In a piston engine, either a timing belt (also called a cambelt) or timing chain or set of timing gears is a perishable component used to synchronize the rotation of the crankshaft and the camshaft. This synchronisation ensures that the engine's valves open and close at the correct times in relation to the position of the pistons.
In most piston engines, the camshaft(s) are mechanically connected to the crankshaft. The crankshaft drives the camshaft (via a timing belt, timing chain or gears), which in turn actuates the intake and exhaust valves. [1] These valves allow the engine to inhale air (or an air/fuel mixture) and exhale the exhaust gasses. [2]
The most common devices to transfer the drive are toothed rubber belts, metal timing chains or a set of gears. The teeth of the belt/chain/gears mesh with both the crankshaft and camshaft(s), thereby synchronising their motion.
In many older overhead valve engines, the camshaft is located in the block near the crankshaft, therefore a simple gear system is often used to drive the camshaft. Overhead camshaft engines mostly use timing belts or timing chains, since these are better suited to transferring drive over larger distances. Timing belts were common on mass-production cars until the 1970s and 1980s,[ citation needed ] however since the 1990s timing chains have become more common due to the replacement intervals required when using timing belts.
The phrase "timing belt" usually refers to a rubber toothed belt. The advantages of timing belts are typically a lower cost, reduced friction losses,[ citation needed ] less noise and that belts traditionally do not require lubrication. [3] The main disadvantage is that belts wear over time, therefore belt replacement is recommended at specific intervals. [4] [5] Replacement of the engine's water pump at the same time is often recommended, since the water pump is also subject to wear and easily accessed during the replacement of the timing belt.
Timing belts are typically located in front of the engine and are often behind a cover for protection against dust and debris. However a few engines since 2008 have used "wet timing belts", whereby the belt is lubricated by engine oil to reduce friction. [6] In some engine designs the timing belt may also be used to drive other components, such as the water pump and oil pump.
A timing belt is typically made from rubber, although some belts are instead made from polyurethane or neoprene. [7] [8] The structure of the belt is reinforced with corded fibres (acting as tension members) [9] and the toothed surface is reinforced with a fabric covering. [10]
Rubber degrades with higher temperatures, and with contact with motor oil. Thus the life expectancy of a timing belt is lowered in hot or leaky engines. Also, the life of the reinforcing cords is also affected by water and antifreeze, so it is important that belt that can be exposed to water is able to drain the water away quickly.
Older belts have trapezoid shaped teeth leading to high rates of tooth wear.[ citation needed ] Newer manufacturing techniques allow for curved teeth that are quieter and last longer.
Manufacturer-specification timing belts may stretch at high rpm,[ citation needed ] retarding the cam and therefore the ignition. [11] Stronger aftermarket belts will not stretch and the timing is preserved. [12] When designing the timing belt, a wider belt increases its strength however a narrower belt reduces weight and friction. [13]
The usual failure modes of timing belts are either stripped teeth (which leaves a smooth section of belt where the drive cog will slip) or delamination and unraveling of the fiber cores. Breakage of the belt, because of the nature of the high tensile fibers, is uncommon. [14] Often overlooked, debris and dirt that mix with oil and grease can slowly wear at the belt and materials advancing the wear process, causing premature belt failure. [15]
Toothed belts were invented in the early 1940s, for use in textile mills. [16] The first known automobile engine to use a timing belt was the American 1954 Devin-Panhard racing car, used an engine converted from pushrods to overhead camshafts through the use of a toothed belt made by the Gilmer Company. [17] [18] This car won the Sports Car Club of America (SCCA) National Championship in 1956. [19]
The 1962 Glas 1004 was the first mass-produced vehicle to use a timing belt. The 1966 Pontiac OHC Six engine was the first US mass-produced vehicle to use a timing belt, [20] [21] while the 1966 Fiat Twin Cam engine was the first mass-produced engine to use a timing belt with twin camshafts.
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Metal timing chains have become more widespread in car engines produced since the 1990s, due to the lack of the regular maintenance task of replacing a rubber timing belt. While the chains themselves are subject to minimal wear, lubrication of the chain or failure of the tensioner and chain guides can cause maintenance issues. By contrast to rubber-based timing belts which give no indication of snapping while one is driving, early symptoms of a timing chain system becoming worn exist, and these include a rattling noise from the front of the engine. [22]
Most pushrod engines, where the crankshaft and camshaft are very close together, use a short chain drive rather than a direct gear drive. This is because gear drives suffer from frequent torque reversal as the cam profiles "kick back" against the drive from the crank, leading to excessive noise and wear.[ citation needed ]
Timing gears are used in various overhead valve engines, due to the close proximity of the camshaft to the crankshaft.
Fiber or nylon covered gears, with more resilience, are often used instead of steel gears where direct drive is used. However, commercial engines and aircraft engines use steel gears only, as these other materials can fail suddenly and without warning. [23]
Failure of the timing system will prevent an engine from running. Many modern cars use interference engines, which can suffer catastrophic damage in the event of timing system failure, [24] since the loss of synchronization between the crankshaft and the camshaft will cause the valves to collide with the pistons.
Warning signs that a timing chain needs to be replaced include: [25]
Aside from the belt/chain itself, also common is a failure of the tensioner, and/or the various gear and idler bearings, causing the belt/chain to derail. Furthermore, in engines where the timing belt drives the water pump, failure of the water pump can cause the pump to seize, which can break the timing belt or chain. For this reason, timing belts and chains are often sold as part of a kit with the water pump, tensioner, and idler pulleys so that these parts can be replaced to prevent timing belt or chain failure due to failure of these parts.
A camshaft is a shaft that contains a row of pointed cams, in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines, mechanically controlled ignition systems and early electric motor speed controllers.
