1 Management System Structure and Circuit Analysis The Audi A8D3 sedan has 70 electronic control units that communicate with each other through a gateway J533 and five data bus systems. The power management system manages the on-board power supply between the onboard power supply and the onboard power load, and is usually composed of a power supply, a current sensor, a battery temperature sensor, an energy management control unit, an onboard network, an electrical appliance, and a controller thereof. The power management system of Audi A8D3 car has no current sensor and battery temperature sensor. The core components of the Audi A8D3 sedan are the emission control of the energy management control unit, and the fault diagnosis technology of automotive electrical appliances and electronic control systems.
J644, which is connected to the comfort CAN bus system, the basic circuit is shown in Figure 2. The energy management control unit J644 can continuously monitor the battery, it detects the state of charge (SOC) and start-up capability of the battery; the control unit J644 is used when the engine is running. Adjusting the generator output charging voltage, it can also perform unloading and raising the idling speed; In order to reduce the quiescent current consumption when the engine is stopped, the energy management controller will cut off the electrical appliance through the CAN bus under special circumstances to avoid excessive discharge of the battery. The battery disconnect relay is a battery separation element whose task is to cut off the starter and the generator in the event of a collision. The battery disconnection element receives the trigger information from the airbag control unit J234 via the wire.
2 The function and principle of the power management system The energy management control unit J644 has 3 function modules, namely battery management module, quiescent current management module and dynamic management module. These function modules are activated in different vehicle states.
The battery management function module is responsible for monitoring the diagnosis of the battery, it is always in the active state; the role of the quiescent current management function module is to turn off some of the used electrical EQUIPMENT in some cases, it is in the active state when the engine is stationary; dynamic The management function module is responsible for charge voltage regulation and unloading, which is active when the engine is running.
2.1 Battery Management The battery current and the battery operating time are detected in the control unit. The battery voltage is measured by the control unit on the positive side of the battery. The battery temperature is calculated using a mathematical algorithm.
The battery startup capability and the current state of charge are displayed in the instrument cluster. The two most pieces of information are the basic data for quiescent current management and dynamic management. When the engine stops rotating, the battery will discharge if the electrical equipment is in operation.
If the engine's starting capability is affected, then the multimedia interface MMI will display the requirement to start the engine to avoid the system being automatically switched off within 3 min.
The charge indicator is installed in the tachometer of the instrument cluster. Unlike previous Audi vehicles, it is controlled by an energy management control unit.
2.2 Static Current Management The quiescent current management function in the energy management control unit J644 facilitates the use of the appliance when required. It is cut off on line 15 or on line 15 but is activated when the engine is not running.
The static current must be reduced after the car is turned off. This is to make the battery discharge less to ensure that the car can start normally after a long period of parking. When the battery reveals that it has been in a very low state of charge, in order to be able to supply power to all consumer appliances that are out of service, consumers of comfort systems and infotainment systems have to be switched off. Which electrical equipment under the control of a control unit is cut off is determined by the cut-off level. The energy management control unit J644 shuts down six levels of electrical equipment. The lower the state of charge of the battery, the higher the level of shutdown.
The energy management controller adjusts the required cut-off level via the CAN bus and informs the driver via the combination meter. During fault diagnosis, it should be noted that an activated cut-off level may be the cause of limited functionality.
In the fault memory of the energy management control unit, the cut-off level activation information is saved as a fault and can be found in the memory using the diagnostic trouble shooting function of the diagnostic device.
According to the state of charge of the battery in the vehicle, the energy management control unit will perform a cut-off level operation. The cut-off level has the following effects: Cut-off level 1: The consumer on the comfort system CAN bus is switched off.
Cut-off level 2: In addition to switching off the consumer electronics on the comfort system CAN bus, there will also be restrictions on the infotainment system.
When the static discharge current is >50 mA and the stop time exceeds 3 h, the cut-off level 2 is activated immediately.
Cut-off level 3: Operation to reduce quiescent current.
Within the cut-off level 1 to 3, the appliance is turned off by the interior control unit to prevent the battery from being discharged further.
Cut-off level 4: the transport mode, it is implemented through the fault diagnostic apparatus. In the transport mode, the car can greatly reduce the battery discharge during long-term parking and transportation. There is a matching channel in the energy management control unit J644 to activate this function. In channel 1 transport mode, 0 = normal mode or 1 = transport mode can be selected. In the transport mode, all comfort functions are almost turned off to ensure that the batteries will not discharge during the longest stay.
Cut-off level 5: The parking heating system shuts off.
Switch-off level 6: At this switch-off level, the battery power is only sufficient to start the engine. In order to save current, the control unit is no longer awakened for any other reason.
The energy management control unit J644 sends the necessary shut-off level information via the data bus when required, and the control unit switched on the bus system will shut down the electrical appliances that should be shut down under the cut-off level according to the read information. Which devices are switched off at the corresponding switch-off level have been determined in the control unit.
When the engine is started, all active cut-off levels except for cut-off level 4 are cancelled. When the charger is connected to the battery in the car, all cut-off levels are also turned off. The priority of the cut-off level is implemented in the order of 1-2-5-3-6.
2.3 Dynamic Management The role of dynamic management is to allocate energy to each independent system reasonably and provide enough charging current to the battery at the same time.
It plays a role when the engine is running. Its functions are battery voltage regulation, unloading, high-power heating system regulation, idling speed, access to the generator, and dynamic adjustment of the generator.
