This invention relates to a brake adjuster for the air brake system of a motor vehicle, particularly, to an adjuster for the automatic lining gap adjustment of vehicle brakes to compensate for wear of the linings and hence maintain a controlled lining gap in operation. Prior art:
Such adjusters and the corresponding brake system wherein they are used are well known to the art.
The essential features of such known brake adjusters are a permanently fixed reference location with respect to the vehicle bracketry, pre-set internal reference gap, which determines the lining clearance during operation, a one-way clutch which allows adjustment only in one direction, either during brake application stroke or during brake release stroke, another clutch which senses the contact of the lining with the brake drum, the said dutch disengaging through sensing of the elastic deformation of the brake drum during braking to prevent excessive adjustment, which may lead to brake binding.
The deficiencies in the prior art are:
In constructions, which adjust the clearance on brake release, the return force to overcome the friction of the internal mechanisms of the adjuster should be provided by the brake chamber return spring. In cases of vehicles after a certain period of service, the return spring load may relax and hence provide insufficient return force, causing brake binding. From this point of view, adjusters that adjust during application are advantageous, but in such cases the one-way clutch is required to take up a higher torque caused by forces generated during brake application. The one-way clutch usually comprises a torsion spring gripped on the outer diameter, which are occasionally known to fail in service through buckling.
Another construction feature of prior art with respect to the clutch, which senses the elastic portion of the stroke, is that such clutches are generally made of two sets of teeth engaging and disengaging against a heavily loaded spring. Such a feature has the disadvantage that the teeth have to slip every time a manual de-adjustment of the brakes are carried out, as during a renewal of the lining. This results in a high level of de-adjustment torque. During automatic adjustment also, the teeth tend to slip partially
Page 2 of 11
before engaging and disengaging. This results in wear of the teeth, which limits the durability of the adjuster.
The prior art brake adjusters also require precise adjustment of the spring force that senses the elastic deformation of the drum, during assembly. This may not be possible to achieve precisely during servicing of the adjuster in the field, which may lead to malfunction.
Advantages of present Invention:
The important feature of the present invention is that it overcomes the above deficiencies through a construction, which incorporates the one-way clutch torsion spring in the adjusting pinion and worm mechanism, in the axis perpendicular to the main worm shaft. This allows a larger motion reduction at the one-way clutch through internal gearing and hence correspondingly lower torque transmission capacity is required for the torsion spring to effect the adjustment. This imposes a lower stress level on this one-way clutch spring and makes this critical component more durable. Another feature of the present invention is that the torsion spring is gripped on the internal diameter of the coils, thereby increasing the stability of the spring against buckling.
Yet another feature of the present invention is the arrangement of the adjustment mechanism, which permits adjustment during brake application, resulting in lower return force requirement of the brake chamber springs.
Yet another feature of this invention is that it employs a friction clutch to sense the elastic deformation of the brake drum, which results in improved durability of the assembly in service and reduced torque for de-adjustment as compared to prior art adjusters whose clutch is constructed of a set of mating teeth. Yet another feature of this invention is that the motion transmitting adjustment mechanism is supported by bearing supports at the two extremities, which facilitates the alignment of the said mechanism with the adjustment worm wheel, thereby reducing the internal friction and facilitating functioning of the one-way clutch more efficiently. Yet another feature of this invention is that the pre-set reference gap, which is built in as the backlash between the worm thread and gear of the adjustment mechanism can be ii selected through the thickness of the separate bearing member (U in figure 2).
According to this invention, the brake adjuster for air brake system of a motor vehicle, which adjusts the brake lining clearance to a pre-determined value during the brake application stroke, comprises a body, and a control arm non-rotatably mounted on a fixed point of the vehicle bracket, the said control arm driving through teeth, a motion transmitting adjustment mechanism, the worm of the adjustment mechanism co¬operating with a adjustment worm wheel which in turn co-operates with a torque limiting friction clutch , whose slipping torque is controlled by a compression spring and, the said clutch in turn transmitting motion to the worm shaft and then to the worm , which in turn co-operates with a worm wheel to effect the adjustment of the lining clearance, characterized in that the said control arm drives the motion transmitting adjustment mechanism through a pinion and a one-way clutch spring located in the axis of the said adjustment mechanism; the said adjustment mechanism is precisely supported by bearings at the two extremities; the backlash of the said adjustment mechanism is seleictable by the thickness of the separate bearing member at one end; the force of the said compression spring is precisely pre-set by the thickness of the washer; said clutch in turn transmits motion through a dog to the worm shaft. The functioning of the brake adjuster as per the present invention is described below according to a preferred embodiment detailed in the accompanying drawings. Brief description of the drawings:
Figure 1 is a side view of the adjuster showing the internal parts in one plane Figure 2 is view along section T-T which is a perpendicular axis to the view in figure 1. Description of the preferred embodiment:
The working of the brake adjuster in co-operation with the brake actuator, foundation brakes and camshaft of the vehicle brakes is well known and not described here in detail.
