Ford Explorer: High Voltage Battery, Mounting and Cables / Description and Operation - High Voltage Battery, Mounting and Cables - System Operation and Component Description

System Diagram

System Operation

  Network Message Chart - Battery Energy Control Module (BECM)

Cell Balancing

Individual cells can deviate over the life of the high voltage battery. The purpose of cell balancing is to equalize the individual cell charges. By balancing the cells the high voltage battery maintains top efficiency. The BECM continuously monitors individual battery cell voltages and will perform balancing when required and when certain conditions are met.

Vehicle Shut Down

A vehicle shut down signal is sent by the BECM when the BECM is about to open the contactors due to an internal fault or has just opened the contactors due to an external input (external module commanding contactors to be opened such as a crash event or interlock circuit failure). When vehicle shut down occurs, the Stop Safely warning indicator is illuminated warning that the vehicle will be shut down within a matter of seconds and the operator should pull off the road as soon as possible. Depending on the fault condition that lead to the shutdown, the vehicle may or may not restart if the condition has corrected itself. If the fault condition is severe enough, the fault will have to be repaired and Diagnostic Trouble Codes (DTCs) cleared before the vehicle will restart.

Component Description

High Voltage Battery

The high voltage battery consists of pouch cells packaged into modules which deliver approximately 300 volts DC to the high voltage system. The high voltage battery supplies electrical energy to the electric motor to move the vehicle when it is operating in electric mode only or to assist the gasoline engine (heavy acceleration). When the engine is operating or the vehicle is moving, the electric motor can be used as a generator creating high-voltage AC electricity. High-voltage AC generated by the electric motor is converted to high voltage DC by the SOBDMC and transmitted through the high voltage cables to recharge the high voltage battery.

The high-voltage DC electrical power is converted to low voltage DC electrical power through the Direct Current/Direct Current (DC/DC) converter control module. This low-voltage high current DC electrical power is then supplied to the 12-volt batteries through the low voltage battery cables.

The high-voltage system has a floating ground. The floating ground is designed to completely isolate the high-voltage system from the vehicle chassis. The high-voltage cables are fully insulated (isolated) from all vehicle components and circuits. There are no common connections (such as body grounds) used to conduct the high-voltage power. The BECM monitors this system for any leakage of current to the normal electrical system (similar to a household ground fault interrupter). There are high voltage circuits from the battery cell arrays to the BECM used to monitor isolation resistance between the high voltage battery and chassis.

Battery Energy Control Module (BECM)

The BECM manages the condition of the high voltage battery to control its charging and discharging. The BECM controls the high voltage battery coolant pump in conjunction with BCMC controlling the diverter valve. When additional high voltage battery cooling is needed (high ambient temperatures and/or during high current flow demand) the coolant diverter valve is energized to allow coolant to be diverted through the high voltage battery chiller. The high voltage battery chiller is part of the HVAC system used to chill the coolant prior to being returned to the high voltage battery.

The BECM monitors the individual cell voltages and temperature sensors internal to the battery arrays. The BECM monitors the battery current using a sensor located in the high voltage battery junction box. This information is needed by the BECM to control the high voltage battery and determine its ability to receive and provide power to the vehicle. The BECM communicates with other vehicle modules on the HS-CAN.

The BECM receives the following hard-wired inputs:

• HEV (Hybrid Electric Vehicle) wakeup
• High voltage battery connector interlock status
• High voltage battery contactor control supply voltage (includes the service disconnect)
• High voltage battery cells sense leads
• High voltage battery cell temperature sensors
• High voltage battery coolant inlet temperature sensor
• High voltage battery coolant pump feedback signal
• Motor electronics coolant pump feedback signal
• Current sensor (part of the high voltage battery junction box)
• Event notification status from the RCM
• HS-CAN

The BECM provides the following outputs:

• High voltage battery coolant pump PWM control signal
• Motor eletronics coolant pump PWM control signal
• High voltage battery junction box pre-charge contactor control
• High voltage battery junction box positive contactor control
• High voltage battery junction box negative contactor control
• HS-CAN information

Direct Current/Direct Current (DC/DC) Converter Control Module

The DCDC is an liquid-cooled component that converts high voltage DC power to low-voltage (12-volt) DC power. The converter provides power to the vehicle 12-volt battery and low-voltage electrical systems. The PCM requests the DCDC to enable power conversion through an enable message over HS-CAN. The PCM sends a charging voltage setpoint request over HS-CAN to the DCDC. For information on the DCDC,
Refer to: Direct Current/Direct Current (DC/DC) Converter Control Module - System Operation and Component Description (414-05 Voltage Converter/Inverter, Description and Operation).

