Method for maximizing the drive torque available when starting an electric vehicle

Abstract

The invention relates to a method for maximizing the drive torque available when starting an electric vehicle, with an electric machine whose rotor is coupled to a drive train of the electric vehicle, wherein, with the rotor decoupled from the drive train, a target angular position of the rotor is set such that, after coupling the rotor to start the electric vehicle, the highest possible torque is provided.

Description

[0001] The invention relates to a method for maximizing the drive torque available when starting an electric vehicle.

[0002] The drive torque of an electric vehicle varies depending on the rotor position of an electric motor in the vehicle's powertrain at the time of acceleration. Therefore, an electric powertrain may not be able to deliver its maximum torque when the vehicle is stationary, depending on the rotor position of the electric motor.

[0003] For example, US 4532460 A describes an electric motor in an electric vehicle with a so-called "Pre-Start Rotor Positioner", which locks the rotor into a specific starting position in order to provide maximum torque at startup.

[0004] DE 10357504 A1 describes a device for determining the rotor position in an electric motor, comprising a detector arranged on the electric motor, sensitive to the rotor's passage through a reference position, and a phase-locked loop synchronizable to the detector's output signal, which provides an output signal representative of the rotor's position. The times of the rotor's passage through a reference position are recorded, and the oscillator's period is adjusted so that the reference passages occur at a predetermined oscillator phase. The rotor position is derived from the oscillator's oscillation between reference position passages.

[0005] German patent DE 10359713 A1 also describes a rotor position sensor arrangement and a method for detecting the rotor position of an electric motor. This involves using a sensor magnet with a plurality of sensor poles, which are arranged on the outer rotor of the electric motor.

[0006] One object of the invention is to provide an improved method for maximizing the drive torque available when starting an electric vehicle.

[0007] The aforementioned problem is solved using the features of an independent claim.

[0008] Favorable embodiments and advantages of the invention will become apparent from the further claims, the description and the drawing.

[0009] According to one aspect of the invention, a method for maximizing the drive torque available when starting an electric vehicle is proposed, with an electric machine whose rotor is coupled to a drive train of the electric vehicle, wherein, with the rotor decoupled from the drive train, a target angular position of the rotor is set such that, after coupling the rotor to start the electric vehicle, the highest possible torque is provided.

[0010] According to the proposed method, with the separating element to the drive train open, the rotor position is adjusted so that the electric machine can provide the highest possible torque. For this purpose, the position of the rotor, decoupled from the drive train, is shifted to an advantageous range.

[0011] This design is advantageous because it allows maximum torque to be achieved even at low engine speeds, for example, below 10 km / h, or from a standstill, even with an unfavorable rotor position after the vehicle has been switched off. This enables faster acceleration from a standstill. Starting on an incline with a trailer load is also made possible. Similarly, driving up to a curb is facilitated.

[0012] According to an advantageous embodiment of the method, to set the target angular position of the rotor, an initial angular position of the rotor can be determined and compared with a predefined characteristic map, which includes the dependence of the rotor's phase currents on its angular position. If the rotor's initial angular position is located in a region of the characteristic map where a maximum current cannot be achieved, the rotor's initial angular position can be adjusted to the target angular position such that the rotor's target angular position is located in a region of the characteristic map where the maximum current can be achieved. Advantageously, this allows the rotor position of the electric machine to be adjusted while the vehicle is stationary, enabling maximum torque during acceleration from a standstill.

[0013] According to an advantageous embodiment of the method, power modules of an inverter can be controlled to change the rotor's initial angular position, thereby generating a magnetic field in the rotor. This field modifies the rotor's initial angular position such that a maximum current can be achieved to meet a demand for drive torque. The rotor position can be adjusted using the electric vehicle's existing inverter to provide maximum drive torque on demand.

[0014] According to an advantageous embodiment of the method, the rotor of the electric machine can be coupled to the drive train via a separating element, wherein the rotor is decoupled from the drive train by means of the separating element. By decoupling the rotor from the drive train, the rotor position at standstill can be set such that a maximum drive torque can be provided on demand for starting from standstill.

[0015] According to an advantageous embodiment of the method, after the target angular position of the rotor has been set, the separating element to the drive train can close automatically. This allows maximum drive torque to be provided on demand for starting from a standstill.

