FR2975142A1 - Load sensing hydraulic system for e.g. farm tractor, has operating slide whose first end is subjected to pressure at flow restrictor device outlet and pressure of calibration spring, and second end is subjected to pressure at device inlet - Google Patents

Abstract

The system has a flow restrictor device (LS) arranged in a pressure channel (10) between a variable flow pump (P) and a hydraulic receiver (R) e.g. hydraulic motor. A correction device (A) has a distributor comprising an operating slide (30) whose first end (31) is subjected to a real load pressure (Pu) at an outlet of the restrictor device and to a pressure (X) of a calibration spring (310), and second end (32) is subjected to a pressure (Pls) at an inlet of the restrictor device. The correction device controls a control device (C) with a load pressure (Pu2) different from the real pressure.

Description

HYDRAULIC SYSTEM FOR UTILITY VEHICLE WITH LOAD DETECTION Description Technical field of the invention.

The invention relates to a hydraulic system for a utility vehicle comprising a load sensing device (also known as "Load Sensing").

State of the art Commercial vehicles, for example agricultural tractors, generally include a load sensing system. This technology makes it possible to have optimum hydraulic power at all times as soon as a hydraulic receiver (for example a cylinder or any other type of equipment or tool) is requested. Load sensing is used to control the flow and pressure in the hydraulic circuit, so that the receiver can almost instantly receive the flow and pressure required for its operation.

Referring to Figure 1, such a hydraulic system comprises: - a pump P variable flow. Its inlet port is connected to a fluid reservoir Re. The pump P generally comprises a movable plate on which the pistons of the pump are fixed. The position of the plate, and therefore the flow rate and the pressure generated, varies according to the stress of the hydraulic circuit. - 2

This plate is itself controlled by a jack 1, actuated by a control device C. This type of pump allows for example to provide a flow rate of about 100 L / min, with a service pressure of about 200 bar (105 Pa). - At least one hydraulic receiver R connected to the discharge port of the pump P by a pressure channel 10, 10 '. This receiver is for example a hydraulic motor, a hydraulic cylinder of a tool, etc. - a flow restrictor device LS (or "load sensing" distributor, hereinafter "the LS distributor") disposed in the pressure channel 10, between the pump P and the hydraulic receiver R. The dispenser LS is set to the value controlling the hydraulic receiver R. It makes it possible to adjust the flow rate of the pump P to the useful flow Qu of the receiver R. This type of dispenser LS is well known to those skilled in the art and will not be described in more detail in the As a result of the description, a regulation channel 20, 20 'makes it possible to transmit the actual charging pressure Pu of the hydraulic receiver R to a control device C adjusting the delivery pressure of the pump P as a function of the said charging pressure. Typically, the control device C adjusts the position of the cylinder 1 of the pump P according to the charging pressure Pu claimed by the hydraulic receiver R. In practice, the control device C is calibrated to an ApLS value. This type of control device C is well known to those skilled in the art and will not be described in more detail in the following description.

The operation of such a hydraulic system will now be described. The charging pressure Pu requested by the receiver R is sent to the control device C via the regulation channel 20, 20 '. The control device C adapts to this load by maintaining the discharge pressure of the pump P to a value Pp = Pu + ApLS. Thus, for a fixed setting of the distributor LS, this servocontrol loop makes it possible to maintain a pressure difference AP = PLs-Pu = Pp-Pu = constant ApLS across said 2975142 -3

dispenser LS and thus maintain a constant flow Qu irrespective of the load variations Pu requested by the receiver R.

However, some parameters outside the LS dispenser may influence the flow Qu. Thus, the parasitic charge losses Apa in the pressure channel 10, upstream of the distributor LS, due to hoses, connections or other, generate a pressure drop right in front of said dispenser LS. This then results in a fall in the theoretical flow rate Qu since the pressure difference across the distributor LS becomes AP = PLs-Pu = Pp-Apa-Pu <ApLS. In addition, the information taken by the charging pressure Pu can be degraded by parasitic pressure losses in the control channel 20, 20 'and / or by a leakage rate that may exist at the level of the control device C In both cases, the charge pressure restored at the control device C is lower than the actual charging pressure Pu. In fact, the pump P provides a lower pressure Pp than that theoretically required.

