APPARATUS FOR INDICATING FLUID LEVEL

Abstract: Apparatus for indicating fluid level which is responsive to the fluid pressure at the bottom of a tank (l0) for indicating fluid level including a fluid pressure amplifier (20) that provides an amplified fluid pressure to a pressure gauge (l8) which is calibrated to provide a measure of fluid level.

Description: This invention relates to an apparatus for indicating the level of fluid in a tank or other container. The fluid pressure at the bottom of a container is directly related to the height of fluid in the container and the density of the fluid. If the density of the fluid is known, the level of fluid in the container can then be determined from the fluid pressure at the bottom of the container. It has been proposed in US patent no. 4,373,388 to provide for a fluid level sensor in which the fluid pressure at the bottom of the container is monitored as an indication of fluid level. However, the variation in fluid pressure in response to changes in fluid level are very small thereby requiring a highly sensitive pressure gauge to detect changes in fluid pressure so as to provide a measure of fluid level. A pressure gauge having the required sensitivity would be very costly and would typically prohibit this form of fluid level sensing in many applications. The object of the present invention is to provide an apparatus to measure the level of fluid in a container based on the fluid pressure at the bottom of the container and wherein a pressure gauge is used that does not require high sensitivity. To this end, an apparatus in accordance with the present invention is characterised by the features specified in the characterising portion of Claim l. In accordance with the present invention, an apparatus for indicating the level of fluid in a container is provided that measures the fluid level in the container based on the fluid pressure at the bottom of the container. By the use of a pressure amplifier including a high pressure source such as the fluid pump for pumping fluid from the container, fluid pressure changes over a wide range as the fluid level varies thereby allowing the use of a pressure gauge having less sensitivity. The invention may be best understood by reference to the following description of a preferred embodiment and the accompanying drawings, in which:- Figure l is a diagram illustrating an apparatus incorporating the principles of this invention; and Figure 2 is a diagram illustrating the pressure amplifier of Figure l. Referring to Figure l, the invention is illustrated with respect to a container in the form of a vented fuel tank l0 from which fuel is delivered to a vehicle engine (not shown) through an intake, including a filter element ll, at the bottom of the vented fuel tank and a fuel line l2 by means of a fluid pump in the form of an electric fuel pump l4. The electric fuel pump l4, which is of the known type, is positioned in the vented fuel tank l0 and is energized via electric leads (not illustrated) to deliver fuel under pressure to the vehicle engine. A fuel gauge to monitor the level of fuel in the vented fuel tank l0 takes the form of a pressure gauge l8 to which fuel at a fluid pressure related to the level of the fuel in the vented fuel tank l0 is applied. A pressure amplifier 20 is positioned at the bottom of the vented fuel tank l0 so as to be exposed to the fluid pressure that is related to the level of fuel in the vented fuel tank l0. The pressure amplifier 20 is vented to the atmosphere via a conduit 22. Fuel at the fluid pressure related to its level in the vented fuel tank l0 is admitted to the pressure amplifier 20 via openings 24 therein. The output of the pressure amplifier 20 is an amplified fuel pressure that is coupled to the pressure gauge l8 through an output pressure line 25. The operating pressure for the pressure amplifier 20 is provided by the electric fuel pump l4. This is accomplished by coupling the pressurized fuel output of the electric fuel pump l4 to the output pressure line 25 via a fluid flow restrictor in the form of an orifice 26. As will be described with respect to Figure 2, the pressure in the output pressure line 25, and which is sensed by the pressure gauge l8, is modulated by the pressure amplifier 20 to a value equal to KP f where K is the gain of the pressure amplifier 20 and P f is the fluid pressure of the fuel dependent upon the level of fuel in the vented fuel tank l0. Referring to Figure 2, the pressure amplifier 20 includes an air chamber 28 formed by opposed first and second diaphragms 30 and 32 respectively and a casing 34. The first diaphragm 30 is captured by crimping the casing 34 which seals the air chamber 28 from the fuel entering the casing via the openings 24. The second diaphragm 32 and casing 34 are captured by a housing 36 of a valve defined by a ball valve 37 and an opposing member 38 such as by threaded bolts 40 to seal the air chamber 28 from fuel entering the interior of the housing 36 through openings (not shown) provided therein. A spacer 42 is carried by the first diaphragm 30 and engages the second diaphragm 32. The air chamber 28 is vented to atmospheric pressure via the conduit 22 previously described. The ball valve 37 includes a movable valve member defined by a ball 44 within the housing 36 that cooperates with a valve seat formed by the end of a tubular fitting 45 extending through the top of the housing 36 to form the ball valve. The output pressure line 25 is pushed over the external end of the tubular fitting 45 to establish fluid communication with the ball valve 37. The ball 44 is engaged by the second diaphragm 32 at a point diametrically opposite the valve seat formed by the end of the tubular fitting 45 for movement therewith, movement of the second diaphram 32 upward tending to close the ball valve 37 and movement downward opening the ball valve 37. Fuel at a fluid pressure dependent upon its level in the vented fuel tank l0 applies a fluid pressure on the bottom side of the first diaphragm 30 tending to displace the first diaphragm 30 in an upward direction against the spacer 42. Fuel at the same fluid pressure is applied to the upper side of the second diaphragm 32 through openings (not shown) tending to displace the second diaphragm 32 in a downward direction against the spacer 42. The area A₁ of the first diaphragm 30 is greater than the area A₂ of the second diaphragm 32 resulting in a net force tending to displace both the first and second diaphragms 30 and 32 and the ball 44 engaged by the second diaphragm 32 in an upward direction to close the ball valve 37. An opposing force acting on the ball 44 tending to displace the ball 44 downward to open the ball valve 37 is created by the fluid pressure in the output pressure line 25 acting on the ball 44 over the area A₃ of the terminal end of the tubular fitting 45. The spacer 42 thereby acts as transmitting means for transmitting the net force exerted by the fuel on the first and second diaphragms 30,32, to the ball 44. The net effect of the forces acting on the ball 44 is to regulate the fluid pressure in the output pressure line 25 to a fluid pressure that is equal to the fluid pressure of the fuel at the bottom of the vented fuel tank l0 times the gain K of the pressure amplifier 20. The gain K can be determined by summing the forces acting on the ball 44 of the ball valve 37. The forces acting on the ball 44 is defined by the following equation: P g A₃ = P f A₁ - P f A₂ + P f A₃ - W (l) where P g is the pressure per unit area in the output pressure line 25 sensed by the pressure gauge l8, P f is the fluid pressure per unit area at the bottom of the vented fuel tank l0, A₁ is the area of the first diaphragm 30, A₂ is the area of the second diaphragm 32, A₃ is the area of the end of the tubular fitting 45 and W is the weight of the ball 44. If the specific gravity of the ball 44 is substantially equal to that of the fuel and if the area A₃ is substantially less than the area A₁, the following equation for the fluid pressure sensed by the pressure gauge l8 results: P g = P f (A₁-A₂)/A₃ . (2) Any errors that may result from the foregoing assumptions relating to the ball weight and area A₃ can be compensated for via calibration of the pressure gauge l8. As can be seen from equation (2) the gain K of the pressure amplifier 20 is equal to (A₁-A₂)/A₃. By making A₂ smaller than A₁ and by making A₃ smaller than the difference between A₁ and A₂, the gain K of the pressure amplifier 20 can be made much greater than unity so that the fluid pressure in the output pressure line 25 at the output of the pressure amplifier 20 is much greater than the fluid pressure at the bottom of the vented fuel tank l0. By amplifying the fluid pressure in the foregoing manner, a wide range of fluid pressures is provided to the fuel gauge in response to the limited range of fluid pressures as the fuel quantity in the vented fuel tank l0 varies from full to empty. This expanded range allows the use of a pressure gauge l8 that is not highly sensitive to small pressure changes and therefore more economical while yet providing an accurate indication of fuel remaining in the vented fuel tank l0.

