Patent Description:
The present disclosure relates to a work vehicle and a controller for a work vehicle.

Some work vehicles for agricultural use, such as tractors, have models equipped with the function of turning at a smaller turning radius than they would in a usual turn. For example, work vehicles are prevalent that have a front wheel speed increaser which, when the front wheel is steered by a predetermined angle or greater, reduces the turning radius by increasing the rotational speed of the outer front wheel over the rotational speeds of the right and left rear wheels. Such a work vehicle is able to smoothly turn while keeping itself from messing the soil on the field surface. <CIT> discloses an example of a work vehicle having such a front wheel speed increaser.

On the other hand, work vehicles equipped with a suspension mechanism at the vehicle front for absorbing vibration and shock during travel for improved riding comfort have also become prevalent. The suspension mechanism provided at the vehicle front is called a "front suspension". In tractors or other work vehicles, the load undergoes large changes. Thus, a hydraulic front suspension is commonly adopted to ensure an adequate suspension stroke. <CIT> discloses an example of a work vehicle having a hydraulic front suspension.

<CIT> discloses a suspension controller for properly preventing a vehicle such as a truck from becoming overturned during a sharp turn. The vehicle disclosed in <CIT> includes a pair of suspension members that allow for vehicle height adjustments. Based on the steering angle and steering angular velocity of the vehicle during travel, the suspension controller, when it is estimated that the turning radius of the vehicle immediately afterwards will be smaller than a predetermined value, controls the suspension members so as to increase the vehicle height on the outer side of the vehicle's turn. Japanese Laid-Open Patent Publication No. <NUM>-<NUM> describes that this can properly prevent the vehicle from becoming overturned during a sharp turn.

<CIT> discloses a motor vehicle characterized by a center of gravity, which comprises a vehicle body, a plurality of wheels for maintaining contact with a road surface, a roll-reduction apparatus configured to resist an impending rollover of the vehicle via at least one of applying a force between the vehicle body and at least one of the plurality of wheels and lowering of the center of gravity of the vehicle, a sensing device configured to detect a roll moment acting on the vehicle and having a threshold magnitude, and a controller configured to trigger the roll-reduction apparatus to generate a moment on the vehicle body opposite to the detected roll moment having the threshold magnitude such that an angle of the vehicle with respect to the road surface during the rollover is reduced.

<CIT> discloses a roll control system for use in a vehicle that is not dependent upon the turning condition of the vehicle.

The present invention is defined by the independent claim. Preferred examples are defined in the dependent claims. When a work vehicle turns with a small turning radius or a high speed, a strong centrifugal force acts in the outer direction of the turn. As a result of this, the tilt of the work vehicle may increase, possibly resulting in poorer riding comfort or loss of balance.

Preferred embodiments of the present invention provide techniques for reducing or preventing tilting when a work vehicle turns with a small turning radius or a high speed to achieve a more stable turn.

A work vehicle according to an implementation of the present disclosure includes a vehicle body, running gear to cause the vehicle body to travel, a height adjuster to change a height of a center of gravity of the vehicle body, and a controller configured or programmed to, in accordance with at least one of a turning radius and an angular velocity of the vehicle body during a turn, control the height adjuster to maintain or lower the height of the center of gravity.

A controller according to another implementation of the present disclosure controls a work vehicle including a vehicle body, running gear to cause the vehicle body to travel, and a height adjuster to change a height of a center of gravity of the vehicle body. The controller includes one or more processors, and one or more memories storing a computer program to be executed by the one or more processors. The one or more processors is configured or programmed to acquire, during a turn, information concerning at least one of a turning radius and an angular velocity of the vehicle body, and control the height adjuster to maintain or lower the height of the center of gravity in accordance with the information.

General or specific aspects of various example preferred embodiments of the present disclosure may be implemented using a device, a system, a method, an integrated circuit, a computer program, a non-transitory computer-readable storage medium, or any combination thereof. The computer-readable storage medium may be inclusive of a volatile storage medium, or a non-volatile storage medium. The device may include a plurality of devices. In the case where the device includes two or more devices, the two or more devices may be disposed within a single apparatus, or divided over two or more separate apparatuses.

According to certain preferred embodiments of the present disclosure, tilting of a work vehicle during a turn is reduced or prevented, and the turning stability is improved.

Hereinafter, preferred embodiments of the present disclosure will be described more specifically. Note however that unnecessarily detailed descriptions may be omitted. For example, detailed descriptions on what is well known in the art or redundant descriptions on what is substantially the same configuration may be omitted. This is to avoid lengthy description, and facilitate the understanding of those skilled in the art. The accompanying drawings and the following description, which are provided by the present inventors so that those skilled in the art can sufficiently understand the present disclosure, are not intended to limit the scope of claims. In the following description, component elements having identical or similar functions are denoted by identical reference numerals.

The following preferred embodiments are only exemplary, and the techniques of the present disclosure are not limited to the following preferred embodiments. For example, numerical values, shapes, materials, steps, and orders of steps, etc., that are indicated in the following preferred embodiments are only exemplary, and admit of various modifications. Any one implementation may be combined with another so long as it makes technological sense to do so.

Hereinafter, preferred embodiments where the work vehicle is a tractor will be described as an example. Without being limited to tractors, the techniques according to the present disclosure are also applicable to other types of agricultural machines, e.g., rice transplanters, combines, vehicles for crop management, and riding lawn mowers. The techniques according to the present disclosure are also applicable to work vehicles for use in non-agricultural applications, e.g., construction vehicles or snowplow vehicles.

<FIG> is a perspective view showing an exemplary appearance of a work vehicle according to an illustrative preferred embodiment of the present disclosure. The work vehicle <NUM> according to the present preferred embodiment is a tractor for use with agricultural work in a field (e.g., an agricultural field, an orchard, or a paddy field). <FIG> is a side view schematically showing the work vehicle <NUM> and an example of an implement <NUM> that is linked to the work vehicle <NUM>.

As shown in <FIG>, the work vehicle <NUM> includes a vehicle body <NUM>, a prime mover (engine) <NUM>, a transmission <NUM>, running gear <NUM> to cause the vehicle body <NUM> to travel, and an adjusting device <NUM> (height adjuster) to change the height of the center of gravity of the vehicle body <NUM>. A cabin <NUM> is provided on the vehicle body <NUM>. The running gear <NUM> includes four wheels (a pair of front wheels 104F and a pair of rear wheels 104R), a wheel axis for rotating the four wheels, and a braking device to apply braking to each wheel. Inside the cabin <NUM>, a driver's seat <NUM>, a steering device <NUM>, an operational terminal <NUM>, and switches for manipulation are provided. The work vehicle <NUM> is able to switch between a four-wheel drive (4W) mode in which all of the front wheels 104F and the rear wheels 104R serve as driving wheels, and a two-wheel drive (2W) mode in which only the front wheels 104F or only the rear wheels 104R serve as the driving wheels.

