High precision vehicle load calculation

Abstract

A method of calculating a vehicle load includes calculating a first vehicle load value based on at least air pressure in an air spring and height data of a suspension of a vehicle axle, determining a second vehicle load value based on a change in track of the vehicle axle, and calculating the vehicle load based on the first vehicle load value and the second vehicle load value.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to motor vehicles, and more particularly to a vehicle load calculation for an air suspension system of a motor vehicle. BACKGROUND

[0002] Suspension systems of motor vehicles provide for a more comfortable ride for the vehicle occupants. The demand of vehicle owners for increased comfort, fuel economy, and more controls and options has led to the development of adjustable air suspension systems. Depending on the current driving surface, the vehicle operator can select different suspension operating modes. The suspension operating modes have preset suspension parameters to provide an ideal suspension arrangement for various driving situations. Typical operating modes that the driver can select include standard driving modes such as comfort or sport mode, snow mode, off-road mode, and the like. In addition to providing selected operating modes for various driving situations, the suspension system can also be adjusted when selected operating conditions are met.

[0003] An air suspension system has four corner assemblies. One corner assembly is located at the suspension position corresponding to each of the vehicle's wheel corners. An air supply unit, including an electronic control unit, is connected to the corner assemblies. The air supply unit is capable of independently adjusting the corner assemblies. The vehicle load calculation system includes a plurality of height sensors, each associated with a corner assembly to measure the current ride height, and at least one pressure sensor to measure the current pressure in each air spring.

[0004] For load detection, the data of the pressure sensors and a number of ride height sensors are used. The pressure sensors sense the air pressure in each air spring. The ride height sensors measure the current ride height at each corner assembly. The signals of those sensors are combined to determine the current vehicle load.

[0005] The vehicle load at individual corner assemblies can be calculated based on the data from the pressure sensors and the plurality of height sensors. Using the vehicle load at each corner, at least one load dependent vehicle characteristic is calculated, which the vehicle system can use to adjust at least one vehicle operating parameter to compensate for the at least one load dependent vehicle characteristic.

[0006] The accuracy of the load detection is limited mainly by the fact that only these signals are used to determine the current vehicle load. But the vehicle frame, and more specifically the corner assemblies, are affected by other forces, which are not considered when determining the vehicle load.

[0007] This leads to a limited accuracy of the load detection algorithm. An inaccurate detected vehicle load leads to an incorrect air pressure in the air springs. In case of high dynamic pressure during driving, the air springs can become damaged. Furthermore, an inaccurate vehicle load leads to an incorrect operation of the dynamic vehicle stability control system, which is essential for the vehicle safety.

[0008] The background description provided herein is for the purpose of generally presenting the context of the disclosure. The work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that can not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the application. SUMMARY

[0009] A vehicle load calculation system comprises an air suspension system with at least four corner assemblies, wherein one corner assembly is located at a suspension position corresponding to each of the vehicle's wheel corners, and the corner assemblies each comprise an air spring; wherein at least two of the corner assemblies are associated with a vehicle axle. An air supply unit, wherein the air supply unit is capable of adjusting the air springs independently from each other. A pressure sensor located at a valve group of the air supply unit, wherein the pressure sensor is capable of measuring the air pressure in each air spring. A plurality of height sensors, wherein one of the height sensors is located at a suspension position corresponding to each of the vehicle's wheel corners, wherein each height sensor is capable of measuring the height of the associated corner assembly. An electronic control unit connected to the corner assemblies, wherein the electronic control unit comprises instructions for calculating a vehicle load. A first vehicle load value is calculated based on at least the data of the pressure sensor and the plurality of height sensors associated with a vehicle axle. A second vehicle load value is determined based on a change in the track width of the vehicle axle. The second vehicle load value is subtracted from at least the first vehicle load value to calculate the vehicle load.

[0010] A method of calculating a vehicle load comprises measuring one of a plurality of air pressures in a plurality of air springs, wherein each air spring is associated with a corner assembly located at a suspension position corresponding to each of the vehicle's wheel corners. A plurality of heights is measured at a suspension position corresponding to each of the vehicle's wheel corners. A first vehicle load value is calculated by means of an electronic control unit based on at least the measured pressures and the height data of a vehicle axle, wherein at least two of the corner assemblies are associated with the vehicle axle. A second vehicle load value is determined by means of the electronic control unit based on a change in the track width of the vehicle axle. The vehicle load is calculated by subtracting at least the second vehicle load value from the first vehicle load value.