To adapt the "pumps" settings of the vehicle to the characteristics of the LS dispenser tools, it is known to integrate an amplifier device A '20 disposed in the control channel 20, 20' of the vehicle. This amplifier device A 'is configured to control the control device C with a higher charging pressure Pu2 than the actual charging pressure Pu. More particularly, patent documents EP 1,760,325 (AGCO) and EP 1,783,378 (AGCO) disclose an amplifier device consisting of a flow distributor combined with a distributor with a two-position operating spool and setting spring. In addition to the fact that such a correction device requires two relatively expensive components (flow distributor + pressure limiter) and must be operated manually by the operator, the result obtained is not totally satisfactory. Indeed, the control pressures of the operating spool absolutely do not allow - 4

to compensate for parasitic load losses between the pump and the distribution block.

In view of this state of affairs, the main objective of the invention is to propose a correction device making it possible to better compensate for the adverse effects related to the environment of the dispenser LS. Another object of the invention is to propose a correction device of simple and inexpensive design.

Disclosure of the invention. The solution proposed by the invention is a hydraulic system for a commercial vehicle, comprising: - a variable flow pump, - at least one hydraulic receiver connected to the discharge port of the pump via a pressure channel, - a restrictor device a flow path disposed in the pressure channel between the pump and the hydraulic receiver, said restricting device being set to the control value of said hydraulic receiver; - a control channel for transmitting the actual load pressure of the hydraulic receiver to a device control device calibrated to a pressure value, said control device adjusting the discharge pressure of the pump as a function of said charging pressure and said set pressure, - a correction device configured to control the control device with a pressure of load different from the actual load pressure of the hydraulic receiver, said correction device consis both in a distributor with two-position operating spool and setting spring, said distributor having at least one outlet port connected to the control device by the control channel. 2975142 -5

This system is notable in that: a first end of the operating spool is subjected to pressure at the outlet of the flow restrictor device and at the pressure of the setting spring; maneuver is subjected to pressure at the inlet of the flow restrictor device. As explained later in the description, such control pressures of the operating spool make it possible to effectively compensate for parasitic losses and to maintain a constant, or almost constant, flow across the flow restrictor regardless of effects related to its environment.

According to a first variant embodiment, the corrector device comprises a first exhausted inlet, and a second inlet connected to the pressure channel upstream of the flow restrictor device, the second end of the operating spool being subjected to pressure. at the inlet of said flow restricting device. In this first variant, the second inlet may be connected to the pressure channel at the discharge port of the pump or near the inlet of the flow restrictor.

According to a second variant embodiment, the corrector device comprises a first input connected to the pressure channel downstream of the flow restrictor device, and a second input connected to the pressure channel upstream of said flow restrictor device, the second end of the spool valve. operating device being subjected to the pressure at the inlet orifice of said flow restricting device. In this second variant, the second inlet may be connected to the pressure channel at the discharge port of the pump or near the inlet of the flow restrictor. And preferentially, the - 6

ApLS calibration value of the control device and the setting value X of the spring of the corrector device A are such that: ApLS-5 (bars) <X <ApLS.

According to a third variant embodiment, the corrector device comprises a first input connected to the pressure channel downstream of the flow restrictor device, and a second input connected to the pressure channel upstream of the flow restrictor device, the second end of the flow restrictor device. maneuver being subjected to the pressure of the outlet of the corrector device.

Description of the figures.

