Control of the Vehicle and Eco-Driving Techniques - Driver CPC Training Manual
Session 2 Objectives and Training Aim
The primary objective of this session is to provide trainee drivers with the technical characteristics and operation of safety controls necessary for vehicle control, the minimization of wear and tear, and the prevention of dysfunction. Per Directive text, the training covers features of hydraulic vacuum servo brake circuits, the limits of brakes and retarders, combined use of these systems, optimizing speed and gear ratios, braking on downhill stretches, and actions to take in the event of failure. By the end of this session, the trainee will understand the following eight key areas: specific features of hydraulic vacuum servo brake circuits; limits to the use of brakes and retarders; the combined use of brakes and retarders; utilizing speed and gear ratios for slowing; techniques for braking on downhill stretches; action in the event of a breakdown; driver assistance technologies; and the objectives and safety contributions of Commercial Vehicle Roadworthiness Testing (CVRT).
Section A: Braking Systems and General Principles
Section A explores the various braking systems used in large vehicles, their technical components, and physical characteristics. There are four main types of braking systems fitted to trucks and buses. The Service Brake is the principal system operated by a foot control, used to control speed and bring the vehicle to a halt; it often incorporates an Anti-lock Braking System (ABS). The Secondary Brake is provided for use if the service brake fails and may be combined with the footbrake or parking brake; it typically operates on fewer wheels and has reduced performance. The Parking Brake, usually a hand control, is intended for use when the vehicle is stationary and must be set to ‘on’ with the engine switched off when the driver leaves the position. The Endurance Brake, commonly known as a retarder, is found on most modern trucks and buses.
Disc brakes consist of brake pads, a caliper containing a piston or pistons, and a disc mounted to the hub; pads apply pressure to the disc to stop the vehicle. Drum brake systems use brake shoes that apply pressure to the inner surface of a rotating drum. Smaller vehicles often use hydraulic systems where an incompressible fluid transmits force evenly. Larger vehicles, generally in excess of g.v.w., utilize air brakes. Key components of a foundation air brake system include the Air Compressor (pumps air), Air Dryer (removes moisture and contaminants), Air Compressor Governor (controls cut-in/out points), and Air Reservoir Tanks (hold pressurized air). The system also utilizes -Way Protection Valves to split air supply between primary, secondary, ancillary (suspension), and parking brake circuits. Other parts include Drain Valves for moisture relief, Brake Pads (steel with friction lining), Foot Valves, Load Sensing Valves (adjust pressure relative to load), Brake Chambers, Slack Adjusters, Brake S-cams, Return Springs, and Spring Brakes, which often apply the brake while air pressure is used to disengage it.
Antilock Braking System (ABS) and Electronic Braking System (EBS)
The Antilock Braking System (ABS) dates back to the mid-, but widespread application occurred after the late . It is now fitted to over of EU vehicles. Its primary function is to maintain steering control during braking on slippery or icy surfaces by preventing wheels from locking, though it does not necessarily shorten stopping distances. The system consists of three main components: a Rotational Speed Sensor, an Electronic Control Unit (ECU), and a Brake Pressure Modulator. The sensor registers deceleration and informs the ECU if a wheel is about to lock; the ECU then signals the modulator to release pressure. This cycle can occur up to times per second. Drivers should apply maximum force to the pedal in an emergency and not “pump” the brakes, as the system does this automatically. For vehicles without ABS, cadence braking (rhythmically pumping the brakes) is used to maintain control. When drawing trailers, two ABS lamps (marked I and II) should illuminate on the dashboard; if a trailer without ABS is used, “trailer swing” or jack-knifing may occur because trailer wheels lock while tractor wheels do not.
The Electronic Braking System (EBS) enhances ABS by using electronic signals to replace air signals, reducing activation time and stopping distances. In EBS, the brake pedal acts as an electric switch transmitting signals to the ECU, which ensures braking force is optimally distributed between front and rear axles. EBS provides benefits such as faster response and release times (reducing brake drag), monitoring of brake lining wear, balanced braking effort across axles, and integrated ABS/ASR/ESC functions. The EBS cable (ISO) with locking rings is essential for transmitting data between the tractor and trailer. Failure to use this correct cable may cause the trailer to swing out of control, unpredictable full-force braking, increased stopping distances, or load shifts. A compatibility table indicates that a drawing vehicle without ABS/EBS should never be connected to a trailer with EBS, as the combination is unsafe.
