JP2014190434A - Work machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a work machine which can control vehicle speed in an operation of an accelerator pedal when an engine rotating speed is held constantly in work.SOLUTION: A normal mode controlling engine rotating speed on the basis of a stepping volume of an accelerator pedal and controlling vehicle speed by controlling a swash plate of an HST pump on the basis of the engine rotating speed, and an attachment mode controlling the vehicle speed by controlling the swash plate of the HST pump on the basis of the stepping value of the accelerator pedal and regardless of the engine rotating speed are provided.

Description

  The present invention relates to a working machine such as a wheel loader.

Conventionally, there is a wheel loader described in Patent Document 1 as a working machine.
This wheel loader includes a front airframe having a front wheel and a rear airframe having a rear wheel. The front airframe is provided with a working device, and the rear airframe is equipped with an engine and an HST (hydrostatic transmission). .
The working device includes a lift arm that can swing up and down, and a bucket that is swingably provided on the tip side of the lift arm. Another attachment can be attached to the tip end side of the lift arm instead of the bucket.

  The HST includes an HST pump including a swash plate type variable displacement pump driven by an engine, and an HST motor connected to the HST pump and a closed circuit by a pair of speed change oil passages. The HST motor is driven by the oil discharged from the HST pump, and the rear wheels are driven by the rotational power output from the HST motor. By changing the angle of the swash plate of the HST pump, the discharge direction and the discharge flow rate of the hydraulic oil discharged from the HST pump are changed. As a result, the wheel loader 1 moves forward or backward and the vehicle speed is steplessly changed. be able to.

Further, the wheel loader includes an accelerator pedal, and the engine speed is controlled by depressing the accelerator pedal, and the control pressure for controlling the swash plate of the HST pump changes according to the change in the engine speed. The vehicle speed is controlled by the engine speed and the control pressure of the swash plate.
The wheel loader includes an inching pedal for decelerating and stopping the wheel loader. When this inching pedal is depressed, the angle of the swash plate of the HST pump is reduced, and the wheel loader is decelerated and stopped.

JP-A-8-40223

In the wheel loader, normal traveling control is performed by operating an accelerator pedal. That is, increasing the amount of depression of the accelerator pedal increases the vehicle speed, and decreasing the amount of depression of the accelerator pedal decreases the vehicle speed.
In addition, in the wheel loader, when an attachment such as a sweeper (cleaning machine) or mower (mower) is attached instead of the bucket, it is necessary to rotate the drive unit at a constant speed. Work with the number held constant. In this case, since the travel cannot be controlled with the accelerator pedal, the inching pedal is used for the travel control.

When running control is performed with this inching pedal, the wheel loader starts when the pedal is returned (released) from the state where the inching pedal is depressed, and when the wheel loader is stopped, the inching pedal is depressed.
Therefore, in the case of the traveling control with the inching pedal, the operation is reverse to the traveling control of the accelerator pedal. Therefore, there is a problem that it is difficult to adjust the vehicle speed unless it is possible.

  In view of the above problems, an object of the present invention is to provide a working machine capable of controlling the vehicle speed by operating an accelerator pedal even when the engine speed is kept constant.

The technical means taken by the present invention to solve the technical problems are characterized by the following points.
In the invention according to claim 1, the HST pump is composed of a swash plate type variable displacement pump driven by an engine, and the HST pump is connected to the HST pump in a closed circuit by a pair of transmission oil passages. An HST motor that drives the traveling device by being driven, a control device that controls the engine and the HST pump, and an accelerator pedal that controls the vehicle speed,
The controller is
A normal mode for controlling the vehicle speed by controlling the engine speed based on the depression amount of the accelerator pedal and controlling the swash plate of the HST pump based on the engine speed;
It has an attachment mode in which the vehicle speed is controlled by controlling the swash plate of the HST pump based on the depression amount of the accelerator pedal, regardless of the engine speed.

