Steering Sensor Torque Calculation Stability

Solution Overview

Problem

Existing sensor devices in electric power steering systems face challenges in handling abnormal sensor signals, leading to fluctuations in calculated physical quantities when switching from abnormal to normal signals, which can result in incorrect steering torque calculations and poor steering feel for drivers.

Innovation Solution

A sensor device comprising a main sensor and a sub sensor, where the sub sensor outputs signals at a shifted timing, allowing the controller to continuously calculate target physical quantities by combining main and sub sensor data during abnormality detection, reducing fluctuations by using a weighted average of pre-abnormal and sub sensor values.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the system switches from using main sensor signals to sub sensor signals when abnormality is detected, then the system reliability is improved, but the calculation stability deteriorates due to fluctuations in the target physical quantity

Engineering Contradiction:

Improvesystem reliabilityVSAvoidcalculation stability

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The system performs preliminary actions by storing the target physical quantity calculated before abnormality detection occurs. During the transition period when abnormality is detected but not yet established, the system retrieves and uses this pre-stored value to maintain calculation stability, avoiding abrupt fluctuations that would occur with direct switching to sub sensor signals.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The stored target physical quantity acts as an intermediary during the transition period. Instead of directly switching from main sensor signals to sub sensor signals, the system uses the previously calculated target physical quantity as a bridge, smoothing the transition and preventing calculation fluctuations while maintaining system reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the system uses only sub sensor signals when main sensor abnormality is established, then the measurement continuity is improved, but the measurement precision deteriorates due to signal timing shifts

Engineering Contradiction:

Improvemeasurement continuityVSAvoidmeasurement precision

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The system performs preliminary actions by storing the target physical quantity calculated before abnormality detection occurs. During the transition period when abnormality is detected but not yet established, the system retrieves and uses this pre-stored value to maintain calculation stability, avoiding abrupt fluctuations that would occur with direct switching to sub sensor signals.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The stored target physical quantity acts as an intermediary during the transition period. Instead of directly switching from main sensor signals to sub sensor signals, the system uses the previously calculated target physical quantity as a bridge, smoothing the transition and preventing calculation fluctuations while maintaining system reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If the system establishes abnormality after a transition period with a predetermined number of cycles, then the reliability is improved by avoiding false detection, but the response time worsens

Engineering Contradiction:

Improveabnormality detection reliabilityVSAvoidresponse time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The system applies partial action by using a predetermined number of cycles (e.g., one cycle) to establish abnormality rather than requiring complete certainty. This partial verification approach balances reliability improvement through false detection avoidance with acceptable response time, avoiding excessive delay while reducing false positives.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS10077069B2Sensor device and electric power steering device using same

Publication Date: 2018.09.18 DENSO CORP

AI summary

A sensor device includes a main sensor, a sub sensor, and an Electronic Control Unit (ECU). The ECU has a torque calculator that sets, as a steering torque, a main steering torque that is calculated based on a main sensor signal when a main output signal is normal. During a transition period between an abnormality detection and an abnormality establishment regarding the main output signal, the torque calculator calculates the steering torque based on (i) a sub steering torque calculated based on a sub sensor signal and (ii) a prior-to-abnormality-detection main steering torque. In such manner, even when abnormality is detected in a part of the sensor signals, a fluctuation of the steering torque due to, or accompanying, the switching of the steering torque calculation to a normal signal only calculation is prevented.