Method for operating an electric machine in a drive train of a motor vehicle

Abstract

The invention relates to a method for operating an electric machine in a drive train of a motor vehicle, wherein the electric machine is used as a drive unit for the motor vehicle and an electronic control and regulating device for the electric machine is provided in the motor vehicle, wherein when a load change of the electric machine from a motor operation to a generator operation, or vice versa, an elastic twist angle (ΔMA) is determined, a total twist angle (ΔG) since the beginning of the load change is determined from the rotational speeds (nR, nW) of a rotor and a wheel by integrating the differential rotational speed (ndiff) over time (t), wherein when the total twist angle (ΔG) exceeds the elastic twist angle (ΔG),MA) exceeds an integral which integrates the same differential speed (ndiff) over time (t), is reset to zero and a control and / or regulation of a game cycle begins, wherein for each twist angle (&PHgr;) in the game cycle a maximum differential speed (ndiff_max) is specified via a characteristic curve which the rotor should not exceed, and wherein if the differential speed (ndiff) is exceeded a proportional controller is used which regulates the difference of the differential speeds (ndiff).;

Description

The invention relates to a method for operating an electric machine in a drive train of a motor vehicle according to the preamble of claim 1.When the torque of a drive, for example an electric drive, changes sign with a transmission for reducing the speed of a rotor to the speed of a wheel of a vehicle, the tooth flank of the transmission changes from the traction flank to the thrust flank or vice versa. Due to the manufacturing process, there are looses and gear clearances in the drive train, which cause a change of the respective flanks of two engaged mechanical components when the power flow changes sign. When the contact of the flanks is released, a differential speed occurs between the rotor-side component and the wheel-side components, which differential speed is indeed required to switch the force path over to the respective other gear flank, but at the same time also leads to a noticeable jerk if the respective other flanks strike one another with a high differential speed. A fast flank change due to this gear backlash is perceptible by persons in the vehicle and, during slow travel, also by persons outside the vehicle. In the case of a strong form, this can also be perceptible as a result of the transmitted structure-borne sound in the vehicle. An important influencing factor for the acoustic characteristic is the speed at which the tooth flanks make contact in the transmission during a change of flank. In the worst case, even multistage beating occurs if the rotor loses contact again for a short time by the impact impulse.The object of the invention is to specify a novel method for operating an electric machine in a drive train of a motor vehicle.The object is achieved according to the invention by a method for operating an electric machine in a drive train of a motor vehicle having the features of claim 1.Advantageous embodiments of the invention are the subject matter of the dependent claims.A method for operating an electric machine in a drive train of a motor vehicle is proposed, wherein the electric machine is used as a drive unit for the motor vehicle and an electronic control and regulating device for the electric machine is provided in the motor vehicle. According to the invention, it is proposed that, when a load change of the electric machine from motor operation to generator operation, or vice versa, is requested, an elastic rotation angle is ascertained and the total rotation angle since the beginning of the load change is ascertained from rotational speeds of a rotor and a wheel by integration of the differential rotational speed over time. When the total twist angle exceeds the elastic twist angle, an integral that integrates the same differential rotational speed over time is reset to zero and control and / or regulation of a backlash pass starts. For each angle of rotation in the clearance passage, a maximum rotational speed difference is specified via a characteristic curve which the rotor should not exceed. When the differential rotational speed is exceeded, a proportional controller is used, which adjusts the difference of the differential rotational speeds.According to the present invention, the clearance pass is recognized by an underlying speed regulation of the drive in the event of a sign change of the required torque on the basis of the speed characteristic which is established in the drive. During the passage of the play, a setpoint rotational speed profile is impressed on the drive, which minimizes the rotational speed difference of the toothed wheels which are in engagement for the contact point of the flanks.With this mechanism, the contact point of the gears can be controlled with its NVH (Noise, Vibration, Harshness) behavior. As a result, the changes in sign of the requested torque can be implemented more comfortably while maintaining the torque dynamics.The method described serves to counteract the jerk during the sign change, wherein with an underlying speed control of the rotor, the differential speed in the transition of the flank change is influenced in such a way that the jerk arising during the impact can be minimized. Underlying speed regulation means a method in which a setpoint torque is predefined for the electric traction machine by a central drive control unit under torque control. In the course of the game itself, however, this is superimposed with a control torque of a speed regulator presented.Exemplary embodiments of the invention are explained in more detail below with reference to drawings.The following are shown: FIG. 1 shows a schematic diagram of a typical profile of a torque of an electric machine over time during a load change, FIG. 2 shows a schematic diagram of a typical profile of a rotational speed over time during the load change, FIG. 3 shows a schematic diagram of a typical profile of a rotation angle of a side shaft over time during the load change, FIG. 4 shows a schematic diagram of a differential speed or differential rotational speed over an angle of a transmission play, and FIG. 5 is a schematic diagram of torque versus time.Corresponding parts are provided with the same reference numerals in all figures.A method is proposed by which a jerk during the sign change of a power flow in a drive with an electric machine and a transmission, in particular for a vehicle, is counteracted, wherein a differential speed in the transition of a flank change is influenced with an underlying speed control of a rotor of the machine in such a way that the jerk that arises during the impact can be minimized.The underlying speed control becomes active when the central drive control unit requests a load change from motor to generator operation, or vice versa. This load change is characterized by the demanded torque M D.Since the torque M is requested to be formed by a low-pass filter for reasons of drivability and comfort, the elastic component of the differential speed or the differential rotational speed n diff can be determined simply by changing a setpoint torque and the torsional spring stiffness of all the involved torsionally soft elements in the drive train via Hooke's law.FIG. 1 is a schematic diagram of a typical profile of a torque M of the electric machine over time t during a load change, here during a load change from generator operation to motor operation. An output torque M A and the torque M D. requested by the central drive control unit are shown. The output torque M A at the start of the load change is used to determine an elastic torsion angle φ of a side shaft shown in FIG. 3 by Hooke's law.FIG. 2 is a schematic diagram of a typical curve of a rotational speed n over time t during the load change. A rotor rotational speed n R of the electric machine and a wheel rotational speed n W of a wheel of the vehicle are shown.The rotor rotational speed n R and the wheel rotational speed n W are detected by measurement technology and are processed by control technology in order to compensate latencies and to filter signals. The differential speed or differential rotational speed n diff is formed on the wheel