JP2012241661A - Wheel loader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine control device of a working vehicle, enhancing lift force of a working machine in response to the demand of an operator.SOLUTION: A wheel loader includes: a variable displacement hydraulic pump and a traveling device, which are driven by a common engine; the working machine driven by pressurized oil from the hydraulic pump; and a controller 7 controlling the output of the engine and the displacement of the hydraulic pump. The controller 7 includes: an excavation state detection means 91 detecting whether or not the working machine is in excavation operation; an operation amount detection means detecting the operation amount of the working machine; a pump displacement control means 92 reducing the pump displacement of the hydraulic pump when the working machine is detected to be in excavation operation; and an engine output reduction means 93 reducing the output of the engine according to a lift operation amount when the working machine is detected to be in excavation operation.

Description

  The present invention relates to a wheel loader.

  Conventionally, a wheel loader is known as a work vehicle having a work machine. In the wheel loader working machine, an attachment such as a bucket is provided at the tip of a boom pivoted on the vehicle body, the boom is provided so as to be movable up and down by a lift cylinder, and the bucket is driven by a tilt cylinder via a so-called link mechanism. The In a wheel loader having a working machine having such a configuration, an operator performs excavation work for lifting a boom while inserting a bucket positioned near a ground position into an object to be excavated, and dumps the bucket from an intermediate position or a top position. To load the truck.

FIG. 20 is a torque distribution diagram in the wheel loader.
In FIG. 20, a line A is a travel drive torque curve showing characteristics of travel drive torque absorbed by the torque converter to generate travel drive force. Further, TW is a work implement driving torque absorbed by the hydraulic pump in order to drive the work implement. The total absorption torque is obtained by adding the work drive torque TW to the travel drive torque indicated by the travel drive torque curve A, and the characteristic is indicated by the total absorption torque curve of line B. In general, a wheel loader obtains a driving force for traveling and a driving force for a work machine from a common engine. For this reason, during excavation work, the engine output is absorbed for driving and working machine driving based on the total absorption torque curve B, and the engine torque is the intersection of the total absorption torque curve B and the engine torque curve C. Match with P.

  Here, at the time of excavation work of the wheel loader, as shown in FIG. 21, since the wheel loader travels with the traveling driving force from the engine, the bucket 32 enters the object to be excavated. The reaction force of the driving force is received from the object. This reaction force acts as a counter-lift force La that cancels the lift force L by the lift cylinder 34. Therefore, in the state where the lift operation is performed to load the excavation object into the bucket 32, the bucket 32 The force obtained by subtracting the anti-lift force La corresponding to the travel drive force from the lift force L by the lift cylinder 34 acts as the actual lift force. That is, in order to obtain a sufficient lift force during excavation work, it is necessary to reduce the travel drive force and reduce the anti-lift force La. Therefore, a wheel loader configured to reduce the traveling driving force by limiting the upper limit value of the accelerator operation amount with respect to the engine when the vehicle speed is equal to or lower than a predetermined value is known (for example, see Patent Document 1). .

  On the other hand, with increasing environmental awareness in recent years, there has been known a wheel loader that controls the capacity of the hydraulic pump during excavation work, which makes the hydraulic pump a variable displacement type that requires hydraulic pressure but requires less hydraulic oil discharge. (For example, refer to Patent Document 2). In this wheel loader, the controller determines that the excavation work is in progress when the driving force, the hydraulic pressure on the bottom side of the lift cylinder, and the hydraulic pressure of the tilt cylinder exceed predetermined values, and changes the capacity of the hydraulic pump. By reducing the pump flow rate, the engine fuel consumption is reduced and the load on the hydraulic circuit is reduced.

JP 2007-182859 A JP 2003-184134 A

  However, in the wheel loader described in Patent Document 2, when it is determined that excavation work is in progress, the capacity of the hydraulic pump changes and the pump flow rate decreases. Here, since the work implement drive torque TW is a product of the discharge pressure of the hydraulic pump and the pump displacement, the work implement drive torque TW decreases as shown in FIG. 22 when the pump displacement decreases. Thus, as shown in FIG. 22, the total absorption torque curve B moves from the broken line state to the solid line state as indicated by the arrow D, and the value of the total absorption torque becomes small. In this case, since the matching point P of the engine moves in the right direction in the figure, the travel drive torque increases from T1 to T2 along the travel drive torque curve A. For this reason, the anti-lift force becomes large, and as a result, a large lift force cannot be obtained. That is, during excavation work, the state where the lift force is reduced continues.

  In contrast to this, like the wheel loader described in Patent Document 1, it is conceivable to reduce the driving force by limiting the upper limit value of the accelerator operation amount. However, in the engine control device described in Patent Document 1, the driving force is reduced when the operator selects a specific work mode using a switch or the like. Therefore, the operator selects the corresponding work mode. If not, there is a problem that the driving force cannot be reduced and a sufficient lifting force cannot be obtained. In addition, as the upper limit value of the accelerator operation amount, since a fixed value set in advance corresponding to the selected work mode is used, the operator wants to obtain a larger lift force depending on the situation. Even if it exists, there exists a problem that it cannot respond to an operator's request | requirement flexibly.