Hybrid Electric Motor Assembly

The hybrid electric motor assembly is mounted to the front of the transmission assembly and is also used as an generator. The assembly also incorporates an electric operated engine disconnect clutch that engages or disengages the electric motor from the gasoline engine.

The electric motor generates high voltage electricity for charging the high voltage battery. The engine is started using either conventional engine block mounted starter (for cold starts only) and a Belt Integrated Starter Generator (BISG) for other starts during normal vehicle operation. The electric motor must be energized and rotated to match gasoline engine cranking speed during starting. If the high voltage system is shutdown due to a malfunction the gasoline engine will not start and the vehicle will be disabled.

The electric motor is used to accelerate the vehicle from a stop when driving under electric power. The electric motor is also used to recover energy during regenerative braking. The electric motor receives power from the high voltage battery after the high voltage battery junction box contactors have closed. For information on the electric motor and its operation,
Refer to: Electric Motor (303-01E Electric Motor, Description and Operation).

During braking and deceleration events the regenerative brake system utilizes the electric motor as a generator to create and capture electrical current. This captured energy is used to charge the high voltage battery. If the high voltage battery is adequately charged, the captured energy is used for gas engine braking to slow the vehicle. The regenerative brake system is a series system which the generator braking is used first, up to the limits of the generator torque capacity and the high voltage battery charging capacity. After optimum regeneration is used, the friction brakes are applied to supplement braking demands. For information on regenerative braking,
Refer to: Anti-Lock Brake System (ABS) and Stability Control - System Operation and Component Description (206-09 Anti-Lock Brake System (ABS) and Stability Control, Description and Operation).

High Voltage Battery Junction Box

The high voltage battery junction box acts as an interface between the high-voltage cable assembly and the high voltage battery. The high voltage battery junction box houses the 3 contactors (precharge, positive and negative) which, when commanded closed by the BECM, connect the high voltage battery to various components for high-voltage consumption and/or charging of the high voltage battery. During initial power up the precharge contactor closes prior to the positive contactor which routes high voltage through the precharge resistor which is also located in the high voltage battery junction box. This reduces the in rush current to the capacitors and prevents contactor arcing. The high voltage battery junction box design enables distribution of high-voltage to the high current side SOBDMC and the low current side (Direct Current/Direct Current (DC/DC) converter control module and the ACCM. The high current side for the SOBDMC is protected by a high-voltage high current 150A fuse. The low current side for the Direct Current/Direct Current (DC/DC) converter control module and ACCM are protected by a high-voltage low current 50A fuse. Any fault resulting in excessive current on the low current side will open the fuse and stop power conversion at the Direct Current/Direct Current (DC/DC) and ACCM. The excessive current will not transfer onto the high-current side. The high voltage battery junction box contains the contactors, the current sensor, high voltage interlock circuit, high-voltage high current 150A fuse, and a high-voltage low current 50A fuse.

The high voltage battery junction box contains a current sensor that is hardwired to and monitored by the BECM. The current sensor helps determine the load or rate of charge of the high voltage battery by sensing current flow into or out of the high voltage battery. The high voltage battery junction box also contains voltage sense points downstream of the high voltage contactors that are used to detect issues with the contactors.

High Voltage Cable Assembly

All cables that carry high voltage are integrated into one high-voltage cable assembly that connects the High Voltage Battery, SOBDMC, DCDC, and the ACCM. There are 4 circuits that connect to the High Voltage Battery. Two main circuits supply high voltage to the SOBDMC. Two auxillary circuits supply high voltage to the DCDC. The DCDC acts as a junction and sends high voltage to the ACCM. There is a seperate 3 phase AC high voltage cable assembly that connects the Hybrid Electric Motor Assembly and the SOBDMC.

High Voltage System Service Disconnect Plug

The high voltage system uses a low voltage disconnect plug that opens the 12-Volt contactor control supply circuit and is located in the engine compartment. When the service disconnect plug is disconnected the high voltage battery contactors that supply high voltage to the vehicle are unable to close. The high voltage system must be depowered prior to disconnecting any high voltage cable (identified by orange color).
Refer to: High Voltage System De-energizing (414-03 High Voltage Battery, Mounting and Cables, General Procedures).