[0011] To compensate for the imprecise vehicle load determination, the vertical acting forces due to the track variation of the first vehicle axle are considered in the load detection algorithm. When the track of the first axle changes, tension forces act on the suspension. Those forces are effective when the vehicle is lowered in a stationary state, for example due to a load change. This leads to a false vehicle load determination.

[0012] Due to the trajectory of the wheels, there is a kinematic correlation between the track and the height variation of the vehicle. If the vehicle is loaded, the height is lowered and the track is increased. Thus, due to the track variation, additional forces are applied to the cornering assembly. This force acts in the opposite way compared to the load force.

[0013] The vehicle load is determined by calculating the vehicle load based on the information of the pressure sensor and the plurality of height sensors, while subtracting the acting forces due to the varying track. This leads to a more precise vehicle load. The corrected vehicle load or the corrected axle load is calculated based on the pressure signal, the height signal and the acting forces due to the variation of the track.

[0014] The described calculation of the vehicle load is not limited to a single vehicle axle. This vehicle load calculation can also be implemented with respect to other vehicle axles. Then, the two calculated vehicle load values are combined to a total vehicle load.

[0015] Other applicable fields of the present disclosure will become apparent from the specific embodiments provided hereinafter. It should be understood that the specific embodiments, while indicating preferred embodiments of the present disclosure, are merely intended to be illustrative and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0016] The present disclosure will become more fully understood from the detailed description and accompanying drawings, wherein:

[0017] Figure 1 is a schematic illustration of an air suspension system according to an embodiment;

[0018] Figure 2 is Figure 1 is a pneumatic wiring diagram of the air suspension system shown in

[0019] Figure 3a and Figure 3b is a diagram illustrating exemplary track variations; and

[0020] Figure 4 is a flow chart of a method for calculating a vehicle load.

[0021] The embodiments, examples, and alternatives of the preceding paragraphs, claims, or following description and drawings, including any of their various aspects or corresponding individual features, can be taken independently or in any combination of one or more features. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. DETAILED DESCRIPTION

[0022] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application, or uses. For clarity, identical numbers can be used throughout the drawings to denote similar elements.

[0023] Figure 1 A vehicle 10, in this example a pickup truck, is illustrated. The vehicle 10 includes an air suspension system 12. The air suspension system 12 is supported by a frame 14. The air suspension system has four corner assemblies 16A-16D located at each of the wheel 18 locations of the vehicle 10. The four corner assemblies 16A-16D can be adjusted independently. Two corner assemblies 16A, 16B are located at the front wheel 18A, 18B corners of the vehicle 10 and two corner assemblies 16C, 16D are located at the rear wheel 18C, 18D corners of the vehicle. The two corner assemblies 16A, 16B are associated with a first axle of the vehicle 10 and the two corner assemblies 16C, 16D are associated with a second axle of the vehicle 10.

[0024] The air suspension system 12 includes an air supply unit 20 fluidly connected to the four corner assemblies 16A-16D. The air supply unit 20 includes an electronic control unit (ECU) 22, a compressor 24, a reservoir 26, and a valve bank 30. The individual components of the air supply unit 20 can be assembled together or supported at separate locations on the vehicle 10. In the illustrated embodiment, the electronic control unit 22 is located away from the compressor 24, the reservoir 26, and the valve bank 30 (electrical connections not shown). Alternatively, the air suspension system 12 can be an open loop system and the air supply unit 20 can not include a reservoir 26.

[0025] The air supply unit 20 is connected to the four corner assemblies 16A-16D by supply lines 28. In the illustrated example, the air suspension system 12 is a closed system. The valve bank 30 is controlled by the electronic control unit 22 to regulate the air supply between the compressor 24, the reservoir 26, and the four corner assemblies 16A-16D. The valve bank 30 can be a single unit defining multiple valves, multiple valves positioned together, or multiple valves located at different locations. Additionally, the reservoir 26 can be a single or multiple tank assemblies.

