Rotary valve and a method of forming a sleeve for such a valve

A rotary valve and a method of forming a sleeve for such a valve. The valve for controlling fluid pressure to a power assisted steering gear has a rotor 3 mounted in the bore 2 of a sleeve 1 so that relative rotation between the rotor and sleeve controls fluid flow through ports 5, 6a, 6b and 7 to actuate the power assistance means. The port 7 is in the form of an axially extending slot in the bore 2, one end 18 of the slot 7 terminating within the bore and the other end opening into an end face 19 of the sleeve to alleviate the requirement for an annular recess (such as 8, 9 or 10) on the sleeve for supply of fluid to the slot 7 and thereby permitting a reduction in length of the sleeve. The slot 7 may be flat bottomed and inclined relative to the sleeve axis and the method comprises rectilinearly machining such a slot--preferably as a single pass with a broaching tool inclined relative to the sleeve axis. In a modification two diametrically opposed slots 7 are provided which open into opposite end faces 19, 27 of the sleeve and have parallel and inclined flat bottoms, and the method comprises forming both said slots simultaneously or consecutively by rectilinear broaching as a single machining operation with the broaching tool inclined relative to the sleeve axis.

TECHNICAL FIELD AND BACKGROUND ART 
This invention relates to a rotary valve and to a method of forming a 
sleeve for such a valve and is primarily concerned with rotary valves of 
the type utilised for controlling fluid (usually hydraulic) to power 
assistance means of a steering gear. Rotary valves for power assisted 
steering gears are well known in the automotive industry and 
conventionally comprise a rotor mounted in the bore of a sleeve so that 
during a steering manoeuvre the rotor and sleeve are rotationally 
displaced relative to each other and in so doing adjust control ports in 
the valve to direct fluid to and from power assistance means as 
appropriate to assist the steering manoeuvre. The power assistance means 
will usually be in the form of a double acting piston and cylinder device 
incorporated in the steering gear. Examples of rotary valves of the type 
aforementioned are to be found in U.K. Patent Specifications Nos. 391,775, 
476,590 and 1,356,172, U.S. Pat. Nos. 1,947,973, 2,328,312, 1,657,412 and 
1,773,794. In each of these examples fluid flow through the valve is 
achieved by providing distributing zones on the rotor which are displaced 
during the aforementioned relative rotation to determine fluid flow 
between ports in the valves, such ports being connected to fluid pressure 
supply, the power assistance means and exhaust/reservoir (low pressure 
return). Since the early 1930s the most favoured sleeve structure has 
comprised a peripherally spaced array of axially extending, blind ended, 
recesses in the bore of the sleeve. Whilst this popular design is 
efficient and reliable in operation, it suffers from two serious 
disadvantages. Firstly, the design does not lend itself to economic 
manufacture on a mass production basis where either several assembly 
stages are required for producing the sleeve as a two or three part 
component as envisaged by the disclosure in Specifications: U.K. Pat. No. 
476,590 and U.S. Pat. No. 1,947,973, or expensive special purpose 
machinery is necessary for manufacturing the sleeve as a one piece 
component as envisaged by the disclosure in U.S. Pat. No. 2,328,312 and 
U.K. Pat. No. 1,356,172. Secondly, the provision of the axially extending 
blind ended recesses calls for a relatively large sleeve and a 
correspondingly large housing within which the sleeve and rotor are 
mounted. This is incompatible with the desirability of providing a small, 
compact, steering gear as called for in modern vehicles. It is therefore 
an object of the present invention to provide a rotary valve for a power 
assisted steering gear and also a method of manufacturing the sleeve for 
such a valve which will lend themselves to the economic manufacture of a 
compact valve assembly without loss of efficiency or reliability when 
compared with conventional forms of rotary valves for power assisted 
steering. 
STATEMENT OF INVENTION AND ADVANTAGES 
According to the present invention there is provided a rotary valve for 
control of fluid to power assistance means of a steering gear which valve 
comprises a sleeve having an axial bore; first port means for connection 
to fluid pressure supply; second port means for connection to the power 
assistance means; third port means for connection to exhaust/reservoir; a 
rotor mounted in said bore, the rotor having fluid distributing zones 
displacement of which during relative rotation between the rotor and 
sleeve determines fluid flow between the port means to control actuation 
of the power assistance means, and wherein at least one said port means 
comprises axially extending slot means formed in the bore of the sleeve, 
one end of said slot means terminating within the bore and the other end 
opening into a radially extending end face of the sleeve. 
