Patent Description:
As an articulated work vehicle , there is disclosed a wheel loader in which a steering angle is changed by controlling a flow rate of oil supplied to a hydraulic actuator arranged across a front frame and a rear frame (for example, see Patent Document No.<NUM>).

In the wheel loader disclosed in Patent Document No. <NUM>, a position control type operation system that outputs a hydraulic cylinder drive command based on a difference between a target articulate angle that matches the lever input angle by operating a joystick lever and an actual articulate angle is used.

<CIT> discloses a steering device for a vehicle which enhance steerability by making the control angle of a steering adjustable to match both the travel of the working vehicle and actual operations. <CIT> shows a steering device for a vehicle which is capable of precisely controlling the steering direction and steering volume of a wheel even for a vehicle with a large steering load, continuously changing a ratio of a change volume of a steering angle relative to a rotation volume of a handle, and surely steering the wheel even with a small rotation amount of the handle. <CIT> discloses a steering system for an articulated vehicle which has a microcomputer connected to a proportional solenoid valve which controls the direction, amount and rate of flow of hydraulic fluid to and from hydraulic articulation cylinders, which provide articulation between the frames of the articulated vehicle. <CIT> discloses a vehicle having a hydraulic system wherein the hydraulic system includes a steering input and a feedback to the steering input.

However, in the case of the position control type operation system, the operator needs to operate the joystick lever by the same angle as the large actual articulate angle, the large lever operation angle causes an unreasonable posture, and the operator is easily tired when operating for a long time.

An object of the present invention is to provide a work vehicle capable of reducing operator fatigue.

A work vehicle according to a first aspect of the invention is an articulated type work vehicle in which a front frame and a rear frame are coupled each other, and which comprises a hydraulic actuator, a lever, a control valve, and a control unit. The hydraulic actuator is driven by hydraulic pressure to change a vehicle body frame angle of the front frame with respect to the rear frame. The lever is rotated to input a target value of the vehicle body frame angle. The control valve controls a flow rate of oil supplied to the hydraulic actuator. The controller sets the target angle of the vehicle body frame angle with respect to an input angle of the lever, and controls the control valve so that an actual angle of the vehicle body frame angle matches the target angle of the vehicle body frame angle. An absolute value of a target value of the vehicle body frame angle corresponding to an absolute value of an input angle of the lever is larger than the absolute value of the input angle of the lever.

According to another aspect of the present invention, a work vehicle, being an articulated type in which a front frame and a rear frame are coupled, comprises a hydraulic actuator configured to be driven by hydraulic pressure to change a vehicle body frame angle of the front frame with respect to the rear frame, a lever configured to be rotated to change the body frame angle, a control valve configured to control a flow rate of oil supplied to the hydraulic actuator, and a controller configured to set a target angle of the vehicle body frame angle with respect to an input angle of the lever and control the control valve such that an actual angle of the vehicle body frame angle matches the target angle of the vehicle body frame angle. Further, values are obtained by differentiating a curve with the input angle of the lever, wherein the values include a value larger than <NUM> and a value smaller than <NUM>, wherein the curve is a relationship between the target angle of the vehicle body frame angle and the input angle of the lever.

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

According to the present invention, it is possible to provide a work vehicle capable of reducing operator fatigue.

The following is an explanation of a wheel loader as an example of a work vehicle according to the present invention with reference to the drawings.

A wheel loader <NUM> according to a first embodiment according to the present invention is explained hereinbelow.

<FIG> is a schematic view of a configuration of the wheel loader <NUM> of the present embodiment. The wheel loader <NUM> of the present embodiment is provided with a vehicle body frame <NUM>, a work implement <NUM>, a pair of front tires <NUM>, a cab <NUM>, an engine room <NUM>, a pair of rear tires <NUM>, a steering system <NUM> (refer to <FIG> described later), and steering cylinders 9a and 9b. In the following explanations, "front," "rear," "right," "left," "up," and "down" indicate directions relative to a state of looking forward from the operator's seat. "Vehicle width direction" and "left-right direction" have the same meaning. In <FIG>, "X" indicates the front-rear direction and "Xf" is used to indicate the forward direction and "Xb" is used to indicate the rearward direction. In addition, the left-right direction is indicated with "Y," and "Yr is used to indicate the right direction and "Yl" is used to indicate the left direction in the following drawings. The wheel loader <NUM> is an example of a work vehicle. The steering cylinders 9a and 9b are examples of hydraulic actuators.

The wheel loader <NUM> is able to carry out work such as earth and sand loading by using the work implement <NUM>. The vehicle body frame <NUM> is a so-called articulated type and includes a front frame <NUM>, a rear frame <NUM>, and a coupling shaft part <NUM>. The front frame <NUM> is arranged in front of the rear frame <NUM>. The coupling shaft part <NUM> is provided in the center in the vehicle width direction, and couples the front frame <NUM> and the rear frame <NUM> to each other in a manner that allows swinging. The pair of front tires <NUM> are attached to the left and right of the front frame <NUM>. The pair of rear tires <NUM> are attached to the left and right of the rear frame <NUM>. The front frame <NUM> is an example of a front frame, and the rear frame <NUM> is an example of a rear frame.

The work implement <NUM> is driven by hydraulic fluid from a work implement pump which is not illustrated. The work implement <NUM> includes a boom <NUM>, a bucket <NUM>, a lift cylinder <NUM>, and a bucket cylinder <NUM>. The boom <NUM> is mounted onto the front frame <NUM>. The bucket <NUM> is attached to the tip of the boom <NUM>.

The lift cylinder <NUM> and the bucket cylinder <NUM> are hydraulic cylinders. One end of the lift cylinder <NUM> is attached to the front frame <NUM> and the other end of the lift cylinder <NUM> is attached to the boom <NUM>. The boom <NUM> swings up and down due to the extension and contraction of the lift cylinder <NUM>. One end of the bucket cylinder <NUM> is attached to the front frame <NUM> and the other end of the bucket cylinder <NUM> is attached to the bucket <NUM> via a bell crank <NUM>. The bucket <NUM> swings up and down due to the extension and contraction of the bucket cylinder <NUM>.

The cab <NUM> is disposed on the rear frame <NUM>. A joystick lever <NUM> (see <FIG> below) for performing steering operations, an lever for operating the work implement <NUM>, and various display devices are arranged inside the cab <NUM>. The engine room <NUM> is arranged to the rear of the cab <NUM> and on the rear frame <NUM> and contains an engine.

<FIG> is a partial side view of the cab <NUM>. An operator's seat <NUM> is provided in the cab <NUM> and a console box <NUM> is arranged to the side of the operator's seat. An arm rest 20a is arranged on the upper side of the console box <NUM>. The joystick lever <NUM> is arranged upward from the front end of the console box <NUM>.

<FIG> is a schematic plan view near the operator's seat <NUM>. As illustrated in <FIG>, as an example, the console box <NUM> is arranged on the left side of the operator's seat <NUM>. Therefore, the joystick lever <NUM> is operated by the left hand. Further, the joystick lever <NUM> is rotatable in a right direction Yr which is an inner side of the operator's seat <NUM> and a left direction Yl which is an outer side of the operator's seat <NUM>.

<FIG> is a configuration view illustrating the steering system <NUM>. The steering system <NUM> changes the flow rate of oil supplied to the steering cylinders 9a and 9b, thereby changing the vehicle body frame angle of the front frame <NUM> with respect to the rear frame <NUM> and changing the traveling direction of the wheel loader <NUM>. The steering cylinders 9a and 9b correspond to an example of a hydraulic actuator.

The pair of steering cylinders 9a and 9b are driven by hydraulic pressure. The pair of steering cylinders 9a and 9b are arranged side by side on the left and right sides in the vehicle width direction with the coupling shaft part <NUM> interposed therein. The steering cylinder 9a is arranged on the left side of the coupling shaft part <NUM>. The steering cylinder 9b is arranged on the right side of the coupling shaft part <NUM>. One end of each of the steering cylinders 9a and 9b is attached to the front frame <NUM> and the other end each is attached to the rear frame <NUM>.

When the steering cylinder 9a extends and the steering cylinder 9b contracts due to hydraulic pressure from the belowmentioned steering system <NUM>, a vehicle body frame actual angle θs_real is changed and the vehicle turns to the right. When the steering cylinder 9a contracts and the steering cylinder 9b extends due to hydraulic pressure from the steering system <NUM>, the vehicle body frame actual angle θs_real is changed and the vehicle turns to the left. In the present embodiment, the vehicle body frame actual angle θs_real when the front frame <NUM> and the rear frame <NUM> are arranged in the front-rear direction is set to zero, the right side is a positive value, and the left side is a negative value. The vehicle body frame actual angle θs_real corresponds to an actual angle of the vehicle body frame angle.

