GB2318886A

GB2318886A - Controlling engine-pump system of hydraulic construction machine

Info

Publication number: GB2318886A
Application number: GB9622593A
Authority: GB
Inventors: Si Cheon Lee; Myung Hoon Song
Original assignee: Samsung Heavy Industries Co Ltd
Current assignee: Samsung Heavy Industries Co Ltd
Priority date: 1996-10-29
Filing date: 1996-10-30
Publication date: 1998-05-06
Anticipated expiration: 2016-10-30
Also published as: GB9622593D0; GB2318886B; DE19644961A1

Abstract

Input torque of the pumps 2,3 is estimated on the basis of output pressures of the pumps detected by a pump output pressure detector, and a power adjustment unit 8 is controlled on the basis of the estimated pump input torque and a reference torque. The power adjustment unit 8 controls the engine 1. The reference torque is adjusted on the basis of engine RPM which is detected at 9. The method permits input power of pumps and output power of an engine to be most suitably matched with each other with respect to working power required according to working environment and characteristic, so that the engine-pump system can have the optimum output characteristic.

Description

2318886 METHOD FOR CONTROLLING ENGINE-PUMP SYSTEM OF HYDRAULIC

CONSTRUCTION MACHINE

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to controlling engine-pump systems of hydraulic construction machines, and more particularly to a method for controlling an engine-pump system of a hydraulic construction machine, in which input power of pumps and output power of an engine are most suitably matched with each other with respect to working power required according to working environment and characteristic, so that the engine-pump system can have the optimum output characteristic.

2. Description of the Prior Art

Referring to Fig. 1, there is schematically shown the construction of a conventional engine-pump system of a hydraulic construction machine. As shown in this drawing, the enginepump system comprises a diesel engine 1 acting as a prime mover, and a plurality of variable displacement hydraulic pumps 2 and 3 being directly connected to the diesel engine 1 to be driven by it. The pumps 2 and 3 are adapted to convert mechanical energy from the diesel engine 1 into hydraulic energy, which is then supplied to hydraulic actuators such as a hydraulic cylinder 5 and a hydraulic motor 6 by a flow control valve 4. The hydraulic actuators are driven by the hydraulic energy from the pumps 2 and 3 to actuate various working elements (not shown).

A pump control system comprises mechanical flow rate/power control means provided with negative control means, cross sensing means and a power adjustment unit 8. The negative control means is adapted to control output flow rate from the pumps 2 and 3 in proportion to the operation of a joystick 7 by the operator. The cross sensing means is adapted to feed output pressures from the pumps 2 and 3 back thereto to control the maximum working power. The power adjustment unit 8 employs electrical auxiliary means for the power adjustment.

Fig. 2 is a graph illustrating the relation between the pump output pressure P and pump output flow rate Q controlled by the pump control system in Fig. 1. In this drawing, a power control curve i shows the maximum power (torque) which can be inputted by the pumps 2 and 3 under the control of the cross sensing means. An flow rate control curve ii shows an flow rate determined by the negative control means when the pumps 2 and 3 are not at a full power control state.

Fig. 3 is a graph illustrating a power characteristic controlled by the pump control system in Fig. 1 and Fig. 4 is a graph illustrating a power characteristic based on an engine output characteristic in Fig. 1. In Fig. 3, curves iii and iv show power states shifted under the control of the power adjustment unit 8. Namely, in response to the magnitude of power shift current, the power adjustment unit 8 shifts the maximum power (torque), which can be inputted by the pumps 2 and 3, from the reference curve to the left or right. In other words, when the engine output has a set characteristic curve T - f(N) in Fig. 4, the pumps 2 and 3 are controlled in such a manner that they can be changed from a no-load state (point B) to a working state (point A) along the characteristic lcurve.

In a conventional power control method, a microcomputer 10 outputs the powershift current to a control input terminal of the power adjustment unit 8 to control the power adjustment unit 8 in such a manner that the RPM of the engine 1 detected by an engine RPM detector 9 can become the same as rated engine RPM which is a reference input corresponding to rated output power (torque). Namely, on the assumption that the pumps 2 and 3 perfectly input the rated output torque from the engine 1 when the controlled RPM of the engine 1 is the rated RPM, the microcomputer 10 controls the pumps 2 and 3 using the powershift current so that the actual RPM of the engine 1 can become the same as the rated RPM corresponding to the rated output power (torque).

