Force analysis of driving gear of starting motor

1.Principle of starting engine with starter motor driving gear

The starting motor of internal combustion engine is to convert electric energy into mechanical energy, and transmit torque to the engine through electrical and mechanical structure to make it rotate continuously. That is to say, the starting motor drives the gear to drive the meshed flywheel ring gear, the flywheel ring gear drives the flywheel, the flywheel is transmitted to the engine crankshaft, and the crankshaft drives the piston to move up and down to start the engine. Under normal circumstances, the driving gear of the starting motor rotates and stretches out at the same time. In the early stage of starting, the driving gear rotates and stretches out slowly at low speed under the action of the control coil. At this time, the rotation torque of the gear is small. In the process of rotation, the position matching with the ring gear is found, and it goes deep enough to make the tooth meshing surface have enough contact area, After the engine starts successfully, the starting motor stops working, the solenoid valve closes, and the driving gear retracts automatically to complete the whole engine starting process.

2.Meshing transmission principle of driving gear and flywheel ring gear

In gear meshing transmission, in order to form lubricating oil film between the meshing tooth profiles and avoid being stuck due to friction, heating and expansion of gears, there must be clearance between the tooth profiles, that is, side clearance. The existence of backlash will produce impact between teeth, which will affect the stability of gear transmission. Reasonable meshing clearance makes the transmission between gears relatively stable, which can meet the normal operation of gears. However, once the gears are loose, the balance state is destroyed, which greatly affects the stability of transmission. Under high-speed operation, the gears will be seriously impacted.

3.Gear force analysis

In the process of gear meshing and transmission, the mechanical model of gear is cantilever beam, and the action point of maximum bending moment is gear meshing point B. under the action of meshing bending moment, the bending stress on the tooth root is the largest, and the tooth root is a dangerous section, as shown in the figure. Under normal operation, the bending stress on the tooth root is less than the allowable stress. In case of severe impact, the bending stress on the tooth root is much greater than the allowable stress.

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