Indicators of the speedometer of the car are necessary to determine and control the speed of the vehicle in accordance with the restrictions in force in the territory of a particular country. It is included in the list of mandatory vehicle equipment.
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What is a speedometer for?
Automotive speedometer (AC) is a device that determines the module of the instantaneous vehicle speed.
Focusing on the performance of the "device" the driver can:
- find out the traffic intensity of the car in real time;
- calculate fuel consumption at each specific speed.
Odometer complete with a car speedometer - a device for measuring the distance traveled. Sometimes these "devices" are not separated and they talk about a speedometer-odometer.
The odometer can be used to determine when to change:
- car oils;
- filters;
- belts (generator and timing).
Types of speedometers
There is a wide variety of speakers, all of them are classified into types according to:
- measurement method;
- type of indicator.
By measurement method
Classification of car speedometers according to the principle of operation:
| Speaker type | Principle of operation |
| Chronometric | Odometer and clock hybrid - the distance traveled is divided by the elapsed time. The result is the vehicle speed. |
| Centrifugal | The spring-held adjuster arm rotates with the spindle and is thrown to the sides by centrifugal force. The offset distance is proportional to the speed. |
| Vibrating | This type of device is used for vehicles that rotate quickly. The mechanical resonance of vibration in the frame or bearings of the machine vibrates the graduated tabs at a frequency corresponding to the speed of the vehicle. |
| Induction | Consists of a system of permanent magnets involved in rotary motion together with a drive spindle. It generates eddy currents in a disk mounted in a magnetic field. The disc is attracted to the rotational movement, which is limited by a special spring. The speed is indicated by an arrow connected to it. |
| Electromagnetic | The movement speed sensor gives electrical signals, and the “device” drive itself moves in accordance with the number of signals. |
| Electronic | The sensor generates a current pulse for every spindle revolution. The signals are sent to the counter, which counts them over a fixed period of time. Further, the information is processed by the microprocessor, where it is converted into speed readings, which are visualized on the vehicle control panel. |
By indicator type
According to the method of data visualization, speedometers are divided into:
- analog or mechanical;
- digital.
Analog
Scheme of operation of a universal analog speaker:
- the arrow of the speedometer is connected to the gearbox shaft;
- the latter, in turn, receives a drive from rotating wheels.
The intensity of movement of the gearbox shaft is proportional to the speed of rotation of the wheels. Therefore, it is this node that most reliably displays the vehicle speed.
The table shows different analog speedometers:
Of all the types of analog speedometers in modern cars, only the pointer is used.
Digital
Features of the digital speaker:
- has the highest accuracy rates;
- indicator - a display showing the speed in digital equivalent;
- on the screen, the driver can see the daily and total mileage;
- has an alarm that is triggered when the vehicle's speed limit is exceeded.
The main disadvantage of a digital car speedometer is the readout lag. As a result, the data is displayed incorrectly when changing the speed.
You can clearly see how a digital car speedometer works using IPHONE 4 in the video captured by the videoSPBLIFE channel.
Photo gallery
The photo shows different types of speakers:
The principle of operation of the speedometer on front-wheel drive and rear-wheel drive cars
There are peculiarities in the principles of operation of the AU on front- and rear-wheel drive vehicles. On cars driven by rear wheels, the speedometer monitors the rotation of the secondary shaft of the gearbox and the speed is calculated from it.
On front-wheel-drive vehicles, the equipment measures the vehicle's traffic using the left-hand drive. In this case, the AC error is large, since the front tires turn the car and the effect of rounding the road is added. When turning to the left, the "fixed speed" is slightly less than when turning straight, and to the right - slightly more.
Speedometer error
All speakers, like any other technical devices, are characterized by inaccurate readings.
Reasons for inaccurate measurement:
- factory calibration of instruments, which is impossible to carry out exactly 100%;
- tire height and diameter - affect the distance that the car will travel in 1 revolution of the drive shaft;
- "Turning effect" on front wheel drive vehicle speedometers.
The rule of automakers is that the AC error should be constructively in the direction of increasing readings, against the actual speed of movement.
