Damper operation control device and damper operation control method for working vehicle

A damper operation control device of a working vehicle, includes: a boom pivotably supported on a vehicle body; a bucket pivotably supported on a tip end of the boom; a lift cylinder which drives the boom; an accumulator connected to the lift cylinder through a branched oil passage; a switching valve connected to the branched oil passage between the lift cylinder and the accumulator, the switching valve switching between a connected state and a disconnected state between the lift cylinder and the accumulator; and a controller which performs switch control of the switching valve, wherein the controller includes: a state detecting unit which detects whether the bucket is in a loaded state; and a switching valve control unit which switches the switching valve to the connected state when the state detecting unit detects that the bucket is in the loaded state.

BACKGROUND OF THE INVENTION

Field of the Invention.

The present invention relates to a damper operation control device and a damper operation control method for a working vehicle and especially relates to the damper operation control device and the damper operation control method for the working vehicle such as a wheel loader, a skid-steer loader, a bulldozer, and a excavator.

In general, the working vehicle such as the wheel loader performs work such as excavation by efficiently using force generated by a power supply, so that this is not equipped with a suspension system to absorb vibration generated in a vehicle body. Therefore, there is a defect that a loaded burden (such as earth and sand) falls due to the vibration generated during travel and that riding quality is deteriorated in a conventional working vehicle.

Then, for example, following Patent Literature 1 discloses technology to provide an accumulator connectable to a fluid pressure lift cylinder for lifting a bucket and connect the fluid pressure lift up cylinder to the accumulator only when a vehicle speed of the working vehicle becomes a predetermined value or higher. According to the conventional technology disclosed in Patent Literature 1, it becomes possible to absorb the vibration generated in the vehicle body during the travel by the accumulator connected to the fluid pressure lift cylinder, so that it is possible to prevent the defect such as falling of the loaded burden such as the earth and sand during the travel and deterioration in the riding quality during the travel from generating.

Also, following Patent Literature 2 discloses the technology to improve stability of the working vehicle at the time of the travel by controlling to accumulate pressure in the accumulator according to a vehicle speed and/or an operating position of a forward/reverse lever and by controlling to absorb variation in pressure generated in a bottom chamber in a boom cylinder.

CITATION LIST

Patent Literature

BRIEF SUMMARY OF THE INVENTION

Technical Problem

However, when use of the accumulator is switched according only to the vehicle speed and the operating position of the forward/reverse lever as in the above-described conventional technology, there is a case in which connection between the accumulator and the bottom chamber is released irrespective of whether the burden is loaded in the bucket, and there is a problem that the burden loaded in the bucket might be fallen in this case.

The present invention is achieved in view of the above description and an object thereof is to provide the damper operation control device and the damper operation control method for the working vehicle capable of efficiently using the force generated by the power supply and of realizing decrease in the falling of the loaded burden and improvement in the riding quality.

Solution to Problem

To overcome the problems and achieve the object, according to the present invention, a damper operation control device of a working vehicle, comprises: a boom pivotably supported on a vehicle body; a bucket pivotably supported on a tip end of the boom; a lift cylinder which drives the boom; an accumulator connected to the lift cylinder through a branched oil passage; a switching valve connected to the branched oil passage between the lift cylinder and the accumulator, the switching valve switching between a connected state and a disconnected state between the lift cylinder and the accumulator; and a controller which performs switch control of the switching valve, wherein the controller includes: a state detecting unit which detects whether the bucket is in a loaded state; and a switching valve control unit which switches the switching valve to the connected state when the state detecting unit detects that the bucket is in the loaded state.

According to the present invention, the switching valve control unit switches the switching valve to the connected state when the working vehicle travels at a speed not lower than a predetermined speed when the state detecting unit detects that the bucket is in a state other than the loaded state, and the switching valve control unit switches the switching valve to the connected state even when the working vehicle travels at a speed lower than the predetermined speed when the state detecting unit detects that the bucket is in the loaded state.

According to the present invention, a damper operation control method for a working vehicle comprises: a boom pivotably supported on a vehicle body; a bucket pivotably supported on a tip end of the boom; a lift cylinder which drives the boom through a branched oil passage; an accumulator connected to the lift cylinder; a switching valve connected to the branched oil passage between the lift cylinder and the accumulator, the switching valve switching between a connected state and a disconnected state between the lift cylinder and the accumulator; and a controller which performs switch control of the switching valve, the method comprising: detecting whether the bucket is in a loaded state; and switching the switching valve to the connected state when the bucket is detected to be in the loaded state in the detecting.

According to the present invention, the working vehicle further includes a transmission for driving, the detecting includes detecting a transition state of at least an unladen state, a state during excavation work, and the loaded state as a working state of the working vehicle and detecting that a current working state of the working vehicle is the loaded state when a bottom pressure of the lift cylinder is detected to be not lower than predetermined unladen pressure for determining that a burden is not loaded in the bucket and an angle of the boom is detected to be smaller than a predetermined angle set in advance or when the bottom pressure of the lift cylinder is detected to be not lower than the predetermined unladen pressure and a direction of the bucket is detected to be horizontal or above a horizontal plane in a case that the current working state of the working vehicle is the unladen state, or when an operation signal to the transmission is detected to be other than forward in a case that the current working state of the working vehicle is the state during the excavation work.

