Description of the LHU/A20NFT charging system
|
|
Description of the LHU/A20NFT charging system
|
|
Control of electric current, overview
|
The electrical control system is constructed to monitor and control the charging system and send diagnostic messages to attract the attention of the driver to any problems with the battery and the alternator. The electrical control system uses mainly the computer capacity of BCM, SCM (Signal Conversion Module) and ECM to improve the charging state and life expectancy of the battery, and to minimise fuel consumption. The charging system performs three functions:
|
•
|
It monitors battery voltage and estimates battery condition.
|
|
•
|
It takes corrective action by increasing idling speed an adjusting control voltage.
|
|
•
|
It performs diagnostic tests, set DTCs and warns the driver.
|
The battery condition is estimated with the ignition off and while the ignition is on. When the ignition is off, the battery's charge state is determined by measuring the battery voltage. The charge state is a function of the acid concentration and the battery's interior resistance, and it is calculated by reading the battery's rest potential when it has been at rest for several hours.
While the ignition is on, the algorithm calculates the charge state continuously based on the original charge state and the current value of the battery sensor.
The electrical control system is also designed to regulate the voltage control so that the battery charge state, battery life expectancy and fuel economy are improved. This is achieved by using information of the battery charge state and temperature to set the battery charge voltage to an optimum battery voltage level for charging without affecting the battery life expectancy negatively.
|
Charging system components
|
Battery sensor
The battery's SOC (State Of Charge) is calculated from the battery voltage after the battery has been at rest for several hours. Once the car is put in use again, the SOC calculated from the rest potential is used, this value is then corrected with the current (charging/discharging) through the battery.
The battery sensor (343) measures the size and direction of the current in order to determine how much current is being charged or discharged. This value is used to calculate the battery's operating SOC. The battery SOC is defined as the battery's current capacity divided by its specified capacity. Capacity is measured in ampere-hours, Ah. In manufacture, the battery capacity (Ah) is programmed into the battery sensor of the new car. When replacing with a new battery, the capacity of the new one must be programmed in again if its capacity is different from the factory value. The current is calculated by measuring the voltage drop across a current shunt that is integrated in the battery sensor. Terminal voltage is measured between B- and a wire for +30. The temperature is measured directly on the battery terminal. The sensor has an integrated processor and an LIN interface.
Body control module (BCM)
Battery voltage, current, temperature and charge are read from the intelligent battery sensor (IBS) via the local interconnect bus (LIN). BCM then sends the following bus data related to the sensor signal:
Battery terminal voltage
Battery input/output current
Battery temperature
Battery state of charge (SOC)
Battery state of health (SOH)
Lowest battery start voltage (SOF)
IBS sensor status (fault/OK)
Battery sensor
The battery sensor is a rugged component that is connected to the negative battery cable on the battery. The battery sensor is a three-wire Hall effect current sensor. The battery sensor monitors the battery current. It feeds directly into BCM. It creates a 5-volt pulse width modulated signal with 128 Hz and pulse length of 0-100 per cent. The normal pulse length is 5-95 per cent. The intervals 0-5 per cent and 95-100 per cent are used for diagnostics.
Signal Conversion Module (SCM)
The software for the charge regulator is in SCM. There are three separate modes of operation:
Charge mode
Fuel economy mode
Start mode
|
Operation of charging system
|
The charging system is intended to maintain the battery charge and the vehicle's load. There are six separate operating modes:
|
•
|
Sulphating reduction mode
|
SCM goes into charge mode when one of the following conditions is met:
|
•
|
Light switch in headlights-on position
|
|
•
|
Battery charge state lower than 78 per cent
|
|
•
|
Vehicle speed is higher than 145 m/h (90 mph)
|
|
•
|
System voltage is lower than 12.3 V.
|
When any of these conditions are met, the system will set the outgoing alternator target voltage to a charge voltage of 13.5-15.5 V, depending on the battery's charge state and calculated battery temperature. Should the charge not be sufficient for idling, the SCM can request an idle increase. This will take place if the battery voltage drops below 12.0 V for longer than 30 seconds. The increase will take place instantly if the voltage drops below 13 V and battery temperature is below -15° C. ECM activates the increase after acceleration or after 130s without acceleration.
