System and method of controlling torque of plural variable displacement hydraulic pumps

A system and method of controlling torque of plural variable displacement hydraulic pumps in construction equipment are provided, which can control torque of the variable displacement hydraulic pumps so that the total amount of torque of the hydraulic pumps does not exceed the preset amount of torque by presetting the torque so that the engine does not stop even at maximum load of the hydraulic pumps or by presetting the speed of the engine or the used torque of the hydraulic pumps in consideration of the fuel economy or working speed. The system includes an engine, at least two variable displacement hydraulic pumps, hydraulic actuators, control levers generating manipulation signals, control lever sensing means detecting the manipulation amounts of the control levers, hydraulic pump pressure sensing means detecting load pressures of the hydraulic pumps, maximum torque setting means setting the total torque inputted to the hydraulic pumps, desired flow rate computing means computing flow rates of the hydraulic pumps, expected torque computing means computing expected torque values of the hydraulic pumps, torque distributing means distributing torque values of the hydraulic pumps, limited flow rate computing means computing the flow rates of the hydraulic pumps, and output means outputting control signals to regulators.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority from Korean Patent Application No. 10-2008-0052098, filed on Jun. 3, 2008 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system and method of controlling torque of plural variable displacement hydraulic pumps in construction equipment that drives working devices by operating an engine and the plural variable displacement hydraulic pumps associated with the engine, which can make it possible to use all the set amount of torque regardless of the load pressure or the number of hydraulic pumps.

More particularly, the present invention relates to a system and method of controlling torque of plural variable displacement hydraulic pumps in construction equipment that operates the plural variable displacement hydraulic pumps by an engine, which can control torque of the variable displacement hydraulic pumps so that the total amount of torque of the hydraulic pumps does not exceed the preset amount of torque by presetting the torque so that the engine does not stop even at maximum load of the hydraulic pumps or by presetting the speed of the engine or the used torque of the hydraulic pumps in consideration of the fuel economy or working speed.

2. Description of the Prior Art

A conventional torque limiting control system for a hydraulic work machine is disclosed in U.S. Pat. No. 5,951,258. The conventional torque limiting system, which is also called an apparatus for controlling an electrohydraulic system of a work machine having an engine that drives variable displacement pumps, includes a pump displacement setting device125adapted to produce a pump command signal indicative of a desired displacement of the variable displacement pumps115and120; pressure sensors130and131adapted to detect the fluid pressure associated with the variable displacement pumps115and120and produce a pressure signal indicative of the detected fluid pressure; an engine speed sensor140adapted to detect the speed of the engine110and produce an actual engine speed signal indicative of the detected engine speed; torque computing means205receiving the pump command and pressure signals of the variable displacement pumps115and120, responsively computing the torque demand on the engine110, and producing a torque demand signal; torque limiting means210receiving the torque demand and engine speed signals, responsively determining a torque limit associated with the engine110, and producing a specified torque limit signal; and a scaling means225receiving the pump command and torque limit signals, determining a scaling factor, and modifying the pump command signal in response to the scaling factor to govern the engine torque.

In the case of scaling the flow rate by using the ratio of an expected torque to the limited torque in the torque limiting control system for a hydraulic work machine, the efficiency of the pump torque in the modified flow rate differs from the efficiency of the pump torque when the expected torque is calculated before the flow rate is modified, and thus the torque limit of the basically causes error occurrence.

Also, there is a limit to individual torque limiting for the plural hydraulic pumps.

In the case of mechanically limiting the torque of the pumps in the conventional torque limiting control apparatus for mechanical variable displacement pumps as illustrated inFIG. 1, the torque limiting mechanism is constructed by a mechanical combination, and thus the maximum torque set for the whole pressure regions cannot be used due to the limitation of the mechanical characteristic even for a single hydraulic pump (InFIG. 1, “a” denotes the flow rate per pressure for the mechanical torque limit, and “b” denotes the ideal flow rate per pressure for a constant torque value).

Also, in the case of performing cross-sensing torque control of plural pumps, the corresponding construction is complicated, and it becomes impossible to use the total amount of torque or 100% of the set torque of the respective pumps.

