GB1568555A

GB1568555A - Mechanical control devices with fluidpressure servo-action

Info

Publication number: GB1568555A
Application number: GB404777A
Authority: GB
Original assignee: Automobiles Citroen SA
Current assignee: Automobiles Citroen SA
Priority date: 1976-02-27
Filing date: 1977-02-01
Publication date: 1980-05-29
Also published as: DE2707991A1; ES455201A1; DE2707991C2; FR2355185A2; IT1082168B; FR2355185B2

Description

(54) IMPROVEMENTS IN OR RELATING TO MECHANICAL CONTROL DEVICES WITCH FLUID-PRESSURE SERVO-ACTION (71) We, SOCIETE ANONYME AUTOMOBILES CITROEN, a French Body Corporate af 117-167, Quail Andre Citron, Paris, France, do hereby declare the invention for which we Pray that a patent may be granted to us and the method by which it is to be performed to be particularly dessnbed in and by the following statement: This invention relates to a tnechanical control device with fluid-pressure servomion for distning fluid under pressure to a two chamber piston and cylinder actuator connected to a mechanisrm to be actuated for control thereof. The control device is par ticularly, Itough not exclusively, suitable for control of the steering gear of a maxmr vehicle.

Accot to various known constructions, a servo-acton mechanical control device of this type comprises essentially a manually operable control member and a distributor of fluid under pressure having a body mechani oally connected to the mechanism and a pair of spool valves slidably mounted therein for controlling the distribution of fluid under pressure to one chamber of the actuator, the spool valves being adapted to be moved in the direction in which the control member is operated, the movements of the spool valves taking place against the force of return means permitting a relative movement between the spool valve concerned and the body only beyond a predetermined threshold of the effort exerted between the control member and the body. Thus, a purely mechanical control action is available up to the peedetermined threshold, and a servo-action is available beyond the threshold, a requirement acknowledged as highly desirable notably in motor vehicle xrvo action steering systems.

Prestressed springs have been used in various ways as return means, with the inconvenience however of introducing as additional and detrimental resistance to the control action during the movement of the distributor spool valve, due to the necessarily limited length of the springs and also to the low flexibility resulting therefrom. According to their specific arrangement in the distribution system, such springs may even interfere with the distributor operation notably when it is desired to use not a continuous or permanentílow distribution but only a selective distribution of the pressurised fluid when required, inasmuch as in this last instance it is possible to provide a distributor capable of nonnally connecting simultaneously both chambers of the actuator (i.e. before the threshold is attained) to the exhaust, so that the pure mechanical control phase of the actuator follower movement can be obtained without any difficulty.

The object of the invention is to provide an improved servo-action mechanical control device of the above described type which is free of the above-listed inconveniences while affording a satisfactory operation without resorting to a continuous or permanent fluid flow, but with only a selective distribution of the power pressure.

According to the invention there is provided a mechanical control device with pressurefluid rvo-action, for distributing fluid under pressure to a two-chamber cylinder and piston actuator connected to a mechanism to be actuated, the device comprising a manually operable control member and a pressure fluid distributor having a body mechanically connectable to the mechanism; two spool valves slidably mounted in the body for controlling the distribution of fluid under pressure to respective chambers in the actuator; an abutment between each spool valve and the body stopping movement of each spool valve in one direction beyond a position of abutment, a respective one of the spool valves being individually movable by the control member from its position of abutment in each direction of movement of the control member; and means for resisting such movement and returning the spool valves to their positions of abut ment, the said means permitting a relative movement between the body and either spool valve only when the force applied to the spool valve exceeds a certain threshold value corresponding to a threshold of effort applied to the control member, and the said means comprising for each spool valve a chamber disposed between the spool valve concerned, or a member co-operating therewith, and the distributor body, these spool valve chambers each being adapted to receive, for determining the said threshold force, a fluid under a common pressure which remains substantially independent of pressure variations in the fluid distributed to the actuator. The fluid under pressure determining the effort threshold may be derived from any suitable source, which may be the source supplying said distributor or another source.

Preferably, for avoiding the risks of producing cavitation in the actuator during the control movements without servo-action, the exhaust pipe lines for returning the fluid to the reservoir are interconnected and provided with a non-return valve opening towards the reservoir only beyond a predetermined pressure value.

Moreover, the pipe line delivering the pressure fluid to each chamber of the actuator may be connected to another chamber formed between the relevant spool valve and the distributor body in order to exert therebetween a servo-action reaction force adding itself to that of the threshold force.

