METHOD FOR DETERMINING WEIGHT AND CENTER OF MASS OF A VEHICULE IN MOTION BY AN ON BOARD SYSTEM

Abstract: A method for determining the weight supported by the suspension (14) of a vehicle (12) in motion by measuring the frequency of vertical motion of the center of mass of the vehicle over a period of time. Preferably, a motion sensor to measure vertical motion (18) and two sensors (20, 22) to measure pitch and roll, respectively, are used.

Description: Method for Determining Weight and Center of Mass of a Vehicle in Motion by an On Board System FIELD AND BACKGROUND OF THE INVENTION The present invention relates to weighing vehicles and, in particular, it concerns a system and corresponding method for determining a total weight of a vehicle in motion or in loading and the position of the center of mass thereof. Vehicle weight is known to be a key parameter in road safety. Overloading of vehicles is often responsible for braking failures as well as roll-overs. Overloading also frequently results in shortening of the mean time between failures (MTBF) of various vehicle subsystems, leading to system malfunction and vehicle failures which may lead to accidents. Overloading is also a major cause of damage to road infrastructure. While the weight is a very important parameter characterizing vehicle loading, it is not the only one. The height of the center of mass, as well as the distribution of the weight between the axles, determined by the horizontal position of the center of mass have considerable influence on vehicle stability, handling and braking ability. Although a weight limit is set for every vehicle, the limit is not always observed. Limits may be exceeded either as a result of miss-estimation of the weight loaded into a vehicle, or through intentional overloading to reduce transportation costs, or as a consequence of payload weight change during travel time, as in the case of bulk load getting wet. Most commonly, vehicle weight is measured by use of external scales or weigh-bridges. Although there are checkpoints for weighing trucks, they are of limited effectiveness. Firstly, since the checkpoints are positioned in a limited number of locations, such as before certain bridges, they can only monitor a small proportion of the possibly overweight vehicles. Secondly, all road based systems lack the ability to log the history of vehicle loading throughout the entire time of operation. Additionally, checkpoints are inefficient, requiring considerable staffing and wasting valuable transport time. Additionally, change of load mass may occur during the travel time, due to wetting of bulk load such as sand or wood, or due to fraud by the operator, in such case there is no indication or measurement available. Finally, a system of checkpoint ' s cannot provide advanced warning to the operator of the vehicle when he begins a journey with an overloaded vehicle. Also, all these means do not give any indication about erroneous load distribution. In the case of aircraft, overload may cause fatal accidents during take-off or on subsequent center-of-mass shift. Miscalculation of the center of mass of an aircraft can have a fatal effect on the stability of the vehicle if it diverges from a designed margin. Monitoring the total load and center of mass of an aircraft is currently done through summation of the weights of several partial loads. In other words, the various loads are added together, either manually or by computer, to estimate the sum total of the weight and the position of the center of mass. As well as the possibility of faulty addition, errors may be introduced during estimation of the weight of the fuel added to the aircraft's tanks, or through error or omission in estimation of the initial weight prior to loading, for example, if some load has mistakenly not been removed from the aircraft. A number of systems have been proposed for on-board weighing of loaded vehicles. U.S. Patents Nos. 4,158,396, 4,580,644, 4796212, 4615404, 5677498 and German Patent DE29521150 teach methods of weight estimation using load cells built into the suspension system of a vehicle. These systems are only operative under static conditions. An alternative system disclosed in U.S. Patent No. 5,410,109 requires installation of a piezo-resistive transducer sensor at each vehicle suspension point. This suffers from similar limitations of requiring design modification and only operating under static conditions. U.S. Patent No. 3,854,540 and British Patent GB2178179 similarly use strain gauges built to the truck structure. U.S. Patent No. 4,588,038 discloses a system which can also weigh during motion of the vehicle, similar systems are described in U.S. Patents 5,119,895 5,528,499 and 5,631,832. The system of U.S. Patent 4,588,038 calculates the weight on each axle by measuring the air pressure in suspension cylinders. Variations due to motion of the vehicle are eliminated by calculating an average value of the measured weight over a period of time. This system also requires adaptation of the existing vehicle systems, making retrofitting difficult. U.S. Patent 4,458,234 describes similar monitoring of shock absorbers while U.S. Patent 5,167,289 describes air-spring load monitoring, U.S. Patent 5,666,295 describes hydraulic pressure monitoring, while U.S. Patent 5,659,470 combines pressure sensors and a tilt sensor. Patent DE4328147 describes the similar integration of an inclination sensor. All