Patent Description:
A work vehicle equipped with a work device, such as a wheel loader, performs a dump approach operation to approach a dump truck, with load materials being in the work device. In this dump approach operation, it is necessary to prevent collision with the dump truck and load spillage by suppressing the vehicle speed while moving the work device upward. In this regard, the brake performance at low speed becomes important for the work vehicle, and therefore, the work vehicle needs to control the brake in detail.

For example, Patent Literature <NUM> discloses a brake control device for a vehicle, comprising: an operation section configured to output an operation signal for operating a brake of the vehicle; an solenoid fluid pressure control valve for the brake which is disposed in a brake working fluid pressure circuit for supplying a fluid pressure to the brake; and a control section configured to output a control signal to the solenoid fluid pressure control valve for the brake based on the operation signal from the operation section to control the brake to be actuated or released Patent Literature <NUM> discloses another work vehicle with a brake control system.

The required brake performance during the dump approach operation differs depending on a specification of a vehicle body, the weight of load materials, or the like. However, since the brake control device disclosed in Patent Literature <NUM> is configured such that the control section merely controls the brake based on the operation signal from the operation section, in order to satisfy the brake performance needed by a user, its hardware configuration has to be changed, for example, by mounting with a special brake. However, changing the hardware configuration increases the number of parts and/or requires special setting for each vehicle body, and accordingly, it is difficult to satisfy the user's demand in a flexible manner.

Therefore, an object of the present invention is to provide a work vehicle capable of satisfying a user's demand to brake performance in a flexible manner.

In order to achieve the object described above, the present invention provides.

According to the present invention, it is possible to satisfy a user's demand to brake performance in a flexible manner. The problems, configurations, and advantageous effects other than those described above will be clarified by explanation of the embodiments below.

Hereinafter, as an aspect of work vehicles according to each embodiment of the present invention, for example, a wheel loader for performing the loading work by excavating such as earth and sand and minerals and loading the excavated materials into a dump truck will be described.

Firstly, a configuration of a wheel loader <NUM> will be described with reference to <FIG>.

<FIG> is a side view of an appearance of a configuration example of the wheel loader <NUM> according to each embodiment of the present invention.

The wheel loader <NUM> is an articulated type work vehicle which is swiveled on a central portion of the vehicle body and steered thereby. Specifically, a front frame 1A that is the front part of the vehicle body and a rear frame 1B that is the rear part of the vehicle body are connected to each other by a center joint <NUM> to swivel in the left and right direction so that the front frame 1A is bent in the left and right direction with respect to the rear frame 1B.

The wheel loader <NUM> includes four wheels <NUM>. Two wheels <NUM> among them are provided, as front wheels 11A, on the left and right sides of the front frame 1A, respectively, and the remaining two wheels <NUM> are provided, as rear wheels 11B, on the left and right sides of the rear frame 1B, respectively. <FIG> illustrates, among the four wheels <NUM>, only the front wheel 11A and the rear wheel 11B provided on the left side. Note that the number of the wheels <NUM> provided on the vehicle body is not particularly limited.

On a front portion of the front frame 1A, a work device <NUM> provided to perform the loading work including operations of moving and loading load materials is attached. The work device <NUM> includes a lift arm <NUM> whose proximal end portion is attached to the front frame 1A, two lift arm cylinders <NUM> for driving the lift arm <NUM> by the extension and contraction of each rod <NUM>, a bucket <NUM> attached to the distal end portion of the lift arm <NUM>, a bucket cylinder <NUM> for driving the bucket <NUM> by the extension and contraction of a rod <NUM>, and a bell crank <NUM> rotatably connected to the lift arm <NUM> and forming a link mechanism between the bucket <NUM> and the bucket cylinder <NUM>. Although the two lift arm cylinders <NUM> are arranged side by side in the lateral direction of the vehicle body, <FIG> illustrates only one of the lift arm cylinders <NUM> which is disposed on the left side by a broken line.

When each bottom chamber of the two lift arm cylinders <NUM> is supplied with hydraulic oil and thus each rod <NUM> extends, the lift arm <NUM> rotationally moves in the upward direction with respect to the front frame 1A. When each rod chamber of the two lift arm cylinders <NUM> is supplied with hydraulic oil and thus each rod <NUM> contracts, the lift arm <NUM> rotationally moves in the downward direction with respect to the front frame 1A. The height of the lift arm <NUM> can be calculated based on an angle of the lift arm <NUM>, and thus an angle sensor <NUM> as a height sensor of the lift arm <NUM> is attached to the lift arm <NUM>.

When the bottom chamber of the bucket cylinder <NUM> is supplied with hydraulic oil and thus the rod <NUM> extends, the bucket <NUM> rotationally moves in the upward direction (tilt) with respect to the lift arm <NUM>. When the rod chamber of the bucket cylinder <NUM> is supplied with hydraulic oil and thus the rod <NUM> contracts, the bucket <NUM> rotationally moves in the downward direction (dump) with respect to the lift arm <NUM>.

The weight of the load materials, such as earth and sand and minerals, loaded in the bucket <NUM> can be detected based on the bottom pressure of the lift arm cylinders <NUM>, and thus a bottom pressure sensor <NUM> as a load sensor is attached to one of the bottom chamber sides of the lift arm cylinders <NUM>. Note that it is sufficient to attach the bottom pressure sensor <NUM> to any one of the two lift arm cylinders <NUM>. <FIG> illustrates the bottom pressure sensor <NUM> attached to the left side lift arm cylinder <NUM> by a broken line.

The rear frame 1B includes an operator's cab <NUM> provided for an operator to get in, a machine room <NUM> for accommodating therein respective devices necessary for driving the wheel loader <NUM>, and a counterweight <NUM> for balancing the vehicle body with the work device <NUM> to prevent the vehicle body from tilting. On the rear frame 1B, the operator's cab <NUM> is provided in the front thereof, the counterweight <NUM> is provided in the rear thereof, and the machine room <NUM> is provided between the operator's cab <NUM> and the counterweight <NUM>.

