Fluid sprinkling – spraying – and diffusing – With means to vibrate or jiggle discharge – By electric transducer
Reexamination Certificate
2002-06-12
2003-07-08
Walczak, David J. (Department: 3751)
Fluid sprinkling, spraying, and diffusing
With means to vibrate or jiggle discharge
By electric transducer
C239S585100, C239S533700, C239S584000, C251S057000
Reexamination Certificate
active
06588678
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an injection system, having a piezoelectric adjuster, a hydraulic booster and a control valve, wherein in continuous operation of the injection system, the stroke of the piezoelectric adjuster can be transmitted to the control valve via a hydraulic medium in the hydraulic booster. The invention also relates to a method for operating an injection system.
2. Description of the Prior Art
An injection system, hereinafter also called a piezoelectric injector, as generically defined above, is used in particular in Diesel storage-type injection systems. In storage-type injection, also known as common rail injection, the pressure generation and the injection are decoupled from one another. The injection pressure of about 120 to 1600 bar is generated independently of the engine rpm and the injection quantity and is available in the rail—that is, the fuel reservoir—for the injection. The instant of injection and the injection quantity are calculated in the electronic control unit and converted by the injector at each engine cylinder. The object of the injector is to adjust the onset of injection and the injection quantity.
Besides triggering the injector via a piezoelectric element, triggering the injector via a magnet valve is also known.
While with magnet valves, adequately long valve strokes for use of the magnet valve as a control valve can be generated, controlling an injector with a piezoelectric element requires that additional measures be taken. This is because with a piezoelectric element, only a very tiny stroke can be generated, which is a fraction in the range of only thousandths of the length of the piezoelectric element. For actuation of the adjusting valve in continuous operation of the injector, this tiny stroke requires conversion. A hydraulic booster, for instance, is used for that purpose.
In
FIG. 3
, a control valve of the prior art for a piezoelectric adjuster is shown. The stroke of a piezoelectric element, not shown, is transmitted to a control valve
110
via a hydraulic booster. In this way, a valve stroke
112
is made available that suffices to move the control valve
110
back and forth between a first valve seat
114
and a second valve seat
116
. The valve control chamber
118
is disposed below the control valve
110
. This valve control chamber
118
is adjoined, via an inflow throttle
120
, by a fuel inlet
122
. On the other side, via an outflow throttle
124
, the control chamber
118
communicates with the control valve
110
. A thrust rod
126
reaches into the control chamber
118
, and by way of this thrust rod the force for the injection nozzle, not shown, is transmitted.
The operating principle of the special piezoelectric injector, equipped with two valve seats
114
,
116
, in accordance with the prior art will now be explained in conjunction with FIG.
3
. In the state shown, the control valve
110
is seated in the first valve seat
114
. At this instant, via the fuel inlet
122
, which communicates with the common rail, and the inflow throttle
120
, a pressure can build up in the control chamber
118
. If a voltage is now delivered to the piezoelectric element, not shown, the piezoelectric element generates a valve stroke, so that the control valve
110
assumes a middle position between the valve seat
114
and the valve seat
116
. The pressure in the control chamber
118
is thus briefly reduced, so that the thrust rod, which is driven by a spring, not shown, in the direction of the control chamber can enter farther into the control chamber. An injection nozzle, not shown, is consequently briefly opened, in the present case for the sake of preinjection. As soon as the control valve
110
reaches the second valve seat
116
, the high pressure made available by the common rail via the inflow throttle
120
can again build up in the control chamber
118
. The thrust rod
126
is consequently forced out of the control chamber
118
, and the injection nozzle closes. In the reverse motion of the control valve from the second valve seat
116
to the first valve seat
114
, which follows an appropriate triggering of the piezoelectric element, a middle position is again assumed, which is however now utilized for the sake of the main injection.
The inflow throttle
120
and the outflow throttle
124
serve on the one hand, via their relative flow quantities, to determine the opening behavior of the nozzle needle. The outflow throttle
124
also serves to return a leakage quantity of fuel from the valve control chamber
118
into the hollow chamber located above it and, via the fuel return
128
, to a fuel tank. The inflow throttle
120
prevents the pressure in the control chamber
118
from being immediately compensated for fully and adapting to the high pressure in the common rail, because only a pressure drop makes the opening of the nozzle needle possible, by retraction of the thrust rod
126
.
In the present special case in the prior art shown in
FIG. 3
, a control valve
110
is shown with two valve seats
114
,
116
. However, the general principles of valve control can also be accomplished with only a single valve seat. For the same injection frequency, the piezoelectric element must then be excited with voltage pulses at twice the frequency, for instance.
A common feature of the systems in the prior art, one of which is shown in
FIG. 3
, is that both in the starting event and in operation, there must be a system pressure in the injector. This makes demands in terms of the capacity of the high-pressure pump of the common rail system, since the leakage quantity for assuring the supply of system pressure must be furnished by the high-pressure pump. Other disadvantages arise in conjunction with the incident leakage quantities, since these quantities must be removed from the system at high pressure. In addition, the systems in the prior art are dependent on environmental factors, since an engine turned off at high temperatures, for example, vaporizes the fuel out of the coupler chamber of the control valve, which makes additional demands of the pressure supply upon restarting of the system.
SUMMARY OF THE INVENTION
The injection system of the invention builds on the prior art in an advantageous way in that the piezoelectric adjuster and the components of the hydraulic booster are disposed relative to the control valve such that at least a portion of the stroke of the piezoelectric adjuster can be transmitted directly to the control valve. The control valve can thus open on the basis of the stroke of the piezoelectric element without there having already been a system pressure present. As soon as the control valve opens as a result of the direct action of the piezoelectric adjuster, the pressure present in the common rail fills the system region with fuel, and the piezoelectric injector is ready for the continuous operation. The system can accordingly assure the supply of a system pressure at anytime, regardless of such environmental factors as high heat or a relatively long period in which the engine is not in operation. It is surprising that a direct or in other words nonhydraulic transmission of force from the piezoelectric element to the control valve is possible at different temperatures, since the piezoelectric element does change its length as a function of the temperature. In the systems of the prior art, this was not a fundamental problem because a force transmission took place only hydraulically in any case. Now, however, since the relative position between the piezoelectric element and the control valve is crucial, the temperature dependency of the length of the piezoelectric element appears to present a fundamental problem. Within the scope of the invention, however, it was discovered that the change in length of the piezoelectric element can be at least nearly compensated for precisely as a result of the change in the stroke capacity. This is due to the following facts. With regard to its longitudinal expansion, the piezoelectric element has a nega
Flynn Amanda
Greigg Ronald E.
Robert & Bosch GmbH
Walczak David J.
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