The steering system <NUM> has an adjusting mechanism <NUM>, a steering device <NUM>, a controller <NUM>, and a vehicle speed sensor <NUM>. The controller <NUM> corresponds to an example of a controller. The adjusting mechanism <NUM> adjusts the drive output of the steering cylinders 9a and 9b. The steering device <NUM> has a joystick lever <NUM> and the like, and an operator inputs a target value of a steering angle of the wheel loader <NUM>. The controller <NUM> instructs the adjusting mechanism <NUM> to adjust the drive output of the steering cylinders 9a and 9b based on the target value of the steering angle input to the steering device <NUM>. The vehicle speed sensor <NUM> detects the vehicle speed V of the wheel loader <NUM>, and transmits the vehicle speed V as a detection signal to the controller <NUM>.

In <FIG>, transmission of signals based on electricity is represented by the dotted lines, and transmission based on hydraulic pressure is represented by solid lines. Further, detection by sensors is represented by a two-dot chain line.

The adjusting mechanism <NUM> adjusts the flow rate of oil supplied to the steering cylinders 9a and 9b. The adjusting mechanism <NUM> has a hydraulic valve <NUM>, a main pump <NUM>, an electromagnetic pilot valve <NUM>, and a pilot pump <NUM>. The hydraulic valve corresponds to an example of a control valve.

The hydraulic valve <NUM> is a flow rate adjusting valve that adjusts the flow rate of oil supplied to the steering cylinders 9a and 9b according to the input pilot pressure. For the hydraulic valve <NUM>, for example, a spool valve is used. The main pump <NUM> supplies the hydraulic fluid that operates the steering cylinders 9a and <NUM> b to the hydraulic valve <NUM>.

The hydraulic valve <NUM> has an obturating element (not illustrated) that can be moved to the left steering position, the neutral position, and the right steering position. When the obturating element of the hydraulic valve <NUM> is arranged at the left steering position, the steering cylinder 9a contracts and the steering cylinder 9b extends, the vehicle body frame actual angle θs_real decrease, and the vehicle body turns to the left.

When the obturating element of the hydraulic valve <NUM> is arranged at the right steering position, the steering cylinder 9b contracts and the steering cylinder 9a extends, the vehicle body frame actual angle θs_real increases, and the vehicle body turns to the right. When the obturating element of the hydraulic valve <NUM> is arranged at the neutral position, the vehicle body frame actual angle θs_real does not change.

The electromagnetic pilot valve <NUM> is a flow rate adjusting valve that adjusts the flow rate of pilot hydraulic pressure supplied to the hydraulic valve <NUM> in accordance with a command from the controller <NUM>. The pilot pump <NUM> supplies hydraulic fluid that operates the hydraulic valve <NUM> to the electromagnetic pilot valve <NUM>. The electromagnetic pilot valve <NUM> is, for example, a spool valve or the like, and is controlled according to a command from the controller <NUM>.

The electromagnetic pilot valve <NUM> has an obturating element (not illustrated) movable to the left pilot position, the neutral position, and the right pilot position. When the obturating element of the electromagnetic pilot valve <NUM> is arranged at the left pilot position, the hydraulic valve <NUM> is in the left steering position. When the obturating element of the electromagnetic pilot valve <NUM> is arranged at the right pilot position, the hydraulic valve <NUM> is in the right steering position. When the obturating element of the electromagnetic pilot valve <NUM> is arranged in the neutral position, the hydraulic valve <NUM> is in the neutral position.

As described above, by controlling the pilot pressure from the electromagnetic pilot valve <NUM> in accordance with the command from the controller <NUM>, the hydraulic valve <NUM> is controlled and the steering cylinders 9a, 9b are controlled.

The steering device <NUM> has an operation unit <NUM>, a lever angle sensor <NUM>, and a vehicle body frame angle sensor <NUM>.

<FIG> is a perspective view of the operation unit <NUM>. <FIG> is a plan view of the operation unit <NUM>. <FIG> is a side sectional view of the operation unit <NUM>, and is a reference arrow cross-sectional view along line B to B' of <FIG>. <FIG> is a reference arrow cross-sectional view along line A to A' of <FIG>. Further, the configuration of the transmission mechanism <NUM> and the like is omitted in <FIG>.

As illustrated in <FIG>, the operation unit <NUM> has a joystick lever <NUM>, a support part <NUM>, a base member <NUM>, and a biasing part <NUM>. The joystick lever <NUM> corresponds to an example of a lever.

The joystick lever <NUM> is operated by the operator. The support part <NUM> is fixed to the console box <NUM> and rotatably supports the joystick lever <NUM>. The base member <NUM> is rotatably supported by the support part <NUM>. The biasing part <NUM> biases the joystick lever <NUM> to a predetermined position with respect to the base member <NUM>.

The joystick lever <NUM> is arranged at a front end part of the console box <NUM>, as illustrated in <FIG>.

As illustrated in <FIG>, the joystick lever <NUM> has a lever portion <NUM>, a pair of connecting plates <NUM> and <NUM>, a connecting portion <NUM>, and a key <NUM>.

The lever portion <NUM> is a rod-shaped member and is operated by an operator. The pair of connecting plates <NUM> and <NUM> connects the lever portion <NUM> and a rotating shaft <NUM> (described later) of the support part <NUM>, and transmits the rotation of the lever portion <NUM> to the rotating shaft <NUM>.

Each of the pair of connecting plates <NUM> and <NUM> is arranged such that the plate-shaped main surface is substantially perpendicular to the front-rear direction X. The pair of connecting plates <NUM> and <NUM> are arranged facing each other along the front-rear direction X with a predetermined space therebetween.

The connecting portion <NUM> is arranged between the pair of connecting plates <NUM> and <NUM> so as to connect upper end portions of the pair of connecting plates <NUM> and <NUM>. A lower end of the lever portion <NUM> is fixed to a upper surface of the connecting portion <NUM>. A through hole is formed in each of the pair of connecting plates <NUM> and <NUM>, and the rotating shaft <NUM> is inserted into the through holes of the connecting plates <NUM> and <NUM>. As illustrated in <FIG>, the key <NUM> fits into a recess formed in an edge of the through hole of the connecting plate <NUM> and a groove formed on the rotating shaft <NUM>, and transmits the rotation of the connecting plate <NUM> to the rotating shaft <NUM>. The rotating shaft <NUM> is rotatably supported by the support part <NUM>.

Further, as illustrated in <FIG> and <FIG>, rod-shaped connecting members <NUM> and <NUM> that connect the connecting plates <NUM> and <NUM> are provided. As illustrated in <FIG>, the connecting member <NUM> and the connecting member <NUM> are arranged below a center P3 of the rotating shaft <NUM> and outside the rotating shaft <NUM> in the vehicle width direction. The connecting member <NUM> is arranged on the right direction Yr side of the rotating shaft <NUM> in the vehicle width direction Y, and the connecting member <NUM> is arranged on the left direction Yl side of the rotating shaft <NUM> in the vehicle width direction Y.

When the lever portion <NUM> is rotated by the operator, the pair of connecting plates <NUM> and <NUM> are also rotated together with the connecting portion <NUM>, and the rotating shaft <NUM> is rotated via the key <NUM>.

The support part <NUM> rotatably supports the joystick lever <NUM>. The support part <NUM> is fixed to, for example, the inside of the console box <NUM> illustrated in <FIG>. As illustrated in <FIG>, the support part <NUM> has a support frame <NUM> and a rotating shaft <NUM>.

The support frame <NUM> is a member formed in a U shape in a side view, as illustrated in <FIG> and <FIG>. The support frame <NUM> has a pair of shaft support portions <NUM> and <NUM> facing each other in the front-rear direction X, and a connecting portion <NUM> that connects the lower end of the shaft support portion <NUM> and the lower end of the shaft support portions <NUM>. A through hole is formed in each of the shaft support portion <NUM> and the shaft support portion <NUM> along the front-rear direction X.

The rotating shaft <NUM> is rotatably inserted into through holes formed in the shaft support portions <NUM> and <NUM>. The rotating shaft <NUM> is arranged in a substantially horizontal direction and along the front-rear direction X.

The base member <NUM> is rotatably supported by the support part <NUM>. As illustrated in <FIG>, the base member <NUM> has a base plate <NUM>, a pair of support plates <NUM> and <NUM>, and a transmission gear portion <NUM>.

