What Is a Tachometer?
A tachometer is a measuring instrument that visualizes the speed of a rotating object by means of scales and numbers.
Tachometers are mainly used to visualize the speed of engines of automobiles and motorcycles, and the shaft speed of motors and electric motors. The “decimal type” uses a volume graph and digital numerals on a screen.
In addition to those originally built into the machine, there are also general-purpose tachometers that use electromagnetic pulse, OBD, and reflective materials.
Uses of Tachometers
It is very important for the user to know the RPM to prevent overloading and breakdowns of the machine.
Especially in the case of cars and motorcycles, engine RPM changes significantly when shifting gears, so downshifting at high RPM without knowing the RPM can lead to breakdowns due to over-rotation.
By using a tachometer, the user can visually check the engine RPM, which not only prevents over-revving, but also enables fuel-efficient driving by cruising at low RPM.
Principle of Tachometers
The following types of tachometers are currently in mainstream use.
As detection methods
- Mechanical Type:Input from rotating parts is extracted using gears and rotating wires, and detected by a rotation sensor in the meter section or displayed by a magnetic meter.
- Electric Type:The voltage applied to the ignition coil of the engine is detected and the number of revolutions is counted (four times per revolution for a four-cylinder engine). Or, the rotation speed is determined by the signal detected by the crank angle sensor.
- Optical Type:A reflective material is attached to the rotating part, and the number of revolutions is determined based on the number of times the light is received.
Display method
- Analog Type:Magnetic type (Foucault type) with a scale or number on the board indicated by a pointer.
- Digital Type:LED or LCD display with segment display, bar graph display, etc.
- Stepping Motor Type:A stepping motor moves the pointer based on detected pulse signals.
In terms of display methods in particular, the digital and stepping motor types, which are less susceptible to external shaking or shock, are currently the mainstream, while the analog type tends to be used for general-purpose, inexpensive products.
What Is a Tachometer’s Tachometer?
Tachometers are used to indicate engine speeds in motorcycles and automobiles.
Tacho is spelled Tacho, and Tacho comes from ancient Greek and means speed. In the olden days, when the car was not yet equipped with gauges, speed was measured by the number of revolutions of the engine. This is why it is called a tachometer.
Tachometers Are No Longer Needed
In the 1900s, when many manual cars were on the road, many automobiles had tachometers to indicate engine speed. In the 2000s, however, an increasing number of cars are now without tachometers.
There are several reasons. One is cost cutting. Before the burst of the bubble economy, there were many manual and luxury cars on the road, and automobiles were equipped with tachometers and various other features. However, after the year 2000, more and more consumers demanded inexpensive cars with automatic transmission, so automakers eliminated tachometers in their lowest-priced models.
Second, computers have become more sophisticated. In manual cars, the driver had to control the gearshift appropriately according to the engine speed. In automatic cars, however, the computer automatically shifts gears, eliminating the need for the driver to pay attention to the tachometer, which indicates engine RPM.
Another major factor is the spread of electric and hybrid vehicles. Instead of a tachometer, these vehicles display a special meter that indicates energy usage. Electric vehicles do not require shifting gears and have meters that indicate energy consumption and regeneration. Drivers can drive more fuel-efficiently by checking the meter.
Hybrid vehicles shift gears according to engine speed like gasoline-powered vehicles, but because engine rotation is also used by the motor to generate electricity, accelerator operation is not linked to engine rotation. Since there is no relationship between engine rotation and fuel consumption, the tachometer has been eliminated and a meter indicating motor operation has been installed.