Next, movements of the wheel loader <NUM> during the loading work will be described with reference to <FIG> and <FIG>. The wheel loader <NUM> performs an excavation operation and a loading operation by a method called "V-shape loading".

<FIG> explains the V-shape loading performed by the wheel loader <NUM>. <FIG> explains the movements of the wheel loader <NUM> during the dump approach operation.

Firstly, the wheel loader <NUM> moves forward toward a pile <NUM> which is an object to be excavated (arrow X1 illustrated in <FIG>), and performs an excavation operation by making the bucket <NUM> thrust into the pile <NUM>. Upon completing the excavation operation, the wheel loader <NUM> temporarily moves backward to the original position (arrow X2 illustrated in <FIG>).

Next, the wheel loader <NUM> moves forward toward a dump truck <NUM> which is a loading destination, stops in front of the dump truck <NUM>, and performs a loading operation to load the load materials in the bucket <NUM> into the dump truck <NUM> (arrow Y1 illustrated in <FIG>). This movement of the wheel loader <NUM> during the loading operation can be referred to as a "dump approach movement". Note that <FIG> illustrates the wheel loader <NUM> which has stopped in front of the dump truck <NUM> by a broken line.

In this dump approach operation, as illustrated in <FIG>, firstly, the operator fully steps on an accelerator pedal (full acceleration), and also performs a lifting operation of the lift arm <NUM> (a state on the right side of <FIG>).

Next, the operator causes the lift arm <NUM> to further move in the upward direction while keeping the full acceleration state, and at the same time, adjusts the vehicle speed by stepping on a brake pedal a little so as to prevent the vehicle body from colliding with the dump truck <NUM> or prevent load collapse (a state on the center of <FIG>).

Then, the operator further steps on the brake pedal to make the vehicle body stop in front of the dump truck <NUM>, and performs a dump operation of the bucket <NUM> (a state on the left side of <FIG>), whereby the load materials in the bucket <NUM> is loaded into the dump truck <NUM>.

As illustrated in <FIG>, upon completing the loading operation, the wheel loader <NUM> moves backward to the original position (arrow Y2 illustrated in <FIG>). In this way, the wheel loader <NUM> performs the excavation operation and the loading operation while reciprocating in a V-shape between the pile <NUM> and the dump truck <NUM>.

Since the wheel loader <NUM> is required to suppress the vehicle speed by applying the brake while moving the lift arm <NUM> in the upward direction, in particular, during the dump approach operation, the brake performance at low speed is important for the wheel loader <NUM>. In the following, a brake control system of the wheel loader <NUM> will be described for each embodiment.

A brake control system according to a first embodiment will be described with reference to <FIG>.

Firstly, a hardware configuration of the brake control system of the wheel loader <NUM> will be described with reference to <FIG>.

<FIG> is a system configuration diagram illustrating a configuration example of the brake control system according to the first embodiment.

The brake control system of the wheel loader <NUM> includes brake devices 41F, 41R configured to apply a brake force to the front wheels 11A and the rear wheels 11B (four wheels <NUM>), respectively, an accumulator <NUM> configured to accumulate pressurized oil, a brake pedal <NUM> for operating the brake devices 41F, 41R, a brake valve <NUM> configured to supply a control pressure to the brake devices 41F, 41R, respectively, a solenoid proportional valve <NUM> configured to output a control pressure (hereinafter, referred to as "brake valve control pressure") to the brake valve <NUM>, a controller <NUM> configured to control the solenoid proportional valve <NUM>, a hydraulic pilot valve <NUM> configured to generate a pilot pressure in accordance with a step-on amount of the brake pedal <NUM>, and a solenoid switching valve <NUM> including two switching positions 47A, 47B.

In <FIG>, the accumulator <NUM> is illustrated as a source of the hydraulic pressure which is a source of the control pressure output from the brake valve <NUM> and the solenoid proportional valve <NUM>. The source of the hydraulic pressure is generally a hydraulic pump, on the other hand, the pressure oil accumulated in the accumulator <NUM> may be used. For example, in the event of an engine failure, the hydraulic oil accumulated in the accumulator <NUM> can be supplied to the braking devices 41F, 41R.

The brake pedal <NUM> is provided in the operator's cab <NUM> (see <FIG>). A step-on amount of the brake pedal <NUM> can be detected based on a step-on angle θ of the brake pedal <NUM> (hereinafter, simply referred to as "pedal angle θ"), and thus a potentiometer <NUM> as a step-on amount sensor is attached to the brake pedal <NUM>.

The brake valve <NUM> is arranged, in the present embodiment, on a position different from and separated away from the brake pedal <NUM> provided in the operator's cab <NUM>, which is a position closer to an axle than the operator's cab <NUM>. Arranging the brake valve <NUM> as above enables reduction of hydraulic vibration (hydraulic pulsation) transmitted from the brake valve <NUM> to the brake pedal <NUM>, thereby making it possible to suppress discomfort that the operator feels due to transmission of the hydraulic vibration and noise caused by the hydraulic vibration. Furthermore, bringing the brake valve <NUM> closer to the axle improves response of the brake more than the case where the brake valve <NUM> is arranged near the operator's cab <NUM>.

The solenoid switching valve <NUM> is configured to be switched, based on a switching command current to be output from the controller <NUM>, between a first switching position 47A for guiding the brake valve control pressure from the solenoid proportional valve <NUM> to the brake valve <NUM> and a second switching position 47B for guiding the pilot pressure generated by the hydraulic pilot valve <NUM> to the brake valve <NUM>. That is, the pilot pressure to be applied to the brake valve <NUM> is changed depending on the switching positions of the solenoid switching valve <NUM>.

As described above, the brake performance at low speed is particularly important for the wheel loader <NUM>, and therefore, the wheel loader <NUM> needs to control the brake in detail using the controller <NUM>. In this case, the solenoid switching valve <NUM> is switched to the first switching position 47A so that the brake valve control pressure from the solenoid proportional valve <NUM> is applied to the brake valve <NUM>.

