Device and method for estimating a longitudinal speed of a vehicle

Abstract

A method for estimating a longitudinal speed of a vehicle is provided, the vehicle comprising two or four wheels. The method comprises obtaining a first estimated longitudinal speed of the vehicle. Then, the method comprises determining whether an uncertainty of the first estimated longitudinal speed is larger than a threshold value. When the uncertainty is larger than the threshold value, the method further comprises controlling the vehicle to adjust a torque of at least one wheel of the vehicle. Next, the method comprises determining a second estimated longitudinal speed of the vehicle after adjusting the torque.

Description

[0001] DEVICE AND METHOD FOR ESTIMATING A LONGITUDINAL SPEED OF A VEHICLE

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a method and a device for estimating a longitudinal speed of a vehicle, the vehicle comprising two or four wheels. The disclosure further provides a computer program to perform the method.

[0004] BACKGROUND

[0005] In chassis control systems, the estimation of the longitudinal velocity (hereinafter denoted as Vx) of a vehicle can lack of accuracy, i.e., it is overestimated or underestimated, when wheel slips are large. The longitudinal slip of a tire or wheel is a speed difference between a tire contract surface and a wheel hub normalized by a wheel hub speed.

[0006] Overestimated or underestimated Vxleads to sub-optimal performance of control systems such as Anti-Lock Braking (ALB) systems or Traction Control Systems (TCS). This means that a vehicle will have lower acceleration and deceleration than the intended capability of the vehicle. Such a sub-optimal estimation stems from the observer dynamics of the Vx. That is, Vxbecomes unobservable in the large slip region due to small and positive normalized longitudinal stiffness of the tire.

[0007] In conventional control systems, a support pulse torque, or simply support pulse, can be applied to the vehicle to make Vxto become observable. However, the torque reduction achieved with current support pulses, as for example the conventional support pulse depicted in FIG. 6(b), leads to a loss of acceleration / deceleration of the vehicle.

[0008] Further, current support pulses are generally heuristic or are based on lookup-table-based algorithms, which reduce the torque on the basis of three main calibration parameters:

[0009] 1. Frequency of the support pulse.

[0010] 2. Duration of the support pulse.

[0011] 3. Amount of torque reduction.

[0012] Ideally, the last two parameters (i.e., the duration of the support pulse and the amount of torque reduction) should be as small as possible. Nevertheless, in order to ensure robustness, these parameters are kept large in practice.

[0013] Moreover, these parameters have mostly constant values in conventional solutions, which is not optimal for the vehicle dynamics, resulting in a loss of the vehicle performance since the reduced level of torque during the support pulse and the duration of the reduced torque lead to a reduced net force on the vehicle tires, which in turn lead to a reduced vehicle acceleration / deceleration.

[0014] SUMMARY

[0015] In view of the above, this disclosure aims to improve conventional solutions for accurately estimating the longitudinal velocity of a vehicle. An objective is to restore the observability of the longitudinal velocity of the vehicle by reducing the torque of at least one wheel without affecting the vehicle acceleration. Another objective is to design the increase and decrease of a torque support pulse value by calculating and further monitoring the normalized longitudinal stiffness of the wheel. These and other objectives are achieved by the solutions of this disclosure as described in the independent claims. Advantageous implementations are further defined in the dependent claims. Furthermore, the disclosure is based on the following considerations.

[0016] In this disclosure, the following convention is used: It is assumed that a positive force exerted in a wheel by the ground refers to a net force applied on the wheel that points to a same direction as, and to an opposite direction to, a tangential speed of the wheel at a contact point between the wheel and the ground during forward motion and reverse motion respectively.

[0017] Accordingly, a negative force exerted on the wheel by the ground refers to a net force that points to an opposite direction to and to a same direction as the tangential speed of the wheel at the contact point during forward motion and reverse motion, respectively.

[0018] In this disclosure, the terms "wheel" and "tire" may be used interchangeably. Further, the terms "linear region" and "stable region" may be used interchangeably. Further the terms "normalized longitudinal stiffness" and "longitudinal stiffness" may be used interchangeably.

[0019] The slip ( ) of a wheel is calculated as equation (1): where Vwheei is a tangential speed of the wheel and Vx,hub is the longitudinal velocity of the vehicle at the wheel hub. Thus, equation (1) determines a sign convention for the slip used in this disclosure. Further, Vxcan be back-calculated from Vx hubusing kinematic equations, which are known in the field of vehicle dynamics. During straight line motion, Vx hub= Vx.

