GB2341158A

GB2341158A - Rotary distributor valve with variable choking for power steering

Info

Publication number: GB2341158A
Application number: GB9918059A
Authority: GB
Inventors: Claudio Ognibene
Original assignee: Ognibene SpA
Current assignee: Ognibene SpA
Priority date: 1998-07-31
Filing date: 1999-07-30
Publication date: 2000-03-08
Anticipated expiration: 2019-07-30
Also published as: ITRE980083A1; GB9918059D0; DE19935020A1; IT1306089B1; GB2341158B

Abstract

A rotary distributor valve comprises an outer casing (not shown) including two internal circumferential grooves, which communicate respectively with supply/outlet ducts of a two-way hydraulic actuator, a circumferential series of holes which communicate with lobes of an orbital flow metering device, and a circumferential groove which communicates with a source of pressurised fluid. A sealed rotary pipe 100 is provided inside the casing and comprises holes (Fig. 1) corresponding to the grooves and the series of holes in the casing. The pipe 100 also has blind axial grooves 102. A sealed rotary hollow shaft 200 is provided inside the pipe 100 and is resiliently connected to it. The shaft 200 has blind millings 201a the upper edges of which are spaced from the inner cylindrical surface of the pipe 100, and extend towards the latter by sections 207, 207a of cylindrical surface which have their centres of curvature C<SB>1</SB>, C<SB>2</SB> inside the shaft 200.

Description

2341158 ROTARY DISTRIBUTOR WITH VARIABLE CHOKING.

FOR POWER OR HYDROSTATIC STEERING SYSTEMS The present invention relates to a rotary distributor with variable choking suitable for hydrostatic or power steering systems for road and industrial vehicles.

These systems comprise a hydraulic actuator which can function in two opposite directions, and generally a piston cylinder unit with a through rod, which is connected to the steering quadrilateral.

The hydraulic actuator is supplied by means of a pipe-type distributor, which conveys to the actuator a controlled quantity of pressurised hydraulic fluid supplied by a pump, and conveys to the outlet the fluid obtained from the actuator. The quantity of fluid which is conveyed to the actuator is controlled by an orbital-type measurer, the rotor of which is connected to the steering wheel.

in particular, the distributor assumes three operative positions, in one of which, which is known as the neutral position, the pressurised fluid which is obtained from the pump is conveyed directly to the outlet, whereas in each of the other two positions, the pressurised fluid is conveyed to the hydraulic actuator which controls the steering in one direction or in the opposite direction, and the fluid obtained from the hydraulic actuator is conveyed to the outlet.

More particularly, the pipe type distributor comprises two cylindrical bodies which are connected in a sealed manner, which can assume different relative angular positions. The inner body is hollow axially, is commonly known as the shaft, and is connected to the steering wheel of the vehicle.

2 The outer body, which is commonly known as the pipe, is connected torsionally to the shaft.

The connection is resilient, for a first rotational section, in one direction and in the other c[ifection, and becomes rigid beyond this section.

Both the bodies are provided with axial holes and grooves, which are distributed along their surface, and are disposed in correspondence with one another, according to the relative angular position between the shaft and pipe.

The resilient means maintain the pipe and the shaft in the relative position which corresponds to the neutral position, whereas actuation of the steering wheel modifies the position of the shaft and pipe relative to one another, in order to direct the hydraulic fluid in one direction or the other, corresponding to the two different directions of steering.

The connection between the steering wheel column and the shaft is rigid, whereas that between the shaft and the pipe is resilient, and consequently, actuation of the steering wheel gives rise to offsetting between the shaft and pipe, which is maintained constant for as long as the steering wheel continues to be turned, whereas when the rotation of the steering wheel ceases, the resilient means return the pipe and shaft into phase with one another.

The hydraulic fluid which is conveyed to the hydraulic actuator is measured by an orbital measurer, the rotations of which correspond to the rotations of the shaft, and thus to the rotations of the steering wheel.

The problem which the present invention intends to solve is derived from the fact that when there is displacement from the neutral position in one direction or the 3 other, progressive closure takes place of the apertures which divert the hydraulic fluid to the tank, and progressive opening takes place of the apertures which supply the hydraulic actuator, in one direction or the other.