On the other hand, in the case where the brake control by the controller <NUM> is not particularly necessary (the brake is to be applied directly by an operator's stepping-on operation of the brake pedal <NUM>), for example, while the wheel loader <NUM> is traveling at medium to high speed, or in the case of disconnection of a signal line connecting the controller <NUM> and the solenoid proportional valve <NUM> or termination of the output of the command current from the controller <NUM>, the solenoid switching valve <NUM> is switched to the second switching position 47B so that the pilot pressure generated by the hydraulic pilot valve <NUM> is applied to the brake valve <NUM>. This allows the wheel loader <NUM> to apply the brake quickly with good responsiveness.

In the present embodiment, the solenoid switching valve <NUM> is switched to the first switching position 47A when a value of the switching command current output from the controller <NUM> becomes more than an urging force of a spring 47C mounted on the solenoid switching valve <NUM>. Accordingly, in the case where the switching command current is not output to the solenoid switching valve <NUM> due to occurrence of an abnormality in an electric system including the controller <NUM> (switching command current=<NUM>), the solenoid switching valve <NUM> is switched to the second switching position 47B by the urging force of the spring 47C.

As described above, the wheel loader <NUM> does not depend only on the electronic brake control by the controller <NUM> but employs the brake control system using both the electronic brake control and the hydraulic brake control. As a result, even in the case where an abnormality occurs in the electric system including the controller <NUM>, it is possible to operate the brake devices 41F, 41R without anxiety.

Next, a configuration of the controller <NUM> will be described with reference to <FIG>.

<FIG> is a function block diagram illustrating functions of the controller <NUM>. <FIG> illustrates a graph showing a first control characteristic Z1 and a second control characteristic Z2 of the brake valve control pressure, which are the hydraulic brake control characteristic and the electronic brake control characteristic. <FIG> illustrates a graph showing a relation between an angle θ of the brake pedal <NUM> and a step-on force F of the brake pedal <NUM>.

The controller <NUM> is configured such that a CPU, a RAM, a ROM, an HDD, an input I/F, and an output I/F are connected to each other via a bus. Then, various operation devices and various sensors such as the bottom pressure sensor <NUM>, the potentiometer <NUM>, and a vehicle speed sensor <NUM> are connected to the input I/F while the solenoid proportional valve <NUM> and the solenoid switching valve <NUM> are connected to the output I/F. Note that the vehicle speed sensor <NUM> is configured to detect the vehicle speed based on the rotational speed of an output shaft of a transmission.

In this hardware configuration, the CPU reads out a control program (software) stored in a recording medium such as the ROM, the HDD or an optical disc, and loads and executes the control program (software) on the RAM, whereby the control program and the hardware collaborate to implement the functions of the controller <NUM>.

In the present embodiment, the controller <NUM> is described as a computer configured by a combination of software and hardware. However, the controller <NUM> is not limited thereto, and as one of the examples of configurations of other computers, an integrated circuit for implementing the functions of the control program executed on the side of the wheel loader <NUM> may be used.

The controller <NUM> stores a plurality of control characteristics each in which a correspondence relation of a brake valve control pressure Pi of the solenoid proportional valve <NUM> with respect to a pedal angle θ (step-on amount) of the brake pedal <NUM> is set. Specifically, each of the plurality of control characteristics is set such that the brake valve control pressure Pi increases as the pedal angle θ of the brake pedal <NUM> increases, and also such that, under the condition where the pedal angle θ is equal to or less than a predetermined pedal angle θth (θ≤θth), an increase rate of the brake valve control pressure Pi of the solenoid proportional valve <NUM> with respect to the pedal angle θ varies. In the present embodiment, the controller <NUM> stores eight control characteristics including the first control characteristic Z1, the second control characteristic Z2, a third control characteristic Z3, a fourth control characteristic Z4, a fifth control characteristic Z5, a sixth control characteristic Z6, a seventh control characteristic Z7, and an eighth control characteristic Z8, however, the number of control characteristics to be stored in the controller <NUM> is not particularly limited.

Note that in the following, "the first control characteristic Z1, the second control characteristic Z2, the third control characteristic Z3, the fourth control characteristic Z4, the fifth control characteristic Z5, the sixth control characteristic Z6, the seventh control characteristic Z7, and the eighth control characteristic Z8" can be collectively referred to as "the first to eighth control characteristics Z1 to Z8".

The first to eighth control characteristics Z1 to Z8 are set such that at least in a range where the pedal angle θ is equal to or less than half the maximum pedal angle θmax (maximum step-on amount) of the brake pedal <NUM> (θ≤θmax/<NUM>), the increase rate of the brake valve control pressure Pi with respect to the pedal angle θ is set to vary. That is, the range where the pedal angle θ is equal to or less than the predetermined pedal angle θth includes the range where the pedal angle θ is equal to or less than half the maximum pedal angle θ (θ≤θmax/<NUM>) of the brake pedal <NUM>, and this range corresponds to a range of the pedal angle θ at the time when the operator steps on the brake pedal <NUM> to suppress the vehicle speed (decelerate) during the dump approach operation of the wheel loader <NUM>.

<FIG> illustrates, as an example, a graph showing the first control characteristic Z1 by a chain line and a graph showing the second control characteristic Z2 by a broken line, respectively. In the range where the pedal angle θ is equal to or less than half the maximum pedal angle of the brake pedal <NUM> (θ≤θmax/<NUM>), an inclination of the graph of the first control characteristic Z1 is steeper than an inclination of the graph of the second control characteristic Z2, and thus, in the first control characteristic Z1, the brake valve control pressure Pi with respect to a certain pedal angle θ1 is Pi1, whereas, in the second control characteristic Z2, the brake valve control pressure Pi is Pi2 which is less than Pi1 (Pi1>Pi2).

Note that <FIG> illustrates the brake control characteristic of the hydraulic brake control by a solid line. In both the first control characteristic Z1 and the second control characteristic Z2 which are the brake control characteristics of the electronic brake control, the inclinations are set to be gentle more than the inclination of the brake control characteristic of the hydraulic brake control.

