Vehicle Speed Monitoring with Low-Speed Sensor Switching
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Solution Overview
Problem
The reliability of vehicle speed detection using vehicle speed sensors is low when vehicles travel at low speeds, as the sensors' output is not reliable at such speeds.
Innovation Solution
A monitoring device that selects between two methods to acquire vehicle speed: one using detection values from vehicle speed sensors and the other using information about the rotational speed of an electric motor, based on the reliability of the detection value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vehicle speed sensor is used to detect vehicle speed, then the detection method is simple and cost-effective, but the reliability of detection value is low when vehicle travels at low speed
Solution Approach 1:
The system dynamically switches between two speed acquisition methods based on vehicle operating conditions. When the vehicle is stationary or moving at very low speeds, the motor rotational speed method is used. When the vehicle is moving at normal speeds, the wheel speed sensor method is used. This dynamic adaptation resolves the contradiction by selecting the appropriate method for each operating regime.
Solution Approach 2:
The system incorporates multiple speed acquisition methods (wheel speed sensor and motor rotational speed) that can serve different purposes. The wheel speed sensor provides reliable data during normal operation, while the motor rotational speed provides reliable data during low-speed or stationary conditions. This multi-functionality ensures reliable speed detection across all operating conditions.
2Reliability
If motor rotational speed information is used to acquire vehicle speed, then the detection reliability at low speed is improved, but the device complexity increases
Solution Approach 1:
The system uses a determination unit that dynamically evaluates whether the vehicle is in a low-speed or stationary state, and switches between acquisition methods accordingly. This dynamic control ensures that the more complex motor rotational speed method is only used when necessary, minimizing overall system complexity while maintaining reliability.
Solution Approach 2:
The system uses existing motor rotational speed information that is already available from the motor control unit, rather than requiring additional dedicated sensors or measurement devices. This self-service approach leverages existing system resources to improve low-speed detection reliability without proportionally increasing device complexity.
3Measurement precision
If wheel speed sensor is used for speed detection, then the system structure is simple, but the detection precision is insufficient at low speeds
Solution Approach 1:
The system dynamically selects the appropriate measurement method based on vehicle speed conditions. At low speeds where wheel speed sensor precision is insufficient, the system switches to motor rotational speed measurement which provides adequate precision. This dynamic selection resolves the precision-complexity contradiction by using the appropriate method for each operating regime.
Solution Approach 2:
The system changes the measurement parameter from wheel rotation speed to motor rotational speed when operating conditions indicate low vehicle speed. This parameter change allows the system to maintain measurement precision across different operating ranges by selecting the parameter that provides adequate resolution for the current speed regime.
Data Source
AI summary
A monitoring device monitors a vehicle that travels through unattended operation using an electric motor as a power source, and includes: a selection unit that selects which one of a first method and a second method is used to acquire a speed of the vehicle according to a status about the speed of the vehicle, the first method being a method of acquiring a speed of the vehicle using a detection value from a vehicle speed sensor that makes an output in synchronization with rotation of a wheel of the vehicle, and the second method being a method of acquiring a speed of the vehicle using information about a rotational speed of the electric motor provided in the vehicle; and a speed acquisition unit that acquires a speed of the vehicle using the method selected by the selection unit.