Drive Motor Battery System Description

Drive Motor Battery System Description

The hybrid energy storage system uses a number of modules and components to store electricity for use by the eAssist system. The hybrid energy storage system stores 115 V DC in two lithium-ion battery sections. Current flows from the battery sections through a series of contactors and a service disconnect. This allows the system to control the disconnect of high voltage from the vehicle and also creates a redundant disconnect to ensure voltage is disabled when servicing high voltage components. To ensure optimum life of the lithium-ion batteries, the hybrid energy storage system monitors the state of charge of each battery cell. The system will equalize the state of charge of each cell through a balancing process. The hybrid energy storage system is also responsible for monitoring and controlling the charging and the discharging of the high voltage battery.

The primary component of the hybrid energy storage system is the hybrid/EV battery pack. The hybrid/EV battery pack is a modular battery pack assembly that not only contains the lithium-ion battery sections, but also many of the control modules and components used by the eAssist system.

The Hybrid/EV Battery Pack contains the following serviceable components:

* Hybrid/EV Battery Section 1

* Hybrid/EV Battery Section 2

* Battery Energy Control Module

* Starter/Generator Control Module

* Main Contactor - located in the generator battery disconnect relay assembly

* Pre-Charge Contactor - located in the generator battery disconnect relay assembly

* Hybrid/EV Battery Pre-Charge Resistor - located in the generator battery disconnect relay assembly

* Hybrid/EV Battery Pack Current Sensor - located in the generator battery disconnect relay assembly

* Hybrid/EV Battery Pack High Voltage Manual Disconnect Lever - located in the battery energy control module wiring junction block assembly

* Generator Battery Fuse - located in the battery energy control module wiring junction block assembly

* High Voltage Interlock Switch

Hybrid/EV Battery Pack

The hybrid/EV battery pack is located in the rear compartment of the vehicle, directly behind the rear passenger seat, and serves as a modular assembly to contain many of the eAssist control modules and system components. The hybrid/EV battery pack may also be referred to as the following names:

* Energy Storage System

* Power Pack

* Generator Control and Battery Module Assembly

The hybrid/EV battery pack first consists of a metal tray that is fixed to the vehicle floor. This provides a strong mount for other components to secure to. Within the hybrid/EV battery pack, the hybrid/EV battery section 1 and hybrid/EV battery section 2 are located nearest to the left side of the vehicle. Directly above the battery sections is the battery energy control module. To the right of the battery sections and nearest to the right side of the vehicle is the starter/generator control module. Above the starter/generator control module is the generator battery disconnect relay assembly and battery energy control module wiring junction block assembly. A case cover is secured over the top of all components, effectively creating the hybrid/EV battery pack and preventing access to any high voltage components without first disabling the high voltage system.

The hybrid/EV battery pack is also integral to the hybrid/EV cooling system. Foam gaskets are adhered to the metal battery pack tray. This seals the underside of the starter/generator control module to ensure proper airflow under the control module for cooling purposes. The hybrid/EV battery pack case cover also provides a mounting surface for the hybrid/EV battery pack cooling fan and has openings where the plastic vents are allowed to pass into the hybrid/EV battery pack to direct air through components which require cooling.

Hybrid/EV Battery Section 1 and Hybrid/EV Battery Section 2

The hybrid/EV battery section 1 and hybrid/EV battery section 2 are a pair of lithium-ion batteries connected in series to make up the 115 V DC battery. The two sections are diagnosed and serviced as a single battery assembly. The individual battery sections are not serviced separately.

The hybrid battery contains a total of 32 cell groups, with each section containing 16 cells that are connected in series using internal bus bars. The two battery sections are externally connected in series using high voltage cable. Each individual cell group is rated at 3.7 V, for a nominal system voltage of 118 V DC.

The hybrid battery sections are air cooled. Each battery case has an air inlet and an air outlet. Air is drawn through the battery case to cool the individual cells. Attached to each case is a vent tube. In the event of a damaged or ruptured battery, any outgassing will be vented to the outside of the vehicle.

A voltage sense circuit is attached to each individual cell. Each of these circuits terminate at a connector located on the top surface of the battery section. A serviceable auxiliary battery wiring harness connects the voltage sense circuits to the battery energy control module, located directly above the battery sections. The sensor itself is a part of the battery cell and is not serviceable.