Furthermore, although not being illustrated in <FIG>, the other control characteristics are set such that, in the third control characteristic Z3, an inclination of the graph is gentle more than the inclination of the graph of the second control characteristic Z2, in the fourth control characteristic Z4, an inclination of the graph is gentle more than the inclination of the graph of the third control characteristic Z3, in the fifth control characteristic Z5, an inclination of the graph is gentle more than the inclination of the graph of the fourth control characteristic Z4, in the sixth control characteristic Z6, an inclination of the graph is gentle more than the inclination of the graph of the fifth control characteristic Z5, in the seventh control characteristic Z7, an inclination of the graph is gentle more than the inclination of the graph of the sixth control characteristic Z6, and in the eighth control characteristic Z8, an inclination of the graph is gentle more than the inclination of the graph of the seventh control characteristic Z7.

As described above, the controller <NUM> can arbitrarily adjust the correspondence relation of the brake valve control pressure Pi with respect to the pedal angle θ by using the first to eighth control characteristics Z1 to Z8 so as to output, from the solenoid proportional valve <NUM>, the brake valve control pressure Pi with respect to the pedal angle θ in accordance with the size of the vehicle body, the weight of the load materials in the bucket <NUM>, and/or the operation state of the vehicle body.

If a plurality of control characteristics is not set in the controller <NUM>, the required brake valve control pressure Pi varies depending on a specification of a vehicle body, the weight of load materials, and/or an operation state of the vehicle body. In this case, when the specification of the vehicle body, the weight of the load materials, and/or the operation state of the vehicle body vary, the relation between the pedal angle θ and the step-on force F of the brake pedal <NUM> also varies in accordance with the brake valve control pressure Pi.

On the other hand, in the case where the first to eighth control characteristics Z1 to Z8 are set in the controller <NUM>, as illustrated in <FIG>, even when the specification of the vehicle body, the weight of the load materials, and/or the operation state of the vehicle body vary, the relation between the pedal angle θ and step-on force F of the brake pedal <NUM> is constant regardless of the brake valve control pressure Pi, and accordingly, the operator can operate the brake devices 41F, 41R without feeling discomfort.

As illustrated in <FIG>, the controller <NUM> includes a data acquisition section <NUM>, a vehicle body state determination section <NUM>, a control characteristic selection section <NUM>, a step-on amount determination section <NUM>, a calculation section <NUM>, a command section <NUM>, a selection processing setting section <NUM>, and a storage section <NUM>.

The data acquisition section <NUM> is configured to acquire a determination signal output from a determination switch <NUM>, which will be described later, and data relating to a lift arm angle α (corresponding to a detected value of the height) detected by the angle sensor <NUM>, a bottom pressure P (corresponding to a detected value of the weight) detected by the bottom pressure sensor <NUM>, a pedal angle θ (corresponding to a detected value of the step-on amount) detected by the potentiometer <NUM>, and a vehicle speed V detected by the vehicle speed sensor <NUM>, respectively.

The vehicle body state determination section <NUM> is configured to determine an operation state of the vehicle body based on the lift arm angle α, the bottom pressure P, the pedal angle θ, and the vehicle speed V acquired by the data acquisition section <NUM>. Specifically, the vehicle body state determination section <NUM> determines whether the bottom pressure P acquired by the data acquisition section <NUM> is equal to or more than a predetermined first threshold value P1, whether the vehicle speed V acquired by the data acquisition section <NUM> is less than a predetermined second threshold value V1, and whether the lift arm angle α acquired by the data acquisition section <NUM> is less than a predetermined third threshold value α1, respectively.

The "predetermined first threshold value P1" is a threshold value serving as a reference relating to whether the load materials in the bucket <NUM> are heavy or light, the "predetermined second threshold value V1" is a threshold value serving as a reference relating to whether the traveling speed of the wheel loader <NUM> is fast or slow, and the "predetermined third threshold value α1" is a threshold value serving as a reference relating to whether the lifting height of the work device <NUM> is high or low. Each of the threshold values can be set to an arbitrary value in accordance with a specification of a vehicle body, preference of an operator, or the like.

The control characteristic selection section <NUM> is configured to select one control characteristic from the first to eighth control characteristics Z1 to Z8 based on the determination result by the vehicle body state determination section <NUM>. A specific method of selection performed by the control characteristic selection section <NUM> will be described later.

The step-on amount determination section <NUM> is configured to determine whether the pedal angle θ acquired by the data acquisition section <NUM> is more than a predetermined switching threshold value θth (predetermined pedal angle θth). The "predetermined switching threshold value θth" is a threshold value serving as a reference for switching the electronic brake control by the controller <NUM> and the hydraulic brake control using the hydraulic pilot valve <NUM>. In the present embodiment, as illustrated in <FIG>, the predetermined switching threshold value θth is a value more than half of the maximum pedal angle θmax of the brake pedal <NUM> (θth>θmax/<NUM>).

The calculation section <NUM> is configured to, in the case where the step-on amount determination section <NUM> determines that the pedal angle θ is equal to or less than the switching threshold value θth (θ≤θth), calculate the brake valve control pressure Pi corresponding to the pedal angle θ based on the one control characteristic selected by the control characteristic selection section <NUM>.

The command section <NUM> is configured to, in the case where the step-on amount determination section <NUM> determines that the pedal angle θ is equal to or less than the switching threshold value θth (θ≤θth), output a switching command current to the solenoid switching valve <NUM>, and output a command current value according to the brake valve control pressure Pi calculated by the calculation section <NUM> to the solenoid proportional valve <NUM>. The command section <NUM> is further configured to, in the case where the step-on amount determination section <NUM> determines that the pedal angle θ is more than the switching threshold value θth (θ>θth), stop the output of the switching command current to the solenoid switching valve <NUM>.

In the present embodiment, the controller <NUM> stores four different types of selection processing (first to fourth selection processing) which allow the control characteristic selection section <NUM> to select one control characteristic from the first to eighth control characteristics Z1 to Z8. The operator's cab <NUM> is provided with the determination switch <NUM> for determining one type of the selection processing from the first to fourth selection processing, and when the data acquisition section <NUM> acquires a determination signal output from the determination switch <NUM>, the selection processing setting section <NUM> sets one type of the selection processing based on the determination signal. The specific processing flows in the first to fourth selection processing will be described later.