By the present invention the important feature that the axially extending 
slot means opens into an end face of the sleeve permits that slot means to 
be formed by relatively inexpensive machining or other techniques (such as 
spark erosion) and avoids the necessity, as in conventionally formed 
sleeves, of forming the blind ended internal recesses in the sleeve. 
Consequently the valve sleeve can be formed as a one piece component by 
relatively inexpensive machining operations. It is appreciated that all of 
the port means in the valve sleeve are unlikely to be in the form of the 
axially extending slot means and accordingly one or more of the port means 
may comprise a passage which extends radially through the sleeve wall. 
This passage or passages may, again, be simply formed by a boring, 
broaching or other conventional machining technique. Furthermore, by the 
present invention the feature that the axially extending slot means opens 
into an end face of the sleeve lends itself to a sleeve design with a 
relatively short axial length since fluid flow to and from the port formed 
by the slot means can be achieved through the side face of the sleeve; in 
this way, the sleeve design can avoid the additional axial length which, 
with conventional designs (having the axially extending recesses which are 
closed at both ends of the sleeve) require fluid communication to those 
recesses by way of passages which open into the cylindrical outer surface 
of the sleeve. 
Where one of the port means comprises a passage which extends radially 
through the sleeve wall such a passage may form control edges in the bore 
which control edges can be axially extending and rectilinear to co-operate 
with the distributing zones for the control fluid flow through that port 
means. With this latter feature in mind the passage may be formed, for 
example by broaching, to be rectangular with a pair of opposed sides of 
the rectangle forming control edges in the bore that are substantially 
parallel to the axis of the sleeve. Preferably the first port means for 
connection to the fluid pressure supply is in the form of an 
aforementioned rectangularly formed port means having the control edges to 
ensure that fluid pressure supply is accurately and efficiently directed 
as appropriate during use of the valve irrespective of whether the valve 
is of the open centre type or closed centre type as are generally known in 
the art. Where a port means in the sleeve or rotor is merely for fluid 
access or egress and has no control edges associated therewith, such a 
port means may comprise a simple bore through the sleeve wall or in the 
rotor. 
The slot means may have a substantially constant depth in the sleeve wall 
over the major part of its axial extent in the bore; in such a design it 
is likely that the end of the slot means which terminates within the bore 
will be radiussed to provide an exit path for a cutting tool by which that 
slot is likely to be formed. Alternatively, the depth of the slot means 
may decrease as the slot means progresses axially along the bore in the 
direction from the end face into which that slot means opens. This 
progressive decrease in depth may provide the base of the slot with a 
curved profile over its axial extent but preferably the base is 
rectilinear to be inclined with respect to the axis of the sleeve. 
Conventional rotary valves have a neutral open-centre or closed centre 
condition so that relative rotation between the rotor and sleeve in one or 
the opposite senses from this neutral condition directs fluid as necessary 
to drive the power assistance means in the appropriate direction to assist 
the steering manoeuvre. To achieve this function it is usual for the port 
means to be symmetrically disposed around the circumference of the valve 
sleeve and preferably two axially extending slot means are provided which 
are located in diametrically opposite sides of the bore. These two slot 
means may open into a common end face of the sleeve or one into each of 
two axially opposite end faces of the sleeve. 
The aforementioned arrangement in which the depth of the slot means 
decreases as the slot means progresses axially along the bore in a 
direction from the end face into which that slot means opens lends itself 
to a particularly advantageous and convenient method of forming the 
sleeve. This method comprises providing an axially extending tubular 
workpiece from which the sleeve is to be formed and rectilinearly 
machining the slot means in an end part length of the bore of the 
workpiece so that said machining is inclined with respect to the axis of 
the workpiece and the depth of the resultant slot decreases as it 
progresses axially from an end face of the workpiece into the bore of the 
workpiece. 
