Electromechanical actuator

Abstract

Electromechanical actuator for operating an electromechanical brake, preferably in a motor vehicle, having at least one structural element with an ohmic resistance which heats up in operation. The electromechanical actuator has a rotary shaft on which a fan wheel is arranged or is driven by the rotary shaft. The fan blades of the fan wheel ventilate and cool the heat-generating structural element of the electromechanical actuator. The fan wheel is fixedly or movably arranged on the rotary shaft. The function of the fan wheel can be reversed so that hot air can heat up a cold transmission.

Description

Technical Field

[0001] This invention relates to an electromechanical actuator for operating an electromechanical brake, preferably for use in motor vehicles, particularly passenger cars. Furthermore, this invention relates to an electromechanical brake having an actuator according to the invention, and a method for operating the electromechanical brake. Background Technology

[0002] As an alternative to known hydraulically operated wheel brakes, electromechanical actuators (EMBs) are also disclosed in the prior art, for example, as known from DE 199 16 955 A1. Here, an electromechanical actuator (EMB actuator or actuator mechanism) moves or presses brake pads, preferably a pair of brake pads or similar components, onto the brake disc, thereby applying braking force to the rotating brake disc. This braking force reduces the movement of the brake disc and thus the wheel, or brings it to full braking.

[0003] One problem with using this type of EMB actuator is that it generates heat during operation. For example, the actuation current needs to be regulated and flows through the coil, where the regulating device (e.g., the inverter) and the coil itself have resistance, which causes the corresponding components to heat up. However, the increased temperature can lead to component melting, increased resistance (e.g., increased resistance of the coil), and demagnetization.

[0004] An attempt has been made to compensate for the temperature rise or subsequent cooling of the brake disc in an EMB brake by estimating the cooling of the braking elements based on a cooling model, for example, see WO 2024165415 A1. However, this method is complex to implement, and it targets the heat generation of the EMB brake itself, not the EMB actuator. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned defects of this type of EMB actuator and the EMB brake operated thereby in the prior art.

[0006] The electromechanical actuator according to the invention has at least one heating or heat-generating structural element with ohmic resistance, particularly a coil or electronic control circuit. Furthermore, the electromechanical actuator includes at least one rotating shaft; preferably, the electromechanical actuator also includes an electric motor, the rotor of which is mounted on the rotating shaft.

[0007] A key element of this invention is a rotatable fan element, preferably a fan impeller, whose rotation axis extends coaxially with the axis of rotation. This fan element has at least one, and particularly multiple, air delivery elements, preferably fan blades, designed to blow air onto or ventilate and / or cool at least one structural element of the electromechanical actuator that has an ohmic resistance. This enables effective cooling of the motor components of the EMB actuator (such as stator windings, permanent magnets, excitation windings, or brush assembly). The advantages of this invention include higher load capacity of the EMB actuator or EMB brake (especially during continuous operation or under anti-lock braking system functionality), thereby achieving a smaller size design and greater availability. Furthermore, it improves the cooling of the electric motor and its controller, and provides possibilities for thermal management within the EMB actuator. Finally, this invention can also be used to reduce fine dust throughout the brake.

[0008] As an alternative to the rotatable fan element being coaxially oriented with the rotating shaft, the fan element's rotational shaft can also advantageously extend parallel to the axial direction of the rotating shaft, or its rotational shaft can be mechanically coupled to the rotating shaft. It is also advantageous to provide additional force transmission interruption elements (such as a freewheel mechanism or clutch, for example in a corresponding gearbox), thereby enabling the fan element to operate continuously.

[0009] The fan impeller, which is arranged on the shaft in a manner that does not allow relative rotation, is disclosed in principle by DE 10 2012 211 080 A1. However, in this document, the fan impeller is associated with a wiper actuator, and its structural requirements are quite different from those of an electromechanical brake.

[0010] If the electromechanical actuator has an electric motor, an advantageous improvement of the invention provides that the electric motor is provided with a fan slot through which cooling air from a rotatable fan element flows to the element of the electric motor to be cooled.

[0011] The rotatable fan element can be a fan or a compressor, especially a radial or axial fan. In this case, it is advantageous that the fan impeller of the EMB actuator is connected to the rotating shaft or a shaft coupled to the rotating shaft (i.e., a second shaft, which is connected to the first shaft via a gearbox or similar component) in a form-fit or force-transmitting manner.

