Dog clutch and internal combustion engine having a dog clutch

Abstract

The invention relates to a switchable dog clutch (1) having a first clutch partner (2) which has a first dog toothing (12) and can be rotated about an axis of rotation (3), a second clutch partner (4) which has a second dog toothing (14) for engagement in the first dog toothing (12), characterized by a blocking element (5) which can be displaced radially with respect to the axis of rotation (3) by centrifugal force, is arranged axially between the two clutch partners (2, 4), in a radially outer position is supported on a first support surface (6) of the first clutch partner (2) and on a second support surface (8) of the second clutch partner (4), in a radially inner position axially overlaps with at least one of the two support surfaces (6, 8). The invention furthermore relates to an internal combustion engine having a dog clutch of this type.

Description

[0001] P241859

[0002] Claw coupling and internal combustion engine with claw coupling

[0003] The invention relates to a switchable jaw coupling with a first coupling partner having a first jaw toothing and a second coupling partner having a second jaw toothing, having the features of the preamble according to claim 1. Furthermore, the invention relates to an internal combustion engine with a generator and such a switchable jaw coupling according to claim 10.

[0004] In motor vehicles, especially hybrid vehicles, particularly plug-in hybrids (PHEVs) and range-extender electric vehicles (REEVs), a clutch is required to disconnect the combustion engine from a generator or electric motor when needed. Disconnecting the combustion engine prevents engine drag during electric operation, reducing efficiency losses and noise. A dog clutch (tooth clutch) is generally suitable for positive-locking disconnection because it provides torsionally rigid power transmission when engaged and generates virtually no drag losses when disengaged. However, rapid shifting, service life, and safety at high speed differentials pose particular challenges.

[0005] Several solutions are known from the prior art. For example, DE 102006 009 750 B4 discloses a selectively operable freewheel torque transmission mechanism in which a friction-actuated actuator is arranged parallel to a freewheel clutch. A fluid-actuated piston acts on a cage mechanism of the freewheel clutch to reverse its locking direction. A disadvantage of this concept, however, is that continuous hydraulic pressure must be applied to maintain a switching state, and thus the clutch function is not self-holding in the event of a malfunction (e.g., pressure loss). Furthermore, the permanent friction activation leads to energy losses and wear.

[0006] From DE 10 2014 211 505 A1, a jaw clutch with a friction brake is known which, when the jaw teeth disengage, presses a friction disc against a counter disc P241859 to dampen relative rotations. This is intended to prevent chattering noises ("rattling") without requiring full synchronization. However, this solution requires additional components (friction discs, springs) and, in the disengaged state, causes hydraulic resistance or drag torque. The continuous friction coupling can impair efficiency and necessitates precise adjustment of the spring forces to ensure effective braking while minimizing unnecessary losses.

[0007] DE 11 2018 002 687 T5 describes an overrunning clutch and control arrangement with a freewheel locking element (pawl) that can hold a control element in a releasable position. The pawl prevents unintentional displacement of the control element due to viscous oil or other parasitic torques at very low temperatures. While this prevents unintentional engagement of the clutch in freewheel mode, the design is complex: it requires separate external actuator components, detent mechanisms, and return springs. Complex tolerance chains can lead to stiffness and necessitate tight manufacturing tolerances.

[0008] German patent DE 11 2023 001 174 T5 discloses a coupling arrangement with at least three operating states. In this design, a jaw coupling ring is axially displaced between an open state, a transition state with one-sided freewheeling, and a locked state. A ratchet arrangement of rockers and ramps allows torque transmission in only one direction in the transition state, while in the locked state, the jaw teeth fully engage. While this solution reduces drag losses and enables a smoother transition, it requires an additional shift ring and several precision components. The overall structure is relatively complex and bulky, as it integrates several rockers, ramps, and springs in addition to the axially displaceable jaw element. This can increase manufacturing costs and presents challenges in the event of a failure (e.g.,Actuator failure also lacks an inherent emergency stop mechanism, as the control unit must remain continuously active to maintain the open position. P241859.

[0009] In summary, known clutch systems for hybrid drives have a number of disadvantages. Either a continuous energy supply (hydraulic or electric) is required to maintain a decoupled state, or friction elements are used, which introduce inefficiencies. Other solutions significantly increase the number of components and complexity. None of the known devices offers a purely mechanical self-holding function that reliably prevents uncontrolled clutch engagement when the actuating force is removed, while requiring minimal additional components.

[0010] Object of the invention

[0011] It is therefore an object of the present invention to provide a coupling device that overcomes the aforementioned disadvantages. In particular, a switchable dog clutch is to be provided in a hybrid vehicle drive system, which, when actuated, reliably disconnects the connection between the combustion engine and the generator and remains automatically closed in the unactuated state, without the possibility of uncontrolled (dangerous) opening or closing of the clutch in the event of a failure of the actuating force.

