2.3. Brake Pad Monitoring - BrkPadMon
Id |
BrkPadMon |
Version |
0.1.0.0 |
Title |
Brake Pad Monitoring |
System |
Braking |
Document Type |
Application Software Component Specification Preview |
2.3.1. Overview
The BrkPadMon software component is responsible for processing the brake pad sensor signals and providing the pad wear status information to other components in the system. It performs the following main functions:
Reads the brake pad sensor and supply voltage signals
Converts the sensor voltage signal to resistance value
Converts the resistance value to wear state
Performs plausibility checks and fault detection on the sensor and supply voltage signals
Performs debounce logic on brake pad wear status
Outputs brake pad wear staus, validity, and fault information
2.3.2. Functions
Title |
Description |
|
|---|---|---|
1 |
Brake Pad Sensor Voltage to Resistance Conversion |
Converts the raw brake pad sensor voltage signal to corresponding resistance value. Performs scaling correction if enabled. Performs plausibility checks on the brake pad sensor and supply signals to detect out-of-range faults. Sets fault status flags and wear status accordingly. |
2 |
Brake Pad Resistance to Wear State Conversion |
Performs selection of the appropriate sensor type. Converts brake pad resistance to wear level and associates wear status based on selected thresholds. Performs debounce logic on brake pad wear status. |
2.3.3. Ports
Id |
Direction |
Data Type |
Dimensions |
Unit |
Description |
Keywords |
|
|---|---|---|---|---|---|---|---|
1 |
BrkPadU |
Incoming |
single |
[1] |
V |
Expected signal: Brake pad voltage measured. |
Brake Pad Voltage |
2 |
ExtRefU |
Incoming |
single |
[1] |
V |
Expected signal: Reference voltage from brake pad |
External Reference Voltage |
3 |
BrkpadmonWearSt |
Outgoing |
Enum: BrkpadmonWearSt |
[1] |
|||
4 |
BrkpadmonDiag |
Outgoing |
Bus: BrkpadmonDiagBus |
[-1] |
inherit |
2.3.4. Parameters
Id |
Data Type |
Dimensions |
Range |
Unit |
Description |
Keywords |
|
|---|---|---|---|---|---|---|---|
1 |
BrkpadmonBrkPadWarnThd |
single |
[1,1] |
Min: 0, Max: 100 |
% |
Brake pad wear percentage threshold for warning |
|
2 |
BrkpadmonDebTi |
single |
[1,1] |
Min: 0, Max: 60 |
s |
Debounce Time For Brake Pad Wear Detection |
|
3 |
BrkpadmonWarnDetnAtLoR |
boolean |
[1,1] |
Min: 0, Max: 1 |
Brake Pad Wear Is Detected At Low Resistance |
||
4 |
BrkpadmonURef |
single |
[1,1] |
Min: 0, Max: 30 |
V |
Supply voltage reference value |
|
5 |
BrkpadmonUseExtRefU |
boolean |
[1,1] |
Min: 0, Max: 1 |
Make use of the external supply voltage value |
||
6 |
BrkpadmonPadURng |
single |
[1,2] |
Min: 0, Max: 30 |
V |
Range of valid sensor voltage readings |
|
7 |
BrkpadmonSplyURng |
single |
[1,2] |
Min: 0, Max: 30 |
V |
Range of valid external supply voltage readings |
|
8 |
BrkpadmonBrkPadSnsrTyp |
uint8 |
[1,1] |
Min: 0, Max: 3 |
Brake Pad Wear Sensor Type: 0 - no sensor, 1 - switch sensor, 2 - analog sensor, 3 - reserved |
||
9 |
BrkpadmonPuUpR |
single |
[1,1] |
Min: 0, Max: 1000000 |
Ω |
Pull-up resistor value |
|
10 |
BrkpadmonHiRThd |
single |
[1,1] |
Min: 0, Max: 1000000 |
Ω |
High Resistance Threshold For Brake Pad Wear Detection |
|
11 |
BrkpadmonLoRThd |
single |
[1,1] |
Min: 0, Max: 1000000 |
Ω |
Low Resistance Threshold For Brake Pad Wear Detection |
|
12 |
BrkpadmonRToWearLutBreakPnt |
single |
[1,2] |
Min: 0, Max: 1000000 |
Ω |
Brake pad resistance to wear level LUT: Resistance break points |
|
13 |
BrkpadmonRToWearLutDa |
single |
[1,2] |
Min: 0, Max: 100 |
% |
Brake pad resistance to wear level LUT: Wear percentage |
2.3.5. Calibration
BrkPadMon must be set up according to the specifications of the brake pad being used.
