JP2009174536A - Load control device of engine of work vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a load control device of an engine of a work vehicle such as a wheel loader which is capable of obtaining the sufficient traction and increasing the vehicle speed in a short time when a high traveling load is applied without degrading any vehicle body performance or causing any trouble such as waste of energy. <P>SOLUTION: An absorbing torque changing means for changing the absorbing torque is provided on each of variable displacement hydraulic pumps 7, 8, 9. A controller 18 determines whether or not a vehicle is in an accelerated state, and executes the control of reducing the absorbing torques of the variable displacement hydraulic pumps 7, 8, 9 when it is determined that the traveling load is in a high state. The control is executed on the condition that a "power mode" is selected by a power mode switch 31 or the like. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a load control device for an engine of a work vehicle.

  The wheel loader is driven by driving wheels (wheels) driven by a torque converter with an engine as a drive source. That is, the engine output is used for the traveling load. In addition, the engine is a drive source for a work machine such as a steering mechanism or a loader. That is, the steering hydraulic pump is driven by the engine, the pressure oil discharged from the steering hydraulic pump is supplied to the steering hydraulic cylinder, and the steering mechanism is operated accordingly. Further, the loader hydraulic pump is driven by the engine, and the pressure oil discharged from the loader hydraulic pump is supplied to the loader hydraulic cylinder, and the loader is operated accordingly. As the steering hydraulic pump and the loader hydraulic pump, a fixed displacement hydraulic pump having a constant capacity is used. Thus, the engine output is used not only for the traveling load but also for the working hydraulic load.

  The traveling speed of the wheel loader changes according to the amount of depression of the accelerator pedal. That is, the engine speed is changed according to the amount of depression of the accelerator pedal, and the vehicle speed is changed accordingly.

  In addition, the wheel loader has an opportunity to work in other vehicle such as a hydraulic excavator under a situation where both a traveling load and a working hydraulic load are applied, for example, a situation where the loader is moved up and down while traveling. Compared to many.

  Here, regarding the hydraulic excavator, the invention of changing the maximum absorption torque and the capacity of the variable displacement hydraulic pump according to various work modes is already known from the patent documents exemplified below.

JP-A-62-58033 Japanese Patent No. 2711833

  Thus, in the wheel loader, the output of one engine is used for both the traveling load and the working hydraulic load. Therefore, the engine output that can be used for running depends on the size of the working hydraulic load.

  FIG. 3 shows the relationship between the engine speed N and the engine torque Te. In FIG. 3, a torque converter matching curve Lt is an absorption torque line of the torque converter and indicates a running load. As indicated by an arrow A, the engine speed N and the engine torque Te increase as the accelerator pedal is depressed. When the loader or steering mechanism is not operating, that is, when there is no working hydraulic load, the torque converter absorption horsepower matches the engine output at the matching point V1 on the maximum torque line R1, and all of the engine output is used as the traveling load. be able to. For this reason, when a large traction force is required or when acceleration is required on a slope, a sufficient traction force can be obtained and the vehicle speed can be increased in a short time.

  However, under conditions where the loader and the steering mechanism are operated while traveling, that is, when a working hydraulic load is generated, the engine output indicated by hatching in FIG. 3 is consumed as the working hydraulic load. Only the engine output can be used for the traveling load.

  For this reason, the matching point between the torque converter absorption horsepower and the engine output is lowered to V2, and the engine output that can be used for running is lowered, so that a high running load must be dealt with while performing work. Under some circumstances, the engine output required for a high travel load cannot be obtained, and therefore sufficient traction force cannot be obtained or the vehicle speed cannot be increased even if it takes a long time.

  Therefore, in order to solve such problems, it is conceivable to reduce the torque itself absorbed by the working machine hydraulic pump, that is, to set the capacity of a fixed displacement hydraulic pump such as a steering hydraulic pump small. . However, if the capacity of the steering hydraulic pump is set to be small, there arises a problem that the steering is not sufficiently cut off at low idle when the engine speed is low. The wheel loader is required to sufficiently turn the steering even when the engine is idling (during low idle rotation). In order to allow a large amount of pressure oil to flow through the steering hydraulic cylinder even during low idle rotation with a low engine speed, it is necessary to secure the pump capacity at a certain level or higher. If the pump capacity is reduced, the maximum flow rate that can be supplied to the hydraulic cylinder at the time of low idle rotation with a low engine speed is reduced, resulting in a problem that the speed at which the steering is turned off becomes slow. Further, if the capacity of the loader hydraulic pump is set to be small, the flow rate is similarly reduced, the speed of raising and lowering the loader is reduced, and work efficiency is impaired. Reducing the capacity of the fixed displacement hydraulic pump in this way leads to a decrease in vehicle body performance.

  Naturally, it may be possible to cope with high driving loads by increasing the engine size and allowing extra engine torque, but this is a situation where work is being performed and acceleration is required on a large traction and slope. Is a small amount of actual work time, and for that reason, increasing the size of the engine causes an increase in cost and fuel efficiency, resulting in wasted energy.

  It is also possible to adjust the loader operation lever so that it can be adjusted to increase the amount of engine output that can be turned to the traveling load when traveling and work are operated simultaneously. Complex operations impose a heavy burden on the operator and it is difficult to actually make such adjustments.

  The present invention has been made in view of such a situation, and in a work vehicle such as a wheel loader, it is sufficient when a high traveling load is applied without causing problems such as a decrease in vehicle body performance and waste of energy. Therefore, it is an object of the present invention to obtain a sufficient traction force and to increase the vehicle speed in a short time.

  Although Patent Documents 1 and 2 describe that the maximum absorption torque and the capacity of the variable displacement hydraulic pump are changed according to various work modes, the traveling load depends on the various modes. The technical idea of changing the distribution of engine output to the work load, that is, a plurality of variable displacement hydraulic pumps are divided into traveling hydraulic pumps and working hydraulic pumps, and traveling hydraulic pumps according to various modes There is no description of the technical idea that the maximum absorption torque and the capacity of the working hydraulic pump are different.

