DE102022213594A1 - Drivetrain with separating clutch unit with torque-limiting safety function - Google Patents

Abstract

Drive train (100) of a vehicle with at least one electric machine (103) with an electrically driven axle (101) of the drive, wherein the electric machine (103) can be connected to the electrically driven axle (101) via a claw clutch (102), wherein the claw clutch (102) with actuation contains an integrated torque limitation in that the claws of the claw clutch (102) have teeth (110) with positively angled tooth flanks, the opening force caused thereby acts against the closing force applied via an actuator device.

Description

The invention relates to a drive train of a vehicle with at least one electric machine with a primary and a secondary axle of the drive, wherein the electric machine can be connected to a primary or a secondary axle via a claw coupling.

State of the art

Vehicles with a hybrid drive structure have at least two drive units. These are usually an internal combustion engine and at least one electric motor. This means that the drive torque can be generated by both drive units or just by one when the hybrid vehicle is in operation.

Certain driving maneuvers can result in torques in the drive train, even in purely electrically powered vehicles, that exceed the nominal torque of the drive.

During such maneuvers, a high acceleration of the wheel is transferred via the transmission to the electric machine, which has a high inertia. The torsionally rigid system, the gear ratio of the transmission and the inertia of the rotor of the electric machine lead to very high torques in the drive train.

This torque increase must be taken into account when designing transmission components such as gears, bearings, shafts, etc. and can lead to larger, heavier and more expensive components.

A limitation of this torque increase can be prevented by slipping in frictional connections such as friction clutches.

Single-speed electric drive units usually do not have a friction clutch or similar installed, as this would lead to additional costs, greater complexity and also higher losses, e.g. due to clutch slip or splashing.

EN 10 2008 042 056 A1 shows a device for a vehicle which has an electric machine and an axle which can be driven by this electric machine, wherein the separable mechanical coupling between the drivable axle and the electric machine is designed as a simple, robust mechanical component.

The electric machine is separated from the driven axle by a claw clutch. Any synchronization required when engaging the clutch is carried out by the electric machine. The advantage of this design is that a robust, maintenance- and wear-free and inexpensive design can be used as the clutch. In various driving situations in a hybrid vehicle, it is advantageous to separate the electric machine from the rear axle. For example, an electric machine cannot deliver any significant torque at high speeds. If there is no gearbox between the electric machine and the driven axle, for example for space or cost reasons, it is energetically advantageous to decouple the electric machine from the drive axle at high speeds in order to avoid the electric machine rotating with its losses. For the same reason, it is advantageous to separate the electric machine from the driven axle when the vehicle is rolling freely.

US 11 167 649 B2 shows a vehicle system comprising: a primary axle and a secondary axle, the secondary axle including a dog clutch with teeth and an actuator for opening and closing the dog clutch; a first electric machine mechanically coupled to the primary axle and a second electric machine mechanically coupled to the secondary axle; and a controller including executable instructions stored in non-transferable memory to accelerate a vehicle via the first and second electric machines, reduce the power output of the second electric machine, and increase the output of the first electric machine when the vehicle reaches a threshold speed, to open the dog clutch when a derivative of a speed of the second electric machine exceeds a threshold. The vehicle system further includes additional instructions to deactivate the second electric machine after opening the dog clutch. The vehicle system further includes additional instructions to maintain power to the electric machine when the derivative of the speed of the second electric machine exceeds the threshold. The vehicle system includes opening the dog clutch via the actuator.

The object of the invention is to limit excessive torque in the drive train so that it can be designed to be lighter and therefore more cost-effective.

Description of the invention

The task is solved with a drive train of a vehicle with at least one electric electrical machine with at least one electrically driven axle, wherein the electrical machine can be connected to the electrically driven axle via a claw coupling, wherein the claw coupling with actuation contains an integrated torque limitation in that the claws of the claw coupling have flanks with an angle deflecting in the axial direction.

