Method and device for operating a claw coupling in a motor vehicle with an electric motor drive

Abstract

Method for operating a dog clutch in a motor vehicle with an electric motor drive, in which the two clutch parts (11a, 11b) of the dog clutch (11) transmit a force between the electric motor drive (2) and an axle (8) having wheels (9, 10) of the motor vehicle and are set to a predetermined speed difference between the axle (8) and the electric motor drive (2) before the dog clutch (11) is closed, wherein the predetermined speed difference is formed from a synchronization speed of the electric motor drive (2) and a speed of the wheel (9, 10) of the motor vehicle, wherein during the operation of the motor vehicle with the dog clutch (11) not closed the electric motor drive (2) is accelerated to a speed which lags behind the synchronization speed, characterized in thatthat, with the claw clutch (11) open, before the moment of an engagement signal, the electric motor drive (2) is operated in a freewheeling state by interrupting a connection between the electric motor drive (2) and an energy source (15) of the electric motor drive (2), whereupon the electric motor drive (2) is accelerated by a drag torque of a transmission (12), the transmission (12) being moved via the axle (8) supporting the wheels (9, 10) of the moving motor vehicle, so that before the moment of the engagement signal the passive electric motor drive is accelerated by the drag torque to a speed which lags behind the synchronization speed.

Description

State of the art The invention relates to a method for operating a dog clutch in a motor vehicle with an electric motor drive, in which the two clutch parts of the dog clutch transmit a force between the electric motor drive and an axle having wheels of the motor vehicle and are adjusted to a predetermined speed difference between the axle and the electric motor drive before the dog clutch is closed, wherein the predetermined speed difference is formed from a synchronization speed of the electric motor drive and a speed of the wheel of the motor vehicle, and to a device for carrying out the method. Dog clutches are used in motor vehicles to transmit rotary motion and torque. The two coupling elements of a dog clutch have teeth arranged at predetermined intervals. One coupling element is connected to the drive, and the other to the driven axle of the vehicle. To engage the dog clutch in a moving vehicle, a differential rotational speed between the two coupling elements is necessary so that the teeth of the two coupling elements mesh. This means that the teeth of one coupling element engage with the spaces between the teeth of the other coupling element, and vice versa. This is ensured when the two coupling elements have a differential rotational speed relative to each other. When a dog clutch is used in hybrid vehicles, which have both an internal combustion engine and an electric motor for propulsion, it often occurs that when the vehicle is being driven by the internal combustion engine, the electric motor is engaged via the dog clutch to assist the vehicle's propulsion. At this point, the electric motor is stationary and must first accelerate to the speed of the axle that carries the wheels. For this purpose, the electric motor requires energy from its power source. Furthermore, the electric motor's start-up time from a standstill is relatively long, during which time it cannot contribute to the desired propulsion. From EP 1 142 743 A2, a method for operating a jaw clutch in a motor vehicle with an electric motor drive is known, in which the synchronization speed between a transmission stage coupled to the electric motor drive and a clutch sleeve mounted on a shaft is achieved by means of mechanical synchronization when closing the jaw clutch, in which a clutch sleeve of the jaw clutch slides onto a synchronization ring until the synchronization speed is reached. US Patent 5,827,148 A discloses a known electromagnetically actuated jaw coupling comprising a central body equipped with permanent magnets and flux guides. The central body is axially displaceable on a shaft by applying a corresponding current to an electromagnetic actuator. Due to the interaction of the permanent magnets with the magnets of the electromagnet, the central body can be switched in three positions. A drive device for an electric vehicle is known from DE 69 623 111 T2. Disclosure of the invention The inventive method for operating a dog clutch in a motor vehicle with an electric motor drive, comprising the features of claim 1, has the advantage that the synchronization speed required for engaging the dog clutch is reached in a very short time. Because, during the operation of the motor vehicle with the dog clutch open, the passive electric motor drive is accelerated, particularly from standstill, to a speed that follows the synchronization speed, the electric motor drive is always in rotational motion, which, however, is not used for propelling the vehicle when the dog clutch is open. When engagement of the dog clutch is required, the synchronization time is very short, since the electric motor drive is already rotating close to the synchronization speed.This eliminates the time required to start the electric motor drive and to overcome the inertia of the electric motor drive. For the dog clutch to engage so that the electric motor transmits its generated torque to the vehicle axle, the clutch element connected to the electric motor must reach a synchronization speed. The clutch element connected to the vehicle