AND CIRCUITS
(Models Without Trim Boost) (Foldout 6)
NOTE:
• Only the system components that differ from those in the manual-electric system and circuits (Para-graph 2–21 and 2–22) are described.
• References to up, down, left, or right refer to posi-tions or movements of components on Foldout 6.
• For electronic control hydraulic system functions, refer to Paragraph 2–18a.
• For electronic control hydraulic system schematics, refer to Paragraph 2–18b.
a. Electronic Control Unit (ECU). The Electronic Control Unit (ECU) (Figure 2–7) contains a micro-computer which receives and processes signals from various switches and sensors. The ECU can then con-trol transmission operation by actuating the appropri-ate solenoids. The ECU can also perform diagnostic functions and identify electronic system problems with a displayed code.
b. Shift Selector
1. The two types of electronic control shift selec-tors are touch-pad (Figure 2–8) and shift lever (Figure 2–9).
NOTE:
• For models with touch-pad selector, proceed with Step (2).
• For models with shift lever selector, proceed to Step (3).
Figure 2–7. Electronic Control Unit (ECU)
Figure 2–8. Typical Electronic Control Touch-Pad Shift Selector
2. The touch-pad selector (Figure 2–8) is totally electronic. The shift selector displays seven snap-dome pads: R (Reverse); N (Neutral); D (automatic shifting, first range through sixth range); 4 (automatic shifting, first range
CHASSIS WIRING HARNESS CONNECTION (J1B) SECONDARY MODE HARNESS CONNECTION (J3) CAB WIRING HARNESS
CONNECTION (J1A) ELECTRONIC
CONTROL UNIT (ECU) IDENTIFYING
LABELS
H00688.01
SHIFT SELECTOR
H00695
through fourth range); 3 (automatic shifting, first range through third range); 2 (automatic shifting, first range to second range); 1 (first range). The shift selector also incorporates a DO NOT SHIFT light. When any one of the touch pads is pressed, a “click” is felt and the pad lights to indicate the transmission is ready to operate in the selected range. Proceed to Step (4).
3. The lever shift selector (Figure 2–9) is electro-mechanical and has a movable lever. Movement of the lever activates electronic circuits within the shift selector (there is no mechanical link-age attached to the lever). A two-finger shift le-ver latch release is located below the lele-ver end cap. The shift lever cannot be moved through the detents until the two-finger shift latch is pulled toward the lever end cap. There are nine separate positions on the shift lever quadrant:
R1 (Reverse-1); R2 (Reverse-2); N (Neutral);
D (automatic shifting, first range through sixth range); 5 (automatic shifting, first range through fifth range); 4 (automatic shifting, first range through fourth range); 3 (automatic shift-ing, first range to third range); 2 (automatic shifting, first range to second range); 1 (first range). The shift selector also incorporates two DO NOT SHIFT lights. When any one of the forward drive ranges is selected, detents within the shift selector will hold the lever in the se-lected position. Also, detents within the shift selector hold the shift lever at N (Neutral) and out of R (Reverse).
4. When a serious irregularity is detected in the system, a buzzing tone is produced and the DO NOT SHIFT lights flash continuously. This in-dicates that the operator is not to shift the transmission because the shift selector and the electronic control will not respond. For models with lock-in-range downshift protection, the transmission will stay in the range it was in at the time the DO NOT SHIFT lights were acti-vated regardless of what range is selected at the shift selector. For models with lock-in-neutral, the transmission will shift to neutral when the DO NOT SHIFT lights are activated.
Figure 2–9. Typical Electronic Control Lever Shift Selector
c. CHECK TRANS Light
1. The OEM-supplied CHECK TRANS light may be located on the equipment instrument panel.
2. This light comes on every time the system is turned on as a lamp check and also when the ECU finds an irregularity in the system. If the CHECK TRANS light comes on and the DO NOT SHIFT light(s) remains off, the irregular-ity is minor. In some cases, the transmission will continue to operate in a normal manner. How-ever, in other cases the ECU will take action to reduce the possibility of damage to the equip-ment or the transmission. For example, the ECU may prevent operation in higher ranges.
d. Throttle Sensor
1. A remote-mounted throttle sensor is located in the engine compartment. This sensor consists of a push-pull cable and a potentiometer. One end of the cable is attached via an OEM-sup-plied bracket to the engine fuel lever (the ad-justable bracket attaches to the governor fuel lever on diesel engines). The other end of the cable is attached to a potentiometer which is inside a protective housing. Voltage readings from the potentiometer are sent to the ECU via the wiring harness.
SHIFT SELECTOR H00696
Figure 2–10. Output Speed Sensor (Magnetic Pickup)
2. Movement of the throttle causes a change in the voltage signal to the ECU, which is pro-grammed to recognize the signal as a percent of throttle. When the throttle is wide open, the ECU will cause upshifts to occur near the en-gine governed speed. Part throttle will cause upshifts to occur at a lower engine speed.
When the throttle is closed, the ECU may de-lay the release of the lockup clutch to provide better engine braking. All modulation of shifts occurs as a result of the throttle sensor.
e. Output Speed Sensor (Figure 2–10)
1. The output speed sensor (magnetic pickup) is located in the rear housing. The magnetic end of the sensor is positioned near the speed sen-sor gear (39- or 41-tooth) located on the trans-mission output shaft. The chassis harness con-nects the speed sensor to the ECU.