of these systems are generally intrusive, requiring redesigning of part of the vehicle structure and typically precluding retrofitting. A further shortcoming of the methods mentioned in the above patents is that, while they may offer some indication about the horizontal position of the center of mass, they fail to give any indication about its vertical position. There is therefore a need for a non-intrusive, retrofϊtable on-board system and corresponding method for determining a total weight of a vehicle in motion. It would also be advantageous to provide a generic system of this type that will fit any vehicle model. SUMMARY OF THE INVENTION The present invention is a non-intrusive, retrofϊtable on-board system and a corresponding method for continuously determining the total weight and the position of the center of mass of a vehicle in motion or during loading. The system is generic and will fit any model of vehicle. The present invention may be employed for continuously estimating and monitoring the weight of any type of wheeled vehicle, including but not limited to automobiles, buses, trucks, trailers, trains as well as aircraft on the wheels. The invention enables estimation of total vehicle weight and payload weight and center of mass, without using any external source of information that could introduce errors. The weight and center of mass estimation may be performed continuously, and is first obtained within a very short time from any vehicle loading. The system output can be used for enforcing weight limitations by police or for weight monitoring and automatic toll collection by road operators, and for self-check of the load by the vehicle driver. Real time remote monitoring of vehicle weight may be provided to enhance the effectiveness of law enforcement or other regulation by adding a communication device that can be remotely interrogated. The system may also be used to provide a log of vehicle loading to be used for law enforcement and for periodic maintenance purposes. The system will guard the interests of the public safety and the interests of vehicle manufacturers against vehicle owners violating the warranty terms. Preferably, the system provides advance warning to the vehicle operator on initial operation or loading of the vehicle under potentially dangerous overloaded conditions or to indicate exceeding of center of mass limitations. The system can additionally be used, in conjunction with instantaneous measurements from the various sensors, to determine parameters such as individual axle loads, in order to assist in performing other functions in the vehicle, such as suspension control or ABS optimization. System output may also be used to monitor the load so as to detect attempted theft or hijack of part of the load from the vehicle. Additionally, the present invention offers an option of chassis to ground displacement measurements, relevent also to techniques applied to a stationary vehicles. Thus option greatly reduces or eliminates the need for periodic re- calibrations over the life span of the vehicle. The present invention thus offers an effective indication of the aging of the suspension system by differentiating between short time changes due to load from long term changes due to aging. Thus, according to the teachings of the present invention there is provided, a method for determining a total weight supported by the suspension system of a vehicle in motion, the method comprising: (a) obtaining information sufficient to calculate a representative value of a spring constant for the suspension system of the vehicle; (b) obtaining measures of vertical motion for the center of mass of the total weight over a period of time; (c) analyzing the measures of vertical motion to identify a frequency of vertical oscillation of the weight; and (d) determining from the frequency and the information an estimate of the total weight supported by the suspension system of the vehicle. According to a further feature of the present invention, the measures of vertical motion are obtained by processing outputs of at least two, and preferably at least three, motion sensors attached to the vehicle. According to a further feature of the present invention, the at least three motion sensors include one linear sensor deployed to measure vertical motion information for a part of the vehicle and two angular sensors deployed to measure pitch and roll information for the vehicle. According to an alternative feature of the present invention, the at least three motion sensors include three linear acceleration sensors deployed to measure vertical acceleration at three non-collinear points on the vehicle. According to a further feature of the present invention, the at least three motion sensors include at least one radiation receiver deployed for receiving energy reflected from a road surface underlying the vehicle. According to a further feature of the present invention, the at least one radiation receiver is used for measuring vertical velocity at a point on the vehicle. According to a further feature of the present invention, the at least one radiation receiver is used for measuring vertical displacement at a point on the vehicle. According to a further feature of the present invention, the at least one radiation receiver is implemented as at least two radiation receivers deployed in different positions on the vehicle for receiving reflected radiation generated by