Rear-Wheel Steering Rate Control for Launch Agility and NVH
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Solution Overview
Problem
Rear wheel steering systems in vehicles are not designed for continuous use when stationary, leading to undesirable noise, vibration, and harshness (NVH) issues during low-speed maneuvers.
Innovation Solution
A control system that limits the maximum steering rate of rear wheel steering based on vehicle speed and time since launch, allowing higher rates initially to enhance agility and responsiveness, while minimizing NVH at low speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If rear wheel steering is used immediately upon launch, then vehicle agility and responsiveness are improved, but noise, vibration and harshness (NVH) increase
Solution Approach 1:
The steering rate limit is made dynamic by introducing a time-based threshold that adjusts the steering rate limit based on the elapsed time since vehicle launch. During the initial period (0 to threshold seconds), a first steering rate limit is applied to maximize agility. After the threshold is exceeded, a second (lower) steering rate limit is applied to reduce NVH. This dynamic adjustment resolves the contradiction by allowing high steering rates only when needed for agility during launch.
Solution Approach 2:
The patent changes the parameter of steering rate limit based on the time parameter. By monitoring the elapsed time since launch and comparing it against a predetermined threshold, the system changes the steering rate limit parameter from a high value during the initial period to a lower value afterward. This parameter change allows the system to optimize for agility during launch and for NVH reduction during steady-state operation.
2Object-affected harmful factors
If steering rate is limited to minimize NVH at low speeds, then noise reduction is improved, but vehicle responsiveness and driver feedback are degraded
Solution Approach 1:
The steering rate limit is dynamically adjusted based on the time threshold. During the initial period after launch, the system applies a higher steering rate limit to maintain responsiveness and driver feedback. After the threshold is exceeded, the system transitions to a lower steering rate limit to minimize NVH. This dynamic approach ensures that responsiveness is not compromised during critical launch phases while still achieving NVH reduction during steady-state operation.
Solution Approach 2:
The system implements periodic monitoring of the elapsed time since launch and periodically adjusts the steering rate limit based on whether the time threshold is exceeded. This periodic action allows the system to switch between different steering rate limits at appropriate intervals, balancing responsiveness and NVH reduction based on the operational phase.
Data Source
AI summary
A control system for a vehicle is described, the control system comprising one or more controllers. The control system configured to receive an indication of current vehicle speed, monitor a time period since vehicle launch, and limit a maximum steering rate of a steering system of the vehicle in dependence on the current vehicle speed and a period of time since launch. In this way, by controlling the limiting of the maximum steering rate in dependence not only on vehicle speed but also on a time since launch, it is possible to permit a greater steering limit (or no directly imposed limit beyond the mechanical capability of the rear wheel steering system) to be used immediately upon launch of the vehicle (and a short period thereafter), providing the vehicle with greater agility as it pulls away, and making the handling of the vehicle (and in particular the steering thereof) feel more responsive to the driver. The increased NVH is seen as an acceptable compromise during this initial time window following launch.