Advantageous Effects of Invention

According to the present invention, the switching valve is switched to the connected state to activate the damper mechanism when the bucket is detected to be in the loaded state, so that it is possible to realize the damper operation control device and the damper operation control method for the working vehicle capable of efficiently using the force generated by the hydraulic pump and of realizing the decrease in the falling of the loaded burden and the improvement in the riding quality.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment for carrying out the present invention is hereinafter described in detail with reference to the drawings. Meanwhile, in a following description, the drawings merely schematically illustrate a shape, a size, and positional relationship such that contents of the present invention may be understood, so that the present invention is not limited only to the shape, the size, and the positional relationship illustrated in the drawings. Also, a value illustrated in the following description is merely a preferable example of the present invention, so that the present invention is not limited to the illustrated value.

A damper operation control device and a damper operation control method for a working vehicle according to one embodiment of the present invention are hereinafter described in detail with reference to the drawings. Meanwhile, in this embodiment, a wheel loader100is described as an example of the working vehicle as illustrated inFIG. 1, and a case in which earth and sand are loaded from a mound200into a dump truck300using the wheel loader100is described.

FIG. 1is a schematic diagram illustrating a schematic flow of loading work described as an example in this embodiment. As illustrated inFIG. 1, the wheel loader100is provided with a bucket101, which performs work such as excavation and work to load a burden to carry, and a boom102, which lifts the bucket101.

In an example illustrated inFIG. 1, the wheel loader100is first arranged in a start position A and moves forward from the start position A to the mound200to move to an excavation position B (step S1). Subsequently, the wheel loader100tilts the bucket101at least once with operation of the boom102while moving forward in the excavation position B, thereby scooping the earth and sand from the mound200by using the bucket101(step S2). Next, the wheel loader100moves backward and then turns to move forward, thereby moving to an earth discharge position C beside a loading platform of the dump truck300(step S3). Subsequently, the wheel loader100puts the boom102into a vertical or substantially vertical standing position in the earth discharge position C and dumps the bucket101in this state, thereby discharging the earth and sand in the bucket101into the loading platform of the dump truck300(step S4). Thereafter, the wheel loader100moves backward while turning, thereby moving to its original start position A (step S5). Thereafter, the wheel loader100repeats steps S1to S5, thereby loading a target amount of earth and sand of the mound200into the loading platform of the dump truck300.

In the above-described loading work, as illustrated inFIG. 2, a working state of the wheel loader100transits among an unladen state (working status St=1), a state during the excavation work (working status St=2), and a loaded state (working status St=3). The unladen state (St=1) is the state in which the burden is not loaded in the bucket101. The state during the excavation work (St=2) is the state in which the wheel loader100performs the work to load the burden in the bucket101by operating the boom102and/or the bucket101while moving forward. The loaded state (St=3) is the state in which the burden is loaded in the bucket101.FIG. 2is a schematic diagram for illustrating transition of the working state of the wheel loader100according to this embodiment.

Herein, when describing a transition condition among the working states (St=1 to St=3), a detailed configuration of the wheel loader100according to this embodiment is described with reference to the drawings.FIG. 3is a side view for illustrating the detailed configuration of the wheel loader100. InFIG. 3, only a part of the wheel loader100on a front wheel103side related to the following description is selectively illustrated.

As illustrated inFIG. 3, the wheel loader100is provided with the bucket101, the boom102, a lift cylinder118, a bucket cylinder121, a first bucket link122, and a second bucket link124.

The bucket101is a so-called shovel for excavating to scoop the burden such as the earth and sand. The boom102is a support column for moving the bucket101in a height direction of which one end is pivotably supported on a vehicle body front frame130by means of a pivot pin. A bottom part of the bucket101is pivotably attached to the other end of the boom102by means of the pivot pin.

The lift cylinder118is configured to drive the boom102and includes a tube118-1of which one end is pivotably attached to the vehicle body front frame130in a position different from that of the boom102by means of the pivot pin and a piston rod118-3slidably fitted into the other end of the tube118-1. The lift cylinder118expands and contracts by insertion and removal of the piston rod118-3to and from the tube118-1by hydraulic pressure. Meanwhile, a middle part of the boom102is rotatably attached to a tip end of the piston rod118-3by means of the pivot pin. Therefore, the boom102rotates around the pivot pin fitted onto the vehicle body front frame130by expansion and contraction of the lift cylinder118.

For example, when the lift cylinder118expands, the boom102rotates in a counterclockwise direction in the drawing around the pivot pin as a pivot, and as a result, the end of the boom102opposite to the end pivotably supported rises and the bucket101attached thereto rises. On the other hand, when the lift cylinder118contracts, the boom102rotates in a clockwise direction in the drawing around the pivot pin as the pivot, and as a result, the end of the boom102opposite to the end pivotably supported lowers and the bucket101attached thereto lowers.

The bucket cylinder121is composed of a tube121-1of which one end is pivotably attached to the vehicle body front frame130in the same position as that of the boom102, for example, by means of the pivot pin and a piston rod121-3slidably fitted into the other end of the tube121-1, and expands and contracts by the insertion and the removal of the piston rod121-3to and from the tube121-1by the hydraulic pressure. One end of the first bucket link122is rotatably attached to a tip end of the piston rod121-3by means of a link pin122-1. A middle part of the first bucket link122is rotatably attached to a support member123fixed to the middle part of the boom102by means of a support pin122-2. One end of the second bucket link124is rotatably attached to the other end of the first bucket link122by means of a link pin122-3. The other end of the second bucket link124is rotatably attached to the bottom part of the bucket101in a position different from that of the boom102by means of the pivot pin. Therefore, when the bucket cylinder121expands and contracts, displacement thereof is transmitted to the bucket101through the first bucket link122and the second bucket link124, and according to this, the bucket101rotates around the pivot pin fitted onto the boom102.