Video
The video from user Viktor Khabibulin compares digital speedometers with GPS and analog ones.
We cannot do without a speedometer. The speeds are great, and their impact on safety is undeniable.
The speedometer not only adorns the dashboard, but saves nerves, money, and sometimes life. Do not determine the speed by the flickering of the bushes behind the roadside! The eye of even an experienced driver becomes blurred on a long trip - and a considerable 100 km / h seems like a snail's pace.
The speed we're talking about is "instantaneous". This is important for emergency braking or vigorous maneuvering. But the speedometer also includes an odometer with a measurement accuracy of a kilometer, sometimes up to 100 meters. Want to be more precise - get a navigation system like GPS.
The most simple mechanical speedometers. They are driven from the transmission by a "flexible shaft" - a special cable that transfers rotation well. Since the same speedometers are found on different cars, the simplest gearbox is used in their drive, the gear ratio of which is matched to the car. On a rear wheel drive, the speedometer usually monitors the rotation of the gearbox output shaft. This means that the readings depend on the tire size, the gear ratio of the rear axle gearbox and the intrinsic error of the device. Example: on "Zhiguli" replacement of the pair 4.44 by 3.9 will change the readings by 14%. In these cases, it is necessary to replace the speedometer reducer. However, the gears of the reducer are not rubber - therefore, there is no ideal match of the speedometer to the size of the tires, and they still wear out ... The total error of readings up to 10% and even more is a common thing. This often explains the records of yard racers.
Front wheel drive transverse engine speedometers usually "service" the left wheel drive after the main pair. This means that to the error of the speedometer and the influence of the tire size, the effect of the road rounding is added: when cornering to the left, the “indicated speed” is slightly less than in the middle of the car, and to the right - a little more.
What is the impact of oversized tires? Replacing a 175 / 70R13 tire with a 165 / 70R13 tire or vice versa changes the speedometer reading by 2.5%. Little? But the question is how this error will add up to the error of the speedometer itself and its gearbox, how will tire wear and pressure in them affect. Low pressure reduces rolling radius. The deformation is "tricky", and the payment for it is both an increase in fuel consumption and a drop in maximum speed, although the speedometer readings themselves are ... overstated!
Odometer - a set of drums with numbers(they are also called "decades"). Each is connected to an adjacent gear train with a ratio of 1:10. With the beginning of the movement, the extreme - kilometer counts units of kilometers, when it makes one revolution, the neighboring 10-kilometer one will show a unit in its window. After 100 km, a 10-km drum will complete the first revolution. And so on. Domestic odometers count up to 99,999 km and then reset to zero. Today, many odometers are six-digit. Some models include a convenient option - a short (usually no more than 1000 km) mileage counter with an accuracy of hundreds of meters. The driver can reset it by pressing a button.
Unfortunately, the performance of a mechanical speedometer is highly dependent on the wear of its own parts as well as the drive. It is important to lay a flexible shaft without sharp bends (otherwise the cable will wear out, the pointer vibrates, the mechanism makes noise) - not every car succeeds. The cable drive makes it difficult to assemble and disassemble the instrument panel. In the end, the cable was abandoned - the speedometer became electronic, it works on the signal of the speed sensor. The shown sensor is combined with a gearbox, which, by the way, can also be installed on an old cable-driven machine: unscrew the knurled cap and screw on the cable. We have electronic speedometers for the first time appeared on the GAZ-3110, VAZ-2110, they were completed with the latest versions of IZH-Oda.
In appearance, the first electronic speedometers are difficult to distinguish from mechanical ones. The arrow is in place, the drums with the numbers too. But from now on, the arrow is a part of an electronic meter for the number of impulses from the speed sensor. Its rotation angle is proportional to the number of pulses per unit of time - we will leave the details of the recalculation technology to specialists. The odometer is similar to a mechanical one, but "decades" are subject to an electronically controlled microelectric motor.
These devices are somewhat more accurate than mechanical ones, but they still have an error of 5-7%, because they got rid of only the weak points of the mechanics itself (backlash, whims of a cable, a card, a return spring, etc.).
