Method for low-noise engagement of a parking lock of an electrically driven vehicle

Abstract

The invention relates to a method for the low-noise engagement of a parking lock (10) of an electrically driven vehicle, which is coupled in a rotationally fixed manner to a rotational axis (30) of a ratchet wheel (18), comprising the following method steps: a) in a "park" position (12) of the parking lock (10), the vehicle, due to a downhill force acting thereon, causes a first torque (32) which acts on the parking lock (10) and jams it; b) an electric machine of the electric drive is acted on by a second torque (40), which is directed in the opposite direction to the first torque (32) acting according to method step a); c) during method step b), a pawl (14) of the parking lock (10) is acted on by a first engagement force (36), which acts on the pawl (14); d) as soon as the second torque (40) exceeds the first torque (32), a jamming of the parking lock (10) within a clamping region (34) is released and the pawl head (52) of the pawl (14) moves almost noiselessly out of a tooth gap (29) of an external toothing (20) of the ratchet wheel (18); and, e) the parking lock (10) assumes its "unlocked" position (50).

Description

[0001] Method for the quiet operation of a parking lock of an electric vehicle

[0002] Technical area

[0003] The invention relates to a method for quietly disengaging a parking lock of a vehicle with an electric drive that is rotationally fixedly coupled to a rotational axis of a ratchet wheel. The invention further relates to the use of the method for quietly disengaging a parking lock of a battery-electric vehicle or hybrid vehicle subjected to a downhill force, or of an electrically driven commercial vehicle.

[0004] State of the art

[0005] DE 10 2004 043 416 A1 relates to a vehicle transmission with multiple shifting elements and a parking lock for positively locking the output of a drive train, as well as a method for controlling the same. If the parking lock is to be deactivated when the road gradient is currently inclining, shifting elements are caused to slip depending on the road gradient in such a way that the output rotates in the opposite direction to the direction of its tension when the parking lock is activated, until tension on the positive locking element of the parking lock is at least partially relieved. The positive locking of the parking lock is then released. The current road gradient can be determined by inclination detection, for example, by measurement (inclination sensor) or calculation (route data from a navigation system), and the operating state can thus be recognized taking the vehicle mass into account.

[0006] DE 10 2016 220 282 B4 discloses a method for operating a motor vehicle, including a transmission with a parking lock. When disengagement of the parking lock is requested, a current inclination of the vehicle is compared with a limit value, and then, with the parking lock still engaged, at least one further shifting element in the transmission is engaged, which, together with each shifting element of the transmission closed in the park position, releases the tension in a direction counter to the inclination. When a transmission input speed of the transmission reaches a limit value, the parking lock is disengaged. If the vehicle is parked uphill, for example, a shifting element in the transmission activates the forward gear and the drive train of the vehicle counter to the inclination of the motor vehicle in order to release the parking lock, which is tensioned in the reverse direction, in the opposite direction, thus relieving the parking lock.This allows a parking lock to be designed particularly conveniently while reducing or avoiding a relief shock.

[0007] DE 10 2011 085 149 A1 relates to a hybrid drive for a motor vehicle, wherein the transmission is designed as a planetary gear. To release an engaged parking lock against the effect of a downhill force, the electric motor can be briefly energized, so that the drive train relaxes the load and the shift elements of the transmission, which have been switched to their closed position, can be easily moved to their open position. If, in a vehicle parked on an incline whose parking lock has been engaged by closing the shift claws, there is not enough electrical energy in the energy storage device to relax the planetary gear and disengage the parking lock by energizing an electric motor before the combustion engine starts moving, the separating clutch is opened and, with the first separating clutch closed, the combustion engine is started by means of the first electric motor.This starting process requires less electrical energy than releasing the planetary gear on a road gradient by building up a sufficiently large drive torque on one of the two electric motors. With a released planetary gear, the shift claw is then opened, and then, with the shift claw closed, a drive-effective starting torque is transmitted via the planetary gear carrier to the transmission output shaft.

[0008] Vehicles with an electric drivetrain, whether purely electric or hybrid drivetrains (PEV or HEV), are parked on a slope using a parking lock, which bears the entire downhill force acting on the vehicle, particularly the gearing of the parking lock or an inserted pawl. In this state, the parking lock is mechanically tensioned by the downhill force. When releasing the parking lock, it must be released from the tensioned gearing, which can lead to mechanical stress and, in particular, noise.

