Method of assembling a hydraulic fluid accumulator

A method of assembling a hydraulic fluid accumulator in a bore defined in a housing structure is disclosed. The method includes (a) inserting an annular seal into a second bore portion of the bore so that the annular seal is positioned in contact with the first ledge, (b) inserting a piston into the bore so that the piston is located in a first bore portion of the bore as well as the second bore portion of the bore, and (c) inserting a cover having an annular rim into the bore so that (i) the annular rim is positioned in contact with the annular seal, and (ii) the annular seal is located in an annular space defined by the first ledge, the annular rim, the piston, and an internal wall of the housing structure that partially defines the second bore portion.

The present invention relates to hydraulic systems generally, and more particularly to apparatus and a process for making a hydraulic reservoir such as a fluid accumulator.

BACKGROUND OF THE INVENTION

Many known anti-lock devices operate by cyclically increasing and decreasing the braking force exerted on the wheels so that a wheel having a tendency to lock is permitted to re-accelerate back toward a speed corresponding to the speed of the vehicle. This is typically achieved by control valves alternately allowing fluid to flow out of and then into the brake cylinder to first lower and then raise the brake pressure in the brake system. Some anti-lock braking systems (ABS) employ a pump-back scheme where fluid is dumped from the wheel cylinder to a local accumulator and the same hydraulic fluid is re-supplied from the local accumulator to the brake pad actuators.

Most of such anti-lock braking systems are further capable of operating in a traction control mode (sometimes called “dynamic rear proportioning”). Traction control and anti-lock operation are both responses to aberrant vehicle wheel behavior. A traction control function is established by detecting conditions where the rotational speed of a first powered wheel substantially exceeds that of a second powered wheel. To provide a power balance in the operation of the vehicle, a braking force is applied to the powered wheel rotating at a higher speed to effectively transfer driving torque back to the other wheel that has better traction. Many anti-lock systems having such a traction control feature employ a motor and hydraulic pump or pumps which operate independent of the service braking system to supply fluid from a local accumulator to brake the wheel which has lost traction. The same local accumulator may be utilized during either mode of operation.

With additional sensors, such as accelerometers, monitoring a plurality of additional vehicle operating parameters, e.g., vehicle yaw, electronic stability programs (ESP) are providing enhanced vehicle safety. Like anti-lock and traction control, the ESP systems utilize hydraulic pumping units with one or more fluid accumulators responsive to the monitored parameters to selectively brake certain wheels and maintain vehicle control.

In all these systems, it is desirable to have an immediately available source of hydraulic pressure to selectively apply a corrective braking force in response to certain sensed anomalies and to provide a temporary storage location to which fluid may be vented. With new designs and additional features, it becomes increasingly important to minimize the size and weight of the pump/reservoir units and to adapt those units to a variety of specific configurations. For example, pistons of various axial lengths may be employed in a common diameter accumulator. Moreover, ease and economy of manufacture are important. Prior designs do not allow spacing the seal ring at an advantageous depth, therefore, the piston length and housing depth is unnecessarily long. The used material is not optimized.

The reservoir bore for ESP brake systems is sealed off by an elastomer seal ring and a staked, crimped or orbital riveted-in closing cover. The reservoir is typically a stroke piston design. The seal ring requires a groove for its retention. This groove is formed by a step in the reservoir bore that is machined into the reservoir bore, and the lip or rim of the closing cover. Due to the reservoir size it is highly desirable to be able to place the seal ring at any desirable depth in the reservoir bore to optimize material, stroke and design and therefore cost. It is also desirable that only one component to be used for the assembly. Two components, a cover and a spacer ring, are possible but would make the design and assembly unnecessary complicated and complex.

SUMMARY OF THE INVENTION

The present invention provides a unique design which allows the seal element to be placed at a step in the ESP housing at any advantageous depth. The collar of the closing cover is uniquely formed in the wall of the cover to allow the seal ring groove to be placed at any desirable depth in the bore. This allows optimizing the length and the stroke of the piston to reduce the size of the components, as well as minimizing the depth of the bore which results in a reduction of material required for the piston and the housing. This feature formed in the wall of the cover also eliminates the need for a separate spacer to be added to the assembly for the purpose of retaining the assembly into the housing.

