Title of Invention

A DEVICE FOR MEASURING A PLURALITY OF FLUID PRESSURES

Abstract

(57) Abstract: To measure a plurity of plurality of fluid pressure the invention proposes a sensor plate (30) having fastening holes (32) which are arranged disrubuted over the sensor, plates (30) in the manner of a matrix. Located b etween the fastening holes (32) are measuring disphrams (18) which form and walls of blind bores (20) in the sensor plate (30). The measuring disphrams (18) can be loaded with pressure through fluid ducts of a hydraulic block to whivh the sensor plate (30) can be screwed. Evaluation. tekes place by means of four strain guages (24,25) which are attached to each measuring diaphram (18) and which are interconnected to form a full bridge (wheatstone bridge). The possibility of stress-optimised attachment of the sensor plate (30) allows measurement of various pressure with the least possible measuring error by means of one sensor plate(30) (Figure 3) PRICE: THIRTY RUPEES

Full Text

Prior art The invention relates to a device for measuring a plurality of fluid pressures according to the pre-characterizing clause of the main claim. It is provided particularly to be mounted on a hydraulic block which serves for the hydraulic control of a vehicle brake system. In hydraulic powex brake systems which are equipped with an electrically driven hydraulic pump for generating brake pressure, it is necessary to measure the brake-fluid pressure in wheel-brake cylinders and at other points of the brake system, for example in a brake master cylinder or a hydraulic accumulator. The measured pressures aire converted into electrical signals and fed to an electronic control unit which controls or regulates the vehicle .brake system. It is known to measure the brake-fluid pressure at the various points of the brake system in each case by means of a pressure sensor which is mounted at the respective point or centrally on the hydraulic block and which communicates with the respective points of the brake system via hydraulic conduits. This has the disadvantage of a high outlay in terms of construction. Advantages of the inveatian The pressure-measuring device according to the invention, having the features of the main claim, posses¬ses a sensor plate with, a plurality of meaouxlag dia-_ phragms for measuring different pressures. It is provided particularly for hydraulic vehicle brake systems, but can be used just as well for measuring pressures of any fluids. The measuring diaphragms are arranged on the sensor plate, being uniformly distributed in the manner of a matrix. They can be located, for example, at corners of imaginary equilateral triangles (triangular matrix) or squares (square matrix) or, for example, also in a manner distributed equidistantly on one or more imaginary concentric circles. Means for fastening the sensor plate, that is to say, for example, screw holes, are arranged uniformly around each measuring diaphragm, with the result that individual fastening means are at the same time sur¬rounded by a plurality of measuring diaphragms. Each measuring diaphragm is surrounded by an equal number of fastening means which are preferably all at the same distance from the respective measuring diaphragm. Thus, for example when the measuring diaphragmis and fastening means are arranged on triangular or square matrices, each measuring diaphragm is located in the middle of aa imaginary equilateral triangle or square, the comers of which are formed by the fastening means surrounding the measuring diaphragm. When the measuring diaphragms are arranged ecfuidistantly on a circle, for example one fastening means is located in the middle of the circle and a n\imber of fastening means identical to the number of measuring diaphragms is located on a mid-bisector between two measuring diaphragms in each case, on a concentric circle surroiinding the measuring diaphragms, so that each measuring diaphragm is located in each case between three fastening means. The advantage of the invention is that a requisite number of measuring diaphragms can be accom¬modated in a simple way on a common sensor plate. The mounting and sealing-off of the sensor plate, for example on a hydraulic block, are simple and can be carried out quickly, and the pressure sensors required are inexpen¬sive to produce. The xmiformly distributed arrangement of the measuring diaphragms between an equal number of fastening means in each case ensures a low-stress mount-ing of the sensor plate, for example on the hydraulic block. The measuring diaphragms are virtually stress-free, this being a precondition for accurate measurements with the least possible error over a long period of use. As a result of the identical arrangement of each measur¬ing diaphragm between an equal number of fastening means, the measuring diaphragms are deformed equally under the same pressure load, so that each measuring diaphragm supplies an identical measurement signal for the same pressure. A further advantage of the invention is that the measuring diaphragms of the sensor plate, which are arranged close to one another, and the selected arrange¬ment of the measuring diaphragms relative to one another