Every car has a simple but
important sensor that helps monitor engine performance - the coolant
temperature sensor. Read the article about what a temperature sensor is, what
its design is, what principles its operation is based on, and what place it
occupies in a car.
What is a temperature sensor
Coolant Temperature Sensor (CTS)
is an electronic sensor designed to measure the temperature of the coolant
(coolant) of the cooling system of an internal combustion engine. The data
obtained from the sensor is used to solve several problems:
Visual
control of the temperature of the power unit - data from the sensor is
displayed on the corresponding device (thermometer) on the dashboard in the
car;
Adjustment
of the operation of various engine systems (power supply, ignition, cooling,
exhaust gas recirculation and others) in accordance with its current
temperature conditions - information from the DTOZH is sent to the electronic
control unit (ECU), which makes the appropriate adjustments.
Coolant
temperature sensors are used in all modern cars; they have a fundamentally the
same design and operating principle.
Types and design of temperature sensors
Modern vehicles (as well as
various electronic devices) use temperature sensors, the sensitive element of
which is a thermistor (or thermistor). A thermistor (thermistor) is a
semiconductor device whose electrical resistance depends on its temperature. There
are thermistors with negative and positive temperature coefficient of
resistance (TCR); for devices with a negative TCR, the resistance decreases
with increasing temperature, for devices with a positive TCR, on the contrary,
it increases. Today, thermistors with negative TCS are most often used, as they
are more convenient and cheaper.
Structurally, all automobile DTOZH are fundamentally the same. The basis of the design is a metal body (cylinder) made of brass, bronze or other corrosion-resistant metal. The housing is designed in such a way that part of it is in contact with the coolant flow - a thermistor is located here, which can additionally be pressed by a spring (for more reliable contact with the housing). In the upper part of the housing there is a contact (or contacts) for connecting the sensor to the corresponding circuit of the vehicle's electrical system. The housing is also threaded and has a hex key for mounting the sensor into the engine cooling system.
- Temperature sensors differ in the way they are connected to the computer:
- With a standard electrical connector - the sensor has a plastic connector (or block) with contacts.
- With a screw contact—the sensor has one contact with a clamping screw.
- With a pin contact - the sensor has one pin or spade contact.
Sensors
of the second and third types have only one contact, the second contact is the
sensor body, connected to the “ground” of the vehicle’s electrical system
through the engine. Such sensors are most often used on commercial vehicles and
trucks, on special, agricultural and other equipment.
The Coolant Temperature Sensor (CTS) is
mounted at the hottest point of the engine cooling system - in the exhaust pipe
of the cylinder head. Modern cars often have two or even three DTOZ installed
at once, each of which performs its own function:
The thermometer sensor (coolant temperature indicator) is the
simplest, has low accuracy, since it only helps to visually assess the
temperature of the power unit.
The ECU sensor at the outlet of the block head
is the most responsible and accurate sensor (with an error of 1-2.5°C),
allowing you to monitor temperature changes of several degrees.
The sensor at the radiator outlet is a
low-precision auxiliary sensor that ensures timely switching on and off of the
electric radiator cooling fan..
Several sensors provide more information about the current
temperature conditions of the power unit and allow more reliable control of its
operation.
Operating principle and location of the temperature sensor in the vehicle
In general, the operating principle of a
temperature sensor is simple. A constant voltage (usually 5 or 9 V) is applied
to the sensor, the voltage drops at the thermistor in accordance with Ohm’s law
(due to its resistance). A change in temperature entails a change in the
resistance of the thermistor (as the temperature rises, the resistance
decreases, as the temperature decreases, it increases), and therefore a voltage
drop in the sensor circuit. The measured value of the voltage drop (or rather,
the actual voltage in the sensor circuit) is precisely what is used by the
thermometer or ECU to determine the current engine temperature.
To visually monitor the temperature of
the power unit, a special electrical device is connected to the sensor circuit
- a ratiometric thermometer. The device uses two or three electrical windings,
between which there is a movable armature with an arrow. One or two windings
create a constant magnetic field, and one winding is included in the
temperature sensor circuit, so its magnetic field changes depending on the
coolant temperature. As a result of the interaction of constant and alternating
magnetic fields in the windings, the armature rotates around its axis, which
entails a change in the position of the thermometer needle on its dial.
To
monitor the functioning of the motor in various modes and control its systems,
sensor readings are fed to the electronic control unit through the appropriate
controller. Temperature is measured based on the voltage drop in the sensor
circuit, for this purpose, the ECU memory contains tables corresponding to the
voltage in the sensor circuit and engine temperature. Based on this data, the
ECU runs various algorithms for the operation of the main engine systems.
Based on the DTOZ readings, adjustments are made to the
operation of the ignition system (change in ignition timing), power (change in
the composition of the fuel-air mixture, its depletion or enrichment, control
of the throttle assembly), exhaust gas recirculation and others. The ECU also
sets the crankshaft speed and other characteristics in accordance with the
engine temperature.
The temperature sensor on the cooling radiator works in a
similar way, it controls the electric fan. On some vehicles, this
sensor can be paired with the main one for more precise control of various
engine systems.
The
temperature sensor plays an important role in any vehicle with an internal
combustion engine, in the event of a breakdown, it must be replaced as soon as
possible - only in this case will the normal operation of the power unit be
ensured in any mode.