Load determination for an internal combustion engine

#This invention relates to internal combustion engines generally, and more particularly, to a method and apparatus for providing a determination of load on internal combustion engines to improve control over engine operational parameters.

#In internal combustion engines it is desirable to schedule various operational parameters of the engine as a function both of the engine speed and the engine load. Determination of engine speed or revolutions per minute (RPM) is well established for internal combustion engines. Prior digital systems determining the timing of engine spark ignition as a function of engine speed (RPM) are disclosed in U.S. Pat. Nos. 5,392,753 and 4,924,831.

#However, to date, there has been no economical method of determining the load on a small internal combustion engine. The conventional methods of determining engine torque involve measuring strain or angular displacement of a segment of the crankshaft, a mounting element or an element of the drive train. These methods are not cost effective for small engine applications. Therefore. small engines have used fuel injection event and/or ignition timing that is either fixed or based on the engine speed.

#These and other objects, features and advantages of this invention will be apparent from the following detailed description of the preferred embodiments and best mode, appended claims and accompanying drawings in which:

#FIG. 1 is a block diagram of the operation of the present invention;

#FIG. 2 is a circuit diagram of the present invention;

#Referring in more detail to the drawings, FIG. 1 diagrammatically illustrates a system 10 and method in which the load on an internal combustion engine 11 is determined to improve control over at least the ignition event within the engine 11. The system 10 and method utilize changes in the speed of rotation of a body driven by the engine, such as a crankshaft or flywheel, corresponding to different portions of the engine cycle to determine the load on the engine or piston and thereafter to use such load information as a parameter to improve control of the timing of at least the ignition event and preferably also the fuel injection event or other engine events. Generally, the system and method comprise determining the crankshaft position based on pulses received from a sensor, calculating the time between pulses and/or pulse durations and thereafter determining the maximum and minimum angular velocities of the crankshaft during an engine cycle which is proportional to the engine load. A representative graph correlating the difference in RPM or engine speed between portions of the engine cycle and the load on the engine is shown in FIG. 4. Preferably, the sensors are located where the maximum and minimum speeds of rotation of the crankshaft occur.

#With a four-stroke engine, a single sensor location may be used with the time between consecutive pulses relating to a full revolution of the crankshaft which is one-half of the engine cycle. In a four-stroke engine, the revolution containing the power stroke is faster, or in other words, at a higher rpm than the revolution containing the compression stroke. This difference between the time of the revolution containing the power stroke and that of the compression stroke is a function of the load on the engine. The greater the difference between these times, the greater the load on the engine. Further, the ignition spark can be controlled to synchronize the ignition to the compression stroke to avoid an unnecessary spark during the exhaust stroke.

#FIG. 1 generally illustrates a system to carry out the method of the invention by receiving and storing the relative time between pulses from a crankshaft or flywheel position sensor and thereafter performing various calculations to average the information received over a plurality of cycles to more accurately determine the average load on the engine which is used to improve control over, for example, the fuel injection and ignition events. In more detail, the system shown in FIG. I has a crankshaft position pickup block 12 (preferably edge 66 FIG. 3B), a time of pulse block 14, a pulse-to-pulse time block 16, a table of pulse-to-pulse times 18, an average alternate time block 20, a high time average minus low time average block 22, an engine load map block 24 and a low average block 26.