Types of brake pad wear sensors and how they work
Modern cars now use friction-type brakes, the operation of which is due to the force of friction. The interaction between the disc and pads as a result of their contact and leads to braking. The most wearing part of the brake mechanism is the friction layer of the brake pads.
Until recently, the remaining thickness of the pads had to be checked by the car owner himself. Now, however, many of them are installed sensor brake pad wear, which greatly simplifies this control. These sensors (signaling devices), placed on or inside the bar, when the friction layer reaches critical wear, they signal the need for their replacement. Modern machines use two types of such signaling devices: mechanical and electronic, which differ in their principle of operation and location on the slat.
At the same time, a variety of sensors can be installed in the machine. They can be attached:
- One – on the single bar of the front wheel.
- Two – on the pads of one front and one rear wheel.
- Four on all wheels.
For several decades, an uncomplicated but effective solution has been used to monitor the wear of the brake bars – a mechanical signaling device.
Its construction consists of a U-shaped steel spring plate, attached to the shoe with one end.
Its other end is located perpendicular to the brake disc at the distance of the minimum wear of the friction layer. The principle of this sensor is simple:
- When the friction material is worn down to the minimum allowable values, the plate begins to make contact with the disc, producing a distinctive rattling sound.
- The occurrence of this sound warns the driver of the need to replace the brake pads.
The design of these sensors allows them to be installed only on disc brakes.
Disadvantages of mechanical sensors
Some manufacturers do not glue signalers to the metal part of the bar, and fasten them with different fasteners. Given our roads, such fastening contributes to its loss while driving.
The second problem, independent of the alarm, can be dust and small gravel, getting between the pad and the disc. The resulting sound can be perceived as the brake pad wear sensor activating.
Electronic warning devices
Manufacturers equip all modern cars with such sensors, considering them to be more advanced. After all, thanks to such signaling devices, it became possible to monitor not only the fact of complete wear, but the degree of amortization of the friction material. This is facilitated by the fact that electronic signaling devices began to be divided into two types:
- External sensors – attached to the side of the brake bar or in a specially designed recess for them. Which allows, in the case of breakage, to replace them.
- Integrated devices – pressed into the friction material during the production of the slats. In this case, their replacement is not possible.
Such signaling devices are arranged simply: there is a core in the plastic body, in order not to spoil the brake disc, it is made of soft varieties of metal. On the back side of the device there is a connector with a lead wire.
The principle of operation of such sensors is based on the processes that occur in an electrical circuit when it closes. When the core begins to touch the disc when the strips are worn and the front part of the housing breaks, the same processes occur. The contact circuit closes and the indicator on the dashboard lights up.
The result of the external and integrated sensors is slightly different by the signal that appears on the dashboard:
- The indicator light when the external sensor is triggered lights up the moment the friction material thickness has reached its critical point and lights up permanently in one color.
- In the case of the integrated warning light, the indicator lamp changes color depending on the wear of the pads. As the friction layer thickness approaches the critical level, it starts to light up yellow. And when the friction material is completely worn out, when immediate replacement of the pads is required, the light turns red.
It is not difficult to understand the principle of how such a multi-level scheme works. As already mentioned in the article covering the question – “when to replace the brake pads” – the friction layer of many pads contains metal additives. Because of this, they can, albeit with high resistance, pass an electric current. This is the property that manufacturers have used to determine how soon the pads will wear. The thickness of the friction layer plays an important role in the electrical resistance of the lining (the thinner the layer, the less it is).
When the ignition is turned on, an electronic circuit is formed, the circuit consists of an indicator, wires, a sensor and a brake disc.
When, as a result of partial wear of the friction layer to a certain percentage, the resistance in this circuit decreases, the yellow light bulb lights up. Which signals that the bar will still serve a certain period of mileage of the car, but its full wear is not far off and should be concerned about the purchase of new pads. Well, if the color of the indicator changes from warning yellow to red, you should immediately replace the bars.
Disadvantages of electronic alarms
Like any signaling device, wear sensors have certain disadvantages:
- The wires with which they are equipped are quite thin and often become frayed and torn.
- The lack of protection of wire connectors against moisture and dirt often causes contacts to oxidize or short out.
- In rainy weather, moisture on the friction layer can change its resistance, leading to false triggering of the indicator.
The only good thing about electronic sensors (based on the disadvantages described above) is that even if the wire is broken, they will still signal that the pads are worn. In this case, they will work as mechanical alarms, when the sensor rod begins to press closely against the disc, there will be a characteristic squeaking sound.
For most modern cars, the wear warning devices are sold separately from the brake pads.
Thus, manufacturers made sure that it is possible to replace the worn or failed part (unfortunately, this does not apply to pads with integrated signal indicators). But, despite this, experts still advise replacing the old sensors along with the installation of new brake pads. Since it is possible that they will not work properly.
Brake pads with an electronic sensor with their own hands
If you want to know when you have worn out brake pads and change them in time, then this tinker will help you to implement it on your car, namely – to install the electronic sensor of the wear pads with their own hands.
If you want to be aware of when you have worn out brake pads and timely change them, then this tip will help you to implement it on your car, namely – to install an electronic sensor pads wear with his hands.
Many cars have sensors of wear, but not electrical, and just inform the squeak, that is, when the wear pads reach the metal plate, then the latter begins to publish a characteristic squeak.
But you can do a little on – more modern, that is, when the panel will just light up an informative light that will inform us that the pads is time to replace.
In any car, you can do this, namely from the simple pads to do with an electronic sensor and bring to the panel informative light or connect to some existing.
So, what we need for this…
Take an ordinary brake pad, take a drill 2 mm in diameter and drill a hole in the pad as close as possible to the metal base of the pad, a depth of 10 – 15 mm. Drill so that after that the wire in no case did not touch the metal base, and the hole was from him at a distance of about 2 mm.
photo for information, it is better to drill a hole, not as shown here.
Then we need a piece of simple wire with a copper core inside, by the way it will be stranded or single core all the same. It is desirable to bend it twice at the end and put it into the hole made, but before that it is better to grease it with superglue or epoxy resin.
An informative photo of how to coil the wire.
how to do it
sticking, gluing the wire
After the glue dries, our pad will be ready to install on the car. The outer end of the wire will serve to connect to the information light in the interior of the car. The wire only needs to be made for one brake pad on the side, for the inside.
Next, how to connect the informative lamp, by which actually we will learn about the depletion of the brake pad.
For this we need a simple, 3 or 5 watt car lamp, a simple car relay
and a little time to connect it all according to the diagram below.
The scheme is simple, there is nothing complicated about it, any car enthusiast will be able to cope with it.
The wire from the sensor brake pads connected to the coil relay (pin 86), the second contact (number 85) relay coil is connected through a fuse for 5A to the plus, which should appear after the ignition.
Well, the light circuit itself is connected through open relay contacts (numbers 30 and 87), that is, a light bulb during normal car operation should not burn, but as soon as the brake pad will be rubbed out, the wire will connect to the common ground and our informative light bulb in the car will be lit.
Here is such a simple method of electronic pads. It is very easy to install it on the car, and it will benefit a lot.