However, the above-mentioned conventional engine-pump system control method has the following disadvantages.

First, in the case where the engine 1 is varied in the output characteristic due to its manufacturing error, it reaches an unexpected result according to a controlled characteristic under a given environment. resulting in a degradation in working performance.

Second, the above-mentioned problem is also caused in the case where the engine output characteristic is degraded due to a variation in working environment or the lapse of a year.

In other words, as shown in Fig. 4, the conventional engine-pump system control method controls the engine-pump system on the basis of only the RPM of the engine 1. In this connection, in the case where the actual output characteristic of the engine 1 is T = freal(N), the RPM of the engine 1 is not set to the point B but a point Breal at the no-load state and not to the point A but a point Areal at the working state. As a result, because the input power of the pumps 2 and 3 becomes higher than the output power of the engine 1, the engine-pump system is subjected, to an overload, resulting in a degradation in working performance.

4 - SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for controlling an engine-pump system of a hydraulic construction machine, in which an output characteristic of an engine is prevented from being degraded due to a manufacturing error of the engine, a variation in working environment or the lapse of a year and input power of pumps and output power of the engine are most suitably matched with each other with respect to working power required according to working environment and characteristic, so that the engine-pump system can have the optimum output characteristic.

In accordance with the present invention, the above and other objects can be accomplished by a provision of a method for controlling an engine-pump system of a hydraulic construction machine which comprises an engine, at least one hydraulic pump, an engine RPM detector for detecting RPM of the engine, a pump output pressure detector for detecting an output pressure of the pump, a power adjustment unit for adjusting input power of the pump, and a microcomputer for controlling the power adjustment unit to adjust the input power of the pump, comprising the step of estimating an input torque of the pump on the basis of the output pressure of the pump detected by the pump output pressure detector and controlling the power adjustment unit on the basis of the estimated pump input torque and a reference torque.

- The reference torque is adjusted on the basis of the engine RPM detected by the engine RPM detector.

The above step includes the first step of receiving the reference torque and a reference engine RPM; the second step of receiving the output pressure of the pump detected by the pump output pressure detector and a present engine RPM detected by the engine RPM detector and checking a present powershift current value to the power adjustment unit: the third step of calculating a difference between the reference engine RPM received at the first step and the present engine RPM received at the second step; the fourth step of performing a control arithmetic operation on the basis of the difference calculated at the third step to obtain a reference torque adjustment value; the fifth step of performing a control arithmetic operation on the basis of the reference torque received at the first step and the reference torque adjustment value obtained at the fourth step to adjust the reference torque; the sixth step of performing a control arithmetic operation on the basis of the output pressure of the pump received at the second step and the present powershift current value checked at the second step to estimate the input torque of the pump; the seventh step of calculating a difference between the reference torque adjusted at the fifth step and the input torque of the pump estimated at the sixth step; the eighth step of performing a control arithmetic operation on the basis of the difference calculated at the seventh step to obtain a new powershift current value; and the ninth step of outputting the new powershift current value obtained at the eighth step to the power adjustment unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a schematic view illustrating the construction of a conventional engine-pump system of a hydraulic construction machine; Fig. 2 is a graph illustrating the relation between pump output pressure and pump output flow rate controlled by a pump control system in Fig. 1:

Fig. 3 is a graph illustrating a power characteristic controlled by the pump control system in Fig. 1; Fig. 4 is a graph illustrating a power characteristic based on an engine output characteristic in Fig. 1; and Fig. 5 is a flowchart illustrating the operation of a microcomputer which performs a method for controlling an engine-pump system of a hydraulic construction machine in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 5 is a flowchart illustrating the operation of a microcomputer which performs a method for controlling an engine-pump system of a hydraulic construction machine in accordance with the present invention. Now, the engine-pump system control method of the present Invention will be mentioned with reference to Figs. 1 to 5.

For example, assume that the present engine output characteristic will be varied from T - f(N) to T - freal(N) as shown in Fig. 4.