  The objective of this invention is providing the wheel loader which can improve the lifting force of a working machine according to the request | requirement of an operator.

A wheel loader according to a first aspect of the present invention includes a variable displacement hydraulic pump and traveling device driven by a common engine, a working machine driven by pressure oil from the hydraulic pump, output control of the engine, and the hydraulic pump A controller for controlling the capacity of the excavation state, the controller detects whether or not the work implement is in excavation work, an operation amount detection means for detecting a lift operation amount of the work implement, Pump capacity control means for reducing the pump capacity of the hydraulic pump when it is detected that excavation work is in progress; and when it is detected that the excavation work is being performed, Engine output reduction means for reducing the output of the engine is provided.
Here, the lift operation of the work machine refers to an operation for rotating a boom constituting a part of the work machine of the wheel loader upward.

  In the wheel loader according to the second aspect of the invention, it is preferable that the engine output reduction means reduces the engine output by limiting engine torque in accordance with the lift operation amount.

  In the wheel loader according to the third aspect of the invention, it is preferable that the engine output reduction means reduces the engine output by limiting the engine speed in accordance with the lift operation amount.

  In a wheel loader according to a fourth aspect of the present invention, the wheel loader includes a pressure detector that detects a discharge pressure of the hydraulic pump, and the excavation state detection unit performs the operation when the discharge pressure is greater than a predetermined value for a predetermined time. It is preferable to determine that the machine is in an excavation operation.

  According to the first aspect of the present invention, in a wheel loader equipped with a variable displacement hydraulic pump driven by a common engine and a traveling device, when it is detected that the work implement is in excavation work, the lift load is adjusted according to the lift operation amount. Therefore, even if the pump flow rate is reduced during excavation work, the driving force can be reduced without requiring any special operation by the operator. Further, since the engine output at this time is reduced according to the lift operation amount, for example, when the operator increases the lift operation amount in order to obtain a larger lift force, the engine output is adjusted in accordance with the lift operation amount. By increasing the output reduction amount, the driving force can be greatly reduced. Since the anti-lifting force can be reduced by reducing the traveling driving force, even when the pump flow rate is reduced during excavation work, the lifting force of the work implement can be improved according to the operator's request.

  According to the second aspect of the invention, the engine torque is limited according to the lift operation amount, so that the lift force can be increased according to the lift operation amount. For this reason, the lift force can be increased smoothly without giving the operator a sense of incongruity, and the fuel consumption rate of the engine can be improved.

  According to the third aspect of the invention, the engine output is reduced by limiting the engine speed in accordance with the lift operation amount. Therefore, it is possible to increase the lift force while suppressing the engine speed. For this reason, it is possible to effectively improve the fuel consumption rate of the engine as well as the lift force.

By the way, during excavation work, the lift cylinder is driven to lift the boom and the tilt cylinder is driven to tilt the bucket, so the discharge pressure of the hydraulic pump that supplies pressure oil to these cylinders is high.
According to the fourth aspect of the present invention, when the state in which the discharge pressure of the hydraulic pump is larger than the predetermined value continues for a predetermined time, the work implement is determined to be in excavation work, so that it is reliably detected that excavation work is in progress. can do. For this reason, the lift force during excavation work can be reliably ensured.

The side view which shows the wheel loader which concerns on 1st Embodiment of this invention. The block diagram of the power part and control system of a wheel loader. The figure which shows the pump capacity | capacitance characteristic of the hydraulic pump mounted in the wheel loader. The figure which shows the engine characteristic of a wheel loader. The control block diagram of the controller of a wheel loader. The figure which shows the request | requirement pump flow map of a wheel loader. The figure which shows the engine torque limitation map of a wheel loader. The control flowchart of a controller. Action | operation explanatory drawing of the engine output control of a controller. Action | operation explanatory drawing of the engine output control of a controller. Action | operation explanatory drawing of the controller which concerns on 2nd Embodiment. The figure which shows the engine characteristic of the wheel loader which concerns on 3rd Embodiment. The block diagram of the motive power part and control system of the wheel loader which concern on 3rd Embodiment. The control block diagram of the controller which concerns on 3rd Embodiment. The control flowchart of the controller which concerns on 3rd Embodiment. Action | operation explanatory drawing of the controller which concerns on 3rd Embodiment. The block diagram of the motive power part and control system of the wheel loader which concern on the modification of this invention. The control block diagram of the controller which concerns on a modification. Explanatory drawing of another modification of this invention. The torque distribution figure for driving | running | working drive of a wheel loader and a working machine drive. The figure which shows the relationship between the driving force of a wheel loader, and lift force. The torque distribution figure for driving | running | working driving | running | working of a wheel loader and a working machine drive.

Hereinafter, each embodiment of the present invention will be described with reference to the drawings.
In the second and subsequent embodiments, the same constituent members as those described in the first embodiment and constituent members having the same functions are denoted by the same reference numerals as those in the first embodiment. The description of is omitted or simplified.

