Valve arrangement, for example a proportional valve

As a result of an appropriate displacement of the control member, a connection of a fluid unit can, for pressure relief, be connected to a line leading to a low-pressure reservoir or be isolated from this line and/or, for the exertion of pressure, connected to a connection of a pressure source. Should the control member jam and be incapable of following an appropriate actuating stroke of a servomotor into the pressure-relieving position, a safety relief valve is opened by means of the actuating stroke.

BACKGROUND AND SUMMARY OF THE INVENTION 
The invention relates to a valve arrangement, for example a proportional 
valve, for controlling the pressure of a connected fluid unit, with a 
control member which is adjustable by means of a servomotor, counter to a 
restoring force loading the control member, out of an initial position, in 
which the fluid unit communicates with a low-pressure reservoir, into an 
operating position, in which the fluid unit communicates with a pressure 
source via a connection controlled by the control member and/or is 
isolated from the low-pressure reservoir. 
A valve arrangement of this type, designed as a proportional valve, is 
known, for example, from German Patent Document DOS 3,144,362. 
Corresponding valve arrangements can serve, for example, on vehicles with 
all-wheel drive, for connecting a connectable driving axle to a main drive 
train or isolating it from this by appropriately actuating a 
fluid-controlled clutch. 
The capacity for isolating the connectable axle from the main drive train 
in drive terms is important, above all, when the vehicle has a brake 
installation with an anti-lock system. In particular, systems of this type 
can as a rule work effectively only when the vehicle axles are uncoupled 
from one another in drive terms, that is to say when the speeds of the 
wheels of one axle are completely independent of the speeds of the wheels 
of another axle. 
Even when the known valve arrangements used in this respect have a high 
degree of reliability, it is still impossible completely to prevent the 
possibility that the control member will jam or become sluggish and that 
the connectable driving axle will accordingly not be isolated from the 
main drive train or only with a long delay. 
A valve arrangement is known from the manual of H. Zoebl "Olhydraulik [Oil 
hydraulics]", Vienna, Springer-Verlag 1963, page 261, Figure 315, and by 
means of this a double-acting piston/cylinder unit can, for a particular 
actuating stroke in one direction or the other, be connected to a pressure 
source or be shut off form the pressure source, in such a way that the 
piston is retained immovably in the cylinder. Arranged at the connections 
of the cylinder chambers in each case are excess-pressure valves which 
limit the maximum pressure in the piston/cylinder unit. Nevertheless, in 
the event of a fault of the valve controlling the direction of movement of 
the piston or its blocking, the piston can remain stationary in a position 
undesirable per se. 
The object of the invention is to guarantee in a valve arrangement of the 
type mentioned in the introduction an especially high operating safety, 
and at the same time, in particular, to obtain in response to an 
appropriate control of the servomotor a pressure relief of the fluid unit 
with an especially high degree of safety. 
According to the invention, this object is achieved in that a passage, 
which leads from the fluid unit or from the connection controlled by the 
control member between the fluid unit and pressure source to the 
low-pressure reservoir, is controllable by means of a safety relief valve, 
the valve body of which is arranged as a transmission element between the 
servomotor and control member and is urged into the closing position by 
the servomotor when the servomotor loads the control member counter to the 
restoring force. 
The invention is based on the general idea of transmitting the actuating 
force of the servomotor counteracting the restoring force of the control 
member to the control member via the valve body of the safety relief 
valve, specifically in such a way that the mutually counteracting 
actuating and restoring forces are exerted on the safety relief valve with 
a closing effect. The safety relief valve is consequently opened 
automatically when, with the control member being jammed or sluggish, the 
servomotor is actuated with the effect of a return to its position 
assigned to the initial position of the control member. 
According to an especially preferred embodiment of the invention, the 
passage controlled by the safety relief valve can go through the control 
member, the valve body of the safety relief valve interacting with a seat 
of the safety relief valve, this seat being located at the low-pressure 
end of the passage. A seat-controlled valve of this type can afford an 
especially high degree of safety against malfunctioning. 
