Method for estimating the value of the dry friction deviation

Abstract

A method for estimating a value of dry friction deviation, which represents the deviation between the actual value of dry friction acting on the power steering system (1) of a vehicle (2) and the nominal dry friction value, comprising the following steps performed by a data processing means: a) determining the value of the force acting on the rack (6) of the power steering system (1); b) determining the nominal dry friction value based on the speed of the vehicle (2); and c) calculating the value of dry friction deviation based on the force value and the nominal dry friction value, assuming that the value of dry friction deviation does not depend on the speed of the vehicle (2).

Description

Technical Field

[0001] The present invention relates to the field of vehicle power steering, more specifically to the estimation of values related to the friction of a power steering system, and even more specifically to a method for estimating the value of the deviation of dry friction that represents the deviation between the actual value of dry friction acting on a vehicle's power steering system and the nominal dry friction value.

Background Art

[0002] An electric power steering system called "EPS" is a system that uses an electric motor to assist the driver in steering the vehicle.

[0003] The first objective of electric power steering is assistance, that is, to reduce the steering wheel / driver torque during a specific operation. The steering wheel / driver torque sensor is configured to measure the torque applied to the vehicle's steering column by the driver, and the control unit determines an appropriate assist level based on the measured torque and driving conditions, controls the motor of the electric power steering, and supplies additional torque to the rack and pinion that is connected to the steering wheel via the steering column on one hand and to the wheel via the tie rod on the other hand.

[0004] The second objective of electric power steering is to provide the driver with a good steering feel, which is called "steer feel" in English.

[0005] The disadvantage of the initial "assist rule" based only on the steering wheel / driver torque is that the driver feels a significant amount of mechanical friction in the steering, which is considered inaccurate.

[0006] In fact, especially for very small movements close to zero, if the steering wheel / driver torque is very small (for example, when the steering wheel is released), the assist stops when moving in one direction, and the driver feels a jarring sensation due to steering friction. This means that the mechanical friction of the electric power steering reduces or cancels out the movement of the rack when the driver's force input is small, which reduces driving precision by causing large, nonlinear changes in steering wheel / driver torque to make fine steering corrections. As a result, hysteresis occurs. That is, the steering wheel / driver torque in one direction is different from the steering wheel / driver torque in the other direction. To improve the feel of the steering, it is necessary to reduce this hysteresis by continuously compensating for the mechanical friction of the steering, even when the driver input is small, i.e., when the displacement velocity is very low.

[0007] Patents FR3073638 and FR3070957 describe solutions for estimating friction in order to compensate for it.

[0008] However, this solution has several drawbacks. In particular, accurately estimating friction remains difficult when vehicle speed changes. Since friction changes with vehicle speed, it takes a considerable amount of time for the computer to estimate the friction at a particular speed and determine the corresponding assist level. As a result, the assist motor does not supply enough torque to compensate for the friction in the steering system. Therefore, the driver's feel is not optimal. Furthermore, in patent FR3070957, the estimation is only possible during vehicle steering operations.

[0009] Therefore, a more effective and reliable solution is needed that allows for the estimation of friction, particularly dry friction, in order to compensate for it in the vehicle's power steering system. [Overview of the Initiative]

[0010] One of the objectives of the present invention is to compensate for dry friction acting on a vehicle's power steering system in a reliable, efficient, and rapid manner.

[0011] To this end, one of the objectives of the present invention is to estimate a dry friction deviation value, which represents the deviation between the estimated actual value and the nominal dry friction value of the dry friction acting on the power steering system of a vehicle, in a reliable, efficient, and rapid manner.

[0012] According to the first phase, a method is proposed for estimating the value of the dry friction deviation, which represents the deviation between the actual value of dry friction acting on the vehicle's power steering system and the nominal dry friction value. This method involves the following steps performed by a data processing means: a) A step of determining the value of the force acting on the rack of the power steering system, b) A step of determining the nominal dry friction value based on the speed of the vehicle, c) Assuming that the value of the dry friction deviation does not depend on the speed of the vehicle, the step of calculating the value of the dry friction deviation based on the force value and the nominal dry friction value, It is equipped with.

