DE102009055246A1 - Method and device for determining a setpoint torque for controlling an electrical machine of a motor vehicle - Google Patents

Abstract

The invention relates to a method for determining a target torque for controlling an electrical machine of a motor vehicle, in which a force is generated between the electrical machine (2) and an axle (8) of the motor vehicle having wheels (9, 10) by engaging a dog clutch (11) is transmitted. So that the claw clutch behaves the same when closing at any ambient temperature of the electric machine, when the claw clutch (11) is open, friction torques of the electric machine (2) are taken into account when determining the target torque.

Description

State of the art

The invention relates to a method for determining a setpoint torque for controlling an electric machine of a motor vehicle, wherein a force is transmitted between the electric machine and a wheel axle of the motor vehicle by closing a dog clutch and a device for carrying out the method.

For the transmission of rotational movements or torques so-called jaw clutches are used in motor vehicles. The two coupling elements of the dog clutch in this case have teeth which are arranged at predetermined distances from each other. A first coupling element is connected to the electric drive and the second coupling element with the driven axis of the motor vehicle. To close the dog clutch in a moving vehicle, it is necessary to set a differential speed between the two coupling elements, so that the teeth of the two coupling elements engage. Ie. the teeth of one coupling element engage in the spaces between the teeth of the other coupling element and vice versa. This is ensured if the two coupling elements to each other have a differential speed.

To engage the dog clutch, the electric drive is controlled by a control unit so that there is a nearly constant differential speed band between the electric drive and driven by the electric drive axle of the vehicle. If the axle is at a standstill or only rotates at a very low speed, it is difficult to set a designed as an electric machine drive to the necessary differential speed band, which is between 20 to 40 revolutions per minute.

At low vehicle speeds or vehicle standstill influences on the rotational behavior of the electric machine must be known exactly to achieve the necessary differential speed band, otherwise no engagement is possible. To engage the dog clutch, the electric machine must be controlled to a small moment so that the axial friction forces on the dog clutch when closing are as small as possible. However, the friction losses caused by the electrical machine are temperature-dependent and different for each electrical machine due to production-related tolerances of the mechanical assembly.

Disclosure of the invention

The inventive method for determining a desired torque for controlling an electric machine of a motor vehicle with the features of claim 1 has the advantage that the dog clutch behaves the same at closing at each ambient temperature of the electric machine. Because friction moments of the electric machine are taken into account in the determination of the setpoint torque when the jaw clutch is open, the real behavior of the electric machine with regard to the friction behavior is corrected. By this procedure, the effects of friction on the speed behavior of the electric machine are accurately taken into account in order to achieve the necessary differential speed band for coupling the dog clutch. This increases the robustness of the engagement process. By taking into account the friction moments, speed, temperature and structure-specific influences on the method for engaging a dog clutch are reliably taken into account.

Advantageously, a factor is determined to determine the friction moments, by means of which a friction characteristic is applied, from which a torque correction value is determined, which is used as a target torque. Such a process can be performed over the entire vehicle life. In addition, it ensures that the torque applied to the dog clutch at the time of engagement are very small, whereby a torque shock is prevented on the drive train during engagement.

In a further development, the factor is determined from the difference between the current rotational speed of the electric machine and a mathematically determined speed curve. Thus, each course of the speed can be stored to achieve the required for the engagement of the dog clutch differential speed band. It is considered that the speed gradient during the passage of the differential speed band may not be too steep, otherwise the time to engage is too short. The speed gradient may also not be too flat, otherwise the coupling process takes too long.

In one variant, the mathematical speed curve is determined from a rotational speed of the electric machine at a starting time, wherein there is no desired torque request to the electric machine at the start time. Thus, the current conditions in the modeling of the speed behavior of the electric machine are taken into account.

In one embodiment, the friction characteristic is determined as a function of a rotational speed of the electric machine. As an initial condition such a friction characteristic is not necessary, but can be determined in a first approach from a theoretical speed curve.

Advantageously, the friction characteristic is determined as a function of a temperature of the electrical machine. In this case, a characteristic field, which represents the temperature dependence of the rotational speed over time, stored, so that in the correction of the friction torque always the friction characteristic can be selected, which corresponds to the current ambient temperature of the electric machine, whereby the temperature dependence of the friction torque is considered sufficient.

In one embodiment, the factor is determined after each opening of the dog clutch and the friction characteristic created in the preceding opening cycle of the dog clutch is corrected by the factor. Due to the speed error determination is a continuous adaptation of the friction characteristic over the term of the process when changing the environmental conditions such as aging, viscosity of the coolant and temperature possible. A subsequent and complex application of a speed control can be omitted.