The invention comprises, in one form thereof, a method of forming a cover and enclosing a piston and annular seal within a bore of a hydraulic reservoir by deep drawing a generally cylindrical cup from a single sheet of metal to have one open end with an annular rim for engaging one seal surface and one closed end, and bending and folding an intermediate portion of the cylinder to create a radially outwardly extending collar intermediate the ends. Thus, the collar is formed at a preferred axial location for accommodating the piston axial length. The step of bending and folding is performed at an axial location closer to the open end to accommodate axially longer pistons and further from the open end to accommodate axially shorter pistons. The bore may be counterbored at a greater diameter to a depth less than the bore depth to form a seal receiving ledge and an annular seal inserted into the bore to engage the seal receiving ledge. The cover open end is inserted into the bore to engage and position the seal in an annular groove defined axially between the cover open end and the seal receiving ledge and radially by the bore counterbore diameter, whereby the seal is appropriately located and retained within the bore. The bore may be counterbored at a second still greater diameter to a lesser depth to form a cover insertion limiting ledge and the bore deformed as by crimping to retain the cover at the insertion location.

Also in general and in one form of the invention, a method of assembling a hydraulic fluid accumulator in a pre-existing cylindrical bore of a predetermined diameter and depth, includes the selection a piston of a preferred axial length and fixed common diameter matched to the bore diameter and counterboring the bore at a greater diameter to a depth determined by the selected piston to form a seal receiving ledge. The annular seal is then inserted into the bore followed by the annular end of a cover which engages and positions the seal in an annular groove defined axially between the cover end and receiving ledge, and radially by the bore counterbore diameter, whereby the seal is appropriately located within the bore for the particular selected piston length. The selected piston and a bias spring are inserted into the bore after inserting the annular seal and prior to inserting the cover. The cover has an annular crimping flange located axially along the cover to match to a particular piston axial length.

An advantage of the present invention is material and component optimization of the components and housing size is achieved by placing the seal ring at an optimized depth in the reservoir bore.

Another advantage is that only one component rather than a separate spacing ring need be assembled.

A further advantage is that the seal groove can be placed at any depth by the closing cover extension and a simple stepped diameter in the housing, whereas in prior designs, the O-ring can be placed only on one location at the closing cover face.

Corresponding reference characters indicate corresponding parts throughout the several drawing views.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings and particularly toFIG. 1, there is shown a hydraulic pump unit11, for example, of an ESP system having a housing13with a pair of caps or covers15and17visible along one edge.FIGS. 2 and 3are orthogonal sectional views along a common accumulator or reservoir center line such as axis35. The housing contains two accumulators with an illustrative accumulator portion shown in greater detail inFIG. 4. The accumulator includes a piston19and a seal ring21positioned within a housing bore and enclosed by cover17.

ComparingFIGS. 4 and 5, the housing bore in which the piston19is positioned is generally cylindrical extending to a depth indicated by end23and of a diameter indicated by sidewall25. There is a counterbored region of greater diameter as indicated by sidewall29bored to a lesser depth forming a step or ledge at27. The ledge27receives the seal ring21and limits the depth to which the seal may be inserted into the bore. A still greater diameter counterbore forms sidewall31to a depth shown by the ledge33. This ledge33receives the cover flange or collar39, limits cover insertion into the bore, and properly locates the cover lip41to complete a groove in which the seal ring21resides. The cover is then retained in this location, for example, by crimping at41.

InFIG. 6, a typical accumulator spring37has been added. Spring37urges piston19upwardly as viewed. When pressure fluid is supplied to port59, the piston moves downwardly against the spring bias and fluid enters the accumulator to be later expelled therefrom by the force of the spring.FIG. 7illustrates an accumulator of lesser capacity having a shorter stroke piston43. ComparingFIGS. 6 and 7, it will be noted that the axial length of piston43is less than the axial length of piston19. The length of the piston43skirt is sufficiently short that the piston skirt would no longer engage the seal21in the location shown inFIG. 6. To compensate, seal45has been relocated to a greater depth in the housing bore as shown inFIG. 7. This relocation requires the ledge27ofFIG. 5to be deeper in the bore. Also, the rim41of cover17would not extend sufficiently far into the bore to appropriately confine the seal. Hence, cover47has been modified to provide rim49at an appropriate location to complete the seal45receiving groove.

The cover17ofFIGS. 2-6is shown separately asFIG. 8while the cover47ofFIG. 7is shown separately asFIG. 9. ComparingFIGS. 8 and 9, the cover ofFIG. 9is deeper and the separation between the flange51and rim49is greater, while the distance from the cup bottom or closed end to the flange remains unchanged. That the covers for theFIGS. 6 and 7accumulators need not be of different overall length is shown by cover53ofFIG. 10. Here, the flange55is located at an appropriate distance from rim57(the same distance as inFIG. 8) to provide proper seal seating and retention crimping in the accumulator ofFIG. 6. Of course, the cover53would extend further beyond the housing13than does the cover17. By this technique, the seal may be located axially as desired by appropriate boring of the depth of a ledge such as27and the separation between the cover flange such as55and cover rim such as57.

