2.

1 Ignition System
2.1.1 Description
The ignition coil is a small transformer that converts battery voltage to 30 kV or
more to create a spark in the spark plug gap inside the cylinder. The ignition module,
embedded in the ignition coil, includes a power transistor and acts as an electronic switch,
with the current being controlled by signals from the Engine Control Module (ECM).
The ignition timing is controlled by the ECM and standard ignition timing data,
based on the engine operating conditions, is stored in the ECM's memory. The engine
operating conditions (speed, load, starting state, etc.) are detected by various sensors.

Figure : Ignition control system diagram

 2.1.2 System components structure
2.1.2.1 Ignition coil

‘
Figure 2.2 : Location of the ignition coil on the Smartstream engine
*Description :
The ignition coil is mounted on top of the cylinder head cover. It consists of a
primary coil, which receives power from the battery, and a secondary coil that generates
high voltage.
 • Structure :

Figure: Ignition coil structure

In the 2023 Santa Fe, high-energy ignition coils (80mJ) are used. These independent
ignition coils are mounted directly on top of each spark plug for each cylinder. This is a
direct ignition system, meaning it doesn't use a distributor or high-tension wires. The PCM
(Powertrain Control Module) activates each ignition coil independently through an output
signal. As a result, each cylinder is controlled independently, and the ignition occurs only
once per combustion cycle during the power stroke.
• Operating principle:
When the current in the primary coil is interrupted by the ignition signal from the
ECM, a rapid change in magnetic flux is induced in the secondary coil due to mutual
induction. This generates a high voltage depending on the winding ratio of the coils. The
high voltage created in the secondary coil jumps across the gap of the spark plug, causing
the electric field to collapse, which results in a spark discharge.

Figure: Ignition coil circuit diagram

 2.1.2.2 Spark plug

Figure: Spark plug

Description:
A spark plug is a device that delivers electric current from the ignition system to the
combustion chamber of a spark-ignition engine to ignite the compressed air-fuel mixture
using an electric spark. It also seals the combustion chamber from the high pressure
generated inside the engine. The spark plug has a metal threaded shell that is electrically
insulated from a central electrode by a ceramic insulator.
Structure:
Spark plugs are threaded into the cylinder head, one for each cylinder. The spark plug
has a metal threaded cover, electrically isolated from the center electrode by a ceramic
insulator. The center electrode contains a resistor that reduces noise in the ignition system,
connected to the ignition system output by a well-insulated wire.
Figure: Spark plug structure
 2.1.3 Circuit diagram and system control principle

