Vehicle Suspension Control Using Wheel Speed for State Variable Computation
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Solution Overview
Problem
Conventional suspension control systems require stroke sensors and vertical G sensors to compute relative velocity between sprung and unsprung masses, which is impractical due to space constraints and reduces precision, especially when the suspension geometry has a small or no caster angle.
Innovation Solution
A suspension control system that uses a wheel rotational speed sensor to compute base input values, which are then used in a vehicle model to calculate state variables like unsprung load, sprung velocity, and suspension stroke speed, eliminating the need for these sensors and accounting for caster angle variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If stroke sensors and vertical G sensors are used to detect relative velocity between sprung and unsprung masses, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the essential measurement function from complex sensor systems and implements it through a simplified wheel rotational speed sensor. By computing relative velocity from wheel speed variations rather than directly measuring it with multiple sensors, the system achieves the necessary measurement precision while dramatically reducing device complexity and cost.
Solution Approach 2:
The patent introduces wheel rotational speed as an intermediary parameter to indirectly determine the relative velocity between sprung and unsprung masses. Instead of directly measuring the difficult-to-obtain relative velocity with complex sensors, the system measures wheel rotational speed variations and computes the desired parameter through mathematical relationships, simplifying the measurement system.
2Measurement precision
If stroke sensors are mounted within the wheelhouse or adjacent vehicle body parts, then measurement precision is improved, but ease of manufacture deteriorates due to space constraints
Solution Approach 1:
The patent removes the requirement for internally mounted stroke sensors by extracting the measurement function to an externally accessible component - the wheel rotational speed sensor. This eliminates the space constraints within the wheelhouse while maintaining the capability to compute relative velocity for skyhook control.
3Device complexity
If relative velocity is computed from wheel rotational speed variations, then device complexity is reduced, but measurement precision deteriorates when caster angle is small or zero
Solution Approach 1:
The patent addresses the caster angle limitation by changing the computational parameters and methodology. Instead of relying on geometric relationships that fail with small caster angles, the system uses wheel rotational speed variations in conjunction with vehicle model-based state variable computation to accurately determine relative velocity regardless of caster angle magnitude.
Solution Approach 2:
The system employs feedback through vehicle model-based state variable computation to compensate for potential inaccuracies in the wheel speed-based relative velocity calculation. By continuously comparing computed state variables with actual system behavior, the system maintains measurement precision across different suspension geometries including those with small or zero caster angles.
Data Source
AI summary
A suspension control system allows a state variable of a vehicle used for the damper damping force control to be computed at a high precision without regards to the caster angle given to the suspension geometry. A suspension control system for a vehicle provided with a variable damper that can adjust a damping force according to an input signal comprises a wheel rotational speed sensor for detecting a wheel rotational speed, a gain circuit for computing the unsprung load of each wheel according to the wheel rotational speed variation detected by the wheel speed sensor, a single wheel model computing unit for computing the sprung velocity and the stroke speed by inputting the unsprung load to a single wheel model representing the behavior of the vehicle, and a damper control unit for controlling a damping force of the variable damper according to the computed sprung velocity and stroke speed.