Field of Invention:
This invention in general relates to automobile industries and in particular relates to auto adjuster. More particularly this invention relates to wheel cylinder based auto adjuster incorporated within the wheel cylinder housing.
Background of Invention:
As the friction material in a drum brake wears off due to repeated brake applications, the brakes must be constantly readjusted to the set diameter; otherwise, the pedal travel will increase, giving an unsafe feeling for the driver. Conventionally, in a drum brake without auto adjuster, the brakes are manually inspected at regular periodic intervals and are manually adjusted. This type of manual adjustment of brakes involves time and hence money. If there were an automatic adjustment feature in a drum brake, which would sense the wear of the friction material and compensate for the wear without having to externally meddle with the brakes, such a feature would reduce down time and hence save a lot of money. Moreover, if this feature would provide a compensation (or adjustment) in such a way that it would maintain constant clearance between the drum and the shoe at all times, the pedal travel will fall within a narrow band, which is a desirable feature
Currently Available Automatic Adjusters for Drum Brakes:
In small size brakes that are normally fitted in cars and SUVs, there are a wide range of automatic adjusters that compensate for the wear of the friction material. Most of these are based on converting the excess travel of the wheel cylinder apply piston (due to lining wear) to linear length increase of an adjustment screw that provides for the wear of the friction material. Whereas such an arrangement might work in a conventional car brake system, in commercial brakes (for brake sizes in excess of 300mm), mounting of such an adjustment system poses

installation difficulties. Secondly, these commercial vehicles are used for an assortment of purposes, including and not limited to sand transport, water transport, etc. Typically, the drivers and the owners of these commercial vehicles are not well informed about maintenance of vehicle in general and brakes in particular. They normally submerge the vehicle up to its cab bottom in water to clean the under body of the vehicle. This means that it is quite likely that water or slush might enter the brake system and cause havoc in its functionality. Therefore, it is desirable that we have an automatic adjustment feature that is concealed and protected from these operating parameters. In hitherto available commercial vehicle brakes, no automatic adjustment feature is available in India. A survey of commercial vehicle drum brakes worldwide, indicate that except for Akebono, no other manufacturer has introduced an automatic adjustment feature for their drum brakes. Even in the Akebono design, the automatic adjuster is external to the wheel cylinder and hence not concealed. Therefore that design, if implemented, would be subject to the same external parameters as the current brakes. In light of the above scenario, an automatic adjuster for commercial vehicle brakes with the following features is the order of the day.
1. An automatic wear adjustment feature for a commercial vehicle brake that compensates for the wear of the friction material, without any manual external intervention.
2. This automatic wear adjustment feature must be concealed so that it is not exposed to water and slush in which these brakes sometimes operate.
3. They must also contain a manual adjustment feature that can be used at will to override the automatic adjustment feature. This feature would help easily dismount the brake in case of a jam.

Description of Drawings:
Now the invention will be described in detail with reference to drawings which accompany the complete specification :
Figures 1A and IB of the drawing shows in elevation and in section the
component details of wheel cylinder based auto adjuster.
Figures 2A, 2B and 2C of the drawing shows in elevation adjuster and
adjusting screw details of the device according to invention.
Figures 3A and 3B of the drawing shows in elevation the construction
details of plunger and adjuster according to invention.
Figures 4A and 4B of the drawing shows in elevation the construction
details of cam screw according to invention.
Figure 5 of the drawing shows in elevation the construction details of
drive ring
Figures 6A and 6B of the drawing shows in elevation the construction
details of wave spring
Figures 7A and 7B of the drawing shows in elevation the construction
details of lock ring
Figures 8A and 8B of the drawing shows in elevation the construction
details of backlash
Figure 9A and 9B of the drawing shows the working principles of the
invention

Description of present Invention:
Our present invention incorporates the above requirements. Our present invention houses the entire automatic adjuster mechanism inside the wheel cylinder, without disturbing the normal wheel cylinder function. Even though multiple variations of the same concept have been developed, we describe here only that concept that went into production. Since the entire mechanism is housed inside the wheel cylinder, there is no possibility of this mechanism coming in contact with water and slush. The mechanism also contains a manual override feature, which can be used to retract the adjuster to the original position.
The accompanying pictures show the working of the auto adjustment mechanism. It comprises of sixteen parts as shown in the accompanying FIG |. The conventional wheel cylinder plunger (6) (alternatively called piston as well) is modified to have a helical groove on its surface (as shown in the FIG 4, Fig 9 and Fig 10). This helical groove mates with a cam screw (5) that is mounted externally from wheel cylinder casting (1) through threads. Inside of the wheel cylinder plunger (6), in a specially shaped grooves are housed are rollers (8) of very high hardness and these rollers are held in the smaller end of these grooves by special springs (13). These springs (13) look like accordion and hence the name accordion springs (13). These rollers act like bearings between the wheel cylinder plunger and the adjusting piston (alternatively called adjuster) during forward motion of the wheel cylinder plunger. During reverse traverse of the wheel cylinder plunger, these rollers move to the smaller radial clearance portion of the wedge and thereby rigidly connect the adjusting piston with wheel cylinder plunger. Therefore, during the return stroke of the wheel cylinder plunger, both the wheel cylinder plunger and the adjusting piston move together as one piece. The adjusting screw (4) carries at its head an