plane. For this purpose, the rotor rotational speed n R is divided by the transmission ratio of the drive train and subtracted from the wheel speed or wheel rotational speed n W. The determined differential speed or differential rotational speed n diff is cumulative and / or integrated over time t. The integral resulting from this forms the angle of rotation Φ, which has been reduced and / or built up since the beginning of the load change from the previously illustrated angle of rotation Φ of the torsionally soft transmission elements.Because the recuperation torque is reduced during the load change, the angle of rotation φ of the side shaft is reduced, which results in a greater rotor speed.FIG. 3 is a schematic diagram of a typical profile of the angle of rotation Φ of the side shaft over time t during the load change. The figure shows an angle of the gear play φ GS as a determined component characteristic value, a proportion φ MA of the angle of rotation φ from the output torque M A from Hooke's law, a total angle of rotation φ G since the start of the load change and a angle of rotation φ SD of the pass through the play.The total twist angle φ G is determined by integrating the differential speed. Reaching the threshold value of the elastic angle of rotation Φ, i.e. the proportion Φ MA of the angle of rotation Φ from the output torque M A from Hooke's law, represents the time t1of the beginning of the game pass. From this point in time t1, the rotational speed difference is integrated (starting value 0°) and evaluated as a traversed transmission play value or angle of rotation Φ SD of the game traverse. A time t2 at which the geometric component characteristic value of the angle of the gear play φ GS is reached is considered to be the end of the play pass.If the measured degraded angle of rotation (the integral), that is to say the total angle of rotation Φ G, exceeds the angle of rotation Φ which results from the torque M of the start of load change to the neutral torque 0 Nm (via the Hooke's law), that is to say the proportion Φ MA of the angle of rotation Φ from the output torque M A from the Hooke's law, it can be stated with a high probability that the tooth flanks of the transmission which hitherto lie one on top of the other start to lose contact at this point in time. This represents the time t1or the beginning of the freewheeling rotor due to the backlash in the transmission and can be additionally corrected by means of an offset characteristic curve.At this time t 1, an integral is reset to 0, which integrates the same differential speed or differential rotational speed n diff over time t. This value represents the currently traversed angle in the game. Since the backlash of the electric drive train can be sufficiently constant and measured at the test stand (thus can be stored as a parameter in the software), the time t2or the end of the backlash pass can also be determined as a threshold value of this integral and the current position of the rotor in this backlash can be determined with a certain probability.FIG. 4 is a schematic diagram of differential speed n diff versus the angle of backlash φ GS. An actual differential rotational speed n diff_ist and a maximum differential rotational speed n diff_max, which is predefined by a characteristic curve over the angle of the gear play φ GS are shown.Between the times t1 and t2, the subordinate speed control becomes active. The maximum rotational speed difference n diff_max is predetermined by means of the characteristic curve via the clearance passage. With the actual differential rotational speed n diff_ist a deviation A is determined. If this deviation A is positive (actual differential rotational speed n diff_ist is greater than the maximum differential rotational speed n diff_max), the underlying rotational speed control system engages and, by means of a P controller, sets a control torque M stell, which is illustrated in FIG. 5 and is intended to brake the rotor.Now, by means of the subordinate speed control, influence is exerted on the differential speed or differential speed n diff during this pass through the play. As a result, a maximum differential speed or maximum differential rotational speed n diff_max is predefined for each location in the backlash pass via a characteristic curve which the rotor should not exceed. At the beginning of the game cycle, the differential speed or differential rotational speed n diff must be high, because the game must necessarily be reduced in order that the load change can be carried out. Towards the end of the game pass, i.e. at the time t 2, when the currently traversed angle approaches the stored value of the game width, it should become smaller, ideally going to zero at the time of the impact of the flanks. Since the values are subject to a certain tolerance, a lower differential speed or differential rotational speed n diff not equal to 0 is predefined at the time t 2. When the differential speed or differential rotational speed n diff is exceeded, a proportional controller (P controller) is used, which adjusts the difference of the differential speeds or differential rotational speeds n diff. This minimizes the impact speed of the flanks somewhat, which reduces the perceptible jerk in the vehicle.FIG. 5 is a schematic diagram of a torque M over time t. A torque M D requested by the central drive control unit is shown, and the above-mentioned actuating torque M stell, is an actually set torque which is influenced by the subordinate rotational speed control.This actuating torque M stell is superimposed on the originally requested torque M D. As a result of the engagement, the rotor is braked shortly before reaching the new pair of flanks in the transmission, in order to reduce the impact and / or impact and / or jerk and to make the passage of play more comfortable.The term "subordinate speed control" is to be understood as a controller which controls the differential speed or differential speed n diff between the wheel and the rotor of the electric machine to a setpoint profile during the gear cycle run-through. Backing is referred to here because the rotor rotational speed n R does not affect the state of the force conditions at the wheel (propulsion neutral). The controller actuating torque is added to the actual setpoint torque of the electric machine.Specifically, the angle of rotation Φ of the torsionally flexible transmission elements of the drive train (relevant to be called the side shaft) known from a stationary or quasi-stationary state with a known torque M (Hooke's Law) is used to draw in the rotational speed difference n diff between the wheel and the rotor movement and to detect the beginning of the backlash pass. In the backlash passage itself, the electric motor does not transmit torque to the wheel. Only after passing through the clearances is a torque M transmitted again from the electric motor via the transmission to the wheel. The end of the clearance passage is considered to be in contact with the other tooth flank of the engaged gears in the transmission. The width of the clearance is measured on the test stand. The already traversed angle of the play is determined by integration of the rotational speed difference n diff. In order to make the passage of the game quick and comfortable, a speed profile is specified as the setpoint rotational speed difference over the cumulative angle of the game. At the beginning, the differential speed or differential rotational speed n diff may be large. Toward the end of the clearance passage, the maximum permissible setpoint speed is reduced in order to minimize the impact speed of the tooth flanks, to reduce the energy of the impact and to minimize the excitation of the drive train (engine mounting and torsional vibration in the side shaft).List of reference charactersA deviation M torque M A output torque M D requested torque M stell actuating torque n rotational speed n diff differential rotational speed n diff_ist actual differential rotational speed n diff_max maximum differential rotational speed n R rotational speed, rotor rotational speed n W rotational speed, wheel rotational speed t time t1 time t2 time φ rotation angle φ G total rotation angle φ GS angle of the gear backlash φMApart of the rotation angle from the output torque from Hooke's law, elastic angle of rotation Φ SD angle of rotation of the game passage