A further development of the invention relates to a device for determining a desired torque for controlling an electric machine of a motor vehicle, wherein between the electric machine and a wheels having axle of the motor vehicle by closing a dog clutch, a force is transmitted. In order for the dog clutch to behave the same at closing at each ambient temperature of the electric machine, means are provided which, when the dog clutch is open, take friction moments of the electric machine into account when determining the setpoint torque. In this case, the friction losses of the electric machine are compensated at no torque request, wherein when closing the dog clutch whose friction losses are reduced. Since the friction losses depend on the environment of the electrical machine such as temperature, viscosity of the surrounding medium of the electric machine or aging of the electric machine, the dog clutch always shows the same behavior during the closing process, regardless of the environmental conditions.

Advantageously, a control unit ( 16 ) with the electric machine ( 2 ) and a speed sensor ( 19 ), which determines the rotational speed of the electric machine ( 2 ) certainly. By determining a speed difference between the speed of the electric machine, on the condition that a target torque of 0 Nm is requested, and a mathematically determined speed can easily determine a speed error, which is due to the friction of the electric machine and in the determination a mechanical target speed torque is taken into account. Thus, no additional structural components are necessary to determine the target torque.

In one embodiment, the electric machine ( 2 ), the dog clutch ( 11 ) and a transmission ( 12 ), which with the axis ( 8th ) in an oil-filled structural unit ( 13 ) arranged. As a result, all elements involved in the process of engaging the dog clutch are subject to the same environmental conditions.

The invention allows numerous embodiments. One of them will be explained in more detail with reference to the figures shown in the drawing.

It shows:

1 : Schematic representation of a hybrid vehicle with an electrically driven axle

2 : schematic flow diagram for the coupling process of the dog clutch

3 : Course of torque and speed of the electric machine over time during the engagement process of a dog clutch

4 : Schematic representation of an adaptive torque control of the electric machine

In 1 a hybrid vehicle is shown, which is a hybrid drive consisting of an internal combustion engine 1 and an electric motor 2 having. The internal combustion engine 1 and the electric motor 2 drive thereby different axes of the hybrid vehicle. The internal combustion engine 1 is about a first gearbox 3 with the front axle 4 the hybrid vehicle connected to which two drive wheels 5 . 6 are arranged. An engine control unit 7 generates the drive signals for the internal combustion engine 1 ,

The electric motor 2 drives the rear axle 8th the hybrid vehicle, which two other drive wheels 9 and 10 wearing. The electric motor 2 makes with a dog clutch 11 and a second transmission 12 a structural unit 13 , The gear 12 leads to the rear axle 8th of the hybrid vehicle and is connected to this. The electric motor 2 , the dog clutch 11 and the gearbox 12 are located in a common oil sump for cooling.

At the claw clutch 11 it is a special design of a clutch. Both coupling elements 11a . 11b the dog clutch 11 have teeth that have predetermined distances from each other. To close the dog clutch 11 grip the teeth of a coupling element 11a in the gaps of the other coupling element 11b , whereby a firm engagement arises and a good power transmission is ensured. The first coupling element 11a the dog clutch 11 is with the electric motor 2 connected while the second coupling element 11b with the gearbox 12 is linked.

The electric motor 2 is still with a power output stage 14 connected in the form of a pulse inverter, which supplies the current for the operation of the electric motor 2 generated. This is the power output stage 14 with a high-voltage battery 15 connected to an electrical voltage of approximately 230 V for the operation of the electric motor 2 provides. The electric motor 2 is formed in the present embodiment as a permanently excited synchronous machine. Furthermore, the electric motor 2 with an electric motor control unit 16 connected, which on a speed sensor 17 that leads at the wheel 10 of the vehicle is arranged and thus measures the speed from which the driving speed of the motor vehicle is determined. It's also on the shaft 18 of the electric motor 2 another, with the control unit 16 connected speed sensor 19 arranged, the speed of the electric motor 2 detected.

In hybrid vehicles occur frequently cases where the vehicle alone by the internal combustion engine 1 is driven. Although the drive, as described, takes place at the front axle 4 of the hybrid vehicle, wherein by the driving movement of the hybrid vehicle, the rear axle 8th with the wheels 9 . 10 is accelerated. Because the rear axle 8th stuck with the gearbox 12 is connected, which in the present case only has a fixed gear ratio, the gear rotates 12 according to the vehicle speed. Through the connection of the transmission 12 with the second coupling element 11b the dog clutch 11 is also this coupling element 11b in a rotary motion.

