JPH02178428A - Hydraulically driven control device for construction machine - Google Patents

Abstract

PURPOSE:To supply a proper flow rate of pressurized oil to actuators by suitably selecting control using a load sensing system mode and control using a flow control mode. CONSTITUTION:A control unit 20 receives detection values of operation command detectors 15a1-15b3, a load pressure detector 17, discharge pressure detectors 16a, 16b, pump capacity detectors 13a, 13b, a rotating speed detector 14, and signals of a selection command dispatcher 18. When the differential pressure between the hydraulic pump side and the actuator side exceeds a regulated value, the control unit commands valves 3a2, 3b2 to reduce the discharge capacities. On the other hand, when the differential pressure is below the regulated value and the discharge capacity reaches a specified value, the capacity is fixed, and when the discharge capacity does not reach the specified value, the capacity is increased. When a flow control mode is selected by the selection command dispatcher 18 and operation command signals for actuators are above the specified value, the discharge capacity is determined in order to obtain the total amount of flow rates required for the actuatores, and when the discharge capacity is below the specific value, the capacity is increased to correspond to the capacity required.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic drive control device for a construction machine that uses pressure oil to drive an actuator provided in the construction machine.

[Conventional technology]

Construction machines, such as hydraulic excavators, are equipped with one or more hydraulic pumps, and the boom cylinder is powered by pressure oil discharged from the hydraulic pumps.

Arm cylinder, packet cylinder, swing motor.

Actuators such as left and right travellers are driven. A directional control valve is provided between each of these actuators and the hydraulic pump, and the directional control valve is activated by the operator arbitrarily operating the operating lever of each actuator provided in the driver's seat of the hydraulic excavator. Acting accordingly, the flow of pressure oil from the hydraulic pump to the actuator is controlled, which in turn controls the operation of the actuator, thereby achieving the intended work of the hydraulic excavator.

Six types of means have been proposed for drive control of such actuators, and one of them includes, for example,
There is a load sensing system disclosed in Japanese Patent No.-11706. This load sensing system detects a differential pressure between the hydraulic pressure on the hydraulic pump side of the directional control valve and the hydraulic pressure on the actuator side (valve loading pressure) (differential pressure generated by the metering orifice of the directional control valve) during drive control of the actuator. This is means for controlling a hydraulic pump (variable displacement hydraulic pump) so that it always maintains a certain predetermined value. More specifically, in a state where the variable displacement hydraulic pump discharges a constant flow rate determined by the tilt angle of its swash plate, etc., and the actuator is being driven by this, the operating lever is pressed to increase the speed of the actuator. When is operated, the opening area of the directional control valve increases accordingly.

Then, the differential pressure inevitably decreases and a deviation from the predetermined value occurs. In accordance with this deviation, a command is output to the variable displacement hydraulic pump to increase its tilt angle to increase the discharge flow rate of pressure oil. As a result, the amount of oil passing through the directional control valve increases and the speed of the actuator is increased, and at the same time, the differential pressure also increases and returns to the predetermined value. In this way, by controlling the variable displacement hydraulic pump so as to always maintain the differential pressure at a predetermined value, the actuator can be driven and controlled in accordance with the operation of the operating lever.

[Problem to be solved by the invention]

The load sensing system described above is an extremely excellent means for controlling the speed of an actuator. By the way, as is well known, the viscosity of the oil used to drive the actuator as described above changes greatly depending on the temperature. When such oil viscosity is taken into account, even if the amount of oil passing through the directional control valve is the same, the differential pressure will have different values depending on the viscosity. On the other hand, construction machinery is usually used outdoors, and is used in a wide range of regions from warm to cold regions, and even in the same location, it is used in different temperature environments in the morning and evening and during the day. be done. Therefore, the viscosity of oil used in construction machinery varies greatly depending on the usage environment.

In contrast, in the conventional load sensing system described above, the differential pressure is always controlled to a predetermined value. However, in reality, the required flow rate cannot be obtained, and conversely, if the viscosity of the oil is low, the required flow rate is >tl
is supplied to the actuator, resulting in a problem that it becomes difficult to drive the actuator as desired.

Furthermore, if pressure loss becomes large for some reason in the pipeline from the point where the discharge pressure of the variable displacement hydraulic pump is derived to just before the directional control valve, or in the flow path within the directional control valve, even if the variable displacement hydraulic pump Even if there is sufficient discharge capacity,
The above-mentioned load sensing system also has a problem in that it becomes impossible to obtain the desired flow rate to the actuator.