SCM goes to fuel economy mode if the battery current is lower than 15 A and higher than -25 A, and the battery charge state is higher than or equal to 85 per cent. None of the conditions for normal charge mode may be met either. Regulator voltage can now be set as low as 12.4 V
When the engine is started, SCM will increase the output target voltage of the alternator by 0.5 V for 60 seconds. Maximum voltage however is 15.0 V.
When SCM has finally calculated the optimum charge voltage, it converts it to a percentage and transmits it on the P bus. The value will then be converted by ECM to a PWM and applied to the alternator L terminal.
|
Commanded pulse length (percent)
|
Alternator output voltage (V)
|
|
10
|
11.00
|
|
20
|
11.56
|
|
30
|
12.12
|
|
40
|
12.68
|
|
50
|
13.25
|
|
60
|
13.81
|
|
70
|
14.37
|
|
80
|
14.94
|
|
90
|
15.50
|
It is then the ECM that forwards the information in the form of a PWM signal to the alternator L terminal.
Engine Control Module (ECM)
When the engine is running, the alternator is started with a PWM signal sent from ECM to the alternator L terminal with information on the requested charge voltage. The alternator voltage regulator regulates the current strength to the rotor and thereby also the output voltage so that it complies with the command from ECM. The rotor current is proportional to the electric pulse width the regulator delivers. When the engine starts, the regulator senses that the alternator is rotating by detecting the alternating current on the stator via an internal wire. When the engine is running, the regulator varies the field voltage by regulating the pulse width. It controls the alternator output voltage so that the correct battery charge and electrical system operation is obtained. The alternator F terminal is internally connected to the voltage regulator and externally to ECM. When the voltage regulator detects a problem in the charging system, it grounds the circuit in order to send a signal to ECM that a problem has arisen. ECM reads the alternator F terminal and sends the PWM value on the bus so that SCM can read it.
Alternator
The alternator is belt driven from the engine. When the rotor is rotating, it induces an alternating current in the stator windings. The AC voltage is then sent through a series of Zener diodes to be rectified. The rectified voltage has been converted to DC voltage, which can be used by the vehicle's electrical system. The voltage regulator integrated in the alternator controls the output voltage of the alternator. The voltage regulator controls the amount of current supplied to the rotor. If the alternator does not receive information on the charge voltage, an output voltage of 13.8 V is set automatically.
Warning indicator for charging
The charge warning indicator advises the driver whether or not the alternator is charging. If the alternator is not charging then a symbol is shown as well as a warning text in the MIU. When no warning message is shown, the alternator is charging. Information on the alternator's charging status is sent via a cable to the engine control module. The MIU receives information via a bus message from the engine control module as to whether or not the alternator is charging. In addition to this, a diagnosis is made of the charging system in BCM and SCM. A warning indicator is shown in the MIU. When the ignition is on and the engine is not running there is no warning message shown in the MIU. A diagnostic trouble code can be found in BCM, SCM or ECM when charging is not working.
Operating the charge indicator
The instrument group turns on the charge indicator and displays a warning message in the trip computer (if one is present) when any of the following occur:
|
•
|
The engine control module (ECM) detects the alternator output voltage is lower than 11 V or higher than 16 V. The instrument group receives a GMLAN message from ECM requesting the lamp be turned on.
|
|
•
|
The instrument group detects that the system voltage is lower than 11 V or higher than 16 V for longer than 30 seconds. The instrument group receives a GMLAN message from the body control module (BCM) specifying there is a problem with the system voltage interval.
|
|
•
|
IPC performs a display test at the beginning of each ignition cycle. The indicator comes on for about three seconds.
|
BATTERY NOT CHARGING SERVICE CHARGING SYSTEM
BCM and ECM send a GMLAN message to the trip computer to display the message BATTERY NOT CHARGING SERVICE CHARGING SYSTEM. It is requested ON when a DTC related to the charging system is a current-related DTC. The message is turned OFF when the conditions for clearing the DTC have been met.
SERVICE BATTERY CHARGING SYSTEM
BCM and ECM send a GMLAN message to the trip computer to display the message SERVICE BATTERY CHARGING SYSTEM. It is requested ON when a DTC related to the charging system is a current-related DTC. The message is turned OFF when the conditions for clearing the DTC have been met.