Claims: 1. An apparatus for indicating the level of fluid in a container (l0), the apparatus comprising: a pressure gauge (l8) responsive to the fluid pressure in an output pressure line (25) for providing a measure of the fluid level in the container; and a fluid pump (l4) for pumping fluid under pressure from the container; characterised by a pressure amplifier (20) comprising a casing (34) disposed at the bottom of the container and having opposed surfaces; first (30) and second (32) diaphragms carried by the opposed surfaces of the casing, the casing and the first and second diaphragms forming an air chamber (28) isolated from the fluid, the external surfaces of the air chamber being exposed to the fluid pressure at the bottom of the container, the fluid exerting a force equal to A₁Pf on the first diaphragm and an opposing force A₂Pf on the second diaphragm, where A₁ is the area of the first diaphragm, A₂ is the area of the second diaphragm and Pf is the fluid pressure per unit area at the bottom of the container and which is proportional to the level of the fluid in the container; a valve (37) including a movable valve member (44) and a valve seat (45) having an area A₃; transmitting means (42) for transmitting the net force Pf(A₁-A₂) exerted by the fluid on the first and second diaphragms to the movable valve member in a sense tending to seat the movable valve member against the valve seat; in that the output pressure line is coupled between the pressure gauge and the valve seat, the output pressure line being vented to the container when the movable valve member is unseated from the valve seat; and by a fluid flow restrictor (26) coupled between the fluid pump and the output pressure line to pressurize the output pressure line, the fluid pressure in the output pressure line generating a force equal to PgA₃ on the movable valve member tending to unseat the movable valve member from the valve seat, where Pg is equal to the fluid pressure per unit area of the fluid in the output pressure line, the movable valve member being moved by the forces acting thereon to modulate the fluid pressure per unit area Pg in the output pressure line to a value substantially equal to Pf(A₁-A₂)/A₃. 2. An apparatus according to claim l, wherein the area A₁ of the first diaphragm (30) is greater than the area A₂ of the second diaphragm (32) and the area A₃ is less than the difference A₁-A₂ so that the fluid pressure in the output pressure line (25) is greater than the fluid pressure at the bottom of the container (l0).

Inventors: FALES, DOUGLAS I.
Applicants: GENERAL MOTORS CORPORATION
Application year: 1986
Main classification: G01F23
IPC codes: G01F23