WO2014000932A1

WO2014000932A1 - Control system for axle load measurement

Info

Publication number: WO2014000932A1
Application number: PCT/EP2013/059451
Authority: WO
Inventors: Thiemo BUCHNER; Martin Stoiber
Original assignee: Agco International Gmbh
Priority date: 2012-06-26
Filing date: 2013-05-07
Publication date: 2014-01-03
Also published as: GB201211295D0

Abstract

A process for calibrating an axle load measuring apparatus of an agricultural vehicle having a sensor, such as a strain sensor, attached to an axle assembly of the vehicle. The process comprises firstly determining (50) a configuration of the vehicle and using the configuration to look up (52) an expected weight or axle load value in a database (54) of vehicle parameters and their respective contributions to vehicle weight. A weight value indicated by the sensor output is compared (56) with the expected weight value for that configuration, and a calibration offset to be applied to subsequent sensor outputs is derived (58).

Description

DESCRIPTION

CONTROL SYSTEM FOR AXLE LOAD MEASUREMENT

The present invention relates to systems for measuring the axle load of a vehicle axle and especially, although not exclusively, the rigid rear axle of an agricultural vehicle such as a tractor, together_with_methods.for_the calibration otsuch systems.

To improve efficiency and reduce damage to the ground during operation, modem tractors may be equipped with tyre pressure control systems or efficiency control systems as described in applicant's co-pending UK patent application No. GB 1 1 12568.9 and GB 1 1 12569.7 filed on 22.07.201 1 . In operation, these systems require a precise knowledge of the wheel load of each wheel or axle to enable, for example, the adjustment of tyre pressures without exceeding the tyre capability, or the generation of an optimised load distribution profile to provide guidance to the operator on ballasting of the tractor.

It is well known, for suspended axles, to determine the wheel load by measuring the pressure in the hydraulic or pneumatic cylinders of the suspension. However, in the case of a tractor, only the front axle is equipped with such a suspension system from which the wheel load may be determined, so the rear axle requires a different solution. According to one approach, it is known to use axle bearings which are equipped with load sensing means. These means require changes in the axle installation and are costly. Furthermore, optional usage is not generally an economic option due to the impact of the changes on the complete axle design and the resulting costs.

United States patent US 4,173,259 describes a load sensing device which senses deformation of the rear drive housing of a tractor to control the draft load by raising or lowering of an implement. The sensing may be electrical or mechanical and the signal produced by the strain on the rear drive is amplified and used to control a hydraulic control valve to a hydraulic weight distribution system. The document indicates that electric strain gauges or sensors may be mounted on any member deforming in response to loading. However, the performance of strain gauges can vary widely with position and less than optimum performance can easily result.

In addition, strain gauge sensors are known which determine wheel load by measuring deformation/strain of a part as described in applicants pending UK patent application No. GB 1200529.4 filed on 13^lh January 2012. In that arrangement, a part of the housing of a rigid rear axle of an agricultural vehicle is provided with a shaped attachment point to receive the sensor and hold it at an orientation chosen to optimise sensor output performance.

A major problem occurs if these sensors are used in mass-produced products. Changing parameters such as sensor position tolerances or tyre width or variations in tractor configuration require that calibration be performed during assembly and later on, during operation or maintenance. A calibration by adding defined weights, as used for test installations, is not suitable during production line assembly as assembly is interrupted and costs are increased. Furthermore, the issue of how to facilitate calibration during operation, by an operator or service personnel, has not yet been satisfactorily resolved and so vehicles equipped with such sensors cannot be calibrated during use and thereby no change in vehicle configuration is possible. For vehicles such as wheel loaders or fork lifters, this is not a serious problem as their configuration does not change during operation time. Agricultural vehicles however, especially tractors, are frequently reconfigured to use different tyres with varying width, to use adjustable tyre assemblies on a adjustable wheel hub, or just to use twin tyres during some operations. All of these variations impact the wheel load measurement so a calibration is necessary each time.

It is an object of the present invention to provide an axle load measuring arrangement which mitigates the above mentioned problems.

