190103f

Heavy Equipment Technician

Electric BrakeFundamentals and Service

Hydraulic Brake Systems

First Period

ALL RIGHTS RESERVED: © 2010 Her Majesty the Queen in right of Alberta, as represented by the Minister of Advanced Education and Technology. All rights reserved. No part of these materials may be reproduced in any form or by any means without the prior written consent of the Minister of Advanced Education and Technology, Province of Alberta. Canada. Copyright inquiries can be directed to ilm@gov.ab.ca

Table of ContentsObjective One.....................................................................................................................................................2

Introduction.....................................................................................................................................................2Components....................................................................................................................................................3

Objective Two.....................................................................................................................................................8Introduction.....................................................................................................................................................8Electric Brake System Faults.........................................................................................................................8Service Checks and Adjustments..................................................................................................................9

Self-Test.............................................................................................................................................................HSelf-Test Answers............................................................................................................................................13

Electric Brake Fundamentals andService

RationaleWhy is it important for you to learn this skill?

Medium duty trailers may use electric brakes rather than other systems. Simplicity of operation makes an electric brake system convenient for someone like a small gravel truck operator who needs to haul a loader or cement mixer to and from a job site. Being aware of the system components and operation helps you provide quality service in the shop or field.

OutcomeWhen you have completed this module, you will be able to:

Explain service procedures of electric braking systems.

PrerequisitesIn order for you to fully understand the information presented in this module, you must first complete the following modules:

• 190103a Hydraulic Brake System Fundamentals

• 190103b Hydraulic Brake System (Drum and Disc)

• 190103c Hydraulic Brake System Diagnosis and Service

Objectives1. Explain the principle of operation for electric braking systems.2. Identify basic electric braking system failures.

IntroductionElectric braking systems are another method used to slow or stop moving equipment. These are typically used on medium duty trailers in and around construction sites as well as in over-the-road applications.

Electric brakes are not designed to halt the motion of a combined truck and trailer unit. You must ensure that the braking system on the towing vehicle is properly matched to the electric brake system components and weight limitations. The information you need to understand and service electric brakes is presented in this module.

Objective OneWhen you have completed this objectivey you will be able to:

Explain the principle of operation for electric braking systems.

IntroductionElectric brake systems are not designed to withstand loads created by the braking requirements of a combined truck and trailer unit. When considering the effectiveness of an electric brake system, you must also determine if the towing vehicle is equipped to properly activate an electric brake system.

In addition, the service brakes on the towing vehicle must be adequate for the braking needs of the towing vehicle. Figure 1 illustrates a truck/trailer unit in which the truck is equipped with hydraulic brakes while the trailer uses electric brakes.

TrailerConnection

Figure 1 - Hydraulic truck/electric trailer braking system. (Courtesy Dexter Axle Company)

Brakelight Wire

Brake Controller

Breakaway Switch Breakaway

BatteryElectric Brakes

Ground WireBrake

Wire

Variable Resistor

Power Wire

Master Cylinder

Battery

Components

ControllerAn electric trailer brake controller (Figure 2) is a device that supplies power from a vehicle to a trailer's electric brakes. The controller allows the user to adjust output or braking power. A manual override trigger can be used to apply the trailer brakes independent of the vehicle brakes. The pendulum style of controller is activated by the vehicles stopping motion, which causes the pendulum to swing and applies a proportional voltage to the trailer's brakes. When properly adjusted the trailer will decelerate at thesame speed as the tow vehicle. The controller can be adjusted to allow for varied trailer loads and road condition, so that the brakes match the application.

Figure 2 - Electric brake controller.

The electrical connector used between the tow vehicle and the trailer provides power to the electric brakes, the running lights, and the auxiliary breakaway battery. An example of connector wiring circuitry and the end views of two types of connector plugs is shown in Figure 3.