Of course, obtaining the threshold force with the assistance of fluid under pressure does not preclude the possibility of utilizing an auxiliary compression spring producing an additive or substractive action, which is free of the inconvenience mentioned in the foregoing when the effort threshold is obtained only by using spring means.

Moreover, with this invention it is possible to vary the fluid pressure determining the threshold force according to at least one selected parameter, such as the vehicle speed, its load, and/or an adjustment controlled by the driver, for instance, where the controlled mechanism is the steering gear of a motor vehicle.

Various embodiments of this invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic general view of the steering gear of a motor vehicle controlled by a control device according to the invention; Figures 2,3 and 4 are fragmentary sections taken across the distributor shown in Figure 1 to illustrate various modifications thereof; Figure 5 is a section showing another distributor; Figures 6 to 9 inclusive are fragmentary sections similar to Figures 2 to 4, showing further modifications of the distributor; Figure 10 is a diagrammatic section showing a servo-action steering distributor associated with a device for for varying the effort threshold as a function of vehicle speed, and Figure 11 is a diagrammatic sectional view showing a servo-action steering distributor associated with a device for varying effort threshold as a function of vehicle load.

In the following description, for the sake of convenience and coherence in the disclosure, and to facilitate the understanding thereof, the same reference numerals will be used for designating the component members or parts which have the same functions in the various embodiments, irrespective of their specific shape or construction.

The servo action steering system for a motor vehicle as illustrated diagrammatically in Figure 1 comprises a double-acting hydraulic actuator shown generally at 1 and comprising a cylinder 2 rigidly fastened to the body of the vehicle in a manner not shown, and a piston 3 having a rod 3a projecting from each end of the cylinder and connected via links 4 to the driven levers 5 of the wheel stub axles having their pivot pins designated by the reference numeral 6.

The piston rod 3a also incorporates a rack 7 in constant meshing engagement with a pinion 8 constituting the member for mechanically actuating the steering, mounted at one end of a rotary shaft 9 having its other end solid with the body 10 of a distributor for delivering fluid under pressure to the actuator, the distributor being designated in general by the reference numeral 11.

This distributor 11 comprises in turn a movable assembly consisting of a pair of spool valves 12 and 13 co-acting with a control member in the form of a rocker 14 rigid with a control shaft 15 carrying the steering wheel 16 of the vehicle.

In this structure, each spool valve 12, 13 is urged simultaneously against one arm of rocker 14 and against the distributor body 10 due to the provision of a chamber 17 at the end of each spool valve which is opposite the end engaging the rocker, the two chambers 17 being interconnected via a passage 18 formed in the distributor body and connected in turn to a source of fluid under pressure shown diagrammatically at 19 in Figure 1 as consisting of a pump, although a pressure accumulator may also be used for the same purpose. Abutment between the spool valve and the distributor body is obtained in this arrangement by the relative engagement between a shoulder 12a or 13a of the spool valve and the bottom 17a of the relevant chamber 17.

Each spool valve 12, 13 comprises a first circular groove 12b, 13b normally (i.e. in the inoperative spool valve position illustrated in Figure 1) connecting the chambers la, 1b of actuator 1 to the exhaust, said chambers la, ib being connected to passages 20, 21 of distributor 11 which open into the correspoad- ing groove 12b, 13b.

These grooves 12b, 13b and therefore the actuator chambers la, ib are normally interconnected via another passage 22 formed in the distributor body 10 and provided with a discharge ball-valve 23 adapted to be unseated beyond a predetermined pressure threshold for discharging the fluid towards the reservoir 24.

Each spool valve 12, 13 is also provided with another circular groove 12c, 13c into which opens a pressure-duid supply passage 18a also formed in the body 10. Each groove 12c, 13c is separated from the adjacent groove 12b, 13b by aland 12d, 13d. These lands normally prevent any communication between said grooves 12c, 13c and said passages 20, 21, but permit the same communication when one of the spool valves 12, 13 is moved as a consequence of the relative movement pro duced between the rocker 14 and the distributor body 10 as permitted by the abutment clearances J1 and J2 provided therebetween in either direction of rotation of the steering wheel 16.

