Method for estimating the longitudinal force difference acting on the steering wheel

Abstract

A method for estimating a longitudinal force difference ΔF acting on wheels (104, 105) of a steering axle (102) of a vehicle (1) x The method comprises: obtaining a steering torque M applied to the vehicle (1) steer The data related to the applied steering torque M steer Associated with the steering axle wheel (104, 105); obtain the kingpin offset value r associated with the steering axle wheel (104, 105) s ; and, based on the data obtained and the kingpin offset r s To estimate the longitudinal force difference ΔF x , the longitudinal force difference is related to the applied steering torque M steer is proportional to and equal to the kingpin offset r s Inversely proportional.

Description

Technical Field

[0001] The present disclosure relates to a method for estimating a longitudinal force difference acting on a wheel of a steering axle of a vehicle, a control unit and a vehicle. Also disclosed are a plurality of applications for use in the vehicle, which applications are at least partially based on the estimated force difference.

[0002] The invention may be applied to heavy vehicles such as trucks and construction equipment.Although the invention will be described primarily with reference to cargo transport vehicles such as semi-trailers, the invention is not limited to this particular type of vehicle but may also be used in other types of vehicles. Background Art

[0003] Advanced vehicle motion control systems are being introduced to, for example, support automated driving functions and improve vehicle safety. These vehicle control systems obtain data related to the current vehicle state from multiple sensors and perform vehicle motion control based on the data.

[0004] A vehicle is typically subject to longitudinal and lateral forces acting on the vehicle's wheels. Longitudinal forces acting on the wheels of the vehicle's steering axle are of particular concern to vehicle motion control systems because they affect the vehicle's steering characteristics.

[0005] To improve vehicle state estimation and motion control, it is desirable to estimate these longitudinal forces, especially the difference between the longitudinal forces acting on a pair of steered wheels on an axle. However, such estimation is not straightforward.

[0006] US2003 / 0221898 discloses a method for determining the longitudinal forces acting on a pair of steering wheels. Signals from a brake pressure sensor and a wheel speed sensor are used to perform calculations. The calculation results are used to determine the steering torque required to compensate for the force difference.

[0007] However, there is a need for an improved method for determining the longitudinal force differential acting on the steering wheel. Summary of the invention

[0008] The present invention aims to provide a method for estimating the longitudinal force difference ΔF acting on the wheels of the steering axle of a vehicle. x The method includes: obtaining a steering torque M applied from the vehicle steer The data related to the applied steering torque M steer The method further comprises: obtaining a kingpin offset value r associated with the steering axle wheel. s , and based on the data obtained and the kingpin offset r s To estimate the longitudinal force difference ΔF x , the longitudinal force difference ΔF x With the applied steering torque Msteer is proportional to and equal to the kingpin offset r s Inversely proportional.

[0009] Thus, a simple and accurate estimate of the longitudinal force difference acting on the wheels of the steering axle of the vehicle is provided. For example, it can be simply calculated from ΔF x =M steer / r s Or use the M steer and r s A more advanced expression is used to estimate the longitudinal force difference. This method does not require advanced and / or expensive sensors or powerful data processing resources, which is an advantage. This method can also realize a variety of applications based on the estimated force difference, which will be described below.

[0010] According to various aspects, the vehicle includes an active steering system, and the obtaining includes: obtaining a steering torque M corresponding to the applied steering torque M from the active steering system. steer Active steering systems implemented in vehicles typically already provide data about the steering torque applied. Therefore, advantageously, some of the methods disclosed herein can be efficiently and cost-effectively implemented in a vehicle by reusing already existing data and control hardware. According to some such aspects, the data obtained from the active steering system includes the steering wheel torque T steering and the combined gain factor K through the vehicle's hydraulic steering mechanism powersteer Then, based on the relationship ΔF x =T steering *K powersteer / r s To estimate the longitudinal force difference ΔF x In other words, considering the hydraulic steering torque gain coefficient K powersteer In the case of x The applied steering wheel torque T steering is proportional to, and again to, the kingpin offset r s Inversely proportional.

[0011] According to various aspects, the data obtained from the active steering system includes the applied steering torque M steer Thus, advantageously, the applied steering torque need not be available, as the method can be implemented based on data inputs that are only indirectly related to the applied steering torque, such as a current value associated with an electric motor of an active steering system.

[0012] According to various aspects, the active steering system includes a steering angle feedback system configured to maintain the steering angle of the vehicle at a requested angle. If the active steering system is running a steering angle control loop to maintain the steering angle of the vehicle at a certain requested steering angle even in the presence of disturbances, the estimation of the longitudinal force difference may become more accurate because the control loop may reduce the influence of certain vehicle dynamics that may otherwise affect the accuracy of the estimation to a certain extent. For example, if the steering angle controller is active and fast enough, then even when ΔF x If the steering angle controller system does not work, then under certain conditions, a large ΔF x Significant variations in the steering angle may result, which in turn means that various aspects of the steering hardware may need to be taken into account in order to maintain the accuracy of the estimate.

[0013] According to various aspects, the vehicle comprises one or more torque sensors or force sensors, which are arranged to be connected to the steering system of the vehicle. Then, the obtaining comprises: obtaining from the one or more torque sensors a torque value corresponding to the applied steering torque M steer Thus, advantageously, some of the methods disclosed herein do not require a vehicle with an active steering system, as torque sensors or force sensors may be used to achieve a similar effect.

[0014] According to various aspects, the estimating comprises filtering the time series of data values ​​obtained from the active steering system or from the one or more torque sensors. By filtering the obtained time series of data values, the accuracy of the estimation can be improved, since measurement noise and other disturbances are suppressed by the filtering, which is an advantage.