The movement of the internal parts during brake application and brake release and method of adjustment of the gap is described here in relation to figures 1 and 2. The adjuster consists of a body A within which the adjustment mechanism is housed and a control arm B which is fixed to a static portion of the foundation brake bracket. The control arm B along with the teeth B' on its periphery is mounted such that, it is
rotatable relative to the adjuster about the axis of the worm wheel C. The control arm B and B' are normally integral.
The spline E on the worm wheel C is slidably located on corresponding spline of the camshaft of the foundation brake (not shown). The worm D' mounted non-rotatably with the worm shaft D engages with the worm wheel C. To reduce (adjust) or increase the gap (de-adjust) of the linings, the worm D' is rotated in the appropriate direction through the worm shaft D, which rotates the worm wheel C, which in turn rotates the camshaft of the foundation brakes.
The teeth B' of the control arm B, engage with the corresponding teeth of the pinion P of the adjustment mechanism F and rotate it.
The adjustment mechanism F consists of the pinion P, a one-way clutch formed by a torsion spring R and a worm Q, which engages with the adjustment worm gear G. In alternate embodiment, as is well known to someone skilled in the art, the worm gear G may be replaced by an equivalent helical gear of like proportions. The one-way clutch spring R engages with the shafts S of the worm Q and S' of the pinion P. The one-way clutch engages and transmits motion from P to Q in the brake apply direction and disengages and decouples P from Q in the brake release direction. The rotary motion of pinion P described earlier is transferred to the worm Q and then to the adjusting worm gear G. The backlash of the worm Q when co-operating with worm wheel G decides the pre-determined clearance of the lining with the brake drum. The adjustment mechanism F is precisely supported at the two ends by a separate bearing member U and a bore in the body U'. The control mechanism experiences radial forces due to forces generated by worm Q rotating worm wheel G. If unsupported at one end (corresponding to U), the control mechanism can go out of alignment with the worm wheel G and create uncontrolled internal friction, which in turn can cause the one-way spring R to slip during adjustment, causing incomplete adjustment. The adjustment mechanism F is kept biased towards body A by a spring SP to prevent relative motion in vibratory condition.
The above mentioned backlash between worm Q and worm wheel G is controlled by the axial play X between adjustment mechanism F and the separate bearing member U. By 1 selecting different thicknesses of U, X can be varied. For different vehicle applications,
the pre-determined lining clearance may have to be varied to prevent brake binding in cold condition. Since this lining clearance is directly controlled by the axial play X, such variant generation for different vehicle applications is easily achieved by replacing the bearing member U of the required tNckness, without disassembling the other parts of the assembly.
One end of the adjusting worm gear G forms one part of the friction clutch H. The friction clutch H consists of one peripheral edge J mating against a cone feature of the clutch part I. The compression spring K is housed in the spring seat O at one end and a recess in the adjusting worm gear G at the other end. The washer L provides precise force control of the compression spring K in fitted condition. Changing the thickness of the washer L can vary the force of the compression spring, which determines the slipping torque of the friction clutch H.
The clutch part I has a hexagon projection N at one end and a dog W at the other end, which engages with a corresponding recess on the worm shaft D. The hexagon projection N is used to manually rotate the worm D' to adjust or de-adjust the adjuster, which happens usually during installation or de-installation of the adjuster on the vehicle. The clutch part I is retained against the force of compression spring K by cover M which buts against a step in the body. Typically the joint between the cover M and body A could be through threads. Another sheet metal cover M' attached to the body A through screws, is used to retain the worm wheel C and adjustment mechanism F, the bearing member U and to prevent dust and water entry into the adjuster. The rotary movement of the adjusting worm gear G, is transferred to the worm D' through the friction clutch H, dog W and worm shaft D. This movement is transferred to the worm wheel C to adjust the gap of the brake lining.
Now the brake application sequence, in the direction of the arrow V, will be described.