2. Rotation of the output shaft causes the gear teeth to pass through the magnetic field at the end of the sensor. The passing of each gear tooth inter-rupts the magnetic field and generates an electri-cal pulse which is directed to the ECU (a 39-tooth gear would produce 39 pulses for each rev-olution of the output shaft). The ECU uses this signal (speed), the throttle sensor signal (power demand), and shift selector position to control upshifts, downshifts, and lockup operation.
OUTPUT SPEED SENSOR
H00697
Figure 2–12. Typical Electronic Control Cab Wiring Harness
ECU CONNECTOR (J1A)
LEVER-TYPE SHIFT SELECTOR CONNECTOR*
INTERFACE WITH EQUIPMENT ELECTRICAL SYSTEM
DIAGNOSTIC DATA READER (DDR) HOOKUP
H00698.01
* For touch-pad shift selector, this connector is round.
Figure 2–13. Typical Electronic Control Secondary Mode Wiring Harness ECU
CONNECTOR (J3)
Interface with stall check switches, secondary mode functions, or other special features
H00700
Figure 2–11. Typical Electronic Control Chassis Wiring Harness ECU CONNECTOR
(J1B)
ELECTRIC LOCKUP CONNECTOR
(MODELS WITH ELECTRIC LOCKUP) H00699
TRIM BOOST CONNECTOR (MODELS WITH TRIM BOOST) MAIN CONTROL
VALVE BODY CONNECTOR
THROTTLE
SENSOR CONNECTOR SPEED
SENSOR CONNECTOR
f. Wiring Harnesses. Three wiring harnesses are used to connect the components of the electronic trol system. The chassis harness (Figure 2–11) con-nects the ECU to the components located in the engine compartment (e.g., transmission, throttle sensor, and speed sensor). The cab harness (Figure 2–12) connects the components located at the instrument panel: the ECU, shift selector, and Diagnostic Data Reader (DDR) hookup. This harness also connects the ECU to the equipment electrical system. The secondary mode harness (Figure 2–13) connects the ECU to special functions (e.g., stall checks, special pumping, or dual-mode operation).
g. Lockup (Models With Electric Lockup)
1. Upon start-up of the transmission, main hy-draulic fluid pressure is supplied to the top of the lockup valve, the side of the lockup valve, and the lockup spring pocket through an ori-fice. The lockup clutch is exhausted through the valve (Figure 2–14).
2. The lockup solenoid is energized by a signal from the ECU, exhausting main pressure from the spring pocket. Although main pressure fluid continues to feed into the spring pocket, the effective orifice in the solenoid is large enough to allow the spring pocket to be ex-hausted since the spring pocket feed is through a smaller orifice. Main pressure at the top of the lockup valve then overcomes the spring force and the valve moves down. The exhaust is then cut off and main pressure is fed to the lockup clutch through the lockup valve.
3. When the solenoid is de-energized, the spring pocket exhaust is closed, main pressure com-bines with the spring force in the spring pocket to overcome the main pressure at the top of the valve, and the valve moves to the up position.
Lockup feed is cut off and the lockup clutch exhausts through the lockup valve.
h. Operation of the Electronic Control System 1. The electronic control system selects the
proper transmission drive ratio for the most ef-ficient operation of the equipment under all conditions of speed, load, throttle position, and range selection.
Figure 2–14. Electronic Lockup — Hydraulic Schematic
2. The operator selects the desired range, which may be any one of eight positions at the shift selector.
3. The shift selector transmits an electronic signal to the ECU. The ECU also receives pulse sig-nals indicating equipment speed from the speed sensor and a signal from the throttle sen-sor indicating throttle position.
4. The three inputs are transmitted to the ECU which sends the electronic signals to the con-trol valve assemblies. The range selected by the operator, the equipment (transmission out-put) speed, and the throttle position determine the signal sent to the solenoids in the control valve assemblies.
5. If a forward range is selected, the transmission starts out in first range and upshifts automati-cally within the selected range. Timing of up-shifts and downup-shifts is based on equipment speed and throttle position. At closed throttle, both upshifts and downshifts occur at lower speeds than at open throttle.
V00701
ORIFICE
MAIN PRESSURE EXHAUST OR SUMP LOCKUP SOLENOID TO LOCKUP CLUTCH
MAIN
6. The ECU includes a program that protects the engine and equipment drive train from down-shifts at excessively high speeds. If an acciden-tal high speed downshift or a premature selection of neutral or reverse occurs, the ECU will prevent engine damage due to an over-speed condition. The transmission will pro-gressively downshift at safe engine speeds until the range selected can be attained. Throt-tle position will not influence such downshifts.
7. Refer to Paragraphs 2–21 and 2–22 for the de-scription and operation of the hydraulic system and circuits. While Paragraphs 2–21p and 2–21q and Paragraph 2–22 pertain specifically to man-ual shifting, the responses of the hydraulic sys-tem and circuits in each range are similar. The control valve assemblies for electronic-control systems without trim boost are similar to those for manual-electric systems.