[0015] As described above, a number of applications are disclosed herein that may be implemented in a vehicle or elsewhere based on the estimated longitudinal force differential.

[0016] According to one such example application, the method includes determining a relationship between a brake control input signal (e.g., a brake chamber pressure value) and a resulting braking force or torque applied to a steering wheel by applying a plurality of brake control input signals at the steering wheel, monitoring a longitudinal force difference value ΔF for each applied brake control input signal x , and determining the relationship based on a plurality of applied brake control input signals and a plurality of generated longitudinal force difference values.

[0017] The relationship between the brake control input signal (e.g., brake pressure value or other brake input amplitude) and the actual braking force achieved can be linear, or can follow some other higher order relationship. Knowing these relationships enables, for example, real-time updating of the control algorithm to account for changes in the relationship between the output signal and the achieved braking force, which is an advantage because more accurate vehicle control can be achieved. For example, according to one example, the method includes based on ΔF x and the system of equations and The solution to estimate the braking gain associated with the vehicle's steering wheel Among them, p1 and p2 are the applied brake pressure values, etc. and are the braking gains associated with the left and right steering wheels, respectively, and R L and R R are the rolling radii associated with the left and right steering wheels, respectively. Advantageously, knowledge of the current brake gain and the most recent brake gain enables a more accurate braking operation, as the actual braking force obtained from a given set of brake control signals can be more accurately determined.

[0018] According to various aspects, the method further includes calibrating a braking system of the vehicle based on the determined relationship between the brake control input signal and the generated braking force. For example, this calibration can be performed by adjusting a known brake gain estimated according to the above example. Moreover, the brake gain can be continuously estimated so that an accurate value of the brake gain is maintained over time (e.g., as brake pad wear and temperature changes occur).

[0019] According to another such example application, the method includes detecting a fault in the vehicle by determining an expected longitudinal force difference ΔF based on requested torques on the left and right steering wheels, respectively, and based on wheel rolling radii. x,expect For example, we can use ΔF x,expect =T L / R L -T R / R R To determine the expected longitudinal force difference, where T L and T R are the requested torques on the left and right steering wheels, respectively, and where R L and R R are the rolling radii associated with the left and right steering wheels, respectively. The method then comprises: calculating the expected longitudinal force difference ΔF x,expect The difference between the estimated force and the x for comparison; and, in ΔF x,expect and ΔF xWhen there is a difference between the two, a fault in the vehicle is detected. The allowed difference amplitude may be, for example, simply a preconfigured threshold, or the difference amplitude may be an adaptive threshold configured according to the scenario. Other more advanced detection criteria are also applicable. Therefore, advantageously, a fault in the vehicle can be reliably detected by the disclosed method, which is an advantage.

[0020] According to aspects, the method further comprises, in case of a detected fault in the vehicle, triggering a warning signal or an emergency maneuver by the vehicle.Thus, advantageously, the disclosed method can be used to trigger a warning signal in a robust manner based on an estimation of a longitudinal force difference value.

[0021] According to yet another example application, the method includes controlling the stability of the vehicle by: based on the relationship M yaw =ΔF x *L w To determine the total yaw moment or torque applied to the vehicle, where L w is the track width of the front axle of the vehicle. The method further comprises: allocating braking torque and / or steering angle to compensate for the total yaw M yaw , thereby controlling the stability of the vehicle. Thus, advantageously, a more stable vehicle operation is provided.

[0022] According to various aspects, the method further comprises: x,1 =ΔF x -F x,2 To estimate the longitudinal force acting on the first steering wheel, is a brake chamber pressure value or other brake control input signal associated with a second wheel, and is the braking gain associated with the second wheel. In this way, improved vehicle control based on the estimated longitudinal force data is provided.

[0023] According to various aspects, the method includes monitoring wheel speed values ​​and / or wheel slip conditions associated with a steering axle wheel of the vehicle, and also detecting a fault in the vehicle and / or classifying a road condition based on the wheel speed values ​​and / or wheel slip conditions.

[0024] By monitoring wheel speed and / or wheel slip, an improved fault detection mechanism is provided. For example, if a large longitudinal force differential is estimated but both wheels are in a free rolling state, it is likely that a fault has occurred in the vehicle's braking system or a tire blowout, etc. However, if a large longitudinal force differential is detected and the wheel slip monitoring indicates that the wheels are slipping, the differential is more likely to be due to road conditions and should not be recorded as a fault.

[0025] A control unit, a computer program, a computer readable medium, a computer program product and a vehicle associated with the above advantages are also disclosed herein.

[0026] Generally, all terms used in the claims should be interpreted according to their ordinary meanings in the art, unless otherwise clearly defined herein. All references to "one / an / the element, device, part, device, step, etc." should be interpreted in an open manner as referring to at least one instance of the element, device, part, device, step, etc., unless otherwise clearly stated. Unless clearly stated, the steps of any method disclosed herein do not have to be performed in the exact order disclosed. Other features and advantages of the present invention will become apparent when reading the attached claims and the following description. Those skilled in the art will recognize that, without departing from the scope of the present invention, the different features of the present invention can be combined to produce embodiments other than those described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] With reference to the accompanying drawings, below follows a more detailed description of embodiments of the invention cited as examples.