The prime mover <NUM> may be a diesel engine, for example. Instead of a diesel engine, an electric motor may be used. The transmission <NUM> can change the propulsion and moving speed of the work vehicle <NUM> through a speed changing mechanism. The transmission <NUM> can also switch between forward travel and backward travel of the work vehicle <NUM>.

The steering device <NUM> includes a steering wheel, a steering shaft connected to the steering wheel, and a power steering device to assist in the steering by the steering wheel. The front wheels 104F are the wheels responsible for steering, such that changing their angle of turn (also referred to as a "steering angle") can cause a change in the traveling direction of the work vehicle <NUM>. The steering angle of the front wheels 104F can be changed by manipulating the steering wheel. The power steering device includes a hydraulic device or an electric motor to supply an assisting force for changing the steering angle of the front wheels 104F. The work vehicle <NUM> may have an automatic steering function. When automatic steering is performed, under the control of a controller disposed in the work vehicle <NUM>, the steering angle of the front wheels 104F may be automatically adjusted by the power of the hydraulic device or electric motor.

A linkage device <NUM> is provided at the rear of the vehicle body <NUM>. The linkage device <NUM> may include, e.g., a three-point linkage (also referred to as a "three-point link" or a "three-point hitch"), a PTO (Power Take Off) shaft, a universal joint, and a communication cable. The linkage device <NUM> allows the implement <NUM> to be attached to or detached from the work vehicle <NUM>. The linkage device <NUM> is able to raise or lower the three-point linkage device with a hydraulic device, for example, thus controlling the position and/or attitude of the implement <NUM>. Moreover, motive power can be sent from the work vehicle <NUM> to the implement <NUM> via the universal joint. While towing the implement <NUM>, the work vehicle <NUM> allows the implement <NUM> to perform a predetermined task. The linkage device may be provided frontward of the vehicle body <NUM>. In that case, the implement may be connected frontward of the work vehicle <NUM>.

Although the implement <NUM> shown in <FIG> is a rotary tiller, the implement <NUM> is not limited to a rotary tiller. For example, any arbitrary implement such as a mower, a seeder, a spreader, a rake implement, a baler, a harvester, a sprayer, or a harrow, may be connected to the work vehicle <NUM> for use. The work vehicle <NUM> may travel without the implement <NUM> being attached thereto.

The running gear <NUM> may include a front wheel speed increaser which causes the outer front wheel 104F to rotate more rapidly than the inner front wheel 104F and the right and left rear wheels 104R during a turn, thus to reduce the turning radius. The front wheel speed increaser may increase the rotational speed(s) of the front wheel(s) 104F when the steering angle of the front wheels 104F has reached a predetermined angle or greater as the driver turns the steering wheel to a great extent, for example. By increasing the rotational speed of the outer front wheel 104F to approximately, e.g., <NUM> to <NUM> times of the rotational speed of the outer rear wheel 104R, the front wheel speed increaser can reduce the turning radius of the work vehicle <NUM>. This allows the work vehicle <NUM> to smoothly turn in a small space, while keeping itself from messing the soil on the field surface. Such a turn may be referred to as a "bi-speed turn" in the present specification. When the front wheel speed increaser increases the rotational speed(s) of the front wheel(s) 104F, a control of automatically braking the inner rear wheel 104R may be performed. Braking the inner rear wheel 104R in addition to increasing the rotational speed(s) of the front wheel(s) 104F allows the turning radius to be further reduced. By manipulating the operational terminal <NUM> or the switches within the cabin <NUM>, the driver is able to set: whether the front wheel speed increasing function is enabled/disabled; how much the rotational speed(s) of the front wheel(s) 104F is to be increased during a turn; and whether or not the rear wheels 104R are braked and the degree of such braking during a turn.

Although a bi-speed turn can be made within a small circle, a stronger centrifugal force will act in a bi-speed turn than in a turn which is made at the same vehicle speed but not in the manner of a bi-speed turn. A strong centrifugal force may cause the body of the vehicle to tilt during a turn, thus detracting from the riding comfort, or resulting in a loss of balance.

<FIG> are diagrams schematically showing a strong centrifugal force at work when the work vehicle <NUM> is making a small turn via bi-speed turn. In <FIG>, a curved arrow (a) in solid line represents an example locus of the work vehicle <NUM> during a usual turn, while a curved arrow (b) in broken line represents an example locus of the work vehicle <NUM> during a small turn via bi-speed turn. A straight arrow in solid line represents a centrifugal force during a usual turn, while a straight arrow in broken line represents a centrifugal force during a small turn. An object having a mass m, which undergoes a circular motion with a velocity v and a radius r (angular velocity v/r), receives a centrifugal force with a magnitude of mv<NUM>/r in the outer direction of the circular motion. Therefore, the turning work vehicle <NUM> is subject to a centrifugal force which is, in the outer direction of the turn, essentially in proportion to its velocity raised to the second power and its weight, and which is in inverse proportion to the turning radius. Therefore, given the same vehicle speed, a greater centrifugal force than in a usual turn is at work during a small turn. Consequently, as shown in <FIG>, the body of the vehicle is more likely to tilt and become unbalanced during a small turn (b) than during a usual turn (a). In particular, when the center of gravity of the work vehicle <NUM> is high or when the interval between the right and left wheels (i.e., tread) of the work vehicle <NUM> is narrow, the body of the vehicle is likely to have a large tilt due to centrifugal force. This problem may occur not only when making a bi-speed turn, but commonly when any turn is made with a small turning radius or a high velocity (i.e., a high angular velocity).

In the present preferred embodiment, in order to reduce or prevent tilting of the body of the vehicle during a small turn and to achieve a stable turn, the work vehicle <NUM> includes the adjusting device <NUM> (height adjuster), which changes the height of the center of gravity of the vehicle body <NUM>. As used herein, "height" means a height (i.e., distance) from the ground surface on which the work vehicle <NUM> is traveling. The adjusting device <NUM> may include a suspension device that changes the height of the front of the vehicle body <NUM>, for example. In the example shown in <FIG>, the adjusting device <NUM> includes a hydraulic suspension device provided at the lower front of the vehicle body <NUM>. By controlling such a suspension device, the height of the center of gravity of the vehicle body <NUM> can be adjusted. Without being limited to a suspension device provided at the front of the vehicle body <NUM>, the adjusting device <NUM> may be configured to adjust the center of gravity of the vehicle body <NUM> by other mechanisms. For example, suspension mechanisms may be provided at both the front and the rear of the vehicle body <NUM>. Alternatively, the adjusting device <NUM> may be implemented by a mechanism that raises or lowers a weight provided at a predetermined position (e.g., the bottom, the front, the side, or the rear) of the vehicle body <NUM>.

