Motor Torque Control for Low Speed Vehicle Stopping

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Solution Overview

Problem

Existing vehicle speed control systems struggle to accurately manage vehicle speed at low speeds, particularly in situations where the driver may not perceive the vehicle as moving, leading to potential rolling or inability to stop the vehicle effectively.

Innovation Solution

The system employs a road load module and closed loop module to determine road load torque and adjust torque limits based on vehicle speed, using a motor torque module to set motor torque commands and control the electric motor, ensuring the vehicle can be brought to a stop and maintain zero acceleration within a predetermined low speed range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If the vehicle speed is reduced to very low speeds (0.1-0.3 km/h), then the vehicle appears stationary to the driver, but the vehicle may continue to roll imperceptibly

Engineering Contradiction:

Improvedriver perception of vehicle motionVSAvoidvehicle stopping accuracy

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

The control system applies motor torque in advance to counteract road load torque before the vehicle reaches the imperceptible speed range, preventing the vehicle from entering the rolling zone where motion cannot be perceived by the driver

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system continuously monitors vehicle speed and dynamically adjusts motor torque based on feedback from the speed sensor, comparing actual speed against target speed to maintain precise stopping control and prevent imperceptible rolling

Inventive Principle:

Principle #23Feedback

2Reliability

If the torque limit is increased to prevent rolling at low speeds, then stopping accuracy improves, but the risk of exceeding maximum torque capacity increases

Engineering Contradiction:

Improvevehicle stopping accuracyVSAvoidtorque limit violation

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The torque limit is made dynamic rather than fixed, adjusting in real-time based on current vehicle speed and road load conditions. The limit increases as speed decreases to the imperceptible range, then decreases again as the vehicle approaches complete stop, optimizing stopping force without exceeding motor capabilities

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the torque parameter dynamically by adjusting the torque limit based on vehicle speed and road load torque calculations, allowing the torque application to adapt to changing conditions and prevent both rolling and torque saturation

Inventive Principle:

Principle #35Parameter changes

3Reliability

If mechanical brakes are used to stop the vehicle at low speeds, then stopping reliability improves, but brake wear increases

Engineering Contradiction:

Improvevehicle stopping capabilityVSAvoidbrake wear

Core Design Contradiction:

ReliabilityVSLoss of substance

Solution Approach 1:

The system replaces mechanical brake application with electric motor torque control for stopping the vehicle. The motor torque counteracts road load torque to bring the vehicle to a complete stop, eliminating the need for mechanical brake engagement and thereby preventing brake wear

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS10259341B2Control systems and methods for preventing low vehicle speed

Publication Date: 2019.04.16 GM GLOBAL TECHNOLOGY OPERATIONS LLC

AI summary

A road load module is configured to determine a road load torque to maintain zero vehicle acceleration. A closed loop (CL) module is configured to determine a CL torque based on a difference between a target vehicle speed and a vehicle speed. A motor torque module is configured to: produce a limited CL torque by limiting the CL torque to a predetermined torque limit when a magnitude of the CL torque is greater than a magnitude of the predetermined torque limit; when the vehicle speed is within a predetermined low speed range and a magnitude of the road load torque is greater than or less than a magnitude of a predetermined maximum torque, adjust the predetermined torque limit; and determine a motor torque command based on the limited CL torque and a motor torque request determined based on a position of an accelerator pedal.