FR2766525A1 - Control circuit for vehicle steering - Google Patents

Abstract

The flow regulators include a throttle (116) with its inlet connected to the pump discharge duct (112) and the outlet connected to the vents (126). The throttle has a fluid drain passage (212) and controls (200,204) to vary the throttle section as a function of the fluid discharge

Description

 The present invention relates to a circuit for supplying fluid to a receiver comprising a first hydraulic discharge pump capable of supplying pressurized fluid to a so-called "discharge line", a receiver connected to said discharge line by a so-called line "receiver" and adjustment means capable of generating, in this receiver line, a fluid pressure dependent on the discharge flow rate of the pump according to a determined pressure law.

 The pump, with fixed displacement, is generally driven by a thermal or electric motor and it is easy to increase or decrease the delivery rate by acting on the speed of the engine, the variation of flow being then proportional to the variation of motor speed.

 The pressure variation in a pipe on either side of an orifice is a direct function of the square of the flow rate through this orifice. Consequently, if there is a single nozzle with a constant section on the receiver pipe, the pressure variation curve on either side of this nozzle as a function of the pump delivery rate is parabolic. For certain applications, we seek to define a pressure law which gives a curve different from a parabola. In particular, it is necessary to obtain a pressure law substantially proportional to the flow for the application of the circuit to the drive of a machine driven by at least one hydraulic motor in driving mode called "automotive driving" which will be explained. in the following.

 Thus, for the automotive pipe, there is a circuit shown in FIG. 1. This circuit includes a first hydraulic pump with fixed displacement 10 which feeds the discharge pipe 12 on which is disposed a first fixed nozzle 14. A section nozzle 16 variable as a function of the pressure drop in the nozzle 14 is placed in series with the latter on the receiver pipe 18 to which the receiver 20 is connected at the output of this variable nozzle, while a second fixed nozzle 22 is arranged in parallel to the receiver on a pipe 24 connected to discharge means 26 the adjustment means which make it possible to determine in the receiver pipe a pressure law proportional to the delivery rate therefore comprise the two fixed nozzles 14, 22 and the variable nozzle 16. It is also necessary to limit the maximum value of the pressure in the circuit by using a pressure limiter 28 q which is connected to the discharge line 12 downstream of the nozzles 14 and 16 and which, when activated, evacuates the excess fluid towards the evacuation means 26.

 This circuit also includes. a second hydraulic pump 30 with variable displacement and two directions of operation, to which is connected at least one hydraulic motor 32 by two pipes 34 and 36, respectively for supplying and exhausting fluid (or vice versa). The first hydraulic pump 10 also serves as a booster pump for the supply line 34 or 36 of the motor 32.

Indeed, a main booster pipe 38 is connected to the discharge pipe 12 downstream of the nozzles 14 and 16. To this pipe 38 are connected booster connections 40 and 42, each equipped with a non-return valve, respectively 41 and 43, and respectively connected to lines 34 and 36.

 The receiver 20 is able to control the means 44 for varying the displacement of the pump 30. This pump being in two directions of operation, a slide selector 46 with three positions (forward, stop, reverse) is interposed on the receiver line 18, upstream of the receiver 20 and serves to orient the control pressure of the latter in one or the other direction, against return means 48 and 50.

 These known circuits have several drawbacks. Firstly, the means which serve to determine the reception law in the receiver pipe 18 comprise several hydraulic components, the nozzles 14, 16 and 22 placed in series or in bypass.

In addition, the presence of the pressure limiter 28 downstream of the nozzles 14 and 16 is necessary. It should also be noted that, for the application to the automotive pipe shown in FIG. 1, the pressure in the main booster pipe 38 is mainly affected by the pressure drop in the nozzle 14, since this pipe 38 is connected to the pipe. 12 downstream of this nozzle.

 The present invention aims to remedy these drawbacks by proposing a simpler circuit and in which the number of components of the adjustment means serving to determine the pressure law is reduced.

 This object is achieved thanks to the fact that the adjustment means comprise a single restriction member, the inlet of which is in communication with the discharge line and the outlet of which is in communication with discharge means, said restriction member comprising a fluid discharge passage and means for varying the section of said discharge passage as a function of the flow rate of fluid discharged by the first pump so as to determine the fluid pressure in the discharge line, and to the fact that the line receiver is connected to the discharge line upstream of the restriction member and in derivation from the latter.

