JPS63154874A - Contorlle for variable displacement hydraulic pump - Google Patents

Abstract

PURPOSE:To enable quick reset to a normal state, by modifying the load mode of an engine upon overheat of the engine. CONSTITUTION:When a heavy load or an intermediate load work mode has been by a work mode changeover switch 9, a controller 10 judges whether an engine 1 is overheated or not based on a detection signal from a temperature sensor 8. When it is judged that the engine is overheated, a target engine rotation being applied onto a proportional solenoid 11 is reduced by a predetermined amount to lower the engine rotation, and a lower characteristic is selected according to an inner work mode of an absorption power characteristic of a variable displacement hydraulic pump 2 prestored in a memory 14. Since the load mode of the engine 1 is modified when the engine 1 is overheated, damage of engine 1 or degradation of workability due to overheat can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for controlling a variable displacement hydraulic pump driven by an engine.

[Conventional technology]

Construction machinery such as power shovels are equipped with variable displacement hydraulic pumps driven by engines. JP-A-60-2 discloses a device that changes the absorption torque of the pump according to the work mode (high-load work, light-load work, etc.).
No. 04987.

[Problem that the invention seeks to solve]

However, the conventional device described above has a drawback in that it cannot deal with engine overheating. Note that as a countermeasure against overheating, it is possible to reduce the output horsepower and rotational speed of the engine, but this countermeasure that does not change the absorption horsepower of the pump, which is a direct load on the engine, does not prevent the engine from overheating. It takes a long time for the engine to return to its normal state, which not only makes it impossible to work satisfactorily, but also shortens the life of the engine.

SUMMARY OF THE INVENTION In view of these conventional problems, it is an object of the present invention to provide a device that can quickly restore a normal state when an engine overheats.

[Means for solving problems]

The present invention includes an engine rotation speed detection means for detecting the rotation speed of the engine, a pressure detection means for detecting the discharge pressure of a variable displacement hydraulic pump driven by the engine, and an overheat detection means for detecting overheat of the engine. and a work mode instruction means for instructing a work mode corresponding to the size of the load, and a pump absorption horsepower characteristic that is set according to the work mode, and when the overheating is detected, the currently set pump absorption horsepower characteristic is set. an absorption horsepower characteristic setting means for setting a pump absorption horsepower characteristic for a light load work mode in place of the horsepower characteristic; means for determining a target swash plate tilting angle of the pump in accordance with horsepower characteristics; means for reducing the rotational speed of the engine when the overheating is detected; and swash plate control means for controlling the swash plate so that the swash plate tilts at the same angle as the swash plate.

[Effect]

According to the above configuration, when the engine overheats, the rotational speed of the engine is reduced and the absorption horsepower of the pump is reduced.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

A variable displacement hydraulic pump 2 shown in the figure is driven by an engine 1, and a discharge flow rate v per revolution is changed by changing the tilt angle of a swash plate 2a by a swash plate driving actuator 3.

The pressure oil discharged from the pump 1 is supplied to a hydraulic actuator (for example, a hydraulic motor, a hydraulic cylinder) that drives a working machine of a construction machine (not shown).

The accelerator sensor 4 shown in the figure outputs a signal corresponding to the operation amount of the accelerator lever 5, the engine rotation sensor 6 outputs a signal indicating the actual rotation speed N of the engine 1, and the pressure sensor 7 indicates the discharge pressure of the pump 2. The signal and further the temperature sensor 8 is
A signal indicating oil dust T (for example, cooling water temperature, exhaust temperature) of the engine 1 is outputted.

The work mode selector switch 9 is operated by the operator according to the work state, and the switch 9 selects H mode for high load work, M mode for medium load work, and H mode for low load work.

The signal output from the accelerator sensor 4 is subjected to processing such as amplification by the controller 10, and then input to the proportional solenoid 11 as a signal indicating the target engine rotation speed Nr.

The proportional solenoid 11 is connected to the cabana 1 as shown in FIG.
The proportional solenoid 11 is provided as an actuator for driving the fuel control lever 13 of No. 2, and the fuel injection amount (engine torque) is changed by the displacement of the control lever 13 due to the biasing force of the proportional solenoid 11.

Now, assuming that the horsepower generated by the engine 1 is WE, and the horsepower absorbed by the variable displacement hydraulic pump 2 is W, these are expressed as follows under a certain load condition.