The first invention is
The engine of the work vehicle in which the output of the engine (1) is transmitted to the drive wheels (5) and the output of the engine (1) is transmitted to the work implement via the variable displacement hydraulic pump (7, 8, 9). A load control device of
Absorption torque changing means (19, 22) for changing the absorption torque of the variable displacement hydraulic pump (7, 8, 9);
Acceleration state determination means (18) for determining that the work vehicle is in an acceleration state;
And a control means (18) for reducing the absorption torque of the variable displacement hydraulic pump (7, 8, 9) when the acceleration state determination means (18) determines that the work vehicle is in an acceleration state. It is a load control device for an engine of a work vehicle.

The second invention is the first invention,
Acceleration state determining means (18),
Acceleration detecting means for detecting the acceleration of the work vehicle;
And means for determining that the acceleration of the work vehicle detected by the acceleration detecting means is equal to or greater than a predetermined threshold value.

The third invention is the first invention,
Acceleration state determining means (18),
An operation amount detection means (17a) for detecting an operation amount of the travel operation element (17);
And a means for determining that the operation amount of the travel operation element (17) detected by the operation amount detection means (17a) is equal to or greater than a predetermined threshold value.

A fourth invention is the first invention,
Acceleration state determining means (18),
A rotational speed difference calculating means for calculating a difference between the target rotational speed of the engine (1) and the actual engine rotational speed;
And a means for determining that the rotational speed difference calculated by the rotational speed difference calculating means is equal to or greater than a predetermined threshold value.

The fifth invention
In the load control device for a work vehicle engine according to any one of the fourth aspect of the present invention to first free the invention,
Further comprising a selection means (31) for selecting a power mode for traveling at a high traveling load,
When the acceleration state determination means (18) determines that the vehicle is in the acceleration state, the fact that the power mode is selected by the selection means (31) indicates that the variable displacement hydraulic pump (7, 8, 9) It is characterized by a condition for executing control for reducing the absorption torque.

The sixth invention, in any one of the fourth aspect of the present invention to the second free invention,
It further comprises selection means (31) for selecting a plurality of travel modes,
The threshold value is changed to a size corresponding to the selected work mode according to the type of the travel mode selected by the travel mode selection means (31).

A seventh invention is any one of the first invention to the sixth invention,
Wherein the output of the engine (1) is transmitted to a drive wheel (5) via the travel hydraulic pump.

Eighth invention, in any one of the seventh invention to the first free invention,
Control that reduces the absorption torque of the variable displacement hydraulic pump when the brake is operated when the absorption torque of the variable displacement hydraulic pump (7, 8, 9) is reduced when it is determined to be in the acceleration state It is characterized by canceling .

A ninth invention is the eighth invention,
When the brake is operated, the control for reducing the absorption torque of the variable displacement hydraulic pump (7, 8, 9) is canceled when the operation amount of the brake exceeds a predetermined threshold value.

  The operation and effect of the present invention will be described with reference to the drawings.

That is, as shown in FIG. 6 or 7, the variable displacement hydraulic pump 7, 8, 9 is provided with an absorption torque changing means 19 or 22 for changing the absorption torque. The controller 18 determines whether or not the traveling load is in a high state. When it is determined that the traveling load is in a high state, the controller 18 executes control to reduce the absorption torque of the hydraulic pumps 7, 8, and 9. This control is executed, for example, on the condition that the “power mode” is selected by the power mode switch 31 (the fifth invention).

  In FIG. 2, a torque converter matching curve Lt is an absorption torque line of the torque converter 2 and indicates a running load. As shown by the arrow A, as the accelerator pedal 17 is depressed, the engine speed N and the engine torque Te increase, and the torque converter absorption horsepower increases.

  The torque converter absorption horsepower is obtained by subtracting the pump absorption horsepower of the variable displacement hydraulic pumps 7, 8, and 9 from the engine output. When the working hydraulic load is increased, the traveling load is relatively reduced, and the traction force and acceleration are reduced.

  When it is determined that the traveling load is low, the torque on the torque line R2 obtained by subtracting the working hydraulic load from the maximum torque line R1 in FIG. 2 is used as the traveling load. The matching point between the torque converter absorption horsepower and the engine output is the point V2 on the torque line R2.

  If it is determined that the traveling load is high, the absorption torque of the variable displacement hydraulic pumps 7, 8, 9 is changed to a small value. As a result, the working hydraulic load is reduced, and the torque on the torque line R3 obtained by subtracting a small working hydraulic load from the maximum torque line R1 in FIG. 2 is used as the traveling load. The matching point between the torque converter absorption horsepower and the engine output is the point V3 on the torque line R3.

  When it is determined that the traveling load is high as described above, the matching point moves from V2 to a point V3 having a larger torque converter absorption horsepower compared to the case where the traveling load is not high. When the load becomes high during traveling, for example, when a large traction force or acceleration on a slope is required, a large traction force can be obtained, and the vehicle speed can be increased in a short time.

  In other words, conventionally, as shown in FIG. 3, even when the traveling load is high, the engine output indicated by the diagonal lines in FIG. Since the engine output that can be turned to the load was small (matching point V2), if the load becomes high during driving while performing work, for example, when a large traction force or acceleration is required on a slope, sufficient traction force is obtained. The vehicle speed could not be increased or the vehicle speed could not be increased over a long period of time, but according to the present embodiment, as shown in FIG. Since the engine output is distributed to the working hydraulic load and the engine output that can be turned to the traveling load is relatively large (matching point V3), the load is higher during traveling while performing the work than in the past. When it becomes, and for example, a large traction force, when the acceleration is needed on a slope, it is possible to obtain a greater tractive force, it is possible to increase more quickly vehicle speed.

  When the loader or steering mechanism is not operating, that is, when there is no working hydraulic load and the traveling load is high, the torque converter absorption horsepower matches the engine output at the matching point V1 on the maximum torque line R1, and the engine output Everything can be used for driving load. For this reason, when a large traction force is required or when acceleration is required on a slope, a sufficient traction force can be obtained and the vehicle speed can be increased in a short time.

  As described above, according to the present invention, when a high traveling load is applied, sufficient traction force can be obtained and the vehicle speed can be increased in a short time. Moreover, the capacity of the fixed displacement hydraulic pump is not set uniformly low, but the capacity or maximum absorption torque of the variable displacement hydraulic pump is only temporarily reduced when the running load is high. Therefore, the vehicle performance is not reduced. In addition, since it is not necessary to increase the size of the engine in order to increase the engine output, problems such as deterioration of fuel consumption and waste of energy are not caused.

