MCI SERVICE INFORMATION

 

Kneeling - J4500 Multiplexed (MUX)

This service tip discusses the function of the kneeling feature on J4500 coaches effective with unit 62032. The operation of the system will be broken into 4 separate phases:

  1. Addition and removal of air during normal ride
  2. Kneeling
  3. Recovery
  4. Recovery when the park brake is released

Both the electrical function and air flow will be discussed in each phase. Before going any further, it is necessary to explain the drawings used in this service tip.

Figure 1
(click image for enlarged printable view*)

Across the top of the drawings are the inputs and outputs of the MCI multiplex modules. The reference name for the input begins with "I" and the outputs begin with"O". The number after the dash represents the input or output LED on the face of the module. See Figure 2

.
Figure 2

In the lower left of Figure 1 are symbols representing the leveling valves in the front axle area. See Figure 3.


Figure 3

The lower RH symbol on the drawing represents the kneeling module located in the spare tire compartment. See Figure 4.


Figure 4

Normal Ride When the coach is in normal ride mode, air flow into and out of the front air bellows is controlled by the RH leveling valve attached to the front axle. Figure 5 shows air being added to the bellows to increase the ride height. Air flows from the leveling valve through the V3 air piloted valve, through a pair of one way check valves, and on to the front air bellows.


Figure 5
(click image for enlarged printable view*)

In Figure 6, air is routed from the front axle air bellows through a pair of orifices, through the V3 air pilot valve, and out the exhaust port on the RH leveling valve. These orifices restrict air flow, causing the suspension to lower slowly to normal ride height.


Figure 6
(click image for enlarged printable view*)

Kneel Phase: When the coach is at normal ride height, the pressure switch on the LH front leveling valve supplies a ground signal to input #6 on the #1 MUX module. See Figure 6.The kneel switch, when pressed, supplies a ground signal to input #25 on the #1 MUX module in the Front Junction Box. With these inputs active, the MUX modules are programmed to activate outputs 14 and 17 on the #1 MUX module. Output 17 activates the exterior alarm and warning light, output 14 energizes the SV2 solenoid. When energized, SV2 supplies air to the V2 and V3 air piloted valves. The V3 valves disconnects the RH leveling valve from the front air bellows and the V2 valve exhausts the air pressure out of the front air bellows, lowering the front suspension. Kneeling occurs only while the kneel switch is pressed. Releasing the switch will stop the kneel function. See Figure 7.


Figure 7
(click image for enlarged printable view*)

When the air pressure in the front bellows drops below 15 psi, the pressure switch on the kneel module closes sending a ground signal to input 7 on the #1 MUX module. Module outputs 14 and 17 are de-activated. This disables the external alarm and light, and stops the exhausting of air from the front suspension. See Figure 8.


Figure 8
(click image for enlarged printable view*)

Recover Phase

When pressed, the Recover switch supplies a ground signal to input #26 on the #1 MUX module. This activates outputs 15 and 17 on the #1 MUX module. Output 17 activates the external alarm and light. Output 15 activates solenoid SV1 in the kneel module. SV1 supplies air pressure to the V1 air pilot valve. The V1 valve connects supply air pressure to the front air bellows for quick recovery of the suspension. See Figure 9.


Figure 9
(click image for enlarged printable view*)

When the coach ride height reaches approximately 10 - 10½ inches, the pressure switch on the LH leveling valve closes sending a ground signal to input #6 on the #1 MUX module. This de-activates outputs 15 and 17 on the #1 MUX module, stopping the quick recovery and the exterior light/alarm. See Figure 10.


Figure 10
(click image for enlarged printable view*)

When the park brakes are released, air pressure supplied by the park brake valve shifts the V3 air pilot valve. This reconnects the RH leveling valve to the front axle bellows and the suspension will raise the remaining 1 - 1½ inches. See Figure 11.


Figure 11
(click image for enlarged printable view*)

Recovery when the park brake is released

If the park brakes are released while the coach is in the kneel position, the MUX modules are programmed to operate the quick recovery feature of the suspension, just as if the recover switch were pressed. Outputs 15 and 17 on the #1 MUX module are activated. Output 17 activates the external alarm and light and output 15 activates solenoid SV1 in the kneel module. SV1 supplies air pressure to the V1 air pilot valve. The V1 valve connects supply air pressure to the front air bellows for quick recovery of the suspension. Air pressure supplied by the park brake valve shifts the V3 air pilot valve. This reconnects the RH leveling valve to the front axle bellows and the suspension will raise the remaining 1 - 1½ inches.

Thanks to Steve Martin of the MCI Technical Department for his creation of the air and electrical schematic used in this tip. If you have any questions, please call the MCI Customer Support Center at (800) 241-2947.

Motor Coach Industries - A New Flyer company: Corporate Address 200 East Oakton Street, Des Plaines, Illinois 60018 | Phone: 866-MCICOACH

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