SsangYong Rodius (2013 year). Manual - part 85

15-11

0000-00

2) ECU Control

(1) Function

a. ECU Function

ECU receives and analyzes signals from various sensors and then modifies those signals into 

permissible voltage levels and analyzes to control respective actuators.

ECU microprocessor calculates injection period and injection timing proper for engine piston speed 

and crankshaft angle based on input data and stored specific map to control the engine power and 

emission gas.

Output signal of the ECU microprocessor drives pressure control valve to control the rail pressure and 

activates injector solenoid valve to control the fuel injection period and injection timing; so controls 

various actuators in response to engine changes. Auxiliary function of ECU has adopted to reduce 

emission gas, improve fuel economy and enhance safety, comforts and conveniences. For example, 

there are EGR, booster pressure control, autocruise (export only) and immobilizer and adopted CAN 

communication to exchange data among electrical systems (automatic T/M and brake system) in the 

vehicle fluently. And Scanner can be used to diagnose vehicle status and defectives.
Operating temperature range of ECU is normally -40 to +85°C and protected from factors like 

oil, water and electromagnetism and there should be no mechanical shocks.

To control the fuel volume precisely under repeated injections, high current should be applied instantly 

so there is injector drive circuit in the ECU to generate necessary current during injector drive stages.

Current control circuit divides current applying time (injection time) into full-in-current-phase and hold-

current-phase and then the injectors should work very correctly under every working condition.

b. Control Function

Controls by operating stages

To make optimum combustion under every operating stage, ECU should calculate proper injection 

volume in each stage by considering various factors.

Starting injection volume control

During initial starting, injecting fuel volume will be calculated by function of temperature and engine 

cranking speed. Starting injection continues from when the ignition switch is turned to ignition 

position to till the engine reaches to allowable minimum speed.

Driving mode control

If the vehicle runs normally, fuel injection volume will be calculated by accelerator pedal travel and 

engine rpm and the drive map will be used to match the drivers inputs with optimum engine power.

-

-

-

15-12

(2) Fuel injection control

a. Multi injection

Fuel injection process consists of 3 steps: Main Injection, Pilot Injection, Post Injection

This is the injection before main injection. This consists of 1st and 2nd pilot injection, and Pre-injection. 

The steps are normally used to control the NOx, noise, idle stability and engine vibration. Inject a small 

amount of fuel before main injection prevents the instant high combustion temperature. It reduces the 

NOx and decreases the engine noise and vibration. The main injection produces the actual output. 

The vehicle output is based on the main injection. The post injection is the injection process after main 
injection and consists of ‘After injection”, “Post 1 injection” and “Post 2 injection”. All of post 

injections are to reduce the PM and harmful exhaust gas. The post injection does not make the actual 

output. The post injection activates the fuel by injecting the fuel to the incompletely combusted gas 

after primary combustion. Through the process, the PM and smoke in the exhaust gas could be 

reduced. There are totally 7 injections as shown in the figure. However, all of 7 injections are not 

performed during driving because it decreases the fuel economy. Totally 5 injections can be performed 

in one cycle.

Injection

Function

Main

Produces engine power

Pilot 1

Reduces PM by injecting   before 
main injection.

After

PM control

Pilot 2

Reduces NOx and noise by 
shortening main injection delay 
due to flammability 

Post 1

Reduces PM by enabling fuel 
activation.

Pre

Controls NOx emission level, 
Combustion noise and
Stable idle 

Post 2

Activates CDPF by increasing 
exhaust gas temperature and 
supplying reduction material

15-13

0000-00

b. Pilot Injection

Injection before main injection. Consists of 1st and 2nd pilot injection, and Pre-injection

Inject a small amount of fuel before main injection to make the combustion smooth. Also, called as 

preliminary injection or ignition injection. This helps to reduce Nox, engine noise and vibration, and to 

stabilize the idling.

The injected fuel volume is changed and stopped according to the coolant temperature and intake air 

volume.

Pilot injection is much earlier than main injection due to higher engine rpm

Too small injection volume (insufficient injection pressure, insufficient fuel injection volume in 

main injection, engine braking)

System failure (fuel system, engine control system)

-

-

-

Pilot injection

Main injection

Combustion pressure with pilot injection

Combustion pressure without pilot injection

1.

2.

1a.

2b. 

Stop conditions

Combustion pressure characteristic curve for pilot injection

▶

15-14

c. Main Injection

The power of the vehicle is determined by the main fuel injection volume. 

Main injection calculates the fuel volume based on pilot injection. The calculation uses the value for 

accelerator pedal position, engine rpm, coolant temperature, intake air temperature, boost pressure, 

boost temperature and atmospheric pressure etc.

d. Post  Injection

Injection after main injection. Consists of After injection, Post 1, Post 2 injection.

Post injection reduces PM and smoke from exhaust gas. No actual output is generated during these 

injections, instead, fuel is injected to the unburned gas after main injection to enable fuel activation.