Battery Energy Control Module

The battery energy control module is located directly above the hybrid/EV battery section 1 and hybrid/EV battery section 2. The module is responsible for monitoring the hybrid/EV battery section 1 and hybrid/EV battery section 2 parameters and reporting this to the starter/generator control module. The battery energy control module may also be known as the BECM, voltage current temperature module, or voltage temperature interface module (VTIM).

The battery energy control module monitors the voltage of each battery cell section. A voltage sense circuit is attached to each individual cell group. Each of these circuits terminate at a connector located on the top surface of the battery section. A serviceable auxiliary battery wiring harness connects the voltage sense circuits to the battery energy control module, located directly above the battery sections. The sensor itself is a part of the battery cell and is not serviceable.

The battery energy control module also measures critical temperatures within the two battery sections and at the hybrid/EV battery section 1 air inlet. Six temperature sensors are used to monitor the battery temperature. The battery temperature sensors are located in the battery sections. Two of the temperature sensors are located on the top of the battery section and the remaining four are located on the bottom of the section. The temperature sensor is a variable resistor that measures the temperature of the battery cell group. The battery energy control module supplies 5 V to the signal circuit and a ground for the low reference circuit. The battery temperature sensor resistance changes with battery temperature. As the temperature decreases, the sensor resistance increases. As the temperature increases, the sensor resistance decreases. The air inlet temperature sensor operates in much the same way, except that it measures the temperature of the incoming air used to cool the hybrid/EV battery pack at the hybrid/EV battery section 1 air inlet. None of the temperature sensors or the temperature sensor harness is serviceable. They are all serviced as part of the battery sections.

The battery energy control module is responsible for the cell balancing process. During operation, individual cells may charge or discharge at different rates. To ensure proper battery health and optimal life, these voltages are balanced, with energy from a higher voltage cell being transferred to a lower voltage cell. This keeps the voltage consistent between all 32 cell groups. Cell balancing is an internal process of the battery energy control module. Internal gates allow energy to flow between cells using the same circuits that are used to monitor cell voltage.

Starter/Generator Control Module

The starter/generator control module is a multifunction module that is involved in many eAssist system operations. The starter/generator control module contains two internal microprocessors: a battery control processor and a motor control processor. The battery control processor is responsible for the following:

* Communicating with the battery energy control module to determine the status of the high voltage battery

* Controlling the battery and starter/generator cooling systems

* Controlling the main and pre-charge contactors

* Monitoring the high voltage interlock loops

* Monitoring for isolation faults

* Supplying 12 V to the vehicle

Internal to the starter/generator control module, the motor control processor is responsible for propulsion activities and the 14 V control module is responsible for maintaining 12 V to the vehicle. The starter/generator control module may also be referred to as the following names:

* SGCM

* Hybrid Powertrain Control Module (HPCM)

* Accessory Power Module (APM)

* Battery Power Inverter Module (BPIM)

* Power Inverter Module (PIM)

Hybrid/EV Battery Control

The starter/generator control module interfaces with the battery energy control module to determine the status of the battery voltage and battery temperature. The starter/generator control module uses voltage information from the battery energy control module to make decisions about the battery state of health, how the battery should be charged or discharged, and when to initiate cell balancing.

Hybrid/EV Battery and Starter/Generator Cooling

The starter/generator control module uses temperature information from the battery energy control module to control the hybrid/EV battery pack cooling fan. The starter/generator control module also monitors the starter/generator coolant temperature sensor and will control the starter/generator coolant pump relay, which controls the starter/generator coolant pump.

High Voltage Contactors

At times, it may be necessary to disconnect high voltage from the vehicle, both during normal operation and when a system fault is identified. The starter/generator control module controls the main contactor and pre-charge contactor to disconnect and connect high voltage from the vehicle.

High Voltage Interlock

The high voltage interlock is a fail-safe to disable high voltage when the starter/generator control module identifies that a high voltage area has been accessed. The hybrid/EV battery pack has a high voltage interlock switch located on the service access cover. The starter/generator also has a high voltage interlock switch on the access cover. When either cover is removed, the interlock loop is opened. The starter/generator control module will open the contactors to prevent technician contact with high voltage.

High Voltage Isolation

The starter/generator control module monitors the electrical potential between high voltage and the vehicle chassis. High voltage should always be isolated from the vehicle chassis by a certain amount of resistance to avoid the potential for a life threatening current path. In the event that a high voltage leak path is detected to the vehicle chassis, the starter/generator control module will set a DTC and open the contactors to remove high voltage.

