine can be used to share a drive load with the electric motor, so that the electric motor can be downsized, whereby a size and a weight can be reduced. Moreover, each of the electric motors may have a capacity enough to be capable of individually driving the pair of sub drive wheels. Therefore, the electric motor can be accommodated in the axle case without difficulty, and the durability of the electric motor can be improved by protecting the electric motor from muddy water or the like. Accordingly, the downsizing of the internal combustion engine can also be realized, and an environment-friendly traveling vehicle can be provided.

Hereinafter, an embodiment which embodies the present invention will be described on the basis of the drawings (<FIG>). In the embodiment, the present invention is applied to a tractor <NUM> as a traveling vehicle. In the following explanation, terms such as "front and rear" and "left and right" are used to specify a direction with a traveling direction of the tractor <NUM> as the front and rear as a reference for specification of the direction. It is needless to say that these terms are used for convenience of explanation and do not limit the technical scope of the present invention.

First, an overview of the tractor <NUM> will be described with reference to <FIG>. The tractor <NUM> of the embodiment includes a traveling machine body <NUM> supported by a pair of left and right sub drive wheels <NUM> and a pair of left and right main drive wheels <NUM>. The main drive wheels are non-steerable wheels that support a side of the vehicle where vehicle weight distribution is large, and in this embodiment, refer to the rear wheels <NUM>. Similarly, the sub drive wheels are steerable wheels that support a side of the vehicle where the vehicle weight distribution is small, and in this embodiment, refer to the front wheels <NUM>. An internal combustion engine <NUM> and a steering column <NUM> having a steering wheel <NUM> are provided on a front side of the traveling machine body <NUM>. The internal combustion engine <NUM> is covered with a bonnet <NUM>. Regarding a capacity of the internal combustion engine <NUM>, it has a degree of rotating the rear wheels <NUM> on the side of the larger weight distribution, and a capacity of an electric motor <NUM>, which will be described later, has a degree of rotating the front wheels <NUM> on the side of the smaller weight distribution.

A driving seat <NUM> on which an operator is seated is disposed behind the steering wheel <NUM>. It is configured such that, when the operator sitting on the driving seat <NUM> rotationally moves/operates the steering wheel7, steering angles of the left and right front wheels <NUM> are changed in accordance with a rotational-movement operation amount. On a rear part of the traveling machine body <NUM>, a transmission case <NUM> incorporating a traveling transmission mechanism <NUM> for driving the front and rear wheels <NUM> and <NUM> by appropriately shifting power of the internal combustion engine <NUM> and a work transmission mechanism <NUM> for driving a agricultural implement are mounted. A hydraulic elevation mechanism <NUM> for elevating up/down a agricultural implement (not shown) such as a scraper, a rake, or a cultivator is disposed on an upper surface of a rear part of the transmission case <NUM>. The agricultural implement is connected to the rear part of the transmission case <NUM> via a link mechanism.

On the side of the steering column <NUM>, a forward/backward-travel switching lever <NUM> for a switching operation of the traveling direction of the traveling machine body <NUM> between forward and backward traveling, and a clutch pedal <NUM> for connecting and disconnecting operations of an output from the internal combustion engine <NUM> to the traveling transmission mechanism <NUM> are disposed. On the side of the steering column <NUM>, a pair of brake pedals (not shown) for an individual braking operation of the left and right rear wheels <NUM>, an accelerator pedal (not shown) for setting a rotation speed of the internal combustion engine <NUM> and the like are also disposed. In a periphery of the driving seat <NUM>, a four-wheel drive switching lever <NUM> for a switching operation of drive modes of the front and rear four wheels <NUM>, <NUM> and a PTO speed selection lever <NUM> for a switching operation of the output of a PTO shaft <NUM>, which will be described later, in plural stages and neutral are disposed. A parking brake lever <NUM> for a maintaining operation of the both left and right rear wheels <NUM> in a braking state is disposed on a front of the four-wheel drive switching lever <NUM>. Although not shown, a main speed-change pedal for stopping the traveling machine body <NUM> and for a continuously changing operation of a vehicle speed thereof in the traveling transmission mechanism <NUM>, a sub shift lever for setting and maintaining the output and the rotation speed of the traveling transmission mechanism <NUM> in a predetermined range in accordance with a work state, An agricultural implement control lever for manually changing and adjusting a height position of the agricultural implement connected to the rear of the traveling machine body <NUM> and the like are also disposed in the periphery of the driving seat <NUM>.

As shown in <FIG>, the traveling machine body <NUM> is configured by connecting the transmission case <NUM> functioning as a rear frame to a front frame <NUM> having a front bumper <NUM>. A rear end side of the front frame <NUM> is connected to left and right outer side surfaces of the internal combustion engine <NUM>. A cooling fan <NUM> is rotatably provided on the front surface side of the internal combustion engine <NUM>. Although not shown, the internal combustion engine <NUM> also includes a cooling water pump. On a side of the internal combustion engine <NUM>, an alternator <NUM> (generator) that generates electric power by the power of the internal combustion engine <NUM> is provided. When the internal combustion engine <NUM> operates, rotation power is transmitted from a front end side of an engine output shaft <NUM> (crank shaft, see <FIG>) to the cooling fan <NUM> and the cooling water pump via a transmission belt <NUM>, and the rotation power is also transmitted to the alternator <NUM>.