Variable valve timing (VVT) is the process of altering the timing of a valve lift event in an internal combustion engine, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combination with variable valve lift systems. There are many ways in which this can be achieved, ranging from mechanical devices to electro-hydraulic and camless systems. Increasingly strict emissions regulations are causing many automotive manufacturers to use VVT systems.
The GM Ecotec engine, also known by its codename L850, is a family of all-aluminium inline-four engines, displacing between 1.4 and 2.5 litres. Confusingly, the Ecotec name was also applied to the final DOHC derivatives of the previous GM Family II engine; the architecture was substantially re-engineered for this new Ecotec application produced since 2000. This engine family replaced the GM Family II engine, the GM 122 engine, the Saab H engine, and the Quad 4 engine. It is manufactured in multiple locations, to include Spring Hill Manufacturing, in Spring Hill, Tennessee, with engine blocks and cylinder heads cast at Saginaw Metal Casting Operations in Saginaw, Michigan.
An overhead camshaft (OHC) engine is a piston engine in which the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion chamber in the engine block.
An overhead valve (OHV) engine, sometimes called a pushrod engine, is a piston engine whose valves are located in the cylinder head above the combustion chamber. This contrasts with flathead engines, where the valves were located below the combustion chamber in the engine block.
The powerplant used in Saturn S-Series automobiles was a straight-4 aluminum piston engine produced by Saturn, a subsidiary of General Motors. The engine was only used in the Saturn S-series line of vehicles from 1991 through 2002. It was available in chain-driven SOHC or DOHC variants.
The Pontiac straight-6 engine is a family of inline-six cylinder automobile engines produced by the Pontiac Division of General Motors Corporation in numerous versions beginning in 1926.
A tappet is a valve train component which converts rotating motion into linear motion in activating a valve. It is most commonly found in internal combustion engines, which converts the rotating motion of the camshaft into linear motion of intake and exhaust valves, either directly or indirectly.
The Volvo B21 is a slanted straight-four engine first used in the Volvo 200 series, meant to replace the B20. The B21 and all derived engines are often referred to as red block engines for the red paint applied to the block. The primary differences when compared to the B20 was the switch to a SOHC in place of the older pushrod configuration, and an aluminum crossflow cylinder head versus the iron head of the B20.
An Injection Pump is the device that pumps fuel into the cylinders of a diesel engine. Traditionally, the injection pump was driven indirectly from the crankshaft by gears, chains or a toothed belt that also drives the camshaft. It rotates at half crankshaft speed in a conventional four-stroke diesel engine. Its timing is such that the fuel is injected only very slightly before top dead centre of that cylinder's compression stroke. It is also common for the pump belt on gasoline engines to be driven directly from the camshaft. In some systems injection pressures can be as high as 620 bar.
A toothed belt; timing belt; cogged belt; cog belt; or synchronous belt is a flexible belt with teeth moulded onto its inner surface. Toothed belts are usually designed to run over matching toothed pulleys or sprockets. Toothed belts are used in a wide array of mechanical devices where high power transmission is desired.
A valvetrain or valve train is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine. The intake valves control the flow of air/fuel mixture into the combustion chamber, while the exhaust valves control the flow of spent exhaust gasses out of the combustion chamber once combustion is completed.
The Volkswagen wasserboxer is a four cylinder horizontally opposed pushrod overhead-valve (OHV) petrol engine developed by Volkswagen. The engine is water-cooled, and takes its name from the German: "wasserboxer" ("Water-boxer"); with "boxer" being another term for horizontally opposed engines. It was available in two displacements – either a 1.9-litre or a 2.1-litre; the 2.1-litre being a longer stroke version of the 1.9-litre, both variants sharing the same cylinder bore. This engine was unique to the Volkswagen Type 2 (T3), having never been used in any other vehicle. Volkswagen contracted Oettinger to develop a six-cylinder version of this engine. Volkswagen decided not to use it, but Oettinger sold a Volkswagen Type 2 (T3) equipped with this engine.
The L-series engine is an automotive diesel engine built by Powertrain Ltd, a sister company of MG Rover.
The following outline is provided as an overview of and topical guide to automobiles:
The oil pump is an internal combustion engine part that circulates engine oil under pressure to the rotating bearings, the sliding pistons and the camshaft of the engine. This lubricates the bearings, allows the use of higher-capacity fluid bearings and also assists in cooling the engine.
The Talbot 14-45 also known as Talbot 65 is a luxury car designed by Georges Roesch and made by Clément Talbot Limited in their North Kensington factory and usually bodied by fellow subsidiary of S T D Limited, Darracq Motor Engineering in Fulham. The car made its first appearance at the London Motor Show in 1926.
The 4 VD 14,5/12-1 SRW is an inline four-cylinder diesel engine produced by the VEB IFA Motorenwerke Nordhausen from 1967 to 1990. The engine was one of the standard modular engines for agricultural and industrial use in the Comecon-countries. Approximately one million units were made.
{{cite book}}: CS1 maint: others (link)In earlier engines, camshafts were often gear-driven off the crankshaft. Later, powerplant designers developed chain drives in OHV (overhead valve) configurations that allowed some flexibility in the placement of the camshaft so that shorter pushrods could be used, for more performance and efficiency. Those engines with long chains sometimes tended to whip about and cause problems. The only alternative was a noisy and complicated multi-gear train until the cogged rubber synchronous timing belt was invented in 1945. Today the timing belt cam drive is used in distinguished automobiles such as Ferrari, Mercedes, Cadillac, Corvette, BMW, Alfa Romeo, Porsche, etc.
Example of an Audi belt that broke before the recommended replacement interval.