[0020] Based on the above definitions, the dynamics of the Vxcan be observed when the longitudinal stiffness is negative, and is not observable when the longitudinal stiffness is positive.

[0021] According to a first aspect, a method for estimating a longitudinal speed of a vehicle is provided, wherein the vehicle comprises two or four wheels. The method comprises: obtaining a first estimated longitudinal speed of the vehicle; determining whether an uncertainty of the first estimated longitudinal speed is larger than a threshold value; when the uncertainty is larger than the threshold value, controlling the vehicle to adjust a torque of at least one wheel of the vehicle; and determining a second estimated longitudinal speed of the vehicle after adjusting the torque.

[0022] When all the wheels of the vehicle he in a large slip region for a long time, the estimated Vxbecomes uncertain. Thus, the first aspect provides the advantage of reducing the uncertainty in the vehicle velocity estimation triggered by the threshold value, without having to compromise the vehicle performance due to torque reduction. Further, this provides the advantage of controlling the torque of only one or more of the wheels of the vehicle, instead of applying support torque pulses to all the wheels. As a result, the amount of net torque reduction during the support pulse can be reduced and the loss of vehicle deceleration can also be reduced.

[0023] In an implementation form of the first aspect, the second estimated longitudinal speed has an uncertainty smaller than the uncertainty of the first estimated longitudinal speed. That is, the torque of the at least one wheel is controlled until it is brought to a stable region, in which the longitudinal velocity can be estimated with higher accuracy.

[0024] In an implementation form of the first aspect, controlling the vehicle to adjust the torque of the at least one wheel of the vehicle comprises controlling the vehicle to apply a support pulse torque on the at least one wheel, the support pulse torque being a function of a longitudinal stiffness of the at least one wheel. Since the longitudinal stiffness of a wheel is a measurable parameter, the applied support pulse torque is a function of the force characteristics of the at least one wheel and, thus, is not based on rule-based logics.

[0025] In an implementation form of the first aspect, controlling the vehicle to apply the support pulse torque on the at least one wheel comprises: controlling the vehicle to reduce the torque of the at least one wheel from an initial value to a reduced value; calculating, at each of a plurality of points in time, the longitudinal stiffness of the at least one wheel; controlling the vehicle to maintain the torque of the at least one wheel at the reduced value until the calculated longitudinal stiffness changes from a positive value to a negative value and remains negative; and controlling the vehicle to increase the torque of the at least one wheel from the reduced value to the initial value until the calculated longitudinal stiffness changes from the negative value to another positive value. This has the advantage of bringing the vehicle into a reliable, observable region by taking into account the actual conditions of the vehicle and the at least one wheel.

[0026] In an implementation form of the first aspect, the longitudinal stiffness of the at least one wheel is determined as a ratio of a rate of change of a force of the at least one wheel to a rate of change of a longitudinal slip of the at least one wheel.

[0027] In an implementation form of the first aspect, the reduced value of the torque of the at least one wheel is at least 50% of the initial value. This provides the advantage that an at least 50% reduction of the torque is sufficient to bring the at least one wheel to a stable region. Moreover, a lower torque reduction leads to a better vehicle performance.

[0028] According to a second aspect, a device for estimating a longitudinal speed of a vehicle is provided, wherein the vehicle comprising two or four wheels, and the device is configured to: obtain a first estimated longitudinal speed of the vehicle; determine whether an uncertainty of the first estimated longitudinal speed is larger than a threshold value; when the uncertainty is larger than the threshold value, control the vehicle to adjust a torque of at least one wheel of the vehicle; and determine a second estimated longitudinal speed of the vehicle after adjusting the torque.

[0029] In an implementation form of the second aspect, the second estimated longitudinal speed has an uncertainty smaller than the uncertainty of the first estimated longitudinal speed. That is, the torque of the at least one wheel is controlled until it is brought to a stable region, in which the longitudinal velocity can be estimated with higher accuracy.

