Hydraulic Circuit Equipped with a System for Controlling a Hydraulic Component

Abstract

A hydraulic circuit includes a pump connected to a tank for supplying hydraulic liquid under pressure to a component via a directional control slide valve provided with a feed port connected to an inlet of the component and with a return port connected to an outlet of the component. The hydraulic circuit further includes a pressure limiter connected to the inlet of the component and the tank, and a feed control system for the hydraulic component including a pressure sensor installed upstream of the hydraulic component downstream of the feed port for supplying information about the pressure of the hydraulic liquid and a setpoint pressure. The feed control system further including an actuator for controlling the movement of the directional control slide valve, and a control unit for generating a control signal for the actuator based on information about the pressure measured at the feed port.

Claims

1. A hydraulic circuit comprising: a directional control slide valve including (i) a feed port connected to an inlet of a hydraulic component, and (ii) a return port connected to an outlet of the component; a pump connected to a tank and configured to supply hydraulic liquid under pressure to the component via the directional control slide valve; a pressure limiter connected to the inlet of the component and connected to the tank; a feed control system for the component comprising: a pressure sensor installed upstream of the component and downstream of the feed port, the pressure sensor configured to supply information about a pressure of the hydraulic liquid and a setpoint pressure, an actuator configured to control a movement of the directional control slide valve, a control unit configured to generate a control signal for the actuator based on (i) the information about the pressure measured at the feed port, (ii) the setpoint pressure, and (iii) a request signal from an operator, and a leakage port in the directional control slide valve configured to create a leakage towards the tank between the feed port and the component in an initial phase of travel of the slide valve.

2. The hydraulic circuit according to claim 1, wherein: the control unit is configured to establish a pressure difference between (i) the information about the pressure from the pressure sensor, and (ii) the setpoint pressure and to convert the pressure difference into a base signal that varies in steps in operating zones in accordance with a position of the directional control slide valve, and the hydraulic circuit further comprises a weighing device configured to receive the request signal from the operator, and the base signal to emit another control signal equal to a smaller of the request signal and the base signal.

3. The hydraulic circuit according to claim 1, wherein: curves of cross sections of the feed, return, and leakage ports of the directional control slide valve are subdivided into operating zones depending on a displacement position of the slide valve, and the operating zones include: a closure zone, being a feed closure zone from an end-of-travel position of the slide valve to a start-of-opening position; a decompression zone that follows the closure zone and in which a feed cross section opens up slowly while being smaller than a leakage cross section, the feed cross section and the leakage cross section being very much smaller than a decompression cross section; a pressure maintaining zone in which the leakage cross section falls again and drops below the feed cross section, a distribution zone in which the leakage cross section of the leakage port intervenes only very weakly; and a full flow zone of full flow rate in which the leakage cross section practically no longer intervenes.

4. The hydraulic circuit according to claim 2, wherein: the control unit has a temperature compensation table which receives the base signal so as to compensate the base signal as a function of a temperature of the hydraulic liquid, which temperature is supplied by a temperature sensor configured to detect the temperature of the hydraulic liquid in the hydraulic circuit, the temperature-compensated signal is applied to the weighing device, and the weighing device is configured to form the control signal as the smaller of the request signal from the operator and the temperature-compensated signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The disclosure will be described below in more detail with the aid of an embodiment of a hydraulic circuit according to the disclosure, which is shown in the appended drawings in which:

[0050] FIG. 1 shows a system for controlling a hydraulic component according to the disclosure;

[0051] FIG. 2 shows a diagram of the control function of the system;

[0052] FIG. 3A shows a graph of the curves of the cross sections of the ports of the directional control slide valve;

[0053] FIG. 3B shows a larger-scale detail of FIG. 3A;

[0054] FIG. 4 shows a graph of the curves of the cross section of the ports of the slide valve as a function of a travel of the slide valve for a reversible hydraulic component, such as a hydraulic motor;

[0055] FIG. 5A shows a diagram of a system for controlling a hydraulic component according to the prior art;

[0056] FIG. 5B shows a graph of the curves of the cross section of the ports of the directional control slide valve of the circuit of FIG. 5A;

[0057] FIG. 6A shows a control diagram for a double-acting hydraulic ram for its first feed position;

[0058] FIG. 6B shows a control diagram for the double-acting ram of FIG. 6A in its second feed position; and

[0059] FIG. 7 shows a graph of the curves of the cross section of the ports of the directional control slide valve for the feed of a double-acting ram.