For example, when the bucket cylinder121expands by increase in the hydraulic pressure, the first bucket link122rotates in the clockwise direction in the drawing around the support pin122-2as the pivot, and according to this, the link pin122-3of the second bucket link124is pulled in a direction toward the vehicle body front frame130. As a result, the bucket101rotates in the counterclockwise direction in the drawing around the pivot pin connected to the boom as the pivot. On the other hand, when the bucket cylinder121contracts, a direction of the bucket101rotates in the clockwise direction in the drawing.

By driving the lift cylinder118and the bucket cylinder121in the above-described manner, a height from a ground surface and the direction of the bucket101are operated. Meanwhile, in this embodiment, the term “direction of the bucket101(hereinafter, referred to as a bucket direction)” is used by setting such that the bucket in a state suitable for performing the excavation work is in a horizontal direction. Specifically, in a case in which the wheel loader100is on a horizontal ground surface, it is possible to determine that the direction of the bucket101is in the horizontal direction by a direction of the bottom part (surface on a side in contact with the ground surface) of the bucket101, a direction of a tooth (small piece indicated on a front-lower part of the bucket in the drawing) attached to the bucket101, or a direction in which an opening of the bucket101in a tray shape faces.

A boom angle sensor102-11, which detects an attitude of the boom102(for example, an elevation angle: hereinafter, referred to as a boom angle) is provided on the end of the boom102on the vehicle body front frame130side. The detected boom angle is input to a controller111(refer toFIG. 4) to be described later. Meanwhile, in this embodiment, the boom angle indicates the angle (elevation angle) between a straight line connecting the pivot pin, which is the pivot of the boom102, and the pivot pin, which is the pivot of the bucket101, and a horizontal plane when the end supported on the vehicle body front frame130of the boom102is set to a start point, for example. However, the angle is not limited thereto and may be variously modified such as an angle with respect to a vertical direction, for example.

Further, a bucket angle sensor122-11for detecting an angle between the bucket101and the boom102is provided on the middle part of the first bucket link122in a position in which the support pin122-2is provided. The bucket angle sensor122-11detects a rotational angle of the first bucket link122with respect to a reference, which is a longitudinal direction of the boom102, for example. The detected rotational angle is input to the controller111(refer toFIG. 4) to be described later as a bucket angle. The controller111calculates the direction of the bucket101(bucket direction) from the boom angle and the bucket angle, which are input.

Subsequently, an extract of a configuration of a damper operation control device110equipped on the wheel loader100according to this embodiment is described in detail with reference to the drawings.FIG. 4is a block diagram illustrating a schematic configuration of the damper operation control device110according to this embodiment. As illustrated inFIG. 4, the damper operation control device110includes the controller111, a shift operation detector112A, a damper function switch112B, a boom operating lever operation amount sensor112C, a bucket operating lever operation amount sensor112D, a vehicle speed sensor113, a fluid reservoir114, a valve system115including a switching valve115aand an EPC (electromagnetic proportional control) valve115b, a pilot pressure supply source116, an accumulator117, at least one lift cylinder118, each of which includes the tube118-1and the piston rod118-3, and a bottom pressure detector119. In this configuration, the fluid reservoir114, the valve system115including the switching valve115aand the EPC valve115b, and the accumulator117serve as a damper mechanism, which decreases vibration of the lift cylinder118. Meanwhile, a hydraulic pump141, which discharges hydraulic oil, and a tank142are connected to the lift cylinder118through an operating valve140. The lift cylinder118expands and contracts by supply and switch of a direction of supply of the hydraulic oil by operation of the operating valve140. Main oil passages145connect the lift cylinder118and the operating valve140. Branched oil passages146branched from the main oil passages145are connected to the accumulator117and the fluid reservoir114. The switching valve115ais provided in the middle of the branched oil passages146. The accumulator117is connected to the lift cylinder118through a branched oil passage146aout of the branched oil passages146and an oil passage on a bottom side of the main oil passages145.

The shift operation detector112A is provided on a shift lever mechanism, which operates a transmission of the wheel loader100, and detects a current operating position indicating forward (F)—neutral (N)—reverse (R) and any of speed stages from first to fourth speeds in the shift lever mechanism to output a shift operation signal indicating the current operating position to the controller111. The damper function switch112B is the switch, which switches between activation/deactivation of the damper function, operated by an operator and outputs a damper function SW signal indicating whether the damper function is activated (ON) or deactivated (OFF) by the operator to the controller111. The boom operating lever operation amount sensor112C detects an operational angle of the boom operating lever operated by the operator (boom lever stroke) and outputs a boom lever stroke signal indicating a boom lever stroke amount to the controller111. The bucket operating lever operation amount sensor112D detects the operational angle of the bucket operating lever operated by the operator (bucket lever stroke) and outputs a bucket lever stroke signal indicating a bucket lever stroke amount to the controller111. The vehicle speed sensor113always detects a current vehicle speed of the wheel loader100and outputs a vehicle speed signal indicating the detected vehicle speed to the controller111. The bottom pressure detector119detects the hydraulic pressure on the bottom side of the lift cylinder118(hereinafter, referred to as boom bottom pressure) and outputs a boom bottom pressure signal indicating the detected boom bottom pressure to the controller111.

The controller111is composed of an information processing unit such as a CPU (central processing unit) and an MPU (micro processing unit), for example, and generates a damper drive signal, which is a control signal for opening and closing the EPC valve115bin the valve system115, from the shift operation signal, the damper function SW signal, the boom lever stroke signal, the bucket lever stroke signal, the vehicle speed signal, and the boom bottom pressure signal, which are input, to output to the EPC valve115b.