The invention according to claim 2 includes a servo cylinder that controls the swash plate of the HST pump, and a swash plate comprising an electromagnetic proportional valve that supplies pressure oil from a hydraulic pump driven by the engine to the servo cylinder as a control pressure of the swash plate. It has a plate control valve and an accelerator position sensor that detects an operation amount of the accelerator pedal and inputs it to the control device,
In the normal mode, a command signal is output from the control device to the engine so as to control the engine speed based on the depression amount of the accelerator pedal, and the control pressure of the swash plate of the HST pump is controlled based on the engine speed. A command signal is output from the control device to the swash plate control valve,
In the attachment mode, the control device outputs a command signal to the swash plate control valve so as to control the control pressure of the swash plate of the HST pump based on the depression amount of the accelerator pedal.

The invention according to claim 3 includes an inching pedal and an inching position sensor that detects an operation amount of the inching pedal and inputs the inching pedal to the control device. In the normal mode and the attachment mode, the HST pump can be operated by depressing the inching pedal. A command signal is output from the control device to the swash plate control valve so that the control pressure of the swash plate decreases.
The invention according to claim 4 is characterized by having an accelerator setting member for setting the engine speed to a constant speed in the attachment mode.

The present invention has the following effects.
According to the first aspect of the present invention, in the normal mode, the engine speed is controlled based on the depression amount of the accelerator pedal, and the swash plate of the HST pump is controlled based on the engine speed. Thus, the vehicle speed can be controlled by a normal accelerator pedal operation of controlling the vehicle speed while controlling the engine speed by depressing the accelerator pedal.

  In the attachment mode, the swash plate of the HST pump is controlled regardless of the engine speed based on the depression amount of the accelerator pedal. Thus, the vehicle speed can be controlled by depressing the accelerator pedal while keeping the engine speed constant. Therefore, even when using an attachment that needs to rotate the drive unit at a constant speed, the vehicle speed can be controlled by the same operation as the normal operation of the accelerator pedal.

According to the invention of claim 2, the vehicle speed control by controlling the engine speed based on the accelerator pedal depression operation and the swash plate of the HST pump regardless of the engine speed based on the accelerator pedal depression operation. It is possible to easily realize a system that can select vehicle speed control by controlling the vehicle speed.
According to the invention of claim 3, the vehicle speed can be satisfactorily reduced in both the normal mode and the attachment mode.

  According to the invention which concerns on Claim 4, an engine speed can be set to a fixed speed with an accelerator setting member at the time of an attachment mode.

It is a side view of a wheel loader. It is the block diagram which showed a part of hydraulic circuit and electric control system of a wheel loader. (A) is a block diagram illustrating a vehicle speed control system in a normal mode, and (b) is a block diagram illustrating a vehicle speed control system in an attachment mode. (A) is the engine rotation control map which concerns on this invention which showed the relationship between engine speed and the depression amount of an accelerator pedal, (b) is the engine rotation control map which concerns on a comparative example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 illustrates a wheel loader 1 as a work machine.
The wheel loader 1 is an articulated working machine, and the traveling machine body 1 </ b> A includes a front machine body 2 and a rear machine body 3. The front machine body 2 is provided with a pair of left and right front wheels 5, and the rear machine body 3 is provided with a pair of left and right rear wheels 6.

A connecting member 4 is provided on the front end side of the rear body 3 so as to be rotatable within a predetermined range around an axial center in the front-rear direction, and the rear end side of the front body 2 swings left and right about the vertical axis in the connecting member 4. It is connected freely.
A steering cylinder 7 comprising a hydraulic cylinder is provided between the connecting member 4 and the front machine body 2, and the front machine body 2 swings left and right with respect to the rear machine body 3 by expanding and contracting the steering cylinder 7. The loader 1 can turn left and right.