[0030] In an implementation form of the second aspect, the device is further configured to control the vehicle to apply a support pulse torque on the at least one wheel, the support pulse torque being a function of a longitudinal stiffness of the at least one wheel. Since the longitudinal stiffness of a wheel is a measurable parameter, the applied support pulse torque is a function of the force characteristics of the at least one wheel and, thus, is not based on rule-based logics. In an implementation form of the second aspect, the device is further configured to: control the vehicle to reduce the torque of the at least one wheel from an initial value to a reduced value; calculate, at each of a plurality of points in time, the longitudinal stiffness of the at least one wheel; control the vehicle to maintain the torque of the at least one wheel at the reduced value until the calculated longitudinal stiffness changes from a positive value to a negative value and remains negative; and control the vehicle to increase the torque of the at least one wheel from the reduced value to the initial value until the calculated longitudinal stiffness changes from the negative value to another positive value. This has the advantage of bringing the vehicle into a reliable, observable region by taking into account the actual conditions of the vehicle and the at least one wheel.

[0031] In an implementation form of the second aspect, the longitudinal stiffness of the at least one wheel is determined as a ratio of a rate of change of a force of the at least one wheel to a rate of change of a longitudinal slip of the at least one wheel. In an implementation form of the second aspect, the reduced value of the torque of the at least one wheel is at least 50% of the initial value.

[0032] The device according to the second aspect provides the same advantages and effects as described above for the method of the first aspect and its respective implementation forms.

[0033] According to a third aspect, a computer program is provided. The computer program includes instructions which, when the program is executed by a computer, cause the computer to carry out the method according to the first aspect and its implementation forms.

[0034] The computer program according to the third aspect provides the same advantages and effects as described above for the method of the first aspect and its respective implementation forms.

[0035] The advantages of the solutions according to this disclosure can be summarized as follows. By using the longitudinal stiffness of the at least one wheel, the solutions can truly inform about the observability (stability) of the wheel and enabling to optimize, for example and not as a limitation:

[0036] • The duration of the torque reduction.

[0037] • The amount of the torque reduction.

[0038] • The frequency of the torque support pulse.

[0039] As a result, the amount of the net torque reduction during the support pulse can be reduced and subsequently the loss of the vehicle deceleration can also be reduced.

[0040] It has to be noted that all devices, elements, units and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof. BRIEF DESCRIPTION OF DRAWINGS

[0041] The above described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which:

[0042] FIG. 1 schematically shows a method for estimating a longitudinal speed of a vehicle, according to this disclosure;

[0043] FIG. 2 shows a flowchart for applying a support pulse torque, according to this disclosure;

[0044] FIG. 3 shows an exemplary plot of the dynamics of the estimated longitudinal speed of a vehicle in a plot of a normalized longitudinal tire force vs. the tire slip characteristic, according to this disclosure;

[0045] FIG. 4 schematically depicts a device for estimating a longitudinal speed of a vehicle, according to this disclosure;

[0046] FIG. 5 schematically depicts a device for estimating a longitudinal speed of a vehicle, according to this disclosure;

[0047] FIG. 6(a) schematically depicts an example of a conventional support pulse torque;

[0048] FIG. 6(b) schematically depicts an example of a support pulse torque according to this disclosure.

[0049] Same elements shown in the figures are labeled with the same reference signs, and may be implemented likewise.

[0050] DETAILED DESCRIPTION OF EMBODIMENTS

[0051] FIG. 1 shows an exemplary embodiment of a method 100 for estimating a longitudinal speed of a vehicle according to this disclosure, the vehicle comprising two or four wheels. For example, the vehicle can be a motorcycle or a car, or any other vehicle with two or four wheels.

[0052] The method 100 comprises a step 101 of obtaining a first estimated longitudinal speed of the vehicle, Vx.

[0053] The first estimated Vxcan be obtained, for example, from the vehicle.

[0054] Then, the method 100 comprises a step 102 of determining whether an uncertainty of the first estimated longitudinal speed is larger than a threshold value. The threshold value can be a predetermined value.

[0055] Further, in step 103, the method 100 comprises controlling the vehicle to adjust a torque of at least one wheel of the vehicle when the uncertainty is larger than the threshold value.

[0056] Next, the method 100 comprises a step 104 of determining a second estimated longitudinal speed of the vehicle after adjusting the torque.

