WO1991013322A1

WO1991013322A1 - An apparatus for determining the level of liquid in a container

Info

Publication number: WO1991013322A1
Application number: PCT/US1990/002254
Authority: WO
Inventors: Arthur Wild
Original assignee: Caterpillar Industrial Inc.
Priority date: 1990-02-26
Filing date: 1990-04-27
Publication date: 1991-09-05

Abstract

An apparatus (100) is adapted to determine the level of liquid in a container (200). The apparatus (100) includes a movable portion (206) and an actuator (222) for moving the movable portion (200) through the liquid. A controller (116) actuates the actuator (222) and senses the rate at which the movable portion (206) moves from a first position towards a second position. The controlled (116) then determines the level of liquid in the container (200) as a function of the rate of movement of the movable portion (206).

Description

AN APPARATUS FOR DETERMINING THE LEVEL OF LIQUID IN A CONTAINER

Technical Field

This invention relates generally to a liquid level sensor and, more specifically, to an apparatus for moving a member from one predetermined position toward another predetermined position and determining the level of the liquid as a function of the rate at which the member moves toward the second position.

Background Art Often, it is necessary to determine the level of liquid in a container so that a correct amount of liquid may be added to the container or so that the amount of liquid taken from the container (or used) may be monitored. For example, in a gasoline or diesel engine, oil is used as a lubricant to decrease the amount of wear and tear on the engine's components. The oil is held in a sump or oil pan and is cycled and dispersed throughout the engine while the engine is in operation. The effectiveness of the oil as a lubricant is dependent on the effectiveness and thoroughness of its dispersement. Therefore, maintaining the correct level of oil in the engine is highly desirable. Typically, a dipstick is supplied to assist in determining the level of oil in an engine during replacement of the oil or during maintenance of the engine. However, the dipstick and the hollow tube providing the dipstick a path to the oil may allow foreign particles to enter the oil pan and contaminate the oil, causing damage to the engine. Also, use of the dipstick is a manual operation requiring that an operator check the oil level. Failure to do so may result in damage to the engine and its components. Therefore, an apparatus to automatically measure oil level is desirable.

One type of device used to determine a low oil level is disclosed in U.S Patent No. 4,610,164, issued to Hideo Sobue, et al., dated September 9, 1986. This device includes an ultrasonic wave transmitter and an ultrasonic wave receiver. The transmitter and receiver are arranged such that when the liquid level is normal, both are submerged and the wave is propagated by the liquid and detected by the receiver. When the liquid is below a certain level such that the transmitter is not submerged, the wave will not propagate through the liquid and will not be detected by the receiver. However, this device can be affected by an unstable or erratic fluid surface, resulting in an invalid level reading.

The same problem occurs with the device disclosed in U.S. Patent No. 3,680,579, issued to Takeo Hisada, et al., dated August 1, 1972. This device uses a source of pressurized air to detect whether or not the liquid is above or below a certain level. This device is susceptible to the same problem discussed above and also may be affected when the device is on an incline.

In an attempt to accurately monitor oil level, some engines are equipped with a sensor based on a float and magnet arrangement. One such arrangement is disclosed in U.S. Patent No. 4,480,469 issued to Charles Tice, dated November 6, 1984. It provides a float with a magnet guided along an upright portion of a container. The magnet affects the state of two switches, allowing an abnormally low oil level to be detected.

One problem with float devices is that they are susceptible to errors due to the erratic movement of the surface of the oil during movement of the engine. Also, placement of the floating device is critical to ensure a proper reading when the engine is on an incline.

The magnet also introduces additional problems into the sensor mechanism. Due to the movement of the metal components of the engine in relation to each other small metal particles or shavings are introduced into the oil. The strength of the magnet must be such that it does not attract these particles and thereby introduce detrimental magnetic effects.

A capacitive probe is sometimes used in an attempt to determine liquid level. U.S. Patent No. 4,083,248, issued to Lawrence Maier, dated April 11, 1978, discloses one such device. The capacitive probe is arranged in the container such that the liquid affects a capacitor in the probe. This capacitance varies according to the level of the liquid in the container. The probe is part of a timing circuit. The timing circuit includes a pulse generator which is adapted to vary the period of the generated pulse proportionally with respect to the capacitance of the probe. However, the capacitance of the probe is dependent on the dielectric constant of the liquid and varies from liquid to liquid. Also, temperature changes in the liquid and contaminants may vary the dielectric constant of the liquid (e.g. the above mentioned metal shavings in the oil) and affect the accuracy of the probe. Another type of sensor uses a resister wire probe to determine the liquid level. One such device is disclosed in U.S. Patent No. 4,584,554, issued to Mario A. Weiss, dated April 22, 1986. The resistor probe is extended into the oil and a current is passed through the probe. The voltage across the terminals varies with immersion of the probe into the oil.

