WO2020065915A1 - Wheel loader - Google Patents

Abstract

A wheel loader is provided which can improve work efficiency even when performing digging operations while climbing a slope. This HST-type travel drive wheel loader 1 is provided with a controller 5, 5A, 5B which, during digging operations by a front work machine 2, performs control to adjust the HST motor 42 and limit the maximum traction of the vehicle body. The controller 5, 5A, 5B determines whether or not a specific condition is satisfied that specifies a digging operation of the front work machine 2 performed while the vehicle climbs a slope, and if the specific condition is satisfied, then the maximum traction of the vehicle is increased to greater than the maximum traction in the case of performing a digging operation with the front work machine 2 in a state in which the vehicle is placed on flat ground.

Description

Wheel loader

The present invention relates to a wheel loader that performs a cargo handling operation.

In a wheel loader having a hydraulic circuit for traveling and a hydraulic circuit for a front working machine for excavation, etc., the balance between the traction force (running driving force) and the excavating force of the front working machine becomes important. . If the traction force is too large for the digging force of the front work machine, the wheels slip when the bucket is pushed into the digging object and the lift arm is operated to lift the bucket upward. On the contrary, the traction force becomes small, and it becomes difficult for a load such as earth and sand to enter the bucket. Further, in this case, when the bucket is pushed into the object to be excavated, the reaction force acting on the lift arm increases, and the reaction force acts as a resistance, so that the bucket or the lift arm may not be lifted upward.

For example, Patent Literature 1 discloses, as a traveling hydraulic circuit, a variable displacement traveling hydraulic pump driven by an engine and a variable displacement traveling hydraulic motor driven by pressure oil from the hydraulic pump. A wheel loader using an HST circuit in which a traveling hydraulic pump and a traveling hydraulic motor are connected in a closed circuit by a pair of main pipelines is disclosed. In this wheel loader, when the vehicle rushes toward the ground to be excavated and takes in the load into the bucket, the maximum traction force of the HST motor is set to the upper limit value so that the maximum traction force reaches the upper limit. This makes it possible to take in sufficient load into the bucket.

Then, when performing the excavating operation of lifting the bucket upward by operating the lift arm, the maximum tilting of the HST motor is limited to about 50 to 70% of the upper limit value, so that the traction force becomes too large. In this way, the balance between the lifting operation force of the lift arm (the digging force of the front working machine) and the traction force is favorably maintained, and the lifting operation of the loaded bucket is facilitated. In this wheel loader, the operator switches the manual switch to limit the maximum tilt of the HST motor during the excavation operation in the L mode, the N mode, and the P mode according to the type of the ground and the road surface condition. Adjustment can be made in three stages.

Japanese Patent No. 5129493

掘 削 Excavation work by a wheel loader may be performed while climbing up the ground in addition to the case where the vehicle body is installed on a flat ground. Specifically, the wheel loader moves forward on a steep slope while operating the lift arm in the upward direction, excavates the slope, and discharges the load to the top of the ground. While the wheel loader is climbing a hill, a force corresponding to (weight of vehicle body × sin θ) acts on the vehicle body toward the rear of the slope. Therefore, when the excavation operation is performed on a slope, the tractive force is reduced by (the weight of the vehicle body × sin θ) as compared with the case where the excavation operation is performed while the vehicle body is installed on a flat ground.

The wheel loader described in Patent Literature 1 is based on the premise that an excavation operation is performed in a state where a vehicle body is installed on a flat ground. Therefore, when the wheel loader performs an excavation operation while climbing the ground, a tractive force is applied. Is insufficient, and it is not possible to climb the hill while operating the lift arm upward. It is conceivable that the traction force is increased by switching to the P mode in which the maximum tilt limit value of the HST motor at the time of the excavation operation is the largest by a manual switch. It is necessary to switch the manual switch to the P mode. Further, when performing an excavation operation on a flat ground after the excavation operation while climbing a slope, the operator must return the manual switch to the L mode in which the limit value of the maximum tilt of the HST motor during the excavation operation is the smallest. However, the operation is troublesome for the operator.

Therefore, an object of the present invention is to provide a wheel loader capable of improving work efficiency even when performing an excavation operation while climbing a hill.

In order to achieve the above object, the present invention provides an engine, a variable displacement traveling hydraulic pump driven by the engine, and a driving force of the engine connected to the traveling hydraulic pump in a closed circuit. To the wheels, a front working machine having a lift arm provided at the front of the vehicle body and rotatable in a vertical direction, and driven by the engine to the front working machine. A hydraulic pump for a working machine for supplying hydraulic oil, a running state detector for detecting a running state of the vehicle body, an operation amount detector for detecting a lifting operation amount of the lift arm, and excavation when the front working machine is operated. When it is determined that the vehicle is in the state, a controller that controls the traveling hydraulic pump or the traveling hydraulic motor to limit the maximum traction force of the vehicle body, The vehicle loader further includes an inclination state detector for detecting an inclination state of the vehicle body, wherein the controller is configured to control a traveling state detected by the traveling state detector, and to raise the lift arm detected by the operation amount detector. Based on the operation amount and the tilt state detected by the tilt state detector, it is determined whether or not a specific condition for specifying that the vehicle body is in an excavation state while climbing a slope is satisfied, and the specific condition is satisfied. , Wherein the maximum traction force of the vehicle body is set to be higher than the maximum traction force when the vehicle body is installed on a flat ground and is in an excavation state.

According to the present invention, the work efficiency can be improved even when the digging operation is performed while climbing a hill. Problems, configurations, and effects other than those described above will be apparent from the following description of the embodiments.

It is a side view showing the appearance of the wheel loader concerning each embodiment of the present invention. (A) is an explanatory view explaining the lifting operation of the wheel loader, and (b) is an explanatory diagram illustrating the operation of the lift arm during the lifting operation. (A) is a graph showing the relationship between the detected body tilt angle and the converted vehicle body tilt angle value, and (b) is a graph showing the relationship between the detected lift arm angle and the converted vehicle body tilt angle value. FIG. 2 is a diagram illustrating a hydraulic circuit and an electric circuit related to a traveling drive of the wheel loader according to the first embodiment of the present invention. 5 is a graph showing a relationship between an accelerator pedal depression amount and a target engine rotation speed. (A) is a graph showing the relationship between the engine speed and the displacement of the HST pump, (b) is a graph showing the relationship between the engine speed and the input torque of the HST pump, and (c) is the engine speed and the HST pump. 6 is a graph showing a relationship between the discharge flow rate and the flow rate. It is a figure showing a hydraulic circuit concerning driving of a front work machine. 4 is a graph showing a relationship between a discharge pressure of a hydraulic pump for a working machine and an opening area of a spool. FIG. 3 is a functional block diagram illustrating functions of a controller according to the first embodiment. 6 is a flowchart illustrating a flow of a process executed by the controller according to the first embodiment. It is a graph which shows the relation between the discharge pressure of the hydraulic pump for work equipment and the maximum displacement of the HST motor in the first embodiment. FIG. 9 is a diagram illustrating a hydraulic circuit and an electric circuit related to traveling drive of the wheel loader according to the second embodiment. It is a flow chart which shows a flow of processing performed by a controller concerning a 2nd embodiment. It is a graph which shows the relation between the discharge pressure of the hydraulic pump for work equipment and the maximum displacement of the HST motor in the second embodiment. It is a flow chart which shows a flow of processing performed by a controller concerning a 3rd embodiment. It is a graph which shows the relation between the discharge pressure of the hydraulic pump for work equipment and the maximum displacement of the HST motor in the third embodiment.