[0013] Depending on their advantageous and unrestricted characteristics, the following may be adopted individually or in any combination: Step c) for calculating the value of the dry friction deviation includes performing a difference calculation between the force value and the nominal dry friction value. In step c), the calculation of the value of the dry friction deviation is further performed based on the viscous friction value acting on the power steering system. In step c), the calculation of the dry friction deviation is further performed, preferably based on the lateral acceleration value of the vehicle, weighted by the gain. The gain is determined by a nominal gain value determined based on the vehicle's speed and a gain deviation value that is assumed to be independent of the vehicle's speed. In step c), the value of the dry friction deviation is calculated using the following formula, namely: This is done by solving TIFF0007881093000002.tif7170, where, TIFF0007881093000003.tif7170 corresponds to the value of the dry friction deviation, TIFF0007881093000004.tif7170 corresponds to the aforementioned force value, TIFF0007881093000005.tif7170 corresponds to the aforementioned nominal gain value, TIFF0007881093000006.tif7170 corresponds to the value of the gain deviation that is independent of the vehicle's speed, TIFF0007881093000007.tif7170 corresponds to the value of the lateral acceleration of the vehicle, TIFF0007881093000008.tif7170 corresponds to the aforementioned nominal dry friction value, TIFF0007881093000009.tif7170 corresponds to the aforementioned viscous friction value. The value of the force is determined by the force from the assist motor to the rack and / or the force from the steering wheel to the rack. In step b), the nominal dry friction value is determined from a predetermined nominal dry friction model. The nominal dry friction value is determined based on other parameters, which are at least one of the following: the angle of the steering wheel, the temperature of the power steering system, and the type of road.

[0014] According to the second phase, a method is proposed to compensate for dry friction acting on the vehicle's power steering system, and this method is... The steps include: estimating a value of dry friction deviation, which represents the deviation between the actual value of dry friction acting on the vehicle's power steering system and the nominal dry friction value, by performing the method for estimating the dry friction deviation value described above; · To compensate for the dry friction acting on the power steering system, a step of correcting the value of the force applied to the rack by the assist motor based on the value of the deviation of the dry friction. including.

[0015] According to a third aspect, a power steering system for a vehicle is proposed, which includes an electronic control unit configured to execute the aforementioned estimating method or the aforementioned compensating method.

[0016] According to a fourth aspect, a computer program product is proposed, which includes code instructions for executing the aforementioned estimating method or the aforementioned compensating method when the program is executed on a computer.

[0017] According to a fifth aspect, a storage means readable by a computer device is proposed, on which the computer program product includes code instructions for executing the aforementioned estimating method or the aforementioned compensating method.

Brief Description of the Drawings

[0018] Other features and advantages of the present invention will become apparent from the following description of the preferred embodiments. This description is made while referring to the accompanying drawings. [Figure 1] FIG. 1 schematically shows a power steering system of a vehicle. [Figure 2] FIG. 2 shows the steps of a method for estimating the value of the deviation. [Figure 3] FIG. 3 shows the steps of a method for compensating for dry friction.

Embodiments for Carrying out the Invention

[0019] System A power steering system 1 is proposed for a vehicle 2, more specifically an automobile for transporting people.

[0020] As is well known and as shown in Figure 1, the power steering system 1 includes a steering wheel 3 that allows the driver to operate the power steering system 1 by applying a force called "steering wheel torque" T3 to the steering wheel 3. The angle θ3 of the steering wheel 3 is measured by an angle sensor 23. The steering wheel torque T3 and the angle θ3 of the steering wheel are transmitted to the electronic control unit 20.

[0021] The steering wheel 3 is preferably mounted on a steering column 4 which is rotationally guided on the vehicle 2, and engages with a steering rack 6 by a steering pinion 5, the steering rack 6 itself is translationally guided within a steering casing 7 which is fixed to the vehicle 2.

[0022] Preferably, both ends of the steering rack 6 are connected to steering tie rods 8 and 9, respectively, which are connected to the steering knuckles of the steering wheels 10 and 11 (left wheel 10 and right wheel 11, respectively), and the steering angle (yaw angle) of the steering wheels can be changed by the longitudinal translational motion of the rack 6.

[0023] The steering wheels 10 and 11 may also preferably be drive wheels.

[0024] The power steering system 1 also includes an assist motor 12 which is intended to supply an assist motor force T12, more specifically an assist motor torque T12, to assist the operation of the power steering system 1.

[0025] The assist motor 12 is preferably a bidirectional electric motor, and preferably a brushless or brushed rotary electric motor.