[0012] In an advantageous alternative embodiment, the fan impeller is not fixedly connected to the rotating shaft or a shaft coupled to the rotating shaft, wherein one of the aforementioned shafts has a drive mechanism designed to drive the fan impeller up to a predetermined rotational speed or a predetermined airflow intensity. That is, the fan impeller operates at a predetermined rotational speed (e.g., proportional to the shaft rotational speed); however, when the predetermined rotational speed is reached, decoupling is achieved, for example through a sliding or ratchet mechanism, thereby limiting the upper limit of the generated airflow.

[0013] In a preferred embodiment, the driving mechanism has a ratchet mechanism, which preferably has a wheel with asymmetrical, particularly axially oriented teeth and fixedly connected to the shaft, and a reset element (such as a spring or magnet), wherein the reset element presses the fan impeller onto the wheel connected to the shaft, wherein the fan impeller also has a ratchet, the teeth of which engage with the teeth of the wheel connected to the shaft.

[0014] In this embodiment, a reset element (e.g., a spring, magnet) is provided, which applies a residual force to keep the fan always pressed back into the ratchet. Furthermore, the lift generated by accelerating the air can be used to move the fan axially, thereby generating a force opposite to that of the reset element. Therefore, the shaft speed and the fan speed are no longer coupled, satisfying the relationship: 𝜔 轴 ≤ 𝜔 风扇 .

[0015] In one improved embodiment, a speed below the motor's maximum speed can generate sufficient lift in the fan to mechanically decouple the fan from the motor shaft. This allows airflow to pass through an upper limit constraint. This corresponds to a decreasing variant of the aforementioned implementation without flexible fan blades.

[0016] In another preferred embodiment of the invention, the electric motor of the EMB actuator is designed as an asynchronous motor. It is particularly advantageous to provide two mechanically decoupled rotating parts for the stator. One rotating part drives the EMB actuator, while the other rotating part carries the fan impeller.

[0017] An asynchronous motor has a stator with stator windings, in which polarity changes are generated by applying an alternating voltage. This produces a rotating magnetic field whose rotational speed depends on the frequency of the applied alternating voltage and the number of pole pairs. Typically, a three-phase alternating voltage from the power grid is used as the alternating voltage in the stator. This is generally not feasible in EMB actuators, so it is advantageous to use a DC / AC inverter. The rotating parts of the asynchronous motor can be designed in different ways; in an advantageous implementation, for cost savings, it is designed as a squirrel-cage rotor without sliding contacts. A voltage is induced in the rotor by the speed difference (slip) between the stator and the rotating parts and the resulting relative motion, thereby generating torque. Using only one stator also reduces the complexity of the motor and its corresponding electronic controller, thus reducing costs.

[0018] The present invention also relates to an electromechanical brake, which is preferably used in motor vehicles, especially passenger cars, having an electromechanical actuator of the type described above.

[0019] For such a brake, an advantageous improvement of the invention includes a mechanism for reversing the function of a rotatable fan element. In this reversal, the rotatable fan element draws in heated air from at least one structural element of the electromechanical actuator with an ohmic resistance and blows it into the transmission of the electromechanical brake to be heated; the mechanism for reversal is designed for this purpose. The electromechanical brake may include a transmission that may lock in a cold state, i.e., it is self-locking. This self-locking can be released by introducing hot air. In other words, this structural design of the invention enables an operating strategy in which the motor continuously operates in both forward and reverse directions within the fan operating range (without generating braking torque drive) at low temperatures and / or during vehicle startup, thereby generating heat. The hot airflow is blown directly into the transmission through the fan impeller, thereby warming the transmission and eliminating its self-locking. Here, the EMB brake may also include a housing that advantageously has one or more openings for air exchange, and / or one or more cooling ribs toward which the hot airflow generated by the reversibly operating fan impeller is blown.

[0020] The present invention also relates to a method for operating an electromechanical brake having an electromechanical actuator having a rotatable fan element, preferably a fan impeller, whose rotation axis extends coaxially with or parallel to the axial direction of the rotation axis, or whose rotation axis is mechanically coupled to the rotation axis, and the fan element having at least one, and in particular multiple, air delivery elements, preferably fan blades. This method comprises two alternative method steps:

[0021] - In the first operating mode, the rotatable fan element operates in such a way that it supplies air to, ventilates, and / or cools at least one structural element of the electromechanical actuator that has an ohmic resistance (which can generate heat). This is the "conventional" operating mode in which the EMB actuator and its structural elements are cooled.

[0022] - In the second operating mode, the rotatable fan element operates such that air heated by the electromechanical actuator's ohmic resistance-bearing structural element is blown into the transmission of the electromechanical brake to heat the transmission. This "reverse" operating mode corresponds to the aforementioned functional reversal of the rotatable fan element.