allow short electrical contacting with a central evaluartion circuit, this likewise increasing the measur¬ing accuracy. In particular, there is no need, between the measuring diaphragms and the evaluation circuit, for plug connections and long cables which may lead to increased transition resistances as a consequence of corrosion and ageing and which falsify the measurement result. The subclaims relate to advantageous embodiments and developments of the invention specified in the main claim. To measure the fluid pressures, according to Claim 4, preferably extensible electrical resistors are attached on the outside or inside of each measuring diaphragm. These are deformed elastically, together with the measuring diaphragm, as a result of the loading of the latter with the fluid, the pressure of which is to be measured, and at the same time change their electrical resistance value. This change in resistance is used for determining the fluid pressure. For example, strain gauges can be applied as extensible electrical resistors to the measuring diaphragms by the thin-film, thick-film or foil technique. To reduce the measuring error, according to Claim 5 four extensible electrical resistors are attached to each measuring diaphragm and are interconnected as a so- called full bridge (Wheatstone bridge), as a result of which, for example, changes in resistance caused by temperature changes can be compensated. The arrangement of the four full-bridge resistors according to Claim 6 likewise serves for improving the measurement result. In each case two resistors are arranged in the middle of a measuring diaphracgm and the other two resistors are arranged diametrically opposite one another on the circximference of the measuring diaphr¬agm. These are the zones of the greatest mechanical stresses directed in opposition. The directions of extension of the four resistors run parallel to one another and to an imaginary diametral line through the two resistors attached to the circumference of the measuring diaphragm. In each case one outer resistor is connected in series with one middle resistor. This arrangement of the four bridge resistors affords maximum pressure sensitivity of the bridge connection. By means of a sheet-like sealing element accor¬ding to Claim 10 with one-piece 0-rings, the blind holes in the sensor plate, which have the measuring diaphragms can be sealed off, for example relative to the hydraulic block, at the least possible outlay. Faces of the sensor plate and of the hydraulic block which confront one another do not need to be provided with recesses for the insertion of sealing rings. The sheet-like sealing element serves for positioning the 0-rings during assemb¬ly. It does not need to be present over the entire area of the sensor plate, for example webs which connect the 0-rings to one another are sufficient. Accordingly, the present invention provides a device for measuring a plurality of fluid pressures, characterized in that it has a sensor plate (12, 30) with a plurality of measuring diaphragms (18) to which the fluid to be measured can be applied from one side through fluid ducts (38) of a component (34) on which said sensor plate (12, 30) is mounted, said measuring diaphragms (18) are located, distributed in the manner of a matrix on the sensor plate (12,30) and said sensor plate (12, 30) has attachment devices (14, 16, 32) for mounting on the component (34) which attachment devices (14, 16, 32) are located, distributed in the manner of a matrix on said sensor plate (12, 30) in such a way that a measuring diaphragm (18) is located in the centre between an equal number of attachment devices (14, 16, 32). The pressure-measuring device according to the invention is explained in more detail below by means of two exemplary embodiments with reference to the accompanying drawings, In this: Figure 1 shows a perspective representation of a round sensor plate according to the invention, shown in section; Figure 2 shows an enlarged detail from Figure 1; Figure 3 shows, in section, a rectangular sensor plate according to a second embodiment of the invention; Figure 4 shows a sectional representation of a pressure-measuring device according to the invention; Figure 5 shows a perspective representation of the pressure-measuring device of Figure 4; Figure 6 shows an exploded representation of the pressure-measuring device of Figure 4; and Figure 7 shows an electrohydraulic vehicle brake system according to the invention. The figures are drawn to scales which differ from one another. Description of the exemplary embodiment The pressure-measuring device 10 according to the invention, represented in Figure 1, has a circular sensor plate 12 made of metal. It can also consist, for example, of ceramic. It has altogether seven screw holes 14, 16 as fastening means for attaching the sensor plate 12 to another component. One of the screw holes 16 is located in the middle of the sensor plate 12, and the other six screw holes 14 are arranged equidistantly to one another near the edge on the circumference of the sensor plate 12. The near-edge screw holes 14 are at the same distance from the middle screw hole 16 as from each of the adjacent