This progressive closure and progressive opening of the apertures, respectively in their end and initial phases, give rise to choking in the apertures for passage of the fluid, thus causing noise.

The noise is caused by the increase in speed of the fluid, which gives rise to the phenomena of cavitation.

According to the known art, this problem is dealt with by constructing the apertures which are present in the pipe and in the shaft, or in at least one of these components, in the form of axial grooves, the edges of which constitute the components, which carry out the choking as they gradually meet.

The noise which is derived from the choking is dealt with according to the known art, by using grooves which are very long in relation to their depth, with values of this ratio of up to 1600 times.

This requires considerable accuracy of mechanical processing, with tolerances approximately +/- 3 microns.

However this has not been found to be sufficient, and an the contrary, has increased the costs of the device to levels which are such as to limit its use.

The accuracy of mechanical processing of the grooves has thus become subordinate to the characteristics of the shape of the edges of the grooves, and the position of the grooves relative to one another.

4 In order to reduce the cavitation phenomena, it is known to use a reciprocal arrangement of the grooves, i.e. circumferential distribution of the latter, by means of which the.groove which is disposed downstream in the direction of reciprocal rotation of the shaft in the pipe, makes available counter- pressure in the preceding groove, by means of which the cavitation is greatly reduced.

Considerable importance is thus attributed to the shape of the edge of the grooves themselves, on which the gradualness of closure and opening of the apertures of the rotary distributor depend.

The state of the art provides many different types of teaching relative to the shape of the edge of the grooves, which teaching has in common the creation of a bevel. However, the bevels according to the known art have characteristics of accuracy and shape such that as a whole they are unsatisfactory, both from the operative point of view and the economic point of view.

An object of the present invention is to provide a specific shape of the edge of the grooves which are present in the outer surface of the shaft, such as to reduce to a minimum the phenomenon of cavitation, and which at the same time is structurally simple.

Accordingly, the invention comprises a rotary distributor for hydrostatic steering, comprising an outer casing, which is provided with at least two inner circumferential grooves, which communicate respectively with a source of pressurised oil and an oil tank.

A pipe is inserted in a sealed manner inside the said casing, and has at least one through hole which corresponds to that of the said circumferential grooves, and leads to the source of pressurised oil.

Two Ixial grooves are disposed symmetrically relative to the sides of.the said hole, and communicate with the outlet when the distributor is in the neutral position.

A rotary hollow shaft is inserted in a sealed manner inside the said pipe, with which it is engaged by a resilient torsional connection, and comprises on its outer surface at least one axial blind groove, which is wide enough, in order, in the neutral position, to face the said hole, and partially the said axial grooves of the pipe, which are disposed laterally relative to the pipe.

is Two axial grooves which communicate with the centre of the shaft are disposed symmetrically relative to the sides of the said blind groove, which has its upper edges spaced from the inner surface of the pipe, and connected to the latter by cylindrical surfaces which have their centre of curvature inside the shaft.

According to an improved embodiment of the invention, the edges of the two axial grooves which are disposed laterally relative to the blind aperture are also spaced from the inner surface of the pipe, and are connected to the latter by cylindrical surfaces which have their centre of curvature inside the shaft.

According to a first embodiment of the invention, the axial grooves which communicate with the centre of the shaft are open at the front.

According to a second preferred embodiment, the axial grooves are on the other hand closed at the front.

6 Various series of holes, which as will be described hereinafter, are distributed on the shell of the pipe and the shaft, constitute the various methods of distribution of the device.