[0023] Other advantages, features and details of the invention will become apparent from the following detailed description of preferred embodiments of the invention and the accompanying drawings.

[0024] The features disclosed about the apparatus should also be regarded as those disclosed about the method, and vice versa.

[0025] The same elements or elements with the same function in the accompanying drawings are given the same reference numerals. Attached Figure Description

[0026] Figure 1 The main components of an electromechanical actuator (EMB actuator) are schematically shown.

[0027] Figure 2 A schematic cross-sectional view of the electric motor of the EMB actuator is shown.

[0028] Figure 3 It shows Figure 2 A perspective view of an electric motor.

[0029] Figure 4 The application of the fan impeller according to the present invention is illustrated schematically.

[0030] Figure 5 A ratchet mechanism for a freely rotating fan impeller is shown, with the teeth displayed in an unfolded form for better illustration.

[0031] Figure 6 A graph illustrating the shaft speed variation curve is shown.

[0032] Figure 7 The characteristic curves of the load torque as a function of speed for an asynchronous motor with two rotating parts (rotors) are shown, and

[0033] Figure 8 A schematic diagram of the structural components of the EMB brake is shown when the fan impeller function is reversed. Detailed Implementation

[0034] Figure 1 An electromechanical (EMB) actuator 1 for an EMB brake in a motor vehicle, particularly a passenger car, is shown schematically. An electric motor 2 (of which four are provided, but only one is shown) drives a transmission 3, which in turn acts on brake pads 5a and 5b via a ball recirculating screw 4. The brake pads 5a and 5b are arranged on and act on opposite sides of a brake disc 6. The force transmission path can also advantageously be interrupted via a freewheel mechanism or clutch in a manner described later.

[0035] EMB actuators may also include, in a manner not shown, an inverter, a control unit (“Electronic Control Unit” ECU), and / or sensing mechanisms, such as one or more current sensors, EMB position sensors, or wheel speed sensors. Such actuators are often referred to as “smart actuators.”

[0036] In electromechanical actuators, electric motors are typically used as energy converters. The maximum temperature of an electric motor is limited. However, electric motors generate heat during operation. This is because the actuation current needs to be regulated and flows through coils, where the regulation / control unit (e.g., an inverter) and the coils themselves have resistance, causing the corresponding components to heat up. Since increased temperature can cause components to melt, increase resistance (e.g., increased coil resistance), and demagnetize, limiting its temperature is important.

[0037] According to Figure 2 In the schematic cross-sectional view of the electric motor 2 of the EMB actuator, the rotor 7 (magnet) and stator 8 (excitation coil) can be seen. Reference numeral 9 indicates the shaft leading to the transmission 3, and reference numeral 10 indicates the ventilation slot.

[0038] Figure 3 A similar view is shown, but in perspective. Reference numeral 2 indicates the electric motor, and reference numeral 9 indicates the rotation axis. The direction of rotation is indicated by reference numeral 11.

[0039] and Figure 3 compared to, Figure 4 The structure shown is equipped with a fan impeller 12 designed and installed according to the present invention. Figure 4 In the illustrated embodiment, the fan impeller 12 is connected to the rotating shaft 9 via a force-transmitting connection or a form-fit connection. Other mounting methods may also be used, such as mounting it on a shaft parallel to shaft 9. The fan impeller may also be mounted such that its rotational shaft is mechanically coupled to the rotating shaft 9, for example, through a suitable gearbox or transmission stage (not shown in the figure). The fan impeller may also operate freely in the manner described later.

[0040] As previously mentioned, the force transmission path in the transmission (not shown in the figures) can also be advantageously interrupted, particularly through a freewheel mechanism or clutch. This allows the electric motor and fan / fan impeller to rotate continuously, resulting in a continuous cooling effect even when the braking elements themselves are not currently operated (e.g., because they are in the final stop). In other words, in this embodiment with a disconnectable transmission, the fan is not always coupled to the load, i.e., the brake pads or brake disc, and therefore, unlike other embodiments of the invention, the fan can operate without time constraints even when the brake pads or brake disc are not currently being adjusted.

[0041] In the illustrated embodiment, the fan impeller 12 blows cool air axially to the electric motor 2, thereby cooling structural components that generate heat due to their ohmic resistance, such as coils, windings, (not shown) brush devices, or modules of control circuitry.

[0042] Figure 4The right side shows a perspective view of the fan impeller 12. It is related to... Figure 4 The left half shows the same structural element. The fan blades are clearly visible.

