Method of detecting an in-range failure of a brake pedal position sensor

A method of detecting an in-range failure of a brake pedal position sensor includes calculating the difference between a minimum position and a maximum position of the brake pedal position sensor. The calculated difference is weighted to define a fast test weighted input value and/or a full test weighted input value. A cumulative test result value is incremented by the fast test weighted input value and/or the full test weighted input value. The cumulative test result value is filtered to define a moving average of the cumulative test result value after each incremented occurrence. The moving average of the cumulative test result value is tracked to determine if the brake pedal position sensor is functioning properly.

TECHNICAL FIELD

The invention generally relates to a method of detecting an in-range failure of a brake pedal position sensor.

BACKGROUND

A brake pedal position sensor senses a position of a brake pedal and sends an electrical signal to an engine control module indicating the current position of the brake pedal. The electrical signal varies within a normal operating range with the change in position of the brake pedal. The electrical signal may be defined as operating in-range when the electrical signal is within the normal operating range.

The engine control module includes onboard diagnostics that continually monitor the electrical signal from the brake pedal position sensor. When the electrical signal from the brake pedal position sensor is out of the normal operating range, i.e., out of range, the onboard diagnostics may easily determine that the brake pedal position sensor is not functioning properly. However, the electrical signal from the brake pedal position sensor may be shorted in such a manner so as to provide a continuous and steady signal to the engine control module that is within the normal operating range, i.e., in-range. Accordingly, the onboard diagnostics are unable to detect that the brake pedal position sensor is not functioning properly because the electrical signal is in-range.

Some vehicles may employ an erratic sensor diagnostic system. The erratic sensor diagnostic system detects a fluctuating electrical signal from the brake pedal position sensor that would not be possible when actuated by an operator's foot. However, as noted above, if the electrical signal form the brake pedal position sensor is shorted in such a manner as to provide a continuous and steady electrical signal, the erratic sensor diagnostic system is unable to identify the malfunctioning brake pedal position sensor. Another method of detecting in-range brake pedal position sensor failures includes comparing the signal from the brake pedal position sensor to a signal from a second or redundant sensor that is designed to correlate with the brake pedal position sensor. However, such redundancy, i.e., a second redundant brake pedal position sensor, is not always available.

SUMMARY

A method of detecting an in-range failure of a brake pedal position sensor for a vehicle is provided. The method includes initializing a full test buffer, and incrementing a full test buffer counter when the full test buffer is initialized to track a total number of instances the full test buffer is initialized. A minimum position of the brake pedal position sensor and a maximum position of the brake pedal position sensor are sensed. A position difference between the sensed minimum position and the sensed maximum position of the brake pedal position sensor is calculated. The method further includes sensing a position of a brake transmission shift interlock of the vehicle, initiating a full test when the brake transmission shift interlock is disposed in a park gear, sensing a depressed position of an accelerator pedal, and sensing a speed of the vehicle. The calculated position difference is weighted to define a full test weighted input value. The calculated position difference is weighted to define the full test weighted input value when the full test counter is greater than a minimum initiated full test value, the brake transmission shift interlock is moved out of the park gear, the speed of the vehicle is less than a pre-defined vehicle speed threshold and the depressed position of the accelerator pedal is less than a pre-defined accelerator pedal position. A cumulative test result value is incremented by the full test weighted input value. The cumulative test result value is filtered to define a moving average of the cumulative test results. The method further includes tracking the moving average of the cumulative test results to determine if the brake pedal position sensor is functioning properly.

