WO2011076485A1

WO2011076485A1 - Method and device for determining desired torque for controlling an electric machine of a motor vehicle

Info

Publication number: WO2011076485A1
Application number: PCT/EP2010/067591
Authority: WO
Inventors: Stefan Spoerhase; Markus Peter
Original assignee: Robert Bosch Gmbh
Priority date: 2009-12-23
Filing date: 2010-11-16
Publication date: 2011-06-30
Also published as: DE102009055246A1; DE102009055246B4

Abstract

The invention relates to a method for determining desired torque for controlling an electric machine (2) of a motor vehicle, in which force is transmitted, between the electric machine (2) and an axis (8) of a motor vehicle comprising wheels (9, 10), by closing a claw coupling (11). The invention is characterised in that when closing, said claw coupling remains constant independent of the ambient temperature of the electric machine (2). As a result, when the claw coupling (11) is open, the friction movements of the electric machine (2) are taken into account when determining the desired torque.

Description

Description title

Method and device for determining a setpoint torque for driving an electric machine of a motor vehicle

State of the art

The invention relates to a method for determining a desired torque for driving an electric machine of a motor vehicle, wherein between the electric machine and a wheels having axis of

Motor vehicle by closing a jaw clutch, a force is transmitted and an apparatus for performing the method.

To transmit rotary 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. That 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 at a very low speed, it is difficult to 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 must

Influences on the rotational behavior of the electric machine to 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 at the claw clutch applied torque at the time of Einkuppeis 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 life of the Procedure for changing the ambient 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 setpoint torque for controlling an electric machine of a motor vehicle, in which 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 corrected at no torque request, and their friction losses are reduced when closing the claw clutch. 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) is connected, which determines the speed of the electric machine (2). By determining a speed difference between the speed of the electric machine, under the condition that a target torque of 0 Nm is requested, and a mathematically determined speed can be easily determine a speed error, which is due to the friction of the electric machine and at the determination of 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 (1 1) and a gear (12) which is connected to the axis (8) arranged in a filled with oil structural unit (13). As a result, all the elements involved in the process of engagement of 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:

Figure 1: Schematic representation of a hybrid vehicle with an electrically driven axle Figure 2: a schematic flow diagram for the engagement of the

claw clutch

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

FIG. 4: Schematic representation of an adaptive torque control of the electric machine FIG. 1 shows a hybrid vehicle which has a hybrid drive consisting of an internal combustion engine 1 and an electric motor 2. The internal combustion engine 1 and the electric motor 2 thereby drive different axes of the hybrid vehicle. The internal combustion engine 1 is connected via a first transmission 3 to the front axle 4 of the hybrid vehicle, on which two drive wheels 5, 6 are arranged. An engine control unit 7 generates the control signals for the internal combustion engine 1.

The electric motor 2 drives the rear axle 8 of the hybrid vehicle, which carries two further drive wheels 9 and 10. The electric motor 2 forms with a dog clutch 1 1 and a second gear 12, a structural unit 13. Das

Transmission 12 leads to and is connected to the rear axle 8 of the hybrid vehicle. The electric motor 2, the dog clutch 1 1 and the transmission 12 are located for cooling in a common oil pan.

The dog clutch 1 1 is a special design of a clutch. Both coupling elements 1 1 a, 1 1 b of the dog clutch 1 1 point Teeth on, the predetermined distances from each other. To close the jaw clutch 1 1, the teeth of a coupling element 1 1 a engage in the gaps of the other coupling element 1 1 b, whereby a firm engagement is formed and a good power transmission is ensured. The first coupling element 1 1 a of the dog clutch 1 1 is connected to the electric motor 2, while the second coupling element 1 1 b is linked to the transmission 12.

The electric motor 2 is further connected to a power output stage 14 in the form of a pulse inverter, which generates the current for the operation of the electric motor 2. For this purpose, the power output stage 14 is connected to a high-voltage battery 15, which provides an electrical voltage of approximately 230 V for the operation of the electric motor 2. The electric motor 2 is formed in the present embodiment as a permanently excited synchronous machine. Furthermore, the electric motor 2 is connected to an electric motor control unit 16 which leads to a speed sensor 17, which is arranged on the wheel 10 of the vehicle and thus measures the speed from which the driving speed of the motor vehicle is determined. In addition, a further, connected to the control unit 16 speed sensor 19 is arranged on the shaft 18 of the electric motor 2, which detects the rotational speed of the electric motor 2.