The base plate <NUM> is a plate-shaped member arranged so as to cover the pair of connecting plates <NUM> and <NUM> from below. The base plate <NUM> is convexly curved downward when viewed in the front-rear direction X (see <FIG>).

The pair of support plates <NUM> and <NUM> rotatably support the base plate <NUM> on the rotating shaft <NUM>, as illustrated in <FIG> and <FIG>. The pair of support plates <NUM> and <NUM> are arranged so as to sandwich the connecting plates <NUM> and <NUM> from the outside in the front-rear direction X. As illustrated in <FIG> and <FIG>, the support plate <NUM> is arranged on the front direction Xf side of the connecting plate <NUM>, and the support plate <NUM> is arranged on the rear direction Xb side of the connecting plate <NUM>.

Through holes are formed in the support plates <NUM> and <NUM> along the front-rear direction X, and the rotating shaft <NUM> is inserted into these through holes. In this way, the support plates <NUM> and <NUM> are rotatably arranged with respect to the rotating shaft <NUM>.

As illustrated in <FIG> and <FIG>, the lower ends of the support plates <NUM> and <NUM> are convexly curved downward, and the base plate <NUM> is arranged so as to connect the lower end of the support plate <NUM> and the lower end of the support plate <NUM>. As illustrated in <FIG>, a groove <NUM> is formed in the vehicle width direction Y on a upper surface 71a of the base plate <NUM>. An end of the groove <NUM> on the right direction Yr side in the vehicle width direction Y is indicated by 76R, and an end on the left direction Yl side is indicated by <NUM>.

The transmission gear portion <NUM> transmits the information about the vehicle body frame angle θs_real to the base member <NUM> via the transmission mechanism <NUM>. As illustrated in <FIG>, the transmission gear portion <NUM> is arranged on the front side of the support plate <NUM> and is connected to the support plate <NUM>. A through hole is formed in the transmission gear portion <NUM> along the front-rear direction X, and the rotating shaft <NUM> is inserted into the through hole. As a result, the transmission gear portion <NUM> is configured to be rotatable with respect to the rotating shaft <NUM>. As illustrated in <FIG>, the transmission gear portion <NUM> has a lower end surface 74a that is convexly curved downward, and a gear shape is formed on the lower end surface 74a. The lower end surface 74a meshes with a transmission gear 96c of the transmission mechanism <NUM>, which will be described later, as illustrated in <FIG>.

The base member <NUM> is rotatable with respect to the rotating shaft <NUM> by the transmission mechanism <NUM> described later (see <FIG> and <FIG> described later). When the transmission gear portion <NUM> rotates with respect to the support part <NUM> via the transmission mechanism <NUM>, the support plates <NUM> and <NUM> and the base plate <NUM> connected to the transmission gear portion <NUM> also rotate.

The biasing part <NUM> biases the joystick lever <NUM> to the base reference position 43b with respect to the base plate <NUM>. Specifically, as illustrated in <FIG>, the biasing part <NUM> biases the joystick lever <NUM> so that the lever portion <NUM> is arranged at the center of the base plate <NUM> in the vehicle width direction Y.

Specifically, the base reference position 43b is a position on a line connecting a center position P1 of between a right end 76R and a left end <NUM> of the groove <NUM> of the base plate <NUM> and a center position P3 of the rotating shaft <NUM>. In the state illustrated in <FIG>, the straight line L1 along the longitudinal direction of the lever portion <NUM> is arranged at the base reference position 43b, and the lever portion <NUM> is not rotated with respect to the base member <NUM>.

The biasing part <NUM> has a spring member <NUM> and a damper <NUM>. The spring member <NUM> is a coil spring, and is arranged around the rotating shaft <NUM> as illustrated in <FIG>.

Accordingly, a counterforce can be generated when the operator operates the lever portion <NUM> from a predetermined position to the left or right with respect to the base plate <NUM>, and a feeling of operation can be given to the operator.

The rotating shaft <NUM> is inserted into the spring member <NUM>. The spring member <NUM> is arranged between the pair of connecting plates <NUM> and <NUM>.

As illustrated in <FIG>, the spring member <NUM> has a coil portion <NUM>, a first end portion <NUM>, and a second end portion <NUM>. The rotating shaft <NUM> inserts through the coil portion <NUM>. The first end portion <NUM> and the second end portion <NUM> extend downward from the coil portion <NUM> and are arranged between the connecting member <NUM> and the connecting member <NUM>.

When the lever portion <NUM> is arranged at the above base reference position 43b, the first end portion <NUM> is arranged on the left direction Yl side of the connecting member <NUM> in a state of being in contact with the connecting member <NUM>. A lower end of the first end portion <NUM> is in contact with the right end 76R of the groove <NUM>. The second end portion <NUM> is arranged on the right direction Yr side of the connecting member <NUM> in a state of being in contact with the connecting member <NUM>. A lower end of the second end portion <NUM> is in contact with the left end <NUM> of the groove <NUM>.

The spring member <NUM> exerts an elastic force so as to push the connecting member <NUM> and the right end 76R toward the right direction Yr side and push the connecting member <NUM> and the left end <NUM> toward the left direction Yl side.

The counterforce generated on the joystick lever <NUM> by the spring member <NUM> will be described. A counterforce is generated by the spring member <NUM> according to the rotation angle of the joystick lever <NUM> with respect to the base member <NUM>.

Here, as illustrated in <FIG>, the rotation angle of the lever portion <NUM> of the joystick lever <NUM> with respect to the support part <NUM> from the support reference position 42b is set as an actual lever input angle θi_real. The support reference position 42b is, as illustrated in <FIG>, a position on a straight line that passes through the center P3 of the rotating shaft <NUM> and is arranged in the vertical direction. The angle when the lever portion <NUM> is rotated in the right direction from the support reference position 42b is a positive value, and the angle when the lever portion <NUM> is rotated in the left direction from the support reference position 42b is a negative value.

Further, as illustrated in <FIG>, the rotation angle of the base reference position 43b from the support reference position 42b of the support part <NUM> is the actual base angle θb_real of the base member <NUM> with respect to the support part <NUM>. The angle when the base member <NUM> is rotated in the right direction from the support reference position 42b is a positive value, and the angle when the base member <NUM> is rotated in the left direction from the support reference position 42b is a negative value.

For example, as illustrated in <FIG> described later, when the lever portion <NUM> is rotated in the right direction, the first end portion <NUM> of the spring member <NUM> is pushed by the connecting member <NUM> in the clockwise direction (left direction Yl side) to move, and the tip end of the first end portion <NUM> is separated from the right end 76R of the groove <NUM> in the left direction Yl side. Further, since the tip end of the second end portion <NUM> is in contact with the left end <NUM> of the groove <NUM>, the second end portion <NUM> cannot move in the clockwise direction (left direction Yl side), and the connecting member <NUM> is separated from the second end portion <NUM> in the left direction Yl side. As a result, the first end portion <NUM> of the spring member <NUM> biases the connecting member <NUM> so as to push the connecting member <NUM> in the counterclockwise direction, so the spring member <NUM> biases the joystick lever <NUM> so that the lever portion <NUM> returns to the base reference position 43b provided on the vertical line passing through the center P3 in the rotating shaft <NUM>.

<FIG> is a view illustrating the relationship between the actual lever relative angle θr_real, which is the difference subtracting the actual base angle θb_real from the actual lever input angle θi_real and the counterforce generated by the spring member <NUM>. The spring member <NUM> has a counterforce characteristic as illustrated in <FIG>. In <FIG>, θr_real of the positive value represents the case where the joystick lever <NUM> is rotated in the right direction with respect to the base member <NUM>, and θr_real of the negative value represents the case where the joystick lever <NUM> is rotated in the left direction with respect to the base member <NUM>. Further, a counterforce of the positive value represents a counterforce generated toward the left direction, and a counterforce of the negative value represents a counterforce generated toward the right direction.

When θr_real has a positive value, θr_real and the counterforce have a proportional relationship, the initial counterforce is F1, and the value of the counterforce increases as the value of θr_real increases. When θr_real has a negative value, the initial counterforce is -F1, and the value of the counterforce decreases as the value of θd_real decreases. That is, the spring characteristic of the spring member <NUM> is formed linearly, and as the absolute value of θr_real increases, the counterforce with respect to the rotating operation of the joystick lever <NUM> also increases.

Thus, by applying a force equal to or larger than the initial counterforce F1 to the joystick lever <NUM>, the joystick lever <NUM> rotates with respect to the base member <NUM>, and the counterforce also increases as the absolute value of θr_real increases.