In accordance with a first aspect of the invention there is provided an axle load measuring apparatus for an agricultural vehicle comprising:

• an axle assembly with at least one sensor to determine axle load;

• data processing means coupled to said at least one sensor to receive an output signal therefrom and arranged to generate an output value representative of axle loading based thereon;

• data storage means coupled with the data processing means and holding a database of vehicle weight or axle load data by reference to vehicle configuration;

wherein the data processing means further comprises an input to receive a vehicle configuration and is arranged to use the configuration to look up an expected weight or axle load value in said database, to compare the loading value indicated by the sensor output, and to determine and store a calibration offset to be applied to subsequent sensor outputs,

wherein the axle assembly is a rigid-type axle assembly with said at least one sensor being a strain sensor mounted to an attachment area thereof and wherein the data processing means is a programmable device controlled to derive a performance curve of strain sensor output against rigid axle loading based on a first sensor output at a first configuration and at least one additional factor

In a further aspect there is provided a method of calibrating an axle load measuring apparatus of an agricultural vehicle having a sensor to determine axle load of an axle assembly of the vehicle, the method comprising:

• determining a configuration of the vehicle;

• using the configuration to look up an expected weight or axle load value in a database of vehicle parameters and their respective contributions to vehicle weight or axle load;

• comparing a loading value indicated by the sensor output with the expected weight or axle load value for that configuration; and

• determining and storing a calibration offset to be applied to subsequent sensor outputs, wherein the sensor is a strain sensor and the axle i a rigid axle, wherein the step of determining and storing includes deriving a performance curve of strain sensor output against rigid axle loading based on a first sensor output at a first configuration and at least one additional factor.

Preferred features of the invention are set out in the dependent claims, the contents of which are incorporated herein by reference.

With such an arrangement, calibration of the measuring system can be provided which is suitable for use during assembly, in operation and for maintenance purposes.

Further advantages of the invention will become apparent from reading the following description of specific embodiments, given by way of example only, with reference to the appended drawings in which:-

Figure 1 shows a side view of a tractor;

Figure 2 shows a perspective view of a rigid axle assembly with an attached strain gauge; Figure 3 is a characteristic map for the strain gauge in Figure 2 showing deformation against load;

Figure 4 is a flow chart showing the principal process steps of a calibration method embodying the invention;

Figure 5 is a schematic representation of a vehicle construction process with reference to calibration steps; Figures 6 to 8 are display screen images of a menu-driven utility supporting the calibration process; and

Figure 9 schematically represents the components of a data processing system for use in an axle load measuring apparatus.

Referring to Figure I , a tractor 1 is shown having a cab 2 and an engine compartment 3. A chassis 4 which is partly visible connects front wheel mounting 5 and rear axle 6. The front wheel mounting 5 is equipped with an independent wheel suspension as described in applicants granted patent EP 1 627 762 with upper and lower transverse links mounting steered wheel hubs to the chassis and with vertical movement of each hub being damped by a respective hydraulic cylinder. As mentioned previously, the load of the front axle can be determined by measuring the pressure in the hydraulic cylinders of the suspension.

Figure 2 shows the structure of rear axle 6 the principal components of which are a central rear axle (differential) housing 8, and one outer trumpet housing 9 on each side. Central rear axle housing 8 has attachment points 8a for the lower links of a three-point linkage and is closed towards the rear end of the tractor by back cover 10. Back cover 10 has an attachment point 10a for the top link of a three point linkage. At the outer end of each outer trumpet housing 9, a hub flange 1 1 is provided to attach wheels which carry a pneumatic tyre (not shown) and are clamped by bolts 12, a clamping ring 13 and nuts 14.

A strain gauge sensor 30 is attached to the trumpet housing 9 by respective screws or bolls 31. Alternatively, the strain gauge sensor 30 could be glued to the respective surface. The strain gauge sensor 30 (and sensors to determine the load on the front axle) are connected with a tractor control unit (described below) which is also connected to a terminal display 32 (Fig. 1) provided for the operator to show information and set various parameters of the vehicle.

The strain gauge sensor 30 can measure deformation in two directions, represented in Figure 2 by arrows S I and S2. This has two major advantages. Firstly, the strain gauge sensor 30 may be provided with temperature compensation based on the relation between the deformation in directions SI and S2. Secondly, in addition to determining vertical loading, the strain gauge sensor 30 can also be used to determine a horizontal deformation in the driving direction (along axis X) which offers determination of the draft force applied.

