Electrical Changes In The Operation Of The Oscillating Axle And The Swing Brake Circuits With The M300 In Year 2000 Update Caterpillar

Electrical Changes In The Operation Of The Oscillating Axle And The Swing Brake Circuits With The M300 In Year 2000 Update

Usage:

EXCAVATORSM312 (6TL951-UP),
M315 (7ML1647-UP),
M318 (8AL2265-UP, 6ES243-UP, 8SS470-UP),
M320 (6WL469-UP, 9PS287-UP) EXCAVATORS

Problem:

Early electrical schematics do not accurately reflect the electrical configuration of the oscillating axle and the swing brake circuits on current production machines (year 2000 configuration).

Solution:

The following publications include updated schematics effective with the above listed serial numbers.Table 1.

An update to the Service Manual Operation section is forthcoming. In the interim the following information is provided to assist in troubleshooting the swing brake and the oscillating axle functions of current production wheeled excavators.

Swing Brake:

The year 2000 update of wheeled excavators includes a new swing drive group. As with the previous configuration, the new swing drive group includes a spring applied disc brake that is released through actuation of a solenoid in the pilot circuit.

There is a significant difference between the swing brake activation of previous machine configuration and the swing brake activation of the year 2000 configuration. The swing brake solenoid is now energized automatically when the hydraulic swing circuit is activated. Refer to Illustration 1.

Once the operator moves the left joystick to activate the swing operation, the AEC Swing Pressure switch (P/N 163-2084) closes and powers terminal 53c of the timer relay (P/N 155-4574). The output from terminal 53e of the same relay then provides current from terminal 15 to the swing brake solenoid through wire BU(9) and GN/BU(1).

There are two ways to interrupt the current to the swing brake solenoid and subsequently apply the swing brake.

1. By closing the swing brake switch (on the left joystick), the swing brake relay is activated which breaks the connection between wires BU(9) and GN/BU(1). The swing brake solenoid is then de-energized and the swing brake is applied.

2. By releasing the swing joystick, the pilot pressure in the swing circuit pilot line drops, which in turn, opens the AEC Swing Pressure Switch. This disconnects power to terminal 53c of the timer relay (P/N 155-4574). The timer relay has a built-in delay of 3.5 seconds. With this feature, the timer relay disconnects power to the swing brake solenoid 3.5 seconds after power to terminal 53c has been disconnected. In this way there is approximately a 3.5-second delay between release of the swing joystick and application of the swing brake.

NOTE: To assist in trouble shooting the connector to the swing brake solenoid includes a built-in LED. This LED is illuminated whenever there is current to the solenoid to release the swing brake refer to Illustration 1.

Illustration 1 - Schematic of Swing Brake Circuit

Illustration 2: Pilot Manifold

(1) Oscillating Axle Solenoid,

(2) AEC Swing Pressure Switch,

(3) Red LED for Swing Brake Solenoid,

(4) Swing Brake Solenoid,

(5) Oscillating Axle Pilot Hose,

(6) Swing PRV Hose, and

(7) Swing Brake Pilot Hose.

Oscillating Axle:

On previous models the oscillating axle was locked or unlocked with a manually operated hydraulic valve. Effective with the above listed serial numbers, the oscillating axle is locked or unlocked electrically from either the "Oscillating Axle Lock Switch" (8) that is located below the brake pedal (refer to Illustration 3), or from the "Oscillating Axle Toggle Switch" (9) that is located on the right console (refer to Illustration 4).

Illustration 3: Brake Pedal

Illustration 4: Right Console

Electrical activation of this circuit is accomplished by incorporating an electrical solenoid in the control circuit for the oscillating axle. Activating this solenoid connects pilot pressure to the oscillating axle cylinders that release their check valves, thus allowing the axle to oscillate.

If current to the oscillating axle solenoid is interrupted, pilot pressure is disconnected from the cylinders. The check valves close and the oscillating axle is locked.

There are "3 Conditions" that must be met before the axle is allowed to oscillate through energizing the oscillating axle out solenoid. Refer to Illustration 5.

1. The left console must be down in order to energize the pilot pressure enable relay .

2. The "oscillating axle toggle switch" (9) that is located on the right console must remain in the "axle free" position. Refer to Illustration 4.

3. The "oscillating axle lock switch" (8) that is located below the brake pedal must remain in the "axle free" position (brake pedal NOT fully depressed). Refer to Illustration 3.

If any of the above conditions is not satisfied, the electrical power to the oscillating axle solenoid is interrupted and the oscillating axle remains locked.

NOTE: If the left console is down and the "oscillating axle toggle switch" (9) is in the "locked" position, the light in the "oscillating axle toggle switch" (9) is powered through GY(12).

If the left console is down and the "oscillating axle lock switch" (8) located below the brake pedal is in the "locked" position, the light in the "oscillating axle toggle switch" (9) is powered through BU(20), BR(11), and GY(13).

Illustration 5. Schematic of the Oscillating Axle Lock Circuit