Also, in compliance with the market requirements, such as fuel economy improvement of the construction equipment, implementation of electronic functions of construction equipment in diverse working environments, and the like, it becomes immediate to adopt electronic hydraulic pumps.

Even in the case of controlling fuel injection to the engine for urgent load, the delay of the engine itself occurs, and the increase of the engine torque is limited by limiting the fuel injection ratio in order to reduce black smoke in compliance with the waste gas regulation.

In addition, trouble may occur in torque matching due to the year elapse of the engine or pumps. That is, in the case of urgent load of the engine, the engine may instantaneously stop or the engine speed may be excessively reduced to cause the output horsepower (hp) of the pumps to be reduced. Also, even in a static state, trouble may occur in torque matching, and in this case, an excessive lowering of engine revolution may continuously occur.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art while advantages achieved by the prior art are maintained intact.

One object of the present invention is to provide a system and method of controlling torque of plural variable displacement hydraulic pumps in construction equipment that operates the plural variable displacement hydraulic pumps associated with an engine, which can accurately limit the total amount of torque of the hydraulic pumps to the preset amount of torque when the used torque of the hydraulic pumps is limited.

Another object of the present invention is to provide a system and method of controlling torque of plural variable displacement hydraulic pumps, which can maintain user manipulation according to a user's intention even on the torque limit condition by reducing the flow rate of the respective hydraulic pumps in the specified ratio with respect to the desired flow rate of the respective hydraulic pumps in the case where the sum of desired torque values of the plural hydraulic pumps is larger than a set torque value and thus it is intended to reduce the discharge flow rate of the respective hydraulic pumps.

Still another object of the present invention is to provide a system and method of controlling torque of plural variable displacement hydraulic pumps, which can improve the workability by suppressing the stop of engine start during the occurrence of urgent load on condition that load is generated in the plural hydraulic pumps, and can maintain the working speed by preventing an excessive speed lowering of an engine during the occurrence of urgent load.

Still another object of the present invention is to provide a system and method of controlling torque of plural variable displacement hydraulic pumps, which can suppress unexpected generation of vibration in working devices even in their abrupt operation through adjustment of the change rate of the torque of the plural hydraulic pumps.

In order to accomplish these objects, there is provided a system for controlling torque of plural variable displacement hydraulic pumps, according to an embodiment of the present invention, which includes an engine; at least two variable displacement hydraulic pumps associated with the engine; hydraulic actuators associated with the hydraulic pumps, respectively, to drive working devices; control levers generating manipulation signals corresponding to manipulation amounts to drive the hydraulic actuators, respectively; control lever sensing means detecting the manipulation amounts of the control levers and generating detection signals; hydraulic pump pressure sensing means detecting load pressures of the hydraulic pumps and generating detection signals; maximum torque setting means setting the total torque inputted from the engine to the hydraulic pumps; desired flow rate computing means computing flow rates of the hydraulic pumps corresponding to the detection signals inputted from the control lever sensing means; expected torque computing means computing expected torque values of the hydraulic pumps in accordance with input signals from the hydraulic pump pressure sensing means and the desired flow rate computing means; torque distributing means distributing torque values of the hydraulic pumps by proportionally reducing allowable torque values of the hydraulic pumps so that the sum of the torque values generated by the hydraulic pumps is limited to the torque value by the maximum torque setting means in accordance with input signals from the expected torque computing means and the maximum torque setting means; limited flow rate computing means receiving the torque values of the hydraulic pumps distributed by the torque distributing means and the load pressures of the hydraulic pumps from the hydraulic pump pressure sensing means, and computing the flow rates of the hydraulic pumps so that the torque values reset in accordance with the load pressures generated by the hydraulic pumps are generated in the hydraulic pumps; and output means outputting control signals to regulators so that the hydraulic pumps are operated in accordance with the flow rates computed by the limited flow rate computing means.