[0012] The problem is solved with a switchable jaw coupling for selective torque transmission, with a first coupling partner having a first jaw toothing and rotatable about an axis of rotation, a second coupling partner having a second jaw toothing for engagement with the first jaw toothing, wherein a locking element, which can be displaced radially to the axis of rotation by centrifugal force, is arranged axially between the two coupling partners, in a radially outer position bearing on a first support surface of the first coupling partner and on a second support surface of the second coupling partner, and in a radially inner position axially overlapping with at least one of the two support surfaces.

[0013] The advantages of this combination lie particularly in a purely inertia-controlled self-holding mechanism that requires no permanent external power supply. P241859

[0014] The radially outward spring-mounted pawl mechanically locks the jaw coupling in the unactuated state. This is achieved solely through the centrifugal force of the locking element – ​​no additional actuator forces are required during normal operation. Compared to the prior art with permanently pressurized couplings or friction-based retaining elements, this eliminates the need for a constantly applied holding force, thus preventing friction losses. Furthermore, the lock provides positive engagement in both directions of rotation, ensuring the coupling remains securely closed even under varying torques (forward-reverse operation). Overall, this results in increased operational reliability, as uncontrolled opening or closing cannot occur even if the actuating force or control unit fails, thus preventing dangerous driving conditions and coupling damage.

[0015] The term self-locking mechanism refers to a mechanical locking system that holds the coupling in a specific state without a continuous external energy supply. This means the coupling remains closed (or locked) on its own until it is actively disengaged. This prevents the coupling from unintentionally opening or closing, especially in the event of a fault.

[0016] It is particularly preferred that the locking element be designed as one or more arc-shaped segments. This allows for optimal use of the available installation space, as an arc-shaped locking element conforms to the round shape of the coupling partners. Several segment-shaped weights can be distributed around the circumference to achieve a more uniform mass distribution and redundancy. The use of arc-shaped segments also makes it possible to accommodate sufficiently large masses for the centrifugal force effect without extending the coupling in the axial direction. In a particular embodiment, the locking element can be held in a recess on the first coupling partner and pivot around the holder.

[0017] It is also preferred that the first support surface be designed as an axial projection of the first coupling partner. This design simplifies the construction by using an integral projection on one coupling partner as a stop. P241859

[0018] Instead of a separate part, the support surface is formed directly by the shape of the first coupling partner. This reduces the number of components and eliminates potential joining or loosening points. Furthermore, the axial projection ensures a precisely defined contact surface, which increases wear resistance and makes manufacturing tolerances more manageable.

[0019] In another preferred embodiment, the axial projection is designed as a ring. An annular projection provides extensive support for the locking element. The ring-segment-like (partially circular) design increases the contact area between the locking element and the support surface. This significantly reduces the surface pressure, so that even at high torques, indentation or settling is minimal. Furthermore, such an annular segment projection can prevent the misalignments or edge pressures that frequently occur in practice, as the load is distributed evenly across the arch.

[0020] It may also be preferable for the second coupling partner to be cup-shaped with a base and a wall, the wall forming a radial stop for the locking element. Due to the cup shape of the second coupling partner, its cylindrical wall automatically forms a guide for the radially movable locking element. The radial stop on the wall limits the maximum outward deflection of the pawl. This has two advantages: First, it reliably prevents the locking element from being ejected or jammed, thus increasing operational reliability. Second, the stop precisely defines the outer locking position in which the element is supported by both support surfaces. Manufacturing the second partner as a cup with an integral stop contour requires no additional components and yet ensures precise positioning of the locking element in its end position.

[0021] Furthermore, it is particularly advantageous that the locking element is spring-loaded by a return spring. The return spring ensures that the locking element reliably returns to its initial position (radially inward) when the engine speed decreases. This guarantees that the locking element does not unintentionally remain in the outer position when the clutch components are stationary or rotating slowly. This is important, for example, to have defined starting conditions when engaging the clutch again. The spring ensures that the clutch is ready to engage even at low engine speeds and prevents rattling noises from the unloaded locking element. Overall, the pre-tensioned return spring increases the functional reserve in the limiting range, such as during vibrations or brief fluctuations in engine speed.

[0022] Furthermore, it is advantageous that one of the coupling partners has a projection around which the return spring is wound, and that the return spring is attached to the coupling partner with the projection as well as to the locking element. This allows for a particularly compact integration of the return spring. The projection—for example, a cylindrical pin or an annular protrusion on the coupling partner—serves simultaneously as a spring guide and anchor. The helical compression spring can thus be arranged around this projection in a space-saving manner. Due to the dual attachment (to the coupling partner and the movable locking element), the spring acts reliably in tension or compression without requiring additional guide components. This design reduces assembly effort and eliminates loose spring ends that could otherwise rub or rattle. In addition, the spring force is transferred directly into the components involved, ensuring precise and low-loss power transmission.

