Method for controlling a brushless DC electric motor - Patents.com

Abstract

A method for controlling a brushless and sensorless DC electric motor (3) for automotive applications, the electric motor (3) having a rotor and phases (A, B, C) powered by pulse width modulation applied to a power inverter (1) of the electric motor (3), wherein a minimum threshold (S) of rotational speed of the rotor is set. min ), the rotor position is determined from measurements of the electromotive forces in the phases (A, B, C) of the electric motor (3), and the control method determines that the speed of rotation of the rotor exceeds a minimum threshold (S) by modifying the pulse width modulation when a command (104) to stop the electric motor (3) is given. min ) and the minimum threshold (S min ) within a range between the nominal speed and more than 10% of the nominal speed to a predetermined rotational speed (V1) (105), and then the electric motor (3) is stopped (106) at a predetermined position by short-circuiting the branches (A, B, C) of the inverter (1) when the predetermined position is reached.

Description

[Technical field]

[0001] The present invention relates to the field of electric motors for automotive applications, and in particular to brushless DC electric motors used for wiper systems. [Background technology]

[0002] Controlling a brushless DC motor requires at least ascertaining the position of the rotor at a certain precise point in order to be able to apply pulse width modulation commands making it possible to achieve the desired rotational speed.

[0003] For this purpose, it is known to use position sensors, in particular Hall effect sensors, which make it possible to ascertain a certain position of the rotor.

[0004] However, to reduce the cost of the electric motor, it may be beneficial to omit these position sensors, the cost of which is not negligible.

[0005] It is also possible to determine the rotor position using the zero-crossing method by measuring the electromotive forces in the phases of the electric motor, but it is necessary for the electric motor to be rotating at a speed above a predefined rotational speed in order for the electromotive forces to be high enough that they can be detected.

[0006] It is therefore possible to drive an electric motor without a sensor by applying a predetermined command at start-up until a predefined rotation speed is reached.

[0007] However, in the case of a wiper device, it is also necessary to stop the motor at a predefined position corresponding to a stop position (or "parking position"). This stop position is generally determined via a sensor associated with the connection of the wiper device. One way to stop the electric motor is therefore to short-circuit the branch of the inverter supplying power to the phases of the motor when the stop position is reached, in order to bring the electric motor to a complete stop. However, such a short-circuit of the inverter branch, when the electric motor is rotating at its nominal speed, causes significant current peaks that can damage the transistors used in the inverter and thus lead to failure of the electric motor. One way to solve this problem is to oversize the transistors so that they can withstand these current peaks, but this involves significant costs that go against the desire to reduce the overall cost of the electric motor. Summary of the Invention [Problem to be solved by the invention]

[0008] It is therefore necessary to find a solution that makes it possible to control brushless and sensorless electric motors, while still allowing the electric motor to be stopped in place without damaging the transistors used to supply power to the electric motor. [Means for solving the problem]

[0009] For this purpose, a method is proposed for controlling a brushless and sensorless DC electric motor for automotive applications, the electric motor comprising a rotor and phases powered by pulse width modulation applied to an inverter of the electric motor, the position of the rotor being determined from measurements of the electromotive forces in the phases of the electric motor when a minimum threshold for the rotational speed of the rotor is exceeded, A control method, characterized in that, when a command to stop an electric motor is given, the rotational speed of the electric motor is reduced from a nominal speed to a second predetermined rotational speed within an interval between a first predetermined rotational speed and more than 10% of said first predetermined rotational speed by modifying the pulse width modulation, and then the motor is stopped at a predetermined position by short-circuiting a branch of the inverter when the predetermined position is reached.

[0010] Use of a method for controlling a brushless and sensorless electric motor, in which when the electric motor is stopped, it is decelerated to a rotational speed substantially equal to the minimum speed at which the electromotive forces in the phases of the motor can be measured, thereby detecting the position of the rotor and then shorting an inverter branch to stop the motor when the desired stopping position is reached, thereby making it possible to reduce the degree of current peaks generated when the inverter branch is shorted, which advantageously makes it possible to stop the electric motor at the desired position without damaging the transistors used to supply power to the electric motor.

