GB2202925A

GB2202925A - Open loop or closed-loop control system for a drive assembly

Info

Publication number: GB2202925A
Application number: GB08801316A
Authority: GB
Inventors: Horst Deininger
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 1987-02-25
Filing date: 1988-01-21
Publication date: 1988-10-05
Anticipated expiration: 2008-01-21
Also published as: FR2611172B1; GB8801316D0; DE3706117A1; JPS63232044A; FR2611172A1; GB2202925B

Abstract

A drive assembly, consisting of an internal combustion engine (1) and an infinitely variable hydrostatic transmission, has an open-loop or a closed-loop control system which includes a compression control system which reduces the output speed of the transmission when the engine speed drops owing to severe loading. In order to provide the loop control system with high control quality, an electric speed sensor (40) fitted on the engine (1) passes a signal to an electronic control (42), which is in connection with an electromagnetic proportional valve (28) via a control magnet (29). The valve (28) is connected via a line (17) to an hydraulically controlled valve (15) connected to the setting element (9) of the adjustable transmission pump (3), and via line (52) to a pressure space of an operating cylinder (50) for the setting of the diesel engine (1) and to the brake pressure line of energy storage brakes (8). Each motor (6) in the transmission has an hydraulically releasable spring-loaded brake (8). The sensor (40) may be an inductive sensor. The proportional valve (28) may have a plurality of mutually separate current paths assigned in each case to a control or operating element. <IMAGE>

Description

"OPEN-LOOP AND CLOSED-LOOP CONTROL SYSTEM FOR A DRIVE ASSEMBLY AND METHOD OF OPERATION OF SAID SYSTEM" This invention relates to an open-loop and closed-loop control system for a drive assembly and to a method of operation of said system.

As hereinafter employed, the words "an openloop and closed-loop control system of the type described" is intended to mean an open-loop and closed-loop system for a drive assembly and, in particular, the travel drive assembly of a motor vehicle, said drive assembly having a primary energy source which is preferably a reciprocating internal combustion engine and in particular a diesel engine, and a transmission which can be adjusted infinitely by means of a control pressure and is preferably hydrostatic, and has a compression control system varying the setting of the setting element of the transmission in the direction of a smaller output speed dependently on the speed of the primary energy source when this speed drops.

Compression controls, which are intended to avoid the stopping of an internal combustion engine (driving a hydrostatic transmission) occurring due to en excessive torque at the output shaft of the internal combustion engine, by reducing the swept volume per revolution of the pump of the hydrostatic transmission and thus its torque take-up whenever the speed of the internal combustion engine drops below a predetermined threshold, are known (see, for example, German Offenlegungschrift No.28 23 559, German Auslegeschrift No.15 55 480 and German Offenlegungschrift No. 35 44 607).In this contect, there are purely hydraulic systems in which a fixed displacement pump is connected to the shaft of the internal combustion engine, in the delivery flow of which pump a measuring restrictor point is arranged, the pressure head, dependent on the speed of the fixed displacement pump, upstream of this measuring restrictor point being used for controlling the transmission setting. In the case of a control system of purely hydraulic design, such a configuration is expedient and can be produced with an appropriate production outlay. However, such an arrangement also has several disadvantages. One which may be mentioned is that quite a considerable level of power is required for the delivery of a liquid stream by the fixed displacement pump against the resistance offered by a measuring restrictor point, which power cannot be utilised but is converted into heat.Another which may be mentioned is that the pressure signal is not precisely proportional to the motor speed but is dependent upon the viscosity (and thus the temperature) of the liquid, the tightness of the pump, the setting accuracy of the measuring restrictor point and any contaminants which may have lodged in the latter. Consequently, the quality of the control is also limited.

On the other hand, there are also purely electronic compression controls and this presupposes that the transmission pump can be activated electrically. Although such systems produce a high control quality, they are very expensive.

The present invention therefore has as its principal object the creation, with minimum possible production outlay, of an open-loop and closed-loop control system of the type described (as defined above) with high control quality but reduced expense when compared with that of some of the existing ones, and the creation of a method of operation of said system. Another object of the present invention is the creation of a method of operation of such a control system.

According to a first aspect, therefore, the present invention consists in an open-loop and closedloop control system of the type described (as defined above), wherein the compression control system includes a sensor for an electric speed signal and wherein there is provided a signal/current converter to the output of which the magnet coil of an electromagnetic proportional valve is connected, to which the setting element of the transmission is connected.