The pilot pressure supply source116supplies the hydraulic pressure to operate the switching valve115a. The EPC valve115bis connected between the pilot pressure supply source116and the switching valve115a. When the damper drive signal for controlling to “open” is input from the controller111to the EPC valve115b, this permits conduction between the pilot pressure supply source116and the switching valve115aand guides pressurized fluid from the pilot pressure supply source116(pilot oil) to the switching valve115aas a hydraulic pilot signal. On the other hand, when the damper drive signal for controlling to “close” is input from the controller111to the EPC valve115b, this blocks the conduction between the pilot pressure supply source116and the switching valve115ato prevent the pressurized fluid from the pilot pressure supply source116from being guided to the switching valve115a. When the switching valve115aand the fluid reservoir114are connected to each other, the switching valve115adischarges pressurized oil to the fluid reservoir114by an action of a spring provided on a side opposite to a side on which the hydraulic pilot signal is applied to move to a pressed-down position in the drawing.

The switching valve115ais a so-called pilot operated valve for opening and closing connection between the lift cylinder118and the accumulator117and controls the conduction between the piston rod118-3side of the lift cylinder118and the fluid reservoir114and the conduction between the tube118-1side of the lift cylinder118and the accumulator117according to the hydraulic pilot signal input through the EPC valve115b. For example, when the hydraulic pilot signal (pressurized fluid) is input, the switching valve115amoves in a direction to contract a spring115cby the pressurized fluid, which flows in. As a result, the switching valve115ais put into an open state and the conduction between the piston rod118-3and the fluid reservoir114and the conduction between the tube118-1and the accumulator117are permitted. According to this, the hydraulic oil on the lift cylinder118side may flow into and out of the fluid reservoir114and the accumulator117. In this manner, by allowing the hydraulic oil on the lift cylinder118side to flow into and out of the accumulator117, it becomes possible to allow the accumulator117to absorb the vibration generated in the wheel loader100, especially, the boom102.

Meanwhile, the fluid reservoir114is a tank, which reserves the hydraulic oil being a medium for transmitting the drive force to the lift cylinder118and the bucket cylinder121. The accumulator117is the accumulator, which serves as an escape of the pressurized oil on the tube118-1side.

In the wheel loader100configured in the above-described manner, the transition condition among the working states (St=1 to St=3) illustrated inFIG. 2is described in detail with reference to Table 1 illustrated below. Table 1 is the table illustrating the transition condition among the working states according to this embodiment.

As illustrated in Table 1, parameters of the transition condition taken into consideration when the working state transits include the boom bottom pressure, the boom angle, the bucket direction, and the shift operation signal.

The boom bottom pressure is the boom bottom pressure detected by the bottom pressure detector119. Herein, in Table 1, the predetermined unladen pressure is the boom bottom pressure detected in a state in which the burden is not loaded in the bucket101. The predetermined impact pressure is the pressure generated by an impact of entry of the bucket101to the mound200at the time of the excavation. The predetermined impact pressure is sufficiently higher than the predetermined unladen pressure. Although the boom bottom pressure increases in association with a rise of the boom102at the time of loading of the burden into the dump truck300and the like, the predetermined impact pressure is set to the pressure higher than maximum pressure by the rise.

The boom angle (attitude) is the angle of elevation of the boom102with respect to the horizontal plane in a case in which the pivot (pivot pin) on the vehicle body front frame130side is set to the start point, for example, as described above. Herein, in Table 1, the predetermined angle is the angle of the boom102when the height of the bucket101during travel is supposed to be highest. The predetermined angle is generally set to the angle above the horizontal plane by several tens of degrees (for example, 20 degrees).

The bucket direction is the direction in which the opening of the bucket101in the tray shape faces as described above. As described above, the shift operation signal is the signal indicating the current operating position of the shift lever mechanism. Meanwhile, the shift lever mechanism indicates forward (F)—neutral (N)—reverse (R) and any of the speed stages from the first to fourth speeds of the transmission, so that two types of signals of forward/reverse and speed stages are mixed in the shift operation signal. However, the speed stages other than forward and the first speed stage (F1) may be optional in this description, so that the speed stage is not referred to unless it is required.

In a case in which the current working state is the unladen state (current working status St=1), the working state of the wheel loader100transits to the state during the excavation work (destination working status St=2) on the condition that the boom bottom pressure not lower than the predetermined impact pressure is detected. The working state of the wheel loader100in the unladen state transits to the loaded state (destination working status St=3) on the condition that the boom bottom pressure is not lower than the predetermined unladen pressure and the boom angle is smaller than the predetermined angle or that the boom bottom pressure is not lower than the predetermined unladen pressure and the bucket direction is horizontal or above the horizontal plane.

When the current working state is the state during the excavation work (current working status St=2), the working state of the wheel loader100transits to the unladen state (destination working status St=1) on the condition that the boom bottom pressure is lower than the predetermined unladen pressure. The working state of the wheel loader100in the state during the excavation work transits to the loaded state (destination working status St=3) on the condition that the shift operation signal is other than the F signal indicating forward.

Further, in a case in which the current working state is the loading work (current working status St=3), the working state of the wheel loader100transits to the state during the excavation work (destination working status St=2) on the condition that the boom bottom pressure not lower than the predetermined impact pressure is detected. The working state of the wheel loader100in the loaded state transits to the unladen state (destination working status St=1) on the condition that the boom angle is not smaller than the predetermined angle and the bucket direction is horizontal or below the horizontal plane or that the boom bottom pressure is lower than the predetermined unladen pressure.

