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Types of EGR Valves

To be sure of fitting the correct replacement Exhaust Gas Return valve it is good to have an understanding of the different types available. There are many different types of EGR valves, some have electronic controls and some have mechanical controls, some of which work strictly on vacuum and others which work on a combination of vacuum and pressure.

Petrol and diesel powered engines have various EGR valve system designs. Vehicles on the road today may use one of six or more different valve configurations.

Vacuum Operated
Vacuum Operated (click to enlarge)
Electronically Operated
Electronically Operated (click to enlarge)

 

On older models, a small diameter vacuum hose operates a basic EGR valve. The hose connects the top of the valve to the throttle body or carburettor. The EGR valve's metal disk typically houses a vacuum diaphragm, spring, and plunger. Newer vehicle models use electronic EGR valve systems that may include additional components, even a digital valve that eliminates the need for vacuum control altogether.

Later models may come equipped with electronic vacuum EGR valves inside a small block or cylinder. The valve works the same way as in older models, except that an electronic EGR position sensor communicates with the cars ECU computer for better control. You may see electric solenoids connected through vacuum lines to the valve as well.

A more radical EGR valve system design is the replacement of the valve with EGR jets at the bottom of the intake manifold. Some newer high-efficiency engines, for example those with variable valve timing (VVT) don't even use an EGR valve system.

Pneumatic EGR Valves

Activated by vacuum through electromagnetic valves which generally have an open – closed function only. The vacuum is generated from the inlet manifold or by a vacuum pump, depending on vehicle type, and may incorporate an EGR position sensor.

Pneumatic EGR Valves Pneumatic EGR Valves

A small pipe from the exhaust manifold or an internal crossover passage in the cylinder head and intake manifold routes exhaust to the valve. When vacuum is applied to the EGR valve, it opens. This allows intake vacuum to suck exhaust into the engine. To prevent the EGR valve from opening when the engine is cold, the vacuum line to the EGR valve may be connected to a parted vacuum switch or an ECU controlled solenoid. Vacuum is not allowed to pass to the valve until the engine is warm, as the EGR valve isn't needed when the engine is cold, only when it is warm and under load.

Electric EGR Valves

Activated directly by the engine control unit (ECU) and no longer needs a vacuum source or electro–pneumatic valves.

Type 1 – Linear Electric EGR Valve
The Linear EGR valve is generally activated under the following conditions:

  • Warm engine operation – using Engine coolant temperature (ECT) sensor
  • Above idle speed and utilises the following signals:
    • TPS
    • MAF Sensor
    • Engine RPM

The engine ECU monitors the EGR position and monitors the pintle position feedback signal and adjusts the pintle accordingly.

Electric EGR Valves Electric EGR Valves

Type 2 - ECU Controlled EGR solenoid with vacuum operated EGR valve.

Type 3 – ECU Controlled EGR Solenoid With Vacuum Operated EGR Valve utilising Differential Pressure Sensor. EGR Differential Pressure Sensor Measures the difference in pressure across a restriction placed in the EGR exhaust gas supply.

Electric EGR Valves with Cooler Modules

The Electric EGR Valve with Cooler Modules offers further reduction of combustion temperatures and control of emissions. More stringent emission regulations require improved pollutant reduction methods. Cooled EGR valves can play a significant role in reducing combustion chamber temperatures and levels of NOx formation.

Electric EGR Valves with Cooler Modules

DC Motor EGR Valve with Hall Sensor Response

Current units fitted for increased opening force and quicker response time in diesel applications.

DC Motor EGR Valve with Hall Sensor Response

EGR Valve Operation on Common Rail Diesel and Direct Petrol Injection

A regulating throttle assembly or intake manifold flap is utilised to create a greater pressure difference between the exhaust and inlet manifolds to allow the exhaust recirculation to enter the inlet in quantities

Applications with No EGR Valve

On many late model engines with Variable Valve Timing (VVT), there is no EGR valve because the VVT system varies the timing of the exhaust valves to provide the same effect as EGR. By changing the point at which the exhaust valves close when the engine is working hard under load, a small amount of exhaust gas can be retained in the cylinders for the next combustion cycle. The big difference is that the VVT system can react to changing engine loads much more quickly and precisely than a traditional EGR valve. Using VVT for EGR also eliminates many of the problems associated with EGR valves such as carbon build up and valve sticking or failure.

Applications with No EGR Valve

Exhaust Gas Return can also be implemented by using a variable geometry turbocharger (VGT) which uses variable inlet guide vanes to build sufficient backpressure in the exhaust manifold. For Exhaust Gas Return to flow, a pressure difference is required across the intake and exhaust manifold and this is created by the VGT.

Another EGR actuation method that has been experimented with is using a throttle in a turbocharged diesel engine to decrease the intake pressure, thereby initiating EGR flow.

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