The damper <NUM> is provided between the rotating shaft <NUM> and the shaft support portion <NUM>. The damper <NUM> causes resistance according to the angular velocity of the lever portion <NUM>.

The lever angle sensor <NUM> is composed of, for example, a potentiometer, and detects the actual lever input angle θi_real, which is the rotation angle of the rotating shaft <NUM> with respect to the support part <NUM> (specifically, also referred to as the support frame <NUM>), as a detection value θi_detect of the lever input angle. As illustrated in <FIG>, the lever angle sensor <NUM> is arranged outside the shaft support portion <NUM> of the support part <NUM> (on the rear direction Xb side).

The detection value θi_detect of the lever input angle detected by the lever angle sensor <NUM> is sent to the controller <NUM> as a detection signal.

The vehicle body frame angle sensor <NUM> detects the vehicle body frame actual angle θs_real as a detection value θs_detect of the vehicle body frame angle. The vehicle body frame angle sensor <NUM> is arranged in the vicinity of the coupling shaft part <NUM> arranged between the steering cylinders 9a and 9b or in the transmission mechanism <NUM> described later. The vehicle body frame angle sensor <NUM> is composed of, for example, a potentiometer, and the detection value θs_detect of the detected vehicle body frame angle is sent to the controller <NUM> as a detection signal.

Futhermore, each of the steering cylinders 9a and 9b may be provided with a cylinder stroke sensor that detects a stroke of the cylinder, and the detection values of these cylinder stroke sensors may be sent to the controller <NUM> to detect the detection value θs_detect of the vehicle body frame angle.

The controller <NUM> has a CPU, a memory, and the like, and executes each function described below. As illustrated in <FIG>, the detecton value θi_detect by the lever angle sensor <NUM>, the detection value θs_detect by the vehicle body frame angle sensor <NUM>, and the vehicle speed Vdetct detected by the vehicle speed sensor <NUM> are input to the controller <NUM>. The controller <NUM> controls the electromagnetic pilot valve <NUM> based on these values.

Here, <FIG> illustrates the relationship between the lever input angle θi_real, the vehicle body frame actual angle θs_real, and the vehicle body frame target angle θtarget. As illustrated in <FIG>, the vehicle body frame target angle is calculated from the lever input angle θi_real, and the control is performed so that the vehicle body frame actual angle θs_real matches the vehicle body frame target angle θtarget. The vehicle body frame target angle θtarget corresponds to an example of a target angle of the vehicle body frame angle.

<FIG> is a control block diagram illustrating input/output and calculation of the controller <NUM>.

The controller <NUM> has a target angle calculator <NUM>, a vehicle body frame actual angle calculator <NUM>, a pulse / vehicle speed converter <NUM>, a difference calculator <NUM>, and an output calculator <NUM>.

The detection value θi_detect of the lever input angle is input to the controller <NUM> from the lever angle sensor <NUM>, and the target angle calculator <NUM> calculates the vehicle body frame target angle θtarget using the map M1. Further, the detection value θs_detect of the vehicle body frame angle is input to the controller <NUM> from the vehicle body frame angle sensor <NUM>, and the vehicle body frame actual angle calculator <NUM> calculates the vehicle body frame actual angle θactual using the map M2. The detection value V_detect of the vehicle speed is input to the controller <NUM> from the vehicle speed sensor <NUM>. The pulse / vehicle speed converter <NUM> converts the input pulse into a vehicle speed and calculates a vehicle speed signal V.

The difference calculator <NUM> calculates a difference angle θdiff between the vehicle body frame target angle θtarget and the vehicle body frame actual angle θactual. Then, the output calculator <NUM> calculates an electromagnetic pilot valve control current output i from the difference angle θdiff and the vehicle speed signal V using the map M3 and outputs the electromagnetic pilot valve control current output i to the electromagnetic pilot valve <NUM> to control the electromagnetic pilot valve <NUM> so that θdiff becomes zero. The maps M1 to M3 are stored in a storage part of the controller <NUM>.

<FIG> is a view illustrating an example of the map M1. The map M1 illustrates the relationship between the actual lever input angle θi_real and the vehicle body frame target angle θtarget. The vehicle body frame target angle θtarget corresponding to the maximum value of the vehicle body frame actual angle θs_real is set to θ2. At this time, the vehicle body frame <NUM> is in the most bent state to the right. The lever input angle θi_real corresponding to θ2 is set to θ1. By setting the relationship of θ1<θ2, it becomes possible to steer at a lever input angle θi_real smaller than the vehicle body frame actual angle θs_real, and it is possible to reduce operator's fatigue.

Further, the vehicle body frame target angle θtarget corresponding to the minimum value of the vehicle body frame actual angle θs_real is set to θ4. At this time, the vehicle body frame <NUM> is in the most bent state to the left. The lever input angle i_real corresponding to θ4 is θ3. By setting the relationship of θ4<θ3, it becomes possible to steer at a lever input angle θi_real smaller than the vehicle body frame actual angle θs_real, and it is possible to reduce operator's fatigue.

Furthermore, the characteristics of the actual lever input angle θi_real and the vehicle body frame target angle θtarget on the left and right need not be symmetrical because the human movements to the left and right is not symmetrical.

<FIG> is a view illustrating another example of the map M1. The relationship between the lever input angle θi_real and the vehicle body frame target angle θtarget is a curve in which the slope (increase rate) is small when the lever input angle θi_real is near zero and the slope is large when the lever input angle θi_real is far from zero. When traveling at high speeds, near zero is used, and when working, the entire range of the lever angle is used. Therefore, by setting the characteristics as illustrated in <FIG>, it is possible to achieve both straight traveling stability during high-speed traveling and fatigue reduction during work.

<FIG> is a view illustrating an example of the map M2. An example of the map M2 illustrated in <FIG> shows a graph of the relationship between the detection value θs_detect of the vehicle body frame angle and the vehicle body frame actual angle θactual. In this example, the detection value θs_detect of the vehicle body frame angle and the vehicle body frame actual angle θactual have a proportional relationship. The controller <NUM> calculates the vehicle body frame actual angle θactual from the detection value θs_detect of the vehicle body frame angle by using this map M2. The vehicle body frame actual angle θactual indicates the actual angle of the vehicle body frame angle. Further, in the map M2 of <FIG>, θactual=<NUM>×θs_detect is set and the value of θactual and the value of θs_detect are equal, but the present invention is not limited to this.

<FIG> is a view illustrating an example of the map M3. The controller <NUM> stores curves about a plurality of vehicle speeds illustrating the value of the electromagnetic pilot valve control current output i with respect to the difference angle θdiff. In the example of the map M3 illustrated in <FIG>, for example, a curve C1 (solid line) when the vehicle speed is <NUM> / h, a curve C2 (dotted line) when the vehicle speed is <NUM> / h, and a curve C3 (one-dot chain line) when the vehicle speed is <NUM> / h are set. The faster the vehicle speed, the smaller the value of the electromagnetic pilot valve control current output i. As a result, as the vehicle speed increases, the speed at which the vehicle body frame actual angle θs_real changes (also referred to as angular velocity) decreases, and it is possible to improve high-speed stability. Further, as the vehicle speed decreases, the speed at which the vehicle body frame actual angle θs_real changes (also referred to as angular velocity) increases, and it is possible to improve the operability at low speed. When the vehicle speed V is between C1, C2 and C3, the electromagnetic pilot valve control current output i is determined by interpolation calculation.

The controller <NUM> transmits an electric current to the electromagnetic pilot valve <NUM> based on <FIG>.

Although omitted in <FIG>, the controller <NUM> may control the main pump <NUM>, the pilot pump <NUM>, and the like.

Further, the transmission and reception of signals between the controller <NUM> and the vehicle body frame angle sensor <NUM>, the lever angle sensor <NUM>, the vehicle speed sensor <NUM>, and the electromagnetic pilot valve <NUM> may each be carried out wirelessly or by wire.

The transmission mechanism <NUM> transmits information on the vehicle body frame actual angle θs_real to the base member <NUM>, and rotates the base member <NUM> to a position corresponding to the vehicle body frame actual angle θs_real.

<FIG> is a schematic view illustrating the configuration of the transmission mechanism <NUM>. As illustrated in the figure, the transmission mechanism <NUM> is a mechanism including links, and has a transmission member <NUM>, a first conversion part <NUM>, a universal joint <NUM>, a bevel box <NUM>, a universal joint <NUM>, and a transmission part <NUM>.