Figure: Ignition system circuit diagram

When turning the ignition switch to the IG or ST position, the power will be supplied
to the direct ignition system, the current will go through the F40 20A fuse and the current
will be divided into 4 controls for 4 bobines. Then, the current is supplied to the 4 primary
coils of the 4 bobines and to the GC201 mass. For bobine number 1, pin 42 PCM will send
a signal to pin number 2 of the bobine, a high voltage current will appear through the
secondary coil. This high voltage current will go to the spark plug to ignite directly in the
cylinder. The control operation is similar for the remaining 3 bobines.
• Operating principle of ignition control system:
Based on the sensor signal and ignition timing data, when the ECM applies an
ignition signal to the ignition coil for a certain period of time, the ignition module is
energized, causing the current to flow and increase gradually in the primary coil, generating
a magnetic field.
When the current in the primary coil is cut off by the ECM's ignition signal, the
magnetic flux changes rapidly due to mutual induction, generating a high voltage in the
secondary coil depending on the winding ratio of the coil. This high voltage is then
conducted to the spark plug gap, where it discharges when the magnetic field is broken,
generating a spark.
The operating principle of the ignition control system in modern engines is based on
information from sensors and control by the ECU (Engine Control Unit) to ensure the
combustion of the fuel and air mixture takes place accurately, optimizing engine
performance. Below is a detailed description of the operating principle:
Input: Sensor signals
Sensors collect data from the engine and send it to the ECU to calculate the
appropriate ignition timing. Some of the main sensors include:
Crankshaft Position Sensor (CKPS): Determines the position of the piston and the
rotation speed of the crankshaft.
Camshaft Position Sensor (CMPS): Determines the position of the camshaft,
allowing the ECU to know the exact position of the valves and cylinders.
Engine Coolant Temperature Sensor (ECT): Measures the coolant temperature to
adjust the ignition timing.
Knock Sensor (KS): Detects engine knocking, notifying the ECU to adjust the
ignition timing if premature detonation occurs.
Manifold Absolute Pressure Sensor (MAPS): Measures the pressure in the intake
manifold to calculate the amount of air entering the engine.
Throttle Position Sensor (TPS): Measures the throttle position to determine the
amount of air entering the engine.
Accelerator Pedal Position Sensor (APPS): Measures the position of the accelerator
pedal, reflecting the power request from the driver.
* Central processing unit: ECU
The ECU receives signals from the sensors and uses algorithms to calculate the most
accurate ignition timing. The ECU must determine when the spark needs to be fired during
the engine's working cycle, usually just before the piston reaches Top Dead Center (TDC)
during the compression stroke. The ECU generates the IGT (Ignition Timing) signal in the
form of a square pulse to initiate the ignition process.
* Actuator: Transistor, Bobbin, Spark plug
The IGT signal is sent by the ECU to the Igniter (ignition IC), controlling the
operation of the Transistor. The transistor acts as a switch to control the current through the
primary coil of the bobine.
Specific ignition process:
When the IGT signal is sent from the ECU to the Igniter, the Transistor in the Igniter
turns on, allowing current from the positive terminal of the battery to pass through the
primary coil of the coil and through the Transistor to ground. This current creates a
magnetic field in the primary coil.
When the IGT signal is lost (the Transistor is turned off), the current through the
primary coil is suddenly interrupted, the magnetic field in the primary coil collapses. This
change in magnetic field creates a high voltage electromotive force in the secondary coil
of the coil. This electromotive force can reach several tens of thousands of volts.
The high voltage is transmitted through the high voltage wire to the spark plug,
where it creates a spark between the electrodes of the spark plug. This spark ignites the
compressed fuel and air mixture in the combustion chamber, generating power for the
engine.
 Figure 2.1 : Ignition system diagram

* For 4-cylinder engines:

Each cylinder will have a separate IGT signal. For a 4-cylinder engine, the ECU will send
4 different IGT signals to control the ignition timing for each cylinder. This process is very
fast and precise to ensure the engine runs smoothly, powerfully and saves fuel.
2.1.4 Ignition timing adjustment

Figure : Factors determining actual ignition timing

Initial ignition advance: This is the ignition timing set by the manufacturer during
the engine's starting phase and does not change during this process.
Basic ignition advance angle: The ESA (Electric Spark Advance) system will rely
on signals from sensors (camshaft position sensor, crankshaft, intake air flow, throttle
position, coolant temperature) to determine the basic ignition advance angle.
Corrected ignition advance angle: The ECU will use data from the sensors to correct
the ignition angle to match the actual operating conditions of the engine.
 Figure 4.36 Adjusting the ignition advance angle
Coolant temperature correction: When the engine is cold, to increase the engine
heating speed, the ECU will advance the ignition angle. This helps improve combustion
efficiency when the engine is at low temperature.
Correction based on air-fuel mixture ratio: When the fuel mixture ratio is too rich
(too much fuel), the ECU will reduce the amount of fuel injected. However, this can reduce
engine power, so the ECU will increase the ignition angle to compensate, helping the
vehicle to operate stably.
Correction when shifting gears: During gear shifting, the ECU will delay the
ignition angle to reduce engine torque. This helps reduce shock and create smoothness
when shifting gears, protect the transmission system and increase driving comfort.
2.2 Fuel supply system
2.2.1 Structure, operating principle and circuit diagram of the system.
* Structure
 Fuel pump: Located in the fuel tank and provides high pressure to push fuel to the
injection system.
Fuel filter: Ensures clean fuel before entering the combustion chamber.
Fuel pressure regulator: Integrated right at the fuel pump, regulates pressure without
the need for a return line to return excess fuel to the tank.
Fuel injectors: Directly inject fuel into the combustion chamber under high pressure
according to the working order of the cylinder.
Fuel rail: Delivers fuel to the injectors.
Operation :
The Smartstream G2.5 Theta III engine uses a fuel system without a return line.
Below is a diagram of the system.