DETAILED DESCRIPTION

[0060] According to FIG. 1, the subject of the disclosure is a hydraulic circuit 100 fed with hydraulic liquid by a pump 20 (motorized pump) that supplies the hydraulic liquid at a variable pressure, limited by a main pressure limiter 9. The hydraulic circuit 100 comprises a directional control slide valve 2 managing the feed for a hydraulic component 7 according to the request DO from the operator actuating a control member 1, such as a lever, and taking account of imposed parameters.

[0061] The hydraulic circuit 100 comprises (i) a branch connecting the pump 20 to the inlet of the hydraulic component 7 through a feed port 3 of the slide valve 2, (ii) a return branch connecting the outlet of the hydraulic component 7 to the tank 21 through the decompression (or return) port 4 of the slide valve 2, and (iii) a bypass, bypassing the inlet of the hydraulic component 7, and leading to the tank 21 via a leakage port 5 of the slide valve 2.

[0062] The hydraulic circuit 100 is supplemented by a direct connection between the inlet of the hydraulic component 7 and the tank 21 via a secondary pressure limiter 6, without passing through the return port 4.

[0063] The secondary limiter 6 is an important high-pressure safety member for limiting the maximum pressure in the event of failure of the electronic part or by cutting off the electrical power supply. By way of example, the range of settings is from 50 bar to 350 bar. The secondary pressure limiter will be calibrated to 360 bar to avoid overpressures that could damage the ducts, hoses or any other component of the hydraulic system if the directional control slide valve were to remain closed following a control error or via a lack of electrical power.

[0064] According to the disclosure, the virtually instantaneous control of the slide valve 2 by the actuator 23 controlled by the unit 10 is independent of the request DO from the operator, that is to say of the position of the actuating member 1.

[0065] The leakage port 5 is connected to the feed port 3 upstream of the component 7, thereby making it possible, in the initial phase, to increase the pressure in the hydraulic circuit or to attenuate or smooth out the increase in pressure and also to operate more effectively in the event of a strong increase in pressure; thus, for example, in the event of jamming of the hydraulic component 7, the increase in pressure upstream of the component is immediately detected by the pressure sensor 8 connected to the inlet of the hydraulic component 7; this pressure is processed by the control unit 10, which immediately returns the directional control slide valve 2 to the decompression zone B so as to reduce the feed cross section 83 and therefore the flow rate Q3 arriving at the hydraulic component 7; this weak flow rate is discharged via the leakage port 5 without having to pass through the limiter 6 with a full flow rate and at high pressure. The available flow rate can be fed to another component.

[0066] As the features of the hydraulic circuit 100 can depend on the temperature T of the hydraulic liquid, in one variant, to take account of this significant dependence in certain cases, the outlet of the pump 20, downstream of the branching of the primary limiter 9, is provided with a temperature sensor 22.

[0067] The directional control slide valve 2 is controlled by a control unit 10 receiving (FIG. 2) (i) the request DO from the operator 1, (ii) the setpoint pressure PC, (iii) the pressure P from the pressure sensor 8, and, as a variant (iv) the temperature T of the hydraulic liquid, which temperature is provided by the sensor 22.

[0068] The setpoint pressure PC is a parameter imposed on the operation of the hydraulic circuit 100 to protect the circuit and its components SES and reduce the losses of power caused by returning the liquid at high pressure and with a substantial flow rate, since these losses do not trigger the pressure limiter 6.

[0069] The leakage cross section S5 of the leakage port 5 opens up more than that of the feed port 3, thus attenuating the feed flow rate in the feed line of the hydraulic component 7, whether the latter is a motor or a ram.