axle rotates at a speed that is a difference higher or lower than the synchronization speed. This ensures that the two clutch elements of the dog clutch can engage, with each tooth of one clutch element engaging a corresponding gap in the other. Because the electric motor is already in motion before the dog clutch engages, very little time is required to reach the synchronization speed, as only the difference between the two speeds needs to be compensated for.This compensation is achieved by electrically driving the electric motor again at the moment the dog clutch closes. With the dog clutch open, before the engagement signal is received, the electric motor operates in a freewheeling state by interrupting the connection between the electric motor and its power source. The electric motor is then accelerated by a drag torque from a gearbox, which is driven by the axle supporting the wheels of the moving vehicle. Thus, before the engagement signal is received, the passive electric motor is accelerated by the drag torque to a speed that lags behind the synchronization speed. In the case of a hybrid engine, the vehicle is kept in motion by the combustion engine, with the drive motion of the vehicle's wheels being transferred to the transmission, which also rotates in this state. Losses and friction within the transmission assembly accelerate the electric motor drive, causing it to passively lag behind the synchronization speed. This behavior significantly contributes to reducing the synchronization time. In the freewheeling operating state, there is no active control of the torque of the electric motor drive, so the electric motor drive is free from any influence by external signals. In this situation, the electric motor drive's movement is influenced solely by the gearbox arrangement. In one variant, an actuator of the electric motor drive is put into idle mode. In the case of an electric motor, this actuator is a pulse inverter whose semiconductor elements are blocked, so that no control signals reach the electric motor drive. Advantageously, the speed of the electric motor drive is accelerated up to a speed threshold that is above the clutch speed at which the jaw clutch engages. This setting ensures that the synchronization speed is always reached. It also prevents the electric motor drive from overspeeding, thus preventing mechanical overload. In one embodiment, after the passive drive phase is completed and the clutch is engaged, the electric motor is subjected to active speed control. This ensures that the torque contributed by the electric motor to the propulsion of the vehicle is fully aligned with the requirements of the driver and / or the vehicle, and normal driving operation with the electric motor resumes. A further development relates to a device for operating a dog clutch in a motor vehicle with an electric motor drive, in which the two clutch parts of the dog clutch transmit a force between the electric motor drive and an axle having wheels of the motor vehicle and are set to a predetermined speed difference between the axle and the electric motor drive before the dog clutch closes, wherein the predetermined speed difference is formed from a synchronization speed of the wheel and a speed of the electric motor drive. In order to shorten the synchronization time, means are provided which, during the operation of the motor vehicle with the dog clutch not closed, accelerate the electric motor drive, in particular from standstill, to a speed that lags behind the synchronization speed, wherein means are provided thatwhich, with the clutch open, operate the electric motor in a freewheeling state before the engagement signal is received. This is achieved by interrupting the connection between the electric motor and its power source. The electric motor can then be accelerated by a drag torque from a transmission, provided the transmission is moved via the axle supporting the wheels of the moving vehicle. This allows the passive electric motor to be accelerated by the drag torque to a speed that lags behind the synchronization speed before the engagement signal is received. Since the electric motor is already rotating close to the synchronization speed at the time of the engagement signal, the time required to reach the synchronization speed is significantly reduced.This eliminates the time required to start the electric motor. Overcoming the inertia of the electric motor is only partially necessary, as the electric motor is already in motion. Advantageously, the claw coupling and a gearbox connected to the vehicle axle form a single structural unit. This results in a more compact design. In one embodiment, the electric motor drive and / or the jaw clutch are arranged in the transmission oil. This means that when the transmission moves, this movement is transferred to the transmission oil, whereby friction and losses in the transmission assembly transmit a drag torque to the two coupling elements of the jaw clutch and the electric motor drive. Even when the jaw clutch is open, a force is exerted on the electric motor drive via the coupling element connected to it, setting it into a rotary motion. The invention allows for numerous embodiments. One of these will be explained in more detail with reference to the figures shown in the drawing. It shows: Fig. 1: Schematic representation of a vehicle with a hybrid drive; Fig. 2: Schematic flowchart for an embodiment of the method according to the invention. Figure 1 shows a hybrid vehicle with 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 drive