US-12617294-B2 - Process for controlling an electric motor of a motor vehicle and motor vehicle with a control unit configured to carry out the process

US12617294B2US 12617294 B2US12617294 B2US 12617294B2US-12617294-B2

Abstract

A process for controlling an electric motor is disclosed. The process includes determining a target torque to be delivered by the electric motor, associating the target torque with a control target for a control input of the electric motor according to a mapping between the target torque and the control target, acquiring a feedback signal of the control input, controlling the electric motor with an error between the feedback signal and the control target, identifying a critical condition where the error diverges, determining a safety control target corresponding to a safety target torque according to the mapping, where the safety target torque is reduced relative to the target torque, and replacing the error when the critical condition is identified with a safety error between the feedback signal and the safety control target.

Inventors

Roberto Betro'
Giorgio Bisceglie
Valerio Dodet
Ugo Sitta

Assignees

FERRARI S.P.A.

Dates

Publication Date: 20260505
Application Date: 20240523
Priority Date: 20230525

Claims (11)

1 . A process for controlling an electric motor of a motor vehicle, the process comprising the steps of: a. determining a target torque to be delivered by the electric motor as a function of a corresponding demand of a driver of the motor vehicle; b. associating the determined target torque with at least one corresponding control target for a control input of the electric motor according to a mapping between the target torque and the control target; c. acquiring a feedback signal of the control input; d. controlling the electric motor according to a control law as a function of an error indicative of a difference between the feedback signal and the control target, wherein the control law is configured to induce convergence of the error to a zero value; e. identifying a critical condition where the error diverges from the zero value during step d.; f. determining a safety control target corresponding to a safety target torque according to said mapping, wherein the safety target torque is reduced relative to the target torque determined in step a.; and g. replacing said error in step d., when the critical condition is identified according to step e., with a safety error indicative of a further difference between the feedback signal and the safety control target.
2 . The process according to claim 1 , wherein the safety target torque is less than or equal to a predetermined percentage of the target torque determined in step a.
3 . The process according to claim 2 , wherein the predetermined percentage is 90%.
4 . The process according to claim 1 , further comprising determining an output speed of the electric motor and having an optimized characteristic curve of the electric motor, the optimized characteristic curve defining a functional relationship between the output speed of the electric motor and a target torque limit, wherein the determined target torque is limited to the target torque limit corresponding to the determined output speed, according to the optimized characteristic curve.
5 . The process according to claim 4 , further comprising determining a safety characteristic curve by lowering the optimized characteristic curve for all values of the output speed, the safety characteristic curve defining a functional relationship between the output speed and a safety target torque limit, wherein the determined safety target torque limit is limited to the safety target torque limit corresponding to the determined output speed, according to the safety characteristic curve.
6 . The process according to claim 1 , wherein steps e., f., g. are performed iteratively during step d. progressively reducing the safety target torque for each iteration until the critical condition ceases to be identified in step e.
7 . The process according to claim 1 , wherein the critical condition is identified in step e. when an increment of the error for a predetermined time interval exceeds a critical threshold.
8 . The process according to claim 1 , wherein the control input comprises an electric current to supply the electric motor.
9 . The process according to claim 1 , further comprising the step of replacing again the safety error in step d. with said error at the expiration of a predetermined time from the execution of step g.
10 . A motor vehicle comprising an electric motor and a control unit configured to carry out the process according to claim 1 .
11 . A process for controlling an electric motor of a motor vehicle, the process comprising: determining a target torque to be delivered by the electric motor as a function of a corresponding demand of a driver of the motor vehicle; associating the determined target torque with at least one corresponding control target for a control input of the electric motor according to a mapping between the target torque and the control target; acquiring a feedback signal of the control input; controlling the electric motor according to an algorithm as a function of an error indicative of a difference between the feedback signal and the control target, wherein the algorithm is configured to induce convergence of the error to a zero value; identifying a critical condition where the error diverges from the zero value during said controlling step; determining a safety control target corresponding to a safety target torque according to said mapping, wherein the safety target torque is reduced relative to the determined target torque; and replacing said error in said controlling step, when the critical condition is identified according to said identifying step, with a safety error indicative of a further difference between the feedback signal and the safety control target.

