Windshield Wiper Operation - E/J Coaches
Windshield
wipers on the E4500 and J4500 coaches are controlled by a single electric
motor. The electrical circuit for this motor can be broken up into 4 separate
phases; intermittent, low speed, high speed, and park. The key to the
correct operation of the wipers is a set of contacts inside the motor
itself.
- When the
wipers are running, 24V power is supplied to the WM2 circuit through
these contacts.
- When the
wipers reach the center windshield post (PARK position), 24V power is
removed from the WM2 circuit and it is connected to system Ground.
In Figure
1, two motors are disassembled. The motor on the right shows three
intact contacts whereas the motor on the left shows contacts that have
been damaged. On close inspection, note that the outermost, or "Ground",
contact on the left motor is completely missing.
Referring
to the motor on the right;
- The center contact is connected to circuit WM2. This contact is connected
continuously to the metal ring on the large gear of the wiper mechanism.
- The inside contact is connected to 24V power. This contact is connected
to the metal ring for the majority of the wiper cycle. When the wiper
motor reaches the "Park" position, this contact is disconnected from
the ring because of the notch in the ring itself.
- The 24V power is used to power the wiper motor after the switch
is shut off, allowing the wipers to reach the "Park" position.
- The outside contact is connected to system Ground. This contact only
connects to the metal ring when the wiper motor reaches the "Park" position.
This ground has two functions:
- To ground the low speed winding in the wiper motor, preventing the
motor from "coasting" through the Park position.
- To provide a signal to the intermittent module, stopping the wipers
and starting the delay timer for intermittent wiper operation. If
this ground isn't received by the intermittent module, the wipers
will continue to operate at low speed.
Figure
1
When the
wiper motor is running, only two of the three contacts are connected to
the metal ring at any time.
Ground for
the intermittent relay, the R1, JRE3, & JRE4 relays is provided through
the grounding module located in the front junction box.
24V power
is provided as follows:
- Module 5 on all coaches prior to unit # 62032
- PDM 1 located in the drag link compartment, outputs 7-12 on all coaches
effective with unit # 62032
See
Figure 2
Figure
2
(click image for enlarged printable view*)
Intermittent
Phase - Powered. See Figure
3.
- When the wiper switch is moved to the intermittent position, 24V power
is routed to the JRE 4 relay and the intermittent relay.
- The JRE 4 relay is energized, connecting the WM2 circuit to the intermittent
relay.
- The intermittent relay is energized, connecting 24V power to the R1
relay.
- The R1 relay closes connecting the WM5 circuit to 24V power coming
from the R1 circuit. The WM5 circuit is connected to the wiper motor
low speed.
- The wipers operate at low speed for one cycle.
Figure
3
(click image for enlarged printable view*)
Intermittent
Phase - Timer Activated. See Figure
4.
- After the wipers complete one cycle and reach the center windshield
post, the WM2 circuit switches from 24V power to ground.
- This signals the intermittent relay to de-energize the R1 relay and
begin the timer function for a 5 second delay before the wipers operate
again.
- When the R1 relay is de-energized, power is removed from the WM5,
low speed, circuit and the wipers stop.
- After the 5 second delay, the intermittent module re-energizes the
R1 relay, the wipers restart and the cycle repeats.
REMINDER:
If the ground signal is not present on the WM2 circuit, the wipers will
not pause; they will continue to operate at low speed. There may be a
slight hesitation at the park position, then the wipers resume operation.
Figure
4
(click image for enlarged printable view*)
When the
wiper switch is moved to the low speed position, 24V power is routed to
the R1 relay, energizing the WM5 (low speed) circuit.
Figure
5
(click image for enlarged printable view*)
High Speed
phase. See Figure
6.
When the wiper switch is moved to the High speed position, 24V power is routed to both the R1 relay and the JRE3 relay.
- When the JRE3 relay is energized, 24V power is removed from the R1 circuit and routed to the WM6 (high speed) circuit.
- When the R1 relay is energized, the WM5 (low speed) circuit is disconnected from the WM2 circuit. This is done to prevent 24V power from being connected to the low speed circuit at the same time as the high speed circuit is energized.
WARNING:
THE LOW SPEED AND HIGH SPEED CIRCUITS SHOULD NEVER BE ENERGIZED AT THE
SAME TIME. THIS CAUSES THE WIPER MOTOR TO RUN SLOW AND EXTREMELY HOT!
Figure
6
(click image for enlarged printable view*)
Park Phase
- Powered. See Figure
7.
With the wiper switch in the OFF position, the R1 relay is de-energized connecting the WM5 (low speed) wire to the WM2 circuit. As long as the wipers are positioned anywhere except at the center windshield post, the WM2 wire is connected to 24V.
- This power is connected to the WM5 wire, keeping the wiper motor energized.
Figure
7
(click image for enlarged printable view*)
Park Phase -
Powered. See Figure
8.
When the
wipers reach the center windshield post, the 24V power supply is removed
from the WM2 circuit. The WM2 now is connected to ground and this acts
like a brake to prevent the motor from "coasting" through the Park position.
Figure
8
(click image for enlarged printable view*)
If you have
any questions, please call the MCI Customer Support Center at (800) 241-2947.
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