near-edge screw holes 14. At the mid-point of an imaginary triangle, the corners of which form two adjacent near-edge screw holes 14 and the middle screw hole 16, a measuring diaphragm 18 is located in each case. As a result of this distribution of the screw holes 14, 16 and measuring diaphragms 18 on the sensor plate 12, the measuring diaphragms 18 remain virtually stress-free when the sensor plate 12 is attached to a component. Any residual stress possibly present despite this stress-optimised placing acts in the same way in each measuring diaphragm 18 by virtue of the identical arrangement of each measuring diaphragm 18 in the middle between three screw'holes 14,16. "Small measuring errors caused by such residual stresses are therefore the same for all six measuring diaphragms 18, that is to say, with the meas- ured values being the same, the same pressure prevails on the measuring diaphragms 18. The measuring diaphragms 18 are in one piece with the sensor plate 12 (Figure 2), and they are formed by a blind hole 2 0 from a fastening side 22 of the sensor plate 12, the said fastening side coming to bear on a component to which the sensor plate 12 is fastened. The blind holes 20 can, for example, be drilled or, when the sensor plate 12 is a sintered part, be made during the sintering operation. One end wall of the blind holes 20 forms the measuring diaphragms 18. The diaphragm dieuneter is 10 mm. In the exemplary embodiment, the diaphragm thickness is between 0.5 and 1 mm, depending on the pressure, for the measurement of which the pressure-measuring device according to the invention is to be used, and on the bursting pressure which the measuring diaphragms 18 must withstand. In the exemplary embodi¬ment, the measured pressure is up to 250 bar, the pre¬scribed bursting pressure being 1200 bar. Four strain gauges 24, 25 are attached to each measuring diaphragm 18 by the thin-film thick-film or foil technique, of which strain gauges two 24 are arranged diametrically opposite one another in the edge region of the measuxing dietphragms L8 and the other two 2 5 are arranged next to one another in their centre. All four strain gauges 24, 25 are arranged parallel to one another and with their longitudinal direction and direc¬ tion of extension parallel to an imaginary diametral line through the two strain gauges 24 attached at the edge. In the event of a deformation of the measuring diaphragm 18 caused by pressure load, the strain gauges 24, 25 are extended or compressed and change their electrical resistance, which is used for determining the pressure. By means of conductor tracks 26, the resistors 24, 25 are 3 5 interconnected to form a full bridge (wheatstone bridge) and are connected electrically conductively to four cohhectihg contacts 28. ~ Figure 3 shows a second embodiment of a sensor plate 3 0 of a pressure-measuring device according to the invention. The sensor plate 30 is rectangular, altogether six measuring diaphragms 18, together with attached resistance bridges 24, 25, being arranged in two rows next to one another, the rows being offset relative to one another by the amount of half the distance between two measuring diaphragms 18, that is to say the measuring diaphragms 18 are "staggered" relative to the measuring diaphragms 18 of the other row in each case. In this way, each measuring diaphragm 18 is at the same distance from the adjacent measuring diaphragms 18, and they are located at corners of imaginary equilateral triangles. Screw holes 32 are arranged between and around the six measuring diaphragms 18 in the manner of a triangular matrix having equilateral triangles. As in the case of the roiind sensor plate 12 too, the measuring diaphragms 18 are therefore located in the middle of an imaginary equilateral triangle, the comers of whivh are formed by three screw holes 32. With the exception of the shape of the sensor plate 3 0 and of the arrangement of the measuring dia¬phragms 18 and screw holes 32, this sensor plate is identical to the sensor plate 12 represented in Figure 1 and functions in the same way. To avoid repetition, reference is made thus far to the statements made with regard to Figures 1 and 2. The pressure—measuring device according to the invention is explained below by means of the rectangular sensor plate 30, the statements also applying accordingly to the round sensor plate 12. Figures 4 and 5 show a pressure-measuring device according to the invention in which the rectangular sensor plate 3 0 is screwed to a hydraulic block 34 by means of screws 3 6 inserted through the screw holes 32 of the sensor plate 30. The section, shovm in Figure 4, through the pressure-measuring device according to the invention passes alternately through a screw hole 32 and through a blind hole 20 of a measuring diaphragm 18 which are actually located in two different planes. A fluid duct 38, through which a measuring diaphragm 18 earn be loaded with fluid, opens in each case into one of the blind holes 20. For sealing, a sealing plate 40 is inserted between the sensor plate 30 and the hydraulic block 34 (Figure 6), the said sealing plate having O-rings 42 which are in one piece with it and which posi¬tion it on