[0011] According to one embodiment, the deceleration of the rotational speed to the predetermined rotational speed comprises multiple increments with different decelerations of the rotational speed of the electric motor.

[0012] According to another embodiment, the electric motor is combined with a gear reduction device to form a geared motor adapted to drive a motor vehicle wiper device comprising at least one wiper arm, the wiper device comprising a stop sensor associated with a stop position of the wiper arm, the predetermined position being provided by the stop sensor and a signal from the stop sensor being used to determine the time at which the rotational speed should be reduced.

[0013] According to another embodiment, the stop sensor is modified to define a deceleration position, for example 5° or 10° before the stop position, at which the rotational speed of the electric motor should be decelerated in order to enable the wiper device to be stopped at the stop position.

[0014] According to another embodiment, the position of the wiper arm is inferred from the position of the rotor determined by the electromotive force and from the gear reduction ratio of the gear reducer when the rotational speed of the electric motor exceeds a minimum threshold value.

[0015] The invention also relates to a geared motor for a motor vehicle wiper device comprising a brushless and sensorless DC electric motor, the electric motor comprising a rotor, a control unit and phases powered by pulse width modulation applied to an inverter of the electric motor, the control unit being configured to determine the position of the rotor from measurements of the electromotive forces in the phases of the electric motor when a minimum threshold value for the rotational speed of the rotor is exceeded.

[0016] When a command to stop the electric motor is given, the control unit is configured to decelerate the rotational speed of the electric motor from the nominal speed to a predetermined rotational speed within an interval between said minimum threshold value and more than 10% of said minimum threshold value by modifying the pulse width modulation, and then stop the electric motor at the predetermined position by short-circuiting a branch of the inverter once the predetermined position is reached.

[0017] According to one embodiment, the predetermined position is given by a stop sensor associated with a stop position of the wiper device, and the control unit is configured to use an output signal from said stop sensor to determine the time at which the rotational speed of the rotor should be reduced.

[0018] According to another embodiment, the stop sensor is modified to define a deceleration position at which the rotational speed of the electric motor should be decelerated in order to enable the wiper device to be stopped in the stop position.

[0019] The invention also relates to a wiper device, in particular for a motor vehicle, which comprises a geared motor as described above.

[0020] Further features and advantages of the invention will become more clearly apparent on reading the following description, given by way of illustrative and non-limiting example, and the accompanying drawings, in which: [Brief description of the drawings]

[0021] [Figure 1] 1 shows a schematic diagram of an electric motor and its controlling inverter. [Diagram 2] 1 shows a schematic perspective view of a portion of a wiper device. [Diagram 3] 1 shows a schematic diagram of a portion of a stop sensor. [Figure 4] 1 shows a schematic diagram of a wheel equipped with a metal track of a stop sensor. [Diagram 5] 2 shows a flow diagram of method steps for controlling an electric motor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] In these figures, identical elements have the same reference numbers.

[0023] The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment or that a feature applies only to one embodiment. Individual features of various embodiments can also be combined or substituted to create other embodiments.

[0024] The present invention relates to a method for controlling an electric motor for a wiper device of a motor vehicle.

[0025] Fig. 1 shows a circuit diagram of a power supply inverter 1 for a three-phase electric motor 3, in particular an electric motor 3 for a motor vehicle wiper device. The inverter 1 comprises three branches, designated B1, B2 and B3, arranged to supply power to the three phases A, B and C of the electric motor 3, respectively, each branch B1, B2, B3 being connected on the one hand to a positive terminal of a power source 5, such as a vehicle battery, and on the other hand to a ground corresponding to the negative terminal of the power source 5. Each branch B1, B2, B3 comprises two switches 7 connected in series, typically formed by transistors. A diode 8 is typically arranged in parallel with each transistor 7. A center tap between the two transistors 7 of each branch B1, B2, B3 is connected to the respective phase A, B, C of the electric motor 3.