On a front part of the front frame <NUM>, a radiator <NUM> for water-cooling the internal combustion engine <NUM> is erected so as to be located on a front surface side of the internal combustion engine <NUM>. By drive of the cooling water pump, cooling water in the radiator <NUM> is supplied to the internal combustion engine <NUM> and cools the internal combustion engine <NUM>. On the front part of the front frame <NUM>, an oil cooler <NUM> for cooling oil and a battery <NUM> for supplying electric power are provided so as to be located on the front surface side of the radiator <NUM>. Cooling air introduced from the outside of the bonnet <NUM> is blown against the oil cooler <NUM> and the radiator <NUM> by the rotation of the cooling fan <NUM> and then, flows toward the internal combustion engine <NUM>. The radiator <NUM>, the oil cooler <NUM>, and the battery <NUM> are covered by a bonnet <NUM> together with the internal combustion engine <NUM>.

A flywheel housing <NUM> that houses a flywheel <NUM> (see <FIG>) is attached to a rear surface side of the internal combustion engine <NUM>. To the rear surface side of the flywheel housing <NUM>, a front surface side of the transmission case <NUM> is connected. On a rear part of the transmission case <NUM>, a rear axle case <NUM> is attached so as to protrude outward in the left-right direction. The left and right rear wheels <NUM> are rotatably disposed on left and right distal end sides of the rear axle case <NUM>. On the rear surface of the transmission case <NUM>, the PTO shaft <NUM> for transmitting a PTO drive force to the agricultural implementis provided so as to protrude rearward.

Subsequently, a power transmission system of the tractor <NUM> will be explained with reference mainly to <FIG>. The tractor <NUM> of the embodiment is configured to drive the front wheels <NUM>, the rear wheels <NUM>, and the PTO shaft <NUM> by transmitting the power of the internal combustion engine <NUM> to the traveling transmission mechanism <NUM> and the work transmission mechanism <NUM> in the transmission case <NUM>. To the engine output shaft <NUM> provided so as to protrude rearward on the rear surface of the internal combustion engine <NUM>, the flywheel <NUM> is directly connected. The flywheel <NUM> and a transmission input shaft <NUM> are connected to each other via a main clutch (not shown) for engaging and disengaging power. The transmission input shaft <NUM> is rotatably supported by the transmission case <NUM> along the machine body front-rear direction. The transmission input shaft <NUM> is directly connected to the work transmission mechanism <NUM>, is branched from a transmission gear <NUM> to a shift input gear <NUM>, and is fixed to a shift input shaft <NUM> of the traveling transmission mechanism <NUM>.

The traveling transmission mechanism <NUM> includes a continuously variable or stepped transmission device (not shown), and a pinion <NUM> is fixed to a shift output shaft <NUM> protruding rearward via the transmission device. On a rear of the traveling transmission mechanism <NUM>, a final reduction-gear mechanism <NUM> in the rear axle case <NUM> that transmits rotation power to the left and right rear wheels <NUM> is disposed. The final reduction-gear mechanism <NUM> includes a differential input gear <NUM> meshed with the pinion <NUM> of the shift output shaft <NUM>, a differential gear case <NUM> fixed to the differential input gear <NUM>, and a pair of rear-wheel differential output shafts <NUM> extending in the left-right direction. The left and right rear-wheel differential output shafts <NUM> are connected to a rear axle <NUM> via a final gear <NUM> and the like. The rear wheel <NUM> is attached to a distal end part of the rear axle <NUM>. On the left and right rear-wheel differential output shafts <NUM>, a brake mechanism <NUM> is provided. The brake mechanism <NUM> applies braking to the both left and right rear wheels <NUM> by simultaneously operating the parking brake lever <NUM> (see <FIG>) and the pair of brake pedals. Note that, when turning, if only the brake pedal on an inner side of the turn is depressed, and a braking force corresponding to the depression force is applied to the rear wheel on the inner side of the turn, the vehicle can turn with a further smaller turning radius in addition to operating the steering wheel <NUM>.

A front-wheel output shaft <NUM> that protrudes forward from the output side of the traveling transmission mechanism <NUM> and extends parallel to the shift input shaft <NUM> is also rotatably supported in the transmission case <NUM>. To the front-wheel output shaft <NUM>, a front-wheel propeller shaft <NUM> extending coaxially with the front-wheel output shaft <NUM> is connected via a switching mechanism <NUM> that switches the drive form of the front and rear four wheels <NUM>, <NUM> among "front-wheel only drive (FWD)", "all (four) wheel drive (4WD)", and "rear-wheel only drive (RWD)". The aforementioned four-wheel drive switching lever <NUM> is operated by an operator so as to select any one of a "four-wheel drive (4WD) position", a "front-wheel drive (FWD) position", and a "rear-wheel drive (RWD) position" shown in the drawing, the switching mechanism <NUM> operates so as to realize those driving states.

The switching mechanism <NUM> of the embodiment is of a clutch type that selectively connects/disconnects the transmission of the rotation power from the internal combustion engine <NUM> via the traveling transmission mechanism <NUM> to the front-wheel propeller shaft <NUM> and thus, to the left and right front wheels <NUM>. The switching mechanism <NUM> of the embodiment has a clutch shifter 47a that is fitted onto the front-wheel output shaft <NUM> and the front-wheel propeller shaft <NUM> non-rotatably and slidably in an axial direction.