In this manner, in this embodiment, the controller111detects whether it is in the state in which the burden is loaded in the bucket101based on the values detected by the bottom pressure detector119, the boom angle sensor102-11, the bucket angle sensor122-11, and the shift operation detector112A and the transition condition (Table 1).

Next, a specific example of the controller111according to this embodiment is described in detail with reference to the drawings.FIG. 5is a schematic diagram illustrating the specific example of the controller111according to this embodiment.

As illustrated inFIG. 5, the shift operation signal is input from the shift operation detector112A to the controller111. The damper function SW signal indicating whether the damper function is activated (ON) or deactivated (OFF) by the operator is input from the damper function switch112B to the controller111. The boom lever stroke signal is input from the boom operating lever operation amount sensor112C to the controller111. The bucket lever stroke signal is input from the bucket operating lever operation amount sensor112D to the controller111. In addition to this, the boom bottom pressure signal indicating the boom bottom pressure detected by the bottom pressure detector119, the vehicle speed signal indicating the vehicle speed measured by the vehicle speed sensor113, a boom angle detection signal indicating the boom angle detected by the boom angle sensor102-11, and a bucket direction detection signal indicating the bucket direction detected by the bucket angle sensor122-11are also input to the controller111.

The controller111includes a state detecting unit111A, which detects the current working state, and a switching valve control unit111B, which turns on/off the damper function, that is to say, which performs switch control of the switching valve115ato switch between a connected state (open) and a disconnected state (close) between the lift cylinder118and the accumulator117. The state detecting unit111A detects the current working state according to Table 1 described above based on the shift operation signal, the boom bottom pressure signal, the boom angle detection signal, and the bucket direction detection signal out of the signals input to the controller111to output a detection result to the switching valve control unit111B.

The detection result by the state detecting unit111A, the boom angle detection signal, the boom lever stroke signal, the bucket lever stroke signal, the vehicle speed signal from the vehicle speed sensor113, and the damper function SW signal from the damper function switch112B are input to the switching valve control unit111B. The switching valve control unit111B generates the damper drive signal to turn on or off the damper function based on the input various signals and outputs the damper drive signal to a solenoid coil for opening and closing the EPC valve115bin the valve system115(refer toFIG. 4). Meanwhile, to turn on the damper function is to output the damper drive signal for controlling to “open” to the switching valve115afor permitting the conduction between the pilot pressure supply source116and the switching valve115aand to turn off the damper function is to output the damper drive signal for controlling to “close” to the switching valve115a.

Next, the damper operation control method according to this embodiment is described in detail with reference to the drawings. Meanwhile, it is described focusing on operation of the controller111in the following description.FIG. 6is a flowchart illustrating schematic operation of the damper operation control method according to this embodiment. This operation may be configured to start together with a start of a power supply (for example, engine) of the working vehicle in this embodiment and stops together with a stop of the power supply unless particularly instructed to stop.

As illustrated inFIG. 6, the controller111first determines whether the wheel loader100is equipped with the damper function (step S101), and finishes this operation when this is not equipped with the damper function (step S101, No) or shifts to next step S102when this is equipped with the damper function (step S101, Yes). Meanwhile, as for whether the wheel loader100is equipped with the damper function, a variety of configurations such as a configuration in which this is registered in advance in a memory not illustrated, for example, may be applied.

Next, the controller111determines whether the damper function switch112B is turned on (step S102) and shifts to step S112to turn off the damper function when this is not turned on (step S102, No). On the other hand, when the damper function switch112B is turned on (step S102, Yes), this shifts to step S103. Meanwhile, steps S101and S102are the steps provided according to the embodiment (for example, the working vehicle without the damper function switch112B).

The controller111determines whether a current speed stage is other than a predetermined stage (F1) at step S103. The wheel loader100is generally operated by using the speed stage not lower than the second speed irrespective of forward/reverse, and the forward first speed is used when performing the excavation work. At the time of the excavation work, when the damper mechanism is turned off for improving working efficiency, relative movement between the vehicle body and a working machine is eliminated and the efficiency is improved. Therefore, it is determined whether the shift operation signal is other than the forward first speed (F1) and when this is “F1” (step S103, No), the procedure shifts to step S112to turn off the damper function. On the other hand, when the current speed stage is other than the forward first speed (step S103, Yes), the procedure shifts to next step S104for further determining whether to activate the damper mechanism.

At step S104, the controller111determines whether the vehicle speed is not lower than a first threshold speed Va, and when the vehicle speed is not lower than the first threshold speed Va (step S104, Yes), this shifts to step S110. On the other hand, when the vehicle speed is lower than the first threshold speed Va (step S104, No), the controller111shifts to step S105.

Next, at step S105, the controller111determines whether the vehicle speed is not lower than a second threshold speed Vd, and when the vehicle speed is not lower than the second threshold speed Vd (step S105, Yes), this shifts to step S106. On the other hand, when the vehicle speed is lower than the second threshold speed Vd (step S105, No), the controller111shifts to step S107.

At step S106branched from positive determination at step S105, the controller111determines whether the damper function is in an on-state at the time at which it shifts to this step. When the damper function is in the on-state (step S106, Yes), the controller111shifts to step S110. On the other hand, when the damper function is not in the on-state (step S106, No), the controller111shifts to step S107.

At steps S104, S105, and S106described above, it is determined whether to turn on the damper function based on a condition according to the vehicle speed. As described above at step S103, when the wheel loader100is operated at a low speed, it is considered that the work has a priority, so that it is more efficient that a relative position between the vehicle body and the working machine (such as the boom102and bucket101) is fixed. When a determination value of the speed is one speed, hunting operation such as turn on/off of the damper function might occur at the time of the travel at a speed near this speed. Therefore, there are two threshold speeds in a viewpoint of providing hysteresis. Meanwhile, the first threshold speed Va is a speed value larger than the second threshold speed Vd.