In another aspect of the present invention, there is provided a method of controlling torque of plural variable displacement hydraulic pumps in construction equipment including an engine, plural variable displacement hydraulic pumps associated with the engine, hydraulic actuators associated with the hydraulic pumps, control levers generating manipulation signals so as to drive the hydraulic actuators, control lever sensing means detecting the manipulation amounts of the control levers, pressure sensing means detecting load pressures of the hydraulic pumps, and torque selecting means, which includes a first step of receiving inputs of the manipulation amounts of the control levers from the control lever sensing means, the load pressures of the hydraulic pumps from the pressure sensing means, and a torque value selected by the torque selection means; a second step of setting the total torque inputted to the hydraulic pumps in accordance with a selected value selected by the torque selection means; a third step of computing desired flow rates of the hydraulic pumps desired in accordance with the manipulation amounts of the control levers; a fourth step of computing expected torque values of the hydraulic pumps from the desired flow rates of the hydraulic pumps and the load pressures of the hydraulic pumps; a fifth step of judging whether the sum of the expected torque values of the hydraulic pumps is larger than the set maximum torque value; a sixth step of outputting the desired flow rates to the hydraulic pumps as they are if the sum of the expected torque values of the hydraulic pumps is smaller than the set maximum torque value in the fifth step; and a seventh step of outputting the desired flow rates of the hydraulic pumps reset so that the sum of the torque values of the hydraulic pumps is limited to the distributed torque values of the hydraulic pumps in accordance with load pressure conditions of the hydraulic pumps if the sum of the expected torque values of the hydraulic pumps is larger than the set maximum torque value in the fifth step.

The seventh step may proportionally reduce the respective maximum torque values of the hydraulic pumps so as to limit the torque values of the hydraulic pumps to the set maximum torque values.

The maximum torque setting means may modify the maximum torque values by comparing an input engine speed with a set engine speed.

The maximum torque setting means may receive the expected torque values and modify the maximum torque values so that the change rate of the sum of the distributed torque values exists within a specified range.

The maximum torque setting means may receive the input signals from the manipulation amount sensing means, and if it is judged that no manipulation amount is detected, it may maintain the maximum torque value lower than the set maximum torque value, while if any manipulation amount of the control levers is detected, it may modify the maximum torque value so that the maximum torque value is gradually increased for a predetermined time.

The torque distributing means may reset the respective distributed torque values so that the change rate of the distributed torque values of the hydraulic pumps exists within a specified range.

If the distributed torque values of the hydraulic pumps reach upper and lower threshold values of torque use of the hydraulic pumps, the torque distributing means may set the torque value of the corresponding hydraulic pump as a threshold value and transfer its variation to the remaining hydraulic pump to reset the torque value.

Pressure sensors may be used as the hydraulic pump pressure sensing means.

The maximum torque setting means may include an engine speed setting function that sets the maximum torque values of the hydraulic pumps in association with an engine speed adjusting step so as to adjust the working speed through setting of the engine speed in multi-steps.

DETAILING DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The matters defined in the description, such as the detailed construction and elements, are nothing but specific details provided to assist those of ordinary skill in the art in a comprehensive understanding of the invention, and thus the present invention is not limited thereto.

As illustrated inFIGS. 3 and 4, a system for controlling torque of plural variable displacement hydraulic pumps in construction equipment according to an embodiment of the present invention includes an engine1; at least two variable displacement hydraulic pumps (hereinafter referred to as “hydraulic pumps”)2and3associated with the engine1; hydraulic actuators (e.g. hydraulic cylinders)5and6associated with the hydraulic pumps2and3, respectively, to drive working devices (a boom, an arm, and the like); control levers (i.e. RCV levers)7and8generating manipulation signals corresponding to manipulation amounts to drive the hydraulic actuators5and6, respectively; control lever manipulation amount sensing means12and13detecting the manipulation amounts of the control levers7and8and generating detection signals; hydraulic pump pressure sensing means9and10detecting load pressures of the hydraulic pumps2and3and generating detection signals; maximum torque setting means11setting the total torque inputted from the engine1to the hydraulic pumps2and3; desired flow rate computing means14and15computing flow rates of the hydraulic pumps2and3corresponding to the detection signals inputted from the control lever sensing means12and13; expected torque computing means16and17computing expected torque values of the hydraulic pumps2and3in accordance with input signals from the hydraulic pump pressure sensing means9and10and the desired flow rate computing means14and15; torque distributing means18distributing torque values of the hydraulic pumps2and3by proportionally reducing allowable torque values of the hydraulic pumps2and3so that the sum of the torque values generated by the hydraulic pumps2and3is limited to the torque value by the maximum torque setting means11in accordance with input signals from the expected torque computing means16and17and the maximum torque setting means11; limited flow rate computing means19and20receiving the torque values of the hydraulic pumps2and3distributed by the torque distributing means18and the load pressures of the hydraulic pumps2and3from the hydraulic pump pressure sensing means9and10, and computing the flow rates of the hydraulic pumps2and3so that the torque values reset in accordance with the load pressures generated by the hydraulic pumps2and3are generated in the hydraulic pumps2and3; and output means21and22outputting control signals to regulators23and24so that the hydraulic pumps2and3are operated in accordance with the flow rates computed by the limited flow rate computing means19and20.