Thus, when the control effort exerted on steering wheel 16 as required for pivating the steerable wheels of the vehicle generates between the rocker 14 and the corresponding spool valve 12 or 13 a force lower than the opposite force applied there-against by the pressure prevailing in the corresponding chamber 17, the assembly comprising the rocker, the spool valve and the distributor body behaves like a rigid coupling between drive shaft 15 and the shaft 9 of pinion 8 meshing with the steering rack 7, while the pston 3 coupled to the rack causes pressure fluid to be transferred between the normally interconnected actuator chambers, as already mentioned in the foregoing, the non-return valve 23 maintaining a certain residual pressure in the circuit concerned.

However, when the control effort exerted the steering wheel 16 and necessary for tuning the steerable road wheels exceeds the threshold beyond which the force generated between the rocker 14 and the relevant spool 12 or 13 is greater than the opposing force exerted on the spool by the pressure prevailing in the corresponding chamber 17, this spool is moved within the limits permitted by the relevant clearance J1 or J2. Whereby the land 12d or 13d will shut off the port connect- ing the corresponding actuator chamber la or 1b to the exhaust, this chamber being thus supplied with fluid under pressure via passage 20 or 21, the other actuator chamber remaining connected to the exhaust. So that the steerable wheels are actuated hydraulically for steering purposes by the fluid pressure exerted on one side of the actuator piston 3, and the assembly including the steering wheel 16, the rocker 14, the distributor body 10, the rack pinion 8 and the rack 7 will follow the servoaction thus exerted on the steerable wheels, this servo-action is discontinued to restore the above-described operating conditions corresponding to a pure mechanical operation when the control effort exerted on the steering wheel 16 drops below the predetermined threshold.

The conventional prestressed spring having unavoidably a low flexibility for determining the threshold is thus advantageously replaced in the present arrangement by a fluid pressure producing an action equvalent to that of a spring of infinite flexibility.

However, this does not imply a complete absence of spring effect for, as illustrated in the modified arrangement shown in Figures 2 and 3, an auxiliary compression spring may be used, this auxiliary spring being either of the additive action type, as shown at 25 in Figure 2, or of the substractive action type, as shown at 26 in Figure 3, the spring in this last case acting as a spool valve abutment member at the end of its compression. In Figure 2, an exemplary separate feed for passages 18 and 18a is illustrated, from two separate sources 19 and 19a, respectively.

Figure 4 illustrates another modification in which, according to an arrangement known per se, a servo-reaction force is exerted on each spool valve which adds itself to the threshold force, raising the threshold effort, and is obtained by connecting each output passage 20 or 21 of the distributor to a chamber 27 provided between the spool valve and the distributor body, independently of chamber 17 formed in this case between an extension of the spool valve stem and the distributor body, this last-mentioned chamber 17 receiving the fluid pressure generating said effort threshold.

Figure 5 illustrates a typical form of embodiment of the spool valve and distributor body arrangement wherein the pressure from the same source and the same passage 18 is utilized for supplying both actuator chambers lo and lb, thus producing the threshold force.

The chamber 17 is supplied with fluid under pressure via an axial passage 28 formed in the spool for constantly interconnecting said chamber 17 and the feed groove 12c or 13c of the corresponding spool valve. In this Figure, it is also dear that the spool valves are driven in a known fashion by means of adjustable screw tappets 29 adapted to be locked in the selected position by means of nuts 30, the tappets co-operating with the spool valves through the medium of thrust rods 31 engaging freely in opposite cavities formed in the tappets and the spool valves.

Figure 6 illustrates a modified embodiment wherein each spool valve comprises an extension emerging from the distributor body, in the form of screw threaded extension 12e, on which a nut 32 for adjusting the abutment position of spool valve 12 is engaged.

Figures 7 and 8 illustrate modified embodiments wherein the fluid pressure producing the threshold force is applied to an additional member co-acting with each spool valve which, in this case, may be simplified. In Figure 7 this additional member is a disc-like piston 33 adapted to slide in fluid-tight relationship in a bore constituting the chamber 17, the groove 12b of the preceding embodiments resulting here from a thinner end tip of the spool valve. In Figure 8 the additional member is a rod-like piston 34 adapted ta slide in fluid tight relationship in a wall separating the bore of the spool valve 12 from a bore constituting the chamber 17, the groove 12b of the preceding embodiments resulting therefore from the co-operating configurations of the spool valve and relevant piston 34, while the stop abutment of spool valve 12, at the opposite end of this valve, may consist of a conventional axial stop ring 33.

Figure 9 illustrates a modified construction wherein the chamber 17 is formed at the location of the feed groove 12c of spool valve 12 which comprises a two-stage chamber in which an end portion 12f of greater diameter than the remaining spool valve portions is adapted to slide, so that this spool valve is normally responsive to a differential effect of the supply pressure urging same against the rocker 14, this movement being controlled by a stop member consisting of an adjustment ring 36 screwed in the distributor body 10.