Testing for loss of isolation requires special tools and procedures. Because of the high voltages present in the hybrid system, a loss of isolation may occur due to insulation breakdown. Insulation breakdown typically occurs only when high voltage is present. Conditions such as insulation breakdown cannot be diagnosed with a typical DMM because high voltage is not used by the DMM when measuring resistance.

12 V Output

The starter/generator control module essentially takes the place of the generator on a traditional vehicle. The starter/generator control module converts high voltage DC to a 12 V DC for accessory electrical operation and to charge the 12 V battery.

Main Contactor, Pre-Charge Contactor, and Pre-Charge Resistor

The high voltage contactors are switches that are controlled like a relay. To disable high voltage from the vehicle, the main and pre-charge contactors are commanded open. This will open the contactors and physically disconnect the hybrid/EV battery positive cable. To connect high voltage to the vehicle, first the pre-charge contactor is closed. With the pre-charge contactor closed, current flows through the pre-charge resistor. This allows high voltage to slowly build in the system. Once high voltage is brought up though the pre-charge contactor, the main contactor is close and high voltage is active. If the high voltage builds too quickly or too slowly, the starter/generator control module will set a fault.

Both the main contactor and the pre-charge contactor are controlled in a similar manner. B+ is applied at all times to each contactor. Each contactor is controlled by an independent low side driver in the starter/generator control module. When the starter/generator control module commands the contactor closed, ground is applied to the contactor through the low side driver and the contactor is closed.

Both contactors and the pre-charge resistor are located in the generator battery disconnect relay assembly. The generator battery disconnect relay assembly is a plastic tray that is secured to the top of the starter/generator control module. The generator battery disconnect relay assembly also contains the hybrid/EV battery pack current sensor and a series of bus bars and cables that electrically connect the hybrid/EV battery to the starter/generator control module.

Hybrid/EV Battery Pack Current Sensor

The hybrid/EV battery pack current sensor is a three-wire hall effect sensor that measures current flow from the hybrid/EV battery. The battery energy control module applies 5 volt and provides a low reference to power the sensor. Current measurement is communicated to the battery energy control module via a signal circuit.

The hybrid/EV battery pack current sensor is located in the generator battery disconnect relay assembly. The generator battery disconnect relay assembly is a plastic tray that is secured to the top of the starter/generator control module. The generator battery disconnect relay assembly also contains the high voltage contactors, pre-charge resistor, and a series of bus bars and cables that electrically connect the hybrid/EV battery to the starter/generator control module. The hybrid/EV battery pack current sensor monitors current on the hybrid/EV battery negative bus bar.

Hybrid/EV Battery Pack High Voltage Manual Disconnect Lever and Generator Battery Fuse

The hybrid/EV battery pack high voltage manual disconnect lever provides a redundant method to disconnect high voltage from vehicle when performing service on the system. With the switch open, high voltage is physically disconnected from the hybrid/EV battery positive cable. Together with the high voltage interlock and the high voltage contactors, the manual disconnect provides a means of disconnecting high voltage at two points in the system. This provides a double-layer of protection.

The generator battery fuse is a 125 A fuse to prevent an overcurrent condition in the 115 V DC system.

The hybrid/EV battery pack high voltage manual disconnect lever and generator battery fuse are located in the battery energy control module wiring junction block assembly. The battery energy control module wiring junction block assembly is a plastic tray that is secured to the top of the starter/generator control module.

High Voltage Interlock Switch

The high voltage system uses two high voltage interlock switches to indicate that an area of the vehicle that contains a high voltage connection has been exposed. These locations are at the starter/generator and the hybrid/EV battery pack. The two interlock switches are completely separate and are not tied together.

The starter/generator control module applies a constant 5 V reference to the high voltage interlock switch and monitors the voltage. Each high voltage interlock switch contains a resistor. With the high voltage interlock connected, the 5 V reference voltage travels through the resistor and is reduced by a specific amount. This indicates that the high voltage interlock switch is closed and no circuit faults have occurred. If the high voltage interlock switch is removed or a circuit fault occurs, the voltage will change and the starter/generator control module will open the contactors.

The hybrid/EV battery pack high voltage interlock switch is part of the hybrid/EV battery pack cable cover. When the cover is removed, the high voltage interlock switch is also removed. To remove the cover, the hybrid/EV battery pack high voltage manual disconnect lever must also be opened, providing a second means of disconnecting high voltage.

The starter/generator high voltage interlock switch is part of the starter/generator cable cover. When the cover is removed, the high voltage interlock switch is also removed.