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This study aimed to visualize crack initiation and propagation of rubber at low temperatures. Typical fatigue behavior such as cracking at only the compressed part of rubber products like dustcovers during oscillation tests at ultra-low temperatures have been reported [1]. Rubber products are usually used at temperatures where good rubber elasticity can be obtained. However, in some cases, they are used near glass transition temperatures at which rubber elasticity is poor. Fatigue failures of rubbers generally occur due to existing defects in the rubber material, and rubber tends to fracture easily near glass transition temperatures due to cracking on the surface of the compressed side of the rubber. The observation of the crack initiation process of rubber is difficult at low temperatures because the fracture patterns on rubber disappear when elasticity is recovered at room temperature.

This paper introduces a new simulation test method by using IR analysis which is capable of evaluating the rate of deterioration of VMQ (Silicone) rubber material applied in engine crankshaft seal applications. IR analysis is used to measure the rate of change of the Si-C/Si-0 ratio which indicates the level of deterioration of VMQ material from the hydrolysis of the siloxane bond. Applying the new analysis method, laboratory test conditions could be improved to more closely simulate field conditions.

In automotive automatic transmissions, seal rings made of cast iron or polytetrafluoroethylene (PTFE) have conventionally been installed between the rotary shaft and housing to prevent oil leakage. Recent trends have indicated that there is an increase in the number of cars with automatic transmissions (1)*, and leakage past the seal rings has become more critical from a functional view point. In this presentation, the leakage phenomena will be discussed, and seal rings with an improved shape and material will be introduced. The result of this design is a lower rate of leakage.

The recent tendency for higher output and high-rotation-speed auto-engines brings an increasing possibility of firing pressure and heat distortion. On the other hand, demands for reducing the consumption of fuel change the material of auto-engine from cast iron to aluminum die-cast. Therefore, the number of cases of engine structure deformation and bore distortion are increasing. As this reason, the new robust type of cylinder head gasket is required for this aluminum block gasoline engine. However, conventional gaskets such as metal reinforced flexible graphite and metal clad non-asbestos millboard have difficulty in maintaining the sealing performance and in reducing the bore distortion. The rubber pre-coated metal gasket can obtain sufficient clamp load on the head gasket and maintain good sealing performance. The rubber-coated metal gaskets include the FKM coated metal gasket, which is called an after-coat type.

Regarding the polyester thermoplastic Elastomer (TPEE) boot used in a Constant Velocity joint(CVJ), it is effective to adopt soft and low frictional coefficient (μ) TPEE material which achieves compact size, low frictional noise and easy assembling. However, in the conventional low hardness TPEE, both grease resistance and heat resistance deteriorate, so it was necessary to improve the structure of TPEE polymers. We developed the new soft TPEE CVJ boot, focusing on the improvement method of TPEE polymers and design factors to achieve the compact and low frictional noise boot.

Transmission manufactures have been required of performance improvement and miniaturization for the AT (automatic transmission) or CVT (continuously variable transmission) unit from car manufactures. Current unit is composed of Aluminum piston, O-ring (or D-ring) and drift ball. We changed design from O-ring to lip type seal and aluminum piston to high strength steel plate piston in order to miniaturize. On the other hand, we changed drift ball to canceler in order to make faster response. At this time, we selected new lip design and developed high tensile strength ACM to keep as same oil pressure resistance and durability as current O-ring. In addition, we could have lower friction with new design of lip shape.

A seal ring of PEEK material was developed and shown to withstand high pressure and high shaft velocity. This was made possible by cooling the ring material using leakage through an engineered passage at the cut junction. The cooling effect of leakage rate was modeled thermodynamically, and calculated leakage rates were compared to measured results.

The oil strainer is used in an automatic transmission in an effort to trap contaminated particles in the transmission oil and protect the valves and other parts from wearing prematurely. Recently in order to increase the reliability of the transmission, non-woven fabric has been used for the filtering material as it has good contamination trapping ability. On the other hand, oil-passing characteristics decrease by using non-woven fabrics as a filtering material. We analyzed the oil flow in an oil strainer by performing a computer simuration and at the same time obtained good results which were confirmed by visualization.

In the seal ring used for the rotating portion of the automatic transmission, we have developed a seal ring in which the wear of the ring is reduced to 1/10 under PV-value of 12MPa · m/s and equivalent at PV-value of 30MPa·m/s and also the frictional torque of the rotating portion is reduced to 1/2 when compared with the conventional PTFE seal ring. This has been achieved by means of improvement of the oil pocket's shape, size, and the distance between oil pockets equally spaced on the side surface of the seal ring.

