Electric vehicles do not require any clutch, torque convertor or multi-speed transmission, and their powertrain can be designed with a simple combination of an electric motor and a constant gear ratio reducer. High rotational speed of motors causes issues of noise, vibration and tribology. Countermeasures on gear tooth and surface finish design, lubrication and cooling system including oil characteristics, and design of bearings and oil seals are explained.
By increasing speed, traction motors can be made lighter and smaller, thereby reducing power consumption in electric vehicles. Thus, speed reducers that withstand high-speed rotation of the traction motor are required. Traction drives, a type of power transmission mechanism, are more suitable than gears for silent rotation at high speeds and are expected to be employed in high-speed traction motors. This paper describes operation principles and related technologies in the design of compact, light, and highly efficient traction drives.
Electric vehicles are being developed around the world. This paper describes the main cooling methods for drive motors of electric vehicles, and in particular, describes the trends of mechanical seals, which are important functional products in rotor shaft water cooling. There are three main motor cooling systems: water jacket system, oil cooling system, and rotor shaft water cooling system. Against the background of higher motor efficiency, a motor with a high cooling efficiency that uses both a water jacket and a rotor shaft water cooling system has been developed mainly in Europe. Mechanical seals use surface texturing to accommodate high sliding speeds. Mechanical seals that use gas lubrication are expected to reduce energy loss from conventional seals while maintaining sealing performance, and spread to actual products.
This paper introduces the approach of lubricant agent to components which contribute to vehicle electrification, including high speed bearing, minute current sliding contact switch and bearing for preventing electrical corrosion. In the high speed bearings, grease thickener is being designed to improve both durability and high speed rotation performance. In the minute current sliding contact switch, electrical contact grease is commercialized to reduce wear of electrical contact materials in electrical components. In order to prevent bearing damage from electrical current, development of conductive grease is in progress, for example by blended with ionic liquid.
As vehicle power unit become quieter, tire related noise is becoming important for vehicle noise. Noise radiated from a tire is transmitted to both vehicle compartment and exterior. Vehicle interior noise is important for comfortability, and exterior noise is for noise emission. To improve interior noise and noise emission, tire dynamic behavior should be properly controlled depending on the frequency. This paper presents some representative mechanisms of tire/road noise and approach to reduce tire noise.
In the market, there has been a new family of Oil Soluble Polyalkylene Glycols that offer many benefits beyond traditional PAGs. They are highly oil soluble and thereby provide the formulator with an additional tool for upgrading hydrocarbon based lubricants. Research has shown they offer a diverse range of functionality. Their inclusion into hydrocarbon oils as a co-base oil or an additive can improve deposit control and extend fluid life. They are also friction modifiers which may lead to more energy efficient lubricants. OSPs also act as extreme pressure and anti-wear additives, and corrosion inhibitor boosters. In ester based lubricants, they can improve their hydrolytic stability at modest treat levels. Finally they have the potential too for replacing esters as seal swell additives.
Phenylether lubricants having a structure in which aromatic rings are bonded by oxygen atoms are used under severe conditions such as high temperature environment and high radiation dose due to their excellent oxidation stability. It is known that these phenyl ether compounds greatly change physical properties and properties due to structural changes, such as introduction of an appropriate alkyl chain or changing the number of aromatic rings. In this report, we introduce the present state of main applications of phenyl ether lubricating oil and outline the function expression including tribological characteristics.