Figure : Fuel system diagram of fuel injection system

1: Suction pump to fill gasoline, 2: Fuel pump, 3: Pressure regulator, 4: Intake
pipe, 5: Manifold pipe, 6: Injectors

The fuel pump supplies fuel from the tank through the fuel filter and then pushes it
into the fuel rail. From the rail, fuel is supplied to the injectors. The fuel injectors open
when receiving a control signal from the ECU, spraying fuel into the intake manifold.
When the intake valve opens, air is drawn in, carrying fuel vapor to form an air-fuel
mixture.
 2.2.2 Components
2.2.2.1 Injector
* Features of injector:

8-hole injector: This design helps to spray fuel into smaller and more evenly
distributed jets in the combustion chamber, improving the mixing of air and fuel, thereby
improving combustion efficiency.
High resistance injector: With a resistance value of 11.4 to 12.6Ω, this type of
injector consumes less current, helping the system operate more stably under high pressure
conditions.
Positioned near the intake valve: This helps to spray fuel directly into the intake
manifold as soon as the intake valve opens, preventing fuel from sticking to the intake port,
optimizing air-fuel mixing.Thiết kế lắp đặt kim phun:
Injector Insulation: Injectors mounted on the manifold must be insulated to prevent
heat from boiling the fuel, preventing the formation of air bubbles in the system.
O-rings: Ensure no fuel leaks occur and maintain stable pressure in the fuel system.
Rubber gaskets: The injector tips are mounted through rubber gaskets into the intake
manifold. This serves to insulate, reduce vibration, and prevent unwanted air from entering
the intake system.
Figure: Fuel injector on Santafe 2023
 Figure: Injector structure

Operating principle of the injector:

Coil in the injector body: Used to control the injector valve. When there is no current
running through the coil, the injector valve is held closed by the force of the spring.
When there is no current: The spring in the injector pushes the injector valve down,
closing the outlet and preventing fuel from being sprayed into the intake port.
 When there is current: The current running through the coil creates a magnetic field,
which lifts the injector valve, opening the way for fuel to be sprayed through the injector
holes and into the intake port.
Control process:

The ECU (electronic control unit) controls the current through the coil according to
the engine's operating order. When the ECU receives a signal that fuel needs to be injected,
it will supply current to the coil, opening the needle valve and fuel is injected into the intake
manifold. When the injection process is finished, the ECU stops supplying current, the
needle valve will return to the closed position by the push of the spring.
Injector circuit diagram:

Figure: Injector control circuit diagram

Each injector in the diagram has two pins, denoted as pin 1 and pin 2. Fuel injection
control of the injectors is performed through the control of the ECU. The ECU will receive
signals from input sensors, calculate the appropriate amount of fuel and injection timing,
then output signals to control the injectors according to the correct engine working cycle.
General principle of injectors:
Pin 1 (High): This pin receives the control signal from the PCM.
Pin 2 (Low): This pin connects to the low current control circuit.
Injector operating steps:
Injection Timing Calculation: The ECU relies on input signals from sensors such as
the camshaft position sensor, crankshaft position sensor, intake manifold pressure sensor,
and other operating parameters to determine when and how much fuel to inject.
Controlling the current to the injector coil: Once the injection timing has been
determined, the ECU sends a control signal to the injector coil. For injector 1, the signal is
sent from pin 73 of the ECU to pin 1 of injector 1, and the current is connected back to the
ECU via pin 74.
Injector activation: Current from the ECU runs through the coil in the injector,
creating a magnetic field that pulls the injector valve up. At this time, high-pressure fuel
from the distribution pipe will be sprayed through the injector holes into the combustion
chamber..
Injector Closing: After the injection time is complete, the ECU will cut off the current
through the coil, causing the magnetic field to disappear, and the spring in the injector will
push the needle valve back to the closed position. Fuel stops being injected.
Operating characteristics of the injector in the diagram:
Each injector has two wires connected to the ECU to control the fuel injection
process. For example, injector 1 has wires connected from pin 73 (High) and pin 74 (Low)
of the ECU, similar to the other injectors:
Injector No. 2: pin 29 (High) and pin 30 (Low).
Injector No. 3: pin 31 (High) and pin 32 (Low).
Injector No. 4: pin 61 (High) and pin 62 (Low).
This arrangement helps ensure that each injector is controlled to spray at the
correct time, according to the engine's operating cycle.
 2.2.2.2 Fuel Pressure Regulator
* Description :
The fuel pressure regulator is responsible for maintaining a stable pressure for the
fuel injection system, ensuring that fuel is injected into the engine at a constant pressure.
On the Smartstream G2.5 Theta III engine, the pressure regulator is located inside the
fuel tank and right above the fuel pump.