A method of detecting an in-range failure of a brake pedal position sensor for a vehicle is also provided. The method includes initializing a fast test buffer, and incrementing a fast test buffer counter when the fast test buffer is initialized to track a total number of instances the fast test buffer is initialized. A full test buffer is incremented when the full test buffer is initialized to track a total number of instances the full test buffer is initialized. The method further includes sensing a minimum position of the brake pedal position sensor, sensing a maximum position of the brake pedal position sensor and calculating a position difference between the sensed minimum position and the sensed maximum position of the brake pedal position sensor. The calculated position difference is weighted to define a fast test weighted input value when the fast test buffer counter is greater than a minimum initialized fast test value, and incrementing a cumulative test result value by the fast test weighted input value. The method further includes sensing a position of a brake transmission shift interlock of the vehicle, initiating a full test when the brake transmission shift interlock is disposed in a park gear, sensing a depressed position of an accelerator pedal, and sensing a speed of the vehicle. The calculated position difference is weighted to define a full test weighted input value when the full test counter is greater than a minimum initiated full test value, the brake transmission shift interlock is moved out of the park gear, the speed of the vehicle is less than a pre-defined vehicle speed threshold and the depressed position of the accelerator pedal is less than a pre-defined accelerator pedal position. The method further includes incrementing the cumulative test result value by the full test weighted input value, and filtering the cumulative test result value to define a moving average of the cumulative test results. The moving average of the cumulative test results is tracked to determine if the brake pedal position sensor is functioning properly.

Accordingly, the change in position of the brake pedal position sensor is tracked to identify an in-range failure of the brake pedal position sensor. Accordingly, if the brake pedal position sensor is not moving, the moving average of the cumulative test results will tend toward a value that indicates that the brake pedal position sensor is not moving, thereby allowing onboard diagnostics to identify a brake pedal position sensor that is not functioning properly yet still providing an in-range signal.

DETAILED DESCRIPTION

Referring to the Figures, wherein like numerals indicate like parts throughout the several views, a brake pedal position sensor is generally shown at20inFIG. 1. Referring toFIG. 1, the brake pedal position sensor20is configured for sensing a position of a brake pedal (not shown) of a vehicle (not shown). The brake pedal position sensor20generates an electrical signal with varying strength with movement of the brake pedal. Accordingly, the signal from the brake pedal position sensor20changes in relation to a change in position of the brake pedal.

The brake pedal position sensor20may include any brake pedal position sensor20capable of generating a first signal22and a second signal24, wherein each of the first signal22and the second signal24indicate the position of the brake pedal. The first signal22is directed to a controller26. The controller26may include but is not limited to an engine control module or a brake control processor. The controller26includes onboard diagnostics that utilize the first signal22to test and/or monitor the brake pedal position sensor20for proper functionality.

The second signal24is directed to a brake control module28. The brake control module28releases a Brake Transmission Shift Interlock30(BTSI) when the second signal24indicates that the brake pedal is depressed. Once the brake transmission shift interlock30is released, the transmission may be moved out of a park gear. Accordingly, brake control module28must receive the second signal24from the brake pedal position sensor20indicating that the brake is depressed in order for the brake control module28to release the brake transmission shift interlock30to allow the transmission to be shifted out of the park gear and into another gear, including but not limited to a reverse gear, a drive gear or a neutral gear.

The brake control module28sends a BTSI signal32to the controller26indicating that the brake transmission shift interlock30has been released, i.e., that the brake transmission shift interlock30has moved out of the park gear and into another gear. The release of the brake transmission shift interlock30may be interpreted by the controller26to indicate that the brake pedal position sensor20is functioning properly because the brake transmission shift interlock30may only be released in response to the second signal24, which indicates that the brake pedal position sensor20has sensed movement of the brake pedal and so indicated the movement of the brake pedal to the brake control module28.

Referring toFIGS. 1 and 2, the first signal22and the second signal24from the brake pedal position sensor20, hereinafter referred to as the sensor signals22,24, include an electrical sensor signal having a variable resistance, generally indicated at34. The level of resistance of the sensor signals22,24indicates and is related to the relative position of the brake pedal. The level of resistance of the sensor signals22,24falls within a normal operating range36. When the level of resistance of the sensor signals22,24is within the normal operating range36, the brake pedal position sensor20may be defined as operating in-range. When the level of resistance of the sensor signals22,24is not with in the normal operating range36, the brake pedal position sensor20may be defined as operating out of range. More specifically, if the level of resistance of the sensor signals22,24is below the normal operating range36, the sensor signals22,24may be defined as operating out of range low, generally indicated at38. Similarly, if the level of resistance of the sensor signals22,24is above the normal operating range36, the sensor signals22,24may be defined as operating out of range high, generally indicated at40. The onboard diagnostics may determine that the brake pedal position sensor20is not functioning properly when the level of resistance of the sensor signals22,24is operating out of range low38or out of range high40.

