GB1572061A - Hydraulic cut-outs - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO HYDRAULIC CUT-OUTS (71) We. Society Anonyme AUTOMO BILES CITROEN. a French Bodv Corporate of 117/167 Ouai Andre Citroënss Paris.

France. do herebv declare the invention for which we pray that a Patent may be granted to us. and the method bv which it is to be performed. to be particularly described in and bv the following stateníent:- This invention relates to a hydraulic cut-out for use between a pump and a pressure accumulator to maintain the fluid pressure in the accumulator between two predetermined limits.

Hydraulic cut-outs are alreadv known wherein the desired predetermined pressure values are obtained bv calibrating a pair of springs co-operating with valve members.

Now this arrangement increases the risks of faulty operation. in comparison with other known arrangements utilizing only one spring and one valve member for controlling a relief passage from the pump deliverv side to the pump intake. However. in this last case anv permanent throttling of the liquid in the vicinitv of the opening and closing positions of the relief passage should be carefully avoided. as well as anv oscillation or noise likelv to be developed when conditions of unbalance in the pressure exerted by the liquid on the valve member are adjusted for obtaining the desired difference between the opening and cut-out pressures.

A known proposition directed to avoid these detrimental effects consisted in associating with said valve member mechanical means capable of promoting a straightforward passage of the valve member from one to the other of its opening or cut-out positions.

However. the sensitivitv of these known means is generallv poor. or the device itself is difficult to construct andior has a short useful life. and for all these various reasons the results thtis obtained are far from satisfactory.

According to the present invention there is provided a hydraulic cut-out for maintaining the pressure in an accumulator supplied by a pump between two limits, the cut-out comprising a non-return valve for preventing flow of fluid in the direction from the accumulator to the pump outlet. and a valve member which in operation is subjected to the force of a spring and. acting in opposition to the spring force. ta a force derived from the pressure in the accumulator, the valve member being moveable to open and close a relief passage which. when open in use of the cut-out. relieves the delivery pressure of the pump. the valve member having two stable positions corresponding to the relief passage being open and closed respectively. these stable positions being established by magnetic means.

For a better understanding of the present invention and to show how it may be carried into effect. reference will now be made by way of example only, to the accompanying drawings in which: Figure 1 is a sectional view of a pump with built-in cut-out. as seen in different planes in order to show more clearly the internal passages also visible in Figure 2; Figure 2 is a sectional view of the pump illustrated in Figure 1. taken along various transverse planes perpendicular to the planes along which Figure 1 is taken. and selected to show more clearly the internal passages of the assembly: Figure 3 is an elevational view of the pump. as seen in the direction of the arrow III of Figure 1: and Figure 4 is an elevational view of the assembly as seen in the direction of the arrow IV of Figure 1. with the lower portion shown in fragmentary section.

The pump illustrated in the drawing comprises a pump body 1 in which a cylindrical liner 2 is held against movement and slidably engaged by an internal piston 3.

c This piston 3 comprises a rod 4 having an enlarged base projecting from the liner 2, and is responsive to a compression spring 5 constants urging this enlarged base against an eccentric member 6 mounted on a driven shaft 7 which is rotatably mounted in a lower pump case la.

The pump body I comprises an inlet port X for the fluid to be pumped. which is connected to a groove 9 communicating in turn with radial passages 10 formed through the wall of the cvlinder liner 2 and adapted to be uncovered bv the piston 3 in the bottom dead center position shown in the drawing.

The pumping chamber 11 formed in the liner 2 above the aforesaid passages 10 is bounded at its upper end by a delivery valve 12 urged to its closed position by a spring 13.

The valve and spring assembly 12. 13 are housed in a member 14. and the assembly comprising this member 14 and the liner 2 is force fitted in the body 1 and engages a stop ring 16 fitted in a corresponding groove formed in the cvlindrical bore of the pump body. as a safetv measure.

The member 14 comprises around the outer periphery of the chamber of valve 12 a pluralitv of lateral or radial apertures 17 such that when the valve is unseated from the top of liner 2 the pumped liquid can flow from the pumping chamber 11 to a deliverv or pressure passage 18 formed centrallv df said member 14. Furthermore. this member 14 encloses a non-return valve. in this case a ball 19. the seat engaged by this ball consisting of the outlet end of the delivery passage 1X. and the cavity enclosing this ball valve 19 comprises a plurality of orifices 'ü opening into a chamber 21 formed in the pump body between a cover 15 screwed in said body and the aforesaid member 14.A union 22 is provided for connecting this chamber 21 to a pressure accumulator. not shown. adapted to be supplied with liquid under pressure hv the pump.

