Electromechanical steering system and method for adaptive position determination of a motor of an electromechanical steering system

Abstract

Method for adaptive position determination of a motor (8) of an electromechanical steering system (1) comprising the steps - Receiving (100) a sine signal (A(sin)) and a cosine signal (B(cos)) from a resolver for position determination, - Creating (300) a first rotor angle setpoint signal (Φsetpoint) based on the sine signal (A(sin)) and the cosine signal (B(cos)), - Determining (400) an angular velocity (Φ') by differentiating from the rotor angle setpoint signal, characterized by - Determining (600) coefficients for a proportional component (P(Φ)) of a pl controller of the steering system (1) as a function of the angular velocity (Φ'), and - Calculating a second rotor angle setpoint signal (Φsetpoint) based on the coefficients.

Description

State of the art

[0001] The present invention relates to an electromechanical steering system and a method for adaptively determining the position of a motor of an electromechanical steering system. In particular, the present invention relates to a way of making the haptics of an electromechanically assisted steering system more pleasant, especially more consistent, for the user.

[0002] Electromechanically assisted steering systems are increasingly being used to generate assistance torque for a steering maneuver initiated by the driver. A so-called "resolver" is often provided to determine the rotor position of an electric motor (e.g. a synchronous motor) in the electromechanical steering system. Direct use of the resolver signal, which contains information about the angular position of the steering system, leads to haptic and acoustic abnormalities on the steering wheel. When developing new motor control concepts, an improvement in steering feel is therefore always the goal. The inventors discovered that the representation accuracy of the measured resolver signals leaves much to be desired. This was attributed, among other things, to the fact that the representation accuracy is always lost when the signals cross zero.These cause an error in the motor position calculation and thus alter the set voltage vector. This results in a fluctuation in the motor torque, which in turn negatively affects the steering feel.

[0003] In the state of the art, phase-locked loops are used to determine the position of supporting electrical machines or the steering column.

[0004] US 2006 / 0 132 338 A1 discloses an angle detection device which is configured to determine an angle of a motor, which may be installed, for example, in a power steering system of a hybrid vehicle, using a phase-locked loop.

[0005] However, the approaches known in the prior art cannot satisfactorily address the disadvantages identified by the inventors of the present invention. Therefore, it is an object of the present invention to satisfy the above-identified need. Disclosure of the invention

[0006] The above-identified object is achieved according to the invention by a method for the adaptive position determination of a motor of an electromechanical steering system with the features of claim 1 and by an electromechanical steering system with the features of claim 10. According to the invention, it is irrelevant whether the position determination is carried out on the motor itself or whether a position determination carried out elsewhere allows conclusions to be drawn about the position of the motor by the position (rotational position) of the motor being determined via a predefined and known transmission ratio. The electromechanical steering system can, for example, be used to steer a road vehicle. In a first step, a sine signal is received by a first sensor and a cosine signal is received by a second sensor from a resolver for position determination. The sine signal and the cosine signal can, for example,can be generated in such a way that the same sensor (e.g. a permanent magnet) of the steering system is detected at different angular positions by the sensors contained in the resolver and converted into electrical signals. A first rotor angle target signal is then created from the sine signal and the cosine signal. The rotor angle target signal can be understood as the basis for controlling or modified controlling an electric motor to generate a steering assistance torque. A time derivative of the rotor angle target signal then generates an angular velocity, which according to the invention is used further in controlling the electric motor. Coefficients for a proportional component of a proportional integrator control system (hereinafter "PI controller") of the steering system are then determined as a function of the angular velocity.In other words, the coefficients (also called "gain factors") are determined using a predefined function of a current angular velocity within the steering system. Finally, a second rotor angle target signal is calculated based on the coefficients determined as described above. In other words, the coefficients determined according to the invention are used to modify the first rotor angle target signal into the second rotor angle target signal. The result is an output value for the PI controller in the form of a signal proportional to the angular velocity, which is summed, for example, using a discrete integrator. The output of the integrator represents a (modified) actual value of the angle and can be used to control the electric motor by forming a difference with a target value. In this way, an adaptive change of a gain factor of the PI control loop takes place.As described in detail, the haptic behavior of the electromechanical steering system designed according to the invention is improved in this way.

[0007] The subclaims show preferred developments of the invention.

[0008] Preferably, the resolver's sine or cosine signals are converted into arctangent signals or angle values ​​using a predefined number of stored results. This avoids the computationally complex "in real time" calculation of the angular position from the sine and cosine signals.

