HT80 데이터 시트보기 (PDF) - Unspecified

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HT80

turbocharger

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HC5A/HX80/82/83/85/HT4B/4C/80 Service Repair Manual

Introduction

Description and Operation of Turbocharger

General Information

A turbocharger is a mechanical device which uses the engine’s exhaust gases to force more air into the engine

cylinders. Hot exhaust gas energy is used to turn a turbine wheel and shaft. At the other end of the shaft is the

compressor impeller (or compressor wheel), which draws in air and forces it into the engine cylinders.

Supplying increased air mass flow to the engine provides improved engine performance, lower exhaust smoke

density, improved operating economy and altitude compensation. The turbocharger has proven to be one of the

most beneficial devices for improving engine performance. It performs its job very well, as long as it is properly

cared for.

Introduction to Turbocharger Matching

The need for optimised matching over the engine speed range

A standard turbocharger can be perfectly matched to only one particular engine condition, eg maximum torque

speed or maximum load speed. At this engine speed, the turbocharger supplies the optimum mass of air to

give the required air/fuel ratio. At other speeds the air/fuel ratio cannot be held at the optimum hence fuel

consumption and emission levels worsen.

Engine emission legislations have forced manufacturers to improve their engine efficiencies, particularly at low

speeds where low air/fuel ratios cause high smoke levels.

The Holset turbocharger is carefully matched to meet the required engine characteristics during application

engineering. It is important that this match is maintained by using only Holset original turbine and compressor

parts.

The importance of correctly servicing the turbocharger

A turbocharger requires accurate assembly at point of manufacture. It is very important to adhere to setting

limits when servicing the turbocharger, as failure to do so could result in turbocharger or engine failure.

Effects of wrong match

Possible consequences if turbocharger boost pressure is too low:-

• Engine runs fuel rich

• Fuel consumption increase

• Exhaust temperature increase

• Smoke levels increase

• Hydrocarbon levels increase

• Risks of failing emissions tests

• High cylinder temperature risks

damage to engine pistons

Possible consequences if turbocharger boost pressure is too high:-

• Engine runs fuel weak (lean)

• Nitrous oxide levels increase

• Excessive boost overspeeds

turbocharger

• Turbocharger bearing failure and

wheel fatigue problems

• Increased cylinder pressure risks damage

to engine head gasket, pistons and valves

• Intercooler load increases causing engine

to overheat, risking piston damage

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