Road Grade Estimation Using Longitudinal Acceleration Sensor
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Solution Overview
Problem
Powertrain control systems inaccurately estimate road grade due to assumptions about vehicle mass, payload, and wind force, leading to incorrect engine and transmission control, especially when the vehicle is stopped or braking, which affects fuel economy.
Innovation Solution
A system that includes a longitudinal acceleration estimation module, a vehicle longitudinal acceleration sensor, a road grade estimation module, and an actuator control module, which estimates road grade based on transmission output speed and wheel speed, accounting for sensor offsets to improve accuracy even when the vehicle is stopped or braking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If road grade is estimated using traditional force balance method with assumed vehicle mass, payload, and wind force, then the estimation can be performed with simple calculations, but the accuracy of road grade estimation deteriorates especially when vehicle is stopped or braking
Solution Approach 1:
The patent replaces the traditional mechanical force balance estimation method with an accelerometer-based measurement system. The accelerometer directly measures longitudinal acceleration, which is then used to calculate road grade through gravitational force relationships, eliminating the need for complex force balance calculations and assumptions about vehicle mass, payload, and wind force.
Solution Approach 2:
The patent changes the fundamental measurement parameter from indirect force balance calculations to direct acceleration measurement. By using the accelerometer output signal that directly reflects longitudinal acceleration, the system transforms the estimation problem into a simpler calculation based on gravitational force and measured acceleration, improving accuracy without sacrificing computational simplicity.
2Device complexity
If traditional force balance method is used to estimate road grade, then the system can operate without additional sensors, but the fuel economy control deteriorates due to inaccurate road grade estimation
Solution Approach 1:
The patent utilizes the vehicle's existing accelerometer (which is part of the standard vehicle instrumentation for other purposes) to enable accurate road grade estimation. This self-service approach allows the system to improve fuel economy control without adding dedicated sensors, as the accelerometer data already captured for other vehicle functions is repurposed for road grade calculation.
Solution Approach 2:
The patent makes the accelerometer serve multiple functions: its primary function for general vehicle dynamics monitoring and its secondary function for road grade estimation. This multi-functionality allows accurate road grade measurement without additional hardware, enabling better fuel economy control through accurate engine stop-start decisions and transmission shift management.
3Loss of energy
If engine automatic stop-start control is implemented based on inaccurate road grade estimation, then fuel economy may be improved on flat roads, but engine reliability deteriorates due to unnecessary stop attempts on steep hills
Solution Approach 1:
The patent implements feedback control by continuously monitoring the accelerometer-based road grade estimation and using this information to make real-time decisions about engine stop-start control. The system compares the estimated road grade against threshold values to determine whether conditions are suitable for engine stopping, ensuring that stop-start actions are only taken when appropriate and avoiding unreliable stops on steep hills.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system accurately estimates road grade and improves fuel economy by preventing unnecessary engine stop-start cycles and optimizing transmission shifts based on precise road grade calculations.
Implementation Method 1
The vehicle longitudinal acceleration sensor measures the longitudinal acceleration of the vehicle
Implementation Method 2
α=sin−1(Fα/mg) where α is the road grade, Fg is the force acting on the vehicle due to gravity, Fα is the force acting on the vehicle due to the road grade, m is the mass of the vehicle, and ag is the acceleration of the vehicle due to gravity
Data Source
AI summary
A system according to the principles of the present disclosure includes a longitudinal acceleration estimation module, a vehicle longitudinal acceleration sensor, a road grade estimation module, and an actuator control module. The longitudinal acceleration estimation module estimates a longitudinal acceleration of a vehicle based on at least one of a transmission output speed and a wheel speed. The vehicle longitudinal acceleration sensor measures the longitudinal acceleration of the vehicle. The road grade estimation module estimates a grade of a road on which the vehicle is traveling based on the estimated longitudinal acceleration and the measured longitudinal acceleration. The actuator control module controls an actuator of the vehicle based on the estimated road grade.