In hybrid vehicles, there are often cases where the vehicle is driven solely by the engine 1. Although the drive, as described, takes place on the front axle 4 of the hybrid vehicle, the rear axle 8 with the wheels 9, 10 being accelerated by the driving movement of the hybrid vehicle. Since the rear axle 8 is fixedly connected to the transmission 12, which in the present case only has a fixed gear ratio, the transmission 12 rotates according to the vehicle speed. By the connection of the transmission 12 with the second coupling element 1 1 b of the dog clutch 1 1 is also this coupling element 1 1 b in a rotational movement.

With an increased slip of the wheels 5, 6 of the front axle 4, the electric motor 2 is switched on and the wheels 9, 10 of the shiftable rear axle 8 are driven by the electric motor 2. The method for engaging a dog clutch is to be described with the aid of FIG. 2, it being assumed that the rotational speed of the wheels 9, 10 of the rear axle 8 driven by the electric motor 2 is less than 300 revolutions per minute.

In block 100 it is queried whether a coupling process is to be performed. If this is the case, the rotational speed of the wheel 10 at the rear axle of the motor vehicle is measured in block 101 with the aid of the tachometer 17 and converted into an electric motor speed n _A , taking into account the ratio of the transmission 12. In block 102, the rotational speed of the wheel 10 converted into an electric motor rotational speed n _{A is} compared with a synchronization rotational speed n _{s of} the electric motor 2. The synchronization speed n _s is formed from the electric motor speed formed from the wheel speed of the wheel 10 plus the differential speed band Δη required for the engagement of the dog clutch of approximately 20 to 40 revolutions per minute. n _s = n _A + Δη

If the determined from the rotational speed of the wheel 10 electric motor speed n _A above the synchronization speed n _s , which is located at a standstill electric motor 2 is started in block 103 and adjusted by the controller 16 such a torque M that the electric motor 2 overcomes a so-called Losreismoment. 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 is to be moved from standstill. If the electric motor 2 is already in motion, a correspondingly smaller torque M is set as the desired value of the control. In block 104, the speed n _{E of} the electric motor 2 is measured by means of the speed sensor 19 and it is determined whether the synchronization speed n _{s is} reached or exceeded. If the instantaneous rotational speed n _{E of} the electric motor 2 is higher than the synchronization rotational speed n _s, the torque control target torque is set to a value of 0 Nm (block 105). This means that the electric motor 2 is no longer regulated. By friction losses and inertia effects occurring, the electric motor 2 is decelerated accordingly. After a predetermined time, it is checked in block 106 whether the rotational speed n _{E of} the electric motor 2 has decayed so far that it has reached the rotational speed difference band Δη, which adjoins the rotational speed of the wheel 10 converted into an electric motor rotational speed n _A. If this is not the case, the system returns to block 105, where, in the absence of torque control, the

Electric motor 2 continues to roll.

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

The behavior of the electric motor 2 during the acceleration from standstill can be seen in FIG. 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 is driven so that it generates an electrical torque M, wherein the torque M starting from 0 increases linearly.

At time T1, the control of the torque is set to 0 Nm. First, the electric motor 2 keeps constant the torque M due to its inherent energy before, due to the inertia and frictional forces, the torque M linearly decreases approximately to 0, which occurs at a time point T2. However, the torque at time T2 but one of

Zero different size, which is due to the frictional forces acting on the electric motor 2.

The speed n _{E of} the electric motor 2 follows the torque M, as can be seen from the diagram 3b. However, the fall in the rotational 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, the dog clutch 11 is moved from the open to the closed state at this point in time T2 (diagram 3c).

In this process, a vibration-resistant as possible behavior is set to a shaft 18 of the electric motor 2, 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 for compensating the friction torque depends on the speed controls. This results in a smooth progression of the speed, since no vibrations can arise through a torque or speed control.