First, the overall configuration and operation of the wheel loader according to each embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a side view showing the appearance of the wheel loader 1 according to each embodiment of the present invention.

The wheel loader 1 includes a vehicle body including a front frame 1A and a rear frame 1B, and a front work machine 2 provided at a front portion of the vehicle body. The wheel loader 1 is an articulated work vehicle that is steered by turning a vehicle body near the center. The front frame 1A and the rear frame 1B are rotatably connected in the left and right direction by a center joint 10, and the front frame 1A is bent in the left and right direction with respect to the rear frame 1B.

A pair of left and right front wheels 11A is provided on the front frame 1A, and a pair of right and left rear wheels 11B are provided on the rear frame 1B. FIG. 1 shows only the left front wheel 11A and the rear wheel 11B of the pair of left and right front wheels 11A and the rear wheels 11B. In the following description, the “front wheel 11A and the rear wheel 11B” may be simply referred to as “ wheels 11A and 11B”.

In the rear frame 1B, the operator's cab 12, the engine room, the controller 13, and the machine room 13 in which various devices such as a hydraulic pump are housed, and the front work machine 2 are kept in balance so that the vehicle body does not tilt. And a counter weight 14 are provided. In the rear frame 1B, the operator cab 12 is disposed at the front, the counterweight 14 is disposed at the rear, and the machine room 13 is disposed between the operator cab 12 and the counterweight 14.

The front working machine 2 includes a lift arm 21 attached to the front frame 1A, a pair of lift arm cylinders 22 that expand and contract to rotate the lift arm 21 in the vertical direction with respect to the front frame 1A, A bucket 23 attached to the tip end, a bucket cylinder 24 that expands and contracts to rotate the bucket 23 in the vertical direction with respect to the lift arm 21, and a bucket 23 and the bucket cylinder that are rotatably connected to the lift arm 21. 24, and a plurality of pipes (not shown) for guiding pressure oil to a pair of lift arm cylinders 22 and bucket cylinders 24. In FIG. 1, only the lift arm cylinder 22 arranged on the left side of the pair of lift arm cylinders 22 is shown by a broken line.

The lift arm 21 rotates upward when the rod 220 of each lift arm cylinder 22 extends, and rotates downward when each rod 220 contracts. The bucket 23 tilts (rotates upward with respect to the lift arm 21) when the rod 240 of the bucket cylinder 24 extends, and dumps (rotates downward with respect to the lift arm 21) when the rod 240 contracts. I do.

The wheel loader 1 is a loading / unloading vehicle for performing a loading / unloading operation, for example, in an open pit mine or the like, for excavating earth and sand, minerals, and the like, and loading the dumped truck and the like. In the excavation work, in addition to the case where the bucket 23 rushes into the object to be excavated to excavate earth and sand, minerals, and the like in a state where the vehicle body is installed on a flat ground, the wheel loader 1 travels forward on the slope of the object to be excavated. In some cases, the bucket 23 excavates the slope. Hereinafter, the case where the wheel loader 1 performs the excavation operation while climbing a hill is referred to as “scraping work”. Next, the "pick-up work" will be specifically described with reference to FIGS.

FIG. 2A is an explanatory view for explaining the lifting operation of the wheel loader 1, and FIG. 2B is an explanatory diagram for explaining the operation of the lift arm 21 during the lifting operation. FIG. 3A is a graph showing a relationship between the detected body tilt angle and the converted value of the vehicle body tilt angle, and FIG. 3B is a graph showing a relationship between the detected angle of the lift arm and the converted value of the vehicle body tilt angle. .

As shown in FIG. 2A, the wheel loader 1 travels on a flat ground toward the ground 100 to be excavated, and operates the front work machine 2 while climbing the ground 100 as it is to cut the slope. Excavate. Then, the earth and sand, minerals, and the like that have been excavated and piled in the bucket 23 are discharged on the top of the ground 100, and then the wheel loader 1 returns to the original place on the slope while moving backward. At the time of the lifting operation, as shown in FIG. 2B, the operator operates to lift the lift arm 21 upward as it goes up the slope.

When the wheel loader 1 is traveling on level ground (state (X) shown in FIG. 2A), the lift arm 21 is at the lowest position in the movable range in the vertical direction (the position shown in FIG. 2B). (X)), when the wheel loader 1 starts climbing the ground 100 (state (Y) shown in FIG. 2A), the lift arm 21 is in the horizontal posture (the position shown in FIG. 2B). (Y), just before the wheel loader 1 discharges the load in the bucket 23 to the top of the ground 100 (state (Z) shown in FIG. 2A), the lift arm 21 is lifted upward. It is at the cut position, that is, the highest position (the position (Z) shown in FIG. 2B) in the vertical movable range.

Note that "when the wheel loader 1 starts climbing the ground 100" means that not only the front wheel 11A but also the rear wheel 11B is located on the slope of the ground 100 as shown in the state (Y) of FIG. State. At this time, the position of the lift arm 21 does not need to be exactly the horizontal position, but may be a position slightly lower than the accurate horizontal position as shown in the position (Y) in FIG. That is, the “horizontal posture” of the lift arm 21 includes an error in the vertical direction from the accurate horizontal position.

Whether or not the wheel loader 1 is climbing a slope can be determined by using a traveling state detector that detects the traveling state of the vehicle body and an inclination state detector that detects the inclination of the vehicle body. As one aspect of the tilt state detector, for example, a vehicle body tilt angle sensor 130 as a vehicle body tilt angle detector that detects a vehicle body tilt angle θ, and a lift as a lift arm angle detector that detects the angle β of the lift arm 21 An arm angle sensor 211 is used. The body tilt angle sensor 130 is attached to the rear frame 1B as shown in FIG. 2A, and the lift arm angle sensor 211 is attached to the base of the lift arm 21 as shown in FIG. I have.

When excavating in a state where the vehicle body is installed on a flat ground, only the bucket 23 is tilted. However, when performing a lifting operation, as described above, in addition to the tilt operation of the bucket 23, the lift arm is used. In order to move the vehicle body 21 upward, the inclination state of the vehicle body can also be detected by detecting the angle β of the lift arm 21. In a work vehicle such as the wheel loader 1, it is necessary to use a strong vehicle body inclination angle sensor 130 having a strong seismic resistance, which is relatively expensive. Is installed as a standard, it is possible to use the lift arm angle sensor 211 without increasing the cost.

When the vehicle body inclination angle sensor 130 is used, as shown in FIG. 3A, when the vehicle body inclination detection angle θ detected by the vehicle body inclination angle sensor 130 is 0 or more and less than a predetermined angle threshold θs, (0 ≦ θ <θs) The converted vehicle body tilt angle value is set to 0, and when the detected vehicle body tilt angle θ becomes equal to or larger than a predetermined angle threshold θs (θ ≧ θs), the converted vehicle body tilt angle value increases from 0 in a positive direction.