The invention will be described in more detail by way of example with reference to the accompanying drawings, wherein:- Figure 1 shows a lateral view of the pipe of a rotary distributor, according to a first embodiment of the invention; Figure 2 shows the cross-section 11-11 in figure 1; Figure 3 shows in lateral view the hollow shaft of the rotary distributor, which is designed to be inserted in the pipe in figure 1 1 Figure 4 shows the cross-section M1V in figure 3; Figure 5 shows the cross-section at right angles to the axis of the shaft inserted in the pipe, designated as V-V in figure 1; Figure 6 shows an enlarged part of figure 5, with the hydraulic circuit in the neutral position; Figure 7 shows the same detail as figure 6, with the hydraulic circuit in the steering position; Figure 8 shows the circuit in figure 6 further enlarged, indicating the critical dimensions; Figure 9 shows the development in plan view of the pipe, indicated as a thick continuous line superimposed on the development in plan view of the shaft, which is indicated as a thin continuous line, in the reciprocal position corresponding to the neutral position of the distributor, Figure 10 shows the lateral view of the pipe of a rotary distributor according to a second embodiment of the invention; Figure 11 shows the cross-section X1-Xl in figure 10; 7 Figure 12 shows in lateral view the hollow shaft of the rotary distributor, which is designed to be inserted in the pipe in figure 10; Figure 13 shows the cross-section X1WX111 in figure 12, Figure 14 shows the cross-section at right angles to the axis of the shaft inserted in the pipe, indicated as XW-XW in figure 10; Figure 15 shows an enlarged part of figure 14, with the hydraulic circuit in a neutral position; Figure 16 shows the same detail as figure 15, with the hydraulic circuit in the steering position; Figure 17 shows further enlarged the circuit in figure 16, indicating the critical dimensions; Figure 18 shows the development in plan view of the pipe, indicated as a continuous line superimposed,on the development in plan view of the shaft, which is indicated as a broken line, in the reciprocal position corresponding to the neutral position of the distributor, Figure 19 shows the circuit in figure 18, in a steering position; Figure 20 shows the pressure control curve according to the known art; and Figure 21 shows the pressure control curve according to the invention.

With reference to figures 1 to 9, the invention comprises an outer pipe 100, which is provided with the following circumferential alignments of through holes, which are equidistant in each alignment; a first alignment of six first holes 101, which open into a circumferential groove in an outer casing, not shown, which communicates with the oleodynamic fluid supply pump; a second alignment of twelve second holes 104, with a differentiated cross section, and with the narrowed part facing the shaft, which is opposite a series of seven equidistant holes in the outer casing, which communicate with the lobes of an orbital measurer; 8 a third alignment of six third holes 105, which open into a circumferential groove in the outer casing, not shown, which communicates with one of the two chambers of the hydraulic actuator 300, for example the one 301 which controls the steering to the right (figure 6); - a fourth alignment of six fourth holes 106, which open into a circumferential groove in the outer casing, not shown, which communicates with the other chamber of the hydraulic actuator 300, for example the one 302 which controls the steering to the left (figure 6).

With reference to figure 9, it can be seen that the holes 101 of the first alignment are offset relative to the holes 104 of the second alignment, and, on the other hand, the holes 104 are aligned alternately respectively with the holes 105 of the third alignment, and the holes 106 of the fourth alignment.

Between two consecutive holes 101, there is disposed a pair of blind axial grooves 102, which are provided in the inner surface of the pipe 100.

The grooves 102 of each pair are separated by a section 103 with a cylindrical surface.

Inside the pipe 100 there is disposed a hollow shaft 200, which in turn comprises (see figure 3):

a first series of six first equidistant blind millings 201, consisting of two aligned sections 201 a and 201b, the plane of symmetry of which passes through the centre C, of the shaft; a second series of six second millings 202, which are open at the front and spaced relative to the said first millings; a third series of six third equidistant millings 203, which are aligned with, and separated from the millings 202; 9 a fourth series of seven equidistant through holes 204, which are spaced from the millings 203; and - a fifth series of eight through holes 205, which are aligned with the holes 204.

It should be noted that the inner cavity 206 of the shaft 200 communicates with the outlet.

The inner surface of the pipe 100 is perfectly cylindrical, including in the vicinity of the edges of the grooves 102.

In the neutral position which is shown in figures 5, 6 and 9, each of the six first equidistant axial millings 201 of the shaft 200 corresponds to one of the holes 101, and part of the two adjacent grooves 102.

In a central position between the grooves 102 of each pair, which are provided in the pipe, as already stated, there are disposed the second miHings 202 of the shaft, which, in the neutral position illustrated in figures 5, 6 and 9 correspond to both these grooves, the said millings being wider than the section which separates them.

The difference between the length of the arc beneath which there is disposed the groove 102, an the inner surface of the pipe, and the length of the arc beneath the outer surface of the shaft, between the millings 201 and 202, is between 0.01 mm and 1.00 mm.