[0016] According to an advantageous embodiment of the method, when the separating element is open, the target angular position of the rotor can be set after the vehicle has come to a standstill, if the initial angular position does not match the target angular position. By decoupling the rotor from the drive train, the rotor position can be set while the vehicle is stationary so that maximum drive torque can be provided on demand for starting from a standstill.

[0017] According to an advantageous embodiment of the method, when the separating element is closed and the vehicle is stationary, a check can be performed to determine whether the separating element has opened automatically or has been requested to open. This allows for a convenient decision as to whether, given increased availability, it is acceptable to wait for the separating element to open automatically, or whether, for example, the separating element must be opened on demand for a race start function or trailer detection.

[0018] According to an advantageous embodiment of the method, if the separating element opens automatically, and the initial angular position does not match the target angular position after the separating element has opened, the target angular position of the rotor can be set, and the separating element can close automatically. This allows the electric vehicle to be ready to deliver maximum drive torque when starting from a standstill.

[0019] According to an advantageous embodiment of the method, if the opening of the separating element is requested when the initial angular position does not match the target angular position, the rotor's angular position can be adjusted and the separating element closed as requested. This allows the electric vehicle to be ready to deliver maximum drive torque when starting from a standstill.

[0020] According to an advantageous embodiment of the method, the initial and target angular positions of the rotor can be determined using a rotor position sensor, in particular a resolver or a TMR sensor. The rotor position sensor can be located within the electric machine. For determining the angular position, a resolver, i.e., an electromagnetic transducer for converting the rotor's angular position into an electrical value, can be used, for example. Alternatively, tunnel magnetoresistance (TMR) sensors, which are based on a magnetoresistive effect used in magnetic tunnel contacts, can be employed.

[0021] Further advantages will become apparent from the following description of the drawings. The drawings illustrate an embodiment of the invention. The drawings, the description, and the claims contain numerous features in combination. A person skilled in the art will expediently consider the features individually and combine them into meaningful further combinations.

[0022] This shows: Fig. 1 a flowchart of a function for setting a drive torque according to the method of an embodiment of the invention; and Fig. 2 a flowchart of the method according to an embodiment of the invention.

[0023] In the figures, identical or similar components are numbered with the same reference symbols. The figures merely show examples and are not to be understood as limiting.

[0024] Fig. Figure 1 shows a flowchart of a function S100 for setting a drive torque according to the method of an embodiment of the invention.

[0025] The proposed method aims to maximize the available drive torque when starting an electric vehicle, using an electric machine whose rotor is coupled to the vehicle's drivetrain. With the rotor decoupled from the drivetrain, a target angular position is set such that, after the rotor is coupled to the drivetrain to start the electric vehicle, the highest possible torque is provided.

[0026] The S100 function allows the target angle position of the rotor to be adjusted when the electric vehicle is stationary.

[0027] The rotor of the electric machine is coupled to the drive train via a separating element, which can be used to decouple the rotor from the drive train. The separating element can be any type of coupling, such as a jaw coupling or a friction disc coupling.

[0028] In step S102, the separating element between the rotor of the electric machine and the drive train is opened.

[0029] In the next step S104, to set the target angular position of the rotor, an initial angular position of the rotor is determined and compared with a predefined characteristic map, which includes a dependence of phase currents of the rotor on an angular position of the rotor.

[0030] The rotor position sensor, which determines the angular position of the rotor, can be, for example, a resolver or a TMR sensor. In particular, the rotor position sensor can be located within the electric machine.

[0031] If the rotor's initial angular position is in a region of the characteristic map where a maximum current cannot be set, in step S106 the rotor's initial angular position is changed to the target angular position so that the rotor's target angular position is in a region of the characteristic map where the maximum current can be set.

[0032] The reason for this is that single-phase current load in the inverter of the electric machine on the AC side is dependent on the rotor position when at standstill and therefore must be avoided.

[0033] In step S106, to change the output angular position of the rotor, power modules of the inverter are controlled to generate a magnetic field in the rotor, which changes the output angular position of the rotor so that a maximum current can be achieved for the rotor to meet a requirement of the drive torque.

[0034] In step S108, after setting the target angle position of the rotor, the separating element to the drive train closes automatically.

[0035] This terminates function S100 for adjusting the target angle position of the rotor when the electric vehicle is stationary.

[0036] In step S110, the maximum torque is available for setting after the rotor's position has changed while at standstill.

[0037] Fig. Figure 2 shows a flowchart of the method according to an embodiment of the invention.