transmitter. According to a further feature of the present invention, the at least three motion sensors include at least three independent lobes of at least one receiver of energy reflected from a road surface underlying the vehicle. According to a further feature of the present invention, outputs of at least three motion sensors are also processed to derive a horizontal position of the center of mass of the vehicle. According to a further feature of the present invention, an output of at least one linear motion sensor deployed to be responsive to a horizontal motion of the vehicle is also processed derive a vertical position of the center of mass of the vehicle. According to a further feature of the present invention, the information sufficient to calculate a representative value of a spring constant for the suspension system of the vehicle is obtained by a calibration process including: (a) determining a calibration weight supported by the suspension system of the vehicle by an alternative method; (b) obtaining measures of vertical motion for the center of mass of the calibration weight over a period of time; and (c) analyzing the measures of vertical motion to identify a frequency of vertical oscillation of the calibration weight. There is also provided according to the teachings of the present invention, a system for determining a total weight supported by the suspension system of a vehicle in motion, the system comprising: (a) an arrangement of motion sensors deployable in fixed relation to the vehicle and configured to provide a first output indicative of vertical motion of a first part of the vehicle and at least a second output affected by a rotational movement of the vehicle in a manner different from the first output; and (b) a processing system associated with the arrangement of motion sensors and configured to: (i) process at least the second output to derive a resonant frequency of rotational oscillation, (ii) identify in the first signal a resonant frequency not equal to the resonant frequency of rotational oscillation as a resonant frequency of vertical oscillation, and (iii) determine from the resonant frequency of vertical oscillation an estimate of the total weight supported by the suspension system of the vehicle. According to a further feature of the present invention, the arrangement of motion sensors includes a rotational sensor for generating the second output. According to a further feature of the present invention, the arrangement of motion sensors includes a second vertical motion sensor for generating the second output, the second output being indicative of vertical motion of a second part of the vehicle. According to a further feature of the present invention, the arrangement of motion sensors includes three motion sensors including at least one linear motion sensor. According to a further feature of the present invention, the arrangement of motion sensors further includes an additional motion sensor deployed to generate an output indicative of horizontal motion of the vehicle. According to a further feature of the present invention, the processing system is further configured to perform at least one Fourrier transform. According to a further feature of the present invention, the processing system is further configured to apply at least one notched filter. There is also provided according to the teachings of the present invention, a method for estimating the weight and center of mass of the suspended part of a vehicle, the method comprising: (a) obtaining measures of a vertical clearance of various points on the vehicle from the ground using at least three sensors receiving energy generated by at least one on-board transmitter and reflected from the ground while the vehicle is substantially stationary; (b) comparing the measures with reference values for the unloaded vehicle so as to obtain displacement values at the points on the vehicle; (c) estimating the forces acting on suspension springs of the vehicle, based on the displacement values; and (d) calculating by vector summation of the forces a total suspended weight and a location of the center of mass of the vehicle. BRIEF DESCRIPTION OF THE DRAWINGS The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: FIG. 1 is a schematic representation of the terminology used herein to describe the motion of a vehicle; FIG. 2A is a schematic top view of a vehicle showing an arrangement of sensors for use in a first embodiment of a system and method for determining a total weight carried by the suspension system of the vehicle when in motion and the center of mass thereof according to the teachings of the present invention; FIG. 2B is a schematic side view of the vehicle of Figure 2 A; FIG. 2C is a schematic rear view of the vehicle of Figure 2 A; FIG. 3 is a block diagram illustrating operation of the system and method of the present invention; FIG. 4A is a schematic top view of a vehicle showing an arrangement of sensors for use in a second embodiment of a system and method for determining a total weight carried by the suspension system of the vehicle when in motion and the center of mass thereof according to the teachings of the present invention; FIG. 4B is a schematic side view of the vehicle of Figure 4A; FIG. 4C is a schematic rear view of the vehicle of Figure 4A; and FIGS. 5A-5C are views similar to Figures 4A-4C, respectively, showing a preferred implementation employing an additional horizontal motion sensor to determine the vertical position of the center of mass of the vehicle. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is a system and corresponding method for determining a total weight carried by the suspension system of a vehicle in motion or during loading and the center of mass thereof. The principles and operation of systems and methods according to the present invention may be better understood with reference to the drawings and the accompanying description. Referring now to the drawings, Figures 1-4 illustrate a system 10 and corresponding method for determining a total weight carried by the suspension system of a vehicle 12 in motion or during loading and the center of mass thereof. The underlying principle of system 10 may be understood with reference to Figure 1 in which vehicle 12 is shown to have components of instantaneous linear acceleration a x , a y and a z , and angular positions θ and φ. It will be apparent that, for any vehicle traveling along the ground, components a x and a y are determined 8 principally by the travel of the vehicle whereas a z results from the reaction of the vehicle suspension system to various shocks and impacts imparted by bumps in the ground, transient responses to vehicle velocity variations, load variations or movements and other stimuli. The response of the vehicle suspension system, including all suspension and shock-absorbing elements can be regarded as equivalent to a single theoretical spring 14 which has a representative value of a spring constant k for the entire suspension system of the vehicle plus appropriate damping. The mass m that is subject to the vibration or motion is comprised from the mass of the chassis the mass of the fuel and the mass of the payload. A lower portion of the vehicle 16, including the wheels, axles and certain other vehicle components, is not supported by spring 14. From the theory of springs, it is known that the frequency of oscillation /of a load m supported by a spring is given by: 2π m Thus, once a representative spring constant has been determined, the total mass of the vehicle chassis and load can be expressed as a function of the frequency of oscillation as: . 1 m *fY By rewriting this relation for arbitrary measured reference values designated 0 and ) and dividing one relation by the other, the mass can be expressed as: m = m yA Thus, generally speaking, the method of the present invention involves obtaining information sufficient to calculate a representative value of a spring constant for the suspension system of the vehicle, for example reference values m 0 and ,, and obtaining measures of the vertical acceleration of the center of mass of the vehicle over a period of time. The measures of the vertical acceleration are then analyzed to identify a frequency of vertical oscillation of the vehicle and this 9 frequency, together with the spring constant information, is used to determine an estimate of the total weight carried by the suspension system of the vehicle. It will be immediately apparent that, unlike the devices of the prior art in which vehicle movement is an unwanted interference, the present invention measures the vehicle weight directly from the motion. Since calculations are based on the frequency of motion monitored over a period of time, the precision of measurements, and even systematic errors in the measurements, have little or no effect on the precision of the final results. The invention is therefore ideally suited to on-board weight measurement. Furthermore, since the invention does not attempt to measure weight directly, no modification of the existing suspension system is required. To the contrary, the solid body motion of the vehicle chassis can be measured by suitable sensors attached to any part of the vehicle chassis, thereby permitting unlimited positioning options for retrofit. Parenthetically, it will be noted that the system and method do not directly determine the total weight of the entire vehicle and load. Instead, they determine the total weight supported by the suspension system of the vehicle. This differs from the total by the constant weight of the wheels, axles, part of the suspension system itself, and any other part of the vehicle directly mounted on the axles. The true total weight, or the net weight of the load alone, can easily be derived from the result by adding or subtracting a predetermined constant value to the derived weight and by regarding the weight of the fuel as part of the payload of the vehicle. Turning now to the features of system 10 in more detail, it will be clear that a basic implementation of the system could be achieved using a single motion sensor deployed for measuring or deriving vertical acceleration. However, in practice, the vertical acceleration measured at any point other than the center of mass is a sum of the true vertical acceleration together with the effects of pitch and roll oscillations. In order to derive the true vertical acceleration, one or two additional motion sensor inputs are preferably provided. Various combinations of sensors may be used to provide sufficient information. By way of example, two 10 particular sensor combinations will be described here, the first with reference to Figures 2A-2C and the second below with reference to Figures 4A-4C. Figures 2A-2C show a first sensor arrangement employing a single linear acceleration sensor 18 deployed to