There is fundamentally the possibility of connecting the valve body of the 
safety relief valve to an output member of the servomotor or to design it 
as part of this, so that, with the control member being jammed or 
sluggish, the valve body can actively be pulled away from the closing 
position by the servomotor when the servomotor seeks to return to its 
position assigned to the initial position of the control member. 
Instead, it is also contemplated and advantageous if the valve body of the 
safety relief valve is arranged separately from the output member of the 
servomotor and is subjected to the pressure of the fluid unit in the 
opening direction. Thus, if the control member cannot follow the output 
member of the servomotor because of jamming or sluggishness, should the 
latter be returned to its position assigned to the initial position of the 
control member, the valve body between the control member and servomotor 
is relieved and pushed open by the pressure of the fluid unit. 
As appropriate, the control member can control a plurality of lines which 
are assigned to different fluid units or different parts of a fluid unit 
and which, in the initial position of the control member, are all 
connected to the low-pressure reservoir and, in the event of a 
displacement of the control member counter to the restoring force, are 
successively isolated from the low-pressure reservoir and connected to the 
pressure source, and the passage leading to the low-pressure reservoir 
branches off from the connection controlled by the control member and, 
depending on the position of the control member, communicates with one or 
more of the lines and with the pressure source. 
This arrangement takes into account the fact that, even when the control 
member jams or becomes sluggish, a safety pressure relief is superfluous 
for those lines which lead to the fluid units and which are already 
connected to the low-pressure reservoir by the control member. The passage 
leading to the low-pressure reservoir controlled by the safety relief 
valve is therefore connected only to the lines or fluid units which 
communicate with the pressure source in the particular position of the 
control member. 
A valve arrangement of this type, by means of which a plurality of fluid 
units can be controlled, is suitable, for example, for vehicles with a 
connectable all-wheel drive and with a plurality of differential locks and 
affords the possibility first of coupling a connectable driving axle to 
the main drive train and then, as appropriate, also of successively 
actuating the lock of a central differential and the lock of axle 
differentials or successively releasing the actuated differential locks 
and then also once again uncoupling the connectable driving axle from the 
main drive train. This uncoupling is thus ensured even when the control 
member jams or becomes sluggish. 
Other objects, advantages and novel features of the present invention will 
become apparent from the following detailed description of the invention 
when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
In the embodiment illustrated in FIG. 1, a stepped bore 2 is arranged 
within a valve housing 1, the long middle portion of which is equipped 
with two annular grooves 3 and 4 spaced axially from one another. A 
connection 5 opens into the annular groove 3 and leads to a pressure 
source or to the delivery side of a pump. From the annular groove 4 a line 
6 branches off via which the annular groove 4 is connected to a 
low-pressure reservoir. Arranged parallel to the line 6 is a line 7 which 
connects the low-pressure reservoir to the narrow region of the bore 2 
adjacent to the annular step 8 on the right in FIG. 1. 
A radial channel 9 branches off from the bore 2 between the annular grooves 
3 and 4 and leads to a fluid unit (not shown). 
The end of the bore 2 on the left in FIG. 1 is connected either to the 
radial channel 9 and to the fluid unit connected to this, as shown, or to 
the connection 5 and the pressure source or delivery side of the pump 
connected to it. 
A piston-like slide 10 is guided with sliding displaceability in the middle 
portion of the bore 2 having the annular grooves 3 and 4. This slide 10 
possesses a middle portion 10' of reduced diameter, such that two annular 
steps 11 and 12 with the annular edges 11' and 12' are formed on the 
circumference of the slide. The axial spacing of the annular steps 11 and 
12 or annular edges 11' and 12' corresponds approximately to the axial 
spacing of the annular edges 3' and 4' on the mutually confronting flanks 
of the annular grooves 3 and 4 on the inside of the bore 2. As stated 
further below, the axial spacing of the annular edges 11' and 12' can be 
somewhat larger, but also somewhat smaller than the axial spacing of the 
annular edges 3' and 4'. 