[0038] If the separating element is open in step S102 as described above, the target angular position of the rotor is set in step S104 after the vehicle has come to a standstill in step S202, if the initial angular position does not match the target angular position.

[0039] In step S106, the target angular position of the rotor is set.

[0040] In step S204, the maximum torque can then be set when a closing request is received for the separating element.

[0041] However, if the separating element is closed, step S200, and the vehicle is stationary, step S206, a check is performed in step S208 to see if the separating element has opened on its own or if it has been requested to open.

[0042] If the separating element opens automatically, and the initial angular position does not match the target angular position after the separating element opens, the target angular position of the rotor is set, and the separating element closes automatically.

[0043] If independent opening of the separating element is available in step S210, for example in case of increased time availability, the process runs in Fig. 1. The described function S100 is for adjusting the target angle position of the rotor when the electric vehicle is stationary.

[0044] In step S110, the maximum torque is again available for setting after the rotor's position has changed while at standstill.

[0045] If step S208 determines that the separating element can only be opened on demand, then in step S212 the separating element is first opened on demand, for example when integrated into a race start function or when a trailer is detected.

[0046] If the opening of the separating element is requested, and the initial angular position does not match the target angular position, the angular position of the rotor is adjusted, and the separating element is closed as requested.

[0047] After opening the separating element, function S100 is performed to adjust the target angle position of the rotor while the electric vehicle is stationary.

[0048] In step S214, the separating element is then closed again upon request.

[0049] If the vehicle is moving, step S216, no further action is necessary, step S218. Reference symbol list S100 function for adjusting the target angle position of the rotor when the electric vehicle is stationary S102 separating element opened S104 Determining the initial angular position of the rotor S106 Setting the target angle position of the rotor S108 Independent closing of the separating element S110 Maximum torque adjustable S200 separating element closed S202 vehicle is standing S204 Maximum torque adjustable when closing request is received S206 vehicle is standing S208 Check for automatic or requested opening of the separating element S210 Independent opening of the separating element S212 Requested opening of the separating element S214 Closing of the separating element on demand S216 vehicle is driving S218 No action required QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 4532460 A

[0003] DE 10357504 A1

[0004] DE 10359713 A1

[0005]

Claims

[1] Method for maximizing the drive torque available when starting an electric vehicle, using an electric machine whose rotor is coupled to a drive train of the electric vehicle, wherein, with the rotor decoupled from the drive train, a target angular position of the rotor is set such that, after coupling the rotor to start the electric vehicle, the highest possible torque is provided. [2] Method according to claim 1, wherein, for setting the target angular position of the rotor, an initial angular position of the rotor is determined and compared with a predetermined characteristic map which includes a dependence of phase currents of the rotor on an angular position of the rotor, wherein, if the rotor is located with its initial angular position in a region of the characteristic map in which a maximum current cannot be set, the initial angular position of the rotor is changed to the target angular position such that the rotor is located with its target angular position in a region of the characteristic map in which the maximum current can be set. [3] Method according to claim 2, wherein power modules of an inverter are controlled to change the output angular position of the rotor in order to generate a magnetic field in the rotor which changes the output angular position of the rotor in such a way that a maximum current for a requirement of the drive torque can be achieved for the rotor. [4] Method according to one of the preceding claims, wherein the rotor of the electric machine is coupled to the drive train via a separating element, wherein the rotor is decoupled from the drive train by means of the separating element. [5] Method according to claim 4, wherein after setting the target angular position of the rotor, the separating element to the drive train closes independently. [6] Method according to claim 4 or 5, wherein, when the separating element is open, after the vehicle has come to a standstill, the target angular position of the rotor is set if the initial angular position does not match the target angular position. [7] Method according to any one of claims 4 to 6, wherein, when the separating element is closed and the vehicle is stationary, a check is carried out to see if the separating element has opened on its own or if it has been requested to open. [8] Method according to claim 7, wherein, if the opening of the separating element is carried out independently, after opening the separating element, if the initial angular position does not correspond to the target angular position, the target angular position of the rotor is set, and the separating element closes independently. [9] Method according to claim 7, wherein, when the opening of the separating element is requested, if the initial angular position does not match the target angular position, the angular position of the rotor is adjusted and the separating element is closed as requested. [10] Method according to one of the preceding claims, wherein the initial angular position and the target angular position of the rotor are determined by means of a rotor position sensor, in particular a resolver or a TMR sensor, in particular wherein the rotor position sensor is arranged in the electric machine.

Images