In the drawings, the reference numerals23and24denote regulators respectively controlling inclination angles of swash plates of the hydraulic pumps2and3in accordance with the input of drive signals,25denotes a pilot pump supplying pilot signal pressure,26denotes a controller,27and28denote main control valves controlling the flow rate and direction of hydraulic fluid being supplied from the hydraulic pumps2and3to the hydraulic actuators5and6in accordance with the pilot signal pressure inputted corresponding to the control levers7and8, and30and31denote electro proportional valves controlling the signal pressure being applied to the regulators23and24in accordance with a control signal from the controller26.

As illustrated inFIG. 5, a method of controlling torque of plural variable displacement hydraulic pumps in construction equipment including an engine1, plural variable displacement hydraulic pumps2and3associated with the engine1, hydraulic actuators5and6associated with the hydraulic pumps2and3, control levers7and8generating manipulation signals corresponding to their manipulation amounts to drive the hydraulic actuators5and6, control lever sensing means12and13detecting the manipulation amounts of the control levers7and8, pressure sensing means9and10detecting load pressures of the hydraulic pumps2and3, and torque selecting means11a, includes a first step S100of receiving inputs of the manipulation amounts of the control levers7and8from the control lever sensing means12and13, the load pressures of the hydraulic pumps2and3from the pressure sensing means9and10, and a torque value selected by the torque selection means11a; a second step S200of setting the total torque Tmax inputted to the hydraulic pumps2and3in accordance with a selected value selected by the torque selection means11a; a third step S300of computing desired displacements Dr1and Dr2of the hydraulic pumps2and3desired in accordance with the manipulation amounts of the control levers7and8; a fourth step S400of computing expected torque values Te1and Te2of the hydraulic pumps2and3from the desired displacements Dr1and Dr2of the hydraulic pumps2and3and the load pressures of the hydraulic pumps2and3; a fifth step S500of judging whether the sum Te1+Te2of the expected torque values of the hydraulic pumps2and3is larger than the set maximum torque value Tmax; a sixth step S600of outputting the desired displacements Dr1and Dr2of the hydraulic pumps2and3as they are if the sum Te1+Te2of the expected torque values of the hydraulic pumps2and3is smaller than the set maximum torque value Tmax (i.e. (Te1+Te2)<Tmax) in the fifth step S500; and a seventh step S700of outputting the desired displacements D1and D2of the hydraulic pumps2and3reset so that the sum of the torque values of the hydraulic pumps2and3is limited to the distributed torque values of the hydraulic pumps2and3in accordance with load pressure conditions of the hydraulic pumps2and3if the sum Te1+Te2of the expected torque values of the hydraulic pumps2and3is larger than the set maximum torque value Tmax (i.e. (Te1+Te2)>Tmax) in the fifth step S500.

Hereinafter, the system and method of controlling torque of plural variable displacement hydraulic pumps according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

As illustrated inFIG. 2, in the case where the control levers7and8are manipulated by a user, pilot signal pressure that corresponds to the manipulation amounts of the control levers is supplied from the pilot pump25to the main control valves27and28to shift inner spools.

Accordingly, hydraulic fluid discharged from the variable displacement hydraulic pumps2and3is supplied to the hydraulic cylinders5and6through the control valves27and28, and thus working devices such as a boom and so on are driven.

