Variable Valve Timing
While many organizations search for ways to reduce pollution and improve fuel consumption in internal combustion engines; one of the most currently touted methods is variable valve timing.
In some demonstrations, this is accomplished by a computer managed electric solenoid to actuate each valve. Because these are conventional valves, the electro mechanical apparatus must be large and very powerful.
Because these valve management devices do the same work as a camshaft, they require just about as much energy. The improved management of the IC process in the engine may be worth the cost, but further improvement would be possible only by finding some entirely different system.
Another highly touted means of managing valve timing is to change the geometric relationship between the cams and the push rods, or rocker arms. There is more than one way to do this, but it isn't simple or inexpensive.
There is a simple and inexpensive means to do this, but none of the larger organizations or manufacturers are yet working with this new method.
| Figure 2 |
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| Cutaway segment of a cylinder head showing the patented pressure actuated Intake Valve and its Variable Tension Spring. |
In our valved two-stroke engines, we at LIM Technology have devised a simple means to retard the opening and advance the closing of the intake valves. LIM uses a controlled spring tension to accomplish this. In the LIM system it is the intake manifold air pressure which opens the valves. This occurs only as exhaust begins, through the piston managed exhaust ports. It is only when the pressure differential exerts force on th floor area of the valve, in excess of the spring tension, that the spring can begin to open.
The more spring force, the later the opening, shorter the stroke, and earlier the closing. The spring may be manipulated a number of ways. Most efficiently, we so far think, is the use of a coiled steel tape anchored at the inside of the coil to a control rod. The outer end of the coil provides a steady force to keep the valve closed, but the main forces keeping the valve closed are compression and combustion pressure.
For starting, idle, and low power, the control rod is relaxed; as the load and speed of the engine increase, the rod is rotated to increase the spring torsion. This works because the faster turning engine provides more pressure in the manifold. The control rods are actually operated much like a throttle.
This system is mechanically simple, far simpler than manipulating the camshaft or managing electro-mechanical devices. It weighs less, costs less, and contributes practically no friction to the process.
A U.S. Patent is pending on our variable spring force valve management system.
| Figure 2a |
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| Exploded view shows more clearly the patent pending
Valve Guide and other parts. LIM Technology, L.L.C., of Baltimore, Maryland has been granted a United States patent for its LIM engine, and has international patents pending. Click here to see patent # 6,257,180 and Click here to see patent # 6,349,691 |
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| In later development, we also experimented with a springless
system, in which we removed the bale at the top of the valve, and added
a collar. The collar moves within a control chamber. Just prior to the
best time for valve closing, compressed air is injected into the camber
below the collar. Click here to see what the
system looks like, and how it works. |
| This engine was actually built and runs. We are now working on a more sophisticated system for conventional four-stroke engines. To see this, including animation, click HERE. |
