| 摘要 |
Internal combustion engines with valves - be they of the gasoline, or Diesel variety - use compression coil springs to close their valves. Statistically speaking, these engines amount to virtually 100% of all motors produced, or in existence today. The said compression coil springs with the valve and its components, such as the valve cap, valve locks, or valve keepers and stem seals, form a "Valve Spring Assembly" which, only with minor changes has seen service in engines produced since the turn of the century. Of note is the fact, that the said assembly remains essentially unchanged throughout all types of valve train categories, such as the OHV (Overhead Valve) engines with pushrods and rockers, the SOHC (Single Overhead Camshaft) engines, with rockers only and the DOHC (Dual Overhead Camshaft) motors with no rockers at all. Only minute changes occur in the said assembly when moving from one of the above categories to another one; the true, or significant changes take place in the components that are 'upstream' of the Valve Spring Assembly, i.e. that lie between the camshaft and the said assembly. In long service over several decades, the "Valve Spring Assembly" has proven itself to be reliable and efficient. However, it has several serious drawbacks that become readily apparent upon close scrutiny; its main shortcomings can be summarized as follow * being extremely tall, it requires other valve train components to access it only from above * because the spring of the said assembly sits directly above the combustion chamber, it is a subject to constant heat-soaking, raising its operating temperatures to dangerously high levels, impairing its life-span and performance * a coil spring is prone to 'coil-bind', a condition occurring when individual windings of the coil spring touch each other and destroy the spring, if not the entire valve train * a coil spring forces the valve stem to be excessively long, reaching almost the top of the spring; along with it, it also produces an uncessarily long valve guide. The overall length of the valve stem adds materially to a high reciprocating mass of the valve train, which is undesirable * finally, the overall height of the "Valve Spring Assembly" forces all valve-actuating components, i.e. the rockers, pushrods, or the camshaft itself, to operate from a very high postion in the cylinder head, creating a tall, heavy and cumbersome structure. It is both the design objective and the claim of the valve trains submitted by Attain to reduce the cylinder head height and the height of the main cylinder head casting by a factor of 50%, with a variance of +/- 5%. A further claim is the reduction of the valve trains' reciprocating weight in the SOHC and DOHC type engines, which shall be reduced by a factor of 15%, or more. Current production methods call for separate castings for the engine block and the cylinder heads. With the only exception known to the writer - GM's Saturn - all motors are produced by a method described above. The exceedingly low cylinder head height in the proposed Attain engines - ranging from 35 mm to 55 mm - when measured vertically up from the deck-line - should entice major engine producers to adopt a method, which Attain has labeled "UNICAST, or UNIBLOC", in which the cylinder head is fabricated with the engine block as one single component. This eliminates a whole host of expensive parts, like cylinder head gaskets, sealants, bolts, nuts and cylinder bolt-bosses and saves a great deal of labour expense in the assembly of the engine. An estimated additional 50 lbs. of dead weight could be saved in a typical, medium size V-8 motor, made out of steel, leading to further significant economies. The "Unicast/Unibloc" production method is almost 100 years old and is not a novelty but the ultra-low cylinder-head casting is. Attains claim here is that of a facilitator, enabling a manufacturer to initiate the said method as an economically viable production process and realize substantial savings in the manufacture of motors. The submitted valve trains by Attain are proposing to replace the century-old "Valve-Spring-Assembly" altogether and to reap far-reaching benefits from the newly developed components, instrumental in creating a "new cylinder head architecture."
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