<FIG> is a rear view illustrating the configuration in the vicinity of the transmission member <NUM>.

The transmission member <NUM> is a rod-shaped member and is arranged substantially along the front-rear direction X. A front end 91a of the transmission member <NUM> is rotatably connected to a bracket <NUM> fixed to the front frame <NUM>. The end 91a of the transmission member <NUM>, which is a connection part with the bracket <NUM>, is arranged near the coupling shaft part <NUM> in the vehicle width direction Y. A rear end 91b of the transmission member <NUM> extends to the rear frame <NUM> and is rotatably connected to a lever 92a of the first conversion part <NUM>.

The first conversion part <NUM> converts the movement of the transmission member <NUM> in the front-rear direction X into movement in the rotation direction. The first conversion part <NUM> has the lever 92a, a rotation shaft 92b, and a shaft support part 92c. The rotation shaft 92b is arranged substantially along the vertical direction. The shaft support part 92c rotatably supports the rotation shaft 92b. The shaft support part 92c is fixed to the rear frame <NUM> and arranged on the floor of the cab <NUM>. The lever 92a is fixed to the lower end of the rotation shaft 92b, and at least a part of the lever 92a is arranged under the floor of the cab <NUM>. That is, the rotation shaft 92b penetrates the floor of the cab <NUM>. Further, as illustrated in <FIG>, a quadrangle connecting the coupling shaft part <NUM>, the end 91a, the end 91b and the rotation shaft 92b is a parallelogram, and a parallel link is formed.

The universal joint <NUM> is expandable and contractable, and is connected to the rotation shaft 92b. The lower end 93a of the universal joint <NUM> is connected to the upper end of the rotation shaft 92b. The upper end 93b of the universal joint <NUM> is connected to the bevel box <NUM>.

The bevel box <NUM> is arranged inside the console box <NUM>, for example. The bevel box <NUM> has a support case 94a, a first rotation shaft 94b, a first bevel gear 94c, a second rotation shaft 94d, and a second bevel gear 94e. The support case 94a is fixed to the console box <NUM>. The first rotation shaft 94b is rotatably supported by the support case 94a. The first rotation shaft 94b is arranged substantially along the vertical direction, and the lower end of the first rotation shaft 94b is connected to the upper end 93b of the universal joint <NUM>.

The first bevel gear 94c is arranged inside the support case 94a and is fixed to the first rotation shaft 94b.

The second rotation shaft 94d is rotatably supported by the support case 94a. The second rotation shaft 94d is arranged substantially along the horizontal direction. The universal joint <NUM> is connected to the front end of the second rotation shaft 94d.

The second bevel gear 94e is arranged inside the support case 94a and is fixed to the second rotation shaft 94d. The second bevel gear 94e meshes with the first bevel gear 94c. With such a bevel box <NUM>, it is possible to convert the rotation about the vertical direction into the rotation about the horizontal direction.

The universal joint <NUM> is expandable and contractable, and is arranged inside the console box <NUM>. The rear end 95a of the universal joint <NUM> is connected to the second rotation shaft 94d. The front end 95b of the universal joint <NUM> is connected to the transmission shaft 96b of the transmission part <NUM>.

The transmission part <NUM> transmits the rotation of the universal joint <NUM> to the base member <NUM>. The transmission part <NUM> has a transmission shaft 96b, and a transmission gear 96c. The transmission shaft 96b is rotatably supported by the support part <NUM> of the operation unit <NUM>, as illustrated in <FIG>. The transmission shaft 96b is arranged substantially along the horizontal direction. The rear end of the transmission shaft 96b is connected to the front end 95b of the universal joint <NUM> as illustrated in <FIG>. The transmission gear 96c is fixed to the transmission shaft 96b inside the shaft support part 96a.

As illustrated in <FIG>, the transmission gear 96c meshes with the transmission gear portion <NUM> of the base member <NUM>.

When the front frame <NUM> is rotated in the right direction (arrow Yr in the rear view of <FIG>) as illustrated by the two-dot chain line, the bracket <NUM> is also rotated, and the transmission member <NUM> is also moved forward (arrow C1). Then, the lever 92a also rotates in the right direction (arrow C2) when viewed from above, and the universal joint <NUM> also rotates in the right direction. The rotation of the universal joint <NUM> is converted by the bevel box <NUM> into the rotation of the left direction (arrow C3) when viewed from the rear, and the transmission shaft 96b and the transmission gear 96c also rotate in the left direction through the universal joint <NUM> when viewed from the rear. As a result, the transmission gear portion <NUM> rotates in the right direction (arrow C4) when viewed from the rear, so that the base member <NUM> also rotates in the right direction.

When the front frame <NUM> rotates in the left direction, the bracket <NUM> moves rearward, and the lever 92a and the universal joint <NUM> rotate in the left direction when viewed from above. Due to the rotation of the universal joint <NUM>, the universal joint <NUM>, the transmission shaft 96b, and the transmission gear 96c are also rotated in the right direction through the bevel box <NUM> when viewed from the rear. As a result, the transmission gear portion <NUM> rotates in the left direction when viewed from the rear, and the base member <NUM> also rotates in the left direction.

Here, the reduction ratio from the transmission gear 96c to the transmission gear portion <NUM> is set so as to match the reciprocal of the inclination of the map M1 illustrated in <FIG>. For example, in the case of θi_real=<NUM>×θtarget, the reciprocal of the inclination is set to <NUM>. When the body frame angle θs_real of the front frame <NUM> with respect to the rear frame <NUM> is <NUM> degrees, the base angle θb_real of the base member <NUM> with respect to the support part <NUM> is set to be <NUM> degrees. As a result, the scales of the rotation angles of the base member <NUM> and the joystick lever <NUM> with respect to the support part <NUM> can be matched.

When the map M1 is a curve as illustrated in <FIG>, the same relationship is realized by using an unequal pitch gear.

The base member <NUM>, the biasing part <NUM>, the transmission mechanism <NUM> and the like described above constitute a counterforce applying mechanism <NUM> that applies a counterforce to the operation of the lever portion <NUM>.

The control operation of the wheel loader <NUM> according to the present embodiment will be described below. <FIG> is a flow chart illustrating the control operation of the wheel loader <NUM> of the present embodiment. <FIG> are sectional views for explaining the control operation of the wheel loader <NUM> of the present embodiment.

As illustrated in <FIG>, in the case where the base reference position 43b of the base member <NUM> matches the support reference position 42b of the support part <NUM>, and the longitudinal direction (L1) of the joystick lever <NUM> also matches the support reference position 42b (also referred to as an initial position. ), the actual lever input angle θi_real by the joystick lever <NUM> is zero.

At this time, the electromagnetic pilot valve <NUM> is in the neutral position. In this case, the hydraulic valve <NUM> is also in the neutral position. Therefore, the oil is not supplied to or discharged from the left and right steering cylinders 9a and 9b, and the actual vehicle body frame angle θs_real is maintained at zero. In this way, since the vehicle body frame actual angle θs_real is also zero, the base member <NUM> is also located at the initial position.

Then, the operator applies an operating force Fin to rotate the joystick lever <NUM> from the support reference position 42b to the right side. When the operating force Fin exceeds the initial biasing force of the spring member <NUM> the lever portion <NUM> rotates in the right direction and the actual lever input angle θi_real increases, as illustrated in <FIG>. Further, the counterforce applied by the spring member <NUM> increases as the lever portion <NUM> is moved to the right direction.

In step S10, the lever angle sensor <NUM> detects the actual lever input angle θi_real of the lever portion <NUM> operated by the operator as illustrated in <FIG> as the detection value θi_detect of the lever input angle.

Next, in step S20, the controller <NUM> calculates the vehicle body frame target angle θtarget from the detection value θi_detect of the lever input angle by using the map M1 as illustrated in <FIG>.

Next, in step S30, the vehicle body frame angle sensor <NUM> detects the vehicle body frame actual angle θs_real as the detection value θs_detect of the vehicle body frame angle, and calculates the vehicle body frame actual angle θactual by using the map M2 as illustrated in <FIG>.

At this time, the body frame actual angle θs_real is zero due to the delay in the reaction of the left and right steering cylinders 9a and 9b. Therefore, the detection value θs_detect of the vehicle body frame angle, which is the detection value by the vehicle body frame angle sensor <NUM>, is zero. Since the body frame actual angle θs_real is almost zero, the base member <NUM> is also not rotating. Therefore, as illustrated in <FIG>, when the lever portion <NUM> is rotated in the right direction, the straight line L1 along the longitudinal direction of the lever portion <NUM> is rotated from the base reference position 43b.

