Engine Mechanical - Mechanism & Function (H4DOTC): Other Subaru Outback BR рестайлинг

General

The engine used in this vehicle is of a horizontally opposed, four-cylinder design. This four-stroke-cycle, water-cooled, DOHC turbocharged engine uses a total of 16 valves and its main components are made of aluminum alloy. It is fueled by a multiple fuel injection system.

The engine's major structural and functional features are as follows

Scheme 56

1. The cylinder head forms pent roof combustion chambers, each having a spark plug located at its center and two each of intake and exhaust valves (four valves per cylinder). The intake and exhaust ports are located in a cross-flow arrangement.
2. A single timing belt drives four camshafts on the left and right banks and the water pump on the left bank. Belt tension is automatically adjusted by a belt tension adjuster, eliminating need for manual adjustment.
3. The crankshaft is supported at five journals with high rigidity and strength.
4. The cylinder block is made of cast aluminum, and cast iron cylinder liners are cast in.

AIM OF NEW ENGINE MOUNT SYSTEM

With new Legacy, the new engine mount system has been developed to improve comfort and to install the environment friendly turbo.

Based on the ideal mounting structure of Subaru's unique horizontally opposed engine, "simple system with highly balanced performance as well as great degree of tuning freedom" was considered.

NEW ENGINE MOUNT LAYOUT

The main mounts are positioned at the height of the torque roll axis and is placed horizontally, while the left-to-right span is extended towards both sides of transmission.

Scheme 57

Each mount is made with aluminum in order to achieve both rigidity and light weight.

Scheme 58

Automatic Belt Tension Adjuster

The automatic belt tension adjuster consists of a tensioner unit and a bracket. It maintains the timing belt tension automatically at a specified level to enable the belt to transmit power correctly, reduce operating noise and increase the life of the belt.

The cylinder of the tensioner unit incorporates an adjuster rod, wear ring, plunger spring, return spring, check ball and silicone oil.

The automatic belt tension adjuster gives tension to the belt by a levering action which is produced by the push force of the tensioner unit's adjuster rod. It operates in the process detailed below.

Scheme 59

1. Timing belt tensioning action When the belt becomes slack, the adjuster rod is pushed upward by the return spring. The oil in the reservoir chamber, which is pressurized by the plunger spring to a certain level, pushes open the check ball and flows into the oil pressure chamber to keep the pressure constant. The thrust force F resulting from extension of the adjuster rod applies a counterclockwise torque to the tensioner bracket, which causes the belt tension pulley at its end to turn in the same direction. This applies tensioning pressure Pb to the timing belt.
2. Timing belt tension balancing action When the belt tension pulley is pushed against the timing belt with pressure Pb, reaction force Tb of the timing belt generates the reaction force P at the point on which the adjustor rod force is acting. This force P pushes the adjuster rod until it balances with the sum of the thrust force F and the pressure of the oil in the oil pressure chamber. Therefore, the timing belt tension is kept constant.
3. Over-tension correction action If the tension of the timing belt increases excessively, the force P becomes larger than the thrust force F and silicone oil is returned from the oil pressure chamber to the reservoir chamber little by little until the force P balances again with the thrust force F. Thus the timing belt tension is maintained at the specified level at all times.

Scheme 60

1. The belt cover is made of lightweight, heat resistant synthetic resin molding. It constitutes a totally enclosed housing with its cylinder block mating edges sealed with rubber gaskets. This effectively protects the inside components from dust and liquid.
2. Rubber seals used between the cylinder block and the belt cover effectively reduces transmission of noise and vibration.
3. The front belt cover has a line mark for ignition-timing checking.

Camshaft

The DOHC engine uses four camshafts in all; intake and exhaust camshafts on each of the right and left banks.

The camshafts are of a composite material type using sintered steel for cam lobes and carbon steel for pipe part.

The sintered steel cams are very high in the resistance to wear, which enables the cam lift to be increased. In addition, use of a hollow pipe material contributes to reduction in weight.

Each camshaft is supported at its three journals and held in position by three camshaft caps. The two flanges on each camshaft supports thrust forces to limit the end play of the camshaft within the tolerance.

For DOHC turbo model engines, slots (notches) for variable valve timing position sensors are provided at the intake side.

Scheme 61

Scheme 62

1. The cylinder head is made of low pressure cast aluminum.
2. Each combustion chamber in the cylinder head is a compact, pent roof design. The spark plug is located at the center of the combustion chamber, which contributes to creation of a wide "squish area" for increased combustion efficiency.
3. The two intake and two exhaust valves are arranged on opposite sides for a cross-flow feature.
4. The cylinder head gasket is a metallic gasket consisting of three layers of the stainless steel sheets. The gasket is highly resistant to heat and maintains high level of sealing performance for a long period.

