VW Polo Teardown (Part 2)

1.2-liter Turbocharged Direct Injection (TDI) diesel engine and suspensions

2014/12/19

Summary

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 As reported earlier in "VW Polo Teardown (Part 1) Engine compartment and driver's seat area" (No. 1354 posted on December 2, 2014), the VW Polo teardown was performed on November 5 and 6, 2014. It was co-organized by the Saitama Industrial Development Corporation and Japan Auto Parts Industries Association. This second report focuses on the 1.2-liter TDI diesel engine and front/rear suspensions.

 The 1.2-liter TDI diesel engine employs a variable nozzle turbocharger with an air-cooled intercooler to deliver high torques from low engine speed ranges. The engine uses common-rail type direct fuel injection, electronically controlled swirl control, electronically controlled exhaust gas recirculation (EGR), and oxidation catalyst with diesel particulate filter (DPF) to meet Euro 5 emission standards for cars in Europe. The VW Polo has strut type suspension in the front and the torsion beam type suspension in the rear. These suspensions have been used for years on the VW Golf and Polo. They are reputed for use on front-wheel drive vehicles in C and smaller segments around the world. The vehicle used for the teardown event was the 2012 British model of the VW Polo fitted with a 1.2-liter diesel engine and not sold in Japan.


Past teardown reports:

Nissan Note (Sep. 2014)
 (Part 1) Major safety technology and advanced
              driver assistance systems

 (Part 2) Drive unit and supercharger

Honda Accord Hybrid (Feb. 2014)
 (Part 1) Sport Hybrid i-MMD PCU and vehicle
              chassis components

 (Part 2) Sport Hybrid i-MMD Battery components
              and electric servo brake system

 (Part 3) Sport Hybrid i-MMD drive unit

Honda Fit Hybrid (Dec. 2013)
 (Part 1) Battery components & brake system
 (Part 2) Engine and transmission

Toyota Aqua (Nov. 2012)
 (Part 1) Part suppliers and battery components
 (Part 2) Hybrid systems behind the 35.4km/liter car

Nissan Leaf
 (Part 1) Benchmarking systems and components (Mar. 2012)
 (Part 2) Main components disassembled (Sep. 2012)
 (Part 3) Body cutaway (Nov. 2012)


Main specifications of VW Polo (2012 British model)

Vehicle VW Polo 2012 British model (right-hand drive)
Dimensions Length: 3,970mm, Width: 1,682mm, Height: 1,462mm, Wheelbase: 2,470mm
Vehicle weight 1,132kg
Fuel efficiency (NEDC) Combined: 26.3, Urban: 21.7, Extra-urban: 30.3 (km/liter)
Diesel engine 1.2-liter inline 3-cylinder (intercooled direct-injection turbo engine),
compliant with Euro 5 emission standard,
DOHC 12-valve, compression ratio: 16.5,
maximum output: 55kW (75PS)/ 4200rpm, maximum torque: 180Nm/ 2000rpm
Transmission 5-speed manual transmission
Price GBP 13,634  (London, U.K.)
Plant name Uitenhage plant, South Africa

Source: Compiled by MarkLines based on "2014 Vehicle Teardown Study Group Data" issued by the Saitama Industrial Development Corporation and Next Generation Automobile Industry



1.2-liter TDI diesel engine

 In order to meet the Euro 5 emission standard, the engine supplies highly pressurized fuel to the common rail for precisely controlled direct injection. It employs swirl, EGR and other controls. It also employs variable nozzle turbocharger and an air-cooled intercooler to generate high torques in low to high engine speed ranges. A balance shaft is used to improve the engine's quietness.

Item Contributing technologies
Low emissions Common rail system and direct fuel injection (solenoid type injectors)
Electronically-controlled swirl control valve
EGR cooler
Electronically-controlled EGR valve
Oxidation catalyst
DPF
High torques in low ranges Variable nozzle turbocharger
Air-cooled intercooler
Silence Balance shaft
High-stiffness cylinder block


Engine system diagram

 

Engine compartment layout and engine assembly

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The common rail is located at the center over the cylinder head cover. Fuel is supplied from the common rail to individual injectors for direct injection into the combustion chamber. The air intake system is located toward the front of the vehicle and the exhaust system to the rear. The turbocharger is located directly behind the engine. The air intake piping connects the parts listed below, from the air intake port to the intake manifold.
* Air intake port on the front end module
* Air cleaner
* Turbocharger
* Intercooler
* Throttle valve
* Intake manifold

 

Fuel line

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Highly pressurized fuel is supplied to the common rail which is connected by piping to the solenoid-type injector for each cylinder. The amount and timing of fuel injection is controlled precisely as the fuel is injected from directly above the combustion chamber. Fuel is injected in several stages so that the combustion pressure peak lasts longer. This helps to reduce fuel consumption and nitrogen oxide (NOx) emissions. It also reduces vibrations and noise. The common rail is supplied by Bosch and the fuel injectors by Delphi.

 

Turbocharger

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* The variable nozzle turbocharger controls the exhaust gas flow rate effectively by altering the nozzle vane angle inside the exhaust gas turbine as the engine speed changes.
* When the exhaust gas flow at low speed and volume, the passage area is reduced to accelerate the exhaust gas flow and the turbine speed. This leads to higher engine response and available torque.
* The passage area is increased at high engine speed to reduce exhaust gas pressure and resistance. This leads to higher engine output.
* The turbocharger is supplied by Honeywell (Garrett).

