SYSTEM FOR DETERMINING THE LOAD OF A VEHICLE OR THE LIKE

Abstract: A system for determining the load of a vehicle or the like, comprising one or more measuring units (22), each to be connected with two measuring points, with a transmitter and a receiver for sound waves, and by a control and processing unit (26) which is connected to the or each measuring unit (22) and is equipped for determining the transit time of the sound waves between the transmitter and the receiver and for deriving therefrom the distance between the two measuring points.

Description: System for determining the load of a vehicle or the like. The invention relates to a system for determining the load of a vehicle or the like according to the preamble of claim 1. Measuring the load condition of a vehicle by means of measuring a distance between two measuring points on the vehicle which is representative of the load is generally known. The object thereof is, for example, to check on overloading or underloading, on volume or weight units supplied and to be supplied for a load to be carried, on illegal loading and/or unloading of loads etc. This can be for lorries with a loading platform, tankers or private cars, but it can also be for aircraft on the ground. The check on overloading and underloading is an absolute measurement which does not have to be very accurate, and in the case of which only a specific maximum load, possibly per wheel or per wheel set of the vehicle, must not be exceeded, and therefore has to be monitored. The check on units of goods for loading and unloading, on the other hand, requires an accurate relative measurement, in order to ensure that small weight changes can still be detected. The known systems for determining the load of a vehicle or the like are based on converters, which convert a distance between two points on a vehicle into an analogue voltage which therewith is a measure of the vehicle load, at least a part thereof. The above- mentioned converters work by means of inductive, capacitive or resistive elements and are very inaccurate and expensive, partly due to the large measuring range required, which is generally of the order of the spring travel of the vehicle. The object of the invention is to diminish these disadvantages by providing an accurate and cheap system for determining the load of a vehicle or the like which is characterized as described in claim 1. Advantageous embodiments of the system according to the invention are described in the sub-claims. Acoustic distance measuring devices, which are known per se, like the corresponding electronic circuits, can currently be manufactured cheaply. In principle, a contactless measurement takes place between two points, so that no mechanical wear of the converter need occur. It is common to control the transmitter of acoustic measuring devices in such a way that it transmits ultrasonic sound waves. The distance between two measuring points can be measured very accurately in this way, in each case about ten times more accurately than in the load checking systems according to the state of the art. The invention is explained with reference to the drawing, in which: Fig. 1 shows a schematic representation of a supporting structure of a vehicle, with remote measuring means according to the invention; Fig. 2 shows a diagram of a system according to the invention; and Fig. 3 shows a schematic representation of the supporting structure of Fig. 1, with other load measuring devices according to the invention. Fig. 1 shows a rear axle 2 of a lorry with rear wheels 4 and 5 and a differential 6. The rear axle 2, by means of springs 8 and 9, supports a chassis 10, on which rests a loading platform 12 which is filled with a load 14, for example sand. A transmitter/receiver 16, 17 for sound waves is fitted near each spring 8, 9 on the chassis 10, and opposite it a reflecting surface 18, 19 respectively. When there is an increase or decrease in the load 14, the springs 8 or 9 will compress or recoil, so that the distance between the transmitter/receiver 16 and the reflecting surface 18 and/or the distance between transmitter/receiver 17 and the reflecting surface 19 will decrease or increase; the transit time of a sound wave transmitted by the transmitter, reflected by the appropriate reflecting surface and picked up by the receiver, will consequently decrease or increase proportionately. The transit time of the sound wave thus constitutes a measure of the compression of the spring and consequently for the load situation of the vehicle. In order to reduce the influence of environmental noise on the sound wave detected by the receiver and to eliminate the influence of water and dust on the elements required for the transit time measurement, these elements are accommodated in a closed, flexible casing, for example, a bellows 20 (shown in cross-section in Figs. 1 and 3) . In the embodiment of the transmitter and the receiver it is also conceivable to connect the transmitter to one measuring point and to connect the receiver to the other measuring point. The transmitter and the receiver can, however, also be fitted next to each other at one measuring point, while the other measuring point is connected to a surface reflecting the sound waves. In the preferred embodiment of the system according to the invention shown in Fig. 1, a converter connected to chassis 10 acts as transmitter and as receiver, so that each measuring unit need be equipped with one converter only. Since the converter is the most vulnerable part of a measuring unit, it is connected to the loadable part of the vehicle or the