21-06-2013, 04:25 PM
THE PROBLEM OF CONTROLLING FOUR-STROKE ENGINES; THE NEED TO ALTER THE CONVENTIONAL METHOD, AS JUSTIFIED BY THE EXAMPLE OF OTTO ENGINE
THE PROBLEM OF CONTROLLING.doc (Size: 143 KB / Downloads: 24)
Proper engine control as precondition of good functioning, and the importance of precision
The principle of operation of four-stroke engines, as suggested by the name, is based on the continuous succession of four cycles, i.e, their operation is realized by the succession of the individual cycles.
These are: - suction
- compression
- power cycle (firing stroke, combustion and expansion)
- exhaust
In order to achieve that the consecutive continuity of these four strokes or cycles is transformed into a rotary movement and to obtain thereby some source of power, it is necessary to regulate - by utilizing the movement of the piston - the pressure conditions inside the cylinder. The four basic cycles are generated in function of the controlled pressure conditions within the cylinder. In fact, the proper control of pressure conditions in each cycle, equals to safeguarding the perfect functioning of the engine. This regulation of pressure conditions is referred to as engine control. With internal combustion engines, kinetic energy is obtained by ensuring the fulfilment of the above criteria. The development of pressure conditions can be represented in a diagram. The formation of pressure conditions regularly required for ensuring correct motor operation, is safeguarded by certain components.
Also the position of said components, expressed in degrees, can be visualized by means of diagrams. They are referred to as valve timing diagrams. Parameters that can be read off of the valve timing diagram are used to guarantee the development of pressure conditions inside the cylinder, required for the economic operation of the engine.
Engine controlling techniques presently applied, and their basic features
With four-stroke engines commonly used today, a certain method of valve control is applied to regulate pressure conditions within the cylinder. The essence of the method is public knowledge, nonetheless, the question does arise, whether due considerations have been given in the course of R&D activities to the limits and constraints of that control method? Said control is of the same age as four-stroke engines themselves, and the basic approach has not been altered ever since.
True, there have been some experiments and trials to realize certain sorts of port control, however, next to all of those attempts were limited to controlling friction only. But there is more than that to it, and as the trials have not been extended to a wider scope, even today the same, over hundred year old technique is being applied to control four-stroke engines. Besides bringing about a huge friction and compression spring force resistance during engine operation
Summary
Based on what has been described above, I consider efforts aimed to alter the present conception of controlling four-stroke engines well-founded and necessary. With the development of infrastructure - with the continuous upgrading of motorways -, we may reach almost any locations by driving our cars at high speed and high power. However, the engine control system presently applied, is simply unable to keep the engine running at the required output values above the medium range of speed. It has become obsolete. Due to the high pollutant emission at high speed, it is harmful to the environment. It is no coincidence that when testing environmental-friendliness, the rate of pollutant emission of the engines is measured up to medium speed-range only (and never in the high-speed range), as the presently applied concept of engine control is capable of safeguarding proper enging operation up to that range of speed only.
I must point out in this context that when testing engines on a test bench in car factories, engines are tested up to the medium speed-range only. Thus, when purchasing a new car, the technical data specified in the manual supplied with the vehicle, necessarily include test values obtained by the above test methods.
All claims made in this paper with respect to valve control, may be proven and verified in practice. To demonstrate this, to model control conditions, I have constructed an electro-mechanical measuring device to be used with the help of a lathe. By gradually increasing the speed of the lathe, the speed follow-up limit of the compression spring and the starting point of ’valve float’ condition can be measured, these points being indicated by a lamp going out. It can be observed that by increasing the speed (rpm), the gap between valve seat and the closing/sealing surface of the valve disc will grow in direct proportion to the speed increase, while the compression final pressure within the cylinder will decrease in the same ratio. When compression final pressure within the cylinder has dropped below 7 bar, the engine is unable to perform its function even at minimum level, it becomes ’lifeless’, in fact that is when the ’death’ of the engine sets in.