Other advantages and characteristics of the invention will appear better on reading the description of a preferred embodiment which follows, with reference to the accompanying drawings, made by way of indicative and non-limiting examples and in which: FIG. 1 is a diagrammatic representation of a load sensing and correction hydraulic system of the type known from the prior art; FIG. 2 schematizes a hydraulic system according to the invention, according to a first variant, in a first embodiment, FIG. 3 schematizes a hydraulic system according to the invention, according to the first variant, in a second embodiment, FIG. 4 schematizes a hydraulic system according to the invention, according to a second variant, in a first embodiment of FIG. FIG. 5 schematizes a hydraulic system according to the invention, according to the second variant, in a second embodiment, FIG. n hydraulic system according to the invention, according to a third variant, in a first embodiment, - Figure 7 schematically a hydraulic system according to the invention, according to the third variant, in a second embodiment.

Embodiments of the invention

The hydraulic system which is the subject of the invention is particularly intended to be used in a utility vehicle of the construction or tractor type. It is particularly suitable for agricultural vehicles such as equipment towed or carried by an agricultural tractor reusing its hydraulic sources.

When elements of the hydraulic system are "connected" or "connected" to each other, in the sense of the present invention, it is meant that ducts (e) allow to circulate the fluid from one element to another.

According to the invention, and as shown diagrammatically in FIGS. 2 to 7, the corrector device A (hereinafter "the corrector") consists of a distributor comprising an operating spool 30 movable between at least two positions I, II. Each end 31, 32 of the slide 30 is subjected to a control pressure. A first end 31 is further subjected to the pressure X of a calibration spring 310. The value of X depends on the configuration of the hydraulic circuit and can be set for example between 1 bar and 50 bar. The design and operation of such a dispenser are known to those skilled in the art and will not be described in more detail in the following description. The corrector A comprises at least one output port S connected to the control device C by the regulation channel 20, 20 '. In the embodiments of Figures 2 to 7, the corrector A further comprises two inputs el, e2. In the first position I, the second input e2 is connected to the output S, while in the second position II, the first input el is connected to said output. The distributor is therefore preferably a 3/2 distributor (3-way and 2-position). The setting spring 310 is disposed at the first end 31 of the slide 30 so that the latter tends to position itself in the first position I. -7 2975142 -8

Three variants of the invention will now be described in more detail.

1) First variant embodiment (FIGS. 2 and 3).

In this preferred embodiment, the first input el of the corrector A is exhausted, in practice being connected to the reservoir Re. The second input e2 is connected to the pressure channel 10, upstream of the dispenser LS, at the level of the inlet of said distributor (Figure 3) or preferably near (substantially the same level) of the discharge port of the pump P (Figure 2) to have the maximum pressure of the circuit.

The first end 31 of the spool 30 is subjected to pressure Pu at the outlet (or actual load pressure) of the dispenser LS and pressure X of the setting spring 310. The second end 32 of the spool 30 is subjected to the pressure Pis at the inlet orifice of the dispenser LS.

When the receiver R is not solicited, the distributor LS is inactive and the flow Qu = 0. And the pressure Pu is zero. With the pump P operating, the pressure Pis increases and becomes greater than the calibration pressure X. The spool 30 switches to the second position II where the first input el is connected to the output S. In this position, the first input el being connected to the reservoir Re, then the pressure Pu2 = 0 at the outlet port S of the corrector A. Thus the standby pressure of the pump P is Pp = ApLS. In the case where X> ApLS, the spool 30 remains in the first position I where the second input e2 is connected to the output S. In this position, the second input e2 being connected to the pressure channel 10, the pressure Pu2 increases by so that the pressure Pp of the pump P increases until it reaches the value X. Thus the waiting pressure of the pump P is Pp = X. - 9

When the receiver R is solicited, the dispenser LS is active and passes a flow Qu. Since the pressure Pu increases, the spool 30 is positioned in the first position I where the second input e2 is connected to the output S. In this position, the second input e2 being connected to the pressure channel 10, the pressure Pu2 increases causing a pressure increase P.sub.P of the pump P. The corrector A equilibrates as soon as PLs = Pu + X and AP = PLs-Pu = X. The pressure difference AP across the LS valve therefore remains constant and independent of the environment of the hydraulic circuit. Thus, for a given flow rate adjustment of the dispenser LS, it is retained, whatever parasitic pressure losses upstream of said dispenser LS and / or parasitic pressure losses in the control channel 20, 20 '.