like which has a great mass inertia. The reflecting surface, which can be made robust in design, is connected to the wheel axle or the guiding part thereof, which vehicle parts are exposed to intensive vibrations with great acceleration forces. In general, the movement of the reflecting surface during changes in the load situation of the vehicle or the like is not such that a sound wave directed at a particular angle onto a flat reflecting surface is reflected in the same direction. This is, for example, the case when the position of rear axle 2 relative to chassis 10 changes as the load of one of the springs 8 or 9 becomes greater than the other. In a preferred embodiment, the reflecting surface therefore comprises three partial faces which are at right angles to one another and are arranged in such a way that, on tilting of the surface about an arbitrary axis during a displacement of the measuring point connected thereto relative to the transmitter/receiver, a sound wave coming from the transmitter is reflected parallel to itself to the receiver through reflection against the three partial faces. Fig. 2 shows different measuring units 22, each comprising a transmitter and a receiver for sound waves, which are connected by means of leads 24 to a control and processing unit 26. Dashed lines 28 and 30 indicate that the number of measuring units 22 and accompanying leads 24 is not a priori fixed, but can be determined according to the actual requirements. The control and processing unit 26 is also connected by means of a lead 32 to a speed measuring apparatus 34. Since, due to uneven road surfaces, acceleration, deceleration and steering movements, a distance measurement of the type mentioned above during movement of the vehicle shows a curve fluctuating around a certain average value so that an average over a certain period of time has to be taken in order to obtain sufficient accuracy, determining the load condition is carried out when the vehicle is stationary, which is determined by the control and processing unit 26 on the basis of the speed measuring apparatus 34. It is assumed here that load changes in the vehicle can in principle take place only when said vehicle is stationary. It is true that, as a result of the fuel consumption of the vehicle, with unchanged load a load difference can be found between two successive moments of stopping, separated by movement. In order to eliminate this influence on a measurement of the load change, the control and processing unit 26 is connected by means of a lead 36 to means 38 for measuring the fuel level in a fuel container, and is equipped to correct the determined load for the fuel consumption. Each time the vehicle stops after movement, the control and processing unit 26 fixes a reference load value, so that subsequent, load changes can be related thereto, in order to increase the measuring accuracy. For the exchange of data, which may or may not be recorded on a data carrier, between the system and the operator thereof, the control and processing unit 26 is connected by means of a lead 42 to an input and output unit 40 present on the vehicle, preferably placed in the driver's cab. The input and output unit 40 may comprise, for example, a display screen 44 for alphanumeric or graphic display of data, a keyboard 46 for controlling the load-checking system, and a slot 48 behind which a read/write unit is provided for reading or writing to a data carrier, e.g. a card with a magnetic strip. The measuring unit need not be fitted directly near the measuring points. Instead of that, the movements which the measuring points make relative to each other can be transmitted by means of a Bowden cable to another place on the vehicle or the like where the measuring unit is situated. Fig. 3 shows a vehicle construction such as that of Fig. 1, in which the measuring point 50 on the rear axle 2 is connected to one end of the core 63 of a Bowden cable 60, and the corresponding measuring point 53 on the chassis 10 is connected to one end of the sheath 66 of the Bowden cable 60. The other end of the sheath 66 is connected to a casing 70, while the other end of the core 63 can move a reflecting surface 18 relative to a transmitter/receiver 16 for sound waves. When the distance between measuring points 50 and 53 decreases or increases, the distance between transmitter/receiver 16 and reflecting surface 18 will also decrease or increase by the same amount, so that load determination is possible. A compression spring 75 ensures here that there is constant tensile stress in the core 63, in order to avoid backlash. Measuring points 51 and 54 are connected in a corresponding way through the core 64 and the sheath 67 respectively of a Bowden cable 61 to the reflecting surface 19 and a casing 71 respectively, a compression spring 76 holding the core 64 taut. The reflecting surface 19 interacts with the transmitter/receiver 17. The velocity of sound in air depends on the pressure, the temperature and the air humidity, factors which thus also will have an influence on the measured values of the measuring unit. In order to compensate for measuring errors caused by these, the control and processing unit 26 is connected to an additional measuring unit in which for reference a predetermined fixed distance is measured, possibly by means of a representative length of Bowden cable, to compensate for length variations in the case of temperature variations therein. Fig. 3 shows the realization of such an additional measuring unit by connecting two measuring points 52 and 55 which are not movable relative to each other to