Combination high pressure pump/attenuator for vehicle control systems

A combination high pressure pump/attenuator suitable for use in vehicle control systems employs a high pressure pump outlet check valve located in the attenuator cavity and compressively loaded against its seat by the compressive force of a volumetrically and axially compressible attenuator element. In one preferred embodiment, the check ball is replaced by a projection molded into the attenuating element itself.

TECHNICAL FIELD 
The present invention pertains to vehicle control systems, particularly 
those suitable for use in anti-lock braking systems and traction control 
systems. More particularly, the subject invention pertains to a 
combination high pressure pump/attenuator for vehicle control systems with 
smaller size and reduced part count and concomitant ease of assembly. 
BACKGROUND ART 
Anti-lock braking systems have now progressed to the point where they are 
standard on many vehicles. The use of traction control systems is now 
becoming increasingly widespread, and it is anticipated that their use 
would parallel that of anti-lock braking systems. In both systems, which 
may be termed "vehicle control systems," rapid deployment of brake 
calipers or brake shoes are necessary in order to perform the intended 
control function. In anti-lock braking systems, when locking of the wheels 
due to over-application of brake pressure or loss of traction due to the 
nature of the surface, i.e., gravel, ice, or snow, is encountered, the 
automotive braking system rapidly pulsates the brakes between an off and 
an on condition, allowing maximal retention of braking ability while yet 
retaining the ability to steer the vehicle in a stable fashion. In 
traction control systems, loss of traction in a driving wheel is countered 
by a momentary application of brake pressure, thus restoring traction. In 
either case, high pressure systems are desirable to affect the rapid 
changes necessary to achieve the desired control. 
During anti-lock operation, it is necessary to rapidly decrease brake 
pressure by pumping brake fluid from the brake cylinders back to the 
master cylinder. This is necessary both for decreasing brake pressures and 
for having this dumped fluid available for subsequent antilock cycles in a 
stop. The motor driven high pressure pump is actuated only when the need 
for high pressure brake releases is sensed by the circuitry associated 
with anti-lock braking system or traction control system, as the case may 
be. 
A typical anti-lock braking system is shown schematically in the 
above-referenced related patent application. In that system, hydraulic 
fluid from the brake pedal actuated master cylinder flows through a line 
through a normally open isolation solenoid valve to a brake caliper slave 
cylinder. Except for the presence of the additional normally open 
isolation valve, the system thus far described is similar to the normal 
braking system of the automobile. In an anti-lock brake system, detection 
of a lock condition actuates a high pressure pump and closes the solenoid 
actuated isolation valve. At the same time, a solenoid actuated hold/dump 
valve is opened, allowing pressure to bleed from the brake cylinder to the 
low pressure accumulator. The brakes are thus momentarily released. The 
low pressure accumulator allows quick initial dumping or decrease in brake 
pressure. The pump, however, empties the low pressure accumulator to allow 
continued decrease of brake pressure if needed and also pumps the brake 
fluid back to the master cylinder for subsequent needed antilock cycles of 
a stop. To reapply the brakes, pressure from either/or the master cylinder 
or the high pressure pump is diverted to the brake cylinder by opening the 
isolation valve and closing the hold/dump valve, once again increasing 
braking pressure. This cycle repeats itself rapidly as needed, resulting 
in rapid increases or decreases of brake pressure thus achieving maximal 
braking while avoiding a locked condition. Although this system is highly 
effective, it may be subject to noise and vibration due to the high 
pressure pulses emanating from the high pressure pump, as well as the 
pressure spikes and rebound pulses emanating from the isolation solenoid 
and the dump valves. In order to minimize these effects, it has proven 
useful to place an attenuator on the outlet side of the pump between the 
pump outlet and master cylinder. The combination of the compressible 
hydraulic fluid or elastomer within the attenuator cavity and a reduced 
diameter orifice adjacent thereto in the line leading therefrom, 
attenuates the pressure pulses and vibrations emanating from the pump. 
Commonly used hydraulic systems in anti-lock and traction control systems 
utilize split or divided systems in which one portion of an opposed, dual 
piston pump supplies hydraulic fluid to two of the vehicle wheels, while 
the other piston of the high pressure pump supplies high pressure 
hydraulic fluid similarly to the other half of the braking system, i.e., 
the other two wheels. The braking circuit to each wheel is generally as 
described above, with the addition of integrated traction control 
requiring basically additional control valves and a high pressure 
accumulator associated with the hydraulic circuits in that portion of the 
system. 
