Brake wear indicator

Brake wear indicator is used to warn the user and/or owner of a vehicle that the brake pad is in need of replacement. The main area of use for this is on motor vehicles with more than three wheels. However brake wear indicators are also useful for brake pads in industrial applications, including wind turbines and cranes.[1][2]

This article refers to disc brakes as an example, but the principle is the same for other types of friction brakes.

Types of indicators

There are different types of wear indicators for brake pads:

  • Ocular inspection: A cut is made in the pad material to the depth where it shall be replaced. Requires manual inspection of the pads.
  • Mechanical:[3][4] A metal plate is designed to scratch the brake disk causing a noise when the pad has worn down to the desired level.
  • Electrical:[5] A metal body is embedded in the pad material that comes in contact with the rotor when the desired wear level is reached. This will light an indicator in the instrument cluster.
  • Position sensor:[6] A sensor that measures the position of the brake mechanics and indicates to the driver when the desired position has been achieved.

Of the alternatives above the first three are simple and cheap since their lifetime coincides with the service life of the brake pad. The last one is more expensive since the sensors needs to be designed to survive the designed service life of the vehicle. This means that the last alternative is usually only seen on heavy duty vehicles.

The idea is that in all cases alert the driver and/or owner of the vehicle that it is time to replace the brake pads to ensure that the traffic safety is preserved for the vehicle.

Detailed description

Pads B are mounted on carriers G. These are pushed against the rotor A by the piston D which is pushed by the brake fluid E. This induces wear on the brake pads. The rotor A also experiences some wear, but to a lesser extent than the brake pads. The modules C are joined to the cylinder that houses the piston D and acts as counter-force to the piston D.

Sufficient wear to validate a change of brake pads is considered when one of the following cases are applicable:

  1. The vXbox gap 1 is no longer visible or soon to be no longer visible.
  2. The embedded sensor in the brake pad 2 contacts the rotor and creates a connection to ground of the sensor.
  3. The metal plate 3 contacts the rotor and creates a noise.
  4. The distance between the cylinder for piston D and the carrier G becomes too large, causing the sensor F to send a signal outside the permitted range through the sensor wire 4, or ground the sensor wire 4 if F is a contact.

F can either be an analog sensor, with an electronic threshold value set to signal an alarm when it has been reached, or an on/off switch, activated at a certain distance.

Under normal conditions, only one of the alternatives are used. Many front wheels on cars are equipped only with wear indicators.

Electric wear indicator

Indication symbol for worn brake pads

Electrical wear indicator is the alternatives 2 and 4 as displayed above.

Embedded in brake pads

The simplest form of this indicator is that the wire 2 is connected to the ground side of a bulb that will light up as soon as contact is made with the rotor. This can result in a flickering light for the indicator.

In some vehicles an electrical wear indicator of type 2 can be doubled and one sensor is on the 50% mark while the other is when the pad is worn out. The 50% mark is stored in the vehicle ECU and can be used by workshops to estimate if the remaining lifetime of the current pads is sufficient until the next regular maintenance or if the pads shall be changed before they have reached end of life in order to save the vehicle owner from an additional visit for changing just the brake pads.

Separate sensor

This sensor (4 in the picture) may be present on heavy duty vehicles and special vehicles as well as in industry applications where maintenance is expensive, which means that planning and proactive maintenance is important to be as cost effective as possible at each maintenance event.

A simpler variant of the separate sensor is that it is a simple contact with the same functionality as the sensor of type 2 in the picture. This may be validated in cases where the actual brake pad is in an environment that would destroy any electrical wiring, for instance high temperatures.

