JP2968558B2 - Hydraulic pump control device for traveling work vehicle with torque converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Field of the Invention The present invention relates to a discharge capacity of a variable displacement hydraulic pump that is mounted on a traveling work vehicle that extracts traveling driving force from a torque converter and discharges hydraulic oil that drives a front actuator. To a device for controlling

B. Prior Art FIG. 10 shows a schematic configuration of a driving device in a conventional wheel loader. Torque converter on output shaft of engine 21
22 and the fixed hydraulic pump 24 are connected, and the torque converter
A traveling drive device 23 is connected to 22. The hydraulic pump 47 has a hydraulic cylinder 27 for driving the front of a work bucket or the like.
Are connected via a control valve 26.

C. Problems to be Solved by the Invention When performing a combined operation in which a bucket is penetrated into soil and scooped while traveling with a wheel loader having such a configuration, the output torque of the engine is given priority to the front hydraulic pump 47. Therefore, when the load on the front side increases and becomes larger than the engine output torque, the engine speed decreases and the input torque of the torque converter 22 decreases, and the traction force via the traveling drive device, that is, the rush force, decreases. Become smaller.

Thus, in the wheel loader, the direction of the resultant force of the thrust force by the torque converter and the lifting force by the front is important. That is, how to distribute the output horsepower of the engine to the running and the front is an important issue in performance. In particular, the case where the torque converter is in a stall state and the front hydraulic circuit is in a relief state is called combined stall, and this state is the most severe load on the engine, and the engine output torque at this time is transmitted to the front side and the traveling side. The question is how to distribute.

 Next, this point will be described in detail.

FIG. 11 shows the torque curve ET of the engine and the input torque curve TT when the torque converter is stalled.
From this engine output torque curve ET, the pump absorption torque
The torque curve of the remaining engine output after subtracting TP is shown.

Now, when the engine is rotating at the rotation speed No, the torque converter 22 absorbs the input torque (hereinafter referred to as torque converter input torque) To when the wheel loader rushes into an excavation target (such as earth and sand). Here, when the front is operated and the total torque used for traveling with the front becomes larger than the engine output, the engine speed decreases, and the sum of the absorption torques of the torque converter and the front hydraulic pump is equal to the engine output torque. Point (matching point) A
Balance in. As a result, the engine speed becomes Δ
N and the input torque of the torque converter 22 is also ΔT
Just drop.

Conventionally, since a fixed displacement pump was used as the hydraulic pump 24, the torque converter input torque (traction force) at the time of combined stall was set to one. For example, when the pump absorption torque was set large, When the front is operated, a decrease in the traction force (thrust force) is increased, and there is a possibility that excavation cannot be performed. In addition, even if work is possible, the engine speed is greatly reduced, the engine output cannot be used effectively, and work efficiency is poor.

If the capacity of the hydraulic pump 24 is reduced to avoid such inconvenience and the pump absorption torque Tp is reduced as Tpo, the matching point at the time of combined stall becomes the point B, and the engine speed at the time of combined stall becomes the matching point A. It is improved and higher than in the case of, and the engine output can be used effectively. However, in this case, when the front is operated alone, there is a problem that the work of the front becomes small even though there is a margin in the engine output, and the engine cannot be used effectively in another aspect.

An object of the present invention is to increase the pump absorption torque of the front hydraulic pump when the sum of the loads during the combined operation is smaller than the engine output torque, and to make the sum of the loads smaller than the engine output torque such as during combined stall. It is an object of the present invention to provide a hydraulic pump control device for a traveling work vehicle with a torque converter that maintains a large traction force when it becomes large and makes effective use of the engine output.

D. Means for Solving the Problems The traveling work vehicle according to the present invention will be described with reference to FIG. 1 which is an embodiment. The present invention provides a command means 31 for commanding a target rotation speed of the engine 21; A torque converter 22 connected to an output shaft of an engine 21;
A traveling drive unit 23 connected to an output shaft of the engine 22 and an engine 21
The present invention is applied to a traveling work vehicle including a variable displacement hydraulic pump 24 driven by a hydraulic pump and an actuator 27 driven by pressure oil discharged from the variable displacement hydraulic pump 24 to drive a work front member.

