Internal-combustion engines – Charge forming device – With fuel pump
Reexamination Certificate
2000-08-18
2001-12-11
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
With fuel pump
Reexamination Certificate
active
06328019
ABSTRACT:
BACKGROUND INFORMATION
The present invention concerns a device directed to a continuous control of a piezoelectric actuator for fuel injection systems.
To control fuel injection valves for internal combustion engines, previously proposed systems, as described in German Published Patent Application No. 195 31 652, use piezoelectric actuators whose piezo stack, that changes in length in response to an electrical control voltage, serves to actuate the valve element. With piezoelectric actuators, a pronounced hysteresis effect arise between the electrical voltage applied to the piezo stack that receives the electrical charge and the generated elongation of the piezo stack during the operating cycle. Due to this dielectric hysteresis, the high precision in the set movements of the fuel injection valves from piezoelectric actuators cannot be maintained.
Furthermore, it is difficult to continuous control the actuators due to alternating conditions of use and operation of i.c. engines such as load and temperature, and to the ageing of the piezo stack.
SUMMARY OF THE INVENTION
It is an object of the present invention to create a piezoelectric actuator to control valves of i.c. engines with a constant actuator function under different conditions of use and operation.
This object is solved according to the invention by the features of patent claim
1
. Developments of the invention are found in the subclaims.
The hysteresis only arises between the received electrical charge and an electrical voltage that cause the charge to be received.
The elongation curve S(Q)—where S stands for the relative elongation of the ceramic and Q stands for the electrical charge received by the ceramic—can be expressed by a mathematical function that follows a quadratic equation S=a (Q−Q
o
)
2
.
Given these facts, a procedure is suggested according to the present invention that advantageously keeps constant the thrust function of a piezoelectric actuator by precisely controlling the receipt of the electrical charge, The influence of external mechanical and/or thermal quantities on the actuator such as the fuel pressure and engine temperature are advantageously eliminated according to the present invention since they are detected via sensors and are entered as parameters in the actuator control. Such sensors are common in modern engine control. The ageing of the piezo actuator can be compensated by measuring the operating hours with sensors.
REFERENCES:
patent: 4732129 (1988-03-01), Masahiro et al.
patent: 4750706 (1988-06-01), Schlagmuller
patent: 6236190 (2001-05-01), Hoffman et al.
patent: 195 31 652 (1977-05-01), None
patent: 196 44 521 (1998-04-01), None
patent: 197 14 610 (1998-10-01), None
patent: 0 856 654 (1998-08-01), None
patent: WO 94/18449 (1994-08-01), None
Daimler-Chrysler AG
Kenyon & Kenyon
Moulis Thomas N.
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