METHOD AND DEVICE FOR DETERMINING AND INDICATING THE CONDITION OF A MEDIUM IN A CONDUIT

Abstract: The invention relates to a device for sensing and indicating the state of a medium in a conduit. The device comprises a sensor means (10) for sensing the value of a parameter of the medium in the conduit (8) and an indicator means (13) which is coupled to the sensor means and is intended to provide an indication which is dependent on the sensed value. The sensor means (10) is coupled into the conduit (8) and is provided with a channel which, when the sensor means is coupled in place, constitutes a portion of the conduit. The sensor means (10) has two electrodes which are electrically isolated from each other and extend into the channel. The indicator means is provided with or is coupled to a current source for applying a voltage between the electrodes of the sensor means (10) and is arranged to provide an optical and/or acoustic signal when the resistance of the medium exceeds a predetermined threshold value. According to the invention, a second sensor means in the form of a measuring probe (23) is coupled to an instrument (12) comprising the indicator means (13). The measuring probe (23), when immersed in a medium, senses a calibration value for calibrating the indicator means (13).

Description: Method and device for determining and indicating the condition of a medium in a conduit The invention relates to a device for sensing and indicating the state of a medium in a conduit in accordance with the preamble to claim 1. The device according to the invention is primarily intended for sensing and indicating the state of a brake fluid in the brake system of a vehicle. Brake fluids for brake systems in vehicles are hygroscopic, i.e. they gradually absorb water to a greater or lesser extent. When the water content in the brake fluid exceeds a predetermined value, the brake fluid is considered unsuitable for use and should be replaced. This can be determined by experience after a certain period of use, but apparatuses have begun to be used of late to check the state of the brake fluid. Such an apparatus measures the resistance of the brake fluid, either by removing a sample from the brake system or by measuring directly in the brake fluid container of the master cylinder. Since the electrical resistance in the brake fluid changes as a function of the water content of the brake fluid, the resistance value provides a good indication of the water content of the brake fluid. The purpose of the present invention is to provide a device of the type described by way of introduction, which is easy to use and provides a reliable indication of when all the old brake fluid has been drained off and new brake fluid has been filled, at the same time as one prevents new brake fluid from being wasted. This is achieved by a device of the type described by way of introduction, which is characterized according to the inven¬ tion by those features which are disclosed in the character¬ izing clause of claim 1. Advantageous embodiments of the invention are disclosed in the subclaims. The invention will be described in more detail below with reference to the accompanying drawing, where Figure 1 is a partially cut-away, schematic view of a brak system in a vehicle and with a device according t one embodiment of the invention, Figure 2 is a cut-away side view of a sensor means include in the device shown i Figure 1, Figure 3 is a schematic perspective view of a vehicle with a brake system comprising a device according to another embodiment of the invention, and Figure 4 is a schematic view of an instrument included in the device according to the invention. Figure 1 shows a brake system with two wheel brake cylinde la, lb, which are connected via brake lines 2a, 2b to a mast brake cylinder 3. The master brake cylinder 3 is provided with a brake fluid container 4, which contains brake fluid and is intended to both fill the system with brake fluid a function as an expansion vessel when braking. A brake peda is connected to pistons in the master brake cylinder to achieve braking when an operator presses his foot 6 on the brake pedal 5. Each wheel brake cylinder la, lb is provided in a known man with a purging nipple 7a,7b which is used to purge the bra system of air if it should be necessary. The purging nippl 7a, 7b are, however, also used to drain off brake fluid fro the brake system when the brake fluid is to be replaced. In Figure 1, a draining hose 8 is connected to the purging nipple 7b to make it possible to replace brake fluid in th portion of the brake system comprising: a part of the mast brake cylinder 3, the brake line 2b and the wheel brake cylinder lb. The purging nipple 7b is in this case open and the draining hose extends down into a collecting container 9 When the brake pedal 5 is depressed, the brake fluid will be forced through the master brake cylinder 3, the brake line 2b, the wheel brake cylinder lb and the draining hose 8. By filling new brake fluid into the brake fluid container 4, this new brake fluid will at the same time replace the old brake fluid. According to the invention, a sensor means 10 is arranged in the draining hose 8. The sensor means 10 is shown in more detail in Figure 2 and will be described in more detail below. The sensor means 10 is coupled by means of an elec- trical conductor 11 to instruments 12, comprising a power source and at least one indicating means 13 for indicating the resistance sensed by the sensor means 10 in the manner described below. The sensor means 10 is shown in more detail in Figure 2. It comprises an essentially cylindrical body 14, preferably of electrically insulating material. The body 14 is provided with connector means 15 for the draining hose 8, and a chan¬ nel 16 extends through the connector means 15 and the body 14 to make possible fluid flow through the sensor means 10, which is thus coupled into the draining hose 8 and forms a portion thereof. Two electrodes 17 and 18 extend through the body 14 and out from the side thereof, and the electrodes 17 and 18 terminate in spaced relationship the channel 16. The electrodes 17 and 18 are connected to the electrical con¬ ductor 11 and by means thereof are coupled to the instrument 12 and the indicator means 13. When using the device according to Figures 1 and 2, the elec- trical resistance sensed in the brake fluid between the tips of the electrodes 17 and 18 in the channel 16 will have a certain value when the old brake fluid flows through the draining hose 8. When a sufficient amount of old brake fluid has been drained off and new brake fluid has been filled in, all of the old brake fluid will have left the relevant po tion of the brake system, so that new brake fluid will be forced out through the purging nipple 7b and flow through draining hose 8. When this new brake fluid reaches the se means 10 and flows into the channel 16 between the electr 17 and 18, the sensed resistance value will be changed. B suitable calibration of the instrument 12, the indicator means 13 can provide an indication as soon as the resistan has increased to a certain value corresponding to the valu for new brake fluid. This means that the indicator means 1 will provide an indication as soon as all the old brake fl has been drained off and new brake fluid has filled the entire relevant portion of the brake system. In this manne it is possible to be certain that all brake fluid has been replaced and at the same time reduce the risk of new brake fluid being drained off. Figure 3 shows another embodiment of a device according to the invention. Those components in the embodiment shown in Figure 3 which have their direct counterparts in the embod ment shown in Figures 1 and 2, are provided with the same reference numerals. As can be seen in Figure 3, the sensor means 10 in this case is connected to a wheel brake cylind 19 in a vehicle 20 (shown only schematically) . The sensor means 10 is of the type which is shown in Figure 2 and it coupled into a brake line 21. The electrical conductor 11 connects the sensor means 10 to the instrument 12, which i this case is arranged to be powered by the vehicle electri system (not shown) . From the instrument 12 an electrical c ductor 22 leads to the indicator means 13, which in this c is mounted at a suitable location in the vehicle 20 instru ment panel (not shown) . The embodiment shown in Figure 3 of the device according t the invention can, through suitable calibration of the sen means 10 and the instrument 12, provide an indication, by means of the indicator means 13, of when the brake- fluid i the brake line 21 has absorbed so much water that it is no longer suitable for use and should therefore be replaced. In this manner, an indication is provided in the vehicle 20 of when it is time to replace the brake fluid. Figure 4 shows an embodiment of the instrument 12, which can be used for calibrating the device, since it has been shown that new brake fluids of different manufacturers and differ¬ ent types have different electrical properties. In order to achieve a calibration of the instrument 12, it is provided, as shown in Figure 4, with a measuring probe which is coupled to the instrument 12 by means of a wire 24. When calibrating the instrument 12, the measurement probe 23 is immersed in the new brake fluid which is to be filled into the brake system, and a calibrating button 25 is pressed down. The electrical resistance in the brake fluid is measur¬ ed by the measuring probe 23 and the measured value is fed into the instrument 12. The brake fluid is then replaced by conducting the new brake fluid through the brake system and thus replacing the old brake fluid which is drained off. When the new fluid has reached the sensor means 10, the instrument 12 will provide an acoustic and/or visible signal when the resistance of the flowing fluid has the same value as the value stored in the instrument 12. This means that new brake fluid has reached the sensor means 10 and the entire brake system is filled with new brake fluid. By measuring the resistance of the new brake fluid and of brake fluid with a predetermined water content and boiling point, it is possible to determine with great accuracy the state of a used brake fluid. The electrical resistance of the brake fluid as a function of the water content, and thus also of the boiling point of the fluid, follows a curve which can be converted into a four-digit code, which can be entered into the instrument 12. The invention is not limited to the embodiments described above. Rather, changes can be made within the scope of the following patent claims.