The various control valves, generally solenoid actuated valves, and the 
attenuators, low pressure accumulators, high pressure accumulators, if 
any, and high pressure pump elements are all commonly assembled in a 
single housing of extruded aluminum into which the various components are 
located in appropriately machined bores. Additional internal bores provide 
the requisite hydraulic circuit interconnections. Even though the body or 
housing of the hydraulic control unit is made of light alloy material, its 
size, and the size of the components located therein, many of whose parts 
are constructed of steel, still represent a significant amount of weight 
in a vehicle. Significant weight savings can be accomplished by reducing 
the overall size of the control unit, and additional savings can be 
effected by reducing the weight of the component parts of the various 
accumulators, attenuators, solenoids, and high pressure pump components. 
In addition to the desirability of effecting weight savings by reduction of 
size and number of components, it is further desirable to reduce 
manufacturing costs by both reducing the number of components as well as 
aiding in ease of assembly of the components. 
SUMMARY OF THE INVENTION 
The present invention pertains to a combination high pressure 
pump/attenuator useful in vehicle control systems. 
More particularly, the present invention pertains to a combination high 
pressure pump/attenuator wherein the outlet check ball of the high 
pressure pump is moved to and incorporated in the attenuator, thus both 
reducing part count and increasing ease of assembly of the high pressure 
pump assembly. Due to the revision of the location of the outlet check 
ball, the length of the hydraulic control unit as measured through the 
axis of the pump pistons is reduced by a total of approximately 16 mm, a 
substantial decrease in size, thereby resulting in an approximate 16% 
decrease in pump element length and allowing a weight reduction of about 
15% and a volume reduction of about 15%. 
Further, unlike conventional pump outlet check valves which have helical 
metal springs, the outlet check ball of this invention, whether it is a 
separate ball or an integral molded elastomer ball, is preloaded by the 
compressive elastic force of the elastomeric attenuator element itself. 
All the attenuator element materials recommended herein have a beneficial 
hysteresis that damps check ball rebound and effectively eliminates check 
ball bouncing which can be a source of noise in antilock systems and in 
piston pump systems. 
The subject invention further pertains to a combination high pressure pump 
for use in vehicle control systems comprising a reciprocable piston member 
sealingly engaged in a bore, and providing a high pressure fluid pump 
cavity; a pump inlet passage capable of supplying fluid to the high 
pressure fluid cavity; an attenuator containing an elastomeric attenuating 
element positioned in an attenuator cavity and having an outlet orifice; 
an attenuator inlet passage connecting the attenuator cavity with the pump 
cavity, the diameter of the inlet passage being larger than the diameter 
of the outlet orifice; and a check valve located within the attenuator 
cavity adapted to allow one way passage of high pressure fluid from the 
high pressure pump to the attenuator. 
The above objects and other objects, features and advantages of the present 
invention are readily apparent from the following detailed description of 
the best mode for carrying out the invention when taken in connection with 
the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
In FIG. 1, as concerns the pump piston assembly, generally designated 10, 
pump piston 11 is urged outwardly by piston return spring 13 against an 
electric motor-driven eccentric (not shown). Upon being driven inwardly by 
the eccentric, high pressure fluid in fluid reservoir 15 exits through 
outlet check ball 17 which is urged against its seat by check ball spring 
19, both located in sleeve 20. High pressure fluid exits via passages 21 
through bore 23 to volumetrically compressible attenuator, generally 
designated 25. The attenuator comprises an elastomeric or other 
volumetrically compressible member 27 residing in cavity 29, and bonded to 
a cap 28 which is held in place by a snap ring 26. High pressure fluid 
pulses cause elastomeric member 27 to be volumetrically compressed. The 
volumetric compression of this member, which is a function of its bulk 
modulus, together with the energy dissipating and damping characteristics 
of the reduced diameter exit orifice 31 causes high pressure pulses and 
their harmonics to be attenuated as the fluid passes from cavity 29 
through one or more radially extending grooves 32 in the annular lip of 
the member 27 to orifice 31. 
During the return stroke of piston 11 against the rotating eccentric, 
facilitated by return spring 13, the outlet check valve 17 closes and 
fluid from the low pressure accumulator (not shown) on the inlet side of 
the pump, may enter the pump cavity through port 33 and through radially 
connecting passage 34 in the piston, through inlet bore 36 and past inlet 
check ball 35 which is only lightly urged against its seat by inlet check 
ball spring 37. The piston is sealed against sleeve 39 by dynamic seal 41, 
shown here schematically as an O-ring. At 43, 45 and 47, are additional 
sealing O-rings necessary to seal the sleeves 20 and 39 with respect to 
the light alloy control unit housing 51, and at 49 is an additional seal 
to seal threaded retainer sleeve 53 to the housing. Sleeve 20 includes 
radial grooves at the end abutting sleeve 39 to provide fluid 
communication from outlet passage 21 to attenuator inlet bore 23. Sleeve 
55 forms the high pressure fluid pump cavity. 