[0043] Figure 5 An embodiment in which the fan impeller rotates freely on the shaft is shown. For simplicity, the teeth of the ratchet mechanism are drawn disengaged here. Reference numeral 13 here indicates the portion of the ratchet mechanism fixedly connected to the rotating shaft, while a second portion 14 of the ratchet mechanism is fixedly connected to the fan impeller. A reset element, such as spring 15 shown here, applies residual force and presses the fan impeller back into the ratchet mechanism. The air motion / acceleration indicated by arrows 16a-16d can be used to move the fan impeller axially in the directions of arrows 17a, 17b, thereby generating a force opposite to that of the reset element. The rotational speeds of the shaft and the fan impeller are thus no longer coupled, as from Figure 6 As can be seen from it. In Figure 6 The horizontal axis represents time, and the vertical axis represents rotational speed. Label 18 indicates the shaft rotational speed, and label 19 indicates the fan impeller rotational speed. It can be seen that from time t1 onwards, the fan rotational speed no longer follows the shaft rotational speed.

[0044] If the electric motor of the EMB actuator is an asynchronous motor, it is also possible to achieve the effect of the fan impeller rotating even when the EMB drive is stationary. For this purpose, two rotating parts can be used for a single stator (one for the EMB drive and one for the fan impeller). The two rotating parts are mechanically decoupled. Using only a single stator reduces the complexity and cost of the motor and ECU.

[0045] An asynchronous motor has a stator with stator windings, in which a polarity reversal is generated by an applied AC voltage. This produces a so-called rotating magnetic field, the speed of which depends on the frequency of the applied AC voltage and the number of pole pairs. Typically, a three-phase AC voltage from the power grid is used as the AC voltage in the stator. This is generally not feasible in EMB actuators, so a DC / AC converter is advantageous. The rotating component of the asynchronous motor can have various designs, but in a preferred embodiment, a squirrel-cage rotor without slip contacts is used for cost savings. A voltage is induced in the rotating component by the speed difference (slip) between the stator and the rotating component, and the resulting relative motion, thereby generating torque.

[0046] Figure 7The figure shows the speed-torque characteristic curve of the asynchronous motor in this embodiment. Reference numeral 20 indicates the relationship between the load torque of the asynchronous motor and the speed, and reference numeral 21 indicates the relationship between the load torque of the fan impeller and the speed. The speed (horizontal axis) is limited by the speed of the rotating magnetic field. This characteristic curve can be modified accordingly if a DC / AC converter with a frequency converter (and, if necessary, variable current and voltage regulation devices) is used. It is evident that even if the asynchronous motor operates more slowly or is stationary, the fan impeller continues to rotate and cool the heat-generating components of the electromechanical actuator. Specifically:

[0047] The load torque of the EMB drive can fluctuate over a wide range, while the fan load torque can be set to a fixed characteristic curve. The slip and speed of the two rotating parts can differ. In extreme cases, the EMB drive speed is zero, and the fan speed is positive. This generates airflow during continuous braking or parking. This can be advantageously used for cooling during braking or for preheating during parking.

[0048] The torque distribution between the EMB driver and the fan depends on both their respective slip rates and the set distribution, which is particularly affected by the effective length of the rotating parts and their windings. Different distributions can also be achieved by varying the frequency of the stator voltage.

[0049] This invention can also be implemented in conjunction with an operating strategy. The purpose of this operating strategy is to heat the cold, and therefore self-locking (or stuck), transmission of the EMB, thereby releasing it from self-lock. This operating strategy can be achieved by continuously reversing the electric motor in both directions within the fan's operating range (without braking torque drive) at low temperatures and / or during vehicle startup, thus generating heat. The hot airflow is then blown directly into the transmission through the fan impeller, thereby warming the transmission and eliminating its self-lock.

[0050] This application, combined with the functional reversal of the fan impeller, is in... Figure 8 As shown in the diagram. At this time, the fan impeller 12 draws in heated air (arrow 23) from the components of the electric motor 2, thereby heating the (still cold and therefore self-locking) transmission 22.

[0051] The EMB brake can be installed in a housing that advantageously has openings to allow for air exchange.

[0052] Cooling fins can also be installed in areas of the housing that are impacted by the "hot" airflow generated by the fan.