[0009] More preferably, the sine signal and the cosine signal are first digitized, and the digital value pairs, which were determined at an identical point in time, are assigned arctangent signals read from a stored table. Digitization, in conjunction with the table, enables particularly rapid and computationally inexpensive retrieval of the current arctangent signal or the determination of the position in the form of a (rotational) angle.

[0010] Preferably, the table described above can be defined for input values ​​in the range from zero to π / 4. For the range from π / 4 to π / 2, for example, the formula Arctan(sin / cos)=π / 2−Arcan(cos / sin) can be used. In this way, the storage space required for the table can be kept as small as possible. However, the computational effort required to determine the information implicitly contained in the table in the range from π / 4 to π / 2 is significantly less than calculating the angles based on trigonometric functions from the resolver's sine and cosine signals.

[0011] Preferably, the angular velocity can be determined by numerical differentiation from the rotor angle target signal. This enables a robust and computationally manageable generation of the angular velocity signal.

[0012] To avoid harmonics and noise signals, which can adversely affect the haptic experience when using an electromechanical steering system, a low-pass filter can be provided that processes the first rotor angle target signal and / or the rotor angle target signals. The low-pass filter can, in particular, be a discrete-time filter. In particular, the angular velocity signal can be subjected to the low-pass filtering described above. Digital processing of all of the aforementioned signals enables interference-free and computationally simple signal processing.

[0013] When determining the coefficients for the proportional component of the steering system's PI controller, a nonlinear dependence on the angular velocity can preferably be used. In other words, the proportional component (also called the "P component") is adaptively changed depending on the filtered angular velocity. This dependence can be implemented, for example, using a pre-calculated and stored table, as described, for example, in connection with the calculation of the arctangent signal. The gain factor of the P component can vary over a wide range, particularly between 400 and 8,000, so that the maximum value of the gain due to the coefficient is 20 times greater than the minimum value.

[0014] Preferably, a coefficient for an integration component (also called the "I component") of the PI controller can be adjusted proportionally to the coefficient for the proportional component. In other words, the coefficients for the integration component are linked to the coefficients for the proportional component via a fixed factor. In particular, the ratio of the coefficient for the integration component to the coefficient for the proportional component can be in a range from 1:8 to 1:16, preferably in a range from 1:9 to 1:11. In tests, a ratio of 1:10 has proven particularly optimal.

[0015] The output signal of the PI controller can be integrated to generate an actual rotor angle signal from the motor of the electromechanical steering system. The integration can also be performed using a discrete integrator. The integrator's output now represents an actual value of the rotor angle and can be fed back with a target value to calculate the difference, creating a feedback loop.

[0016] According to a second aspect of the present invention, an electromechanical steering system is proposed, which comprises a resolver, a PI controller, and an evaluation unit. As explained in connection with the method according to the invention, the resolver can output a sine signal and a cosine signal of an angular position of the motor to generate an assist torque. The evaluation unit, which comprises, for example, a programmable processor (e.g., a microcontroller, a nanocontroller, or similar), is configured according to the invention to generate a first rotor angle target signal based on the sine signal and the cosine signal. For this purpose, the evaluation unit can use a data storage device, which can also be implemented as a component of the electromechanical steering system. In addition, the evaluation unit is configured to determine an angular velocity by differentiating from the rotor angle target signal.As described above, differentiation can also be carried out digitally (time- and value-discrete). The evaluation unit can determine coefficients for a proportional component of the PI controller as a function of the angular velocity and calculate a second rotor angle target signal based on the coefficients. According to the invention, it is particularly provided that the coefficients (gain factors) are not selected to be constant or time-invariant. The function for determining them, which is dependent on the angular velocity and is provided according to the invention, enables a more natural and pleasant steering feel for the user of the electromechanical steering system. The features, combinations of features, and the resulting advantages of the electromechanical steering system according to the invention correspond to those explained in connection with the method according to the invention. To avoid repetition, reference is made to the above explanations.