[0026] The assist motor 12 can, if necessary, engage with the steering column 4 itself via a gear reducer to form a so-called "single pinion" mechanism, or it can directly engage with the steering rack 6 by a second pinion 13 different from the steering pinion 5 that meshes with the rack 6, for example, to form a so-called "double pinion" mechanism as shown in Figure 1, or it can directly engage with the steering rack 6 by a ball screw that cooperates with the corresponding threads of the rack 6 at a position away from the steering pinion 5.

[0027] This section describes a mechanical electric power steering system, that is, a system in which a mechanical link exists between the steering wheel and the rack.

[0028] However, the present invention is also applicable to an electric power steering system 1 (called "steer-by-wire" in English) that does not have mechanical couplings, although this is not shown in the illustration, in which the steering wheel is mechanically disconnected from the rack. In this case, the steering system comprises a steering wheel unit that is mechanically independent from the rack unit.

[0029] In the steering wheel unit, the control regulator controls the control motor in such a way that the driver is particularly aware of the rack's inertia, i.e., the weight of the rack.

[0030] In the rack unit, the assist regulator controls the assist motor that applies assist motor torque to the rack. More specifically, the steering wheel angle is measured or calculated to determine the set angle achieved by the angular position of the rack. The assist regulator controls the angular position of the operating motor to the set angle by controlling the motor torque that the assist motor applies to the rack. The angular position of the assist motor corresponds to the angular position of the rack, modified by the value of the mechanical stiffness between the assist motor and the rack, and the virtual stiffness programmed into the assist regulator, which represents the stiffness between the assist motor and the steering wheel.

[0031] The present invention is not limited to any particular type of power steering system.

[0032] The power steering system 1 includes an electronic control unit (ECU) 20 equipped with data processing means 201 such as a processor and configured to control the assist motor 12.

[0033] The data processing means 201 is configured to perform a method for estimating a value of dry friction deviation, which represents the difference between the actual dry friction value and the nominal dry friction value acting on the power steering system 1 of the vehicle 2. This method will be described in detail later.

[0034] By using this deviation value, it becomes possible to estimate the dry friction acting on system 1. Using this deviation value, the dry friction can be taken into account by the assist motor.

[0035] In other words, the idea of ​​the present invention is not to directly determine the actual dry friction value, which is very complex, but simply to estimate the value of the "deviation" from the "nominal" dry friction value, which is a theoretical approximation, and this value of deviation can actually be estimated much more easily by the method of the present invention.

[0036] Advantageously, the data processing means 201 of the electronic control unit 20 is configured to correct the value of the force applied to the rack 6 by the assist motor 12 based on the value of the deviation. In this way, the electronic control unit 20 controls the assist motor 12 based on the corrected assist motor force value, thereby reliably compensating for the dry friction acting on the power steering system 1.

[0037] method Referring to Figure 2, a method is proposed for estimating the value of the dry friction deviation, which represents the difference between the actual value of dry friction acting on the power steering system 1 of vehicle 2 and the nominal dry friction value. This method is advantageous because it is performed when vehicle 2 is traveling at a constant speed.

[0038] The speed refers to the longitudinal speed of vehicle 2, that is, the speed in the direction of vehicle 2's movement.

[0039] Dry friction and viscous friction are distinguished. Dry friction is independent of the displacement velocity of the rack-and-pinion mechanism of the steering system. Dry friction arises from surface contact (with or without lubrication) between two solids, particularly the pinion and the rack. Viscous friction depends on (and is sometimes proportional to) the velocity of the rack-and-pinion mechanism.

[0040] Since dry friction is highly dependent on vehicle speed, compensating for it is complex. This invention aims to provide a solution to this problem.

[0041] This method advantageously includes a preliminary step a0) of determining a predetermined nominal dry friction model. This model is intended to allow the determination of a nominal dry friction value based on the speed of vehicle 2.

[0042] The nominal dry friction value is the expected dry friction value when vehicle 2 is traveling at a constant speed. In other words, when vehicle 2 is traveling at a constant speed, a specific dry friction value equal to the nominal dry friction value is expected.