Figure : Pressure regulator

Structure:

Figure : Structure of fuel pressure regulator

1: Intake manifold; 2: Spring; 3: Retaining valve; 4: Diaphragm; 5: Valve; 6: Fuel
in; 7: Return fuel
Intake manifold: Connects to the engine's intake system, where the vacuum behind
the throttle acts on the diaphragm to regulate fuel pressure.
 Spring: Located at the top of the regulator, it exerts a force on the valve through the
diaphragm to keep the fuel pressure stable. The spring force is balanced by the vacuum
pressure from the intake manifold.
Holding valve: Holds the fuel control valve in place, allowing for precise pressure
adjustment as fuel passes through.
Diaphragm: Divides the regulator into two parts (the lower part contains the fuel,
the upper part contains the spring). The diaphragm oscillates as the pressure changes,
regulating the opening and closing of the valve.
Valve: Controls the fuel flow, opening to allow excess fuel to return to the tank when
the pressure exceeds the allowable level.
Fuel inlet: Fuel from the pump is fed into the lower part of the regulator.
Fuel return: Excess fuel after being regulated by the valve will be returned to the
fuel tank through this line.
Operation principle :

Figure : Operation of the pressure regulator

 When the fuel pressure in the pipeline is higher than the required level (over 3.3-3.7
bar), the diaphragm is pushed up by the high pressure, opening the valve and allowing
excess fuel to return to the tank.
When the engine is running at low load and the vacuum behind the throttle increases,
the spring will be compressed less and the pressure regulator will adjust the fuel pressure
lower, suitable for the operating conditions.
On the contrary, when the engine load increases, the vacuum decreases, the spring
will push harder on the valve, increasing the fuel pressure to ensure sufficient fuel supply
to the injectors.
2.2.2.3 Fuel pump
* Description:
The fuel pump on the 2023 Santafe is located inside the fuel tank and is integrated with
the fuel filter, pressure regulator, and fuel level sensor. The pump is responsible for
drawing fuel from the fuel tank and supplying it with stable pressure to the entire fuel
system. The arrangement of the pump inside the fuel tank has the advantage of providing
good sound insulation and keeping the pump cool. However, the disadvantage of this
design is that maintenance and replacement become more complicated and difficult.

Figure : Fuel pump on Hyundai Santafe 2023

 Structure :

Figure : Structure of fuel pump

The structure of the fuel pump on a vehicle usually includes the following main
components:
Electric Motor: This is the main part of the fuel pump, which rotates and creates suction
to pump fuel from the fuel tank through the system. This motor usually operates at 12V
voltage, controlled by the ECU and sensor.
Gear or Rotor: Inside the pump are gears or rotors, which help push fuel out of the pump
as the motor rotates. Depending on the pump design, either a vane pump or a gear pump
can be used.
Fuel Filter: Integrated in the pump to filter impurities in the fuel before it is fed into the
engine, ensuring that other parts in the fuel system are not damaged.
One-Way Valve: This valve prevents fuel from flowing back into the fuel tank when the
pump stops operating, ensuring fuel pressure is always maintained in the system.
Fuel Pressure Regulator: Integrated to keep fuel pressure stable within the standard range
(3.3 – 3.7 kgf/cm²) and return excess fuel to the tank.
Fuel Level Sensor: Measures the remaining fuel level in the tank and sends a signal to the
ECU, displayed on the vehicle's dashboard.
Pump Housing: The housing protects the entire pump, helping to protect against water
and harmful external agents. It also plays an important role in soundproofing, reducing
noise from the pump during operation.
Fuel lines: Carry fuel from the pump through the filter, pressure regulator, and to other
components in the fuel system.
• Operating principle
When the 12V DC power source is supplied in the correct direction, the fuel pump's
electric motor starts to operate. The rotating motor causes the vanes to rotate, creating
suction to draw fuel from the tank. The fuel after being sucked up will go through a coarse
filter to remove dirt and impurities, helping to clean the fuel before reaching the injector
system. The fuel will flow through the gap between the rotor and stator in the pump, going
up to the upper chamber. When the fuel pressure is large enough, the one-way valve will
open, allowing fuel to enter the pipeline to supply the injectors. Inside the fuel pump, there
is a safety valve, which helps reduce excessive pressure on the pump. When the pressure
in the system exceeds the allowable limit, the safety valve will open to release excess
pressure, protecting the fuel pump system from damage. The one-way valve is installed at
the pump outlet, helping to maintain an excess pressure in the system when the engine
stops running. This residual pressure plays an important role in helping the engine restart
easily, especially in the case of engine stop at high temperature. This pressure prevents
foaming in the fuel, keeps the fuel in a stable liquid state, ensuring the system is ready to
operate when restarted.
 2.2.2.4 Fuel Sender

