Grease Lithium grease Molybdenum disulfide lithium grease
With the development of wheel bearings, brakes and other automotive technologies, the requirements for wheel bearing greases are also more demanding. In order to adapt to this change, the development of new grease types has continued without interruption, and the work to modify and formulate new test methods has also gone hand in hand. The relubrication cycle of hub bearings has been continuously extended and the goal of lifetime lubrication is gradually becoming a reality.
In the process of formulating standards for hub bearing greases, people in the automotive industry and the grease community agreed that it must be considered that the use of grease in the use of automotive hub bearings (especially for disc brakes) must be considered. The properties are: leakage, high and low temperatures, turning torque and life; the operating conditions that have to be considered are: temperature, load and speed. This can be said to be a basic requirement. Good hub bearing grease should also meet some other requirements.
The temperature of the automobile hub bearing is determined by the heat and heat dissipation conditions of the hub bearing and its surroundings.
The heat of the hub bearing mainly comes from the frictional heat of the hub bearing and the frictional heat of the brake. The fourth generation of unitized wheel hub bearings is under development. Because the hub bearings and the universal joints are completely integrated, the friction heat of the universal joints will become the third heat source of the hub bearings.
The heat generated by the internal friction caused by the mechanical friction of the hub bearings and the viscosity of the grease is proportional to the speed, that is, the higher the speed, the higher the temperature rise. The use of grease with good lubricity, small friction coefficient, and low base oil viscosity generates less heat and lower bearing temperature rise. Wheel hub bearing too much fat, bearing temperature rise is high.
The brakes are braked by the resistance created by forced friction. The brake is close to the hub, and the large amount of friction heat generated during braking is transmitted to the hub of the vehicle, which is the main heat source for the temperature rise of the hub. The size of the frictional heat is related to the braking intensity. When the traffic conditions or geographical conditions require strong braking or frequent braking or even continuous braking, the heat generated by the brake rises more and the temperature of the hub bearing increases accordingly.
How much heat is transferred from the brake to the hub bearing is related to the distance between the brake and the hub bearing and the heat dissipation. In the past, drum brakes were commonly used in automobiles. The friction points were relatively far from the hub bearings and had a larger heat dissipation area. Since the 1970s, floating-clamp disc brakes have gradually replaced fixed-clamp disc brakes and are used as wheel brakes in cars and trucks at all levels. Because there is no need to cross the brake oil channel, the floating-clamp disc brakes may be placed closer to the wheel hub; some heavy-duty vehicles use full-disc brakes as wheel brakes. The fixed discs and the rotary discs of the multi-disc brakes are all enclosed in the housing and have poor heat dissipation conditions. Therefore, the temperature rise of automobile hub bearings with disc brakes is much higher than that of drum brakes. The application of disc brakes has made heat resistance a top priority for wheel bearing greases.
In the 1970s, the Beijing Highway Research Institute of the Ministry of Transport measured the temperature of the hub bearing during a driving trial conducted with the Lithium-branded (CA-10) truck (4t) using No. 3 industrial lithium grease. The high stability temperature achieved in rear-wheel bearings is 45°C (above the air temperature 15°C) when driving on a flat road (speed 40 to 50km/h); on the uphill, it is the same as on flat roads; the bearing temperature rise on downhill depends on the system Number of moves and braking intensity. When the normal downhill driving, the temperature of the brake drum is 210-450°C, and the high temperature of the bearing in the rear wheel is 49-85°C. When the brake is consciously forced, the temperature of the bearing in the rear wheel reaches 105°C. In the mountain slopes of Yunnan Province, the temperature of the brake drum is 270-480°C, and the bearing temperature in the rear wheel is 68-125°C. Abroad also believes that the automotive hub bearings under the influence of strong braking, the high temperature up to 130 °C. For taxis equipped with disc brakes, the front hub bearing temperature will briefly exceed 150°C under severe braking conditions. Some high temperatures range from 149 to 163°C. This temperature has exceeded the scope of application of ordinary soap-based grease.