In order to determine when the brake pedal position sensor20is not functioning properly when the sensor signals22,24are operating in-range, i.e., not operating out of range low38or out of range high40, a method of detecting an in-range failure of the brake pedal position sensor20is provided. The method is shown generally at42inFIG. 3. The method42may be embodied as an algorithm operable by the controller26.

The method42includes initializing a fast test buffer, indicated at44. The fast test buffer initializes each time the controller26is turned on, i.e., each time the vehicle is turned on. Initializing the fast test buffer allocates memory in the controller26for receiving and temporarily storing data related to the operation of the brake pedal position sensor20. The data related to the operation of the brake pedal position sensor20is utilized by the controller26to analyze the operation of the brake pedal position sensor20. The data related to the operation of the brake pedal position sensor20that is stored in the fast test buffer may include but is not related to a first position of the brake pedal, hereinafter referred to as a minimum position of the brake pedal, and a second position of the brake pedal, hereinafter referred to as a maximum position of the brake pedal. The controller26may calculate a position difference between the minimum position and the maximum position of the brake pedal, and store the position difference in the fast test buffer as well.

The method42further includes sensing a minimum position of the brake pedal position sensor20, indicated at46, and sensing a maximum position of the brake pedal position sensor20, indicated at48. The minimum position and the maximum position of the brake pedal are sensed by the brake pedal position sensor20and provided to the controller26through the first signal22. The controller26may receive the first signal22and interpret the minimum position and the maximum position of the brake pedal from the varied level of resistance of the first signal22. As indicated above, the minimum position and the maximum position of the brake pedal are stored in the fast test buffer.

The method42further includes calculating a position difference between the sensed minimum position and the sensed maximum position of the brake pedal position sensor20, indicated at50. The controller26may calculate the position difference by subtracting the minimum position of the brake pedal from the maximum position of the brake pedal. The position difference may be calculated as percentage of the total possible movement of the brake pedal. Accordingly, if the maximum position is equal to a position associated with a relative movement of the brake pedal equal to forty percent (40%) of the total range of motion of the brake pedal, and the minimum position is equal to a position associated with a relative movement of the brake pedal equal to fifteen percent (15%) of the total range of motion of the brake pedal, then the position difference would be equal to forty percent (40%) minus fifteen percent (15%), or twenty five percent (25%) of the total range of movement of the brake pedal.

The method42may further include incrementing a fast test buffer counter, indicated at52, when the fast test buffer is initialized. The fast test buffer counter is used to track a total number of instances the fast test buffer is initialized. Accordingly, the fast test buffer counter initially starts at zero (0) and increments by one (1) every time the fast test buffer is initialized. Therefore, if the fast test buffer has been initialized one hundred seventy four (174) times, then the fast test buffer counter would equal one hundred seventy four (174). As indicated above, the position difference of the brake pedal is stored in the fast test buffer.

The method42further includes weighting the calculated position difference to define a fast test weighted input value, indicated at54. The position difference is weighted to define the fast test weighted input value when the fast test buffer counter is greater than a minimum initialized fast test value. Accordingly, the vehicle is allowed to cycle on and off, i.e., the vehicle may be turned on and off, a minimum number of occurrences equal to the minimum initialized fast test value before the fast test algorithm begins to track the operation of the brake pedal position sensor20. This operates to ensure that the fast test algorithm is not operating to test the brake pedal position sensor20prior to all of the components of the vehicle being installed and/or tested. Once the fast test buffer counter is greater than the minimum initialized fast test value, then the fast test algorithm may continue to test and/or monitor the brake pedal position sensor20.

Weighting the calculated position difference to define a fast test weighted input value may include referencing a fast test look-up table, which converts the calculated position difference to the fast test weighted input value. For example, a calculated position difference having a higher value, indicating greater movement between the sensed minimum position and the sensed maximum position of the brake pedal, may be weighted higher than a calculated position difference having a lower value, indicated less movement between the sensed minimum position and the sensed maximum position of the brake pedal. The larger values of the calculated position difference may be weighted more heavily than the smaller values of the calculated position difference because the larger values of the calculate position difference provide better evidence that the brake pedal position sensor20is not stuck at a constant resistance, i.e., that the electrical signal is not stuck on a constant value such as when the wiring is shorted to a fixed resistance. In other words, the greater the calculated difference, the more likely the brake pedal position sensor20is not stuck at a fixed electrical resistance.

