DEVICE FOR SENSING AND INDICATING THE STATE OF A FLOWING MEDIUM

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 said sensed value. According to the invention, the sensor means (10) is coupled into the conduit (8) and is provided with a channel which, when coupled, is a portion of the conduit. The sensor means (10) has two electrodes insulated from each other, which 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 lies beyond a predetermined threshold value.

Description: Device for sensing and indicating the state of a flowing medium. The invention relates to a device for sensing and indicating the state of a medium in a conduit, said device comprising a sensor means for sensing the value of a parameter of the medium in the conduit and an indicator means which is coupled to the sensor means and is intended to provide an indication depending on the sensed value. The device according to the invention is primarily intended for sensing and indicating the state of a brake fluid in a vehicle brake system. Brake fluids for vehicle brake systems are hygroscopic, which means that 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 to be unsuitable for use and should therefore be replaced. This can be done after a certain period of use determined by experience, but lately apparatii have begun to be used to check the state of the brake fluid. One such 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 resistance of the brake fluid changes as a function of the percentage of water in the brake fluid, measuring re¬ sistance may provide a good measure of the water content of the brake fluid. The known devices for checking the brake fluid are, however, difficult to use, and they cannot be used to provide an indi¬ cation, during replacement of brake fluid in the brake sys- tem, of when a sufficient amount of old brake fluid has been drained off at the same time as new brake fluid is put in. One can never be sure that all brake fluid has been removed from the braking system without wasting new brake fluid. The purpose of the present invention is to provide a device of the type described by way of introduction which is of simple construction and is easy to use as well as reliably providing an indication of when all old brake fluid has been drained off as new brake fluid is poured in, at the same time preventing 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 in- vention by those characterizing features disclosed in the characterizing 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, in which Figure 1 is a partially cut-away, schematic view of a vehicle brake system with a device according to one embodiment of the invention, Figure 2 is a sectional side view of a sensor means included in the device according to claim 1, and Figure 3 is a schematic perspective view of a vehicle with a brake system comprising a device according to another embodi¬ ment of the invention. Figure 1 in the drawing shows a brake system with two wheel brake cylinders la,lb, which are connected via brake lines 2a,2b to a master brake cylinder 3. The master brake cylinder 3 is provided with a brake fluid container 4, which contains brake fluid and is intended, on the one hand, to permit filling of brake fluid into the system and, on the other hand, functions as an expansion vessel during braking. A brake pedal 5 is connected by means of pistons to the master brake cylinder to provide braking when an operator presses his foot 6 down on the brake pedal 5. Each wheel brake cylinder la, lb is provided in a known manner with a bleeder nipple 7a,7b, which is used to bleed the brake system if this should be necessary. The bleeder nipples 7a,7b are, however, also used to drain brake fluid from the brake system when brake fluid is to be changed. In Figure 1, a drain hose 8 is connected to the bleeder nipple 7b to make it possible to replace brake fluid in the portion of the brake system comprising part of the master brake cylinder 3, the brake line 2b and the wheel brake cylinder lb. The bleeder nipple 7b is in that case open and the drain hose extends into a collector bottle 9. When the brake pedal 5 is depressed, brake fluid will be forced through the master brake cylinder 3, the brake line 2b, the wheel brake cylinder lb and the drain hose 8. By filling in 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 drain hose 8. The sensor means 10 is shown in more detail in Figure 2 and is described in more detail below. The sensor means 10 is coupled by means of an electric cable 11 to instruments 12, comprising a current source and at least one indicator 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 an electrically insulating material. The body 14 is provided with connector means 15 for the drain hose 8, and a channel 16 extends through the connector means 15 and the body 14 to make possible fluid flow through the sensor means 10, which is coupled into the drain hose 8 and forms a part thereof. Two electrodes 17 and 18 extend from outside the body 14 through the body 14, terminating in the channel 16 spaced from each other. The electrodes 17 and 18 are connected to the cable 11 and are coupled thereby to the instrument 12 and the indicator means 13. When the device shown in Figures 1 and 2 is used, the resis¬ tance sensed in the brake fluid between the tips of the elec¬ trodes 17 and 18 in the channel 16 will have a certain value when the old brake fluid flows through the drain hose 8. When a sufficient amount of old brake fluid has been drained off and new brake fluid has been filled, all of the old brake fluid will have left the operative portion of the brake system, so that new brake fluid will flow out through the bleeder nipple 7b and through the drain hose 8. When this new brake fluid reaches the sensor means 10 and flows into the channel 16 between the electrodes 17 and 18, the sensed resistance value will change. By suitable calibration of the instrument 12, the indicator means 17 can provide an indica¬ tion as soon as the resistance has risen to a value corre¬ sponding to the value for new brake fluid. This means that the indicator means 13 provides an indication as soon as all the old brake fluid has been drained off and new brake fluid has filled the entire operative portion of the brake system. In this manner, one can be sure that all brake fluid has been replaced and at the same time has reduced the risk of wasting new brake fluid. Figure 3 shows a second embodiment of a device according to the invention. The components in the embodiment according to Figure 3 which have direct counterparts in the embodiment according to Figures 1 and 2, have been 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 cylinder 19 in a schematically shown vehicle 20. The sensor means 10 is of the type shown in Figure 2, and it is coupled into a brake line 21. The electric cable 11 connects the sensor means 10 to the instrument 12, which in this case is arranged to be powered by the vehicle electrical system (not shown) . From the instrument 12, electrical wires 22 lead to an indicator means 13, which in this case is placed at a suitable location on the vehicle instrument panel (not shown) . The embodiment of the device shown in Figure 3 can, by suit¬ able calibration of the sensor means 10 and the instrument 12, provide an indication by the indicator means 13 of when the brake fluid in the brake line 21 has absorbed so much water that it is no longer suitable for use and should be changed. In this manner, an indication is provided in the vehicle 20 of when it is time to change brake fluid. The invention is not limited to the examples described above, but rather changes can be made within the scope of the fol¬ lowing patent claims.

Claims: Claims 1. Device for sensing and indicating the state of a medium in a conduit, said device comprising a sensor means (10) for sensing the value of a parameter of the medium in the con¬ duit, and indicator means (13) which is coupled to the sensor means (10) and is intended to provide an indication dependent on the sensed value, characterized in that the sensor means (10) is coupled into the conduit (8) and is provided with a channel (16) which, when coupled, is a portion of the conduit (8) , that the sensor means (10) has two electrodes (17,18) insulated from each other and extending from outside the sensor means (10) and into the channel (16) , that the indica¬ tor means (13) is provided with or is coupled to a current source for applying a voltage between the electrodes (17,18) of the sensor means (10) , and that the indicator means (13) is 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) lies beyond a predetermined threshold value. 2. Device according to Claim 1, characterized in that the conduit (8) is a conduit for brake fluid, intended to be used for purging a brake system in a vehicle. 3. Device according to Claim 1, characterized in that the conduit (8) is a conduit in a vehicle brake system. 4. Device according to Claim 3, characterized in that the indicator means (13) is disposed on the vehicle instrument panel.

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