[0026] To control the rotation of the electric motor 3, a pulse width modulation command is applied to the phases A, B, C of the electric motor 3. This command is applied by commanding the opening and closing of the transistors 7 via the control unit 18. During normal operation, the two switches 7 of the branches B1, B2, B3 are in the opposite state (one open, the other closed). Furthermore, there is always a phase A, B or C that is not powered (switch 7 connected to the positive terminal of the power supply in the open position).

[0027] The electric motor 3 comprises a rotor. When the rotor rotates fast enough, i.e. above a minimum threshold value S min At speeds above 0.5 V, it is possible to infer the position of the rotor of the electric motor 3 by measuring the emf at the unpowered phases A, B or C and detecting the time when the measured voltage passes through zero, a technique called the “zero-crossing” technique.

[0028] The pulse width modulation commands are applied, for example, by the control unit 18 for controlling the electric motor 3. In addition, when the electric motor 3 is started, there is no need to ascertain the position of the rotor and therefore the rotational speed S can be determined without using a position sensor. minIt is possible to apply a predefined sequence of commands that allows reaching the desired stopping position. Similarly, it is possible to apply another predefined sequence of commands to stop the motor without needing a position sensor, but such a method does not allow to stop the electric motor 3 in the desired stopping position.

[0029] FIG. 2 shows a schematic diagram of a wiper device 9 for a motor vehicle. The wiper device 9 comprises an electric motor 3, controlled by an inverter 1 shown in FIG. 1. A gear reduction mechanism (not visible) is arranged on the output side of the electric motor 3 so as to form a geared motor 10. The gear reduction ratio of the gear reduction mechanism is, for example, 1 / 69°. The output side of the gear reduction mechanism is connected to a linkage 11, which allows a mechanical connection between the output side of the gear reduction mechanism and one or more wiper arms (not shown) of the wiper device 9. The linkage 11 comprises, for example, a set of connecting rods and a crank, which allows converting the rotary movement of the electric motor 3 into a reciprocating movement of one or more wiper arms. To ensure that the wiper arms are stopped in a predefined stop position, a stop sensor 13, also called a "park finger", is arranged on the wiper device 11, for example on the linkage 11 or on the output side of the gear reduction mechanism.

[0030] 3 and 4 show an exemplary embodiment of such a stop sensor 13. The sensor 13 comprises a metallic, and therefore conductive, track 15, for example with a resistance of less than 10 milliohms. The metallic track 15 is arranged on a wheel 17, made of a non-conductive material, for example plastic. The metallic track 15 comprises a circular portion 15a, from which an appendage 15b extends outwardly over a limited angular portion. The sensor 13 also comprises two contacts 19a and 19b, for example formed by two metal blades, arranged to come into contact with the metallic track 15. The first contact 19a is configured to contact the circular portion 15a of the metal track 15 and to be in permanent contact with the metal track 15, while the second contact 19b is configured to contact the appendage 15b such that the second contact is in contact with the metal track 15 only in a limited angular portion corresponding to the appendage 15b and is in contact with the non-conducting wheel 17 the rest of the time.

[0031] Thus, by measuring the electrical resistance between the two contacts 19a and 19b, it is possible to detect the time when the appendage 15b of the metal track 15 is in contact with the second contact 19b, since the resistance between the two contacts 19a and 19b is substantially zero due to the conductive nature of the metal track 15. The wheel 17 is therefore configured such that the angular region with the appendage 15b corresponds to the stop position. Nevertheless, it is possible to modify the configuration of the wheel (and in particular of the metal track 15) so that the position of the appendage 15b corresponds to a position other than the stop position, for example 5° or 10° before the stop position.