When the lift arm angle sensor 211 is used, as shown in FIG. 3B, if the lift arm detection angle β detected by the lift arm angle sensor 211 is equal to or greater than 0 and less than a predetermined angle threshold βs, (0 ≦ β <βs) The vehicle body inclination angle conversion value is set to 0, and when the lift arm detection angle β becomes equal to or larger than a predetermined angle threshold βs (β ≧ βs), the vehicle body inclination angle conversion value increases from 0 in a positive direction.

Here, the “predetermined angle thresholds θs, βs” are angles corresponding to when the front wheel 11A approaches the slope of the ground 100, respectively. Therefore, when the vehicle body inclination detection angle θ is equal to or greater than 0 and less than a predetermined angle threshold θs (0 ≦ θ <θs), and when the lift arm detection angle β is equal to or greater than 0 and less than a predetermined angle threshold βs ( 0 ≦ β <βs) is the state (X) shown in FIGS. 2A and 2B, respectively.

2A and 2B when the vehicle body inclination detection angle θ is the first angle threshold θ1 (θ = θ1) and when the lift arm detection angle β is the first angle threshold β1 (β = β1). This is the state of (Y) shown in (b). Therefore, the “first angle thresholds θ1, β1” are angles corresponding to when the wheel loader 1 starts climbing the ground 100, that is, when the lift arm 21 takes a horizontal posture.

2A and FIG. 2 when the vehicle body inclination detection angle θ is the second angle threshold value θ2 (θ = θ2) and when the lift arm detection angle β is the second angle threshold value β2 (β = β2). This is the state of (Z) shown in (b). Therefore, the “second angle thresholds θ2, β2” correspond to immediately before the wheel loader 1 discharges the load in the bucket 23 to the top of the ground 100, that is, when the lift arm 21 is completely lifted upward. Angle.

When the vehicle body inclination angle sensor 130 is used, as shown in FIG. 3A, it is also possible to detect the vehicle body inclination angle when the wheel loader 1 is moving down the slope while moving backward. is there.

When the wheel loader 1 performs the lifting operation, as shown in FIG. 2A, assuming that the angle of the slope with respect to the flat ground at the ground 100 is α, the force of the sin α component with respect to the weight W of the vehicle body (= W sin α) Acts toward the rear of the slope. The inclination angle α of the ground 100 is, for example, 15 ° to 25 °, and the slope of the ground 100 is relatively steep. Assuming that a traction force (driving driving force) required when performing an excavation operation in a state where the vehicle body is installed on a flat ground is F, the traction force when performing an excavation operation on a slope such as a lifting work is (F −W sin α), and the traction force is reduced by W sin α as compared with the case where the excavation operation is performed in a state where the vehicle body is installed on a flat ground.

Next, a drive system of the wheel loader 1 will be described for each embodiment.

<First embodiment>
A drive system of the wheel loader 1 according to the first embodiment of the present invention will be described with reference to FIGS.

(About the driving system)
First, a traveling drive system of the wheel loader 1 according to the first embodiment will be described with reference to FIGS.

FIG. 4 is a diagram showing a hydraulic circuit and an electric circuit of the wheel loader 1 according to the first embodiment. FIG. 5 is a graph showing the relationship between the accelerator pedal depression amount and the target engine speed. 6A is a graph showing the relationship between the engine rotation speed and the displacement of the HST pump 41, FIG. 6B is a graph showing the relationship between the engine rotation speed and the input torque of the HST pump 41, and FIG. 4) is a graph showing the relationship between the engine rotation speed and the discharge flow rate of the HST pump 41.

The wheel loader 1 according to the present embodiment includes an HST-type traveling drive device having a closed-circuit hydraulic circuit. As shown in FIG. 4, the HST-type traveling drive device stores the engine 3 and hydraulic oil. A hydraulic oil tank 40, an HST pump 41 as a traveling hydraulic pump driven by the engine 3, an HST charge pump 41A for replenishing pressure oil for controlling the HST pump 41, and a pair of HST pumps 41 An HST motor 42 as a traveling hydraulic motor connected to the HST pump 41 in a closed circuit via 400L and 400R, a forward / reverse switching valve 43 for switching the forward / backward movement of the vehicle body, and an HST pump 41, an HST motor 42, and the like. It has a controller 5 for controlling each device.

The HST pump 41 is a swash plate type or oblique axis type variable displacement hydraulic pump whose displacement is controlled according to the tilt angle. The tilt angle is adjusted by a tilt cylinder 44 driven by the action of pressure oil discharged from the HST charge pump 41A.

The HST motor 42 is a swash plate type or oblique axis type variable displacement hydraulic motor whose displacement is controlled according to the tilt angle, and transmits the driving force of the engine 3 to the wheels 11A and 11B. The tilt angle is adjusted by the regulator 420 according to the command signal output from the controller 5.

In the HST type traveling drive device, first, when an operator depresses an accelerator pedal 61 provided in the cab 12, the engine 3 rotates, and the HST pump 41 is driven by the driving force of the engine 3. The HST charge pump 41A is also driven by the driving force of the engine 3, and the pressure oil discharged from the HST charge pump 41A is guided to the tilt cylinder 44 via the forward / reverse switching valve 43.

The forward / reverse switching valve 43 is provided between the HST charge pump 41A and the tilt cylinder 44. The forward / reverse switching valve 43 is connected to a discharge line 800 connected to the discharge side of the HST charge pump 41A by a pair of main lines 800A and 800B. Further, the forward / reverse switching valve 43 is connected to left and right oil chambers 44L, 44R of the tilt cylinder 44 by a pair of pilot lines 800L, 800R.

The forward / reverse switching valve 43 has a forward position 43A for moving the vehicle forward, a reverse position 43B for moving the vehicle backward, and a neutral position 43N for stopping the vehicle, and a forward / backward switching lever provided in the cab 12. 62 is operated.

As shown in FIG. 4, when the forward / reverse switching valve 43 is at the neutral position 43N, the pressure oil discharged from the HST charge pump 41A flows through the throttle cylinder 44 via the throttle 401 provided on one main pipeline 800B. And act equally on the left and right oil chambers 44L, 44R. Accordingly, since the rod of the tilting cylinder 44 is located at the neutral position, the displacement of the HST pump 41 becomes zero, and the discharge amount of the HST pump 41 becomes zero. Therefore, the vehicle body is stopped.

On the other hand, when the forward / reverse switching valve 43 switches to the forward position 43A, the upstream pressure of the throttle 401 acts on the oil chamber 44L on the left side of the tilt cylinder 44, and the downstream side of the throttle 401 on the right oil chamber 44R. Pressure acts. Then, the rod of the tilting cylinder 44 operates rightward in FIG. 4 due to the pressure difference generated between the left and right oil chambers 44L and 44R. As a result, the tilt angle of the HST pump 41 increases, and the hydraulic oil from the HST pump 41 is guided to the HST motor 42 through the pipeline 400L, and the HST motor 42 rotates forward to move the vehicle forward.

