DE102021200754A1 - Electric drive device for a vehicle and method for operating an electric drive device - Google Patents

Abstract

The present invention creates an electric drive device (10) for a vehicle (F), comprising an electric machine (EM); a drive shaft (AW) which is connected to the electric machine (EM) and through which the electric machine (EM) can be connected to at least one drive wheel of the vehicle (F); an eddy current brake (WB) which is arranged on the drive shaft (AW); and a control device (SE), which is connected to the electrical machine (EM) and to the eddy current brake (WB), and with which a first braking torque (B1) of the electrical machine ( EM) can be supplemented by a second braking torque (B2) from the eddy current brake (WB).

Description

The present invention relates to an electric drive device for a vehicle and a method for operating an electric drive device.

State of the art

In eddy current brakes, a rotor and an associated stator are usually used, with eddy currents being able to be generated in the rotor by its rotation, which can then generate a braking torque.

Eddy current brakes usually have a stator with an excitation coil, in which case eddy currents can then flow in the rotor and kinetic energy can thus be converted into heat in the rotor. The eddy currents are induced in the conductor, which in turn can generate their own induction voltages, which oppose the external magnetic field according to Lenz's law, and consequently their own magnetic fields, which can ultimately slow down the movement of the conductor material.

Traditionally, there can be two different components for traction and braking in vehicles, such as an electric machine and a brake as separate elements. In addition to the drive, the electric machine can also be used for recuperation and thus for braking. In the event that the electric machine is used at speeds which are greater than the corner speed of the machine, this machine can then have a lower maximum torque, in which case the full torque is not available as braking torque over the entire speed range.

the DE 10 2014 210 444 A1 describes an electric vehicle with a retarder mechanically connected to a wheel.

Disclosure of Invention

The present invention provides an electric drive device for a vehicle according to claim 1 and a method for operating an electric drive device according to claim 9.

Preferred developments are the subject of the dependent claims.

Advantages of the Invention

The idea on which the present invention is based is to specify an electric drive device for a vehicle and a method for operating an electric drive device, wherein the electric machine can be supported by an eddy current brake when operating above a cut-off speed when providing a braking torque on the vehicle, in order to thereby to be able to generate such a total braking torque as corresponds to the maximum braking torque of the electrical machine below the cut-off speed.

According to the invention, the electric drive device for a vehicle comprises an electric machine; a drive shaft which is connected to the electric machine and through which the electric machine can be connected to at least one drive wheel of the vehicle; an eddy current brake arranged on the drive shaft; and a control device which is connected to the electric machine and to the eddy current brake and with which a first braking torque of the electric machine can be supplemented by a second braking torque from the eddy current brake in a speed range of the electric machine above a corner speed.

The drive shaft can extend through the electric machine, for example from a second side, on which a gearbox can be arranged on the drive shaft, to the first side, which can face away from the gearbox. On the first side, the drive shaft can also extend beyond the electric machine by a predetermined distance, on which the eddy current brake can then be arranged. In this case, the eddy current brake can comprise a rotor which can be connected in a rotationally fixed manner to the axis of rotation and can rotate with it. The electrical machine can be connected to at least one wheel via the second side and the transmission.

The eddy current brake can advantageously be designed and dimensioned in such a way that it can generate the difference between the possible and the maximum value of the braking torque in that speed range in which the electric machine cannot provide the maximum braking torque. The "possible" braking torque is the braking torque that can be generated by the machine at the current speed or less than this. In the area above the cut-off speed, this is lower than the maximum braking torque (from recuperation), with the possible braking torque below and at the cut-off speed also being the maximum (maximum value) braking torque of the electrical machine, or less. The maximum value of the braking torque of the electric machine can be that braking torque which the electric machine can generate maximum below and at the corner speed. Above the corner speed, the braking torque of the machine that is possible at this speed must be supplemented in order to be able to generate a total braking torque equal to the maximum value. This difference can be generated (compensated) by an eddy current brake.

In this way, it is possible to use a combination of an electric machine and a very small, compact eddy current brake to call up the full braking torque over the entire speed range at or above the maximum value of the braking torque of the electric machine.

The torque of the electrical machine that can be generated for braking below the cut-off speed can also be lower than the situation-related braking torque requires.

Furthermore, the eddy current brake can generate a braking torque even at lower speeds than the cut-off speed and supplement the braking torque from the electrical machine.

