Internal Piston Press

Technical Field

This invention relates to small tools and more particularly to small tools useful to the automotive industry in the assembly and repair of disc brake equipment.

Background Art

The prior art, U.S. Patent No. 3,835,522, provides a tool for retracting disc brake pistons, specifically in the operation of replacing worn disc brake pads. The tool comprises two thin plates, one of which plates is immovably fixed to a guide rod while the other plate is secured to a member which is slideably mounted on the guide rod. The force required to retract the pistons is applied by means of a screw whose line of action is offset from the line of action of that force applied to the piston faces themselves through the two thin plates. The thin plates may thus be subject to bending stresses that may become particularly significant when the pistons are subject to binding frictional forces within the walls of their cylinders.

Disclosure of Invention

In accordance with the present invention, an internal piston press is provided in which a piston, having moved to some position not fully within its cylinder, may be retracted in a safe, easy and uncomplicated manner. A tool piston plate and a tool caliper plate, the expanding members, are caused to move in a direction apart from each other so as to force the piston fully into its cylinder.

The inventive device exhibits the notable advantage that the line of action of the force causing retraction of the piston into its cylinder coincides with the line of action of the applied force. For example, in a one- cylinder system, the tool piston plate will bear against the piston and the tool caliper plate will bear against the caliper with the actuating member, an expander bolt, acting between them and along the central axis of the piston and cylinder. In operation, the internal piston press tool becomes wholly contained within the caliper space so that it may be applied in a situation in which space is at a premium.

An alignment utility, a dowel pin centrally secured in the tool piston plate and insertable in a centrally axial dowel aperture provided in the expander bolt, prevents the tool from becoming canted with respect to the piston and caliper faces thus preventing scoring of the cylinder wall by the piston. Fabrication of the tool piston plate and tool caliper plate, for example, may be had by machining from soliα metal , however, it has been found to be advantageous to construct these parts from plastic material, for example, from molded glass fiber-reinforced plastic material such as Fiberglas lay-up or similar

material so as to ensure, adequate strength while at the same time assuring that the piston face will not be scored by these elements of the tool.

Further features and advantages of the inventive device will be more fully apparent to those skilled in the art to which the invention pertains from the ensuing Best Mode detailed description thereof, regarded in conjunction with the accompanying drawing wherein like reference characters refer to like parts throughout.

Brief Description of Drawings

The details of the invention will be described in connection with the accompanying drawing, in which:

Fig. 1 is an idealized schematic showing a disc brake caliper in relation to a wheel disc.

Fig. 2 is a cross sectional view taken along the sight 1ines 2 - 2 of Fig. 1.

Fig. 3 is a cross-sectional view in profile showing the internal piston press tool in place in a disc brake caliper.

Fig. 4 is an exploded perspective view showing the parts of the internal piston press as disassembled.

F g. 5 is a cross-sectional view in profile like Fig. 3 showing the internal piston press in expanded configuration so as to retract the disc brake piston into its cylinder.

Best Mode for Carrying Out the Invention

Although specific embodiment of the invention will now be described with reference to the drawing showing application of the invention to a one-piston disc brake system, it should be understood that the embodiment is by way of example only and merely illustrative of an application of the principles of the invention. Various changes and modifications, obvious to one skilled in the art to which the invention pertains, are deemed to be within the spirit, scope and contemplation of the invention as further defined in the appended claims.

Referring to Fig. 1 with greater particularity, a disc brake caliper 20 is shown in its relation to wheel brake disc 27, shown in phantom outline. Disc brake piston 22 is further shown in its relation to a pad support plate, identified by the numeral 25.