The effectiveness of the resistor probe decreases with movement of the oil surface. As with the float arrangement, the placement of the probe is critical to ensure a proper reading when the engine is on an incline. And as with the capacitive probe, changes in the temperature of the liquid may affect the accuracy of the probe. Another problem exists with the resistor probe in applying the sensor to an explosive and/or flammable liquid such as gasoline. With an electrical current through such a resistive load there is always the possibility of an electrical spark which may ignite the liquid. The subject invention is directed at overcoming one or more of the problems as set forth above.

Disclosure of the Invention In one aspect of the present invention, an apparatus for determining the level of liquid in a container is provided. The apparatus includes a liquid engaging member having a mounting portion and a movable portion and being orientable with the liquid. The mounting portion is connectable to the container. Also included is an actuator for moving the movable portion between first and second positions relative to the container and logic for controllably operating the actuator, sensing the rate of movement of the movable portion, and determining the level of liquid in the container as a function of the rate of movement.

In another aspect of the present invention, a method for determining the level of liquid in a container is provided. The container includes a liquid engaging member having a mounting portion and a movable portion and being oriented with the liquid surface. The mounting portion is connected to the container. The method includes the steps of moving the movable portion from a first position toward a second position, sensing the rate of movement of the movable portion from the first position toward the second position, and determining the level of liquid in the container as a function of the time period.

Brief Description of the Drawinσs

Fig. 1 is a block diagram of an embodiment of the apparatus in an system for determining the level of oil in an engine; Fig. 2 is a diagrammatic side view of a liquid level sensor having a logic means, a plunger, and an electrical actuator;

Fig. 3 is a diagrammatic front view of the plunger of Fig. 2 having a rectangularly shaped end portion; and

Fig. 4 is a schematic of a first embodiment of the logic means of Fig. 2.

Best Mode for Carrying Out the Invention With reference to Fig. 1, an apparatus 100 for determining the level of liquid is adapted to determine the level of oil in an engine 102. A starter switch 104 activates a starter motor 106 for starting the engine 102. The starter switch 104 has four positions: Off 108, Test 110, Run 112, and Crank 114. A logic means 116 determines the status of the engine (i.e. temperature, battery condition, etc..) and displays the status information on a display panel 118. It should be noted that the apparatus 100 can be adapted to determine the level of liquid in a variety of containers (for example storage and fuel tanks) .

With reference to Fig. 2, the apparatus 100 for determining the level of liquid in a container 200 includes a liquid engaging member 202. The liquid engaging member 202 consists of a mounting portion 204 and a movable portion 206. Preferably the movable portion 206 is a plunger, as shown, and the mounting portion 204 includes a casing 208. The casing 208 is mounted to the container 200 by brackets 210 in a conventional manner. The movable portion 206 has an end portion 212 and a shaft 214 which passes through an aperture 216 in the container 200. Preferably the end portion 212 has a rectangular surface area, as shown in Fig. 3, but the present invention is not limited to such and may include a movable portion with an end portion having different configurations (for example, a circular surface area) .

A sealing means 218 allows the shaft 214 to slidably move- relative to the container 200 along an axis 220 while forming a liquid-tight juncture between the container 200 and the shaft 214. The sealing means 218 may consist of a rubber 0 ring or rings and connectors (not shown) utilized in a conventional manner. Thus, in the preferred embodiment, the liquid engaging member 202 has a linear motion, however, it is recognized that the motion of the liquid engaging member 202 could be otherwise (e.g. radial motion) . Therefore, the present invention is not limited to a linear motion. An actuating means 222 moves the movable portion 206 along the axis 220 between a first position and a second position. The first and second positions are a fixed distance apart. Preferably, the actuating means 222 includes an electrical actuator 224. The electrical actuator 224 includes a spring means 226 and a coil 228. The spring means 226 exerts a first force on the movable portion 206, preferably in a direction away from the container 200. The first force urges the movable portion 206 towards the first position and holds the movable portion 206 at the first position when the coil 228 is deactuated.. The coil 228 is actuated by a current passing through the coil 228 which generates a magnetic field. The electrical actuator 224 is constructed such that a magnetic field exerts a second force on the movable portion 206 and causes the movable portion 206 to move towards the second position. Preferably, the second force causes movement of the movable portion 206 towards the container 200, as shown.

However, it is understood that the electrical actuator 224 could be arranged such that the first force acts to move the movable portion 206 towards the container 200 and the second force moves the movable portion 206 in the opposite direction.

