Patent Application
20050087067
This invention relates to vacuum brake boosters, and more particularly to a vacuum brake booster having diaphragm supports attached to a power piston for sealing high and low pressure cavities within the booster from one another.
Vehicles such as automobiles, trucks, buses, and motor homes typically include a dashboard at the front of the passenger compartment, having a power brake booster on the front of the dashboard connected by a push rod to a brake pedal mounted on the rear of the dashboard in the passenger compartment. Such power brake boosters typically include a power piston that is sealed to the inside of a booster housing by one or more rolling diaphragms.
Extending radially outward from the power piston 116, in the secondary chamber 114 of the housing 102, is a secondary diaphragm support 122. In similar fashion, a primary diaphragm support 124 extends radially outward from the power piston 116 in the primary chamber 112. The primary and secondary diaphragm supports 122, 124 are fixed to the power piston 116 and move axially along an axis of motion 126 with the power piston 116.
A flexible rolling secondary diaphragm 128 has an outer periphery sealed to the inner walls of the secondary chamber 114 of the front housing 106, an inner periphery sealed to the power piston 116, and a skirt extending along the secondary diaphragm support 124 between the inner and outer peripheries of the secondary diaphragm 128, to thereby form a secondary low pressure chamber 130 between the secondary diaphragm 128 and the front wall 132 of the front housing 106 and a secondary high pressure chamber 134 between the secondary diaphragm 128 and the divider 110.
A flexible rolling primary diaphragm 136 has an outer periphery sealed to the inner wall of the primary chamber 112 of the rear housing 102, an inner periphery sealed to the power piston 116, an inner periphery sealed to the power piston 116, and a skirt extending between the inner and outer peripheries of the primary diaphragm 136, along the secondary diaphragm support 122, to thereby form a primary low pressure chamber 138 between the primary diaphragm 136 and the divider 110, and a primary high pressure chamber 140 between the primary diaphragm 136 and the rear wall 142 of the rear housing 102.
One or more air tubes 144 extend through the primary low pressure chamber 138 to connect the primary and secondary high pressure chambers 140, 134. The primary and secondary diaphragms 136, 128 include integrally formed grommets that provide a sliding seal between the air tubes 144 and the primary and secondary diaphragms 136, 128. The primary and secondary low pressure chambers 138, 130 are connected by holes 146 passing through the power piston 116.
The booster 100 includes valve elements, indicated generally by arrow 148, operably attached to the push rod 118 within the power piston 116, for selectively connecting all four chambers 138, 140, 130, 134 (i.e. the primary low pressure, secondary low pressure, primary high pressure, and secondary high pressure chambers) to a source of vacuum (not shown), such as the interior passages of an engine intake manifold, when the brake pedal 120 is not depressed. When the brake pedal 120 is depressed, the push rod 118 moves the valve elements 148 to a position where the primary and secondary low pressure chambers 138, 130 remain connected to the source of vacuum, but the primary and secondary high pressure chambers 140, 134 are connected to atmospheric air pressure around the brake booster 100.
The difference in pressure between the atmospheric pressure operating against the rear side of the primary and secondary diaphragms 136, 128, and the vacuum operating against the front side of the primary and secondary diaphragms 136, 128, generates a force against the primary and secondary diaphragm supports 124, 122 that drives the power piston 116 forward, (to the left in
When the brake pedal 120 is released, after a braking event, a booster return spring 154 disposed between the front housing 106 and the power piston 116 causes the power piston 116 to move back to poise position, illustrated in
It is desirable to reduce the complexity and cost of the booster 100 by eliminating the first and second diaphragm support retainers.
Large rolling diaphragms, having large thin wall sections, such as the primary and secondary diaphragms 136, 128 shown in
The present invention provides an improved booster, meeting the requirements discussed above, through use of a first diaphragm support having a central hole for passage therethrough of the power piston, and an integral locking collar disposed about the central hole for locking engagement with an annular groove in a booster power piston. A booster, according to the invention, may also include a second diaphragm support that is also locked into the annular groove in the power piston by the integral locking collar on the first diaphragm support.
The locking collar of the diaphragm support may include one or more spring tangs that expand for sliding the first diaphragm support along the power piston, to position the locking collar in the annular groove, and spring back for engaging and locking the first diaphragm support into the annular groove of the power piston.