Figure: Fuel level sensor

To measure the fuel level, a float is used in the fuel tank. As the float moves with
the fuel level, the slider position on the sensor changes. This change affects the
potentiometer, changing the output current, which is then sent to the control panel to
display the fuel level. To accurately measure different fuel volumes, manufacturers
increase the angle of rotation of the fuel float to improve measurement accuracy.
2.2.2.5 Fuel filter
The fuel filter on the Santafe is made of plastic.
 Figure : Fuel filter on Hyundai Santafe 2023
• Description :
The fuel filter is responsible for filtering out impurities and harmful substances in the fuel
to ensure the correct operation of the fuel system. After being filtered, the fuel will be
distributed and the injector. The fuel filter removes dirt, rust, water and other impurities in
the fuel before the fuel reaches the injector. Large filters are designed to remove particles
that are 10 to 20 micrometers in size or larger.
2.2.3 Adjustment of injection timing and fuel injection quantity.
Adjustment of injection timing:
The basic injection timing is determined by input signals from sensors such as the
Manifold Absolute Pressure Sensor (MAPS), Intake Air Temperature Sensor (IAT), and
Crankshaft Position Sensor (CKP). ECU receives and processes these signals to calculate
the appropriate fuel injection timing based on the engine's operating conditions.
For effective injection timing, the ECU adjusts the injector's opening duration by
altering the pulse width. When more fuel is required, the injector stays open longer; when
less fuel is needed, it opens for a shorter period. This optimizes the air-fuel (A/F) ratio,
ensuring the vehicle operates efficiently under various driving conditions..
 • Fuel injection quantity adjustment:
ECU calculates the fuel injection amount based on input signals from sensors. Once
calculated, it sends control signals to the injectors to adjust the fuel quantity delivered into
the engine. The amount of fuel injected depends on the size of the injector nozzles and the
fuel pressure in the fuel rail. These factors remain constant, but the fuel quantity is adjusted
by varying the injector open time. This ensures the engine receives an adequate and
efficient fuel supply for combustion.
2.3 Electronic Throttle Control System
2.3.1 Description of structure, operating principle and parameters

Figure : Electronic throttle on Hyundai Santafe 2023

• Structure :
Throttle Assembly:
Includes the control motor and integrated Throttle Position Sensor (TPS).
Accelerator Pedal Position Sensor (APS):
Replaces the traditional throttle cable, detecting driver input (how much the accelerator
pedal is pressed).
Engine Control Unit (ECM):
The "brain" of the system, processes signals from sensors and controls the throttle opening
angle.