Further, the first end portion <NUM> of the spring member <NUM> is pushed and moved in the clockwise direction (left direction Yl side) by the connecting member <NUM>, and the tip end of the first end portion <NUM> is separated from the right end 76R of the groove <NUM> in the left direction Yl side. Further, since the tip end of the second end portion <NUM> is in contact with the left end <NUM> of the groove <NUM>, the second end portion <NUM> cannot move in the clockwise direction (left direction Yl side), and the connecting member <NUM> is separated from the second end portion <NUM> in the left direction Yl side. Accordingly, since the first end portion <NUM> of the spring member <NUM> pushes the connecting member <NUM> in the counterclockwise direction, the spring member <NUM> biases the joystick lever <NUM> so that the lever portion <NUM> returns to the base reference position 43b.

Next, in step S40, the controller <NUM> calculates a difference angle θdiff between the body frame target angle θtarget and the body frame actual angle θactual.

Next, in step S50, the controller <NUM> uses the calculated difference angle θdiff and the vehicle speed signal V calculated from the vehicle speed sensor <NUM> to determine the electromagnetic pilot valve control current output i from the stored map M3 illustrated in <FIG> and give a command to the electromagnetic pilot valve <NUM>.

Since the lever portion <NUM> is rotated in the right direction, the electromagnetic pilot valve <NUM> is in the right pilot position, and the pilot pressure controlled by the electromagnetic pilot valve <NUM> is supplied to the hydraulic valve <NUM>. By supplying the pilot pressure, the hydraulic valve <NUM> is in the right steering position, and the main hydraulic pressure is supplied to the steering cylinders 9a and 9b so as to extend the steering cylinder 9a and contract the steering cylinder 9b.

As a result, the vehicle body frame actual angle θs_real gradually increases, and the front frame <NUM> is oriented in the right direction with respect to the rear frame <NUM>.

This change in the vehicle body frame actual angle θs_real is reflected on the angle of the base plate <NUM> via the transmission mechanism <NUM>. As a result, the base plate <NUM> rotates clockwise (in the direction of arrow H) in <FIG> about the center P3 of the rotating shaft <NUM>. When the base plate <NUM> is rotated toward the rotating position of the lever portion <NUM>, the deviation angle between the actual lever input angle θi_real and the actual base angle θb_real becomes small, so the biasing force of the spring member <NUM> becomes small.

As illustrated in <FIG>, when the operator stops the lever portion <NUM> at a predetermined actual lever input angle θi_real = θa, the difference angle θdiff becomes smaller because the vehicle body frame actual angle θs_real gradually increases. Then, when the vehicle body frame actual angle θs_real catches up with the vehicle body frame target angle θa_target obtained by converting the lever input angle θa using the map M1 of <FIG>, the difference angle θdiff becomes zero. At this time, the electromagnetic pilot valve <NUM> is in the neutral position, and the hydraulic valve <NUM> is also in the neutral position. Therefore, the oil is not supplied to or discharged from the left and right steering cylinders 9a and 9b, and the vehicle body frame actual angle θs_real maintains the vehicle body frame target angle θa_target obtained by converting the lever input angle θa using the map M1 in <FIG>. Further, as illustrated in <FIG>, the base member <NUM> also rotates clockwise by θa, and the straight line L1 passing through the center of the lever portion <NUM> is arranged at the base reference position 43b. The positional relationship between the base member <NUM> and the joystick lever <NUM> is the same as that in the state illustrated in <FIG>.

Next, when the operator returns the lever portion <NUM> from the right side position (θi_real = θa) toward the central position (θi_real = zero), the joystick lever <NUM> rotates in the left direction so that the straight line L1 is positioned in the vertical direction (support reference position 42b) as illustrated in <FIG>.

Before returning the lever portion <NUM> to the support reference position 42b (state illustrated in <FIG>), the positional relationship between the joystick lever <NUM> and the base member <NUM> is the same as that in <FIG>. Therefore, the counterforce at the start movement when moving the lever portion <NUM> is the same as the counterforce at the start movement from the initial position. That is, in the present embodiment, since the base member <NUM> rotates to the position corresponding to the vehicle body frame actual angle θs_real, the counterforce applied to the operation is determined according to the state of the electromagnetic pilot valve <NUM> (intermediate position, right pilot position, left position) regardless of the position of the lever portion <NUM>.

At this time, the body frame actual angle θs_real is in the state of θa_target due to the delay in the reaction of the left and right steering cylinders 9a and 9b. Further, since the actual base angle θb_real is θa, in which is the same as the vehicle body frame actual angle θs_real, the second end portion <NUM> of the spring member <NUM> is pushed by the connecting member <NUM> and is rotated counterclockwise (the right direction Yr side) to be separated from the left end <NUM> of the groove <NUM> as shown in <FIG>. On the other hand, the first end portion <NUM> of the spring member <NUM> presses the right end 76R of the groove <NUM>. As a result, the second end portion <NUM> of the spring member <NUM> pushes the connecting member <NUM> in the clockwise direction, so that the spring member <NUM> biases the joystick lever <NUM> with respect to the base plate <NUM> so as to be in the state of <FIG>.

As described above, since the actual body frame actual angle θs_real is in the state of θa_target, the difference angle θdiff decreases from zero and becomes negative. Then, the electromagnetic pilot valve <NUM> is in the left pilot position, the pilot pressure is supplied to the hydraulic valve <NUM>, and the hydraulic valve <NUM> is in the left steering position. As a result, the hydraulic pressure is supplied so that the steering cylinder 9b extends and the steering cylinder 9a contracts.

As a result, the vehicle body frame actual angle θs_real gradually decreases from the rotation angle θa_target. This change in the vehicle body frame actual angle θs_real is reflected on the base member <NUM> via the transmission mechanism <NUM> as described above, and the base member <NUM> also rotates in the same manner as the change in the vehicle body frame actual angle θs_real.

Then, when the vehicle body frame actual angle θs_real becomes zero, the difference from the actual lever input angle θi_real (=<NUM>) becomes zero. At this time, the electromagnetic pilot valve <NUM> is in the neutral position, and the hydraulic valve <NUM> is also in the neutral position. Therefore, the oil is not supplied to or discharged from the left and right steering cylinders 9a and 9b, and the vehicle body frame actual angle θs_real returns to zero and is maintained. As a result, the front frame <NUM> is returned to the direction that is the direction along the front-rear direction with respect to the rear frame <NUM>.

Furthermore, the base member <NUM> is rotated by the transmission mechanism <NUM> so that the actual base angle θb_real becomes zero as the vehicle body frame actual angle θs_real decreases, and returns to the initial position (θb_real = <NUM>) as illustrated in <FIG>.

Further, the control operation when the joystick lever <NUM> is rotated to the left is the same as the above, and therefore is omitted.

Next, the wheel loader <NUM> of the second embodiment according to the present invention will be described. Unlike the steering system of the first embodiment, the wheel loader <NUM> of the second embodiment does not have the transmission mechanism <NUM>. In the second embodiment, the same configurations as those in the first embodiment are designated by the same reference numerals as those in the first embodiment, and the description thereof will be omitted.

<FIG> is a view illustrating the configuration of the steering system <NUM> of the wheel loader <NUM> according to the second embodiment.

The steering system <NUM> according to the second embodiment has the adjusting mechanism <NUM>, the steering device <NUM>, the controller <NUM>, and the vehicle speed sensor <NUM>. The controller <NUM> corresponds to an example of a controller. In <FIG>, transmission of signals based on electricity is indicated by dotted lines, and transmission based on hydraulic pressure is indicated by solid lines. Further, the detection by the sensor is illustrated by a two-dot chain line.

The steering device <NUM> has an operation unit <NUM>, a lever angle sensor <NUM>, and a vehicle body frame angle sensor <NUM>. The operation unit <NUM> has a joystick lever <NUM>, a support part <NUM> that rotatably supports the joystick lever <NUM>, and a counterforce applying mechanism <NUM> that applies a counterforce to the operation of the joystick lever <NUM>.

The joystick lever <NUM> has, for example, a through hole at the proximal end, and the shaft 242a of the support part <NUM> is inserted through the through hole. With such a configuration, the joystick lever <NUM> can be rotatably supported by the support part <NUM>.

The counterforce applying mechanism <NUM> applies a counterforce to the rotating operation of the joystick lever <NUM> from the support reference position 242b. The counterforce applying mechanism <NUM> has an electric motor <NUM>. For example, a gear is fixed to the output shaft of the electric motor <NUM>, and the gear meshes with a gear shape formed on the outer periphery of the proximal end of the joystick lever <NUM>, whereby a counterforce can be applied to the operation of the joystick lever <NUM>.