In the distributor illustrated in Figure 10, each spool valve 12, 13 is also. urged against the rocker 14 and for abutment in the distributor body 10 by the provision of a chamber 17 formed at the spool valve end opposite the rockerengaging valve end, both chambers 17 communicating with a fluid pressure supply passage 18.

In this example, this fluid pressure supply is obtained via a regulator 32 of a type known per se, of which the output pressure is a function of the vehicle speed. This regulator comprises another separate spool valve 33 provided with a land 34 adapted to co-act with a passage connected to the supply passage 18, and two grooves disposed on either side of the land 34, one groove 35 being connected to the source of fluid pressure 19 supplying also the other passage 18a of the distributor, while the other groove 36 is connected to the reservoir of the hydraulic system. This spool valve is responsive to the opposite forces of the output pressure exerted in an end chamber 37 connected via a passage 38 to the passage 18, and of a coil compression spring 39 interposed between the opposite end of the spool valve 33 and a centrifugal governor comprising a push member 40 responsive to a pair of inertia weights 41 fulcrumed to a rotary shaft 42 rotatably driven from the transmission system. driving the vehicle road wheels. Thus, the output pressure of regulator 32 is exactly proportional to the degree of compression of spring 39 and therefore to the vehicle speed.

For controlling the angular position of the steerable wheels of the vehicle with this arrangement, it is clear that the higher vehide speed, the higher the threshold of steering effort without servo-action, depending on the pressure in chambers 17 which pressure determines the threshold force required to move one of the spool valves 12, 13. In other words, under normal road driving conditions, the higher the vehicle speed, the higher the maximum torque produced through the mechanical steering gear without exerting any servoaction, thus improving considerably the steering stability, whereas at low vehicle speeds, and notably during parking manoeuvers, since the effort threshold resulting from threshold force consequent upon the pressure in chambers 17 remains very low, the servo-action is substantially immediate, a quite desirable feature since the mechanical resistance to any steering movement is relatively high in this case.

The value of the effort threshold without servo-action can thus be preset as desired, or made adjustable by the driver, by providing means for controlling the degree of compression of spring 39, for instance by axially moving the support (not shown) of the centrifugal governor in relation to the regulator body 32 enclosing the additional spool valve 33.

Of course, one may also contemplate to give the driver the possibility of adjusting at will the effort threshold without any servoaction, and in this case the centrifugal governor of Figure 10 would simply be replaced by a push member adapted to adjust the degree of compression of spring 39, the regulator acting in this case as an adjustable pressure reducing device.

Figure 11 illustrates another possibility of adapting the effort threshold without servoaction but as a function of the vehicle load, this possibility being particularly valuable in vehicles likely to be operated with extremely variable loads and which, being equipped with a known type of hydropneumatic suspension system with automatic ground clearance correction means, are capable of producing through simple means the desired variation by connecting the chambers 17 directly to the hydraulic section of the hydro-pneumatic elements 43 of the vehicle axle concerned (in this case these elements communicate with each other), of which the known ground clearance correcting device is not shown since it is not an integral part of this invention.

Of course, other modifications and changes may be contemplated, notably by providing an arrangement in which the control member, instead of c-operating with the pair of parallel-arranged spool valves, would co operate with a pair of spod valves disposed in axial alignment to each other, the control member being mounted therebetween.

For more details conoerning the arrangement comprising a distributor with a rotary seal between the distributor and a fixed union to which the various feed and exhaust lines together with the line leading to the actuator chambers would be connected, reference may be made to the Applicants' British Patent No.

753,821.

WHAT WE CLAIM IS: 1. A mechanical control device with pressureqfluid servo-action, for distributing fluid under pressure to a two-chamber cylinder and piston actuator connected to a mechanism to be actuated, the device comprising a manually operable control member and a pressure fluid distrior having a body mechanically connecable to the mechanism; two spool valves slidably mounted in the body for controlling the distribution of fluid under pressure to respective chambers in the actuator; an abutment between each spool valve and the body stopping movement of each spool valve in one direction beyond a position of abutment, a respective one of the spool valves being individually movable by the control member from its position of aburent in each direction of movement of the control member; and means for resisting such movement and returning the spool valves to their positions of abutment, the said means permitting a relative movement between the body and either spool valve only when the force applied to the spool valve exceeds a certain threshold value colrres- poncing to a threshold of effort applied to the control member, and the said means composing for each spool valve a chamber disposed between the spool valve concerned, or a member co aperating therewith, and the distributor body, these spool valve chambers each being adapted to receive, for determining the said threshold force, a fluid under a common pressure which remains substantially independent of pressure variations in the fluid distribeeed to the actuator.