(1) Battery voltage regulation In the control unit J644, the battery manager obtains the proper generator rated voltage value from the battery temperature and state of charge. This rated voltage value is passed to the dynamic management function module and then transmitted to the power generation through the data cable. The machine is finally regulated by the generator voltage regulator module.
In the guided fault search, a data reading block is used to detect the rated voltage of the generator and the data cable is used to detect the communication.
In the diagnostic tool, the generator rated voltage can be changed for diagnostic purposes.
(2) Unloading During the engine acceleration process, the energy management control unit can reduce the engine load as required by the engine control unit. When the engine control unit asks for the unloading request, in order to reduce the power consumed by the generator, the energy management control first reduces the high-power electrical appliances, and the second step reduces the generator voltage. For this purpose, the energy management control unit sends a request to the automatic air conditioning unit control unit J255 via the comfort system CAN bus to regulate various heating systems such as front window heating, seat heating, rear window heating and PTC heating.
(3) Turning speed increase In order to optimize grid power supply and battery charging, the energy control unit J644 can request the engine control unit to step up the idle speed.
(4) Generator start-up In order to optimize the startability of the internal combustion engine, the energy control unit J644 minimizes the power consumed by the generator during engine start-up.
(5) Dynamic adjustment of the generator When the driver opens the rear window heating system, the generator voltage will not rise immediately, but will increase in delay within a few seconds according to the rotation speed and temperature, so that the engine is evenly loaded.
3 Power supply and power management system maintenance methods The data exchange between the fault diagnostic device and the various control units of the vehicle is implemented through a gateway, so that the diagnostic data of each control unit is sent to the gateway through the respective data bus system, and then the gateway The diagnostic plug is sent to the scan tool.
3.1 Power Management System Fault Diagnosis Use VAS5051 or VAS5052 diagnostic power supply and its management system as follows: First connect the diagnostic instrument, turn on the ignition switch, select the guided function search, and then select the vehicle system or function selection interface, and then select 61- Battery control, enter, J644 menu, according to the need to select the relevant menu.
(1) Battery diagnosis The battery is checked on the Audi A8D3 sedan with the aid of an energy management control unit. It is not necessary to carry out a load inspection on the battery. The use of a guided fault query can activate the function and component selection menu, select the pull-down menu battery, and check the battery level to perform the battery test. The control unit reports the state of charge of the battery, the internal resistance of the battery, and the current flow. At the same time, it calculates whether the battery is normal, whether it needs to be charged or whether it needs to be replaced.
(2) Reading history data The VAS5051/2 diagnostic instrument can be used to read data from J644. These data are helpful for analyzing the power supply status of the vehicle and whether the battery is aged.
(3) Reading the measurement data block In the data block, the measured value can be retrieved through a guided fault query to provide a basis for analyzing the failure of the power management system.
Battery Internal Resistance (4) Query Fault Code Memory When J644-Energy Management is selected and the fault code memory menu is queried, the fault records are reported in the Energy Management Control Unit, such as generator mechanical faults, generator power faults, etc. More detailed information is available in the corresponding fault record data, such as the status of the fault and the date of occurrence.
(5) When replacing the control unit When replacing the control unit, the standard state value set by the new control unit is: the state of charge (SOC) is 80%, and the capacity loss due to aging is 0 Ah, so the code and history of the battery on the original car The data must be overlaid inside the new EEPROM of the control unit. Otherwise, the electrical equipment in the electrostatic flow management system may cause delayed or delayed adjustment of the feedback, and the control unit may generate a large error during operation.
(6) Generator voltage control component test This menu function tests whether the communication between the generator and J644 is normal. The component test can be used to adjust the generator setpoint voltage to two types: generator setpoint voltage 15.OV and generator setpoint voltage 13.5V. The generator setpoint voltage can be measured on the generator or battery.
(7) The energy management control unit measures the no-load current menu The function of the no-load current measured by the energy management control unit is to test the amount of no-load current when the vehicle enters sleep mode. The normal value should be below 50mA.
3.2 Maintenance of Audi A8D3 Car Battery
(1) Battery Charging When using an external charging device to charge the battery, the positive electrode clamp of the charging device's output terminal must be properly clamped on the positive terminal of the battery. The negative electrode clamp of the output terminal should be connected across the external starter connector of the energy management control unit. Do not directly connect to the negative pole of the battery.
In principle, the battery should be recharged in the vehicle, so that the energy management control unit can account for this inflow current when calculating the battery charge value.
In order to avoid damage to the in-vehicle vehicle network when charging with an external charging device, the rapid charging of the in-vehicle battery is prohibited in principle. For example, if the charging voltage is higher than 14.8V, the energy manager cannot record the value of fast charging, and the battery charging cannot be determined. Status and predictive startup performance.
(2) Replacement of battery Since the value stored in the EEPROM of the power manager before replacement of the battery is the charge state of the old battery and the capacity loss due to the aging of the old battery, the energy management control unit must be replaced when the battery is replaced. coding. The new battery must pass the diagnostic test. In the guided fault query system, a battery code menu is provided by the battery manager's self-diagnosis system. The serial number of the battery must be provided when coding. The serial number is marked on the battery.
(3) External start When using an external power supply to start, the ground wire of the start line is connected to the external start connector of the energy management control unit, and the positive wire is connected to the external starter clamp.
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