  The front machine body 2 is provided with a work device 8 (front work device). The working device 8 includes a pair of left and right lift arms 9 and a bucket 10. The left and right lift arms 9 are supported at their base ends on a support frame 11 provided on the front machine body 2 so as to be rotatable about a left and right axis, and can swing up and down. The bucket 10 is pivotally connected to the distal end side of the left and right lift arms 9 so as to be swingable about a horizontal axis. The left and right lift arms 9 are driven by a lift cylinder 12, and the bucket 10 is driven by a bucket cylinder 13. The lift cylinder 12 and the bucket cylinder 13 are constituted by hydraulic cylinders.

The bucket 10 is detachably provided, and an attachment such as a sweeper, a mower, or a breaker can be attached to the tip side of the lift arm 9 instead of the bucket 10.
The rear body 3 includes a driver's seat 14, a four-post canopy 15 as a driver's seat protection device, a steering wheel 16 that operates the steering cylinder 7, and a working device operation lever 17 that operates the working device 8. And an engine 18 (diesel engine).

FIG. 2 shows a part of the hydraulic circuit and electric control system of the wheel loader 1.
In FIG. 2, 18 is an engine, 19 is an HST (hydrostatic transmission) for a traveling device, 20 is a control device for controlling the engine 18 and the HST 19, 21 is an accelerator pedal for increasing and decelerating the wheel loader 1, and 22 is a wheel. An inching pedal for decelerating and stopping the loader 1, 23 is a main pump, and 24 is a sub pump (charge pump).

  The HST 19 includes an HST pump 26 driven by the engine 18, and an HST motor 29 connected in a closed circuit by the HST pump 26 and a pair of speed change oil passages 27 and 28. The HST motor 29 is driven by the oil discharged from the HST pump 26, and the front wheels 5 and the rear wheels 6 are driven by the rotational power output from the HST motor 29 in this embodiment.

  The HST pump 26 is a swash plate type variable displacement pump. By changing the angle of the swash plate of the HST pump 26, the discharge direction and the discharge flow rate of the hydraulic oil discharged from the HST pump 26 are changed. As a result, the rotational speed of the output shaft of the HST motor 29 is stepless in the direction in which the wheel loader 1 moves forward (direction in which the HST motor 29 rotates forward) or in the direction in which the wheel loader 1 moves backward (direction in which the HST motor 29 reverses). It is possible to change the speed (change the vehicle speed of the wheel loader 1).

The HST motor 29 is a swash plate type variable capacity motor, and the angle of the swash plate of the HST motor 29 (tilt angle of the swash plate) can be controlled by a command signal from the control device 20. It is possible to apply the HST brake force by increasing the angle. The output shaft 30 of the HST motor 29 is transmitted to the transmission shaft 32 via the gear transmission mechanism 31, and power is transmitted from the rear end side of the transmission shaft 32 to the left and right rear axles 34 via the rear wheel differential device 33. Then, power is transmitted from the rear axle 34 to the rear wheel 6 to drive the rear wheel 6. Further, power is transmitted from the front end side of the transmission shaft 32 to the front wheel 5 via a drive shaft, a front wheel differential device, a front axle, and the like, so that the front wheel 5 is driven.

The traveling device includes a front wheel 5 and a rear wheel 6, a support case that supports the front wheel 5 and the rear wheel 6, a power transmission system that transmits power from the HST motor 29 to the front wheel 5 and the rear wheel 6, and the like.
The rotational speed of the transmission shaft 32 can be detected by a rotation sensor 35. The rotation sensor 35 is connected to the control device 20, and a detection value of the rotation sensor 35 is input to the control device 20. The controller 20 calculates the vehicle speed based on the detection value of the rotation sensor 35.

When the actual vehicle speed obtained based on the detection value of the rotation sensor 35 is lower than the target vehicle speed obtained from the engine rotational speed command value output from the control device 20 (that is, the vehicle speed has been reduced), the wheel It is determined that a traveling load has acted on the loader 1. Further, the degree of travel load is determined by the difference between the target vehicle speed and the actual vehicle speed.
The traveling load means a load applied to the wheel loader 1 when traveling on an uphill road or entering a corner.