The number of types of selection processing for selecting one control characteristic from the plurality of control characteristics is not necessarily four. The controller <NUM> may store a plurality of types of selection processing, or may store only one type of selection processing.

The storage section <NUM> is a memory, and stores the first threshold value P1, the second threshold value V1, the third threshold value α1, the switching threshold value θth, the first to eighth control characteristics Z1 to Z8, and the first to fourth selection processing, respectively.

Next, the specific flows of processing executed by the controller <NUM> will be described with reference to <FIG>.

<FIG> is a flowchart illustrating a flow of the entire processing executed by the controller <NUM>. Each of <FIG> and <FIG> is a flowchart illustrating a flow of the first selection processing. <FIG> is a flowchart illustrating a flow of the second selection processing. <FIG> is a flowchart illustrating a flow of the third selection processing. <FIG> is a flowchart illustrating a flow of the fourth selection processing.

In the present embodiment, firstly, in the controller <NUM>, when the data acquisition section <NUM> acquires the determination signal from the determination switch <NUM> (step S501/YES), the selection processing setting section <NUM> sets one type of the selection processing in accordance with the determination signal acquired in step S501 (step S502). Subsequently, the controller <NUM> executes the selection processing set in step S502 (step S503).

On the other hand, when the data acquisition section <NUM> does not acquire the determination signal from the determination switch <NUM> (step S501/NO), the selection processing setting section <NUM> cannot set one type of the selection processing from among the first to fourth selection processing.

In the first selection processing, as illustrated in <FIG>, firstly, the data acquisition section <NUM> acquires the bottom pressure P detected by the bottom pressure sensor <NUM> (step S610). Next, the vehicle body state determination section <NUM> determines whether the bottom pressure P acquired in step S610 is equal to or more than the first threshold P1 (step S611).

When it is determined in step S611 that the bottom pressure P is equal to or more than the first threshold value P1 (P≥P1) (step S611/YES), the control characteristic selection section <NUM> selects the first control characteristic Z1 from among the first to eighth control characteristics Z1 to Z8 (step S612), and the controller <NUM> ends the first selection processing.

On the other hand, when it is determined in step S611 that the bottom pressure P is less than the first threshold value P1 (P<P1) (step S611/NO), the control characteristic selection section <NUM> selects the second control characteristic Z2 from among the first to eighth control characteristics Z1 to Z8 (step S613), and the controller <NUM> ends the first selection processing.

In the first selection processing illustrated in <FIG>, the first control characteristic Z1 or the second control characteristic Z2 is selected from among the first to eighth control characteristics Z1 to Z8 based on the bottom pressure P detected by the bottom pressure sensor <NUM>, however, the first selection processing is not limited thereto. As illustrated in <FIG>, the first control characteristic Z1 or the second control characteristic Z2 may be selected from among the first to eighth control characteristics Z1 to Z8 based on the vehicle speed V detected by the vehicle speed sensor <NUM>.

Specifically, firstly, the data acquisition section <NUM> acquires the vehicle speed V detected by the vehicle speed sensor <NUM> (step S610A). Next, the vehicle body state determination section <NUM> determines whether the vehicle speed V acquired in step S610A is less than the second threshold value V1 (step S611A).

When it is determined in step S611A that the vehicle speed V is less than the second threshold value V1 (V<V1) (step S611A/YES), the control characteristic selection section <NUM> selects the first control characteristic Z1 from among the first to eighth control characteristics Z1 to Z8 (step S612), and the controller <NUM> ends the first selection processing.

On the other hand, when it is determined in step S611A that the vehicle speed V is equal to or more than the second threshold value V1 (V≥V1) (step S611A/NO), the control characteristic selection section <NUM> selects the second control characteristic Z2 from among the first to eighth control characteristics Z1 to Z8 (step S613), and the controller <NUM> ends the first selection processing.

That is, in the first selection processing, the controller <NUM> selects one of the first control characteristic Z1 and the second control characteristic Z2 based on either a more or less relation (whether the load materials in the bucket <NUM> are heavy or light) between the bottom pressure P detected by the bottom pressure sensor <NUM> and the first threshold value P1, and a more or less relation (whether the vehicle speed is high or slow) between the vehicle speed V detected by the vehicle speed sensor <NUM> and the second threshold value V1.

In the second selection processing, as illustrated in <FIG>, firstly, the data acquisition section <NUM> acquires the vehicle speed V detected by the vehicle speed sensor <NUM> and the bottom pressure P detected by the bottom pressure sensor <NUM>, respectively (step S620). Next, the vehicle body state determination section <NUM> determines whether the vehicle speed V acquired in step S620 is less than the second threshold V1 (step S621).

When it is determined in step S621 that the vehicle speed V is less than the second threshold value V1 (V<V1) (step S621/YES), subsequently, the vehicle body state determination section <NUM> determines whether the bottom pressure P acquired in step S620 is equal to or more than the first threshold value P1 (step S622).

When it is determined in step S622 that the bottom pressure P is equal to or more than the first threshold value P1 (P≥P1) (step S622/YES), the control characteristic selection section <NUM> selects the first control characteristic Z1 from among the first to eighth control characteristics Z1 to Z8 (step S623), and the controller <NUM> ends the second selection processing.

On the other hand, when it is determined in step S622 that the bottom pressure P is less than the first threshold value P1 (P<P1) (step S622/NO), the control characteristic selection section <NUM> selects the second control characteristic Z2 from among the first to eighth control characteristics Z1 to Z8 (step S624), and the controller <NUM> ends the second selection processing.

Furthermore, when it is determined in step S621 that the vehicle speed V is equal to or more than the second threshold value V1 (V≥V1) (step S621/NO), similarly to step S622, the vehicle body state determination section <NUM> determines whether the bottom pressure P acquired in step S620 is equal to or more than the first threshold value P1 (step S622A).

