Adaptive Cruise Braking With Negative Speed Setpoint at Low Speed
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Solution Overview
Problem
Existing adaptive cruise control systems in motor vehicles face reliability issues when measuring low speeds, leading to potential activation of parking brakes while the vehicle is still moving due to inaccurate speed sensor readings.
Innovation Solution
The method involves setting a speed setpoint to a negative value when stopping, ensuring continuous braking control without modifying the control law, using existing sensors, and maintaining the vehicle stationary after complete stop, by determining the control setpoint based on the difference between the speed setpoint and measured speed, and incorporating external data such as the preceding vehicle's speed and distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If speed sensors are used to measure vehicle speed in adaptive cruise control, then the system can control vehicle speed and maintain safety distance, but the measurement becomes unreliable at very low speeds (less than 1 km/h)
Solution Approach 1:
The invention changes the speed setpoint parameter from zero to a negative value when stopping is required. This parameter change allows the control system to continue functioning reliably at low speeds by maintaining a non-zero speed difference between setpoint and measured speed, thereby ensuring continuous braking control without being affected by sensor measurement unreliability at very low speeds
2Productivity
If the system extrapolates stopping based on speed evolution and activates parking brake when vehicle is considered stationary, then stopping control is implemented, but the parking brake may be activated while the vehicle is still moving
Solution Approach 1:
The invention applies preliminary anti-action by setting a negative speed setpoint before the vehicle actually stops. This creates a preemptive braking command that ensures the vehicle will stop accurately without relying on extrapolation or premature parking brake activation, thereby preventing the harmful effect of activating brakes while the vehicle is still moving
Solution Approach 2:
The control system continuously calculates the difference between the negative speed setpoint and the measured speed, using this feedback to maintain appropriate braking control. This feedback mechanism ensures accurate stopping detection and prevents premature or incorrect activation of the parking brake
3Ease of operation
If the speed setpoint is set to zero when stopping, then the vehicle is considered stationary, but the control law cannot distinguish between actual stationary state and low-speed movement due to sensor errors
Solution Approach 1:
The invention changes the speed setpoint parameter from zero to a negative value when stopping is required. This parameter change allows the control system to continue functioning reliably at low speeds by maintaining a non-zero speed difference between setpoint and measured speed, thereby ensuring continuous braking control without being affected by sensor measurement unreliability at very low speeds
Data Source
Figure 1~4
AI summary
The invention relates to a method for controlling a drive unit of a motor vehicle, comprising: - a step of acquiring a speed instruction (Cv), - a step of measuring the speed (VM) of the motor vehicle, and - a step of computing a control instruction for said drive unit on the basis of the measured speed and of the speed instruction. According to the invention, when the motor vehicle is moving forwards and should be stopped, the speed instruction is determined so as to be strictly less than zero.