[0043] It should be reiterated that the nominal dry friction value is a theoretical value, and therefore, in reality, the actual dry friction value is close to the nominal dry friction value but not equal to it, and as mentioned above, the actual dry friction value has a deviation value from the nominal dry friction value. The actual dry friction value refers to the dry friction value that is considered to represent the dry friction actually acting on system 1. This actual dry friction value is unknown at the start of this method and is assumed to be expressed based on the nominal dry friction value and the deviation value of the dry friction. This method aims to accurately calculate the value of the dry friction deviation, thereby characterizing and further calculating the actual dry friction value.

[0044] As explained, while the nominal dry friction value depends on vehicle speed, this method estimates the deviation value assuming that it is independent of vehicle speed, that is, unrelated to vehicle speed. In other words, the actual dry friction value is expressed based on a component that depends on vehicle speed (i.e., the nominal dry friction value) and a component that is judged to be independent of vehicle speed (i.e., the value of the dry friction deviation). In this way, the actual dry friction value is cleverly decomposed into a component that depends on vehicle speed and a component that does not depend on vehicle speed, and as will be described later, this makes it possible to reliably compensate for dry friction at all vehicle speeds, even when the vehicle speed changes.

[0045] Modeling this deviation as a quantity independent of velocity significantly simplifies calculations while, paradoxically, maintaining a high level of estimation quality.

[0046] As explained, the nominal dry friction value can be determined using a model, which is advantageously determined in step a0).

[0047] Step a0) consists of constructing a model that allows for the determination of the nominal dry friction value based on the vehicle's speed.

[0048] The model can be any kind of mathematical model, such as a function or a calculation chart.

[0049] This model is advantageously constructed empirically by driving the vehicle and measuring dry friction at various vehicle speeds.

[0050] Dry friction can be measured, for example, by steering on a flat track using a reference vehicle and a reference power steering system. Steering is typically performed sinusoidally (alternating left and right steering operations, with the steering wheel angle following a sinusoidal time progression) at a maximum lateral acceleration of 0.1g, a very low steering wheel speed (less than 10° / sec), and a constant vehicle speed. Measurements are preferably performed at different speeds, such as 20 km / h, 40 km / h, and 60 km / h. After measurement, in the plane of rack force versus lateral acceleration, the curve can be summarized as two parallel lines representing hysteresis. The semi-hysteresis as a whole corresponds to friction (dry friction and viscous friction). Due to the very low steering wheel speed, the semi-hysteresis is considered to represent dry friction. The slopes of these lines preferably correspond to the nominal gain values, which will be detailed later. Choosing the "rack force" versus "lateral acceleration" plane is advantageous as it replaces the "rack force" versus "angle" plane. This is because the change in the slope of the line is smaller in the selected plane. In any case, a person skilled in the art would know how to perform such measurements and construct a model.

[0051] Advantageously, this model allows for the determination of nominal dry friction values ​​based on the speed of vehicle 2, as well as other parameters relating to the vehicle, its movement, and / or its environment. For example, these parameters include at least one of the following: steering wheel angle, power steering system temperature, road type, and signs of wear in the power steering system.

[0052] Therefore, preferably, step a0) consists of building a model based on the vehicle speed, as well as other parameters relating to the vehicle, its movement, and / or its environment. In other words, dry friction measurements are performed under a variety of conditions.

[0053] Advantageously, this model is associated with a vehicle type and / or model so that it is particularly suited to the operation of the vehicle. Therefore, step a0) can be performed on multiple reference vehicles to obtain a model corresponding to each vehicle type / model in multiple reference vehicles.

[0054] Step a0) is advantageously performed only once on a reference vehicle designed for this purpose, after which the model can be implemented in the data processing means 201 of any suitable vehicle. Thus, step a0) is preferably performed by the data processing means, which are in practice different from the data processing means 201 that perform the remaining processing (i.e., steps a), b) and c)). Therefore, step a0) is not performed every time the method is executed.

[0055] This method includes step a) determining the value of the force acting on the rack 6 of the power steering system 1.

[0056] Advantageously, the force values ​​depend on the force applied from the assist motor 12 to the rack 6, and / or the force applied from the steering wheel 3 to the rack 6.

[0057] In some cases, such as in a power steering system without mechanical links or in an autonomous vehicle, the force value depends solely on the force applied from the assist motor 12 to the rack 6. Alternatively, in these cases, the force value depends on both the force applied from the assist motor 12 to the rack 6 and the force applied from the steering wheel 3 to the rack 6, but the force applied from the steering wheel 3 is considered zero.

