Data processing: measuring – calibrating – or testing – Calibration or correction system – Circuit tuning
Reexamination Certificate
2001-04-02
2004-11-30
Nghiem, Michael (Department: 2863)
Data processing: measuring, calibrating, or testing
Calibration or correction system
Circuit tuning
Reexamination Certificate
active
06826504
ABSTRACT:
The present invention concerns a method and an apparatus for controlling system parameters, in particular for controlling the voltage applied to piezoelectric elements within a circuit for charging and discharging piezoelectric elements.
Control systems generally comprise a control unit typically but not necessarily comprising a central processing unit (CPU), at least one controlled element and utilization means which transform CPU signals if and as necessary and apply them to the controlled element. For this purpose, the CPU and the utilization means need to be connected to each other by communication means such as a bus system. Moreover, external data may need to be communicated to the CPU and/or the utilization means on a corresponding way.
As an example, piezoelectric elements may be used as actuators in fuel injection nozzles (in particular in so-called common rail injectors) of an internal combustion engine. The use of piezoelectric elements with double acting, double seat valves to control corresponding injection needles in a fuel injection system is shown in German patent applications DE 197 42 073 A1 and DE 197 29 844 A1, which are incorporated by reference herein in their entirety.
Fuel injection systems using piezoelectric actuators are characterized by the fact that, to a first approximation, piezoelectric actuators exhibit a proportional relationship between applied voltage and the linear expansion. In a fuel injection nozzle, for example, implemented as a double acting, double seat valve to control the linear stroke of a needle for fuel injection into a cylinder of an internal combustion engine, the amount of fuel injected into a corresponding cylinder is a function of the time the valve is open, and in the case of the use of a piezoelectric element, the activation voltage applied to the piezoelectric element.
FIG. 5
is a schematic representation of a fuel injection system using a piezoelectric element
2010
as an actuator. Referring to
FIG. 5
, the piezoelectric element
2010
is electrically energized to expand and contract in response to a given activation voltage. The piezoelectric element
2010
is coupled to a piston
2015
. In the expanded state, the piezoelectric element
2010
causes the piston
2015
to protrude into a hydraulic adapter
2020
which contains a hydraulic fluid, for example fuel. As a result of the piezoelectric element's expansion, a double acting control valve
2025
is hydraulically pushed away from hydraulic adapter
2020
and the valve plug
2035
is extended away from a first closed position
2040
. The combination of double acting control valve
2025
and hollow bore
2050
is often referred to as double acting, double seat valve for the reason that when piezoelectric element
2010
is in an unexcited state, the double acting control valve
2025
rests in its first closed position
2040
. On the other hand, when the piezoelectric element
2010
is fully extended, it rests in its second closed position
2030
. The later position of valve plug
2035
is schematically represented with ghost lines in FIG.
5
.
FIGS. 6
a
,
6
b
, and
6
c
show the double acting control valve in the first closed position, open position, and in the second closed position respectively.
The fuel injection system comprises an injection needle
2070
allowing for injection of fuel from a pressurized fuel supply line
2060
into the cylinder (not shown). When the piezoelectric element
2010
is unexcited or when it is fully extended, the double acting control valve
2025
rests respectively in its first closed position
2040
or in its second closed position
2030
, as shown in
FIGS. 6
a
and
6
c
, respectively. In either case, the hydraulic rail pressure maintains injection needle
2070
at a closed position. Thus, the fuel mixture does not enter into the cylinder (not shown). Conversely, when the piezoelectric element
2010
is excited such that double acting control valve
2025
is in the so-called mid-position with respect to the hollow bore
2050
, then there is a pressure drop in the pressurized fuel supply line
2060
. This situation is illustrated in
FIG. 6
b
. This pressure drop results in a pressure differential in the pressurized fuel supply line
2060
between the top and the bottom of the injection needle
2070
so that the injection needle
2070
is lifted allowing for fuel injection into the cylinder (not shown).
Within the example of
FIG. 7
, the use of having two open positions resp. two voltages corresponding to open positions is as follows: Generally, it may be desired that the first and second open position of the valve plug
2035
within the hollow bore
2050
are equal to each other. However, in order to achieve this aim it has to be taken into account, that in one case the open position is approached from the first or bottom closed position and in the other case from the second or top closed position. While recalling
FIG. 6
a
through
FIG. 6
c
, this means, that in the first case the valve plug
2035
is moved against a force applied by the pressure p
rail
in the pressurized fuel supply line
2060
and in the second case it is moved with the force applied by the pressure p
rail
in the pressurized fuel supply line
2060
. Hence, in the first case a larger force is to be applied than in the second case. Since the valve
2025
is driven by the piezoelectric element
2010
, this again means, that in the first case a higher voltage is required than in the second case in order to obtain the desired expansion of the piezoelectric element and hence the desired open position of the valve plug
2035
.
In addition, in the above example, the movement of the double-acting valve and hence of the injector needle is influenced by any changes of the occurring pressure p
rail
, since so far it is only taken into account, that different voltages are required in order to similarly position the valve plug
2035
while moving it against and with the pressure p
rail
. However, so far it is not taken into account what further modifications are required in order to deal with changing pressures p
rail
which occur in practice. In order to nevertheless control the movement of the injector needle with high precision respectively to control the corresponding amount of injected fuel with high precision these influences have to be taken into account. Hence, the occurring rail pressures are measured by measuring means and the target voltages which are to be applied to the piezoelectric elements for desired actions are modified in a corresponding way. As a result, a feedback system is implemented, in which rail pressures p
rail
are measured by measuring means, the measured values are communicated to the control unit, corresponding target voltages for the piezoelectric actuators are calculated within the control unit (for example by means of adding an offset to a more general target voltage) and are communicated from the control unit to an utilization unit, for example an activation IC, from which they are applied to the piezoelectric actuators.
It is to be understood, that the above examples are introduced only in order to allow a better understanding of the inventive approach However, any further environment, particularly having a single-acting control valve or using a double-acting control valve in a single acting mode (i.e. temporarily or permanently not using the second or top closed position of the valve plug
2035
, for example due to very cold temperatures which may cause difficulties to a full expansion of the piezoelectric element
2010
) may be an environment for the present invention without any limitations. Furthermore, any other driving profile than the one mentioned above may be used. Moreover, control systems having a totally different technical background may be an environment for the present invention as well.
In the control system of above examples as well as in other control systems, there is a need for obtaining a good correspondence of the target values and the obtained values of each control procedure in order to achieve a high p
Mrosik Matthias
Pitzal Volker
Rueger Johannes-Jörg
Schulz Udo
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