[First Embodiment]
[1] Overall Configuration FIG. 1 shows a wheel loader 1 as a work vehicle according to a first embodiment of the present invention. The wheel loader 1 includes a vehicle main body 2, a work machine 3, a cab 4, a traveling device 5, a power unit 6, and a controller 7.
The vehicle main body 2 is composed of a steel frame body that supports the work machine 3, the cab 4, and the power unit 6. A structure 21 is provided on the front side of the vehicle body 2 so as to be rotatable in the left-right direction with respect to the vehicle body 2, and a work implement 3 is provided further on the front side of the structure 21.

The work implement 3 includes a boom 31 pivoted on the structure 21, a bucket 32 pivoted up and down on the boom 31, and a bell crank 33 pivoted on the boom 31 at an intermediate portion of the boom 31. .
A pair of booms 31 are arranged in the vehicle width direction, and pivotally pivoted up and down with respect to the structure 21. A lift cylinder 34 is pivoted at an intermediate portion of the boom 31, and a base end portion of the lift cylinder 34 is pivoted on the structure 21. The boom 31 is rotated up and down by expanding and contracting the lift cylinder 34 by hydraulic pressure.

The bucket 32 is a portion for loading excavated soil and the like. In the bucket 32, a link 35 is pivoted above the pivot position with respect to the boom 31, and the other end side of the link 35 is pivoted on the lower end portion of the bell crank 33.
The bell crank 33 is pivoted between the pair of booms 31, and the base end portion of the link 35 is connected to the lower end of the bell crank 33. A tilt cylinder 36 is pivoted on the upper end of the bell crank 33, and a base end portion of the tilt cylinder 36 is pivoted on the structure 21.

  Then, when the bucket 32 moves forward with the bucket 32 being positioned near the ground position and the lift cylinder 34 is extended while the bucket 32 enters the excavation target such as earth and sand, the boom 31 is loaded with the excavated soil in the bucket 32. Can rotate upward to perform excavation work. Further, when the tilt cylinder 36 is contracted in a state where the bucket 32 is positioned above, the upper end portion of the bell crank 33 rotates toward the vehicle main body 2 and the lower end portion of the bell crank 33 rotates toward the vehicle front side. Then, the upper part of the bucket 32 is pushed to the front side of the vehicle by the link 35, whereby the bucket 32 is rotated, and the excavated soil loaded in the bucket 32 can be lowered onto a loading platform such as a dump truck.

  The cab 4 is provided at substantially the center of the vehicle body 2, and an operator gets on the cab 4 to operate the wheel loader 1. Inside the cab 4, as shown in FIG. 2, there are operating levers 41 and 42 for operating the work implement 3, a shift lever 43 for changing the speed stage (shift position) during traveling, engine output and engine rotation. An accelerator pedal 44 for adjusting the number, a brake pedal (not shown), a steering wheel, and the like are provided.

  The traveling device 5 includes drive wheels 51 provided at four positions on the side surface of the vehicle main body 2, an axle that is not shown in FIG. 1 but supports the drive wheels 51 rotatably with respect to the vehicle main body 2, The axle and the vehicle body 2 are connected to each other through a differential at a substantially central portion in the width direction, and a drive shaft to which power is transmitted from the power unit 6 is provided.

FIG. 2 shows an outline of the power unit 6 and the control system of the wheel loader 1.
The power unit 6 includes an engine 61, a transmission 62, and a hydraulic pump 63. The rotation of the output shaft of the engine 61 is transmitted to the drive shaft through the transmission 62, and the wheel loader 1 travels by rotating the drive wheel 51 through the differential. Further, by driving the hydraulic pump 63 with the engine 61, the lift cylinder 34 and the tilt cylinder 36 of the work machine 3 can be expanded and contracted.

  The engine 61 includes a fuel injection device 611 that adjusts the fuel injection amount in accordance with a command from the controller 7, and an engine speed detector 612 that detects the engine speed. The output torque and the rotational speed of the engine 61 are adjusted according to the fuel injection amount of the fuel injection device 611, and the engine rotational speed signal from the engine rotational speed detector 612 is sent to the controller 7.

  The transmission 62 includes a torque converter 621 coupled to the output shaft of the engine 61. The speed stage of the transmission 62 is controlled by the controller 7 in accordance with the operation position of the transmission lever 43. For this reason, the shift lever 43 is provided with a shift position detector 431 such as a position sensor for detecting the operation position of the shift lever 43.

  The hydraulic pump 63 is a variable displacement hydraulic pump including a regulator 631 that adjusts the capacity of the hydraulic pump 63 and a control valve 632 that controls the regulator 631. The control valve 632 changes the pilot pressure from the pilot hydraulic power source 633 to a magnitude corresponding to a command from the controller 7 and outputs it to the regulator 631. The regulator 631 is configured to change the pump capacity of the hydraulic pump 63 by being driven by receiving the pilot pressure from the control valve 632 and the discharge pressure of the hydraulic pump 63.

