How Spedometers Work

Introduction to How Speedometers Work:

The dashboard instrument cluster in a car organizes a variety of sensors and gauges, including the oil pressure gauge, coolant temperature gauge, fuel level gauge, tachometer and more. But the most prominent gauge, and perhaps the most important, at least in terms of how many times it is looked at while someone is driving is the speedometer. The job of the speedometer is to indicate the speed of your car in miles per hour, kilometers per hour or both. Even in late-model cars, it's an analog device that uses a needle to point to a specific speed, which the driver reads as a number printed on a dial.

As with any emerging technology, the first speedometers were expensive and available only as options. It wasn't until 1910 that automobile manufacturers began to include the speedometer as standard equipment. One of the first speedometer suppliers was Otto Schulze Autometer (OSA), a legacy company of Siemens VDO Automotive AG, one of the leading developers of modern instrument clusters. The first OSA speedometer was built in 1923 and its basic design didn't change significantly for 60 years. Otto Schulze was the first to figure out how do you measure a wheel's rate of rotation (through his speedometer). In this report, we're going to look at the how speedometers in automobiles work and the design of it (mechanical and electronical).

Types of Speedometers:

There are two types of speedometers: electronical and mechanical. Because the electronic speedometers is actually relatively new invention the first all-electronic speedometer didn't appear until 1993. This kinematics report will focus primarily on the mechanical speedometer, also known as the eddy-current speedometer. But, it will also look at how electrin speedometers work since they are very useful in our everyday lives.

Mechanical (Eddy-Current) Speedometer Parts:

To measure the speed of a car, one must be able to measure the rotational speed of either the wheels or the transmission and send that information to some sort of gauge. In most cars, measurement takes place in the transmission. And the job of measuring the rotational speed generated by the transmission falls to something called a drive cable (drive shaft).

The drive cable (also known as the speedometer cable) consists of a number of superimposed, tightly wound, helical coil springs wrapped around a center wire, or mandrel. Because of its construction, the drive cable is very flexible and can be bent, without fracture, to a very small radius. This is handy because the cable must snake its way from the transmission to the instrument cluster, which houses the speedometer. It is connected to a set of gears in the transmission, so that when the vehicle moves, the gears turn the mandrel inside the flexible