On the other hand, when the forward / reverse switching valve 43 is switched to the reverse position 43B, the downstream pressure of the throttle 401 acts on the oil chamber 44L on the left side of the tilt cylinder 44, and the upstream side of the throttle 401 on the oil chamber 44R on the right side. Pressure acts. Then, the rod of the tilt cylinder 44 operates to the left in FIG. 4 due to the pressure difference generated between the left and right oil chambers 44L and 44R. As a result, the tilt angle of the HST pump 41 increases, and the hydraulic oil from the HST pump 41 is guided to the HST motor 42 through the pipeline 400R, and the HST motor 42 reverses and the vehicle moves backward.

As described above, when the HST motor 42 rotates with the hydraulic oil guided from the HST pump 41, the output torque from the HST motor 42 is transmitted to the front wheel 11A and the rear wheel 11B via the axle 15, and the wheel loader 1 To run. Therefore, the output torque of the HST motor 42 becomes a driving force for driving the wheel loader 1, that is, a traction force of the vehicle body.

The output torque of the HST motor 42 is represented by the product of the displacement (tilt angle) of the HST motor 42 and the traveling load pressure (= pressure of the line 400L−pressure of the line 400R). By controlling the displacement of the vehicle, the traction force of the vehicle body can be controlled.

The rotation speed of the engine 3 is adjusted by the amount of depression of the accelerator pedal 61, and the discharge amount of the HST charge pump 41A connected to the engine 3 is proportional to the rotation speed of the engine 3. Therefore, the differential pressure across the throttle 401 is proportional to the rotation speed of the engine 3, and the tilt angle of the HST pump 41 is also proportional to the rotation speed of the engine 3.

The depression amount of the accelerator pedal 61 is detected by a depression amount sensor 610 attached to the accelerator pedal 61. The number of revolutions of the engine 3 is controlled in accordance with the target engine speed in accordance with the stepping amount detected by the stepping amount sensor 610.

As shown in FIG. 5, the depression amount of the accelerator pedal 61 is proportional to the target engine rotation speed, and the target engine rotation speed increases as the depression amount of the accelerator pedal 61 increases. Then, when the depression amount of the accelerator pedal 61 becomes S2, the target engine rotation speed becomes the maximum rotation speed Nmax1.

In FIG. 5, the range of the depression amount of the accelerator pedal 61 in the range of 0 to S1 (for example, the range of 0% to 20 or 30%) is the target engine rotation speed at the predetermined minimum rotation speed Nmin regardless of the depression amount of the accelerator pedal 61. It is set as a fixed dead zone. In the range of the depression amount S2 to 100 of the accelerator pedal 61 (for example, 70 or 80% to 100%), the target engine rotation speed is maintained at the maximum target engine rotation speed Nmax regardless of the depression amount of the accelerator pedal 61. Is set to These ranges can be arbitrarily set and changed.

(6) Next, the relationship between the engine 3 and the HST pump 41 is as shown in FIGS.

As shown in FIG. 6A, when the engine rotation speed is between N1 and N2, the rotation speed N of the engine 3 is proportional to the displacement q of the HST pump 41, and the rotation speed of the engine 3 is N1. As the speed increases from N to N2 (N1 <N2), the displacement increases from 0 to a predetermined value qc. When the engine speed is equal to or higher than N2, the displacement of the HST pump 41 is constant at a predetermined value qc regardless of the engine speed.

The input torque of the HST pump 41 is the sum of the displacement and the discharge pressure (input torque = displacement volume × discharge pressure). As shown in FIG. 6B, when the engine rotation speed is between N1 and N2, the rotation speed N of the engine 3 is proportional to the input torque T of the HST pump 41, and the rotation speed of the engine 3 is N1. The input torque increases from 0 to a predetermined value Tc as the speed increases from 0 to N2. When the engine speed is equal to or higher than N2, the input torque of the HST pump 41 is constant at a predetermined value Tc regardless of the engine speed.

As shown in FIG. 6C, when the engine rotation speed is between N1 and N2, the discharge flow rate Q of the HST pump 41 and the rotation speed N of the engine 3 are in a quadratic proportional relationship, and the rotation speed of the engine 3 is As the speed increases from N1 to N2, the discharge flow rate of the HST pump 41 increases from 0 to Q1. When the engine rotation speed is equal to or higher than N2, the rotation speed N of the engine 3 and the discharge flow rate Q of the HST pump 41 have a linear proportional relationship.

Therefore, when the rotation speed N of the engine 3 increases, the discharge flow rate Q of the HST pump 41 increases, and the flow rate of the pressure oil flowing from the HST pump 41 into the HST motor 42 increases, so that the rotation speed of the HST motor 42 increases and the vehicle speed increases. Is faster. The vehicle speed is detected by the motor rotation speed sensor 72 as the rotation speed of the HST motor 42 (see FIG. 4).

As described above, in the HST traveling drive system, since the vehicle speed is controlled (shifted) by continuously increasing or decreasing the discharge flow rate of the HST pump 41, the wheel loader 1 can smoothly start and stop with less impact. Become.

As shown in FIG. 4, the pressure oil discharged from the HST charge pump 41A is also guided to the pipelines 400L and 400R through the throttle 401 and the check valves 402A and 402B. The downstream pressure of the throttle 401 is limited by a charge relief valve 403 provided on a pipe connecting the forward / reverse switching valve 43 and the hydraulic oil tank 40, and the maximum pressure of the pipes 400 </ b> L and 400 </ b> R is limited by a relief valve 404. Is done.

The HST traveling drive device according to the present embodiment is provided with a high-pressure selection valve 405 that selects the higher one of the pipeline pressures of the pipelines 400L and 400R that guide the hydraulic oil from the HST pump 41 to the HST motor 42. The pressure selected by the high-pressure selection valve 405 is input to the controller 5. Further, in the present embodiment, the vehicle body tilt angle sensor 130 is used as a tilt state detector that detects the vehicle body tilt state, and the vehicle body tilt detection angle θ detected by the vehicle body tilt angle sensor 130 is input to the controller 5. .

(About the drive system of the front work machine 2)
Next, a drive system of the front work machine 2 will be described with reference to FIGS. 4, 7, and 8. FIG.

FIG. 7 is a diagram illustrating a hydraulic circuit related to driving of the front work machine 2. FIG. 8 is a graph showing the relationship between the discharge pressure of the working machine hydraulic pump 45 and the opening area of the spool.

As shown in FIGS. 4 and 7, the wheel loader 1 includes a working machine hydraulic pump 45 driven by the engine 3 to supply hydraulic oil to the front working machine 2, and each of the lift arm cylinder 22 and the bucket cylinder 24. Operate the lift arm 21 and a control valve 46 provided between the work machine hydraulic pump 45 and controlling the flow of pressurized oil supplied from the work machine hydraulic pump 45 to the lift arm cylinder 22 and the bucket cylinder 24, respectively. And a bucket operation lever 230 for operating the bucket 23.

In this embodiment, a fixed hydraulic pump is used as the working machine hydraulic pump 45, and is connected to the control valve 46 via a first conduit 801 as shown in FIG. The discharge pressure from the working machine hydraulic pump 45 is detected by a discharge pressure sensor 75 provided on the first conduit 801, and a signal related to the detected discharge pressure is input to the controller 5. The discharge pressure sensor 75 is an example of a discharge pressure detector that detects the discharge pressure of the working machine hydraulic pump 45.