The rectilinear machining operation is conveniently achieved by a broaching 
technique in which the teeth of the broaching tool progressively increase 
in size to cut the slot means to the required dimensions and profile in a 
straight single pass of the tool over the workpiece. In the aforementioned 
construction where two slot means are located in diametrically opposite 
sides of the bore to open one into each of the opposite end faces of the 
sleeve, it is preferred that the two slot means are rectilinear and 
inclined at substantially the same angle with respect to the axis of the 
sleeve and are substantially parallel with each other. This latter design 
lends itself to a simple and convenient application of the aforementioned 
broaching technique for forming the sleeve whereby the two slot means are 
rectilinearly machined simultaneously or consecutively as a single 
machining operation. This proposal may again be achieved by use of a 
rectilinear broaching tool carrying two sets of progressively increasing 
sized teeth, one for each of the slot means, and which tool is passed 
through the bore of the sleeve to cut the respective slot means, 
conveniently, in a single pass. 
One or more of the slot means may be formed by at least two substantially 
parallel and adjacent similarly formed slots. This has the advantage of 
providing a bearing surface zone for the rotor in the region of the bore 
circumferentially between the two adjacent slots. 
At least one of the slot means will usually form axially extending 
rectilinear control edges in the bore which edges co-operate with the 
distributing zones of the rotor to control fluid flow through the port 
means which comprises that slot means. Although the slot means can be 
formed by broaching as discussed above, it is envisaged that alternative 
methods of forming will be available such as spark erosion techniques, 
milling, shaping and possibly honing or grinding as a finishing operation. 
The sleeve can also be formed by use of a casting or sintering process. 
A particular advantage of the present invention is that the sleeve can be 
formed as a one piece component (other than, of course, for sealing and 
bearing means which are conventionally applied to the sleeve). It is to be 
realised however that the sleeve may be an integral part of a shaft or 
attached to a shaft which is intended to form part of a steering gear. It 
is also to be realised that each of the first, second and third port means 
may comprise one or more discrete ports in the sleeve and also that one or 
more of the port means may comprise one or more discrete ports in the 
rotor and which communicate with passage means extending through the rotor 
.

DETAILED DESCRIPTION OF THE DRAWINGS 
The rotary valve in the arrangement of FIG. 1 has a sleeve 1 with a 
cylindrical bore 2. Mounted in the cylindrical bore 2 is a rotor 3 having 
a circumferentially spaced array of rectangular distributing zones 4. The 
sleeve 1 has first port means 5 for connection to a fluid pressure supply, 
second port means 6a, 6b for connection to power assistance means of the 
steering gear and third port means 7 for connection to exhaust/reservoir 
(sometimes referred to in the art as "low pressure return"). In the 
present example, the first port means 5 in each case is formed by a 
rectangularly sectioned passage which extends radially through the wall 
thickness of the sleeve 2 to open into an annular recess 8 in the exterior 
of the sleeve. The second port means 6a, 6b in each case, comprises a bore 
which extends radially through the wall of the sleeve. Conventionally the 
power assistance means will be in the form of a double acting piston and 
cylinder device which is incorporated in the steering gear so that fluid 
pressure is directed to one or the other side of the device whilst the 
opposite side is exhausted to displace the piston and cylinder as 
appropriate to provide assistance to the steering manoeuvre; consequently, 
at least two ports 6a and 6b are provided which communicate one with each 
of two axially spaced annular recesses 9 and 10 in the exterior surface of 
the valve sleeve. The valve sleeve is rotatably mounted in a cylindrical 
bore 11 of a housing 12 which forms part of the steering gear. The rotor 3 
has a shaft 13 which extends from the housing 12 and is intended to be 
rotated in response to a steering input. The sleeve 1 has an integral 
skirt 14 by which the sleeve is connected through pins 15 for rotation 
with a steering shaft 16 (which may be connected to a pinion in the case 
of a rack and pinion steering gear or a worm in the case of a worm and nut 
steering gear) so that rotation of the shaft 16 provides a steering output 
from the gear. A resilient coupling 17 is provided between the rotor 3 and 
the shaft 16. The coupling 17 is conveniently in the form of a torsion rod 
and permits relative rotation between the rotor 3 and the shaft 16 (and 
thereby the sleeve 1) in response to a steering manoeuvre and this 
relative rotation between the distributing zones 4 and the ports in the 
sleeve 1 is intended to control fluid flow to and from the power 
assistance piston and cylinder device. 
