Encapsulating arrangement for an electrical component
The invention provides an encapsulating arrangement for an electrical component comprising first and second insulating layers and an electrically charged conductive layer, preferably in the form of a metal foil, intermediate the first and second insulating layers, and arranged to prevent the passage of ionic species across the encapsulating arrangement. The encapsulating arrangement of the invention has particular application to piezoelectric actuator arrangements for fuel injectors of internal combustion engines.
1 . An encapsulating arrangement for an electrical component comprising:
first and second separate insulating layers; and
a third layer in the form of an electrically charged conductive layer intermediate the first and second insulating layers which is arranged to prevent the passage of ionic species across the encapsulating arrangement.
2 . The encapsulating arrangement of claim 1 , wherein the conductive layer is a metal.
3 . The encapsulating arrangement of claim 1 , wherein the conductive layer is a self-supporting metal foil.
4 . The encapsulating arrangement of claim 1 , wherein the conductive layer is a metallic film carried on a non-conductive supporting substrate.
5 . The encapsulating arrangement of claim 4 , wherein the non-conductive supporting substrate is the first or second insulating layer.
6 . The encapsulating arrangement of claim 1 , wherein the conductive layer is substantially continuous.
7 . The encapsulating arrangement of claim 1 , wherein the conductive layer is discontinuous.
8 . An electrical component protected by an encapsulating arrangement as claimed in claim 1 .
9 . The electrical component of claim 8 , wherein the electrical component is a piezoelectric device.
10 . The piezoelectric device of claim 9 , including a charging arrangement to permit charging of the conductive layer at least during operation of the piezoelectric device.
11 . The piezoelectric device of claim 10 , wherein the charging arrangement includes an electrical connector arrangement for connecting the device to a power source.
12 . The piezoelectric device of claim 11 , including first and second external electrodes for generating an electrical field across the device when the device is connected to the power source, in use, wherein the electrical connector arrangement includes first and second electrical terminals connected, respectively, to the first and second external electrodes.
13 . The piezoelectric device of claim 11 , wherein the electrical connector arrangement is provided with a third terminal in electrical contact with the conductive layer, the third terminal being provided with a connection to an uninterruptible power supply to enable charging of the conductive layer in circumstances when the first and second electrical terminals are inoperative.
14 . The piezoelectric device of claim 9 , wherein the conductive layer is charged through mutual capacitance with the device.
15 . The piezoelectric device of claim 14 , for use in a fuel injector having an injector body housing the piezoelectric device, the conductive layer being at a floating voltage with respect to a voltage of the injector body.
16 . The piezoelectric device of claim 9 , including an earthed component, wherein the conductive layer is connected to the earthed component.
17 . A piezoelectric device for use in a fuel injector having an injector body housing the piezoelectric device, the piezoelectric device being protected within the injector body by an encapsulating arrangement including first and second separate insulating layers, and an electrically conductive layer intermediate the first and second insulating layers which is arranged to prevent the passage of ionic species across the encapsulating arrangement and wherein the conductive layer is charged through mutual capacitance with the piezoelectric device and is at a floating voltage with respect to the injector body.
18 . An electrical component protected by an encapsulating arrangement comprising:
first and second insulating layers; and
an electrically charged conductive layer intermediate the first and second insulating layers which is arranged to prevent the passage of ionic species across the encapsulating arrangement;
the electrical component further comprising a charging arrangement to permit charging of the conductive layer at least during operation of the component.
19 . The electrical component of claim 18 , including an electrical connector arrangement for connecting the electrical component to a power source, and first and second external electrodes for generating an electrical field across the electrical component when the electrical component is connected to the power source, in use, and wherein the electrical connector arrangement includes first and second electrical terminals connected, respectively, to the first and second external electrodes.
20 . A fuel injector incorporating the piezoelectric device of claim 9 .