Description And Operation
DESCRIPTION
The battery system consists of the following components:
| 1. | Refer to VOLTAGE STABILITY MODULE (VSM) . |
| 2. | Refer to BODY CONTROL MODULE (BCM) . |
| 3. | Refer to BATTERY . |
| 4. | Refer to INTELLIGENT BATTERY SENSOR (IBS) . |
| 5. | Refer to BATTERY TRAY . |
| 6. | Refer to BATTERY CABLES . |
OPERATION
The battery system is designed to provide a safe, efficient, reliable and mobile means of delivering and storing electrical energy. This electrical energy is required to operate the engine starting system, as well as to operate many of the other vehicle accessory systems for limited durations while the engine and/or the charging system are not operating. The battery system is also designed to provide a reserve of electrical energy to supplement the charging system for short durations while the engine is running and the electrical current demands of the vehicle exceed the output of the charging system. In addition to delivering, and storing electrical energy for the vehicle, the battery system serves as a capacitor and voltage stabilizer for the vehicle electrical system. It absorbs most abnormal or transient voltages caused by the switching of any of the electrical components or circuits in the vehicle.
| Refer to COMPONENT INDEX . |
The battery is designed to store electrical energy in a chemical form. When an electrical load is applied to the terminals of the battery, an electrochemical reaction occurs. This reaction causes the battery to discharge electrical current from its terminals. As the battery discharges, a gradual chemical change takes place within each cell. The sulfuric acid in the electrolyte combines with the plate materials, causing both plates to slowly change to lead sulfate. At the same time, oxygen from the positive plate material combines with hydrogen from the sulfuric acid, causing the electrolyte to become mainly water. The chemical changes within the battery are caused by the movement of excess or free electrons between the positive and negative plate groups. This movement of electrons produces a flow of electrical current through the load device attached to the battery terminals.
As the plate materials become more similar chemically, and the electrolyte becomes less acid, the voltage potential of each cell is reduced. However, by charging the battery with a voltage higher than that of the battery itself, the battery discharging process is reversed. Charging the battery gradually changes the sulfated lead plates back into sponge lead and lead dioxide, and the water back into sulfuric acid. This action restores the difference in the electron charges deposited on the plates, and the voltage potential of the battery cells. For a battery to remain useful, it must be able to produce high-amperage current over an extended period. A battery must also be able to accept a charge, so that its voltage potential may be restored.
The battery is vented to release excess hydrogen gas that is created when the battery is being charged or discharged. However, even with these vents, hydrogen gas can collect in or around the battery. If hydrogen gas is exposed to flame or sparks, it may ignite. If the electrolyte level is low, the battery may arc internally and explode. If the battery is equipped with removable cell caps, add distilled water whenever the electrolyte level is below the top of the plates. If the battery cell caps cannot be removed, the battery must be replaced if the electrolyte level becomes low.
Supplemental Battery - A supplemental battery is used in vehicles equipped with Engine Stop Start (ESS) in place of the VSM (certain ESS models only).
| Refer to COMPONENT INDEX . |
The battery cables connect the battery terminal posts to the vehicle electrical system. These cables also provide a path back to the battery for electrical current generated by the charging system for restoring the voltage potential of the battery. The female battery terminal clamps on the ends of the battery cable wires provide a strong and reliable connection of the battery cable to the battery terminal posts. The terminal pinch bolts allow the female terminal clamps to be tightened around the male terminal posts on the top of the battery. The eyelet terminals secured to the opposite ends of the battery cable wires from the female battery terminal clamps provide secure and reliable connection of the battery cables to the vehicle electrical system
| Refer to COMPONENT INDEX . |
The molded plastic battery tray is located in the left front corner of the engine compartment. On this vehicle, the battery tray also provides an anchor point for the Powertrain Control Module (PCM).
One wire has an eyelet terminal that connects the battery positive cable to the B(+) terminal stud of the BCM, and the other wire has an eyelet terminal that connects the battery positive cable to the B(+) terminal stud of the engine starter motor solenoid. The battery negative cable terminal clamp has one wire as an eyelet terminal that connects the battery negative cable to the vehicle powertrain through a ground connection, typically on the engine cylinder block.
| Refer to COMPONENT INDEX . |
The BCM communicates with the IBS to provide load shedding.
Load shedding is activated under the following conditions:
- The engine must be running with an engine speed equal to or higher than 400 rpm for greater than 50 seconds.
- The battery state of charge supplied by the IBS over the Local Interface Network (LIN) to the BCM must be less than or equal to 70%.
- The battery voltage measured by the IBS and supplied to the BCM over the LIN bus must be less than or equal to 12.2 volts.
Any transition of the ignition state will rest all of the load shed output signals and therefor cancel load shedding operation.