Then, detection means 29 for detecting the actual rotation speed of the engine 21
And discharge capacity setting means 28 and 32 for setting the discharge capacity of the variable displacement hydraulic pump 24 based on the rotation speed detected by the detection means 29 and the command value of the target rotation speed. Is the traveling drive device 23 and the actuator 27
When the sum of the loads is smaller than the output torque of the engine 21, the command value of the target rotation speed is used. , The discharge capacity of the variable displacement hydraulic pump 24 is controlled, and the reduction rate of the discharge capacity of the pump 24 when the sum of the loads is larger than the output torque of the engine 21 and the command value is constant, The above object is achieved by controlling the sum so as to be smaller than the output torque of the engine 21 and larger than the reduction rate of the discharge capacity of the pump 24 due to the decrease in the command value.

E. Operation The engine output is distributed between the driving power and the front driving power. If the sum of the running load and the front load exceeds the output torque of the engine 21 during the combined operation of the running and the front, the engine speed drops from the current speed according to the engine output torque curve even if the speed command value is constant, and the torque converter The input torque of 22 decreases in proportion to the decrease of the engine speed. As the rotation speed decreases, the discharge capacity of the variable displacement hydraulic pump 24 decreases, and the pump absorption torque decreases. Then, matching is performed at a point where the sum of the pump absorption torque and the torque converter input torque becomes equal to the engine output torque.

On the other hand, when the rotational speed command value decreases, the rotational speed decreases, the discharge capacity decreases at a predetermined reduction rate, and the pump absorption torque decreases. According to the present invention, the discharge capacity of the variable displacement hydraulic pump 24 is set such that the reduction rate of the discharge capacity due to the reduction in the number of revolutions due to the load when the command value is constant is larger than the reduction rate of the discharge capacity due to the change in the command value. Is controlled.

Therefore, even when a variable displacement hydraulic pump having a large maximum displacement is used, the matching point at the time of combined stall can be set to a higher rotation speed side than before, and the input torque of the torque converter 22 can be increased. As a result, a large traction force can be maintained during the combined operation, and the workload of the front alone can be increased. In addition, the engine output can be used effectively.

In the above sections D and E for describing the configuration of the present invention, the drawings of the embodiments are used for easy understanding of the present invention, but the present invention is not limited to the embodiments.

F. Embodiment An embodiment of the present invention will be described with reference to FIGS.

The engine 21 has a governor 21a, and the number of revolutions is controlled by a governor lever (not shown) operated by depressing an accelerator pedal 31. An input shaft of a torque converter 22 is connected to the engine 21, and an output shaft of the torque converter 22 is connected to an input shaft of a transmission constituting the traveling drive device 23. On the other hand, a variable displacement hydraulic pump 24 and a fixed displacement pump 25 for the front are also connected to the engine 21. The discharge oils of the variable displacement hydraulic pump 24 and the fixed displacement pump 25 are merged and guided to a front drive hydraulic cylinder 27 via a control valve 26. Variable displacement hydraulic pump
The discharge capacity (tilt angle) of 24 is controlled by a pump regulator 28 for tilt angle control.

The pump regulator 28 has two piston chambers 281 and 282. The piston chamber 281 has a piston 283 connected to the tilting lever 24a of the variable displacement hydraulic pump 24,
Spring 2 that always biases 283 to the right, that is, the minimum tilt direction
84 and are arranged. Here, when the engine is stopped, the spring force of the spring 284 is determined such that the tilt angle of the variable displacement hydraulic pump 24 becomes zero. Piston chamber 282
Has a piston 285 with a piston rod 285a at the tip inserted into the left chamber 281l of the piston chamber 281;
A spring 286 is provided for constantly biasing 85 to the left.

A proportional electromagnetic variable throttle 29 is provided in the discharge line of the fixed displacement hydraulic pump 25, and the pressure upstream of the throttle 29 is guided to the right chamber 281r of the piston chamber 281 via the line 30r, and the downstream of the throttle 29. Is led to 281 l of the left ventricle via the line 30 l.
Therefore, the front-rear pressure of the throttle 29 acts on the left and right of the piston 283. On the other hand, the left chamber 282l of the piston chamber 282 is connected to the output port of the pressure reducing valve 32 linked to the accelerator pedal 31, and a pressure proportional to the depression amount of the accelerator pedal 31 is introduced.

Next, the pump displacement control operation of such a wheel loader will be described.

When the accelerator pedal 31 is depressed, the rotation speed of the engine 21 increases, the pressure difference ΔP across the throttle 29 increases, and at the same time, the pressure corresponding to the amount of depression is applied to the output port of the pressure reducing valve 32. As a result, the piston chamber 281 of the pump regulator 28
The front and rear pressures of the throttle 29 are guided to the left and right chambers 281l and 281r, respectively, and the output pressure of the pressure reducing valve 32 is guided to the left chamber 282l of the piston chamber 282.