Description

CROSS-REFERENCE TO RELATED APPLICATION This patent application claims priority from Italian patent application no. 102023000010545 filed on May 25, 2023, the entire disclosure of which is incorporated herein by reference. TECHNICAL FIELD The invention relates to a process for controlling an electric motor of a motor vehicle, as well as a motor vehicle comprising a control unit configured to carry out the process. BACKGROUND Some motor vehicles include electric motors as an exclusive means of propulsion (called fully electric motor vehicles) or as an auxiliary means of propulsion (called hybrid motor vehicles with at least one electric motor). Usually, an electric motor of a motor vehicle is controlled in feedback based on a target torque delivered, which in turn is obtained as a function of a corresponding driver demand, e.g., an acceleration demand, in particular which can be expressed by pressing an accelerator pedal. In more detail, a motor vehicle control unit converts the driver's demand into the target torque according to known algorithms. The target torque can be limited as a function of an angular motor output speed according to a torque-speed characteristic curve. In particular, for each value of the angular output speed, the target torque is equalled to the maximum deliverable torque for that same value according to the characteristic curve if the target torque is greater than such a maximum deliverable torque. The characteristic curve is typically calibrated experimentally on the bench with reference to maximised performance. This especially applies to electric motors supplied for sports cars. In more detail, the target torque translates into a target electric current which enters into a closed-loop control law, or algorithm, of the motor, where the variable controlled in feedback is precisely the electric current supplying the motor. More in particular, the closed-loop control law can, for example, be of the proportional-integrative type. The translation of the target torque into the target current can occur by means of specific mappings or mathematical functions, which can be theoretical in nature (e.g., models known by the acronyms MTPA, FW, MTPV, and the like) or more preferably experimental. In any case, each manufactured electric motor will have its own characteristics which differ relative to the others and, above all, will be able to operate under very different conditions, e.g., temperature, health of the power supply network, surrounding humidity, etc. Given the pursuit of maximised performance, the variability of operating conditions, and the ideal nature of the aforementioned mapping with respect to the actual link between torque and electric current, there is a real risk that the target electric current will be unattainable by means of the designed closed-loop control law. This would mean that the error given by the difference between the actual current and the target electric current would tend to diverge, so that a complete loss of control of the motor vehicle could occur with consequent danger to the driver and for his/her passengers. Therefore, some motor vehicles are provided with instruments for recognising an error divergence condition and for commanding a motor vehicle stop or a speed limiter insertion. Although such instruments are important for safety matters, the insertion of the speed limiter or, even worse, the stopping of the motor vehicle, is a major inconvenience, not least because it forces the motor vehicle owner to remedy the situation by taking the motor vehicle to a garage. Therefore, the need is felt to overcome the drawback just mentioned, while not compromising or jeopardising the safety of the motor vehicle. An aim of the invention is to fulfil the above requirement, preferably in a simple and repeatable manner. DESCRIPTION OF THE INVENTION In one aspect, the invention can be a process for controlling an electric motor of a motor vehicle, the process comprising the steps of: a. determining a target torque to be delivered by the electric motor according to a corresponding demand of a driver of the motor vehicle;b. associating the determined target torque with at least one corresponding control target for a control input of the electric motor according to a mapping between the target torque and the control target;c. acquiring a feedback signal of the control input;d. controlling the electric motor according to a control law as a function of an error indicative of a difference between the feedback signal and the control target, wherein the control law is configured to induce convergence of the error to a zero value;e. identifying a critical condition where the error diverges from the zero value during step d.;f. determining a safety control target corresponding to a safety target torque according to said mapping, wherein the safety target torque is reduced relative to the target torque determined in step a.; andg. replacing said error in step d., when the critic