#3 - License Tail& Running Lights

#2 - Electric Brake

#1 - ElectricBrake Ground

White #1 - Common Ground

Green #3 - To Tail Running& License Lights

Clearance &Tail Lights

BatteryCharge

9- Circuit Receptacle

Stop &LH Turn

Clearance &Tail Lights

BatteryCharge

Figure 3 - Trailer connector wiring. (Courtesy Dexter Axle Company)

#4 - Battery Charge

#1 - Common Ground

#9 - Auxiliary Circuit

Red #5-Stop & Left Turn

Black #4 - Battery Charge

Yellow #7-Auxiliary Circuit

Orange #9 - Auxiliary Circuit

Brown #6 - Stop & Right Turn

Blue #2 - Electric Brake

Gray #8 - Auxiliary Circuit

#6 - Stop & Right Turn

7-Circuit Receptacle

Stop & LH Turn

Ground

Stop & RH Turn

Brakes

L Auxiliary

Ground

CAUTIONCheck manufacturer's specifications on plug wiring to preventcomponent damage.

#5 - Stop and Left Turn

#7 - Auxiliary Circuit

Auxiliary

Brakes

Auxiliary Stop & RH Turn

Auxiliary

#9 - Auxiliary Circuit

Breakaway Switch

Breakaway Switch and Auxiliary Breakaway BatteryAn emergency method to halt the trailer is needed in case the trailer breaks free from the towing vehicle. When the trailer uses electric brakes, a breakaway switch and an auxiliary battery are used for this purpose. The breakaway switch is located on the trailer, as is the auxiliary breakaway trailer battery (see Figure 4). A steel cable from this switch is attached to the tow vehicle frame or trailer hitch. If the trailer separates from the tow vehicle, the steel cable releases a pin in the breakaway switch. Power from the auxiliary breakaway battery is immediately directed to the trailer brakes. Full braking will occur.

The charging system on the tow vehicle normally charges the auxiliary breakaway trailer battery through a pin on the trailer electrical connector.

To insure proper function of this device, you must comply with the following installation instructions.• Mount break away device or normally open switch on the hitch of the trailer.• Position the bracket so there is no strain on the lanyard between the trailer and the horizontal plane, as close as possible to centreline of the hitch• Connect wires as shown in the schematic wiring diagram.

CAUTIONMake sure the trailer is disconnected from the tractor before testing the breakaway. Consult the manufacturer's manual before testing the breakaway, to avoid component damage.

Make sure the pin is securely in place each time before using trailer. Keep trailer battery charged at all times to insure safe operation.

Splice to Brake f12 V Wire

N/O Switch Mounted on Trailer Hitch or Frame

Trailer Battery

Cable Fastened to Frame

Brake+12 V Wire

Brake Ground

+12 V From Brake Controller

Ground

Splice to Brake Ground

To Trailer Brakes

Figure 4 - Breakaway switch.

Electric Brake AssemblyThe electric brake assembly, as illustrated in Figure 5, is similar in appearance to a servo type hydraulic drum brake assembly. The brake assembly includes a backing plate, two brake shoes with bonded or riveted linings, return springs, shoe hold-downs and an adjuster assembly, perhaps with a self-adjusting feature. The major difference from hydraulic systems is the method of activation. A horseshoe-shaped actuating lever is attached to an actuating block on one end, and an electromagnet at the other end.

When the operator activates the trailer brakes, either through the tow vehicle service brakes or by manually applying the controller, the electromagnet attempts to clamp itself to the side surface of the internal brake drum. This means the brake drum must have a smooth friction surface for the brake shoes and a smooth machined surface for the magnet.

As the magnet tries to move with the rotating brake drum, it moves the actuating lever. The lever pivots the actuating block which moves the brake shoes. Servo-action and self- energizing action improves braking action.

Secondary Shoe

Actuating Lever (Horseshoe Shaped)

Primary Shoe

Actuating Block

Hold Down

Spring

Electro Magnet

Retractor Spring

Figure 5 - Basic electric brake assembly. (Courtesy Dexter Axle Company)

Adjuster AssemblyAdjuster Spring

Backing Plate

The position of the electromagnet in relation to the drum surface is shown in Figure 6.

ElectromagnetsThe electromagnets are critical to the operation of the brake system. It is important to inspect them for evidence of wear. Figure 7 illustrates the use of a straight edge for this purpose.

