Modern Truck Electrical Systems

Copyright © 2014 Delmar, Cengage Learning

Modern Truck Electrical Systems

Instructor Name: (Your Name)

15CHAPTER


Learning Objectives

• Explain the basic functionality of an electronically controlled automatic transmission

• Discuss the functionality of an automated manual transmission

• Define the terms PRNDL, NSBU, VIM, chuff test, differential braking, and ABS modulator

• Explain how an air ABS system and traction control operate


Learning Objectives (continued)• Test an ABS wheel sensor circuit• Describe how a fault detected by a trailer

ABS ECU causes the trailer ABS warning lamp to illuminate in the truck instrument panel

• Discuss the operation of an Eaton electric hybrid system

• Discuss the difference between a series hybrid and parallel hybrid truck

• List the steps to troubleshoot a wiring problem with the J1939 data link


Allison World Transmission

• Currently the most common in North America• Full authority control; transmission will only shift

when commanded by the transmission ECU• WTEC – World Transmission Electronic

Controls• Electronic shift control; no hard line to the

transmission• Transmission ECU can use information from the

J1708/1587 & J1939 data link


World Transmission Controls

Figure 15-2 World transmission components.


Allison WT Electronic Shift Selectors

Figure 15-3 Allison WT electronic shift selectors.


Allison World Transmission (continued)

• WT Transmissions uses 3 reluctance type speed sensors: engine, turbine, and tail shaft

• There are two types of solenoids used: normally open and normally closed

• Allison Diagnostic Optimized Connection (DOCTM) troubleshooting software

• WT Generation 4 can display diagnostic trouble codes on digital display


WT Speed Sensors

Figure 15-4 WT speed sensors.


Figure 15-6 WT normally closed solenoid. Figure 15-7 WT normally open solenoid.

WT Solenoids


WT Hydraulic Schematic – Third Range Setting

Figure 15-9 WT hydraulic schematic – third range attained.


Automated Manual Transmissions

• AMT – Automated manual transmission• Manual transmission with automatic

control• One or two pedal system• Eaton Fuller is currently the most common• Driver interface and transmission ECU

communicate via private J1939 network called the EPL


Eaton Driver Interface

Figure 15-11 Eaton driver interface.


Automated Manual Transmissions (continued)

• Primary inputs to ECU are from three transmission mounted speed sensors and rail select and gear select position sensors

• Eaton AutoShift – Three pedal system• Eaton UltraShift – Two pedal system• Eaton ServiceRanger™ is a PC-based

EST used to diagnose an Eaton AMT


Eaton AMT Speed Sensors

Figure 15-12 Eaton AMT speed sensors.


Gear and Rail Select Position Sensors

Figure 15-13 Gear and rail select position sensors.


Antilock Brake System

• Reluctance-type speed sensors on both front and at least two rear wheels on a tandem axle tractor

• Typical ABS tone wheel has 100 teeth• The ABS ECU measures the frequency of the

waveform produced• ABS modulators control air flow to service brake

chambers to prevent brake lock up• Modulators are designed to revert to non-ABS in

the event of failure


ABS Schematic For Straight Truck

Figure 15-15 ABS schematic for straight truck.


Four Channel ABS With ATC

Figure 15-18 Four-channel ABS with ATC.


ABS Modulator with Integral Relay Valve

Figure 15-19 Air ABS brake modulator with integral relay valve.


Antilock Brake System (continued)

• A chuff test is a brief actuation of the modulation coil at start up

• A drive axle event can trigger a signal to the transmission and engine ECU or a signal on the J1939 data link

• Automatic traction control (ATC) will limit wheel slip under acceleration


WARNING

Differential braking can cause a truck to drive off a jack stand if only one drive axle wheel end is lifted off the ground and the driveline is operated. Traction control must also be disabled if truck is operated on a dyno.


Advanced ABS Features

• Steering wheel angle sensor• Air application pressure sensor• Air suspension pressure sensor • Yaw rate sensor• Lateral acceleration sensor• VORAD – Vehicle onboard radar


Advanced Air ABS Sensors

Figure 15-24 Advanced air ABS sensors.


ABS Warning Lamp

• FMVSS 121 requires an amber-colored ABS warning lamp in clear view of the operator

• Three methods of controlling ABS warning lamp:1) Direct control by ECU2) Control by fail safe relay3) Controlled by J1939 data link with a J1939

multiplexed IPC


Direct-Wired ABS Warning Lamp

Figure 15-27 Direct-wired ABS warning lamp.


Fail Safe Relay Used to Control ABS Warning Lamp

Figure 15-27 Direct-wired ABS warning lamp.


Diagnosing ABS Systems

• Most Meritor-Wabco ABS ECS use warning lamp to retrieve DTCs

• Some Bendix systems use a blink code switch

• Bendix remote diagnostic unit (RDU) can be plugged into the 9-pin diagnostic connector


Blink Codes Displayed Using ABS Warning Lamp

Figure 15-30 Blink codes displayed using ABS warning lamp flash sequence.


Bendix RDU

Figure 15-31 Bendix remote diagnostic unit (RDU).