[0032] According to a first embodiment, in order to limit the extent of these current peaks, when the electric motor 3 is stopped, the stop sensor 13 is modified to correspond to a deceleration position in which the appendage is located before the stop position, for example 5° or 10° before the stop position. In addition, during operation and when the wiper device 11 is stopped, the control unit 18 is configured to decelerate the rotational speed of the electric motor 3 when the deceleration position is reached and detected via the stop sensor 13. The control unit 18 is therefore configured to receive and use an output signal from the stop sensor 13. The rotational speed of the electric motor 3 is determined by a minimum threshold value S, which allows the position of the rotor to be determined from the electromotive forces measured in phases A, B, C. min , or the minimum threshold S min The rotation speed V1 is reduced to a predetermined rotation speed V1, which corresponds to a speed slightly exceeding a minimum threshold value S min and the minimum threshold S min The rotational speed is within the interval between 10% and

[0033] Thus, when the electric motor 3 is stopped, the speed is reduced from the nominal operating speed (there will typically be multiple nominal speeds) to a minimum threshold S min The deceleration from the nominal speed to the predetermined rotational speed V1 is performed substantially linearly or gradually, via various intermediate speeds for various predetermined positions, so as to reach the predetermined speed V1 just before reaching the stop position. In particular, the configuration of the increments may differ depending on the nominal speed at the time the command to stop the electric motor 3 is sent.

[0034] The control unit 18 is configured to stop the rotor of the electric motor 3 by short-circuiting the branches B1, B2, B3 of the inverter 1 when a stop position is reached. This stop position is determined from the electromotive forces measured in the phases of the electric motor 3 and from the gear reduction ratio of the gear reducer.

[0035] In fact, the electromotive force makes it possible to determine the position of the rotor (this is because a given rotation speed exceeds a minimum threshold S min1.0 Hz), the gear reduction ratio makes it possible to infer the position of one or more wiper arms from the position of the rotor.

[0036] Shorting the branches of the inverter 1 when the stop position is reached therefore leads to a lower degree of current peaks due to the reduced rotational speed (compared to the nominal rotational speed of the electric motor 3).

[0037] According to the second embodiment, the stop sensor 13 is not corrected and indicates the stop position. The first predetermined position is then determined from the position of the rotor deduced from the electromotive force and the gear reduction ratio of the gear reducer.

[0038] In fact, as indicated above, the position of one or more wiper arms is determined so that the rotation speed of the electric motor is sufficient, in other words the minimum threshold value S min can be deduced from the rotor position, which is determined from the electromotive force, if

[0039] However, since the determination of the rotor position is the result of a measurement of the relative position, it is necessary to use the stop sensor 13 in order to have a position reference. All forms of sensorless control, for example the measurement of the electromotive force, make it possible to estimate the position of the wiper arm between two positions of the wiper arm or arms. This makes it possible to determine the position of the arm just before it reaches the stop position, in particular to reach a first predetermined position, for example located 5° before the stop position. The speed is then reduced to a predetermined rotation speed V1 when the estimated position corresponds to the first predetermined position. Then, when the stop position given by the stop sensor 13 is reached (at speed V1), the branches B1, B2, B3 of the inverter 1 are short-circuited in order to stop the electric motor 3 in this stop position. As in the previous embodiment, the current peaks generated in the transistors 7 of the inverter 1 are reduced (compared to the peaks generated when a short circuit is created when the electric motor 13 is rotating at the nominal speed).

[0040] The various steps of the method for controlling the electric motor 3 of the wiper device described above will now be explained on the basis of figure 5. The invention relates more particularly to controlling the electric motor 3 when it is stopped, but the steps associated with the start-up and nominal operation of the electric motor 3 are also explained.

[0041] The first step 101 involves activating the wiper device 11. This activation corresponds, for example, to the initiation of a manual command by the user of the vehicle, which causes an activation signal to be sent to the control unit 18.

[0042] The second step 102 involves starting the electric motor 3. Following receipt of the start command, the control unit 18 for controlling the electric motor 3 applies a predefined sequence of pulse width modulated commands to the inverter 1. This step can be performed with or without knowledge of the position of the rotor of the electric motor 3.