 It is understood that, thanks to these provisions, the restriction member plays not only the role of the adjustment means of the prior art but in addition, insofar as its output is connected to evacuation means, that of the limiter pressure of the prior art. Thus, thanks to the unique component that constitutes the restriction member, judiciously placed in bypass with respect to the receiver, it is possible both to generate the pressure law in the receiver pipe and to limit the pressure in the circuit to a value maximum.

 The means for varying the section of the evacuation passage to the variable section make it possible to generate in the discharge pipe a variable fluid pressure as a function of the flow rate discharged by the pump. During the transient phases (starting, acceleration, deceleration of the drive of the fixed displacement hydraulic pump), the flow evacuated by the restrictor is temporarily lower than the pumped flow, because it is slightly reduced by the little fluid withdrawn by the receiver. In steady state operation, the flow evacuated at the outlet of the restriction member is equal to the flow discharged by the first pump.

 Advantageously, the restriction member is formed by a valve comprising a drawer capable of being controlled hydraulically by the pressure of fluid prevailing in the discharge line in the direction of its movement against a return means for gradually open a fluid discharge passage to the discharge means.

 This return means may include one or more mechanical springs, possibly suitably prestressed.

 According to an advantageous embodiment of this valve, the drawer is disposed in a bore having a discharge hole and comprises a wall having at least one opening capable, when the drawer is moved, of being placed in communication with the bore d 'evacuation so that the communication section between said opening and said bore is variable depending on the position of the drawer.

 The circuit according to the invention is particularly suitable for the automotive driving of a machine driven by at least one hydraulic motor. In this case, the circuit comprises a second hydraulic displacement pump with variable displacement associated with means for progressive variation of its displacement and the receiver is able to control said variation means as a function of the pressure prevailing in the receiver pipe.

 In general, the first hydraulic pump, the displacement of which is fixed, and the second hydraulic pump, the displacement of which is variable, form the same assembly, which is driven by a heat engine. The speed of the heat engine is detected and used to vary the displacement of the second hydraulic pump thanks to the delivery rate of the first hydraulic pump which therefore serves as a tachometric and generic detector, depending on the pressure law given by the member. restriction through which the fluid delivered by the first hydraulic pump passes, a pressure law determined in the receiver pipe which acts on the means for varying the displacement of the second pump.

 The rotational speed of the hydraulic motor, therefore the speed of advance of the machine driven by the latter, is proportional to the displacement of the second pump. The delivery rate of the first pump is a direct function of the speed of the heat engine. By determining, using the restriction member, a pressure law for the receiver as a function of the delivery rate of the first pump (we will generally choose a proportionality law) and by controlling the progressive variation of the displacement of the second pump using the receiver, we finally obtain a direct dependence (in general a proportionality) between the variation of the displacement of the second pump (the one that feeds the hydraulic motor) and the rotation speed of the heat engine. Furthermore, when the second pump is driven by the heat engine, the speed of rotation of its rotor obviously depends directly on the speed of the heat engine.

 The discharge flow of the second pump, which conditions the speed of rotation of the hydraulic motor and therefore the speed of advance of the machine, is the product of the speed of the rotor of this second pump and its displacement; it therefore depends in two ways on the speed of the engine. Finally, by correctly choosing the pressure law to which the receiver is subjected by means of the restriction member, it is ensured that the operator of the machine has practically the same impression of driving as if the machine was driven by a heat engine and hydrokinetic transmission, since the hydraulic motor reacts directly and gradually to variations in the speed of the heat engine, variations obtained using an accelerator pedal actuated by the driver.

 For greater efficiency, it is preferable to ensure that the pressure law applied to the receiver is such that the maximum displacement of the second hydraulic pump is obtained for an engine speed corresponding to the maximum torque of said engine. For example, for a thermal engine rotating at a maximum of 2500 rpm, one could choose to have the maximum displacement of the second pump correspond to a rotation speed of 2000 rpm of this engine.

 Conventionally, the second hydraulic pump is a pump with a tilting cam plate and the means for varying its displacement include a lever which varies the inclination of this cam plate.

 Of course, the second hydraulic pump is advantageously reversible to rotate the hydraulic motor in both directions and the inclination of the cam plate can vary between two opposite extreme values.