[0057] As explained above in the disclosure, the estimated Vxis uncertain when the wheel slip is large. Thus, in this exemplary embodiment, when the uncertainty of the first estimated Vxexceeds the threshold value, there is the need to bring the vehicle into a stable (observable) region where Vx can be estimated accurately. This is achieved by adjusting the torque of at least one of the wheels. When the uncertainty of the first estimated Vxis less than or equal to the threshold value, the torque of the at least one wheel may not be modified.

[0058] Once the vehicle is in the observable region, the second Vxis estimated. Hence, the second estimated longitudinal speed has an uncertainty that is smaller than the uncertainty of the first estimated Vx.

[0059] The second estimated longitudinal speed of the vehicle can be provided as a result, and can be provided, for example, to the vehicle.

[0060] The step 102 of controlling the vehicle to adjust the torque of the at least one wheel of the vehicle comprises: controlling the vehicle to apply a support pulse torque on the at least one wheel. The support pulse torque is a function of a longitudinal stiffness of the at least one wheel, as explained later on in this disclosure.

[0061] Controlling the vehicle to apply the support pulse torque on the at least one wheel comprises the steps explained as follows: First, the vehicle is controlled to reduce the torque of the at least one wheel from an initial value to a reduced value.

[0062] The torque reduction can be performed by the vehicle, for example, by increasing a brake torque on at least one wheel, or by reducing powertrain torque on at least one wheel, or utilizing torque transfer actuators comprising e.g. electronic limited-slip differential (e-LSD), clutches, or the like.

[0063] The reduced value of the torque of the at least one wheel is at least 50% of the initial value. Notably, reducing the initial value of the torque of the at least one wheel by at least 50% of is sufficient to bring back the wheel to a stable region and, thus, a further reduction of the torque brings no further benefits. This is in contrast to conventional support pulses that reduce the torque up to 10% of the total drive torque, resulting in a loss of performance of the vehicle as 90% of the drive torque is lost on the wheel.

[0064] The reduced value of the torque may be obtained as a function of the force characteristics of the at least one wheel and can be calculated from tire model parameters or calibration parameters, which describe a maximum tire force reduction at higher slips (slip>50%).

[0065] Next, controlling the vehicle to apply the support pulse torque on the at least one wheel comprises calculating, at each of a plurality of points in time, the longitudinal stiffness of the at least one wheel.

[0066] As it was explained above in this disclosure, the longitudinal stiffness of the at least one wheel is calculated (or determined) as the ratio of the rate of change of the force of the at least one wheel to the rate of change of the longitudinal slip of the at least one wheel, dpx / dZ

[0067] Thus, after the method step 101 of obtaining the first estimated longitudinal speed of the vehicle, the method 100 may comprise a step of obtaining the ratio of the rate of change of the force of the at least one wheel, dpxand the rate of change of the longitudinal slip of the at least one wheel, dZ thereby the longitudinal stiffness of the at least one wheel can be calculated.

[0068] Alternatively, before calculating the longitudinal stiffness of the at least one wheel at each of the plurality of points in time, the step of controlling the vehicle to apply the support pulse torque on the at least one wheel may comprise calculating (or determining) the ratio of the rate of change of the force of the at least one wheel, dpxand the rate of change of the longitudinal slip of the at least one wheel, dZ so that the longitudinal stiffness of the at least one wheel can be calculated. Once the longitudinal stiffness is calculated at each time step, the controlling the vehicle to apply the support pulse torque on the at least one wheel may comprise determining whether the calculated longitudinal stiffness is positive or negative.

[0069] Further, the controlling the vehicle to apply the support pulse torque on the at least one wheel comprises controlling the vehicle to maintain the torque of the at least one wheel at the reduced value until the calculated longitudinal stiffness changes from a positive value to a negative value and remains negative.

[0070] That the longitudinal stiffness remains negative means that the ratio dpx / dZ has the negative value, or has another negative value that is different from the negative value; this is not limiting in this disclosure. In other words, the magnitude of the longitudinal stiffness is not limiting in this disclosure, but the sign (positive or negative) is.

[0071] Next, the controlling the vehicle to apply the support pulse torque on the at least one wheel comprises controlling the vehicle to increase the torque of the at least one wheel from the reduced value to the initial value until the calculated longitudinal stiffness changes from the negative value to another positive value. Another positive value can be equal to or different from the positive value disclosed above.