Fully electronic devices are better. But here the usual arrows are in their places: it turns out that most people understand their "language" better than any numbers on the display. Such a dashboard can be found on the "Samara" VAZ-2113 ... 2115 and parts of the "tenth" family cars. On the other hand, this complex is a work of art. All arrows are commanded by the electronics via the control motors. Displays (odometer and air temperature) are liquid crystal.
With all the possibilities of electronics, the basis of the measurement, that is, the control of the rotation of the drive wheel with the tire, remains. This means that measurement errors associated with this are inevitable, and the developers of "advanced" speedometers, it seems, are not interested in the possibility of their fine tuning. Why is an open question. This is hardly an insoluble problem - this function is provided for in trip computers! The photo shows one of them. Among the tasks of MK is fuel consumption accounting. Here you can not do without measuring the distance traveled. How to account for measurement errors? The computer allows you to enter a correction. The procedure is described in the instructions for it. The "base" is the path measured by the kilometer posts - they are dug in with an accuracy that many speedometers never dreamed of. Nowadays, the position of reference points is easy to check with modern navigation aids. Road builders are also familiar with them.
Analog speedometer
1. The first speedometer, installed in a car in 1899, worked on the principle of a centrifugal governor. After that, the principle of operation and the design of the speedometer changed many times, as a result of which for many years, up to the present day, the design of the speedometer with an induction transmission clutch has become a classic (see. Figure: 2.11).
The leading part of the clutch is a cylinder forged from light aluminum alloy. The cylinder rotates in the field of a permanent magnet, as a result of which a current is induced in the cylinder, which forms an electromagnetic field around the cylinder. The interaction of two magnetic fields leads to the fact that the internal permanent magnet is carried away after the cylinder.
2. The drive shaft of the speedometer also drives the daily and total mileage counter, which is similar to a bicycle counter.
A speedometer of this type has one drawback - the need to pull the cable from the gearbox to the dashboard, so designers are looking for new technical solutions.
Digital speedometer
3. The sensor of such a speedometer is located in the transmission. The principle of operation of the sensor can be different: inductive, hall generator, photovoltaic, etc. (see. Figure: 2.12). The output signal of the sensor is voltage pulses, the frequency of which is proportional to the vehicle speed. After passing through the formation block ( schmidt trigger) rectangular pulses enter the multiplexer.
After the multiplexer, the pulses enter the time gate, which opens for a certain period of time. The number of pulses passed through the gate and counted by the counter is proportional to the vehicle speed. From the counter, the number is transmitted to the microprocessor, where it is converted into speed, and then through the demultiplexer and decoder it is sent to the digital display. After reading and processing the next measurement, the counter is reset to zero and is ready to receive the next pulse packet.
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Today there are many ways to improve your vehicle, one of them is to put an electronic speedometer drive. Do you hear for the first time? Then let's figure it out!
Functions and device of the speedometer
The speedometer is the most important element in a car, bus, motorcycle or moped, because when we drive, we definitely need to monitor the speed so as not to break the rules. However, speed detection is not the only function of this device. The mechanism includes another device - an odometer, which shows the distance traveled. The main parts for the speedometer are the drive cable and the flexible shaft, through which the rotational movement is transmitted from the transmission to the device. They, in essence, connect the dashboard, which is located in the passenger compartment on the dashboard and shows the current values, with the drive located directly in the gearbox.
Almost any speedometer has high-speed magnetic assemblies, the rotation of the magnet forms a flow, which, passing through the coil, contributes to the induction of eddy currents in it. These currents, in turn, create another magnetic field. These fields begin to interact, and the arrow of the device moves along the scale in proportion to the frequency with which the magnet rotates.
In order to choose the right gear ratio for the car, there is a special gearbox in the speedometer. In rear wheel drive vehicles, it monitors the output shaft. As for the cars on which it is installed, here the data comes from a sensor installed on the left front wheel. That is, in the first case, the error will depend only on the size of the tires, and in the second, also on the rounding of the road.
