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Chapter 3
High-Voltage Vehicle Safety Systems
High-Voltage Safety Systems •
Interlock Systems • Service
Disconnect Services • Isolation Fault
Detection Systems
Chapter 3 — High-Voltage Vehicle Safety Systems
The J1673 standard
provides a visual means
of identifying high-voltage
wires and cables.
Chapter 3 — High-Voltage Vehicle Safety Systems
A serial interlock loop (SIL)
connects each high-voltage
device in series.
Chapter 3 — High-Voltage Vehicle Safety Systems
Each wire that carries
high voltage has a
serial interlock loop
circuit that reports the
status to the batterypack controller.
Chapter 3 — High-Voltage Vehicle Safety Systems
A local interlock loop
(LIP) connects each
high-voltage device on a
LAN bus.
Chapter 3 — High-Voltage Vehicle Safety Systems
A grounded switch
interlock is a modified
LIP system with
switches located within
its components.
Chapter 3 — High-Voltage Vehicle Safety Systems
An active bus-discharge
circuit is typically located
within the power inverter.
Chapter 3 — High-Voltage Vehicle Safety Systems
The op-amp output voltage in
the saturated state is equal to
the supply positive voltage.
The op-amp output voltage in
the low state is approximately
equal to the voltage on the
op-amp ground.
Chapter 3 — High-Voltage Vehicle Safety Systems
A window comparator permits the op-amps to sense
whether a voltage input is within a specific voltage
window.
Chapter 3 — High-Voltage Vehicle Safety Systems
A high-voltage cutoff switch
and an inertia fuel shutoff
switch work with the interlock
circuit and open in the event
of a collision.
Chapter 3 — High-Voltage Vehicle Safety Systems
The service disconnect system permits
a technician to
manually isolate the
battery-pack system
from other vehicle
systems.
Chapter 3 — High-Voltage Vehicle Safety Systems
An isolation-fault detection
system monitors the
vehicle chassis ground to
determine if high voltage is
acquiring an electrical path
to the chassis.
Chapter 3 — High-Voltage Vehicle Safety Systems
DC isolation fault
detection measures
DC leakage to
chassis ground.
Chapter 3 — High-Voltage Vehicle Safety Systems
AC isolation fault
detection injects
an AC signal
onto the bus.
Chapter 3 — High-Voltage Vehicle Safety Systems
The voltage-sensing
stage monitors the
voltage on both the
analog and chassis
grounds.
Chapter 3 — High-Voltage Vehicle Safety Systems
The differential-amplifier
stage amplifies the
difference between its
inverting and noninverting inputs.
Chapter 3 — High-Voltage Vehicle Safety Systems
The voltage-comparator
stage senses voltages
and compares those
voltages to a voltage
reference value.
Chapter 3 — High-Voltage Vehicle Safety Systems
The controller uses
logic to determine
whether a voltage
level is within a
safe range.
Chapter 3 — High-Voltage Vehicle Safety Systems
A simple voltage-regulator circuit can be constructed
with zener diodes, resistors, and capacitors in
parallel and one resistor in series.