[0017] According to a third aspect of the present invention, a means of transport (e.g. a car, a van, a truck, a motorcycle, an aircraft and / or a watercraft) is proposed which has an electromechanical steering system according to the second aspect of the invention. Short description of the drawings

[0018] Embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawings: Fig. 1 a schematic view of an embodiment of a means of transport equipped according to the invention with an embodiment of an electromechanical steering system designed according to the invention; Fig. 2 a flow chart which enables the inventive production of a rotor angle target signal by means of a method designed according to the invention; Fig. 3 a flowchart illustrating steps of an embodiment of a method according to the invention. Embodiments of the invention

[0019] Fig. Figure 1 shows a passenger car 10 as a means of transport, in which an embodiment of an electromechanical steering system 1 according to the invention is provided. A steering wheel 9 is connected via a steering column 7 and a transmission 23 (with a gear ratio of 1:x) to an electromechanical drive in the form of a motor 8, which is designed as an electric motor, whose rotor is mechanically coupled in a predefined manner to a rotation of the steering wheel 9 by an angle Φ. Two sensors 2, 3 of a resolver provide sine signals and cosine signals, respectively, which are converted into a current angle signal by an electronic control unit as an evaluation unit 6 using a data memory (not shown). In other words, the output signals of the sensors 2, 3 are converted into arctangent signals via a stored table. The table is stored in a data memory 5, which is informationally connected to the electronic control unit as an evaluation unit 6.

[0020] Fig. 2 shows a flowchart whose input side is fed by a sine signal A(sin) from a first sensor 2 and a cosine signal B(cos) from a second sensor 3. Based on a stored table 11, in which discrete values ​​are stored for calculating an arctangent signal atan2(A, B) for predefined value pairs of the signals A(sin), B(cos). In a summer 12, the output signal of table 11 is added to an angular offset 15 to correct a mechanically induced angular difference between the resolver and a synchronous motor of the electromechanical steering system, thereby removing any DC component that may be present. The output signal of the summer 12 Φsoll is fed on the one hand to a discrete differentiator 4 and on the other hand to a subtractor or subtractor 16.The output signal of the discrete differentiator 4, which is shown as angular velocity Φ', is then fed to a low-pass filter (13), which is designed as a digital low-pass filter, via which harmonics and any noise present are removed from the rotor angle target signal Φsoll. The output signal of the low-pass filter (13), which is designed as a low-pass filter, is designated as Φ'f and represents an output signal at the output 21 of the flow diagram. According to the invention, the filtered angular velocity signal Φ'f is converted into a coefficient for the proportional component of the PI controller contained in the flow diagram via a predefined relationship 14 that is dependent on the angular velocity Φ'. In a first multiplier 18, the coefficient generated from the relationship 14 is multiplied by an output signal of the subtractor orSubtractor 16, in which the rotor angle target signal Φsoll is subtracted from an actual rotor angle signal Φist present at output 22, is multiplied to generate a proportional component P(Φ) dependent on the angle or angular velocity. In a second multiplier 18, the coefficient from relationship 14 is multiplied by a constant factor (in the example 1:10) in a memory 17, and the result is fed to a third multiplier 18, which also receives the output signal of the subtractor or subtractor 16 as a second input signal and feeds the product to a digital integrator 19. The output signal of the digital integrator 19 is added to the proportional component P(Φ) in a second summer 12 and converted into an actual rotor angle signal Φactual in an integrator 20 and fed to the second output 22 of the flow chart.Relationship 14 can result in a gain factor of the proportional component in a range from 400 to 8,000. The constant factor reflects a ratio of the integrating component to a proportional component. In other words, using the constant factor, the proportional component is weighted approximately 9 times higher than the integrating component. Table 11 can also be understood as an "arc tangent function" with two arguments. The signal present at output 22 represents a rotor angle that has been optimized according to the invention.

[0021] Fig.3 shows a flowchart illustrating steps of an embodiment of a method according to the invention for adaptively determining the position of a motor of an electromechanical steering system. In step 100, a sine signal and a cosine signal are received from a resolver for position determination. The sine signals or cosine signals can be digitized in advance and, in particular, quantified in order to simplify an assignment to value pairs provided in the table in step 200. In step 200, an arctangent signal is created on the basis of the sine signal and the cosine signal and with the aid of a stored table. In step 300, a first rotor angle target signal is created on the basis of the sine signal and the cosine signal. In step 400, an angular velocity is determined by differentiating the created rotor angle target signal. The rotor angle target signal orThe rotor angle target signals are filtered in step 500 using a time-discrete low-pass filter. In step 600, coefficients for a proportional component of the PI controller range of the steering system are determined as a function of and as a predefined function of the angular velocity. This method step represents a core aspect of the present invention. In step 700, a difference signal is generated which reduces the rotor angle target signal Φtarget by the rotor angle actual signal Φactual and divides the result by a difference signal δ Φ (difference between the previous rotor angle target signal Φtarget and the previous rotor angle actual signal Φactual). In step 800, the proportional component is determined by multiplying the difference signal δ Φ by the coefficient K determined according to the invention. In step 900, the integration component is determined by multiplying the difference signal δ Φ by the coefficient K and a weighting factor of 0.1.In step 1000, the integration component is integrated using an integrator. In step 1100, the proportional component and the integration component are summed. In step 1200, the output signal of the PI controller is integrated to obtain a new actual rotor angle signal Φactual. In step 1300, the actual rotor angle signal Φactual is stored to be kept ready for the next calculation cycle of the inventive method for adaptive position determination.