The logic means 116 controllably actuates the electrical actuator 224. With reference to Figs. 1 and 4, the starter switch 104 is used to actuate the logic means 116. When the starter switch 104 is in the Run position 112 or the Crank position 114 a level switch 402 is closed. One end of the level switch 402 is connected to input voltage, V+ (normally battery voltage or a fraction of the battery voltage) . A timing capacitor 404 is connected in series between the other end of the level switch 402 and one end of the coil 228. The other end of the coil 228 is connected to battery ground. A position switch 406 has one end connected to the junction between the level switch 402 and the timing capacitor 404. The other end of the position switch 406 is connected to a control terminal (gate) of a silicon-controlled rectifier (SCR) 408 through a first resistor 410. The SCR 408 is connected to the junction between the timing capacitor 404 and the level switch 402 through a second resistor 412 at an anode, and to battery ground at a cathode. A third resistor 414 is connected between the gate of the SCR 408 and battery ground.

The display panel 118 includes a liquid level indicator 416. In the preferred embodiment, the liquid level indicator 416 includes a light emitting diode (LED) 420.

The SCR 408 is initially blocked, allowing no current to pass from the anode to the cathode. Therefore, no current passes through the LED 420 (the LED 420 remains off) . To activate the apparatus 100, the level switch 402 is closed and a positive voltage appears at the anode of the SCR 408. When the level switch 402 is closed, a pulse of current begins to flow through the timing capacitor 404, energizing the coil 228, and moving the movable portion 206 from the first position towards the second position. As the timing capacitor 404 charges with time, the pulse of current decays until movement of the movable portion 206 stops and the movable portion 206 is returned to the first position by the spring means 226.

If the movable portion 206 is immersed in liquid, movement of the movable portion 206 is slowed by the physical resistance of the liquid against the end portion 212. The timing capacitor 404 is chosen such that the pulse of current through the coil 228 decays before the movable portion 206 reaches the second position if the end portion 212 is emerged in the liquid. A constant voltage is produced at the anode of the SCR 408, the SCR 408 remains blocked and the LED 420 remains off.

Since the physical resistance of air against the end portion 212 is less than that of liquid, the movable portion 206 will move more quickly towards the second position if the end portion 212 is not immersed in the liquid. Preferably, the position switch 406 will be a Hall effect device, as is well known in the art. When the movable portion 206 reaches the second position, the position switch 406 closes and a voltage appears at the gate of the SCR 408. The SCR 408 is now in the conducting state, allowing current to flow between the anode and cathode of the SCR 408. Therefore, the voltage at the anode of the SCR 408 drops to or near battery ground. A low voltage at the anode of the SCR 408 allows current to flow through the LED 420, indicating a low liquid level. The SCR 408 remains in the conducting state even after the position switch 406 is opened and the gate voltage of the SCR 408 drops to battery ground. In this manner, the LED 420 (indicating a low liquid level) is left on until level switch 402 is opened.

A sheath 230 with a drainage hole 232, as shown in Figs. 2 and 3, may be needed for some applications. The sheath 230 would act to increase the difference in the physical resistance the movable portion 206 encounters while moving in air as opposed to moving in-the liquid. The drainage hole 232 would allow the liquid to leave the sheath 230 while the movable portion 206 is moving. Alternatively, the logic means 116 may include a microcomputer (not shown) . The end portion 212 would be fashioned such that a portion of the end portion 212 would be immersed at any level within the desired liquid level range. To calibrate the microcomputer, the container would be filled to a known level and the movable portion 206 moved from the first position to the second position. The microcomputer would determine the time needed to move the movable portion 206 from the first position to the second position. This would be done at a number of different liquid levels. With a rectangularly shaped end portion 212 the physical resistance of the liquid against the end portion 212 would increase linearly with liquid level. The known liquid levels and the corresponding time intervals would be stored in the microcomputer. Any unknown liquid level can therefore be interpolated or extrapolated, given the time needed to move the movable portion 212 from the first position to the second position.

The viscosity of liquid may vary with temperature (for example, oil) and will affect the physical resistance of the liquid against the end portion 212. A temperature sensor (not shown) may be electronically connected to the microcomputer. The liquid level sensor could therefore be calibrated for different temperatures and the level of liquid can be determined as a function of the time needed to move the movable portion 212 from the first position to the second position and of the temperature of the liquid.

Industrial Applicability

With reference to the drawings, and in operation, the apparatus 100 is adapted for determining the level of oil in an engine 102. The starter switch 104 is used to test the display panel 118, actuate the logic means 116, and start the engine 102. To start the engine 102, the starter switch

104 is moved from the Off position 108 to the Crank position 114. However, the starter switch 104 first passes through the Test and Run positions 110,112 before it reaches the Crank position 114. A starter switch 104 of this type is well known in the art.

In the Test position 110, the display panel 118 is lit up so that an operator can see that the indicators (not shown) are working properly.

In the Run position 112, the level switch 402 is closed and an oil level reading is taken (as described above) . The starter switch 104 is then placed in the Crank position 114 and the starter motor 106 starts the engine 102. After the operator releases the starter switch 104, it moves back and remains in the Run position 80.

