DEVICE FOR BALANCING SUBATMOSPHERIC PRESSURE IN CONTAINERS FOR GAS OR LIQUID

Abstract: Device for automatically equalizing subatmospheric pressure in vehicle fuel tanks. The device comprises an electronic control circuit connected to the vehicle ignition lock (10) and contains a pressure monitor (7, 8) which controls a magnet valve (1). A circuit (11) with a temperature controlled switch (12) is coupled in parallel to the ignition lock in order to connect current to the automatic control circuit when the ambient temperature is low.

Description: DEVICE FOR BALANCING SUBATMOSPHERIC PRESSURE IN CONTAINERS FOR GAS OR LIQUID The present invention relates to a device for equalizing subatmospheric pressure in a container with a fluid medium, comprising an electromagnetic venting valve disposed between the interior of the container and an outlet from the con- tainer, and a control circuit connected for controlling the valve with a pressure sensor arranged to sense the sub- atmospheric pressure in the container and provide a signal to the control circuit, and to open the venting valve at a certain pre-determined subatmospheric pressure. Pressure monitoring systems with venting valves of this type are used in a wide range of applications. In order for these systems to work, they must be constantly connected to opera¬ ting voltage. These systems are thus not suitable for use in monitoring subatmospheric pressure in fuel tanks in vehicles where the current must be broken when the vehicle is not in operation. The present invention is directed to the development of a system for pressure monitoring, in particularly monitoring of subatmospheric pressue for uεe in particular, but not e :- clusively, for monitoring and compensating subatmospheric pressure in fuel tanks for motor vehicles to prevent deforma¬ tion caused by partial vacuum in the tank. In modern automobiles, for the purpose of saving weight, more and more use has been made of fuel tanks in non-metallic materials, e.g. plastics, with relatively thin walls. Even at a relative slight partial vacuum, e.g. on the order of magni- tude of 3 kPa, a relatively heavy deformation of the tank can occur due to the thinness of the walls, and this can lead to damage to sensitive components mounted in the tank, e.g. the fuel pump, the level sensor, etc. Most modern engines with direct injection are fed from the tank with excess fuel, the excess being returned to the tank. This results in raised temperatures in the fuel in the tank, so that the temperature, when the engine is shut off, can be as much as 70°C. The tank must therefore be dimensioned in its material and wall thickness to be able to resist the partial vacuum which can arise in the tank when the fuel cools off. The purpose of the present invention is in general to provide a device of the type described by way of introduction, which can be used in containers in which the partial vacuum arising in the fluid medium due to the dropping temperature can be equalized even if a switch for the control circuit governing the venting valve has been switched off. This is achieved according to the invention in a device of the type described by way of introduction by virtue of the fact that the control circuit is connected to a current source via a manually operated switch, and in that a separate circuit with a temperature controlled switch is coupled in parallel to the manual switch. Such a device applied to an automobile with a low pressure sensor makes it possible for the control circuit, even though the automobile is parked and the ignition is turned off, to open the venting valve and equalize the partial vacuum in the tank when the fuel cools in the parked car. The invention will be described in more detail with reference to an example shown in the accompanying drawing, where Figure 1 shows a circuit diagram of a device according to the invention. Figure 2 shows a cross-section through a pressure sensor, particularly designed to be used in a device according to the invention, and Figure 3 is a partially cut-away plan view of the pressure sensor of Figure 2. In the circuit diagram in Figure 1, 1 designates an electro- magnetically controlled valve, and 2 designates a venting hose to a tank 3, e.g. a fuel tank in a car. The valve 1 is opened and closed by a relay 4, which is controlled by a control circuit containing a transistor 5 and the pressure sensor 6 including an LED 7 and an LDR resistor 8. When the valve 1 is open, the tank is connected via the hose 2 to the atmosphere or to a container under atmospheric pressure, e.g. a filter with activated charcoal. At atmospheric pressure or over pressure, the pressure sensor 6 provides a low voltage at the point 9 by virtue of the fact that the resistance of the LDR resistor is low, e.g. about 600a. The relay 4 is open and the valve 1 is closed. As the pressure drops to subatmospheric pressure, e.g. 0.5 kPa, the resistance in the resistor 8 rises to about 0.5Ma, thereby increasing the voltage at the point 9 so that as the switch 10, which can be an ignition lock, is turned on, current will be conducted through the relay 4 and the collector emitter path of the transistor, thus activating the relay and opening the valve 1. As soon as pressure equalization has been com¬ pleted, the valve 1 will return to its closed position, and this takes place when the voltage at the transistor base drops as the resistance in the LDR resistor drops. When the current is broken by the switch 10 (the ignition lock) , the valve 1 is normally closed. If the temperature of the fuel is high and the surrounding air temperature is low, the pressure sensor 6 will be activated, when the temperature drops, to open the venting valve, since the fuel, as it cools off, creates a partial vacuum in the tank. Under these cir¬ cumstances, to create an automatic venting of the tank, an extra switch circuit 11 is arranged in parallel to the switch 10, according to the invention. This circuit contains, inter alia, a tyristor 12, an NTC resistor 13, and a resistor 14 serving as a voltage divider. At low temperature, the resist¬ ance in the resistor 13 is high, and when the voltage has reached a certain level (0.8 volts), due to the resistance increase caused by the low temperature, the tyristor 12 will start to conduct and the relay circuit will conduct current. If the pressure sensor 6 in these circumstances indicates a partial vacuum, the valve 1 will open and vent the tank. As soon as the switch 10 is closed, the tyristor 12 will return to its rest position, and only be activated again at low temperature. The control circuit described is particularly suited for use in combination with a pressure sensor of the type shown in Figures 2 and 3. It shows a housing 20 of plastic, for examp¬ le, comprising a cylindrical wall portion 22, a circular bottom portion 23 and a circular cover 24, which are fixed to the cylinder 22. The bottom portion 3 is fixed to the cylin¬ der 22 with an intermediate 0-ring 25, and it defines to- gether with a bottom plate 26 made in one piece with the cylinder, a space which is divided into lower and upper chambers 28 and 29, respectively, by a thin membrane 30 stretched between the lower edge of the cylinder 22 and the bottom portion 23. The bottom plate 26 is provided with a bracket 31 and a pair of protecting walls 32, 33 with circular holes 34, 35. The LED 7 is fixed to the bottom plate 26 in front of the opening 34, and the LDR resistor 8 is fixed to the bottom plate in front of the opening 35. A semaphore-like arm 38 is pivotally mounted in a shaft 39 carried by the bracket 31 and is biased by a spring 40 towards the plate 26. The arm 38 has an outer screening portion 41 lying between the screen walls 32, 33, and which, in its position shown in Figure 2 with solid lines, covers the openings 34, 35. Furthermore, the arm 38 has approximately in its middle a heel 41 which extends through an opening 42 in the plate 26 and is held in contact with the membrane 30 by the spring 40. A tube 43 with a channel 44 leading into the lower chamber 28 is intended to be connected to the container where the pressure is to be monitored, e.g. the expansion space in a fuel tank for a motor vehicle. The LDR resistor 8 can be a resistor, in which the resistance can be changed from about 0.5MQ in the dark to about 600c at full illumination. The space above the bottom plate 26 is ventilated to the surroundings, so that the atmospheric pressure prevails in this space. As the pressure in the lower chamber varies, the membrane 40 will bulge upwards or down¬ wards depending on whether there is overpressure or subat¬ mospheric pressure, and the arm 38 can swing between the position shown with solid lines to the position shown with dash-dot lines. The cooperating components, i.e. the membrane 30, the arm 38 and the spring 40, can be adapted to each other so that the arm 38 assumes the position shown with solid lines when there is a subatmospheric pressure of about 0.5 kPa, whereupon the LDR resistor is kept in the dark. When there is pressure compensation between the lower chamber 28 and the chamber above the bottom plate, the central portion of the membrane is moved upwards, thus swinging the arm 18 up. When the screening portion 41 of the arm has been moved away so that the LDR resistor is once again fully illu i- nated, the resistance in the resistor 8 will drop and the control circuit will brake the current to the relay 4, where¬ upon the venting valve 1 is closed. The device described contains simple and inexpensive com- ponents requiring very little space. Due to its very small space requirements, it can be integrated with other com¬ ponents, e.g. a level sensor for the fuel tank. The pressure sensor with the electronic control circuit and the venting valve can be manufactured at very low cost.