The clutch shifter 47a is configured to slide to three predetermined positions by drive of a clutch actuator 47b and to select any one of engagement of the front-wheel propeller shaft <NUM> with the front-wheel output shaft <NUM> (four-wheel drive position), disengagement of the front-wheel output shaft <NUM> and fixing of the front-wheel propeller shaft <NUM> (front-wheel drive position) non-rotatably, disengagement of the front-wheel output shaft <NUM> and allowing of free rotation of the front-wheel propeller shaft <NUM> (rear-wheel drive position). The clutch actuator 47b is of a push-pull type and can drive so as to cause the clutch shifter 47a to select the three positions described above. In the embodiment, the clutch actuator 47b switches and operates the clutch shifter 47a in response to a switching operation of the four-wheel drive switching lever <NUM>. Note that the clutch actuator 47b preferably has electricity as a drive source, but the electricity is not necessarily limiting. For example, a linear solenoid may be used, or an electric pump combined with a hydraulic piston or a pneumatic piston may be used.

As shown in <FIG>, in the embodiment of the switching mechanism <NUM>, a shifter claw portion 47c is provided on the front end side of the clutch shifter 47a. To the inner surface side of the front part of the flywheel housing <NUM>, a housing claw portion 30a is fixed so as to face the shifter claw portion 47c. When the four-wheel drive switching lever <NUM> is switched to the front-wheel drive position and the clutch shifter 47a is switched and operated to the front-wheel drive position by the clutch actuator 47b, the clutch shifter 47a is disconnected from the front-wheel output shaft <NUM>, and the shifter claw portion 47c is engaged with the housing claw portion 30a. As a result, the front-wheel propeller shaft <NUM> is held non-rotatable. When the four-wheel drive switching lever <NUM> is switched to the four-wheel drive position and the clutch shifter 47a is switched and operated to the four-wheel drive position by the clutch actuator 47b, the engagement between the shifter claw portion 47c and the housing claw portion 30a is released, and the front-wheel output shaft <NUM> and the front-wheel propeller shaft <NUM> are connected so as to be integrally rotatable by the clutch shifter 47a. As a result, the rotation power of the front-wheel output shaft <NUM> is transmitted to the front-wheel propeller shaft <NUM>. When the four-wheel drive switching lever <NUM> is switched to the rear-wheel drive position and the clutch shifter 47a is switched to the rear-wheel drive position by the clutch actuator 47b, the clutch shifter 47a is disconnected from the front-wheel propeller shaft <NUM>, and the front-wheel propeller shaft <NUM> becomes freely rotatable.

A front end side of the front-wheel propeller shaft <NUM> is connected to an input shaft <NUM> at a laterally intermediate part of a front axle case <NUM> disposed on a lower side of a front part of the traveling machine body <NUM>. As shown in <FIG> and <FIG>, the input shaft <NUM> is rotatably supported by bearings in a cylinder portion 200a provided on an outer side surface of a cover <NUM> which closes a rear-surface opening of the front axle case <NUM> with an axial direction thereof following the longitudinal direction of the machine body.

In the front axle case <NUM>, as will be described later, a space other than a defined motor accommodating chamber 94a is a gear accommodating chamber 94b. That is, a counter shaft <NUM> to which power is transmitted from the input shaft <NUM> via a bevel gear mechanism 49a is rotatably supported by bearings on the rear side of the cover <NUM> so as to follow the left-right direction, and is inserted from the rear-surface opening of the front axle case <NUM> and is located inside the front axle case <NUM>. Power distributing gears <NUM> for transmitting power to each of ring gears <NUM>, <NUM> of a planetary gear mechanism <NUM>, which will be described later, are fixed to both left and right end parts of the counter shaft <NUM>.

A pair of left and right electric motors <NUM> for individually driving the both left and right front wheels <NUM> are accommodated in the motor accommodating chamber 94a defined and formed in a front center part of the front axle case <NUM>, and the planetary gear mechanisms <NUM> for drivingly connecting the electric motors <NUM> to corresponding left and right front-wheel differential output shafts <NUM> are accommodated in the front axle case <NUM> on the left and right outer sides of the motor accommodating chamber 94a. An axle housing201, which rotatably supports the front-wheel differential output shaft <NUM> therein, is fixed to both outer side ends of the front axle case <NUM>.

The left and right electric motors <NUM> are respectively accommodated in two spaces defined side by side in a center part of the front axle case <NUM> so as to be distributed to both left and right sides with respect to a virtual extension line A (a center position in the vehicle width direction) of the front-wheel propeller shaft <NUM>. A pear of motor shafts <NUM> protruding outward in the left-right direction from the left and right electric motors <NUM> are arranged concentrically (on the axis of left and right front-wheel differential output shafts <NUM>, which will be described later). The corresponding planetary gear mechanisms <NUM> are disposed on the left and right outer sides of each of the motor shaft <NUM>, <NUM>, respectively. Therefore, combinations of the left and right electric motors <NUM> and the planetary gear mechanisms <NUM> are disposed by being distributed to the both left and right sides with a virtual extension line A (the center position in the vehicle width direction) of the front-wheel propeller shaft <NUM> interposed therebetween. In other words, the combinations of the left and right electric motors <NUM> and the planetary gear mechanisms <NUM> are disposed symmetrically with respect to a laterally intermediate part of the front axle case <NUM>, which is on the virtual extension line A of the front-wheel propeller shaft <NUM>.