measure vertical acceleration of a part of the vehicle and two angular sensors 20, 22 deployed to measure pitch and roll information of the vehicle, respectively. Sensors 20 and 22 can be used to determine the frequencies of pitch and roll oscillations directly and these frequencies can be filtered out of vertical acceleration information. This embodiment allows all sensors to be combined into a single sensor unit located together on the vehicle. It should be further noted that the frequencies of pitch and roll oscillation as determined above may be used to determine the longitudinal and lateral position of the center of mass. A notched filter can be used to exclude all acceleration frequencies except at the pitch and roll oscillation frequencies respectively. Based on these frequencies the maximum values of the pitch and roll angular acceleration can be calculated. The linear acceleration values peculiar of the pitch and roll oscillation frequencies (as measured using notched filters at the said frequencies) are also of oscillating nature and feature a maximum value. The maximum linear vertical acceleration at the pitch oscillation frequency divided by maximum angular acceleration at the said frequency yield the longitudinal distance of the center of mass from the point of acceleration measurement. The signs of the said maximum (or minimum) linear and angular accelerations enable to determine the sign of the said distance of the said center of mass (according to well-known sign conventions). The maximum linear vertical acceleration at the roll oscillation frequency divided by maximum angular acceleration at the said frequency yield the lateral distance of the center of mass from the point of acceleration measurement. The signs of the said maximum (or minimum) linear and angular accelerations enable to determine the sign of the said distance of the said center of mass (according to well-known sign conventions). 11 It should be appreciated that the sensors employed in the present invention may be of a very wide range of types. The linear sensors may be direct acceleration sensors of any type, including but not limited to mechanical inertial and piezoelectric sensors. Alternatively, the linear sensor may measure other information from which oscillatory frequency can be derived, including vertical velocity or position relative to the road surface, relative to the axles or relative to any other frame of reference not moving vertically with the chassis. Thus, further examples of sensors include, but are not limited to, laser, optical, microwave, radar or ultrasonic range sensors measuring perturbations of vehicle chassis-to-ground distance and Magnetic or Hall Effect sensors installed to measure perturbations of vehicle chassis-to-axle distance. All such sensors are referred to generically as "linear sensors". Thus, the sensors may in fact be receivers of energy reflected from ground, such as micro-wave or radio-frequency sensors or acoustic sensors, the energy being transmitted from at least one transmitter mounted on the vehicle. For instance, by placing a receiver or a transceiver at each sensor position, one can measure at various locations the local vertical velocity and/or displacement relative to the ground and from the said measures determine the various frequencies as explained above. Optionally, the type and design of sensor may be chosen to be sensitive only to relatively low frequency movements, for example responding to frequencies below about 5 or below about 10 Hz. This avoids picking up the higher frequency vibrations caused by the vehicle engine or other higher frequency mechanical noise. Alternatively, such vibrations can be filtered out during later processing as will be described below. With respect to the angular sensors, these too may be angular acceleration sensors, velocity sensors or displacement sensors of any conventional type, all such sensors being referred to generically as "angular sensors". As an alternative to independent linear and angular sensors, one can deploy a combination sensor which includes a transmitter of energy such as 12 electromagnetic or acoustic energy at one location on the vehicle, and a corresponding receiver, the receiver having at least three independent lobes; the summation of the measures of the lobes is indicative of the vertical motion at the point of measurement while the pitch and roll motions are derived from a combination of the measures of the lobes. For the purposes of the description and claims, such a combination sensor is functionally equivalent to, and will be referred to as, a corresponding number of independent sensors. Figure 4 shows a block diagram of one possible processing sequence according to the present invention. First, after suitable pre- filtering where required, the outputs of angular sensors 20, 22 are processed (step 26) to derive resonant frequencies of pitch and roll oscillations. This may be simply achieved by Fourrier analysis followed by peak detection within a range appropriate to the vehicle in question. For a small domestic vehicle, such resonant frequencies are typically in the range between about 1 and about 5 Hz, whereas for a large, fully laden truck, lower frequencies are to be expected. Then, at step 28, these resonant frequencies are used as inputs to adaptive notched filters for removing these frequencies from the signal provided by linear acceleration sensor 18. Pre- filtering