Jack-Knife and Trailer Swing Conditions
A ‘Jack-knife’ refers to an accident involving vehicles towing trailers (Classes BE, CE, CE, DE, and DE) where drive wheels lose adhesion. A Power Jack-knife occurs when drive wheels spin excessively, often during overtaking or on roundabouts; it can be recovered by releasing the throttle and correcting steering. A Brake Jack-knife occurs when drive wheels lock under excessive braking, causing the tractor to be pushed to the side; recovery from this is remote. Trailer Swing happens when trailer wheels lock under hard braking while the tractor remains straight, causing the trailer to swing across the road or onto the nearside footpath.
Questions & Discussion: Braking Systems
Q.1: List events that will cause an ABS to activate. A: Heavy braking or braking on slippery/icy surfaces.
Q.2: What action must a driver take if the ABS light illuminates whilst driving? A: Stop as soon as it is safe and seek expert assistance, as the system is registering a fault.
Q.3: List common types of braking systems. A: Service brake, secondary brake, parking brake, and endurance brake.
Q.4: What is the purpose of an air dryer? A: It is a filtration system that removes moisture and contaminants from the compressed air to prevent ice or system failure.
Q.5: How does a load sensing valve work? A: It adjusts the brake pressure relative to the load being carried by the vehicle.
Q.6: List possible consequences of not using the correct EBS cable. A: Trailer swinging out of control, brakes applying on the trailer with full force and then releasing unexpectedly, increased stopping distance, and load shifting causing instability.
Q.7: What is known as cadence braking? A: Pumping the brakes rhythmically to maintain steering control during heavy deceleration in vehicles without ABS.
Q.8: When should an ISO cable be used? A: It should be used at all times between an EBS-equipped tractor and trailer to provide electrical feeds for braking, ABS, and load sensing functions.
Q.9: Is a tractor unit without EBS compatible with a trailer with EBS? A: No, the combination is considered unsafe and not roadworthy.
Q.10: Can a -pin wiring harness be used in place of a -pin harness? A: No, a -pin harness provides ABS but not full EBS functionality.
Q.11: What causes a Power Jack-knife? A: Drive wheels spinning excessively, usually from heavy acceleration on slippery surfaces.
Q.12: What causes a Brake Jack-knife? A: Drive wheels on the tractive unit locking under excessive braking.
Section B: Retardation Devices and Endurance Brakes
Retardation devices allow drivers to control speed without using wheel-mounted service brakes, reducing maintenance costs and preventing brake fade. Brake fade occurs when continuous use causes brakes to over-heat and lose effectiveness. There are four primary types: Exhaust Brakes, Engine Brakes, Retarders (Electromagnetic or Hydrodynamic), and Intarders. The Exhaust Brake uses a ‘Butterfly Valve’ in the exhaust manifold to restrict gas flow and create back pressure; it is most effective at high engine speeds (often marked by a blue zone on the tachometer). The Engine Brake combines an exhaust brake with a compression brake, potentially providing retardation effects in excess of .
Retarders are staged (usually to stages) to increase effect. Electromagnetic Retarders use current passed through magnets to slow a rotor on the driveline. Hydrodynamic Retarders use liquid (hydraulic oil) to achieve the same. Intarders are integrated directly into the transmission and may use transmission oil for cooling. Because these devices absorb vast energy and create high temperatures, they are often linked to the engine cooling system. Drivers must monitor engine temperature during prolonged use. On slippery or icy roads, extreme caution is required as endurance brakes can cause drive wheels to lock.
Questions & Discussion: Retardation Devices
Q.1: Why should a driver use a retardation device? A: To maximize braking effect, reduce maintenance costs, and prevent brake fade on long descents.
Q.2: What are the main types of retardation systems? A: Exhaust brake, engine brake, retarders, and intarders.
Q.3: Where is the ‘Butterfly Valve’ located? A: Inside the engine's exhaust manifold.
Q.4: How does the engine brake improve on the effectiveness of an exhaust brake? A: It combines the exhaust brake with a compression brake, releasing pressurized gas to increase braking effort on the crankshaft.
Q.5: Describe the difference between a retarder and an intarder. A: Retarders are individual units separate from the gearbox acting on the drive shaft; Intarders are integrated into and act directly on the transmission.
Q.6: Which of the following statements is true? A: Statement A: Endurance brakes are most effective at higher engine speeds above the ‘Green’ band.
Q.7: During prolonged use of an Engine Brake or Retarder what must the driver be aware of? A: The engine temperature, as these devices create significant heat.