In Fig. 2, the brake caliper 20 is shown in cross- section as taken along sight lines 2 - 2 of Fig. 1, so as to clearly show in profile the position of disc brake piston 22 within fluid cavity or cylinder 21. A fluid line 19 is illustrated showing the means by which brake fluid pressure may be transmitted into fluid cavity or cylinder 21 so as to operate disc brake piston 22 when brake pressure is to be applied to the wheel brake disc 27 shown in phantom outline. The lip seal 23 is commonly provided in the form of an O-ring so as to prevent brake fluid from escaping from the fluid cavity or cylinder 21. Brake pads 24, shown as situated on each side of wheel brake disc 27, are applied to that disc by means of the thrusting of disc brake piston 22 out of its fluid cavity or cylinder caused by transmission of increased pressure

in fluid line 19 into fluid cavity 21. These brake pads 24 are shown as attached to first pad support plate 25 on brake caliper 20 and second pad support plate 26 on the face of piston 22.

Referring now to Fig. 3, the caliper 20 is illustrated after having had brake pad support plates 25 and 26 removed and the internal piston press tool now situated in place preparatory to causing the retraction of disc brake piston 22. The threaded expander bolt 16 is shown as fully threaded into threaded metal insert boss member 11 of tool caliper plate 12 with tool piston plate 14 attached through bolt head 18 by means of dowel 15. Dowel

15 is inserted through bolt head 18 and into expander bolt

16 by way of dowel hole 17 (Fig. 4). Thus, continued alignment of piston plate 14 and caliper plate 12 is maintained.

Fig. 4 shows the internal piston press in exploded detail. The simplicity of the tool is abundantly evident. The tool consists essentially of only three relatively movable members. The first member is a tool caliper plate 12 having a threaded metal insert boss member 11 fixedly- inserted into boss 29. The tool caliper plate 12 may be fabricated from all metal or preferably from a plastic material such as a molded glass fibei—reinforced plastic material similar to Fiberglas or the like and may then advantageously employ structural strengthening ribs 28. In making the tool piston plate 14 and the tool caliper plate 12 from Fiberglas, or the like, scoring of the caliper and piston faces may be prevented.

A threaded expander bolt 16 having a bolt head 18 and a centrally axial dowel receiving aperture 17 drilled along

the central axis thereof comprises the second member. The expander bolt 16 has threads that are threadably attachable to the tool caliper plate 12 by means of threaded metal insert boss member 11.

The third member, tool piston plate 14, has a centrally located, perpendicular dowel 15 for insertion into dowel hole 17 of expander bolt 16. The insertion of dowel 15 provides for the continued alignment of the tool so as to prevent the application of any sideways or shearing forces when retracting the piston 22 into its cylinder 21. Rotation of expander bolt 16 in a direction threading it out of threaded metal insert boss member 11 causes tool caliper plate 12 and tool piston plate 14 to move apart from each other so as to exert an axial force against any constraint, for example, the resistance of piston 22 to a force tending to move it into fluid cavity or cylinder 21.

In Fig. 5, the internal piston press, denoted generally by numeral 10, is shown in its expanded configuration after having forced retraction of disc brake piston 22 into its cylinder 21 by rotation of expander bolt 16 in a direction tending to remove that bolt from the tool caliper plate 12 through threaded metal insert boss member 11. Continued expansion of the internal piston press tool may be provided by means of continued rotation of expander bolt 16. A set of longer bolts having dowel holes 17, not specifically shown, may be provided so as to effectuate greater distances traveled when more retraction is needed. It is also to be noted that in double piston systems, as provided for some disc brake applications, the internal piston press will provide for the retraction of both pistons into their related cylinders in the same manner.

Thus there has been described an internal piston press that will provide for the retraction of a piston into its cylinder. Great improvements in usability, flexibility, ease of operation, safety and economy have been provided through the novel advantages of this invention.

It is pointed out that although the present invention has been shown and described with reference to a particular embodiment, nevertheless various changes and modifications, obvious to one skilled in the art to which the invention pertains, are deemed to lie within the purview of the invention.

Industrial Applicab lity

The present invention finds application wherever opposing pistons must be retracted for any purpose and where a piston works against an immovable member, for example, to press upon an element in between. Configurations wherein there is a necessity to push elements apart for some form of maintenance or the like. The most obvious application appears to lie with the embodiment described.