[0028] In these figures:

[0029] Figure 1 A vehicle for cargo transportation is schematically shown;

[0030] Figure 2 Example forces acting on a vehicle are shown;

[0031] Figure 3 The active steering arrangement is schematically shown;

[0032] Figure 4a The caster angle is shown;

[0033] Figure 4b The scrub radius is shown;

[0034] Figure 5 An example vehicle steering device is shown;

[0035] Figure 6 is a graph showing an example relationship between braking force and brake pressure;

[0036] Figure 7 is a flow chart used to illustrate the method;

[0037] Figure 8 A control unit is schematically shown; and

[0038] Fig. 9 An example computer program product is shown. DETAILED DESCRIPTION

[0039] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain aspects of the invention are shown. However, the present invention may be implemented in many different forms and should not be construed as limited to the embodiments and aspects set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. Throughout the specification, the same reference numerals refer to the same elements.

[0040] It should be understood that the present invention is not limited to the embodiments described herein and shown in the drawings; rather, those skilled in the art will recognize that many modifications and variations are possible within the scope of the appended claims.

[0041] Figure 1 A vehicle 1 in the form of a truck is shown. The vehicle 1 includes a power source 10, illustrated here as a combustion engine. The vehicle 1 also includes one or more control units 101 arranged to control various systems and functions included in the vehicle 1. For example, the vehicle control unit 101 is arranged to implement at least some of the methods and techniques described herein.

[0042] The vehicle 1 has a pair of steerable wheels 104, 106, which are arranged on the left and right sides of the front axle 102 of the vehicle 1, respectively. The front axle 102 is the frontmost axle of the vehicle 1. The vehicle 1 also includes a pair of first rear wheels 108, 110 connected to the first rear axle 112, and a pair of second rear wheels 114, 116 connected to the second rear axle 118. As seen in the longitudinal direction of the vehicle 1, the first rear axle 112 is arranged in front of the second rear axle 118. The pair of first rear wheels 108, 110 and the pair of second rear wheels 114, 116 are usually (but not always) arranged as non-steerable wheels. The vehicle 1 also includes a pair of first rear wheels 108, 110 connected to the first rear axle 112, and a pair of second rear wheels 114, 116 connected to the second rear axle 118. The front axle 102 of the vehicle 1 has a wheelbase L w .

[0043] Figure 2 1 shows some example forces acting on the vehicle 1 and its wheels. The pair of steerable wheels 104, 106 are performing a turning maneuver and are therefore arranged to have a steering angle δ relative to the vehicle forward direction. For simplicity, for the left steerable wheel 104 and the right steerable wheel 106, the steering angle δ is Figure 2are shown as being identical and are the angles of these wheels relative to the longitudinal axis of the vehicle 1. The vehicle 1 is travelling at a vehicle speed, denoted as V. The steerable wheels 104, 106 further comprise respective wheel torque actuators 103, 105.

[0044] The following will be combined Figure 3 An example vehicle steering system is discussed in greater detail.

[0045] The front axle 102 is arranged at a distance l1 from the center of mass 202 of the vehicle 1, the first rear axle 112 is arranged at a distance l2 from the center of mass 202 of the vehicle 1, and the second rear axle 118 is arranged at a distance l3 from the center of mass 202 of the vehicle 1. The center of mass 202 is a position of the vehicle 1 at which the total global forces affecting the vehicle 1 can be represented in a known manner.

[0046] In the following, the x-axis extends in the longitudinal direction of the vehicle 1, the y-axis extends in the lateral direction of the vehicle 1, and the z-axis extends in the vertical direction of the vehicle 1. During a turning maneuver, the vehicle 1 is subjected to a torque M at the center of mass 202. z Furthermore, the vehicle is subjected to a global longitudinal force F x and the global lateral force F y .

[0047] Furthermore, when the steerable wheels 104, 106 of the front axle 102 are subjected to a steering angle δ, the left steerable wheel 104 is subjected to a longitudinal force F x,104 and the lateral force F y,104 , while the right steerable wheel 106 is subjected to a longitudinal force F x,106 and the lateral force F y,106 .

[0048] The sum of the lateral forces of the left steerable wheel 104 and the right steerable wheel 106 can be expressed as the total front wheel lateral force. For example, when the vehicle is propelled or braked, the sum of the front wheel longitudinal forces may increase and decrease.

[0049] The first rear wheels 108, 110 are subjected to respective lateral forces F y,108 and F y,110 , and the second rear wheels 114, 116 are subjected to respective lateral forces F y,114 and F y,116 .exist Figure 2 In the example of FIG. 1 , the longitudinal forces of the pair of first rear wheels 108 , 110 and the pair of second rear wheels 114 , 116 are set to zero, ie, each wheel is not subjected to any forces due to propulsion or braking.

[0050] Now go to Figure 4a to Figure 4b , these figures show different views of the left steerable wheel 104 according to an example embodiment. In detail, Figure 4a is a side view of the left steerable wheel 104, and Figure 4b It is a rear view of the left steerable wheel 104 .

[0051] from Figure 4a Initially, the figure is a side view of the left steerable wheel 104. The suspension (not shown) of the wheel 104 is arranged so that the wheel 104 has a suspension caster angle γ, which is defined as the angular displacement of the steering axis 402 relative to the vertical axis 404 of the left steerable wheel 104, measured in the longitudinal direction of the vehicle 1. The distance between the intersection of the road surface 401 and the steering axis 402 and the intersection of the road surface 401 and the vertical axis 404 (also called "mechanical trail") is denoted as t m Under the action of the wheel suspension, the point of application of force on the contact surface 406 between the wheel 104 and the road surface 401 will be slightly offset in the longitudinal direction relative to the intersection of the road surface 401 and the vertical axis 404. This offset (also called "pneumatic trail") is denoted as t p The contact surface is the area where the tire is in contact with the ground. Therefore, the force application point of the contact surface 406 between the wheel 104 and the road surface 401 depends on the suspension caster angle γ.