The invention will be well understood and its advantages will appear better by referring to the accompanying drawings in which
FIG. 1, previously described, shows the prior art,
FIG. 2 shows a circuit in accordance with the invention, applied to automotive driving,
FIG. 3 is a view similar to FIG. 2 showing an alternative embodiment, and
- Figure 4 is a diagram showing the conformation of the restriction member.

 It should be understood that Figures 2 to 4 are appended to illustrate exemplary embodiments of the invention without limitation.

 The circuit shown in FIG. 2 comprises a first hydraulic discharge pump, or "booster pump" 110 which supplies pressurized fluid with a discharge line 112. A receiver 120 is connected to the discharge line 112 by a receiver line 118.

 In the application to the automotive line, this receiver makes it possible, according to the pressure in the receiver line 118, to vary the displacement of a hydraulic pump 130 with variable displacement using means 144 of displacement variation . The two pumps 110 and 130 are driven by a motor (not shown). For automotive driving, it is sought to vary the displacement of the pump 130 gradually as a function of the variation in the speed of rotation of the motor (most often, substantially proportional to the latter). It is therefore necessary to generate a pressure law in the conduct of the receiver which will determine this progressiveness. To this end, the circuit comprises a restriction member 116 whose inlet 1 16A is supplied with fluid by a pipe 122 connected to the discharge pipe 112 at node N122, and whose outlet 116B is connected to discharge means 126 via an evacuation pipe 124.

 The restriction member 116 serves to evacuate a greater or lesser fluid flow rate as a function of the discharge flow rate of the pump 110 and to determine the pressure of the fluid (discharged by the pump 110) in the conduits 112, 118 and 122.

 For this, the fluid evacuation passage at the outlet of the member 116 opens more or less, against a return means 119 such as a spring, depending on the flow of fluid to be evacuated at the outlet 1 i 6B of this restriction member 116, which generates in the discharge passage a variable pressure drop.

 The second hydraulic pump 130 with variable displacement is used to supply pressurized fluid to at least one motor 132 for driving a vehicle. The motor 132 and the pump 130 are connected by two lines 134 and 136 which, depending on the direction of actuation of the pump, play the role of a line for supplying the motor with fluid or that of an exhaust line . There is also a leakage return pipe 137 which connects the interior of the motor housing to the discharge means 126. As previously indicated, the speed of rotation of the motor 132 is conditioned by the delivery rate of the pump 130, itself a function both of the speed of the rotor of this pump 130 (driven by the same motor as the rotor of the pump 110 with fixed displacement) and of the displacement of this pump 130. The means 144 of adjustment of the displacement of the pump 130 may be a system for adjusting the inclination of the latter's cam plate, controlled by a hydraulic cylinder which constitutes the receiver 120.

 This cylinder 120 has at least a first chamber 147 capable of being supplied with fluid by the receiver pipe against a first return means 148 (for example a spring) to move the piston of this cylinder in a first sense, so as to actuate the means for varying the displacement of the pump.

 Advantageously, as in the example shown, the pump being in two directions of operation, the jack has a second chamber 149 which is capable of being supplied with pressurized fluid against a second return means 150 for moving the piston of the jack in a direction opposite to its first direction of movement. To control the supply of fluid to the chambers 147 and 149, the circuit includes a selection device 146 for example constituted by a three-position solenoid valve, to which the chambers 147 and 149 are respectively connected by secondary receiver lines, respectively 147 'and 149'. In its neutral position, the selector 146 places the two pipes 147 'and 149' in communication with the discharge means 126, by a discharge pipe 151. In each of its active positions, it connects one of the pipes 147 'and 149' to the receiver line 118, while it puts the other of these two lines in communication with the evacuation line 151.

 It is understood that, thanks to the restriction member 116, the first pump 110 serves to make the displacement of the pump 130 depend on the speed of the motor (thermal or electric) which drives these pumps. In operating situation, the pump 110 is also used for boosting the high pressure lines of the supply circuit of the hydraulic motor 132, that is to say it is used to maintain a minimum pressure of at least a few bars (in generally 15 to 25 bars) in these pipes. To do this, the pump 110 feeds a booster line 138 located in bypass at the node N138 on the discharge line 112, upstream from the node N122. This line 138 is separated into two lines 140 and 142 which, by means of the non-return valves 141 and 143, are used respectively for feeding the lines 134 and 136 when they act as supply lines. In other words, the main booster line 138 is located bypassing the main discharge line 112 on which all the components (restriction member 116, receiver 120) which are used for adjusting the displacement of the pump 130 are placed. relative to the drive speed of the pumps.