[0026] While the disclosed embodiments have four corner assemblies 16A-16D, the suspension system 12 can also be a system in which the front and rear axles can be adjusted separately and not necessarily require separate adjustment at each of the corner assemblies 16A-16D. The four corner assemblies 16A-16D are adjustable to accommodate various driving conditions. Based on the selected suspension mode, the electronic control unit 22 will adjust the air supply between the compressor 24, the reservoir 26, and the four corner assemblies 16A-16D to adjust the four corner assemblies 16A-16D from their current position to the desired position. When lowering any of the corner assemblies 16A-16D, the excess air is sent to the reservoir 26 for storage. When raising any of the corner assemblies 16A-16D, the required air is sent from the reservoir 26 to the appropriate corner assembly 16A-16D. The compressor 24 ensures that the air pressure within the system 12 is maintained at the desired level. Alternatively, in the case of an open system, the excess air is released to the environment, or drawn from the environment and pressurized as needed. The compressor 24 ensures that the air pressure within the system 12 is maintained at the desired level.

[0027] The air suspension system 12 can be adjusted at the direction of the vehicle operator by moving the selector or when there are predetermined operating conditions, such as the vehicle 10 accelerating above a certain speed, lowering the suspension system 12, and raising the suspension system 12 when the vehicle 10 decelerates below a predetermined threshold. Thus, the air suspension system 12 can be adjusted while the vehicle 10 is in motion. In this case, the front corner assemblies 16A, 16B can be adjusted together, and the rear corner assemblies 16C, 16D can be adjusted together. To provide the greatest possible aerodynamic adjustment, when the vehicle is traveling in the forward direction, the rear corner assemblies are adjusted to the new position first when raising the suspension system 12. However, the front corner assemblies 16A, 16B are adjusted to the new position first when lowering the suspension system 12. Alternatively, each corner 16A-16D can be adjusted individually, or all of the corners 16A-16D can be adjusted simultaneously. The air suspension system 12 can also be adjusted in a stationary state of the vehicle. The corner assemblies 16A-16D can be adjusted after the vehicle 10 has been loaded. For example, the vehicle 10 is then raised back to the normal ride height to compensate for the load.

[0028] Reference Figure 1 and Figure 2The solenoid valve assembly 30 includes an exhaust valve, a pressure sensor 32, and four air spring valves. Fluid line 28 connects the reservoir 26 to the compressor 24 (e.g., fluid line 28 is a 6x1 mm pipe), connects the compressor 24 to the valve assembly 30 (e.g., fluid line 28 is a 6x1.5 mm pipe), and connects the valve assembly 30 to the air springs (e.g., fluid line 28 is a 6x1.5 mm pipe). The pressure sensor 32 can be connected close to or directly to the valve assembly 30.

[0029] Solenoid valve assembly 30 is used to manage airflow between system components 16A-16D, 24, and 26. The vehicle load can be determined using signals from pressure sensor 32. The electronic control unit 22 then uses this vehicle load information to help determine desired adjustments to the air suspension system 12, such as increasing height to accommodate heavy vehicle loads.

[0030] Therefore, the vehicle load calculation system includes an air suspension unit 12 with four air spring corner assemblies 16A-16D. Each air spring corner assembly 16A-16D is located at a suspension position corresponding to each of the wheel corners 18A-D (18A-18D) of the vehicle 10, and an air supply unit 20, including an electronic control unit 22, is fluidly connected 28 to the air spring corner assembly 16A-16D. The air supply unit 20 is capable of independently adjusting the air spring corner assemblies 16A-16D.

[0031] A method for determining the vehicle load of a vehicle 10 equipped with an air suspension system 12 includes detecting a pressure signal from a sensor 32 located within a valve assembly 30 of the air suspension system 12. The pressure sensor 30 determines the air pressure within each air spring. The vehicle load is calculated based at least on this pressure signal.

[0032] The method for determining vehicle load also includes signals from height sensors. A driving height sensor is associated with each corner assembly 16A-16D. These sensors can collect information about the current height at each of the corner assemblies 16A-16D. These sensors can also collect information about the current height of the vehicle whether it is stationary or moving.