[0052] Go to Figure 4b , which is a rear view of the left steerable wheel 104. It can be seen that the effective wheel radius R is represented as the distance between the front wheel axle 102 and the road surface 401, and the wheel 104 is connected to the suspension via an inclined kingpin axis 408, the inclination of which is represented as τ. During the turning maneuver, the wheel 104 rotates around the kingpin axis 408. The point of application of the contact surface 406 between the wheel 104 and the road surface 401 is located at the intersection between the vertical axis 404 and the road surface 401. The vehicle 1 (especially the steerable wheels 104, 106) has a positive wheel kingpin offset r s . Wheel kingpin offset r s The wheel suspension kingpin offset is defined as the distance between the intersection point 403 between the kingpin axis 408 and the road surface 401 and the force application point of the contact surface 406. When the intersection point between the kingpin axis 408 and the road surface 401 is located inside the vertical axis 404, a positive wheel suspension kingpin offset r is generated. s ,like Figure 4b When a braking torque is applied, for example, to the left steerable wheel 104, the wheel will be steered due to the positive kingpin offset r s The rotation around the kingpin axis 408 causes the vehicle to turn left.

[0053] Kingpin offset and caster angle are well-known concepts and therefore will not be discussed in further detail in this article.

[0054] Figure 5 An example vehicle steering system 500 is shown. Steering torque is transmitted via a steering gear ( Figure 5 ) is applied to the wheels via one or more connecting rods ( Figure 5 The tie rod 510 connects the steerable wheels 104, 106. When the wheels turn, the tie rod moves laterally (530). The steering torque discussed herein is the torque acting on the wheel that also causes the tie rod to move laterally. Alternatively, the steering torque can be applied to the steering device via an actuator 520 arranged to be connected to the tie rod, but this type of configuration is not common for trucks.

[0055] Longitudinal force difference ΔF x =F x,104 -F x,106 Generates steering torque M steer =ΔF x *r s The basic mechanism of this steering torque has been discussed, for example, in WO 2019 / 072379 A1 and will therefore not be discussed in more detail in this article.

[0056] The method and control unit disclosed herein are based on the following recognition: the steering torque M steer , or equivalently, the lateral steering force acting on the tie rod 510, or the force acting on the connecting rod or the steering knuckle can be obtained from a torque sensor, a force sensor, or from an active steering system that reacts to the torque to maintain a given turning maneuver of the vehicle. Since the kingpin offset is fixed and can be obtained, for example, from vehicle design data, it can be based on the relationship ΔF x =M steer / r s (i.e., longitudinal force difference ΔF x With the applied steering torque M steer The direct proportional relationship between the longitudinal force difference ΔF x Distance from kingpin r s The inverse proportional relationship between the longitudinal force and the longitudinal force difference is used to estimate the longitudinal force difference.

[0057] Reference Figure 7 , a method for estimating a longitudinal force difference ΔF acting on wheels 104, 105 of a steering axle 102 of a vehicle 1 is disclosed herein. x The method includes: obtaining S1 from the vehicle 1 and the applied steering torque M steer The data related to the applied steering torque M steer Associated with the steering axle wheels 104, 105; obtain S2 and the steering axle wheels 104, 105 associated with the kingpin offset value r s; and based on the data obtained and the kingpin offset r s To estimate the S3 longitudinal force difference ΔF x , the longitudinal force difference ΔF x With the applied steering torque M steer is proportional to and equal to the kingpin offset r s Inversely proportional.

[0058] For example, the longitudinal force difference can be simply determined as ΔF x =M steer / r s However, it should be appreciated that the longitudinal force difference can be estimated in many different ways based on the direct proportional relationship between the longitudinal force difference and the applied steering torque and the inverse proportional relationship between the longitudinal force difference and the kingpin offset. For example, the proportionality constants a and b can be used in the equation given by ΔF x =a*M steer / b*r s The more general expression given in . Other more advanced expressions can also be used to achieve similar results. For example, at larger steering angles, the factors a and b may not be constant, but are known. This relationship is most accurate when there is little or no movement in the steering system (i.e., the steering angle is close to constant). When the steering angle is not in a steady state, there will be acceleration, inertia, and friction terms that can be taken into account to improve accuracy.

[0059] For example, the difference may be calculated directly, or it may be estimated based on a model built around the relationship between the longitudinal force difference and the applied steering torque and the kingpin offset. x =M steer / r s It is to be interpreted broadly so as to also include similar expressions for this longitudinal force difference as a function of kingpin offset and applied steering torque.

[0060] Vehicles equipped with active steering systems can often provide measurements of the applied steering torque of these vehicles. When there is a longitudinal force difference on both sides of the steering axle, this can be observed in the applied torque of the active steering system (i.e., the greater the longitudinal force difference acting on the wheels on the steering axle, the greater the active steering system torque required). According to some aspects, the method disclosed herein includes obtaining S11 from the active steering system 300 of the vehicle 1 and the applied steering torque M steer Relevant data.

[0061] According to some other aspects, the active steering system may include a feedback system configured to maintain a steering angle of the vehicle at a requested angle.

[0062] This data can also be obtained indirectly, for example, in addition to the hydraulic gain applied to the torque generated by the electric motor, the steering wheel torque applied by the electric motor can also be known. In other words, the data obtained from the active steering system 300 can include the steering wheel torque T steering and a combined gain factor K of the hydraulic steering mechanism 340 of the vehicle 1 powersteer , therefore, based on the relationship ΔF x =T steering *K powersteer / r s To estimate the longitudinal force difference ΔF x .

