Under the Bonnet: Confessions of a 1970s & '80s Car Mechanic by Brian Cunningham

Author:Brian Cunningham [Cunningham, Brian]
Language: eng
Format: epub
ISBN: 9780750995665
Google: XlUJzgEACAAJ
Publisher: History Press Limited
Published: 2021-05-24T00:14:40.030523+00:00

11

The Differential

Clever though Nikolaus Otto was with his four-stroke engine, there is an even more ingenious piece of kit in your car and it is called a differential. The differential is mind-blowingly clever. Its invention predated the motor car by many years: in 1827 it was introduced for steam-driven vehicles by a Frenchman, Onésiphore Pecqueur, and he was a genius. The technology has not substantially changed in the nearly 200 years since.

Here’s how it works, but first things first, your car will either be front-wheel drive, or, less commonly these days, rear-wheel drive, or possibly even four-wheel drive. When I was a mechanic, rear wheel drive was the most common set-up and the simplest from a mechanical point of view because it meant that the front wheels did the steering while the rear wheels delivered the momentum. These days, front-wheel drive is the most common layout, so the front wheels have to both steer the car and deliver the driving force, while the rear wheels just tag along behind.

Front-wheel drive has primarily become the norm because if you don’t have to deliver power to the rear wheels, then you don’t have to find space for a bulky rear axle and a long propeller shaft connecting it to the back of the gearbox. That additional space can be used to create more room within the passenger cabin or load area.

For the purposes of trying to explain the differential, I will use the rear-wheel-drive scenario for simplicity, but the principle is the same whichever set-up you have. We know already that the Otto cycle drives pistons up and down and this movement is turned into circular motion by attaching the pistons to a crankshaft by means of connecting rods on lubricated bearings. With an engine and gearbox aligned front to rear, the circular motion of the crankshaft is transmitted rearward via a heavy flywheel to provide momentum and balance, then through the various shafts and cogs of the gearbox and a long propshaft all the way back to the rear axle.

Here that spinning motion has to change course. We need it redirected by 90 degrees to the left and 90 degrees to the right, and then out to the road wheels, and this is done by a pinion gear attached to the end of the propshaft, meshed with a crown wheel in the axle. The crown wheel drives two drive shafts, one each leading out to the left- and right-hand road wheels. Simple, eh?

Here’s where the problems start. The directly connected nature of the shafts and gears I have described leads to identical force being delivered to both road wheels; ideal if travelling in a straight line. But what if you want to go around a corner? Try to visualise what happens when a car turns a corner. The road wheel on the inside of the turning circle does not have to travel as far as the outer wheel, yet the engine is driving them both at the same speed (very early

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.