anti-rotation clip (9) into the slot of which the web (10) gets positioned in an assembled brake. The anti-rotation clip is of spring steel material that provides positive non-rotary connection between the adjusting screw and the brake web, thereby communicating any forward movement of the adjusting screw to the brake web. The anti-rotation clip contains raised impressions in its structure that gets housed between two teeth on the outer diameter of the adjusting screw as shown in Fig. 4. Since the anti-rotation clip is of spring steel material, the adjusting screw can be rotated against the spring force of the clip in both clockwise and anticlockwise directions. Since the anti-rotation clip is held by the brake web, any rotation of the adjusting screw will force the adjusting screw to move either in a forward or in a reverse direction. This forward or reverse movement would help retract the brake (or collapse the brake), when necessary.
When the cam screw is seated inside the helical groove, there will be a gap between the wall of the helical groove and the cam screw. This gap (or the distance) is called backlash. During normal operation of the brakes, when no adjustment is demanded by the system, the wheel cylinder plunger would axially move the set clearance between the lining and the drum. In order that the wheel cylinder piston moves this distance freely and without any problem, there must be sufficient gap between the cam screw and the wall of the helical groove. In addition, no adjustment must take place, when the system is having an elastic deformation due to brake application, temporary heat swell of the lining and the system, etc. The backlash contains not only the axial movement required for the wheel cylinder plunger for normal brake application, when no adjustment is demanded by the system, but also account for the above identified additional parameters.
During normal brake applications, the wheel cylinder plunger moves forward an amount equivalent to the running clearance between

the shoe and the drum. As the friction material wears off, this running clearance will keep increasing. When this clearance becomes more than the backlash designed, then cam screw will hit the other wall of the helical groove. This would force the wheel cylinder plunger to rotate. Once the cam screw touches the spiral groove, further movement of the wheel cylinder would be dictated by the spiral groove. Any further movement of the wheel cylinder would be a combination of rotary and linear motion. During forward movement of the wheel cylinder plunger, no rotary motion of the wheel cylinder plunger would be transmitted to the adjuster, as the rollers would move to the bigger end of the gap thereby acting like a bearing. During reverse traverse of the wheel cylinder piston, the rollers would move to the smaller end of the gap thereby locking the wheel cylinder piston and the adjuster into one unit and therefore they move as one unit.
The sequence of movement of the wheel cylinder piston during forward and reverse traverse is as follows. During forward movement, the wheel cylinder piston would initially have a liner motion only till all of the backlash distance is consumed. After the backlash distance is consumed, wheel cylinder piston would have a combination of linear and rotary motion. During return movement, the wheel cylinder piston would have liner motion initially till all of the backlash distance is consumed. After the backlash distance is consumed, it would have a combination of liner and rotary motion. Therefore, wheel cylinder piston would have a linear motion followed by a combination of linear and rotary motion during both forward and return travel. However, the direction of rotation during forward and return travels is opposite to each other. During the return travel, as the wheel cylinder piston and the adjuster move together and the adjusting screw is held by the web through the slot in the anti-rotation clip, the adjusting screw must unscrew to compensate for the extra travel of the wheel cylinder plunger (this extra travel is equal to the wear of the friction material).

Advantages :
The following are the advantages of wheel cylinder based auto adjuster :
This concept is very simple and can be packaged inside an existing
wheel cylinder housing.
It is incremental in terms of adjustment and hence fine adjustment is
possible.
The adjuster makes it very amenable for individual shoe adjustment.

We Claim :
1. Wheel cylinder based auto adjuster incorporated within the wheel
cylinder housing, comprising a housing (1) lip seal, (2) plunger, (3)
adjuster, (4) the said adjuster axially butts against the plunger, (5)
adjusting screws, the said adjusting screw and adjuster being connected
by means of threaded joint roller, (6) dust cover , (7) a cam screw, (8)
copper washer, (9) thrust bearing and (10) excluder assembly.
2. Wheel cylinder based auto adjuster incorporated within the wheel
cylinder housing as claimed in claim-1 wherein there is a sliding fete
between the plunger diameter and adjuster outer diameter in such way
that the adjuster can slid inside the plunger.
3. Wheel cylinder based auto adjuster incorporated within the wheel
cylinder housing as claimed in claim 1 needle roller thrust bearing being
assembled between the plunger and adjuster to avoid friction during
plunger rotation.