When magnets become worn or damaged they must be replaced, preferably in pairs (two on an axle). At the same time, the drum surface should be machined.

BackingPlate

Actuating

Lever

Adjusting

Spring

Adjuster

Link

INormal Wear

Anchor

PostBalanced Return

Spring

Adjuster Pawl

Abnormal Wear (Replace Magnet)

Electromagnet

Figure 6 - Heavy-duty electric brake assembly. (Courtesy Dexter Axle Company)

Straight Edge

Figure 7 - Checking electromagnet surfaces. (Courtesy Dexter Axle Company)

Objective TwoWhen you have completed this objective, you mil be able to:

Identify basic electric braking system failures.

IntroductionAn operator may indicate that the electric trailer brakes on a unit are developing certain problems. Information relating to the tow vehicle and trailer combination is very important. Other problems may become noticeable during an inspection or testing of trailer brakes in the field.

Electric Brake System Faults

Operator Abuse or Misuse

When an operator can activate a trailer braking system independently from the vehicle service brakes, operator abuse of the trailer brakes is possible. When trailer brakes alone are used to slow or stop a vehicle and trailer combination, rapid wear of the trailer brakes can occur. Electric trailer brakes are not designed for this type of braking load.

An operator may use a tow vehicle that is not properly equipped for, or matched to, the electric trailer brake system. As well, the controller or variable resistor may not be adjusted correctly to ensure balanced braking.

Mechanical ComponentsExcessive wear may have worn or severely damaged the magnets, brake shoes or drums, making the system inoperative. The actuating levers or blocks may be damaged or seized. The brake shoe linings and drums may be worn beyond specifications. The wheel bearings may be excessively loose. These types of problems can result in unpredictable braking action.

Electrical ComponentsProblems with electrical connections are the prime causes of for electric brake malfunctions. These include broken, bare, loose, undersized and missing conductors. Temporary splice connectors used to bypass mismatched connectors between the tow vehicle and the trailer brakes can also create electrical problems.

Breakaway system components that are either missing, damaged or inoperative put the trailer and cargo at risk. An auxiliary battery that is not kept fully charged while out of service is a common problem. Corroded battery posts and cables can make the auxiliary battery inoperative.

Service Checks and AdjustmentsBegin the inspection and service by first ensuring that the brake shoes are properly adjusted. You must also consider the condition of the service brakes on the tow vehicle.

Synchronizing Truck and Trailer BrakesSynchronizing the braking of the truck and trailer can only be accomplished through a series of road tests. For best results, follow the instructions provided by the controller manufacturer. Adjustment is critical. If the trailer brakes take too much of the overall braking load, trailer tire skid can occur as well as rapid trailer brake wear.

When the brakes are lightly applied the controller must supply a low voltage to the brake system. As greater pedal pressure occurs more voltage is required. Maximum foot pressure results in full battery voltage to the trailer brake system. During the road tests, gradually adjust the controller to balance truck and trailer braking until the trailer brakes apply slightly ahead of the truck brakes.

This setting is suitable only for the load and road conditions at the time of testing. When either of these conditions change, the process must be repeated to ensure maximum balanced braking.

Electromagnet ActionThe effectiveness of the electromagnets is dependent on the cleanliness and free action of the actuating levers, the actuating blocks and the brake shoes. Binding or restriction of these components results in unpredictable brake action from one side of the axle to the other side. Follow the manufacturer's recommendations regarding lubrication of components. A badly scored magnet or drum surface prevents quick and positive electromagnetic action. Mismatched magnets on the same axle cause uneven braking. Machine or replace parts as recommended by the manufacturer.

Voltage ChecksThe ability of the truck to supply the voltage needs of the trailer system depends on the tow vehicle's battery condition, alternator output and electrical loads.

Measure system voltage at the magnet leads, as shown in Figure 8. The tow vehicle engine must be running. Voltage starts at zero and moves gradually to full battery voltage as the controller lever is slowly moved. A high voltage reading resulting from only a small amount of controller lever movement means a harsh, sudden brake application could occur. Check the specifications carefully.