The lift arm operating lever 210 and the bucket operating lever 230 are both modes of an operating device for operating the front work machine 2, and are provided in the cab 12 (see FIG. 1). For example, when the operator operates the lift arm operation lever 210, a pilot pressure proportional to the operation amount is generated as an operation signal.

As shown in FIG. 7, the generated pilot pressure is guided to a pair of pilot lines 64L and 64R connected to a pair of pressure receiving chambers of the control valve 46, and acts on the control valve 46. Thereby, the spool in the control valve 46 strokes according to the pilot pressure, and the direction and the flow rate of the hydraulic oil are determined. The control valve 46 is connected to a bottom chamber of the lift arm cylinder 22 by a second pipe 802, and connected to a rod chamber of the lift arm cylinder 22 by a third pipe 803.

作 動 Hydraulic oil discharged from the working machine hydraulic pump 45 is guided to the first pipeline 801 and is guided to the second pipeline 802 or the third pipeline 803 via the control valve 46. When the hydraulic oil is led to the second conduit 802, it flows into the bottom chamber of the lift arm cylinder 22, whereby the rod 220 of the lift arm cylinder 22 is extended and the lift arm 21 is raised. On the other hand, when the hydraulic oil is guided to the third conduit 803, it flows into the rod chamber of the lift arm cylinder 22, the rod 220 of the lift arm cylinder 22 contracts, and the lift arm 21 descends.

In this embodiment, each of the lift arm operation lever 210 and the bucket operation lever 230 is a hydraulic lever, but an electric lever may be used. In this case, a current value corresponding to the operation amount is used as an operation signal. Is generated as

The pilot pressure is detected by a pilot pressure sensor 76 as an operation signal sensor for detecting an operation signal according to the lift operation amount of the lift arm 21. The pilot pressure sensor 76 is provided on a pilot line (the pilot line 64R in FIG. 7) corresponding to the lifting operation of the lift arm 21. The pilot pressure sensor 76 is an embodiment of an operation signal detector that detects an operation signal from a lift arm operation lever 210 as an operation device.

As shown in FIG. 8, the lifting operation amount of the lift arm operation lever 210 and the opening area of the spool of the control valve 46 are in a proportional relationship, and the opening area of the spool increases as the lifting operation amount of the lift arm operation lever 210 increases. Become. Therefore, when the lift arm operation lever 210 is largely operated in the direction in which the lift arm 21 is raised, the amount of hydraulic oil flowing into the lift arm cylinder 22 increases, and the rod 220 elongates quickly. That is, as the operation amount of the lift arm operation lever 210 increases, the operation speed of the lift arm 21 increases.

In FIG. 8, the range of 0 to 10% of the lifting operation amount of the lift arm operation lever 210 is set as a dead zone where the spool does not open even when the lift arm operation lever 210 is operated and the opening area is 0%. In the range of 85-100% of the lifting operation amount of the lift arm operation lever 210, the opening area of the spool is constant at 100%, and the full lever operation state is maintained. Note that these setting ranges can be arbitrarily changed.

Since the discharge pressure of the working machine hydraulic pump 45 and the pilot pressure, which is an operation signal, respectively correspond to the lifting operation amount of the lift arm 21, both the discharge pressure sensor 75 and the pilot pressure sensor 76 This is an embodiment of an operation amount detector that detects the amount of operation of raising the lift arm 21 by the arm operation lever 210.

In order to accurately detect the lifting operation amount of the lift arm 21, it is desirable to use both the values detected by the discharge pressure sensor 75 and the pilot pressure sensor 76, respectively. 75 and / or pilot pressure sensor 76 may be used. In the present embodiment, the controller 5 determines the lifting operation of the lift arm 21 using the discharge pressure Pa detected by the discharge pressure sensor 75.

Regarding the operation of the bucket 23, similarly to the operation of the lift arm 21, the pilot opening generated according to the operation amount of the bucket operation lever 230 acts on the control valve 46, so that the opening area of the spool of the control valve 46 is controlled. Then, the amount of hydraulic oil flowing into and out of the bucket cylinder 24 is adjusted. Although not shown in FIG. 7, sensors and the like for detecting the operation of the bucket 23 are also provided on each pipeline of the hydraulic circuit.

(Configuration of controller 5)
Next, the configuration of the controller 5 will be described with reference to FIG.

FIG. 9 is a functional block diagram illustrating functions of the controller 5 according to the first embodiment.

The controller 5 includes a CPU, a RAM, a ROM, a HDD, an input I / F, and an output I / F connected to each other via a bus. Various operating devices such as a forward / reverse switching lever 62 and various sensors such as a discharge pressure sensor 75, a stepping amount sensor 610, and a vehicle body tilt angle sensor 130 are connected to an input I / F, and a regulator 420 of the HST motor 42 is connected. Are connected to the output I / F.

In such a hardware configuration, the CPU reads an arithmetic program (software) stored in a recording medium such as a ROM, an HDD, or an optical disk, expands the arithmetic program on a RAM, and executes the expanded arithmetic program to execute arithmetic processing. The program and the hardware cooperate to realize the function of the controller 5.

In the present embodiment, the configuration of the controller 5 is described by a combination of software and hardware. However, the present invention is not limited to this, and an integrated circuit that realizes the function of an arithmetic program executed on the wheel loader 1 side may be used. You may comprise using it.

As shown in FIG. 9, the controller 5 includes a data acquisition unit 51, a specific condition determination unit 52, a motor control unit 53, and a storage unit 54.

The data acquisition unit 51 outputs a forward / reverse forward / backward switching signal output from the forward / backward switching lever 62, a depression amount of the accelerator pedal 61 detected by the depression amount sensor 610, and a working machine detected by the discharge pressure sensor 75. Data on the discharge pressure Pa of the hydraulic pump 45 and data on the vehicle body inclination detection angle θ (the amount of inclination) detected by the vehicle body inclination angle sensor 130 are acquired.

The specific condition determination unit 52 determines whether or not a specific condition for specifying that the wheel loader 1 is in an excavation state while climbing a slope is based on the signal and each data acquired by the data acquisition unit 51.

Specifically, the specific condition determination unit 52 determines the forward traveling of the wheel loader 1 based on the forward / reverse switching signal and the amount of depression of the accelerator pedal 61, and determines the front based on the discharge pressure Pa of the hydraulic pump 45 for work equipment. A determination on the excavation operation of the work implement 2 and a determination on the tilt state of the vehicle body based on the vehicle body tilt detection angle θ are performed. The specific condition determination unit 52 determines whether or not the specific condition is satisfied by performing the determination on these three conditions.

Here, each of the forward / reverse switching lever 62 and the depression amount sensor 610 is one mode of a traveling state detector that detects the traveling state of the vehicle body of the wheel loader 1. In the present embodiment, the forward traveling of the vehicle body is determined based on the forward / backward switching signal indicating forward traveling output from the forward / backward switching lever 62 and the depression amount of the accelerator pedal 61 detected by the depression amount sensor 610. The traveling state detected by another traveling state detector mounted on the vehicle body, such as, for example, detecting whether the traveling direction of the vehicle body is forward or backward based on the rotation direction of the propeller shaft. Based on this, the forward running of the vehicle body may be determined comprehensively.