  FIG. 3 is a pump capacity map showing the relationship among the discharge pressure of the hydraulic pump 63, the command current value from the controller 7 to the control valve 632, and the pump capacity of the hydraulic pump 63. As shown in FIG. 3, if the discharge pressure of the hydraulic pump 63 is equal to or less than a predetermined value, the pump capacity becomes maximum, and if the discharge pressure of the hydraulic pump 63 exceeds the predetermined pressure, the pump capacity gradually decreases in accordance with the increase. The predetermined pressure used here shifts to the low pressure side as the command current value to the control valve 632 increases. That is, when the command current value to the control valve 632 is 0 ampere, the relationship between the discharge pressure of the hydraulic pump 63 and the pump capacity has a characteristic indicated by a solid line in the figure, and the command current value is 0.2 ampere, 0 As the voltage increases to .4 ampere and 0.6 ampere, as shown by the broken line in the figure, there is obtained a characteristic that the gradually decreasing portion is shifted to the low pressure side. For this reason, by controlling the command current value to the control valve 632 according to the discharge pressure of the hydraulic pump 63, the pump capacity can be controlled to a desired capacity.

  On the discharge circuit 64 of the hydraulic pump 63 in FIG. 2, a tilt operation valve 65 for switching the connection state between the discharge circuit 64 and the tilt cylinder 36 and a connection state between the discharge circuit 64 and the lift cylinder 34 are switched. A lift operation valve 66, a relief valve 67 that regulates the maximum pressure of the pressure oil in the discharge circuit 64, and a pressure detector 68 that detects the pressure in the discharge circuit 64 are provided.

In such a power unit 6, the engine 61, the hydraulic pump 63, the tilt operation valve 65, and the lift operation valve 66 are operated by operation means such as the lift operation lever 41, the tilt operation lever 42, and the accelerator pedal 44.
The lift operation lever 41 is an operation means for performing a lift operation of the work machine 3. The boom 31 is controlled by adjusting the discharge amount of the hydraulic pump 63 and driving the lift operation valve 66 according to a command output from the controller 7 in accordance with the operation amount (lift operation amount) of the lift operation lever 41. Moves up and down. The lift operation lever 41 is provided with a lift operation amount detector 411 as operation amount detection means for detecting the operation amount of the lift operation lever 41. Examples of the lift operation amount detector 411 include a potentiometer and a stroke sensor.

  The tilt operation lever 42 is an operation means for performing a tilt operation of the work machine 3. The discharge amount of the hydraulic pump 63 is adjusted by a command output from the controller 7 in accordance with the operation amount of the tilt operation lever 42, and the bucket 32 is tilted by driving the tilt operation valve 65. It has become. The tilt operation lever 42 is provided with a tilt operation amount detector 421 such as a potentiometer and a stroke sensor for detecting the operation amount of the tilt operation lever 42.

  The accelerator pedal 44 is means for instructing the rotational speed of the engine 61, and the engine 61 is driven at a rotational speed corresponding to the operation amount of the accelerator pedal 44, that is, the accelerator operation amount. The accelerator pedal 44 is provided with an accelerator operation amount detector 441 such as a potentiometer and a stroke sensor for detecting an accelerator operation amount.

  The controller 7 is configured as a control unit that performs output control of the engine 61 based on various information input to the controller 7, and performs control such as displacement control of the hydraulic pump 63 and shift control of the transmission 62. Configured to do. The controller 7 includes a lift operation amount detector 411, a tilt operation amount detector 421, a shift position detector 431, an accelerator operation amount detector 441, a transmission 62, a pressure detector 68, a fuel injection device 611, an engine speed. The detector 612 and the control valve 632 of the hydraulic pump 63 are electrically connected.

FIG. 4 shows an engine torque map showing the characteristics of the engine output torque with respect to the engine speed.
The wheel loader 1 performs all speed governor control that suppresses fluctuations in the engine speed against fluctuations in engine load so that the work can be performed stably. Therefore, in the engine torque map shown in FIG. 4, a plurality of regulation lines that define the relationship between the engine speed and the engine torque are set according to the accelerator operation amount. In FIG. 4, for example, a broken line displayed as 0% is a regulation line when the accelerator operation amount is 0%, and a broken line displayed as 80% is a regulation line when the accelerator operation amount is 80%. is there.

  The controller 7 controls the command to the fuel injection device 611 so that the engine torque corresponding to the actual engine speed is obtained on the regulation line corresponding to the accelerator operation amount shown in FIG. Thus, the engine is controlled so that the engine output torque and the engine speed change along the regulation line.

  Furthermore, the controller 7 performs control to improve the lift force during excavation work. That is, the controller 7 sends a control command for reducing the engine output during excavation work to the fuel injection device 611, thereby reducing the travel driving force of the wheel loader 1 and increasing the lift force acting on the bucket 32.

[2] Control Structure by Controller Next, a control structure by the controller 7 will be described with reference to FIGS.
As shown in FIG. 5, the controller 7 includes a storage device 8 such as a memory and an arithmetic processing device 9 configured to be accessible to each other.