[0058] Preferably, the force applied from the assist motor 12 to the rack 6 is torque, which is called assist motor torque.

[0059] Preferably, the force applied from the steering wheel 3 to the rack 6 is a torque called the steering wheel torque.

[0060] Conveniently, this force value is called the rack force estimate (RFe), which is the sum of the forces applied to the rack by the steering wheel and the assist motor.

[0061] Therefore, preferably, the force value corresponds to the sum of the force value applied from the assist motor 12 to the rack 6 and the force value applied from the steering wheel 3 to the rack 6.

[0062] This method includes step b) determining the nominal dry friction value based on the speed of vehicle 2.

[0063] The nominal dry friction value is determined favorably from the speed of vehicle 2 using a predetermined nominal dry friction model.

[0064] Preferably, the nominal dry friction value is further determined based on at least one parameter relating to the vehicle, its movement, and / or the environment. This at least one parameter favorably includes the steering wheel angle, the temperature of the power steering system, and / or the type of road.

[0065] Therefore, at the end of step b), the data processing means 201 determines a nominal dry friction value, which is the dry friction value measured on a reference vehicle during the construction of the model, at the same speed, and possibly with the same parameters relating to the vehicle, its movement, and / or its environment.

[0066] Therefore, as described above, the data processing means 201 determines the components of the actual dry friction value that depend on the vehicle speed.

[0067] Next, the method includes step c) calculating the value of the dry friction deviation based on the force value and the nominal dry friction value, assuming that the value of the dry friction deviation does not depend on the vehicle speed.

[0068] In other words, it was based on the assumption that the value of the deviation does not depend on the vehicle speed. That is, changes in vehicle speed do not change the value of the deviation. The vehicle speed-dependent component of the actual dry friction value, i.e., the nominal dry friction value, had already been determined and was rapidly calculated using a given model. In the prior art, due to the changes in speed, it is complex, time-consuming, and therefore impossible to efficiently estimate a reliable dry friction value. In fact, in the prior art, it was necessary to obtain measurements at a large number of time points (hundreds of measurement points) in order to make it possible to determine the friction, which was extremely time-consuming. The present invention makes it possible to consider changes in speed and to efficiently estimate a reliable actual dry friction value by separating and determining the vehicle speed-dependent component from the vehicle speed-independent component of the actual dry friction value.

[0069] More specifically, assuming that the value of the dry friction deviation does not depend on the vehicle speed means, for example, that when calculating the value of the dry friction deviation, the mathematical hypothesis is that this value of the dry friction deviation does not change with the vehicle speed.

[0070] Advantageously, step c) for calculating the value of the dry friction deviation includes performing a difference calculation between the force value and the nominal dry friction value.

[0071] Preferably, in step c), the value of the dry friction deviation is further calculated based on the viscous friction value acting on the power steering system. This determines the value of the dry friction deviation by taking viscous friction into account, which is closer to reality and therefore more reliable.

[0072] In one embodiment, the viscous friction value is determined using a model that allows for the determination of the viscous friction value based on various parameters, particularly the vehicle speed. Advantageously, this model is constructed similarly to a model that allows for the determination of the dry friction value, but preferably for steering wheel speeds exceeding 10 degrees / second. For the construction of the model, the viscous friction measurement can be determined by varying the steering wheel speed. For example, when the steering wheel speed is greater than 10 degrees / second (e.g., 30 degrees / second), the difference between the measured total friction (i.e., dry friction and viscous friction) and the measured dry friction corresponds to the viscous friction. Viscous friction is considered to be proportional to the steering wheel speed. Those skilled in the art can construct the model by performing such measurements in any case.

[0073] Advantageously, in step c), the calculation of the dry friction deviation is further performed based on the vehicle's lateral acceleration value, which is preferably weighted by a gain. Lateral acceleration is the force acting on the vehicle when it turns or changes direction. The gain is multiplied by the lateral acceleration to allow for a representation of an equivalent lateral acceleration that is less affected by the vehicle's velocity. Thus, the value of the dry friction deviation becomes more reliable as it approaches reality.

[0074] Those skilled in the art can calculate the lateral acceleration, for example, based on the vehicle's speed, steering wheel angle, and intrinsic gains that primarily depend on the vehicle's shape. These intrinsic gains are different from and should not be confused with the gains mentioned in the remainder of this description.