The purpose of the present invention is to solve the problems in the above-mentioned prior art,
An object of the present invention is to provide a hydraulic drive control device for construction machinery that can properly control the supply of pressure oil to an actuator even if various conditions such as the viscosity of oil or the loss of a pipe member change.

[Means to solve the problem]

In order to achieve the above object, a first aspect of the present invention includes a variable displacement hydraulic pump, a plurality of actuators driven by pressure oil of the variable displacement hydraulic pump, and a directional control valve for controlling each of these actuators. , maximum pressure selection means for selecting the highest pressure among the load pressures of each of the actuators, discharge pressure detection means for detecting the discharge pressure of the variable displacement hydraulic pump, and a differential pressure between the maximum pressure and the discharge pressure. and a control means for controlling the capacity of the variable displacement hydraulic pump to achieve a specified pressure, the variable displacement hydraulic pump for obtaining a total flow rate of pressure oil required for each of the actuators. means for determining the discharge capacity of the variable displacement hydraulic pump, another control means for controlling the displacement of the variable displacement hydraulic pump based on the determined discharge capacity, and selection means for selecting one of the control means and the other control means. It is characterized by having been established.

Further, in a second aspect of the present invention, in the hydraulic drive control device for construction machinery according to the first aspect, when the other control means is selected by the selection means, the other control means is controlled only for a predetermined actuator. The present invention is characterized in that an actuator selection means is provided to apply control by the control means to other actuators, and to apply control by the control means to other actuators.

Furthermore, in the hydraulic drive control device for construction machinery according to the first invention, when the other control means is selected by the selection means, the operation amount of the operated actuator is set to a predetermined amount. The invention is characterized in that a manipulated variable discriminating means is provided for applying control by the control means to the actuator when the value is smaller than the value.

[Effect]

In the first invention, in addition to one control means (control means using a load sensing system), the discharge capacity of the variable displacement hydraulic pump to obtain the required total meteor is determined from the required total flow rate of the actuator. Another control means (flow rate control means) is provided to control the variable displacement hydraulic pump so as to achieve a discharge capacity of the variable displacement hydraulic pump, and a selection means selects one of the control means when controlling the drive of the actuator.

Further, in a second invention, in the first invention, when the flow rate control means is selected by the selection means, the type of actuator is determined, and if the actuator is a predetermined actuator, control by the flow rate control means is applied. , if the actuator is not a predetermined actuator, control of the control means by the load sensing system is applied.

Furthermore, in a third invention, when the flow rate control means is selected by the selection means in the first invention,
The operation amount of the actuator is compared with a predetermined value, and control by the flow control means is applied to the actuator whose operation amount is greater than the predetermined value, and when the operation amount is larger than the predetermined value, the control means by the load sensing system is applied. Apply controls.

〔Example〕

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is a system diagram of a hydraulic drive control device for a hydraulic excavator according to an embodiment of the present invention. In the figure, la.

2b is two variable capacity hydraulic pumps (hereinafter simply referred to as hydraulic pumps) mounted on the hydraulic excavator, and 1c is a fixed capacity hydraulic pump that supplies pilot pressure oil and the like. 2a, 2
3a and 3b are pump capacity operating mechanisms for operating the swash plates 2a and 2b, respectively. The pump capacity operating mechanisms 3a, 3b are comprised of cylinders 3al, 3b+ connected to the swash plates 2a, 2b, respectively, and control valves 3az, 3bz for driving and controlling the cylinders 3al, 3b+.

5a+, 5az, 5at, 5b+, 5bz, 5b3
are actuators driven by the pressure oil discharged from the hydraulic pumps la and 2a. These correspond to the boom cylinder, arm cylinder, packet cylinder, swing motor, left and right travel motors, etc. of a hydraulic excavator. ” a+ +
6 a z + 6 a 3 are directional switching valves that control the drive of actuators 5 '' + 5321 5 a 3, respectively, and 6 kl +, 61) z 6 b3 are directional valves that control the drive of actuators 5 b + , 5 bz , and 5 bs, respectively. Yes. 7a+, 7at
7a*, 7b+, 7bx, and 7b* are throttle valves provided on the hydraulic pump la and lb sides of the directional control valves 6a, 6at, 6ax, 6b+6bz, and 6b+, respectively. The functions of these throttle valves 7a+ to 7b3 will be described later. F
Hydraulic pilot valves 3a and 8bt are driven by control levers (not shown) that operate the actuators 5a and 5b, and control pilot pressure according to the direction and amount of operation of each control lever. It is supplied to the pilot ports of the corresponding directional switching valves 5a+ to 5b, and drives these directional switching valves. 9 is a hydraulic pump la;
This is a relief valve that defines the maximum pressure of the IbO main circuit and the pilot circuit of the constant displacement hydraulic pump IC.