First, the microcomputer 10 receives a reference torque Tref and a reference engine RPM Nref set according to working environment at step SI. Noticeably, the microcomputer 10 controls the power adjustment unit 8 in such a manner that the engine 1 can output the reference torque Tref at the reference engine RPM Nref and the pumps 2 and 3 can input the reference torque Tref from the engine 1, namely, the output power of the engine 1 and the input power of the pumps 2 and 3 can accurately be matched with each other.

Under the condition that the microcomputer 10 receives the reference torque Tref and the reference engine RPM Nref at the above step S1, it receives output pressures P1 and P2 of the pumps 2 and 3 detected by a pump output pressure detector 11 in Fig. 1 and a present engine RPM N detected by the engine RPM detector 9 and checks a present powershift current value ips to the power adjustment unit 8 at step S2.

At step S3, the microcomputer 10 calculates a difference eN between the reference engine RPM Nref received at the above step S 1 and the present engine RPM N received at the above step S2, namely, eN = Nref - N. In the case where the present engine output characteristic is at the reference set state T = f(N) as shown in Fig. 4, the engine-pump system is controlled in such a manner that the output torque of the engine 1 and the input torque of the pumps 2 and 3 can be matched with each other at the reference torque state Tref. In this case, the present engine RPM N becomes the reference engine RPM Nref. As a result, the difference eN between the reference engine RPM Nref and the present engine RPM N is 0.

Then, in the case where the present engine output characteristic is varied from T = f(N) to T = freal(N) as shown in Fig. 4 due to a manufacturing error of the engine 1 or the lapse of a year, the engine- pump system is controlled in such a manner that the output torque of the engine 1 and the input torque of the pumps 2 and 3 can be matched with each other at the reference torque state Tref. In this case. the present engine RPM N cannot become the reference engine RPM Nref. As a result, the difference eN between the reference engine RPM Nref and the present engine RPM N has a value other than 0.

When the engine-pump system is controlled in such a manner that the output torque of the engine 1 and the input torque of the pumps 2 and 3 can be matched with each other at the reference torque state Tref, the following cases can be inferred on basis of the engine RPM.

First. in the case where the set reference torque Tref is lower than - the actual output of the engine 1, the present engine RPM N becomes higher than the reference engine RPM Nref. This case has no effect on the operator's sense of operation but results in a degradation in working performance. In other words, in this case, the actual engine output characteristic becomes higher than the reference engine output characteristic due to a manufacturing error of the engine 1. For this reason, the reference torque Tref must be adjusted to a higher value.

Second, In the case where the set reference torque Tref is higher than the actual output of the engine 1, the present engine RPM N becomes lower than the reference engine RPM Nref. This case causes the operator to feel the application of an overload to the engine 1 and results in a degradation in working performance. In other words, in this case, the actual engine output characteristic becomes lower than the reference engine output characteristic due to a variation in working environment or the lapse of a year. For this reason, the reference torque Tref must be adjusted to a lower value.

Then, at step S4. the microcomputer 10 performs a control arithmetic operation [Tref - f(eN)] on the basis of the difference eN calculated at the above step S3 to obtain a reference torque adjustment value Tref.

At step S5, the microcomputer 10 performs a control arithmetic operation (Tref - Tref + Tref) on the basis of the reference torque Tref received at the above step S1 and the reference torque adjustment value Tref obtained at the above step S4 to adjust the reference torque Tref.

At step S6, the microcomputer 10 performs a control arithmetic operation [Tcal = g(Pl,P2,ips)l on the basis of the output pressures P1 and P2 of the pumps 2 and 3 received at the above step S2 and the present powershift current value ips checked at the above step S2 to estimate the input torque of the pumps 2 and 3. Noticeably, the input torque of the pumps 2 and 3 can be expressed as a function of the output pressures P1 and P2 of the pumps 2 and 3 and the displacements of the pumps 2 and 3. Also, the displacements of the pumps 2 and 3 can be expressed as a function of the output pressures P1 and P2 of the pumps 2 and 3 and the powershift current value ips, as shown in Fig. 3. Such a pump input torque function is initially stored in the microcomputer 10 for the estimation of the input torque of the pumps 2 and 3.

