Global automotive supplier DENSO has developed an exhaust gas recirculation (EGR) valve unit, a major component of EGR systems that helps make diesel engine emissions cleaner. The new unit, the first in the world to integrate an air intake throttle valve and an EGR valve, is half the size of conventional models and requires fewer components, thus reducing costs. The unit will be installed in a diesel passenger vehicle to be sold in Europe from later this year.
Conventionally, air intake throttle valves and EGR valves were separately installed to vehicles. The air intake throttle valve controls the amount of air entering the engine and the EGR valve controls the amount of exhaust gas to be recirculated into the engine. By integrating the two valves into one unit, Denso combined the ducts and reduced the connectors, resulting to reducing the size to half compared to previous models. As the EGR system needs to be installed in a limited space close to the engine, a smaller system enables automakers to design engines more flexibility.
Conventionally, a motor for valve opening and closing, paired with a sensor to detect the valve opening and closing angle, were needed for both the air intake throttle valve and EGR valve. However, Denso’s new unit, which integrates the two valves, needs only one motor and one sensor, thus reducing the cost.
The air intake throttle valve and EGR valve are connected through a highly flexible coupling (cam-link mechanism), allowing the new unit to be applied to various engine parameters, including displacement and output, merely by changing the shape of the connection between the two valves (cam profile).
The diesel engine EGR system, which consists of an EGR valve, an air intake throttle valve, and an EGR cooler, recirculates a portion of the exhaust gas into the engine to lower the combustion temperature and hence reduce emissions of oxides of nitrogen (NOx). With the introduction of stricter exhaust emission regulations worldwide, including Euro 6 standards in Europe, this system has attracted much attention.
The main type of EGR system used today is the high pressure loop (HPL) EGR system where the exhaust gas to be recirculated is taken from an upstream section of the exhaust passage. However, this system has a disadvantage: diverting a fraction of the exhaust gas before the turbocharger that uses exhaust gas energy to force extra air into the engine reduces the amount of exhaust gas energy which can be used by the turbocharger, which makes it difficult for the forced induction device to produce high power. Therefore, the combination of a high pressure loop EGR with low pressure loop (LPL) EGR that takes the exhaust gas to be recirculated from a downstream section of the exhaust passage, is expected to be widely used in the future.
Denso has been mass-producing its first EGR valves used in LPL EGR systems since February 2011. It has also been mass-producing LPL EGR systems with a separate air intake throttle valve and EGR valve since November 2012. Denso’s new EGR valve unit is designed for LPL EGR systems.