Mechanism of deposit formation on an electronic throttle body

Abstract

The buildup of deposits on the electronic throttle body (ETB) used to control the intake air flow in an internal combustion engine causes various problems. To obtain information that can be used to prevent the buildup of such deposit, the characteristics and mechanism of the deposit formation were investigated by analysis of the components of the deposit, measurement of the distribution of the deposit thickness, and numerical analysis of the intake air flow. The deposit was found to comprise a complex of fuel and engine oil, high molecular components, and inorganic matter, with engine oil being the major component. The distribution of the deposit thickness was also observed to be similar to that of the temperature decrease across the butterfly valve, indicating that the temperature decrease was related to the deposit formation. In addition, it was established that the deposit component on the downstream side of the butterfly valve was transported very close to the butterfly valve by a circulatory flow. Based on the study results, it is postulated that the mechanism of the ETB deposit formation involves the initial transportation, by the blow-by gas, of hydrocarbons to the ETB air passage, where the hydrocarbons are condensed and adhere to the passage wall just behind the butterfly valve, owing to sudden drop in the air temperature under small valve opening angle conditions. The formed deposit subsequently builds up by attracting fuel, engine oil, combustion products, and suspended solids in the atmospheric air intake passing through the air cleaner.