The adjusting device <NUM> is controlled by a controller, such as an electronic control unit (ECU), that is included in the work vehicle <NUM>. In accordance with at least one of the turning radius and the angular velocity of the vehicle body <NUM> during a turn, the controller is configured or programmed to control the adjusting device <NUM> to maintain or lower the height of the center of gravity of the vehicle body <NUM>. For example, the controller controls the adjusting device <NUM> to lower the center of gravity when a state of a small turn is entered during a turn, i.e., a state where the turning radius is smaller than a reference radius, and if the height of the center of gravity of the vehicle body <NUM> is higher than a reference height. Even in a state of a small turn, if the height of the center of gravity is equal to or lower than the reference height, the controller does not lower the center of gravity but maintains its height. For example, if at the beginning of the turn the center of gravity of the vehicle body <NUM> is already close to the lowest height within a controllable range, then the controller maintains that height of the center of gravity.

<FIG> is a diagram schematically illustrating an effect obtained by lowering the center of gravity of the vehicle body <NUM> when the turning radius is small (i.e., the angular velocity is high). The left side of <FIG> depicts an example of the work vehicle <NUM> during a turn where the control for the center of gravity is not performed. The right of <FIG> depicts an example of the work vehicle <NUM> during a turn where the control for the center of gravity according to the present preferred embodiment is performed. As shown in the right side of <FIG>, by lowering the center of gravity, the tilt of the work vehicle <NUM> caused by centrifugal force is reduced or prevented. This achieves improvement in the stability of the work vehicle <NUM> during a small turn.

As described above, the running gear <NUM> may include a front wheel speed increaser. In that case, the running gear <NUM> can operate in a small turn mode where the rotational speed of the outer front wheel 104F is made higher than the rotational speed(s) of the two rear wheels 104R during a turn so that the turning radius becomes smaller than the reference radius. A turn made in the small turn mode corresponds to the aforementioned "bi-speed turn". The controller may include a first control circuit to control the running gear <NUM> and a second control circuit to control the adjusting device <NUM>. When the angle of rotation of the steering wheel or the steering angle of the front wheels 104F has exceeded a reference angle, the first control circuit causes the running gear <NUM> to operate in the small turn mode. When the small turn mode is begun while the height of the center of gravity of the vehicle body <NUM> is higher than the reference height, the second control circuit causes the adjusting device <NUM> to lower the center of gravity of the vehicle body <NUM>. With such a configuration, the second control circuit is able to cause the adjusting device <NUM> to lower the center of gravity of the vehicle body <NUM> in response to a signal which is output from the first control circuit indicating the start of the small turn mode. Thus, adjustments of the center of gravity can be made without having to separately provide a sensor to detect a state of a small turn.

In the small turn mode, the running gear <NUM> may have the function of automatically braking the inner one of the two rear wheels 104R. In that case, the first control circuit may be configured to control the presence or absence of braking or intensity of braking on the inner rear wheel. The second control circuit may cause at least one of the amount of lowering the center of gravity and the reference height to vary in accordance with the presence or absence of braking or intensity of braking. When the inner rear wheel 104R is braked, the turning radius is further reduced such that the centrifugal force is further increased. Therefore, in the case where a small turn is made with the braking of the inner rear wheel 104R, the condition for lowering the center of gravity may be more relaxed than when a small turn is made without such braking.

The controller may perform the aforementioned control for the center of gravity even in the case where a bi-speed turn is not enabled, or in the case where the work vehicle <NUM> lacks bi-speed turn functionality. The work vehicle <NUM> may include an angular velocity sensor that is capable of measuring the angular velocity of the vehicle body <NUM>, e.g., an inertial measurement unit (IMU). In that case, the controller may cause the adjusting device <NUM> to lower the center of gravity when the angular velocity of a yawing (i.e., rotational motion around an axis in the top-bottom direction of the vehicle) of the vehicle body <NUM> as measured by the angular velocity sensor has become equal to or greater than a threshold, and if the height of the center of gravity is higher than the reference height. With such a configuration, it is possible to adjust the center of gravity based on the result of measurement by the angular velocity sensor, even in the case where a bi-speed turn is not enabled or where the work vehicle <NUM> lacks bi-speed turn functionality.

The controller may change at least one of the amount of lowering the center of gravity and the reference height in accordance with at least one of the turning radius, the angular velocity, and the weight of the work vehicle. Moreover, the controller may change the reference radius in accordance with at least one of the speed and the weight of the work vehicle <NUM>. The magnitude of the centrifugal force depends on the turning radius, the speed of the work vehicle <NUM>, the angular velocity of the work vehicle <NUM>, and the weight of the work vehicle <NUM>. Therefore, based on these conditions, the controller may change at least one of the amount of lowering the center of gravity, the reference height, and the reference radius. For example, the controller may increase the amount of lowering the center of gravity or lower the reference height as the turning radius decreases (or the angular velocity increases) or as the weight increases. Moreover, the controller may increase the reference radius as the speed of the work vehicle <NUM> increases or as the weight increases.

The controller may change at least one of the amount of lowering the center of gravity, the reference height, and the reference radius in accordance with the type of the implement <NUM> linked to the work vehicle <NUM> or the presence or absence of the implement <NUM>. Once the implement <NUM> is attached, the center of gravity of the system combining the work vehicle <NUM> and the implement <NUM> may become higher than the center of gravity of the work vehicle <NUM> alone, etc., which makes tilting more likely. Therefore, when the implement <NUM> has been attached, the controller may increase the amount of lowering the center of gravity, lower the reference height, or increase the reference radius, relative to when no implement <NUM> is attached.

As in the example shown in <FIG>, when the adjusting device <NUM> includes a suspension device, the controller may control the suspension device to change the height of the center of gravity. Hereinafter, an exemplary configuration and an exemplary control for the suspension device will be described.