The determination that the traveling load is high can be made by determining that the wheel loader 100 is in the acceleration state ( first invention).

Specifically, the controller 18 determines whether or not the acceleration of the vehicle body is greater than or equal to a predetermined threshold value, and when it is determined that the acceleration of the vehicle body is equal to or greater than the predetermined threshold value, the hydraulic pump 7 , 8 and 9 are reduced, and the torque converter absorption torque is relatively increased ( second invention).

Further, when the controller 18 determines whether or not the amount of depression of the accelerator pedal 17 is equal to or greater than a predetermined threshold, and when it is determined that the amount of depression of the accelerator pedal 17 is equal to or greater than a predetermined threshold, The absorption torque of the hydraulic pumps 7, 8, and 9 may be reduced to relatively increase the torque converter absorption torque ( third invention).

Further, the controller 18 calculates a difference between the target engine speed of the engine 1 and the actual engine speed Nr, and determines whether or not the engine speed difference is equal to or greater than a predetermined threshold value. If it is determined that the value is equal to or greater than the predetermined threshold value, the absorption torque of the hydraulic pumps 7, 8, and 9 may be decreased to relatively increase the torque converter absorption torque ( fourth invention).

The determination that the traveling load is high is made by actually measuring the traveling load transmitted to the drive wheels 5 and determining that the measured traveling load is equal to or greater than a predetermined threshold value. It is Ru can.

Specifically, the controller 18 calculates a travel load based on the torque converter input shaft rotational speed N1, the transmission output shaft rotational speed N2, and the speed stage currently selected in the transmission 3, and the calculated travel load. Is determined to be greater than or equal to a predetermined threshold value, and if it is determined that the calculated traveling load is equal to or greater than the predetermined threshold value, the absorption torque of the hydraulic pumps 7, 8, 9 is reduced. , relatively, not good by increasing the torque converter absorption torque.

  Further, it may be determined whether or not the vehicle body is in a decelerating state, and when it is determined that the vehicle body is in a decelerating state, the control for reducing the absorption torque of the hydraulic pumps 7, 8, and 9 may be released. That is, when it is determined that the vehicle body is in a decelerating state, the control for reducing the maximum absorption torque of the hydraulic pump in the direction of arrow D in FIG. 4 is canceled, or the capacity of the hydraulic pump in the direction of arrow E in FIG. As shown in FIG. 2, from the matching point V3 where the working hydraulic load is reduced (the traveling load is increased) to the matching point V2 where the working hydraulic load is increased (the traveling load is reduced), as shown in FIG. It is made to return (8th invention).

Each threshold value described above may be changed according to the selected travel mode. That is, when the “power mode” is selected, the threshold is set to a low value because the operator is willing to travel with a high travel load. For example, the threshold value of the depression amount of the accelerator pedal 17 is set to a low value, and even when the depression amount of the accelerator pedal is small, the absorption torque of the hydraulic pumps 7, 8, 9 is immediately reduced to relatively Control to increase torque converter absorption torque is executed. Thereby, it is possible to cope with a high traveling load early. On the other hand, when the “normal mode” is selected, the operator does not intend to travel at such a high driving load, and therefore the threshold value is set to a high value. For example, the threshold value of the depression amount of the accelerator pedal 17 is set to a high value, and when the accelerator pedal depression amount is greatly depressed, the absorption torque of the hydraulic pumps 7, 8, 9 is reduced, Control to increase torque converter absorption torque is executed. Thereby, it is possible to cope with a high traveling load while giving priority to the working hydraulic load ( sixth invention).

  Further, the control for reducing the absorption torque of the hydraulic pumps 7, 8, 9 may be executed only by operating the switch on the operation panel 30. That is, when “power mode” is selected, in FIG. 4, control is performed to reduce the maximum absorption torque of the hydraulic pump in the direction of arrow D, or in FIG. 5, the capacity of the hydraulic pump is reduced in the direction of arrow E. As shown in FIG. 2, the control is executed to shift to a matching point V3 where the working hydraulic load is reduced (travel load is increased).

On the other hand, when the “normal mode” is selected, the control for reducing the maximum absorption torque of the hydraulic pump in the direction of arrow D in FIG. 4 is released, or the capacity of the hydraulic pump is reduced in the direction of arrow E in FIG. As shown in FIG. 2, the control is released so that the working hydraulic load is reduced (the traveling load is increased) to the matching point V2 where the working hydraulic load is increased (the traveling load is reduced). you to.

By the way, depending on the type of work vehicle, the output of the engine 1 is not transmitted to the drive wheels 5 through the torque converter 2 and the transmission 3, but the output of the engine 1 is transmitted through the traveling hydraulic pump and the traveling hydraulic motor. Some of them are transmitted to the drive wheels 5. The present invention can also be applied to a work vehicle having such a configuration ( seventh invention).

Drawing 1 is a figure showing the composition of the work vehicle of an embodiment. FIG. 2 is a diagram showing the relationship between the engine speed and the engine torque. FIG. 3 is a diagram for explaining the prior art and corresponds to FIG. FIG. 4 is a diagram illustrating control for changing the maximum absorption torque of the hydraulic pump. FIG. 5 is a diagram illustrating control for changing the capacity of the hydraulic pump. FIG. 6 is a diagram showing a configuration example for performing PC control. FIG. 7 is a diagram illustrating a configuration example for performing LS control.

  Embodiments of an engine load control device for a work vehicle according to the present invention will be described below with reference to the drawings.

  FIG. 1 shows a configuration of a wheel loader according to an embodiment of the present invention with respect to a portion according to the present invention.

  As shown in FIG. 1, the output shaft of the engine 1 of the wheel loader 100 is connected to the PTO shaft 6. The PTO shaft 6 is connected to the torque converter 2 and is also connected to a steering hydraulic pump 7, a loader hydraulic pump 8, a fan hydraulic pump 9, and a torque converter lubrication hydraulic pump 10.

  The steering hydraulic pump 7, the loader hydraulic pump 8, and the fan hydraulic pump 9 are variable displacement hydraulic pumps, and the pump displacement q (by changing the tilt angles of the swash plates 7a, 8a, 9a, respectively. cc / rev) is changed.