[0009] Description of the invention

[0010] According to the invention, a method is proposed for the low-noise disengagement of a parking lock of a vehicle with an electric drive which is coupled in a rotationally fixed manner to a rotational axis of a ratchet wheel, in which the following method steps are carried out: a) In a "parking" position of the parking lock, the vehicle causes a first torque due to a slope force acting on it, which acts on the parking lock and jams it, b) an electric machine of the electric drive is subjected to a second torque which is directed in the opposite direction to the first torque acting according to method step a).c) during process step b), a pawl of the parking lock is subjected to a first release force which acts on the pawl, d) as soon as the second torque exceeds the first torque, a jamming of the parking lock within a clamping range is released and a pawl head of the pawl extends almost silently from a tooth gap of an external toothing of the ratchet wheel and e) the parking lock assumes its "unlocked" position.

[0011] The method proposed according to the invention can ensure that, in the case of an electric vehicle parked on a slope, the mechanical loads on the parking lock caused by the downhill force are considerably minimized and a significant reduction in the noise level when the parking lock is disengaged is achieved.

[0012] In an advantageous development of the method proposed according to the invention, according to method step d), the first release force acting on the pawl according to method step c) is increased to an increased release force. This ensures that the pawl extends safely from the external toothing of the ratchet wheel of the parking lock.

[0013] In an advantageous development of the method proposed according to the invention, the duration of a control of the electric drive for generating the second torque is carried out over a defined period of time or until a defined angle of rotation is passed through.

[0014] In the method proposed by the invention, the duration of the activation of the electric drive is also determined depending on the current gradient at which the vehicle is parked with the parking lock in the "Park" position and / or depending on the vehicle load. This allows the local parking conditions of an electrically powered vehicle and its load to be taken into account, since a more heavily loaded vehicle on a steep slope requires a longer activation time of the electric drive until the second torque builds up to a point where it exceeds the first torque.

[0015] In an advantageous development of the method proposed according to the invention, the degree of the gradient generating the downhill force in the parking position of the vehicle is determined on a map-based basis and / or via at least one acceleration sensor installed in the vehicle or via values ​​stored in the drive control unit when the vehicle is stopped.

[0016] The method proposed according to the invention also enables the determination or calculation of the gradient from a measured deceleration of the vehicle due to the slope force when the weight of the vehicle is known or estimated.

[0017] In an alternative embodiment of the method proposed by the invention, the release force acting on the pawl is regulated or controlled between the value corresponding to the first release force and the increased release force. This also allows for quiet release of the parking lock without the need for time or angle control. In the method proposed by the invention, at the beginning of the release of the parking lock from the "Park" position, the release force is set, for example, between 30% and 50% before the electric motor is started to generate the second torque.

[0018] In the method proposed according to the invention, it is further possible that after a defined period of time, the release force is increased to a value that ensures the release of the parking lock.

[0019] Furthermore, the invention relates to the use of the method for the low-noise disengagement of a parking lock of a battery-electric vehicle or a hybrid vehicle or an electrically driven light commercial vehicle subjected to a downhill force.

[0020] Advantages of the invention

[0021] The solution proposed by the invention allows the mechanical parking lock system, which is subject to significant mechanical stress at certain points, particularly when an electrically powered vehicle is parked on a slope, to be relieved before the parking lock is moved from its "parked" position to its "unlocked" position. Furthermore, the solution proposed by the invention ensures that noise generation when the parking lock is disengaged is ideally completely eliminated or at least significantly reduced.Before the parking lock is released, its mechanical system is relaxed by the electric drive of the electrically powered vehicle moving the gearbox blocked by the parking lock by a very small degree of rotation, so that there is no vehicle movement and the jammed toothing between the parking lock pawl and its ratchet wheel can be released without great effort and accordingly with very little noise.

[0022] The solution proposed by the invention ideally allows for a silent transfer of the parking lock from the "Park" position to the "Unlocked" position. The duration of activation of the electric drive to generate the second torque or to traverse a rotational angle that releases the jam between the tooth of the external toothing of the ratchet wheel and the pawl can be controlled either over a fixed period of time or over a rotational angle. This can be achieved, in particular, by controlling or regulating the fixed activation time or the rotational angle to be traversed depending on the current gradient on which the electrically powered vehicle is parked and the vehicle's load.This allows for the fact that, for example, a heavily loaded vehicle on a very steep slope is subject to greater mechanical stress on the components of the parking lock than a light vehicle in a parking position with only a slight gradient.