2. A control device as clained in claim 1, wherein the fluid under pressure determenxng the threshold force is received from a pressurefluid source provided for feeding said actuator chambers through the distributor.

3. A control device as claimed in claim 1, wherein the fluid pressure applied to each chamber of the distributor has a predeter- mined value adjustable and/or variable automatically.

4. A control device as claimed in claim 1, claim 2 or claim 3 wherein an auxiliary coil compression spring capable of exerting an additive or subtractive effect, is disposed in each chamber of the said spool return means.

5. A control device as claimed in any one of claims 1 to 4, wherein a conduit supplying fluid under pressure to each actuator chamber is connected to another chamber disposed between the relevant spool valve and the distributor body in order to impart to the body a servo-action reaction force capable of adding itself to the threshold force.

6. A control device as claimed in any one of claims 1 to 5, wherein exhaust passages from the spool valves of the distributor are interconnected and provided with a discharge non-return valve opening only beyond a predetermined pressure valve.

7. A control device as claimed in claim 2, wherein each spool valve has an internal passage connecting a groove comunicating the fluid under pressure from the said source to the spool valve and to the chamber of the said spool return means.

8. A control device as claimed in claim 2, wherein each spool valve has a groove for supplying fluid under pressure from the said source, the groove being disposed in a doublestage chamber of the spool valve which determines the threshold force by exerting a pressure differential effect on the spool valve.

9. A control device as claimed in any one of claims 1 to 6 wherein each spool valve is adapted to co-act with a piston slidably mounted in the chamber receiving the fluid under pressure for determining the threshold force.

10. A control device as claimed in any one of claims 1 to 6 wherein each spool valve is adapted to co-act with a push-rod slidably fitted through a partition separating the spool valve sliding compartment from the chamber receiving the fluid under pressure for determining the threshold force.

11. A control device as claimed in claim 3, wherein the pressure exerted in the distributor chambers is derived from an adjustable pressure reducing device.

12. A control device as claimed in claim 3, wherein the pressure exerted in the distributor chambers is derived from a regulator responsive to vehicle speed, the mechanism being the steering gear of a motor vehicle.

13. A control device as claimed in claim 12, wherein the regulator is adjustable by the driver of the vehicle.

14. A control device as claimed in claim 3, wherein the pressure exerted in the distributor chambers is a function of vehicle load, the mechanism being the steering gear of a motor vehicle.

15. A control device as claimed in claim 14, wherein the pressure exerted in the distributor chambers is the pressure of at least one hydropneumatic element of a suspension system.

16. A control device substantially as described herein with reference to any one of the Figures of the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. an arrangement in which the control member, instead of c-operating with the pair of parallel-arranged spool valves, would co operate with a pair of spod valves disposed in axial alignment to each other, the control member being mounted therebetween. For more details conoerning the arrangement comprising a distributor with a rotary seal between the distributor and a fixed union to which the various feed and exhaust lines together with the line leading to the actuator chambers would be connected, reference may be made to the Applicants' British Patent No. 753,821. WHAT WE CLAIM IS:

1. A mechanical control device with pressureqfluid servo-action, for distributing fluid under pressure to a two-chamber cylinder and piston actuator connected to a mechanism to be actuated, the device comprising a manually operable control member and a pressure fluid distrior having a body mechanically connecable to the mechanism; two spool valves slidably mounted in the body for controlling the distribution of fluid under pressure to respective chambers in the actuator; an abutment between each spool valve and the body stopping movement of each spool valve in one direction beyond a position of abutment, a respective one of the spool valves being individually movable by the control member from its position of aburent in each direction of movement of the control member; and means for resisting such movement and returning the spool valves to their positions of abutment, the said means permitting a relative movement between the body and either spool valve only when the force applied to the spool valve exceeds a certain threshold value colrres- poncing to a threshold of effort applied to the control member, and the said means composing for each spool valve a chamber disposed between the spool valve concerned, or a member co aperating therewith, and the distributor body, these spool valve chambers each being adapted to receive, for determining the said threshold force, a fluid under a common pressure which remains substantially independent of pressure variations in the fluid distribeeed to the actuator.