[0063] The applied steering torque can also be obtained, for example, from the applied steering torque M steer The relevant pressure value, current value or voltage value can be inferred.

[0064] Moreover, some vehicles include a torque sensor capable of outputting the applied steering torque. Therefore, according to some aspects, the vehicle 1 includes one or more torque sensors 360, 360', which are arranged to be connected to the steering system of the vehicle 1. Then, the method includes obtaining S12 from the one or more torque sensors 360, 360' and the applied steering torque M steer Relevant data.

[0065] It will be appreciated that various known filtering techniques and noise suppression signal processing techniques (e.g. Kalman filtering) may be applied to the obtained data values ​​to improve the performance of the force difference value estimation. In other words, the estimation optionally comprises filtering S31 the time series of data values ​​obtained from the active steering system 300 or from the one or more torque sensors 360, 360'.

[0066] Compared with the known methods, given the ΔF obtained by the above method x Many applications and vehicle functions can be implemented and / or improved without the estimated values ​​of Figure 7 An overview of these applications is given. These applications do not directly rely on the method for determining longitudinal force differential values ​​disclosed herein, but can be used with any method for determining longitudinal force differential values.

[0067] Unintentional uneven brake torque distribution on the front axle of a truck may result in severe "pulling" of the vehicle to one side and possible vehicle instability. This may occur when the brake system does not correctly calculate the forces generated at each front wheel; this may be due to, for example, improper calibration of the brake pressure sensor, wrong pressure estimation, different brake gains at different wheels, mechanical failure of the brake actuator, etc.

[0068] If the actual difference in braking force between two wheels on the same axle can be determined, the vehicle motion controller can use this information to adjust the actuator requests to account for this situation and prevent vehicle instability. By adjusting the actuator requests in this way, it is possible to relax the requirements on the braking system hardware, for example, which is an advantage.

[0069] Large variations in the "brake gain", i.e., the proportionality factor between the brake control input signal (e.g., brake chamber pressure value) and the actual braking force in the brake system, can be observed during normal driving. This brake gain can be affected, for example, by brake pad wear, temperature, dirt, corrosion, mechanical adjustments in the brake actuator, etc. During normal driving, it is difficult to sense the "actual" brake gain. An accurate knowledge of the current vehicle brake gain is required to be able to achieve a predictable and accurate brake torque response from the brake system.

[0070] Reference Figure 6 , a method for estimating the braking gain will now be described. The respective braking gains on the left steering wheel 104 and the right steering wheel 106 Represents the brake control input signal p and the actual braking force or torque T on the left and right wheels respectively L , T R The conversion ratio coefficient between . That is, Where T L is the braking torque in Newton metres applied to the left wheel 104 of the vehicle 1. This braking torque can be converted into a braking force (in Newtons) by taking into account the wheel rolling radius in a known manner.

[0071] Braking gain K BG Making an accurate estimate is very important to ensure that the braking system correctly meets the global request (e.g., for a given acceleration). Since there are usually no direct torque measurement sensors at the wheels, the brake gain is usually preprogrammed to a fixed value (although this brake gain may vary significantly).

[0072] According to the example method, during a normal braking event, the braking torque distributed to the front axle may be intentionally sent in certain circumstances, such as a slightly higher braking torque request on one wheel of the steering axle than on the other wheel (e.g., a higher torque request is sent to the left brake device than to the right wheel). In a subsequent braking event, a higher request may be given to the other wheel (the right wheel in this example).

[0073] Preferably, the different brake control input signals should be spaced apart in amplitude to make it easier to distinguish the system responses.

[0074] According to various aspects, these calibration events should preferably be performed only when there is no anti-lock braking system (ABS) intervention (eg, when there is no significant wheel slip during braking), and also preferably when the vehicle is traveling in a nearly straight line.

[0075] By comparing the achieved brake pressure (at each wheel) with the ΔF measured from the steering system x Combined, it can be Figure 6 The respective brake gain for each of the two wheels is determined as shown in FIG.

[0076] exist Figure 6 In the example 600 shown, the braking gain 610 on the right wheel is greater than the braking gain 620 on the left wheel - note that in this figure, the gradient of each line is the braking gain divided by the rolling radius of the wheel. This difference in braking gain may be due to brake pad wear, brake temperature, dirt, etc. Data from two braking events were used, where the total required braking force was similar.

[0077] In the first braking event, a braking control signal p1 is requested on the left wheel 621 and a braking control signal p2 is requested on the right wheel 612 (where p2 is higher than p1). The longitudinal force difference ΔFx is measured by the steering system a In the second braking event, p1 is instead requested from the right wheel 611 and p2 is requested from the left wheel 622. Again the longitudinal force difference ΔFx is measured in the steering system b .

[0078] The individual braking gains can now be deduced by rearranging the balance equation for the total torque for these two braking events, namely:

[0079]

[0080] As long as the rolling radius R L , R R It is known that the above equation can be solved and

[0081] Again it will be appreciated that the brake control input signals p1 , p2 are preferably spaced apart to provide a more distinct and measurable longitudinal force difference.

[0082] An advantage of this brake gain estimation method over other known methods is that it can be used even when other wheels on the vehicle are braking, whereas brake gain estimation methods based on vehicle acceleration must take into account all longitudinal forces acting on the entire vehicle combination.

[0083] Figure 6The example 600 in FIG. 1 assumes a strictly linear proportional relationship between the braking force and the brake pressure or brake control input signal. It should be understood that this relationship may be more complex, such as following a second-order or higher-order relationship. Such a more complex relationship may also be estimated by the disclosed method, such as by using more than two detection control signals (e.g., four or five brake pressure test signals).