the core 65 and the sheath 68 respectively of a Bowden cable 62, the core 65 being connected to a reflecting surface 80 which interacts with a transmitter/receiver 81, the last-mentioned two being placed inside a casing 73. A spring 77 also holds the core 65 taut inside this casing 72. The casings 70, 71 and 72 can be placed together at a suitable point on the vehicle, it being possible to adapt the number of casings and the relative positioning thereof to the required number of measuring points. The transmitters/receivers inside each casing are connected by means of leads 90 to a control and processing unit, as described with reference to Fig. 2. The system for determining the load of a vehicle according to the invention is not only suitable for establishing the total load of the vehicle through adding together the load measured for the different wheels or wheel sets, but by means of the system, provided that it is equipped for the purpose, it is also possible to establish overloading of specific wheels as a result of incorrect loading. The above-mentioned system can also be used for vehicles with pneumatic and/or hydraulic suspension, in which the distance from the axle to the chassis is kept essentially constant by regulating the pressure in the appropriate spring. Instead of the above- mentioned Bowden cable, a pressure line is then connected to the pressure chamber of the appropriate spring, which at the other side is connected to a cylinder whose piston, which is under spring tension or a similar reference counterpressure, is connected to the corresponding surface 18, 19, the displacement of which then corresponds to the pressure in the spring, and thus to the load. It is, of course, also possible to connect these pressure cylinders directly to the corresponding spring, and to connect the piston thereof to a Bowden cable of the above-mentioned type.

Claims: C L I M S 1. System for determining the load of a vehicle or the like, comprising means for determining the distance between a measuring point fixed to a loadable part of the vehicle or the like and a measuring point fixed to a wheel axle or a guiding part moving proportionately thereto relative to the first-mentioned measuring point, the distance being a measure of the load condition of the vehicle or the like, characterized by one or more measuring units (22) , each to be connected with two measuring points, with a transmitter and a receiver for sound waves, and by a control and processing unit (26) which is connected to the or each measuring unit (22) and is equipped for determining the transit time of the sound waves between the transmitter and the receiver and for deriving therefrom the distance between the two measuring points. 2. System according to claim 1, characterized in that each measuring unit (22) comprises a transmitter/receiver (16; 17) for sound waves connected to one measuring point and a surface (18; 19) connected to the other measuring point, the surface reflecting the sound waves transmitted by the transmitter/receiver back thereto. 3. System according to claim 2, characterized in that the reflecting surface (18; 19) is connected to the wheel axle (2) or the guiding part thereof. 4. System according to claim 2 or 3, characterized in that the reflecting surface (18; 19) comprises three partial faces which are at right angles to each other and are arranged in such a way that a sound wave coming from the transmitter, after reflection against the partial faces, is reflected parallel to itself to the receiver. 5. System according to any of the preceding claims, characterized by a Bowden cable (60; 61) , of which one end of the sheath is connected to one measuring point (53; 54) , and the end of the core lying at said sheath end is connected to the other measuring point (50; 51) , while the other ends of sheath and core are connected to a measuring unit. 6. System according to any of claims 1 - 5 for a vehicle with pneumatic and/or hydraulic suspension, characterized in that the surfaces (18, 19) are each connected to the piston of a compression cylinder standing under a reference counterpressure, which cylinder is connected by means of a pressure line to the pressure chamber of the corresponding spring. 7. System according to any of the preceding claims, characterized in that the control and processing unit (26) is connected to a speed measuring apparatus (34) and is equipped for carrying out the load determination when the vehicle or the like is stationary. 8. System according to any of the preceding claims, characterized in that the control and processing unit (26) is connected to means (38) for measuring the fuel consumption and is equipped for correcting the determined load for the fuel consumption. 9. System according to Claim 7 or 8, characterized in that the control and processing unit (26) is equipped for establishing a reference load value when the vehicle or the like is stationary. 10. System according to any of the preceding claims, characterized in that the or each measuring unit is accommodated in a casing. 11.. System according to any of the preceding claims, characterized by an additional measuring unit (22) in which both measuring points (16, 18; 80, 81) are connected with fixed points of the vehicle, said additional unit (22) serving as a reference unit for compensating for temperature, pressure and humidity variations.

Inventors: VAN ZEGGEREN WILHELM AART, VAN ZEGGEREN, WILHELM, AART
Applicants: STICHTING CENTRA VOOR MICRO EL, STICHTING CENTRA VOOR MICRO-ELEKTRONICA
Application year: 1990
Main classification: G01G19
IPC codes: G01G19