CASE AS-TRANSMISSION 1246082 - 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 Lever pwm is used as a primary direction input. The PWM can read a position of"FORWARD", "NEUTRAL", OR "REVERSE". As a backup, in case the Direction Lever sensor is faulted or missing, at that time the Direction Switches, "FORWARD SWITCH", or "REVERSE SWITCH"will be used to detect when the direction selector is in Forward or Reverse.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, causing an increase in oil pressure and 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. Differential Steering Operation
The steering control lever (tiller) uses two rotary position sensors in order to send a signal to the pump control solenoid valves through the Power Train ECM. The steering motor utilizes a dual Hall Effect sensor in order to provide speed and direction output information to the Power Train ECM. The dual Hall Effect sensor contains two sensing elements. As the steering motor rotates, the rotation of the internal parts of the motor induce a current (signal) into both elements in the sensor. The difference in the timing between the signals determines motor speed. Direction is determined by sensing which element provides the signal first, then second.The steering pump control solenoids (left and right) are installed in the steering control valve and are energized by the Power Train ECM. The Power Train ECM determines the amount of current and which pump control solenoid to energize based on the signals received from the steering lever position sensors. As the solenoids are energized, the solenoid pin pushes against the end