[0072] The above steps for controlling the vehicle to apply the support pulse torque on the at least one wheel according to this disclosure can also be understood in terms of an exemplary flowchart according to this disclosure, depicted in FIG. 2.

[0073] In the exemplary flowchart of FIG. 2, a first step, labelled as "1 ", the torque reduction starts when the uncertainty of the first estimated Vxis larger than the threshold value.

[0074] In a second step, labelled as "2" in FIG. 2, the tire longitudinal stiffness dpx / dZ is calculated at each of the plurality of time steps. The wheel torque is kept in the reduced value until dpx / dZ changes from a first positive value to a negative value and stays negative.

[0075] Next, in a third step labelled as "3" in FIG. 2, at each time step, the longitudinal stiffness djix / dZ is still calculated, and the torque of the at least one wheel is increased, at a respective time step, from the reduced value to the initial value until d px / dZ changes from the negative value to another positive value. The wheel torque is no further increased after dpx / dZ becomes positive again.

[0076] An exemplary support pulse torque according to this disclosure obtained by applying the flowchart of FIG. 2 is depicted in FIG. 6(b). The three steps, labelled "1", "2" and "3", according to the flowchart of FIG. 2 are also depicted in FIG. 6(b).

[0077] The amount of torque reduction in the support pulse torque according to this disclosure and shown in FIG. 6(b), which is calculated as a function of the wheel dynamics, is smaller than the one obtained with conventional solutions, as depicted in FIG. 6(a) and that is calculated using fixed parameters, for example the duration of the support pulse, tsp, and / or the amount of torque reduction, AT. Further, the total duration of the support pulse torque of FIG. 6(b) according to this disclosure can be smaller than the duration of the conventional support pulse according to FIG. 6(a).

[0078] FIG. 3 depicts an example of the dynamics of the estimated Vxin a plot of the normalized longitudinal tire force ( ix) vs. the tire slip characteristic (X), obtained when the support pulse torque according to the flowchart of FIG. 2 is applied. FIG. 3 shows that the estimated Vxis unobservable (e.g., is in a non-linear region) when all the heels of the vehicle are in the large slip region, and it becomes observable (e.g., is in a linear region) when the longitudinal stiffness of all the wheels is negative. The steps "1 " , "2" and " 3 " according to the algorithm shown in FIG. 2 are also indicated in FIG. 3.

[0079] FIG. 4 shows an exemplary embodiment of a device 400 for estimating a longitudinal speed of a vehicle according to this disclosure, the vehicle comprising two or four wheels.

[0080] The device 400 can be part of, or can be implement in, the vehicle. Further, the device 400 is configured to perform the method 100 according to FIG. 1 and its implementation forms.

[0081] The device 400 according to this disclosure may comprise a processor or processing circuitry (not shown) configured to perform, conduct or initiate the various operations of the device 400 described herein. The processing circuitry may comprise hardware and / or the processing circuitry may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or multi-purpose processors. The device 400 may further comprise memory circuitry, which stores one or more instruction(s) that can be executed by the processor or by the processing circuitry, in particular under control of the software. For instance, the memory circuitry may comprise a non-transitory storage medium storing executable software code which, when executed by the processor or the processing circuitry, causes the various operations of the device 400 to be performed. The processing circuitry may comprise one or more processors and a non-transitory memory connected to the one or more processors. The non-transitory memory may carry executable program code which, when executed by the one or more processors, causes the device 400 to perform, conduct or initiate the operations or methods described herein.

[0082] The device 400 is configured to obtain a first estimated longitudinal speed 401 of the vehicle. For example, the device 400 may obtain the first estimated longitudinal speed 401 from the vehicle.

[0083] Next, the device 400 is configured to determine whether an uncertainty of the first estimated longitudinal speed 401 is larger than a threshold value.

[0084] When the uncertainty is larger than the threshold value, the device 400 is further configured to control the vehicle to adjust a torque 402 of at least one wheel of the vehicle.

[0085] For example, the device 400 may communicate with the vehicle and may instruct the vehicle to adjust the torque 402 of the at least one wheel.

[0086] Further, the device 400 is configured to determine a second estimated longitudinal speed 403 of the vehicle after the torque 402 of the at least one wheel was adjusted by the vehicle.

[0087] The device 400 may further provide the second estimated longitudinal speed 403 to the vehicle.