The slide 10 and the portion of the bore 2 having the annular grooves 3 and 
4 are so calculated that the annular space formed within the annular 
groove 4 and located on the valve housing and the annular space formed 
between the annular steps 11 and 12 and located on the slide communicate 
with one another, without a throttle effect, via a wide annular gap formed 
between the annular edges 4' and 12', when the slide 10 assumes its 
initial position in which the end face of the slide 10 on the right in 
FIG. 1 bears against the annular step 8 of the bore 2. 
Moreover, the slide 10 can be displaced so far to the left that the annular 
space formed within the annular groove 3 and located on the valve housing 
and the annular space formed between the annular steps 11 and 12 and 
located on the slide communicate with one another, essentially free of 
throttling, via an annular gap formed between the annular edges 3' and 
11'. 
Arranged within the slide 10 is an axial blind bore 13 which opens out on 
the right end face of the slide 10 and which communicates via a radial 
bore 14 with the annular space located on the slide between the annular 
steps 11 and 12. 
The opening of the axial blind bore 13 on the right end face of the slide 
10 forms a valve seat 15 for a spherical valve body 16 which is normally 
held in its closing position shutting off the opening of the axial blind 
bore 13, because the slide 10 is urged to the right, by means of a 
restoring spring 17 tensioned against its left end face, against a 
tappet-shaped output or actuating member 18 of an electromagnet 19 
designed as an abutment for the spherical valve body 16. The arrangement 
is therefore such that the spherical valve body 16 is arranged between the 
slide 10 and the output or actuating member 18 as a force transmission 
member which transmits to the slide 10 a holding or actuating force 
generated by means of the electromagnet 19 and counteracting the force of 
the restoring spring 17. 
When an appropriate current flow through the electromagnet 19, its output 
or actuating member 18 is displaced to a greater or lesser extent to the 
left in FIG. 1 or is held in a position displaced to the left. Insofar as 
the current flow through the electromagnet 19 is reduced sufficiently or 
cut off, the output or actuating member 18 is pushed to the right in FIG. 
1 in the direction of an end position by a restoring spring 20, the slide 
10 normally being advanced correspondingly by the restoring spring 17 and 
the spherical valve body 16 accordingly remaining in its closing position 
resting on the valve seat 15. 
To guarantee that the output or actuating member 18 of the electromagnet 19 
remains free of self-locking with a high degree of safety, ball bearings 
21 are provided for mounting the output or actuating member 18. 
The valve arrangement illustrated in FIG. 1 functions as follows: 
When the slide 10 assumes a position in which the annular space formed 
between the annular steps 11 and 12 and located on the slide communicates 
solely either with the annular space located on the valve housing and in 
the annular space located on the valve housing and in the annular groove 3 
or with the annular space located on the valve housing and in the annular 
groove 4, then the radial channel 9 leading to a fluid unit is connected 
either to the pump or pressure source connected to the connection 5 or to 
the line 6 leading to the low-pressure reservoir. At the same time, the 
connecting paths between the radial channel 9 and the connection 5 or 
between the radial channel 9 and the line 6 are throttled to a greater or 
lesser extent according to the width of the annular gap between the 
annular edge 11' located on the slide and the annular edge 3' located on 
the valve housing or between the annular edge 12' located on the slide and 
the annular edge 4' located on the valve housing. 
When, as shown in FIG. 1, the axial spacing of the annular steps 11 and 12 
located on the slide is somewhat smaller than the axial spacing of the 
annular edges 3' and 4' located on the valve housing and on the mutually 
confronting flanks of the annular grooves 3 and 4, the slide 10 can also 
assume an intermediate position, in which the fluid unit connected to the 
radial channel 9 is shut off both from the connection 5 of the pump or 
pressure source and from the line 6 leading to the low-pressure reservoir. 
