Speedometer. Types and device. Accuracy and features

Almost with the first serial production of cars, they began to be equipped with the necessary instruments, among which there is a speedometer. Automotive devices help control the necessary processes, technical condition, level and temperature of liquids.

What is a car speedometer?

The speedometer is a measuring device that shows the real speed of the vehicle. For cars, a mechanical and electronic speedometer is used, and the speed is indicated in miles or kilometers per hour. The speedometer is located on the dashboard, usually in front of the driver, integrated with the odometer. There are also options in which the instrument panel is shifted to the center of the torpedo and facing the driver.

What is a speedometer for?

This device helps the driver in real time to learn about:

• vehicle traffic intensity;
• speed of movement;
• fuel consumption at a specific speed.

By the way, often on the speedometers the maximum speed mark is slightly higher than that indicated in the characteristics of the car.

History of creation

The very first speedometer installed on a passenger car appeared in 1901, and thus the car was Oldsmobile. However, there is an opinion on the Internet that the first analogue of the speedometer was invented by the Russian craftsman Yegor Kuznetsov. For the first time, the speedometer became a mandatory option in 1910. OS Autometer was the first manufacturer to release vehicle speedometers.

In 1916, Nikola Tesla invented a speedometer with a fundamentally its own design, the basis of which is still used today.

From 1908 to 1915, drum and pointer speedometers were produced. Later they began to use digital and pointer. By the way, all automakers have opted for dial gauges because of the ease of reading the readings.

From the 50s to the 80s of the last century, belt speedometers were used, most often on American cars, like drum ones. These types of speedometer were abandoned due to low information content, which can lead to dangerous situations on the road.

In the 80s, the Japanese are gradually introducing digital speedometers, but this did not receive mass use due to some inconvenience. It turned out that analog indicators are better readable. Digital speedometers have found their way into sports motorcycles, where it has proven to be really convenient.

Types

Despite the fact that there are a lot of variations in speedometers, they are classified in two types:

• what method of measurement is used;
• what type of indicator.

The variety is divided into 3 categories:

• mechanical;
• electromechanical;
• electronic.

To understand the speed of the variable movement of a car, which the speedometer shows, and how the measurement is provided, we will consider in detail the specifics of work and data processing.

measurement method

In this category, car speedometers are divided into the following classifications:

• chronometric. Operation is based on odometer and clock readings - distance divided by elapsed time. The method relies on the laws of physics;
• centrifugal. The method is based on the work of centrifugal force, where the regulator arm cuff fixed by the spring moves to the sides due to centrifugal force. The offset distance is equal to the traffic intensity;
• vibrating. Due to the resonance of vibrations of the bearing or frame, a vibration graded equal to the number of wheel rotation is created;
• induction. The work of the magnetic field is taken as a basis. Permanent magnets are used on the spindle, where an eddy current is generated when the wheel rotates. A disc with a spring is involved in the movement, which is responsible for the correct readings of the speedometer arrow;
• electromagnetic. The speed sensor, when moving, sends signals, the number of which is equal to the number of movements of the sensor drive;
• electronic. Here, the mechanical part is provided by current pulses that are transmitted when the spindle rotates. The information is received by the counter, which determines the frequency for a fixed period of time. The data is converted to kilometers per hour and displayed on the dashboard.

Interesting fact! Massive introduction of mechanical speedometers began in 1923, since then their design has changed little to our time. The first electronic speed meters appeared in the 70s, but became widespread after 20 years.

By type of indication

According to the indication, the speedometer is divided into analog and digital. The first works by transmitting torque due to the rotation of the gearbox, which is connected to the gearbox or axle gearbox.

The electronic speedometer wins with the accuracy of the indicators, and the electronic odometer always indicates the exact mileage, daily mileage, and also warns of mandatory maintenance at a certain mileage. 

How a mechanical device works, principle of operation

A mechanical speed meter consists of the following main components:

• gear vehicle speed sensor;
• flexible shaft transmitting information to the instrument panel;
• the speedometer itself;
• distance traveled counter (node).

The magnetic induction assembly, taken as the basis of a mechanical speedometer, includes a permanent magnet connected to the drive shaft, as well as a cylindrical aluminum coil. The center is supported by a bearing. To prevent errors in readings, the top of the coil is covered with an aluminum screen that protects against magnetic field effects. 

The gearbox has a plastic gear, or a set of gears, which communicates with one of the gears of the gearbox, and transmits primary information through the cable. 

The speedometer works like this: when the coil rotates, eddy currents are created, because of which it begins to deviate by a certain angle, which in turn depends on the speed of the car.

The speedometer is driven by transmitting torque through the sensor and flexible shaft to the gear cluster. The minimum reading error is provided by a direct connection with the rotation of the driving wheels.

Electromechanical speedometer operation

This type of speed meter is more popular, especially on domestically produced cars. The essence of the work intersects with the mechanical, but differs in the implementation of the process. 