Claims

Method for operating an electric machine in a drive train of a motor vehicle, wherein the electric machine is used as a drive unit for the motor vehicle and an electronic control and regulating device for the electric machine is provided in the motor vehicle, characterized in that, if a load change of the electric machine from a motor to a generator operation, or vice versa, is requested, an elastic angle of rotation (Φ MA) is determined, the total angle of rotation (Φ G) since the start of the load change is determined from rotational speeds (n R, n W) of a rotor and of a wheel by integration of the differential rotational speed (n diff) over time (t), wherein, then, when the total twist angle (Φ G) exceeds the elastic twist angle (Φ MA) an integral which integrates the same differential rotational speed (n diff) over the time (t) is reset to zero and a control and / or regulation of a backlash pass begins, wherein a maximum differential rotational speed (n diff_max) is specified for each twist angle (Φ) in the backlash pass via a characteristic curve which the rotor should not exceed, and wherein when the differential rotational speed (n diff) is exceeded a proportional regulator is used which adjusts the difference of the differential rotational speeds (n diff).Method according to Claim 1, characterized in that the elastic angle of rotation (Φ MA) is determined via the change in a setpoint torque and a torsional spring stiffness of all the involved torsionally flexible elements in the drive train of the vehicle via Hooke's law.Method according to Claim 1 or 2, characterized in that the total torsion angle (Φ G) is formed by a rotor rotational speed (n R) and a wheel rotational speed (n W) being detected by measurement technology and processed by regulation technology, the differential rotational speed (n diff) being formed on the wheel plane, for which purpose the rotor rotational speed (n R) is divided by a transmission ratio of the drive train of the vehicle and is subtracted from the wheel rotational speed (n w) the difference rotational speed (n diff) determined being cumulative and / or integrated over the time (t).

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