The differential pressure ΔP before and after the throttle 29 is the second depending on the engine speed N.
The output pressure Pr of the pressure reducing valve 32 changes as shown by a solid line a in the drawing, and changes as shown by a solid line b in FIG. When the work load is equal to or smaller than the engine output torque, the depression amount S of the accelerator pedal is proportional to the engine speed N, so that S = N. This can be expressed as follows.

ΔP = α · f1 (N) (1) Pr = β · f2 (S) = β · f2 (N) (2) where f1 (N) and f2 (N) represent functions of the engine speed and α , Β are constants.

In FIG. 2, f1 is used to simplify the description.
(N) and f2 (N) are linear functions.

Here, assuming that the force for driving the piston 283 to the left against the spring force of the spring 284 is Pa, this driving force Pa is represented by Pa = ΔP−Pr (3)

Torque converter input torque Tr and pump absorption torque Tp
Is within the range of the engine output torque Te, that is, when the work load is small and the engine speed increases in proportion to the amount of depression of the accelerator pedal 31, the driving force Pa
Increases according to the engine speed N as shown by the solid line c in FIG.

On the other hand, when the sum of the torque converter input torque Tr and the pump absorption torque Tp exceeds the engine output torque Te, that is, when the work load is large and the depression amount of the accelerator pedal 31 is constant, the engine rotation speed is determined from the rotation speed (No) at that time. When ΔN ′ decreases according to the engine output torque curve, the pressure P acting on the left chamber 282l of the piston chamber 282
Although r does not change, since the pressure ΔP acting on the piston 283 decreases, the driving force Pa decreases as the engine speed decreases (ΔN ′) as shown by the broken line d in FIG.

 This can be expressed as follows.

ΔP = α · f1 (No−ΔN ′) (4) Pr = β · f2 (No) (5) Pa = ΔP−Pr = α · f1 (No−ΔN ′) − β · f2 (No) (6) Where No is the engine speed before the load is increased ΔN 'is the engine speed reduced by the load Further, the discharge capacity D of the variable displacement hydraulic pump 24 and the driving force Pa of the piston 283 are the solid line e in FIG. (D
= Γ · Pa: where γ is a constant), the engine speed N and the discharge capacity D are equal to the solid line f in FIG. 5 when the work load is smaller than the engine output torque. When it is large, it becomes like a broken line g.

 This can be expressed as follows.

B) When the work load is smaller than the engine output torque, D = γ ｛α · f1 (No) −β · f2 (No)｝ (7) b) When the work load is larger than the engine output torque, D = γ ｛α · f1 (No-ΔN ')-β · f2 (No)｝
(8) FIG. 6 shows the engine speed N obtained by the above operation.
FIG. 4 is a diagram illustrating torque and torque T.

ET indicates the output torque curve of the engine 21, TT indicates the input torque curve of the torque converter 22, and L1 to L3 indicate the remaining engine output torque curves obtained by subtracting the pump absorption torque Tp from the engine output torque ET. L1 is an example when the work load is smaller than the engine output torque, L2 is an example when the work load is larger than the engine output torque, and L3 is an example when the opening degree of the variable throttle 29 is larger than that at the time of L2. Show.

As described above, when the front and traveling are simultaneously operated, the torque of the front pump is used with priority. When the front load is small, the sum of the input torques of the front pumps 24 and 25 and the torque converter 22 does not exceed the output torque of the engine 21, so the engine speed increases and decreases in proportion to the amount of depression of the accelerator pedal 31. . In this case, the displacement is expressed by the equation (7) and changes with respect to the engine speed N as shown by a solid line f in FIG. Here, since the pump absorption torque is represented by (discharge capacity (D) × pump pressure (P)), the pump absorption torque increases and decreases in proportion to the engine speed as shown by a solid line L1 in FIG.

When the front load increases and the sum of the input torques of the front pumps 24, 25 and the torque converter 22 exceeds the output torque of the engine 21, the engine rotation is performed even if the depression amount of the accelerator pedal 31 is kept constant. The number decreases from the rotational speed (No) at that time according to the engine output torque curve. The discharge capacity is expressed by equation (8), changes as shown by a broken line g in FIG. 5, and the pump absorption torque increases and decreases in proportion to the engine speed as shown by L2 in FIG. In this case, as can be seen from the broken line g, the rate of change of the discharge capacity with respect to the engine speed is larger than that of the solid line f when the load is small. Therefore, the rate of change of the pump absorption torque with respect to the engine speed is also large. This can be easily understood from the fact that the change in the distance between L2 and ET in FIG. 6 is greater than the change in the distance between L1 and ET.