The control arm B remains stationary and hence rotates the pinion P. The one-way clutch spring R engages and rotates the worm Q, which in turn rotates the adjusting worm wheel G. The friction clutch H, which remains in engagement and clutch part I drives the worm D' through the dog W and worm shaft D. The movement of the worm adjusts the excess clearance of the lining by rotating the worm wheel C, which in turn rotates the camshaft. Once the lining touches the brake drum, the torque required to turn the worm wheel C and worm D' suddenly increases causing the clutch H to slip. This prevents the adjuster from adjusting the lining gap further. By this process of clutch slipping, the elastic deformation of the brake drum is sensed and the device avoids over adjusting.
The brake release sequence, in the direction opposite to the arrow V is described further.
The clutch H continues to remain in a slipping condition till the force on the adjuster is reduced and the brake drum recovers from the elastic deformation and thereafter the lining loses contact with the brake drum. At this point the clutch H engages again. In the brake release direction, the control arm B again transmits rotary motion to the pinion P in the reverse direction. The one-way clutch spring R slips in this direction and hence the rotary motion from the pinion P is not transmitted to the adjusting worm Q. Therefore, even though the clutch H is engaged, the worm wheel G does not rotate and hence the worm shaft D and worm D* do not rotate and hence there is no de-adjustment of the brake lining in the brake release direction.
Another feature of this invention is that, the spring force of compression spring K is not controlled in the assembly process. The force is controlled through a selection of the thickness of the washer L that is carried out externally. This facilitates generation of different variants with different slipping torque of clutch H to suit different vehicle applications.
Like other adjusters known to the art, the present invention also is capable of adjusting the excess gap in the linings in very small increments with every brake application, which prevents over adjustment and brake binding.
Naturally the invention and embodiment must not be considered restricted to the details described above and illustrated in the drawings, but may be modified in different ways within the scope of the appended claims.
claim:
A brake adjuster for air brake system of a motor vehicle, which adjusts the brake
lining clearance to a pre-determined value during the brake application stroke, the
said brake adjuster comprising a body, and a control arm non-rotatably mounted
on a fixed point of the vehicle bracket, the said control arm driving through teeth, a
motion transmitting adjustment mechanism, the said motion transmitting
adjustment mechanism supported precisely at two bearings located at the
extremities, one of the bearing members at one extremity being selectable to
/
control the required backlash in the said motion transmitting mechanism, the worm of the adjustment mechanism co-operating with a adjustment worm wheel which in turn co-operates with a torque limiting friction clutch , whose slipping torque is controlled by a compression spring and, the said clutch in turn transmitting motion to the worm shaft and then to the worm, which in turn co-operates with a worm wheel to effect the adjustment of the lining clearance, characterized in that the said control arm drives the motion transmitting adjustment mechanism through a pinion and a one-way clutch spring located in the axis of the said adjustment mechanism; the force of the compression spring of the said torque limiting friction clutch is precisely pre-set by the thickness of the washer; said friction clutch in turn transmits motion through a dog to the worm shaft. ^Art>rake adjuster for air brake system of a motor vehicle as claimed in claim 1, wherein the adjustment-meehanism is supported at two bearings located at the extremities havin^lmprov^cl^ignment with the adjustment worm, which results in lowgnnternal friction andlmproved Decision of adjustment. Wbrake adjuster for air bwk&syat&n of a motor vehicle as claimed in claim 1, wherein one of the bearing members of the adjustment mechanism, located at one extremity adjacent to the cover, is selectable by thickness and replaceable easily to achieve the required axial play and hence backlash of the worm of the adjustment^" mSShanism7
HMorake adjuster for air brake system of a motor vehiete-as^imed in claim 1 and 2, wherein the axtejoithe adjustment mechanism, has a large/notion reduction gearing requiring a low torque capacity of the said one-way clutch spring.
I 5frf A Drake adjuster for air brake system of a motor vehicle as claimed in claims 1,2 Vyjand 3, wherein the one-way clutch spring grips the driving and driven members on itsinner diameter.
6. TWbrake adjuster for air brake system of a motor vehicle as claimed in any one of
ine claims 1 to 4 wherein the torque limiting clutch has a slipping torque limit which is precisely pre-settable by selection of the thickness of washer for controlling the j. force of the compression spring.
7. \A)>rake adjuster for air brake system of a motor vehicle as claimed in claims 1 to 5
wherein the dog in the clutch co-operates with a corresponding recess in the worm shaft.
^ /uY^brake adjuster as claimed in any one of the claims 1 to 7 substantially as herein described and as illustrated in the accompanying drawings