Vehicle Input Switch Circuit for Voltage-Based Fault Detection
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Solution Overview
Problem
Existing input devices for motor vehicles cannot reliably detect faults in switching contacts, such as breaks or resistance changes, which prevents their use in safety-critical applications like autonomous driving.
Innovation Solution
The input device incorporates an evaluation circuit to detect and distinguish actuation and fault states by measuring voltages at a measuring node, using resistors and power supply terminals, and optionally includes a dome- or cup-shaped switching contact for haptic feedback and enhanced fault detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a simple switching element is used, then the device complexity is reduced, but the reliability of fault detection deteriorates
Solution Approach 1:
The switching element is divided into multiple independent terminals (first terminal, second terminal, third terminal) with separate connection paths. The first resistor connects to the first terminal, the second resistor connects to the second terminal, and the third resistor connects to the third terminal. This segmentation allows independent monitoring of each path, enabling reliable fault detection without requiring complex integrated circuits.
Solution Approach 2:
Three resistors are introduced as intermediary elements to create measurable voltage drops across different paths. The first resistor between the first power supply terminal and first terminal, the second resistor between the second power supply terminal and second terminal, and the third resistor between the first power supply terminal and third terminal serve as mediators that convert switching states into distinguishable voltage signals for fault detection.
2Measurement precision
If voltage-based detection is implemented, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The circuit is designed to create equipotential relationships in different switching states. When the switching contact connects specific terminals, it creates predictable voltage equalization patterns that can be detected by the evaluation circuit. The resistors are selected to create distinct voltage levels at the measuring node for each possible switching state, enabling precise measurement without complex instrumentation.
Solution Approach 2:
The mechanical switching action is replaced with electrical voltage measurement for detection. Instead of mechanically sensing the switching contact position, the invention uses voltage-based detection through resistive dividers and evaluation circuits that convert mechanical switching states into electrical signals, enabling more precise and reliable detection.
3Reliability
If multiple terminals are used for fault detection, then the reliability is improved, but the ease of operation deteriorates
Solution Approach 1:
The switching element with multiple terminals serves multiple functions simultaneously: it enables normal switching operation, provides fault detection paths, and allows state monitoring. The same physical structure (switching contact and terminals) is used for both actuation and diagnostic purposes, eliminating the need for separate test switches or additional operational complexity.
Solution Approach 2:
The switching element performs self-diagnostics through its own terminal structure. By incorporating multiple terminals and resistors connected to power supply terminals, the device monitors its own operational state and detects internal faults automatically during normal operation, without requiring external testing equipment or additional user actions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables clear identification of actuation and fault states, ensuring reliable operation and safety in safety-critical applications by providing distinct voltage values for each state, enhancing safety and reliability.
Implementation Method 1
a first resistor (9) connected to a second power supply terminal (8), wherein a measuring node (10) is located between the first resistor (9) and the first terminal (4)
Data Source
Figure 1a~2c
Figure 3a~4c
Figure 5a~5b
AI summary
The invention relates to an input device (1) for safety-relevant functions of a motor vehicle, having a switch contact (3) with a first connection (4) and a mating contact (5) with a second connection (6). A first resistor (9) is connected between a voltage supply connection (8) and one connection (4, 6) of the switch element (2) and a second voltage supply connection (7) is connected to the other connection (4, 6) of the switch element (2). A measuring node (10), via which an actuation-dependent voltage can be captured, is provided between the first resistor (9) and the associated connection (4, 6). The problem addressed by the invention is that of developing input devices of the type in question such that they can be used for safety-relevant applications in the motor vehicle. This problem is solved by the switch contact (3) having a third connection (12) at which a second resistor (13), which is connected to the second connection (6) of the switch element (2), is provided.