Formation and assembly of the reservoir and cover includes an initial boring of the housing19to a depth forming the cylindrical end23and sidewall25as seen inFIG. 5. A piston of a preferred axial length and a diameter matched to the sidewall diameter is then selected, that is, the specifications or parameters of piston to be employed are determined. Identification of a particular piston need not occur until assembly of that piston into the bore. The piston axial length determines the depth27to which a second larger diameter counterboring is performed to form a seal receiving ledge at27. After an annular seal21is inserted into the bore, the cover such as17,47or53having an annular end41,49or57is inserted into the bore to engage and position the seal in an annular groove defined axially between the cover end and receiving ledge, and radially by the bore counterbore diameter29, whereby the seal is appropriately located within the bore for the particular selected piston. Of course, the piston19or43and spring37are typically inserted into the bore after inserting the annular seal and prior to inserting the cover. The counterboring also includes counterboring the bore at a second still greater diameter forming sidewall31and to a lesser depth to form a cover insertion limiting ledge at33. The depth27of the greater diameter counterbore varies for various diameter pistons while the still greater diameter bore depth33is constant and independent of the piston selected. Finally, the bore is deformed as by crimping at41to retain the cover at the insertion location.

A cover having an annular crimping flange39,51or55located axially along the cover at a location matched to a particular axial length piston is formed by deep drawing a generally cylindrical cup from a single sheet of metal to have one open end with an annular rim for engaging one seal surface and one closed end, and bending and folding an intermediate portion of the cylinder to create a radially outwardly extending collar39,51or55intermediate the cover ends. The collar is formed at a preferred axial location for accommodating the piston axial length which is closer to the open end to accommodate axially longer pistons and further from the open end to accommodate axially shorter pistons. The bending and folding of a collar on deep drawn components are state of the art for assembly purposes. Similar designs and forming of a collar are known from, e.g., fuel damper housings.

As stated above, the housing13contains two accumulators with an illustrative accumulator shown in greater detail inFIG. 4. Another manner of describing the method of assembling the accumulator of the present disclosure is set forth below with reference to the flow chart200depicted inFIG. 11. Note the housing structure13defines a bore as shown inFIG. 5. As clearly shown inFIG. 5, the bore includes a first bore portion having a first diameter, (ii) a second bore portion having a second diameter that is greater than the first diameter, and (iii) a third bore portion having a third diameter that is greater than the second diameter. Also, as shown inFIG. 5, the housing structure13includes a first ledge27that partially defines the second bore portion, and a second ledge33that partially defines the third bore portion. With reference toFIG. 11, the method of assembling the accumulator includes the step202of inserting the annular seal21into the second bore portion so that the annular seal21is positioned in contact with the first ledge27. The method further includes the step204of inserting a piston19,43into the bore so that the piston is located in the first bore portion and the second bore portion as shown inFIGS. 4,6, and7. The method further includes the step206of inserting a spring37into the bore. Note that the piston19,43defines a first cavity, and a first end portion of the spring37is inserted into the first cavity of the piston19,43as shown inFIGS. 6 and 7. The method further includes the step208of inserting the cover17,43,53having an annular rim41,49,57into the bore so that (i) the annular rim41,49,57is positioned in contact with the annular seal21, and (ii) the annular seal21is located in an annular space defined by the first ledge27, the annular rim41,49,57, the piston19,43, and an internal wall of the housing structure13that partially defines the second bore portion. Note that the cover17,43,53defines a second cavity, and a first end portion of the spring37is inserted into the second cavity of the cover as shown inFIGS. 6 and 7. Note also that the housing structure13further includes the second ledge33that partially defines the third bore portion. The cover17,47,53further has a sidewall and an annular flange39,51,55extending outwardly from the sidewall. The step208includes positioning the cover17,47,53in the third bore portion so that the annular flange39,51,55contacts the second ledge33. The method further includes the step210of deforming the housing structure13so that a shape of the bore is altered and a retention portion is created as shown inFIGS. 4,6, and7. Note that, as shown inFIGS. 4,6, and7, the annular flange39,51,55of the cover17,47,53is interposed between the second ledge33and the retention portion.

Thus, while a preferred embodiment has been disclosed, numerous modifications will occur to those of ordinary skill in this art. Accordingly, the scope of the present invention is to be measured by the scope of the claims which follow.