Flathead engine
The SV valve controller ( Side Valve ) or side -valve arrangement referred to a construction in a four -stroke engine, wherein the valves are disposed laterally next to the cylinders. For this design, the term standing valves is used in the English-speaking dominated the designation Flathead wherein the particularly low profile design of the cylinder head is expressed. A characteristic feature of an SV engine is that the cylinder head contains no parts of the valve train. At first glance, therefore SV engines are interchangeable with two-stroke engines. The valves can - on both sides of the piston - opposite each other (T- head engine) or close to one another - on the same side of the piston - (L- head engine ) can be arranged. Motors with T- head have two down camshafts.
Picture Notes
The top image shows a Norton engine of most produced type 16H. The British Army used it with a few hundred thousand units built during World War II. The valve stems are hidden behind the silver casing cap with the word " Norton " on the cylinder. The small dark lever is the decompression, more correctly, a valve lifter: It allows keeping open the exhaust valve by hand to facilitate the starting procedure.
The middle image shows the open valve engine of the motorcycle BMW R 42 from the 1920s. The centrally positioned camshaft to the crankshaft actuated via tappets the exposed valves ( above the cylinder, left above the exhaust pipe ). The valve springs are open lying. Because of the smaller here Zylinderhubräume ( 250 cc ), no decompression is required for the engine start.
The lower picture shows a cylinder with piston and valves. The valves are adjacent and can be operated by an underlying camshaft.
Historical
The need for control of gas exchange cycle engines is as old as the steam engine. However, the valve system of the steam engine is not suitable for controlling combustible gases. Therefore, Nikolaus August Otto had for the four-stroke engine build something else: a gas exchange with valves that allow controlled the working area with fresh gases to fill and empty the working space of the burned gases allow. In the early days of the engine art, it was usual to control only the exhaust valve, or more precisely to open against the closing force of a spring, while a spring-loaded " automatic" valve admitting fresh gas enabled: the " poppet ". However, it soon became apparent that the power requirements, in addition to overcome by means of suction, the spring force of the poppet valve, a good performance yield was considerably in the way. So we went over to the controlled inlet valve having a gas guide " from the bottom up " to the cylinder head logically linked from the initial updraft spray-nozzle carburetor according Maybach with an inlet valve that controls the sealing plate " above " has and his operation down through the cams on the cam shaft which is driven by the crankshaft close. This is the SV - work principle.
Because of the disadvantages (see below) were quickly sought more efficient combustion space designs for sport use, requiring the installation of the valves "up" into the cylinder head, and a more complex operation, either by bumpers ( OHV ), or be it with an overhead camshaft ( OHC ). However, these designs are clearly bauaufwendiger why they stayed for about three decades of the sport and cash vigorous audience reserved.
An interim solution was the attempt with their plates in the combustion chamber to order the valves against each other, usually in a line, in which the exhaust valve is at the bottom as in the SV order and the intake valve against him in the cylinder head, and over there with a single bumper and deflection rocker arm is operated. Therefore, the English name for this: " Inlet over Exhaust " inlet ( valve) above the outlet ( valve), IOE.
SV engines came from 1900 to the late 1950s for use. Last German car with such an engine was produced until 1962 Taunus 12M of Ford In vehicle side-valve engines were replaced with a few exceptions of OHV and OHC engines. Known examples of the SV - type are the Ford Model B from the 1930s (V8 - cylinder with 90 PS) and most bikes of the 1930s and 1940s. Even today, the SV valve train in some sidecar motorcycle models from Russian ( Dnepr, Ural ) and Chinese manufacturing ( Donghai, Chang Jiang) is installed: These motorcycles are evolved copies of the 750 BMW motorcycles of the 1930s (BMW R 71 ).
Pros and Cons
Benefits
Since the valves of a SV engine are actuated by the cam shaft only over short plunger and the cam shaft is in turn driven by a simple spur gear, or a timing chain short, the valve operation is only a few individual parts. For the oil circulation no separate pump is required as all the moving parts in the crankcase. SV engines fall from compact because the cylinder head contains no parts of the valve train. The manufacture of the motors is low due to the smaller number of parts. Both criteria make this type still in small engines for power generators, irrigation pumps, lawn mowers and (more rarely) power saws popular.
Thanks to the slow combustion of the fuel mixture in the cylinder, as well as the reduced number of moving parts to SV engines are characterized by a smoother running as " top -driven " ( OHV / OHC ) engines. Because of the little streamlined management of the intake and exhaust this type of engine has little torque at higher engine speeds, ie a flatter power curve, which tends to require gearing with a smaller coefficient. Thus, both an effective solution is possible with manual transmission, as also given a good suitability for automatic transmissions.
Although long before the Second World War was the know -how for OHV and OHC engines available, SV engines were primarily built. The reason was the lower expected damage by a torn due to poor material quality valve. This might not fall into the cylinder and there damage to the piston head in the rule.
Disadvantages
Due to the larger sealing surface between the cylinder and cylinder head gasket problems of the risk is higher than for engines with overhead valves. The elongated, jagged combustion chamber shape is quite far from the ideal spherical. The consequence is that the gas mixture will take longer to burn. This results in low maximum speeds, relatively low specific power and higher fuel consumption with relatively low emission values , including carbon monoxide and hydrocarbons ( C m H n ), as well as soot formation. When Ricardo heads these disadvantages are reduced, the combustion chamber is more compact because the cylinder head above the pistons with a step ( " squish band " ) is provided. To lubricate the valve stems must, if lubrication is not otherwise possible, the top oil fuel are mixed, which also contributes to increased CmHn - pollutant in the exhaust. The piston head is not directly cooled by the incoming fuel-air mixture. The piston is therefore exposed to higher thermal loads, making the performance enhancement potential is also limited. Also because of the required minimum height above the valves increase the performance and energy efficiency are set by higher compression limits.