References

  1. Wind Turbine Brake Pads”.
  2. “Crane Brakes”.
  3. “How Stuff Works: How Disc Brakes Work”.
  4. “Installing Subaru 4-Pot Brakes”. Archived from the original on 2013-10-05.
  5. “Professional Motor Mechanic; Brake Pads – Questions and Answers”.
  6. “Gill Sensors; Through-Hole Position Sensor”.
Brake pad Brake pads are a component of disc brakes used in automotive and other applications. Brake pads are steel backing plates with friction material bound to the surface that faces the disc brake rotor. Function Brake pads convert the kinetic energy of the vehicle to thermal energy through friction. Two brake pads are contained in the brake caliper, with their friction surfaces facing the rotor. When the brakes are hydraulically applied, the caliper clamps or squeezes the two pads together onto the spinning rotor to slow/stop the vehicle. When a brake pad heats up due to contact with the rotor, it transfers small amounts of its friction material onto the disc, leaving a dull grey coating on it. The brake pad and disc (both now having the friction material), then "stick" to each other, providing the friction that stops the vehicle. In disc brakes, there are usually two brake pads per disc rotor. These are held in place and actuated by a caliper affixed to the wheel hub or suspension upr...
Parking brake In road vehicles, the parking brake, also called hand brake, emergency brake, or e-brake, is used to keep the vehicle stationary and in many cases also perform an emergency stop. Parking brakes on older vehicles often consist of a cable connected to two wheel brakes at one end and the other end to a pulling mechanism which is operated with the driver's hand or foot. The mechanism may be a hand-operated lever, at floor level beside the driver, or a straight pull handle located near the steering column, or a (foot-operated) pedal located beside the drivers leg. In most automobiles the parking brake operates only on the rear wheels, which have reduced traction while braking. Some automobiles have the parking brake operate on the front wheels, for example most Citroens manufactured since the end of World War II, and the early models of the Saab 900. Hand brake lever from a Geo Storm. In this photo, the lever mechanism is shown not installed in the car. Brake warning light ISO symb...
Brake bleeding Brake bleeding is the procedure performed on hydraulic brake systems whereby the brake lines (the pipes and hoses containing the brake fluid) are purged of any air bubbles. This is necessary because, while the brake fluid is an incompressible liquid, air bubbles are compressiblegas and their presence in the brake system greatly reduces the hydraulic pressure that can be developed within the system. The same methods used for bleeding are also used for purging, where the old fluid is replaced with new fluid, which is necessary maintenance. The process is performed by forcing clean, bubble-free brake fluid through the entire system, usually from the master cylinder(s) to the calipers of disc brakes (or the wheel cylinders of drum brakes), but in certain cases in the opposite direction. A brake bleed screw is normally mounted at the highest point on each cylinder or caliper. There are four main methods of bleeding: The pump and hold method, the brake pedal is pressed while one b...
Transmission brake A transmission brake or driveline parking brake is an inboard vehicle brake that is applied to the drivetrain rather than to the wheels. Historically, some early cars used transmission brakes as the normal driving brake and often had wheel brakes on only one axle, if that. In current vehicles, these brakes are now rare. They are found in some makes, notably Land Rover, usually for light off-road vehicles. Simple transmission brakes could be found in large vehicles too, such as the 16 inch single disc parking brake used in the M19 Tank Transporter of World War II. The transmission brake is provided solely as a parking brake or handbrake. Normal wheel brakes are still provided for use when driving, drum brakes originally, now almost always disc brakes. Driver's manuals usually caution against using the transmission brake when driving, as it is neither powerful enough nor robust enough and so will not work effectively and may even be damaged by trying to stop a moving vehicle. ...
Electric park brake Electric park brakes (EPB) are used on passenger vehicles to hold the vehicle stationary on grades and flat roads. This was accomplished traditionally using a manual parking brake. With electric park brakes, the driver activates the holding mechanism with a button and the brake pads are then electrically applied onto the rear brakes. This is accomplished by an electronic control unit (ECU) and an actuator mechanism. There are two mechanisms that are currently in production: 1. Cable puller systems and 2. Caliper integrated systems. EPB systems can be considered a subset of Brake-by-wire technology. First installed in the 2002 BMW 7 Series (E65), electric park brakes have since appeared in a number of vehicles. Electric park brake in the center console in a Volkswagen Touran Functionality Apart from performing the basic vehicle holding function required of park brakes, the EPB systems provide other functions like automatic release of the park brakes when the driver presses the...