<FIG> is a conceptual diagram showing a schematic configuration of the suspension device. By hydraulic action, this suspension device is able to change the height of a front wheel axis frame <NUM> that is provided at the front of the vehicle body <NUM>. As an example of the controller, <FIG> illustrates an ECU <NUM>. Without being limited to the illustrated position, the ECU <NUM> may be disposed at any arbitrary position. The running gear in this example includes two supports <NUM> for respectively supporting the two front wheels 104F. The suspension device includes: two hydraulic suspension cylinders <NUM> which are provided near the right and left front wheels 104F; and a hydraulic circuit <NUM> that is connected to the two hydraulic suspension cylinders <NUM>. In <FIG>, the front wheel 104F, the support <NUM>, and the suspension cylinder <NUM> on the left side are illustrated. The support <NUM> is mounted to the front wheel axis frame <NUM> at one end thereof, so as to be capable of swinging up and down around a spindle <NUM>. The suspension cylinder <NUM> interconnects a portion of the support <NUM> and the front wheel axis frame <NUM>. The hydraulic circuit <NUM> adjusts the amount and pressure of hydraulic oil to be supplied to each suspension cylinder <NUM>. By controlling the hydraulic circuit <NUM>, the ECU <NUM> controls the extension/retraction action of the suspension cylinders <NUM>.

On the front wheel axis frame <NUM> and the support <NUM>, a stroke sensor <NUM> is mounted to detect an extended or retracted state of the suspension cylinder <NUM>. The stroke sensor <NUM> shown in <FIG> includes a rotary displacement potentiometer. The stroke sensor <NUM> outputs a signal which is in accordance with the stroke length of the suspension cylinder <NUM>. Based on the signal which is output from the stroke sensor <NUM>, the ECU <NUM> calculates the stroke length of the suspension cylinder <NUM>. By controlling each control valve in the hydraulic circuit <NUM> based on the results of calculation, the ECU <NUM> is able to adjust the stroke length to a desired length.

<FIG> is a side view showing a more specific example of the structure of the suspension device. The rear end of the support <NUM> is supported by the spindle <NUM>, which is located below the front wheel axis frame <NUM> and which extends along the right-left direction with respect to the vehicle's traveling direction. The support <NUM> is supported so as to be capable of swinging around the spindle <NUM>. The front wheel axis <NUM> is located frontward and upward from the support <NUM>. To the front wheel axis <NUM>, a transmission system to transmit a motive force for traveling via a universal joint and the like is connected. The front wheels 104F are mounted on the front wheel axis <NUM>.

Between the front ends of the right and left supports <NUM> and the two positions at the front of the front wheel axis frame <NUM>, two hydraulic suspension cylinders <NUM> are respectively connected. The two suspension cylinders <NUM> are controlled by the ECU <NUM> to extend or retract in conjunction with the up and down movements of the front wheel 104F. To each suspension cylinder <NUM>, hydraulic oil is supplied from the hydraulic circuit <NUM>. As the ECU <NUM> controls supply and discharge of the hydraulic oil, the suspension cylinders <NUM> function as springs. As a result of this, shocks during travel are absorbed so as to provide an improved riding comfort.

<FIG> is a diagram showing an exemplary schematic configuration for the hydraulic circuit <NUM>. The suspension cylinders <NUM> are disposed in such an attitude that piston rods protrude downward therefrom. Each suspension cylinder <NUM> includes a head-side oil chamber 441a and a rod-side oil chamber 441b. A first oil channel <NUM> is connected to the upper (head-side) oil chamber 441a. A second oil channel <NUM> is connected to the lower (rod-side) oil chamber 441b.

To the first oil channel <NUM>, a head-side accumulator <NUM> is connected via a pilot-operated double check valve <NUM>. In an oil channel between the head-side accumulator <NUM> and the double check valve <NUM>, a pilot-operated variable orifice <NUM> is provided. To an oil channel between the double check valve <NUM> and the first oil channel <NUM>, a pressure sensor <NUM> is connected. A rod-side accumulator <NUM> is connected to the second oil channel <NUM>.

A gas, e.g., nitrogen, is sealed inside the accumulators <NUM> and <NUM>. The gas compresses as pressure increases in the oil channel connected thereto, and the gas expands as the pressure in the oil channel decreases. Through this action, a spring property is imparted to each suspension cylinder <NUM>.

The variable orifice <NUM> has three positions associated with different orifice diameters. Two switching control valves <NUM> and <NUM> are provided, which allow the variable orifice <NUM> to be manipulated through control of a pilot pressure. By adjusting the flow of hydraulic oil to be supplied and discharged to and from the head-side accumulator <NUM>, the variable orifice <NUM> is able to vary the stiffness (corresponding to the spring modulus) of the suspension. As the ECU <NUM> drives solenoids <NUM> and <NUM> in the switching control valves <NUM> and <NUM>, the aperture of the variable orifice <NUM> can be switched in three steps of large, medium, and small. This allows the damping force of the suspension cylinders <NUM> to be switched in three steps. If the ECU <NUM> turns both solenoids <NUM> and <NUM> OFF, an aperture at the "large" position is inserted in the oil channel, whereby the damping force becomes minimum. If the ECU <NUM> turns the solenoid <NUM> ON, an aperture at the "medium" (left) position is inserted in the oil channel, whereby the damping force becomes intermediate. If the ECU <NUM> turns the solenoid <NUM> ON, an aperture at the "small" (right) position is inserted in the oil channel so that the damping force becomes maximum.

The hydraulic circuit <NUM> further includes an open/close control valve <NUM> to cause a pilot pressure to act on the double check valve <NUM>. Through pilot pressure control by the open/close control valve <NUM>, the double check valve <NUM> is switched between a closed state and an open state. By driving a solenoid <NUM> in the open/close control valve <NUM>, the ECU <NUM> causes a pilot pressure to act on the double check valve <NUM> so as to open the double check valve <NUM>. When the double check valve <NUM> is opened, hydraulic oil flows between the head-side oil chamber 441a and the head-side accumulator <NUM>, thus enabling suspension functionality. In the present specification, this state may be referred to as "suspension-ON". Conversely, when the double check valve <NUM> is in a closed state, the flow of hydraulic oil between the head-side oil chamber 441a and the head-side accumulator <NUM> is blocked. This keeps the suspension fixed. In the present specification, this state may be referred to as "suspension locking".

The hydraulic oil from the hydraulic pump <NUM>, which is driven by the prime mover <NUM> (engine), is supplied to the pilot-operated main control valve <NUM>. To the oil channel between the hydraulic pump <NUM> and the main control valve <NUM>, a relief valve <NUM> is connected. When the pressure of the hydraulic oil reaches an upper limit value that was previously set, the relief valve <NUM> is opened to allow a portion of the hydraulic oil to return to the tank <NUM>, so as to reduce or prevent an excessive pressure increase of the hydraulic oil.