Trailer ABS

• All trailers built after March 1, 1989 are required to have ABS

• Power to the trailer ABS is provided through pin 7 of the J560 trailer socket

• Trucks and trailer built after March 1, 2001 are required to have a trailer ABS warning lamp on ICP of truck

• PLC – Power line carrier


PLC Signal Generated by Trailer ABS ECU

Figure 15-32 Power line carrier (PLC) signal generated by trailer ABS ECU.


Tech Tip

A problem with the trailer ABS power supply circuit may cause the trailer ABS warning lamps to flash when the service or trailer brakes are applied.


Hydraulic ABS Systems

• Required on all trucks built after March 1, 1999

• Functions similar to air ABS systems • Hydraulic fluid is returned to the reservoir

during an ABS event


Hydraulic ABS System

Figure 15-33 Hydraulic ABS system.


Hydraulic ABS Disc Brake Rotor

Figure 15-34 Hydraulic ABS disc brake rotor with cast tone wheel.


Hydraulic Power Brakes

• Uses two electric pump motors to charge gas filled accumulators with brake fluid under pressure

• HCU – Hydraulic compact unit• The HPB system is connected to the J1939 data

link• Accumulator pressure is maintained at

approximately 2320 psi• If pressure drops below 1523 a low pressure lamp

illuminates


WARNING

Never attempt to drive a vehicle with HPB that has the brake warning lamp illuminated. You may not be able to stop the vehicle.


Hydraulic Power Brakes (continued)

• Ignition off, vehicle not moving, service brakes released, unit will go into sleep mode

• If ignition is turned on or brake pressed, system will wake and control pump motors as needed

• SAHR – Spring-applied hydraulically released parking brake

• Meritor-WABCO Toolbox™ is the EST used to diagnose the HPB system


WABCO HPB SAHR Park Brake

Figure 15-35 Wabco HPB spring-apply hydraulic-release (SAHR) park brake.


Twisted Wiring for ABS Speed Sensors and Modulators

Figure 15-36 Twisted wiring for ABS wheel-speed sensors and modulators.


Electronic On Board Data Reader (EOBR)

Figure 15-37 Electronic on-board recorder (EOBR).


Satellite Link Between Truck/Trailer and Fleet Management

Figure 15-38 Satellite link between truck/trailer and fleet management.


Hybrid Electric Trucks

• Parallel System – Internal combustion engine is supplemented by electric motor

• Series System – Truck is propelled only by electric motor and internal combustion engine charges batteries

• A three-phase motor/generator is used to propel vehicle and charge batteries

• A battery bank with up to 340V DC power and inverter producing up to 500V AC


WARNING

Lethal voltage levels are used in hybrid electric systems. You should not attempt to work on the high-voltage components of an HEV until you have had proper training and have all of the proper protective equipment including insulated gloves. High-voltage wiring is identified by orange-colored insulation. Never splice into this high-voltage wiring.


Online Service Information Systems (SYS)

• Caterpillar Service Information System• Cummins QuickServe Online• Mack Trucks Electrical Information System• Navistar Service Information• Paccar DAVIE and ServiceNet• Volvo IMPACT


J1939 Bus Type Network

Figure 15-42 J1939 bus-type network.


J1939 Data Link

Figure 15-43 J1939 data link modeled as a pair of wires with two 120Ω resistors in parallel.


Damaged J1939

Figure 15-44 Damaged J1939 data link will act as two separate networks.


Summary

• Allison electronic automatic transmissions use three variable reluctance speed sensors to measure engine, turbine, and output speeds. The transmission ECU controls a series of normally open and closed solenoids using PWM. These solenoids control the flow of transmission fluid to apply clutches for specific ranges.


Summary (continued)

• Eaton automated manual transmissions (AMTs) use two electric motors to activate the shift mechanism. AMTs are divided into two- and three-pedal systems, indicating if the clutch is controlled by the operator or the transmission ECU. Inputs to the ECU include three speed sensors and rail and gear select positions.


Summary (continued)• Air ABS systems use wheel-speed sensors to

determine if a wheel lock up is occurring or is about to occur. The ABS ECU then controls modulators to block air flowing to the brake chambers and exhaust air out of the brake chambers to prevent wheel lock up.

• Testing wheel-speed sensors and the associated circuits may involve raising each wheel end and rotating the wheel by hand while watching for the amplitude of the AC voltage that is generated by the variable reluctance sensor.


Summary (continued)

• Trailer air ABS ECUs on modern trucks use the power line carrier technique to signal the truck or tractor ABS ECS that a trailer ABS fault is active. A variable frequency signal is placed onto the 12V power supply by the trailer ABS ECU. This signal is detected by the truck ABS ECU in its 12V power supply, causing the truck ABS ECU to energize the trailer ABS warning lamp on the truck’s instrument panel.


Summary (continued)• Electronic on-board recorders (EOBRs) are electronic

truck operator log books designed to record the hours of service (HOS) for each truck operator.

• In a parallel hybrid system, a diesel engine and electric motor/generator are coupled together. The electric motor is used to supplement the diesel engine. In a series hybrid system, the electric motor alone is used to propel and the engine is used as a generator for the electric motor. A dual-mode hybrid system acts as a series hybrid system during acceleration and a parallel hybrid system at higher speeds.

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Modern Truck Electrical Systems