The method42further includes incrementing a cumulative test result value by the fast test weighted input value, indicated at56. The cumulative test result value is the ongoing summation of all test result values. Accordingly, each time the fast test algorithm calculates a fast test weighted input value, that fast test weighted input value is added to the previous cumulative test result value to define a current cumulative test result value.

The method42further includes initializing a full test buffer, indicated at58. The full test buffer initializes each time the controller26is turned on and the fast test algorithm completes to define a fast test weighted input value. Initializing the full test buffer allocates memory in the controller26for receiving and temporarily storing data related to the operation of the brake pedal position sensor20. The data related to the operation of the brake pedal position sensor20is utilized by the controller26to analyze the operation of the brake pedal position sensor20. The data related to the operation of the brake pedal position sensor20that is stored in the full test buffer may include but is not related to the minimum position of the brake pedal, the maximum position of the brake pedal and the calculated difference between the minimum position and the maximum position of the brake pedal.

The method42may further include incrementing a full test buffer counter when the full test buffer is initialized, indicated at60. The full test buffer counter is used to track a total number of instances the full test buffer is initialized. Accordingly, the full test buffer counter initially starts at zero (0) and increments by one (1) every time the full test buffer is initialized. Therefore, if the full test buffer has been initialized one hundred twenty two (122) times, then the full test buffer counter would equal one hundred twenty two (122).

The method42includes sensing a position of a brake transmission shift interlock30of the vehicle, indicated at62. The position of the brake transmission shift interlock30may be sensed by the brake control module28through the second signal24of the brake pedal position sensor20, and signaled to the controller26. Accordingly, the controller26indirectly utilizes the second signal24from the brake pedal position sensor20by identifying when the brake control module28has released the brake transmission shift interlock30, which requires an indication form the second signal24that the brake pedal is depressed, i.e., an indication of movement of the brake pedal position sensor20.

The method42further includes initiating the full test algorithm when the brake transmission shift interlock30is disposed in a park gear, i.e., when the brake control module28has not yet released the brake transmission shift interlock30. This ensures that the vehicle is not being started from a neutral transmission gear. Initiating the full test algorithm when the brake transmission shift interlock30is disposed in a park gear may occur only once during a vehicle on cycle. The vehicle on cycle is defined as the cycle beginning when the vehicle is turned on and ending when the vehicle is turned off.

In order to identify two footed acceleration of the vehicle, i.e., depressing an accelerator pedal while simultaneously pressing the brake pedal, the method42further includes sensing a depressed position of the accelerator pedal, indicated at64, and sensing a speed of the vehicle, indicated at65. The full test algorithm may only continue if the position of the accelerator pedal is less than a pre-defined accelerator pedal position, and the speed of the vehicle is less than a pre-defined vehicle speed threshold.

The method42further includes weighting the calculated position difference to define a full test weighted input value, indicated at66. The calculated position difference is weighted to define the full test weighted input value when the full test counter is greater than a minimum initiated full test value, the brake transmission shift interlock30is moved out of the park gear, the speed of the vehicle is less than the pre-defined vehicle speed threshold and the depressed position of the accelerator pedal is less than the pre-defined accelerator pedal position. Accordingly, the controller26is allowed to cycle on and off, i.e., the controller26may be turned on and off, a minimum number of occurrences equal to the minimum initialized full test value before the full test algorithm begins to track the operation of the brake pedal position sensor20. This provides sufficient data for the buffer in the controller26to accurately track the operation of the brake pedal position sensor20, as well as requires a minimum number of complete tests for the exponentially weighted moving average, described below. Additionally, this operates to ensure that the full test algorithm is not operating to test the brake pedal position sensor20prior to all of the components of the vehicle being installed and/or tested. Additionally, the full test algorithm may only continue when the brake transmission shift interlock30is released and the transmission is moved out of the park gear and into another gear, thereby providing additional indication that the brake pedal position sensor20has moved.

