VARIABLE SHIFT CONTROL CIRCUIT

Control Switch 1 2 3 4 BK 18 GN 18 BU 18 BR 18

Power Train ECM

J2-32 J1-32 Ground

Variable Shift Control (E conomy)

Variable Shift Control (P ower)

Variable Shift Control (M id) J2-33

J2-34

BK 16 BK 16 BK 16 BK 16

VARIABLE SHIFT CONTROL CIRCUIT

Variable Shift Control

The 966H and the 972H Wheel Loaders feature Variable Shift Control on electrohydraulic machines. Variable Shift Control allows the transmission to shift at lower engine speeds. The variable shift control switch (arrow) is a three-position switch (POWER, MID, ECONOMY) that will change the shift points stored in the Power Train ECM. When the switch is rotated to the ECONOMY position (clockwise), the switch sends a signal to the Power Train ECM to shift the transmission at a lower engine rpm for increased fuel economy. When the switch is rotated to the POWER position (counterclockwise), the transmission shifts when the engine reaches 2100 rpm.

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Integrated Brake System

The 966H and the 972H Wheel Loaders are equipped with the Integrated Brake System (IBS). This system allows the operator to downshift the transmission and neutralize the transmission using the left brake pedal.

The left service brake pedal (1) is attached to a PWM rotary position sensor (2) and a mechanical linkage (not shown). The position sensor continuously monitors the left brake pedal position. The position sensor sends an input signal to the Power Train ECM indicating left brake pedal position.

The mechanical linkage is connected to the brake control valve (not shown) located below the cab. The right service brake pedal (not shown) is also connected to the brake control valve independent of the left brake pedal.

NOTE: The amount of brake pedal travel can be displayed on the ET Service Tool

screen or the Caterpillar Monitoring System main display module. Pedal travel is displayed as a percentage (%) in ET and by counts (ct.) on the Caterpillar Monitoring System. Three percent of brake pedal travel is about 2 ct. or 1°, and 100 percent of pedal travel is about 66 counts or 33°.

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Left Brake Pedal Actions

This view shows the actions that occur as the brake pedal is depressed.

In approximately the first nine percent of brake pedal travel (dead band), no braking or downshift occurs. Brake pedal travel between the pedal dead band and the calibrated initial brake pressure point is the initial Mode. In the Initial Mode, the transmission downshifts, but the service brakes are not engaged and the transmission is not neutralized.

In the Normal Mode, the left brake pedal is further depressed between the calibrated initial brake pressure point and the maximum pedal travel. In the Normal Mode, the transmission downshifts and the service brakes are engaged.

When the left pedal is depressed in Initial and Normal Modes, and if the transmission is in third or fourth gear, the transmission will downshift one gear at a time until second gear is reached. Each downshift will occur when the transmission output speed decreases to the shift point of the current transmission speed.

Deadband Calibrated Neutralization Set Point Maximum Pedal Travel Calibrated Initial Brake Pressure Point

LEFT BRAKE

PEDAL POSITIONS

transmission neutralizer override switch is in the OFF position, the Transmission ECM will DE-ENERGIZE the direction clutch solenoid to neutralize the transmission when the following conditions exist:

- The auto/manual selector switch is NOT in the 1-4 position - The transmission is in 2nd gear

- The ground speed is 6.5 mph or

- The auto/manual selector switch is in the 1-4 position - The transmission is in 1st gear

- The ground speed is 4.5 mph

If the left brake pedal is raised 4° above the Neutralization Set Point, a signal is sent to the modulating valve to engage the direction clutch. At this time, the drive train will be

re-engaged. Normally, the travel of the left brake pedal will overshoot the Neutralization Set Point. Each time the brake travel overshoots the Neutralization Set point without being released into the dead band zone, the New Neutralization point moves down the point of the overshoot. The Power Train ECM will retain the New Neutralization Point until the left brake pedal is released and the pedal is into the dead band zone.

In normal conditions, the best gear for loading trucks is 2nd, or "Second Auto." The operator pushes the bucket into the pile, and then manually shifts the transmission down to Forward 1. When the bucket is full, the operator changes the direction of the machine to Reverse. In Second Auto, the transmission automatically reverses in Reverse 2, instead of Reverse 1.

The auto/manual selector switch sets parameters in the ECM that influence the Integrated Brake System. On machines equipped with the optional Command Control Steering (CCS), the switch has 5 positions: 1-4, 2, 3, 4, and MANUAL. The switch position for the smoothest neutralization during truck loading in normal applications is 2. Smoothest means high engine speed with the following limitations: unacceptable jerkiness during slowdown, unacceptable engine overspeed during slowdown, and unacceptable transmission overspeed during

slowdown.

On machines equipped with the standard Hand Metering Unit HMU steering, the auto/manual selector switch has 3 positions: 1-4, 2-4, and MANUAL. With the speed selector on the steering column in the 2 position, the ideal auto/manual selector switch position for the smoothest neutralization during truck loading in normal applications is 2-4.

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