  The output of the engine 1 is transmitted to the drive wheels 5 through the torque converter 2, the transmission 3, and the differential gear 4. The transmission 3 is composed of a forward hydraulic clutch, a reverse hydraulic clutch, a speed clutch, that is, a first speed hydraulic clutch, a second speed hydraulic clutch, a third speed hydraulic clutch, and a fourth speed hydraulic clutch. Any one of the forward hydraulic clutch and the reverse hydraulic clutch is selected, and any one of the speed stage clutches is selected to perform a shift.

  The output of the engine 1 is transmitted to a steering hydraulic pump 7, a loader hydraulic pump 8, a fan hydraulic pump 9, and a torque converter lubrication hydraulic pump 10.

  When the steering hydraulic pump 7 is driven, the discharge pressure oil is supplied to the steering hydraulic cylinder 13 via the steering control valve 11.

  The steering hydraulic cylinder 13 is connected to a steering mechanism. When pressure oil is supplied to the steering hydraulic cylinder 13, the steering mechanism is activated and the vehicle body is turned. The spool of the steering control valve 11 is moved in response to an operation of a steering handle (not shown), the opening area of the control valve 11 is changed accordingly, and the flow rate supplied to the steering hydraulic cylinder 13 is changed.

  When the loader hydraulic pump 8 is driven, the discharge pressure oil is supplied to the loader hydraulic cylinder 14 via the loader control valve 12.

  The loader hydraulic cylinder 14 is connected to a loader at the front of the vehicle body. When pressure oil is supplied to the loader hydraulic cylinder 14, the loader is activated. That is, the boom constituting the loader is raised or lowered, and the bucket is tilted. The spool of the loader control valve 12 is moved according to the operation of a loader operation lever (not shown), and the opening area of the control valve 12 is changed accordingly, and the flow rate supplied to the loader hydraulic cylinder 14 is changed. The

  When the fan hydraulic pump 9 is driven, the discharge pressure oil is supplied to the fan hydraulic motor 15 and the cooling fan 16 is operated.

  When the torque converter lubrication hydraulic pump 10 is driven, the discharge pressure oil is supplied to the torque converter 2 and the torque converter 2 is lubricated.

  On the output shaft of the engine 1, an engine speed detection sensor 1a for detecting the actual speed Nr of the engine 1 is provided. The engine speed Nr detected by the engine speed detection sensor 1a is input to the controller 18.

  On the input shaft of the torque converter 2 (output shaft of the engine 1), a torque converter input shaft rotational speed detection sensor 2a for detecting the rotational speed N1 of the input shaft of the torque converter 2 is provided. The rotational speed N1 detected by the torque converter input shaft rotational speed detection sensor 2a is input to the controller 18.

  The output shaft of the transmission 3 is provided with a transmission output shaft rotational speed detection sensor 3 a that detects the rotational speed N 2 of the output shaft of the transmission 3. The rotational speed N2 detected by the transmission output shaft rotational speed detection sensor 3a is input to the controller 18.

  The accelerator pedal 17 is operated by an operator, an operation amount (depression amount) is detected by a stroke sensor 17 a provided on the accelerator pedal 17, and a signal indicating the operation amount is input to the controller 18.

  The drive wheel 5 is provided with a hydraulic brake that brakes the drive wheel 5. The brake pedal 29 is operated by an operator, an operation amount (depression amount) is detected by a stroke sensor 29 a provided on the brake pedal 29, and a signal indicating the operation amount is input to the controller 18. The controller 18 controls the hydraulic brake so that the brake pressure is in accordance with the depression amount of the brake pedal 29.

  The controller 18 controls the engine 1 so as to achieve a target rotational speed corresponding to the operation amount of the accelerator pedal 17.

  The operation panel 30 is provided with a power mode switch 31, a transmission mode switch 32, a forward / reverse switch 33, and a speed stage switch 34.

  The shift mode switch 32 is a switch that selects the timing of automatic shift of the transmission 3, the forward / reverse switch 33 is a switch that selects the forward hydraulic clutch and the reverse hydraulic clutch of the transmission 3, and the speed stage switch 34 is , A switch for selecting a speed stage clutch (a first speed hydraulic clutch, a second speed hydraulic clutch, a third speed hydraulic clutch, a fourth speed hydraulic clutch).

  The controller 18 controls the transmission 3 so that the speed stage changes at the shift timing selected by the shift mode switch 32. Further, the controller 18 controls the transmission 3 so as to automatically shift in the range of the speed stage selected by the speed stage switch 34 in the forward direction or the reverse direction selected by the forward / reverse switch 33.

  The power mode switch 31 is a switch that selects a traveling state (power mode) that requires a large engine output for traveling with a high traveling load. When the “power mode” is not selected by the power mode switch 31 (when the switch is off), the traveling state (normal mode) in which the traveling load is low and the engine output is not so large for traveling is selected.

  The engine 1 is a diesel engine, and its output is controlled by adjusting the amount of fuel injected into the cylinder. This adjustment is performed by controlling a governor attached to the fuel injection pump of the engine 1. As the governor, an all-speed control type governor is generally used, and the engine speed and the fuel injection amount are adjusted in accordance with the load so that the target speed is in accordance with the accelerator pedal depression amount. That is, the governor increases or decreases the fuel injection amount so that there is no difference between the target engine speed and the actual engine speed. The output characteristics of the engine 1 are represented in FIG. The horizontal axis in FIG. 2 is the engine speed N, and the vertical axis is the engine torque Te.

  In FIG. 2, the region defined by the maximum torque line R1 indicates the performance that the engine 1 can produce. The governor controls the engine 1 so that the torque does not exceed the maximum torque line R1 and the exhaust smoke limit is not reached, and the engine speed N does not exceed the high idle speed NH and does not overspeed.

(First embodiment)
In this embodiment, the variable displacement hydraulic pumps 7, 8, 9 are provided with absorption torque changing means for changing the absorption torque. In the controller 18, it is determined whether or not the traveling load is high. When it is determined that the traveling load is high, the controller 18 performs control to reduce the absorption torque of the variable displacement hydraulic pumps 7, 8, and 9. Execute. This control is executed on condition that the “power mode” is selected by the power mode switch 31.