When it is determined in step S622A that the bottom pressure P is equal to or more than the first threshold value P1 (P≥P1) (step S622A/YES), the control characteristic selection section <NUM> selects the third control characteristic Z3 from among the first to eighth control characteristics Z1 to Z8 (step S625), and the controller <NUM> ends the second selection processing.

On the other hand, when it is determined in step S622A that the bottom pressure P is less than the first threshold value P1 (P<P1) (step S622A/NO), the control characteristic selection section <NUM> selects the fourth control characteristic Z4 from among the first to eighth control characteristics Z1 to Z8 (step S626), and the controller <NUM> ends the second selection processing.

In the second selection processing, the controller <NUM> selects one of the first to fourth control characteristics Z1 to Z4 based on the more or less relation between the bottom pressure P detected by the bottom pressure sensor <NUM> and the first threshold value P1, in addition to the more or less relation between the vehicle speed V detected by the vehicle speed sensor <NUM> and the second threshold value V1. That is, the controller <NUM> selects one of the first to fourth control characteristics Z1 to Z4 based on whether the traveling speed of the wheel loader <NUM> is high or slow and whether the load materials in the bucket <NUM> are heavy or light.

In the third selection processing, as illustrated in <FIG>, firstly, the data acquisition section <NUM> acquires the vehicle speed V detected by the vehicle speed sensor <NUM> and the lift arm angle α detected by the angle sensor <NUM>, respectively (step S630). Next, the vehicle body state determination section <NUM> determines whether the vehicle speed V acquired in step S630 is less than the second threshold value V1 (step S631).

When it is determined in step S631 that the vehicle speed V is less than the second threshold value V1 (V<V1) (step S631/YES), subsequently, the vehicle body state determination section <NUM> determines whether the lift arm angle α acquired in step S630 is less than the third threshold value α1 (step S632).

When it is determined in step S632 that the lift arm angle α is less than the third threshold value α1 (α<α1) (step S632/YES), the control characteristic selection section <NUM> selects the first control characteristic Z1 from among the first to eighth control characteristics Z1 to Z8 (step S633), and the controller <NUM> ends the second selection processing.

On the other hand, when it is determined in step S632 that the lift arm angle α is equal to or more than the third threshold value α1 (α≥α1) (step S632/NO), the control characteristic selection section <NUM> selects the second control characteristic Z2 from among the first to eighth control characteristics Z1 to Z8 (step S634), and the controller <NUM> ends the second selection processing.

When it is determined in step S631 that the vehicle speed V is equal to or more than the second threshold value V1 (V≥V1) (step S631/NO), similarly to step S632, the vehicle body state determination section <NUM> determines whether the lift arm angle α acquired in step S630 is less than the third threshold value α1 (step S632A).

When it is determined in step S632A that the lift arm angle α is less than the third threshold value α1 (α<α1) (step S632A/YES), the control characteristic selection section <NUM> selects the third control characteristic Z3 from among the first to eighth control characteristics Z1 to Z8 (step S635), and the controller <NUM> ends the second selection processing.

On the other hand, when it is determined in step S632A that the lift arm angle α is equal to or more than the third threshold value α1 (α≥α1) (step S632A/NO), the control characteristic selection section <NUM> selects the fourth control characteristic Z4 from among the first to eighth control characteristics Z1 to Z8 (step S636), and the controller <NUM> ends the second selection processing.

In the third selection processing, the controller <NUM> selects one of the first to fourth control characteristics Z1 to Z4 based on a more or less relation between the lift arm angle α detected by the angle sensor <NUM> and the third threshold value α1, in addition to the more or less relation between the vehicle speed V detected by the vehicle speed sensor <NUM> and the second threshold value V1. That is, unlike the case of the second selection processing, the controller <NUM> selects one of the first to fourth control characteristics Z1 to Z4 based on whether the traveling speed of the wheel loader <NUM> is high or slow and whether the lifting height of the work device <NUM> is high or low.

In the fourth selection processing, as illustrated in <FIG>, firstly, the data acquisition section <NUM> acquires the vehicle speed V detected by the vehicle speed sensor <NUM>, the bottom pressure P detected by the bottom pressure sensor <NUM>, and the lift arm angle α detected by the angle sensor <NUM>, respectively (step S640). Next, the vehicle body state determination section <NUM> determines whether the vehicle speed V acquired in step S640 is less than the second threshold V1 (step S641).

When it is determined in step S641 that the vehicle speed V is less than the second threshold value V1 (V<V1) (step S641/YES), subsequently, the vehicle body state determination section <NUM> determines whether the bottom pressure P acquired in step S640 is equal to or more than the first threshold value P1 (step S642).

When it is determined in step S642 that the bottom pressure P is equal to or more than the first threshold value P1 (P≥P1) (step S642/YES), the vehicle body state determination section <NUM> further determines whether the lift arm angle α acquired in step S640 is less than the third threshold value α1 (step S643).

When it is determined in step S643 that the lift arm angle α is less than the third threshold value α1 (α<α1) (step S643/YES), the control characteristic selection section <NUM> selects the first control characteristic Z1 from among the first to eighth control characteristics Z1 to Z8 (step S644), and the controller <NUM> ends the fourth selection processing.

On the other hand, when it is determined in step S643 that the lift arm angle α is equal to or more than the third threshold value α1 (α≥α1) (step S643/NO), the control characteristic selection section <NUM> selects the second control characteristic Z2 from among the first to eighth control characteristics Z1 to Z8 (step S645), and the controller <NUM> ends the fourth selection processing.

Furthermore, when it is determined in step <NUM> that the bottom pressure P is less than the first threshold value P1 (P<P1) (step S642/NO), similarly to step S643, the vehicle body state determination section <NUM> determines whether the lift arm angle α acquired in step S640 is less than the third threshold value α1 (step S643A).

When it is determined in step S643A that the lift arm angle α is less than the third threshold value α1 (α<α1) (step S643A/YES), the control characteristic selection section <NUM> selects the third control characteristic Z3 from among the first to eighth control characteristics Z1 to Z8 (step S646), and the controller <NUM> ends the fourth selection processing.