different axles of the hybrid vehicle. The internal combustion engine 1 is connected to the front axle 4 of the hybrid vehicle via a first transmission 3, 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 a structural unit 13 with a dog clutch 11 and a second gearbox 12. The gearbox 12 connects to the rear axle 8 of the hybrid vehicle. The electric motor 2, the dog clutch 11, and the gearbox 12 are located in a common oil pan. The jaw coupling 11 is a special type of coupling. Both coupling elements 11a and 11b of the jaw coupling 11 have teeth spaced at predetermined intervals. To close the jaw coupling 11, the teeth of one coupling element 11a engage with the gaps of the other coupling element 11b, creating a tight connection and ensuring efficient power transmission. Coupling element 11a of the jaw coupling 11 is connected to the electric motor 2, while the second coupling element 11b is connected to the gearbox 12. The electric motor 2 is connected to a power output stage 14 in the form of a pulse inverter, which generates the current for operating 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 operating the electric motor 2. In the present embodiment, the electric motor 2 is designed as a permanent magnet synchronous machine. The power output stage 14 also includes a control unit (not shown) which generates the clock signals for the semiconductor switches of the power output stage 14, which control these switches and thereby set the electric motor 2 into rotational motion. In hybrid vehicles, situations frequently arise where the vehicle is driven solely by the combustion engine 1. Although the drive, as described, is at the front axle 4 of the hybrid vehicle, the rear axle 8 with wheels 9 and 10 is nevertheless accelerated by the vehicle's movement. Since the rear axle 8 is rigidly connected to the transmission 12, which in this case has only one fixed gear ratio, the transmission 12 rotates according to the vehicle speed. Due to the connection of the transmission 12 with the second clutch element 11b of the dog clutch 11, this clutch element 11b is also in a rotational motion. In the event of increased slippage of the wheels 5, 6 of the front axle 4, the wheels 9, 10 of the switchable rear axle 8 are driven by the electric motor 2. The method for reducing the synchronization time when engaging the dog clutch at medium and high speeds of the hybrid vehicle will be explained in more detail with reference to Fig. 2. Block 100 detects whether the dog clutch 11 is open. If so, block 101 switches the electric motor 1 into freewheel mode. This puts the semiconductor switches of the pulse inverter of the power output stage 14 of the electric motor 2 into a blocking state, thereby interrupting the energy flow from the high-voltage battery 15 to the electric motor 2, as the pulse inverter no longer sends clock signals. The electric motor is therefore no longer able to generate any electrical torque. Block 102 checks whether the hybrid vehicle is in motion. If the hybrid vehicle is traveling at high speed, high wheel speeds result, which are transmitted to the transmission 12 and the second dog clutch element 11b, causing them to rotate as well. At high speeds, the movement of the transmission 12 induces friction in the transmission oil, which is transmitted to the electric motor 2. Due to these losses in the transmission 12, the electric motor also begins to rotate. The synchronization speed of the electric motor 2, which is necessary for closing the claw coupling 11, is determined in block 103 from the vehicle speed. If a signal to engage the dog clutch 11 is received in block 104, the speed of the electric motor 2 is measured by means of a speed sensor (not shown) and the difference to the synchronization speed required to close the dog clutch 11 is determined (block 105). This synchronization speed always differs from the speed of the rear axle 8 by a predetermined amount. This difference is necessary so that the dog clutch 11 engages correctly, tooth to tooth. In block 106, the electric motor 2 is switched from the freewheeling operating state to the driven operating state by switching the semiconductor switches of the pulse inverter of the power output stage 14 back to forward bias, and the pulse inverter of the power output stage 14 again supplies clock signals to build up an electric torque by the electric motor 2. The electric torque supplied by the electric motor 2 in this case is only such that only the difference in torque, in which the electric motor 2 is already operating due to the drag torque of the gearbox 12, needs to be compensated for until the synchronization speed is reached, which is why only a very short synchronization time is required. Once this synchronization speed is achieved by the actively controlled operation of the electric motor 2, the jaw clutch 11 is closed in block 107. The speed of electric motor 2 is limited to a predetermined speed in block 108, with this predetermined speed being higher than the synchronization speed. The predetermined speed is maintained until the speed of the second clutch element 11b, and thus the speed of the rear axle 8, decreases again, at which point the synchronization speed also decreases. During the described procedure, the temperature of electric motor 2 is monitored. Since electric motor 2 is designed as a permanent magnet synchronous machine, the rotor is heated by the constantly rotating field, which can lead to overheating of electric motor 2. If such an overheating occurs, active regulation of electric motor 2 is initiated.