The main control valve <NUM> is a <NUM>-port <NUM>-position directional control valve including a position-to-raise where hydraulic oil is supplied to the first oil channel <NUM> so as to extend the cylinders <NUM> and raise the vehicle height; a position-to-lower where hydraulic oil is supplied to the second oil channel <NUM> so as to retract the cylinders <NUM> and lower the vehicle height; and a neutral position where hydraulic oil is neither supplied nor discharged to/from the cylinders <NUM>. Two operable valves <NUM> and <NUM> are provided in order to manipulate the main control valve <NUM> by allowing a pilot pressure to act thereon. To the first oil channel <NUM>, a pilot-operated check valve <NUM> and a throttle <NUM> are connected. To the second oil channel <NUM>, a pilot-operated check valve <NUM>, a check valve <NUM> that opens or closes with hydraulic oil pressure, and a throttle <NUM> are connected. A relief valve <NUM> is connected to the oil channel between the check valve <NUM> and the check valve <NUM>.

As the ECU <NUM> drives solenoids <NUM> and <NUM> in the operable valves <NUM> and <NUM>, the raising and lowering of the cylinders <NUM> can be controlled. If the ECU <NUM> turns the solenoid <NUM> ON, the pilot pressure places the main control valve <NUM> in the position-to-raise such that hydraulic oil is supplied from the pump <NUM> to the head-side oil chamber 441a. As a result of this, the cylinders <NUM> extend, thus raising the center of gravity of the vehicle body <NUM>. On the other hand, if the ECU <NUM> turns the solenoid <NUM> ON, the pilot pressure places the main control valve <NUM> in the position-to-lower such that hydraulic oil is supplied from the pump <NUM> to the rod-side oil chamber 441b. As a result of this, the cylinders <NUM> are retracted, thus lowering the center of gravity of the vehicle body <NUM>. If the ECU <NUM> turns both solenoids <NUM> and <NUM> OFF, the main control valve <NUM> is switched to the neutral position. In this state, the cylinders <NUM> are isolated from the pump <NUM> and the tank <NUM> by the check valves <NUM> and <NUM>. In this state, if the ECU <NUM> turns the solenoid <NUM> ON, the accumulators <NUM> and <NUM> and the cylinders <NUM> are coupled, so that the cylinders <NUM> act as springs extending or retracting in conjunction with up and down movements of the front wheel 104F. As the oil channel between the head-side oil chamber 441a and the head-side accumulator <NUM> is narrowed by the variable orifice <NUM>, the moving speed of the hydraulic oil is regulated, so that the cylinders <NUM> function as dampers.

<FIG> is a block diagram showing an exemplary configuration for a front suspension control system <NUM> according to the present preferred embodiment. The control system <NUM> includes a front suspension ECU <NUM>, an engine ECU <NUM>, and a main ECU <NUM>. The front suspension ECU <NUM> controls the operation of the front suspension. The engine ECU <NUM> controls the operation of the engine. The main ECU <NUM> controls the overall operation of the work vehicle <NUM>.

The ECUs <NUM>, <NUM> and <NUM> may communicate with one another according to a vehicle bus standard such as CAN (Controller Area Network). Although the ECUs <NUM>, <NUM> and <NUM> are illustrated as individual corresponding blocks in <FIG>, each of these functions may be distributed among a plurality of ECUs. Alternatively, an onboard computer that integrates some or all of the functions of the ECUs <NUM>, <NUM> and <NUM> may be provided. The control system <NUM> may include ECUs other than the ECUs <NUM>, <NUM> and <NUM>, and any number of ECUs may be provided in accordance with functionality. Each ECU includes a control circuit including one or more processors and one or more memories. The processor(s) operate by executing a computer program(s) stored in the memory(s). In the present preferred embodiment, the main ECU <NUM> is configured or programmed to perform the function of the aforementioned first control circuit, whereas the front suspension ECU <NUM> is configured or programmed to perform the function of the aforementioned second control circuit. Therefore, in the present preferred embodiment, a combination of the front suspension ECU <NUM> and the main ECU <NUM> has the functions of the aforementioned "controller".

The front suspension ECU <NUM> is connected to a plurality of switches <NUM> to <NUM>, the pressure sensor <NUM>, the stroke sensor <NUM>, and the solenoids <NUM> to <NUM>. The plurality of switches <NUM> to <NUM> are provided in the cabin <NUM> of the work vehicle <NUM>. The plurality of switches <NUM> to <NUM> include a suspension-auto switch (SW) <NUM>, a suspension-OFF switch <NUM>, a suspension-soft switch <NUM>, a suspension-hard switch <NUM>, and a suspension-manual switch <NUM>.

The main ECU <NUM> is connected to an electronic meter <NUM>, a buzzer <NUM>, and an angle-of-turn sensor <NUM>. In accordance with a command from the main ECU <NUM>, the electronic meter <NUM> displays the operating status of the work vehicle <NUM>. The electronic meter <NUM> displays the operating status of the front suspension, the bi-speed turn operating status, and so on, for example. The buzzer <NUM> generates an alarm sound in accordance with a command from the main ECU <NUM>. The buzzer <NUM> may generate an alarm sound while the user is manually adjusting the vehicle height, for example. The angle-of-turn sensor <NUM> measures the angle of turn (steering angle) of the front wheels 104F or the angle of rotation of the steering wheel, and outputs a signal indicating the result of measurement to the main ECU <NUM>.

During travel of the work vehicle <NUM>, the engine ECU <NUM> consecutively sends information representing the revolutions of the engine per unit time to the front suspension ECU <NUM>. The information of engine revolutions is used in the relief-stopping control described below.

During travel of the work vehicle <NUM>, the main ECU <NUM> consecutively sends to the front suspension ECU <NUM> information representing: the state of a shuttle lever (forward travel/backward travel); the speed of the work vehicle <NUM> (vehicle speed); the temperature of the hydraulic oil (oil temperature) in the hydraulic circuit <NUM>; the states of braking (brakes) on the right and left wheels; and the bi-speed turn operating status. Upon detecting that the steering angle of the front wheels 104F or the angle of rotation of the steering wheel has exceeded the reference angle based on the signal which is output from the angle-of-turn sensor <NUM>, the main ECU <NUM> causes the running gear <NUM> to operate in the small turn mode. As a result, a bi-speed turn is made. The main ECU <NUM> sends information indicating that a bi-speed turn is to be made to the front suspension ECU <NUM>. The main ECU <NUM> may control the braking devices to apply braking to the inner rear wheel 104R or both of the right and left rear wheels 104R during a bi-speed turn. These controls are to be made in accordance with user-designated settings concerning bi-speed turns.

<FIG> is a block diagram showing a hardware configuration of the front suspension ECU <NUM>. The front suspension ECU <NUM> includes a processor <NUM>, a ROM <NUM>, a RAM <NUM>, a storage device <NUM>, and a communicator <NUM>. These component elements are connected so as to be capable of communicating with one another via a bus.