If the end portion 212 is immersed in oil, the LED 410 remains unlit (signifying a correct oil level) .

If the apparatus 100 determines that the oil level is low, the LED 420 is lit (as described above) . While the starter switch 104 remains in the Run position 112, the level switch 402 remains closed, keeping current flowing through the LED 420. This ensures that the LED 420 remains lit. When the starter switch 104 is turned to the Off position 108, the engine 102 is turned off and the logic means 116 is reset, turning off power to the LED 420.

Claims

1. An apparatus (100) for determining the level of liquid in a container (200) , comprising: a liquid engaging member (202) having a mounting portion (204) and a movable portion (206) and being orientable with said liquid, said mounting portion (204) being connectable to said container (200) ; actuating means (222) for moving said movable portion between first and second positions relative to said container (200) ; and, logic means (116) for controllably operating said actuating means (222) , sensing the rate of movement of said movable portion (206) , and determining the level of liquid in said container (200) as a function of said rate of movement.

2. An apparatus (100), as set forth in claim 1, wherein said actuating means (222) includes an electrical actuator (224) having a coil (228) , said logic means (116) being adapted to controllably actuate and deactuate said coil (228) , said movable portion (206)* being adapted to move from said first position toward said second position upon actuation of said coil (228) .

3. An apparatus (100), as set forth in claim 2, wherein said actuating means (222) includes spring means (226) for positioning and holding said movable portion (206) at said first position upon deactuation of said coil (228) .

4. An apparatus (100), as set forth in claim 1, wherein said movable portion (206) is a plunger and includes: a shaft (214) having an axis (220) oriented substantially parallel with the surface of said liquid; and, an end portion (212) engagingly and transversely oriented with said surface.

5. An apparatus (100) , as set forth in claim

4, wherein said shaft (214) passes through an aperture (216) in said container (200) and including a sealing means (218) for providing a liquid-tight juncture between said shaft (214) and said aperture (216) .

6. An apparatus (100), as set forth in claim 4, wherein movement of said plunger (206) between said first and second positions is along said axis (220) .

7. An apparatus (100), as set forth in claim

6, wherein said end portion (212) is adapted to intersect the surface of the liquid in a generally perpendicular manner.

8. An apparatus (100), as set forth in claim

7, wherein said end portion (212) has a rectangular shape.

9. An apparatus (100), as set forth in claim 7, wherein said end portion (212) has a circular shape.

10. An apparatus (100) , as set forth in claim 7, wherein said end portion (212) is adapted such that said rate of movement of said plunger (206) has a substantially linear relationship with said liquid level.

11. An apparatus (100) , as set forth in claim 1, including a sheath (230) having a constant cross sectional shape and being connectable to said container (200) , said sheath (230) extending from said container (200) and surrounding said movable portion (206) .

12. An apparatus (100), as set forth in claim 1, wherein the velocity of the movement of said movable portion (206) is restricted by a restraining force caused by the movement of said movable portion (206) through said liquid, the magnitude of said restraining force being dependent on the level of said liquid.

13. An apparatus (100) for determining the level of liquid in a container (200) , comprising: a liquid engaging member (202) having a mounting portion (204) and a plunger (206) and being oriented with said liquid, said mounting portion (204) being connected to said container (200) , said plunger (206) having a shaft (214) having an axis (220) substantially parallel with the surface of said liquid and an end portion (212) engagingly and transversely oriented with said surface, said shaft (214) passing through an aperture (216) in said container (200) , said end portion (212) being adapted to intersect said surface in a generally perpendicular manner; an electrical actuator (224) having a coil (228) and being mounted to said container (200) , said plunger (206) being adapted to move from a first position to a second position upon actuation of said coil (228) , the velocity of said plunger (206) being restricted by a restraining force caused by said movement of said plunger (206) through said liquid, the magnitude of said restraining force being dependent on the level of said liquid; spring means (226) for positioning and holding said plunger (206) at said first position upon deactuation of said coil (228) ; and, logic means (116) for controllably operating said electrical actuator (224) means, sensing the rate of movement of said plunger (206) , and determining the level of liquid in said container (200) as a function of said rate of movement.

14. A method for determining the level of liquid in a container (200) having a liquid engaging member (202) , said liquid engaging member (202) having a mounting portion (204) and a movable portion (206) and being oriented with the surface of said liquid, said mounting portion (204) being connected to said container (200) , comprising the steps of: moving said movable portion (206) from a first position to a second position; sensing the rate of movement of said movable portion (206) from said first position toward said second position; and, determining the level of liquid in said container (200) as a function of said rate of movement.

15. A method, as set forth in claim 14, including the step of moving said movable portion (206) from said second position to said first position.