If the desired torque M = 0 Nm is requested by the electric motor 2 through the torque control, the friction of the electric motor 2 is additionally compensated by the electric motor 2 via a friction characteristic which is dependent on the rotational speed in the control unit 16. This means that the electric torque of the electric motor 2 is not equal to 0, but minimizes the mechanical torque on the shaft 18 of the electric motor 2 by providing an additional torque to compensate for the friction.

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 stored in the control unit 16 electric motor-specific friction characteristic is dependent on the temperature of the environment. Since the electric motor 2 is oil-cooled and is arranged with the dog clutch 1 1 and the transmission 12 in a transmission housing 13, in addition to the temperature, the viscosity of the oily medium affects the friction characteristic.

At low speeds or in a vehicle standstill, these influences on the speed behavior of the electric motor 2 must 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 is adaptively tracked at low speeds or standstill of the vehicle. FIG. 4 shows a corresponding method. At time tO is required that the jaw clutch 1 1 is to be engaged. In this case, the target torque of the electric motor 2 is set to 0 Nm. From the current rotational speed n _{E of} the electric motor 2, a starting rotational speed n ₀ is determined at the time t ₀ , where n ₀ = n _E (t ₀ )

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 is stored in the control unit 16 determines (block 200). This mathematically determined speed curve n _math (t, n ₀ ) is continuously compared at point 201 with the measured actual speed n _{E of} the electric motor 2, 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 ), which is regarded as an error. Depending on the size of this error, an adaptation factor f (An _D ) is determined in block 202. This is fed to the block 203, where the friction characteristic stored in the control unit 16 is represented as a characteristic field as a function of the oil temperature. The adaption factor f (An _D ) and the consideration of the temperature are used to adapt this friction characteristic, whereby the adaptation factor f (An _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 fed to a torque interface 204, where it is used to compensate for unwanted mechanical deviations to determine the torque TrqEMDesCalc of the electric motor 2 to be controlled. 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 is stored in the control unit 16 and used in the next request. This requirement is when a new command for engaging the dog clutch 1 1 is issued. In the case, the stored friction characteristic curve is retrieved according to the method described and checked in dependence on the current speed n _{E of} the electric motor 2.

Claims

Claims 1. Method for determining a setpoint torque for controlling an electric machine of a motor vehicle, in which a force is transmitted between the electric machine (2) and an axle (8) of the motor vehicle by closing a claw coupling (11), characterized in that friction moments of the electric machine (2) are taken into account in the determination of the target torque when the jaw clutch (1 1) is open.

2. The method according to claim 1, characterized in that for determining the friction moments, a factor (Δη ₀ ) is determined, by means of which a friction characteristic is applied, from which a torque correction value (TrqFrc) is determined, which is used as a target torque (TrqEMDesCal).

3. The method according to claim 2, characterized in that the factor (Δη ₀ ) 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.

4. The method according to claim 3, characterized in that the mathematical see speed curve n _math (t, n ₀ ) from a rotational speed (n ₀ ) of the electric machine (2) at a start time (tO) is determined, wherein at the start time (tO ) there is no desired torque request to the electric machine (2).

5. The 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.

6. The method according to claim 2, characterized in that the friction characteristic is determined as a function of a temperature of the electric machine (2). Method according to at least one of the preceding claims, characterized in that after each opening of the dog clutch (1 1) the factor (Δη ₀ ) is determined and in the previous opening cycle of the dog clutch (1 1) created friction characteristic with the newly determined factor (Δη ₀ ) is corrected.

Device for determining a setpoint torque for controlling an electric machine of a motor vehicle, in which a force is transmitted between the electric machine (2) and a wheel (9, 10) having the axle (8) of the motor vehicle by closing a dog clutch (11), characterized in that means (16) are present, which take into account when the jaw clutch (1 1) friction moments of the electric machine (2) in determining the target torque.

Apparatus according to claim 8, characterized in that a control device (16) with the electric machine (2) and a speed sensor (19) is connected, which determines the rotational speed of the electric machine (2).

0. Device according to claim 8 or 9, characterized in that the

electric machine (2), the dog clutch (1 1) and a gear (12) which is connected to the axis (8) are arranged in a filled with oil structural unit (13).