of this signal, such as by a low pass filter, may also be performed at this stage. The signal is then analyzed (step 30), typically also by Fourrier analysis followed by peak detection, to determine a resonant frequency of vertical (heave) oscillations. An estimated weight supported by the suspension system of the vehicle is then calculated from the resonant frequency taken together with the pre-determined spring properties of the suspension (step 32). A similar procedure may be used for estimating the position of the longitudinal and lateral position of the center of mass: for estimating the longitudinal position of the center of mass relative to any point of measurement, the resonant frequencies of the heave and roll motions are filtered out, while only the vertical accelerations at the pitch resonant frequency pass through a notched filter at this frequency; accordingly, the longitudinal position of the center of mass relative to the said point of measurement can be readily calculated by dividing the 13 maximum vertical acceleration measured at such frequency by the maximum pitch acceleration measured at the pitch resonant frequency . For estimating the lateral position of the center of mass relative to any point of measurement, the resonant frequencies of the heave and pitch motions are filtered out, while only the vertical accelerations at the roll resonant frequency pass through a notched filter at this frequency; accordingly, the lateral position of the center of mass relative to the said point of measurement can be readily calculated by dividing the maximum vertical acceleration measured at such frequency by the maximum roll acceleration measured at the roll resonant frequency According to an additional, or alternative, aspect of the present invention, one can also obtain estimates for the vehicle weight and center of mass in a stationary condition, such as at loading, employing the aforementioned arrangement of three sensors: measures of the distance to the ground at loading and comparison with reference values for an unloaded vehicle result in displacement values at various points of the vehicle. Given the displacements, the forces acting in the various suspension springs can be conveniently estimated, assuming the spring constants are known from appropriate calibration or a priori information. Once all the forces are known, their vector summation will give the total suspended weight while the location of the resultant will give the center of mass. Thus, displacement sensors measuring displacement relative to the ground provide an alternative sufficient set of parameters parallel to those obtained under dynamic measurement. Preferably, the two types of measurement (static and dynamic) are combined for the purposes of verification or for improved accuracy, to achieve continuous dynamic calibration updates, and for dynamic maintenance monitoring of the suspension. The estimated weight and center of mass position, may be made available via a display directly to the driver, or may be recorded electronically or otherwise in a vehicle log, or may serve as an input to other vehicle safety or control systems and/or may be transmitted immediately or at a later time as a response to an interrogation by an external monitoring authority. 14 It should be noted ' that, while certain preferred implementations of the present invention do provide center of mass information as described, such information is not a prerequisite for more basic weighing-only implementations of the invention. In the latter case, the "measures" of the vertical motion obtained may in fact be scaled by some unknown factor. Since, however, the invention depends only on measurements of the frequency of oscillations, the true magnitude of the acceleration is not critical. When a priori information about the motion or center of mass of the vehicle is available, it may be possible to omit one or both of the angular sensors. For example, in cases where the center of mass can be assumed to always lie roughly on the longitudinal center-line of the vehicle, mounting of linear acceleration sensor 18 on or near the center-line may render roll sensor 22 unnecessary. A priori information about the motion may be available when the vehicle is actually standing stationary and the vertical oscillating motion is induced directly by an externally applied impulse such as, for example, the actual loading procedure. In some of the embodiments, such motion sensors are used that have a secondary ability to perform ground clearance measurements which may be used to enhance static measurements of the systems implemented, such as in the case of the embodiments of measuring energy reflected from the ground. As mentioned earlier, the weight calculation is based on some reference information sufficient to calculate a representative value of a spring constant for the suspension system of the vehicle. Typically, this information is in the form of a pair of reference values m 0 and/ obtained through a calibration process as follows. First, a calibration weight m 0 of the part of the vehicle 12 supported by the suspension system is determined by a theoretical calculation based on vehicle part specifications, or equivalent information provided by the manufacturer. Measures are then obtained of the vertical motion of the center of mass of the vehicle over a period of time, and these are analyzed to identify a calibration