[0023] Furthermore, it is advantageous that the jaw coupling has an actuator that is radially mounted in one of the coupling partners and axially supported on the other coupling partner by an axial roller bearing. The use of a radially mounted actuator allows the jaw coupling to be kept very slim, as no axially positioned cylinder is required. The actuator – for example, an electromagnetic switching bolt or a hydraulic actuating piston – engages radially within one coupling partner. An axial roller bearing is provided on the opposite coupling partner so that the force exerted by the actuator can be axially supported without impeding relative movements between the partners. This roller bearing (an axial roller or ball bearing) thus absorbs the reaction forces and enables low-friction axial displacement between the actuator and the coupling partner.This makes the shifting motion very smooth, minimizing wear and friction losses. Overall, this contributes to shorter shift times, reduced actuator stress, and an increased clutch service life.

[0024] A particularly advantageous feature is that the actuator has a ramp for interaction with a counter-ramp on the locking element. This ramp-like coupling positively translates the movement generated by the actuator into a radial movement of the locking element. When the actuator is actuated, the inclined ramp surfaces slide over one another, forcing the locking element in the desired direction (typically radially inwards to release the lock). This principle is self-reinforcing – a small axial or radial movement of the actuator can transmit a relatively large force to the locking element. This allows strong return springs or high centrifugal forces to be reliably overcome without requiring an oversized actuator. Furthermore, locking and unlocking are very fast because the ramps provide continuous force transmission and there are no dead legs.The combination of ramp and counter-ramp thus ensures precise and rapid operation of the locking element even under difficult conditions.

[0025] The problem is ultimately solved by an internal combustion engine with a generator and a switchable dog clutch according to one of the preceding claims, with which the generator can be disconnected from the internal combustion engine. Such a drive makes it possible to decouple the generator—or, in a hybrid vehicle, the electric motor—from the internal combustion engine as needed. Advantages arise particularly in driving conditions where the internal combustion engine is not required: By opening the dog clutch according to the invention, the engine can be completely switched off and decoupled from the drivetrain without the latter being dragged along. This significantly increases efficiency in purely electric driving mode. When the generator is re-engaged, the positive-locking clutch allows lossless torque transmission for recuperation or the hybrid drive. In addition, the detachable connection improves the start-stop system.

[0026] Comfort and shifting behavior: The engine can be engaged smoothly because the clutch locks and releases in an optimal relative position. Overall, starting comfort, the efficiency of the entire system, and the vehicle's operational safety are significantly improved, as unwanted interaction between the combustion engine and the electric motor is eliminated when decoupled.

[0027] Brief description of the drawings

[0028] The invention is explained in more detail using the figures as examples. They show:

[0029] Fig. 1 shows a longitudinal section of the switchable claw coupling according to the invention in the switched state (actuator off), in which the first coupling partner represents the torque input side,

[0030] Fig. 2 shows the claw coupling according to Figure 1 in the switched state (actuator off), in which the first coupling partner represents the torque output side,

[0031] Fig. 3 shows the claw coupling according to Figure 1 in the actuated state (actuator on), in which the coupling partners are stationary.

[0032] Fig. 4 shows the claw coupling according to Figure 1 in the actuated state (actuator on), in which the second coupling partner rotates,

[0033] Fig. 5 shows a cross-section of the jaw coupling according to Figure 1 at rest and

[0034] Fig. 6 shows a cross-section of the claw coupling according to Figure 1, in which the locking element is displaced outwards by centrifugal force.

[0035] Detailed description of drawings P241859

[0036] Figure 1 shows a jaw coupling 1 according to the invention with a first coupling partner 2, which has a first shaft toothing 24 for a shaft (not shown). The second coupling partner 4 is formed in two parts, consisting of a cup part 23 and a cranked disc 27. The disc 27 engages with an external toothing in an internal toothing of the cup part 23, so that the disc 27 is axially displaceable relative to the cup part 23. The cup part 23 has a second shaft toothing 25 on its base 20 for a shaft (also not shown). The wall 21 of the cup part 23 is formed by spaced-apart ring segments 17. Both coupling partners 2, 4 are rotatable about a common axis of rotation 3.

[0037] An axial roller bearing 18 is provided for the axial support of an actuator 10 radially integrated into the first coupling partner 2. By applying a force F, the actuator 10 can be displaced axially against the preload force of a return spring 19, for example, a disc spring. The actuator 10 acts on the disc 27 via an axial bearing disk 28.