 In the circuit of FIG. 2, the pressure of the fluid in the line 118 comes directly to supply one of the chambers 147 and 149 of the jack 120 to control the displacement of the pump 130 on a non-zero value. To prevent the displacement of the pump 130 from being placed too quickly at a non-zero value by putting the motor 132 into gear before the discharge flow from the pump 110 has reached a sufficient value, it is advantageous to prestress the return means 148 and 150 to ensure that the piston of the cylinder 120 does not move until the pressure in the chambers 147 and 149 reaches a sufficient value. It may be one or more springs adapted so that the stiffness of the resulting return means possibly varies in stages.

In addition, it is possible to choose a return means 119 which is weakly opposed to the opening of the discharge passage of the restriction member 116 for low flow rates to ensure a so-called "booster" pressure sufficient to guarantee the good operation of the second pump.

 FIG. 3 shows a circuit which, in addition to the components of that of FIG. 2, comprises a servo-control member which progressively controls the supply of the chambers 147 or 149 as a function of the pressure in the circuit. To simplify, in FIG. 3, the elements common to the circuit of FIG. 2 are given the same references.

The servo-control member 170 comprises a distribution slide which, in its position 0 puts the two secondary receiver pipes 147 'and 149' in communication with the discharge pipe 151 and which, from this position 0, is continuously displaceable towards one or the other of its extreme positions in which it respectively places one of the lines 147 'and 149' in communication with the receiver line 118 and the other of said lines with the line 151.

 The distribution slide of the servo-control member is moved to one or other of its extreme positions by hydraulic control, against return means. In fact, the circuit comprises a selector 172 constituted by a three-position solenoid valve, supplied by a line 174 connected in derivation of the receiver line 118 upstream of the servo-control member 170.

This selector is connected to the two chambers of the servo-control member by two selector pipes, respectively 176 and 178. In its position 0, it places the two pipes 176 and 178 in communication with a discharge pipe 179. In each of its two active positions, it places one of the lines 176 and 178 respectively in communication with the line 174, and the other of these lines in communication with the line 179.

 Thus, by hydraulically controlling the servo-control member 170 by the fluid pressure, the law of which is determined using the restriction member 116, the "degree of communication" of the chamber 147 or 149 of the jack 120 with the receiver line is adjusted according to this fluid pressure.

 In particular, it is possible to choose to preload the return means 171 and 171 ′ of the dispenser drawer of the servo-control member 170 against its movement under the effect of the pressure of the fluid so that this drawer continues occupy its position 0 as long as the pressure in the circuit supplied by the pump 110 remains below a threshold pressure. This will avoid placing the displacement of the pump 130 on a non-zero value until the pressure has reached this threshold value. By suitably choosing the return means 171 and 171 ′ of the distribution slide of the selection member 170 and the return means 148 and 150 of the jack 120, it is also possible to ensure that there is an intermediate threshold pressure for which the displacement of the pump 130 can be set to a non-zero value which allows it to power the motor 132 just enough to release the brake without causing it to start, while it is only from the pressure starting threshold that the displacement of the pump 130 will increase enough to supply the motor 132 with a pressure allowing it to start.

 In the example shown in FIG. 3, the servo-control member 170 also takes into account the inclination of the cam plate of the pump 130 to adjust the communication between the chambers 147 and 149 of the jack 120 with the receiver line. It is therefore in a way a servo which receives in return ("feed back") information on the inclination of the cam plate. We already know the advantage of servos of this type which compensate for the increase in the reactive force of the pistons of the pump on the cam plate when the inclination of the latter increases. Thus the dispenser drawer of the servo-control member 170 can be connected to the means 144 for varying the displacement of the pump 130 by an arm or a lever 180 which, with the hydraulic supply by one of the conduits 176 and 178 , helps manage the movement of this dispenser drawer.