Alternatively, a strain gauge sensor 30 which can measure deformation in only one direction, preferably in direction S I , could be installed. The temperature compensation may then be provided by determining the temperature of the housing (which is more or less equal to the sensor temperature) by using a surface temperature sensor. Alternatively the temperature sensor may be integrated in the strain gauge sensor 30. Furthermore, an ambient temperature sensor or a sensor measuring oil temperature in the housing may be used to determine sensor temperature with a stored characteristic map showing the relation between both parameters and thereby enabling compensation for temperature influence.

The strain gauge sensor 30 thereby shows a linear relationship between applied load and the deformation/strain as shown in a graph in Figure 3 whereby the load is shown on the vertical axis and deformation/strain is shown on the horizontal axis in the graph. The position of the linear curve can change for various reasons:

• Depending on tolerances during assembly of the axle structure 6, or of the sensor 30 itself, the curve may have different inclination, compared to reference curve CR, as shown by dashed curve C I .

• Depending on the wheel track width (the distance of the theoretical contact point between two tyres in a transverse direction) the curve inclination may change as shown by dashed curve C2. This track width can be changed for example by mounting different tyres with changed rim geometry, or by use a rear axle with adjustable track width.

• There may be an offset of the zero-point. If a load is applied perpendicular to the theoretical contact point between wheel and ground (defined by track width), the inclination of the characteristic of the sensor 30 is not changed, but an offset of the characteristic results as shown at C3. This may result for example if new tyres have the same track width but are heavier, if wheel weights are attached or if the tyre is filled with water. Adding twin tyres results in both a change in inclination (as track width is adapted) and zero-point offset (as twin tyres are heavier) as shown at C4.

Variations of inclination and offset of the zero-point by tolerances, track width and overall weight configuration require a method to calibrate the measuring system according the present invention, the basic steps of which are shown in the flow chart of Figure 4.

The process starts at 50 by determining a configuration of the vehicle. During construction the configuration is indicated by the stage reached in the construction process: after construction, the configuration will specify whether additional features such as double wheels are fitted. At 52, the configuration is used to look up an expected weight value in a database 54 of vehicle parameters and their respective contributions to vehicle weight. The database may contain individual weights for separate components of the vehicle, or it may be a simpler listing of total weight at known steps during the assembly process.

At 56, the weight value (axle loading) indicated by the strain sensor 30 output is compared with the expected loading for that configuration as read from the database 54, and a calibration offset (whether slope angle or zero offset) to be applied to subsequent strain sensor outputs is derived 58 and stored 60.

Prior to derivation, a check 62 may be performed as to whether additional data is required: if so, this is obtained at step 64. The additional data may comprise sensor characteristics 65a (such as the inclination of the sensor graph or curve), track width 65b, or additional loading 65c perpendicular to the wheel contact point. The additional data suitably also comprises an input from a further sensor 70 representative of the loading on the front axle 5.

Referring again to Figure 3, the calibration may require one or two measurements. If the inclination of the sensor graph is known, the system only requires only one measuring point PI is required to enable the system to calculate the load depending on deformation. This may be suitable if the tolerances within the assembly process are mitigated and parameters influencing the inclination can be determined by characteristic maps. Modern tractors are assembled according to customer demands so, before starting the assembly process, the final configuration and construction sequence is known and often stored on the assembly information system or in the tractor engine control unit (ECU). Based on the configuration, especially information related to track width, wheel size and loads applied to the wheel by wheel weights or water filling, the system can determine the current conditions and thereby inclination of the sensor graph. For example, for each tyre/rim size and track width, the inclination of the graph can be saved and restored.

If the inclination of the sensor graph is not known, the system requires a second measuring point P2 to define the inclination and thereby the relationship between load and deformation/strain. This is further represented by dashed line 66 in Figure 4. This must be considered for any calibration whereby the configuration during as semb I y/producti on and subsequently in operation varies and is described separately.