[0070] The pressure maintaining zone C: the leakage cross section S5 decreases, thereby making it possible to implement a controlled repressurization of the feed line of the hydraulic component 7 in order to prepare the conditions for obtaining a movement controlled by the leakage.

[0071] At the end of the zone C, the leakage cross section C5 meets the feed curve C3, which continues to rise.

[0072] A small leakage cross section S5 is maintained for the leakage port 5 to avoid possible instability, in particular when the system is being excited upon activation of an indicial response (response to a step change).

[0073] The slide valve 2 distributes the flow rate in proportion with the pressure drop at the edge of the equivalent port following the opening law of the curve C3.

[0074] The distribution zone D: the slide valve 2 distributes the volumetric flow rate in proportion with the pressure drop across the equivalent port of the hydraulic component 7 following the opening law of the curve C4.

[0075] The zone of full flow rate E: in this zone, the maximum hydraulic power is reached. The increase in the feed cross section 3 causes the pressure in the load (component 7) to drop. To ensure a stabilized pressure, the return cross section C4 is decreased to obtain a pressure ratio of close to 1 in the case of a hydraulic motor.

[0076] At full flow rate travel, the directional control slide valve 2 completely closes the leakage cross section 5 to avoid a needless drop in flow rate.

[0077] In the event of jamming of the hydraulic component 7, the increase in the load pressure is immediately detected by the sensor 8 and processed by the control unit 10, which instantaneously returns the slide valve 2 to the zone B to reduce the feed flow rate Q3 via the reduction of the cross section S3 and the compensation via the cross section S5 of the leakage port 5.

[0078] Since the measured pressure exceeds the setpoint pressure PC, the difference Ec becomes negative and generates a control signal SCmin, immediately returning the slide valve to the decompression zone B irrespective of the current request DO from the operator.

[0079] The feed is thus reduced immediately and the return is carried out via the leakage port 5.

[0080] In the case of a hydraulic component 7 constituted by a hydraulic motor, the incoming flow rate is the same as the outgoing flow rate and the curves as set out in FIG. 3A apply.

[0081] In the case of a hydraulic ram, the control is done similarly to reduce the feed cross section of the ram in the event of jamming of the instrument associated with the ram.

LIST OF KEY PARTS

[0082] 100 Hydraulic circuit [0083] 1 Control member/lever [0084] 2 Directional control slide valve [0085] 2a Known directional control slide valve [0086] 3 Feed port of the component 7 [0087] 4 Return port of the component 7 [0088] 5 Leakage port upstream of the component 7 [0089] 6 Secondary pressure limiter [0090] 7 Hydraulic component [0091] 7a,b Hydraulic ram [0092] 8 Pressure sensor at the inlet of the component 7 [0093] 9 Main pressure limiter [0094] 10 Control unit [0095] 101 Temperature compensation table [0096] 102 Weighing means [0097] 20 Feed pump for the hydraulic circuit [0098] 21 Hydraulic liquid tank [0099] 22 Temperature sensor for the hydraulic liquid at the outlet of the pump 20 [0100] 23 Actuator of the directional control slide valve 2 [0101] P Pressure measured by the sensor 8 [0102] PC Setpoint pressure [0103] DO Request from the operator [0104] SCo Base signal [0105] SCC Compensated signal [0106] SC Control signal [0107] Ec Difference between the measured pressure and the setpoint pressure [0108] T Temperature supplied by the sensor 22 [0109] A-E Zones of the opening curves for the ports 3, 4, 5 [0110] C3 Curve representing the cross section of the feed port [0111] C4 Curve representing the cross section of the decompression port [0112] C5 Curve representing the cross section of the leakage port [0113] C6 Pressure curve [0114] A Closure zone [0115] B Decompression zone [0116] C Pressure maintaining zone [0117] D Distribution zone [0118] E Zone of full flow rate [0119] S3 Feed cross section [0120] S4 Decompression or return cross section [0121] S5 Leakage cross section