the blind holes 20 of the measuring diaphragms 18. When the sealing plate 40 is not fitted, a cord diameter of the 0-rings 42 is larger than the sealing plate 40 is thick. To measure the electrical resistance values of the strain gauges 24, 25 and to determine the pressure prevailing in the blind holes 20 from the resistance values, the connecting contacts 2 8 of the strain-gauge measuring bridges 24, 25 are connected to an evaluation circuit 46 by means of thick-wire bonds 44, that is to say by means of aluminium wires, which are attached to Che connecting contacts 2 8 by friction welding. The evaluation circuit 46 is mounted on a flat carrier 48 which, in top view, has the shape of a double-T and which is screwed with its web to the hydraulic block 34 so as to extend at a sight distance above the sensor plate 30. The connecting contacts 28 are located freely accessibly close to one edge of the carrier 48 on the sensor plate 30. This also applies to the use of the round sensor plate 12, represented in Figure 1, in which the connec¬ting contacts of any three measuring diaphragms 18 are arranged on a straight line. The evaluation circuit 46 is located at the centre of the six measuring diaphragms 18, so that short electrical connection distances, preferably of equal length, from the strain gauges 24, 25 to the evaluation circuit 46 are obtained. This allows accurate pressure measurements with the smallest possible measur¬ing errors. The evaluation circuit 46 can evaluate the resis-tance values of the strain gauges 24, 25 of all six measuring diaphragms 18 separately. In one embodiment of the invention, the resistance values of the strain gauges 24, 25 of the measuring diaphragrames.8 are measured and evaluated in succession in the multiplex mode, so that therefore the resistance values of all six measuring diaphragms 18 are evaluated by the same electronic components. Different measurement results in the case of identical pressure conditions at various measuring diaphragms 18 are thereby avoided. Figure 7 shows a hydraulic vehicle brake system according to the invention using the pressure-measuring device described. The vehicle brake system has two brake systems supplementing one another, namely a service brake system, which generates brake-fluid pressure by means of a hydraulic ptunp 50 and which acts on wheel-brake cylin¬ders 52, 54 of all the vehicle wheels, and an auxiliary brake system which procures its brake-fluid pressure from a pedal-operated brake master cylinder 55, which acts only on the wheel-brake cylinders 52 of two vehicle wheels of one axle. Each wheel-brake cylinder 52, 54 has a first shut-off valve 56 opened in the basic position and a second shut-off valve 58 closed in the basic position. When a brake pedal 62 of the brake master cylin¬der 55 is operated, a pedal-position sensor 64 and a pressure sensor 74 transmit an electrical signal to a control circuit, not shown, for the brake system, the said control circuit controlling all the valves and an electric pump motor 66 of the vehicle brake system a according to the invention. The second shut-off valves 58 are opened and the wheel-brake cylinders 52, 54 are thereby loaded with pressure from a hydraulic accumulator 6 8 which is itself put under pressure by the hydraulic pump 50, so that brake fluid under pressure is present even when the hydraulic pump 50 is not in operation. The pressure in the hydraulic accumulator 6 8 is monitored by a pressure sensor 72. A pressure-relief valve 60 protects the hydraulic accumulator 68 against overload. When a brake-fluid pressure dependent on the pressure generated by the brake master cylinder 55 is reached in the wheel-brake cylinders 52, 54, the second shut-off valves 58 are closed. In this case, the first shut-off valves 5€—are closed, so that no brake fluid can escape through them from the wheel brake cylinders 52, 54 during braking by means of the service brake system. The brake-fluid pressure in the wheel-brake cylinders 52, 54, in the brake master cylinder 55 and in the hydraulic accumulator 68 is fed to the measuring diaphragms 18 through conduits and the fluid ducts 3 8 in the hydraulic block 34. The measuring diaphragms 18, together with the strain gauges 24, 25 attached to them and together with the evaluation circuit 46, form pres¬sure sensors 70, 72, 74. Their signal is fed to the control circuit of the vehicle brake system according to the invention. When the brake-fluid pressure in the wheel-brake cylinders 52, 54 is higher than corresponds to the pressure generated by the brake master cylinder 55 and measured by the pressure sensor 74, brake-fluid pressure is reduced by c3pening the fixsl: shut-off valves 56 in the wheel-brake cylinders 52, brake fluid flowing into a reservoir 76 of the brake master cylinder 55. Insofar as a sufficient brake pressure does not prevail in the hydraulic accumulator 58 in the event of a fault in the service brake system, when the brake pedal 62 is operated the first shut-off valves 56 of all four wheel-brake cylinders 52, 54 remain open and the second shut-off valves 58 closed. The two wheel-brake cylinders 52, which are connected to the auxiliary brake system, are loaded