With increased slip of the wheels 5 . 6 the front axle 4 becomes the electric motor 2 switched on and the wheels 9 . 10 the switchable rear axle 8th through the electric motor 2 driven.

With the help of 2 the method for engaging a dog clutch is to be described, it being assumed that the speed of the wheels 9 . 10 that of the electric motor 2 driven rear axle 8th less than 300 revolutions per minute.

In the block 100 a query is made as to whether a coupling process is to be carried out. If this is the case, in the block 101 with the help of the tachometer 17 the speed of the wheel 10 measured at the rear axle of the motor vehicle and this involving the translation of the transmission 12 converted into an electric motor speed n _A. In the block 102 becomes the rotational speed of the wheel converted into an electric motor rotational speed n _A 10 with a synchronization speed n _{S of} the electric motor 2 compared. The synchronization speed n _S is determined from the wheel speed of the wheel 10 formed electric motor speed plus the required for the engagement of the dog clutch differential speed band .DELTA.n of about 20 to 40 revolutions per minute. n _S = n _A + Δn

Is this from the speed of the wheel 10 determined electric motor speed n _A above the synchronization speed n _S , which is located at a standstill electric motor 2 in the block 103 started and through the control unit 16 such a torque M is set that the electric motor 2 overcomes a so-called Losreiismoment. It is a very strong torque M, which is necessary to overcome the inertia and the associated mechanical friction, which occurs when the electric motor 2 to be moved from standstill. Is the electric motor 2 already in motion, a correspondingly smaller torque M is set as the setpoint of the control. In the block 104 becomes the speed n _{E of} the electric motor 2 by means of the speed sensor 19 measured and determined whether the synchronization speed n _{S is} reached or exceeded. Is the instantaneous speed n _{E of} the electric motor 2 higher than the synchronization speed n _S , the torque control torque setpoint is set to a value of 0 Nm (block 105 ). This means that the electric motor 2 is no longer regulated. Due to friction losses and occurring inertial effects of the electric motor 2 decelerated accordingly.

After a given time is in the block 106 checked whether the speed n _{E of} the electric motor 2 has decayed so far that it has reached the speed difference band Δn, which is above the converted into an electric motor speed n _A speed of the wheel 10 followed. If not, it becomes the block 105 returned, where in the absence of torque control of the electric motor 2 continues to roll.

If the electric motor speed n _{E has reached} the differential speed band Δn, is in the block 107 the dog clutch closed.

The behavior of the electric motor 2 when accelerating from standstill is off 3 seen. The diagram 3a shows the behavior of the torque M of the electric motor 2 over time t. To overcome the breakaway torque of the electric motor 2 so driven that it generates an electrical torque M, wherein the torque M increases linearly starting from 0. At time T1, the control of the torque is set to 0 Nm. First, the electric motor retains 2 as a result of its inherent energy, the torque M constant before, due to the inertia and frictional forces, the torque M linearly decreases approximately to 0, which takes place at a time T2. However, the torque reaches a non-zero size at time T2, which is due to the frictional forces acting on the electric motor 2 act.

The speed n _{E of} the electric motor 2 follows the torque M, as shown in the diagram 3b is apparent. However, the fall in the speed n _{E is} not linear, but asymptotic, so that the electric motor 2 at time T2 still has a measurable speed. If this speed measured at time T2 lies in the differential speed band, then at this point in time T2 becomes the dog clutch 11 moved from the open to the closed state (diagram 3c ).

In this process, a vibration-resistant as possible behavior on a shaft 18 of the electric motor 2 set, since too high torsional vibrations of the coupling operation can not be performed. In the present method, no torque control is performed, but the torque controlled to compensate for the friction torque speed dependent. This results in a smooth progression of the speed, since no vibrations can arise through a torque or speed control.

By the torque control, the target torque M = 0 Nm from the electric motor 2 is requested by the electric motor 2 via one in the control unit 16 stored friction characteristic, which is dependent on the speed, in addition to the friction of the electric motor 2 balanced. This means that the electric torque of the electric motor 2 which is not equal to 0, but which by adding an additional torque to compensate for the friction, the mechanical torque on the shaft 18 of the electric motor 2 minimized as possible. Ideally, the mechanical moment goes to zero. In this case, no torque control is performed, but controlled the torque to compensate for the friction torque speed dependent.

The in the control unit 16 Stored electric motor-specific friction characteristic is dependent on the temperature of the environment. As the electric motor 2 oil cooled and with the dog clutch 11 and the transmission 12 in a gearbox 13 is arranged, in addition to the temperature and the viscosity of the oily medium affects the friction characteristic.