Referring to Figure 5A and 5B, assembly production is schematically represented by a timeline running from left to right, with a first component C I introduced at time tO and subsequent components (Cm, Cm+ I , Cx, Cx+ I ) being added in a known sequence until the vehicle is fully assembled (at point F). At a first stage, the axle load measuring step CAL1 is introduced. The load on the rear axle structure 6 (mainly caused by component weight plus fluid in the fuel tank or other reservoirs) would result in a deformation of the rigid axle. As at this stage, axle load is known as the influence of the various configuration on the wheel load is known from characteristic maps stored in the database 54 on the tractor ECU or the assembly information system, so P I (Fig. 3) is defined. This stage should be installed in the assembly process as early as possible to mitigate the influence of configuration so that characteristic maps may be simplified. For example, this stage could be at a time when only the housing plus driveline is mounted which is not varying very much. As these parts are taken in a defined order during assembly, the deformation can be measured while the load is known due to configuration.

Preferably the stages of the determination take place when the electric supply system of the tractor is in operation. Alternatively, the sensor (together with the ECU to save settings) may be externally supplied. With known, constant inclination, one point is sufficient to define the position of the graph.

If the sensor graph inclination is not known or may change, a further step CAL2 must be involved. As shown in Figure 5A, the step may happen at a construction stage such as when the tyres are fitted and the vehicle stands on the ground so that the rigid axle deformation can again be measured. As before, configuration (wheels/rim size etc) and the influence on the wheel load is known from characteristic maps, so the second measuring point P2 is gained. The system can then calculate the graph inclination with the first point PI . A system described above can be easily integrated in the production means without any additional steps required.

Coming now to the calibration during operation, this is represented by Figure 5B in which the further step CAL2 is performed subsequent to assembly finishing at F. In this operation, user input will generally be required (by owner or service personnel) to provide the configuration data, and suitably a menu-driven system is provided to obtain the necessary information.

Figures 6 to 8 show screen layouts as part of a terminal display 32 such as that described in applicants published patent application WO 201 1/033014. The screen layout is dedicated to the calibration function of the above described wheel load measuring system. The screen has a touch sensitive display area 40 showing, in the layout of Figure 6, a graphic representation of a tractor and columns 41 representing wheel load values, whereby:

41a is the current wheel load value for the front axle

41b is the current wheel load value for the rear axle

41 c is the default wheel load value for the front axle

41 d is the default wheel load value for the rear axle

The area below shows the numerical value for the current (or default) values in kg or as a percentage. Thereby the operator can compare current values with the default values set after or during assembly to evaluate whether the current values are plausible. There may be a questionnaire to suggest different changes which caused the variations in wheel load display: if the difference cannot be explained, the driver/operator may consult his service technician.

On the right side of display area 40, buttons 42are provided to enable operator selection of several functions. Button 42a is assigned to enter the menu for settings relevant to calibration, button 42b starts the calibration procedure and button 42c shows the display of Figure 6 as described above.

If button 42a is pressed, the display area 40 changes to display the layout shown in Figure 7 wherein the operator can enter relevant parameters relevant for axle load measurement. At the top of the display area 40, buttons 43a and 43b can be used to switch from settings related to front axle (43a) or rear axle (43b). The parameters to be entered are:

Area 44a - Wheel width: Distance of the contact points between left and right wheel. This may be a list of allowed wheel width configurations. Alternatively, this may be measured easily if, for example, adjustable wheel-width axles are used which are common in North America.

Area 44b - Tyre and rim size: The tyre size, but also the shape of the rim influences wheel width. A menu may be offered for the operator to select an allowed tyre/rim combination. If one is chosen, settings are adopted accordingly.

Area 44c and 44d - Provided to enter set-up for twin-tyre application. If button 44c is switched to the YES condition, indicating that twin tyres are used, area 44d shows a list of wheels rim combinations to be chosen. If button 44c is not activated and the status is NO, indicating that twin tyres are not used, the list in 44d is not selectable and highlighted in grey letters. Area 44e and 44f - Provided to enter set-up for wheel weight application. If button 44e is switched to YES condition, indicating that wheel weights are attached, area 44f shows a list of weights to be chosen. If button 44e is not activated and the status is NO, indicating that no wheel weight is used, the list is not selectable and highlighted in grey letters.

Area 44g and 44h - Provided to enter set-up for water filled tyres. If button 44g is switched to YES condition, indicating that tyres are filled with water, area 44h can be used to select the volume inserted in the tyre. If button 44g is not activated and the status is NO, indicating that no water filing is used, the list is not selectable and highlighted in grey letters.