with pressure by the brake master cylinder 55 through a brake master cylinder shut-off valve 78 which is opened in its basic position and which, when the service brake system is used, is closed and then separates the brake master cylinder 55 from the wheel-brake cylinders 52, 54 and from the service brake system. When the service brake system is used, a non¬return valve BO, which is closed in its basic position, is opened. Brake fluid can flow through the opened non¬return valve 80 out of the two wheel-brake cylinders 52 connected to the auxiliary brake system back into the reservoir 76 of the brake toaster cylinder 55 when the first shut-off valves 56 are opened. When the auxiliary brake system is used, the closed non-return valve prevents brake fluid from flowing out of the brake master cylinder 55 back into the reservoir 76. A travel simulator 84 known per se is connected to the brake master cylinder 55 via a shut-off valve 82, which is closed in its basic position, and the said travel simulator can receive brake fluid in dependence on the pressure in a way known per se, in order, when the service brake system is used and the auxiliary brake system operated by the brake master cylinder 55 is blocked, to give a driver the customary brake-pedal sensation occurring when the brake pedal 62 gives way according to the foot force exerted on it. WE CLAIM; 1. A device for measuring a plurality of fluid pressures, characterized in that it has a sensor plate (12, 30) with a plurality of measuring diaphragms (18) to which the fluid to be measured can be applied from one side through fluid ducts (38) of a component (34) on which said sensor plate (12, 30) is mounted, said measuring diaphragms (18) are located, distributed in the manner of a matrix on the sensor plate (12, 30) and said sensor plate (12, 30) has attachment devices (14, 16, 32) for mounting on the component (34) which attachment devices (14, 16, 32) are located, distributed in the manner of a matrix on said sensor plate (12, 30) in such a way that a measuring diaphragm (18)is located in the centre between an equal number of attachment devices (14, 16, 32). 2. The device according to claim 1, wherein the measuring diaphragms (18) are designed as end walls of blind holes (20) in the sensor plate (12, 30). 3. The device according to claim 1 or 2, wherein the measuring diaphragms (18) are in one piece with the sensor plate (12, 30). 4. The device according to one of claims 1 to 3, wherein there is attached to each measuring diaphragm (18) at least one extensible electrical resistor (24, 25), of which the length and therefore at the same time its resistance value change during the deformation of the measuring diaphragm (18). 5. The device according to claim 4, wherein there are attached to each measuring diaphragm (18) four extensible electrical resistors (24, 25) which are interconnected to form a full-bridge connection. 6. The device according to claim 5, wherein two resistors (25) are arranged in the middle of a measuring diaphragm (18) and the other two resistors (24) are arranged diametrically opposite one another on the circumference of the measuring diaphragm (18), directions of extension of the four resistors (24, 25) running parallel to a diametral line through the two outer resistors (24), and in each case an outer resistor (24) being connected in series with a middle resistor (25). 7. The device according to one of claims 4 to 6, wherein it has a common electronic evaluation circuit (46) for the resistors (24, 25) of all the measuring diaphragms (18) of the sensor plate (12, 30). 8. The device according to claim 7, wherein a flat carrier (48) for the electronic evaluation circuit (46) engages over the measuring diaphragms (18) in the sensor plate (12, 30), and in that connecting contacts (28) of the electrical resistors (24, 25) attached to the measuring diaphragms (18) are located freely on the sensor plate (12, 30) next to one edge of the carrier (48) and are connected to the electronic evaluation circuit (46) by electrical connection means (44). 9. The device according to claim 7 or 8, wherein the evaluation circuit (46) works in the multiplex mode. 10. The device according to one of claims 2 to 9, wherein a sheet-like sealing element (40) can be inserted between the sensor plate (12, 30) and the component (34) having the fluid ducts (38), the said sealing element having 0-rings (42), which are in one piece with it and which surround mouths of the blind holes (20) in the sensor plate (12, 30), and having fluid passage orifices within the O-rings (42). 11. A hydraulic brake system with a device for measuring a plurality of fluid pressures as claimed in any one of the preceding claims. 12. A device for measuring a plurality of fluid pressures, substantially as herein described with reference to the accompanying drawings.

Documents:

0856-mas-1996 abstract.pdf

0856-mas-1996 claims.pdf

0856-mas-1996 correspondence-others.pdf

0856-mas-1996 correspondence-po.pdf

0856-mas-1996 description (complete).pdf

0856-mas-1996 drawings.pdf

0856-mas-1996 form-1.pdf

0856-mas-1996 form-26.pdf

0856-mas-1996 form-4.pdf

0856-mas-1996 others.pdf

0856-mas-1996 petition.pdf