Depending on the amount of displacement travel of the slide 10 in relation 
to this intermediate position, there is then a more or less sharply 
throttled connection of the channel 9 to the connection 5 or line 6. 
If, in contrast to the representation of FIG. 1, the axial spacing of the 
annular steps 11 and 12 located on the slide or of the annular edges 11' 
and 12' located on the slide is somewhat larger than the axial spacing of 
the annular edges 3' and 4' located on the valve housing and on the 
mutually confronting flanks of the grooves 3 and 4, the slide 10 can also 
assume intermediate positions, in which the annular space on the slide, 
formed between the annular steps 11 and 12 located on the slide, 
communicates with the two annular spaces located on the valve housing in 
the two annular grooves 3 and 4. In these intermediate positions, there is 
established between the annular steps 11 and 12 located on the slide and 
therefore at the channel 9 leading to the fluid unit a pressure of which 
the valve is between the low value of the pressure of the low-pressure 
reservoir at the line 6 and the high value of the pressure of the pressure 
source or pump at the line 5. Thus, the value of the pressure on the 
channel 9 can be finely regulated by displacing the slide 10, because, 
whenever the slide 10 is displaced, one of the annular gaps between the 
annular edges 3' and 11' or 4' and 12' is narrowed, whilst the other 
annular gap is widened, that is to say the throttle effect of one annular 
gap is increased, whilst the throttle effect of the other annular gap is 
reduced. 
As already stated above, the valve formed by the valve seat 15 and valve 
body 16 is normally closed because the slide 10 is tensioned by the 
restoring spring 17 against the output or actuating member 18 of the 
electromagnet 19. In the example shown in FIG. 1, the fluid pressure 
prevailing at the channel 9 acts, so as to assist the restoring spring 17 
on the end face of the slide 10 on the left in FIG. 1. The slide 10 
therefore normally follows the movements of the output or actuating member 
18. 
However, should the slide 10 become sluggish or jam, it can no longer 
follow a movement of the output or actuating member 18 to the right in 
FIG. 1. This is equivalent to saying that, in such a case, the valve body 
16 is relieved when the electromagnet 19 is activated with the effect of a 
displacement of its output or actuating member 18 to the right. 
Consequently, the valve formed by the valve seat 15 and by the valve body 
16 can be pushed open by the pressure prevailing at the channel 9 and 
acting on the valve body 16 via the radial bore 14 and the axial bore 13 
in the slide 10, with the result that the channel 9 is connected, via the 
bores 13 and 14 arranged in the slide, to the portion of the valve-housing 
bore 2 on the right of the slide 10 and therefore to the line 7 leading to 
the low-pressure reservoir. Accordingly, the fluid unit connected to the 
channel 9 is also relieved of the pressure when, with the slide 10 jammed, 
the output or actuating member 18 of the electromagnet 19 moves to the 
right in FIG. 1. 
The valve formed by the seat 15 and by the valve body 16 therefore performs 
the function of a safety relief valve for the fluid unit connected to the 
channel 9 and guarantees, even when the slide 10 jams, that this unit can 
be made pressure-free. 
Thus, if the valve arrangement illustrated in FIG. 1 is intended for 
controlling the pressure in a clutch which, on a vehicle with all-wheel 
drive, serves to couple a connectable driving axle to the main drive 
train, this clutch can be made pressure-free and therefore opened even 
when, because of sluggishness or jamming, the slide 10 cannot follow a 
displacement of the output or actuating member 18 of the electromagnet 19 
to the right in FIG. 1. 
In contrast to the arrangement illustrated in FIG. 1, the portion of the 
valve-housing bore 2 on the left of the slide 10 can also be connected to 
the connection 5 of the pressure source or pump, so that the pressure of 
the pressure source or pump always acts on the left end face of the slide 
10 so as to assist the restoring spring 17. 
It is also possible, furthermore, for the end portion of the bore 2 on the 
left of the slide 10 always to be pressureless, so that the slide 10 is 
urged to the right in FIG. 1 solely by the restoring spring 17. 