A main flow illustrated inFIG. 6is described again and step S110branched from steps S104and S106at the time of the positive determination is to be described later.

At step S107, the controller111determines whether the current working status is the loaded state (St=3), and when it is not in the loaded state (step S107, No), this shifts to step S112to turn off the damper function. On the other hand, as a result of the determination at step S107, when the current working status is the loaded state (St=3) (step S107, Yes), the controller111shifts to step S108.

At step S108, the controller111determines whether the boom angle is below the horizontal plane, which is the predetermined attitude, and when the boom angle is not below the horizontal plane (step S108, No), this shifts to step S112to turn off the damper function. On the other hand, as a result of the determination, when the boom angle is below the horizontal plane (step S108, Yes), the controller111shifts to step S109for checking a state in which the direction of the bucket101is operated. That is to say, the controller111determines whether the attitude of the boom102is controlled to be a predetermined attitude (attitude with the angle of elevation above the horizontal plane) from the boom angle obtained by a detection value from the boom angle sensor102-11, and turns off the damper function when the boom102is controlled to be in the predetermined attitude.

It is determined whether stable travel is possible with the damper function turned on at this step. Since a heavy burden is loaded in the bucket in the loaded state (St=3), a barycentric position of the wheel loader100is lower when the boom is located on a lower position and the stable travel becomes possible. In such a case, the damper function is turned on. On the other hand, when the barycentric position is high, the damper function is turned off. There also is operation to load the burden into the loading platform of the dump truck300in a state in which the boom102is raised above the horizontal plane or substantially vertically. In such a case, when the damper function is in the on-state, the bucket position is unstable and a predetermined or longer time might be taken to approach the dump truck300. That is to say, step S108also is substantially the step at which it is determined whether to load the burden in the bucket101into the loading platform of the dump truck300. By turning on/off the damper function based on a determination result at this step, it becomes possible to prevent occurrence of a defect such as contact of the boom102and the bucket101with the loading platform and the like of the dump truck300by swing of the boom102, for example. Meanwhile, it goes without saying that a boom angle condition at this step and the boom angle condition of the transition condition to the loaded state (St=3) indicated in Table 1 may be identical to or different from each other, and they may be set according to an object.

Then, at step S109, the controller111detects from the bucket lever stroke signal to operate the direction of the bucket101to determine whether the bucket lever stroke is not smaller than a first threshold stroke. As a result of the determination at step S109, when the bucket lever stroke is smaller than the first threshold stroke (step S109, No), the controller111shifts to step S112to turn off the damper function. On the other hand, as the result of the determination, when the bucket lever stroke is not smaller than the first threshold stroke (step S109, Yes), the controller111shifts to step S110.

The bucket lever stroke signal indicates the operation in a tilt direction and the operation in a dump direction by positive and negative values, respectively, and it is set such that the absolute values thereof becomes larger as the operation amount of the lever is larger. The bucket lever stroke signal at the time of neutral, that is to say, when there is no operation of the bucket lever is set to 0. Herein, the first threshold stroke is set to an optional value in the dump direction (negative value). This is for allowing small dump operation and tilt operation when performing operation to arrange a shape of the loaded burden and determining that large operation of the bucket101in the dump direction is performed. In this manner, by allowing the first threshold stroke to have a certain degree of margin with respect to neutral, this serves as the threshold for determining whether the operator of the wheel loader is to discharge the burden in the bucket101.

Meanwhile, it is not required to determine at steps S108and S109described above in this order and the order may be changed. Further, it may be said that it is determined to turn off the damper function at the time of the operation to load the burden into the truck300at both of two steps, so that there is a modified example to integrate them into a step at which it is determined whether to be in a loading state by further providing a switch indicating transition to the “loading state” to check on/off and by providing a “loading state” as the working state illustrated in Table 1 to allow the transition of the state according to conditional determination at steps S108and S109.

Next, at step S110, the controller111detects from the boom lever stroke signal, which operates the angle of elevation of the boom102(boom angle), and determines whether the boom lever stroke is not smaller than a second threshold stroke. Meanwhile, it shifts to this step not only from step S109but also from the determination to turn on the damper function at steps S104and S106described above.

The boom lever stroke signal determined at this step S110is set such that the signal in a neutral state without the operation is 0, the operation to raise the boom and the operation to lower the boom are represented by the positive and negative values, respectively, and the larger the operation amount of the lever, the larger the absolute value thereof. The second threshold stroke value is set to a negative value. That is to say, a state in which the value is smaller than the second threshold stroke value is a state in which large and rapid lowering of the boom is performed.

In such operation, the pressurized oil on the bottom side of the lift cylinder is rapidly drained, so that pressure of the pressurized oil on the bottom side becomes the pressure near atmosphere pressure. Therefore, when the damper function is in the on-state, pressure in the accumulator117connected to the bottom side is decreased to the pressure near the atmosphere pressure. A case in which the damper function is turned off and then turned on in this state is considered. The damper function is turned on when it transits to the loaded state (St=3), so that the hydraulic pressure capable of bearing a weight of the burden is generated on the bottom side of the lift cylinder. Then, if the pressure in the accumulator is substantially 0 (near the atmosphere pressure) when the damper function is turned on, the pressurized oil on the bottom side flows into the accumulator, and as a result, a phenomenon that the boom is temporarily lowered occurs. It is required that the accumulator117maintains certain pressure in order to decrease the lowering phenomenon and prevent the operator from feeling discomfort when the dump function is turned on. Then, at step S110, it is determined that the boom is rapidly lowered when the operation signal of the boom stroke lever is smaller than the second threshold stroke value to turn off the damper function. According to this, the communication of the pressurized oil between the bottom side and the accumulator is blocked. However, since step S110is for obtaining the above-described function, this may be made the step to make the detected pressure of the bottom pressure detector119the signal to turn off the damper function when a pressure value is not larger than an optional threshold.

