Measuring and testing – Liquid level or depth gauge – Immersible electrode type
Reexamination Certificate
1998-09-16
2001-10-30
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Immersible electrode type
C073S149000, C073S075000, C073S335050, C073S025050, C073S295000, C338S038000, C374S021000, C374S027000
Reexamination Certificate
active
06308564
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention relates to a method and an apparatus for determining and/or monitoring the quantity and quality of a fluid in which a lowering of the boiling temperature is symptomatic of a deterioration in quality. This is the case in particular with hygroscopic fluids, for example with glycol-based brake fluids or with engine oil.
Since the boiling point of brake fluid is known to be lowered by absorption of water, with the result that the serviceability of the brake is reduced if the brake fluid is strongly heated, monitoring the state of the brake fluid is particularly important. Furthermore, it is also expedient in this connection to establish the filling level of the brake fluid in the hydraulic system.
DE 36 39 664 C2 already discloses a method and an apparatus for monitoring the state or the condition of a hydraulic fluid, the boiling point being determined with the aid of sensor elements. Apart from the boiling point, the momentary temperature of the fluid is measured. As a measure of the temperature difference between the boiling point and the momentary temperature, a so-called “thermal reserve” is formed and displayed.
DE 41 13 443 C2 discloses an apparatus for detecting a liquid or gaseous medium, in particular a fluid filled to a certain level in a vessel, having at least one sensor unit which can be brought into contact with the medium. For this purpose, a heating element and a temperature sensor are used, the influencing of the temperature sensor by the heating element taking place in a way dependent on the presence or absence of fluid of the medium to be tested.
SUMMARY OF THE INVENTION
Against this background, the invention is based on the object of specifying a method and apparatus with which both the filling level or the quantity and the condition or quality of a fluid are automatically determined in a simple but reliable way.
This object is achieved according to the invention by both the filling level and the condition of the fluid—in particular a hygroscopic fluid—being determined successively one after the other by a single sensor of a measuring instrument.
The method according to the invention has the advantage that the determination or measurement of the quantity and quality of the brake fluids in the system can be carried out at any time and by personnel who are not specially trained, without taking an inordinate amount of time. Apart from monitoring brake fluid, the method according to the invention is also suitable for monitoring other fluids, such as engine oil for example.
It has proven to be particularly advantageous for determining the filling level to heat a temperature-dependent resistance element which is located in the system and represents the sensor by applying a current to it and at the same time measuring the voltage across the resistance element, at least two voltage values being used for determining the filling level.
A further advantageous design of the invention comprises determining the condition or quality of the fluid by raising the temperature of the temperature-dependent resistance element by applying to it a current of such an intensity that the boiling temperature of the fluid to be tested is not quite reached if it is of a given quality, by at the same time measuring the voltage across the temperature-dependent resistance element and by comparing this voltage characteristic with the voltage characteristics typical of different qualities.
It is expedient here that the determination of the quality of the fluid takes place only when the entire temperature-dependent resistance element is covered with fluid.
In another embodiment of the invention, it is proposed that, for determining the quality of the fluid, the temperature of a heating. resistance element is increased by applying to it a current of such an intensity that the boiling temperature of the fluid to be tested is not quite reached if it is of a given quality, by at the same time measuring the voltage across the temperature-dependent resistance element when it is supplied with current of low intensity and by comparing this voltage characteristic with the voltage characteristics typical of different qualities.
It has proven to be expedient here for the measured voltage value to be used for calculating the ambient temperature immediately after switching on the current and for the value obtained from this to be stored and taken into consideration when supplying current to the heating resistance element.
It has been found to be an advantageous variant of the invention for the temperature of the fluid to be initially increased by applying current to the sensor containing a temperature-dependent resistance element, by at the same time determining the filling level by measuring the voltage across the temperature-dependent resistance element, by then using this voltage as a criterion for initiating the quality determination or not initiating it if the fluid level is low, by then, if proceeding with the determination of the quality of the fluid, applying to a heating resistance element contained in the sensor a current of such an intensity that the boiling temperature of the fluid to be tested is not quite reached if it is of a given quality, by at the same time measuring the voltage across the temperature-dependent resistance element supplied with current of low intensity and by finally comparing this voltage characteristic with the voltage characteristics typical of different qualities, an automatic signaling of the filling level and quality of the fluid taking place optically and/or acoustically.
In various applications of the method according to the invention, measurements need be performed only at relatively large time intervals, measurements while the motor vehicle is at a standstill being preferable. For this purpose, it is provided in a development of the method according to the invention that the determination of the filling level and/or the determination of the quality of the fluid take(s) place in the time between opening a motor vehicle and starting the engine of the motor vehicle.
An apparatus for carrying out the method according to the invention comprises the sensor arranged in the fluid system being connected to a measuring instrument, which includes on the one hand a current source for supplying current to the sensor and on the other hand a voltmeter for determining the voltage at the sensor, and furthermore comprises the provision of a computer for controlling the measuring sequence and also an optical and/or acoustic display device.
In a development of this apparatus, it is provided that the sensor comprises a temperature-dependent resistance element.
Another development of this apparatus provides that the sensor has in addition to the temperature-dependent resistance element a heating resistance element.
In this case, it is advantageous that the two resistance elements are arranged close to each other. It has proven to be expedient for the heating resistance element to be arranged underneath the temperature-dependent resistance element.
An advantageous application of the apparatus according to the invention is that the hydraulic fluid system is a braking system with a glycol-based brake fluid.
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Acht Joachim
Porth Wolfgang
Wallrafen Werner
Wehrmeyer Volker
Cygan Michael
Farber Martin A.
Mannesmann VDO AG
Williams Hezron
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