By writing the equilibrium of the pressures in the hydraulic circuit, it appears that: - PLs = Pp-Apa (parasitic losses in the pressure channel 10, upstream of the dispenser LS) - PLs = Pu + X - Pp = Pu2 -Apc + ApLS (Apc = parasitic losses in the control channel 20 ', downstream of the corrector A) Pu2 = Pp + Apc-ApLS = PLs + Apa + Apc-ApLS = Pu + X + Apa + Apc-ApLS

The additional interest of this embodiment lies in its two-way action. When X> ApLS, the corrector A acts as a signal amplifier to compensate for the pressure losses due to the environment of the hydraulic circuit (parasitic losses in pressure channel 10 and / or in control channel 20 ', ...). When X <ApLS, the corrector A acts as a signal reducer to compensate, for example, for a too large initial setting of the ApLS of the control device C. 2) Second variant embodiment (FIGS. 4 and 5). In this variant embodiment, the first input el of the corrector A is connected to the pressure channel 10 'downstream of the dispenser LS, in particular at the outlet orifice of said dispenser. Compared to the first variant 5 (Figures 2 and 3) where the first input el is connected to the tank Re, this configuration reduces the number of connections, avoiding the connection to said tank.

The second inlet e2 is connected to the pressure channel 10, upstream of the dispenser LS, near the inlet orifice of said dispenser (FIG. 5) or preferably near (substantially at the same level) of the discharge orifice. pump P (Figure 4).

The first end 31 of the spool 30 is subjected to pressure Pu at the outlet (or actual load pressure) of the dispenser LS and pressure X of the setting spring 310. The second end 32 of the spool 30 is subjected to the pressure Pis at the inlet orifice of the dispenser LS.

When the receiver R is not solicited, the dispenser LS is inactive: the flow Qu = 0 and the pressure Pu = 0. With the pump P operating, the pressure Pis increases and becomes greater than the calibration pressure X. The spool 30 switches to the second position II where the first input el is connected to the output S. In this position, the first input el being connected at the output terminal of the dispenser LS, the pressure Pu2 = Pu = 0 at the outlet port S of the corrector A. Thus the waiting pressure of the pump P is Pp = ApLS.

When the receiver R is solicited, the dispenser LS is active and passes a flow Qu. Since the pressure Pu increases, the spool 30 is positioned in the first position I where the second input e2 is connected to the output S. In this position, the second input e2 being connected to the pressure channel 10, the pressure Pu2 increases causing an increase of 2975142 -11-

Pp pressure of the pump P. The corrector A is balanced as soon as PLs = Pu + X and AP = PLs-Pu = X. The pressure difference AP across the LS valve therefore remains constant and independent of the environment of the hydraulic circuit. Thus, for a given flow control of the dispenser LS, this is retained, whatever the parasitic losses of upstream of the LS distributor and / or parasitic losses losses in the control channel 20, 20 '.

The applicant has demonstrated that for an adjustment of the setting value X such that: ApLS-5 (bars) <X <ApLS, then the operation of the hydraulic system is optimal.

3) Third variant embodiment (FIGS. 6 and 7).

In this variant embodiment, the first input el of the corrector A is connected to the pressure channel 10 'downstream of the dispenser LS, in particular at the outlet orifice of said dispenser. The second inlet e2 is connected to the pressure channel 10, upstream of the dispenser LS, near the inlet orifice of said dispenser (FIG. 7) or preferably close to (substantially the same level) of the discharge orifice. pump P (Figure 6).

The first end 31 of the spool 30 is subjected to the pressure Pu (or actual load pressure) at the outlet of the dispenser LS and at the pressure X of the setting spring 310. The second end 32 of the spool 30 is subjected to the pressure Pu2 at the output port S of the corrector A.

