electronically HOIST RAISE SOLENOID BACK-UP ALARM STARTER RELAY SHIFT LEVER POSITION SENSOR KEY START SWITCH UPSHIFT SOLENOID LOCKUP SOLENOID BODY UP SWITCH
INPUT COMPONENTS OUTPUT COMPONENTS
TRANSMISSION GEAR SWITCH TRANSMISSION OUTPUT SPEED SENSOR PARKING/SECONDARY BRAKE PRESSURE SWITCH SERVICE/RETARDER BRAKE PRESSURE SWITCH CONVERTER OUTPUT SPEED SENSOR ENGINE OUTPUT SPEED SENSOR HOIST LEVER POSITION SENSOR LOW STEERING PRESSURE SENSOR
ARC AND TCS CONTROL ENGINE CONTROL ELECTRONIC SERVICE TOOL CAT DATA LINK
MESSAGE CENTER MODULE °C kPaMiles KM RPM Liter SERV
CODE X10 . . . DOWNSHIFT SOLENOID HOIST LOWER SOLENOID SECONDARY STEERING RELAY AUTO LUBE SOLENOID
TRANSMISSION AND CHASSIS CONTROL ELECTRICAL SYSTEM
The purpose of the EPTC III is to determine the desired transmission gear and energize solenoids to shift the transmission up or down as required based on information from both the operator and machine.
The EPTC III receives information from various input components such as the shift lever sensor, Transmission Output Speed (TOS) sensor, transmission gear switch, body up switch and the hoist lever sensor. Based on the input information, the EPTC III determines whether the transmission should upshift, downshift, engage the lockup clutch or limit the transmission gear. These actions are accomplished by sending signals to various output components.
NOTE: The torque Converter Output Speed (COS) sensor is not installed on the D-series update trucks.
¥ Shifts controlled by electrical signals
Output components include the upshift, downshift and lockup solenoids, the back-up alarm and others.
The EPTC III also provides the service technician with enhanced
diagnostic capabilities through the use of onboard memory, which stores possible diagnostic codes for retrieval at the time of service.
The Advanced Diesel Engine Management (ADEM II) engine control, the Automatic Retarder Control (ARC) and Traction Control System (TCS) control, the Caterpillar Monitoring System or the Vital Information Management System (VIMS) and the EPTC III all communicate with each other through the CAT Data Link. Communication between the electronic controls allows the sensors of each system to be shared. Many additional benefits are provided, such as Controlled Throttle Shifting (CTS). CTS occurs when the EPTC III tells the engine ECM to reduce engine fuel during a shift to lower stress to the power train.
The EPTC III is also used to control the hoist and secondary steering system on the D-series update trucks.
The Electronic Control Analyzer Programmer (ECAP) and the Electronic Technician (ET) Service Tools can be used to perform several diagnostic and programming functions (see Slide No. 23).
Some of the diagnostic and programming functions that the service tools can perform are:
- Display real time status of input and output parameters - Display the internal clock hour reading.
- Display the number of occurrences and the hour reading of the first and last occurrence for each logged diagnostic code and event. - Display the definition for each logged diagnostic code and event. - Display load counters.
- Display the lockup clutch engagement counter. - Display the transmission gear shift counter.
- Program the top gear limit and the body up gear limit - Upload new Flash files
INSTRUCTOR NOTE: In the following slides, only some of the input and output components of the transmission and chassis control will be shown. Other components will be shown when the system they control is discussed (hoist raise and lower solenoids for example).
¥ Benefits of electronic communication
¥ EPTC III used to control hoist and secondary steering system ¥ Service tool diagnostic and programming functions ¥ EPTC III outputs
1. Shift lever sensor - PWM duty cycle input 42 2 1
The shift lever (also referred to as the "Cane" or "Gear Selector") sensor (1) is located inside the cab in the shift console and provides an input signal to the transmission and chassis control (EPTC III). The shift lever sensor controls the desired top gear selected by the operator. The sensor provides a PWM duty cycle signal that is unique for each position of the shift lever sensor.