[0084] In summary, refer to Figure 7 The method disclosed herein includes determining the relationship between the S4 brake control input signal and the braking force generated on the steering wheels 104, 105 by applying a plurality of brake control input signals at the steering wheels 104, 105, monitoring the longitudinal force difference ΔF for each applied brake control input signal x , and determining the relationship based on a plurality of applied brake control input signals and a plurality of generated longitudinal force difference values.

[0085] For example, the method may include based on ΔF x And based on the system of equations and The solution to estimate the braking gain associated with the steering wheels 104 and 105 in S41 Where p1 and p2 are the applied brake pressure values, and are the braking gains associated with the left steering wheel 104 and the right steering wheel 105, respectively, and R L and R R are the rolling radii associated with the left steerable wheel 104 and the right steerable wheel 105 , respectively.

[0086] The determined relationship between the brake control input signal (e.g. brake chamber pressure) and the generated braking force or brake torque can be advantageously used for brake system calibration. Therefore, a method for calibrating S42 a brake system of a vehicle 1 based on the determined relationship between the brake control input signal and the generated braking force is disclosed herein.

[0087] A similar method can be designed based on acceleration rather than brake pressure, where the vehicle acceleration a is measured when a deliberate braking force differential is requested from any two wheels on the vehicle. x (rather than steering wheel torque). Again, at least two braking events are required, where uneven braking is intentionally applied in a similar manner as described above (note that a x The signal is used to measure the sum of the forces in the longitudinal direction, i.e., ∑F=ma, rather than comparing the difference in steering wheel torque). Again, two separate equations can be generated for the two braking events and solved to obtain the individual braking gains:

[0088]

[0089]

[0090] in, is the longitudinal acceleration measured for the first braking event, and is the longitudinal acceleration obtained for the second braking event. m is the total vehicle mass, and F resist is the sum of all drag forces acting on the vehicle in the longitudinal direction (air resistance, rolling resistance, slope resistance, etc.) - in the above equation, F resist is defined in the negative longitudinal direction.

[0091] This acceleration-based approach may be combined with the steering torque-based approach discussed above to improve, for example, the estimation of brake gain, or to calibrate vehicle steering, or to detect faults in the vehicle steering system.

[0092] As will now be discussed, the method disclosed herein can also be used to detect faults in the vehicle 1. During normal operation, the vehicle control unit 101 (e.g., a vehicle motion management controller (VMM)) can generate separate braking torque requests on the left and right wheels of the steered axle and other axles of the vehicle to control vehicle motion. The requested wheel torques on the wheels of the steered axle (T L and T R ) can be used to calculate the expected difference in longitudinal braking force ΔF x,expect =T L / R L -T R / R R , where T L and T R are the requested torques on the left steering wheel 104 and the right steering wheel 105, respectively, and where R L and R R are the rolling radii associated with the left steered wheel 104 and the right steered wheel 105 on the front axle, respectively. Then, ΔF x,expect can be compared with the ΔF estimated by the method disclosed herein x When a large difference is detected between the expected longitudinal force difference and the estimated longitudinal force difference, this can be interpreted as a fault in the braking system on the front axle; this can be reported to the human driver and / or to some VMM fault handler. This check is preferably only performed without ABS intervention (i.e., no significant wheel slip on either wheel). This check is also preferably only performed when the steering angle is constant or at least close to constant, because otherwise there will be inertial effects that affect the final result.

[0093] In summary, refer to Figure 7 , the method disclosed herein includes detecting a fault in S5 vehicle 1 by:

[0094] According to ΔF x,expect =T L / R L -T R / R R To determine the expected longitudinal force difference of S51, where T L and T R are the requested torques on the left steering wheel 104 and the right steering wheel 105, respectively, and where R L and R R are the rolling radii associated with the left steering wheel 104 and the right steering wheel 105, respectively,

[0095] The expected longitudinal force difference ΔF x,expect The difference between the estimated force and the x Compare S52, and

[0096] In ΔF x,expect and ΔF x When there is a difference between them, a fault in the vehicle 1 is detected S53.

[0097] The detection principle used (i.e. the detection principle for determining when there is a sufficiently large difference between the expected longitudinal force difference value and the estimated longitudinal force difference value) may vary from implementation to implementation. In many applications, a preconfigured threshold value may be sufficient, possibly in combination with a certain time window function, i.e. a difference is an event in which the magnitude of the difference between the expected force difference value and the estimated force difference value is above a certain threshold value at least for some predetermined time period. However, of course, more advanced detection algorithms may also be applied, such as statistical detection methods or the like. Such detection principles and algorithms are known and will therefore not be discussed in more detail herein.

[0098] According to aspects, the method further comprises, in the event of a detected fault in the vehicle 1 , triggering ( S54 ) a warning signal or an emergency maneuver by the vehicle 1 .

[0099] Preferably, the wheel speed and / or wheel slip condition should also be monitored. x But if both wheels are rolling freely (no significant slip), it is likely that a fault in the brake system or a tire blowout has occurred. On the other hand, if a large ΔF is estimated x and one wheel is in slipping at the same time, for example due to poor road friction, then it is indicated instead that the difference may be due to slippery road conditions and should not be recorded as a fault. In this case, the ΔF from the braking system on the non-slipping wheel can be more "trusted"x Estimated value.