A diaphragm support, according to the invention may include an imperforate, generally annular plate extending radially outward from the power piston and defining an outer periphery thereof adapted for fixed attachment of a seal for sealing a juncture between the outer periphery of the first diaphragm support and a booster housing of the booster. The booster may include a seal in the form of a rolling diaphragm having an internal bead thereof for attachment to the outer periphery of the diaphragm support and an external bead thereof adapted for attachment to the booster housing.
The present invention may also take the form of a method for assembling a booster or a power piston apparatus, according to the invention.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.
The booster housing 12 includes a rear housing 16, adapted for attaching the booster 10 to a panel (not shown), a front housing 18, adapted for attachment of a master cylinder (not shown), and a divider 20. The front and rear housings 18, 16 and the divider 20 are all joined and sealed from the environment at a common juncture 22 of the booster housing 12. The booster housing 12 defines a longitudinal axis 25 of the booster 10.
The power piston apparatus 14 includes a booster power piston 24, a secondary diaphragm support 26, a diaphragm support seal 28, and a primary diaphragm support 30 having an integral locking collar 32 for engaging an annular groove 34 in an outer surface 36 of the power piston 24 and clamping radially inner edges of the primary and secondary diaphragm supports 26, 30, with the diaphragm support seal 28 therebetween, in the annular groove 34.
The booster power piston 24 is mounted within the booster housing 12 for movement along the longitudinal axis 25 of the booster 10, and defines a radially outer surface 36 thereof including the annular groove 34 for receiving the integral locking collar 34 of the primary diaphragm support 30.
As shown in
The term imperforate, as used herein with respect to the primary and secondary diaphragm supports 30, 26, means that once the booster 10 is assembled, the primary and secondary diaphragm supports 30, 26 define a barrier to air flow. In embodiments of the invention including tie rods extending axially through the booster housing 12, for example, the primary and secondary support diaphragms 30, 26 may include holes 44, 46, such as the ones shown in
The primary rolling diaphragm 42, as shown in
It will be recognized, by those having skill in the art, that the primary rolling diaphragm 42, and the secondary rolling diaphragm 64 (described below) of the present invention, are smaller in size than the rolling diaphragms used in prior vacuum boosters, and do not include large thin-walled areas. Also, the thinner areas of the primary and secondary rolling diaphragms 42, 64 of the present invention are located relatively close to the internal and external beads 50, 52, 66, 68 of the primary and secondary rolling diaphragms 42, 64. This construction results in rolling diaphragms 42, 64 that are more readily manufactured than prior rolling diaphragms, which had large thin-walled areas extending considerable distances beyond thicker-walled areas, and a construction which reduces the problems, discussed above, caused by hard particles of carbon black.
In the exemplary embodiment, the external bead 52 of the primary rolling diaphragm 42 is crimped into the common juncture 22 of the front and rear housings and divider 18, 16, 20, for sealing the common juncture 22. The outer periphery 40 of the primary diaphragm support 30, in the exemplary embodiment includes a formed annular groove for receiving and retaining the internal bead 52 of the rolling diaphragm 42. The internal bead 52 and outer periphery 40 may be sized so that the internal bead 52 is retained in the groove of the outer periphery by a radial interference fit. Other methods of attaching the internal bead 52 may also be used, in other embodiments of the invention, such as, rolling or crimping the outer periphery 40 around the internal bead 52, or adhesive bonding.
As shown, in
As shown, in
The secondary rolling diaphragm 64, as shown in
In the exemplary embodiment, the external bead 68 of the secondary rolling diaphragm 64 is crimped into a juncture 70 of the front housing 18 and the divider 20, for sealing the juncture 70 of the front housing 18 and the divider 20. The outer periphery 62 of the secondary diaphragm support 26, in the exemplary embodiment includes a formed annular groove for receiving and retaining the internal bead 66 of the secondary rolling diaphragm 64. The internal bead 66 and outer periphery 62 may be sized so that the internal bead 66 is retained in the groove of the outer periphery 62 by a radial interference fit. Other methods of attaching the internal bead 66 may also be used, in other embodiments of the invention, such as, rolling or crimping the outer periphery 62 around the internal bead 66, or adhesive bonding.
As shown in
Those skilled in the art will readily recognize that, while the embodiments of the invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. For example, the invention can be utilized in a tandem booster as shown in
The scope of the invention is indicated in the appended claims, and all changes or modifications within the meaning and range of equivalents are intended to be embraced therein.