[0038] A radially movable locking element 5 is arranged radially outside the actuator 10. In this case, the locking element 5 is formed by two arc-shaped segments (Figs. 5 and 6) which are held in the cup part 23 by a recess 15. Each locking element 5 is provided with a retaining spring 9 which, in the absence of centrifugal forces, ensures that the locking element assumes its radially inner position. The retaining spring 9 is arranged on a pin-like projection 7 and is attached both to the locking element 5 and to a recess 30 located between the ring segments 17 of the cup part 23. Stops 29 are provided to determine its inner end position.

[0039] In the position of the actuator (OFF) shown in Figures 1 and 2, a torque can be transmitted either from the first coupling partner 2 to the second coupling partner 4 (Figure 1), represented by the torque flow 26, or from the second coupling partner 4 to the first coupling partner 2 (Figure 2). The locking element 5 is in its radially inner position. P241859

[0040] Figures 3 and 4 show the actuator in the ON position, so that the two coupling partners 2, 4 are separated from each other and no torque is transmitted.

[0041] In Figure 3, no centrifugal forces are acting. A ramp 11 arranged on the actuator 10 allows it to interact with a counter-ramp 13 on the locking element 5, initiating its radial outward movement. In Figure 4, centrifugal forces are added, causing the locking element 5 to abut one of the ring segments 17, which thus forms a radial stop 22 for the locking element 5. As long as the centrifugal forces are effective, the axial width of the locking element 5 prevents the two coupling partners 2 and 4 from being pushed together. This means that even without an applied actuating force F, the two coupling partners 2 and 4 remain securely separated. In the operating position shown, the locking element 5 is located radially outward and therefore rests against the first support surface 6 of the first coupling partner 2 and the second support surface 8 of the second coupling partner 4. In this position, it holds the jaw coupling 1 open.

[0042] P241859

[0043] Reference symbol

[0044] 1 claw coupling

[0045] 2 first coupling partner

[0046] 3. Axis of rotation

[0047] 4 second coupling partner

[0048] 5 Locking element

[0049] 6 first support surface

[0050] 7th extension

[0051] 8 second support surface

[0052] 9 Retaining spring

[0053] 10 Actuator

[0054] 11 Ramp

[0055] 12 first claw teeth

[0056] 13 Counter ramp

[0057] 14 second claw teeth

[0058] 15 Exclusion

[0059] 16 Axial projection

[0060] 17 ring segment

[0061] 18 axial bearings

[0062] 19 Return spring

[0063] 20 floor

[0064] 21 wall

[0065] 22 Radial stop

[0066] 23 pot part

[0067] 24 first shaft toothing

[0068] 25 second shaft gearing

[0069] 26 Moment Flow

[0070] 27 discs

[0071] 28 Axial bearing disc

[0072] 29 attacks

[0073] 30 Return P241859

[0074] F force

Claims

P241859 Patent claims 1. Switchable claw coupling (1 ) with - a first coupling partner (2) which has a first jaw toothing (12) and is rotatable about an axis of rotation (3), - a second coupling partner (4) which has a second claw toothing (14) for engagement with the first claw toothing (12), characterized by a locking element (5) which - can be displaced radially to the axis of rotation (3) by centrifugal force, - is arranged axially between the two coupling partners (2, 4), - in a radially outer position, it is supported on a first support surface (6) of the first coupling partner (2) and on a second support surface (8) of the second coupling partner (4), - in a radially inner position with at least one of the two support surfaces (6, 8) axially overlapping.

2. Switchable claw coupling according to claim 1, characterized in that the locking element (5) is designed as one or more arc segments.

3. Switchable claw coupling according to claim 1 or 2, characterized in that the first support surface (6) is designed as an axial projection (16) of the first coupling partner (2).

4. Switchable claw coupling according to claim 3, characterized in that the axial projection (16) is designed as a ring.

5. Switchable claw coupling according to one of the preceding claims, characterized in that the second coupling partner (4) is designed as a disc- P241859 is formed, which is pre-tensioned against a pot part (23) by a return spring (19).

6. Switchable claw coupling according to one of the preceding claims, characterized in that the locking element (5) is spring-loaded by a return spring (9).

7. Switchable claw coupling according to claim 6, characterized in that one of the coupling partners (6, 8) has a projection (7) around which the return spring (9) is wound and that the return spring (9) is attached to the coupling partner (6, 8) with the projection (7) and to the locking element (5).

8. Switchable jaw coupling according to one of the preceding claims, characterized in that the jaw coupling (1 ) has an actuator (10) which is radially mounted in one of the coupling partners (2, 4) and axially supported on the other coupling partner (4, 2) by an axial rolling bearing (18).

9. Switchable claw coupling according to claim 8, characterized in that the actuator (7) has a ramp (11) for interacting with a counter ramp (13) on the locking element (5).

10. Internal combustion engine with a generator and a switchable claw coupling according to one of the preceding claims, with which the generator can be separated from the internal combustion engine.

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