  In FIG. 2, a torque converter matching curve Lt is an absorption torque line of the torque converter 2 and indicates a running load. As shown by the arrow A, as the accelerator pedal 17 is depressed, the engine speed N and the engine torque Te increase, and the torque converter absorption horsepower increases.

  The torque converter absorption horsepower is obtained by subtracting the pump absorption horsepower of the variable displacement hydraulic pumps 7, 8, and 9 (including the torque converter lubrication hydraulic pump 10) from the engine output. When the working hydraulic load is increased, the traveling load is relatively reduced, and the traction force and acceleration are reduced.

  When it is determined that the traveling load is low, the torque on the torque line R2 obtained by subtracting the working hydraulic load from the maximum torque line R1 in FIG. 2 is used as the traveling load. The matching point between the torque converter absorption horsepower and the engine output is the point V2 on the torque line R2.

  If it is determined that the traveling load is high, the absorption torque of the variable displacement hydraulic pumps 7, 8, 9 is changed to a small value. As a result, the working hydraulic load is reduced, and the torque on the torque line R3 obtained by subtracting a small working hydraulic load from the maximum torque line R1 in FIG. 2 is used as the traveling load. The matching point between the torque converter absorption horsepower and the engine output is the point V3 on the torque line R3.

  When it is determined that the traveling load is high as described above, the matching point moves from V2 to a point V3 having a larger torque converter absorption horsepower compared to the case where the traveling load is not high. When the load becomes high during traveling, for example, when a large traction force or acceleration on a slope is required, a large traction force can be obtained, and the vehicle speed can be increased in a short time.

  In other words, conventionally, as shown in FIG. 3, even when the traveling load is high, the engine output indicated by the diagonal lines in FIG. Since the engine output that can be turned to the load was small (matching point V2), if the load becomes high during driving while performing work, for example, when a large traction force or acceleration is required on a slope, sufficient traction force is obtained. The vehicle speed could not be increased or the vehicle speed could not be increased over a long period of time, but according to the present embodiment, as shown in FIG. Since the engine output is distributed to the working hydraulic load and the engine output that can be turned to the traveling load is relatively large (matching point V3), the load is higher during traveling while performing the work than in the past. When it becomes, and for example, a large traction force, when the acceleration is needed on a slope, it is possible to obtain a greater tractive force, it is possible to increase more quickly vehicle speed.

  When the loader or steering mechanism is not operating, that is, when there is no working hydraulic load and the traveling load is high, the torque converter absorption horsepower matches the engine output at the matching point V1 on the maximum torque line R1, and the engine output Everything can be used for driving load. For this reason, when a large traction force is required or when acceleration is required on a slope, a sufficient traction force can be obtained and the vehicle speed can be increased in a short time.

  Next, a specific configuration example of means for changing the absorption torque of the hydraulic pump will be described.

  FIG. 6 shows a configuration for PC control of the loader hydraulic pump 8. In FIG. 6, the loader hydraulic pump 8 is shown as a representative, but the same applies to the case where the other variable displacement hydraulic pumps 7 and 9 are PC-controlled.

  The PC valve 19 tilts the swash plate 7a of the hydraulic pump 8 so that the product of the discharge pressure Pp (kg / cm 2) of the hydraulic pump 8 and the capacity q (cc / rev) of the hydraulic pump 8 does not exceed a certain torque. Control the corners. If the rotational speed of the engine 1 is constant, the hydraulic pump 8 so that the product of the discharge pressure Pp (kg / cm 2) of the hydraulic pump 8 and the flow rate Q (l / min) of the hydraulic pump 8 does not exceed a constant horsepower. The swash plate 8a is controlled.

  When the hydraulic pumps 7, 8, 9 are collectively controlled by the PC, the average value of the discharge pressures of the pumps 7, 8, 9 is input to the PC valve 19.

  The PC valve 19 inputs the discharge pressure Pp of the hydraulic pump 8 as a pilot pressure, and supplies the drive pressure oil corresponding to the discharge pressure Pp to the servo valve 20 to control the capacity q of the hydraulic pump 8.

  The contents of the PC control will be described with reference to FIG. 4, the horizontal axis represents the discharge pressure Pp (kg / cm 2) of the hydraulic pump 8, and the vertical axis represents the capacity q (cc / rev) of the hydraulic pump 8, that is, the tilt angle of the swash plate 8a.

  As shown in FIG. 4, when the discharge pressure Pp of the hydraulic pump 8 is equal to or lower than a predetermined pressure, the tilt angle of the swash plate 8a of the hydraulic pump 8 is set to the maximum, and the maximum capacity qmax is obtained. When the working hydraulic load increases and the pump discharge pressure Pp exceeds a certain pressure, the pump displacement q is decreased according to the characteristic LN1, and the swash plate tilt angle is minimized and the minimum displacement qmin.

  As described above, in the hydraulic pump 8, the pump displacement q is controlled according to the pump discharge pressure Pp in a range where the working hydraulic load, that is, the absorption torque does not exceed the maximum absorption torque Tp1.

  A control signal i1 is applied to the PC valve 19 from the controller 18, and the maximum absorption torque is changed according to the control signal i1.

  If it is determined that the traveling load is low, the maximum absorption torque of the hydraulic pump 8 is set to a large value of Tp1, and the hydraulic pump 8 is controlled according to the characteristic LN1. When it is determined that the traveling load is high, as indicated by an arrow D, the value changes from the characteristic LN1 to the characteristic LN2, and the pump discharge pressure value at which the pump capacity starts to decrease decreases. The maximum absorption torque value is set to a small value Tp2.

  FIG. 7A shows a configuration for LS controlling the loader hydraulic pump 8. In FIG. 7A, the loader hydraulic pump 8 is shown as a representative, but the other variable displacement hydraulic pumps 7 and 9 are configured similarly in the case of LS control.

  The LS valve 22 adjusts the tilt angle of the swash plate 8a of the hydraulic pump 8 so that the differential pressure ΔP between the discharge pressure Pp of the hydraulic pump 8 and the load pressure PLS of the loader hydraulic cylinder 14 becomes a constant differential pressure ΔPLS. Control.