 Referring to Figure 4, we now describe the conformation of the restriction member. In this figure, the first hydraulic pump 110, the discharge line 112, the receiver 120, the discharge line 124 and the discharge means 126. have been shown very schematically. The restriction member 116 is formed by a valve which comprises a slide 200 which moves in a bore 202 against a return means such as a spring 204 held by a holding means such as a plug 206. At its end opposite to this plug , the spring 204 is disposed in an end part of the drawer 200 which has the shape of a sleeve 208. The drawer 200 has a tubular body 210 open on the side of the fluid inlet by the line 122 and closed on the side of the spring 204. The axial wall of this tubular body 210 is provided with several openings 212. The bore 202 in which the drawer slides has a discharge hole 214 (generally disposed transversely to the direction of movement of the drawer 2 00) in communication with the discharge line 124. It is understood that, when the delivery rate of the pump 110 is zero or substantially zero, the slide is pushed back under the effect of the spring 204 in a position in which the openings 212 are closed by the part of the axial wall 203 of the bore 202 which is located opposite these openings. When the delivery rate increases, the fluid tends to push the slide in direction F, against the reaction force of the spring 204, so as to progressively place the openings 212 of the wall 211 of the tubular body in the discharge hole 214. The flow of fluid passing through these openings 212 is the cause of a pressure drop determining the pressure of the fluid in the circuit supplied by the pump 110.

 The openings 212 make it possible to communicate the pipe 122 with the evacuation means 126. To vary the communication section, it is possible, as in FIG. 4, to provide a plurality of openings 212 successively arranged on the wall 211 of the tubular body of drawer 210.

 Obviously, the more the flow delivered by the pump 110 increases, the more the pressure in the delivery line increases, the more the flow to be evacuated, so that the drawer is moved more in the direction F and the number of openings located in the discharge hole 214 (whose axial length is sufficiently large) increases. A person skilled in the art will be able to choose the size and distribution of the openings 212 so as to generate, in line 118, the pressure law which is suitable for him as a function of the delivery rate of the pump 110. More precisely, the number and the distribution of openings 212 make it possible to generate a variable pressure drop as a function of the flow rate passing through the restriction member 116, therefore as a function of the discharge flow rate of the pump 110, which consequently makes it possible to vary the pressure in the pipes supplied by the pump 110. The spring 204 can be preloaded so that the fluid does not pass through the restriction member until a certain threshold pressure is reached.

Thus, up to this threshold pressure, the receiver 120 is directly subjected to the pressure generated by the pump 110, while from this threshold pressure, the displacement of the valve slide establishes the determined pressure law, which ultimately will depend on the flow delivered by the pump 110, possibly reduced or increased by the flow taken or supplied by the receiver 120.

 It should be noted that the pressure law depends not only on the number and distribution of the openings 212, but also on the stiffness of the spring 204. It is thus possible to choose a single mechanical spring as shown in FIG. 4, the stiffness of which is a constant. One can also choose to use, as a means of returning the valve spool, several combined springs which would thus determine a non-linear evolution of the displacement of spool 200 as a function of the pressure acting on the tubular body of the spool.

It should be noted that the restriction member 116 makes it possible to partially compensate for the variation in the pressure in the circuit which is due to the variation in viscosity of the fluid, for example under the effect of a variation in temperature. Indeed, as we have seen, the movement of the drawer 200 is a function of the pressure exerted on the body of this drawer, and insofar as the movement of the body of the drawer allows the passage of fluid, it is also itself at the origin of the determination of the pressure law. Overall, if the pressure drop increases due to the increase in viscosity, the slide is moved further in the direction
F, which increases the passage section, therefore limits the pressure variation to stabilize this pressure substantially to the value it would have if the viscosity had not increased.

 At all times, the flow of fluid passing through the openings 212 of the drawer is the cause of a pressure drop in the restriction member 116, that is to say a pressure variation between the upstream of the member 116 (that is to say in particular in the pipes 112 and 118) and downstream of this member (the discharge pipe 124 in which the pressure is generally zero). This pressure drop and its evolution as a function of the movement of the slide create the pressure law in the conduits 112 and 118. This law is dependent on the initial preload of the spring or springs 204 which define the minimum pressure from which the valve formed by the restriction member opens, from the variation of the opening section of this valve as a function of its stroke (number of openings 212 located in the discharge bore 214) and from the variation of the force of reaction exerted by the spring or springs 204 against the movement of the slide according to the stroke of the latter (possibly non-linear variation if one chooses to have several springs).

