Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-08-15
2001-12-25
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06333585
ABSTRACT:
The invention relates to a discharge circuit for a capacitive actuator, especially for a piezoelectrically operated fuel injection valve for an internal combustion engine, according to the preamble of claim
1
.
A piezoelectric actuator consists of a plurality of piezoceramic layers which are piled one on the other to form a so-called “stack” which changes its dimensions, especially its length when an electrical voltage is applied, or when mechanical pressure or traction is applied it produces and electric current.
In the use of such a piezoelectric actuator in a fuel injection system an electric voltage is applied to the actuator which is thus electrically charged to inject fuel, while in the uncharged state of the actuator no fuel is injected. It is therefore necessary after an injection to restore the actuators back to the safe state wherein the actuators are uncharged and accordingly no fuel injection takes place. In the previously published German Patent Application 196 52 801.1 a discharge switch is used for this purpose, which is connected parallel to the actuators and short-circuits them to discharge them, so that the electric charge of the actuators is rapidly discharged. It is disadvantageous, however, that the discharge switch for the discharge of the actuators must be actively operated, so that the discharging of the actuators will not take place if the power supply of the control circuit drops out or the control circuit fails to operate.
The invention is thus addressed to the problem of creating a discharge circuit for a capacitive actuator which will permit a reliable discharge of the actuators after an actuation, even if power to the control circuit drops out and even in case of a failure of the control circuit.
The problem is solved, setting out from the above-described, known discharge circuit according to the preamble of claim
1
, by the distinctive features of claim
1
.
The invention includes the general technical teaching of providing in the discharge circuit not only for a conventionally operated discharge, but also for an automatic discharge which operates automatically whenever the operation of the conventional discharge fails, which can be the case, for example, due to a power failure or to a malfunction.
The discharge circuit according to the invention therefore has preferably a discharge switch and a short-circuit switch, the discharge circuit acting only when the short-circuit switch fails due, for example, to a power failure. In this case the discharge switch is automatically activated by the charge present in the actuator and then discharges the actuator except for a residual charge voltage at which the discharge switch again closes automatically and thus ends the discharging action.
The discharge switches are preferably in the form of MOSFET switches, but other kinds of controlled devices can be used in which the electrical resistance can be influenced by a controlling input.
The controlling input of the discharge switch is preferably connected with the actuator to be discharged, so that the voltage decreasing through the actuator operates the discharge switch. If the charge stored in the actuator is sufficiently great, the discharge switch is automatically made conductive, so that the actuator is short-circuited. The charge stored on the actuator then flows away until the voltage dropping across the actuator is no longer sufficient to make the discharge switch conductive, thereby ending the discharge action.
The controlling input of the discharge switch, however, is preferably operated not by the electrical charge in the actuator alone, but it can also be grounded by the control circuit in order to close the discharge switch independently of the charge of the actuator and thus prevent any automatic discharge of the actuator, which is important in the normal operation of the actuator.
In an advantageous variant of the invention, the controlling input of the discharge switch is connected through a voltage divider to the actuator, so that it is not the full voltage of the actuator that is applied to the controlling input of the discharge switch, but only a fraction of this voltage corresponding to the size of the voltage divider. If the voltage divider consists, for example, of a resistor R1=100 k&OHgr; and a resistor R2=50 k&OHgr;, the control voltage amounts to only ⅓ of the charge voltage of the actuator. Such an arrangement with a voltage divider for operating the discharge switch is especially advantageous if the short-circuit switch shorts the actuator through a battery, since then the battery voltage is applied to the actuator and thus also to the controlling input of the discharge switch. The discharge switch is then conductively operated by the battery voltage applied to its controlling input, so that a large current flows through the discharge switch, which can result in the destruction of the discharge switch. The voltage divider is therefore preferably of such a size that the residual discharge voltage is above the battery voltage, so that the battery voltage does not suffice to make the discharge switch conductive.
In another variant of the invention the controlling input of the discharge switch is connected to the actuator through a Zener diode, so that the discharge begins only when the actuator voltage is greater than the sum of the voltage threshold of the discharge switch and the Zener diode voltage. The residual discharge voltage can in this case, therefore, be established by an appropriate sizing of the Zener diode so that the battery voltage does not suffice to make the discharge switch conductive, thereby prevent destruction of the discharge switch by the battery current.
REFERENCES:
patent: 4109174 (1978-08-01), Hodgson
patent: 4732129 (1988-03-01), Takigawa et al.
patent: 4767959 (1988-08-01), Sakikabara et al.
patent: 4947074 (1990-08-01), Suzuki
patent: 5036263 (1991-07-01), Yamada et al.
patent: 5208505 (1993-05-01), Mitsuyasu
patent: 5214340 (1993-05-01), Suzuki
patent: 5543679 (1996-08-01), Morino et al.
patent: 6081061 (2000-06-01), Reineke et al.
patent: 6204591 (2001-03-01), Nariai
patent: 17 63 686 B2 (1972-01-01), None
patent: 196 52 801 C1 (1998-04-01), None
patent: 197 09 717 C1 (1998-09-01), None
patent: 0 464 443 A1 (1992-01-01), None
Freudenberg Hellmut
Gerken Hartmut
Hecker Martin
Hoffmann Christian
Pirkl Richard
Budd Mark O.
Siemens Aktiengesellschaft
LandOfFree
Discharge circuit for a capacitive actuator does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Discharge circuit for a capacitive actuator, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Discharge circuit for a capacitive actuator will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2559865