1, overhead cam
English full camshaft Overheadcamshaft, referred OHC. Camshaft mounting position of the engine are generally underlying, center, overhead three forms. Overhead camshaft is a camshaft placed in the cylinder head above the combustion chamber, to directly drive the rocker arm, a valve, without going through a long putter. Compared to the same number of valve pushrod engine (i.e., overhead valve configuration), overhead camshaft arrangement reciprocating member needs much less, thus greatly simplifying the valve structure, significantly reduce weight of the engine, while also improve the transmission efficiency and reduce operating noise. Although overhead cam engine structure is more complex, but it brings better overall engine performance (in particular, a significant increase in ride comfort) and a more compact engine structure, the engine manufacturer soon widely used in products this design. Driving manner with overhead valve overhead cam configuration is not necessarily different. Power can be transferred to the overhead cam shaft through a timing belt, chain or even gear set.
In addition, overhead camshaft engine structure using this design to achieve higher than the overhead valve engine with a camshaft structure or unitary structure of the rotational speed. Today, many OHC engines have adopted the structure of multi-valve timing or variable valve structure to improve efficiency and dynamic performance of the engine.
according to the number of the camshaft within the valve structure comprises, overhead camshaft can be divided into two forms:
single overhead camshaft (Singleoverheadcamshaft, SOHC)
DOHC (Doubleoverheadcamshafts, DOHC)
OHC
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2, SOHC
is a single overhead camshaft disposed in a cylinder head onlyArticle camshaft design. This design uses only an in-line cylinder engine camshaft placed in the cylinder head side, and a V-shaped cylinder engine two camshafts is required, are placed on the side of the cylinder bank.
single overhead cam design, the need for pushrod engines reciprocating member and the total mass of significantly reduced compared with the same condition. Thus SOHC engine speed can be improved, thereby improving the power output of the engine in the case where the output torque is the same. In this design, the camshaft can be opened and closed either directly or via a rocker arm control valve, as without pushrod overhead valve engine of the kind required by the tappet, rocker arm, and the long pushrod engine group movement of the cam on the camshaft is transmitted to the valve cover in the cylinder.
than the pusher structure, single overhead camshaft design enables the engine structure (mainly valve structure) is more compact. This advantage is particularly significant when at the same time using multi-valve design (ie a cylinder with more than two valves). However, sometimes adjusting typical single overhead camshaft engine. Hillman urchin is a small two-door sedan design and manufacture of a early 1960s. Thereafter alloy engine by Coventry opposed vertices (CoventryClimax) series of improvements comes racing engines. In this engine, the intake and exhaust valves of the engine is placed on the same side of the body, and thus the cylinder head without using a crossflow (crossflowcylinderhead) design, while facilitating the work of the spark plug.
However, single overhead camshaft has its drawbacks. Since the intake and exhaust valves at different locations in the intake port, the accuracy of the valve opening and closing time will be affected. In the early 1980s, Toyota (Toyota) and VW (Volkswagen) have also been used to directly drive the two valves per cylinder single overhead camshaft engine, the structure of the parallel valve so that the volume further compact. Toyota uses hydraulic tappets, and uses the Volkswagen barrel tappet, also equipped with a gasket lash adjuster to precisely control the valve opening and closing time. In all the valve arrangement form single overhead camshaft engine, such a design may be the most compact and simple.
single counter cam
3, DOHC
equipped with a DOHC valve arranged in the form of two camshafts in the cylinder head. Two camshafts control the intake and exhaust valves. The different engine configuration (mainly different forms of cylinder arrangement), a general DOHC engine cars can have up to two to four ranging camshaft.
DOHC engine configuration is not necessarily more than two intake valves and exhaust valves, but if a multi-valve engine valve to be driven directly (although generally driven by a ram) , then double overhead camshaft is essential. Not all are multi-valve DOHC – the universal prior art multi-valve, the two valve engine are often equipped with two camshafts. But today, DOHC multi-valve technology and has the equal sign, because in almost all DOHC engines, each cylinder has three to five valves.
4 Characteristics
Such a device is suitable for installation is available with the camshaft. However, if the mounted or mounted in a camshaft, the camshaft and the valve because distance farther, auxiliary part required valve tappet and tappet, resulting in more valve train parts, complicated structure, large volume of the engine, and in the high-speed operation is also prone to noise, while the use of overhead camshaft may change this phenomenon. Therefore, modern car engines are generally employed overhead camshaft, the camshaft is disposed above the engine, to shorten the distance between the camshaft and the valve, the valve tappet is omitted and the tappet, the cam shaft to simplify the valve a transmission mechanism between the structure of the engine becomes more compact. More importantly, this installation may reduce the quality of the reciprocating system, transmission efficiency is increased.
by number of how many of the camshaft, can be divided into single overhead camshaft (SOHC) and double overhead camshaft (DOHC) are two,Since the high-end cars and multi-valve engine is generally V-shaped cylinder arrangement, it requires the use of dual camshafts control the intake and exhaust valves, so DOHC engine designer many be employed.
5, historical introduction
the first batch of dual-overhead camshaft engine are designed by Fiat (Fiat, in 1912), Peugeot (1913), Alfa Romeo (1914) design and manufacture. Wherein the latter also uses a four-valve per cylinder design. In later Alfa Romeo 6C (1925), the Masala Titi wave 26 (MaseratiTipo26, 1926), the Bugatti Type 51 (BugattiType51, 1931 years) and early Audi (Audi) and other car also adopted this technology. Moreover, the early use of two valves per cylinder technology Ferrari (Ferrari) is often used a double overhead camshaft.
When DOHC technology was initially introduced into the mainstream auto market, car manufacturers of this technology has been a lot of promotion. In the mid-1960s, just as the technology is also limited to a small number of limited production of cars and sports car, the Fiat Group decisively full use of its product line, including a coupe, sedan, convertible and station wagon, including belt-driven double overhead camshaft technology, and thus became the first comprehensive application of this technology