Brakes – With condition indicator – Electrical
Patent
1995-02-21
1997-05-27
Graham, Matthew C.
Brakes
With condition indicator
Electrical
188 717, F16D 6602
Patent
active
056323590
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a disk brake for a motor vehicle, comprising:
two brake elements which can move with respect to one another, one of which is a caliper straddling a brake disk, and the other of which is a carrier fixed to the vehicle;
braking means comprising a cylinder secured to the caliper and, facing the disk, having an opening which is closed by a piston;
guide means allowing the caliper to slide with respect to the carrier when the braking means are actuated, these guide means comprising at least one guide pin fitted to one of the brake elements, and a bore formed in the other brake element and in which the guide pin slides;
two friction pads, the first of which is located between the piston and a first face of the disk, and the second of which is located between a second face of the disk and a jaw of the caliper, these pads being applied to the disk when the clamping means are actuated; and
at least one electrical wear indicator for monitoring the state of wear of at least one of the pads, this indicator including two parts at least one of which is displaced with respect to the other when the braking means are actuated, and comprising means for varying an electrical parameter, substantially continuously, as a function of the relative position occupied by the first and second parts of this indicator.
A brake of this type is illustrated, for example, by documents FR-A-2,485,132 and EP-A-0,168,303.
In practice, essentially three types of wear indicators are known today, namely electrical indicators connected to the pads, acoustic indicators also connected to the pads, and electrical indicators, such as the one which the previously mentioned documents describe, which are provided on the brake itself.
Whatever its embodiment, such a wear indicator is subject to a high risk of failure, stemming from the very hostile nature of the environment in which it must work.
Under these conditions, there is always a non-negligible risk that even substantial wear of the brake pads might not be indicated by any signal despite the presence of a wear indicator, it always being possible for the latter to have broken down.
What is more, a wear indicator like the one described in document EP-A-0,168,303 assumes the use of coils and of magnetically appropriate materials which have an overall size and additional cost which are not negligible.
The present invention is located in this context and its object is to propose a disk brake in which the risk of significant wear of the pads passing unnoticed is substantially reduced, but without being subject to substantial constraints in terms of cost and overall size.
To this end, the brake of the invention is essentially characterized in that the wear indicator comprises a capacitive sensor having two electrodes, each of the parts of this indicator constituting a corresponding electrode of this sensor, in that one of the electrodes of the capacitive sensor is mounted so that it can slide in the other, these electrodes participating in forming said guide means and having a variable overlap area, and in that this brake further comprises monitoring means capable of periodically measuring the electrical parameter, of comparing its value to at least one predetermined threshold, and of delivering a failure signal when the result of the comparison differs from a previously recorded normal result.
The monitoring means advantageously comprise an electronic circuit which is sensitive to the capacitance between the two electrodes, secured to one of the parts of the indicator and capable of producing, as an output signal, a signal which is modulated over time as a function of the value of the capacitance formed between the electrodes of the sensor.
In a very effective embodiment, the electronic circuit produces, as an output signal, a modulation of an electrical energy signal which it receives coming from a power source.
Moreover, one of the electrodes of the wear indicator may, for example, comprise the guide pin or an axial electrode secured to the cylinder, the other electro
REFERENCES:
patent: 3802257 (1974-04-01), Jorenda et al.
patent: 4374375 (1983-02-01), Allori et al.
Bacardit Juan S.
Camps Josep O.
Bendix Espana S.A.
Graham Matthew C.
McCormick Jr. Leo H.
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