frequency / of vertical oscillation of the vehicle. This is preferably achieved by executing steps 26, 28 and 30 described above. Optionally, the values m 0 and / 15 may be used to calculate a representative value of the spring constant for the vehicle suspension system, or a scaled value thereof, for use in the subsequent calculations. It is particularly advantageous to choose the unloaded state of the vehicle for the calibration process. This allows provision of a user-operated reset function to be actuated periodically when the vehicle is unloaded. The reset function checks, and if necessary changes, the stored value of the calibration frequency/ to correct for variations due to wear in the suspension system, the resulting updates may be recorded in the system to enable tracing of possible attempted frauds. Additionally, by analyzing records kept of variations in the calibration frequency over an extended period, the system may be programmed to detect and provide warning of deterioration of the suspension system or sudden changes which may be indicative of a dangerous fault. Alternatively, application of time criteria to dynamically collected suspension behavioral data may be used for autonomous discrimination between real-time changes of load and long-term aging changes of the suspension calibration values, to be used for maintenance monitoring and prompting. Turning now to Figures 4A-4C, these show an alternative sensor arrangement employing three linear acceleration sensors 34, 36 and 38 deployed to measure vertical accelerations designated a , a 2 , α 3 , respectively, at three non- collinear points on vehicle 12. Clearly, the exact form of analysis of the sensor outputs depends on their positioning, but for any positioning, the three measurements can be transformed into the equivalent of the vertical acceleration a v , pitch acceleration 3 and roll acceleration φ measured or calculated from sensors outputs according to the same method as detailed in the first embodiment. In the case shown here, pitch oscillations will affect sensors 36 and 38 in a like manner opposite to the effect on sensor 34. Roll, on the other hand, will 16 generate opposite outputs in sensors 36 and 38, while sensor 34 is relatively unaffected by roll. Thus, ignoring scaling factors and assuming small angles: a x = a v - θ a 2 = a v + θ+ φ a 3 = ay θ- φ In all other respects, the implementation of the method and system remain similar to those of the first embodiment. In embodiments where the motion sensors used are based on energy transmission to the ground and reception of reflected energy from ground, part of the measures may be enhanced in static conditions such as during the loading process by using the secondary ability of the sensors to perform ground clearance measures. For this purpose, system implementations may preferably use at least three RF Micro- Wave sensors or Optical Laser sensors or Acoustic sensors rather than inertial accelerometers. Finally, turning now to Figures 5A-5C, it will be noted that the embodiments illustrated thus far only provide information about the position of the center of mass in the x-y directions. Optionally, in order to determine the vertical position of the center of mass, an additional linear accelerometer 50 is deployed for measuring a horizontal linear acceleration a h , preferably the longitudinal or lateral acceleration a x or a y . A notched filter is then applied, passing the acceleration a h at the pitch (or roll) oscillation frequency while filtering out other motion. The vertical distance of the center of mass from the position of the horizontal accelerometer is then determined by division of the maximum linear acceleration at the corresponding resonant frequency by the corresponding maximum angular acceleration, in a manner similar to that described above for the longitudinal (or lateral) position of the center of mass. The result may be expressed: Z cg = (a m- ω ^ pitch 0r Z cg = (« y > ' ΦmzA '* _roll Although additional accelerometer 50 is shown here schematically as mounted separately from the other sensors, it will be appreciated that it may readily 17 be combined in a single unit with one or more other sensors. Particularly, in the case of a single-unit implementation as shown in Figures 2A-2C, accelerometer 50 may also be combined with the other sensors to provide a highly convenient retrofit system. It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the spirit and the scope of the present invention. 18

Claims: WHAT IS CLAIMED IS: 1. A method for determining a total weight supported by the suspension system of a vehicle in motion, the method comprising: (a) obtaining information sufficient to calculate a representative value of a spring constant for the suspension system of the vehicle; (b) obtaining measures of vertical motion for the center of mass of the total weight over a period of time; (c) analyzing said measures of vertical motion to identify a frequency of vertical oscillation of the weight; and (d) determining from said frequency and said information an estimate of the total weight supported by the suspension system of the vehicle. 2. The method of claim 1, wherein said measures of vertical motion are obtained by processing outputs of at least two motion sensors attached to the vehicle. 3. The method of claim 1, wherein said measures of vertical motion are obtained by processing outputs of at least three motion sensors attached to the vehicle. 