When the specific condition determination unit 52 determines that the specific conditions are satisfied, the motor control unit 53 performs a maximum displacement volume qs (hereinafter, referred to as a “displacement volume”) when the excavation operation is performed by the front work machine 2 in a state where the vehicle body is installed on a flat ground. A command signal based on a maximum displacement larger than “maximum displacement qs at the time of flat ground excavation operation” is output to the regulator 420 of the HST motor 42, and the maximum displacement qmax of the HST motor 42 is set at the maximum during the flat land excavation operation. The displacement is increased above the displacement volume qs.

If the specific condition determination unit 52 does not satisfy the specific condition and the vehicle body is installed on a flat ground and is in an excavation state, the motor control unit 53 outputs a command signal based on the maximum displacement qs during the flat ground excavation operation to the HST. Output to the regulator 420 of the motor 42 to limit the maximum displacement qmax of the HST motor 42 to the maximum displacement qs at the time of level ground excavation operation.

The storage unit 54 stores a discharge pressure Ps (a discharge pressure of a hydraulic pressure source for extending the lift arm cylinder 22) of the work machine hydraulic pump 45 necessary for the excavation operation, a first angle threshold θ1 that is a threshold related to a vehicle body inclination angle, and a second angle threshold. The angle threshold value θ2 and the maximum displacement qs at the time of the flat ground excavation operation are stored.

(Processing in Controller 5 and Operation of Wheel Loader 1)
Next, the flow of a specific process executed in the controller 5 and the operation of the wheel loader 1 under the control of the controller 5 will be described with reference to FIGS.

FIG. 10 is a flowchart showing a flow of processing executed by the controller 5 according to the first embodiment. FIG. 11 is a graph showing the relationship between the discharge pressure Pa of the working machine hydraulic pump 45 and the maximum displacement qmax of the HST motor 42 in the first embodiment.

First, the data acquisition unit 51 acquires the depression amount of the accelerator pedal 61 output from the depression amount sensor 610 and the forward / reverse switching signal output from the forward / reverse switching lever 62 (step S501). Next, the specific condition determination unit 52 determines whether or not the wheel loader 1 is traveling forward based on the stepping amount and the forward / reverse switching signal acquired in step S501 (step S502).

When it is determined in step S502 that the wheel loader 1 is traveling forward (step S502 / YES), the data acquiring unit 51 determines the discharge pressure Pa of the working machine hydraulic pump 45 output from the discharge pressure sensor 75. It is acquired (step S503).

Next, the specific condition determination unit 52 determines whether or not the discharge pressure Pa is equal to or higher than the discharge pressure Ps of the working machine hydraulic pump 45 necessary for the excavation operation, based on the discharge pressure Pa acquired in step S503. (Step S504).

If it is determined in step S504 that the discharge pressure Pa is equal to or higher than the discharge pressure Ps of the work equipment hydraulic pump 45 required for the excavation operation (Pa ≧ Ps) (step S504 / YES), the data acquisition unit 51 determines whether the vehicle body tilt The vehicle body inclination detection angle θ output from the angle sensor 130 is obtained (step S505).

Subsequently, the specific condition determination unit 52 determines whether or not the vehicle body inclination detection angle θ is equal to or greater than 0 and less than the first angle threshold θ1 based on the vehicle body inclination detection angle θ acquired in step S505. (Step S506).

If it is determined in step S506 that the vehicle body inclination detection angle θ is equal to or greater than 0 and less than the first angle threshold θ1 (0 ≦ θ <θ1) (step S506 / YES), the vehicle body is not climbing a hill. The motor control unit 53 limits the maximum displacement qmax of the HST motor 42 to the maximum displacement qs at the time of the flatland excavation operation (step S507).

If it is determined in step S506 that the vehicle body inclination detection angle θ is equal to or greater than 0 and is not less than the first angle threshold θ1 (step S506 / NO), the specific condition determination unit 52 then proceeds to step S506. It is determined whether the angle is equal to or more than the first angle threshold θ1 and less than the second angle threshold θ2 (step S508).

If it is determined in step S508 that the vehicle body inclination detection angle θ is equal to or larger than the first angle threshold θ1 and smaller than the second angle threshold θ2 (θ1 ≦ θ <θ2) (step S508 / YES), the specific condition is satisfied. Therefore, the motor control unit 53 limits the maximum displacement qmax of the HST motor 42 to a first maximum displacement q1 (> qs) that is larger than the maximum displacement qs at the time of level digging operation (step S509). That is, in step S509, the motor control unit 53 raises the maximum displacement qmax of the HST motor 42 to be larger than the maximum displacement qs during the level ground excavation operation.

When it is determined in step S508 that the vehicle body inclination detection angle θ is equal to or greater than the first angle threshold θ1 and not less than the second angle threshold θ2 (step S508 / NO), the specific condition determination unit 52 subsequently performs the vehicle body inclination detection It is determined whether or not the angle θ is the second angle threshold θ2 (step S510).

If it is determined in step S510 that the vehicle body inclination detection angle θ is the second angle threshold θ2 (θ = θ2) (step S510 / YES), the motor control unit 53 determines that the HST motor 42 The maximum displacement qmax is limited to a second maximum displacement q2 (> q1) that is even larger than the first maximum displacement q1 (step S511). That is, in step S511, the motor control unit 53 further increases the maximum displacement qmax of the HST motor 42 beyond the maximum displacement qs and the first maximum displacement q1 during the leveling operation.

{Circle around (5)} When the respective processes of step S507, step S509, and step S511 are executed, the controller 5 returns to step S503. When it is determined in step S502 that the vehicle is not traveling forward (step S502 / NO), the discharge pressure Pa is less than the discharge pressure Ps of the work machine hydraulic pump 45 required for the excavation operation (Pa <Ps) in step S504. ) (Step S504 / NO) and when it is determined in step S510 that the vehicle body inclination detection angle θ is not the second angle threshold θ2 (θ ≠ θ2) (step S510 / NO), Since the condition is not satisfied, the processing in the controller 5 ends.

As described above, when the specific conditions are satisfied, that is, during the lifting operation of the wheel loader 1, the maximum displacement qmax of the HST motor 42 is automatically increased as shown in FIG. Since the maximum traction force of the vehicle body is higher than the maximum traction force at the time of level ground excavation operation by raising the vehicle body, the traction force of Wsinα, which has been reduced as compared with the level at the time of level ground excavation, can be compensated. This improves the work efficiency not only in the case of performing the excavation operation in a state where the vehicle body is installed on a flat ground, but also in the case of the lifting operation in which the vehicle body performs the excavation operation while traveling forward (uphill) on a steep slope. I can do it.