The both left and right motor accommodating chambers 94a are provided symmetrically with respect to a partition wall 20a by extending a peripheral wall 20b having a cylindrical inner surface laterally outward from the partition wall 20a formed on a front part side of the laterally intermediate part in the front axle case <NUM>. The electric motor <NUM> is of a type in which a heat generation spot is cooled by oil, and is configured to be usable for cooling by introducing lubricant oil stored in the gear accommodating chamber 94b of the front axle case <NUM> into the motor accommodating chamber 94a. That is, the both left and right motor accommodating chambers 94a communicate with a common opening <NUM> formed in a front surface of the laterally intermediate part of the front axle case <NUM> via the through hole of the partition wall 20a. At a center part of the left and right cylindrical peripheral walls 20b, a rear-part communication port <NUM> communicating with the both motor accommodating chambers 94a is formed. A side communication port <NUM> communicating with the corresponding motor accommodating chamber 94a is formed in a motor cover 20c which defines the motor accommodating chamber 94a by covering outer side openings of the left and right cylindrical peripheral walls 20b.

Each of the electric motors <NUM> in each of the motor accommodating chambers 94a includes a ring-shaped stator <NUM> fixed to the inner surface of the cylindrical peripheral wall 20b, and a rotor <NUM> disposed inside the stator <NUM> and having the motor shaft <NUM> inserted through the center part thereof. The inner end of each of the motor shafts <NUM> is rotatably supported by bearings by the partition wall 20a, respectively, and the outer end thereof is supported by bearings by the motor cover 20c. The electric motor <NUM> is accommodated in the motor accommodating chamber 94a in a posture that the motor shaft <NUM> protrudes outward in the left-right direction from the motor cover 20c. The stator <NUM> includes a plurality of coils as usual.

A rotation speed sensor (not shown) of the motor shaft <NUM> is also provided. Wiring cables <NUM> electrically connected to the coils and sensors provided in the left and right electric motors <NUM> are collected in the common opening <NUM> via a concentration pocket portion <NUM> provided in the partition wall 20a, respectively.

Each of the left and right planetary gear mechanisms <NUM> is constituted by a sun gear <NUM> driven by the motor shaft <NUM> of the corresponding electric motor <NUM>, a plurality of planetary gears <NUM> meshed with the sun gear <NUM>, the ring gear <NUM> meshed with a group of the planetary gears <NUM>, and a carrier <NUM> rotatably supporting the group of the planetary gears <NUM> on the same circumference to drive the front-wheel differential output shaft <NUM>.

Sun-gear shafts 55a, 55b are integrally formed at a rotation center part of both side surfaces of the sun gear <NUM>. The sun gear shaft 55a facing the inside of the case is hollow and includes a coupling for the motor shaft <NUM> at its inner peripheral part. The motor cover 20c includes a support portion for the sun gear shaft 55a concentrically with the support portion for the motor shaft <NUM>, and when the motor shaft <NUM> is connected to the sun gear shaft 55a, the outer peripheral end part of the sun gear shaft 55a is supported by the motor cover 20c.

The sun gear <NUM> is meshed with a planetary gear <NUM> group disposed on the carrier <NUM>. The left and right ring gears <NUM> are supported by the sun gear shaft 55a capable of relative rotation in a state in which internal teeth formed on inner peripheral surfaces thereof are meshed with the planetary gear <NUM> group from a radially outer side.

At the rotation center parts of the left and right carriers <NUM>, a coupling for rotatably supporting a distal end part of the corresponding motor shaft <NUM> by bearings and for connecting a front-wheel differential output shaft <NUM> incapable of relative rotation is provided adjacent to that.

External teeth formed on outer peripheral surfaces of the left and right ring gears <NUM> are meshed with the power distribution gears <NUM> disposed at both end parts of the counter shaft <NUM> all the time so that the power of the internal combustion engine side from the input shaft <NUM> is also input.

During a switching operation of the switching mechanism <NUM> to the "front-wheel only drive" position, the front-wheel output shaft <NUM> and the front-wheel propeller shaft <NUM> are disconnected from each other, and the input shaft <NUM> is held non-rotatable and thus, a state in which the ring gears <NUM> of the left and right planetary gear mechanisms <NUM> meshed with the power distribution gears <NUM> are also restricted non-rotatably is maintained. Therefore, when the electric motors <NUM> are driven in this state, only the rotation power of the corresponding electric motor <NUM> is transmitted to the left and right planetary gear mechanisms <NUM> via each of the sun gears <NUM>, and the left and right front wheels <NUM> are driven only by the rotation power. In this case, even without driving the internal combustion engine <NUM>, the tractor <NUM> can be moved only by the both left and right electric motors <NUM>. However, since the capacity of the electric motor <NUM> is only enough to rotate the front wheels <NUM> of the tractor <NUM>, damage to the electric motor <NUM> is avoided at the "front wheel only drive" position, which is effective for traveling in a short time and a short distance, for example, when changing a parking place indoors. It is to be noted that traveling time and a traveling distance are measured at the "front-wheel only drive" position, and when the value exceeds a threshold value, a controller <NUM>, which will be described later, preferably controls to issue an alarm or to stop power feed to the electric motor <NUM>.