The processor <NUM> is a semiconductor integrated circuit including a central processing unit (CPU), for example. The processor <NUM> may be implemented as a microprocessor or a microcontroller. Alternatively, the processor <NUM> may be implemented as an FPGA (Field Programmable Gate Array), a GPU (Graphics Processing Unit), an ASIC (Application Specific Integrated Circuit), or an ASSP (Application Specific Standard Product) incorporating a CPU; or a combination of two or more circuits selected from among such circuits. The processor <NUM> executes a computer program in which instructions for performing at least one process are stated, this being stored in the ROM <NUM>, and performs a desired process.

The ROM <NUM> may be a writable memory (e.g., a PROM), a rewritable memory (e.g., a flash memory), or a read-only memory, for example. The ROM <NUM> stores a program to control the operation of the processor <NUM>. The RAM <NUM> provides a work area for a control program stored in the ROM <NUM> to be laid out once at boot time. Each of the ROM <NUM> and the RAM <NUM> does not need to be a single storage medium, but may be an aggregation of multiple storage media. The storage device <NUM>, which may be, e.g. a magnetic storage device or a semiconductor storage device, stores data generated through computation by the processor <NUM>. An example of a magnetic storage device is a hard disk drive (HDD). An example of a semiconductor storage device is a solid state drive (SSD).

The communicator <NUM> is a communication module to perform communications with the engine ECU <NUM> and the main ECU <NUM>. The communicator <NUM> performs communication in accordance with CAN or other vehicle bus standards, for example.

The engine ECU <NUM> and the main ECU <NUM> also have a similar hardware configuration to the configuration shown in <FIG>. Therefore, descriptions concerning the hardware configuration of the engine ECU <NUM> and the main ECU <NUM> will be omitted.

<FIG> is a schematic diagram showing an example of the operational terminal <NUM> and operation switches <NUM> to be provided in the cabin <NUM>. In the cabin <NUM>, switches (including levers) <NUM>, which are a multitude of switches that are manipulable to the user, are disposed. The operation switches <NUM> may include, for example, a switch to select the gear shift as to a main gear shift or a range gear shift, a switch (shuttle lever) to switch between forward travel and backward travel, a switch to switch between a bi-speed turn enabled state and a bi-speed turn disabled state, a switch to switch between the presence or absence of braking and the degree of braking on the rear wheels 104R during a bi-speed turn, a switch to switch the mode of the front suspension, a switch to adjust the damping force of the front suspension, a switch to raise or lower the implement <NUM>, and so on. Among these switches, switches <NUM>, <NUM> and <NUM> to switch the mode of the front suspension, and switches <NUM> and <NUM> to adjust the damping force of the front suspension are shown in <FIG>.

The suspension-auto switch <NUM> is a switch to enable the automatic control on the front suspension by the ECU <NUM>. The suspension-OFF switch <NUM> is a switch to disable the automatic control on the front suspension. The suspension-manual switch <NUM> is a switch to enable the function of manually setting the front suspension. The suspension-soft switch <NUM> is a switch to reduce the damping force of the front suspension. The suspension-hard switch <NUM> is a switch to increase the damping force of the front suspension. The front suspension ECU <NUM> operates based on signals which are output from these switches.

Hereinafter, specific examples of the operation of the front suspension ECU <NUM> will be described. The front suspension ECU <NUM> according to the present preferred embodiment is able to perform controls (<NUM>) to (<NUM>) below, for example. Note that controls (<NUM>) to (<NUM>) below are mere examples, and the ECU <NUM> may be configured to perform only some of controls (<NUM>) to (<NUM>) below.

When the suspension-auto switch <NUM> is set ON, the ECU <NUM> performs an automatic vehicle height control. The ECU <NUM> prevents the suspension cylinders <NUM> from being extended all out or retracted all in because of fluctuations in the load on the front wheels 104F of the work vehicle <NUM>, and controls each cylinder <NUM> to maintain a state of extending or retracting always near midway of the stroke on average. Specifically, the ECU <NUM> calculates a stroke length based on a signal which is output from the stroke sensor <NUM>, and controls the suspension based on the calculated stroke length. For example, if the calculated stroke length is longer than the midway stroke length, the ECU <NUM> turns the suspension lowering solenoid <NUM> ON to retract the cylinders <NUM> and lower the vehicle height. Conversely, if the calculated stroke length is shorter than the midway stroke length the ECU <NUM> turns the suspension raising solenoid <NUM> ON to extend the cylinders <NUM> and raise the vehicle height. As a result, the cylinders <NUM> are always allowed to make a relatively large move in the extending direction or in the retracting direction, thus maximizing the suspension's effect of vibration reduction.

Now, with reference to <FIG>, an exemplary method of calculating the stroke length of the suspension will be described.

<FIG> is a diagram showing an exemplary relationship between the output voltage of the stroke sensor <NUM> and the stroke length of the suspension. The suspension cylinders <NUM> in this example has a difference in length of about <NUM> between the most extended state and the most retracted state. In <FIG>, the amount of extension of the cylinder <NUM> is expressed as a stroke length against the length in the most retracted state. The ECU <NUM> calculates the stroke length from the output voltage of the stroke sensor <NUM>, based on the data (e.g., a table or a mathematical function) recorded in the storage device representing the relationship shown in <FIG>. The ECU <NUM> may calculate the stroke length as often as about <NUM> times in one second, for example.

<FIG> is a graph showing an example of change in stroke length over time. The ECU <NUM> stores stroke lengths over a period of, e.g., about <NUM> seconds in the past (about <NUM> data points) in a memory, and defines an intermediate value between the maximum value and the minimum value in this period as a current stroke length. Regarding a target range which is supposed to be the neighborhood of the center movable range of stroke length, for any current stroke length that is outside the target range, the ECU <NUM> controls it to be closer into the target range.

(i) In order to ensure that a proper amount of damping is always attained irrespective of an increase or decrease in the load on the front wheels 104F, the ECU <NUM> performs a control of switching the aperture size of the variable orifice <NUM> to regulate the flow rate of hydraulic oil going in and out of the cylinder <NUM>. Specifically, in accordance with the pressure of hydraulic oil as measured by the pressure sensor <NUM>, the ECU <NUM> switches the aperture size of the variable orifice <NUM>. This solves problems such as difficulties to stop wobbling of the body of the vehicle under a large load, or the excessive stiffness of the suspension preventing vibrations from being absorbed in the presence of a light load, and makes it possible to constantly maintain a high suspension performance.