11a+ is a shuttle valve that selects the higher pressure of the load pressures of actuators 5al and 5at; 1laz;
is a shuttle valve that selects the higher pressure between the pressure selected by the shuttle valve 11al and the load pressure of the actuator 5az, 11b1 is a shuttle valve that selects the higher pressure of the load pressure of the actuators 5bl and 5b2, l
1bz is a shuttle valve that selects the higher pressure between the pressure selected by shuttle valve 11b+ and the load pressure of actuator 5bz, and 1lab is shuttle valve 11a211b.
This is a shuttle valve that selects the higher pressure among the pressures selected in step 2. In the end, the pressure selected by the shuttle valve 11ab is the maximum pressure among the load pressures of the actuators 5a to 5b3, and this maximum pressure is the pressure selected by the shuttle valve 11ab.
7bi is supplied to one pilot port. In addition,
The load pressure of the corresponding actuator is supplied to the other pilot port of each throttle valve 7a, to 7b'+. Reference numeral 12 denotes a pressure control valve (unload valve) that controls the pump discharge pressure so as not to exceed a predetermined maximum pressure of the load pressure.

13a and 13b are pump capacity detectors that detect the capacities of the hydraulic pumps 1a and 1b (tilting amounts of the swash plates 2a and 2b), respectively; 14 is a rotation speed detector that detects the rotation speed of each of the hydraulic pumps 1a and 1b; be. Reference numerals 15a1 to 15b3 are operation command detectors that detect the amount of operation of each operating lever, that is, the output pressure of each hydraulic pilot valve 8aI to 8b+.

16a.

16b is a discharge pressure detector that detects the discharge pressure of the hydraulic pumps la and lb, respectively, and 17 is a load pressure detector that detects the pressure (the highest pressure of each load pressure) selected by the shuttle valve 11ab. Reference numeral 18 denotes a selection command device for selecting a control mode, which will be described later.

20 indicates a control unit, which includes pump capacity detectors 13a and 13b.
, rotation speed detector 14. Operation command detector 15a to 15bs
, discharge pressure detectors 16a, 16b, load pressure detector 17
Input each detection value and command signal of the 1 selection command device 18,
Based on these, necessary calculations and controls are performed, and necessary command signals are output to the control valves 3at, 3bz of the pump capacity operating mechanisms 38, 3b.

Next, the operation of this embodiment will be explained with reference to the flowchart shown in FIG. Now, when the operator operates a corresponding control lever to drive one or more of the actuators 5a, ~5bi, the corresponding hydraulic pilot valve 8a+~8b A pilot pressure is outputted from the control valve 6b, and the corresponding directional switching valves 6a+ to 6b3 are opened according to the operating direction and operating amount of the operating lever. As a result, the hydraulic pump 1a,
lb of pressure oil flows through the throttle valves 7a+ to 7b and the directional control valve 6.
Corresponding actuators 5a, ~5 via a1~6bi
b3. These supply flow rates are controlled by the directional control valve 5a.
, ~6b, and the actuator is driven at a speed proportional to the flow rate. When multiple actuators are driven simultaneously by a combined operation, the highest pressure among the load pressures of the actuators being driven is supplied to one pilot port of each of the throttle valves 7a and 7bs, and the highest pressure is supplied to the other pilot port. Since the pressure of hydraulic pumps la and Lb is supplied,
When the total required flow rate of the actuators being driven exceeds the maximum capacity of the hydraulic pumps Ia, lb, each throttle valve 7a
, ~7b, are further throttled from the normal state, and as a result, the distribution of pressure oil to each actuator is proportionally distributed according to the required flow rate, although the absolute amount of distribution decreases, and the throttle valve 7a , ~7b3 is not provided, the phenomenon of uneven pressure oil supply to the low-load actuator is prevented. Note that it is also possible to detect the discharge pressure and the maximum load pressure of the hydraulic pumps la and Ib, and to electrically control the throttle valves 7a and 7bi based on the pressure difference between them.

On the other hand, the control unit 20 normally executes necessary control according to the differential pressure between the hydraulic pump side and the actuator side (this differential pressure is expressed as ΔPLff) generated by the pressure oil flowing into the driven directional switching valve. The operation of the control unit 20 will be explained below using a second flowchart.

The control unit 20 first operates the operation command detectors 15a+ to 15
b3', load pressure detector 17. discharge pressure detector 16a,
16b, pump capacity detectors 13a and 13b3, the detection value of the rotation speed detector 14 and the command signal of the selection command device 18 are input (step S1 shown in FIG. 2).