[0053] Finally, the fan impeller can also be used to employ active airflow for exhausting drum brakes. This exhaust can be combined with a filter to reduce fine dust. This is particularly advantageous when combined with a second fan impeller, which is specifically positioned outside the housing wall. This application is also found in… Figure 8 As shown in the diagram, the airflow 24 from the drum brake passes through the filter cartridge 25, then through the fan cylinder 26, and then exits from the housing in the direction of arrow 27. The fan cylinder 26 is driven here by the rotating shaft 9 of the fan impeller.

Claims

1. An electromechanical actuator (1) for operating an electromechanical brake, wherein the electromechanical actuator is preferably used in motor vehicles, particularly in passenger cars, wherein, The electromechanical actuator (1) has at least one heating or heat-generating structural element with an ohmic resistance, particularly a coil or electronic control circuit. The electromechanical actuator (1) has at least one rotating shaft (9) and preferably includes an electric motor (2), the rotor (7) of which is mounted on the rotating shaft (9). The feature is that it is provided with a rotatable fan element, preferably a fan impeller (12), whose rotation axis extends coaxially or parallel to the axial direction of the rotation axis (9), or whose rotation axis is mechanically coupled to the rotation axis (9), and the fan element has at least one, especially multiple, air delivery elements, preferably fan blades, which are designed to supply air or ventilation and / or cool at least one structural element of the electromechanical actuator (1) with ohmic resistance.

2. The electromechanical actuator (1) according to claim 1, wherein, The electromechanical actuator (1) has an electric motor (2), characterized in that the electric motor (2) is provided with a fan slot (10) through which cooling air from a rotatable fan element flows to the element to be cooled in the electric motor (2), such as a stator winding (8), one or more permanent magnets, one or more excitation windings or the brush assembly of the electric motor.

3. The electromechanical actuator (1) according to claim 1 or 2, wherein, Rotating fan components are fans or compressors, especially radial or axial fans.

4. The electromechanical actuator (1) according to claim 3, wherein the electromechanical actuator has a fan impeller, wherein, The fan impeller is shaped to fit or force-transmittingly connected to the rotating shaft (9) or a shaft coupled to the rotating shaft (9), and is preferably connected to an additional force transmission interruption element, such as a freewheel mechanism or a clutch.

5. The electromechanical actuator (1) according to claim 3, wherein the electromechanical actuator has a fan impeller, wherein, The fan impeller is not fixedly connected to the rotating shaft (9) or a shaft coupled to the rotating shaft (9), wherein one of the shafts has a drive mechanism designed to drive the fan impeller up to a predetermined rotational speed or a predetermined airflow intensity of the shaft.

6. The electromechanical actuator (1) according to claim 5, wherein, The drive mechanism has a ratchet mechanism (13, 14), preferably with an asymmetrical, particularly axially oriented toothed wheel (13) fixedly connected to the shaft, and a reset element, such as a spring or magnet, which presses the fan impeller onto the wheel (13) connected to the shaft. The fan impeller also has a ratchet (14) whose teeth engage with the teeth of the wheel (13) connected to the shaft.

7. The electromechanical actuator (1) according to at least one of the preceding claims, the electromechanical actuator having an electric motor (2) designed as an asynchronous motor, characterized in that, It has two mechanically uncoupled rotating parts, preferably a squirrel-cage rotor, one of which carries a fan impeller (12).

8. An electromechanical brake, preferably used in motor vehicles, especially passenger cars, the electromechanical brake having an electromechanical actuator (1) according to at least one of the preceding claims.

9. The electromechanical brake according to claim 8, characterized in that, The mechanism has a function reversal mechanism for a rotatable fan element, which is designed to draw in hot air from at least one structural element with an ohmic resistance of the electromechanical actuator (1) and blow it into the heated transmission (22) of the electromechanical brake when the function is reversed. Preferably, the mechanism also has a housing with one or more openings and / or one or more cooling ribs.

10. A method for operating an electromechanical brake, the electromechanical brake having an electromechanical actuator (1) having a rotatable fan element, preferably a fan impeller (12), whose rotation axis extends coaxially or parallel to the axial direction of a rotation shaft (9), or whose rotation axis is mechanically coupled to the rotation shaft (9), and the fan element having at least one, particularly multiple, air delivery elements, preferably fan blades. Its features are, It has two execution methods, namely: - In the first operating mode, the rotatable fan element operates in such a way that it supplies air or ventilation and / or cooling to at least one structural element of the electromechanical actuator (1) that has an ohmic resistance, and - In the second operating mode, the rotatable fan element operates in such a way that air heated by the structural element with ohmic resistance of the electromechanical actuator (1) is blown into the transmission (22) of the electromechanical brake to heat the transmission.

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