  The storage device 8 stores a pump capacity map and an engine torque map described above, a requested pump flow rate map and an engine torque limit map, which will be described later, respectively, and maps and parameters necessary for other controls. These maps may be stored in the form of a table or may be stored as mathematical expressions.

The arithmetic processing unit 9 includes excavation state detection means 91, pump capacity control means 92, and engine output reduction means 93.
The excavation state detection means 91 detects whether the work implement 3 is in the excavation state based on the discharge pressure of the hydraulic pump 63. That is, the excavation state detection unit 91 determines that excavation work is being performed when the discharge pressure of the hydraulic pump 63 is greater than a predetermined value for determining the excavation state for a predetermined time. In the present embodiment, the excavation state is determined using the pressure value from the pressure detector 68 provided on the discharge circuit 64 of the hydraulic pump 63.

  The pump capacity control unit 92 controls the pump capacity of the hydraulic pump 63 based on the determination result of the excavation state detection unit 91. Specifically, the pump capacity control unit 92 reduces the pump capacity to a preset target pump capacity when the excavation state detection unit 91 determines that the work implement 3 is in the excavation state. For example, when the target pump capacity is 60% of the maximum capacity, the command current value corresponding to the current pump discharge pressure Pp is calculated on the pump capacity 60% line shown by a two-dot chain line in FIG. Then, by outputting this command current value to the control valve 632 and driving the regulator 631, the pump capacity can be set to 60%.

  The engine output reduction means 93 includes an actual pump capacity calculation means 94, an actual pump flow rate calculation means 95, an actual absorption torque calculation means 96, a required pump flow rate calculation means 97, a required absorption torque calculation means 98, and a command generation means 99. Yes.

  The actual pump capacity calculating means 94 calculates the actual pump capacity of the hydraulic pump 63 using the pump capacity map stored in the storage device 8 based on the discharge pressure of the hydraulic pump 63 and the command current value to the control valve 632. . As described above, during excavation work, the pump capacity is controlled so as to become the target pump capacity. Therefore, if the influence of fluctuations in the discharge pressure of the hydraulic pump 63 and the control delay is not a problem, the target is set. The pump capacity may be used as the actual pump capacity.

  The actual pump flow rate calculating means 95 calculates the actual pump flow rate based on the actual pump capacity calculated by the actual pump capacity calculating means 94 and the engine speed received from the engine speed detector 612. That is, the actual pump flow rate calculation means 95 calculates the actual pump flow rate by multiplying the calculated actual pump capacity by the engine speed.

  The actual absorption torque calculating unit 96 calculates the actual absorption torque of the hydraulic pump 63 based on the discharge pressure of the hydraulic pump 63 and the actual pump flow rate calculated by the actual pump flow rate calculating unit 95. Specifically, the actual absorption torque calculating unit 96 calculates the actual absorption torque of the hydraulic pump 63 by multiplying the discharge pressure of the hydraulic pump 63 by the calculated actual pump flow rate.

  The required pump flow rate calculation means 97 calculates the required pump flow rate of the hydraulic pump 63 based on the lift operation amount at the lift operation lever 41. At this time, as shown in FIG. 6, the required pump flow rate calculation means 97 calculates the required pump flow rate using a required pump flow rate map in which the required pump flow rate corresponding to the lift operation amount is stored.

  The required absorption torque calculating means 98 calculates the required absorption torque of the hydraulic pump 63 based on the discharge pressure of the hydraulic pump 63 and the required pump flow rate calculated by the required pump flow rate calculating means 97. That is, the required absorption torque calculating means 98 calculates the required absorption torque of the hydraulic pump 63 by multiplying the discharge pressure of the hydraulic pump 63 by the calculated required pump flow rate.

  The command generation means 99 calculates an engine torque reduction amount based on the required absorption torque and the actual absorption torque. That is, the command generation means 99 calculates the engine torque reduction amount by subtracting the actual absorption torque from the required absorption torque. Then, the command generation means 99 generates a limit command for reducing the engine torque by the engine torque reduction amount, and outputs the control command to the fuel injection device 611. In the present embodiment, the fuel injection device 611 is commanded to limit the upper limit value of the engine torque with the torque value of the engine torque limit map shown in FIG. 7, as will be described later. Note that the display from 0% to 100% in FIG. 7 indicates the ratio of the engine torque after the restriction to the engine torque of 100%.

[3] Action by Controller Next, the action of the controller 7 will be described with reference to FIGS.
In FIG. 8, first, when the controller 7 reads various input values (step ST1), the excavation state detecting means 91 determines whether or not the state in which the discharge pressure of the hydraulic pump 63 is greater than a predetermined value has continued for a predetermined time. Thus, it is determined whether or not the work machine 3 is in the excavation state (step ST2). In step ST2, when the discharge pressure of the hydraulic pump 63 is less than or equal to the predetermined value, or when the discharge pressure of the hydraulic pump 63 is greater than the predetermined value for less than the predetermined time, the excavation state detection means 91 It is determined that excavation work is not being performed, and the process returns to step ST1. The output of the engine 61 at this time is controlled according to the accelerator operation amount so as to obtain the engine characteristics shown in FIG.