Claims: Claims 1. Device for sensing and indicating the state of a mediu in a conduit, said device comprising a sensor means (10) sensing the value of a parameter of the medium in the con¬ duit, and an indicator means (13) which is coupled to the sensor means (10) and is intended to provide an indicatio dependent on the sensed value, the sensor means (10) bein coupled into the conduit (8) and being provided with a ch nel (16) which, when coupled in, constitutes a portion of the conduit (8), and having two electrodes (17,18) which a electrically isolated from each other and extend from the outside of the sensor means (10) and project into the chan (16) , the indicator means (13) being provided with or bein coupled to a current source for applying a voltage between the electrodes (17,18) of the sensor means (10) and being disposed to provide an optical and/or acoustic signal when the resistance of the medium between the electrodes (17,18 of the sensor means (10) exceeds a predetermined threshold value, characterized in that a second sensor means in the form of a measuring probe (23) is coupled to an instrument (12) comprising the indicator means (13) , said measuring probe (23), when immersed in a medium, sensing a calibrati value for calibrating the indicator means (13) . 2. Device according to Claim 1, characterized in that the conduit (8) consists of a conduit for brake fluid, intende to be used for purging air from a brake system in a vehicl 3. Device according to Claim 1, characterized in that the conduit (8) consists of a conduit in a brake system in a vehicle. 4. Device according to Claim 3, characterized in that the indicator means (13) is disposed on the instrument panel o the vehicle. 5. Process for calibrating a device according to a device according to one of Claims 1-4, characterized in that the measuring probe (23) is immersed in a medium and that the value of the parameter in question is fed into the indicator means to serve as a starting value for subsequent measurement for the sensor means (10) .

Inventors: GUSTAFSSON MORGAN, GUSTAFSSON, MORGAN
Applicants: GUSTAFSSON MORGAN, NYBERG BO ERIK, GUSTAFSSON, MORGAN, NYBERG, BO, ERIK
Application year: 1995
Main classification: G01N27
IPC codes: B60T17, G01N27, G01N33