[0043] A third step 103 involves stabilizing the rotational speed of the electric motor 3 at a nominal speed, which is equal to or exceeds a minimum threshold value S min This means that the pulse width modulation control to achieve this nominal speed is performed by the rotor position, which is determined from the electromotive forces measured in the branches of the inverter 1. The wiper device 1 may be equipped with several nominal speeds, typically two, so that the user can vary the nominal speed over time if required. The electric motor 3 is regulated in all cases using the electromotive forces measured in the branches B1, B2, B3 of the inverter 1.

[0044] A fourth step 104 involves the command to stop the wiper device 1. This command corresponds, for example, to a manual command from the user, causing a stop signal to be sent to the control unit 18.

[0045] A fifth step 105 involves decelerating the rotational speed of the electric motor 3 to a predefined rotational speed. This deceleration is carried out when the wiper device 1 is in a predefined position, for example 5° before the stop position.

[0046] According to a first embodiment, this position is given by a stop sensor 13, which is modified to detect this predetermined position, in other words the deceleration position.

[0047] According to a second embodiment, this position is determined from the rotor position estimated by the electromotive forces measured in branches B1, B2, B3 of the inverter 1, the gear reduction ratio of the gear reducer and the previous signal from the stop sensor 13.

[0048] The rotational speed deceleration can be linear or incremental (a first speed deceleration is applied between the -15° and -10° positions (before the stop position corresponding to the 0° reference position), then a second speed deceleration is applied between the -10° and -5° positions). Non-linear deceleration can also be applied.

[0049] A sixth step 106 involves stopping the electric motor 3 at the stop position by short-circuiting the branches B1, B2, B3 of the inverter 1 once the stop position has been reached.

[0050] According to a first embodiment, the reaching of the stop position is determined from the rotor position estimated by the electromotive forces measured in branches B1, B2, B3 of the inverter 1, the gear reduction ratio of the gear reducer and the previous signal from the stop sensor 13 corresponding to the 5° position.

[0051] According to a second embodiment, the stop position is given by the stop sensor 13. A short circuit of the branches B1, B2, B3 of the inverter 1 leads to a very rapid stop of the electric motor 3 and therefore corresponds to a stop of the wiper device 11 in the stop position. In addition, the reduced speed before the short circuit reduces the current peaks generated in the transistors 7 of the inverter 1, thereby making it possible to avoid the use of oversized transistors 7 and thus limit the costs of the inverter 1.

[0052] The above-described management of the stopping of the electric motor 3 of the wiper device 11 thus makes it possible to use in such a device a brushless and sensorless DC electric motor 3 while at the same time using transistors 7 of limited capacity and therefore of limited cost. The overall cost of the wiper device 11 can thus be reduced while still maintaining the same operating quality for the user (stopping the wiper arms in the stop position).

Claims

1. A method for controlling a brushless and sensorless DC electric motor (3) for automotive applications, said electric motor (3) having a rotor and phases (A, B, C) powered by pulse width modulation applied to an inverter (1) for supplying power to said electric motor (3), said method comprising: determining a minimum threshold (S) for the rotational speed of said rotor; ｍｉｎ ), the position of the rotor is determined from measurements of the electromotive forces in the phases (A, B, C) of the electric motor (3), When a command (104) is given to stop the electric motor (3), the rotational speed of the rotor is adjusted to the minimum threshold (S ｍｉｎ ) and the minimum threshold value (S ｍｉｎ ) within an interval between the nominal speed and a given rotational speed (V １ ) (105), and then the electric motor (3) is stopped (106) at a predetermined position by short-circuiting the branches (A, B, C) of the inverter (1) when the predetermined position is reached. the electric motor (3) is coupled with a gear reduction device to form a geared motor (10) configured to drive a wiper device (11) comprising at least one wiper arm, the wiper device (11) comprising a stop sensor (13) associated with a stop position of the wiper arm, the stop sensor (13) having a circular portion, a conductive track having an appendage extending outwardly from a portion of the circular portion, a wheel of non-conductive material surrounding the circular portion, a first contact that contacts the circular portion during rotation of the rotor, and a second contact that contacts either the wheel or the appendage depending on the rotational position of the rotor; 4. A method of controlling a sensor, comprising: detecting the predetermined position by measuring an electrical resistance between the first contact and the second contact.