[0033] The detected information (including the height at each corner assembly 16A-16D and the air pressure in each air spring) is reported to the electronic control unit 22. The load calculation system uses the suspension electronic control unit 22 to calculate the vehicle load based at least on this information. The vehicle load at each corner assembly 16A-16D or at the front and rear axles can be calculated based on this information.

[0034] Furthermore, the determined vehicle load is corrected by subtracting the load resulting from the wheel track constraint. The total vehicle load is calculated by subtracting a wheel track based load value from the load value based on pressure and height data. The wheel track based load value is a result of the vertical force exerted to the wheel axle when lowering or levelling up the vehicle. These kinematic properties (wheel track) can be measured in advance and are available by the vehicle test application by levelling up and down with the help of the slide plates. The height data points will be assigned to the wheel track. This results in a predetermined value of the vehicle load based on the varying wheel track.

[0035] Referring to Figure 3a and Figure 3b a change in wheel track of a vehicle axle is exemplarily shown. In Figure 3a the vehicle is in a static state and for example at its lowest height h0. At this first height the wheel track 0 is for example 1610 mm. At this time the proposed method stores the current wheel track at the current height. Following is a request to level up. Therefore, as shown in Figure 3b the vehicle height is increased to a second height hi. For example, the vehicle is levelled up by 60 mm. At this height hi the wheel track 1 will be 1590 mm. This means that the wheel track changes from 1610 mm to 1590 mm due to the request to level up. Therefore, the change in wheel track is 20 mm. When the vehicle is levelled up the tire is pulled inwards. Due to this kinematic property a vertical force is exerted to the corner assembly of this wheel axle. The road friction force results in a counter force on the tire indicated by the bold arrow shown outwards.

[0036] Due to the wheel track this force translates into a vertical force on the corner assembly. This force distorts the correct calculation of the vehicle load. Therefore, a correction load value is determined. The proposed determination takes into account the change in wheel track. The changed wheel track value will be multiplied by a constant stiffness factor. This constant stiffness factor is predefined for the specific suspension properties of each vehicle. Furthermore, the current road surface friction coefficient can be applied to the constant stiffness factor. By multiplying the changed wheel track value with the constant stiffness factor the vertical force on the corner assembly is calculated. To calculate the correction load value the vertical force is divided by the gravitational acceleration (9.81 m / s2). This calculation results in a correction load value which can then be subtracted from the standard vehicle load calculation. The standard vehicle load calculation is based on the air spring pressure and the vehicle height. Therefore, by taking into account the change in wheel track a more precise vehicle load calculation is implemented.

[0037] The increased accuracy of the load detection can be used to adjust the suspension system 12 more finely based on the provided readings. Additionally, the increased accuracy can be used to more closely monitor the load, especially on the rear axle of a pickup truck, to prevent overload situations and provide a more robust measure for safe operation in overload situations. In fact, due to the increased accuracy of the measurements available to the system, the overall high effective load rating can even be increased, as the load measurements are more accurate, the design margin to prevent overload situations can be smaller.

[0038] Reference Figure 4 which is a flow chart illustrating a method of determining a vehicle load. The method comprises the following steps. In step S1 the vehicle speed is reduced to 0 mph, so the vehicle is in a stationary state. In step S2 the current wheelbase for the current height is stored in the electronic control unit.

[0039] In step S3 there is a request to raise the height. This is initiated by the driver or the autonomous vehicle itself. Thereafter, the vehicle height is raised. In step S4 a change in load of the vehicle occurs. Thus, i.e. the vehicle height is lowered.

[0040] In step S5 the measurement of air pressure and current height is completed. This leads to a calculation of a first vehicle load value load_m in step S6 based on the pressure and height measurements.

[0041] In step S7 a second vehicle load value load_tw is determined by taking into account the wheelbase at the current height. The wheelbase of the axle exerts a certain vertical force on the suspension at a certain height. Due to this kinematic property, a lookup table is provided which contains certain load values for each class of vehicle.

[0042] Finally, in step S8 the overall and accurate vehicle load can be calculated by subtracting the second vehicle load value from the first vehicle load value.

