TERMINAL-BUS 1135100 - Caterpillar

Transmission Shifting Operation
Table 1
Transmission Gear and Solenoid Valve Logic
Gear
Engaged Solenoid
Valves On Clutches
Engaged
1F 5 and 2 5 and 2
2F 4 and 2 4 and 2
3F 3 and 2 3 and 2
Neutral 3 3
1R 5 and 1 5 and 1
2R 4 and 1 4 and 1
3R 3 and 1 3 and 1 The direction switch, the upshift switch, the downshift switch, and the position sensor for the direction lever informs the ECM of the shifting that is requested from the operator. The requests are "FORWARD", "NEUTRAL", "REVERSE", "UPSHIFT", or "DOWNSHIFT". The ECM activates the transmission solenoid valves in order to shift the transmission. Each transmission clutch has a corresponding transmission solenoid valve. The transmission solenoid valves control the hydraulic circuits that engage the transmission clutch pressures. The ECM applies electrical current to the appropriate transmission solenoid valve. For the movement of the machine, two clutch solenoids are activated. One solenoid is activated for the direction and one solenoid is activated for speed. Under normal conditions, the ECM shifts the transmission. The shifting is based on the information from the sensor and from the switches. Electronic Clutch Pressure Control (ECPC)
The ECM selects the transmission clutches that must be engaged. The clutch pressure is MODULATED ELECTRONICALLY. The ECM controls the modulation of clutch pressure. The ECM uses the transmission speed, the torque converter output speed and the transmission temperature in order to control the smooth engagement of the clutches. The ECM uses the transmission solenoid valves to directly modulate the oil pressure to each transmission clutch. The solenoid valves are the proportional type. The ECM uses a pulse width modulated signal (PWM) in order to vary the current to the solenoid. The current to the solenoid determines the amount of oil pressure that is applied to the clutch. The distance of travel of the plunger is proportional to the electrical current of the solenoid. The position of the plunger controls the amount of oil pressure and the amount of clutch engagement. An increase in electrical current will open the solenoid valve further. This causes an increase in oil pressure and an increase in clutch engagement. The ECM responds to a request for shifting by opening the appropriate solenoid valves. The solenoid valves are opened to a position which initially fills the corresponding clutches with oil. Then, the ECM opens the valve gradually in order to increase the pressure to the clutches. The pressure is increased until the clutches are fully engaged. Braking Operation
The brakes are applied by a spring and hydraulically released. The service brake pedal and the parking brake switch tell the ECM the braking requests of the operator. The left brake solenoid and the right brake solenoid on the brake control valve are de-energized. When the proportional solenoid valves are de-energized, the brake control valve closes. The pressure for the power train oil is not available in order to release the brakes. The brakes are fully engaged. When no braking is requested, the proportional solenoid valves are energized and