ABS Rear Wheel Speed Calculation via Output Shaft Sensor
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Solution Overview
Problem
Rear wheel speed sensors in anti-lock braking systems (ABS) are prone to failure due to harsh environments and aftermarket damage, leading to increased warranty costs and system unreliability, with no mechanism to prevent Powertrain Control Module or Output Shaft Speed sensor failures, and are considered redundant.
Innovation Solution
The system calculates rear wheel speed using the Output Shaft Speed sensor signal, eliminating the need for a differential speed sensor by modifying the CAN message list to send this information to the ABS module, allowing for the elimination of the differential speed sensor and its associated components, wiring, and enhancing ABS reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a differential speed sensor (DSS) is used to calculate rear wheel speed, then rear wheel speed information can be obtained, but the system complexity and cost increase due to additional sensors, wiring, and components
Solution Approach 1:
The patent extracts the rear wheel speed measurement function from the dedicated differential speed sensor (DSS) and relocates it to the existing output shaft speed (OSS) sensor. By eliminating the DSS and using only the OSS sensor along with axle ratio information from the CAN bus, the system removes unnecessary components and wiring while maintaining the required speed measurement capability for ABS operation
Solution Approach 2:
The OSS sensor, originally designed for powertrain control, is made multi-functional by using it for both engine management and ABS rear wheel speed calculation. The patent leverages the existing OSS sensor and its data already present on the CAN bus, eliminating the need for a separate DSS and making the OSS sensor serve dual purposes in the vehicle system
2Measurement precision
If a differential speed sensor (DSS) is installed in harsh environments, then rear wheel speed can be measured, but the sensor becomes prone to failure from heat, acceleration, and physical damage
Solution Approach 1:
The patent introduces an intermediary approach by using the OSS sensor data transmitted through the CAN bus as a mediator between the powertrain system and the ABS system. Instead of placing a sensor directly in the harsh rear wheel environment, the system uses the remotely located OSS sensor in the powertrain compartment, which experiences less extreme conditions, and transmits its data electronically to the ABS module for rear wheel speed calculation
3Ease of operation
If three speed sensors are used in the ABS system, then complete wheel speed information is available, but the cost and potential failure points increase
Solution Approach 1:
The patent discards the redundant differential speed sensor (DSS) that was traditionally considered necessary for rear wheel speed measurement. By recovering and reusing the existing OSS sensor data that was already being collected by the powertrain control module and made available on the CAN bus, the system eliminates the need for the third sensor while maintaining full ABS functionality and diagnostic capability
Data Source
AI summary
An anti-lock braking system (ABS) calculates driven wheel speed without any sensors on the driven axle assembly. A powertrain control module (PCM) receives signals from an output shaft speed (OSS) sensor and adds the speed and axle ratio information to a control network bus. Access to the CAN bus is provided to enable calculation of the rear wheel speed based on such information so that ABS may implement anti-lock braking functionality by taking into account such information.