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A thermal vacuum switch (TVS) is a component commonly found in automotive engines, particularly those equipped with vacuum-operated systems such as exhaust gas recirculation (EGR) valves and vacuum advance distributors. Its primary function is to regulate vacuum levels or routing based on temperature changes, ensuring optimal engine performance and emissions control under various operating conditions.

Here are some key functions and features of a thermal vacuum switch:

  1. Temperature Sensing: The TVS is equipped with a temperature-sensitive mechanism that responds to changes in temperature within the engine or its surroundings. It typically measures parameters such as coolant temperature, underhood temperature, or ambient air temperature.
  2. Vacuum Control: Based on the temperature readings, the TVS controls the level of vacuum applied to specific components in the engine system. For example, in engines equipped with EGR valves, the TVS regulates the amount of vacuum supplied to the EGR valve based on temperature conditions.
  3. Vacuum Routing: In addition to controlling vacuum levels, the TVS may also govern the routing of vacuum lines within the engine compartment. This routing may vary depending on temperature requirements for different engine functions.
  4. Switching Mechanism: The TVS employs a switching mechanism that activates or deactivates vacuum flow based on temperature thresholds. For example, when coolant temperature reaches a certain level (e.g., approximately 107°C), the TVS may switch from ported vacuum to manifold vacuum, altering the timing or operation of vacuum-operated components.
  5. Emissions Control: By regulating vacuum levels and routing, the TVS contributes to effective emissions control in the engine system. It helps optimize the operation of emission control devices such as EGR valves, ensuring compliance with emissions standards.
  6. Integration with Engine Management System: The TVS is often integrated into the engine management system, working in conjunction with other sensors and actuators to achieve precise control over engine functions. It may communicate with the engine control unit (ECU) or other control modules to coordinate vacuum-related operations.

Overall, the thermal vacuum switch plays a crucial role in maintaining engine performance, emissions control, and efficiency by adjusting vacuum levels and routing based on temperature variations encountered during engine operation.

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