The third port means in the sleeve is in the form of one or more axially 
extending slots 7 which are formed in the bore of the sleeve 1 so that one 
end 18 of the slot is closed and terminates within the bore while the 
other end opens into a radially extending end face 19 of the sleeve. The 
housing 12 has a fluid pressure supply port 20 which is in constant 
communication with the annular recess 8; a port 21 which is in constant 
communication with annular recess 9 and a port 22 which is in constant 
communication with recess 10. These ports 21 and 22 communicate with 
opposite sides of the power assistance means in conventional manner while 
a port 23 in the housing 12 provides for low pressure return to reservoir. 
The port 23 is in constant communication with an exhaust chamber 24 which 
is formed between the end face 19 of the sleeve and annular seals 25 
within which the shaft 13 rotates; the axial slots 7 open into the chamber 
24 to be in constant communication with exhaust. The recesses 8 to 10 and 
chamber 24 are sealed by annular seals 26 on the sleeve which seals 
rotatably mount the sleeve in the housing. The arrangement of the ports 5 
to 7 and distributing zones 4 will be described in greater detail 
hereinafter. However, it will be apparent from FIG. 1 that the arrangement 
of the port means 7 as an axially extending slot which opens into the end 
face 19 of the sleeve (and thereby to the chamber 24 and return) 
alleviates the requirement for an additional annular recess to be provided 
on the exterior of the sleeve which would be necessary if the third port 
means 7 were in the form of a passage through the wall thickness of the 
sleeve (similar to the passages 6a, 6b) as is conventional practice--the 
preferred arrangement shown in FIG. 1 therefore permits the valve sleeve 
to have an axial length which is less than that which would normally be 
provided. 
The rotary valve shown in FIG. 2 is substantially the same as that shown in 
FIG. 1, the major difference being that the axially extending slot means 7 
are located to open into the opposite end face 27 of the sleeve. Over its 
region which carries the distributing zones 4 the rotor 3 may be of 
generally square section as shown in FIG. 3 so that four distributing 
zones are provided each being a substantially rectangular flat 28. 
Alternatively, the distributing zones can be in the form of recesses as 
indicated at 29 and well known in the relevant art. 
The rotary valve in FIGS. 2 and 3 has its ports symmetrically disposed 
relative to the circumference of the sleeve to be of the open centre type 
whereby in a neutral (inoperative) condition fluid pressure supply from an 
hydraulic pump or otherwise passes freely through the valve to the low 
pressure return or reservoir. This is best illustrated in the flat 
development of FIG. 4 where the sleeve has two diametrically opposed 
rectangular ports 5 and two diametrically opposed axially extending slots 
7 which open into the same end face 27 of the sleeve. Both slots 7 
communicate with the return line 23 while both ports 5 communicate with 
the pressure line 20. In the neutral condition (as shown) each of the four 
distributing zones 28 circumferentially bridges a pressure port 5 and a 
return slotted port 7. In addition two ports 6a which communicate with the 
line 21 to one side of the power assistance means and two ports 6b which 
communicate with the line 22 to the other side of the power assistance 
means are in constant communication, as appropriate, one with each of the 
distributing zones 28 so that the valve is both open centre to the pump 
and open return to both sides of the power assistance means in its neutral 
condition. It will be apparent from FIG. 4 that during relative rotary 
displacement between the rotor 3 and sleeve 1 in one sense of direction 
fluid pressure will progressively be directed to one side of the power 
assistance means while the other side is exhausted and vice versa during 
relative rotation between the sleeve and rotor in the opposite sense of 
direction so that power assistance is available to assist the steering 
manoeuvre which causes the aforementioned relative rotation. 
The ports 5, 6a and 6b, slots 7 and distributing zones 28 can be formed 
relatively simply and inexpensively by conventional machining techniques. 
In forming these parts the ports 5, slots 7 and zones 28 are preferably 
provided with accurately machined control edges 29, 29' which extend 
axially parallel to the sleeve axis and it is the movement of the control 
edges 29 on the rotor circumferentially relative to the control edges 29' 
in the sleeve which controls the fluid flow through the ports 5 and 24 
(and thereby to the power assistance means). The axial extent of the 
control edges 29 for the distributing zones need only be as long as is 
necessary to provide an appropriate axial overlap with the associated 
control edges 29' of the ports 5 and 7 but it is likely that the control 
edges 29 will be longer than necessary to facilitate manufacture of the 
distributing zones 28. 