 Rather than providing on the wall 211 of the tubular body 210 of the drawer a plurality of small openings of substantially circular sections, one or more openings could be provided in the form of oblong slots, slots whose transverse dimension would be variable along their axial length. In general, at least one of the axial walls 211 of the drawer and 203 of the bore 202 would then have at least one slot having a determined shape and extending in the direction of movement of the drawer.

Claims (12)

1. Fluid supply circuit for a receiver comprising a first hydraulic delivery pump (110) capable of supplying pressurized fluid to a pipe (112) called "delivery", a receiver (120) connected to said pipe discharge (112) by a line (118) called "receiver" and adjustment means capable of generating, in this receiver line, a fluid pressure depending on the discharge rate of the pump according to a determined pressure law,  characterized in that the adjustment means comprise a single restriction member (116), the inlet (116A) of which is in communication with the discharge line (112) and the outlet of which (116B) is in communication with means of discharge (126), said restriction member comprising a fluid discharge passage (212, 214) and means (200, 204) for varying the section of said discharge passage as a function of the flow rate of fluid discharged by the first pump to determine the fluid pressure in the discharge line (112), and in that the receiver line (118) is connected to the discharge line (112) upstream of the restrictor (116) and in derivation from the latter. 2. Circuit according to claim 1, characterized in that the restriction member is formed by a valve comprising a slide (200) capable of being hydraulically controlled by the fluid pressure prevailing in the discharge line (112) in the direction of its movement against a return means (204) to gradually open the discharge passage (212, 214) of the fluid towards the discharge means (126). 3. Circuit according to claim 2, characterized in that the slide (200) is arranged in a bore (202) having a discharge hole (214) and comprises a wall (211) having at least one opening (212) capable , when the drawer is moved, to be placed in communication with the discharge bore (214) so that the communication section between said opening and said bore is variable depending on the position of the drawer. 4. Circuit according to any one of claims 1 to 3, characterized in that it comprises a second hydraulic delivery pump (130) with variable displacement associated with means for progressive variation of its displacement (144) and in that the receiver (120) is able to control said means (144) of variation as a function of the pressure prevailing in the receiver line (118). 5. Circuit according to claim 4, characterized in that the receiver is formed by a jack (120) having at least a first chamber (147) capable of being supplied with fluid by the receiver line (118) against a first return means (148) for moving the piston of said cylinder in a first direction. 6. Circuit according to claim 5, characterized in that the jack has a second chamber (149) capable of being supplied with fluid by the receiver line (118) against a second return means (150) for moving the piston of said cylinder in a second direction opposite to said first direction and in that it comprises selection means (146) for selectively connecting the first or the second chamber (147,149) to the receiver line (118). 7. Circuit according to any one of claims 5 and 6, characterized in that it further comprises a servo-control member (170) comprising means for varying the communication section between the chamber or chambers (147, 149) of the jack (120) and the receiver line (118) as a function of the pressure prevailing in said line. 8. Circuit according to claim 7, characterized in that the servo-control member is capable of varying the communication section between the chamber or chambers (147, 149) of the jack (120) and the receiver line (118) in as a function of the pressure prevailing in said pipe and as a function of the situation of the means (144) of progressive variation of the displacement of the variable displacement hydraulic pump (130). 9. Circuit according to any one of claims 1 to 8, characterized in that the first hydraulic discharge pump (110) is used to supply at least one booster line (138, 140, 142) and in that the line delivery (112) and the booster pipe are connected in bypass (N138) to the outlet of said first hydraulic pump (110). 10. Valve intended to form a restriction member (116) for a circuit according to any one of claims 1 to 9, characterized in that it comprises a slide (200) axially movable in a bore (202) which comprises a first axial wall (203) having a discharge hole (214), the drawer having a second axial wall (211) having at least one opening (212) capable, when the drawer is moved, of being put in communication with the discharge hole so that the communication section between said opening and said hole is variable depending on the position of the drawer.  11. Valve according to claim 10, characterized in that at least one of the first and second axial walls (203, 211) has at least one slot, having a determined shape and extending in the direction of movement of the drawer ( 200). 12. Valve according to claim 10 or 11, characterized in that at least one of the first and second axial walls (203, 211) has a plurality of openings (212) arranged successively in the axial direction (F).