Figure: Electronic throttle system structure

• Operating principle
Driver Input:
When the driver presses the accelerator pedal, the Accelerator Pedal Position Sensor
(APS) detects the amount of pressure and converts the mechanical action into an electrical
signal.
Signal Processing by the ECM:
The signal from the APS is sent to the Engine Control Unit (ECM), which calculates the
desired throttle opening angle based on the driver input and other engine conditions.
Throttle Control:
The ECM sends a control signal to the electronic throttle motor, which adjusts the position
of the butterfly valve (throttle valve) inside the throttle assembly to achieve the desired
opening angle.
Throttle Position Feedback:
The Throttle Position Sensor (TPS) in the throttle assembly monitors the actual position
of the butterfly valve and sends feedback to the ECM, allowing the system to make the
necessary adjustments to maintain the desired opening.
Specifications
Throttle Position Sensor (TPS)
Output Voltage (V)
Throttle Angle (°) TPS1 TPS2
0 0.0 5.0
10 0.48 4.52
20 0.95 4.05
30 1.43 3.57
40 1.90 3.10
50 2.38 2.62
60 2.86 2.14
70 3.33 1.67
80 3.81 1.19
90 4.29 0.71
100 4.76 0.24
105 5.0 0
C.T (6 - 15°) 0.29 - 0.71 4.29 - 4.71
W.O.T (93 - 102°) 4.43 - 4.86 0.14 - 0.57
 TPS1 and TPS2 sensors operate in opposite directions. When one sensor outputs an
increased voltage according to the throttle valve opening angle, the other sensor will
decrease. This symmetrical operation allows the ETC system to accurately control and
monitor the throttle valve position. TPS2 acts as a backup to ensure safety. If one sensor
fails, the remaining sensor can still provide an accurate signal to the ECM, thereby ensuring
the system continues to operate stably.
Item Sensor Resistance (kΩ)
TPS1 0.875 - 1.625 [20°C (68°F)]
TPS2 0.875 - 1.625 [20°C (68°F)]
ETC Motor
Item Specification
Coil Resistance (Ω) 1.2 - 1.8 [20°C (68°F)]
 Figure: Schematic Diagram ECT
The ECM continuously monitors the engine's operating conditions and adjusts the
throttle valve position via the ETC motor to control airflow into the engine. It uses the
feedback from the TPS to maintain optimal performance.
 Figure : Circuit Diagram ECT
The throttle position sensor (TPS 1 and TPS 2) sends data about the throttle position
to the ECM.
The ECM calculates the throttle opening based on the signal from the accelerator
pedal position sensor (APS) and other signals.
The ECM then sends a control signal to the ETC motor to adjust the throttle to the
correct position, helping to control the amount of air entering the engine accurately.
This system provides more precise control and eliminates the use of mechanical
cables.
2.3.2 Control modes
Normal mode control: This is the basic control mode to maintain the balance
between ease of operation and smooth movement.
High power mode control: In this mode, the throttle valve opens wider than in
normal mode. Therefore, this mode gives the feeling that the engine responds quickly to
the accelerator pedal and the vehicle operates more powerfully.
 Snow/slippery mode control: This control mode keeps the throttle valve opening
angle smaller to avoid slipping when driving on snow

Figure : Schematic diagram of operating modes

Active Torque Control: In this mode, the control system will open or close the throttle
automatically, not completely dependent on the accelerator pedal angle. The purpose is to
maintain smooth acceleration and minimize sudden changes in acceleration during
operation, providing a more comfortable driving experience.
 Figure 4.42 Schematic diagram of active power transmission control
Vehicles with active torque control: When the driver steps on the accelerator, the
throttle valve opens slowly, helping the longitudinal acceleration of the vehicle increase
gradually, not suddenly. This creates a smoother driving experience.
Vehicles without active torque control (vehicles using a throttle cable): The throttle
valve opening will be almost synchronized with the movement of the accelerator pedal, the
longitudinal acceleration of the vehicle may increase suddenly in a short time, causing
jerking or impact.
Reduced shift shock:
When shifting, the control system reduces the throttle opening to minimize vibration
and shock during shifting. This makes shifting smoother and more comfortable.
Cruise Control: The electronic throttle system combined with the ECU will maintain
the selected speed without the driver having to keep the accelerator pedal pressed
continuously. When cruise control is activated, the throttle will be automatically adjusted
to keep the vehicle at a stable speed, making the driver more comfortable when traveling
long distances.
2.4 Continuously Variable Valve Timing System
2.4.1 Description
CVVT stands for Continuously Variable Valve Timing. This is a system that controls
the valve timing to optimize engine performance based on actual operating conditions.
In conventional engines, the valve timing is fixed and is designed based on the
specific operating conditions of the engine. This happens because the cam is driven directly
from the crankshaft through gears or chains. However, for the 2023 Hyundai Santafe engine
equipped with the CVVT system, the valve timing can change depending on the engine's
operating conditions. The CVVT system adjusts the opening angle of the intake camshaft
through the use of hydraulic pressure controlled by a solenoid valve, which changes the
valve timing to optimize performance.

