UNIT INJECTORS, VW Self Study Box

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Service Training
Self-study Programme 352
Unit Injectors with Piezo Valves
Design and Function
Low consumption and excellent performance have
made the rise of the diesel engine unstoppable.
Nevertheless the targets for diesel engines in terms of
emissions, driving comfort and engine performance
are also being raised constantly. Customer
satisfaction, environmental protection and the
fulfilment of legal requirements are always at the
forefront and can only be achieved through continued
development.
The introduction and ongoing development of unit
injectors has created considerable competitive
advantages in the areas of injection pressure,
injection precision and efficiency. In collaboration with
Siemens VDO Automotive AG, we have developed a
unit injector with the same or even greater
advantages. It also allows new flexibility in the
configuration of the pilot, main and secondary
injection phases.
Improved mixture, higher efficiency and lower noise
emissions are the innovative results.
S352_002
NEW
Important
Note
The self-study programme shows the design and
function of new developments.
The contents will not be updated.
For current testing, adjustment and repair
instructions, refer to the relevant service literature.
2
Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
The Piezo Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Nozzle Spring Chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Injection Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Pilot Injection Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Main Injection Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Secondary Injection Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Test Yourself . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3
Introduction
General Information
The unit injector with piezo valve (version:
PPD 1.1) is a further development of the solenoid-type
unit injector. As the name says, the solenoid valve has
been replaced by a faster and more controllable
piezo
valve. Furthermore the mechanical control of the
varying injection pressures within the unit injector has
been improved so that there is no need for a
retraction piston. It has therefore been possible to
reduce the high-pressure volume in favour of
efficiency.
This new type uses the same fitting as the unit injector
with solenoid valve (PDE-P2) and is also secured with
2 screws to avoid additional engine assembly costs.
In future, the new unit injectors will be used in the new
2.0l-125kW 4V TDI engine and later in other
4-valve TDI engines.
S352_005
Volkswagen Mechatronic GmbH & Co. KG has been
founded for production of the unit injector with piezo
valve in collaboration with Siemens VDO Automotive
AG. The new production site is located in Stollberg in
Saxony.
200 employees are currently working on the
production of the new unit injector.
4
Improvements
Control of the injection phases
Pilot injection
Main injection
As the new piezo valve switches approximately four
times faster than the previous solenoid valve, it is now
possible to close the switching valve and open it
again for each injection phase. This allows more
precise control of the injection phases and flexible
control of the injection quantities.
Secondary injection
(if required)
Time
S352_007
Var ia ble
injection intervals
Injection pressure
Pilot injection
Each injection phase has different requirements in
terms of injection pressure. For example, the pilot
injection phase requires a lower injection pressure
and the main injection phase a very high injection
pressure. The extended injection pressure range (130-
2200bar) has allowed a further change in this area.
As a result, the emission levels are improved and
greater performance is possible.
Main injection
Secondary injection
(if required)
Time
S352_008
Minimum
injection pressure
Maximum
injection pressure
Noise emissions
The typical noise emissions occur when TDI engines
are idling above all due to the noise generated by the
unit injectors, not due to the combustion. These noises
are caused by rapid, large-scale pressure changes
within the unit injector that are transmitted to the
engine via the unit injector drive.
The mechanical noises transferred by the drive are
reduced by the smaller pump plunger diameter. The
power required to drive the unit injector is therefore
also lower.
The pressure changes can now be influenced with the
aid of the faster and more precise piezo valve to
reduce the noise.
The piezo valve can be controlled so precisely that the
pressure build-up and pressure reduction of the
individual injection phases can be influenced.
5
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