Then, as a result of the determination at step S110, when the boom lever stroke is smaller than the second threshold stroke (step S110, No), the controller111shifts to step S112to turn off the damper function. On the other hand, when the boom lever stroke is not smaller than the second threshold stroke as the result of the determination at step S110(step S110, Yes), the controller111turns on the damper function (step S111), and thereafter shifts to step S113. When the damper function is turned off at step S112, the controller111thereafter shifts to step S113.

At step S113, the controller111determines whether an instruction to finish the damper operation control process is input by a key switch and the like not illustrated (step S113), and when the instruction to finish is input (step S113, Yes), this finishes this damper operation control process. On the other hand, when the instruction to finish is not input (step S114, No), the controller111returns back to step S102to repeat the process at step S102and subsequent steps described above.

By operating in the above-described manner, in this embodiment, when the working status is the loaded state (St=3), the damper function is turned on irrespective of the vehicle speed, so that it is possible to prevent the burden in the bucket101from falling and ride quality during the travel from being deteriorated by the vibration and the like generated in the boom102and the like at the time of the turn. Also, in this embodiment, the damper function is turned off according to the angle (angle of elevation) of the boom102, so that it is possible to prevent contact of the boom102and the bucket101with the dump truck300by the vibration and the like of the boom102generated when loading the burden into the loading platform of the dump truck300. Further, in this embodiment, in a case in which the working status is other than the loaded state (St=3) (step S107, No), when the wheel loader100travels at a predetermined speed (first threshold speed Va or second threshold speed Vd) or higher (step S104, Yes or step S105, Yes), the damper mechanism is activated, and in a case of the loaded state (St=3) (step S107, Yes), the damper mechanism is activated even when the speed of the wheel loader100is lower than the predetermined speed (first threshold speed Va or second threshold speed Vd) (step S104, No or step S105, No). Therefore, it becomes possible to adequately activate/deactivate the damper function according to the working state such as the excavation work and carrying work.

Next, a flow of the loading work illustrated inFIG. 1is described in detail as a specific example with reference to the drawings.FIG. 7is a view for illustrating a schematic flow of the loading work illustrated inFIG. 1.FIG. 8is a sequence diagram illustrating change in each parameter in a process illustrated inFIG. 7.

As illustrated inFIG. 7, in the loading work illustrated inFIG. 1, the wheel loader100first moves forward from the start position A toward the excavation position B just before the mound200(FIG. 7(a)). In this process, as illustrated inFIG. 8(a), the working status is the unladen state (St=1) and the wheel loader100starts moving forward with a shift gear not lower than a forward second speed (F2), and thereafter, the vehicle speed becomes the first threshold speed Va or higher at timing t1. The controller111of the wheel loader100turns on the damper function on the condition that the vehicle speed becomes the first threshold speed Va or higher at the timing t1.

Next, the wheel loader100starts reducing the speed before the excavation position B (FIG. 7(b)). In this process, as illustrated inFIG. 8(b), the working status is the unladen state (St=1). The wheel loader100shifts from the shift gear not lower than the forward second speed stage (F2) to the forward first speed stage (F1) at timing t2, so that the controller111turns off the damper function at the timing t2. Thereafter, the vehicle speed is reduced from the vehicle speed not lower than the first threshold speed Va and further becomes the vehicle speed not higher than the second threshold speed Vd at timing t3. Meanwhile, in the process illustrated inFIG. 7(b), the wheel loader100reduces the speed in a state of lowering the boom102while maintaining the direction of the bucket101horizontally such that the bucket101is brought into contact with the ground.

Next, when the wheel loader100arrives at the excavation position B, this lifts up (lifts off) and tilts the bucket101several times, thereby excavating the mound200by the bucket101to load the earth and sound in the bucket101(FIG. 7(c)). In this process, as illustrated inFIG. 8(c), the working status is initially the unladen state (St=1) and the wheel loader100sticks the bucket101to the mound200at timing t4in a state in which the bucket101is brought into contact with the ground. At that time, the boom bottom pressure drastically increases at the timing t4. The controller111detects the drastic increase in the boom bottom pressure and allows the working status to transit from the unladen state (St=1) to the state during the excavation work (St=2) (refer toFIG. 1and Table 1). Thereafter, the wheel loader100tilts the bucket101several times (turns the bucket opening upward) while gradually increasing the boom angle (lifting up) to load the earth and sand in the bucket101. Therefore, the boom bottom pressure at that time changes according to the lift-up and the tilt.

Next, the wheel loader100moves backward in a state in which the earth and sand are loaded in the bucket101, thereby returning to the vicinity of the start position A (FIG. 7(d)). In this process, as illustrated inFIG. 8(d), the working status is the state during the excavation work (St=2) and the wheel loader100starts moving backward after the shift lever mechanism is moved to reverse (R) at timing t5and thereafter stops in the vicinity of the start position A. At that time, the vehicle speed becomes the first threshold speed Va or higher at timing t6, and thereafter, the vehicle speed becomes the second threshold speed Vd or lower at timing t7. The controller111detects that the shift lever mechanism is moved to reverse at the timing t5and allows the working status to transit from the state during the excavation work (St=2) to the loaded state (St=3) (refer toFIG. 1and Table 1). The controller111turns on the damper function. However, the controller111does not turn off the damper function at timing t7even when the vehicle speed becomes the second threshold speed Vd or lower because the working status is the loaded state (St=3) (refer to Table 1). According to this, it becomes possible to decrease the vibration generated in the boom102at the time of the turn, and as a result, falling of the burden from the bucket101and deterioration in the riding quality may be decreased.