Claims

A method for operating a dog clutch in a motor vehicle with an electric motor drive, in which the two clutch parts (11a, 11b) of the dog clutch (11) transmit a force between the electric motor drive (2) and an axle (8) having wheels (9, 10) of the motor vehicle and are set to a predetermined speed difference between the axle (8) and the electric motor drive (2) before the dog clutch (11) is closed, wherein the predetermined speed difference is formed from a synchronization speed of the electric motor drive (2) and a speed of the wheel (9, 10) of the motor vehicle, wherein during the operation of the motor vehicle with the dog clutch (11) not closed, the electric motor drive (2) is accelerated to a speed which lags behind the synchronization speed, characterized in thatthat, with the claw clutch (11) open, before the moment of an engagement signal, the electric motor drive (2) is operated in a freewheeling state by interrupting a connection between the electric motor drive (2) and an energy source (15) of the electric motor drive (2), whereupon the electric motor drive (2) is accelerated by a drag torque of a transmission (12), the transmission (12) being moved via the axle (8) supporting the wheels (9, 10) of the moving motor vehicle, so that before the moment of the engagement signal the passive electric motor drive is accelerated by the drag torque to a speed which lags behind the synchronization speed. Method according to claim 1, characterized in that the passive electromechanical drive (2) is accelerated from standstill to the speed which follows the synchronization speed. Method according to claim 1, characterized in that an actuator (14) of the electromechanical drive (2) is put into an idle state. Method according to one of the preceding claims, characterized in that the rotational speed of the electric motor drive (2) is accelerated up to a rotational speed threshold which is above a clutch speed at which the jaw clutch (11) is closed. Method according to claim 3, characterized in that the electromechanical drive (2) is subjected to active speed control after the completion of the passive drive phase. Device for operating a dog clutch in a motor vehicle with an electric motor drive, in which the two clutch parts (11a, 11b) of the dog clutch (11) transmit a force between the electric motor drive (2) and an axle (8) having wheels (9, 10) of the motor vehicle and are set to a predetermined speed difference between the axle (8) and the electric motor drive (2) before the dog clutch (11) is closed, wherein the predetermined speed difference is formed from a synchronization speed of the wheel (9, 10) of the motor vehicle and a speed of the electric motor drive (2), wherein means (12) are provided which, during the operation of the motor vehicle with the dog clutch (11) not closed, accelerate the electric motor drive (2) to a speed which lags behind the synchronization speed, characterized in that means are provided,which, with the claw clutch (11) open, operate the electric motor drive (2) in a freewheeling state before the moment of an engagement signal, by interrupting a connection between the electric motor drive (2) and an energy source (15) of the electric motor drive (2), whereupon the electric motor drive (2) can be accelerated by a drag torque of a transmission (12) when the transmission (12) is moved via the axle (8) supporting the wheels (9, 10) of the moving motor vehicle, so that before the moment of the engagement signal the passive electric motor drive can be accelerated by the drag torque to a speed which lags behind the synchronization speed. Device according to claim 6, characterized in that the claw coupling (11) and a transmission (12) which is connected to the axle (8) of the motor vehicle form a structural unit (13). Device according to claim 7, characterized in that the electric motor drive (2) and / or the claw coupling (11) is arranged in the transmission oil.

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