Speedometer drive - basic faults
The first and main sign that repair of the speedometer drive is necessary is that its arrow stops responding to changes in speed. There may be several reasons for this behavior. It is quite possible that you just need to tighten the nut by means of which the flexible shaft is attached to the device itself (to its drive). The second reason may lie in the breakage of this shaft, or in the failure of the mechanism, which is located on the dashboard of the car.
Also, sometimes you can hear a characteristic knock, this also not in the most favorable way affects the performance of the device. After all, its causes may be contamination of the checkpoint bore hole, where the flexible cable is connected, incorrect installation of the device, or loosening of its fastening. But the "growling" noise indicates that it is necessary to lubricate the cable. When the arrow of the device goes off scale, then the opposing spring has broken, and the speedometer must be completely replaced.
If the device shows incorrect data, then, most likely, the cable is simply incorrectly attached to the shaft. Sometimes you also have to execute and.
Do-it-yourself speedometer drive repair
In the case when it is necessary to replace the O-ring, gear or housing, the speedometer drive should be dismantled, the VAZ device of the insides of the car allows you to reach it almost without difficulty, but in a foreign car you have to tinker. Having established the location of the mechanism using the car manual, proceed to the removal. To do this, unscrew the fastening bolt by means of which the unit is attached to the gearbox, and pry it off with a screwdriver.
After that, we carry out a visual check of both the gear itself and the seat in which the end of the flexible rod of the device is located. They must be free from any defects and contamination. Also carefully inspect the box body, if you find oily stains on it, then immediately replace the O-ring... To get to it, first the driven gear of the speedometer drive is removed, and then the seal itself changes. Before assembly, all elements should be thoroughly rinsed in kerosene.
Speedometer(from the English speed - speed) - a device for measuring the speed of movement and the distance traveled by a vehicle. the speedometer provides measurements up to a kilometer, sometimes up to 100 meters.
Mechanical speedometers are driven from the transmission by a "flexible shaft" - a special cable that transmits rotation well. Since the same speedometers are found on different cars, a simple gearbox is used in their drive, the gear ratio of which is matched to the car. On a rear wheel drive, the speedometer usually monitors the rotation of the gearbox output shaft. This means that the readings depend on the tire size, the gear ratio of the rear axle gearbox and the intrinsic error of the device. Example: on "Zhiguli" replacement of the pair 4.44 by 3.9 will change the readings by 14%. In these cases, it is necessary to replace the speedometer reducer. However, the gears of the gearbox are not rubber - so there is no perfect match of the speedometer to the tire size. The total error of readings is up to 10%. Front-wheel drive transverse engine speedometers usually "service" the left wheel drive after the main pair. The error in speedometer measurement is influenced by the size of the tires and the effect of rounding the road: when cornering to the left, the "indicated speed" is slightly less than in the middle of the car, and slightly more to the right.
Replacing a 175 / 70R13 tire with a 165 / 70R13 tire or vice versa changes the speedometer reading by 2.5%. The error is added with the error of the speedometer itself and its reducer, tire wear and pressure in them. Low pressure reduces rolling radius.
History
Both old and new cars use the standard version, where the usual arrow indicates the speed of movement on the scale.
Like any new technology, the first speedometers were very expensive and were only optional devices for the car. This continued until 1910, when car factories began to include the speedometer in the car as standard equipment. One of the first companies to manufacture speedometers was the Otto Schulze Autometer (OSA), the predecessor of the current Siemens VDO Automotive AG, which develops various auto parts and parts.
The first "OSA" speedometer was manufactured in 1923 and its basic configuration has not changed much for 60 years.
Few people know that the first inventor of the Speedometer was a self-taught serf mechanic Kuznetsov (Rzepinsky) Yegor Grigorievich (1725-1805).
One of his most famous inventions, a mechanical droshky with a verstometer, was planned by Yegor Kuznetsov when he was 60 years old. He gave this invention 16 years of life. It is not known for whom they were created. But it is known that the name was invented by the author himself and that the product turned out to be great.
