Chery A15. Manual - part 251

8. Idle speed control function
Idle speed control logic
The idle speed air flow control enables the engine control system to: maintain the targeted
turning speed when the throttle is fully closed and avoid runaway; maintain a stable turning
speed when the engine load changes at idle speed. Idle speed control function refers to the
system’s control over the engine speed when the throttle is closed. The system’s control over idle
speed refers to the adjustment of the following parameters to match the actual turning speed with
the targeted idle speed.
- Air quantity control at idle speed;
- Fuel injection quantity control
- Ignition timing control
Design control timing at idle speed
- Stability demarcation at idle speed
- Acceleration working condition demarcation
- Deceleration working condition demarcation
- Deceleration fuel cutoff
- Engine instantaneous transition working condition fuel supply demarcation
- Even speed driving demarcation
- Mechanical and electrical load increase/decrease demarcation
Targeted idle speed is determined by various input signals:
- When the engine water temperature is relatively low, the system will set a relatively high
targeted idle speed to speed up the car heating; for engines that use mechanical fans, in the case
of engine cooling fluid over temperature, the system will set a relatively high idle speed to
increase the air flow into the cooling water tank;
- When external load (e.g. air conditioner, power steering and all kinds of electrical loads, etc)
changes, the system will increase the idle speed to compensate the increased load and maintain a
stable idle speed.

Basic targeted idle speed

speed under different cooling fluid temperatures:

Coo

rature

Target idle

基本

目标怠速

车速补偿

大灯补偿

电压补偿

减速调节

目标怠速计算

目标怠速

空调补偿

Voltage
compensation

Headlight
compensation

Air conditioner
compensation

Targeted idle
speed

Deceleration
adjustment

Car speed
compensation

Basic targeted
idle speed

风扇补偿

Fan
compensation

-
Th setting of basic targeted idle

ling fluid Target idle

Cooling

Target

Cooling

Target

Cooling

temperature
℃

speed

fluid
temperature
℃

idle spe

rpm

fluid
temperature
℃

idle spe

rpm

fluid
tempe
℃

speed

< -28

1100

1150

800

104

750

-28 1100 20

1000

68 750

116 1300

-16 1100 32

1000

80 750

116

1300

-4 1100 44

900

750

- System voltage compensation

, the s

matically increase the targeted idle speed

leration adjustment

, the targeted idle speed during car

itioner compensation

on at parking idle speed, the targeted idle speed will be

When the system voltage is <12 V

ystem will auto

to increase the engine power generation. The system will increase the speed by 12.5rpm and the
maximum speed will reach 150rpm.
- Car speed compensation and dece
In order to improve the driving performance during parking
traveling will be 50rpm higher than the idle speed for car parking. When the car slows down an
stops, the idle speed will be gradually decreased until it reaches the targeted idle speed for car
parking.
- Air cond
When the air conditioner is turned
increased by 150rpm to compensate for the compressor’s power consumption.
- Headlight compensation

After the dipped headlight is turned on, the targeted idle speed will be increased by 50rpm in

es and the water tank fan is turned on, the targeted

. Self-diagnosis

ystem faults is an essential function of the engine management system; when

stem may also launch the emergency scheme to control the

0. Three-way catalyst overheating protection function

ease tendency according to the

the

es can predict the exhaust emission after

pressor control

d on, the system will receive the signal called air-conditioner

ntrol the

ntrols

llowing conditions are satisfied;

than 3.75℃

℃

Air

er output or protect the engine or air conditioning system under

order to compensate for its power consumption.
- Cooling water tank fan compensation
When the cooling fluid temperature increas
idle speed will be increased by 50rpm in order to compensate for the power consumption by the
fan.

9
Self-diagnosis of s
one or more system components are in trouble, the system will inform the driver to check and
repair by the fault indicator lights.
In the case of the above faults, the sy
engine running so that the driver may be able to drive the car up to the maintenance station
instead of having the car broken down on the roadside.

