WO2011076487A1 - Method and device for engaging a claw coupling for driving an axis of a motor vehicle - Google Patents

Abstract

The invention relates to a method for engaging a claw coupling for driving a motor vehicle, said claw coupling (11) transmitting force between an electric motor (2) and the axis (8) of the motor vehicle supporting the wheels (9, 10). In order to engage, an approximately constant rotational speed differential range is formed from a synchronisation speed (n_s) of the electric machine (2) and a rotational speed (n_A) of the axis. In order to obtain, in a precise manner, the differential speed range required for engaging when the axis, which is to be driven, is at a low speed or at a standstill, the electric machine (2) is accelerated above the synchronisation speed (n_s) and subsequently, the speed (n_E) of the electric motor (2) is reduced and the claw coupling (11) is engaged when the reduced speed (n_E) of the electric machine (2) reaches the differential speed range (Δn).

Description

 Description title

 Method and device for engaging a dog clutch for driving an axle of a motor vehicle

State of the art

The invention relates to a method for engaging a dog clutch for driving an axle of a motor vehicle, wherein the dog clutch transmits a force between an electric machine and a wheel-carrying axle of the motor vehicle, wherein for engaging an approximately constant speed difference band from a synchronization speed of the electric machine and a Speed of the axle is formed 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 intervals 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 a nearly constant speed difference band between the electric drive and the axis to be driven Vehicle results. The axis is at a standstill or rotates only 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. Below a speed of 300 revolutions per minute, the electric machine can no longer be controlled precisely enough to set such a small speed difference as required by the differential speed range.

Disclosure of the invention

The inventive method for engaging a dog clutch for driving an axle of a motor vehicle having the features of claim 1 has the advantage that at low speeds or the stoppage of the driven axle the necessary for the clutch differential speed band can be reached exactly. Characterized in that the electric machine is accelerated beyond the synchronization speed and then the speed of the electric machine is withdrawn, wherein the dog clutch is engaged when the reduced rotational speed of the electrical machine has reached the differential speed band, can on a control of the electric machine at Speeds below 300 revolutions per minute are dispensed with. There is only a control of the electric machine and a monitoring of the speed behavior of the electric machine after the control. These steps are easy to perform and do not require additional hardware overhead.

Advantageously, the synchronization speed is determined from the vehicle speed. The speed of synchronization is understood to mean the speed which the electric machine must at least reach in order to come within the range of the rotational speed of the wheels of the motor vehicle, which is necessary in order to initiate a coupling process at all. It is assumed that the required differential speed range of 20 to 40 revolutions per minute is added to the synchronization speed or subtracted from this. When the speed of rotation of the electric machine approaches, the speed approaches that above the syn- rungsdrehzahl lying differential speed band, this speed is still above the synchronization speed.

In one embodiment, the speed of the electric machine is taken back by the electric machine is switched to a generator mode. The electric machine is braked and can roll out. That is, the speed of the electric machine decreases. At the same time, the mechanical energy of the electric machine is converted into electrical energy with which a high-voltage battery is charged, which supplies it with energy in the active state of the electric machine.

Alternatively, the speed of the electric machine is withdrawn by switching off the control of the electric machine. This only causes the electric machine to roll out, where its speed is reduced by the mass inertia of the electric machine. If the speed of the electric machine has fallen within the range of the differential speed band, a command for engaging the dog clutch is issued.

In a further development, a torque control of the electric machine requires a torque of 0 Nm. In such an embodiment remains the

Torque control of the electric machine is active and is set only to such a target torque, which reliably causes the speed of the electric machine is reduced to reach the differential speed band of 20 to 40 revolutions per minute between the electric machine and the vehicle axle.

Advantageously, the electric machine is accelerated from standstill. Since the electric machine from standstill can reach a maximum torque very quickly, the required synchronization speed or a speed above this synchronization speed is reached in a very short period of time, so that the coupling process can be initiated at short notice.

In one embodiment, the vehicle is during Einkuppeins at a standstill. The proposed method can thus also be used simply to engage the dog clutch in order to drive the vehicle. In In this case, a force is transmitted by the electric machine to the stationary vehicle axle, whereby the motor vehicle is put into a driving movement. In one variant, the axle of the vehicle during the engagement one

Speed of less than 300 revolutions per minute. Thus, a reliable engagement of the dog clutch is possible even at very slow movements of the vehicle, which is reflected in the low speed of the axle.