  The swash plate of the HST pump 26 is operated to change the angle by a servo cylinder 36. The servo cylinder 36 is connected to a forward / reverse switching valve 39 via a forward oil passage 37 and a reverse oil passage 38. The forward / reverse switching valve 39 is a four-port three-position electromagnetic switching valve, and is held at the neutral position 39a by the spring 41 when the solenoid 40 is demagnetized. 39b or reverse position 39c.

When the forward / reverse switching valve 39 is switched to the forward movement position 39b, the swash plate of the HST pump 26 can be tilted so as to rotate the HST motor 29 in the forward rotation direction, and the forward / backward switching valve 39 is switched to the reverse movement position 39c. The swash plate of the HST pump 26 can be tilted so as to rotate the HST motor 29 in the reverse direction.
The forward / reverse switching valve 39 is connected to a swash plate control valve 43 through a control pressure supply path 42. The swash plate control valve 43 controls the pressure of the pressure oil supplied to the servo cylinder 36 (the control pressure of the swash plate of the HST pump 26). The swash plate control valve 43 is constituted by an electromagnetic proportional valve, and the pressure of the pressure oil supplied to the servo cylinder 36 can be controlled by a command signal (command current value) from the control device 20.

The control device 20 is connected to a forward / reverse selector switch 44. By operating the forward / reverse selector switch 44, the forward / reverse selector valve 39 is excited and switched to the forward position 39b or the reverse position 39c.
Further, a neutral switch 45 is connected to the control device 20, and by operating the neutral switch 45, the forward / reverse switching valve 39 is demagnetized and switched from the forward position 39b or the reverse position 39c to the neutral position 39a.

  The accelerator pedal 21 controls the vehicle speed by depressing it. The depression amount (depression condition) of the accelerator pedal 21 is detected by an accelerator position sensor 46 including a potentiometer. The accelerator position sensor 46 is connected to the control device 20, and a detection value of the accelerator position sensor 46 (a depression amount of the accelerator pedal 21) is input to the control device 20.

The inching pedal 22 can be depressed, and is configured such that the travel brake master cylinder 47 is operated by further depressing it after depressing a predetermined amount. The operation area of the inching pedal from the state where the inching pedal 22 is not depressed to the position before the master cylinder 47 is operated is referred to as an inching operation area A.
The master cylinder 47 is connected to a brake mechanism 48 that brakes the rear axle 34 via a brake oil passage 49. When the master cylinder 47 is operated by the inching pedal 22, the brake mechanism 48 is operated and the left and right rear axles 34 are moved. Braked.

The depression amount (depression condition) of the inching pedal 22 is detected by an inching position sensor 51 including a potentiometer. The inching position sensor 51 is connected to the control device 20, and a detection value (depression amount of the inching pedal 22) of the inching position sensor 51 is input to the control device 20.
In the inching operation area A, a command signal is output from the control device 20 to the solenoid 52 of the swash plate control valve 43 so that the control pressure of the swash plate of the HST pump 26 decreases as the inching pedal 22 is depressed.

  The main pump 23 and the sub pump 24 are constituted by constant displacement hydraulic pumps driven by the power of the engine 18. The main pump 23 supplies hydraulic oil to hydraulic actuators (steering cylinder 7, lift cylinder 12, bucket cylinder 13, etc.) mounted on the wheel loader 1 and attachment hydraulic actuators mounted instead of the bucket 10.

