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Lecture Engineering drawing and design - Lecture 18: Mechanical elements – Gears

Lecture Engineering drawing and design - Lecture 18: Mechanical elements – Gears. introduction, gear types, how gears work? How is a gear tooth formed? Module and pitch, relations between gear parameters, gear forming – rack generation, gear force calculation,. | Design web Design web Introduction ME 1110 – Engineering Practice 1 Engineering Drawing and Design - Lecture 18 Gears and most of other transmission elements are used to transmit power or to transform rotational movement to translation. Gears are most often used in speed reducers: Mechanical Elements – Gears » Speed is easy to generate, because voltage is easy to generate » Torque is difficult to generate because it requires large amounts of current Other driving elements have similar means of action LONDON EYE Tip speed 0.26 m/s Rotational speed 0.033 rpm {30 min/rev} Drive power 200 kW !? Prof Ahmed Kovacevic Motor speed = 3000 rpm Motor power = 200 kW Motor Torque = 640 Nm School of Engineering and Mathematical Sciences Room CG25, Phone: 8780, E-Mail: a.kovacevic@city.ac.uk www.staff.city.ac.uk/~ra600/intro.htm 1 Ahmed Kovacevic, City University London 2 Design web Ahmed Kovacevic, City University London nπ T 30 Ahmed Kovacevic, City University London Design web Gear types London eye photographs 3 Pow = ωT = Wheel speed = 0.033 rpm Driving power = 200 kW Wheel Torque = 600,000,000 Nm 4 Ahmed Kovacevic, City University London Design web Design web How gears work? How is a gear tooth formed? Law of Gearing: Involute gears: »A common normal to the tooth profiles at their point of contact must, in all positions of the contacting teeth, pass through a fixed point on the line-of-centres called the pitch point. The fundamental premise of gearing is to maintain a constant relative rotation rate of gears. This can be achieved with a tooth shape called INVOLUTE. »Any two curves or profiles engaging each other and satisfying the law of gearing are conjugate curves Pitch point Pitch circle Basic circle 5 Imagine that the pressure line is cut in two. Trace of the half line end, when the line wraps around the base circle, is the involute of the base circle. Pressure angle Pressure line Ahmed Kovacevic, City University London 6 Ahmed .