The present invention relates to a method for estimating the wheelbase length of at least one trailer of a vehicle combination comprising a towing vehicle and at least one towed trailer. The method is especially suited for vehicle combinations having more than one towed trailer.
In order to reduce the number of heavy vehicles on the roads, longer vehicle combinations comprising more than one towed trailer are proposed for the use on regular roads in some countries. Apart from reducing the required number of towing vehicles for a specific load, the energy consumption and the emission of exhaust gases will also be reduced compared with traditional vehicle combinations. Normally, the length and the weight of the vehicle combination are controlled by law and regulations. One vehicle combination that at the moment is allowed in some European countries is a truck-dolly-semitrailer combination, which is slightly longer than a normal truck-trailer combination. Such a combination allows a truck to tow a semitrailer using a small trailer often referred to as a dolly or dolly trailer. A dolly is a small trailer that can be coupled to a truck or trailer in order to support a semi-trailer. The dolly is equipped with a fifth wheel to which the semi-trailer is coupled.
In some countries, longer and/or heavier vehicle combinations are also allowed under restricted conditions. Such vehicles may comprise several trailers and may be over 50 meters long and more. They are often used in remote areas and for specific purposes. In Australia, road trains comprising more than 4 trailers are used in some states and on some roads. Longer combination vehicles (LCV's) are also used in e.g. USA, Canada and Argentina. All these LCV's are used under strict regulations.
One problem that may arise when longer and varying vehicle combinations are used, is to determine the effective wheelbase of each towed trailer. Knowledge of the effective wheelbase is e.g. advantageous to have when slow speed driving of the vehicle combination is to be assisted by an autonomous or semi-automatic function, e.g. when marshalling, in order to simplify the positioning of the vehicle combination at a loading ramp. It is especially important to know the effective wheelbase when automatic or semi-automatic reversing is to be implemented.
The effective wheelbase is a well-known expression. When a vehicle is provided with more than one axle at one end, these axles can be approximated with only one virtual axle. A vehicle having only this virtual axle would in the ideal case behave almost exactly in the same way as the original vehicle with more axles. For a vehicle combination, i.e. a towing vehicle followed by one or several towed units, each vehicle unit will thus have one effective wheelbase. In FIG. 1, a vehicle combination 1 comprising a truck 2, a dolly 3 and a semitrailer 4 is shown. The effective wheelbase is the distance between the connection point of the trailer and the virtual wheel axle. For the dolly 3, the effective wheelbase is the distance L2 between the trailer coupling 5 and the virtual axle 6 of the dolly, which is derived from the regular axles 7 of the dolly. For the semitrailer 4, the effective wheelbase is the distance L3 between the kingpin 8 of the semitrailer and the virtual axle 9 of the semitrailer, which is derived from the regular axles 10 of the semitrailer. In FIG. 1, the virtual wheel axles are shown with dashed lines.
The easiest way of determining the effective wheelbase of a trailer is to measure the distance from the connection point to the wheel axles and to determine the tyre characteristic and the axle loads. The effective wheelbase can then be calculated using available explicit formulas. This may be a reliable method when the same trailer is used exclusively and is running with the same load, or when trailer axle longitudinal position, tyre properties and load is continuously made available to all control units that require the information. In reality this is most often not the case. The effective wheelbase, i.e. the position of the virtual axle, is dependent on each axle load and the tyre characteristics, which means that the effective wheelbase may vary depending on how the trailer is loaded. Further, for a trailer having a liftable axle, the wheelbase will change when the axle is raised.
U.S. Pat. No. 6,301,548 discloses a method for determining the wheelbase of steerable vehicles when cornering, in which the wheelbase is determined from at least one defined track width, measured wheel circumference speeds and/or measured steering angles. In this method, the radius of the curve is used as an input to the method which means that the vehicle must drive through a curve with a constant radius.
EP 2 324 323 B1 discloses a method for determining a wheelbase of a vehicle having at least two axles by which measurement signals of the vehicle are recorded at least during travel of the vehicle through a curve, and where the wheelbase is determined from at least the measured signals. A yaw rate and the rotational speeds of the wheels for determining the wheel speeds are measured and the wheelbase is determined from geometrical calculations. In this method, the radius of the curve is used as an input to the method which means that the vehicle must drive through a curve with a constant radius.
These methods are mainly adapted to determine the wheelbase for a vehicle combination comprising one towing vehicle and one towed trailer driving through a continuous curve. There is thus still room for an improved method and arrangement adapted for vehicle combinations having at least one towed trailer and where steering is not restricted to steady state cornering.
It is desirable to provide an improved method for estimating the effective wheelbase length of a trailer in a vehicle combination comprising a towing vehicle and at least one towed trailer. It is also desirable to provide an improved arrangement for estimating the effective wheelbase length of a trailer in a vehicle combination comprising a towing vehicle and at least one towed trailer.