When the switching mechanism <NUM> is at the "four-wheel drive" position, the rotation power from the internal combustion engine <NUM> is transmitted from the front-wheel output shaft <NUM> to the counter shaft <NUM> in the front axle case <NUM> via the input shaft <NUM>, and each of the ring gears <NUM> of the left and right planetary gear mechanisms <NUM> is simultaneously driven at a constant rotation. When the left and right electric motors <NUM> drive the respective sun gears <NUM> in this state, the rotation power of the both gears <NUM>, <NUM> are synthesized by the respective planetary gear mechanisms <NUM>, and the synthesized power is output from the carrier <NUM> so as to drive the left and right front wheels <NUM>.

The rear wheels <NUM> are driven by the internal combustion engine <NUM>.

When the switching mechanism <NUM> is at the "rear-wheel only drive" position, the rotation power from the internal combustion engine <NUM> is not transmitted to the counter shaft <NUM> in the front axle case <NUM> or does not restrict the counter shaft <NUM> and the ring gear <NUM> non-rotatably, either. In this case, when the ring gear <NUM> becomes free, the transmission function by the planetary gear mechanism <NUM> is lost regardless of a cogging torque of the electric motor <NUM>. As a result, the left and right front wheels <NUM> idle. The left and right rear wheels <NUM> are driven only by the rotation power from the internal combustion engine <NUM>.

In the embodiment, the left and right planetary gear mechanisms <NUM> are configured to be capable of rotating and driving the left and right front wheels <NUM> by synthesizing the rotation power from the internal combustion engine <NUM> and the rotation power of the left and right electric motors <NUM>. That is, each of the planetary gear mechanisms <NUM> of the embodiment is that of an output-coupled (input-split) type. In each of the planetary gear mechanisms <NUM>, the sun gear <NUM> fixed to the motor shaft <NUM> of the electric motor <NUM> corresponds to a first element. The carrier <NUM> connected to the front-wheel differential output shaft <NUM> for transmitting the rotation power to the left and right front wheels <NUM> corresponds to a second element. The ring gear <NUM> to which the power of the internal combustion engine <NUM> is transmitted corresponds to a third element. Which of the internal combustion engine <NUM>, the electric motor <NUM>, and the front wheels <NUM> is combined with each of the elements (the sun gear <NUM>, the carrier <NUM>, and the ring gear <NUM>) of the left and right planetary gear mechanisms <NUM> is not limited to that of the embodiment, and various combinations may be adopted.

As shown in <FIG>, a PTO input shaft <NUM> is connected to the transmission input shaft <NUM> in the transmission case <NUM> via a PTO clutch <NUM> for connecting and disconnecting power. The PTO shaft <NUM> extending in parallel to the PTO input shaft <NUM> is rotatably supported. When the PTO shift lever <NUM> located in the periphery of the driving seat <NUM> is operated to shift to a position other than the neutral position, the PTO clutch <NUM> is brought into a power connected state, and the transmission input shaft <NUM> and the PTO input shaft <NUM> are connected to each other, incapable of relative rotation.

Between the PTO input shaft <NUM> and the PTO shaft <NUM>, low-speed gear trains <NUM>, <NUM> and high-speed gear trains <NUM>, <NUM> are disposed in parallel, and by causing a shift clutch <NUM> to slide and move along the PTO shaft <NUM>, the rotation power via the low-speed gear trains <NUM>, <NUM> or the high-speed gear trains <NUM>, <NUM> is selectively transmitted to the PTO shaft <NUM>.

As shown in <FIG> and <FIG>, the controller <NUM> (control device) that manages various controls of the electric motor <NUM> and the clutch actuator 47b is mounted on the traveling machine body <NUM>.

The controller <NUM> of the embodiment is disposed in the vicinity of the steering column <NUM> in the bonnet <NUM>. A disposed spot of the controller <NUM> is not particularly limited and may be disposed below the driving seat <NUM> or the like, for example. It is to be noted that, though details are omitted, the controller <NUM> includes a CPU that executes various types of arithmetic processing and controls, storing means such as EPROM and a flash memory, a RAM for temporarily storing control programs and data, a communication interface (I/F) and the like.

The controller <NUM> is electrically connected to a steering potentiometer <NUM> for detecting a rotational-movement operation amount (steering angle) of the steering wheel <NUM>, a switching potentiometer <NUM> for detecting an operation position of the four-wheel drive switching lever <NUM>, a speed-change potentiometer for detecting an operation position of the main speed-change pedal, a sensor for detecting an output-side rotation state of the traveling transmission mechanism <NUM>, a sensor for detecting a rotation state of the front-wheel differential output shaft <NUM>, the clutch actuator 47b of the switching mechanism <NUM>, and the left and right electric motors <NUM>. The left and right electric motors <NUM> are electrically connected to the controller <NUM> via an inverter <NUM>. The inverter <NUM> is also electrically connected to the battery <NUM>, which is power storage means. To the controller <NUM>, electric power is supplied from the battery <NUM> via a key switch <NUM>. The battery <NUM> is electrically connected to the alternator <NUM> (generator), which generates electricity during the operation of the internal combustion engine <NUM>, via a converter <NUM>. The electricity generated by the alternator <NUM> is charged in the battery <NUM>.