As will be recognised, the lists shown in areas 44a, 44b, 44d, 44f and 44h change depending whether front or rear axle menu is activated (by button 43a b)

So far, the calibration after end of line and the necessary input by the operator (Wheel width) for proper calculation were described. A recalibration (after sales) should be done by a service technician and alternative procedures are described hereinafter with reference to Figure 8. After pressing button 42b, menu is switched to that shown in Figure 8, whereby the methods can be chosen by pressing respective buttons.

Recalibration 1 : Weighing method (by pressing button 45a)

The tractor is driven on a stationary weighing means (used for example for weighing loads of delivered goods) with its rear axle. The rear axle load can then be determined. The offset value graph can then be determined. Alternatively, mobile wheel load measuring devices (used by police to check overloading), could be used to determine current wheel load.

Recalibration 2: Workshop Modus (by pressing button 45b)

The tractor is equipped with a service mode which means that the rear linkage can be used to lift the rear axle from the ground. In a further step the front lifting unit is taken to bring the tractor in a horizontal position. The weight of the tyre/rim and respective width can be calculated according the drivers input, and the applied force on the sensor can be determined, so the graph can be determined.

Recalibration 3: End of Line Condition (by pressing button 45c)

The third method includes default parameters set during an End of Line (EOL) calibration carried out at F in Figure 5 with the data being logged in the ECU. In this mode, the system checks whether any changes have been made compared to end of line calibration. First of all, the service personnel must make sure that no weights, front loaders or other accessories are attached. Furthermore, all fluids (oil, diesel) must be at same level as for EOL. If this is true, the default values can be taken from the ECU.

Figure 9 schematically represents components of a system to receive the output from one or more strain sensors 30 and provide an axle load measuring apparatus including the rear axle assembly described above. The system provides the tractor control unit and ECU referenced above.

A first processor CPU 100 is coupled with random access memory RAM 1 12 and read only memory ROM 1 14 by an address and data bus 1 16. RAM 1 12 will typically hold the captured sensor data for processing whilst ROM 1 14 stores reference data such as characteristic maps of the relation between temperature and sensor output and the above- mentioned database 54. Also connected to CPU 100 via the address and data bus 1 16 is at least one further processor COPROC 142, which may be a further CPU sharing tasks with the first CPU 100, or may be a coprocessor device supplementing the function of the CPU 100, handling background or lower level processes such as floating point arithmetic and signal processing. Each of these internal hardware devices 100, 1 12, 1 14, 142 includes a respective interface (not shown) supporting connection to the bus 216. These interfaces are conventional in form and need not be described in further detail.

Also connected to the CPU 100 via bus 1 16 are a number of external hardware device interface stages (generally denoted 1 18). A first interface stage 120 supports the connection of external input/output devices, such as a joystick or mouse 122 and/or keyboard 124. Also connected to the first interface stage 120 are two strain sensors 30 from the rear axle assembly, together with a further sensor 70 which provides an output indicative of the front wheel/axle loading. Other sensors such as a temperature sensor may also be connected.

The configuration of the first interface stage 120 may vary in dependence on, for example, the type of devices connected thereto and the format of communications on address and data bus 1 16. In relation to the sensors 30, however, it will typically include an amplification stage and one or more analog to digital converters. Based on the digitised sensor output values received via the bus 1 16, CPU 100 and or coprocessor 142 calculates (following a stored computer program) the front and rear wheel loadings for the vehicle, which loadings may then be used to guide adjustment of ballasting for example.

A second interface stage 126 supports the connection of external output devices such as a display screen 128 and/or audio output device 130, such as headphones or speakers. The display screen 128 may be used to present the derived wheel loadings to a user. As indicated by dashed line 32', the functions of keyboard 124 and display screen 128 may be combined in a touch-screen terminal display (32; Fig. I ). A third interface stage 132 supports the connection to external data storage devices in the form of computer readable media: such external storage may as shown be provided by a removable optical or magnetic disc 134 (accessed by a suitably configured disc reader 136). Alternatively or additionally the external storage may be in the form of a solid state memory device such as an extension drive or memory stick device. The external storage may contain a computer program.

A fourth interface stage 138 supports connection of the system to remote devices or systems via wired or wireless networks 140, for example over a local area network LAN, via the internet, or another data source, for example for the downloading of program or database updates or updated reference data tables.