W E-W P -, -P-Q- 2
*p* N*V...(1) However, P; pump discharge pressure (kg/ci) Q;
Pump discharge flow W (ff/l1in) N; engine rotational speed (rprA) V; pump discharge flow rate per revolution (cc/rev) K, 2. From the constant and equation (1), ■-11112111...(2) K2
The relationship φPΦN is obtained. Incidentally, as is well known, V represents the swash plate 2a.
Therefore, V shown in equation (2>) indicates the swash plate tilt angle.

In FIG. 3, symbol A indicates the rated horsepower curve of the engine 1, that is, the horsepower curve when the accelerator lever 5 is operated to the full position.

Normally, construction machinery is operated with the accelerator lever 5 operated to its full position, and the maximum horsepower point of the engine 1 at this time is Pl.

Lines B, C, and D shown in the figure are preset absorption horsepower characteristics of the pump. These horsepower characteristics are each expressed by a monotonically increasing function f +
(N), f2 (N) and i3 (N), and P
It intersects the rated horsepower curve A of the engine at points 1, P2, and 23, respectively.

These horsepower characteristics are stored in the memory 14 in advance.

In order to change the absorption horsepower Wp of the pump 2 shown in equation (2) according to the above self-functions f1 (N), f2 (N) and f3 (N)l, the following equations (3) and (4
) and (5) are obtained by controlling the swash plate tilt angle of the pump 2.

v, fl (N) ... (3) K2
Parable P@N ■-f2 (Σengineering...(4) K2-P
llN v-f3cN> ...(5) K2
#P・N Then, when the swash plate tilt angle of the pump 2 is controlled according to formulas (3), (4), and (5) above while the slot lever 5 is operated to the full position, the angle of the swash plate of the engine 1 is Generated horsepower W. and absorption horsepower WP of pump 2 are respectively the p1. This results in matching at p2 and 23 points.

Furthermore, when the operation amount of the throttle lever 5 is decreased and the target engine speed is lowered by ΔN, that is, when the horsepower curve of the engine 1 is set as shown by the symbol A' in FIG. , by controlling the swash plate tilt angle according to equations (3), (4), and (5-) above, the generated horsepower W of the engine 1 and the absorbed horsepower Wp of the pump 2 are determined.
are matched at point P1', point P2' and point P3', respectively.

FIG. 5 shows the processing means of the controller 0 shown in FIG.

In this procedure, it is first determined whether work mode L is instructed by the work mode changeover switch 9 (step 100), and if the mode L is not instructed, work mode M is changed in the next step 101. It is determined whether an instruction has been given or not.

If both modes L and M are not specified,
That is, if mode H is instructed, it is determined in the next step 103 whether or not the engine 1 is overheating, and if the determination result is NO, the memory 14
Absorption horsepower characteristics B, C and D shown in Fig. 3 stored in
Among them, the characteristic B−f+(N) is selected (step 1
08).

On the other hand, if the determination result in step 101 is YES,
In step 109, it is determined whether or not the engine 1 is overheating. If the engine 1 is not overheating, the characteristic C-f2 (N) shown in FIG. 3 is selected in step 104. Further, if the judgment result in step 100 is YES, step 111 shows the characteristic D=
f3 (N) is selected.

Note that the determination of whether or not the temperature is overheated in steps 102 and 109 is made based on the output of the temperature sensor 8.

After the selection process in any one of steps 108, 109 and 111 is executed, the rotation speed N of the engine 2 is determined based on the output of the engine rotation sensor 6, and the discharge of the pump 1 is determined based on the output of the pressure sensor 7. Each pressure P is detected (step 105).

When characteristic B=f+(N) is selected in step 108, the calculation shown in equation (3) above is performed based on the characteristic f+(N) and N and P detected in step 105. executed in step 106, whereby pump 2
The pump discharge flow rate V that makes the absorption horsepower Wp of the engine a value according to f+(N) is determined.

Further, when the characteristic C-f 2 (N) is selected in step 104 and the characteristic D-f3 (N) is selected in step 111,
N) is selected, the calculations shown in equations (2) and (3) above are executed in step 106, thereby changing the absorption horsepower WP of the pump 2 to f2 (N) and f3 (N). Pump discharge flow mV to be made to the value according to
are required respectively.

In the next step 107, a swash plate tilt angle command (a value corresponding to V) for obtaining the pump discharge flow mV determined in step 106 is created, and this command is applied to the swash plate drive actuator 3. is output to.

As a result, the accelerator lever 5 is set to the full position,
And when engine 1 is not overheating, characteristics B = f 1 (N), C - f 2 (N) and D
When -f3 (N) is selected, the absorbed horsepower of the generating pump 2 and the generated horsepower of the engine 1 match at points P, , P2 and 23 shown in FIG. 3, respectively.