FIG. 2 illustrates one embodiment of the present invention. In FIG. 2, the 
four sleeves of the pump, inclusive of the retainer, have been replaced 
with but a single sleeve. Like elements are numbered as in FIG. 1, and 
perform like functions. Sleeve 57 replaces sleeves 20, 39, 53 and 55, and 
no longer carries an outlet check valve assembly. In operation, the 
outwardly moving piston on the pump stroke forces high pressure fluid 
through bore 23, lifting outlet check valve 17, compression loaded by the 
volumetrically compressible and resilient attenuator element 59 against 
its seat, and flows into attenuator cavity 29 as substantial portion of 
the side area of the resilient attenuator element 59 as well as the area 
of one of its two ends being exposed to the fluid. The high pressure 
pulses are partially absorbed by the volumetric compressibility of 
attenuator element 59 and damped by energy dissipative reduced diameter 
orifice 31. Further details on the specifics of the volumetrically 
compressible attenuator per se, e.g. without check ball 17, are disclosed 
in copending application Ser. No. 08/163,658, as referenced earlier. 
As a result of the relocation of the outlet check ball to the attenuator, 
the number of machined sleeves has been reduced from four to one, with 
retention of the device in the housing made possible by means described 
earlier in regard to FIG. 1. In addition, three sealing O-rings 43, 45, 47 
are required instead of four, and the outlet check ball spring has been 
eliminated. 
Also, the length of the hydraulic control unit as measured through the axis 
of the pump piston has been reduced considerably. For example, comparing 
FIG. 1 to FIG. 2, the axial length taken up by the check ball 17, spring 
19, and end cap or sleeve 20 has been eliminated. The length of piston 11, 
pump chamber or reservoir 15, and enclosing sleeve 55, 57 virtually remain 
the same. Thus, the overall reduction in axial length is on the order of 
16%, with a near equal reduction in volume and weight of the entire 
hydraulic control unit. 
The outermost end of the movable piston member 11 bears against a 
conventional piston driving means as described earlier. 
As a matter of further detail, it will be noted that the return spring 13 
and the inlet check valve spring 37 are concentrically nested, one within 
the other, with innermost spring 37 being seated within a pocket 61 in 
sleeve 57 and spring 13 being seated on a collar 63 at the end of piston 
11. The cylindrical pump chamber 15 is sized to closely receive spring 13 
to preclude spring misalignment, as is well known to those skilled in the 
art. Sleeve 13 includes a stop shoulder 65 locating the pump assembly 10 
fixed relative to the housing against a corresponding annular seat formed 
within the housing piston bore. 
Check ball 17 may advantageously be made of material such as nylon or other 
thermoplastic, thus further reducing noise and vibration which would 
otherwise occur when a steel or ceramic ball hits its seat. Moreover, the 
separate check ball itself may be eliminated, thus further reducing part 
count and assembly time, by molding the check ball as a protrusion of the 
elastomeric attenuator element. Three embodiments of such a combination 
elastomeric attenuator element/check device are shown in FIGS. 3a, 3b, and 
3c, with the projecting check valve portion of the compressible attenuator 
member 27 being identified as 18. 
In operation, the combination high pressure pump/attenuator with revised 
check ball location serves to attenuate and damp not only the high 
pressure pulses, vibrations, and harmonics at the output of the 
attenuator, i.e., the master cylinder line, but also attenuate and damp 
high pressure pulses at the pump cavity itself, thus reducing noise 
causing shocks and vibrations on the pump bearing and motor. 
FIG. 4 illustrates a bar graph showing the pressure pulses which occur 
during dump cycles. The first set of bars, those closest to the pressure 
axis, show, from front to back, the first and second harmonics at the 
master cylinder and the first and second harmonics at the high pressure 
pump as are produced in a standard hydraulic fluid filled attenuator. The 
second and third sets of bars illustrate the improvement in lowering 
pressure pulses using elastomeric attenuator members of 40 durometer butyl 
rubber and 45 durometer silicone rubber, respectively. These materials 
have a bulk modulus (i.e. a volumetric compressibility) of 325,000 and 
192,000 psi, respectively. My invention, as it pertains generally to the 
attenuator has been found to work best in vehicle ABS systems where the 
bulk modulus is selected from a range of about 350,000 psi to as low as 
possible. The upper limit is approximately equal to the bulk modulus of 
the brake fluid in the system. The most practical lower limit to date 
based on available materials is about 290,000 psi. Silicone rubber, while 
compatible with some brake fluids, and having a desireable lower bulk 
modulus of about 190,000 psi, would be considered incompatible with a 
silicone based brake fluid. 
Having now fully described the invention, it will be apparent to one of 
ordinary skill in the art that many changes and modifications can be made 
thereto without departing from the spirit or scope of the invention as set 
forth herein.