Many control valves utilizing the vacuum pressur of engines are used to control the engine, fuel supply, and driving speed. The authors established an empirical formula regarding sealing performance of control valves made of rubber. This formula clarifies the relationship amoung the rubber valve design factors, the counter surface conditions, and the vacuum conditions, with the sealing performance. By applying this formula, it became possible to predict the sealing performance of control valves at a design stage to satisfy the customer's specification.

We have developed a diaphragm which has low gas permeability and is used in the accumulator for the automotive hydraulic brake system, adopting the sandwich structure of rubber and resin films. Improvement of the diaphragm's gas permeability is absolutely necessary to achieve a maintenance-free and also light-weight and small-sized accumulator used for the automotive hydraulic brake system. We will discuss the development of the new resin films and investigation of the design factors of the accumulator focusing on the low gas permeability and durability under low temperature conditions.

In a diaphragm used for an accumulator, the relationship between design factors and durability in low temperature is discussed from the occurrence of buckling phenomenon through the observation results. The durability of the diaphragm which has a sandwich structure of rubber and resin films, is greatly influenced by the buckling phenomenon which occurs during deformation of the diaphragm when used for an accumulator in low temperature condition.

Regarding the sprag type stator which is in a torque converter used in the automatic transmission of automobiles, the authors succeeded in substituting plastic material for the aluminum material by molding the stator inserting outer race into the plastic material. By this change, both weight and cost were reduced without losing durability.

The characteristics of the elastomer material and the fiber cloth reinforcing material have been analyzed as related to diaphragm durability. Investigated were diaphragms used for waste gate actuators for controlling the boost pressure of turbochargers. In this presentation, the authors verify the importance of the elastomer material fatigue resistance under high temperatures and the elongation properties, including directional properties of the fiber cloth reinforcing material for the durability of the diaphragms.

Wear of a seal is greatly dependent on the environmental conditions such as the temperature, the speed, the lubrication condition and the design factors such as the total contact load and the contact width of the seal lip. In this presentation, the authors discuss the phenomenon of abnormal wear of the reciprocating seal for an automatic transmission by investigating from a lubrication theory viewpoint. An improved seal usable in severe conditions was developed as a result of this study and is also explained.

Upgrading of the performance and the durability of bellow boots used to seal constant-velocity joints are essential to seet the demand for higher performance and longer life automobiles. In this discussion about bellows boots for sealing constant-velocity joints, examples and analysis results of bench tests for studying wear and fatigue durability are presented.

For either case for rotary shaft or reciprocating shaft motion, rubber lip type seal leakage problems are often encountered under low temperature conditions. As for causes of leakage under low temperature conditions, there are several factors such as following ability of the sealing lip for runout of a shaft or rod, roughening of the sealing surface of the rubber material at the stage of initial motion and so on. Sealing performance is essentially dependent upon the low temperature property of the rubber materials. In this paper, the leakage phenomena is explained through visco-elastic characteristics of the rubber materials.

The flow behavior of rubber compounds inside a mold is very complicated including various phenomena such as heat transfer from the mold, wall slip and swell at the divergent cavity. A slit rheometer which can measure the flow behavior inside a mold during curing was developed. The rheometer has a window which enables the observation of the flow behavior directly under 50 MPa. The pressure loss gradient along the flow direction and shear viscosity were found to be independent on the degree of cure but wall slip was observed. The wall slip phenomena could not be explained by slip analysis, because plug flow occurred due to little effects of the poiseuille flow. The pressure behavior inside the slit could be well predicted by using the equation obtained by assuming stress relaxation of visoelastic fluid occurs without share along the wall. The stress relaxation phenomena were predicted by taking into account the short and log relaxation time.

NBR (acrylonitrile butadiene rubber) has been used for the oil seal equipped on a power steering. However, lack of heat resistance was occasionally observed for NBR, with the recent trend of customer's demand for increasing the life of oil seals in high temperature environmental condition. We developed an oil seal with H-NBR material, which could exhibit the superior performance in the heat resistance; however, it had a weak point in low temperature environment. We have developed HNBR1, the new H-NBR, which has been improved in the performance for low temperature [1]. HNBR1 has been applied for power steering seals as the rubber material, which has superior heat resistance, cold resistance and oil resistance.