DService BulletinVolvo Trucks North AmericaGreensboro, NC USA

Date Group No. Page

11.2006 253 66 1(9)

Trucks

Engine BrakeDesign and Function

D13F

Engine Brake, Design and Function

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This information covers the design and function of the Volvo Engine Brake (VEB) onthe Volvo D13F engine.

Contents• “Engine Brake” page 2

Note: Information is subject to change without notice.Illustrations are used for reference only and can differ slightly from the actual vehiclebeing serviced. However, key components addressed in this information arerepresented as accurately as possible.

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Service Bulletin 11.2006 253 66 2(9)

Design and FunctionEngine BrakeThe engine (compression) brake operates by openingthe exhaust valves during the inlet stroke and just beforebottom dead center (BDC) on the compression stroke,which utilizes the braking force of the compression stroke.This is achieved mechanically with the aid of a camshaftwith an extra braking cam with two lobes, a brake rockerarm and a control valve that regulates the lubricating oilpressure to the rocker shaft. The control valve is locatedon the cylinder head between cylinders three and four.The inlet of the control valve is connected to a lubricatingoil channel in the engine block, and the outlet of the valveis connected to the rocker arm shaft through a tube. If theengine is equipped with an engine brake, this is shownon the front engine identification label, on the left side ofthe rocker cover.

Compared with the earlier VEB system, the mechanicalloads are now shared by two rocker arms, whichmeans that the braking power can be increased withoutincreasing mechanical stress. Using the engine brakeincreases the gas flow through the cylinder which reducesthe thermal stress on the injector spray nozzles. Theincreased gas flow cools the nozzles.

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Service Bulletin 11.2006 253 66 3(9)

System Components

CamshaftOn engines with a compression brake, the camshaft isdesigned with an additional cam at each cylinder foroperation of the VEB. There are now four distinct cams,operating the intake valves, the unit injectors, the exhaustvalves and the VEB, respectively. The lift height of theVEB lobes on the brake cam are very low compared tothat of normal exhaust cam lobes.

As mentioned, the camshaft (1) on an engine with acompression brake has four cams for each cylinder; theinlet cam, injection cam, exhaust cam and braking cam.

The brake cam has two lobes, the charging lobe (3) andthe decompression lobe (4) which lifts the exhaust valvesat the appropriate time to eliminate the power strokedriving power and fully utilize the braking power.

Inside the exhaust valve rocker arm (5) are two pistons,the pump piston (7) and the power piston (14), alongwith a non-return valve (6), another piston (10) and aspring (13). The power piston is located directly abovethe exhaust valve bridge and it is the power piston thatpresses down on the bridge to open the exhaust valves.The pump piston is located directly underneath the enginebrake rocker arm (9) and is what the brake rocker armpushes against. The exhaust rocker arm (5) is shaped sothat the brake rocker arm is positioned above the exhaustrocker arm. When the lubricating oil pressure is sufficient,the clearance between the rocker arms is taken up bythe pump piston. Both pistons in the exhaust rocker armare linked by an oil channel. When the pump piston ispressed down, the oil underneath the piston is pumpedto the power piston. At the same time, the non-returnvalve closes and the higher oil pressure causes the powerpiston to be pressed down to open the exhaust valves.

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Service Bulletin 11.2006 253 66 4(9)

Control ValveThe control valve is mounted on the cylinder head underthe valve cover and is connected to the oil system aheadof the rocker arm shaft. Its purpose is to reduce oilpressure to the rocker arms while the engine is operating.There is always full system oil pressure to the controlvalve inlet. A seal connects the inlet to the lube oil galleryin the cylinder head. Oil pressure to the rocker arm shaftcan be increased by the solenoid valve which is a partof the control valve, from about 100 kPa (14.5 psi) whilethe engine is operating to over 200 kPa (29 psi) duringcompression braking. The control valve regulates theoil pressure to the rocker arm shaft assembly and iscontrolled by the Engine Electronic Control Unit (EECU).1. Locking Ring2. Sleeve3. Valve Slider4. Balance Spring5. Spring Seat with Ball Holder6. Valve Ball7. Cylinder8. Rod9. Solenoid Coil10. Piston11. Electrical Connection12. Pressure Regulation Hole for Flow Control13. Return Hole14. Calibration Hole15. Hole for Oil Flow to Rocker Arm

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NeutralThe VEB valve is shown in its neutral position, whichmeans that the engine is stationary. The solenoid coil (9)is not energized and the valve slider (3) is up against thelocking ring (1).

Normal DrivingDuring normal engine running, the solenoid coil (9) isnot energized. The solenoid valve is in regulation modeand forces oil through the hole (15) to the rocker armswhile allowing oil to flow through the calibration hole (14)and onwards to the return hole (13). This reduces theoil pressure to 100 kPa (14.5 psi), which is enough tolubricate the camshaft bearings and valve rocker arms.

Engine Brake ActivatedWhen the engine is running and the engine brake isactivated, the solenoid coil (9) is energized and thevalve slider (3) is forced to its end position which is fullyopen. The trapped oil acts as a hydraulic lock. Full oilpressure is now delivered to the rocker arm shaft and thecompression brake comes into action.