 

Air intake system

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The air-cooled intercooler is built into the front module and located under the radiator. The amount of fuel injection, swirl control valve and throttle valve are controlled electronically.
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* The intake manifold sends intake air from two ports (primary and secondary ports) to the cylinder head.
* The swirl control valve is located in the secondary port. It regulates the valve opening so that an adequate amount of swirl flow enters the combustion chamber depending on the amount of intake air.
* When the engine output is low, the swirl control valve is closed and air is allowed only from the primary port. A powerful swirl is created inside the combustion chamber to reduce uneven combustion.
* When the engine output is high, the swirl control valve opens up and air is allowed from the secondary port as well. A sufficient amount of air is supplied as needed to deliver high output.
* The intake manifold is made of plastics.
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* The EGR cooler uses coolant to cool a portion of exhaust gas from the exhaust manifold and returns it back to the intake manifold. This lowers the exhaust gas temperature, reduces the NOx emission and increases fuel efficiency.
* A high-pressure type EGR is used. The EGR takes exhaust gas from the exhaust manifold in upstream of the turbocharger. When the supercharging pressure from the turbocharger is high, the pressure inside the intake manifold is higher than in the exhaust manifold. This prevents recirculation of the exhaust gas. The EGR has a check valve function in the EGR control valve to correct this problem.

 

Engine body

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The diesel engine has a cylinder block made of cast iron. The cylinder block has a thicker wall than the aluminum-made cylinder block of recent gasoline engines. The thicker wall design achieves high stiffness to reduce vibrations and rattles. A long-skirt type block is used to fit the central axis of the crankshaft and maintain enough stiffness around the crankshaft.
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* The primary and secondary ports are built into the intake side of the cylinder head. The amount of air entering the secondary port is regulated by the swirl control valve opening in proportion to the engine output.
* The cylinder head has a perfectly flat bottom to achieve a high compression ratio. The combustion chamber is located in the piston side.
* The camshafts are fixed by an integrated frame that includes independent bearing caps to strongly support camshaft bearings.
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The piston has a recess at the top which forms the combustion chamber. The balance shaft is assembled to the lower surface of the cylinder block and located under the crankshaft. It is chain-driven by the crankshaft. The photo shows the assembled balance shaft as seen from under the engine.
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The engine oil filter and the engine oil cooler (water-cooling) are made of plastics and are fitted to the side of the engine block. The flywheel is of the conventional solid type rather than a double-counterweight type. It has an extra thickness to provide sufficient inertia mass and reduce vibrations.

 

Exhaust system

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The oxidation catalyst converter (OCC) and the lean NOx trap (LNT) are located directly behind the turbocharger in the engine compartment. The diesel particulate filter (DPF) is connected by flexible pipe and located under the floor. The turbocharger and the oxidation catalyst are rigid-mounted to the engine with a long overhang. Flexible pipe is used to absorb the amplitude of vibration. This exhaust system mounted on the 2012 model is compliant with Euro 5 emission standard. The 2014 model is equipped with a Euro 6-compliant 1.4L TDI engine, which includes newly added urea-Selective Catalytic Reduction (SCR) system.

 

 

 



Front and rear suspensions

 The VW Polo has the strut type suspension in the front and the torsion beam type suspension in the rear.

 The 1974 first-generation Golf was the first VW model that adopted this combination. These suspensions have been improved and used on the Golf and the Polo since then. The rear suspension on the Golf was changed to the multi-link type starting with the 5th-generation model. The torsion beam type is re-adopted on the lower grades of the 7th-generation Golf. The Golf was not the world's first vehicle that used the specific front and rear suspension combination. However, other automakers started to use the same combination for their front-wheel drive vehicles because of Golf's superb performance and cabin spaciousness. The same combination is used today in many C segment and smaller vehicles.

 

Front suspensions

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The suspension members are fastened at low points of the body side members. They are fastened at sections with small offset and high stiffness. The side member is designed to support large impacts and vibrations from the suspension effectively. This provides efficient handling, riding comfort and quietness without need for reinforcement.
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The driver's seat side of the steering gear is rigid-mounted on the suspension member. This method is chosen to increase steering stiffness and ensure better response and accuracy of steering dynamic performance. The other end of the steering gear (left side of the vehicle) is soft-mounted via rubber insulator to reduce vibrations. The VW Polo has a hydraulic power steering which is driven by an electric pump. The hydraulic power steering has been replaced by an electric power steering starting with the 2014 model.
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* The transverse link is about 390mm long, long enough for a compact class vehicle. This allows for setting adequate suspension geometry and minimizing the twisting of the suspension bushing caused by a wheel stroke. The end effect is the handling and riding comfort.
* The stabilizer is located with the shorter longitudinal distance from the front wheel axle. This reduces the arm length of the stabilizer. The shorter arm length makes it possible to reduce the stabilizer diameter and its weight.
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The suspension ball joint is bolted to the transverse link. The load wheel is fastened by wheel bolts, not by the stud bolts from the axle.

 

Rear suspensions

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The torsion beam suspension is used in an orthodox layout. The torsion beam between the right and left wheels is located toward the front. The jacking motion of either wheel is absorbed by the twisting of the torsion beam which functions as a semi-independent suspension. The lateral force becomes larger with the use of wide tires. Hence, the torsion beam and the trailing arm have closed cross-sections to ensure adequate lateral stiffness.
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The shock absorber is positioned upright inside the tire house that connects to the outer edge of the side member. This layout is chosen to benefit best from the shock absorber performance characteristics. The bumper rubber is made of urethane.
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The body contact end of the coil spring and the suspension bushing mounting are located under the side member where stiffness is high.

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