The sub pump 24 is connected to the swash plate control valve 43 via a hydraulic oil supply path 53 so as to supply hydraulic oil to the servo cylinder 36. The sub-pump 24 supplies pressure oil to a pilot valve that operates a pilot control valve that controls the hydraulic actuator, a charge circuit that replenishes pressure oil to the transmission oil passages 27 and 28 on the low-pressure side of the HST, and the like.
The control device 20 includes a normal mode, an attachment mode, and an eco mode. When the engine 18 is started, the normal mode is set, the attachment switch 54 switches to the attachment mode, and the eco switch 55 switches to the eco mode. The attachment switch 54 and the eco switch 55 are connected to the control device 20.

  In the normal mode, the rotational speed of the engine 18 (target engine rotational speed) is controlled by the accelerator pedal 21 as shown in FIG. That is, when the accelerator pedal 21 is not depressed, the rotational speed of the engine 18 is the idling rotational speed, and a command signal is output from the control device 20 to the engine 18 so that the rotational speed of the engine 18 increases as the accelerator pedal 21 is depressed. . Note that the reverse is true when the accelerator pedal 21 is returned.

  In the normal mode, the control pressure of the swash plate of the HST pump 26 is controlled based on the rotational speed of the engine 18. That is, a map having a characteristic line indicating the relationship between the engine speed and the control pressure of the swash plate of the HST pump 26 is incorporated in the control device 20, and the control pressure of the swash plate of the HST pump 26 is based on this map. Command signal is output from the control device 20 to the solenoid 52 of the swash plate control valve 43 so that the control pressure corresponds to the rotational speed of the engine 18 (the control of the swash plate of the HST pump 26 increases as the engine speed increases). The control device 20 controls the swash plate control valve 43 so that the control pressure of the swash plate of the HST pump 26 decreases when the pressure increases and the engine speed decreases.

As described above, in the normal mode, when the inching pedal 22 is not depressed, the engine speed based on the depression of the accelerator pedal 21 (the rotation of the HST pump 26) and the control of the swash plate of the HST pump 26 based on the engine speed. The discharge flow rate of the HST pump 26 is determined by the pressure, and the vehicle speed is determined.
In this normal mode, when the forward / reverse switching valve 39 is neutral, the servo cylinder 36 is balanced so that the swash plate angle (tilt angle of the swash plate) of the HST pump 26 is minimized. Pressure oil does not discharge.

When the forward / reverse switching valve 39 is changed from the neutral position 39a to the forward position 39b or the reverse position 39c, the control pressure of the swash plate of the HST pump 26 is minimum when the engine speed is the idle speed (the swash plate angle of the HST pump 26 is The wheel loader 1 remains stopped.
When the accelerator pedal 21 is depressed from this state, the engine speed increases, the control pressure of the swash plate of the HST pump 26 increases, the swash plate angle increases, and the vehicle moves forward or backward. Further, when the accelerator pedal 21 is depressed to the maximum and the engine speed reaches the maximum speed, the control pressure of the swash plate of the HST pump 26 becomes maximum.

  Further, when the inching pedal 22 is depressed while the accelerator pedal 21 is depressed, a command signal is sent from the control device 20 to the solenoid 52 of the swash plate control valve 43 so that the control pressure of the swash plate of the HST pump 26 is lowered. Is output. As a result, the swash plate angle of the HST pump 26 is reduced, and the wheel loader 1 is decelerated while the rotational speed of the engine 18 remains at the rotational speed determined by the accelerator pedal 21.

  On the other hand, in the attachment mode, as shown in FIG. 3B, even if the accelerator pedal 21 is depressed, the rotational speed of the engine 18 does not change, and when the accelerator pedal 21 is depressed, the controller 20 inclines from the control device 20 according to the depression amount. A command signal is output to the solenoid 52 of the plate control valve 43, and the control pressure of the swash plate of the HST pump 26 changes according to the depression amount of the accelerator pedal 21. That is, in the attachment mode, the swash plate of the HST pump 26 is controlled on the basis of the depression amount of the accelerator pedal 21 regardless of the rotation speed of the engine 18, and when the accelerator pedal 21 is not depressed, the inclination of the HST pump 26 is controlled. A command signal is output from the control device 20 to the solenoid 52 of the swash plate control valve 43 so that the control pressure of the plate is minimized, and the control pressure of the swash plate of the HST pump 26 increases as the accelerator pedal 21 is depressed. The control device 20 outputs a command signal to the swash plate control valve 43 (so that the swash plate angle of the HST pump 26 is increased).

