I’m a mechanical engineering student and I know generally how HEVs operate, but I can’t seem to find anywhere that explicitly explains how torques are “added together” to increase overall torque of the vehicle.
Is there a particular device that allows two shafts to drive one (thus adding their torques), and does that mean that both these shafts would need to have the same rotational velocity to avoid excess torsion on the driven shaft?
Any explanation would be greatly appreciated!
In: Engineering
You use something called an overrun clutch. This is already a really common part in automatic transmissions so they’re easy to come by.
An overrun clutch is like a diode or check valve but for rotary motion… it transmits torque in one direction but spins freely in the other. So you put two gears on the driveshaft, each with an overrun clutch between the gear and the shaft (the clutch is a cylinder). Each motor drives one gear. If they try to drive the gear faster than the driveshaft the clutch engages and they transmit torque to the shaft. If they try to go slower (that motor is off) the clutch disengages and the gear just free wheels. It’s a mechanism for summing torques. If they’re engaged, driven shafts have to go the same speed as the driveshaft.
There’s an alternate way to do it with fluid couplings (“torque converters”) where they don’t have to go the same speed, this is how the main “clutch” of an automatic transmission works.
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