The chamber 21 is also connected by a passage 23 to a safet! valve 24 consisting for example of a ball 24a adapted to close the passage 23 under the pressure of a suitabkv calibrated spring 25. the force of the spring 25 being transmitted by a push-rod 26 to the ball 24a. The delivery or discharge chamber 27 of the valve 24 communicates via a passage r.Y with the lower case la of the pump body which comprises a union or like means leading to the fluid reservoir (not shown) from which liquid is drawn by the pump.

The chamber 21 also communicates via a passage 3t) with a chamber 31 forming an integral part of the cut-out incorporated in the pump Irod! . This chamber 31 is bounded in the pump body by a cover 3' and a spool-valve body 33 force fitted and locked in a corresponding bore of said body: slidably fitted in this body 33 is a valve member consisting of a spool valve 34 in this example.The end of the spool valve 34 which extends through said chamber 31 carries a cup-shaped member 35 having its outer peripheral flange engaged by a coil compression spring 36 housed in the chamber 31. The spool valve 34 is provided with a groove 37 extending between a pair of fluid-tight seals and communicates with a pair of radial passages 38. 39 formed at axially spaced intervals in the spool valve body 33. The passages 38. 39 communicate with passage 40 and 41. respectively. formed in the pump body.

The first passage 40 opens into the space left between the delivery valve 12 and the non-return valve 19. via a notch 42 formed at the end of liner '. and the passage 41 leads to the discharge passage 28.

The other end of spool valve 34 also projects from the spool-valve body 33 and carries a cylindrical member 43 force fitted and locked thereon: this cvlindrical member 43 has formed at either ends a shoulder and each shoulder has fitted thereon and retained by spring rings 44 a pair of spaced ferromagnetic disc-shaped armatures 45. 46 between which there is a stationary permanent annular magnet 47. This permanent magnet 47 is held against axial movement at its outer periphery by means of a set ring 48 locked in the pump body by means of a cover 49 closing the chamber containing the magnet and the corresponding movable assembly.

The above described cut-out incorporated in the pump operates as follows: The armature 45 is attracted magnetically and spool valve 34 held in the position shown in the drawing as long as the force exerted thereon by spring 36 and the magne- tic pull exerted by armature 45 are greater than the force exerted by the liquid pressure in chamber 31 against the cross-sectional area of the spool valve. that is. the service pressure prevailing in the accumulator.

Under these circumstances the pumped liquid is forced towards the accumulator by opening simultaneously the delivery valve 19 and non-return valve 19.

When the pressure prevailing in chamber 31 exerts on spool valve 34 a force greater than the above-mentioned forces. thus detaching the armature 45. the magnetic pull of this armature decreased suddenlv to a substantial degree so that the spring 36 yields and the spool valve 34 with its movable assembly 43. 45. 46 assumes sharp ly its other distribution position in which the other armature 46 engages the magnet 47 while the groove of spool valve 34 interconnects passages 38 and 39. As a result. a relief passage is opened from the pump. through the spool valve groove and the passages 41 and 28. to the pump body 1 and the reservoir. and therefore to the pump intake, after lubricating the rotation parts enclosed in said body.

In this case. the delivery valve 12 keeps operating normallv while the non-return valve 19 remains seated by the operating pressure prevailing in the accumulator.

Since the magnetic pull exerted on the armature 46 of said movable assembly has now the same direction as the force exerted by the operating pressure in the accumulator on the spool valve 34, both forces thus counteracting the force of spring 36. it is clear that this second stable condition of the spool valve 34 will change onlv if this value of the operating or service pressure becomes substantially lower than the pressure value having separated armature 45 from magnet 47. the difference between these values being determined bv properly calculating the characteristics of the spring and the magnetic svstem. as those conversant with the art will readilv understand.

When the service pressure drops to the predetermined lower limit whereat the armature 46 separates from the magnet 47. the suddent decrement of this magnetic pull will now cause the spool valve to resume suddenly its initial distribution position illustrated in the drawing. which corresponds to the position of magnetic engagement of armature 45.

This bistable operation of the spool valve will thus be repeated as a function of the predetermined pressure values controlling the opening and closing of the communication between the pump and the accumulator.

