Methods of operating a control system of a vehicle and vehicle systems
Methods for operating a control system of a vehicle and vehicle systems are provided. A method includes receiving a first output signal from a longitudinal accelerometer during a first travel condition of the vehicle including a first vehicle speed of the vehicle and a first road grade substantially equal to zero, wherein the first vehicle speed is a constant speed and the first output signal represents a first measurement including a first vehicle acceleration component and a bias offset component, receiving a second output signal during a second travel condition of the vehicle including a second vehicle speed of the vehicle and a second road grade, wherein the second output signal represents a second measurement including a second vehicle acceleration component and the bias offset component, and determining the bias offset component and gravity component to obtain an estimated road grade factor.
1. A method of operating a control system of a vehicle, the method comprising the steps of:
receiving a first output signal from a longitudinal accelerometer, while the vehicle is subjected to a first travel condition, the first travel condition including a first vehicle speed of the vehicle and a first road grade, wherein the first vehicle speed is a substantially constant speed, the first road grade is substantially equal to zero, and the first output signal represents a first measurement including a first vehicle acceleration component and a bias offset component;
receiving a second output signal from the longitudinal accelerometer while the vehicle is subjected to a second travel condition, the second travel condition including a second vehicle speed of the vehicle and a second road grade, wherein the second output signal represents a second measurement including a second vehicle acceleration component and the bias offset component, and subtracting the bias offset component from the second output signal to obtain an intermediate longitudinal acceleration output signal; and
determining a first gravity component included in the intermediate longitudinal acceleration output signal by calculating a derivative of a wheel speed component included in a third measurement represented by a first output signal from a wheel speed sensor and calculating a difference between the intermediate longitudinal acceleration and the derivative of the wheel speed component, wherein the difference of represents the first gravity component.
2. The method of claim 1 , further comprising the step of:
processing the first gravity component to produce a final gravity component, wherein an estimated road grade factor comprises the final gravity component and the bias offset component.
3. The method of claim 2 , wherein the step of processing the first gravity component comprises filtering the first gravity component to remove one or more frequencies present in the first gravity component that are outside of a predetermined frequency range.
4. The method of claim 1 , further comprising the step of:
receiving a third output signal from the longitudinal accelerometer while the vehicle is subjected to a third travel condition, the third travel condition including a third vehicle speed and a third road grade, wherein the third output signal represents a third vehicle acceleration component, a second gravity component, and the bias offset value; and
producing a final adjusted longitudinal acceleration signal by subtracting the bias offset component from the third output signal and subtracting the final gravity component from the third output signal.
5. The method of claim 1 , wherein:
the second road grade is not substantially equal to zero.
6. The method of claim 1 , wherein:
the step of receiving the first output signal occurs at a first time instance;
the step of receiving the second output signal occurs at a second time instance; and
the method further comprises the step of updating the bias offset component by receiving a third output signal from the longitudinal accelerometer while the vehicle is subjected to a third travel condition at a third time instance, the third travel condition including a third vehicle speed and a third road grade, wherein the third vehicle speed is a substantially constant speed, the third road grade substantially equals zero, and the third output signal represents a third vehicle acceleration component and an updated bias offset component.
7. The method of claim 1 , further comprising the step of continuously reiterating the steps of receiving a second output signal, determining a first gravity component, and processing the first gravity component to obtain real-time estimated road grade factors at selected time instances.
8. The method of claim 1 , further comprising the step of storing the bias offset component in a memory.
9. A vehicle system, comprising:
a longitudinal accelerometer adapted to sense an acceleration of a vehicle and to provide an output signal including a vehicle acceleration component, a gravity component, and a bias offset component;
a speed sensor adapted to sense a vehicle speed and to provide an output signal including a wheel speed component; and
a controller in operable communication with the longitudinal accelerometer and the speed sensor and adapted to (1) receive a first output signal from the longitudinal accelerometer while the vehicle is subjected to a first travel condition, the first travel condition including a first vehicle speed of the vehicle and a first road grade, wherein the first vehicle speed is a substantially constant speed, the first road grade is substantially equal to zero, and the first output signal represents a first measurement including a first vehicle acceleration component and a bias offset component, (2) receive a second output signal from the longitudinal accelerometer while the vehicle is subjected to a second travel condition, the second travel condition including a second vehicle speed of the vehicle and a second road grade, wherein the second output signal represents a second measurement including a second vehicle acceleration component and the bias offset component, (3) subtract the bias offset component from the second output signal to obtain an intermediate longitudinal acceleration output signal, and (4) determine a first gravity component included in the intermediate longitudinal acceleration output signal by calculating a derivative of a wheel speed component included in a third measurement represented by a first output signal from a wheel speed sensor and calculating a difference between the intermediate longitudinal acceleration and the derivative of the wheel speed component, wherein the difference of represents the first gravity component.
10. The vehicle system of claim 9 , wherein the controller is further adapted to process the first gravity component to produce a final gravity component, wherein an estimated road grade factor comprises the final gravity component and the bias offset component.
11. The vehicle system of claim 10 , wherein the controller is further adapted to continuously reiterate receiving the second output signal, determining the first gravity component, and processing the first gravity component to obtain real-time estimated road grade factors at selected time instances.
12. The vehicle system of claim 9 , wherein the controller is further adapted to receive a third output signal from the longitudinal accelerometer while the vehicle is subjected to a third travel condition, the third travel condition including a third vehicle speed and a third road grade, wherein the third output signal represents a fourth measurement including a third vehicle acceleration component, a second gravity component, and the bias offset value, and to produce a final adjusted longitudinal acceleration signal by subtracting the bias offset component from the third output signal and subtracting the final gravity component from the third output signal.
13. The vehicle system of claim 12 , wherein the controller is further adapted to receive the first output signal occurs at a first time instance and the second output signal at a second time instance, and to update the bias offset component by receiving a third output signal from the longitudinal accelerometer while the vehicle is subjected to a third travel condition at a third time instance, the third travel condition including a fourth vehicle speed and a fourth road grade, wherein the fourth vehicle speed is a substantially constant speed, the third road grade substantially equals zero, and the third output signal represents a third vehicle acceleration component and an updated bias offset component.
14. The vehicle system of claim 9 , further comprising a memory in operable communication with the controller, wherein the memory is adapted to store the bias offset component.
15. The vehicle system of claim 9 , further comprising a filter in operable communication with the controller, wherein the filter is adapted to filter the first gravity component to remove one or more frequencies present in the first gravity component that are outside of a predetermined frequency range.