  On the other hand, when the state in which the discharge pressure of the hydraulic pump 63 is greater than the predetermined value continues for a predetermined time in step ST2, the excavation state detection unit 91 determines that the work implement 3 is performing excavation work and proceeds to the next step. move on.

  When it is determined in step ST2 that the work implement 3 is under excavation work, the pump capacity control unit 92 instructs the control valve 632 to reduce the pump capacity of the hydraulic pump 63 to a predetermined capacity (step ST3). For example, the pump capacity control unit 92 changes the command current value to the control valve 632 to reduce the pump capacity to 60% of the maximum capacity.

  Next, the actual pump capacity calculation means 94 calculates the actual pump capacity of the hydraulic pump 63 from the pump capacity map based on the discharge pressure of the hydraulic pump 63 and the command current value to the control valve 632 (step ST4). The actual pump flow rate calculation means 95 calculates the actual pump flow rate by multiplying the calculated actual pump capacity by the engine speed (step ST5), and the actual absorption torque calculation means 96 calculates the discharge pressure of the hydraulic pump 63. The actual absorption torque of the hydraulic pump 63 is calculated by multiplying the calculated actual pump flow rate (step ST6).

  Next, the required pump flow rate calculation means 97 calculates the required pump flow rate of the hydraulic pump 63 from the required pump flow rate map shown in FIG. 6 based on the lift operation amount at the lift operation lever 41 (step ST7). Then, the required absorption torque calculating means 98 calculates the required absorption torque of the hydraulic pump 63 by multiplying the discharge pressure of the hydraulic pump 63 and the calculated required pump flow rate (step ST8).

  Subsequently, the command generation means 99 calculates the engine torque reduction amount by subtracting the actual absorption torque from the required absorption torque (step ST9). Then, the command generation means 99 generates a limit command for reducing the engine torque by the engine torque reduction amount, and outputs the control command to the fuel injection device 611 (step ST10).

  As an example, when the engine 61 is driven with 100% torque, a case where the engine torque is reduced by the engine torque reduction amount ΔT from the matching point P at which the engine torque and the total absorption torque match is shown in FIG. This will be described with reference to FIG. First, the command generation means 99 of the controller 7 refers to the engine torque limit map (see FIG. 7) and calculates what percentage of the engine torque the value obtained by reducing the engine torque reduction amount ΔT from the engine torque at the matching point P corresponds to. To do. For example, as shown in FIG. 9, when the reduced engine torque is 60%, the command generation means 99 generates a control command for limiting the engine torque to a ratio of 60% and outputs it to the fuel injection device 611. .

  In FIG. 10, TW is the work machine drive torque absorbed by the hydraulic pump 63, and the total absorption torque curve B is obtained by adding TW to the travel drive torque curve A. When the command generation means 99 outputs a control command for limiting the engine torque to a ratio of 60% to the fuel injection device 611, as shown in FIG. The matching point P is lowered to the point P1 along the total absorption torque curve B. Along with this, the travel drive torque decreases along the travel drive torque curve A and decreases from T11 to T12. For this reason, even when the capacity of the hydraulic pump 63 is reduced, the traveling drive torque absorbed by the torque converter 621 can be reduced as compared with the conventional case shown in FIG. Therefore, since the travel driving force of the wheel loader 1 can be reduced, the lift force of the bucket 32 by the lift cylinder 34 can be improved by reducing the anti-lift force.

[Second Embodiment]
In the first embodiment, the controller 7 reduces the traveling driving force of the wheel loader 1 by limiting the upper limit value of the engine torque when it is detected that the work implement 3 is in the excavation state.
On the other hand, the second embodiment is different in that the controller 7 limits the upper limit value of the engine speed to reduce the travel driving force of the wheel loader 1.

  Here, the hardware configuration of the wheel loader 1 is the same as that of the first embodiment, but the function of the command generation means 99 in the controller 7 is different. Specifically, the command generation means 99 calculates the engine torque reduction amount ΔT as in the first embodiment. Then, the command generation means 99 generates a control command for limiting the upper limit value of the engine speed so that the engine torque is reduced by the engine torque reduction amount ΔT, and outputs the control command to the fuel injection device 611.

Hereinafter, with reference to FIG. 8 used in the description of the first embodiment, the operation of the controller 7 of the present embodiment will be described.
Steps ST1 to ST9 are the same as those in the first embodiment, and a description thereof will be omitted.
After step ST9, the command generation means 99 generates a control command for limiting the upper limit value of the engine speed so that the engine torque decreases by the calculated engine torque reduction amount ΔT, and outputs the control command to the fuel injection device 611. (Step ST10).