(ii) Through the user's manipulations of the switches <NUM> and <NUM>, stiffness (i.e., damping force) of the suspension can be changed in three steps of "hard", "normal", and "soft". When the user turns the suspension-soft switch <NUM> ON, the ECU <NUM> turns both of the medium damping force-selecting solenoid <NUM> and the large damping force-selecting solenoid <NUM> OFF to increase the flow rate through the variable orifice <NUM>. This results in the stiffness of the suspension being "soft". When the user turns neither the suspension-soft switch <NUM> nor the suspension-hard switch <NUM> ON, the ECU <NUM> turns the medium damping force-selecting solenoid <NUM> ON and the large damping force-selecting solenoid <NUM> OFF, so that the flow rate through the variable orifice <NUM> is intermediate. This results in the stiffness of the suspension being "normal". When the user turns the suspension-hard switch <NUM> ON, the ECU <NUM> turns the medium damping force-selecting solenoid <NUM> OFF and the large damping force-selecting solenoid <NUM> ON to make the flow rate through the variable orifice <NUM> small. This results in the stiffness of the suspension being "hard". With this function, regardless of how the work vehicle <NUM> is equipped or how the work vehicle <NUM> is supposed to work, the body of the vehicle will always achieve stable behavior to the feeling of the user.

During a braking manipulation, in order to prevent a sudden deceleration G-force from causing the suspension to be completely retracted instantaneously, the ECU <NUM> performs a control of switching the aperture size of the variable orifice <NUM>, which regulates the flow rate of hydraulic oil. For example, the ECU <NUM> calculates an acceleration based on temporal change in the traveling speed of the work vehicle <NUM>, and adjusts the aperture size of the variable orifice <NUM> in accordance with the magnitude of a G-force that is estimated from the acceleration. This enhances the behavioral stability of the body of the vehicle.

When the user turns the suspension-OFF switch <NUM> ON, the ECU <NUM> turns the suspension unlocking solenoid <NUM> OFF to immobilize the extension/retraction action of the suspension cylinders <NUM>. This disables suspension functionality, and reduces change in vehicle height, which will be effective in situations where implement stability is important, such as during plowing work in soft terrains.

An operator is able to extend or retract the suspension cylinders <NUM> through manipulations of switches. In the manual operation mode, automatic vehicle height control is not at work, and therefore the height of the front of the work vehicle <NUM> can be fixed to any arbitrary height.

When the load on the front wheels 104F exceeds the tolerable range, the suspension can no longer be raised, and the relief valves <NUM> and <NUM> of the hydraulic circuit <NUM> keep operating. In order to avoid this state, and prevent an excessive load from acting on the hydraulic pump <NUM>, the ECU <NUM> inhibits any raising output of the cylinders <NUM> when the load on the front wheels 104F exceeds the tolerable range. In the case where the pump <NUM> has a low performance (e.g., the oil temperature is high and the engine revolutions are low), the raising output of the cylinders <NUM> is inhibited to prevent the flow rate of hydraulic oil from becoming less than is needed for the power steering device.

When a bi-speed turn is being made, the ECU <NUM> automatically retracts the suspension cylinders <NUM>, and fixes the vehicle height in a low state. Once the bi-speed turn is finished, the ECU <NUM> restores the original state of the suspension cylinders <NUM>, and restarts automatic control of the suspension. Through this control, tilt of the vehicle during a bi-speed turn is reduced or prevented, and the turning stability can be enhanced.

Hereinafter, some example methods of controlling the vehicle height when making a bi-speed turn will be described.

<FIG> is a flowchart showing an example of vehicle height control operation executed by the ECU <NUM> when a bi-speed turn is made. In the example shown in <FIG>, during travel of the work vehicle <NUM>, based on information representing the bi-speed turn operating status which is sent from the main ECU <NUM>, the ECU <NUM> determines whether a bi-speed turn has been begun or not (step S101). Upon determining that a bi-speed turn has been begun, the ECU <NUM> determines whether automatic vehicle height control is ON or not (step S102). If automatic vehicle height control is OFF, control returns to step S101. If automatic vehicle height control is ON, the ECU <NUM> retracts the suspension cylinders <NUM>, and fixes the vehicle height in a lowered state (step S103). The ECU <NUM> may fix the suspension cylinders <NUM> in the most retracted state, or adjust the amount of lowering the vehicle height in accordance with conditions such as the vehicle speed or turning radius. Based on information representing the bi-speed turn operating status which is sent from the main ECU <NUM>, the ECU <NUM> determines whether the bi-speed turn has been finished or not (step S104). When the bi-speed turn is finished, the ECU <NUM> restarts automatic vehicle height control (step S105).

Through the above operation, if a bi-speed turn is made while automatic vehicle height control is being performed, the ECU <NUM> automatically lowers the vehicle height (to, e.g., the lowest state). As a result, the turning stability can be improved.

<FIG> is a flowchart showing another example of the operation of the ECU <NUM>. The flowchart shown in <FIG> is obtained by replacing steps S102 and S105 in the flowchart of <FIG> with steps S112 and S115, respectively. In the example of <FIG>, when a bi-speed turn is begun, the ECU <NUM> determines whether it is possible to further lower the vehicle height by retracting the suspension cylinders <NUM> (step S112). For example, if automatic vehicle height control is ON, or automatic vehicle height control is OFF but the vehicle height is not in the lowest state, it is deemed possible to further lower the vehicle height. If it is possible to further lower the vehicle height, similarly to the earlier example, the ECU <NUM> retracts the suspension cylinders <NUM>, and fixes the vehicle height in a lowered state (step S103). In this example, too, the ECU <NUM> may fix the suspension cylinders <NUM> in the most retracted state, or adjust the amount of lowering the vehicle height in accordance with conditions such as the vehicle speed or turning radius. Thereafter, when the bi-speed turn is finished, the ECU <NUM> restores the state of the suspension before the turn (step S115).

With the operation shown in <FIG>, irrespective of whether automatic vehicle height control is ON or not, when a bi-speed turn is made, the ECU <NUM> automatically lowers the vehicle height (to, e.g., the lowest state). As a result, even when the suspension is locked with the vehicle height being high, tilting of the body of the vehicle during a bi-speed turn is reduced or prevented, and the turning stability can be improved.

<FIG> is a flowchart showing still another example of the operation of the ECU <NUM>. The flowchart shown in <FIG> is obtained by replacing steps S112 and S103 in the flowchart of <FIG> with steps S122 and S123, respectively. In the example of <FIG>, when a bi-speed turn is begun, the ECU <NUM> determines whether the stroke length of the suspension is equal to or higher than a threshold or not (step S122). The threshold may be, for example, a lower limit value of stroke length that is tolerated for a stable bi-speed turn to be made. The ECU <NUM> may determine the threshold in accordance with the speed of the work vehicle <NUM> or turning radius. The stroke length is determined based on a signal which is output from the stroke sensor <NUM>. When the stroke length is below the threshold, control returns to step S101. If the stroke length is equal to or higher than the threshold, the ECU <NUM> retracts the suspension cylinders <NUM>, and fixes the stroke length below the threshold (step S103). In this example, too, the ECU <NUM> may fix the suspension cylinders <NUM> in the most retracted state, or adjust the amount of lowering the vehicle height in accordance with conditions such as the vehicle speed or turning radius. Thereafter, when the bi-speed turn is finished, the ECU <NUM> restores the state of the suspension before the turn (step S115).