4. The method of claim 3, wherein said at least three motion sensors include one linear sensor deployed to measure vertical motion information for a part of the vehicle and two angular sensors deployed to measure pitch and roll information for the vehicle. 5. The method of claim 3, wherein said at least three motion sensors include three linear acceleration sensors deployed to measure vertical acceleration at three non-collinear points on the vehicle. 19 6. The method of claim 3, wherein said at least three motion sensors include at least one radiation receiver deployed for receiving energy reflected from a road surface underlying the vehicle. 7. The method of claim 6, wherein said at least one radiation receiver is used for measuring vertical velocity at a point on the vehicle. 8. The method of claim 6, wherein said at least one radiation receiver is used for measuring vertical displacement at a point on the vehicle. 9. The method of claim 6, wherein said at least one radiation receiver is implemented as at least two radiation receivers deployed in different positions on the vehicle for receiving reflected radiation generated by transmitter. 10. The method of claim 3, wherein said at least three motion sensors include at least three independent lobes of at least one receiver of energy reflected from a road surface underlying the vehicle. 11. The method of claim 3, wherein said processing includes applying at least one notched filter. 12. The method of claim 3, further comprising processing outputs of at least three motion sensors to derive a horizontal position of the center of mass of the vehicle. 13. The method of claim 12, further comprising processing an output of at least one linear motion sensor deployed to be responsive to a horizontal motion of the vehicle to derive a vertical position of the center of mass of the vehicle. 14. The method of claim 1, wherein said analyzing includes performing at least one Fourrier transform. 20 15. The method of claim 1, wherein said information sufficient to calculate a representative value of a spring constant for the suspension system of the vehicle is obtained by a calibration process including: (a) determining a calibration weight supported by the suspension system of the vehicle by an alternative method; (b) obtaining measures of vertical motion for the center of mass of the calibration weight over a period of time; and (c) analyzing said measures of vertical motion to identify a frequency of vertical oscillation of the calibration weight. 16. A system for determining a total weight supported by the suspension system of a vehicle in motion, the system comprising: (a) an arrangement of motion sensors deployable in fixed relation to the vehicle and configured to provide a first output indicative of vertical motion of a first part of the vehicle and at least a second output affected by a rotational movement of the vehicle in a manner different from said first output; and (b) a processing system associated with said arrangement of motion sensors and configured to: (i) process at least said second output to derive a resonant frequency of rotational oscillation, (ii) identify in said first signal a resonant frequency not equal to said resonant frequency of rotational oscillation as a resonant frequency of vertical oscillation, and (iii) determine from said resonant frequency of vertical oscillation an estimate of the total weight supported by the suspension system of the vehicle. 17. The system of claim 16, wherein said arrangement of motion sensors includes a rotational sensor for generating said second output. 21 18. The system of claim 16, wherein said arrangement of motion sensors includes a second vertical motion sensor for generating said second output, said second output being indicative of vertical motion of a second part of the vehicle. 19. The system of claim 16, wherein said arrangement of motion sensors includes three motion sensors including at least one linear motion sensor. 20. The system of claim 19, wherein said arrangement of motion sensors further includes an additional motion sensor deployed to generate an output indicative of horizontal motion of the vehicle. 21. The system of claim 16, wherein said processing system is further configured to perform at least one Fourrier transform. 22. The system of claim 16, wherein said processing system is further configured to apply at least one notched filter. 23. A method for estimating the weight and center of mass of the suspended part of a vehicle, the method comprising: (a) obtaining measures of a vertical clearance of various points on the vehicle from the ground using at least three sensors receiving energy generated by at least one on-board transmitter and reflected from the ground while the vehicle is substantially stationary; (b) comparing said measures with reference values for the unloaded vehicle so as to obtain displacement values at said points on the vehicle; (c) estimating the forces acting on suspension springs of the vehicle, based on said displacement values; and (d) calculating by vector summation of said forces a total suspended weight and a location of the center of mass of the vehicle. 22

Inventors: ELAD SHALOM, TAL REUVEN, ELAD, SHALOM, TAL, REUVEN
Applicants: CONTROLOAD LTD, ELAD SHALOM, TAL REUVEN, CONTROLOAD LTD., ELAD, SHALOM, TAL, REUVEN
Application year: 1999
Main classification: G01G9
IPC codes: G01G19