A further development of the invention relates to a device for engaging a dog clutch for driving an axle of a motor vehicle, wherein the dog clutch transmits a force between an electric machine and an axle supporting the wheels of the motor vehicle, wherein for engaging peln an approximately constant speed difference band from a Synchronisie - Speed of the electrical machine and a speed of the axis is formed. In order to precisely reach the differential speed band necessary for engagement at low speeds or when the axis to be driven is stopped, means are provided which accelerate the electric machine beyond the synchronization speed and then retract the speed of the electric machine, whereby the dog clutch is engaged, when the withdrawn speed of the electric machine reaches the differential speed band. There is only a control of the electric machine and a monitoring of the speed behavior of the electrical machine after the activation. On a regulation of the rotational speed of the electric machine for setting the required differential speed band can thus be dispensed with.

In one variant, a control unit is connected to the electric machine and a speed sensor, wherein the control unit, the electric machine in

Depending on the signals of the speed of the wheel or the axis measuring speed sensor drives. The setting of the differential speed band between the electric machine and the axle or the wheels of the motor vehicle is thus possible without much design effort, since wheel speed sensors are already present in the motor vehicle for the execution of other vehicle functions. 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 wheel of the rear axle 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. 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 measured at the time T2 speed in the differential speed range, so at this time T2, the dog clutch 1 1 from the open to the closed

Move state (diagram 3c).

In this process, a vibration-resistant as possible behavior is set to a shaft 18 of the electric motor 2, since at high torsional vibrations of the engagement 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 be enhanced by 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 setpoint 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 (tO)

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 (block 200). This mathematically determined speed curve n _math (t, n ₀ ) is compared in point 201 continuously 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 ) is formed. Depending on the size of this difference, 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 based on a torque interface

204, where it is used with compensation of 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 A method for engaging a dog clutch for driving an axle of a motor vehicle, wherein the dog clutch (1 1) transmits a force between an electric machine (2) and a, wheels (9, 10) supporting axle (8) of the motor vehicle, wherein for engaging a approximately constant differential speed band (Δη) is formed from a synchronization rotational speed (n _s ) of the electric machine (2) and a rotational speed (n _A ) of the axle (8), characterized in that the electric machine (2) exceeds the synchronization rotational speed (Δ n _s ) is accelerated and then the rotational speed (n _E ) of the electric machine (2) is withdrawn, wherein the dog clutch (1 1) is engaged when the withdrawn rotational speed (n _E ) of the electric machine (2) the differential speed band ( Δη). A method according to claim 1, characterized in that the synchronization speed (n _s ) from the vehicle speed is determined. A method according to claim 1, characterized in that the rotational speed (n _E ) of the electric machine (2) is withdrawn by the electric machine (2) is switched to a generator mode. A method according to claim 1, characterized in that the rotational speed (n _E ) of the electric machine (2) is withdrawn by the activation of the electric machine (2) is switched off. A method according to claim 3 or 4, characterized in that a torque control of the electric machine (2) requests a torque of 0 Nm. 6. The method according to any one of the preceding claims, characterized in that the electric machine (2) is accelerated from standstill. 7. The method according to claim 1, characterized in that the vehicle is at standstill during engagement. 8. The method according to claim 1, characterized in that the axis (8) of the vehicle during engagement has a speed (n _A ) of less than 300 revolutions per minute. 9. A device for engaging a dog clutch for driving an axle of a motor vehicle, wherein the dog clutch (1 1) transmits a force between an electric machine (2) and a, wheels (9, 10) supporting the axle (8) of the motor vehicle, wherein Engaging an approximately constant speed difference band (Δη) from a Synchrondrehdrehlzahl (n _s ) of the electric machine (2) and a rotational speed (n _A ) of the axis (8) is formed, characterized in that means (16, 17) are present which accelerate the electric machine (2) beyond the synchronization speed (n _s ) and then retract the speed (n _E ) of the electric machine (2), wherein the dog clutch (1 1) is engaged when the withdrawn speed ( n _E ) of the electric machine (2) reaches the differential speed band (Δη). 10. The device according to claim 9, characterized in that a control unit (16) with the electric machine (2) and a speed sensor (17) is connected, wherein the control device (16), the electric machine (2) in response to the signals of the Speed (n _A ) of the wheel (9, 10) or the axis (8) measuring speed sensor (17) controls.