Power line high current cutoff device

The present invention relates to a device for cutting off high current along a power line without generating arcs or sparks, and therefore especially suitable for use in the presence of inflammable liquid, vapour or gas.

The cutoff device according to the present invention is particularly suitable for automotive applications, for safeguarding against fire in the event of a crash, in which case, the generation of a spark caused by shorting of the vehicle electrical system is a serious fire hazard, particularly in accidents involving damage to critical parts of the vehicle, such as the fuel supply lines or control members.

To reduce the danger of fire caused by fuel leakage in the event of a crash, use is commonly made of inertial safety systems activated by sharp deceleration of the vehicle (as produced, for example, by impact) and based on solenoid valves controlled by inertial switches for cutting off the supply of fuel or other inflammable liquids or gas.

Before (or even despite) operation of the safety system, however, small amounts of inflammable liquid, particularly fuel, may still be dispersed and set on fire by sparks or electric discharges caused by accidental pinching of the positive cables of the vehicle electrical system close to the point of impact. As such, a device must be provided for enabling rapid, sparkfree disconnection of the vehicle battery from the electrical system, even when this is supplied with strong current (roughly 300 A for cars, and up to 800 A for vans).

At present, the problem can only be solved using complex electronic control circuits which considerably increase the cost of the vehicle electrical system.

It is an object of the present invention to provide a solution to the problem designed to overcome the complexity and high cost of those currently available. The object of the present invention is therefore primarily to provide a device for cutting off high current along a power line without generating sparks or electric arcs; and also to provide a device of the above type that is straightforward, inexpensive and compact in design, and that can be operated both manually and automatically, e.g. by means of the same inertial switch controlling the fuel supply cutoff solenoid valve.

According to the present invention, there is provided a power line high current cutoff device comprising an electrically insulating casing; a first and second contact member housed inside said insulating casing and connected in series between two terminals of said line, at least one of said contact members being movable in relation to the other; and control means for selectively moving said contact members between a first work position wherein they are positioned facing and contacting each other to shortcircuit said terminals of said line, and a second safety position wherein they do not contact each other; characterized in that said contact members comprise carbon brushes of the type used for sliding contacts for supplying the rotors of electric motors.

Using carbon brush contact members has surprisingly been found to eliminate any possibility of sparking, even when the circuit being cut off, and hence the contact members, are supplied with strong currents of 300 A or more. In conjunction with an inertial switch, the above cutoff device therefore provides for effectively eliminating any risk of a vehicle involved in a crash being set on fire due to pinching of the positive cables.

A number of preferred, non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which:

• Figure 1 shows a schematic view of the cutoff device according to the present invention as applied to a car;
• Figures 2 and 3 show longitudinal sections of the Figure 1 device in two different operating positions;
• Figure 4 shows a detail of manual operation of the Figure 2 device;
• Figure 5 shows a manual-only variation of the cutoff device according to the present invention;
• Figures 6 and 7 show a top plan view and longitudinal section of the Figure 5 device in two different operating positions.

With reference to Figure 1, A indicates schematically a body portion (in this case, the engine compartment) of any known vehicle; B indicates the battery for supplying current along a complex line L defined by the vehicle electric circuit; and line L is fitted with a known normally-closed inertial switch I for controlling supply to a known solenoid valve E - in turn controlling fuel supply along a conduit C downstream from a supply pump P - and, according to the invention, for also controlling supply to a current cutoff device 1 series connected to line L immediately downstream from battery B.

With reference to Figures 2, 3 and 4, device 1 comprises a hollow, substantially parallelepiped casing 2 made of insulating material, e.g. synthetic plastic resin; two electric contact members or contactors 10, 11 housed inside casing 2 and movable in relation to each other in opposition to elastic means 12 also housed inside casing 2; and a pair of electric terminals 13, 14 which are stably connected in known manner to line L in the Figure 1 position to form two opposite terminals of line L, which in use are series connected electrically to each other by device 1.

In the example shown, contact 11 is fixed inside casing 2; contact 10 is housed inside casing 2 so as to slide axially between the two positions shown in Figures 2 and 3; contact 11 is series connected to terminal 14 by a flexible cable 16; and contact 10 is similarly series connected to terminal 13 by a flexible cable 18 of such a length as to permit contact 10 to move between the Figure 2 and 3 positions.

Device 1 also comprises control means 20 for moving contact 10 back and forth between the Figure 2 and 3 positions.

According to the present invention, contacts 10 and 11 comprise carbon brushes of the type used on vehicle engine starters for supplying current to the rotor, and therefore comprise two substantially parallelepiped blocks made from a sintered mixture of carbon powder and copper particles and housed inside casing 2 so as to present respective opposite flat faces 21 and 22 facing each other. Block or brush 10 is fixed to a support 23 made of electrically conductive material, to which cable 18 is soldered, and which in turn is mounted so as to slide along guides 24 inside casing 2, and is fitted integrally to the end of a rod 25 facing brush 11.

The opposite end 26 of rod 25 slides through the end wall 4 of casing 2, and is fitted outside casing 2 with a knob 27. Casing 2 is also fitted inside, in a fixed position, with a known electromagnetic actuator 28 fitted through axially with rod 25 which forms the armature. Actuator 28 is mounted between support 23 and wall 4, and supports a helical spring 12 wound coaxially about rod 25 and gripped between actuator 28 and a washer 29 fitted in a predetermined axial position to end 26 of rod 25.