Figure: CVVT system

Continuous Variable Valve Timing (CVVT) system advances or retards the valve timing
of the intake and exhaust valve in accordance with the ECM control signal which is
calculated by the engine speed and load.
 By controlling CVVT, the valve over-lap or under-lap occurs, which makes better fuel
economy and reduces exhaust gases (NOx, HC) and improves engine performance
through reduction of pumping loss, internal EGR effect, improvement of combustion
stability, improvement of volumetric efficiency, and increase of expansion work.

Figure : CVVT system operation diagram

2.4.2 CVVT Components
The structure of the CVVT system includes the main components:
CVVT controller: This is the part that adjusts the valve timing.
Engine ECU: The central control unit, calculates and sends control signals to the
system components based on data collected from sensors.
Crankshaft position sensor: Determines the position of the crankshaft to calculate
the valve timing.
Mass air flow sensor: Measures the amount of air entering the engine to help adjust
the valve timing and fuel injection.
 Throttle position sensor: Helps the system know the position of the throttle and
adjusts the valve timing to suit the engine speed and load.
Camshaft position sensor: Determines the position of the camshaft to adjust the
opening and closing timing of the valves.
In which, the two most important parts of the system are:
Control Valve (OCV): Controls the flow of oil to create hydraulic pressure, adjusting
the opening angle of the camshaft.
CVVT controller: Is the component that changes the opening and closing timing of
the intake and exhaust valves to optimize engine performance.
2.4.2.1 Structure and operating principle of CVVT controller

Figure : CVVT controller structure

1-CVVT body, 2- Lock pin, 3- fan blade, 4- camshaft.
a-when stopped; b- in operation.
Structure:
Controller: The controller is mounted directly on the intake camshaft and controls the
rotation of the intake camshaft according to the signal from the ECU (electronic control
system of the engine).
Structure: The controller consists of an outer shell driven by a timing chain, and the
blades are fixed on the intake camshaft by bolts and locating pins. In the blades there is
an oil passage that connects to the camshaft, supplying oil to the chambers inside the
controller for lubrication and control functions.
The operating principle of the intake camshaft timing control system is described as
follows:
Changing valve timing: When the engine is running, the controller rotates the vanes in
the corresponding direction to change the valve timing. This takes place within the
camshaft rotation angle range of 200 ± 10 degrees. The oil pressure in the system can
vary from 0 to 1000 KPa, and this change will adjust the vanes to rotate the camshaft to
"advance" or "retarded" depending on the engine's requirements.
When the engine stops: The intake camshaft will automatically return to its latest position
to ensure the best starting ability for the engine the next time it is started.
When the engine is running: In the speed range from 650 to 6000 rpm (r/min), the timing
will be adjusted to open the valve early or late depending on the operating conditions of
the engine. When the engine has just started and the oil pressure is not enough to supply
the controller, the locking system will keep the parts in a locked state to avoid unwanted
knocking or vibration.
2.4.2.2. Structure and Operating Principle of Oil Control Valve (OCV):

Figure : Structure of OCV valve controller

a-Spring, b- Bushing, c- Spool, d- Oil line (early chamber), e – Oil line (delay chamber),
f – Return oil line, g – Incoming oil line, h- Coil, j- Piston.
The operating principle of the intake camshaft timing control system operates
according to the following steps:
 Receive signal from ECU: When the engine is running, the ECU (electronic control
system of the engine) will send a control signal through the connector to the solenoid
valve. This signal determines whether the solenoid valve will control the oil line to the
controller in the direction of early or late operation, based on the engine's working
mode.
Camshaft timing oil control valve: This valve selects the oil path to the controller based
on the signal from the ECU, which is regulated by the magnitude of the current from the
engine ECU. When the oil flows into the controller, the intake camshaft will rotate in the
corresponding direction to adjust the valve timing. This timing can be advanced,
retarded, or maintained at a fixed valve timing.
Calculation from ECU: ECU calculates the optimal timing to open/close the valve based
on engine operating conditions such as: engine speed, intake air flow, throttle position,
coolant temperature. From these parameters, ECU controls the oil valve to change the
camshaft timing to optimize performance.
Feedback control: The ECU also uses signals from sensors such as the camshaft position
sensor and crankshaft position sensor to calculate the actual valve timing. If necessary,
the feedback control system adjusts the valve timing to achieve the most optimal
accuracy, helping the engine operate efficiently and stably.
4.3.2. Operating Principle of Continuously Variable Valve Timing System
* The system operates in 3 modes
Working principle of the controller in the latest valve opening mode
Latest open mode:
The intake camshaft controller will be in the latest open position when the engine is
operating in situations such as starting, stopping, idling or when the engine temperature is
low.
These modes require a rich fuel mixture for easy starting and to ensure stable engine
operation at idle. At the same time, the throttle valve opens small in these modes, making
the vacuum pressure in front of the intake valve not large.
Low pressure and difficult air intake into the cylinder:
Due to the small pressure difference between before and after the intake valve, new
intake air has difficulty entering the cylinder.
 In this case, the control valve adjusts the intake camshaft to rotate backward, thanks
to the signal from the ECU. Oil pressure is compressed into the retarder side vane chamber
to rotate the camshaft in the backward direction.
Reduce orchestration duplication:
When the controller holds the intake camshaft at its most advanced position, the
intake camshaft timing is retarded and valve overlap is reduced. This reduces the intake
ratio and limits the amount of residual exhaust gas flowing back into the intake manifold.
In this case, only a small amount of fuel needs to be injected into the intake manifold
but still ensures a rich fuel mixture, helping the engine operate stably and improving fuel
efficiency at start-up.