  The rotation speed of the engine 18 in the attachment mode is set by an accelerator setting dial 56 (accelerator setting member). That is, the accelerator setting dial 56 is connected to the control device 20, and a command signal is output from the control device 20 to the engine 18 so that the engine speed set by the accelerator setting dial 56 is obtained. Further, by turning the accelerator setting dial 56, the rotational speed of the engine 18 can be set or changed stepwise or steplessly from 1700 rpm to 2400 rpm, for example, and the rotational speed of the engine 18 is set to the set rotational speed. Can be held.

In this attachment mode, when the forward / reverse switching valve 39 is in the neutral position 39a, the swash plate angle of the HST pump 26 is the smallest and pressure oil is not discharged from the HST pump 26, as in the normal mode.
Further, even when the forward / reverse switching valve 39 is changed from the neutral position 39a to the forward drive position 39b or the reverse drive position 39c and the engine speed is set higher than the idling speed by the accelerator setting dial 56, the accelerator pedal 21 is not depressed. The control pressure of the swash plate of the HST pump 26 is minimal (the swash plate angle of the HST pump 26 remains minimal) and does not move forward or backward.

When the accelerator pedal 21 is depressed from this state, the wheel loader 1 starts, and as the accelerator pedal 21 is depressed, the control pressure of the swash plate is controlled to increase so that the swash plate angle of the HST pump 26 increases. At this time, the rotational speed of the engine 18 remains the rotational speed determined by the accelerator setting dial 56.
Further, when the inching pedal 22 is depressed while the accelerator pedal 21 is depressed, a command signal is sent from the control device 20 to the solenoid 52 of the swash plate control valve 43 so that the control pressure of the swash plate of the HST pump 26 is lowered. As a result, the swash plate angle of the HST pump 26 is reduced, and the wheel loader 1 is decelerated while maintaining the engine speed determined by the accelerator setting dial 56.

In the normal mode and the attachment mode, the final control pressure of the swash plate of the HST pump 26 (the current value instructed to the swash plate control valve 43 that controls the control pressure of the swash plate of the HST pump 26) is Y × (Z / 100).
Y is the control pressure of the swash plate of the HST pump 26 determined by the accelerator pedal 21. Z is the degree of depression of the inching pedal 22 in the inching operation area A. This Z is 100% when the inching is released (when the inching pedal 22 is not depressed), and 0% when the maximum depression in the inching operation area A is performed.

Therefore, in the normal mode and the attachment mode, regardless of the depression amount of the accelerator pedal 21, when the inching pedal 22 is depressed to the point before operating the master cylinder 47, the control pressure of the swash plate of the HST pump 26 becomes minimum (zero), The wheel loader 1 stops.
As described above, in the normal mode, the engine speed is controlled based on the depression amount of the accelerator pedal 21, and the swash plate of the HST pump 26 is controlled based on the engine speed. As a result, the vehicle speed can be controlled by a normal operation of the accelerator pedal 21 that controls the vehicle speed while controlling the engine speed by depressing the accelerator pedal 21.

  In the attachment mode, the swash plate of the HST pump 26 is controlled regardless of the engine speed based on the depression amount of the accelerator pedal 21. Thus, the vehicle speed can be controlled by depressing the accelerator pedal 21 while keeping the engine speed constant. Therefore, even when using an attachment that needs to rotate the drive unit at a constant speed, the vehicle speed can be controlled by the same operation as the normal operation of the accelerator pedal 21.