Amperage ChecksMeasure individual wheel brake amperage readings at the magnet leads, as shown in Figure 9, while the tow vehicle engine is running. Note that wires are disconnected for this test. If a resistor is used in the system it must be set to zero or bypassed for this test. Low amperage readings could indicate poor electrical connections, wire size too small or controller or resistor problems. High amperage readings could indicate shorted magnet coils or bare wires grounding on a metal surface.

Voltmeter

Figure 8 - Circuit testing with a voltmeter. (Courtesy Dexter Axle Company)

Ammeter

Figure 9 - Circuit testing with an ammeter. (Courtesy Dexter Axle Company)

Self-Test1. In an electric brake wheel assembly, which components are similar to those used in

hydraulic drum brake systems?

2. In an electric brake wheel assembly, which components are unique to the electric brake system?

3. What is the function of the electric brake controller?

4. In an emergency situation the electric trailer brakes will be able to provide the total braking requirements needed by the truck and trailer combination.

a) trueb) false

5. When you are using an ammeter to check the trailer brakes, a high amperage draw reading could indicate:

a) an open circuit.b) a wire size too small for the application.c) a short circuit in the electromagnet.d) a broken wire in the circuit.

6. Explain the function of the auxiliary breakaway battery located on the trailer.

7. Provide four (4) reasons why electric brake systems may develop electrical problems between service intervals.

a) ________________________________________________________

b) ______________________________________________________________c) ______________________________________________________________d) ______________________________________________________________

8. When testing an electric brake wheel assembly with a voltmeter, you notice a high voltage when the controller lever is moved very slightly. This indicates a normal condition.

a) trueb) false

9. If you were testing the relationship between controller lever movement and wheel brake voltages, explain when

a) a low voltage reading would be normal.

b) a high voltage reading would be normal.

c) the highest voltage reading would be expected.

10. The truck brakes and the trailer brakes are synchronized by adjusting the brake controller during a series of road tests.

a) trueb) false

190l03fp5.0.docx© 2010, Her Majesty the Queen in right of the Province of Alberta

Self-Test Answers1. brake shoes, return springs and associated hardware

brake drum friction surface provides a similar functionbacking plate and anchor assembly

2. electromagnets, actuating lever and block assemblybrake drum inner machined surface is special

3. Used to synchronize or balance braking action of tow vehicle and trailer. Can bemanually operated as well as by action of brake pedal.

4. b) false; The trailer brakes will never be able to provide total braking required bythe combined tow vehicle and trailer.

5. c) a short circuit in the electromagnet.

6. When a trailer breaks free of the tow vehicle the electrical connection to the truckbattery is lost. The auxiliary breakaway battery provides full available battery powerto the trailer brakes. Maximum braking should occur.

7. Any four (4) of the following are correct.a) looseness of terminals and connectors over timeb) road salt or water contamination and corrosion of electrical components and

connectionsc) broken conductors and damaged trailer connectorsd) corrosion at truck battery terminals and cablese) reduction of alternator outputf) chafed and damaged conductors, insulation worn

8. b) false; Small movement should cause small voltage increase.

9. a) small lever movement - low voltage to brakeb) large lever movement - higher voltage to brakec) full lever movement - maximum voltage to brake

10. a) true

This learning material is the result of a collaborative effort between Alberta Advanced Education and Technology, and the apprenticeship training providers in Alberta.

Grande Prairie Regional College • Keyano CollegeLakeland College • Lethbridge College • Medicine Hat College

Northern Alberta Institute of Technology • Olds College • Red Deer CollegeSouthern Alberta Institute of Technology

The Individual Learning Modules Initiative is committed to continuous updating and is interested in your comments regarding technical accuracy and clarity of presentation. Please visit our web site to register your comment. To view the ongoing discussion, go to the Bulletin Board.

www.tradesecrets.gov.ab.ca/ilm

The Individual Learning Modules Initiative would like to thank the many companies for their contribution and gratefully acknowledges their valuable input. A complete listing of contributors can be found at our web site.

Module Number 190103f

Version 5.0