Claims: CLAIMS 1. Device for equalizing subatmospheric pressure in a con¬ tainer with a fluid medium, comprising an electromagnetic venting valve disposed between the interior of the container and an outlet from the container, and a control circuit connected for controlling the valve with a pressure sensor arranged to sense the subatmospheric pressure in the con¬ tainer and provide a signal to the control circuit, and to open the venting valve at a certain pre-determined sub- atmospheric pressure, c h a r a c t e r i z e d in that the control circuit is connected to a current source via a manually operated switch (10) , and that a circuit (11) with a temperature controlled switch (12) is coupled in parallel to the manual switch. 2. Device according to Claim 1, c h a r a c t e r i z e d in that said separate circuit (11) contains a thyristor (12) and an NTC resistor (13) . 3. Device according to Claim 1 or 2, c h a r a c t e r¬ i z e d in that the container (3) is a fuel tank in a motor vehicle, that the magnetic valve (1) is arranged in a venting conduit (2) to an expansion space in the tank, and that the manual switch (10) is included in the ignition lock of the vehicle. 4. Device according to one of Claims 1-3, c h a r a c t e r¬ i z e d in that said separate ciruit (11) and said tempera¬ ture controlled switch (12) are coupled into a control cir- cuit with a pressure sensor (20) , comprising a pressure actuated element (38) with a light screening portion disposed between a light source (17) and a light sensitive signal emitter (8) illuminated by said light source.

Inventors: HARDE BO, HARDE, BO
Applicants: VOLVO AB, AB VOLVO
Application year: 1991
Main classification: B60K15
IPC codes: B60K15