[0075] More preferably, the gain depends on a nominal gain value determined based on the vehicle speed and a gain deviation value assumed to be independent of the vehicle speed. This gain and this gain value are different from the intrinsic gains mentioned in the previous paragraph. Advantageously, the nominal gain value is determined from a model using the vehicle speed, and this model can be constructed in a similar manner to the model constructed in step a0). One method for obtaining the nominal gain value is detailed in the description of step a0). This gain decomposition also makes it possible to represent the value of the dry friction deviation in a more realistic way, thus providing an accurate and reliable value that enables precise friction compensation.

[0076] Conveniently, in step c), the value of the dry friction deviation is calculated using the following formula, namely, TIFF0007881093000010.tif7170

[0077] This is performed by solving the equation. Here, TIFF0007881093000011.tif7170 corresponds to the value of the dry friction deviation, TIFF0007881093000012.tif7170 corresponds to the force value, TIFF0007881093000013.tif7170 corresponds to the nominal gain value, TIFF0007881093000014.tif7170 corresponds to a gain deviation value that is independent of vehicle speed. TIFF0007881093000015.tif7170 corresponds to the vehicle's lateral acceleration value. TIFF0007881093000016.tif7170 corresponds to the nominal dry friction value. TIFF0007881093000017.tif7170 corresponds to the viscous friction value.

[0078] Therefore, by solving this equation, we can find the value β of the dry friction deviation. Note that the left side of this equation contains terms (α and β) that do not depend on the vehicle's speed, while the right side contains only terms that depend on the vehicle's speed. This decomposition makes it possible to represent the system in a way that is closer to reality.

[0079] In this equation, the values ​​of α and β are unknown. The other values ​​are determined based on velocity, for example, using a model.

[0080] This solution makes it possible to determine the values ​​of α and β, especially the value of β.

[0081] Assuming that the value of the dry friction deviation does not depend on the vehicle speed means that the constraint imposed when attempting to solve this equation (for example, the constraint imposed on the data processing means responsible for solving the equation) is that the value of the dry friction deviation β does not change with the vehicle speed.

[0082] The value (β) of the dry friction deviation obtained by this invention is a simple value that can be obtained easily and quickly, and enables improved performance of algorithms that use this value as input.

[0083] The value of the dry friction deviation (β) can be advantageously used as input to the dry friction correction algorithm of the electronic control unit 20. For example, this algorithm knows the nominal dry friction value and also accepts the value of the dry friction deviation as input, and from these values ​​it can determine how to correct the assist force that the assist motor 12 should apply to the rack 6 to compensate for the dry friction, thereby providing the driver with a high-quality steering feel. The present invention makes it possible to compensate for dry friction very quickly (the system can adapt after driving less than 2 km). In contrast, with the prior art, it may be necessary to wait for hundreds of kilometers of (continuous) driving before the electronic control unit can adapt to the friction, and if the speed changes, compensation for friction becomes virtually impossible. Therefore, thanks to the value of the dry friction deviation in the present invention, the efficiency of the compensation algorithm is improved.

[0084] Alternatively, the data processing means 201 may be configured to estimate the actual dry friction value from the dry friction deviation value and the nominal dry friction value. For example, the actual dry friction value may be calculated by summing the dry friction deviation value and the nominal dry friction value. This estimated actual dry friction value can be used as input to a compensation algorithm, thereby correcting the assist force that the assist motor 12 should apply to the rack 6.

[0085] Therefore, advantageously, with reference to Figure 3, a method for compensating for the dry friction acting on the power steering system 1 is proposed. This compensation method is advantageously performed by the electronic control unit 20. This compensation method includes step A) estimating a value of the dry friction deviation, which represents the deviation between the actual dry friction value and the nominal dry friction value acting on the power steering system 1, by performing the estimation method described above. Next, this compensation method includes step B) correcting the value of the force applied to the rack 6 by the assist motor 12 based on the value of the dry friction deviation in order to compensate for the dry friction acting on the power steering system 1.

[0086] Computer program product and readable storage means A computer program product has also been proposed that includes code instructions for performing a method to estimate a value of dry friction deviation, which represents the deviation between the actual dry friction value and the nominal dry friction value acting on the power steering system 1 of vehicle 2 when the program is executed on a computer.