It is also conceivable that the eddy current brake can be designed to be larger than is necessary to generate the maximum total braking torque, in order to still have sufficient braking torque available in the event of a fault in the electric machine, with the sufficient amount being able to be based on the respective torque situation and evaluated adaptively can be or in advance during the manufacture of the eddy current brake. Such a design can be independent of the gap in field weakening operation.

With the electric drive device according to the invention, an eddy current brake can be placed on the shaft of the electric machine and used in combination with the electric machine as the sole brake on the axle, thus replacing the hydraulic brake.

According to a preferred embodiment of the electric drive device, the drive shaft extends beyond the electric machine on a first side thereof, which faces away from a transmission and the eddy current brake is arranged on the drive shaft on this first side.

Due to the arrangement on the first side, the eddy current brake can advantageously be easily exchanged or at least easily mountable, for example mountable as a module on the drive shaft. Cooling of the eddy current brake can also be implemented easily from the first side, for example in combination with a cooling device for the electrical machine.

According to a preferred embodiment of the electric drive device, the eddy current brake comprises a rotor which is connected to the drive shaft in a rotationally fixed manner and comprises cast iron.

The rotor can be formed entirely of cast iron.

According to a preferred embodiment of the electric drive device, the eddy current brake includes a rotor, which includes a coating that forms a surface of the rotor.

The coating can form all surfaces of the rotor.

According to a preferred embodiment of the electric drive device, the coating comprises copper and/or aluminum.

According to a preferred embodiment of the electric drive device, an electrical conductivity and/or a thermal expansion coefficient of the coating corresponds, within a tolerance range, to those electrical conductivities and/or the thermal expansion coefficient of the rotor.

The braking torque (torque for braking), which the eddy current brake can generate, can mainly depend on the speed and the material of the rotor, in addition to the geometric dimensions. The speed at which the eddy-current brake can generate its maximum braking torque can therefore be influenced by selecting suitable material properties, for example for their electrical and magnetic conductivity. Since the electrical and magnetic properties of the eddy current brake usually cannot be combined arbitrarily, the rotor can advantageously be made of cast iron with good magnetic properties and a coating of a material such as copper or aluminum with an electrical conductivity that matches the cast iron. Furthermore, it can be taken into account that similar coefficients of thermal expansion of the composite structure made of cast iron and conductive layer can be present in order to prevent or at least reduce mechanical detachment of the coating from the rotor due to different expansions during the high temperature rises occurring during operation. "Similar" can then be understood to mean that the material is different from the conductive gen layer does not peel off with high temperature fluctuations.

A combination of iron with another material (on the rotor) is possible to combine the advantages of the iron (magnetic conductivity) and the other metal (e.g. copper with good electrical conductivity). As a result, a low magnetic resistance can be achieved using iron and the electrical conductivity in the surface of the rotor can be selected using the other metal in such a way that the maximum speed is at the desired point (the better the surface of the rotor conducts, the lower the speed, where the torque is maximum). Furthermore, the aim can be to turn it so high that cast iron can be the right material and thus a composite of two materials can be dispensed with.

According to a preferred embodiment of the electric drive device, the corner speed is between 4000 and 6000 revolutions per minute.

According to a preferred embodiment of the electric drive device, a sum of the first braking torque and the second braking torque corresponds to a maximum braking torque that can be generated by the electric machine, which can be achieved by the electric machine below the corner speed.

The maximum braking torque that can be generated is the already mentioned maximum value of the braking torque that can be achieved below and at the corner speed. However, this maximum braking torque that can be generated can also be higher or lower, depending on the vehicle and the requirement.

According to the invention, in the method for operating an electric drive device, an electric drive device according to the invention is provided; determining whether a speed of the electric machine exceeds a corner speed; and generating a first braking torque by the electric machine and a second braking torque by the eddy current brake, wherein the first braking torque is supplemented by the second braking torque to form a total braking torque.

It can be assumed that the electric machine can generate the maximum value of the braking torque itself below and at the cut-off speed and that above the cut-off speed the braking torque that the electric machine can generate is lower than the maximum value, this has already been referred to as the possible braking torque . If it is determined that the electric machine is being operated above the corner speed, the eddy current brake can also be used to generate the total braking torque on the vehicle in order to be able to advantageously reach the maximum value. In the event of emergency braking, the eddy current brake can also be supplied with maximum current and thus deliver its maximum torque and the electric machine can take over the dynamics, ie regulation/control of the total torque required.

