284 Automatic Transmissions and Transaxles Copyright by Goodheart-Willcox Co., Inc. Line pressure also travels to the actuator feel limit (AFL) valve. The AFL valve limits the amount of pressure in the pressure control and shift solenoid feed circuits, since excess pressure could damage the solenoids. AFL oil is directed to the pressure control solenoid, which is a pulsed solenoid operated by the ECM based on sensor inputs. The pressure control solenoid sends oil pressure to the main pressure regulator boost valve. This pressure moves the boost valve and increases the pressure on the pressure regulator spring. The amount of pressure on the spring varies the pressure output of the main pressure regulator. AFL oil pressure is also delivered to the shift valves and solenoids. The ECM energizes both shift solenoids in Park. AFL oil from the accumulator limit valve cannot exit through the solenoids and pushes the shift valves to the left. However, the solenoids are not supplied with drive oil and, therefore, cannot apply any holding members. The main pressure regulator also directs some oil to the torque converter clutch valve. The torque converter clutch valve is in the released position at this time. Oil passes through the upper part of the valve to the torque converter release circuit, through the torque converter, and out through the torque converter apply circuit. The converter oil then passes through the bottom part of the torque converter valve to the oil cooler. In Park, the operation of the solenoid has no effect, since line oil pressure is stopped at the converter clutch valve until the transmission shifts into second gear. Oil flows through the release and apply sides of the converter clutch plate, and the converter is unlocked. Neutral, Engine Running In Neutral with the engine running, Figure 12-31, the pump is turning and supplying pressure to the main pressure regulator just as it was in Park. AFL oil through the pressure control solenoid continues to regulate line pressure through the main pressure regulator boost valve. AFL pressure is also sent to the shift valves but has no effect. The main pressure regulator also continues to send oil to the torque converter clutch valve, which remains inoperative. In Neutral, the manual valve is positioned to cut off oil to the low reverse clutch piston. Therefore, no holding members are applied in Neutral. Drive, First Gear When the driver places the vehicle in Drive (some- times called Overdrive) with the vehicle not moving, Figure 12-32, line oil is sent to the forward clutch piston, engaging the forward clutch. This oil is called D4 oil. Under normal conditions, the check ball (#12) seals the oil passage, forcing the D4 oil to travel through the smaller orifice next to it. This ensures that the shift is made gently. Some forward clutch oil is also diverted to the forward clutch accumulator. The accumulator uses this oil to compress a spring, reducing the force of the oil sent to the clutch. When the spring is fully compressed, full oil pressure is available at the clutch piston. Notice that D4 oil is called FWD clutch feed oil when it reaches the forward clutch and the forward clutch accumulator piston. If the engine speed is above idle, the pressure control solenoid will raise line pressure. This will cause the D4 oil to be higher than normal, opening the forward abuse valve. When the forward abuse valve is open, D4 oil is sent directly to the forward clutch piston, bypassing the orifice and check ball assembly. The forward abuse valve prevents clutch plate damage by quickly and firmly applying the clutch when the vehicle is placed in Drive at high engine RPM. D4 oil is also directed to the accumulator valve, which fills and pressurizes the 1-2 and 3-4 accumulators for later use. Notice that the accumulator valve is affected by oil pressure from the pressure control solenoid. D4 oil is also delivered to one of the pressure switches in the pressure switch assembly. This normally open (N.O.) switch closes when it is pressurized to tell the ECM that the transmission is in Drive. D4 oil is also sent to the 1-2 shift valve for use in later gears. The shift solenoids are both energized. The 1-2 shift solenoid sends oil pressure to the 3-4 shift valve, but this has no effect on transmission operation since no other oil pressure is present at the valve. Mechanically, the operation of the transmission is the same as in the older version dis- cussed in Chapter 11. Drive, Second Gear When the ECM decides the transmission should be shifted into second gear, it de-energizes (turns off) 1-2 shift solenoid. Since the 1-2 shift solenoid is a normally open (N.O.) type, oil exits through the solenoid when it is de-energized. Spring pressure pushes the 1-2 shift valve to the right, allow- ing D4 oil to pass through the valve and apply the 2-4 band servo, Figure 12-33. This oil pressure, called 2nd oil, applies the band and shifts the transmission into second gear. The check ball and orifice, shown directly above the 3-2 down- shift valve (#8), are used to restrict 2nd oil pressure to the servo and cushion the shift. Pressure also becomes available at the 3-2 downshift valve. To further cushion the shift, some 2nd oil is sent to the 1-2 accumulator. This oil moves the 1-2 accumulator piston against spring pressure, diverting some pressure from the servo. The initial band apply will be soft, followed by full pressure to hold the band tightly. The 2nd oil is also sent to the 2-3 shift valve, 3-4 relay valve, 4-3 sequence valve, and the converter clutch valve for use in other gears. The converter clutch may apply in second gear, as explained on the next page. Note: In the left corner of Figure 12-33, a previously unseen valve and solenoid have been added. The solenoid and valve are supplied with AFL oil. The purpose of this valve and solenoid will be explained in the section on downshifts.