The straight longitudinal edges of the first millings 201 are connected to the outer cylindrical surface of the shaft 200 by means of curved sections 207, with a circular straight cross-section, with a radius of curvature R, which is slightly larger than the radius of curvature IR, of the outer cylindrical surface of the shaft 200.

The curved sections 207 are disposed on a cylinder which is not tangent 5 internally relative to the cylinder defined by the outer surface of the shaft 200.

R, is advantageously between 15 and 20 mm, whereas R, is between 18 and 22 mm.

The centre of curvature C, of each of the curved sections 207 is disposed at a distance of preferably between 2 and 5 mm from the centre of curvature C. of the outer surface of the shaft, and is spaced from the axis of symmetry of the closest milling 201, by a distance of preferably between 0 mm and 1. 15 mm.

is This centre is disposed on the exterior of the circular segment defined by the said axis of symmetry and the said radius Ft., which connect the cavities 201 and 202 to the outer surface of the shaft 200 defined by R, C The second embodiment of the invention, which is illustrated in figures 10 to 19, differs from that previously described in the following details.

With reference to the outer pipe 100, it can be seen that the holes 10 1 of the first alignment of holes are pairs of holes 101 a and 101 b which are aligned axially.

The holes 101 a and 101 b of each pair of holes is offset relative to the holes 104, which on the other hand are aligned alternately with the holes 105 of the third alignment, and the holes 106 of the fourth alignment.

VVith reference to the shaft 200, it can be seen that six second millings 202a of the second series of millings pass through an internal circumferential groove in the shaft, and are no longer open at the front.

The longitudinal straight edges of the second millings 202a are connected to the outer surface of the shaft 200 by means of curved sections 207a, with a circular straight cross-section, which have a radius of curvature R2 which is slightly larger than the radius of curvature Ro of the outer cylindrical surface of the shaft 200.

The curved sections 207a are not tangent internally relative to the outer surface of the shaft.

The centres C2 of the sections 207a (see figure 17) are disposed at a distance of preferably between 2 mm and 5 mm from the centre Co and are spaced from the axis of symmetry of the closest milling 201, by a distance of between 1.2 mm and 3.2 mm.

The distributor functions as follows.

In the neutral position illustrated in figures 9 and 18, the oleodynamic fluid enters the pipe via the holes 101, or the pairs of holes 101 a and 101 b, and fills the millings 201 a and 201 b of the shaft.

The fluid passes from the millings 201 a to the adjacent blind grooves 102 which are provided in the pipe, and from the latter to the millings 202 which convey it to the outlet.

This can also be seen in figure 15.

12 When wishing to steer the wheels to turn to the right, the shaft 200 is rotated clockwise (figure 5), and this corresponds to translation towards the left of the part in a broken line, relative to the part in a continuous line in figures 9 and 18, which translation is apparent in figure 19.

In this new situation, the blind grooves 102 are alternately offset relative to the millings 201 a and relative to the miffings 202, and thus the pressurised fluid which is conveyed by the pump can no longer be discharged through the millings 202, and creates a proportional increase of pressure in the miffings 201 a and 201 b.

Via the narrowed section of a first half of the holes 104 and the miHings 201b, the fluid reaches the volumetric measurer 600, which conveys the same quantity of fluid to the second half of the alternate holes 104, as to the preceding holes. Simultaneously, by means of the rotation, the miHings 203 pass beneath the narrowed part of the second half of the holes 104, and into correspondence with the holes 105.

Via the second half of the holes 104, the millings 203 and the holes 105, the fluid is then supplied to the groove which exists in the outer casing, not shown, and from there it is conveyed to the chamber 301 of the hydraulic actuator 300, and the steering is actuated to the right (figure 7 and figure 1 g).

The fluid which is obtained from the chamber 302 of the actuator 300 reaches the groove in the outer casing, not shown, which is disposed against the holes 106.

The rotation of the shaft relative to the pipe has brought the holes 205 in the shaft partially below the holes 106, and thus the fluid which is obtained from the chamber 302 of the actuator can reach the centre of the shaft, and thus the outlet.

13 Actuation of the steering to the left takes place in the same manner, and can be understood from figure 19, in which the part shown as a broken line is made to move towards the right, relative to the part shown as a continuous line.