[0023] The gradient at the parking position can be determined either map-based or using acceleration sensors installed on the vehicle. It is also possible to determine the gradient based on a value stored in the drive control unit when the electrically powered vehicle is stopped. The gradient can be calculated, for example, in the drive control unit from a measured deceleration of the electrically powered vehicle due to the downhill force, assuming a known or estimated vehicle weight.

[0024] If the release force required to open the parking lock, i.e. to disengage the pawl from the external teeth of the ratchet wheel, can be regulated, the release force can initially be kept quite low, for example 30% of a nominal force. The nominal force is the maximum force that the pawl actuator can apply, i.e. 100%. The respective release force is then the currently effective force. Without jamming, the release force is very low, but with jamming it is close to 100%. This procedure ensures that the parking lock releases automatically as soon as the clamping force is reduced sufficiently. Clamping force is the force that acts in the "parking" position between the pawl head on the one hand and a flank of a tooth on the other.

[0025] In this embodiment of the method proposed by the invention, no time period or angle control would be required. Finally, the solution proposed by the invention also allows for the specification of a specific time period, after which the release force is increased to a nominal value and thus to the maximum value, in order to reliably release the parking lock in every case.

[0026] In addition to avoiding noise occurring when unlocking the parking lock, the method proposed according to the invention can also significantly reduce the mechanical load on the components of the parking lock, so that a longer service life of the parking lock system can be achieved.

[0027] Short description of the drawings

[0028] Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

[0029] They show:

[0030] Figure 1 shows the parking lock in the “Park” position, where the first torque generated by the downhill force acts,

[0031] Figure 2 The parking lock in the “Park” position according to Figure 1 , whereby the second torque counteracting the first torque is gradually built up by the electric machine,

[0032] Figure 3 shows the point in time at which the second torque exceeds the first torque and the pawl head of the locking pawl is within a tooth gap and

[0033] Figure 4 shows the pawl extended from the tooth gap according to Figure 3, which is subjected to an increased release force.

[0034] Embodiments of the invention

[0035] In the following description of the embodiments of the invention, identical or similar elements are designated by the same reference numerals, whereby a repeated description of these elements is omitted in individual cases. The figures only schematically illustrate the subject matter of the invention.

[0036] Figure 1 shows a parking lock 10 in its "Park" position 12. The parking lock 10 includes a pawl 14 that is movable about a rotational axis 16. The actuator of the pawl 14, which applies a release force acting on the pawl 14, is not shown in detail here.

[0037] The parking lock 10 further comprises a ratchet wheel 18. The ratchet wheel 18 comprises an external toothing 20, which is constructed from a sequence of teeth 22 along the circumference of the external toothing 20, with tooth gaps 29 between the individual teeth 22. Each of the teeth 22 of the external toothing 20 of the ratchet wheel 18 comprises a first tooth flank 26 and a second tooth flank 28. A tooth tip of a tooth 22 is designated by reference numeral 24. The ratchet wheel 18 is movable about a rotational axis 30. The rotational axis 30 of the ratchet wheel 18 is rotationally fixedly coupled to an electric drive (not shown in detail here) of an electrically powered vehicle. If the ratchet wheel 18 is in the “Park” position 12 shown in Figure 1 by the parking lock 10, the vehicle is secured against rolling away.

[0038] If the electrically powered vehicle is parked on an incline, either in a forward or reverse direction, in the "parking" position 12 shown in Figure 1, a first torque 32 acts on the mechanical components of the parking lock 10 due to the downhill force acting on the vehicle. In particular, in this state, which is shown in Figure 1, a large surface pressure occurs within a clamping area 34 between a pawl head 52 of the locking pawl 14, on the one hand, and the opposite second tooth flank 28 of the corresponding tooth 22. The pawl head 52 of the locking pawl 14 is almost completely immersed in the resulting tooth gap 29 between two spaced-apart teeth 22 of the external toothing 20 of the ratchet wheel 18.