[0043] While several embodiments have been described in detail, the true scope of the present disclosure should not be so limited as the skilled person familiar with the field to which the present disclosure relates will recognize various alternative designs and embodiments for practicing the scope of the appended claims.

Claims

1. A vehicle load calculation system, comprising: An air suspension system having four corner assemblies, wherein the corner assemblies of the four corner assemblies are located at suspension positions corresponding to each of the wheel corners of the vehicle, and each of the four corner assemblies includes an air spring, wherein two of the four corner assemblies are associated with the vehicle axle. An air supply unit configured to adjust the air pressure within each air spring; A pressure sensor located at the valve assembly of the air supply unit, wherein the pressure sensor is configured to measure the air pressure in each air spring; Multiple height sensors, wherein a height sensor of the multiple height sensors is located at the suspension position corresponding to each wheel corner of the vehicle, and wherein each height sensor of the multiple height sensors is configured to measure the height of an associated corner assembly among the four corner assemblies; as well as An electronic control unit connected to the four corner assemblies, wherein the electronic control unit is configured to calculate a vehicle load from a first vehicle load value and a second vehicle load value, the first vehicle load value being calculated based on the air pressure in each air spring measured by the pressure sensor and the height measured by the plurality of height sensors associated with the vehicle axle, the second vehicle load value being determined based on the wheelbase variation of the vehicle axle, wherein the second vehicle load value is subtracted from the first vehicle load value to calculate the vehicle load, wherein the wheelbase variation is multiplied by a constant stiffness factor to calculate the vertical force acting on the two corner assemblies of the axle, and wherein the road surface friction coefficient is applied to the constant stiffness factor.

2. The vehicle load calculation system according to claim 1, wherein the wheelbase variation is determined by the vehicle height variation from the first vehicle height to the second vehicle height.

3. The vehicle load calculation system according to claim 2, wherein the first vehicle load value is calculated at the second vehicle height.

4. The vehicle load calculation system according to claim 1, wherein the second vehicle load value is calculated by dividing the vertical force acting on the two corner assemblies of the axle by the gravitational acceleration.

5. The vehicle load calculation system according to claim 1, wherein the constant stiffness factor is predefined for the suspension of each vehicle.

6. The vehicle load calculation system according to claim 1, wherein the vehicle is in a stationary state.

7. The vehicle load calculation system according to claim 1, wherein the vehicle load calculation is performed on the vehicle axles.

8. A method for calculating vehicle load, the method comprising: Measure the air pressure in multiple air springs located at suspension positions corresponding to each wheel corner of the vehicle; Measure multiple heights at the suspension positions corresponding to each of the wheel corners of the vehicle; A first vehicle load value is calculated based on the air pressure among the plurality of air pressures and the height among the plurality of heights associated with the vehicle's axles; Determining a second vehicle load value based on the wheel track variation of the vehicle axle includes calculating the vertical force acting on the corner assembly of the axle by multiplying the wheel track variation by a constant stiffness factor and applying the road friction coefficient to the constant stiffness factor. as well as The vehicle load is calculated based on the first vehicle load value and the second vehicle load value, wherein the second vehicle load value is subtracted from the first vehicle load value to calculate the vehicle load.

9. The method for calculating vehicle load according to claim 8, further comprising determining the wheelbase change based on the vehicle height change from a first vehicle height to a second vehicle height.

10. The method for calculating vehicle load according to claim 9, wherein calculating the first vehicle load value includes calculating the first vehicle load value at the second vehicle height.

11. The method for calculating vehicle load according to claim 8, wherein determining the second vehicle load value comprises calculating the second vehicle load value by dividing the vertical force acting on the corner assembly of the axle by the acceleration due to gravity.

12. The method for calculating vehicle load according to claim 8, wherein the constant stiffness factor is predefined for the suspension of the vehicle.

13. The method for calculating vehicle load according to claim 8, wherein calculating the vehicle load includes calculating the vehicle load in a stationary state.

14. The method for calculating vehicle load according to claim 8, wherein calculating the first vehicle load value includes calculating the first vehicle load value based on the air pressure of the plurality of air pressures and the height of the plurality of heights associated with each axle of the vehicle.

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