That is, when mode H is selected and high-load work is performed, 11 points of horsepower are absorbed by the pump 2. In addition, when medium-load work is performed with mode M selected and when light-load work is performed with mode L selected, 22 and 23 points of horsepower are absorbed by pump 2, respectively. Become.

By the way, when work is performed in mode H or mode M, the engine 1 may overheat due to an increase in load.

In the procedure shown in FIG. 5, if overheating is determined in step 102 when mode H is instructed,
In step 103, processing to lower the engine speed by ΔN is executed, and in step 104, the absorption horsepower characteristic C-f is
2 (N) is selected.

Further, if overheating is determined in step 109 when mode M is instructed, a process to similarly lower the engine speed by ΔN is executed in step 110, and in step 111, absorption horsepower characteristic D-f3 (N
) is selected.

Note that the processing in step 103 or 110 is as follows:
This means changing the signal indicating the target engine speed N applied to the proportional solenoid 11 to a signal indicating the rotation speed N - ΔN. It becomes A'.

Thereafter, the processes described above are executed in steps 105, 106 and 107, so if overheating occurs while mode H is instructed, pump 2
If the matching point between the absorbed horsepower Wp of the engine 1 and the generated horsepower WE of the engine 1 is shifted from point 11 in FIG. The above matching points are 2
It will be moved from 2 points to 23 points.

Note that step 1 of reducing the target engine speed by ΔN
The process of 03 is continued until the overheat condition is resolved.

When the matching point is changed from 11 points to P2' or from 22 points to P3', the load on the engine 1 is significantly reduced.

Therefore, the engine 1 can quickly return to a normal state from an overheated state. Since the swash plate control of the pump 1 continues even while the above-mentioned process is being executed, the work can be continued without inconveniences such as a significant drop in engine speed. can.

In the embodiment, the characteristics B, C, and D shown in FIG. 3 are stored in the memory 14, but it is also possible to have the controller 10 calculate the pump absorption horsepower according to these characteristics.

Further, in the above embodiment, the embodiment was shown when the accelerator lever 5 was operated to the full position, but of course the same control as described above is possible even when the lever 5 is operated to the intermediate operation position. be.

In this case, of course, the characteristics f1 (N), f2 (N) and f3 (N) for the individual intermediate positions are stored in the memory 14.

Furthermore, in the embodiment, the pump absorption horsepower characteristic C-f2
(N) and D f3 (N) are each monotonically increasing functions with respect to engine speed N, but as shown in Figure 4, a constant function (equal horsepower characteristic) with respect to N is adopted as these characteristics. There is no practical problem.

〔Effect of the invention〕

According to the present invention, since the load mode of the engine is changed when the engine overheats, it is possible to prevent damage to the engine and decrease in workability due to overheating.

[Brief explanation of the drawing]

FIG. 1 is a block diagram conceptually showing an embodiment of the control device according to the present invention, FIG. 2 is a conceptual diagram showing the arrangement of the proportional solenoid with respect to the fuel control lever, and FIGS. 3 and 4 are Engineering 1...Engine, 2...
Variable displacement hydraulic pump, 2a... Swash plate, 3... Swash plate drive actuator, 4... Accelerator sensor 1.6
...Engine rotation sensor, 7...Pressure sensor, 8.
...Temperature sensor, 9...Work mode changeover switch, 1
0...Controller, 11...Proportional solenoid, 1
2...Governor, 14...Memory. Fig. 1 Fig. 2 Fig. 11 Figure 3 Engine speed Fig. 4

Claims (1)

[Claims] A device for controlling a variable displacement hydraulic pump driven by an engine, comprising: engine rotation speed detection means for detecting the rotation speed of the engine; and pressure detection means for detecting the discharge pressure of the pump. and overheat detection means for detecting overheating of the engine, work mode instruction means for instructing a work mode corresponding to the size of the load, and setting pump absorption horsepower characteristics according to the work mode,
and absorption horsepower characteristic setting means for setting a pump absorption horsepower characteristic for a light load work mode in place of the currently set pump absorption horsepower characteristic when the overheating is detected; means for determining a swash plate tilting angle command of the pump for obtaining absorption horsepower according to the absorption horsepower characteristic based on the rotational speed of the engine and the discharge pressure of the pump; and swash plate control means for controlling the swash plate so that the tilt angle of the swash plate of the pump becomes a magnitude according to the swash plate tilt angle command. Control device for variable displacement hydraulic pump.