The sleeve 1 is a one piece component which may be sintered or cast to form 
the port means in situ. More likely however the sleeve will be formed from 
a cylindrical workpiece by appropriate machining where, for example, the 
passages 6a and 6b may be simple bores and the ports 5 broached to their 
rectangular section. The slots 7 may be accurately formed by a spark 
erosion process where, for example, the closed end 18 may terminate 
abruptly--as shown in FIG. 2; alternatively the slot 7 may have its closed 
end 18 rounded or tapered as shown in FIG. 1 to provide a lead-out path 
for a shaping, milling or grinding tool by which the slot can be cut with 
a cyclical action. 
In each of the arrangements shown in FIGS. 1 and 2 the slot 7 has a 
substantially constant depth in the sleeve wall over the major part of its 
axial extent. However, in the modification shown in FIG. 5 the slot means 
indicated at 7a has a depth which decreases as the slot progresses axially 
along the bore 2 in a direction from the end face 27 into which the slot 
opens. The slot 7a is rectilinear and has a flat bottom which is inclined 
as indicated by the line 30 with respect to the axis of the sleeve 1 so 
that the slot tapers continuously from its opening in the end face 27 to 
where it terminates within the bore 2. This particular configuration for 
the slot means 7a lends itself to a most convenient manufacturing 
technique where the slots 7a are simply broached along the line 30 by a 
single pass from a rectilinear broaching tool. 
The open ended slots 7 are not necessarily restricted for use as the low 
pressure return ports; for example designs are envisaged in which one set 
of open ended slots which communicate with one end face of the sleeve can 
provide low pressure return ports whilst a second set of open ended slots 
which communicate with an opposite axial end face of the sleeve can 
provide communication to one side of the power assistance means. Such an 
arrangement is possible with the rotary valve shown in FIGS. 6 and 7 where 
the previously proposed passages 6b are replaced by axially extending 
slots 7b which are formed similarly to the slots 7 but extend to open into 
the opposite end face 19 of the sleeve. These slots 7b will communicate 
with a chamber which will be in constant communication with the line 22 to 
one side of the power assistance means. 
FIG. 6 includes a possible modification whereby an auxilliary passage 31 
communicates from each slot 7 radially through the wall of the sleeve 1 to 
an annular recess in the exterior of the valve sleeve which is intended 
for communication with the low pressure return line 23. Such passages 31 
(which are also indicated in FIG. 7) can be provided where the end of the 
slot 7 in the face 27 is closed, for example by a bearing 32 for the rotor 
(which bearing obturates fluid flow from the slot 7 by means of the route 
envisaged in the FIG. 4 arrangement). 
The steering gear illustrated in FIG. 8 embodies a rotary valve 
construction similar to that discussed with reference to FIGS. 6 and 7 
where two sets of open ended slots 7 and 7b are provided which open one 
into each of the opposite end faces of the sleeve and the slots 7 in one 
set communicate with an auxilliary passage 31 through the wall of the 
sleeve 1 to permit free flow of fluid from that slot. The steering gear of 
FIG. 8 is, generally, a conventional form of a worm and nut gear in which 
a worm shaft 16 drives a piston/nut 33 in response to rotation of the worm 
by rotation of an input shaft 13--the shafts 13 and 16 being coupled 
together by an axially extending torsion rod 34. The nut 33 is toothed and 
engages a toothed sector 35, rotation of which in response to axial 
displacement of the nut 33 provides a steering output. The nut 33 
constitutes a piston with opposed pressure chambers 36, 37 for use as a 
power assistance double acting piston and cylinder device, the hydraulic 
fluid supply for which is controlled by the rotary valve actuated in 
response to relative rotation between the sleeve 1 and the rotor 3 which 
is incorporated at the end of the shaft 18 in a conventional manner. The 
sleeve 1 is coupled for rotation with the worm shaft 16 and passages 22a 
are provided within this coupling to communicate between the open ends of 
the set of slots 7b and the piston chamber 37. Fluid flow to and from the 
chamber 37 is therefore effected by way of the passages 22a and slots 7b. 