[0087] A storage means readable by a computer device has also been proposed, which includes code instructions for a computer program product to perform a method for estimating a value of dry friction deviation, which represents the deviation between the actual dry friction value and the nominal dry friction value acting on the vehicle's power steering system.

Claims

1. A method for estimating the value of the dry friction deviation, which represents the deviation between the actual value of the dry friction acting on the power steering system (1) of a vehicle (2) and the nominal dry friction value, comprising the following steps performed by a data processing means, namely, a) A step of determining the value of the force acting on the rack (6) of the power steering system (1), b) A step of determining the nominal dry friction value based on the speed of the vehicle (2), c) Assuming that the value of the dry friction deviation does not depend on the speed of the vehicle (2), the step of calculating the value of the dry friction deviation based on the force value and the nominal dry friction value, A method that includes [a certain feature].

2. Step c) for calculating the value of the dry friction deviation includes performing a difference calculation between the force value and the nominal dry friction value. The method according to claim 1.

3. In step c), the calculation of the value of the dry friction deviation is further performed based on the viscous friction value acting on the power steering system (1). The method according to claim 1.

4. In step c), the calculation of the value of the dry friction deviation is further performed based on the value of the lateral acceleration of the vehicle (2). The method according to claim 1.

5. The value of the lateral acceleration of the vehicle (2) is weighted by a gain, The method according to claim 4.

6. The gain is determined by a nominal gain value determined based on the speed of the vehicle (2) and a gain deviation value that is assumed to be independent of the speed of the vehicle (2). The method according to claim 5.

7. Step c) for calculating the value of the dry friction deviation includes performing a difference calculation between the force value and the nominal dry friction value, In step c), the calculation of the dry friction deviation is further performed based on the viscous friction value acting on the power steering system (1), In step c), the calculation of the dry friction deviation is further performed based on the lateral acceleration value of the vehicle (2), The lateral acceleration value of the vehicle (2) is weighted by a gain. The gain is determined by a nominal gain value determined based on the speed of the vehicle (2) and a gain deviation value that is assumed to be independent of the speed of the vehicle (2). In step c), the value of the dry friction deviation is calculated using the following formula, namely: This is done by solving the equation, where, This corresponds to the value of the deviation of the dry friction, This corresponds to the value of the aforementioned force, This corresponds to the aforementioned nominal gain value, This corresponds to the value of the gain deviation that is independent of the speed of the vehicle (2), This corresponds to the value of the lateral acceleration of the vehicle, This corresponds to the nominal dry friction value mentioned above. This corresponds to the aforementioned viscous friction value, The method according to claim 1.

8. The value of the force is determined by the force from the assist motor (12) to the rack (2) and / or the force from the steering wheel (3) to the rack (6). The method according to claim 1.

9. In step b), the nominal dry friction value is determined from a predetermined nominal dry friction model. The method according to claim 1.

10. The nominal dry friction value is determined based on other parameters, which are at least one of the following: the angle of the steering wheel (3), the temperature of the power steering system (1), and the type of road. The method according to claim 9.

11. A method for compensating for dry friction acting on the power steering system (1) of a vehicle (2), - The steps of estimating a value of dry friction deviation, which represents the deviation between the actual value of dry friction acting on the power steering system (1) of the vehicle (2) and the nominal dry friction value, by performing the method according to claim 1, - A step of correcting the value of the force applied to the rack (6) by the assist motor (12) based on the value of the deviation of the dry friction in order to compensate for the dry friction acting on the power steering system (1), Methods that include...

12. A power steering system (1) for a vehicle (2), The system comprises an electronic control unit (20) configured to perform the estimation method described in claim 1 or the compensation method described in claim 11. Power steering system.

13. It is a computer program, The computer program comprises a code instruction for performing, when executed on a computer, the method according to claim 1, which estimates a value of dry friction deviation representing the deviation between the actual value of dry friction acting on the power steering system (1) of the vehicle (2) and the nominal dry friction value, or the method according to claim 11, which compensates for the dry friction acting on the power steering system (1) of the vehicle (2). Computer program.

14. A storage medium that can be read by computer equipment, The storage means includes a code instruction for a computer program to perform the method according to claim 1, which estimates a value of dry friction deviation representing the deviation between the actual value of dry friction acting on the power steering system (1) of the vehicle (2) and the nominal dry friction value, or the method according to claim 11, which compensates for the dry friction acting on the power steering system (1) of the vehicle (2). storage medium.

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