On the other hand, when it is determined in step S643A that the lift arm angle α is equal to or more than the third threshold value α1 (α≥α1) (step S643A/NO), the control characteristic selection section <NUM> selects the fourth control characteristic Z4 from among the first to eighth control characteristics Z1 to Z8 (step S647), and the controller <NUM> ends the fourth selection processing.

When it is determined in step S641 that the vehicle speed V is equal to or more than the second threshold V1 (V≥V1) (step S641/NO), similarly to step S642, the vehicle body state determination section <NUM> determines whether the bottom pressure P acquired in step S640 is equal to or more than the first threshold P1 (step S642A).

When it is determined in step S642A that the bottom pressure P is equal to or more than the first threshold value P1 (P≥P1) (step S642A/YES), similarly to step S643 and step S643A, the vehicle body state determination section <NUM> determines whether the lift arm angle α acquired in step S640 is less than the third threshold value α1 (step S643B).

When it is determined in step S643B that the lift arm angle α is less than the third threshold value α1 (α<α1) (step S643B/YES), the control characteristic selection section <NUM> selects the fifth control characteristic Z5 from among the first to eighth control characteristics Z1 to Z8 (step S648), and the controller <NUM> ends the fourth selection processing.

On the other hand, when it is determined in step S643B that the lift arm angle α is equal to or more than the third threshold value α1 (α≥α1) (step S643B/NO), the control characteristic selection section <NUM> selects the sixth control characteristic Z6 from among the first to eighth control characteristics Z1 to Z8 (step S649), and the controller <NUM> ends the fourth selection processing.

Furthermore, when it is determined in step S642A that the bottom pressure P is less than the first threshold value P1 (P<P1) (step S642A/NO), similarly to step S643, step S643A, and step S643B, the vehicle body state determination section <NUM> determines whether the lift arm angle α acquired in step S640 is less than the third threshold value α1 (step S643C).

When it is determined in step S643C that the lift arm angle α is less than the third threshold value α1 (α<α1) (step S643C/YES), the control characteristic selection section <NUM> selects the seventh control characteristic Z7 from among the first to eighth control characteristics Z1 to Z8 (step S651), and the controller <NUM> ends the fourth selection processing.

On the other hand, when it is determined in step S643C that the lift arm angle α is equal to or more than the third threshold value α1 (α≥α1) (step S643C/NO), the control characteristic selection section <NUM> selects the eighth control characteristic Z8 from among the first to eighth control characteristics Z1 to Z8 (step S652), and the controller <NUM> ends the fourth selection processing.

In the fourth selection processing, the controller <NUM> selects one of the first to eighth control characteristics Z1 to Z8 based on the more or less relation between the vehicle speed V detected by the vehicle speed sensor <NUM> and the second threshold value V1, the more or less relation between the bottom pressure P detected by the bottom pressure sensor <NUM> and the first threshold value P1, and the more or less relation between the lift arm angle α detected by the angle sensor <NUM> and the third threshold value α1. That is, the controller <NUM> selects one of the first to eighth control characteristics Z1 to Z8 based on every factor relating to the dump approach operation of the wheel loader <NUM> (whether the traveling speed of the wheel loader <NUM> is high or slow, whether the weight of the load materials in the bucket <NUM> is heavy or light, and whether the lifting height of the work device <NUM> is high or low).

As described above, the controller <NUM> stores the first to fourth selection processing which are different to each other in the methods of selecting one control characteristic from among the first to eighth control characteristics Z1 to Z8, and the operator can set the optimum one type of the selection processing from among the first to fourth selection processing by considering the working state and the traveling state, thereby enabling the wheel loader <NUM> to efficiently control the brake with high accuracy.

As illustrated in <FIG>, when the control characteristic selection section <NUM> selects one control characteristic in step S503, subsequently, the data acquisition section <NUM> acquires the pedal angle θ detected by the potentiometer <NUM> (step S504). Next, the step-on amount determination section <NUM> determines whether the pedal angle θ acquired in step S504 is more than the switching threshold value θth (step S505).

When it is determined in step S505 that the pedal angle θ is more than the switching threshold value θth (θ>θth) (step S505/YES), the command section <NUM> stops the output of the switching command current to the solenoid switching valve <NUM> (step S506), and the processing in the controller <NUM> is completed. Thus, the solenoid switching valve <NUM> is switched to the second switching position 47B so that the pilot pressure generated by the hydraulic pilot valve <NUM> is applied to the brake valve <NUM>.

On the other hand, when the step-on amount determination section <NUM> determines in step S505 that the pedal angle θ is equal to or less than the switching threshold value θth (θ≤θth) (step S505/NO), the calculation section <NUM> calculates the brake valve control pressure Pi corresponding to the pedal angle θ based on the one control characteristic selected in step S503 (step S507).

Then, the command section <NUM> outputs a switching command current to the solenoid switching valve <NUM> and outputs a command current value according to the brake valve control pressure Pi calculated in step S507 to the solenoid proportional valve <NUM> (step S508), and the processing in the controller <NUM> is completed.

Next, a controller 5A according to a second embodiment of the present invention will be described with reference to <FIG>. In <FIG>, the constituent elements common to those described for the brake control system according to the first embodiment are provided with the same reference signs, and explanation therefor is omitted. This is also applied to the third embodiment.

<FIG> is a flowchart illustrating a flow of the entire processing executed by the controller 5A according to the second embodiment.

The controller 5A according to the present embodiment differs from the controller <NUM> according to the first embodiment in the method of determining one type of selection processing from among the first to fourth selection processing. Specifically, firstly, the data acquisition section <NUM> acquires the vehicle speed V detected by the vehicle speed sensor <NUM> (step S511). Next, the selection processing setting section <NUM> determines whether the vehicle speed V acquired in step S511 is equal to or less than a determination threshold value Vth (step S512).

The "determination threshold value Vth" is a value more than the second threshold V1 (Vth>V1), which is the vehicle speed serving as a reference for determining whether which factors, namely, the vehicle speed, the weight of load materials, and the height of the lift arm <NUM>, is to be considered at the time when the controller <NUM> selects one control characteristic.