The controller <NUM> has a CPU, a memory, and the like. The similarly to the controller <NUM> of the first embodiment, the detection value θi_detect by the lever angle sensor <NUM>, the detection value θs_detect by the vehicle body frame angle sensor <NUM>, and the detection value θi_detect by the vehicle speed sensor <NUM> are input to the controller <NUM>, and the controller <NUM> controls the electromagnetic pilot valve <NUM> based on these values.

As illustrated in <FIG>, the controller <NUM> calculates the vehicle body frame target angle θtarget from the detection value θi_detect of the lever input angle detected by the lever angle sensor <NUM> by using the map M1 illustrated in <FIG>, calculates the vehicle body frame actual angle θactual from the detection value θs_detect of the vehicle body frame angle by using the map M2, and calculates the difference angle θdiff.

Then, the controller <NUM> determines the electromagnetic pilot valve control current output i transmitted to the electromagnetic pilot valve <NUM> based on the calculated difference angle θdiff and the vehicle speed V detected by the vehicle speed sensor <NUM> from the stored graph of <FIG>.

Further, the controller <NUM> applies a counterforce to the operation of the joystick lever <NUM> based on the value of θdiff. For example, a counterforce characteristic such as a graph in which θr_real on the horizontal axis of <FIG> is replaced by θdiff can be added. That is, the controller <NUM> sends a command to the electric motor <NUM> so that the counterforce increases as the absolute value of θdiff increases, and the counterforce decreases as the vehicle body frame target angle θtarget calculated from the lever rotation angle θi_real of the joystick lever <NUM> approaches the vehicle body frame angle θs_real. The command from the controller <NUM> to the electric motor <NUM> may be wired or wireless.

In this way, the control is performed so that the vehicle body frame target angle θtarget becomes larger than the absolute value of the input angle θi_real of the joystick lever <NUM> or <NUM>. As an example, when the input angle θi_real of the joystick lever <NUM> or <NUM> is set to <NUM> degrees, the vehicle body frame target angle can be set to <NUM> degrees, for example.

Therefore, the operation angle of the joystick lever <NUM> or <NUM> can be small, so it is possible to reduce the burden on the operator.

Furthermore, the characteristic of <FIG> is mentioned as an example of "partially larger". In the map M1 of <FIG>, there is a portion where the absolute value of the lever input angle θi_real and the absolute value of the vehicle body frame target angle θtarget match by the straight line of θi_real = θtarget near zero, but in the vicinity of the absolute value of the vehicle body frame target angle θtarget corresponding to the absolute value of the lever input angle θi_real is larger than the absolute value of the lever input angle θi_real.

(<NUM>)
The wheel loader <NUM> or <NUM> of the first or second embodiment is articulated type work vehicle in which a front frame <NUM> and a rear frame <NUM> are coupled to each other, has steering cylinders 9a and 9b, joystick lever <NUM> or <NUM>, the hydraulic valve <NUM> and the controller <NUM> or <NUM>. The steering cylinders 9a and 9b are hydraulically driven to change the vehicle body frame angle θs_real of the front frame <NUM> with respect to the rear frame <NUM>. The joystick lever <NUM> or <NUM> are rotated to change the vehicle body frame angle θs_real. The controller <NUM> or <NUM> controls the flow rate of oil supplied to the steering cylinders 9a and 9b. The controller <NUM> or <NUM> sets the vehicle body frame target angle θtarget with respect to the input angle θi_real of the joystick lever <NUM> or <NUM>, and control the hydraulic valve <NUM> so that the vehicle body frame actual angle θs_real matches the vehicle body frame target angle θtarget.

As illustrated in <FIG>, a value obtained by differentiating the vehicle body frame target angle θtarget by the input angle θi_real of the joystick lever <NUM> or <NUM> includes a value larger than <NUM> and a value smaller than <NUM>.

As a result, it is possible to reduce the burden on the operator.

Furthermore, "a value obtained by differentiating the vehicle body frame target angle θtarget by the input angle θi_real of the joystick lever <NUM> or <NUM> includes a value smaller than <NUM>" is illustrated in the map M1 of <FIG> as an example. In the vicinity of zero of the map M1 in <FIG>, referring to the straight line θi_real=θtarget, the value obtained by differentiating the vehicle body frame target angle θtarget by the input angle θi_real of the joystick lever <NUM> or <NUM> is smaller than <NUM>. Further, "a value obtained by differentiating the vehicle body frame target angle θtarget by the input angle θi_real of the joystick lever <NUM> or <NUM> includes a value larger than <NUM>" is illustrated in the map M1 of <FIG> as an example. In the map M1 of <FIG>, in the vicinity of the portion intersecting the straight line of θi_real=θtarget the value differentiated by the input angle θi_real of the joystick lever <NUM> or <NUM> is larger than <NUM> (see the straight line of θi_real=θtarget).

(<NUM>)
In the wheel loader <NUM> or <NUM> of the first or second embodiment, the joystick lever <NUM> or <NUM> is arranged on the left side of the operator's seat <NUM>, and when the joystick lever <NUM> or <NUM> are rotated to the left side, the vehicle body frame actual angle is decreased, and at least the value θ4 of the vehicle body frame target angle θtarget that matches the minimum value of the vehicle body frame actual angle θs_real is smaller than the value θ3 of the corresponding lever input angle θi_real of the joystick lever <NUM> or <NUM>.

In particular, when the operator operates the joystick lever <NUM> toward the outside (left side in the present embodiment) with respect to the operator's seat <NUM>, the burden on the wrist is large, so by decreasing the operation angle of the joystick lever <NUM> toward the outside (left side), it is possible to improve operator fatigue. Furthermore, when the joystick lever <NUM> or <NUM> is arranged on the right side of the operator's seat <NUM>, the outside is on the right side.

In the first and second embodiments, the value θ2 of the vehicle body frame target angle θtarget that matches the maximum value of the vehicle body frame actual angle θs_real is the corresponding lever input angle θi_real of the joystick lever <NUM> or <NUM> on the inner side (right side), and the operator's fatigue is improved even when the operator operates the joystick lever <NUM> toward the inside (right side) with respect to the operator's seat <NUM>.

As described above, in the first and second embodiment, the present configuration is used so as to improve the fatigue of the operator regardless of whether the wrist is moved to the left side (outer side) or the right side (inner side). The present configuration may be used for only one side. However, since it is more difficult to operate by turning the wrist to the outside, it is preferable to use this configuration at least on the outside.

Further, in the present embodiment, when the joystick lever <NUM> or <NUM> is turned to the left side, the vehicle body frame actual angle θs_real is decreased, and when the joystick lever <NUM> or <NUM> is turned to the right side, the vehicle body frame actual angle θs_real is increased. But these may be reversed. In this case, using <FIG>, the vehicle body frame actual angle θs_real is increased by rotating the joystick lever <NUM> or <NUM> to the left side, and at least the value θ2 of the vehicle body frame target angle θtarget that matches the maximum value of the vehicle body frame actual angle θs_real is larger than the value θ1 of the corresponding lever input angle θi_real of the joystick lever <NUM>, or <NUM>.

(<NUM>)
The wheel loader <NUM> or <NUM> of the first or second embodiment further has a counterforce applying mechanism <NUM> or <NUM>. The counterforce applying mechanism <NUM> or <NUM> applies a counterforce to the joystick lever <NUM> toward the lever input angle θi_real corresponding to the vehicle body frame target angle θtarget.

That is, the counterforce applying mechanism <NUM> or <NUM> applies the counterforce in the direction of making θdiff zero according to the magnitude of the difference angle θdiff.

As a result, a counterforce corresponding to the difference angle between the vehicle body frame angle θs_real and the vehicle body frame target angle θtarget can be applied to the operation of the joystick lever <NUM> or <NUM>.

(<NUM>)
The wheel loader <NUM> of the first embodiment further has a support part <NUM>. The support part <NUM> is arranged inside the cab <NUM> provided on the rear frame <NUM>. The counterforce applying mechanism <NUM> has a base member <NUM>, a biasing part <NUM>, and a transmission mechanism <NUM>. The base member <NUM> is rotatably supported by the support part <NUM>. The biasing part <NUM> biases the joystick lever <NUM> to a predetermined position with respect to the base member <NUM>. The transmission mechanism <NUM> includes a link, transmits the vehicle body frame angle θs_real to the base member <NUM>, and rotates the base member <NUM> to an angle corresponding to the vehicle body frame angle θs_real. The joystick lever <NUM> is rotatably supported by the support part <NUM> or the base member <NUM>.