According to a preferred embodiment of the method, a maximum value of the first braking torque is determined below the cut-off speed of the electric machine and if the electric machine is operated above the cut-off speed, the current first braking torque is determined and the eddy-current brake is operated in such a way that above the cut-off speed there is a difference between the current first braking torque and the maximum value of the first braking torque is compensated by the second braking torque.

However, this step of supplementing the braking torques can also take place below and/or at the corner speed.

The method can advantageously also be characterized by the features of the electric drive device already mentioned, and vice versa.

Further features and advantages of embodiments of the invention result from the following description with reference to the accompanying drawings.

character list

The present invention is explained in more detail below with reference to the exemplary embodiments given in the schematic figures of the drawing.

• 1 eine schematische Darstellung einer elektrischen Antriebseinrichtung für ein Fahrzeug gemäß einem Ausführungsbeispiel der vorliegenden Erfindung;
• 2 eine schematische Darstellung einer Abhängigkeit des Bremsmoments an der elektrischen Antriebseinrichtung von der Drehzahl der elektrische Maschine;
• 3 eine Blockdarstellung von Verfahrensschritten eines Verfahrens zum Betreiben einer elektrischen Antriebseinrichtung gemäß einem Ausführungsbeispiel der vorliegenden Erfindung.

Show it:

• 1 a schematic representation of an electric drive device for a vehicle according to an embodiment of the present invention;
• 2 a schematic representation of a dependence of the braking torque on the electric drive device on the speed of the electric machine;
• 3 a block diagram of method steps of a method for operating an electric drive device according to an embodiment of the present invention.

In the figures, the same reference symbols designate the same elements or elements with the same function.

1 shows a schematic representation of an electric drive device for a vehicle according to an embodiment of the present invention.

The electric drive device 10 for a vehicle F includes an electric machine EM; a drive shaft AW, which is connected to the electric machine EM and through which the electric machine EM can be connected to at least one drive wheel of the vehicle F; an eddy current brake WB arranged on the drive shaft AW; and a control device SE, which is connected to the electric machine EM and to the eddy-current brake WB, can be arranged in a housing of the electric machine, for example, and with which a first braking torque of the electric machine EM is applied in a speed range of the electric machine EM above a corner speed can be supplemented by a second braking torque from the eddy current brake WB.

The drive shaft AW can extend beyond this on a first side A1 of the electric machine EM, which can face away from a transmission GT and the eddy current brake WB can be arranged on the drive shaft AW on this first side A1.

By placing the eddy current brake WB on the first side A1, which can be a high-speed transmission side, and dividing the total braking torque between the electric machine EM and the eddy current brake WB, the eddy current brake WB can be shaped in such a way that it can be very small, light and can be built with simple components and materials.

Alternatively (not shown), the eddy current brake can also be arranged between the transmission and the electric machine, or in such a way that the drive shaft goes through the transmission and the eddy current brake sits on the opposite side of the transmission from the machine.

The speed level allows using a simple cast iron rotor. However, another material with electrically and magnetically similar properties can also be used.

An eddy current brake can have a speed-dependent braking torque, which can decrease towards low speeds and can be zero at standstill. Since the braking torque in electrical machines can decrease at high speeds, the electrical machine and the eddy current brake can advantageously complement each other perfectly in order to be able to generate a required total braking torque, approximately the maximum value of the braking torque.

2 shows a schematic representation of a dependence of the braking torque on the electric drive device on the speed of the electric machine.

In the 2 shows a dependency of a torque of the electrical machine and the eddy current brake, which can each correspond to a total braking torque M, as a function of a speed D of the electrical machine and the eddy current brake. The upper figure shows the (maximum) first braking torque B1 of the electrical machine, which below and at the corner speed ED can reach a maximum value max of the braking torque, advantageously a constant. Above the base speed ED, the maximum (possible) first braking torque B1 can then fall asymptotically to the abscissa (zero value of the braking torque).

The bottom picture of the 2 shows a mirrored view of the image above, with the first braking torque B1 also being drawn in and it can correspond to that in the image above. In addition to this, the second braking torque B2 of the eddy current brake is also shown, which can supplement the first braking torque B1 in order to achieve approximately the maximum value max as the total braking torque.

Conventional traction drives can typically have a corner speed ED in the range of 4000-6000 rpm (revolutions per minute), from which they can no longer generate the full torque. The maximum speed can typically be between 10,000 and 20,000 rpm. For this speed range above the cut-off speed, cast iron is advantageously well suited as a rotor material with regard to both the magnetic and the electrical properties. This circumstance and the fact that the eddy current brake only has to apply a part of the total braking torque allows for a very simple and therefore inexpensive design.

