Air Injection: Description and Operation

Air Injection Reactor System:

To reduce HC and CO emissions, this system injects air into the exhaust ports to accelerate oxidation. The air switching valve (ASV) directs air flow from the air pump. A vacuum switching valve (VSV) actuated by the electronic control module (ECU) controls the mode of the ASV.

AIR PUMP

The air pump consists of the pump body, cover, rotor, vanes and relief valve. It is belt-driven by the engine.
Air is drawn through the air cleaner and suction hose into the pump suction chamber. As the rotor turns, the vanes trap the air and carry it to the outlet chamber and then to the air manifold.
The relief valve is closed by spring tension under most conditions. When pressure exceeds spring tension, the valve opens to release excess air that would otherwise surpass pump outlet air pressure.

AIR MANIFOLD AND AIR INJECTION NOZZLES

Pressurized air flows from the air pump, through the check valve and into the air manifold. When directed by the system, air is injected into the exhaust manifold through nozzles near the exhaust valves.

Air Injection System Schematic:

AIR SWITCHING VALVE (ASV)

The purpose of the ASV is to direct air flow from the air pump. It is actuated by intake manifold vacuum and air pump pressure flowing through the vacuum switching valve (VSV) as directed by a signal from the ECU. Air pump output is directed to the check valve and air manifold or vented to the atmosphere through a hose and silencer. The ECU determines ASV mode by calculating various inputs, including throttle position and coolant temperature.



VACUUM SWITCHING VALVE (VSV)

The VSV has three ports, one connected to intake manifold vacuum and two operated by an electric solenoid plunger which is energized when the coolant temperature is below 122~F or for 10 seconds after the wide open throttle (WOT) switch is energized with the coolant temperature above 122~F. The solenoid is de-energized immediately after the WOT switch is turned off during this 10 second period.
When energized, the VSV connects the diaphragm chamber of the ASV to intake manifold vacuum and causes air pump output to be diverted to the atmosphere. When de-energized, the VSV ports are closed and and the ASV directs air pump output to the check valve and air manifold.

Check Valve:

CHECK VALVE

The check valve is designed to allow air to pass through in only one direction. The valve is pushed open when the pressure of air supplied from the air pump overcomes the valve spring tension and closes with the counterflow of exhaust gas from the manifold. This protects the air pump and hoses against damage when air supply from the air pump is stopped due to a broken drive belt or when backfiring occurs.