2.3.5.1. Step 1 - Set Pull-Up Resistor Value and Reference Supply Voltage
To compute the brake pad’s resistance, the vlaue of the pull-up resistor and the reference supply voltage to the brake pad must be know. Set the pull-up resistor value using the parameter BrkpadmonPuUpR, and the reference supply voltage using the parameter BrkpadmonURef.
2.3.5.2. Step 2 - Configure Reference Supply Voltage
The brake pad resistance is calculated using the voltage reading from Inport #1: BrkPadU. In a real-world application, it is possible that the actual reference (source) voltage of the brake pad can vary slightly from the ideal voltage set by the parameter BrkpadmonURef (typically 5V or 12V). In such case, the voltage reading of Inport #1 also includes a deviation. To remedy this, a scaling factor can be activated to adjust the brake pad voltage reading based on the deviation of the actual external voltage reference given by Inport #2: ExtRefU compared to the ideal voltage reference from BrkpadmonURef. This scaling correction can be activated by setting BrkpadmonUseExtRefU to true and ensuring that the expected reference voltage is correctly set in BrkpadmonURef and Inport #2: ExtRefU is connected to the measured supply voltage of the brake pad.
To disable this scaling correction, set BrkpadmonUseExtRefU to false, and ground Inport #2: ExtRefU.
2.3.5.3. Step 3 - Configure Brake Pad Voltage Range Monitor
There are two voltage range checks, one for the brake pad voltage measurement (Inport #1) and one for the reference voltage measurement (Inport #2). The range of valid voltage values can be set using the parameters BrkpadmonPadURng and BrkpadmonSplyURng respectively. Both parameters are of dimension [1x2] with the first value being the lowest acceptable voltage reading and the second value the highest acceptable voltage reading.
If BrkpadmonUseExtRefU is set to false in Step 2, the voltage monitor uses the ideal reference voltage from parameter BrkpadmonURef instead of Inport #2: ExtRefU and checks that it is within range.
If any of the input voltages exceed their validity bounds, the validity flag of the brake pad’s resistance value is set to false and the corresponding wear level is set to NA. In such case, information about the error can be found in the diagnostic bus from Outport #2: BrkpadmonDiag.
2.3.5.4. Step 4 - Select Brake Pad Type
The BrkPadMon can handle different types of brake pad sensors, selectable with the parameter BrkpadmonBrkPadSnsrTyp.
The first type is a simple two-state switch sensor (wire connected, wire cut), where the resistance is either very low (closed circuit) or very high (open circuit) based on whether or not the electrical wire inside the brake pad has been severed. Set BrkpadmonBrkPadSnsrTyp to 1, and define a low resistance threshold using BrkpadmonLoRThd under which the wear level of the brake pad shall switch from Ok to Worn.
In some applications, the brake pad sensor works in the opposite way; its resistance is high when good, and low when worn. If this is the case, BrkpadmonWarnDetnAtLoR to true and define a high resistance threshold using BrkpadmonHiRThd above which the wear level of the brake pad shall switch from Ok to Worn.
The second type is an analog sensor with continuous resistance readings as the brake pad wears down. Set BrkpadmonBrkPadSnsrTyp to 2, and define the look-up table values mapping the sensor’s resistance to wear using BrkpadmonRToWearLutBreakPnt for the resistance breakpoints and BrkpadmonRToWearLutDa for the corresponding wear percentage levels. Then, define the wear percentage threshold using BrkpadmonBrkPadWarnThd, above which the wear level of the brake pad shall switch from Ok to Worn.
If no brake pad sensor is available, Set BrkpadmonBrkPadSnsrTyp to 0. The output wear state will be NA regardless of the input values.
2.3.5.5. Step 5 - Set The Debounce Timer
The output wear state is equipped with a debounce timer to avoid undesired switching and oscillations around the wear resistance thresholds. The debounce time can be set using the parameter BrkpadmonDebTi.