Q.8: How are endurance braking system temperatures prevented from overheating? A: They are often connected to the standard engine cooling system.
Q.9: In what road conditions must a driver exercise extreme caution when using a retarder? A: Slippery or icy road conditions.
Q.10: Name one of the driveline components that a retarder acts on. A: The drive shaft.
Section C: Road Speed Limiters (RSL)
Road Speed Limiters (RSL) are statutory requirements under EU Directives (originally No , replaced by ) and Irish law (S.I. No. ). Goods vehicles in excess of DGVW are restricted to , and passenger vehicles with more than seats (exclusive of the driver) are restricted to . The device stops fuel delivery to the engine at a pre-set speed. Vehicles must display a plaque detailing "Speed Limiter Fitted," the type approval number, fitter details, the maximum set speed, tyre size, and the date of calibration/sealing. Non-conformance can result in fines up to or imprisonment. Note that while the RSL restricts trucks to , Irish law limits them to on roads other than motorways ( on motorways). Buses are limited to on motorways/dual carriageways and elsewhere ( if carrying standing passengers).
Section D: Driver Assistance Technologies
Modern vehicles use a CAN-bus (Controller Area Network) to allow sensors and ECUs to exchange information instantaneously. Key technologies include: Anti Skid Control (ASC), which stops drive wheels from spinning; Adaptive Cruise Control (ACC), which uses radar to maintain distances; and Predictive Cruise Control (PCC), which uses GPS and topography maps ( to ahead) to reduce fuel consumption by up to . Advanced Emergency Braking Systems (AEBS) became mandatory for new trucks and buses from . Electronic Stability Programme (ESP) monitors dynamics and applies individual wheel brakes to prevent loss of control. Lane Departure Warning (LDW) uses cameras to warn of drifting, while Lane Changing Assistance (LCA) monitors blind spots. Other systems include Tyre Pressure Monitoring Systems (TPMS)—which can prevent a fuel increase and reduction in tyre life—and Silent Mode for low noise zones, which limits noise to . Lift axles and steering axles (positive or self-steer) improve maneuverability and reduce tyre wear.
Section E: Action in the Event of a Breakdown
In the event of a front tyre failure, drivers must hold the wheel firmly, signal left, and reduce speed gradually without harsh braking. For rear failures, stability is less affected but caution is required. Regular maintenance prevents lost wheels; wheel nut indicators are visual aids but not foolproof. To prevent unintended acceleration, drivers should perform a cockpit drill: ensure the parking brake is on, gear is in neutral/park, seat and mirrors are adjusted, and gauges are functioning. In general breakdowns, stop as far left as possible, use hazard lights, and wear hi-visibility clothing. On motorways, do not place a warning triangle; contact Gardaí. In tunnels, switch off the engine, use the emergency phone, and check electronic signs/radio for instructions. Daily walk-around checks (documented) are mandatory to identify safety issues before travel.
Section F: CVRT (Commercial Vehicle Roadworthiness Testing)
The CVRT is an annual roadworthiness test for commercial vehicles over one year old. Light Commercial Vehicles (LCV) include small goods vehicles up to ; Heavy Commercial Vehicles (HCV) include those over , buses, and ambulances. Retests must occur within and . The test covers brakes, lights, wheels/tyres, steering, tachograph, and speed limiters. All HGV operators must register for an online account and make a Self-Declaration to the RSA. Roadside inspections by RSA Transport Officers (checking hours/tachographs/CPC) and Vehicle Inspectors (checking roadworthiness/CRW signals) are conducted with Garda assistance. Failure to produce a CPC card or a valid Certificate of Roadworthiness (CRW) disk is an offense. Since May , CRWs include up to two previous odometer readings to deter clocking. Presenters must provide ID (licence or passport) to receive the CRW.
Appendix Reference Data
Speed limits for HGVs are in built-up areas, on regional/national roads and dual carriageways, and on motorways ( for most, with specific motorway exceptions). Buses not carrying standing passengers are permitted on motorways and dual carriageways. Since , a national weight limit was introduced for six-axle rigid/drawbar combinations, provided they have air suspension, EBS, and specified axle spacing ( between towing vehicle rear-axle and trailer foremost-axle). Manual shut-off taps for trailer brake lines are now prohibited and must be replaced with self-sealing couplings. Penalty points for offenses such as driving a defective vehicle, using a vehicle without a CRW, or mobile phone use usually range from to points on payment, or to on conviction; points lead to automatic disqualification ( points for those on first learner permits/licences since August ).