When the receiver R is not solicited, the dispenser LS is inactive: the flow Qu = 0 and the pressure Pu = 0. Corrector A acts as a pressure reducer maintaining Pu2 = X. So the waiting pressure of the pump P is Pp = Pu2 + ApLS = X + ApLS. 2975142 -12- When the receiver R is solicited, the dispenser LS is active and passes a flow Qu. The equilibrium of the pressures at the level of the corrector A gives: Pu2 = Pu + X. The pressure at the discharge of the pump P becomes: Pp = Pu2 + ApLS = Pu + X + ApLS.

By writing the equilibrium of the pressures in the hydraulic circuit, it appears that: - PLs = Pp-Apa (parasitic losses in the pressure channel 10, upstream of the distributor LS) - Pp = Pu2-Apc + ApLS ( Apc = parasitic losses in the control channel 20, downstream of the corrector A) - Pu2 = Pu + X The pressure difference across the LS distributor: AP = PLs-Pu = X- Apc-Apa + ApLS

The X bars added by the corrector A make it possible to compensate the pressure losses upstream and downstream of the dispenser LS.

Claims (8)

REVENDICATIONS1. Hydraulic system for a utility vehicle, said system comprising: - a pump (1) with variable flow rate, - at least one hydraulic receiver (R) connected to the discharge port of the pump (P) via a pressure channel (10, 10 '), - a flow restrictor device (LS) disposed in the pressure channel (10), between the pump (P) and the hydraulic receiver (R), said restrictor device being set to the control value of said hydraulic receiver a control channel (20, 20 ') for transmitting the actual load pressure (Pu) of the hydraulic receiver (R) to a control device (C) calibrated to a pressure value (ApLS), said control device control adjusting the discharge pressure of the pump (P) according to said charging pressure (Pu) and said calibration pressure (ApLS), - a correction device (A) configured to control the control device (C) with a charge pressure (Pu2) different from the charge pressure real one (Pu) of the hydraulic receiver (R), said correction device consisting of a distributor with operating slide (30) with two positions (I, II) and setting spring (310), said dispenser comprising at least one exit orifice (S) connected to the control device (C) by the control channel (20, 20 '), characterized in that: - a first end (31) of the operating spool (30) is subjected to pressure ( Pu) at the outlet of the flow restrictor device (LS) and at the pressure (X) of the setting spring (310), a second end (32) of the operating spool (30) ) is subjected to pressure (PLs) at the inlet of the flow restrictor (LS). 5 2. System according to claim 1, wherein: the corrector device (A) comprises: a first input (el) exhausted, a second input (e2) connected to the pressure channel (10) upstream of the flow restriction device (LS), the second end (32) of the operating spool (30) is pressurized (PLs) at the inlet of the flow restrictor (LS). 3. System according to claim 2, wherein the second inlet (e2) is connected to the pressure channel (10) near the discharge port of the pump (P). The system of claim 2, wherein the second inlet (e2) is connected to the pressure channel (10) at the inlet of the flow restrictor (LS). 5. System according to claim 1, in which: the correction device (A) comprises: a first input (el) connected to the pressure channel (10 ') downstream of the flow restricting device (LS); second inlet (e2) connected to the pressure channel (10) upstream of the flow restricting device (LS), - the second end (32) of the operating spool (30) is subjected to the pressure (PLs) at the level of the inlet port of the flow restrictor device (LS). 2975142 -15- 6. System according to claim 5, wherein the second inlet (e2) is connected to the pressure channel (10), near the discharge port of the pump (P). 5 The system of claim 5, wherein the second inlet (e2) is connected to the pressure channel (10) at the inlet of the flow restrictor (LS). 8. System according to one of claims 5 to 7, wherein the setting value (ApLS) of the control device (C) and the setting value (X) of the spring (310) of the corrector device (A) are such as: ApLS-5 (bars) <X <ApLS.