Power steering hydraulic system with a low pressure expansible reservoir

A power steering system has a pump, a steering gear and pressure and return passages. The pump does not include a cover member which conventionally provides space for the storage of excess fluid. The return passage has an expansible chamber included therein which accommodates the fluid volume change within the system resulting from fluid temperature changes thus permitting hermetic sealing of the system. An aspirator can also be included within the expansible chamber to improve the inlet pressure condition at the pump.

This invention relates to power steering systems and more particularly to 
hermetically sealed power steering systems having an expansible fluid 
storage chamber. 
Conventional power steering systems include a pump member with cover such 
as shown in U.S. Pat. Nos. 3,253,548 issued to Zeigler et al, May 31, 
1966, and 3,207,077 issued to Zeigler et al, Sept. 21, 1965, and assigned 
to the assignee of the present invention. The cover for such pumps 
includes a cap which is removable to permit fluid to be added to the 
system and is vented to atmosphere so that the fluid contained therein can 
expand and contract in response to temperature changes. 
The present invention utilizes some of the components of a conventional 
power steering system such as the pumping components (cam ring, vanes, 
etc.) and flow control valve shown in the above-mentioned United States 
patents. However, the vented reservoir is omitted with the present system 
and temperature change induced volume changes within the system are 
accommodated by an expansible storage chamber disposed in the low pressure 
or return line of the system. 
In a system incorporating the present invention, the fluid is delivered 
from the pump to the steering gear and from the steering gear the fluid is 
returned to the pump through the expansible chamber. To improve the inlet 
pressure at the pump, an aspirator can be included in the expansible 
chamber. It is well known that aspirators will function to increase the 
volume of fluid downstream from the throat of the aspirator. 
It is an object of this invention to provide an improved power steering 
system which is hermetically sealed and has an expansible chamber disposed 
in the low pressure portion thereof to accommodate fluid volume changes 
resulting from fluid temperature changes. 
It is a further object of this invention to provide an improved power 
steering system which is hermetically sealed and has an expansible chamber 
disposed in the low pressure portion thereof to accommodate fluid volume 
changes resulting from fluid temperature changes and an aspirator is 
disposed within the expansible chamber to increase the inlet pressure at 
the pump.

Referring to the drawings, wherein like characters represent the same or 
corresponding parts throughout the several views, there is seen in FIG. 1, 
a hydraulic pump generally designated 10 which is adapted to be driven by 
an engine, not shown. The pump 10 delivers fluid under pressure to a 
steering gear generally designated 12 through a hose or passage 14. Fluid 
returning from the steering gear, at low pressure, is directed through a 
hose or passage 16 to an expansible chamber 18. The fluid in the 
expansible chamber 18 is directed to the pump 10 through a hose or passage 
20. The steering gear 12 is assembled in a vehicle in a conventional 
manner to provide vehicle steering in a well known manner. The expansible 
chamber 18 is secured to a vehicle panel 22 by a bracket 24. The vehicle 
panel 22 can be any of the available panels such as the engine compartment 
wall or inner fender liner. 
As can be seen in FIG. 2, the expansible chamber 18 has a bellows-shaped 
body 26 which is connected to the hose 16 by a cylindrical passage 28 and 
is connected to the hose 20 through a cap member 30. The cap member 30 is 
secured to the bracket 24 by a fastener 32 which also seals an opening 34 
formed in the cap member 30. The opening 34 permits the power steering 
system to be filled with hydraulic fluid at assembly after which the 
opening 34 is sealed by the insertion of fastener 32. 
As is well known in power steering systems, the hydraulic fluid within the 
system operates at a wide range of temperatures which results in an 
increase in volume as the temperature rises and a decrease in volume as 
the temperature is reduced. The bellows 26 is expansible and can therefore 
accommodate the volume changes which occur within the system so that 
venting to atmosphere is not necessary. 
FIG. 3 shows another embodiment of an expansible chamber generally 
designated 18a. The expansible chamer 18a includes a generally cylindrical 
outer housing 36 made of expansible material such as rubber. The housing 
36 is secured to a fitting 38 which in turn is connected to the hose 16. 
The fitting 38 is also connected to a passage or tube 40 which is disposed 
substantially parallel to the walls of housing 36. The housing 36 is also 
connected to an outlet fitting 42 which is adapted to be connected to the 
hose 20. The outlet fitting 42 has formed therein a passage 44 which is 
coaxially aligned with the passage 40 and which passage 44 is also in 
communication through a frustoconical section 46 with the interior of 
housing 36. 
As fluid returning, from the steering gear 12, to the pump 10 flows through 
passage 40 and into passage 44, the frustoconical section 46 cooperates 
therewith to form an aspirator such that a low pressure region is created 
substantially adjacent the intersection of passage 44 and frustoconical 
section 46 so that the fluid within the housing 36 and external of the 
passage 40 is drawn into passage 44, in a well known manner, to provide a 
supercharging effect on the pump 10 which is located downstream of the 
aspirator. The housing 36 will expand and contract to accommodate volume 
changes which result from temperature changes in the hydraulic fluid 
during power steering operation. 
There is shown in FIG. 4 a further embodiment of an expansible chamber 
generally designated 18b, which includes an expansible cup shaped body 48, 
a funnel shaped outlet fitting 50 and an inlet fitting 52. A passage 54 is 
secured in the inlet fitting 52 and terminates at an end 56 within the 
flared portion 58 of outlet fitting 50. The other end 60 of passage 54 is 
adapted to be connected to hose 16 and the outlet fitting 50 is adapted to 
be connected to the hose 20. The inlet fitting 52 has an opening 62 which 
is maintained closed and sealed during operation by a fitting 64. However, 
at assembly, the fitting 64 can be removed to fill the system with 
hydraulic fluid. The passage 54 and funnel shaped outlet fitting 50 
cooperate to form an aspirator which operates in a manner similar to that 
described above in FIG. 3. The expansible cup shaped body 48 will expand 
and contract to accommodate volume changes which result from temperature 
changes.