At low driving speeds or in the event of a vehicle standstill, these influences must affect the speed behavior of the electric motor 2 be known exactly to achieve the necessary differential speed band, since a clutch is otherwise not possible. For this reason, the torque of the electric motor 2 adaptively tracked at low speeds or standstill of the vehicle. 4 shows a corresponding method. At time t0, it is required that the dog clutch 11 to be engaged. In this case, the target torque of the electric motor 2 set to 0 Nm. From the current speed n _{E of} the electric motor 2 At time t0, a starting speed n _{0 is} determined, where n ₀ = n _E (t0) is.

The course of the speed in this state is determined by a mathematical function n _math (t, n ₀ ) over time with an initial condition of the starting speed n ₀ , which in the control unit 16 is stored, determined (block 200 ). This mathematically determined speed curve n _math (t, n ₀ ) is in the point 201 continuously with the measured actual speed n _{E of} the electric motor 2 compared, wherein a difference between the measured actual speed n _{E of} the electric motor 2 and the mathematically modeled speed n _math (t, n ₀ ) is formed, which is regarded as an error. Depending on the size of this error is in the block 202 an adaptation factor f (Δn _D ) is determined. This one becomes the block 203 fed, where in the control unit 16 stored friction characteristic as a function of the oil temperature is shown as a map. The adaption factor f (Δn _D ) and the consideration of the temperature are used to adapt this friction characteristic, whereby the adaptation factor f (Δn _D ) is added as an offset to the characteristic curve. As the output of the block 203 a torque correction TrqFrc is output as a friction torque. This torque correction TrqFrc is based on a torque interface 204 where it compensates unwanted mechanical deviations to determine the torque to be controlled TrqEMDesCalc the electric motor 2 is being used. The requested mechanical torque TrqDesMech is also set to zero at this time.

After the friction characteristic has been adapted, this newly determined and adapted characteristic curve will be displayed in the control unit 16 filed and used at the next request. This requirement exists when a new command to engage the dog clutch 11 is issued. In the case, the stored friction characteristic is retrieved according to the described method and in dependence on the current speed n _{E of} the electric motor 2 checked.

Claims (10)

Method for determining a setpoint torque for controlling an electrical machine of a motor vehicle, in which between the electric machine ( 2 ) and a wheel ( 9 . 10 ) axis ( 8th ) of the motor vehicle by closing a dog clutch ( 11 ) a force is transmitted, characterized in that when the jaw clutch is open ( 11 ) Frictional moments of the electric machine ( 2 ) are taken into account in the determination of the target torque. A method according to claim 1, characterized in that for determining the friction torque, a factor (Δn _D ) is determined, by means of which a friction characteristic is applied, from which a torque correction value (TrqFrc) is determined, which is used as the desired torque (TrqEMDesCal). A method according to claim 2, characterized in that the factor (Δn _D ) from the difference of the current speed (n _E ) of the electric machine ( 2 ) and a mathematically determined speed curve n _math (t, n ₀ ) is determined. A method according to claim 3, characterized in that the mathematical speed curve n _math (t, n ₀ ) from a rotational speed (n ₀ ) of the electric machine ( 2 ) is determined at a start time (t0), wherein at the start time (t0) no desired torque request to the electric machine ( 2 ) is present. A method according to claim 2, characterized in that the friction characteristic as a function of a rotational speed (n _E ) of the electric machine ( 2 ) is determined. A method according to claim 2, characterized in that the friction characteristic as a function of a temperature of the electric machine ( 2 ) is determined. Method according to at least one of the preceding claims, characterized in that after each opening of the dog clutch ( 11 ) the factor (Δn _D ) is determined and that in the previous opening cycle of the dog clutch ( 11 ) is corrected with the newly determined factor (Δn _D ). Device for determining a setpoint torque for controlling an electric machine of a motor vehicle, in which between the electric machine ( 2 ) and a wheel ( 9 . 10 ) axis ( 8th ) of the motor vehicle by closing a dog clutch ( 11 ) a force is transmitted, characterized in that means ( 16 ), which with open claw clutch ( 11 ) Frictional moments of the electric machine ( 2 ) when determining the setpoint torque. Apparatus according to claim 8, characterized in that a control device ( 16 ) with the electric machine ( 2 ) and a speed sensor ( 19 ), which determines the rotational speed of the electric machine ( 2 ) certainly. Apparatus according to claim 8 or 9, characterized in that the electrical machine ( 2 ), the dog clutch ( 11 ) and a transmission ( 12 ), which with the axis ( 8th ) in an oil-filled structural unit ( 13 ) are arranged.

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