[0022] Even if the aspects and advantageous embodiments of the invention have been described in detail with reference to the exemplary embodiments explained in conjunction with the attached drawing figures, modifications and combinations of features of the illustrated exemplary embodiments are possible for those skilled in the art without departing from the scope of the present invention, the scope of protection of which is defined by the attached claims. List of reference symbols 1 steering system 2 sensors 3 Sensor 4 Differentiators 5 data storage 6 Evaluation unit 7 Steering column 8 Engine 9 Steering wheel 10 cars 11 Table 12 summators 13 Low pass 14 Relationship between angular velocity and the coefficients of the proportional part 15 Angle offset 16 subtractors 17 storage 18 multipliers 19 Integrator 20 Integrators 21 Output / filtered angular velocity 22 Output (of the adjusted rotor angle) 23 gearboxes 100 - 1300 process steps K coefficient I(Φ) integration part P(Φ) Proportional part Φ angle Φ' angular velocity A(sin) sine signal B(cos) cosine signal atan2(A, B) Arcus-Tangens-Signal Φsoll Rotorwinkelsollsignal

Claims

[1] Method for adaptive position determination of a motor (8) of an electromechanical steering system (1) comprising the steps - receiving (100) a sine signal (A(sin)) and a cosine signal (B(cos)) from a resolver for position determination, - creating (300) a first rotor angle target signal (Φsoll) based on the sine signal (A(sin)) and the cosine signal (B(cos)), - determining (400) an angular velocity (Φ') by differentiating from the rotor angle target signal, characterized by - determining (600) coefficients for a proportional component (P(Φ)) of a PI controller of the steering system (1) as a function of the angular velocity (Φ'), and - Calculating a second rotor angle command signal (Φsoll) based on the coefficients. [2] The method according to claim 1 further comprising the step: - Creating (200) an arctangent signal (atan2(A, B)) based on the sine signal (A(sin)) and the cosine signal (B(cos)). [3] Method according to claim 2, - wherein the arc tangent signal (atan2(A, B)) is read out from a table (11) as a function of the sine signal (A(sin)) and the cosine signal (B(cos)). [4] Method according to claim 3, wherein the table (11) has values for input values in the range between 0 and π / 4 and values for input values in the range between π / 4 and π / 2 are calculated. [5] Method according to one of the preceding claims, wherein the determination (400) of the angular velocity (Φ') is carried out by numerical differentiation from the rotor angle target signal (Φsoll). [6] Method according to one of the preceding claims further comprising the step - low-pass filtering (500) of the first rotor angle target signal (Φsoll) and / or the second rotor angle target signal (Φsoll), in particular by means of a time-discrete low-pass filter (13). [7] Method according to one of the preceding claims, wherein a non-linear dependence on the angular velocity (Φ') is used as a basis for determining the coefficients for the proportional component (P(Φ)) of the PI controller of the steering system (1). [8] Method according to one of the preceding claims further comprising - Adjusting a coefficient for an integration component (I(Φ)) of the PI controller proportional to the coefficient for the proportional component (P(Φ)), wherein in particular a ratio of the coefficient for the integration component (I(Φ)) to the coefficient for the proportional component (P(Φ)) of 1 to 8 to 1 to 16, preferably of 1 to 9 to 1 to 11 is selected. [9] Method according to one of the preceding claims further comprising - Integrating (1200) an output signal of the PI controller to generate an actual rotor angle signal (Φist) of the motor (8) of the electromechanical steering system (1). [10] Electromechanical steering system (1) comprising - a resolver, - a PI controller, and - an evaluation unit (6), wherein - the resolver is configured to generate a sine signal (A(sin)) and a cosine signal (B(cos)) for determining the position of a motor (8) for steering assistance, - the evaluation unit (6) is set up, - to create a first rotor angle target signal (Φsoll) based on the sine signal (A(sin)) and the cosine signal (B(cos)), - to determine an angular velocity (Φ') by differentiating from the rotor angle target signal (Φsoll), - to determine coefficients for a proportional component (P(Φ)) of the PI controller as a function of the angular velocity (Φ'), and - to calculate a second rotor angle command signal (Φsoll) based on the coefficients.

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