The controller <NUM> drives the electric motors <NUM>, <NUM> in the following manner. (<NUM>) When the switching potentiometer <NUM> detects the "four-wheel drive" position; and (<NUM>-<NUM>) when the steering potentiometer <NUM> detects the "straight traveling" state of the steering wheel <NUM>, each of the left and right electric motors <NUM>, <NUM> is driven at a rotation speed synchronized with output-side rotation of the traveling transmission mechanism <NUM>. As a result, during the traveling, the front wheel <NUM> rotates without being dragged by the rear wheel <NUM> and can exert a traction force.

Subsequently, a structure of the front axle case <NUM> and its periphery will be explained with reference to <FIG>. The front axle case <NUM> is attached to a pair of front and rear support brackets <NUM> fastened to the front frame <NUM> via front and rear pivot members <NUM>, <NUM> so that each of the front wheels <NUM> can swing (roll) up and down with an intermediate part in the vehicle width direction as a center of rotational movement. When a difference is generated in a ground-contact pressure between the both left and right front wheels <NUM>, the front axle case <NUM> rotationally moves up and down around the laterally intermediate part, and the left and right front wheels <NUM> elevate up and down in directions opposite to each other. As a result, the ground-contact pressures of the both left and right front wheels <NUM> are maintained substantially equal.

The front axle case <NUM> has a hollow shape, which is elongated to left and right. As described above, the counter shaft <NUM>, the pair of left and right electric motors <NUM>, the pair of left and right planetary gear mechanisms <NUM>, the front-wheel differential output shaft <NUM> and the like are accommodated inside the front axle case <NUM>. A fixed gear case <NUM> for supporting an upper end of a king pin <NUM> faced in an up-down direction by bearings is mounted on each of the both left and right end sides of the front axle case <NUM>. A steering gear case <NUM> for supporting a lower end of the king pin <NUM> by bearings is mounted on a lower end of the fixed gear case <NUM> so as to be capable of rotational movement around the king pin <NUM>. A laterally facing front axle <NUM> is rotatably supported by the left and right steering gear cases <NUM>. The front wheels <NUM> are removably attached to parts in the front axle <NUM> that protrude outward to the left and right from the steering gear case <NUM>. Although not shown, a knuckle arm is attached to each of the steering gear cases <NUM> and is mechanically interlocked with the steering wheel <NUM>.

Each of the left and right front-wheel differential output shafts <NUM> in the front axle case <NUM> is interlockingly connected to the upper end side of the king pin <NUM> via a front bevel-gear mechanism <NUM>. A lower end side of the king pin <NUM> is interlockingly connected to a front axle <NUM> via a final gear <NUM> in the steering gear case <NUM>.

The front pivot member <NUM> includes a front center pin <NUM> and a front-center-pin receiving body <NUM> which are fitted with each other so as to be relatively rotatable. An annular flange <NUM> protruding radially outward is formed at a base part of the front center pin <NUM>, and with the axis thereof directed in a machine-body front-rear direction, the annular flange <NUM> is fastened to the front surface of the laterally intermediate part of the front axle case <NUM> so as to close the common opening <NUM>.

The front-center-pin receiving body <NUM> is formed with a cylindrical shape to be mounted to cover the front center pin <NUM> capable of relative rotation, and is fixed to the laterally intermediate part of the front support bracket <NUM> with an opening directed in the front-rear direction. The front center pin <NUM> is inserted into the front-center-pin receiving body <NUM> from the rear side and is supported by bearings.

The rear pivot member <NUM> includes a rear center pin <NUM> and a rear-center-pin receiving body <NUM> which are fitted with each other so as to be relatively rotatable. The cylinder portion 200a which supports the input shaft <NUM> therein by bearings also serves as the rear center pin <NUM>, and the centers of the front center pin <NUM> and the rear center pin <NUM> are matched with respect to an axis of the cylinder portion 200a along the machine-body front-rear direction.

The rear-center-pin receiving body <NUM> is formed with a cylindrical shape to cover and to support the rear center pin <NUM> by bearings, capable of relative rotation, and is fixed to the laterally intermediate part of the rear support bracket <NUM> with an opening directed in the front-rear direction. The rear center pin <NUM> is inserted into the rear-center-pin receiving body <NUM> from the front side, to be capable of relative rotation. In a state where the rear center pin <NUM> is inserted into the rear-center-pin receiving body <NUM>, a rear cover body <NUM> is mounted to cover the rear end sides of the rear center pin <NUM> and the rear-center-pin receiving body <NUM> (the rear pivot support member <NUM>). The rear cover body <NUM> is removably mounted on the rear surface of the rear support bracket <NUM> so as to close the rear openings of the rear center pin <NUM> and the rear-center-pin receiving body <NUM>, thereby limiting the axial movement of the rear center pin <NUM>. Moreover, the rear cover body <NUM> supports the input shaft <NUM> by bearings at a part that closes the rear opening of the cylindrical portion 200a (rear center pin <NUM>).