The shakes were designed for a couple of horses or one horse, harnessed to shafts with an arc, were distinguished by their lightness and agility. A coachman was sitting in a droshky in front, and the passengers behind them, backs to each other, behind the seats for the passengers was an organ, and behind the organ was a verstometer. A portrait of the inventor on a metal sheet was attached under the verstometer above the rear axle of the droshky.
The verstometer mechanism received rotation from the right rear wheel by means of a gear train. The arrows of the verstometer indicated the distance traveled, and the bell, set in motion by the mechanism of the verstometer, marked each mile passed. The organ mechanism received rotation from the rear left wheel. Music could be switched from one melody to another and turned off altogether.
The bowls were also distinguished by an elegant finish, they were painted with red and black paint, lacquered, the seats were reinforced with soft green velvet.
In 1801 the droshky was shown to Empress Maria Feodorovna. The invention has safely survived to this day, finding its refuge in the State Hermitage in St. Petersburg.
Classification
By measurement method
■ Chronometric - a combination of odometer and clockwork.
■ Centrifugal — A spring-held governor arm rotates with the spindle and is thrown to the sides by centrifugal force so that the offset distance is proportional to the speed.
■ Vibrating - used for high speed machines. The mechanical resonance of the vibration of the frame or the bearings of the machine causes the graduated tabs to vibrate at a frequency corresponding to the number of revolutions of the machine.
■ Induction - A system of permanent magnets rotating with a drive spindle generates eddy currents in a copper or aluminum disc placed in a magnetic field. The disc is thus drawn into a circular motion, but its rotation is slowed down by the limiting spring. The disc is connected to an arrow showing the speed.
■ Electromagnetic - the speed is determined by the EMF generated by the tachogenerator connected to the spindle.
■ Electronic - optical, magnetic or mechanical sensor generates a current pulse for every spindle revolution. The pulses are processed by an electronic circuit and the speed is displayed on the indicator.
■ By satellite positioning system - the speed is determined by the satellite positioning system GPS electronically as the distance traveled divided by the travel time.
By indicator type
■ Analog
1. Pointer - the most common; the speed is indicated by an arrow rotating around the axis;
2. Tape - used on the GAZ-24 until 1975, many American and some European and Japanese models; the speed is shown by the tape passing by the divisions on a fixed scale;
3. Drum - used on many pre-war cars, some American cars of the sixties, as well as relatively modern Citroen models; the divisions are drawn on the rotating drum and, as it rotates, appear in the window, displaying the current speed.
■ Digital
The sensor of such a speedometer is located in the transmission.
The output signal of the sensor is voltage pulses, the frequency of which is proportional to the vehicle speed.
After passing through the shaping unit, the rectangular pulses enter the multiplexer. After the multiplexer, the pulses enter the time gate, which opens for a certain period of time. The number of impulses passed through the gate and counted by the counter is proportional to the vehicle speed. From the counter, the number is transmitted to the microprocessor, where it is converted into speed, and then through the demultiplexer and decoder it is fed to the digital display. After reading and processing the next measurement, the counter is reset to zero and is ready to receive the next burst of pulses. Such a system is designed to display a more accurate travel speed than a typical arrow speedometer.
The digital speedometer indicator is a liquid crystal or similar display that shows the speed in numbers.
In the latter case, the main problem is the delay in the readings: in the absence of a delay in displaying the speed value or too little delay, the driver is not able to correctly perceive the numbers constantly "jumping" before his eyes; when a significant delay is introduced, the indicator starts to display incorrectly the speed data at a given time during acceleration and deceleration due to delay.
Because of this, analog indicators are still very widely used, and digital indicators have spread to a relatively small number of models; a surge in their popularity occurred in the United States in the late seventies and eighties, from where this fashion was passed on to Japanese manufacturers, but later on most models they were replaced by traditional pointer speedometers.
Often the speedometer is combined in one housing with a distance traveled counter - an odometer.
Sources used
1.ru.wikipedia.org/wiki.
2.moikompas.ru.
3.belinka.ur.ru.
4.devichnick.ru.