When it is determined in step S512 that the vehicle speed V is equal to or less than the determination threshold value Vth (V≤Vth) (step S512/YES), the selection processing setting section <NUM> sets, for example, the first selection processing from among the first to fourth selection processing (step S513). When the first selection processing is set in step S513, the controller 5A executes the first selection processing (step S514).

On the other hand, when it is determined in step S512 that the vehicle speed V is more than the determination threshold value Vth (V>Vth) (step S512/NO), the selection processing setting section <NUM> sets, for example, the second selection processing from among the first to fourth selection processing (step S515). When the second selection processing is set in step S515, the controller 5A executes the second selection processing (step S516).

As described above, the controller 5A may be configured to determine the traveling state of the wheel loader <NUM> in order to set one type of the selection processing from among the first to fourth selection processing. In this case, it is not necessary to provide the determination switch <NUM> which is provided in the first embodiment, and thus the controller 5A can automatically set the selection processing.

In <FIG>, the selection processing setting section <NUM> sets either the first selection processing or the second selection processing based on the vehicle speed, however, it is not limited thereto. As long as the executed processing is configured to set one type of the selection processing from among the first to fourth selection processing, the determination threshold value Vth may be arbitrarily set in accordance with the working state of the wheel loader <NUM> or the like.

Next, a brake control system according to a third embodiment of the present invention will be described with reference to <FIG>.

<FIG> is a system configuration diagram illustrating a configuration example of a brake control system according to the third embodiment.

In the first embodiment, as an example of the case where an abnormality occurs in the electric system in the brake control system, the case where a signal line connecting the controller <NUM> and the solenoid proportional valve <NUM> is disconnected or the case where the output of the command current from the controller <NUM> is terminated has been described. In the third embodiment, as another example of the case where an abnormality occurs in the electric system in the brake control system, the case where the software in a controller 5B is out of control and thus the command current continues to be output to the solenoid proportional valve <NUM> and a solenoid switching valve <NUM> will be described.

For example, in the case where the switching command current more than the urging force of the spring 47C in the solenoid switching valve <NUM> continues to be output from the controller 5B to the solenoid switching valve <NUM>, the solenoid switching valve <NUM> remains switched to the first switching position 47A. In this case, the brake valve <NUM> will continue to be controlled by the brake valve control pressure Pi from the solenoid proportional valve <NUM>, and thus the hydraulic brake control using the hydraulic pilot valve <NUM> cannot be performed.

With this regard, unlike the configuration of the solenoid switching valve <NUM> of the first embodiment, the solenoid switching valve <NUM> includes a pilot oil chamber 47D configured to cause the hydraulic pressure to be applied in the same direction as the urging force of the spring 47C. The pilot oil chamber 47D is connected to the hydraulic pilot valve <NUM> which receives the pilot pressure generated by the hydraulic pilot valve <NUM>.

Accordingly, the solenoid switching valve <NUM> is switched to the first switching position 47A when the switching command current more than the combined force of the urging force of the spring 47C and the pilot pressure applied to the pilot oil chamber 47D is applied. The pilot pressure which is set for the pilot oil chamber 47D may be arbitrarily set.

As described above, in the case where there is a possibility that the software in the controller 5B is out of control, when the operator strongly steps on the brake pedal <NUM> so as to cause the hydraulic pilot valve <NUM> to generate the pilot pressure more than the set pilot pressure of the solenoid switching valve <NUM>, the solenoid switching valve <NUM> can be switched from the first switching position 47A to the second switching position 47B. As a result, the pilot pressure generated by the hydraulic pilot valve <NUM> is applied to the brake valve <NUM>.

In the above, the embodiments of the present invention have been descried. The present invention is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above have been explained in detail in order to clarify the present invention, but are not necessarily limited to those having all the configurations described. In addition, a part of the configuration of one embodiment of the present invention can be replaced with that of other embodiments, and the configuration of other embodiments can be added to the configuration of the one embodiment. Furthermore, it is possible to add, delete, or replace another configuration with respect to a part of the configuration of the present embodiments.

For example, in the embodiments described above, the wheel loader <NUM> has been described as an aspect of work vehicles, however, the present invention is not limited thereto. The present invention can be applied to other work vehicles such as forklifts. Meanwhile, the present invention is particularly effective in the case of the wheel loader <NUM> which performs the work of loading load materials in the work device <NUM> into the dump truck <NUM> or a hopper while climbing a slope.

Claim 1:
A work vehicle comprising:
a plurality of wheels (<NUM>) provided on a vehicle body;
a work device (<NUM>) provided on a front portion of the vehicle body to perform operations of moving and loading load materials;
a brake device (41F, 41R) configured to apply a brake force to the plurality of wheels;
a brake pedal (<NUM>) for operating the brake device;
a brake valve (<NUM>) configured to control a brake pressure to be output to the brake device based on a step-on amount of the brake pedal;
a solenoid proportional valve (<NUM>) configured to output a pilot pressure to the brake valve; and
a controller configured to control the solenoid proportional valve,
wherein
the work vehicle further comprises:
a step-on amount sensor configured to detect the step-on amount of the brake pedal;
a vehicle speed sensor (<NUM>) configured to detect a vehicle speed; and
a load sensor configured to detect a weight of the load materials loaded in the work device,
the controller stores a plurality of control characteristics each of which is set such that a control pressure of the solenoid proportional valve increases as the step-on amount of the brake pedal increases, and in a case where the step-on amount is equal to or less than a predetermined step-on amount, an increase rate of the control pressure of the solenoid proportional valve with respect to the step-on amount of the brake pedal varies, and
the controller is further configured to:
in a case where the step-on amount detected by the step-on amount sensor is equal to or less than the predetermined step-on amount, select one control characteristic from among the plurality of control characteristics based on at least one of the vehicle speed detected by the vehicle speed sensor and the weight detected by the load sensor;
calculate the control pressure corresponding to the step-on amount detected by the step-on amount sensor based on the selected one control characteristic; and
output a command current value according to the calculated control pressure to the solenoid proportional valve.