2. The predetermined rotation speed (V １ 2. The method of claim 1, wherein the reduction (104) of the rotational speed of the rotor to 1 / 2 comprises a number of increments with different reductions in the rotational speed of the electric motor (3).

3. 3. A control method as claimed in claim 1 or 2, wherein the predetermined position is given by the stop sensor (13), and an output signal from the stop sensor (13) is used to determine the time at which the rotational speed of the rotor should be reduced.

4. 4. A control method according to claim 3, wherein the stop sensor (13) is modified to define a deceleration position at which the rotational speed of the electric motor (3) should be decelerated to enable the wiper device (11) to be stopped at the stop position.

5. The position of the wiper arm is such that the rotational speed of the rotor is equal to or exceeds the minimum threshold value (S ｍｉｎ 5. The method according to claim 3, wherein the rotational speed of the rotor is inferred from the position of the rotor determined by the electromotive force and from the gear reduction ratio of the gear reduction device when the rotational speed of the rotor exceeds the rotational speed of the gear device.

6. A geared motor (10) for driving an automobile wiper device (11) comprising a gear reduction gear and a brushless and sensorless DC electric motor (3), the electric motor (3) comprising a rotor, a control unit (18) and phases (A, B, C) powered by pulse width modulation applied to an inverter (1) of the electric motor (3), the control unit (18) determining a minimum threshold (S) for the rotational speed of the rotor. ｍｉｎ ) is exceeded, the control unit (18) is adapted to determine the position of the rotor from measurements of the electromotive forces in the phases (A, B, C) of the electric motor (3), and when a command is given to stop the electric motor (3), the control unit (18) adjusts the pulse width modulation to the minimum threshold value (S ｍｉｎ ) and the minimum threshold value (S ｍｉｎ ) within an interval between the nominal speed and a given rotational speed (V １ ), and then, when a predetermined position is reached, the electric motor (3) is stopped at the predetermined position by short-circuiting the branches (B1, B2, B3) of the inverter (1); The electric motor (3) is coupled with the gear reduction device to form the geared motor (10) configured to drive a wiper device (11) comprising at least one wiper arm, the wiper device (11) comprising a stop sensor (13) associated with a stop position of the wiper arm, the stop sensor (13) having a circular portion, a conductive track having an appendage extending outwardly from a portion of the circular portion, a wheel of non-conductive material surrounding the circular portion, a first contactor contacting the circular portion during rotation of the rotor, and a second contactor contacting either the wheel or the appendage depending on the rotational position of the rotor; A geared motor (10) characterized in that the predetermined position is detected by measuring an electrical resistance between the first contact and the second contact.

7. 7. A geared motor (10) as claimed in claim 6, wherein the predetermined position is given by a stop sensor (13) associated with a stop position of the wiper device (11), and the control unit (18) is configured to use an output signal from the stop sensor (13) to determine the time at which the rotational speed of the rotor should be reduced.

8. 8. The geared motor (10) according to claim 7, wherein the stop sensor (13) is modified to define a deceleration position at which the rotational speed of the electric motor (3) should be decelerated to enable the wiper device (11) to be stopped at the stop position.

9. The control unit (18) determines whether the rotational speed of the rotor exceeds the minimum threshold value (S ｍｉｎ 9. The geared motor (10) according to claim 7 or 8, configured to infer the position of the wiper arm from the position of the rotor determined by the electromotive force and from the gear reduction ratio of the gear reduction device when the electromotive force exceeds a predetermined value.

10. A windshield wiper device (11) for a motor vehicle, comprising a geared motor (10) according to one of claims 6 to 9.

Images