In a method for estimating the effective wheelbase of a trailer in a vehicle combination comprising a towing vehicle and at least one towed trailer, the steps of driving the vehicle combination forwards, recording the speed of the vehicle combination, recording the steering angle of the towing vehicle, recording the yaw rate of the towing vehicle and of the towed trailers or recording the articulation angle for each towed trailer, recording the steering angle of each towed trailer, and using the determined values to calculate a value for the effective wheelbase for each towed trailer are comprised.
By this first embodiment of the method, the method can estimate the effective wheelbase of the at least one towed trailer. The estimation of the effective wheelbase is done when the vehicle combination is driven forwards for a predetermined time interval, where the time interval may be between a few seconds up to several minutes. The duration of the time interval may e.g. depend on the type of road on which the vehicle combination is driven. Since the steering angles and the yaw rates and/or the articulation angles are used for the estimation, it is advantageous that the vehicle combination at least drives through one curved portion of the road. During the time interval, the different values are determined and recorded with a predetermined sample frequency, such that a series of recorded value sets, which may be arranged in matrixes, are obtained. One or more of these recorded value sets or matrixes are then used to calculate the effective wheelbase for the towed trailers of the vehicle combination.
It is possible to sort the value sets before the effective wheelbase is calculated. When the vehicle combination drives absolutely straight, the recorded values for e.g. the steering angles or the articulation angles of the towed trailers will be substantially zero, which means that there is no point in calculating an effective wheelbase using these value sets. Thus, such value sets can be discharged before the effective wheelbase is calculated. It is also possible that such values are not recorded. It is e.g. possible that some or all values are compared with threshold values before a value set is recorded. If one of the values is below or above the threshold level, the value set is not recorded. When the vehicle combination has traveled for the predetermined time interval, a number of value sets have been recorded. One or more of these value sets are used to calculate an effective wheelbase. It is possible to calculate a number of wheelbases using different value sets and to average these effective wheelbase values.
The estimation of the effective wheelbase is preferable done by fitting a vehicle model using a least square condition. In this way, the deviations in the used values are minimized. Deviations in the values may e.g. come from disturbances or noise in the measured signals. This may e.g. arise from the road conditions, which may not always be perfect. A pot hole may e.g. influence the yaw rate of the truck or the steering angle value of a trailer. Other types of road defects may also influence the estimation. By using a least square approximation, and by performing several estimations for different value sets, an effective wheelbase estimation that differ a few percent or less from the actual effective wheelbase value can be obtained.
The different recorded values are either obtained by measuring the values directly using sensors or by estimating the required values with the use of other measured signals.
One measure that can be estimated is the yaw rate. The yaw rates of the vehicles are e.g. coupled to the articulation angles of the following vehicles. The yaw rate of the first towed trailer can e.g. be approximated by using the yaw rate of the towing vehicle and adding the time derivative of the articulation angle between the towing vehicle and the first towed trailer.
The yaw rate of the towing vehicle can e.g. be determined either by estimation or by a measurement. The estimation may be done by using an estimation method based on vehicle combination properties, such as wheel speed of the vehicle, vehicle mass, vehicle length, steering angle etc. Yaw rate measurements are done by using a yaw rate sensor.
In an arrangement for estimating the effective wheelbase length of a trailer in a vehicle combination comprising a towing vehicle and at least one towed trailer, comprising means for obtaining the speed of the vehicle combination, means for obtaining the steering angle of the towing vehicle, means for obtaining the steering angle of each towed trailer, the arrangement further comprises means for obtaining the yaw rate of the towing vehicle and each towed trailer or for obtaining the articulation angle for each towed trailer, means for recording the obtained values in a data set, and means for calculating a value for the effective wheelbase for each towed trailer.
By this first embodiment of the arrangement, the arrangement comprises means for estimating the effective wheelbase of the at least one towed trailer. The estimation of the effective wheelbase is done by recording appropriate values obtained either by measurements or estimations when the vehicle combination is driven forwards during a time interval, where the time interval may be between a few seconds up to several minutes. The duration of the time interval may e.g. depend on the type of road on which the vehicle combination is driven. Since the steering angles, the yaw rate and/or the articulation angles are used for the estimation, it is advantageous that the vehicle combination at least drives through one curved portion of the road. However, the curve must not be continuous with a specified radius. During the time interval, the different values are determined and recorded with a predetermined sample frequency, such that a series of recorded value sets, which may be arranged in matrixes, are obtained. One or more of these recorded value sets or matrixes are then used to calculate the effective wheelbase for the towed trailers of the vehicle combination. The arrangement comprises means for calculating a value for the effective wheelbase, and the means preferably uses a least square fit to a one track linear vehicle model for the estimation of the effective wheelbase.