The valve 34 provides the usual safetv preventing any undesired overstepping of a predetermined maximum pressure in the load circuit. which pressure is higher than the predetermined cut-out pressure.

Of course. various modifications and changes may be brought to the hydraulic cut-out shown and described herein which constitutes but an exemplary embodiment of the invention: in particular. the cut-out may be a separate component from the pump.

WHAT WE CLAIM IS: 1. A hydraulic cut-out for maintaining the pressure in an accumulator supplied bv a pump between two limits. the cut-out comprising a non-return valve for preventing flow of fluid in the direction from the accumulator to the pump outlet. and a valve member which. in operation. is subjected to the force of a spring and. acting in opposition to the spring force. to a force derived from the pressure in the accumulator. the valve member being movable to open and close a relief passage which. when open. in use of the cut-out, relieves the delivery pressure of the pump, the valve member having two stable positions corresponding to the relief passage being open and closed respectively, these stable positions being established by magnetic means.

2. A hydraulic cut-out as claimed in claim 1, in which two spaced armatures are rigidly attached to the valve member. and in which a stationary permanent magnet is disposed between the armatures. one of the armatures being in contact with the magnet in one stable position of the valve member, and the other armature being in contact with the magnet in the other stable position.

3. In combination, a pump and a hydraulic cut-out as claimed in claim 1 or 2, the components of the hydraulic cut-out being disposed within the body of the pump.

4. A combination as claimed in claim 3, in which the relief passage. when open.

conveys fluid delivered by the pump to the intake of the pump.

5. A hydraulic cut-out substantially as described herein with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. the spool valve groove and the passages 41 and 28. to the pump body 1 and the reservoir. and therefore to the pump intake, after lubricating the rotation parts enclosed in said body. In this case. the delivery valve 12 keeps operating normallv while the non-return valve 19 remains seated by the operating pressure prevailing in the accumulator. Since the magnetic pull exerted on the armature 46 of said movable assembly has now the same direction as the force exerted by the operating pressure in the accumulator on the spool valve 34, both forces thus counteracting the force of spring 36. it is clear that this second stable condition of the spool valve 34 will change onlv if this value of the operating or service pressure becomes substantially lower than the pressure value having separated armature 45 from magnet 47. the difference between these values being determined bv properly calculating the characteristics of the spring and the magnetic svstem. as those conversant with the art will readilv understand. When the service pressure drops to the predetermined lower limit whereat the armature 46 separates from the magnet 47. the suddent decrement of this magnetic pull will now cause the spool valve to resume suddenly its initial distribution position illustrated in the drawing. which corresponds to the position of magnetic engagement of armature 45. This bistable operation of the spool valve will thus be repeated as a function of the predetermined pressure values controlling the opening and closing of the communication between the pump and the accumulator. The valve 34 provides the usual safetv preventing any undesired overstepping of a predetermined maximum pressure in the load circuit. which pressure is higher than the predetermined cut-out pressure. Of course. various modifications and changes may be brought to the hydraulic cut-out shown and described herein which constitutes but an exemplary embodiment of the invention: in particular. the cut-out may be a separate component from the pump. WHAT WE CLAIM IS:

1. A hydraulic cut-out for maintaining the pressure in an accumulator supplied bv a pump between two limits. the cut-out comprising a non-return valve for preventing flow of fluid in the direction from the accumulator to the pump outlet. and a valve member which. in operation. is subjected to the force of a spring and. acting in opposition to the spring force. to a force derived from the pressure in the accumulator. the valve member being movable to open and close a relief passage which. when open. in use of the cut-out, relieves the delivery pressure of the pump, the valve member having two stable positions corresponding to the relief passage being open and closed respectively, these stable positions being established by magnetic means.

2. A hydraulic cut-out as claimed in claim 1, in which two spaced armatures are rigidly attached to the valve member. and in which a stationary permanent magnet is disposed between the armatures. one of the armatures being in contact with the magnet in one stable position of the valve member, and the other armature being in contact with the magnet in the other stable position.

3. In combination, a pump and a hydraulic cut-out as claimed in claim 1 or 2, the components of the hydraulic cut-out being disposed within the body of the pump.

4. A combination as claimed in claim 3, in which the relief passage. when open.

conveys fluid delivered by the pump to the intake of the pump.

5. A hydraulic cut-out substantially as described herein with reference to the accompanying drawings.