In a control system as described in the preceding paragraph, the transmission is preferably an hydrostatic transmission, in which the setting element of the pump is connected to an hydraulic control element, which adjusts to a constant pressure gradient upstream and downstream of a measuring restrictor in the delivery line between pump and consumer, said proportional valve being connected to a sensor valve of the control element.

In a control system as described in either of the two preceding paragraphs, there may be a primary energy source, with an operating cylinder which can be actuated by control pressure and is connected to the setting element of the primary energy source, at least one pressure space of the operating cylinder of the setting element of the primary energy source being connected to the proportional valve.

In a control system as described in any one of the three preceding paragraphs, the drive assembly preferably operates a further adjustable pump, assigned to at least one further consumer, preferably a pump with a control element which adjusts to a constant pressure gradient at a measuring restrictor in the delivery line of the pump, the control element of said further adjustable pump also being connected to the proportional valve.

The input shaft of the drive assembly may be connected to an energy-storage brake, the brake pressure line also being in effective connection with the proportional valve.

The sensor for the electric speed signal is preferably an inductive sensor.

Lastly, the proportional valve preferably has several mutually separate current paths assigned in each case to a control or operating element.

According to a second aspect, the present invention consists in a method of operation of the open-loop and closed-loop control system described in the seventh preceding paragraph, wherein an electric speed signal is generated and wherein an electric current, the size of which is dependent on this speed signal, is passed through the magnet coil of the electromagnetic proportional valve which influences the control elements for the setting of the transmission.

In a preferred embodiment of said method of operation described in the preceding paragraph, an evaluation of the control pressure set value vis-avis the magnetic force influenced by the speed actual value signal is preferably effected in the proportional valve.

All paths of the proportional valve which has several paths may be activated simultaneously to the same extent.

The individual current paths of the proportional valve, which paths are established by the arrangement of the control edges in said valve,may be opened and closed in predetermined sequence.

One embodiment of an open-loop and closedloop control system of the type described (as defined above)according to the present invention will now be explained in detail by way of example only, with reference to the accompanying drawing in which there is illustrated an internal combustion engine 1 which drives via a shaft 2 a transmission pump 3, which is connected via two hydraulic lines 4 and 5 in the closed circuit to two hydraulic motors 6. Each of the hydraulic motors 6 has a shaft 7 and an hydraulically releasable springloaded brake 8 is arranged at each of the shafts 7.

The engine 1 may be a diesel engine in a motor vehicle.

A setting element 9 of the pump 3 is connected to an operating piston 10, which can be displaced in an operating cylinder between two springs 12. Each of the two pressure spaces within the operation cylinder is connected via a line 13, in which a restrictor point 14 is arranged in each case, to an hydraulically controlled valve 15 whose right-hand-side control pressure space is connected to a line 16 and whose left-hand-side control pressure space is connected to a line 17. Furthermore, a direction change-over valve 19 is actuated via an actuating element which is not indicated.

Also driven by the shaft 2 is a second adjustable pump 20, to the delivery line 21 of which further consumers 23, 24, 25 and 26 of hydraulic energy are connected via a block control unit 22.

A load-sensing signal line 27 is connected to the block control unit 22 and this line 27 leads to one inlet of a proportional valve 28, which can be actuated by means of a control magnet 29. A second inlet of this valve 28 is connected via a line 30 to the line 17. The control pressure space, opposing the control magnet 29, of the proportional valve 28 is connected via a line 31 to the outlet of a pressure-dependent switching change-over valve 32, to the two inlets of which control pressure signal lines 34 and 35 are connected, so that the higher of the two pressures carried in the lines 34 and 35 is always fed via the line 31 to the control pressure space of the valve 28.

An inductive speed sensor 40 is arranged on the shaft 2 of the engine 1, which sensor is connected via a line 41 to the electronic control 42, which is connected to a battery 43 and in which the speed-related signal, brought to it through the line 41, is converted into a certain current fed through a line 44 to the control magnet 29, or into a certain voltage which (taking into account the known resistance of the control magnet 29) effects a certain current flow through the latter.