With the operation shown in <FIG>, vehicle height adjustments are made only when the stroke length of the suspension cylinders <NUM> is equal to or higher than the threshold. The threshold can be set in accordance with conditions such as the vehicle speed or turning radius. As a result, the condition for lowering the center of gravity of the vehicle body <NUM> can be flexibly set in accordance with the vehicle speed, the turning radius, or the like.

In the above examples, the main ECU <NUM> causes the running gear <NUM> to operate in the small turn mode when the angle of rotation of the steering wheel or the steering angle of the front wheels has exceeded a reference angle. The front suspension ECU <NUM> causes the suspension device to lower the center of gravity of the vehicle body <NUM> when the small turn mode is begun while the height of the center of gravity of the vehicle body is higher than the reference height. The main ECU <NUM> may control the braking devices to apply braking to the inner one of the two rear wheels 104R in the small turn mode. The main ECU <NUM> may control the presence or absence of braking and the intensity of braking on the inner rear wheel 104R in accordance with switch manipulations by the user. In accordance with the presence or absence of braking or intensity of braking on the rear wheels 104R, the front suspension ECU <NUM> may change the amount of lowering the center of gravity or the condition for lowering the center of gravity. For example, in the case where a bi-speed turn is made with the braking of the rear wheels 104R, the amount of lowering the center of gravity may be increased or the condition for lowering the center of gravity may be more relaxed than in the case where a bi-speed turn is made without braking the rear wheels 104R.

In the examples shown <FIG>, a control to lower the vehicle height is performed only when making a bi-speed turn. However, a similar control may be applied also when not making a bi-speed turn. For example, the ECU <NUM> may calculate an angular velocity of yawing during a turn, based on a signal which is output from a sensor that can measure angular velocity (e.g., an IMU included in the work vehicle <NUM>), and perform a similar control when the angular velocity becomes equal to or higher than a threshold.

<FIG> is a block diagram showing an exemplary configuration where the ECU <NUM> controls the front suspension based on an angular velocity of yawing. In the example shown in <FIG>, the main ECU <NUM> relies on a signal which is output not from the angle-of-turn sensor <NUM> but from the angular velocity sensor <NUM> to determine an angular velocity of yawing during a turn, and sends information representing this angular velocity to the front suspension ECU <NUM>. Based on the information representing the angular velocity, the front suspension ECU <NUM> determines whether the work vehicle <NUM> is in a state of a small turn or not.

<FIG> is a flowchart showing an example of vehicle height control based on the angular velocity of yawing of the work vehicle <NUM>. The flowchart shown in <FIG> is obtained by replacing step S101 in the flowchart shown in <FIG> with step S141. In the example of <FIG>, the ECU <NUM> determines whether an angular velocity of yawing as measured by the angular velocity sensor is equal to or higher than a threshold or not. The threshold may be set to a different value depending on the speed of the work vehicle <NUM>, presence or absence of the implement <NUM>, or the like. For example, the threshold may be made smaller as the speed increases. Alternatively, the threshold may be made smaller when the implement <NUM> is attached than when the implement <NUM> is not attached. If the angular velocity is equal to or higher than the threshold, control proceeds to step S102. The subsequent operation is similar to the operation illustrated in <FIG>.

With the control shown in <FIG>, regardless of the bi-speed turn operating status, the vehicle height is lowered whenever the angular velocity during a turn is high, whereby the turning stability can be enhanced. Therefore, even in a work vehicle that lacks bi-speed turn functionality, for example, the traveling stability during a rapid turn can be improved. It may be not only in <FIG>, but also in the example of <FIG> or <FIG>, that the operation of step S101 can be replaced by the operation of step S141 shown in <FIG>. A similar control may be performed based on an angular velocity of rolling, rather than yawing, of the work vehicle <NUM>.

The ECU <NUM> may perform a similar control based on a signal which is output from a sensor that measures the centrifugal acceleration of the work vehicle <NUM> during a turn. For example, the ECU <NUM> may perform a control of lowering the center of gravity of the vehicle body <NUM> when a centrifugal acceleration as measured by a sensor (such as a gyroscope that is included in an IMU provided in the work vehicle <NUM>) is higher than a threshold. Such a control allows the turning stability to be improved without calculating an angular velocity of yawing or rolling.

Instead of the control of extending or retracting the suspension in each of the above examples, other methods may also be used to control the height of the center of gravity of the vehicle body <NUM>. For example, the height of the center of gravity may be controlled by using a mechanism to raise or lower a weight that is provided at a predetermined position (e.g., the bottom or the front) of the work vehicle <NUM>.

The controller to perform vehicle height control during a small turn in the above preferred embodiment can be mounted on a work vehicle lacking such functionality as an add-on. Such a controller may be manufactured and sold independently from the work vehicle. A computer program for use in such a controller may also be manufactured and sold independently from the work vehicle. The computer program may be provided in a form stored in a computer-readable, non-transitory storage medium, for example. The computer program may also be provided through downloading via telecommunication lines (e.g., the Internet).

The techniques according to the present disclosure are applicable to work vehicles for use in agricultural applications, e.g., tractors, rice transplanters, combines, harvesters, vehicles for crop management, vegetable transplanters, and riding mowers. The techniques according to the present disclosure are also applicable to work vehicles for use in non-agricultural applications, e.g., construction vehicles or snowplow vehicles.

Claim 1:
A work vehicle (<NUM>) comprising:
a controller configured to control the work vehicle (<NUM>);
a vehicle body (<NUM>);
a running gear (<NUM>) configured to cause the vehicle body (<NUM>) to travel; and
a height adjuster (<NUM>) configured to change a height of a center of gravity of the vehicle body (<NUM>),
wherein the controller comprises:
one or more processors; and
one or more memories storing a computer program to be executed by the one or more processors; and
wherein
the one or more processors is configured or programmed to:
acquire, during a turn, information concerning at least one of a turning radius and an angular velocity of the vehicle body (<NUM>); and
control the height adjuster (<NUM>) to maintain or lower the height of the center of gravity in accordance with the information,
characterized in that
the controller is configured or programmed to control the height adjuster (<NUM>) to lower the center of gravity when a state of a small turn where the turning radius is smaller than a reference radius is entered during a turn, and if the height of the center of gravity is higher than a reference height.