Fluid flow to and from the opposing piston chamber 36 is achieved by way 
of axially extending passageways 38, 39 and 40 in the worm shaft 16, 
piston/nut 33 and rotor 13 respectively and a radially extending passage 
21a in the rotor 3. The passage 21a communicates with the passage 40 and 
fluid flow to and from this passage is determined by the control ports in 
the rotary valve. 
The open ends of the slots in the set 7 communicate, without effect, with 
an annular chamber 41 formed between the shaft 13 and the housing 12; this 
chamber 41 is in constant communication (through the slots 7 and 
auxilliary passage 31) with the return passage 23. 
It will be seen from FIG. 8 that by provision of the axially extending sets 
of slots 7a and 7b it is only necessary to provide two axially spaced 
annular recesses in the external surface of the sleeve 1, one of these 
recesses providing constant communication with the fluid pressure feed 
line 20 and the other providing constant communication with the return 
line 23; as a consequence the sleeve 1 can have a relatively small axial 
extent which can be reflected in a reduced size for the rotary valve and 
its housing in the steering gear. 
Generally the ports in a rotary valve of a power steering gear of the type 
with which the present invention is concerned are symmetrically disposed 
circumferentially with respect to the sleeve so that fluid control is 
effected similarly during relative rotation between the rotor and sleeve 
in one or the opposite senses from a neutral condition of the valve. With 
this in mind the valve sleeve will usually have two axially extending 
slots 7c and 7d (see FIGS. 9 and 10) which slots are located in 
diametrically opposite sides of the sleeve bore 2 to lie in a common plane 
which includes the axis of the sleeve. These two slots may open one into 
each of two axially opposite end faces 19 and 27 of the sleeve and be 
substantially rectilinear to have flat bottoms which are inclined as shown 
in FIG. 9 so that the depth of each slot 7c and 7d decreases as the slot 
progresses axially along the bore 2 from the end face 19 or 27 into which 
that slot opens. Each of the slots 7c and 7d can be formed by a 
rectilinear broaching technique along the broach line 30 in a similar 
manner to that previously discussed with reference to FIG. 5. However, the 
particular arrangement shown in FIG. 9 with the slots 7c and 7d inclined 
at substantially the same angle with respect to the axis of the sleeve and 
in parallel alignment with each other lends itself to rectilinearly 
broaching the slots 7c or 7d simultaneously or consecutively as a single 
machining operation (thereby reducing manufacturing time and cost). 
The flat development of the sleeve shown in FIG. 11 includes a possible 
modification in the structure of the axially extending open ended slots 7 
whereby each such slot as incorporated in the previously described 
arrangements can be effectively replaced by two similarly formed slots 
which are located adjacent and parallel to each other; these two adjacent 
slots shown at 7e and 7f in FIGS. 11 and 12 provide control ports which 
co-operate with the rotor 13 in a similar manner to that previously 
described but have the additional advantage in that they form a bearing 
surface zone 42 for the rotor 13 in the region of the bore 2 
circumferentially between the two adjacent slots 7e and 7f. It will, of 
course, be appreciated that the slots 7e and 7f can be formed similarly to 
the previously described slots 7, 7a, 7c or 7d. 
In the modification shown in FIG. 13 each of the flats or recesses which 
form the distributing zones 4 of the rotor is displaced axially with 
respect to the two distributing zones 4 to which it is adjacent and 
peripherally between which it is positioned. By such a staggered layout 
for the distributing zones 4, opposed part-cylindrical bearing surface 
zones which are provided between the rotor and the bore 2 of the sleeve 
are staggered axially around the bore; it is believed that such an axial 
distribution can be used to alleviate distortion in the sleeve and improve 
the bearing which the sleeve bore provides for the rotor. 
In each of the above described arrangements the sleeve is formed as a 
discrete component in the rotary valve; this arrangement is by no means 
essential and as shown in FIG. 14 the sleeve 1a is formed integral with 
and at the end of a worm shaft 16a of a worm and nut power steering gear 
that is similar in many respects to that previously described with 
reference to FIG. 8. 
In the FIG. 14 arrangement only one set of axially extending slots 7 are 
provided which open into the free end face of the valve sleeve 1a while 
the slots 7b in the FIG. 8 arrangement have effectively been replaced by a 
bore 6a which communicates through the wall of the sleeve between the 
piston chamber 37 and the distributing zones 4 in the rotor 3.