  For example, in FIG. 11, in order to reduce the engine torque from the matching point P where the engine torque matches the total absorption torque by the engine torque reduction amount ΔT, the total absorption torque curve is obtained even when the accelerator operation amount is 100%. It is necessary to limit the amount of accelerator operation corresponding to point P1 that is smaller than the matching point P by ΔT on B. In FIG. 11, the case where the accelerator operation amount corresponding to the point P1 is 60% is taken as an example.

Therefore, the controller 7 generates a control command for limiting the engine speed to the engine speed when the accelerator operation amount is 60%, and outputs the control command to the fuel injection device 611. Due to the limitation of the engine speed, the engine torque is reduced and the matching point P is lowered along the total absorption torque curve B to the point P1. Accordingly, the travel drive torque decreases along the travel drive torque curve A, and the travel drive torque decreases from T21 to T22. Therefore, the travel drive torque absorbed by the torque converter 621 can be reduced. Therefore, since the travel driving force of the wheel loader 1 can be reduced, the lift force of the bucket 32 by the lift cylinder 34 can be improved by reducing the anti-lift force.
Further, since the engine speed can be suppressed, the fuel efficiency of the engine can be improved.

[Third Embodiment]
In the first embodiment, the controller 7 of the wheel loader 1 reduces the driving force of the wheel loader 1 by limiting the upper limit value of the engine torque using the engine torque limit map shown in FIG.
In contrast, the wheel loader 1 according to the third embodiment is configured to be able to switch the engine output mode between the power mode and the economy mode. During excavation work, the controller 7 limits the upper limit value of the engine torque to the economy mode torque value, thereby reducing the traveling driving force of the wheel loader 1.

  Here, the power mode is a mode in which the output of the engine 61 is used to the maximum in order to increase the working efficiency, and has an engine characteristic indicated by a line PM in FIG. On the other hand, the economy mode is a mode for suppressing the fuel consumption of the engine 61 by suppressing the output of the engine 61, and has an engine characteristic indicated by a line EM in FIG.

  As shown in FIG. 13, the wheel loader 1 of this embodiment includes a mode switch 45. The mode changeover switch 45 is a switch for changing the engine output mode, and the operator performs an operation for changing the engine output mode with the mode changeover switch 45. As the engine output mode, a power mode and an economy mode are set in advance, and an operator can select these modes as necessary. The mode changeover switch 45 is electrically connected to the controller 7, and an engine output mode signal corresponding to the selected position of the mode changeover switch 45 is sent to the controller 7.

  As shown in FIG. 14, an engine output mode signal corresponding to the selected position of the mode switch 45 is input to the controller 7 from the mode switch 45. Accordingly, as described later, the functions of the excavation state detection means 91 and the command generation means 99 are different from those of the first embodiment.

Hereinafter, the operation of the controller 7 will be described with reference to FIGS. 15 and 16.
In FIG. 15, first, the controller 7 reads various input values (step ST1). Then, the excavation state detection unit 91 determines whether or not the power mode is selected and the work implement 3 is performing excavation work (step ST22). Whether or not excavation work is being performed is determined by whether or not the state in which the discharge pressure of the hydraulic pump 63 is greater than a predetermined value has continued for a predetermined time, as in the first embodiment.

  In step ST22, when the economy mode is selected or the state where the discharge pressure of the hydraulic pump 63 is greater than the predetermined value does not continue for a predetermined time, the excavation state detection unit 91 determines that the work implement 3 is not in excavation work. To do. In this case, the output of the engine 61 is controlled according to the accelerator operation amount in accordance with the characteristics of the selected engine output mode.

  On the other hand, when it is determined in step ST22 that the power mode is selected and the state where the discharge pressure of the hydraulic pump 63 is greater than a predetermined value has continued for a predetermined time, the excavation state detection unit 91 causes the work implement 3 to perform excavation work. It judges that it is inside and proceeds to the next step.

Since the next steps ST3 to ST9 are the same as those in the first embodiment, description thereof will be omitted.
Then, the command generation means 99 controls the engine torque to be limited by the torque value in the economy mode when the calculated engine torque reduction amount ΔT is larger than the difference value of the engine torque between the power mode and the economy mode. Is output to the fuel injection device 611 (step ST10).

  When the controller 7 outputs a limit command for limiting the engine torque to the torque value in the economy mode to the fuel injection device 611, the engine torque is reduced and the matching point P becomes the total absorption torque curve as shown in FIG. It goes down along B to P1 point. Along with this, the travel drive torque decreases from T31 to T32, so the travel drive torque absorbed by the torque converter 621 can be decreased. Therefore, also in the wheel loader 1 of this embodiment, the lift force of the bucket 32 by the lift cylinder 34 can be improved. Furthermore, since the control software structure of the controller 7 can be simplified, the load on the controller 7 can be reduced. Therefore, since the controller 7 can be configured at low cost, the manufacturing cost of the wheel loader 1 can be reduced.

It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
For example, in each of the above embodiments, the controller 7 sends a control command to the fuel injection device 611 so that the fuel injection device 611 adjusts the fuel injection amount to limit the engine torque and the engine speed. The means for performing is not limited to this. In short, it is only necessary to be able to limit the engine torque and the engine speed. For example, the engine torque and the engine speed may be limited by adjusting the ignition timing of the engine.