Figure: Controller schematic diagram in latest mode

The working principle of the controller in the earliest intake valve opening mode is
as follows:
Operating conditions:
This mode appears when the engine is operating at low to medium speed and heavy
load. This is the operating range that the engine normally uses.
 As the engine load increases, the throttle valve opens wider, reducing airflow
resistance, thereby reducing the pressure on the intake manifold, and the pressure in front
of the intake valve becomes higher.
Early mixing time:
At 100% load, the valve timing is adjusted as early as possible to take advantage of
the intake air flow into the cylinder, when the pressure in the cylinder is less than the
pressure before the intake valve.
Opening the intake valve early increases the amount of internal exhaust gas
recirculation (EGR), reduces aerodynamic losses and improves fuel economy. At the same
time, it also reduces the concentration of harmful emissions.
ECU Control:
The engine ECU receives information from sensors, including the crankshaft
position sensor, throttle position sensor, mass air flow sensor, and camshaft position sensor
to determine the current operating mode of the engine.
Based on this information, the ECU controls the camshaft timing valve to move to
the left, forcing oil pressure into the vane chamber on the early opening side. This force
pushes the controller's vane to the early opening side and communicates with the oil
passage on the late opening side.
The vane moves to the position where the intake valve opens earliest, optimizing
the process of filling the cylinder with air.
 Figure : Schematic diagram of the controller in the earliest open mode.
The working principle of the controller in hold mode is as follows:
Increase speed and load:
When the engine accelerates or increases load, the ECU (electronic engine control unit)
controls the oil supply valve so that the camshaft controller rotates towards the intake
valve, helping to open the valve earlier to match the engine's air intake needs.
This optimizes the timing of the fuel injection according to the engine's operating
conditions.Ensures a lean fuel mixture
As load and speed increase to a certain level, the engine requires a leaner fuel-air mixture
to improve fuel economy. The ECU adjusts the oil supply valve to the timing controller
so that the camshaft rotates at the correct timing calculated by the ECU.
Control valve operation:
The control valve moves to the left, allowing oil to enter the late opening passage at high
pressure. This high oil pressure pushes the lock pin and unlocks the lock pin, and at the
same time oil also enters the early opening chamber to push the camshaft control vane
counterclockwise, causing the intake valve to open early. Oil in the oil line connected to
the late opening chamber will flow to the catte (crankshaft box).
Hold status:
When the intake camshaft has rotated to the correct position according to the angle that
the ECU has calculated based on the current working conditions of the engine (through
the feedback signal from the crankshaft position sensor), the ECU controls the air
distribution valve to close the oil lines to the crankcase, preventing oil from entering the
controller anymore. At this point, the controller switches to the holding state, meaning
that the camshaft stays in a stable position and does not change until there is a change in
load or engine speed.
Adjust if necessary:
If there is a change in load or speed, the ECU will re-control to adapt to the new engine
operating mode, ensuring the camshaft adjusts promptly and accurately according to
demand.

Figure : Schematic diagram of the controller working in hold mode.