[0100] In summary, refer to Figure 7 , the method disclosed herein includes: monitoring S8 wheel speed values ​​and / or wheel slip conditions associated with wheels 104, 105 of a steering axle 102 of the vehicle 1, and detecting a fault in the vehicle 1 and / or detecting a slippery road condition based on the wheel speed values ​​and / or wheel slip conditions.

[0101] In the event of wheel slip (e.g. during ABS intervention), the torque response of the brake device becomes more complex due to the dynamics of the wheels and the nonlinear behavior of the tire-road contact patch. With ABS engaged, large longitudinal force differences may occur on the left and right sides of the vehicle, which may not be apparent from the brake control signal (e.g. brake pressure signal) (depending on the friction conditions on the road present on either side of the truck). In this case, the estimated ΔF x A direct measure of the difference in braking force achieved during an ABS event can be provided. The total yaw moment / torque applied to the vehicle due to this difference can be calculated via the relationship M yaw =ΔF x *L w To calculate, where L w yes Figure 2 The track width of the front axle of the vehicle 1 is shown in FIG. yaw Given this, the vehicle control unit 101 can distribute the braking torque and the steering angle to achieve opposite moments (e.g., by countersteering some axles). This approach has the advantage over other conventional stability control systems in that the required M can be calculated before any significant yaw rate or sideslip occurs. yaw correction, whereas with traditional stability control methods, intervention is only made when the vehicle actually starts to "slip".

[0102] In summary, refer to Figure 7 , the method disclosed herein includes controlling the stability of the S6 vehicle 1 by:

[0103] According to M yaw =ΔF x *L w To determine S61 the total yaw moment or torque applied to the vehicle 1, where L w is the track width of the front axle of vehicle 1, and

[0104] Braking torque and / or steering angle are distributed S62 to compensate for the total yaw, thereby controlling the stability of the vehicle 1 .

[0105] "Split friction" braking is a difficult scenario for both human and automated drivers. In this scenario, emergency braking is requested when the vehicle encounters different tire-road friction conditions on the left and right sides of the vehicle (e.g. the left side of the vehicle may be driving on asphalt while the right side is driving on ice).

[0106] It is important that the vehicle's motion control system be able to detect such hazardous conditions and adjust the braking requests sent to the different sides of the vehicle to prevent the vehicle from "skidding" or otherwise losing control. The detection and adjustment must be relatively fast (e.g., less than one second response time) to prevent accidents in many situations.

[0107] In a braking situation where one side of the vehicle is on a slippery surface (e.g., ice) and is controlled by the ABS (to prevent its wheels from locking) and the other side is on a less slippery surface (e.g., dry asphalt), the estimated ΔF x This may be combined with the estimated braking torque produced from the braking system to calculate the actual braking force achieved on the low friction side of the vehicle.

[0108] For example, if the right side of the vehicle is on a high friction surface and its wheels are not slipping, then it can be believed that the brake pressure at that wheel is the F applied at that wheel. x Reasonable estimates of:

[0109]

[0110] If the other side of the vehicle is on a low friction surface, the vehicle is likely to experience wheel slip (and possible ABS intervention), which can be observed in the wheel speed signal. While the wheel is slipping, the braking system cannot easily estimate Fx L , but can be obtained from the estimated longitudinal force difference ΔF x Subtract the estimated force Fx generated on the high friction side from R To calculate Fx L .

[0111] Then, Fx L This can be normalized by the normal load of the vehicle's tires to estimate the maximum available friction on this side of the vehicle. This can then be used to calculate the maximum torque capability of all wheels on that side of the vehicle (calculated in a known manner using the known wheel loads). The control unit 101 can use this capability information to ensure that the control unit allocates actuator requests that are actually achievable given the current road conditions.

[0112] In summary, refer to Figure 7 , the method disclosed herein comprises: according to F x,1 =ΔF x-F x,2 To estimate the longitudinal force of S7 acting on the first steering wheel, is the brake chamber pressure value associated with the second wheel, and is the brake gain associated with the second wheel.

[0113] Optionally, the disclosed method further comprises: based on the estimated longitudinal force F acting on the first steering wheel x,1 To control S71 the vehicle 1. For example, by limiting the braking force on the high friction wheel so that the vehicle does not become unbalanced during the separation friction braking, the vehicle stability can be maintained even in a difficult separation friction braking situation. It should be understood that the first steering wheel can be the left wheel 104 or the right wheel 106, and the second steering wheel is another wheel.

[0114] Figure 8 Components of a control unit 101 according to the embodiments discussed herein are schematically shown in the form of a plurality of functional units. The control unit 101 may be included in a vehicle 1. The processing circuit 810 is provided using any combination of one or more of a suitable central processing unit CPU, a multiprocessor, a microcontroller, a digital signal processor DSP, etc., which are capable of executing software instructions stored in a computer program product (e.g. in the form of a storage medium 830). The processing circuit 810 may also be provided as at least one application specific integrated circuit ASIC or a field programmable gate array FPGA.

[0115] In particular, the processing circuit 810 is configured to cause the control unit 101 to perform a set of operations or steps, such as combining Figure 8 For example, the storage medium 830 may store the set of operations, and the processing circuit 810 may be configured to retrieve the set of operations from the storage medium 830 to cause the control unit 101 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuit 810 is thereby arranged to perform the method disclosed herein.

[0116] The storage medium 830 may also include a persistent storage, which may be, for example, any one or combination of magnetic storage, optical storage, solid-state storage, or even remotely mounted storage.

[0117] The control unit 101 may also include an interface 820 for communicating with at least one external device. As such, the interface 820 may include one or more transmitters and receivers including analog and digital components and a suitable number of ports for wired or wireless communication.