From reading of the present disclosure, other modifications will be apparent to those skilled in the art. Such modifications may involve other features which are already known in the field of vehicle suspension systems and component parts therefore and which may be used instead of or in addition to features described herein. For example, alternative methods for attachment of the sensor 30 may be provided, including mounting by gluing or a combination of screwing and gluing. Furthermore, other configurations of strain sensor, such as a strain bore sensor which is inserted into a bore and deformed by the bore geometry, may be installed.

Claims

1. An axle load measuring apparatus for an agricultural vehicle comprising:

a. an axle assembly with at least one sensor to determine axle load; b. data processing means coupled to said at least one sensor to receive an output signal therefrom and arranged to generate an output value representative of axle loading based thereon;

c. data storage means coupled with the data processing means and holding a database of vehicle weight or axle load data by reference to vehicle configuration;

wherein the axle assembly is a rigid-type axle assembly with said at least one sensor being a strain sensor mounted to an attachment area thereof and

wherein the data processing means is a programmable device controlled to derive a performance curve of strain sensor output against rigid axle loading based on a first sensor output at a first configuration and at least one additional factor.

2. Apparatus as claimed in claim 1 , wherein the at least one additional factor comprises one of:

a. a known performance characteristic of the strain sensor;

b. a track width of wheels mounted on the rigid axle;

c. a second sensor output measured at a second configuration;

d. extent of an additional load applied vertically perpendicular to the contact point between the ground and wheels mounted on the rigid axle;

e. known loading on a further axle of the vehicle.

3. Apparatus as claimed in Claim 1 , in which the rigid axle assembly comprises a pair of trumpet housings, a pair of wheel hubs each being mounted to a respective one of same trumpet housings and being rotatable about a longitudinal axis of the axle assembly, a differential coupled to transfer torque to the wheel hubs, and a differential housing partly surrounding the differential and to which the trumpet housings are attached, with the at least one strain sensor being mounted to an attachment area of one of the trumpet housings.

4. Apparatus as claimed in Claim 1 , wherein the vehicle has an additional axle and the data processing means is arranged to receive and subtract a measured axle loading for the additional axle when determining the calibration offset.

5. Apparatus as claimed in Claim 4, wherein the additional axle is a suspended axle, the apparatus further comprising a fluid pressure sensor with the axle loading of the suspended axle being determined by hydraulic fluid pressure in a suspension system of the axle.

6. Apparatus as claimed in any of Claims 1 to 5, further comprising user-operable input means for the supply of configuration data to the data processing means.

7. Apparatus as claimed in Claim 6, wherein the input means comprises a touch-screen display device coupled with the data processing means.

8. A method of calibrating an axle load measuring apparatus of an agricultural vehicle having a sensor to determine axle load of an axle assembly of the vehicle, the method comprising:

a. determining a configuration of the vehicle;

b. using the configuration to look up an expected weight or axle load value in a database of vehicle parameters and their respective contributions to vehicle weight or axle load;

c. comparing a loading value indicated by the sensor output with the expected weight or axle load value for that configuration; and

d. determining and storing a calibration offset to be applied to subsequent sensor outputs,

wherein the sensor is a strain sensor and the axle is a rigid axle, wherein the step of determining and storing includes deriving a performance curve of strain sensor output against rigid axle loading based on a first sensor output at a first configuration and at least one additional factor.

9. A method according to claim 8, performed during assembly of the vehicle according to a predetermined construction sequence wherein the configuration is determined by the point reached in the construction sequence.

10, A method according to claim 9, performed at two or more different points in the construction sequence.

1 1 . A method as claimed in Claim 8, further comprising storing the database in a control unit of the vehicle.

12. A method as claimed in Claim 1 1 , further comprising providing a menu-driven means to prompt a user of the vehicle to supply data determining the configuration of the vehicle.

13. A method as claimed in claim 8, wherein the at least one additional factor comprises one of:

a. a known performance characteristic of the strain sensor;

b. a track width of wheels mounted on the rigid axle;

c. a second sensor output at a second configuration;

d. extent of an additional load applied vertically perpendicular to the contact point between the ground and wheels mounted on the rigid axle; e. a known loading on a further axle of the vehicle.