In the present embodiment, when the vehicle body inclination detection angle θ is equal to or larger than the first angle threshold θ1 and smaller than the second angle threshold θ2 (θ1 ≦ θ <θ2), the controller 5 sets the maximum of the HST motor 42 to the maximum. While the displacement qmax is increased from the maximum displacement qs during the flat terrain excavation operation to the first maximum displacement q1 (from the two-dot chain line shown in FIG. 11 to the one-dot chain line shown in FIG. 11), the vehicle body inclination detection angle θ becomes the second displacement. When the angle threshold value is θ2 (θ = θ2), the maximum displacement qmax of the HST motor 42 is increased from the maximum displacement qs during the flat terrain operation to the second maximum displacement q2 (> q1) (see FIG. 11). From the two-dot chain line to the solid line shown). That is, the larger the vehicle body inclination detection angle θ is, the larger the rate of increase of the maximum displacement of the HST motor 42 is. For this reason, the maximum traction force of the vehicle body can be more accurately controlled according to the angle of the slope of the ground 100.

<Second embodiment>
Next, a wheel loader 1 according to a second embodiment of the present invention will be described with reference to FIGS. 12 to 14, the same components as those described for the wheel loader 1 according to the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 12 is a diagram illustrating a hydraulic circuit and an electric circuit related to traveling drive of the wheel loader 1 according to the second embodiment. FIG. 13 is a flowchart illustrating a flow of a process executed by the controller 5A according to the second embodiment. FIG. 14 is a graph showing the relationship between the discharge pressure Pa of the working machine hydraulic pump 45 and the maximum displacement qmax of the HST motor 42 in the second embodiment.

As shown in FIG. 12, the wheel loader 1 according to the present embodiment has a vehicle body during an excavation operation according to the hardness and specific gravity of earth and sand, minerals, and the like forming the ground 100, the state of the road surface at the work site, and the like. Is provided with a mode changeover switch 60 for switching the maximum traction force into three stages of a P mode, an N mode and an L mode. The mode switch 60 is a manual switch, and is provided in the cab 12 (see FIG. 1). The mode switching signal output from the mode switch 60 is input to the controller 5A.

The P mode is a mode in which the maximum traction force is minimized, the N mode is a case in which the maximum traction force is larger than that in the P mode, and the L mode is a case in which the maximum traction force is larger than that in the N mode. This is the case. The operator can perform the excavation work efficiently according to the environment of the site by switching the mode changeover switch 60 and selecting the optimum mode.

Further, in the present embodiment, unlike the first embodiment, a lift arm angle sensor 211 (lift arm angle detector) for detecting the angle of the lift arm 21 is used for the tilt state detector for detecting the tilt state of the vehicle body. . Therefore, in the controller 5A, the specific condition determination unit 52 determines the tilt state of the vehicle body based on the lift arm detection angle β output from the lift arm angle sensor 211.

Furthermore, the controller 5A is different from the controller 5 according to the first embodiment in how to increase the maximum traction force when specific conditions are satisfied. Specifically, as the lift arm detection angle β detected by the lift arm angle sensor 211 increases, the controller 5A determines that the discharge pressure Pa () of the working machine hydraulic pump 45 at the time of starting to limit the maximum traction force of the vehicle body. The value of the lift operation amount of the lift arm 21) is increased.

As shown in FIG. 13, when it is determined in step S504 that the discharge pressure Pa is equal to or higher than the discharge pressure Ps of the work machine hydraulic pump 45 required for the excavation operation (Pa ≧ Ps) (step S504 / YES), The acquisition unit 51 acquires the lift arm detection angle β (Step S505A).

Subsequently, the specific condition determination unit 52 determines whether or not the lift arm detection angle β is equal to or larger than 0 and smaller than the first angle threshold β1 based on the lift arm detection angle β acquired in step S505A ( Step S506A).

If it is determined in step S506A that the lift arm detection angle β is equal to or greater than 0 and less than the first angle threshold β1 (0 ≦ β <β1) (step S506A / YES), the motor control unit 53 determines in step S503. When the acquired discharge pressure Pa is the discharge pressure Ps necessary for the excavation operation (Pa = Ps), the maximum displacement qmax is limited to any of qP, qN, and qL (step S507A).

When it is determined in step S506A that the lift arm detection angle β is equal to or greater than 0 and is not less than the first angle threshold β1 (step S506A / NO), subsequently, the specific condition determination unit 52 determines that the lift arm detection angle β It is determined whether or not the angle is equal to or larger than the first angle threshold β1 and smaller than the second angle threshold β2 (step S508A).

If it is determined in step S508A that the lift arm detection angle β is equal to or larger than the first angle threshold β1 and smaller than the second angle threshold β2 (β1 ≦ β <β2) (step S508A / YES), the specific condition is satisfied. Therefore, when the discharge pressure Pa acquired in step S503 is the first pressure threshold P1 (> Ps) larger than the discharge pressure Ps necessary for the excavation operation (Pa = P1), the motor control unit 53 sets the maximum displacement qmax. Is limited to qP, qN, or qL (step S509A).

It should be noted that the limit value qP is set when the P mode is selected by the mode changeover switch 60, the limit value qN is set when the N mode is selected by the mode changeover switch 60, and the limit value qL is set by the mode changeover switch 60. This is a limit value relating to the maximum displacement volume qmax of the HST motor 42 when the L mode is selected.

When it is determined in step S508A that the lift arm detection angle β is equal to or greater than the first angle threshold β1 and is not less than the second angle threshold β2 (step S508A / NO), the specific condition determination unit 52 subsequently performs lift arm detection. It is determined whether the angle β is the second angle threshold β2 (step S510A).

If it is determined in step S510A that the lift arm detection angle β is the second angle threshold β2 (β = β2) (step S510A / YES), the motor control unit 53 acquires the information in step S503 because the specific condition is satisfied. When the discharged discharge pressure Pa is a second pressure threshold P2 (> P1) that is still larger than the first pressure threshold P1 (Pa = P2), the maximum displacement qmax is limited to any of qP, qN, and qL (step). S511A).

As shown in FIG. 14, when the lift arm detection angle β is equal to or larger than the first angle threshold β1 and smaller than the second angle threshold β2 (β1 ≦ β <β2), the maximum displacement qmax of the HST motor 42 is reduced. The discharge pressure Pa at the start of the restriction is set to a first pressure threshold P1 (> Ps) larger than the discharge pressure Ps necessary for the excavation operation, and the lift arm detection angle β is the second angle threshold β2 (β = β2 In ()), the discharge pressure Pa at the start of the limitation of the maximum displacement qmax of the HST motor 42 is set to the discharge pressure Ps necessary for the excavation operation and the second pressure threshold P2 larger than the first pressure threshold P1.

It is desirable that the discharge pressure Pa when the limitation of the maximum traction force of the vehicle body is started be equal to or higher than the discharge pressure when the lift arm 21 takes a horizontal posture. In the present embodiment, this corresponds to the first pressure threshold value P1, which is the discharge pressure at the time when the limitation of the maximum traction force of the vehicle body is started when the lift arm detection angle β reaches the first angle threshold value β1.

Also in the present embodiment, the maximum towing force of the vehicle body can be controlled more accurately according to the angle of the slope of the ground 100 in the same manner as in the first embodiment. Improvement can be achieved.

<Third embodiment>
Next, a wheel loader 1 according to a third embodiment of the present invention will be described with reference to FIGS. In FIGS. 15 and 16, the same components as those described for the wheel loader 1 according to the first embodiment and the second embodiment are denoted by the same reference numerals, and description thereof is omitted.