Next, it is determined whether the signal from the selection command device 18 is a signal for selecting a second control mode (flow rate control mode) which is not the normal load sensing system control mode (step S2). If the selection controller has not been operated for 1 day and the flow rate control mode has not been selected (when executing the normal load sensing system), the process proceeds to step S.
Move on to 3.

That is, in step S3, it is determined whether the differential pressure ΔPLS is larger than a certain prescribed value (this is a prescribed value in the load sensing system, and is expressed as Δptso). The differential pressure Δpts is the specified value Δpts. If it exceeds the control valve 3 of the pump capacity operation mechanism 3a, 3b.
A command to reduce the pump discharge capacity is output to az and 3bz (step S4). On the other hand, in step S3, the differential pressure ΔPL
S is the specified value Δpts. When it is determined that the discharge capacity of the hydraulic pumps la, lb is insufficient, -1, the pump discharge capacity is set to a predetermined value (
A value commensurate with the requirements of the actuator or hydraulic pump la
, lb) has been reached (step S). This judgment is based on the detection signals of the pump capacity detectors 13a, 13b, and the swash plates 2a, 2b.
By checking whether the amount of tilting of
3 and the discharge itt obtained from the rotation speed detector 14 and pump capacity detectors 13a and 13b.
This is done by comparing the If it is determined in step S5 that the discharge flow rate has reached the predetermined value, no higher discharge flow rate can be expected, so the capacities of the hydraulic pumps 1a and Ib are reduced to the previous capacity for the control valves 3az and 3bz. A command to fix the capacity as it is is output (step S6). Further, if the pump discharge flow rate has not reached the predetermined value, a command to increase the pump discharge capacity is output to the control valves 3az and 3bz (procedure St). Procedure S.

The amount of decrease and amount of increase in pump discharge capacity in the process of S7 are both predetermined unit amounts. that's all,
By repeating steps S to S7, drive control of the actuator in the load sensing system mode is executed.

On the other hand, when the hydraulic excavator operator or the like operates the selection command 1 day, the control unit 20 determines that the selection command 1 day has been operated in step S2 during the repetition of the steps S to S7, that is, the flow rate control mode. is selected.

In this case, the process moves to step S8. That is, in step S8, input signals from the operation command detectors 15a1 to 15b3 are checked, and it is determined whether a predetermined actuator is being operated (steps S, 1). If the actuator being operated is an actuator that does not use flow rate control, the process moves to step S, and even if the selection command device 18 is operated, control by the load sensing system is thereafter performed.

Procedure S. When it is determined that the actuator being operated is an actuator that can control the flow rate, it is then determined whether the magnitude of the operation command signal for the actuator is greater than or equal to a certain predetermined value ( Procedure S,
). When it is smaller than the predetermined value, that is, when the required flow rate of the actuator is small, the process moves to step S3, and even if the selection command device 18 is operated, control by the load sensing system is thereafter performed. The reason why the flow rate control mode is not set when the required flow rate is small is that with a normal variable displacement hydraulic pump, it is necessary to secure a predetermined minimum flow rate for cooling and lubrication of the pump itself, so the pump discharge rate control is not possible. This is because it is not possible to control a small flow rate below the minimum flow rate. Therefore, in the case of a hydraulic pump that takes special consideration to cooling and lubrication, it is possible to control from the flow ff1O, and the flow rate control mode can be set over the entire range.

On the other hand, if it is determined that the actuator operation command signal is greater than or equal to the predetermined value, the discharge capacity of the hydraulic pump to obtain the total required flow rate to the actuator is determined (hand 1 + f - f [S + o). This discharge capacity can be calculated by assuming the rotational speed of the hydraulic pumps la, lb or based on the detected value of the rotational speed detector 14, or even if it is not calculated by calculation, it can be determined by a certain predetermined value for the total required flow rate. It can also be obtained using a function generator with the same characteristics.

Regarding the discharge capacity obtained in this way, this discharge capacity is the predetermined capacity determined for the hydraulic pumps la and lb,
That is, it is determined whether the discharge capacity is greater than or equal to the maximum discharge capacity or a certain predetermined limit value (Step S, 1). If the discharge capacity is equal to or greater than the predetermined capacity, the process moves to step S, and the discharge capacity remains fixed at the same value as before.

