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| Illustration 1 | g03666238 |
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(1) Left pedal position sensor
(2) Left pedal (3) Mechanical linkage (4) Right service brake pedal | |
Left pedal position sensor (1) is located in the cab in the left brake pedal assembly. The position sensor (left brake pedal) sends an input to the transmission ECM. The sensor continuously generates a PM signal. The duty cycle varies in proportion to the position of the left brake pedal position sensor. The left pedal position sends a change in the input signal to the transmission ECM. The ECM measures the duty cycle in order to determine the position of the pedal for downshifting the transmission and neutralizing the clutches.
The transmission is in neutral when all FNR switches are in Neutral position.
The transmission is locked into Neutral when :
- Actual Gear is Neutral
- Ground speed is zero
- Left armrest stowed
- Left armrest DOWN and steering is not aligned
Transmission is allowed to shift out of Neutral when:
- All FNR switches are in neutral then one switch transitions to FORWARD or REVERSE
- Left armrest down with operator not present or steering enabled
- Parking brake released only required when going into first gear
Transmission Neutralizer Function
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| Illustration 2 | g03662484 |
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Left brake pedal positions (A) Transmission Downshift (B) Level Mode (C) Moderate Mode (D) Aggressive Mode (E) Calibrated Initial Brake Pressure Point (F) Brake Application (1) Left Brake Position Sensor (5) Stop Lamp Switch | |
The 824K, 825K, and 826K machines are equipped with an Integrated Brake System (IBS). This system allows the operator to downshift the transmission and neutralize the transmission using the left brake pedal.
The left pedal is attached to a PWM rotary position sensor and a mechanical linkage. 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 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 Cat ET screen. Pedal travel is displayed as a percentage (%) in Cat ET. Three percent of brake pedal travel is about 1°, and 100 percent of pedal travel is about 33°.
Illustration 2 shows the actions that occur as the left brake pedal is depressed. The Integrated Brake System (IBS) works the same as the previous machines.
The left brake pedal allows the operator to control the IBS and the transmission neutralizer of the machine. In approximately the first 9% of brake pedal travel (dead band), no braking or downshifting occurs.
Brake pedal travel between the pedal dead band and the calibrated initial brake pressure point (E) will cause the transmission to downshift. When the left pedal is depressed further, and if the transmission is in third or fourth gear, the transmission will downshift one gear at a time until second gear is reached. IBS downshifts the transmission to use the engine and other parasitic loads to reduce the ground speed of the machine without applying the service brakes. When the transmission is in SECOND FORWARD, the transmission neutralizer can be activated if the correct conditions are met.
The transmission neutralizer has a Level Mode (B), Moderate Mode (C), or Aggressive Mode (D) when the left brake pedal is further depressed between the calibrated initial brake pressure point and the maximum pedal travel.
The Level Mode is best suited for level ground operation. The Power Train ECM will neutralize the transmission when the left brake pedal is depressed slightly.
The Aggressive Mode is best suited for working on a steeper grade. In Aggressive mode, the left brake pedal should be depressed further to increase the pressure to the service brakes.
Increasing the pressure sent to the service brakes prevents the machine from rolling back before the transmission is neutralized.
The modes can be selected by the operator through the message display. The Power Train ECM determines when the transmission directional clutch will be neutralized by the mode selected by the operator and the left brake position sensor (1).
When the left pedal is depressed 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.
When the brake pedal reaches the neutralization set point and the transmission neutralizer is enabled, the Power Train ECM will DE-ENERGIZE the directional clutch solenoid to neutralize the transmission when the following conditions exist:
- The autoshift mode is in automatic mode
- IBS is enabled in manual mode
- The transmission is in FIRST or SECOND gear
or
- The autoshift mode is in manual mode
- IBS is disabled
- The transmission is in FIRST, SECOND, THIRD, or FOURTH gear
Note: The 826K machine does not have a clutch 4 (Third Speed).
If the left brake pedal is raised 4° above the Neutralization Set Point, a signal is sent to the modulating valve to engage the directional 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 1-4. The operator pushes the bucket into the pile, and then the transmission automatically downshifts to FIRST FORWARD. The transmission will automatically downshift to FIRST FORWARD when the torque and speed requirements have been met. When the bucket is full, the operator changes the direction of the machine to REVERSE. In 1-4, the transmission automatically shifts into SECOND REVERSE.
The autoshift mode sets parameters in the Power Train ECM that Influence the Integrated Brake System. The autoshift mode has five options: 1-2, 1-3, 1-4, 2-4, and MANUAL. With the speed on the message display in the SECOND speed position, the ideal autoshift mode for the smoothest neutralization during truck loading in normal applications is 2-4. Smoothest means high engine speed with the following limitations: no unacceptable jerkiness during slowdown, no unacceptable engine overspeed during slowdown, and no unacceptable transmission overspeed during slowdown.
The stop lamp switch (5) illuminates the brake lights when the left brake pedal is fully depressed.