The term claw coupling is to be understood broadly and generally includes a positive-locking, separable coupling or a positive-locking, separable driving toothing.

The invention relates to a functional integration of a drive train with at least one electrically driven axle and a switchable positive-locking separating clutch arranged between the electric machine and the driven axle.

The claw clutch has an actuation that keeps the claw clutch closed up to a rated torque.

The actuator includes a bistable electromagnetically actuated switching actuator and/or a locking device to apply the closing force up to the nominal torque.

The claw coupling is provided in one embodiment with a spring mechanism so that it can remain closed even when de-energized

The torque limiter is integrated into the claw coupling as a decoupling unit, so that no additional components need to be installed. It is a positive connection that does not cause any additional losses.

By limiting excessive torques in the drive train, smaller bearings, narrower gears and a lighter, cheaper and more efficient system can be installed.

High load peaks lead to larger bearings and thus to a heavier and less efficient system. In particular, the non-load-dependent torque losses are significantly influenced by the bearing size. From this point of view, reducing these maximum load peaks leads to a smaller, more cost-effective and more efficient system.

Description of the characters

• 1 shows an embodiment of a claw coupling from the prior art,
• 2 shows a detail of a clutch tooth, after 1 ,
• 3 shows a second embodiment of a claw coupling,
• 4 shows a detail of a clutch tooth,
• 5 and 6 represent the operation of the claw clutch,
• 7 Principle representation,
• 8th shows an example of the control strategy for supplying current to the actuator.

7 shows a schematic diagram of a drive with an electrically driven axle 100, which has an electrical machine 103 and an electrically driven axle 101 with the drive wheels 104 and a differential 105. The mechanical coupling between the electrical machine 103 and the electrically driven axle 101 is realized by means of a claw clutch 102. When the claw clutch 102 is closed, a torque can be transmitted from the electrical machine to the driven axle or vice versa. When the claw clutch is open, no torque can be transmitted from the electrical machine to the driven axle or vice versa.

Such a claw coupling 102 is in the 1 and 2 To prevent the claw clutch from opening, either teeth 110 with straight tooth flanks or as in 2 shown, teeth 110 with tooth flanks in undercut are used.

The core of the invention is a structural modification of the existing axial claw coupling 102.

The teeth 110 of the claw clutch are - as in the 3 and 4 shown - designed in such a way that they generate an axial force F_a, which opens the decoupling unit, i.e. the claw coupling 102, at impermissibly high torques.

Secondary electric drives are often mounted on the front axle 101 of a vehicle. Due to the vehicle's braking force distribution, higher operating errors, namely torque peaks, can occur on the front axle during certain driving maneuvers.

The invention consists in designing the teeth in such a way that they generate an opening force F_a under load F_t. In 4 the positively angled teeth 110 of the claw coupling 102 are shown. It is a tooth profile whose flanks have an angle that is directed away in the axial direction.

A positively angled claw receptacle in the clutch disc 102a is easier to manufacture than a tooth profile with an undercut and enables faster and more cost-effective manufacturing processes such as sintering or fine forging. The tooth profile is a tooth profile whose flanks have an angle that is deflected in the axial direction.

In addition to changing the tooth shape, the actuation 106 of the claw clutch 102 must also be adjusted in order to actively open and close the claw clutch 102.

The actuation 106 must be able to generate a closing force that is greater than the resulting opening force of the teeth 110 at the nominal torque. If this nominal torque is exceeded, the axial forces of the teeth 110 exceed the actuation force and the claw clutch opens. Due to the tooth profile, the flanks of which have an angle that is directed away in the axial direction, a return spring in the actuator arrangement can be omitted. The opening force of the teeth must therefore be balanced with the closing force of the drive 107 of the actuation 106 at nominal and smaller torques.

This can be realized by a bistable electromagnetically actuated actuator according to 5 The electromagnet must be active while the clutch is closed and acts on the actuator rod 108, which is also guided inside the actuator.