To view the shift lever sensor positions or diagnose problems with the sensor, use Mode 7.5 of the Caterpillar Monitoring System display window or the status screen of the service tool and observe the "Gear Lever" status. As the shift lever is moved through the detent positions, the Gear Lever status should display the corresponding lever position shown on the shift console.
The position of the shift lever can be changed to obtain better alignment with the gear position numbers on the shift console by loosening the three nuts (2) and rotating the lever. The position of the shift lever sensor is not adjustable.
2. Shift lever adjustment nuts ¥ Shift lever diagnostics
43
3
2 1
The service/retarder brake switch (1) is located in the compartment behind the cab. The switch is normally closed and opens when service/retarder brake air pressure is applied. The switch has two functions for the EPTC III:
- Signals the EPTC III to use elevated shift points, which provides increased engine speed during downhill retarding for increased oil flow to the brake cooling circuit.
- Signals the EPTC III to allow rapid shifting during braking by overriding the anti-hunt timer.
A diagnostic code is stored if the EPTC III does not receive a closed (ground) signal from the switch within seven hours of operation time or an open signal from the switch within two hours of operation time. The Traction Control System (TCS) also uses the service/retarder brake switch as an input through the CAT Data Link (see Slide No. 80).
1. Service/retarder brake switch
¥ Service/retarder brakes engaged: - Raises shift points - Eliminates anti-hunt
timer
¥ Service/retarder switch used as TCS input
The parking/secondary brake switch is in location (2) (trust me, it's in there somewhere) in the parking/secondary brake air pressure line. The normally open switch is closed during the application of air pressure. The purpose of the switch is to signal the EPTC III when the parking/
secondary brakes are engaged. Since the parking/secondary brakes are spring applied and pressure released, the parking/secondary brake switch is closed when the brakes are not applied and opens when the brakes are applied. This signal is used to override the anti-hunt timer for rapid downshifting and is used to sense when the machine is parked.
A diagnostic code is stored if the EPTC III does not receive a closed (ground) signal from the switch within seven hours of operation time or an open signal from the switch within one hour of operation time.
The back-up alarm relay (3) is also located behind the cab. When the operator moves the shift lever to REVERSE, the EPTC III provides a signal to the back-up alarm relay, which turns ON the back-up alarm.
Another input to the EPTC III is the hoist lever sensor (see Slide No. 124). The main function of the hoist lever sensor is to raise and lower the body, but it is also used to NEUTRALIZE the transmission. If the transmission is in REVERSE when the body is being raised, the hoist lever sensor is used to shift the transmission to NEUTRAL. The
transmission will remain in NEUTRAL until:
1. The hoist lever is moved into the HOLD or FLOAT position; and
2. the shift lever has been cycled into and out of NEUTRAL.
The EPTC III provides a Pulse Width Modulated (PWM) signal to the torque converter lockup solenoid to control the lockup clutch pressure (see Slide No. 33 and 34). When the lockup solenoid is energized, the lockup valve supplies oil to ENGAGE the lockup clutch in the torque converter.
2. Parking/secondary brake switch location
3. Back-up alarm relay ¥ Parking/secondary brakes engaged: - Eliminates anti-hunt timer - Signals parked machine
¥ Hoist lever sensor - Reverse inhibitor
operation
44
2 1
The body up switch (1) is located on the frame near the body pivot pin. This magnetic switch is normally open. When the body is raised, a magnet (2) mounted on the body passes by the switch and causes the switch to close. The resulting ground signal is sent to the EPTC III. This signal is used to limit the top gear into which the transmission will shift. The top gear value is programmable utilizing the ECAP or ET Service Tool. The EPTC III comes from the factory with this value set to FIRST gear. When driving away from a dump site, the transmission will not shift past FIRST gear until the body is down. If the transmission is already above the set limit gear when the body is raised, no limiting action will take place.
The body up switch signal is also used to control the snubber position of the hoist control valve. When the body is being lowered and the magnet passes by the body up switch, the transmission and chassis control (EPTC III) signals the hoist lower solenoid to move the hoist valve spool to the snubber position. In the snubber position, the body float speed is reduced to prevent the body from contacting the frame too hard.