1
The system will predict the engine exhaust temperature incr
engine’s actual running status and reduce the engine fuel temperature by way of controlling
AFR in order to protect the three-way catalyst.
Three-way catalyst accelerated aging techniques
The three-way catalyst accelerated aging techniqu
80,000 kg road driving.
11. Air conditioner com
Air conditioner control logics
When the air conditioner is turne
request, make the preparations for loading the air conditioner according to the working
conditions of the engine and then connect with the air conditioner compressor; it will co
on/off status of the air conditioner according to the air conditioner’s needs for protection.
- ECM monitors the A/C request input and A/C evaporator temperature switch input and co
the air conditioner compressor clutch by way of the air conditioner relay. The system can
recognize the air conditioner system once it is plugged in.
Working conditions for the air conditioner
- The air conditioner will start running if the fo

• The car is equipped with air conditioning;
• Engine has been running for over 5 seconds

•  The air conditioner is switched on
•  The air intake temperature is higher
•  The cooling water temperature is higher than 3.75
•  The engine speed is higher than 600rpm

• No air conditioner cutoff mode works

co ditioner cutoff mode

- In order to guarantee the pow
some circumstances, ECM must cut off power supply to the air conditioner compressor or
disable the startup of the air conditioning system. Meanwhile, in order to avoid the frequen
switching on/off of the compressor clutch, ECM will somehow ensure that the air conditione

clutch can only be reactuated only after a certain period of time once the air conditioner cutoff
mode is entered. There are primarily the following modes:
-Engine heavy load air conditioner cutoff mode: to ensure power supply

• No TPS and car speed sensor fault

• The engine speed is lower than 3,600rpm (not at heavy load cutoff mode) or engine speed

is lower than 4,000rpm (at heavy load cutoff mode);

• The car speed is lower than 10kmh (not at heavy load cutoff mode) or engine speed is

lower than 15kmh (at heavy load cutoff mode);

• The throttle opens 70% of the maximum (not at heavy load cutoff mode) or the throttle

opens over 60% of the maximum (at heavy load cutoff mode).

- Wide open throttle (WOT) air conditioner cutoff mode: to ensure power supply

• The engine speed is lower than 5,000rpm;
• No TPS fault;

• TPS is bigger than 90%, and TPS has been lower than this value ever since the previous

WOT air conditioner cutoff.

- Engine overspeed air conditioner cutoff mode: to protect the air conditioning system

• When A/C is turned off, the compressor is only allowed to be started up after the engine

speed is lower than 6,000rpm.

• When A/C is turned on, the compressor will be turned off after the engine speed is higher

than 6,200rpm.

- Engine cooling water over-temperature air conditioner cutoff mode: to protect the engine

• When A/C is turned off, the compressor is only allowed to be started after the cooling

water temperature is below 105℃.

• When A/C is turned on, the compressor will be turned off after the cooling water

temperature is above 108℃.

- Air conditioner evaporator under-temperature air conditioner cutoff mode: to protect the
air conditioning system
The system will turn off the air conditioner under certain circumstances in order to ensure
sufficient power output and to protect the engine.

12. Control of the cooling fan
A double-speed cooling fan is adopted for the system.
Electrical fan control function: the system can control the double-speed cooling fan and turn on
different fans according to the water temperature to reduce the internal power consumption of the
engine.

13. Mileage accumulation
The mileage accumulation is based on the pulse signals from the car speed sensor. The
accumulated mileage range is from 0.0 to 9,999,999.9 km with an accuracy of 0.1km. After a
driving distance of 5 km or when the engine is turned off, the accumulated mileage will be
recorded into the EEPROM and resumed therefrom once the power is on again; moreover, the
accumulated mileage will still be saved even after the ECM is fully out of power. When the
system does not detect any car speed sensor fault and its circuit fault (P0500), the system will
keep accumulating the mileage by 0.1 km for every ten pulse signals received from the car speed
sensor.

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