The electromechanical speedometer uses sensors such as:

• gear with a secondary shaft of efficiency and a left wheel drive;
• pulse (Hall sensor);
• combined;
• induction.

The modified high-speed node uses the indication of magnetoelectric devices. A milliammeter was used for the accuracy of the indicators. The operation of such a system is ensured by a microcircuit that transmits signals to the electronic unit, transmitting readings to the speedometer needle. The current strength is directly proportional to the speed of the car, so here the speedometer shows the most reliable information.   

Electronic device operation

The electronic speedometer differs from the ones described above in that it is directly linked to the odometer. Now all cars are equipped with this system, which rarely allows simple ways to adjust the mileage, which is “memorized” by some control units. 

Why is he lying: the existing error

It has been proven that in most cars, with a high probability, the speedometer does not show an accurate speed. A 10% difference is allowed at a speed of 200 km / h, at 100 km / h the excess will be about 7%, and at 60 km / h there is no error.

As for the external reasons for the error, there are several of them:

• installation of wheels and tires of larger diameter;
• replacement of the axle gearbox with another main pair;
• replacement of the gearbox with other pairs of gears.

The main malfunctions of speedometers

There are 5 main types of malfunctions that occur during the long-term operation of a car:

• natural wear and tear of plastic gears;
• breakage of the cable at the junction with the rotating part;
• oxidized contacts;
• damaged power wiring;
• defective electronics (requires complex diagnostics, including speed sensor).

In most cases of breakdowns, you do not need to be an expert, the main thing is to correctly diagnose the malfunction and equip yourself with a minimum set of tools with a multimeter.

Mechanical Instrument Diagnostics and Troubleshooting

For correct diagnosis, use the following algorithm of actions:

1. Raise the passenger side of the vehicle using a jack. 
2. Using the instructions for the repair and operation of your car, we properly dismantle the instrument panel.
3. Remove the fixing nut of the speedometer cable, remove the shield, start the engine and engage 4th gear.
4. In the protective casing, the cable must rotate. If this happened, twist the tip of the cable, re-enable 4th gear with the engine running and evaluate the readings on the indicator. A malfunction will be indicated by a changing position of the arrow. 

If the cable does not rotate, then it must be dismantled from the gearbox side and make sure that the shape of its tip is square. Try pulling the cable yourself - the rotation should be the same at both ends, and if so, the problem is in the gear. 

Repair and diagnostics of electronic speedometer

Here, the repair is complicated by the fact that it is necessary to have at least an indicator, as a maximum, an oscilloscope or a scanner to read the operation of engines with electronic fuel injection. Absolutely all foreign-made cars after 2000 have an on-board computer that performs self-diagnosis before starting the car. If there is an error, its code can be deciphered by referring to the table of error codes for a particular brand of car. 

If there is an error related to the lack of operation of the speedometer, then with the help of an oscilloscope we connect to the middle contact of the speed sensor, and throw “+” on the battery. Then the motor starts and the gear is engaged. The frequency of the working sensor varies from 4 to 6 Hz, and the voltage is at least 9 volts.  

 Features of operation

The main disadvantage that other devices lack is inaccuracy. As mentioned above, the correct speed reading depends on external interference in the video of installing large wheels and transmission units with different gear ratios. In case of critical gear wear, the speedometer readings “walk” by another 10%. 

Electronic sensors can show speed and mileage without error, subject to the rules of operation and without exceeding the permissible wheel dimensions. 

If the speedometer is out of order, it is prohibited to operate the car, with such a malfunction, according to the rules of the road.

Differences: speedometer and odometer

An odometer is a sensor that reads the total and daily mileage of the car. The odometer shows the mileage, the speedometer shows the speed. Previously, odometers were mechanical, and mileage was actively rolled up by unscrupulous car sellers. Electronic mileage counters have also learned how to edit, but there are many control units in the car that record the mileage. And the engine control unit, in its memory, fixes all the errors that occur at a certain mileage.

Questions and answers:

What is the name of the speedometer in the car? Some motorists call the odometer a speedometer. In fact, the speedometer measures the speed of the car, and the odometer measures the distance traveled.

What does the second speedometer mean in the car? It is correct to call it the odometer. It measures the total mileage of the vehicle. the second digit of the odometer is the daily mileage counter. The first is not discarded, while the second can be discarded.

How do I know the exact speed of a car? For this, there is a speedometer in the car. In many cars in gear 1 car accelerates to 23-35 km / h, 2nd - 35-50 km / h, 3rd - 50-60 km / h, 4th - 60-80 km / h, 5 th - 80-120 km / h. but it depends on the size of the wheels and the gear ratio of the gearbox.

What is the name of the speed measured by the speedometer? The speedometer measures how fast the car is moving at a particular moment. In American models, the indicator gives out miles per hour, in the rest - kilometers per hour.