Patent Application
20050199833
This invention relates to a device for measuring fluid level in a reservoir. More specifically, the present invention describes an optical fluid measuring device useful for checking the level of oil, power steering fluid, washer fluid, etc. in a motor vehicle.
There are many different types of level sensors for monitoring fluid level in a reservoir or tank in common use. The simplest method for determining fluid level is through the use of a dipstick. When the fluid reservoir is in a vehicle, the dipstick is usually housed so that it extends into the tank all the time. Monitoring the fluid level requires removing the dipstick, wiping it clean, reinserting it, and then removing it a second time to check the level. While simple and inexpensive, the dipstick has a number of drawbacks: The process of checking the fluid is rather involved. It requires the use of a cloth or similar material to wipe the dipstick. And dipping into the reservoir creates the likelihood that foreign material will be introduced into the tank.
The most common type of remote level sensor uses a float to determine the liquid level. In its simplest form, a float is connected mechanically to an indicator. As the float moves in response to changes in fluid level, these changes are reflected in the indicator. While more convenient than a dipstick, a completely mechanical float often involves complicated linkages and an opening through which foreign material can be introduced to the reservoir or tank.
In response to a need for reliable sensors a large variety of electric devices have been developed. Typically electronic devices employ a sensor that generates an electrical signal indicative of fluid level. The signal is transmitted via wires to an output device such as a digital or analog indicator. The sensors themselves can be float based or capacitance based, i.e. partially mechanical or wholly electrical. In addition a high degree of reliability, electronic devices can be designed to function well in high NVH (noise-vibration-harshness) environments, and work in harsh fuels and chemicals. (See, for example, U.S. Pat. No. 6,624,755 B1.)
Unfortunately, electronic sensors have a number of drawbacks. Float based electronic sensors have a mechanical component and thus the inherent manual problems. And certain electronic sensors for conductive liquids that utilize conductivity in making a level determination (see, U.S. Pat. No. 6,624,744 B1) are of little use with fuels. The biggest drawback of electronic sensors is that making them function accurately and reliably for use in a variety of applications increases their cost.
In response to the plethora of electronic devices, a variety of optical devices have been designed with the goal of increasing reliability and safety. For example, U.S. Pat. No. 5,687,687 describes a sensor having a series of LED's where each is surrounded by a receiving lens. This sensor is connected to the vehicle ECU which interprets the transmitted signal and displays a low or high indication on the vehicle dash.
An additional type of optical sensor is described in U.S. Pat. Nos. 6,173,609 and 6,668,645. Both these patents describe using a light source, bundled wave guides, and a sensor. The bundled wave guides are configured so that the amount of light from the light source that reaches the sensor is indicative of the fluid volume.
Increased reliability and safety unfortunately comes with increased complexity and increased cost. While these devices could easily be substituted for a dipstick, they lack the simplicity, reliability, and very low cost that a dipstick provides.
One object of the present invention is a fluid measurement device having the simplicity of a dipstick without its inherent drawbacks.
Another object of the present invention is a fluid measurement device that is inexpensive and reliable.
These and other objects of the invention are satisfied by an optical sensor for detecting a level of a liquid in a reservoir, the optical sensor including: a display; a light pipe optically connected to the display and extending to a level of interest in the reservoir, where the light pipe is formed from a material having a refractive index higher than air's refractive index and less than or equal to the liquid's refractive index; and a light optically connected to the light pipe.
The present invention takes advantage of the behavior of light in a light pipe (i.e., glass rod, plastic rod, or optical fiber) having a specific refraction index when the light pipe is surrounded by air or simultaneously surrounded by air and touching a liquid. Where a light pipe has a refraction index higher than air's refractive index, and if the light pipe is illuminated at one point and surrounded by air, the light stays in the light pipe. In addition, when the light pipe's refractive index is also less the refraction index of a liquid to be measured, when the light pipe is illuminated and touches the liquid, all the light escapes from the light pipe through the liquid.
The light pipe 30 must be formed of a material having an index of refraction greater than air and less than or equal to the index of refraction for the liquid whose level is to be determined. In the example shown in
In the example illustrated in
The number of light pipes used may be varied according to the particular application. The present invention is intended to cover the use of one, two, three, four, to any plurality of light pipes. For example, a bundle of fiber optics may be utilized and arranged at levels of interest in the fluid so as to permit the monitoring of the fluid level in the reservoir from zero to completely full.
In addition, the present invention can be configured in a number of ways. If used as a direct replacement for the dipstick, the display can be placed at a location that is visible only when the hood of the vehicle is open. By configuring the light source 50 to illuminate only when the hood is open, energy is conserved and the useful life of the light source extended. As a dipstick replacement the present invention is ideal. It is easy and inexpensive to manufacture, completely avoids the problem of introducing foreign material into the oil pan, and can be checked whenever necessary merely by opening the hood. Within the scope of the present invention is the replacement of all the various dipsticks and other methods used to monitor fluid levels such as power steering fluid, brake fluid, battery electrolyte levels, windshield washer fluid, etc. and/or the use of an unified display for all the monitored reservoirs. Further, although the invention has been described with the display mounted under the hood, it would also be possible to mount the display in a variety of other locations such as on the dashboard or at any other convenient location.
It is to be understood that although the invention has been described with particular reference to specific embodiments thereof, the forms of the invention shown and described are to be taken as a non-limiting embodiment and various changes and modifications may be made to the invention without departing from its spirit and scope as defined by the Claims.