The front and rear center pins <NUM>, <NUM> are located concentrically with each other and are located at the center in the width direction of the machine body and function as the center of rotational movement of the front axle case <NUM>. The input shaft <NUM> is also located concentrically with the front and rear center pins <NUM>, <NUM>. A cable outlet <NUM> of the front cover body <NUM>, a wiring hole <NUM> of the front center pin <NUM>, and an insertion hole <NUM> of the front axle case <NUM> are also located concentrically with the front and rear center pins <NUM>, <NUM>.

The front center pin <NUM> includes the wiring hole <NUM> disposed concentrically with the rotation axis thereof, and an inner end of the wiring hole <NUM> is opened in an end surface of the annular flange <NUM>. In a state where the front center pin <NUM> is fastened to the front surface of the front axle case <NUM>, the wiring hole <NUM> of the front center pin <NUM> communicates with the common opening <NUM> of the front axle case <NUM>. On the other hand, an outer end of the wiring hole <NUM> is opened into an internal space 87a of the front cover body <NUM>. The cable outlet <NUM> is opened in the front cover body <NUM> so as to face the wiring hole <NUM>. The wiring cables <NUM> collected in the common opening <NUM> are drawn out to the outside of the front axle case <NUM> via the wiring hole <NUM> of the front center pin <NUM>, the internal space 87a of the front cover body <NUM>, and the cable outlet <NUM>, and are electrically connected to the controller <NUM> and the inverters <NUM>. Reference numeral <NUM> denotes a grommet made of an elastic body having a sealing function, which prevents coating of the wiring cable <NUM> from being damaged by vibration or the like and maintains a liquid-tight state inside the internal space 87a.

Therefore, the wiring cable <NUM> can be positioned concentrically with the center of rotational movement of the front axle case <NUM>, and even if the front axle case <NUM> swings up and down (rolls) around the front center pin <NUM> during traveling, the wiring cable <NUM> in the front center pin <NUM> is hardly twisted or repeatedly bent and stretched. Therefore, the wiring cable <NUM> drawn out of the front axle case <NUM> in which the electric motor <NUM> is incorporated can be markedly suppressed from being damaged such as disconnection fatigue.

As shown in <FIG>, oil for lubricating various gears and bearings and for cooling the electric motor <NUM> is stored in the front axle case <NUM>. A height position of an oil level when the various rotating bodies in the front axle case <NUM> are stopped is set to such an extent that lower half parts of the left and right motor shafts <NUM>, the front-wheel differential output shaft <NUM>, the counter shaft <NUM> and the like are in contact with the oil. For this reason, the various rotating bodies in the front axle case <NUM> do not rotate in a state of being completely immersed under the oil level, and an increase in stirring resistance (increase in power loss) is suppressed.

When the electric motor <NUM> is cooled by the lubricating oil stored in the front axle case <NUM>, its oil temperature tends to increase. In order to avoid lowering in performance of the electric motor <NUM> due to the temperature rise of each part of the motor, the rise in the oil temperature needs to be suppressed. Thus, as shown in <FIG>, <FIG> and <FIG>, an oil reservoir in the front axle case <NUM> is fluidly connected to the oil cooler <NUM> disposed in the front part of the front frame <NUM> via a feed piping <NUM> and a return piping <NUM>. An end of the feed piping <NUM> connected to a discharge side of the oil cooler <NUM> is mounted on the rear cover body <NUM> of the rear support bracket <NUM> and is connected in communication with the oil reservoir chamber 92a. The oil reservoir chamber 92a is connected in communication with the gear accommodating chamber 94b in the front axle case <NUM> through a supply oil passage <NUM> also used by the rear center pin <NUM> to insert and support the input shaft <NUM>. An end of the return piping <NUM> connected to a suction side of the oil cooler <NUM> is mounted on the front cover body <NUM> of the front support bracket <NUM> and is connected in communication with the internal space 87a.

Since the feed piping <NUM> and the return piping <NUM> can be fixed to the rear cover body <NUM> and the front cover body <NUM> without being bent and extended when the front axle case <NUM> swings, a rigid pipe material such as a durable metal can be used.

The oil is fed from the oil cooler <NUM> to the gear accommodating chamber 94b in the front axle case <NUM> via the feed piping <NUM>, the rear cover body <NUM>, and the supply oil path <NUM> of the rear center pin <NUM>. In a hydraulic fluid in the front axle case <NUM>, the hydraulic fluid that has entered the motor accommodating chamber 94a from the rear communication port <NUM> and the left and right side communication ports <NUM> oil-cools the left and right electric motors <NUM> and then, it is returned to the oil cooler <NUM> via the common opening <NUM> in the front part of the front axle case <NUM>, the wiring hole <NUM>, the front cover body <NUM>, and the return piping <NUM>. As described above, the lubricating oil in the front axle case <NUM> cools the left and right electric motors <NUM> and then, moves to the oil cooler <NUM> to be cooled and then, is introduced into the front axle case <NUM> again to be circulated. Therefore, an amount of the lubricating oil in the front axle case <NUM> can be maintained at a predetermined amount all the time, and the temperature of the lubricating oil can be maintained at an appropriate temperature for the electric motor <NUM>.