On the other hand, if the discharge volume is less than the predetermined volume, that is,
When there is sufficient discharge capacity of the hydraulic pumps la and lb, the control unit 20 controls the control valves 3a of the pump capacity operating mechanisms 3a and 3b.
2 and 3bz to make the discharge capacity of the hydraulic pump 1a1b match the discharge capacity determined in step S1° (step S1□). Thereby, the actuator is controlled by the flow rate control mode, and a desired flow rate can be obtained regardless of the differential pressure ΔP11. Selection command device 18
are being operated, steps St, S2. S8～S1□
The process is repeated to control the flow rate, and the selection command unit 1
When daily gravel harvesting is canceled, control returns to steps 81 to S7 by the load sensing system.

In this way, in this embodiment, flow control can be performed in addition to control by the load sensing system, so the actuator can be controlled regardless of various conditions such as oil viscosity or piping loss. It is possible to supply an appropriate flow rate to. Furthermore, even if a relatively small capacity directional valve is used and a large flow rate is required from the control actuator, selecting flow control will force a sufficient flow rate. can be supplied. In other words, a smaller capacity directional switching valve can be used as the directional control valve.

Furthermore, since the flow rate control is applied only to predetermined actuators, only load sensing is required for actuators for which the effect of flow rate control is small, and the control configuration can be simplified.

Furthermore, even if the actuator is a specified actuator, if the operation command signal is less than a predetermined value, the load sensing system will control the actuator, so the unloading will be performed even if the required flow rate is less than the minimum pump discharge flow rate. Depending on the function of the valve, the flow rate characteristics can be set according to the opening area of the switching valve.

Although the above embodiment has been described using a hydraulic excavator as an example, it is obvious that the present invention can be applied to other construction machines. Further, it is also suitable to use a differential pressure sensor as a means for determining the differential pressure between the load pressure and the pump discharge pressure in order to obtain high accuracy. In addition, in the above embodiment, when the flow rate control mode is selected, the process is performed to determine whether or not it is applicable based on the type of actuator. This process is not necessarily required if a command device is provided and activated at the same time as the grip is grasped. Furthermore, in the description of the above embodiment, the example in which the process of determining whether or not to apply the actuator is performed based on the magnitude of the operation command signal is described above. At the same time, control using the flow rate control mode can be performed, so that an appropriate flow rate can be supplied to the actuator regardless of various conditions or even if a small capacity directional control valve is used.

Further, in the second invention, even when performing flow rate control, the actuator to be controlled is selected, so that the above-mentioned first invention
As a result of the invention described above, the control configuration can be simplified.

Furthermore, in the third invention, even when flow rate control is performed, the flow rate control is performed when the operation amount of the actuator is equal to or greater than a predetermined value, so in addition to the effect of the first invention, the pump minimum discharge flow rate is regulated. Even when the flow rate is 0, smooth flow control is possible from a flow rate of 0.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a hydraulic drive device for a hydraulic excavator according to an embodiment of the present invention, and FIG. 2 is a flowchart illustrating the operation of the device shown in FIG. 1. 1a, 1b---hydraulic pump, 3a,
3 b---------PfNR1 made by Bonfuyoff1t
5a 1 to 5 b 3-------Actuator,
6 a + ~6 b 3---One-way switching valve, 13
a. 13b・------Pump capacity detector, l 4------
--One rotation speed detector, 15 a + ~ 15 b 3-
-----One rotation speed detector, 16 a, l 6
b------Discharge pressure detector, 17----Load pressure detector, 20-----Control section, 22----Selection command means.

Claims (3)

[Claims] (1) Select a variable displacement hydraulic pump, a plurality of actuators driven by the pressure oil of this variable displacement hydraulic pump, a directional control valve that controls each of these actuators, and the highest pressure among the load pressures of each of the actuators. a maximum pressure selection means for detecting the discharge pressure of the variable displacement hydraulic pump; a discharge pressure detection means for detecting the discharge pressure of the variable displacement hydraulic pump; A hydraulic drive control device for construction machinery, comprising: a means for determining a discharge capacity of the variable displacement hydraulic pump to obtain a total flow rate of pressure oil required for each actuator; A hydraulic drive control device for construction machinery, comprising: another control means for controlling the capacity of the variable displacement hydraulic pump based on the control means; and a selection means for selecting one of the control means and the other control means. . (2) In the hydraulic drive control device for construction machinery according to claim (1), when the other control means is selected by the selection means, the control by the other control means is applied only to a predetermined actuator. A hydraulic drive control device for construction machinery, characterized in that actuator selection means is provided for applying control by the control means to other actuators. (3) In the hydraulic drive control device for construction machinery according to claim (1), when the other control means is selected by the selection means and the operation amount of the operated actuator is smaller than a predetermined value, the actuator is A hydraulic drive control device for a construction machine, characterized in that a control amount discriminating means for applying control by the control means to the hydraulic drive control device for construction machinery is provided.