Also, the secondary pressure passing through the control levers7and8from the pilot pump25, which corresponds to the manipulation amounts of the control levers7and8, is supplied to the regulators23and24through the electro proportional valves30and31. Accordingly, the inclination angles of the swash plates of the hydraulic pumps2and3are controlled to optimize the discharge flow rate.

As illustrated inFIGS. 3 to 5, the manipulation amounts of the control levers7and8from the control lever sensing means12and13, the load pressures of the hydraulic pumps2and3from the pressure sensing means9and10, and the torque value selected by the torque selection means11aare inputted (step S100).

The total torque Tmax inputted to the hydraulic pumps2and3is set in accordance with the selected value selected by the torque selection means11a(step S200). In this case, the torque selection means11ais used to set the working speed in addition to the setting of the engine speed.

The engine speed set in accordance with the value selected by the torque selection means11ais outputted to the engine1, and preset values of input torques of the hydraulic pumps2and3to be used in a set speed range are stored in a memory of the controller26to compute the torque values corresponding to the selected value.

Desired displacements Dr1and Dr2of the hydraulic pumps2and3are computed in accordance with the manipulation amounts of the control levers7and8outputted from the control lever manipulation amount sensing means12and13(step S300).

The desired displacements Dr1and Dr2of the hydraulic pumps2and3and the load pressures of the hydraulic pumps2and3from the hydraulic pump pressure sensing means9and10are inputted, and expected torques Te1and Te2of the hydraulic pumps2and3are computed (step S400).

The expected torque Te1of the hydraulic pump2is Te1=K1×P1×Dr1, and the expected torque Te2of the hydraulic pump3is Te2=K2×P2×Dr2.

Here, Ki is Ki=fi(P,Dr) (an expected torque constant according to pressure and displacement).

Tmax indicates the maximum torque set by the torque setting means11. Generally, the working speed is adjusted by setting the engine speed in multi-steps, and the maximum torque of the hydraulic pumps is set in association with the engine speed adjusting step.

Then, it is judged whether the sum (Te=(Te1+Te2)) of the expected torque values of the hydraulic pumps2and3is larger than the set maximum torque value Tmax (step S500).

If the sum (Te=(Te1+Te2)) of the expected torque values of the hydraulic pumps2and3is smaller than the set maximum torque value Tmax (i.e. (Te1+Te2)<Tmax ), the output means21and22output the desired displacements Dr1and Dr2of the hydraulic pumps2and3to the regulators23and24as they are (step S600).

If the sum (Te=(Te1+Te2)) of the expected torque values of the hydraulic pumps2and3is larger than the set maximum torque value Tmax (i.e. (Te1+Te2)>Tmax ), the output means21outputs the desired displacements D1and D2of the hydraulic pumps2and3reset so that the sum of the torque values of the hydraulic pumps2and3is limited to the distributed torque values of the hydraulic pumps2and3in accordance with load pressure conditions of the hydraulic pumps2and3(step S700).

As in step S700A, the maximum torques of the hydraulic pumps2and3are proportionally reduced.

The maximum input torque to act on the hydraulic pump2is Tmax1=(Te1×Tmax)/Te(Te=Te1+Te2), and the maximum input torque to act on the hydraulic pump3is Tmax2=(Te2×Tmax)/Te(Te=Te1+Te2).

Accordingly, the sum (Tmax=(Tmax1+Tmax2)) of the torques distributed to the hydraulic pumps2and3is kept at the torque limit value Tmax, the torque matching of the engine1and the hydraulic pumps2and3is achieved.

Then, as in step S700B, P1value is confirmed with respect to the maximum input torque Tmax1of the hydraulic pump2, and specified displacement, which corresponds to the maximum input torque Tmax1in a formula or a table, is confirmed. In this case, the table is provided by experimentally obtaining a torque value for pressure and displacement.

As illustrated inFIG. 5, it is assumed that input torque data of the hydraulic pumps2and3for setting four kinds of displacements has been provided. If Tmax is determined, the displacement of “C” value is searched for by linear interpolation using torque values A and B for the displacement of ¾ and 2/4 Dmax at the corresponding pressure. If experimental torque values are provided for more diverse displacements, the degree of computation can be heightened.

