Combustion Type Power Heater System System Description

While the engine offers excellent combustion efficiency, it generates low levels of heat. Therefore, depending on the operating condition, the engine coolant temperature may be too low to ensure proper heating. In this case, the heater assembly is used to provide the additional heating.

This heater system provides a heater assembly between the engine and heater core. Air and fuel are introduced into the combustion chamber of the heater and a glow plug is used to ignite this mixture. By heating the engine coolant that flows around the combustion chamber, this system ensures proper heating.

This system, which consists of a heater assembly, heater switch assembly (power heater switch) and heater pump assembly, operates when the engine is idling and the heater switch assembly (power heater switch) is turned on.

1. The heater assembly consists of an ECU, flame sensor, surface sensor, temperature control sensor, glow plug and air blower motor. It cannot be disassembled.
   
2. The ECU in the heater assembly controls this system in accordance with the signals received from the sensors and switches.
   

When the engine is idling, turning the heater switch assembly (power heater switch) on causes the air fan to operate for several seconds for verification purposes. Then, the glow plug starts to preheat the combustion chamber. After that, the heater pump assembly and air fan turn on in order to start low combustion. The heater pump assembly speed is then increased in steps, and this is accompanied by a gradual increase in the speed of the air fan, thus leading to high combustion.

When the engine switch is turned off or the power heater switch is turned off, the heater pump stops, causing the combustion to stop. For the purpose of after-purge, current is applied again to the glow plug, and the air fan is activated for several seconds. Then, the entire system comes to a stop.

While the system is in operation, it controls the heater pump speed, switches between high combustion and low combustion, and always keeps the engine coolant temperature between 75°C (167°F) and 85°C (185°F). If the coolant temperature exceeds 85°C (185°F), the heater pump assembly stops automatically to stop the combustion. Thereafter, when the engine coolant temperature reaches 75°C (167°F) or below, ignition occurs again. The operation of the glow plug, air fan and heater pump assembly during extinguishing and re-igniting is the same as when these are operated by switch as mentioned previously.

If the glow plug breaks, the ECU detects the problem and stops automatic operation to prevent heater assembly operation.

If the temperature detected by the temperature control sensor or surface sensor exceeds 125°C (257°F), the ECU determines that the heater assembly is operating without engine coolant and automatically stops the system.

If the difference in temperature detected by the temperature control sensor and surface sensor exceeds 25°C (77°F), the ECU determines that the flow volume of the engine coolant is insufficient and automatically stops the system.

If the temperature of the exhaust gas detected by the flame sensor is low, the ECU determines that a non-ignition or a misfiring condition exists and automatically stops the system.

If an open or short circuit exists in the sensors or actuators, the ECU automatically stops the system.

If the air fan seizes, the ECU automatically stops the system.