In the eco mode, the rotation speed of the engine 18 (target engine rotation speed) is controlled based on the engine rotation control map 57 shown in FIG.
The engine rotation control map 57 sets the relationship between the amount of depression of the accelerator pedal 21 and the engine speed, and the amount of depression of the accelerator pedal 21 is taken on the horizontal axis and the engine speed is taken on the vertical axis.

  The engine speed control map 57 has a first control characteristic line 58, a second control characteristic line 59, and a third control characteristic line 60, and the control device 20 determines the engine speed according to the first control characteristic line 58. A first engine speed control unit 61 that performs control, a second engine speed control unit 62 that controls engine speed according to a second control characteristic line 59, and a third engine speed that controls engine speed according to a third control characteristic line 60. An engine rotation control unit 63.

The first control characteristic line 58 is set so as to control the rotation speed of the engine 18 at a high rotation speed giving priority to the work speed of the work device 8. For example, the engine rotation speed is reduced when the accelerator pedal 21 is fully depressed. It is set to be the rated speed.
The second control characteristic line 59 is set to control the rotational speed of the engine 18 at a low rotational speed (revolving speed lower than the first control characteristic line 58) giving priority to fuel saving.

The third control characteristic line 60 is located between the first control characteristic line 58 and the second control characteristic line 59, and has a rotational speed between the first control characteristic line 58 and the second control characteristic line 59. The rotation speed of the engine 18 is set to be controlled.
In the present embodiment, the maximum engine speed at the first control characteristic line 58 (the speed when the accelerator pedal 21 is fully depressed) is set to 2400 rpm, and the maximum engine speed at the second control characteristic line 59 is set. Is set to 1800 rpm, and the maximum engine speed in the third control characteristic line 60 is set to 2200 rpm.

When the work device 8 is working, the first engine rotation control unit 61 of the control device 20 controls the rotation speed of the engine 18 according to the first control characteristic line 58. Thus, efficient work can be performed.
When working with the work device 8, the inching pedal 22 is operated to repeatedly start and stop the wheel loader 1 in small increments (the wheel loader 1 is moved forward or backward by jogging), so-called inching operation (inching traveling) is performed. . Further, when working with the work device 8, in order to speed up the operation of the work device 8, the engine speed is kept increased with the accelerator pedal 21, and the start, stop, and vehicle speed increase / decrease operations are performed with the inching pedal 22. Do. Accordingly, since the inching pedal 22 is used when the work device 8 performs work, in the present embodiment, the time when the work device 8 is operated is specified by operating the inching pedal 22. That is, when the inching pedal 22 is operated, the first engine rotation control unit controls the engine speed according to the first control characteristic line 58.

In order to specify when the work device 8 is working, the operation of the lift arm 9 or the bucket 10 or the operation of the operation lever 17 for the work device may be detected, but in that case, a detection means such as a sensor is required separately. Become. In contrast, in the wheel loader 1 of the present embodiment, in order to control the control pressure of the swash plate of the HST pump 26, the operation amount of the inching pedal 22 is detected by the inching position sensor 51 and input to the control device 20. Therefore, the detection of the pedal depression operation by the inching position sensor 51 can be used to specify when the working device 8 is working. As a result, there is an effect that it is not necessary to separately provide a detection means in order to specify the time of work by the work device 8.

  On the other hand, during traveling (when only traveling without performing work), when the traveling load is smaller than the predetermined load, the second engine rotation control unit 62 of the control device 20 follows the second control characteristic line 59. When the running load is equal to or greater than the predetermined load, the third engine rotation control unit 63 of the control device 20 controls the rotation speed of the engine 18 according to the third control characteristic line 60.