[0088] That the device 400 is configured to control the vehicle to adjust the torque 402 of the at least one wheel of the vehicle comprises: the device 400 is configured to control the vehicle to apply a support pulse torque on the at least one wheel. The support pulse torque is a function of the longitudinal stiffness of the at least one wheel. This comprises the following: The device 400 may be configured to control the vehicle to reduce the torque 402 of the at least one wheel from an initial value to a reduced value. The reduced value of the torque 402 of the at least one wheel is at least 50% of the initial value.

[0089] The torque reduction can be performed by the vehicle by increasing a brake torque on at least one wheel, or by reducing powertrain torque on at one wheel, or utilizing torque transfer actuators comprising e.g. electronic limited-slip differential (e-LSD), clutches, or the like.

[0090] Next, the device 400 may be configured to calculate, at each of a plurality of points in time, the longitudinal stiffness of the at least one wheel.

[0091] Further, the device 400 may be configured to control the vehicle to maintain the torque 402 of the at least one wheel at the reduced value until the calculated longitudinal stiffness changes from a positive value to a negative value and remains negative.

[0092] The device 400 may be further configured to control the vehicle to increase the torque 402 of the at least one wheel from the reduced value to the initial value until the calculated longitudinal stiffness changes from the negative value to another positive value.

[0093] As explained above, the longitudinal stiffness of the at least one wheel is determined as the ratio of the rate of change of the force of the at least one wheel to a rate of change of the longitudinal slip of the at least one wheel.

[0094] Thus, the device 400 may be further configured to calculate (or determine) the ratio of the rate of change of the force of the at least one wheel, dpxand the rate of change of the longitudinal slip of the at least one wheel, dZ so that the longitudinal stiffness of the at least one wheel is calculated.

[0095] Additionally or alternatively, after the device 400 obtains the first estimated longitudinal speed of the vehicle, the device 400 may be configured to obtain the ratio of the rate of change of the force of the at least one wheel, dpxand the rate of change of the longitudinal slip of the at least one wheel, dZ: thereby the longitudinal stiffness of the at least one wheel can be calculated.

[0096] FIG. 5 shows an exemplary embodiment of a device 400 for estimating a longitudinal speed of a vehicle, which builds on the device 400 shown in FIG. 4. Same elements are labelled with the same reference signs. Hereinafter, only the differences between FIG. 4 and FIG. 5 are explained.

[0097] In the exemplary embodiment according to FIG. 5, the device 400 may further comprise a controller 504 and a processor 505, which are in communication with each other.

[0098] The controller 504 may be configured to obtain the first estimated longitudinal speed 401 of the vehicle, and may send the first estimated longitudinal speed 401 to the processor.

[0099] Then, the processor 505 may be configured to determine whether the uncertainty of the first estimated longitudinal speed 401 is larger than a threshold value.

[0100] When the uncertainty is larger than the threshold value, the processor 505 may be further configured to determine that the torque 402 of the at least one wheel has to be adjusted, and may notify it to the controller 504. For example, the processor 505 may send to the processor 504 information indicating that the torque 402 of the at least one wheel has to be adjusted. Then, the controller 504 may be configured to control the vehicle to adjust the torque 402 of the at least one wheel.

[0101] Next, the processor 505 may be further configured to determine the second estimated longitudinal speed 403 of the vehicle after the torque 402 of the at least one wheel was adjusted by the vehicle.

[0102] Optionally, the processor 505 may be configured to send to the controller 504 the determined the second estimated longitudinal speed 403 of the vehicle, and the controller 504 may provide it to the vehicle.

[0103] Further, the device 400 may be configured to control the vehicle to apply a support pulse torque on the at least one wheel, wherein the support pulse torque is a function of a longitudinal stiffness of the at least one wheel. This comprises the following: The processor 505 may be configured to determine the reduced value of the torque 402 of the at least one wheel, and may send it to the controller 504. Then, the controller 504 may be configured to control the vehicle to reduce the torque 502 of the at least one wheel from an initial value to the reduced value.

[0104] Further, the processor 505 may be configured to calculate, at each of a plurality of points in time, the longitudinal stiffness of the at least one wheel.

[0105] The processor 505 may be configured to calculate (or determine) the ratio of the rate of change of the force of the at least one wheel, dpxand the rate of change of the longitudinal slip of the at least one wheel, dZ so that the longitudinal stiffness of the at least one wheel is calculated.