Accordingly, the biasing part <NUM> can apply a counterforce to the rotating operation of the joystick lever <NUM>.

(<NUM>)
In the wheel loader <NUM> of the first embodiment, the ratio of the target value of the vehicle body frame angle θs_real to the input angle θi_real of the joystick lever <NUM> is the reciprocal of the reduction ratio when the vehicle body frame angle θs_real is transmitted to the base member <NUM> by the transmission mechanism <NUM>.

As a result, the angle scale of the rotation angle of the joystick lever <NUM> and the angle scale of the rotation angle of the base member <NUM> can be made to coincide with each other, and a counterforce can be applied by the biasing part <NUM> according to the deviation angle between the rotation angle of the joystick lever <NUM> and the vehicle body frame angle.

(<NUM>)
In the wheel loader <NUM> of the second embodiment, the counterforce applying mechanism <NUM> has the electric motor <NUM>. The electric motor <NUM> generates a counterforce.

As a result, a counterforce can be applied to the rotating operation of the joystick lever <NUM> by using the electric motor <NUM>.

While an embodiment of the present disclosure has been explained above, the present disclosure is not limited to the above embodiment and various changes are possible within the scope of the present disclosure, as defined in the appended claims.

The base member <NUM> of the operation unit <NUM> illustrated in <FIG> and <FIG> further includes a detection gear portion <NUM> as compared with the base member <NUM> of the first embodiment. The detection gear portion <NUM> is used to detect the rotation angle of the base member <NUM>. As illustrated in <FIG>, the detection gear portion <NUM> is arranged on the front direction Xf side of the transmission gear portion <NUM> and is connected to the transmission gear portion <NUM>. A through hole is formed in the detection gear portion <NUM> along the front-rear direction X, and the rotating shaft <NUM> is inserted into the through hole. As a result, the detection gear portion <NUM> is configured to be rotatable with respect to the rotating shaft <NUM>. The lower end surface 375a of the detection gear portion <NUM> is formed to be convexly curved downward, and a gear shape is formed on the lower end surface 375a. As illustrated in <FIG>, the lower end surface 375a meshes with the gear <NUM> of the base angle detection unit <NUM>.

As illustrated in <FIG> and <FIG>, the base angle detection unit <NUM> has a base member angle sensor <NUM>, a detection shaft <NUM>, and a gear <NUM>.

The base member angle sensor <NUM> is configured by, for example, a potentiometer, and detects an actual base angle θb_real that is a rotation angle of the base member <NUM> with respect to the support part <NUM> (specifically, also referred to as a support frame <NUM>) as the detection value θb_detect of the base member angle. The base member angle sensor <NUM> is fixed to the outside of the shaft support portion <NUM>.

The detection shaft <NUM> is an axis whose rotation angle is detected by the base member angle sensor <NUM>. The detection shaft <NUM> extends from the base member angle sensor 101to inside the shaft support portion <NUM> through the shaft support portion <NUM>.

The gear <NUM> is fixed to the detection shaft <NUM>. The gear <NUM> meshes with the lower end surface 375a of the detection gear portion <NUM> of the base member <NUM>.

When the base member <NUM> is rotated by the transmission mechanism <NUM> described later, the detection gear portion <NUM> is also rotated, and the rotation also causes the detection shaft <NUM> to rotate via the gear <NUM>. The rotation of the detection shaft <NUM> is detected by the base member angle sensor <NUM>, and the rotation angle of the base plate <NUM> with respect to the support part <NUM> is detected.

The base plate angle detection value θb_detect detected by the base member angle sensor <NUM> is sent to the controller <NUM> as a detection signal. The controller <NUM> performs control by using a block diagram in which the detection value θs_detect of the vehicle body frame angle in <FIG> is replaced with the detection value θb_detect of the base angle. The controller <NUM> converts the detection value θb_detect of the base angle by using the map M2 to calculate the vehicle body frame actual angle θactual. Here, since the actual base angle θb_real of the base member <NUM> corresponds to the vehicle body frame actual angle θs_real by the transmission mechanism <NUM>, by using the map M2 corresponding to the reduction ratio of the transmission mechanism <NUM> and the detection gear portion <NUM>, the vehicle body frame actual angle θactual can be calculated. The steering cylinders 9a and 9b can be controlled based on the vehicle body frame actual angle θactual as in the first embodiment.

(B)
In the first embodiment described above, the lever angle sensor <NUM> that detects the lever rotation angle of the joystick lever <NUM> with respect to the support part <NUM> and the vehicle body frame angle sensor <NUM> are provided, and the deviation angle θd_detect is calculated, but the present invention may not be limited to this. For example, an angle sensor that detects the angle of the joystick lever <NUM> with respect to the base member <NUM> may be provided. In this case, the difference angle θdiff can be calculated by converting the detection value into the angle scale of the body frame angle, and it is possible to control the steering cylinders 9a and 9b by using the difference angle θdiff as in the first embodiment.

(C)
In the second embodiment described above, the electric motor <NUM> is used for the counterforce applying mechanism <NUM> that applies the counterforce to the joystick lever <NUM>, but it is not limited to the electric motor, and a hydraulic motor or the like may be used. In short, any actuator or the like that can generate a counterforce may be used.

(D)
In the first and second embodiments, the amount of oil supplied from the hydraulic valve <NUM> to the steering cylinders 9a and 9b is controlled according to the pilot pressure input from the electromagnetic pilot valve <NUM>. However, the oil from the electromagnetic pilot valve <NUM> may be directly supplied to the steering cylinders 9a and 9b without passing through the hydraulic valve <NUM>. That is, an electromagnetic main valve may be used instead of the electromagnetic pilot valve <NUM>.

(E)
In the first embodiment described above, the biasing part <NUM> is provided with the damper <NUM> in addition to the spring member <NUM>. However, not limited to the damper, a friction brake may be provided, or the damper or the friction brake may not be provided.

(F)
In the first embodiment, the controllers <NUM> and <NUM> perform the calculation using θi_detect=<NUM>×θtarget, and the inclination is not limited to <NUM>, but it is preferable that the inclination is less than <NUM> because the operator can greatly change the vehicle body frame angle with a small rotation angle. In short, the controllers <NUM> and <NUM> may control only need to be able to control the hydraulic valve <NUM> so that the vehicle body frame target angle θtarget becomes larger than the input angle θi_real of the joystick lever <NUM>.

(G)
In the first and second embodiments described above, the rotation angle of the joystick lever <NUM> may be electrically or mechanically restricted to less than <NUM> degrees. In the case of the first embodiment, for example, the support part <NUM> may be provided with a portion with which the joystick lever <NUM> comes into contact when the joystick lever <NUM> is rotated to the left side by <NUM> degrees and when the joystick lever <NUM> is rotated to the right side by <NUM> degrees. Further, in the case of the second embodiment, by restricting the drive of the electric motor <NUM>, the rotation of the joystick lever <NUM> can be restricted within a predetermined range.

(H)
In the above embodiment, the joystick lever <NUM> is supported by the support part <NUM>, but may be rotatably supported by the base member <NUM>, or <NUM>.

(I)
While the wheel loader <NUM> is used in the explanations as an example of the work vehicle in the above embodiments, an articulated type dump truck, a motor grader, or the like may be used.

Claim 1:
A work vehicle, being an articulated type in which a front frame (<NUM>) and a rear frame (<NUM>) are coupled, comprising;
a hydraulic actuator (9a, 9b) configured to be driven by hydraulic pressure to change a vehicle body frame angle (θs_real) of the front frame (<NUM>) with respect to the rear frame (<NUM>);
a lever (<NUM>) configured to be rotated to change the body frame angle (θs_real);
a control valve (<NUM>) configured to control a flow rate of oil supplied to the hydraulic actuator (9a, 9b); and
a controller (<NUM>) configured to set a target angle (θtarget) of the vehicle body frame angle (θs_real) with respect to an input angle (θi_real) of the lever (<NUM>) and control the control valve (<NUM>) such that an actual angle of the vehicle body frame angle (θi_real) matches the target angle (θtarget) of the vehicle body frame angle (θs_real),
characterized in that
an absolute value of the target value of the vehicle body frame angle (θs_real) corresponding to an absolute value of the input angle (θi_real) of the lever (<NUM>) is larger than the absolute value of the input angle (θi_real) of the lever (<NUM>).