The area in which the cavitation which is responsible for the noise tends to occur, is that which is close to the edges of the millings 201a, which, as they approach the edges of the blind grooves 102, gradually choke the passage of the fluid to the outlet, until it is stopped completely.

By means of the shape of the edges according to the invention, i.e. owing to the presence of the curved sections 207, and optionally 207a, the choking is made progressive and continuously variable, such as to reduce the noise drastically, or even to eliminate it completely.

The advantages of the invention are also apparent from comparison of the pressure control curves, according to the angle of offsetting between the pipe and shaft (BOOST CURVE) illustrated in figures 20 and 21.

It can be seen that there is elimination of the area out of control included in rotations of -+ 2040' around the neutral position. The above-described embodiments relate to a so-called open centre distributor, but the solution according to the invention can easily be applied by persons skilled in the art also to closed-centre distributors.

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Claims

1 Rotary distributor with variable choking, comprisingan outer casing including first and second inner circumferential grooves for communication respectively with two supply/outlet ducts of a two-way hydraulic actuator, a circumferential series of holes for communication with lobes of an orbital device, and a third circumferential groove for communication with a source of pressurised fluid..

a sealed rotary pipe inside the outer casing, including at least one first through hole which communicates with the third circumferential groove, at least two second through holes which correspond with the said circumferential series of holes of the outer casing, at least one third through hole which corresponds with one of the said first and second circumferential grooves, at least one fourth through hole which corresponds with the other of the said first and second circumferential grooves, and two blind axial grooves which are disposed symmetrically relative to the sides of the said first through hole., and a sealed rotary hollow shaft inside the said pipe, with which there is engaged a resilient torsional connection, said shaft comprising, on its outer surface, at least one first blind axial milling which, in a neutral position, is wide enough to face the said first through hole of the pipe and partially the said axial grooves of the pipe, at least two second axial millings which communicate with the cavity in the shaft and are disposed symmetrically relative to the sides of the said first blind milling, at least one third axial milling which, in the neutral position, is disposed between the said at least two second through holes of the pipe, and at least one first hole and at least one second hole which are respectively in phase with the third and fourth holes in the pipe, the upper edges of the said at least one first blind axial milling being spaced from the inner cylindrical surface of the pipe and being connected to the latter by a section having a cylindrical surface, which has its centre Cl of curvature inside the shaft.

2. Rotary distributor according to claim 1, wherein the first holes of the pipe which communicate with the third groove in the casing are pairs of through holes which are aligned axially.

3. Rotary distributor according to claim 1 or 2, wherein the second axial millings of the shaft are open at the front.

4. Rotary distributor according to claim 1 or 2, wherein the second axial millings of the shaft are closed at the front, and pass through an internal groove in the shaft.

5. Rotary distributor according to any preceding claim, wherein the upper edges of the second axial millings of the shaft are spaced from the inner cylindrical surface of the pipe and are connected to the latter by a further section with a cylindrical surface, which has its centre C2 of curvature inside the shaft.

6. Rotary distributor according to any preceding claim, wherein the radius of the outer surface of the shaft is between 15 mm and 20 mm.

7. Rotary distributor according to claim 5, characterised in that the centres Cl and C2 of the sections of cylindrical surface are spaced from the centre CO of the shaft by a distance of between 2 mm and 5 mm.

8. Rotary distributor according to any preceding claim, wherein the centres Cl of the sections of the cylindrical surface are spaced from the axis of symmetry of the closest milling by a distance of between 0 mm and 1. 15 mm.

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9. Rotary distributor according to claim 5, characterised in that the centres C2 of the sections of the cylindrical surface are spaced from the axis of symmetry of the closest milling by a distance of between 1.2 mm and 3.2 mm.

10. Rotary. distributor according to any preceding claim, wherein the difference between the length of the arc beneath the inner surface of the pipe of the blind milling and the length of the arc beneath the outer surface of the shaft, between one wall of the groove and the closest wall of the adjacent groove is between 0.05 mm and 1.00 mm.

11. Rotary distributor substantially as herein described with reference to Figs. 1 to 9 or 10 to 19 of the accompanying drawings.