  The LS valve 22 is provided with a spring for setting a constant differential pressure ΔPLS. The discharge pressure Pp of the hydraulic pump 8 is applied as a pilot pressure to the pilot port on the opposite side of the spring side of the LS valve 22, and the load pressure PLS of the loader hydraulic cylinder 14 is applied as a pilot pressure to the pilot port on the spring side. Added. The drive pressure oil is supplied from the LS valve 22 to the servo valve 20 so that the capacity q of the hydraulic pump 8 is controlled.

When the opening area of the loader control valve 12 is A and the resistance coefficient is c, the discharge flow rate Q of the hydraulic pump 8 is
Q = c · A · √ (ΔP)
It is represented by Since the differential pressure ΔP becomes constant by the LS valve 22, the pump flow rate Q changes only depending on the opening area A of the spool of the control valve 12.

  When the loader operation lever is operated, the opening area A of the loader control valve 12 increases according to the operation amount, and the pump flow rate Q increases as the opening area A increases. At this time, the pump flow rate Q is not affected by the working hydraulic load and is determined only by the operation amount of the loader operation lever. By providing the LS valve 22 in this way, the pump flow rate Q changes according to the operator's intention (according to the operation position of the loader operation lever) without increasing / decreasing depending on the working hydraulic load, so that fine control performance, that is, an intermediate operation region The operability is improved.

  However, even in a region where the maximum flow rate of the hydraulic pump 8 is not exceeded, such as during fine control, in order to always supply a flow rate as required by the loader hydraulic cylinder 14, the same discharge as in the high rotation region even in the low rotation region. It becomes flow rate.

  For this reason, the controller 18 performs control to lower the discharge flow rate by lowering the differential pressure set value ΔPLS when the rotational speed of the engine 1 is low. The LS valve 22 is provided with a differential pressure setting unit 23 for changing the spring setting spring force. When the controller 18 outputs a control signal i2 to the differential pressure setting unit 23, the differential pressure setting unit 23 The set spring force of the 22 spring is changed to change the differential pressure set value ΔPLS.

  As shown in FIG. 7B, even if the control signal i2 is applied to the electromagnetic solenoid of the LS valve 22, the set spring force of the spring of the LS valve 22 is changed to change the differential pressure set value ΔPLS. Good.

  The contents of such differential pressure set value change control will be described with reference to FIG. The horizontal axis in FIG. 5 is the discharge pressure Pp (kg / cm 2) of the hydraulic pump 8, and the vertical axis is the capacity q (cc / rev) of the hydraulic pump 8, that is, the tilt angle of the swash plate 8a.

  As shown in FIG. 5, when the discharge pressure Pp of the hydraulic pump 8 is a certain value Pp1 and the pump displacement q is the maximum value qmax, the differential pressure set value ΔPLS is changed to a small value. This corresponds to the fact that the right side of the above equation (Q = c · A · √ (ΔP)) has become smaller, and as shown by the arrow E, the pump capacity q is changed from the maximum value qmax to a smaller value q1. The By reducing the pump capacity q, the absorption torque of the hydraulic pump 8, that is, the working hydraulic load is reduced.

  When the controller 18 determines that the traveling load is low, the controller 18 outputs a control signal i2 that sets the differential pressure setting value ΔPLS to a large value and increases the absorption torque of the hydraulic pump 8 with respect to the LS valve 22. To do. If it is determined that the traveling load is high, a control signal i2 for setting the differential pressure setting value ΔPLS to a small value and reducing the absorption torque of the hydraulic pump 8 is output to the LS valve 22.

  The combination of the control for changing the maximum absorption torque of the hydraulic pump shown in FIG. 4 and the control for changing the pump capacity of the hydraulic pump shown in FIG. 5 allows the absorption torque of the hydraulic pump when the working hydraulic load is high. You may implement control which reduces.

  Note that the maximum absorption torque or the capacity may be reduced for all the variable displacement hydraulic pumps 7, 8, 9, and one or two of the variable displacement hydraulic pumps 7, 8, 9 are variable displacement hydraulic pressures. For the pump, the maximum absorption torque or capacity may be reduced.

  As described above, according to the present embodiment, when a high traveling load is applied, sufficient traction force can be obtained and the vehicle speed can be increased in a short time. Moreover, the capacity of the fixed displacement hydraulic pump is not set uniformly low, but the capacity or maximum absorption torque of the variable displacement hydraulic pump is only temporarily reduced when the running load is high. Therefore, the vehicle performance is not reduced. In addition, since it is not necessary to increase the size of the engine in order to increase the engine output, problems such as deterioration of fuel consumption and waste of energy are not caused.

(Second embodiment)
In the first embodiment, when it is determined that the traveling load is high, the absorption torque of the hydraulic pump is reduced to relatively increase the torque converter absorption torque, but the traveling load is high. Can be determined by determining that the wheel loader 100 is in an acceleration state.

  Specifically, the controller 18 determines whether or not the acceleration of the vehicle body is greater than or equal to a predetermined threshold value, and when it is determined that the acceleration of the vehicle body is equal to or greater than the predetermined threshold value, the hydraulic pump 7 , 8 and 9 are decreased, and the torque converter absorption torque is relatively increased. The acceleration of the vehicle body may be calculated as a change amount per unit time of the rotational speed detected by the engine rotational speed detection sensor 1a, the torque converter input shaft rotational speed sensor 2a, or the transmission output shaft rotational speed sensor 3a. A sensor may be provided to obtain the output of the acceleration sensor.

  Further, the controller 18 determines whether or not the acceleration of the vehicle body is equal to or greater than a predetermined threshold value, determines whether or not the vehicle body is in a deceleration state, and the acceleration of the vehicle body is equal to or greater than the predetermined threshold value. If it is determined that the vehicle body is not in the decelerating state, the absorption torque of the hydraulic pumps 7, 8, and 9 may be reduced to relatively increase the torque converter absorption torque. Whether or not the vehicle body is in a decelerating state may be determined based on whether or not the brake pedal 29 is not depressed, or whether or not the amount of depression of the brake pedal 29 is equal to or less than a predetermined threshold value. Alternatively, it may be determined that the vehicle body is not in a decelerating state by detecting the pressure of the hydraulic brake hydraulic oil and determining that the hydraulic pressure is below a predetermined threshold.