The snubber feature will only function if the body up switch is adjusted correctly.
A diagnostic code occurs if the Electronic Control does not receive a closed (ground) signal from the switch within four hours of operation time or an open signal from the switch within one hour of operation time.
1 Body up switch 2. Magnet
¥ Body up signal used for hoist snubber control
¥ Body up switch must be adjusted
¥ Body up diagnostic code
45 5 2 1 4 3 STEERING SYSTEM
The D-series update trucks use a load sensing, pressure compensated, type steering system which is a substantial change from the steering system used on the D-series pre-update trucks. Very little horsepower is used by the new steering system when the truck is traveling in a straight path. Steering hydraulic horsepower requirements depend on the amount of steering pressure and flow required by the steering cylinders.
Located on the right platform behind the air filters is the steering system tank.
Check the steering system oil level at the sight gauge (1).
The steering system oil filter (2) is located on the side of the steering tank. Steering system oil samples can be taken from the Scheduled Oil
Sampling (S¥O¥S) tap (3) located on top of the steering filter.
The steering system uses a pressure compensated piston type pump. Case drain oil from the steering pump returns to the hydraulic tank through a screen (4) that is part of the fitting installed in the side of the steering tank.
Before removing the cap to add oil to the steering system, depress the pressure release button (5) on the breather to release any remaining pressure from the tank.
¥ Steering system tank
1. Steering system oil level sight gauge 2. Steering system oil
filter
3. Steering system S¥O¥S tap
4. Case drain oil filter screen
5. Steering tank pressure release button and breather ¥ Steering system
requires less horsepower
46
2
1
3
4
The D-series update trucks are equipped with a load sensing, pressure compensated, piston-type pump (1). The steering pump is the third pump mounted in tandem to the engine flywheel housing.
The steering pump operates only when the engine is running and provides the necessary flow of oil for steering system operation. The steering pump contains a load sensing controller with two valves. The high pressure cutoff valve (2) is used as the primary steering system relief valve. To adjust the primary steering system pressure setting (high pressure cutoff), loosen the jam nut and turn the adjusting screw IN to increase the pressure or OUT to decrease the pressure. The primary steering system pressure setting is 23500 ± 350 kPa (3400 ± 50 psi). To verify the new pressure setting, operate the truck in NEUTRAL with the engine at HIGH IDLE and turn the steering wheel hard against the stops to the left or right.
The flow compensator valve (3) is used to adjust the low pressure standby pressure. When the truck is traveling in a straight path, there is virtually no flow or pressure required to the steering cylinders and the pump destrokes to low pressure standby. To adjust the low pressure standby setting, loosen the jam nut and turn the adjusting screw IN to increase the pressure or OUT to decrease the pressure. The low pressure standby setting should be between 2100 and 3600 kPa (300 and 525 psi). To verify the new pressure setting, operate the truck in NEUTRAL with the engine at HIGH IDLE and DO NOT turn the steering wheel.
Load sensing (LS) signal pressure from the Hand Metering Unit (HMU) (see Slide No. 52) enters the load sensing controller at port (4).
1. Steering pump
3. Flow compensator valve
- Low pressure standby
2. High pressure cutoff valve
- Main steering system relief
4. Load sensing signal pressure port
47
1 3
2
Shown is the steering pump in a 775D update truck. The steering pump pulls supply oil from the steering tank through hose (1). Steering oil flows from the pump through hose (2) to the steering valve located on the frame behind the right front suspension cylinder (see Slide No. 50). All piston type pumps produce a small amount of internal leakage for lubrication and cooling. The internal leakage is referred to as case drain oil and flows to the steering tank through hose (3). Before entering the steering tank, the case drain oil flows through a case drain screen (see Slide No. 45).
¥ Steering pump 1. Steering oil supply
hose
2. Steering outlet hose 3. Case drain return
48
¥ Steering pump at minimum flow low pressure standby PUMP OUTPUT LOAD SENSING PRESSURE LOAD SENSING CONTROLLER FLOW COMPENSATOR SWASHPLATE PISTON ACTUATOR PISTON