Next, the wheel loader100moves toward the earth discharge position C beside the loading platform of the dump truck300by moving forward while turning (FIG. 7(e)) and subsequently reduces the speed while lifting up the bucket101to a target height (for example, height equal to or higher than the loading platform of the dump truck300) by driving the boom102, thereby moving to the earth discharge position C beside the loading platform of the dump truck300(FIG. 7(f)). In the process illustrated inFIG. 7(e), as illustrated inFIG. 8(e), first, the working status is the loaded state (St=3) and the wheel loader100starts moving forward with the shift gear not lower than the forward second speed (F2), and thereafter, the vehicle speed becomes the first threshold speed Va or higher at timing t8. However, since the damper function is already turned on at the timing t8, the controller111maintains the on-state. Subsequently, in the process illustrated inFIG. 7(f), as illustrated inFIG. 8(f), the wheel loader100starts reducing the speed with the shift gear in the forward second speed and lifts up the boom102, and thereafter, the angle of the boom102is horizontal or above the horizontal plane at timing t9. The controller111turns off the damper function on the condition that the angle of the boom is horizontal or above the horizontal plane at the timing t9. According to this, the vibration of the boom102relative to the vehicle body of the wheel loader100is less likely to be generated, so that it becomes possible to prevent the contact of the boom102and the bucket101with the dump truck300by the vibration generated in the boom102when the wheel loader100approaches the dump truck300. Meanwhile, although the vehicle speed becomes the second threshold speed Vd or lower at subsequent timing t10, the damper function is already turned off at the timing t10.

Next, the wheel loader100discharges the earth and sand in the bucket101into the loading platform of the dump truck300by dumping the bucket101in the earth discharge position C (FIG. 7(g)). In this process, as illustrated inFIG. 8(g), the working status is initially the loaded state (St=3), and thereafter, the boom bottom pressure becomes threshold pressure Tp or lower at timing t11because the earth and sand in the bucket101are gradually discharged. The controller111detects that the boom bottom pressure becomes the threshold pressure Tp or lower and allows the working status to transit from the loaded state (St=3) to the unladen state (St=1).

Next, the wheel loader100starts moving backward from the earth discharge position C and lifts down and tilts the bucket101by driving the boom102(FIG. 7(h)). In this process, as illustrated inFIG. 8(h), the working status is the unladen state (St=1) and the wheel loader100starts moving backward, and thereafter, the vehicle speed becomes the first threshold speed Va or higher at timing t12. The controller111turns on the damper function on the condition that the vehicle speed becomes the first threshold speed Va or higher at the timing t12. However, the boom angle is set to the predetermined angle (for example, 20 degrees) or smaller before the timing t12.

Next, the wheel loader100starts reducing the speed in the vicinity of the start position A and thereafter stops at the start position A (FIG. 7(i)). In this process, as illustrated inFIG. 8(i), the working status is the unladen state (St=1) and the wheel loader100starts reducing the speed and the vehicle speed becomes the second threshold speed Vd or lower at timing t13. The controller111turns off the damper function on the condition that the vehicle speed becomes the second threshold speed Vd or lower at the timing13.

One cycle of the excavation work and earth discharging work (loading work) is finished through the above-described processes. The wheel loader100repeats the cycle at least once to load a target amount of earth and sand into the loading platform of the dump truck300.

Meanwhile, although the switching valve control unit111B turns on the damper function also at times other than the time at which the state detecting unit111A detects that the state is the loaded state in the above-described embodiment, there is no limitation and it is also possible that the damper function is turned on when the state detecting unit111A detects that the state is the loaded state.

The above-described embodiment and the modified example thereof are merely examples for carrying out the present invention. The present invention is not limited thereto and various modifications according to specification and the like fall within the scope of the present invention, and further, it is obvious from the description above that other various embodiments are possible within the scope of the present invention. For example, it goes without saying that the modified example appropriately illustrated for each embodiment may also be applied to another embodiment.

For example, although the wheel loader is described as an example of the working vehicle in the above-described embodiment, the present invention is not limited thereto and may be applied to various working vehicles such as a skid-steer loader and a excavator. Also, although the working vehicle (wheel loader100) equipped with a hydraulic system in which the hydraulic oil is used as a transmitting medium of the drive force from the power supply is described as an example in the above-described embodiment, there is no limitation and it is also possible to apply the present invention to the working vehicle equipped with a fluid pressure system in which water and another liquid are used as the transmitting medium of the drive force.

REFERENCE SIGNS LIST

110Damper Operation Control Device

111A State Detecting Unit

111B Switching Valve Control Unit

112A Shift Operation Detector

112B Damper Function Switch

112C Boom Operating Lever Operation Amount Sensor

112D Bucket Operating Lever Operation Amount Sensor

113Vehicle Speed Sensor

116Pilot Pressure Supply Source

119Bottom Pressure Detector

122First Bucket Link

124Second Bucket Link

130Vehicle Body Front Frame

145Main Oil Passage

146,146aBranched Oil Passage

A Start Position

B Excavation Position

C Earth Discharge Position