  Further, when the controller 18 determines whether or not the amount of depression of the accelerator pedal 17 is equal to or greater than a predetermined threshold, and when it is determined that the amount of depression of the accelerator pedal 17 is equal to or greater than a predetermined threshold, The absorption torque of the hydraulic pumps 7, 8, and 9 may be reduced, and the torque converter absorption torque may be relatively increased.

  Further, the controller 18 determines whether or not the amount of depression of the accelerator pedal 17 is equal to or greater than a predetermined threshold value, and also determines whether or not the vehicle body is in a decelerating state, and the amount of depression of the accelerator pedal 17 is predetermined. When it is determined that the vehicle body is not in a decelerating state, the absorption torque of the hydraulic pumps 7, 8, and 9 may be reduced to relatively increase the torque converter absorption torque. .

  Further, the controller 18 calculates a difference between the target engine speed of the engine 1 and the actual engine speed Nr, and determines whether or not the engine speed difference is equal to or greater than a predetermined threshold value. When it is determined that the value is equal to or greater than the predetermined threshold value, the torque absorption torque of the hydraulic pumps 7, 8, and 9 may be reduced to relatively increase the torque converter absorption torque.

  Further, the controller 18 calculates the difference between the target engine speed of the engine 1 and the actual engine speed Nr, determines whether or not the engine speed difference is equal to or greater than a predetermined threshold value, and decelerates the vehicle body. It is determined whether or not the engine is in a state, and when it is determined that the difference in rotational speed is equal to or greater than a predetermined threshold value and the vehicle body is not in a decelerating state, the absorption torque of the hydraulic pumps 7, 8, and 9 is reduced. Thus, the torque converter absorption torque may be relatively increased.

(Third embodiment)
In the first embodiment, when it is determined that the traveling load is high, the absorption torque of the hydraulic pump is reduced to relatively increase the torque converter absorption torque, but the traveling load is high. This determination can be made by actually measuring the traveling load transmitted to the drive wheels 5 and determining that the measured traveling load is equal to or greater than a predetermined threshold value.

  Specifically, the controller 18 calculates a travel load based on the torque converter input shaft rotational speed N1, the transmission output shaft rotational speed N2, and the speed stage currently selected in the transmission 3, and the calculated travel load. Is determined to be greater than or equal to a predetermined threshold value, and if it is determined that the calculated traveling load is equal to or greater than the predetermined threshold value, the absorption torque of the hydraulic pumps 7, 8, and 9 is reduced The torque converter absorption torque may be relatively increased.

  Further, the controller 18 calculates a travel load based on the torque converter input shaft rotational speed N1, the transmission output shaft rotational speed N2, and the speed stage currently selected in the transmission 3, and the calculated travel load is a predetermined value. It is determined whether or not the vehicle is above a threshold value, and whether or not the vehicle body is in a deceleration state, and the calculated traveling load is not less than a predetermined threshold value and the vehicle body is not in a deceleration state. In such a case, the absorption torque of the hydraulic pumps 7, 8, and 9 may be reduced to relatively increase the torque converter absorption torque.

  The traveling load may be obtained by calculation as described above, or the traveling load may be detected directly by attaching a stress gauge or the like to the output shaft of the torque converter 2, the output shaft of the transmission 3, or the like.

(Fourth embodiment)
In the above embodiment, the conditions for executing the control for reducing the absorption torque of the hydraulic pumps 7, 8, and 9 have been described. Conversely, it is determined whether or not the vehicle body is in a decelerating state, and the vehicle body is in a decelerating state. When it is determined that there is, control for reducing the absorption torque of the hydraulic pumps 7, 8, 9 may be released. That is, when it is determined that the vehicle body is in a decelerating state, the control for reducing the maximum absorption torque of the hydraulic pump in the direction of arrow D in FIG. 4 is canceled, or the capacity of the hydraulic pump in the direction of arrow E in FIG. As shown in FIG. 2, from the matching point V3 where the working hydraulic load is reduced (the traveling load is increased) to the matching point V2 where the working hydraulic load is increased (the traveling load is reduced), as shown in FIG. Try to bring it back.

(5th Example)
In the first to fourth embodiments described above, the control for reducing the absorption torque of the hydraulic pumps 7, 8, 9 is executed on the condition that the “power mode” is selected by the power mode switch 31. Explained as a thing. However, even if “power mode” is not selected by the power mode switch 31 (even if “normal mode” is selected), it is determined that the traveling load is high. If it is determined that the vehicle body is in an accelerating state or if the measured traveling load is determined to be high, the absorption torque of the hydraulic pumps 7, 8, 9 may be reduced.

(Sixth embodiment)
In the second embodiment and the third embodiment described above, the control for reducing the absorption torque of the hydraulic pumps 7, 8, and 9 is executed when the threshold value is exceeded. The size may be changed according to the type of the selected travel mode.

  In this embodiment, the control for reducing the absorption torque of the hydraulic pumps 7, 8, 9 is executed regardless of whether the “power mode” is selected or the “normal mode” is selected. . However, the magnitude of the threshold value is changed between when the “power mode” is selected and when the “normal mode” is selected. When “power mode” is selected, the threshold is set to a low value because the operator is willing to travel with a high travel load. For example, the threshold value of the depression amount of the accelerator pedal 17 is set to a low value, and even when the depression amount of the accelerator pedal is small, the absorption torque of the hydraulic pumps 7, 8, 9 is immediately reduced to relatively Control to increase torque converter absorption torque is executed. Thereby, it is possible to cope with a high traveling load early. On the other hand, when the “normal mode” is selected, the operator does not intend to travel at such a high driving load, and therefore the threshold value is set to a high value. For example, the threshold value of the depression amount of the accelerator pedal 17 is set to a high value, and when the accelerator pedal depression amount is greatly depressed, the absorption torque of the hydraulic pumps 7, 8, 9 is reduced to relatively reduce the torque converter. Control to increase the absorption torque is executed. Thereby, it is possible to cope with the traveling load while giving priority to the working hydraulic load.

