Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-08-31
2001-12-25
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S341000, C310S346000
Reexamination Certificate
active
06333587
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is directed to improvements in a piezoelectric actuators, in particular for actuating control valves or injection valves in internal combustion engines in motor vehicles, having a piezoelectric actuator body, in particular in the form of a multilayer laminate of stacked layers of piezoelectric material and intervening metal or electrically conductive layers acting as electrodes, in which one of the face ends of the actuator body is fixed on a highly heat-conducting or metal actuator base.
One such piezoelectric actuator is disclosed in German Patent Disclosure DE 196 50 900 A1 of Robert Bosch GmbH.
As is well known, piezoelectric actuators can for instance be used for injection valves of a vehicle motor and in brake systems with anti-lock and traction control systems.
Such injection valves equipped with piezoelectric actuators have an injection nozzle controlled by a tappetlike closure device. An operative face toward the nozzle is disposed on the tappet and is acted upon by the pressure of the fuel supplied to the nozzle; the pressure forces seek to urge the tappet in the opening direction of the closure device. The tappet protrudes with a plungerlike end, whose cross section is larger than the aforementioned operative face, into a control chamber. The pressure effective there seeks to urge the tappet in the closing direction of the closure device. The control chamber communicates with the fuel supply, which is at a high pressure, via an inlet throttle and with a fuel return line that has only low pressure, via an outlet valve that is throttled as a rule or is combined with an outlet throttle. When the outlet valve is closed, a high pressure prevails in the control chamber, by which the tappet is moved in the closing direction of the closure device, counter to the pressure on its operative face toward the nozzle, or is kept in the closing position. Upon opening of the outlet valve, the pressure in the control chamber drops; the magnitude of the drop in pressure is determined by the size of the inlet throttle and by the throttle resistance of the opened outlet valve, or the outlet throttle combined with it. As a result, the pressure in the control chamber decreases when the outlet valve is opened, in such a way that the tappet is moved in the opening direction of the closure device, or held in the open position, by the pressure forces that are operative on its operative face toward the nozzle.
In comparison with electromagnetically actuated injection valves, piezoelectric actuators can switch faster. However, in the design of a piezoelectric actuator, it must be noted that internal losses in the piezoelectric body of the actuator cause lost heat, which has to be dissipated so that the actuator will not overheat. Since the ceramic materials of the piezoelectric ceramic have poorer heat conductivity, the dissipation inside the actuator body, which substantially comprises ceramic material, is unfavorable, especially in long actuators, whose length is greater than their width.
OBJECT OF THE INVENTION
It is therefore the object of the invention to make a piezoelectric actuator, in particular a long one, according to the invention possible in such a way that cooling during its operation can be done without liquid media, that simple mounting of the piezoelectric actuator is possible, and that neither liquid coolants nor special seals are necessary.
SUMMARY OF THE INVENTION
A piezoelectric actuator according to the invention thus avoids overheating caused by the power loss from it, makes do without liquid coolant media and without the seals and coolant paths required for them, so that leakage of such coolants is not possible, and the mounting of the piezoelectric actuator is simplified and the piezoelectric actuator can be produced economically as a result.
The invention resides in the fact that at least one cooling body with good thermal conductivity is joined highly heat-conductively to the side faces of the actuator body and to the actuator base.
In the invention, it is advantageous to be providing that the electric lead lines to the metal or electrically conductive electrodes of the actuator body, embodied as a multi-layer laminate, are extended to the actuator body on only two sides thereof, so that the two other opposed side faces of the actuator body remain free and can be joined highly heat-conductively to the aforementioned cooling body or cooling bodies.
Preferably, the cooling body or cooling bodies comprise metal, and especially preferably copper.
Either two separate cooling bodies, or a single U- shaped cooling body designed such that it is joined on the bottom portion of its U to the face end of the actuator body pointing toward the actuator base, can be joined to the two opposed side faces of the actuator body. This joining is preferably done by an elastic, heat-conductive adhesive between the cooling body and the side faces of the actuator body. A heat-conductive adhesive of this kind comprises a silicone elastomer, for instance, which is optionally filled with an electrically insulating, heat-conductive filler, such as AlN or Al
2
O
3
.
To allow the expansion or shrinkage of the actuator body when the electric voltage is applied, without tearing of the elastic, heat-conductive adhesive, the portions of the cooling body or bodies that border on the side faces of the actuator body can be corrugated, or in other words can have the form of a metal corrugated band.
To utilize the good thermal conductivity of the cooling body or cooling bodies and to dissipate the heat carried by them, the cooling body or cooling bodies are soldered or welded to the actuator base, or alternatively joined to it thermally conductively by means of a silver conductive adhesive. Thus the lost heat generated by the piezoelectric actuator is reliably dissipated from the cooling body to the actuator base, which is a good thermal conductor.
If an actuator body is used whose two face ends are each prestressed by a band spring, and the band springs are located along the side faces not covered by the cooling bodies, spaced apart from the actuator body, it is also recommended that the band springs be used for heat dissipation as well, since they are also fixed to the actuator base. To that end, the interstices between the actuator body and the band springs are filled with heat-conductive elastomer, optionally with the addition of a heat-conductive filler. Furthermore, the electrical terminals of the electrodes of the piezoelectric actuator body can additionally be used for heat dissipation, if these electrical connection lines have an adequately large line cross section.
It should be noted that the shapes mentioned above for the cooling body or bodies are merely examples, and that other expedient shapes can be used, for instance with actuator bodies of round cross section.
Various exemplary embodiments of a piezoelectric actuator designed according to the invention will be described in further detail below in conjunction with the drawings.
REFERENCES:
patent: 3598506 (1971-08-01), O'Neill
patent: 4011474 (1977-03-01), O'Neill
patent: 4752712 (1988-06-01), Tomita et al.
patent: 5239223 (1993-08-01), Miyoshi
patent: 5389851 (1995-02-01), Kimura et al.
patent: 6172445 (2001-01-01), Heinz et al.
patent: 01-027228 (1990-08-01), None
patent: 03-060082 (1991-03-01), None
patent: 05-218519 (1993-08-01), None
patent: 08-172227 (1996-07-01), None
patent: 11-214760 (1999-08-01), None
patent: 2000-022228 (2000-01-01), None
patent: 2000-134958 (2000-05-01), None
Heinz Rudolf
Sugg Bertram
Greigg Ronald E.
Medley Peter
Robert & Bosch GmbH
Tamai Karl
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