Brakes – With condition indicator – Wear
Reexamination Certificate
1999-07-20
2001-09-18
Rodriguez, Pam (Department: 3613)
Brakes
With condition indicator
Wear
C188S00111E
Reexamination Certificate
active
06290027
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a brake pad wear detector for detecting wear of brake pads of a disk brake for automobiles.
There is known a method of predicting when to replace brake pads by mounting a detector (hereinafter called probe) at a wear limit position of the brake pads to detect wear of lining of a brake pad, and electrically detecting breakage of a lead wire based on a change in voltage. The probe is easily attachable to and detachable from brake pads which are expendable. In order to accurately detect the wear limit of linings, various mounting structures have been proposed.
FIG. 4
shows a structure for mounting a brake pad wear detector proposed in Japanese utility model publication 6-22637 filed by the present applicant. A probe
101
is provided inside of the outer edge of a lining
1
of a brake pad
3
, and is resiliently mounted by a resilient clip
5
in a cutout
4
formed in a back plate
2
of the brake pad
3
at its outer edge.
FIG. 5
is an enlarged perspective view of the cutout. The cutout
4
, into which the probe
101
is inserted from the outer periphery of the brake pad
3
in a radial direction of the disk rotor (not shown), has straight guide rails
4
a
extending in the direction of thickness of the back plate
2
and slightly narrower than guide grooves
101
a
formed in the probe
101
(FIG.
6
). A curved cutout
4
b
is provided at a side of the back plate
2
opposite the lining
1
and has shoulders
4
c.
FIG. 6
is a perspective view of the probe
101
. A lead wire
102
for detecting the wear of the lining
1
is bent in the shape of the letter U and buried in the probe
101
which is made from e.g. a resin. The guide rails
4
a
of the back plate
2
(
FIG. 5
) are adapted to engage in guide grooves
101
a
formed in both sides of the probe
101
. When the lining
1
gets worn to some degree by the disk rotor (not shown), the lead wire
102
will be exposed and thus abraded by the disk rotor until eventually cut. When the wire is cut, a warning lamp goes on.
FIG. 7
is a perspective view of the resilient clip
5
for retaining the probe
101
inserted in the back plate
2
. The clip
5
comprises two substantially U-shaped strips
5
c
connected together by a connecting strip
5
b
having projections
5
a
at both ends. The projections
5
a
engage the shoulders
4
c
and prevent the resilient clip
5
from dropping.
FIG. 8
is a top plan view in which the cutout
4
is viewed from above with the brake pad
3
, probe
101
and resilient clip
5
assembled together. In
FIG. 8
, to mount the probe
101
on the back plate
2
, the guide grooves
101
a
of the probe
101
are slid along the guide rails
4
a
of the cutout
4
formed in the back plate
2
to engage the back plate. Then the resilient clip
5
is pressed onto the back plate
2
of the brake pad
3
so that its strips
5
c
engage both sides of the plate
2
. The strips
5
c
of the clip
5
will deflect along the tip shapes of the two projections
5
a
at both ends of the connecting strip
5
b
. When they snap in and engage the shoulders
4
c
of the cutout
4
, they are assembled together.
In this state, the probe
101
is bound by the engagement between the shoulders
4
c
of the cutout
4
and the projections
5
a
of the clip
5
, so that there is no freedom of movement in the vertical direction. Also, bound by the engagement between the guide rails
4
a
of the cutout
4
and the guide grooves
101
a
of the probe
101
, there is no freedom in the groove direction. But they are formed such that clearances S (
FIG. 8
) are present between the back plate
2
and the side faces of the guide grooves
101
a
of the probe
101
in the thickness direction due to the resilience of the strips
5
c
of the clip
5
.
The reason why the clearances S are present is described with reference to sectional views
9
A and
9
B in which the probe
101
in the cutout
4
is viewed from the side.
FIG. 9A
shows the lining
1
when it is brand-new.
FIG. 9B
shows a state in which the lining
1
has been worn to the wear limit X until the lead wire
102
has been cut by the disk rotor
10
, so that the warning lamp is now on. As the lining
1
is abraded, the probe
101
made of resin is brought into contact with and abraded by the disk rotor
10
, which is made of cast iron.
During this process, if there were no clearances S and thus there were no freedom of movement between the guide rails
4
a
of the cutout
4
and the guide grooves
101
a
of the probe
101
, the lining
1
and the disk rotor
10
would collide impulsively against each other upon abrupt braking and the probe
101
and the rotor be exposed to shock, so that the probe
101
, made from a weaker material, would be broken, making it impossible to stably detect the wear limit X. The clearances S serve to absorb such shocks. The probe
101
is thus abraded in a normal manner, so that the lead wire
102
is cut at a predetermined position.
In this conventional arrangement, the straight guide rails provided in the cutout of the back plate are adapted to engage in the guide grooves of the probe. The probe is snapped in and engaged with the shoulders of the cutout of the back plate, held by the resilient clip, so that it can be easily attached and detached. Since the probe is kept resiliently fastened to the disk rotor by the resilient clip, it is protected against collision against the disk rotor, so that it is possible to stably detect the wear limit.
But when expandable brake pads are repeatedly replaced, the disk rotor will become slender as shown in FIG.
10
. In order that the lining is used effectively, the lining
1
of the brake pad is usually mounted so that its outer edge will be 1-2 mm radially inside the outer edge of the rotor
10
. This means that the outer annular edge of the rotor does not contact the lining, so that an annular rib
10
a
is formed along the outer edge of the rotor
10
. When the disk rotor
10
has been abraded by the lining to the depth of H, the lead wire
102
will be cut by the rib
10
a
even though the thickness of the liner
1
is still Y, which is larger than the wear limit X by an amount H.
If only the brake pad is replaced repeatedly with the same disk rotor, the rib
10
a
will increase and thus the thickness Y of the lining when the wire is cut by the rib
10
a
will become larger. This means that the warning lamp goes on even though the lining
1
is still sufficiently thick and usable. When the lamp goes on, an operator will check the lining. But since the lining is still sufficiently thick, he will judge that the alarm is false and keep on using the pad instead of replacing it with a new one, not knowing the fact that the disk rotor is getting dangerously thin. When the height of the rib
10
a
increases to a certain value, the piston will have to move a distance beyond a point at which the piston disengages from the fluid seal member to move the lining into frictional contact with the rotor. If this happens, fluid will leak.
An object of the present invention is to provide a lead wire shaped such that it will be cut at a use limit height H of the rib
10
a
of the rotor, or at the wear limit X of the lining
1
.
SUMMARY OF THE INVENTION
According to the invention, there is provided a brake pad wear detector for detecting the wear of brake pads each having a lining and a back plate and arranged at both sides of a disk rotor, the brake pad wear detector comprising a probe detachably mounted in the outer peripheral portion of the back plate of the brake pad, and a lead wire buried in the probe, the lead wire being curved so as to protrude by a predetermined distance toward the disk rotor, the predetermined distance being larger than a predetermined maximum allowable height of an annular rib formed on the disk rotor at an outer peripheral portion thereof after continued use in a prolonged time of period.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying dra
Greenblum & Bernstein P.L.C.
Rodriguez Pam
Sumitomo Electric Industries Ltd.
LandOfFree
Brake pad wear detector does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Brake pad wear detector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Brake pad wear detector will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2489947