[0106] Additionally or alternatively, after the controller 504 obtains the first estimated longitudinal speed of the vehicle, the controller 504 may be configured to obtain the ratio of the rate of change of the force of the at least one wheel, dpxand the rate of change of the longitudinal slip of the at least one wheel, dZ and may send them to the processor 505: thereby, the longitudinal stiffness of the at least one wheel can be calculated by the processor 505.

[0107] The processor 505 may then determine whether the longitudinal stiffness of the at least one wheel changes from a positive value to a negative value and remains negative.

[0108] If the longitudinal stiffness changes from a positive value to a negative value and remains negative, the processor 505 may notify it to the controller 504. Subsequently, the controller 504 may be configured to control the vehicle to maintain the torque 402 of the at least one wheel at the reduced value until the calculated longitudinal stiffness changes from the positive value to the negative value and remains negative.

[0109] Then, the processor 505 may be configured to determine, at each time step, whether the calculated longitudinal stiffness changes from the negative value to another positive value, and may notify it to the controller 504.

[0110] The controller 504 may then be configured to control the vehicle to increase the torque 402 of the at least one wheel from the reduced value to the initial value until the calculated longitudinal stiffness changes from the negative value to another positive value.

[0111] This disclosure further provides a computer program comprising instructions for carrying out, when the program is executed by a computer, the method 100 according to FIG. 1, and its implementation forms. The computer program may be included in a computer readable medium of a computer program product. The computer readable medium may comprise essentially any memory, such as a ROM (Read-Only Memory), a PROM (Programmable Read-Only Memory), a 15 EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a hard disk drive.

[0112] The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. Elowever, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word "comprising" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

CLAIMS1. A method (100) for estimating a longitudinal speed of a vehicle, the vehicle comprising two or four wheels, and the method comprising: obtaining (101) a first estimated longitudinal speed of the vehicle; determining (102) whether an uncertainty of the first estimated longitudinal speed is larger than a threshold value; when the uncertainty is larger than the threshold value, controlling (103) the vehicle to adjust a torque of at least one wheel of the vehicle; and determining (104) a second estimated longitudinal speed of the vehicle after adjusting the torque.

2. The method (100) according to claim 1, wherein the second estimated longitudinal speed has an uncertainty smaller than the uncertainty of the first estimated longitudinal speed.

3. The method (100) according to claim 1 or 2, wherein controlling (103) the vehicle to adjust the torque of the at least one wheel of the vehicle comprises: controlling the vehicle to apply a support pulse torque on the at least one wheel, the support pulse torque being a function of a longitudinal stiffness of the at least one wheel.

4. The method (100) according to claim 3, wherein controlling the vehicle to apply the support pulse torque on the at least one wheel comprises: controlling the vehicle to reduce the torque of the at least one wheel from an initial value to a reduced value; calculating, at each of a plurality of points in time, the longitudinal stiffness of the at least one wheel; controlling the vehicle to maintain the torque of the at least one wheel at the reduced value until the calculated longitudinal stiffness changes from a positive value to a negative value and remains negative; and controlling the vehicle to increase the torque of the at least one wheel from the reduced value to the initial value until the calculated longitudinal stiffness changes from the negative value to another positive value.

5. The method (100) according to claim 3 or 4, wherein the longitudinal stiffness of the at least one wheel is determined as a ratio of a rate of change of a force of the at least one wheel to a rate of change of a longitudinal slip of the at least one wheel.

6. The method (100) according to claim 4 or 5, wherein the reduced value of the torque of the at least one wheel is at least 50% of the initial value.

7. A device (500) for estimating a longitudinal speed of a vehicle, the vehicle comprising two or four wheels, and the device being configured to: obtain a first estimated longitudinal speed (501) of the vehicle; determine whether an uncertainty of the first estimated longitudinal speed (501) is larger than a threshold value; when the uncertainty is larger than the threshold value, control the vehicle to adjust a torque (502) of at least one wheel of the vehicle; and determine a second estimated longitudinal speed (503) of the vehicle after adjusting the torque (502).

8. A computer program comprising instructions which, when the program is executed by a processor, cause the processor to carry out the method (100) according to claims 1 to 6.

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