Weighting the calculated position difference to define a full test weighted input value may include referencing a full test look-up table, which converts the calculated position difference to the full test weighted input value. For example, a calculated position difference having a higher value, indicating greater movement between the sensed minimum position and the sensed maximum position of the brake pedal, may be weighted higher than a calculated position difference having a lower value, indicated less movement between the sensed minimum position and the sensed maximum position of the brake pedal. The larger values of the calculated position difference may be weighted more heavily than the smaller values of the calculated position difference because the larger values of the calculate position difference provide better evidence that the brake pedal position sensor20is not stuck at a constant resistance, i.e., is not free to move. In other words, the greater the calculated difference, the more likely the brake pedal position sensor20is free to move.

The method42further includes incrementing the cumulative test result value by the full test weighted input value, indicated at68. The cumulative test result value is the ongoing summation of all test result values, i.e., both the fast test result values and the full test result values. Accordingly, each time the full test algorithm calculates a full test weighted input value, that full test weighted input value is added to the previous cumulative test result value to re-define the current cumulative test result value.

The method42further includes filtering the cumulative test result value to define a moving average of the cumulative test results, indicated at70. The cumulative rest result value may be filtered with either a first order lag filter or an Exponential Weighted Moving Average (EWMA) filter. Accordingly, an average value for each incremented cumulative test result value is calculated, and a plot line connecting all of the averages is the moving average. As such, filtering the cumulative test result value is an ongoing analysis that provides an indication or trend line of whether the brake pedal position sensor20is moving or is stuck in place at a constant in-range resistance.

Therefore, the method42further includes tracking the moving average of the cumulative test results to determine if the brake pedal position sensor20is functioning properly. The method42may further include signaling that the brake pedal position sensor20is functioning properly when the moving average of the weighted input is greater than a passing level, signaling that the brake pedal position sensor20is not functioning properly when the moving average of the weighted input is less than a failing level, or signaling that proper functionality of the brake pedal position sensor20is undeterminable when the moving average of the weighted input is less than a passing level and greater than a failing level.

As noted above, the moving average of the cumulative test result value provides an indication of whether the brake pedal position sensor20is moving or is stuck in place and sending a constant signal at a resistance within the normal operation range of the brake pedal position sensor20. If the moving average of the cumulative test result value trends upward, i.e., trends toward larger values, then the moving cumulative test result value indicates that the brake pedal position sensor20is freely moving. Alternatively, if the moving average of the cumulative test result value trends downward, i.e., trends toward smaller values, then the moving cumulative test result value indicates that the brake pedal position sensor20may not be freely moving. Accordingly, even if the moving average of the cumulative test result value falls between the passing level and the failing level, thereby preventing the controller26from determining if the brake pedal position sensor20is functioning properly or is not functioning properly, review of the plot line of the moving average may give an indication of the performance of the brake pedal position sensor20. For example, a recently repaired brake pedal position sensor20would trend upwardly, whereas a recently failed brake pedal position sensor20would trend downward.

The method42further includes incrementing a sample counter for the cumulative test result value, indicated at72. The sample counter for the cumulative test result values is used to track a number of instances the cumulative test result value has been incremented. Accordingly, the sample counter for the cumulative test result value increases by one (1) every time the cumulative test result value is incremented. Therefore, if the cumulative test result value has been incremented fifty five times (55), then the sample counter for the cumulative test result value is equal to fifty five (55).

The method42further includes calibrating the cumulative test result value to a pre-defined starting value of the cumulative test result value, indicated at74, when the sample counter for the cumulative test result value reaches a maximum limit. The maximum limit of the sample counter for the cumulative test result value is the total number of times the cumulative test result value may be incremented within a cycle. Upon reaching the maximum limit, the controller26resets the sample counter for the cumulative test result value to zero, and resets the value of the cumulative test result to the pre-defined starting value. The pre-defined starting value of the cumulative test result value may be a value somewhere between the failing level and the passing level. Furthermore, the cumulative test result value and the sample counter for the cumulative test result value may also be manually reset is required for maintenance or other reasons.