If it is assumed that three variable displacement hydraulic pumps P1, P2, and P3are used, the expected torque Te1of the hydraulic pump P1is Te1=(K1×P1×Dr1), the expected torque Te2of the hydraulic pump P2is Te2=(K2×P2×Dr2), and the expected torque Te3of the hydraulic pump P3is Te3=(K3×P3×Dr3).

That is, the sum Te of the expected torques of the hydraulic pumps P1, P2, and P3becomes Te=(Te1+Te2+Te3).

At this time, if the sum Te of the expected torques of the hydraulic pumps P1, P2, and P3is larger than the set maximum torque Tmax (i.e. Te(=Te1+Te2+Te3)>Tmax ), the set torque values of the respective hydraulic pumps P1, P2, and P3are distributed in such a manner that the maximum input torque to act on the hydraulic pump P1becomes Tmax1=(Te1×Tmax)/Te(=Te1+Te2+Te3), the maximum input torque to act on the hydraulic pump P2becomes Tmax2=(Te2×Tmax)/Te(=Te1+Te2+Te3), and the maximum input torque to act on the hydraulic pump P3becomes Tmax3=(Te3×Tmax)/Te(=Te1+Te2+Te3).

By contrast, if Tmax1among the distributed torque values is smaller than the torque value for the minimum displacement at the present load pressure, the actual displacement cannot be lowered any further. Accordingly, Tmax1is set to Tmin, which has a minus value at Tmax, and the scaling is performed again in the remaining hydraulic pumps to distribute the torques.

Also, if it is assumed that the set Tmax1exceeds the mechanical limit of the hydraulic pump, Tmax1is set to the limit value, which has a minus value at Tmax, and the scaling is performed again in the remaining hydraulic pumps to distribute the torques.

In the case of using more than three hydraulic pumps, the total allowable torque, which is limited for each hydraulic pump, is relatively small in comparison to Tmax, and thus the torque of a specified hydraulic pump should be often limited even if the sum of the expected torques does not exceed Tmax. In this case, it is first checked whether the torque of the respective hydraulic pump exceeds the allowable torque, and if the torque of the hydraulic pump exceeds the allowable torque, the torque of the corresponding hydraulic pump is set to the allowable torque, which has a minus value at the total torque, and the torques are distributed to the remaining hydraulic pumps in the same manner.

As described above, by proportionally reducing the distributed torques of the hydraulic pumps with respect to the total limit torque, the speeds of the respective working devices are proportionally reduced according to a user's intention in a region where the variation of the efficiency of the hydraulic pumps is not large. That is, the relative speeds of the respective working devices can be harmonized.

If it is intended to give different priorities to the respective working devices for the maximum manipulation amount of the manipulation means while the working devices are simultaneously manipulated, the flow rates of the hydraulic pumps and valves for the manipulation amounts are differently set.

For example, in the case where the priorities of the working devices are not separately designated and the manipulation means of two working devices are simultaneously manipulated at maximum, the preferable maximum flow rates for individual operations of the working devices are set as the maximum flow rates of the respective hydraulic pumps.

By contrast, in the case where the priorities of the working devices are designated, a relatively high flow rate may be mapped for the manipulation amount of one working device in the order of priority, or a relatively low flow rate may be mapped for the manipulation amount of the other working device. In this case, by applying the method of controlling torque of hydraulic pumps according to an embodiment of the present invention thereto, the discharge flow rates of the hydraulic pumps in consideration of the priorities of the working devices can be achieved during the torque limiting.

For example, even in the case of limiting the torque of a working device connected to the hydraulic pump2while working devices designated to the respective hydraulic pumps are simultaneously operated at maximum, the flow rate for the working device designated to the hydraulic pump2can be set to be twice the flow rate for the working device designated to the hydraulic pump3in response to the following equations to limit the torques.
Te1=K1×P1×Dr1(=2×Dmax),
Te2=K2×P2×Dr2(=Dmax),
Te=(Te1+Te2),
Tmax1=(Te1×Tmax)/Te(=Te1+Te2), and
Tmax2=(Te2×Tmax)/Te(=Te1+Te2).