In use, actuator 28 is supplied by line L via switch I and a pair of cables 30. When actuator 28 is de-energized (Figure 2), spring 12 acts on washer 29 to withdraw rod 25 towards wall 4 so that it is partly extracted from casing 2; in which position, contacts 10 and 11 are detached so that faces 21 and 22 are separated by a gap D; and terminals 13 and 14 are isolated so that line L is cut off. Conversely, when actuator 28 is energized (Figure 3), rod 25 is drawn, in opposition to spring 12, towards brush 11 so as to bring brushes 10 and 11 into close contact with each other; in which position, surfaces 21 and 22 contact and are pressed against each other by the force determined by actuator 28; terminals 13 and 14 are shorted by mutually contacting brushes 10 and 11; and line L is connected and supplied by battery B.

In actual use, when the vehicle ignition key is inserted to supply line L, normally-closed switch I supplies current to actuator 28 and solenoid valve E, so that battery B supplies line L and pump P supplies conduit C. In the event of a crash, the sharp deceleration on impact is detected by known switch I which opens to de-energize both solenoid valve E and actuator 28; solenoid valve E closes to cut off fuel supply to conduit C by pump P; and spring 12 expands to rapidly detach brushes 10, 11 and so cut off line L. As such, no sparks are generated even in the event of accidental pinching of the positive cables in the collision, and neither, surprisingly, are any sparks generated between brushes 10 and 11 when these are detached, thus eliminating any danger of fire.

In the event of a fault on actuator 28, the line L circuit can be closed manually to operate the vehicle. In the example shown, this is done by simply pressing knob 27 in the direction of the arrow in Figure 3 to compress spring 12 and bring brushes 10 and 11 into contact with each other, and by rotating knob 27 in the direction of the arrow in Figure 4 to rotate rod 25 through 180° together with a pin 40 fitted integrally through and projecting radially from one side of rod 25. When rotated, pin 40, which during the axial movement of rod 25 normally travels through an opening 41 in wall 4 (Figure 3), thus contacts wall 4 when subjected to the thrust of spring 12 (Figure 4) so that brushes 10 and 11 are maintained contacting each other even when actuator 28 is de-energized.

With reference to the Figure 5, 6 and 7 variation indicated as a whole by 100 and wherein any details similar to those already described are indicated using the same numbering system, the device according to the present invention may also be exclusively manually operated, e.g. to disconnect battery B when the vehicle is left stationary for prolonged periods, or for preventing theft. As shown, device 100 comprises a parallelepiped plastic casing 2 defined by a flat bottom wall 3, two lateral end walls 4, 5 fitted integral with respective terminals 13, 14, two longitudinal lateral walls 6, 7, and a cover 8 resting on and fitted integral with the top edges of lateral walls 4, 5, 6, 7 in any known manner (screwed, ultrasonic welded, etc.). At the wall 5 end, casing 2 houses two contact members comprising parallelepiped carbon brushes 10, 11 resting on and sliding along bottom wall 3 and contacting walls 6, 7.

Brush 11 is fitted in fixed manner to a pin 16 connecting it electrically to terminal 14; brush 10 is mounted so as to slide in opposition to a spring 12 gripped between wall 4 and brush 10 so as to push flat wall 21 of brush 10 into contact with flat wall 22 of brush 11; and brush 10 is connected electrically to terminal 13 by a flexible cable 18 of appropriate length. As shown, on faces 21, 22 and the top faces facing cover 8, brushes 10 and 11 present respective symmetrical step-shaped recesses 51, 52 facing each other and which, when walls 21 and 22 are positioned contacting, define inside casing 2 a chamber 53 (Figure 6) of predetermined width (measured parallel to walls 6, 7). Chamber 53 houses a cam 55 fitted for rotation to cover 8 and connected, by means of a prismatic shaft 56, angularly integral with an outer knob 27 also fitted to cover 8 on the opposite side.

Cam 55 selectively assumes two positions: a first (Figure 6) in which it is housed inside chamber 53 without interfering with brushes 10, 11; and a second (Figure 7) in which it is rotated 90° so that it is housed lengthwise inside chamber 53, and interferes with brushes 10, 11 by virtue of the length of cam 55 being greater than the width of chamber 53 when brushes 10, 11 are positioned contacting. As such, device 100 provides for supplying line L when cam 55 is set to the Figure 6 position, and for directly disconnecting line L at its terminals, represented by terminals 13, 14, when knob 27 is turned to set cam 55 to the Figure 7 position wherein the cam pushes brush 10 away from brush 11 in opposition to and by compressing spring 12, so as to form gap D between brushes 10 and 11.

As casing 2 is not normally fluidtight, gap D formed between brushes 10 and 11 contains air, which is nevertheless an excellent dielectric. According to further variations, however, casing 2 may be made fluidtight and a vacuum formed inside; or it may be filled with gaseous fluids or liquids of good insulating characteristics and/or for effectively damping electric discharges between the two contactors. Whichever the case, tests conducted by the Applicant have shown that the main characteristic of the invention whereby the carbon brushes used for the rotors of electric motors are employed as the contact members is in itself sufficient to eliminate any possibility of sparking, even under high current flow conditions.

Using a device identical to 100 in Figures 5, 6 and 7, a test circuit was formed comprising, in addition to device 100, a 12V, 90 Amph vehicle battery, a user device consisting of a rheostat, and an ammeter; the carbon brushes of a Magnetic Marelli E95R-2.2/12 starter were used as contacts 10, 11; and casing 2 was made of plexiglass to observe any sparks. Working in the dark, various tests were conducted involving 2-4 mm detachment of contacts 10, 11 under different current conditions. The results are shown in Table 1.

Current between contacts (A)

Spark (Yes / No)

50

no

100

no

300

no

400

no

500

no

600

no

As can be seen, no spark is generated even in the presence of over 500 A through brushes 10, 11, and despite the fact that the brushes are detached manually and relatively "slowly" as compared with automatic detachment by device 1.