Engine Brake DeactivatedWhen the engine is running and the engine brake isreleased, the solenoid coil (9) is de-energized. Thehigh pressure oil inside the rocker arm shaft causes thevalve slider (3) to quickly move and open the oil returnconnection (13) so that the oil can drain out. When the oilpressure has fallen to approximately 100 kPa (14.5 psi),the valve slider returns to its regulation position.

Exhaust Rocker ArmsThe exhaust rocker arms on an engine with a compressionbrake are larger than those of a conventional engine.The rocker arm is equipped with a non-return valve anda piston with a pressure-limiting valve. Its purpose is toregulate oil flow during compression braking.

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Service Bulletin 11.2006 253 66 6(9)

Non-Return ValveThe non-return valve, consisting of a piston, spring andball is located in the exhaust rocker arm. When oil fromthe rocker arm shaft is forced into the valve, the springforce and the oil pressure determine movement of thepiston.

When the oil pressure is low, about 100 kPa (14.5 psi),the control valve is in its engine operating position. Duringthis time, the piston will not move out of its rest positionbecause the oil pressure cannot overcome the springforce. The piston pin prevents the ball from seating andthe oil can flow freely through the valve in both directions.

When the control valve begins compression braking, oilpressure to the non-return valve increases. The springforce in the non-return valve is such that when the oilpressure exceeds about 200 kPa (29 psi), it overcomesthe spring force and moves the piston to where it nolonger controls the ball. The spring forces the ball againstits seat and the oil contained above the piston cannotflow past the ball. As a result, high oil pressure is formedabove the piston.

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Rocker Arm PistonThe rocker arm (pump) piston is located in the armoffset, facing upward and aligned with the VEB rockerarm adjustment screw. The purpose of the piston is toeliminate all valve clearance during compression brakingwhich it does by closing the gap between the exhaustrocker arm and the engine brake rocker arm.1. Rocker Arm (Pump) Piston2. Non-Return Valve Location

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Service Bulletin 11.2006 253 66 7(9)

Normal Engine Operation — No Compression BrakingWhile the engine is running, the control valve reduces theoil pressure in the rocker arm shaft to approximately 100kPa (14.5 psi). The non-return valve is kept open by thepiston being pushed forward. The oil channels fill, butthe low pressure is not able to push the pump piston toits upper position. The brake rocker arm does not contactthe exhaust valve rocker arm (5). In this situation, theexhaust valves are not affected by the cam lobes on theengine brake cam.

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Compression BrakingDuring compression braking, the control valve raisesthe oil pressure to system oil pressure in the rocker armshaft. The piston is moved back, but the non-return valveis held open by the oil flow. The higher pressure is ableto push the pump piston to its upper position. When thepump piston is pushed to its upper position, the clearancebetween the engine brake rocker arm and the exhaustvalve rocker arm is taken up.

Oil pressure pushes the pump piston to its upper positionand fills the volume beneath the piston. Once the oil hasfilled the system and no longer flows, the non-return valvecloses. When the brake rocker arm travels over one of thetwo lobes, the pump piston is pushed down and the oilvolume beneath the piston applies pressure to the powerpiston. The piston is pushed down and the exhaust valvesopen. The non-return valve is kept closed by the high oilpressure while the exhaust valves are open.

After the exhaust valves close and the brake rocker armis no longer exerting pressure on the pump piston, theoil that was pushing the power piston down runs backto the pump piston. The system then refills because thenon-return valve opens to allow the amount of oil thatleaked out during the previous cycle to come through.

Deactivation takes place when the oil pressure in therocker shaft falls to approximately 100 kPa (14.5 psi). Thenon-return valve piston opens the non-return valve so thatoil can flow back to the rocker arm shaft. The pump pistonspring forces the pump piston back to its lower positionand the brake rocker arm cannot come into contact withthe pump piston.

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Control SystemThe engine brake is associated with accelerator pedalmovement and is activated when the pedal is completelyreleased based on the selection made with the enginebrake switch on the instrument panel.

The selection made with this switch also regulates enginebraking activated by the cruise control.

Note: The engine brake functions as long as the enginecontrol system has received signals from engine sensorsindicating that the required preconditions for enginebraking have been met. For example, the engine speedmust be greater than 1100 rpm, the vehicle speed mustbe greater than 12 km/h (7.5 mph) and the engine coolanttemperature must be above 70 C (160 F).

SwitchThe compression brake is controlled by a switch locatedon the dash.

A typical switch can have the following selections:

0 Compression brake not engaged1 LO — Half compression braking power2 HI — Full compression braking power

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VEB Induction (Charging) PhaseThe induction phase begins at the end of the intake strokeand continues just before BDC on the compression stroke.

The piston travels downward toward bottom dead centerand the VEB cam charging lobe opens the exhaust valveslong enough to fill the cylinder with exhaust backpressurecaused by the turbocharger.

When the charging lobe closes the exhaust valves,the cylinder has a backpressure at the start of thecompression stroke. This backpressure increasescompression considerably during the compression strokewhich, in turn, creates a powerful braking effect when thepiston moves upward.

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VEB Decompression PhaseAt the end of the compression stroke, as the pistonapproaches top dead center, the engine brake camdecompression lobe opens the exhaust valves andreleases the built-up pressure from the cylinder. Shortlybefore bottom dead center, the ordinary exhaust lobeopens the exhaust valves.

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