(Seventh embodiment)
In the embodiment described above, when it is determined that the traveling load is high (when the vehicle body is determined to be in an acceleration state or when the measured traveling load is determined to be high), the hydraulic pump is not used for the first time. Although it has been described that the control for decreasing the absorption torque of 7, 8, 9 and relatively increasing the torque converter absorption torque is executed, such a determination itself is omitted, and the switch operation on the operation panel 30 is performed. However, the control for reducing the absorption torque of the hydraulic pumps 7, 8, and 9 may be executed.

  In this embodiment, when “power mode” is selected, in FIG. 4, control is performed to reduce the maximum absorption torque of the hydraulic pump in the direction of arrow D, or in FIG. As shown in FIG. 2, the control is performed to reduce the working hydraulic load to a matching point V3 where the working hydraulic load is reduced (the traveling load is increased).

  On the other hand, when the “normal mode” is selected, the control for reducing the maximum absorption torque of the hydraulic pump in the direction of arrow D in FIG. 4 is released, or the capacity of the hydraulic pump is reduced in the direction of arrow E in FIG. As shown in FIG. 2, the control is released so that the working hydraulic load is reduced (the traveling load is increased) to the matching point V2 where the working hydraulic load is increased (the traveling load is reduced). To.

  The various determination methods described in the second embodiment and the third embodiment described above may be combined as appropriate. For example, the hydraulic pumps 7, 8, 9 are not met until the two conditions that the amount of depression of the accelerator pedal 17 is equal to or greater than a predetermined threshold and that the measured traveling load is equal to or greater than the predetermined threshold are met. Control for reducing the absorption torque of the motor may be executed.

  In the above-described embodiment, the case where the driving mode is two types of “power mode” and “normal mode” has been described as an example. However, the number of driving modes is three or more, and the control contents are set according to each driving mode. You may make it change the magnitude | size of a threshold value.

  By the way, depending on the type of work vehicle, the output of the engine 1 is not transmitted to the drive wheels 5 through the torque converter 2 and the transmission 3, but the output of the engine 1 is transmitted through the traveling hydraulic pump and the traveling hydraulic motor. Some of them are transmitted to the drive wheels 5. The present invention can also be applied to a work vehicle having such a configuration. In this case, the “travel load” of each embodiment may be replaced with a travel hydraulic load, and the control of each embodiment may be performed in the same manner. That is, when it is determined that the traveling hydraulic load is high (when it is determined that the vehicle body is in an acceleration state or when the measured traveling hydraulic load is high), the working hydraulic pumps 7 and 8 are used. , 9 may be performed to reduce the absorption torque (working hydraulic load) and relatively increase the absorption torque (traveling hydraulic load) of the traveling hydraulic pump.

  The present invention is not limited to the wheel loader, and can be similarly applied to any work vehicle in which the engine output (engine torque) is distributed to both the travel load and the work hydraulic load.

  DESCRIPTION OF SYMBOLS 1 Engine 1a Engine rotational speed detection sensor 2 Torque converter 3 Transmission 2a Torque converter input shaft rotational speed detection sensor 3a Transmission output shaft rotational speed sensor 5 Drive wheel 7, 8, 9 Variable displacement hydraulic pump 17 Accelerator pedal 18 Controller 19 PC valve 22 LS valve 29 Brake pedal

Claims (9)

The engine of the work vehicle in which the output of the engine (1) is transmitted to the drive wheels (5) and the output of the engine (1) is transmitted to the work implement via the variable displacement hydraulic pump (7, 8, 9). A load control device of
Absorption torque changing means (19, 22) for changing the absorption torque of the variable displacement hydraulic pump (7, 8, 9);
Acceleration state determination means (18) for determining that the work vehicle is in an acceleration state;
And a control means (18) for reducing the absorption torque of the variable displacement hydraulic pump (7, 8, 9) when the acceleration state determination means (18) determines that the work vehicle is in an acceleration state. A load control device for an engine of a work vehicle. Acceleration state determining means (18),
Acceleration detecting means for detecting the acceleration of the work vehicle;
The engine load control device for a work vehicle according to claim 1, further comprising means for determining that the acceleration of the work vehicle detected by the acceleration detection means is equal to or greater than a predetermined threshold value. Acceleration state determining means (18),
An operation amount detection means (17a) for detecting an operation amount of the travel operation element (17);
The operation according to claim 1, comprising means for determining that the operation amount of the travel operation element (17) detected by the operation amount detection means (17a) is equal to or greater than a predetermined threshold value. Load control device for vehicle engine. Acceleration state determining means (18),
A rotational speed difference calculating means for calculating a difference between the target rotational speed of the engine (1) and the actual engine rotational speed;
The engine load control device for a work vehicle according to claim 1, further comprising means for determining that the rotational speed difference calculated by the rotational speed difference calculating means is equal to or greater than a predetermined threshold value. The load control device for an engine of a work vehicle according to any one of claims 1 to 4 ,
Further comprising a selection means (31) for selecting a power mode for traveling at a high traveling load,
When the acceleration state determination means (18) determines that the vehicle is in the acceleration state, the fact that the power mode is selected by the selection means (31) indicates that the variable displacement hydraulic pump (7, 8, 9) A load control device for an engine of a work vehicle, characterized in that a condition for executing control for reducing the absorption torque is made. The load control device for an engine of a work vehicle according to any one of claims 2 to 4,
It further comprises selection means (31) for selecting a plurality of travel modes,
Depending on the type of the running mode selected by the drive mode selection means (31), the threshold of the work vehicle, characterized in that changing to a size associated with the working mode selected engine Load control device. The engine load control device for a work vehicle according to any one of claims 1 to 6,
An engine load control device for a work vehicle, wherein an output of the engine (1) is transmitted to a drive wheel (5) via a traveling hydraulic pump. Control that reduces the absorption torque of the variable displacement hydraulic pump when the brake is operated when the absorption torque of the variable displacement hydraulic pump (7, 8, 9) is reduced when it is determined to be in the acceleration state load control device for a work vehicle engine according to any one of claims 1 to 7, characterized in that to release the. When the brake is operated, the control for reducing the absorption torque of the variable displacement hydraulic pump (7, 8, 9) is canceled when the brake operation amount exceeds a predetermined threshold value. Item 9. The load control device for the engine of the work vehicle according to Item 8.

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