An hydrostatic steering power assistance system, which acts on a steering cylinder 46, is indicated by the reference numeral 45 and a control pressure sensor with override control, which serves to control the output speed of the shafts 7, is indicated by the reference numeral 147. Two actuating elements 48 for the control of the output speed and 49 for the control of the brakes 8 are provided in said sensor.

The open-loop and closed-loop control system of the type described (as defined above) according to the invention provides a combination of an electronic control and, a hydraulic control, which utilises the advantages of both systems with a minimum of production outlay; in particular, it provides a very precise control.

The engine 1 is provided with a setting element 51 whose actuating lever is connected to an operating piston which can be displaced in an operating cylinder 50; said piston, in the cylinder 50, separates two pressure spaces from each other, one of which is connected via a line 52 to the line 31 leading to the control pressure space of the proportional valve 28 and the other of which is connected via the control pressure line 53 to the outlet of the direction dependent switching multiway (directional control) valve 19.

It is to be pointed out that control system according to the present invention can be used to good effect not only in the case of hydrostatic transmissions operating in closed circuit but also in the case of pumps operating in open circuit.

In the case where several current paths are controlled by the proportional valve 28, the edges at the control valve may be arranged in such a way that said current paths are enabled simultaneously or in a predetermined sequence so that priorities are/can be set as to which operating cylinder is influenced first and which is influenced second, for example, when two adjustable pumps, each of which serves a different consumer from the other, are driven by the internal combustion engine 1 or else the operating cylinder of the setting element of said engine 1 is connected to the proportional valve 28.

It is a particularly expedient arrangement if the tachometer generator is an inductive pick-up sensor which is influenced, for example, by the teeth of toothing on the flywheel of the internal combustion engine 1.

Claims

CLAIMS:

1. An open-loop and closed-loop control system of the type described (as defined above), wherein the compression control system includes a sensor for an electric speed signal and wherein there is provided a signal/current converter to the output of which the magnet coil of an electromagnetic proportional valve is connected, to which the setting element of the transmission is connected.

2. A control system according to Claim 1, wherein the transmission is an hydrostatic transmission, in which the setting element of the pump is connected to an hydraulic control element, which adjusts to a constant pressure gradient upstream and downstream of a measuring restrictor in the delivery line between pump and consumer, said proportional valve being connected to a sensor valve of the control element.

3. A control system according to Claim 1 or Claim 2, wherein there is a primary energy source, with an operating cylinder which can be actuated by control pressure and is connected to the setting element of the primary energy source, at least one pressure space of the operating cylinder of the setting element of the primary energy source being connected to the proportional valve.

4. A control system according to any one of the preceding Claims, wherein the drive assembly operates a further adjustable pump, assigned to at least one further consumer, preferably a pump with a control element which adjusts to a constant pressure gradient at a measuring restrictor in the delivery line of the pump, the control element of said further adjustable also being connected to the proportional valve.

5. A control system according to any one of the preceding Claims, wherein the input shaft of the drive assembly is connected to an energy-storage brake, the brake pressure line also being in effective connection with the proportional valve.

6. A control system according to Claim 1, wherein the sensor for the electric speed signal is an inductive sensor.

7. A control system according to any one of Claims 3 to 6, wherein the proportional valve has several mutually separate current paths assigned in each case to a control or operating element.

8. Method of operation of the open-loop and closed-loop control system according to Claim 1, wherein an electric speed signal is generated and wherein an electric current, the size of which is dependent on this speed signal, is passed through the magnet coil of the electromagnetic proportional valve which influences the control elements for the setting of the transmission.

9. Method of operation according to Claim 8 for a control system according to Claim 3, wherein an evaluation of the control pressure set value vis-avis the magnetic force influenced by the speed actual value signal is effected in the proportional valve.

10 Method of operation according to Claim 8, wherein all paths of the proportional valve which has several paths are activated simultaneously to the same extent.

11. Method of operation according to Claim 8 or Claim 9, wherein the individual current paths of the proportional valve, which paths are established by the arrangement of the control edges in said valve, are opened and closed in predetermined sequence.

12. An open-loop and closed-loop control system of the tyre described (as defined above), said system being constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

13. A method of operation of an open-loop and closed-loop control system of the type described (as defined above), said method being substantially as hereinbefore described with reference to the accompanying drawing.

14. Any features of novelty, taken singly or in combination, of the embodiments of the invention hereinbefore described with reference to the accompanying drawing.