In FIG. 1, the spherical valve body 16 is arranged separately from the 
output or actuating member 18. It is also possible, in principle, for the 
valve body 16 to be connected to the output or actuating member 18 or to 
form part of this member. This changes nothing in the functioning of the 
safety valve 15/16. 
According to FIG. 2, the valve arrangement can be modified in such a way 
that, in the event of the displacement of the slide 10 to the left, a 
plurality of connections 9a to 9c connected to fluid units or parts of 
these can be connected successively to the connection 5 of a pressure 
source or pump or, in the event of the adjustment of the slide 10 to the 
right, can be connected in reverse order to the connection 6 of a 
low-pressure reservoir. 
The slide 10 once again has a middle portion which is arranged between the 
annular steps 11 and 12 and the diameter of which is smaller than the 
inside diameter of the valve-housing bore 2. At the same time, the axial 
spacing of the annular steps 11 and 12 is calculated so that, in the event 
of a corresponding displacement of the slide 10, the annular space 
remaining between these annular steps 11 and 12 within the bore 2 can 
communicate with the connection 5 of the pressure source or pump and with 
all the channels 9a to 9c of the fluid units. In contrast, if the slide 10 
is displaced so far to the right in FIG. 2 that the channels 9a to 9c are 
located on the left of an annular step 22 of the slide 10 confronting the 
left end face of the latter, whilst the connection 5 of the pressure 
source or pump still remains on the right of this annular step 22, then 
all the channels 9a to 9c are connected, via the region of the 
valve-housing bore, to the line 6 branching off on the left of the slide 
10 from the bore 2 to the low-pressure reservoir. 
If the slide assumes a position between the two above-mentioned positions, 
in which all the channels 9a to 9c are connected either to the connection 
5 of the pump or pressure source or to the line 6 leading to the 
low-pressure reservoir, some of the channels, for example the channels 9a 
and 9b in FIG. 2, are connected to the connection 5 of the pressure source 
or pump, whilst others of these channels, for example the channel 9c in 
FIG. 2, communicate with the line 6 leading to the low-pressure reservoir. 
Depending on the amount by which the portion of the slide 10 between the 
annular steps 11 and 22 overlaps the openings of the channels 9a to 9c 
into the valve-housing bore 2, the connection to the line 6 of the 
low-pressure reservoir or to the connection 5 of the pressure source or 
pump is throttled to a greater or less extent. 
The axial spacing between the annular steps 11 and 22 located on the slide 
should be smaller than the diameter of the channels 9a to 9c in the 
direction of displacement of the slide 10, to guarantee that each of the 
channels 9a to 9c is connected to the line 6 of the low-pressure reservoir 
and/or to the connection 5 of the pressure source or pump in any position 
of the slide 10. 
Should the slide 10 ever be incapable of following a lifting movement of 
the output or actuating member 18 of the electromagnet 19 to the right in 
FIG. 2 because of sluggishness or jamming, all the channels 9a to 9c are 
nevertheless relieved of pressure because, once again, the safety relief 
valve 15/16 is opened in the same way as was explained previously with 
reference to FIG. 1. Insofar as channels 9a to 9c cannot communicate with 
the line 6 leading to the low-pressure reservoir because of the particular 
blocked position of the slide 10, a passage to the line 7 leading to the 
low-pressure reservoir is then provided via the slide bores 13 and 14 by 
means of the open safety relief valve. 
In contrast to the arrangement illustrated in FIG. 2, as appropriate, 
annular grooves corresponding to the annular grooves 3 and 4 in FIG. 1 can 
be arranged on the valve-housing bore 2 in the region of the openings of 
the lines, channels or connections 5, 6 and 9a to 9c. 
Although the invention has been described and illustrated in detail, it is 
to be clearly understood that the same is by way of illustration and 
example, and is not to be taken by way of limitation. The spirit and scope 
of the present invention are to be limited only by the terms of the 
appended claims.