Jeep 1997 Grand Cherokee Service Manual page 320

8B - 2 STARTING SYSTEMS
DESCRIPTION AND OPERATION
STARTING SYSTEM
The starting system components form two separate
circuits. A high-amperage feed circuit that feeds the
starter between 150 and 350 amperes, and a low-am-
perage control circuit that operates on less than 20
amperes.
If the vehicle is equipped with an automatic trans-
mission, battery voltage is supplied through the low-
amperage control circuit to the coil battery terminal
of the starter relay when the ignition switch is
turned to the Start position. The park/neutral posi-
tion switch is installed in series between the starter
relay coil ground terminal and ground. This normally
open switch prevents the starter relay from being
energized unless the automatic transmission gear
selector is in the Neutral or Park positions.
If the vehicle is equipped with a manual transmis-
sion, it has a clutch pedal position switch installed in
series between the ignition switch and the coil bat-
tery terminal of the starter relay. This normally open
switch prevents the starter relay from being ener-
gized unless the clutch pedal is depressed, preventing
starter operation while the clutch disc and the fly-
wheel are engaged. The starter relay coil ground ter-
minal is always grounded on vehicles with a manual
transmission.
When the starter relay coil is energized, the nor-
mally open relay contacts close. The relay contacts
connect the relay common feed terminal to the relay
normally open terminal. The closed relay contacts
energize the starter solenoid coil windings.
The energized solenoid pull-in coil pulls in the sole-
noid plunger. The solenoid plunger pulls the shift
lever in the starter. This engages the starter overrun-
ning clutch and pinion gear with the starter ring
gear on the automatic transmission torque converter
(5.2L/5.9L engine),
torque converter drive plate (4.0L engine), or the
manual transmission flywheel.
As the solenoid plunger reaches the end of its
travel, the solenoid contact disc completes the high-
amperage starter feed circuit and energizes the sole-
noid plunger hold-in coil. Current now flows between
the solenoid battery terminal and the starter motor,
energizing the starter.
Once the engine starts, the overrunning clutch pro-
tects the starter from damage by allowing the starter
pinion gear to spin faster than the pinion shaft.
When the driver releases the ignition switch to the
On position, the starter relay coil is de-energized.
This causes the relay contacts to open. When the
relay contacts open, the starter solenoid plunger
hold-in coil is de-energized.
the automatic transmission
When the solenoid plunger hold-in coil is de-ener-
gized, the solenoid plunger return spring returns the
plunger to its relaxed position. This causes the con-
tact disc to open the starter feed circuit, and the shift
lever to disengage the overrunning clutch and pinion
gear from the starter ring gear.
STARTER
The starter motor incorporates several features to
create a reliable, efficient, compact, and lightweight
unit. A planetary gear system (intermediate trans-
mission) is used between the electric motor and the
pinion gear. This feature makes it possible to reduce
the dimensions of the starter. At the same time, it
allows higher armature rotational speed and delivers
increased torque through the pinion gear to the
starter ring gear on the automatic transmission
torque converter or torque converter drive plate, or
on the manual transmission flywheel.
The use of a permanent magnet field also reduces
the size and weight of the starter. The permanent
magnet field consists of four high-strength perma-
nent magnets. The magnets are aligned according to
their polarity, and are permanently mounted in the
starter field frame.
The starter motors for all engines are activated by
a solenoid mounted to the overrunning clutch hous-
ing. However, the starter motor and solenoid are ser-
viced only as a complete assembly. If either
component is faulty or damaged, the entire starter
assembly must be replaced.
CAUTION:
•
Permanent magnet starters are highly sensi-
tive to hammering, shocks, and external pressure.
The permanent magnets may be damaged and the
starter rendered unserviceable, if subjected to any
of these conditions.
•
The starter motor must not be clamped in a
vise by the starter field frame. Doing so may dam-
age the permanent magnets. The starter should
only be clamped by the mounting flange.
•
Do not connect the starter motor incorrectly
when testing. Reverse polarity may damage the per-
manent magnets and render the starter unservice-
able.
STARTER RELAY
The starter relay is a International Standards
Organization (ISO) micro-relay. The terminal desig-
nations and functions are the same as a conventional
ISO relay. However, the micro-relay terminal orienta-
tion (or footprint) is different, the current capacity is
lower, and the relay case dimensions are smaller
than those of the conventional ISO relay.
ZG