At step S7, the microcomputer 10 calculates a difference eT between the reference torque Tref adjusted at the above step S5 and the input torque Tcal of the pumps 2 and 3 estimated at the above step S6, namely, eT Tref - Tcal. At step S8, the microcomputer 10 performs a control arithmetic operation [ips = h(eTfl on the basis of the difference eT calculated at the above step S7 to obtain a new powershift current value ips. At step S9, the microcomputer 10 outputs the new powershift current value ips obtained at the above step 58 to the power adjustment unit 8 and then returns to the above step S2 to form an endless loop.

In brief, in the conventional engine-pump system control method, on the assumption that the pumps 2 and 3 perfectly input the rated - 12 output torque from the engine 1 when the controlled RPM of the engine 1 is the rated RPM, the microcomputer 10 controls the pumps 2 and 3 using the powershift current so that the actual RPM of the engine 1 can become the same as the rated RPM corresponding to the rated output power (torque). However, in the engine-pump system control method of the present invention, the microcomputer 10 estimates the input torque of the pumps 2 and 3 us-ing the pump input torque function prestored therein on the basis of the output pressures of the pumps 2 and 3 detected by the pump output pressure detector 11 and the present powershift current value. The microcomputer 10 obtains a new powershift current value on the basis of the estimated pump input torque and the reference torque. Then, the microcomputer 10 outputs the obtained new powershift current value to the power adjustment unit 8 to match the output torque of the engine 1 and the input torque of the pumps 2 and 3 with each other. Further, the reference torque is controlled on the basis of the reference engine RPM and the actual engine RPM to cope with a variation in the output characteristic of the engine 1 due to a manufacturing error of the engine 1 or the lapse of a year.

As apparent from the above description, according to the present invention, the engine-pump system control method can flexibly cope with a variation in the output characteristic of the engine due to a variation in working environment or the lapse of a year. Therefore, the input power of the pumps and the output power of the engine can always become the same so that the enginepump system can have the optimum output characteristic.

Further, the engine output characteristic is prevented from being degraded due to a manufacturing error of the engine, a variation in working environment or the lapse of a year and the input power of the pumps and the output power of the engine are most suitably matched with each other with respect to working power required according to working environment and characteristic. Therefore, the engine-pump system control method of the present invention has the effect of enhancing the basic performance of a hydraulic construction machine employing the engine-pump system.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

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Claims

WHAT IS CLAIMED IS:

1. A method for controlling an engine-pump system of a hydraulic construction machine which comprises an engine, at least one hydraulic pump, an engine RPM detector for detecting RPM of said engine. a pump output pressure detector for detecting an output pressure ef said pump, a power adjustment unit for adjusting input power of said pump, and a microcomputer for controlling said power adjustment unit to adjust the input power of said pump, comprising the step of estimating an input torque of said pump on the basis of the output pressure of said pump detected by said pump output pressure detector and controlling said power adjustment unit on the basis of the estimated pump input torque and a reference torque.

2. A method for controlling an engine-pump system of a hydraulic construction machine, as set forth in Claim 1, wherein the reference torque is adjusted on the basis of the engine RPM detected by said engine RPM detector.

3. A method for controlling an engine-pump system of a hydraulic construction machine, as set forth in Claim 1, wherein said step includes the steps of.

(a) receiving the reference torque and a reference engine RPM; (b) receiving the output pressure of said pump detected by said pump output pressure detector and a present engine RPM detected by - 15 said engine RPM detector and checking a present powershift current value to said power adjustment unit; (c) calculating a difference between the reference engine RPM received at said step (a) and the present engine RPM received at said step (b); (d) performing a control arithmetic operation on the basis of the difference calculated at said step (c) to obtain a reference torque adjustment value:

(e) performing a control arit hmetic operation on the basis of the reference torque received at said step (a) and the reference torque adjustment value obtained at said step (d) to adjust the reference torque; (f) performing a control arithmetic operation on the basis of the output pressure of said pump received at said step (b) and the present powershift current value checked at said step (b) to estimate the input torque of said pump; (g) calculating a difference between the reference torque adjusted at said step (e) and the input torque of said pump estimated at said step (f); (h) performing a control arithmetic operation on the basis of the difference calculated at said step (g) to obtain a new powershift current value; and (i) outputting the new powershift current value obtained at said step (h) to said power adjustment unit.

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