1.5.3 Chains for Automotive Engines
Transmission: Camshaft driving, balancer driving
Automotive Chains are used for driving the camshafts in engines, counterbalance shafts, or oil pumps. Some manufacturers use cog belts instead of chains in this application. (See Figure 1.20.)
Camshaft drives transmit the crankshaft rotation to the camshaft of the overhead cam (OHC) engine at a ratio of 2:1. The counterbalance shaft and oil pump are also driven by the crankshaft. Both of these drives are installed inside the engine and are not visible from the outside.
These chains work at the temperature range of −30°C to 130°C, and rotate at about 600 to 7,000 rpm. Counterbalance drive sprockets rotate at 1,200 to 14,000 rpm, which is equivalent to a speed of 1,800 m/min.! This is twice the speed of engine drive chain. Motorcycles also use camshaft drives, but this discussion is limited to automobiles that use roller chains, which are usually offered by Japanese or European manufacturers. In the United States, Silent Chains are usually used for camshaft drives in automobiles, but roller chains are being increasingly used.
Figure 1.20 Engine Cutaway to Show Chain Drive
Construction and Features
- Single strand chain with a pitch of 9.525 mm or 8.0 mm is usually used. (See Figure 1.21.) In diesel engines or other high-load engines, double strand chains may be used.
- The chains are used at high speed. Therefore, the wear between the pins and bushings is the main concern. The surface of the pin is usually hardened with Hmv 1,600 or more.
Figure 1.21 Automotive Drive Chain and Sintered Metal
- Tooth shapes are either ANSI- or BS-type. Currently the BS-type is used more frequently.
- Automotive engines are produced on a large scale. The sprockets for both the crankshaft and the camshaft are mass-produced from sintered metal.
Selection and Handling
- These chains are used with chain guides, levers, and tensioners to reduce chain elongation, vibration, and noise.
- Generally, the chains are selected according to the transmission torque, small-sprocket speed, and the layout. In mid- to high-speed transmission, vibration and lubrication must also be considered.
- These chains need forced lubrication.
Manufacturers are focusing attention on the following issues:
- Making lighter-weight, smaller-sized chains.
- Improving reliability of the entire transmission system, including sprockets, guides, levers, and tensioners.
- Decreasing noise from the chain, and throughout the entire drive system.