The combination of the eddy current brake with the electrical machine can be a design designed for emergency braking (as a supplement to the electrical machine). Eddy-current brakes for the arrangement according to the invention, which need to ensure a braking torque only above the cut-off speed, can be compared to those over the entire speed space can be made significantly smaller and simpler, and can have a simpler and more robust thermal design.

The invention can be used for small and light electric vehicles to avoid a hydraulic brake on the rear axle.

According to the invention, a maximum value max of the first braking torque B1 can be determined below the corner speed of the electrical machine and if the electric machine is operated above the corner speed, the current first braking torque B1 can be determined and the eddy current brake can be operated in such a way that above the corner speed there is a difference between the current first braking torque B1 and the maximum value of the first braking torque B1 can be compensated for by the second braking torque B2.

the 2 also shows the second braking torque (not marked) that is already present below the base speed, which can increase parabolically from the origin. In general, it should also be mentioned that the maximum value max shows the possible value of the first braking torque, it is not absolutely necessary for this to always be generated below the cut-off speed.

the 3 shows a block diagram of method steps of a method for operating an electric drive device according to an embodiment of the present invention.

In the method for operating an electric drive device, an electric drive device according to the invention is provided S1; determining S2 whether a speed of the electric machine exceeds a corner speed; and generation S3 of a first braking torque by the electrical machine and a second braking torque by the eddy current brake, the first braking torque being supplemented by the second braking torque to form a total braking torque.

Although the present invention has been fully described above with reference to the preferred exemplary embodiment, it is not restricted thereto but can be modified in a variety of ways.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102014210444 A1 [0005]

Claims (10)

Electric drive device (10) for a vehicle (F), comprising: - an electric machine (EM); - A drive shaft (AW) which is connected to the electric machine (EM) and through which the electric machine (EM) can be connected to at least one drive wheel of the vehicle (F); - An eddy current brake (WB), which is arranged on the drive shaft (AW); and - A control device (SE), which is connected to the electrical machine (EM) and to the eddy current brake (WB), and with which a first braking torque (B1) of the electrical machine (B1) in a speed range of the electrical machine (EM) above a corner speed EM) can be supplemented by a second braking torque (B2) from the eddy current brake (WB). Electrical drive device (10) after claim 1 , in which the drive shaft (AW) on a first side (A1) of the electric machine (EM) extends beyond this, which is a gear (GT) facing away and on this first side (A1) the eddy current brake (WB) on the Drive shaft (AW) is arranged. Electrical drive device (10) after claim 1 or 2 , In which the eddy current brake (WB) comprises a rotor which is non-rotatably connected to the drive shaft (AW) and includes cast iron. Electric drive device (10) according to one of Claims 1 until 3 wherein the eddy current brake (WB) includes a rotor including a coating forming a surface of the rotor. Electrical drive device (10) after claim 4 , in which the coating comprises copper and/or aluminum. Electric drive device (10) according to one of Claims 4 or 5 , in which an electrical conductivity and/or a thermal expansion coefficient of the coating corresponds within a tolerance range to those electrical conductivities and/or the thermal expansion coefficient of the rotor. Electric drive device (10) according to one of Claims 1 until 6 , at which the corner speed is between 4000 and 6000 revolutions per minute. Electric drive device (10) according to one of Claims 1 until 7 , in which a sum of the first braking torque (B1) and second braking torque (B2) corresponds to a maximum braking torque that can be generated by the electric machine (EM), which can be achieved by the electric machine (EM) below the corner speed. Method for operating an electric drive device (10), comprising the steps: - Providing (S1) an electric drive device (10) according to one of Claims 1 until 8th ; - Determine (S2) whether a speed of the electric machine (EM) exceeds a corner speed; and - generating (S3) a first braking torque (B1) by the electric machine (EM) and a second braking torque (B2) by the eddy current brake (WB), the first braking torque (B1) being combined by the second braking torque (B2) to form a total braking torque is added. procedure after claim 9 , at which a maximum value of the first braking torque (B1) is determined below the cut-off speed of the electrical machine and when the electric machine is operated above the cut-off speed, the current first braking torque (B1) is determined and the eddy-current brake is operated in such a way that above the cut-off speed a Difference between the current first braking torque (B1) and the maximum value of the first braking torque (B1) is compensated by the second braking torque (B2).

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