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Types of boot seals for rack and pinion gear of automotive steering and their characteristics are given, and necessary items for designing seals are clarified based on experiments and experiences upon required performances of products.

New type oil seals - nonwoven fabric secondary lip type oil seals are recently widely used for one of the sealing apparatus for automotive application. Basic improvement of this type of seals is in a secondary lip which prevents solid foreign matters such as dust and sand from entering into the rubbing portion between a primary lip of oil seals and a shaft. This secondary lip is superior in anti-dust property, wear resistance, following ability to the shaft eccentricity and air permeability to the conventional secondary lip of rubber. And the sealing performance of new type seals with the secondary lip made of special nonwoven fabrics is more stable than that of the conventional rubber seals.

In order to improve the reliability of oil seals in practical use, it is considered that further basic investigation for maintaining good sealing characteristics of seals are necessary. However, the result of analysing phenomena in oil seals which has caused the oil leakage in the market shows that about 60 % of oil leakage is caused by the seal installation to housing bore or shaft, about 30 % thereof by unsuitable operating condition and remaining 10 % by the design of oil seals. From the point, oil leakage troubles and their countermeasures on oil seals for automotive application are discussed.

Valve stem seals are important to control consumption of lubricating oil for engines and to prevent an air pollution problem by unclean exhaust. It is required for valve stem seals to have stable characteristics of a controlled oil leakage related to frictional characteristics. In this papor, the concept of designing valve stem seals which possess the above characteristics have been discussed by applying an inverse problem of hydrodynamic lubrication.

For purpose of clarifying the effect of quantity of lubricating oil supplied to the seal lip portion on sealing characteristics of oil seals, relations between the typical constructional applications of the fitting portion for oil seals and the quantity of the lubricating oil supplied to the oil seals are discussed. Then the necessary minimum quantity of the lubricating oil for preventing the seal lip from wear is investigated. And it is clarified that the decrease in sealing characteristics occurs when the lubricating oil is supplied insufficiently to the seal lip portion and, finally, the countermeasure is discussed.

It becomes clear that the suction coefficient of oil, K, and the sealing characteristic constant, Φ (=fG-1/3), are closely connected with the rubbing surface state of oil seals. And, investigations have done on K-, Φ-value, etc. in oil seals after the practical use in automobiles and the results have been compared with the test results in the laboratory.

From the analysis of observational results of the many dust cover seals to be used on passenger cars, it has become clear that the control of the seal design functions such as the working envelope (space available for seal side-wall), the contact face load of the sealing lip, the axial rebound load by the side-wall component, and the anti-ozone property of side-wall materials are necessary to maintain the sealing performance, and that the present dust cover seals satisfy needs requested by the costomers. Therefore, these characteristics should be sufficient when considering the designing of the seal.

Fine solid particles in a lubricating oil affect the sealing characteristics of oil seals, and their lives are shortened by the wear of oil seals and shafts created by the particles. Tests were carried out by using various kinds of foreign matters. The results showed that foreign matters in oil film between the sealing lip and the shaft surface directly caused the leakage. Consequently, it was reconfirmed that the practical application of dust lip and the countermeasure in the construction of seals or their housings were indispensable to obtain the long life and the stable operation of oil seals.