According to the above configuration, the sun gear <NUM>, which is the first element of the three elements of each of the planetary gear mechanisms <NUM>, is interlockingly connected to the corresponding left and right electric motors <NUM>, the carrier <NUM>, which is the second element, is interlockingly connected to the corresponding left and right auxiliary drive (front) wheels <NUM>, and the ring gear <NUM>, which is the third element, is interlockingly connected to the output side of the traveling transmission mechanism for driving the main drive (rear) wheels <NUM> by the internal combustion engine <NUM> and thus, in rotating and driving the left and right front wheels <NUM>, drive loads can be shared by the internal combustion engine <NUM> and the left and right electric motors <NUM>. Thus, each of the electric motors <NUM> can be downsized so as to achieve reduction in size and weight. For example, a relationship of the outputs between the electric motors <NUM> and the internal combustion engine <NUM> is set to <NUM>:<NUM> or <NUM>:<NUM> in accordance with front-rear weight distribution of the vehicle body, and the both left and right electric motors <NUM> can be downsized by independently driving each of the left and right front wheels <NUM>, <NUM> by using a pair of the electric motors <NUM>. Since the left and right electric motors <NUM> are driven independently of each other, rotation of the left and right front wheels <NUM> can be finely controlled, and, for example, a turning radius can be made smaller than before, and the straight traveling performance can be improved.

On the lower side of the front part of the traveling machine body <NUM>, the front axle case <NUM> swingable around the center pins <NUM>, <NUM> located at the laterally intermediate part is provided, the front wheels <NUM> as the drive wheels are provided at the both left and right end parts of the front axle case <NUM>, and the left and right front wheels <NUM> can move in the vertical direction depending on the unevenness of the road surface. The pair of electric motors <NUM> are accommodated in the front axle case <NUM> by being distributed to both the left and right sides with the center pins <NUM>, <NUM> interposed therebetween and thus, the electric motors <NUM> capable of size reduction can be accommodated in the front axle case <NUM> with a good balance. The front axle case <NUM> smoothly swings in the traveling on a bad road or the like so as to realize stable traveling.

The wiring hole <NUM> communicating with the inside and outside of the front axle case <NUM> is formed inside the center pins <NUM>, <NUM>, and the wiring cable <NUM> for the respective electric motors <NUM> is drawn out to the outside of the front axle case <NUM> through the wiring hole <NUM> and thus, the wiring cable <NUM> for each of the electric motors <NUM> can be disposed concentrically with the swing center of the front axle case <NUM>. Thus, even if the front axle case <NUM> swings up and down (rolls), the wiring cable <NUM> is hardly twisted and is not bent and stretched, so that the concern of damage such as disconnection can be markedly suppressed.

Since the oil is stored in the axle case, and the front axle case is connected to the oil cooler <NUM> mounted on the traveling machine body <NUM> so that the stored oil can flow freely via the through hole of the center pin, when the front axle case <NUM> swings, the connection piping (feed and return pipings <NUM>, <NUM>) is not bent and stretched and thus, a connection piping made of a rigid material with durability can be used.

The traveling machine body <NUM> is supported by the both left and right front wheels <NUM> and the both left and right rear wheels <NUM>, and the switching mechanism <NUM> for switching the drive form of the front and rear wheels <NUM>, <NUM> to the front-wheel drive, the four-wheel drive, and the rear-wheel drive is accommodated in the transmission case <NUM>, and it is configured such that, when the switching mechanism <NUM> is switched to the front-wheel drive position, the ring gear <NUM>, which is the third element of the both left and right planetary gear mechanisms <NUM>, is fixed to the transmission case <NUM> and is brought into a breaking state, the drive of the both left and right electric motors <NUM> is transmitted via the sun gears of the both left and right planetary gear mechanisms <NUM>, and the both left and right front wheels <NUM> are rotated and driven and thus, only by the switching operation of the switching mechanism <NUM> to the front-wheel drive position, the traveling only by the front-wheel drive by the both left and right electric motors <NUM> is made possible.

Claim 1:
A traveling vehicle (<NUM>) in which an internal combustion engine (<NUM>), a main drive wheel (<NUM>), and a pair of sub drive wheels (<NUM>) are supported on a traveling machine body (<NUM>), and the internal combustion engine (<NUM>) drives the main drive wheel (<NUM>) through a traveling transmission mechanism (<NUM>), the traveling vehicle (<NUM>) comprising:
an electric motor (<NUM>) and a planetary gear mechanism (<NUM>) that are provided inside an axle case (<NUM>) that supports the pair of sub drive wheels (<NUM>), wherein
in three elements of the planetary gear mechanism (<NUM>), a first element is interlockingly connected to the electric motor (<NUM>), a second element is interlockingly connected to the pair of sub drive wheels (<NUM>), and a third element is interlockingly connected to an output side of the traveling transmission mechanism (<NUM>), and wherein
the axle case (<NUM>) is supported on the traveling machine body (<NUM>), to be swingable around a center pin (<NUM>; <NUM>) disposed at an intermediate part in a vehicle width direction, and the pair of sub drive wheels (<NUM>) is attached, capable of moving up and down; and
each of a pair of electric motors (<NUM>), included in the electric motor (<NUM>), and each of a pair of planetary gear mechanisms (<NUM>), included in the planetary gear mechanism (<NUM>), are accommodated in the axle case (<NUM>) by being distributed to both left and right sides with the center pin (<NUM>; <NUM>) interposed therebetween.