  In each of the above embodiments, the controller 7 changes the pump capacity of the hydraulic pump 63 by issuing a control command to the control valve 632 of the hydraulic pump 63. However, a controller for controlling the capacity of the hydraulic pump 63 separately from the controller 7. And the pump capacity of the hydraulic pump 63 may be changed by a control command from the other controller.

  In each of the above embodiments, the excavation state detection unit 91 determines whether the state in which the discharge pressure of the hydraulic pump 63 is greater than a predetermined value has continued for a predetermined time, thereby determining whether the work implement 3 is in excavation work. However, the method for determining the excavation state is not limited to this.

  For example, as shown in FIG. 17, the wheel loader 1 is provided with a stroke sensor 69 that detects the stroke amount of the lift cylinder 34, and based on the cylinder stroke amount from the stroke sensor 69 and speed stage information to the transmission 62. Further, it may be detected whether or not the work machine 3 is in the excavation state. Here, the height of the bucket 32 from the ground surface depends on the tilt angle of the boom 31, and the tilt angle of the boom 31 depends on the stroke amount of the lift cylinder 34. For this reason, by detecting the stroke amount of the lift cylinder 34, it is possible to determine whether or not the bucket 32 is at the height during excavation work, and thus whether or not the work implement 3 is in the excavation state is detected. can do.

  In this case, as shown in FIG. 18, the structure of the controller 7 needs to change the input signals and functions of some means as compared with the case of the first embodiment. Specifically, a stroke sensor 69 is electrically connected to the controller 7. In this controller 7, the excavation state detection means 91 detects whether or not the work implement 3 is in the excavation state based on the cylinder stroke amount from the stroke sensor 69 and the speed stage information to the transmission 62. .

Further, the wheel loader 1 may be provided with a pressure detector that detects the bottom pressure of the lift cylinder 34, and based on the bottom pressure of the lift cylinder 34, it may be detected whether or not the work implement 3 is in the excavation state. .
Furthermore, an angle detector that detects the rotation angle of the boom 31 with respect to the structure 21 may be provided in the wheel loader 1, and the angle from the angle detector may be used to detect whether or not the excavation state is present. .
The above-described excavation state detection method can be applied to any embodiment including the above-described embodiments.

  In each of the above embodiments, the difference value between the required absorption torque and the actual absorption torque is calculated as the engine torque reduction amount. However, the engine torque reduction amount may be obtained from the operation amount of the lift operation lever 41. Specifically, as shown in FIG. 19, a map of the engine torque reduction amount with respect to the operation amount of the lift operation lever 41 is stored in advance in the storage device 8, and the command generation means 99 performs engine torque based on this map. What is necessary is just to obtain | require reduction amount.

In each of the above embodiments, the operation of the work machine 3 is configured to be performed by the lift operation lever 41 and the tilt operation lever 42. However, if the operation amounts of the boom 31 and the bucket 32 can be detected independently, You may make it operate the working machine 3 with one operating lever.
In each of the above embodiments, the accelerator pedal 44 is provided as the operation means of the engine 61. However, if the accelerator operation amount can be detected, the accelerator operation may be performed by another operation means such as a dial. Good.

  The present invention can be used not only for a wheel loader but also for other work vehicles having a hydraulic pump driven by a common engine and a traveling device.

  DESCRIPTION OF SYMBOLS 1 ... Wheel loader, 3 ... Working machine, 5 ... Traveling apparatus, 61 ... Engine, 63 ... Hydraulic pump, 68 ... Pressure detector, 91 ... Excavation state detection means, 93 ... Engine output reduction means, 411 ... Lift operation amount detector (Operation amount detection means).

Claims (4)

A variable displacement hydraulic pump and a traveling device driven by a common engine;
A working machine driven by pressure oil from the hydraulic pump;
A controller that performs output control of the engine and capacity control of the hydraulic pump;
The controller is
Excavation state detection means for detecting whether or not the working machine is in excavation work;
An operation amount detection means for detecting a lift operation amount of the work implement;
A pump capacity control means for reducing the pump capacity of the hydraulic pump when it is detected that the excavation work is in progress;
A wheel loader comprising engine output reduction means for reducing the output of the engine in accordance with the lift operation amount when it is detected that the excavation work is being performed. The wheel loader according to claim 1,
The wheel loader characterized in that the engine output reduction means reduces the output of the engine by limiting engine torque according to the lift operation amount. The wheel loader according to claim 1,
The wheel loader characterized in that the engine output reduction means reduces the output of the engine by limiting an engine speed according to the lift operation amount. The wheel loader according to any one of claims 1 to 3,
A pressure detector for detecting the discharge pressure of the hydraulic pump;
The wheel loader is characterized in that the excavation state detection means determines that the work implement is in excavation work when a state where the discharge pressure is larger than a predetermined value continues for a predetermined time.