For example, when traveling on a flat road, the rotational speed of the engine 18 is controlled according to the second control characteristic line 59. When traveling on an uphill road and a traveling load greater than a predetermined load is applied to the wheel loader 1, the third control is performed. The rotational speed of the engine 18 is controlled according to the characteristic line 60. As a result, a sufficient reduction in fuel consumption can be achieved.
That is, the engine 18 is based on the engine rotation control map 64 (a map having only the first control characteristic line 58 and the second control characteristic line 59 and not having the third control characteristic line 60) as shown in FIG. When the number of rotations is controlled, if the traveling load is frequently more than a predetermined load during traveling, the engine speed is controlled at a high level, and sufficient fuel consumption cannot be reduced. If the engine speed when the load exceeds a predetermined load is set lower than the engine speed when controlled by the first control characteristic line 58, the operation of the work device 8 is performed when the work device 8 is operated. Become slow. Therefore, in consideration of work efficiency when working with the work device 8 (decrease in work speed), the engine speed when the load exceeds a predetermined load cannot be reduced too much.

  Therefore, as shown in FIG. 4A, when the third control characteristic line 60 is provided in addition to the first control characteristic line 58 and the second control characteristic line 59 and the vehicle is traveling with a traveling load smaller than a predetermined load. By changing the control characteristic line that controls the engine speed between when the running load exceeds a predetermined load and when working with the work device 8, both sufficient fuel consumption reduction and efficient work can be achieved. Can be made.

Note that when the inching pedal is depressed while only traveling without performing work, the engine speed is switched to a higher speed controlled by the first control characteristic line 58, but only traveling is performed. When decelerating sometimes, the accelerator pedal is usually released to decelerate, so there is no problem.
Further, in the normal mode and the attachment mode, the rotational speed of the engine 18 is controlled according to the first control characteristic line 58 regardless of the travel load. Accordingly, it is possible to select between a case where traveling with emphasis on speed is performed and a case where traveling with emphasis on fuel saving is performed.

18 Engine 20 Control device 21 Accelerator pedal 22 Inching pedal 24 Sub pump (hydraulic pump)
26 HST pump 27 Oil passage for shifting 28 Oil passage for shifting 29 HST motor 36 Servo cylinder 43 Swash plate control valve 46 Accelerator position sensor 51 Inching position sensor 56 Accelerator setting member

Claims (4)

An HST pump consisting of a swash plate type variable displacement pump driven by an engine, and a closed circuit connected to the HST pump by a pair of speed change oil passages, and driven by oil discharged from the HST pump, the traveling device is An HST motor for driving, a control device for controlling the engine and the HST pump, and an accelerator pedal for controlling the vehicle speed;
The controller is
A normal mode for controlling the vehicle speed by controlling the engine speed based on the depression amount of the accelerator pedal and controlling the swash plate of the HST pump based on the engine speed;
A work machine having an attachment mode for controlling a vehicle speed by controlling a swash plate of an HST pump based on a depression amount of the accelerator pedal, regardless of an engine speed. A servo cylinder for controlling the swash plate of the HST pump, a swash plate control valve comprising an electromagnetic proportional valve for supplying pressure oil from a hydraulic pump driven by the engine to the servo cylinder as a control pressure of the swash plate, and an accelerator pedal An accelerator position sensor that detects the operation amount and inputs it to the control device;
In the normal mode, a command signal is output from the control device to the engine so as to control the engine speed based on the depression amount of the accelerator pedal, and the control pressure of the swash plate of the HST pump is controlled based on the engine speed. A command signal is output from the control device to the swash plate control valve,
2. The operation according to claim 1, wherein in the attachment mode, a command signal is output from the control device to the swash plate control valve so as to control the control pressure of the swash plate of the HST pump based on the depression amount of the accelerator pedal. Machine.   It has an inching pedal and an inching position sensor that detects the amount of operation of the inching pedal and inputs it to the control device. In normal mode and attachment mode, the control pressure on the swash plate of the HST pump is lowered by depressing the inching pedal. The work machine according to claim 2, wherein a command signal is output from the control device to the swash plate control valve.   The work machine according to any one of claims 1 to 3, further comprising an accelerator setting member that sets the engine speed to a constant speed in the attachment mode.

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