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Plastic gears for applications inside of internal combustion engines
In these applications the operating temperature, always higher than 120°C, the torque to be transmitted and the rotation speed require a toothing sizing particularly precise and reliable. In this way it is possible to choose the most suitable resin for each application and be sure that the gears not to give any problem for the entire engine life.
In this case the same gear is mounted on the crank shaft and on the balancing shaft.
In this case the same gear is mounted on the crank shaft and on the balancing shaft.
The mating gear is made of steel
Driving gear is by steel and driven gear is by plastic. In this case the tooth of the plastic gear has a circular thickness different from that of the ring gear, to maximize the transmittable torque.
A constraint, very often present in internal combustion engines, is the fixing system of the gear on the shaft. It is chosen according to cost and reliability, and almost always is very suitable for metal gears but not for plastic gears. In this case, for example, the metal crown gear is forced on the crank shaft and this operation of course is not possible with a plastic ring, instead the gear is fixed on the balancing shaft with a screw. To be able to hold the same fixing type, in the plastic gear is over molded a metal bushing, which can hold in time the driving torque of the screw and transmit the torque from gear to balancing shaft.
When in a gears chain for power transmission one of the gears is by plastic and the other by steel, the toothing parameters must be chosen according to mechanical characteristics of resin and metal teeth must adapt to plastic.