Now, let ET and TT in FIG. 6 be equal to those in FIG.
It is assumed that the magnitude of the engine speed and the torque corresponding to the intersection C between TT and TT are equal to those corresponding to the matching point A in FIG.

When the engine speed is No, the torque converter absorbs the input torque To. Here, when the front is operated and the total torque becomes larger than the engine output torque, in this embodiment, the variable displacement hydraulic pump is
24, the point at which the pump absorption torque changes like L2 and the engine speed decreases by ΔN '(<ΔN), the sum of the pump absorption torque Tp and the torque converter input torque Tt becomes the engine output torque Te. And the matching point is D. As a result, the decrease in the engine speed is ΔN ′ (<NΔ) and the decrease in the input torque of the torque converter is ΔT ′ (<ΔT). And the engine output can be used effectively.

On the other hand, when the sum of the pump absorption torque and the torque converter input torque does not exceed the engine output torque, for example, when the front is operated alone, the discharge capacity D of the variable displacement hydraulic pump 24, that is, Since the torque changes like L1, the pump absorption torque can be set larger than that of the ETL in FIG. 11, and the front work can be improved.

 The operation of the above embodiment is summarized as follows.

(1) When the work load is smaller than the engine output torque, the pump displacement increases in proportion to the target rotation speed commanded by the accelerator pedal 31.

(2) If the work load is larger than the engine output torque and the actual engine speed is lower than the target speed,
The pump displacement decreases in proportion to the rotational speed deviation from the pump displacement described in (1), and the traveling torque can be increased accordingly.

In the above description, the engine speed is detected by the discharge oil of the fixed pump 25 that merges with the variable displacement hydraulic pump 24 to drive the regulator 28.However, the regulator 28 is driven by a dedicated pump, It may be driven using a pump for use.

FIG. 7 shows a main part of another embodiment, in which a controller 41 composed of a microcomputer or the like controls a regulator 128 to control the discharge capacity of the variable displacement hydraulic pump 24.

That is, the angle of the engine speed sensor 42 for detecting the engine speed, the potentiometer 43 for detecting the depression amount of the accelerator pedal 32, the pressure sensor 44 for detecting the circuit pressure P, and the tilt lever 24a of the pump regulator 28 And a tilt angle sensor 45 for detecting the tilt angle of the pump 24, that is, the discharge capacity D. The detection output of each sensor is input to the controller 41, and the controller executes the procedure shown in FIG. 8 to adjust the discharge pressure of the proportional electromagnetic pressure reducing valve 46 to adjust the discharge capacity of the variable displacement hydraulic pump 24. Pressure reducing valve
When discharge pressure of 46 is large, piston 128 of regulator 128
a moves leftward against the spring 128b, and the discharge capacity increases.

When the program shown in FIG. 8 is executed, in step S1, the rotation speed sensor 42, the potentiometer 43, the pressure sensor
The engine speed is calculated from the detection output of 44 and the tilt angle sensor 45.
N, accelerator pedal depression amount S, circuit pressure P and discharge capacity D are read. In step S2, based on the detection output of each sensor, the engine output torque Te
It is determined whether the input torque Tt and the pump absorption torque Tp are larger than the sum of the input torque Tt and the pump absorption torque Tp. If Te> Tt + Tp is denied (if the load is small) in step S2, the process proceeds to step S3, and if affirmative (if the load is large), the process proceeds to step S4. In step S3, the displacement D is obtained from the engine speed N, which is the output of the revolution sensor 42, according to a map of the engine speed N and the displacement D as shown in the figure. In step S4, the accelerator pedal depression amount is determined. S and engine speed N
When the discharge capacity D is obtained in accordance with the three-dimensional map shown in FIG. 5, a signal corresponding to the discharge capacity D obtained in step S3 or S4 is converted to a proportional electromagnetic pressure reducing valve in step S5.
The pressure is supplied to the right chamber 128r of the regulator 128 to obtain a desired tilt angle.