Cylinder Block

1. The cylinder block is made of aluminum die casting. A semi-closed deck structure is used to obtain a higher rigidity to hold the cylinder liners.
2. The cylinder liners are made of cast iron. As they are of a dry type, their outer surfaces are entirely in contact with the cylinder block.
3. The cylinder block supports the crankshaft at its five journals. The journal supporting portions are designed such that sufficient stiffness and quiet operation are ensured.
4. Sintered material is fit in the casting at the #5 journal to achieve further quietness.
5. The oil pump is located in the front center of the cylinder block and the water pump is located at the front of the left-cylinder bank. At the rear of the right-cylinder bank is an oil separator which removes oil mist contained in blow-by gas.

Crankshaft

The crankshaft is supported in the cylinder block at five journals. Each corner formed by a journal or pin and a web is finished by fillet-rolling method, which increases strength of that area. The five crankshaft bearings are made of aluminum alloy and the No. 5 bearing is provided with a flanged metal to support thrust forces.

Scheme 63

Scheme 64

1. The pistons are of a slipper skirt design for reduced weight and friction. The piston is also a thermal flow type whose oil control ring groove is provided with round oil drain holes.
2. The piston pin is offset toward the thrust side (No. 1 and No. 3 downwards, No. 2 and No. 4 upwards) to reduce piston slap noises.
3. The piston head has recesses to prevent interference with the intake and exhaust valves. It also has engraved marks to identify the piston size and the direction of installation. All the pistons are common in their design.
4. Three piston rings are used for each piston; two compression rings and one oil control ring. The top piston ring has inner bevels and the second piston ring has a cut on the bottom outside to reduce oil consumption.

Variable Valve Timing System

This engine has a variable valve timing system, which adjusts the opening and closing timings of the valves optimally by continuously changing the phase angle of the camshaft sprocket relative to the camshaft.

1. The ECM determines the optimal cam angle relative to the crank angle by making reference to the engine speed, vehicle speed, throttle opening and other relevant parameters.
2. Under the control of the ECM, the oil flow control solenoid valve moves its spool to switch the hydraulic passage to/from the advance and retard chambers that are formed in the camshaft sprocket to change continuously the phase angle between the camshaft sprocket and camshaft.

PHASE ANGLE ADVANCES

In response to an advance signal from the ECM, the oil flow control solenoid valve moves its spool such that hydraulic pressure is applied to the advance chamber in the camshaft sprocket. The sprocket is then turned in the direction in which its phase angle advances relative to the camshaft.

Scheme 65

PHASE ANGLE RETARDS

In response to a retard signal from the ECM, the oil flow control solenoid valve moves its spool such that hydraulic pressure is applied to the retard chamber in the camshaft sprocket. The sprocket is then turned in the direction in which its phase angle retards relative to the camshaft.

Scheme 66

A CERTAIN PHASE ANGLE IS RETAINED

When the ECM issues a signal to keep the phase angle unchanged, the oil flow control solenoid valve moves its spool to the position at which the hydraulic pressures to/from both the chambers are blocked. The pressures in the chambers are thus maintained, so the phase angle does not change and the intake valves' opening and closing timings also remain unchanged.

Scheme 67

Sodium-filled Exhaust Valves

Each exhaust valve contains pure sodium in its hollow stem. Sodium has high thermal conductivity.

The entrapped sodium will liquefy at high temperatures and move inside the stem as the valve is operated. Thus the sodium will effectively transfer heat from the valve head to the valve stem, contributing to cooling down the valve head faster.

Scheme 68

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Scheme 70

1. Stretch type belt uses elastic material in its core, resulting in eliminating a tensioner pulley and in a weight reduction.
2. The stretch type belt eliminates the need to adjust tension of the belt.

STRUCTURE

The stretch type belt is built as shown in the following figure providing the elastic feature.

Scheme 71

The dual AVCS (Active Valve Control System) changes the camshaft phase angle in relation to the camshaft sprocket to optimize valve timing of the intake and exhaust valves, improving torque in a low and medium speed range, output performance in a high speed range, emission performance, and fuel efficiency.

1. The ECM determines the best camshaft angle in relation to the crankshaft angle based on engine speed, vehicle speed, throttle angle, and other relevant parameters.
2. Under the control of the ECM, the oil flow control solenoid valve moves its spool to change the phase angle between the camshaft sprocket and camshaft successively by switching the oil path designed between the advance angle chamber and the retard angle chamber.

Scheme 72

ADVANCEMENT IN PHASE ANGLE

The oil flow control solenoid valve applies oil pressure to the advance angle chamber of the camshaft sprocket by moving its spool in response to an advance angle signal from the ECM. As the pressure is applied, the camshaft that is attached to the vanes rotates in the phase angle advance direction in relation to the camshaft sprocket.

Scheme 73

RETARD IN PHASE ANGLE

The exhaust oil flow control solenoid valve applies oil pressure to the retard angle chamber of the camshaft sprocket by moving its spool in response to an retard angle signal from the ECM. As the pressure is applied, the camshaft that is attached to the vanes rotates in the phase angle retard direction in relation to the camshaft sprocket.

Scheme 74

CONSISTENT PHASE ANGLE IS RETAINED

When the ECM commands a signal preventing a change in phase angle, the oil flow control solenoid valve move its spool to block oil pressure that is applied to both chambers. Therefore the oil pressure in the chambers are held and the phase angle is retained.

Scheme 75