To avoid electrical power system instability and to minimize driver's anxiety and concern, load shed operation is conducted in an orderly and progressive manner. It is categorized as seven levels and critical state, according to a net charge loss of the battery, which is summarized in the table below.
| Levels | Battery Charge Reduction [Ah] | Devices to be affected |
|---|---|---|
| Level 1 | 5 | Heated seat/Vented seat/Heated Wheel |
| Level 2 | 7.5 | Heated seat/Vented seat/Heated Wheel |
| Level 3 | 10 | Heated/cooled cupholders |
| Level 4 | 12.5 | Rear defroster and heated mirrors |
| Level 5 | 15 | HVAC system |
| Level 6 | 17.5 | Power inverter system |
| Level 7 | 20 | Audio and telematics system |
| Critical State | (SOC<=35%, and Battery voltage <=11.8V) | |
| Or (SOC <= 70%, and Battery voltage <= 10.9V) |
If the battery state of charge is equal to or less than 35%, and the battery voltage is equal to or less than 11.8 V, a "Battery Reached Critical State" output signal is broadcast. Another condition to set this output signal is that the battery voltage is less than or equal to 10.9 volts and the state of charge is less than or equal to 70%.
When the battery reaches critical state, only electrical loads essential to vehicle operation are allowed to be turned on. The following actions are recommended to be taken:
- "Heated seats and heated steering wheel" are disabled for the duration of the ignition cycle
- "Heated/cooled cupholders" are disabled for the duration of the ignition cycle
- "Rear defroster and heated mirrors" time out in 30 seconds each time the customer turns them on, for the duration of the ignition cycle
- "HVAC" systems is allowed only minimal loads for visibility requirements, for the duration of the ignition cycle
- "Power inverter" is disabled for the duration of the ignition cycle
- "Audio & Telematics Systems" will only allow minimal loads for communications and emergency requirements, for the duration of the ignition cycle.
| Refer to COMPONENT INDEX . |
The IBS contains a low value resistor, or shunt. The shunt creates voltage drop, which is read by an internal microcontroller to determine the current flow in and out of the battery. In addition to the shunt, the IBS contains a sensor to monitor the battery's temperature. Data gathered by the IBS, including temperature, voltage, and current measurements, are transmitted over a communication bus to either the BCM. The IBS serves two primary purposes. The first is to provide the PCM with both immediate and historical battery information, so the PCM can precisely control the charging system. The second purpose is to provide data to the BCM for operation of the load-shedding feature. A fused power circuit and the bus are connected to the IBS though a two-terminal connector.
In addition to real-time measurements, the IBS transmits some calculated battery data over the bus, including state of charge, state of health, and state of function. These values are calculated by storing measurements over time.
The battery sensor is readable/diagnosable via a scan tool that can display all of the available parameters needed for vehicle servicing or trouble shooting.
Information the IBS transmits out on the Controller Area Network (CAN) bus is:
- SOC = Battery state of charge (or SOC) is expressed as a percentage. The IBS calculates the SOC based on measured voltage, and charge and discharge rates. Therefore, SOC is not a direct percentage of battery voltage.
- SOF = Battery State of Function: Battery state of function (or SOF) is a calculated prediction of the lowest voltage the battery will drop to during engine cranking.
The PCM and BCM use this calculated information to optimize vehicle power management for increased fuel efficiency. The data transmitted from IBS is interpreted and sent over the CAN network by the module connected to the IBS's bus.
When the IBS is powered up for the first time or is powered after a power disconnection, it enters a "recalibration" phase, where the IBS must recognize the type of battery and its characteristics and state. In this phase the tolerances on the state functions (SOC, SOF) are greater than in normal working condition. When IBS is disconnected from the battery, the device loses its stored memory. When power is restored, the IBS starts a relearn process. Until the relearn process is complete, accurate battery state information is unavailable to other vehicle systems. The IBS relearn process requires one start and at least 4 hours of quiescent time (vehicle off, electrical system asleep). Remember, the relearn process is restarted every time power is reconnected to the IBS. This has a major effect on the stop/start feature.
If the IBS is faulty it cannot be serviced, it must be replaced.
| Refer to COMPONENT INDEX . |
The VSM keeps power accessories functional between the stop/start events. The VSM monitors the battery voltage and maintains a constant voltage level in the electrical system while the vehicle is in autostop mode.
The VSM operation is most prevalent during autostop, the main function maintains operating voltage to the radio, instrument cluster and instrument panel displays. Battery voltage tends to drop slightly during an autostop event, if headlamp flickers or dash light dimming takes place during an autostop, diagnose the VSM to ensure proper operation of the driver informational displays. All motors (e.g. windows, blowers, etc) running during stop will slow down but all should continue to operate normally after restart.
The BCM will gateway messages from CAN-IHS to CAN-C and from CAN-C to CAN-IHS. If a malfunction occurs in the VSM, DTCs will set in the BCM and / or PCM. A scan tool is necessary to retrieve the DTCs. The VSM cannot be repaired and is serviced as an assembly.