Vehicle Creep Torque Stabilization via Acceleration-Based Gradient Estimation
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Solution Overview
Problem
Existing vehicle control systems for hybrid and electric vehicles experience abrupt changes in creep torque when transitioning from standstill to motion on upward slopes, leading to unpleasant sliding sensations for the driver due to sudden changes in estimated road surface gradients, which are calculated based on wheel speed sensor outputs.
Innovation Solution
A control apparatus and method that includes an acceleration detecting device, a rotation speed detecting device, and an estimating portion to calculate and limit the change in estimated road surface gradient when vehicle speed is below a certain threshold, and optionally corrects the gradient based on detected acceleration to stabilize creep torque output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the road surface gradient is calculated based on the derivative value of the rotation speed detected by the wheel speed sensor, then the gradient can be estimated after the vehicle has started to move, but the derivative value at the point where detection signal starts is large causing abrupt change in estimated gradient and creep torque fluctuation
Solution Approach 1:
The control apparatus applies preliminary action by detecting vehicle acceleration before the wheel speed sensor can provide reliable detection signals. The acceleration detecting device operates from standstill, providing gradient estimation data before the vehicle reaches several km/h, thus preventing the abrupt changes that occur when derivative values are calculated from noisy speed signals at low speeds.
Solution Approach 2:
The invention introduces an intermediary approach by using acceleration detection as a mediator between the vehicle's motion state and the gradient estimation. Instead of directly calculating gradient from wheel speed derivative (which causes instability), the acceleration signal serves as an intermediate measurement that is then integrated over time to estimate gradient, providing a more stable basis for creep torque control.
2Loss of information
If the wheel speed sensor is used to detect rotation speed for gradient calculation, then gradient information can be obtained, but the detection signal is delayed until vehicle speed reaches several km/h causing the vehicle to slide downhill backwards on upward slopes
Solution Approach 1:
The acceleration detecting device performs preliminary detection of vehicle motion state from standstill, providing gradient estimation information before the wheel speed sensor becomes operational. This preliminary action ensures that gradient information is available immediately when the vehicle starts moving, preventing the information loss that occurs during the delay period.
Solution Approach 2:
The invention substitutes the mechanical wheel speed sensing system with an acceleration-based detection system for the specific function of gradient estimation at low speeds. By replacing the derivative calculation from speed signals with direct acceleration measurement and integration, the system eliminates the mechanical delay inherent in wheel speed sensor operation.
3Use of energy by moving object
If creep torque is generated using the motor to prevent brake drag and vehicle sliding, then fuel efficiency is improved and vehicle stability is enhanced, but abrupt changes in estimated gradient cause creep torque fluctuation and driver discomfort
Solution Approach 1:
The control apparatus implements feedback by continuously monitoring vehicle acceleration and using it to adjust the gradient estimation in real-time. This feedback loop ensures that creep torque adjustments are based on accurate, up-to-date gradient information, preventing the torque fluctuations that cause driver discomfort while maintaining the fuel efficiency benefits of motor-based creep torque generation.
Data Source
AI summary
An HV_ECU executes a program including a step of calculating an estimated gradient, a step of performing rate limit processing on a change in the estimated gradient when on a hill and an absolute value of the vehicle speed is equal to or below V(0), a step of performing hysteresis processing, a step of calculating a creep increase coefficient, and a step of calculating a creep increase torque.