[0118] The processing circuit 810 controls the general operation of the control unit 101, for example, by sending data and control signals to the interface 820 and the storage medium 830, by receiving data and reports from the interface 820, and by retrieving data and instructions from the storage medium 830. Other components of the control node and related functions are omitted so as not to obscure the concepts presented here.

[0119] Fig. 9 A computer readable medium 910 is shown carrying a computer program comprising program code components 920 for executing a program product when the program product is run on a computer. Figure 7 The computer readable medium and the code components may together form a computer program product 900.

Claims

1. A method for estimating a longitudinal force difference ΔF acting on a wheel of a steering wheel axle (102) of a vehicle (1) x method, the method include: S1: Obtaining the steering torque M applied from the vehicle (1) steer The data related to the applied steering torque M steer associated with the wheels of said steering axle, S2: Obtain the kingpin offset value r associated with the wheel of the steering axle s ,as well as S3: Based on the data obtained and the kingpin offset r s To estimate the longitudinal force difference ΔF x , the longitudinal force difference ΔF x With the applied steering torque M steer is proportional to the kingpin offset r s Inversely proportional.

2. The method according to claim 1, in, The vehicle (1) includes an active steering system (300), and wherein S1 includes S11: obtaining from the active steering system (300) a steering torque M steer Relevant data.

3. The method according to claim 2, in, The data obtained from the active steering system (300) include the steering wheel torque T steering and a combined gain factor K of a hydraulic steering mechanism (340) of the vehicle (1) powersteer , and where, based on the relationship ΔF x =T steering *K powersteer / r s To estimate the longitudinal force difference ΔF x .

4. The method according to claim 2 or 3, in, The data obtained from the active steering system (300) include the applied steering torque M steer Relevant pressure value, current value or voltage value.

5. The method according to claim 2 or 3, in, The active steering system comprises a feedback system configured to maintain the steering angle of the vehicle (1) at a requested angle.

6. The method according to claim 2 or 3, in, The vehicle (1) comprises one or more torque sensors (360, 360') and / or one or more force sensors, wherein the one or more torque sensors and / or the one or more force sensors are arranged to be connected to a steering system of the vehicle (1), wherein S1 comprises S12: obtaining a steering torque M corresponding to the applied steering torque M from the one or more torque sensors (360, 360') and / or the force sensors steer Relevant data.

7. The method according to claim 6, in, The S3 comprises S31: filtering a time series of data values ​​obtained from the active steering system (300) or from the one or more torque sensors (360, 360').

8. The method according to any one of claims 1 to 3, comprising S4: determining the relationship between the braking control input signal and the braking force generated on the steering wheel by applying a plurality of braking control input signals at the steering wheel, monitoring the longitudinal force difference ΔF for each applied braking control input signal x , and determining the relationship based on a plurality of applied brake control input signals and a plurality of generated longitudinal force difference values.

9. The method according to claim 8, comprising S41: based on ΔF x And based on the system of equations and The solution to estimate the braking gain associated with the steering wheel is in, p1 and p2 are the applied brake pressure values, and are the braking gains associated with the left and right steering wheels, respectively, and R L and R R are the rolling radii associated with the left and right steering wheels, respectively.

10. The method according to claim 8, comprising S42: calibrating a braking system of the vehicle (1) based on the determined relationship between the brake control input signal and the generated braking force.

11. The method according to any one of claims 1 to 3, comprising S5: detecting a fault in the vehicle (1) by: S51: Determine the expected longitudinal force difference ΔF based on the requested torque on the left steering wheel and the right steering wheel, respectively, and based on the rolling radius associated with the left steering wheel and the right steering wheel, respectively x,expect , S52: The expected longitudinal force difference ΔF x,expect The difference between the estimated force and the x To compare, and S53: In ΔF x,expect and ΔF x In the event that there is a difference between the two, a fault in the vehicle (1) is detected.

12. The method according to claim 11, comprising S54: triggering a warning signal or an emergency maneuver by the vehicle (1) in the event of a detected fault in the vehicle (1).

13. The method according to any one of claims 1 to 3, comprising S6: controlling the stability of the vehicle (1) by: S61: According to M yaw =ΔF x *L w To determine the total yaw moment or torque applied to the vehicle (1), where L w is the wheelbase of the front axle of the vehicle (1), and S62: Distribute braking torque and / or steering angle to compensate for total yaw, thereby controlling the stability of the vehicle (1).

14. The method according to any one of claims 1 to 3, comprising S7: according to F x,1 =ΔF x -F x,2 to estimate the longitudinal force acting on the first steering wheel, in, pc2 is the brake chamber pressure value associated with the second wheel, and is the braking gain associated with the second wheel.

15. The method according to claim 14, comprising: S71: based on the estimated longitudinal force F acting on the first steering wheel x,1 To control the vehicle (1).

16. The method according to any one of claims 1-3 comprises S8: monitoring wheel speed values ​​and / or wheel slip conditions associated with the wheels of the steering axle (102) of the vehicle (1), and also detecting faults in the vehicle (1) and / or classifying road conditions based on the wheel speed values ​​and / or wheel slip conditions.

17. A computer-readable medium (910) carrying a computer program comprising program code components for executing the steps of the method of any one of claims 1 to 16 when the computer program is run on a computer or on a processing circuit of a control unit (101).

18. A control unit (101) for estimating a longitudinal force difference ΔF acting on a wheel of a steering axle (102) of a vehicle (1) x , the vehicle (1) comprises an active steering system (300), the control unit (101) being configured to perform the steps of the method according to any one of claims 1 to 16.

19. A vehicle (1) comprising a control unit (101) according to claim 18.

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