That is, the torque value Tmax1becomes twice the torque value Tmax2after the application of the priority function, and thus the priority function is maintained as it is even in the case of limiting the torque.

As described above, in the case of limiting the torques of the hydraulic pumps so that the priority function for setting the flow rates of valves of the respective working devices and for setting the corresponding flow rates of the hydraulic pumps can be implemented in the valve controller, the priority function can be implemented in diverse manners only through computation of desired flow rates of the valves or hydraulic pumps in diverse flow rate limiting states, even without separate correction of the hydraulic pump control. Even in a static state, the torque matching of the engine and the hydraulic pumps can be achieved.

As illustrated inFIG. 6, in the case of applying the conventional engine speed sensing control a to the maximum torque setting means11, the lowering of an initial engine speed can be prevented during urgent load of the engine1even if the torque matching is not achieved due to the difference in responsibility between the engine1and external loads, or the year elapse of the engine1and hydraulic pumps2and3.

As illustrated inFIG. 7, in the case of the urgent load of the engine1, the transient characteristic due to the limit of the responsibility and fuel injection rate of the engine can be improved. If the control levers7and8are not manipulated, the torques of the hydraulic pumps2and3are lowered. By contrast, if the manipulation of the control levers7and8is sensed by the control lever manipulation amount sensing means12and13, the torques are gradually increased up to the set Tmax. The time constant T is varied in accordance with the manipulation speed of the control levers7and8after the manipulation thereof is sensed. That is, in the case of an abrupt manipulation thereof, a large attenuation effect is secured, while in the case of a soft manipulation thereof, the initial responsibility can be guaranteed.

As illustrated inFIG. 8, in the case where the expected torque is abruptly changed, the instantaneous speed of the engine1is expected to be lowered, and by controlling the change rate of the whole Tmax value in accordance with the Te value, the change rate of the torques to be inputted to the hydraulic pumps2and3is controlled to prevent the instantaneous lowering of the speed of the engine1.

That is, by making torque-limit start points b and d differ from each other in accordance with the torque sizes a and c at time points where the torques start rising after the falling torques are maintained for a specified time in accordance with the expected torque value and the expected torque change rate, and by limiting the torque change rate through the change of the torque rising slope, the output reduction due to the frequent torque limiting in a load-changing work can be minimized.

As described above, according to the system and method of controlling toque of plural variable displacement hydraulic pumps according to the embodiments of the present invention, the stability of working device against the unexpected operation thereof can be improved by limiting not only the total torque for the instantaneous torque matching with the engine but also the set torques distributed in consideration of the characteristics of the working devices designated to the respective hydraulic pumps.

Although not described in the foregoing description, if torque load caused by other additional devices acting as engine power take-off (PTO) devices is estimated or measured, it can be subtracted from the torque value set by the maximum torque setting means to achieve complete torque matching with the engine.

As described above, the system and method of controlling toque of plural variable displacement hydraulic pumps according to the embodiments of the present invention have the following advantages.

In the case of operating the plural variable displacement hydraulic pumps associated with the engine, the total amount of torque of the hydraulic pumps can be accurately limited to the preset amount of torque when the used torque of the hydraulic pumps is limited.

In the case where the sum of desired torque values of the plural hydraulic pumps is larger than a set torque value and thus it is intended to reduce the discharge flow rate of the respective hydraulic pumps, user manipulation can be maintained according to a user's intention even on the torque limit condition by reducing the flow rate of the respective hydraulic pumps in the specified ratio with respect to the desired flow rate of the respective hydraulic pumps.

The workability can be improved by suppressing the stop of engine start during the occurrence of urgent load on condition that load is generated in the plural hydraulic pumps, and the working speed can be maintained by preventing an excessive speed lowering of the engine during the occurrence of urgent load.

Unexpected generation of vibration in working devices can be suppressed even in their abrupt operation through adjustment of the change rate of the torque of the plural hydraulic pumps, and thus the manipulation thereof can be improved.