FIG. 15 is a flowchart showing the flow of processing executed by the controller 5B according to the third embodiment. FIG. 16 is a graph showing the relationship between the discharge pressure Pa of the working machine hydraulic pump 45 and the maximum displacement qmax of the HST motor 42 in the third embodiment.

コ ン ト ロ ー ラ The controller 5B according to the present embodiment is different from the controller 5 according to the first embodiment and the controller 5A according to the second embodiment in how to increase the maximum traction force when specific conditions are satisfied. Specifically, as the lift arm detection angle β detected by the lift arm angle sensor 211 increases, the controller 5B increases the rate of increase of the discharge pressure Pa of the working machine hydraulic pump 45 with respect to the maximum amount of traction of the vehicle body. I'm making it big.

As shown in FIG. 15, when it is determined in step S506A that the lift arm detection angle β is equal to or larger than 0 and smaller than the first angle threshold β1 (0 ≦ β <β1) (step S506A / YES), the motor control is performed. As shown in FIG. 16, the unit 53 increases the discharge pressure Pa of the working machine hydraulic pump 45 from a discharge pressure Ps necessary for excavation operation to a fourth pressure threshold P4 (> Ps) larger than the discharge pressure Ps. , The maximum displacement qmax of the HST motor 42 is gradually limited from 100% to any one of qP, qN, qL (step S507B).

As shown in FIG. 15, when it is determined in step S508A that the lift arm detection angle β is equal to or larger than the first angle threshold β1 and smaller than the second angle threshold β2 (β1 ≦ β <β2) (step S508A). / YES), as shown in FIG. 16, the motor control unit 53 determines that the discharge pressure Pa of the working machine hydraulic pump 45 is greater than the fourth pressure threshold P4 from the discharge pressure Ps required for the excavation operation. As it increases to P5 (> P4), the maximum displacement qmax of the HST motor 42 is gradually limited from 100% to any of qP, qN, and qL (step S509B).

Then, as shown in FIG. 15, when it is determined in step S510A that the lift arm detection angle β is the second angle threshold β2 (β = β2) (step S510A / YES), the motor control unit 53 performs the processing shown in FIG. As the discharge pressure Pa of the working machine hydraulic pump 45 increases from the discharge pressure Ps required for excavation operation to a sixth pressure threshold P6 (> P5) larger than the fifth pressure threshold P5, as shown in FIG. The maximum displacement qmax of 42 is gradually limited from 100% to any of qP, qN, qL (step S511B).

As described above, also in the present embodiment, the maximum traction force of the vehicle body can be controlled more accurately in accordance with the angle of the slope of the ground 100 as in the first embodiment and the second embodiment. In addition, the work efficiency during the scraping operation can be improved.

The embodiments of the present invention have been described above. Note that the present invention is not limited to the above embodiments, and includes various other modifications. For example, each of the above embodiments has been described in detail in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to those having all the described configurations. Further, a part of the configuration of each embodiment can be replaced with the configuration of another embodiment, and the configuration of each embodiment can be added to the configuration of each embodiment. Furthermore, for a part of the configuration of each embodiment, it is possible to add, delete, or replace another configuration.

For example, in each of the above embodiments, the working machine hydraulic pump 45 is a fixed displacement hydraulic pump, but is not limited thereto, and a variable displacement hydraulic pump may be used.

In the above embodiments, the maximum displacement of the wheel loader 1 is controlled by adjusting the maximum displacement qmax of the HST motor 42. However, the present invention is not limited to this. For example, the displacement of the HST pump 41 is adjusted. Thereby, the maximum traction force of the wheel loader 1 may be controlled.

1: Wheel loader 2: Front work machine 3: Engine 5, 5A, 5B: Controller 11A: Front wheel (wheel)
11B: rear wheel (wheel)
21: Lift arm 41: HST pump (hydraulic pump for traveling)
42: HST motor (hydraulic motor for traveling)
45: Hydraulic pump for work equipment 62: Forward / backward switching lever (running state detector)
75: Discharge pressure sensor (operating amount detector)
76: Pilot pressure sensor (operation signal detector, operation amount detector)
130: Body tilt angle sensor (body tilt angle detector, body tilt state detector)
211: Lift arm angle sensor (lift arm angle detector, body tilt state detector)
610: Depressed amount sensor (running state detector)

Claims (8)

1. An engine, a variable displacement traveling hydraulic pump driven by the engine, and a variable displacement traveling hydraulic motor connected to the traveling hydraulic pump in a closed circuit to transmit the driving force of the engine to wheels A front working machine provided at a front portion of a vehicle body and having a lift arm rotatable in a vertical direction; a working machine hydraulic pump driven by the engine to supply hydraulic oil to the front working machine; A traveling state detector that detects a traveling state of the vehicle body, an operation amount detector that detects an operation amount of raising the lift arm, and an operation amount detector that is operated when the front work machine is operated and is in an excavation state. A controller that controls a hydraulic pump or the traveling hydraulic motor to limit a maximum traction force of the vehicle body, and a wheel loader including:
   Having an inclination state detector for detecting an inclination state of the vehicle body,
   The controller is
   Based on the traveling state detected by the traveling state detector, the lift operation amount of the lift arm detected by the operation amount detector, and the inclination state detected by the inclination state detector, the vehicle body climbs uphill. While determining whether or not a specific condition for specifying that the state is excavation,
   A wheel loader, wherein when the specific condition is satisfied, the maximum traction force of the vehicle body is made higher than the maximum traction force when the vehicle body is installed on a flat ground and is in an excavation state.
2. The wheel loader according to claim 1,
   A discharge pressure detector for detecting a discharge pressure of the working machine hydraulic pump,
   An operation signal detector that detects an operation signal according to a lifting operation amount of the lift arm,
   The wheel loader, wherein the operation amount detector is at least one of the discharge pressure detector and the operation signal detector.
3. The wheel loader according to claim 1,
   The wheel loader according to claim 1, wherein the controller increases the rate of increase of the maximum traction force of the vehicle body as the amount of inclination detected by the inclination state detector increases.
4. The wheel loader according to claim 1,
   The wheel wherein the controller increases the value of the lift operation amount of the lift arm at the time of starting the limitation of the maximum traction force of the vehicle body as the inclination amount detected by the inclination state detector is larger. loader.
5. The wheel loader according to claim 4,
   A wheel loader, wherein a lift operation amount of the lift arm when the limitation of the maximum traction force of the vehicle body is started is equal to or larger than a lift operation amount of the lift arm when the lift arm takes a horizontal posture. .
6. The wheel loader according to claim 1,
   The wheel loader according to claim 1, wherein the controller increases the rate of increase of the lift operation amount of the lift arm with respect to the limit amount of the maximum traction force of the vehicle body as the inclination amount detected by the inclination state detector increases.
7. The wheel loader according to claim 1,
   The wheel loader, wherein the controller controls a maximum traction force of the vehicle body by adjusting a maximum displacement of the traveling hydraulic motor.
8. The wheel loader according to claim 1,
   The wheel loader, wherein the tilt state detector is a vehicle body tilt angle detector that detects a tilt angle of the vehicle body, or a lift arm angle detector that detects an angle of the lift arm.

Images