Control systems

The lack of a crank mechanism brings many advantages, however it considerably complicates the motor control system considerably. While a well adjusted common motor can operate with minimum control requirements, the LCE doesn't allow for that.

To demonstrate this it's good to take a look at the common combustion engine design.

To achieve specific rotations at a given output the following requirements will suffice:

  • proper throttle valve adjustment (defines amount of air intake)
  • appropriate amount of fuel (provided by carburetor in older cars)
  • right ignition timing with respect to a crank shaft

Fulfilling these requirements will allow the engine to work for an extended period of time without any further intervention. In case of an accidental error - e.g. when the fuel doesn't ignite in one cylinder - the flywheel will take care of bridging the gap, preventing the engine from stalling.

The situation is a lot more complicated in case of the Free Piston Engine. If - for whatever reason - the fuel ignition fails, the piston could crash against the cylinder head which would result in engine damage. Apparently, it is impossible to ensure a constantly stable engine operation without a precise piston control. The LCE unit in the system allows us to control pistons movement and - according to a need - use electromotor to ensure a desired position of pistons at any given moment. The electromotor system is also used for an ignition part.

Therefore a quick enough position sensor is a must. Also the LCE needs to be connected to a power converter which will provide a correct winding excitation in both, motor and generator regime. Let's presume now that one of the cylinders ignites pushing pistons one direction. Some of the energy is used for fuel compression on the opposite side and the rest has to be directed out in form of electricity via electric generator winding. Just adding a load wouldn't be enough here. The control unit has to manage the take-off precisely so that the piston stops at the required position (the top center) at the end of the cycle so that the whole process could be repeated. If, for some reason, the fuel combustion on the opposite side failed, the control unit immediately detects the failure and the return motion would be performed by an electric motor keeping the system running. The electric motor uses power collected in capacitors in a power converter. This system works as a replacement of a flywheel known from common engines.

The control unit's mathematical complexity goes beyond the scope of this description. Just for an imagination; the piston's position is measured with an accuracy of 0.05mm and all calculations run 10,000 times per second.