The locking 109 in the actuation 106 with the claw coupling 102 is realized by a spring-loaded ball pressure piece, which locks the rod 108 of the drive 107 of the actuator in the "claw coupling closed" position. In the locked position, the drive 107 can be deactivated. The drive must be able to overcome the force of the locking 109

The axial opening force F_a is a function of coupling diameter, friction parameters such as friction coefficient µ and tooth angle a.

If a monostable actuator 106 with a spring mechanism in the rotating system is used, the claw clutch can be designed as normally closed so that the shift fork is not loaded. To do this, the closing spring must be arranged in the rotating system, between the shift sleeve and the shift claw.

The torque transmitted via the positive drive teeth causes a reaction force acting in the axial direction due to the tooth profile. There is a directly proportional relationship between the torque transmitted instantly via the drive teeth and the axial force component acting in the opening direction, which is influenced by the coefficient of friction in addition to the geometry parameters. In combination with a suitable actuator arrangement limited in terms of its maximum actuation or locking force, a torque-limiting function can be achieved.

8th shows an exemplary control strategy for supplying current to a monostable actuator in accordance with 5 .

The actuator current is designated by I, the torque by T and the position of the switching element by s. Indices “actual”, “desired” and “max” stand for the respective current values, target values and maximum values.

In step S1, a current torque requirement T _soll is determined. In step S2, the proportional actuator current I _soll ~ |T _soll | is determined and the position of the switching element is monitored, for example using a position sensor. Step S3 determines whether the switching element is in the end position, S _ist < S _soll .

Step S4 checks whether the actuator current is below the permissible limit or not, I _is < I _max . If this is not the case, an overload O is diagnosed and the process jumps to step S8.

Step S5 checks whether the actuator current is below a setpoint, I _ist < I _soll . Depending on the result of the query, step S6 or S7 follows with an increase in the actuator current Isoll = list + ΔI or a reduction in the actuator current $${\text{I}}_{\text{should}}={\text{I}}_{\text{is}}-\Delta \text{I}.$$

In step S8, the position of the switching element is queried.

Position changes can be responded to with a current change.

In combination with a sufficiently precise position determination, e.g. by means of a position sensor integrated in the actuator arrangement, and a suitable control strategy, the torque transmitted instantaneously via the drive gearing can be determined via the relationship between actuator force and actuator position. In this way, a torque-sensing function can be implemented in addition to or as an alternative to the torque-limiting function.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 102008042056 A1 [0008]
• US 11167649 B2 [0010]

Claims (7)

Drive train (100) of a vehicle with at least one electric machine (103) with at least one electrically driven axle (101), wherein the electric machine (103) can be connected to the electrically driven axle (101) via a claw clutch (102), wherein the claw clutch (102) contains an integrated torque limitation when actuated, in that the claws of the claw clutch (102) have teeth (110) with a tooth profile whose flanks have an angle deflecting in the axial direction. Drivetrain (100) to Claim 1 , characterized in that the claw clutch (102) has an actuator (106) which keeps the claw clutch (102) closed up to a nominal torque. Drivetrain (100) to Claim 2 , characterized in that the actuation includes a bistable electromagnetic actuator to apply the closing force up to the nominal torque. Drivetrain (100) to Claim 2 , characterized in that the actuator includes a locking device (106) to apply the closing force up to the nominal torque. Drivetrain (100) to Claim 3 and 4 , characterized in that the actuator includes a bistable electromagnetic actuator and a lock (106) to apply the closing force up to the nominal torque. Drivetrain (100) to Claim 1 , characterized in that the claw clutch is provided with a spring mechanism so that it is closed in the normal de-energized state. Method for controlling the torque of a drive train according to one of the preceding claims, wherein a sufficiently precise position determination is carried out by a position sensor integrated in the actuator arrangement, and the currently transmitted torque is determined via the relationship between actuator force and actuator position.

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