As shown in FIG. 9, if the front load increases and the work load becomes larger than the engine output torque when the engine speed is No and the discharge capacity Do is the low load state, for example, the accelerator depression amount S A curve i is selected, and the discharge capacity D according to the front load is determined according to the curve i.
Is required, and the regulator is
128 is operated, whereby the variable displacement hydraulic pump 24 is set to the required displacement D.

In such an embodiment, the same operation and effect as those of the embodiment described above can be obtained.

In the embodiment shown in FIG. 1, since the throttle 29 is a variable throttle, the torque curve of the variable displacement hydraulic pump 24 can be set to L3 as shown in FIG. Can be set in any manner as desired. Also, in the embodiment of FIG. 7, the matching point can be arbitrarily changed similarly by changing the curve i in FIG.
Further, although the wheel loader has been described, the present invention can be applied to other similar traveling work vehicles.

In the configuration of the above embodiment, the accelerator pedal 31 and the potentiometer 43 constitute the command means, the variable throttle 29 and the engine speed sensor 42 constitute the detection means, and the regulators 28 and 128 constitute the discharge capacity setting means.

G. Effect of the Invention According to the present invention, the reduction rate of the discharge capacity of the variable displacement hydraulic pump when the sum of the loads during the combined operation becomes larger than the engine output torque is set to the discharge capacity due to the decrease in the rotational speed command value. When the sum of the loads becomes larger than the engine output torque, such as during combined stall during combined operation of running and front, the pump absorption torque and torque converter input torque Is set on the high rotation speed side,
When a large traction force can be maintained and the sum of the loads is smaller than the engine output torque, the absorption torque of the front hydraulic pump can be increased, and the engine can be effectively used.

[Brief description of the drawings]

1 to 6 illustrate one embodiment of the present invention.
FIG. 1 is a configuration diagram showing a traveling drive system and a front drive system,
FIG. 2 shows the relationship N-.DELTA.P between the engine speed and the differential pressure and the relationship S- between the accelerator pedal depression amount and the pressure reducing valve output.
A graph showing Pr, FIG. 3 is a graph showing a relationship N-Pa between the engine speed and the regulator driving force, FIG. 4 is a graph showing a relationship Pa-D between the regulator driving force and the discharge capacity, and FIG. FIG. 6 is a graph showing the relationship between the engine speed and the engine output torque, the input torque of the torque converter, and the pump absorption torque. 7 to 9 illustrate a modified embodiment. FIG. 7 is a diagram showing the main part, FIG. 8 is a flowchart showing an example of the procedure, and FIG. 9 is a graph explaining the operation. . FIGS. 10 and 11 illustrate a conventional example. FIG. 10 is a graph corresponding to FIG. 1, and FIG. 11 is a graph corresponding to FIG. 21: Engine, 22: Torque converter 23: Travel drive, 24: Variable displacement hydraulic pump 25: Fixed displacement hydraulic pump, 27: Hydraulic cylinder 28: Pump regulator, 29: Throttle 31: Accel pedal, 32: Pressure reducing valve 41: Controller, 42: Rotation speed sensor 43: Potentiometer, 44: Pressure sensor 45: Tilt angle sensor, 46: Pressure reducing valve 47: Fixed displacement hydraulic pump, 128: Regulator

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomoo Takahashi 650, Kandamachi, Tsuchiura-shi, Ibaraki Prefecture Within Hitachi Construction Machinery Engineering Co., Ltd. (56) References JP-A-49-65448 (JP, A) JP-A-2-45668 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F04B 49/00-51 / 00

Claims (1)

(57) [Claims] 1. Command means for commanding a target engine speed, a torque converter connected to an output shaft of the engine, a traveling drive device connected to an output shaft of the torque converter, and a drive unit driven by the engine. In a hydraulic pump control device for a traveling work vehicle having a variable displacement hydraulic pump and an actuator for driving a work front member with pressure oil discharged from the variable displacement hydraulic pump, a detecting means for detecting an actual engine speed. And a discharge capacity setting means for setting a discharge capacity of the variable displacement hydraulic pump based on a rotation speed detected by the detection means and a command value of the target rotation speed. When the sum of the loads of the traveling drive device and the actuator is smaller than the output torque of the engine, the target rotation speed command value When the sum of the loads is larger than the output torque of the engine, the discharge capacity of the variable displacement hydraulic pump is controlled based on the command value of the target rotational speed and the sum of the loads. Is smaller than the output torque of the engine when the sum of the loads is smaller than the output torque of the engine. A hydraulic pump control device for a traveling work vehicle, wherein the control is performed so as to be greater than a capacity reduction rate.