[0039] The pawl 14, which is immersed in the tooth gap 29 as shown in Figure 1, forms a positive locking and prevents free rotation of the ratchet wheel 18. In the illustration according to Figure 1, a slight, first release force 36 acts on the end of the pawl 14 opposite the pawl head 52 of the pawl 14. In the state shown in Figure 1, ie the “parking” position 12 shown there, the first release force 36 is not sufficient to release the pawl 14 gently and silently.

[0040] The illustration in Figure 2 shows that when the electric machine of the electric drive is appropriately controlled, a second torque 40 is applied to the rotational axis 30 of the ratchet wheel 18. The second torque 40 is applied by the electric drive (not shown in detail here) and acts in a counterclockwise direction 42. The second torque 40 counteracts the first torque 32 acting in a clockwise direction 33, which results from the downhill force acting on the parked vehicle. In the event that the vehicle is parked on an opposite incline, the resulting forces and moments are also directed in exactly the opposite direction. In the state shown in Figure 2, however, the second torque 40 counteracting the first torque 32 in a counterclockwise direction 42 is not yet sufficient to design the pawl 14 to be silent or at least to reduce noise.In the state shown in Figure 2, the surface pressure between the pawl head 52 and the second tooth flank 28 within the clamping area 34 between the pawl 14 and the tooth 22 is reduced, but the surface pressure prevailing there in the clamping area 34 is not yet completely eliminated.

[0041] In the illustration according to Figure 3, however, this is the case because the second torque 40 generated by the electric machine is now large enough to release the tension within the clamping area 34 between the second tooth flank 28 of the tooth 22 and the pawl head 52 of the locking pawl 14. The first release force 36, which acts on the end of the locking pawl 14 opposite the pawl head 52, still acts on the locking pawl 14. According to the illustration in Figure 3, the pawl head 52 of the locking pawl 14 is located within the tooth gap 29 between the two opposing teeth 22 of the external toothing 20 of the ratchet wheel 18 due to the first release force 36 acting on the locking pawl 14 about the rotation axis 16. An opening gap 44 now releases the clamping area 34. The opening gap 44 essentially corresponds to a rotation angle a 46. If the rotation angle a 46 is passed through, ieIf the second torque 40 exceeds the first torque 32, the state shown in Figure 3 is reached; the pawl head 52 of the locking pawl 14 is now free, without it contacting a tooth 22 of the external toothing 20 of the ratchet wheel 18. The illustration according to Figure 4 shows that the parking lock 10 has now been transferred to its "unlocked" position 50. The pawl head 52 of the locking pawl 14 has completely extended out of the tooth gap 29 facing the pawl head 52 in this rotational position. Thus, due to the lack of mechanical contact, a silent disengagement of the parking lock 10 into the "unlocked" position 50 shown in Figure 4 is possible. Figure 4 shows that, in comparison to Figures 1 to 3, an increased release force 48 acts on the end opposite the pawl head 52 of the pawl 14.The increased release force 48 is further increased for safety reasons, so that a safe disengagement of the pawl 14 or of its pawl head 52 from the tooth gap 29 of the external toothing 20 of the ratchet wheel 18 is ensured.

[0042] By the procedure described above with reference to Figures 1 to 4, instead of immediately releasing the parking lock 10, the electric drive can apply a second torque 40 to the rotational axis 30 of the ratchet wheel 18, which counteracts the first torque 32 acting on the vehicle due to the downhill force that clamps the parking lock 10 in the "Park" position 12. This releases the clamping, allowing the parking lock 10 to be released almost silently into its "Unlocked" position 50. The duration of activation of the electric drive or the size of the angle of rotation a 46 can be controlled or regulated either over a fixed period of time or depending on the angle of rotation a 46.This makes it possible to take into account the fact that, depending on the currently existing gradient and the load of the electrically powered vehicle, the fixed period within which the drive is activated in order to build up the second torque 40 or to pass through the angle of rotation a 46 can be adjusted accordingly. For a heavily loaded vehicle on a very steep gradient, a greater relaxation, i.e. a larger second torque 40 must be applied by the electric drive, compared to a second torque 40 that acts on a relatively light vehicle on a gentle gradient. The degree of the gradient can either be determined using a map-based method or detected via acceleration sensors installed on the vehicle or via a stored value in the drive control unit when the electrically powered vehicle comes to a stop.For example, the degree of the gradient can be determined from a measured deceleration of the vehicle due to the downhill force with a known or estimated weight of the vehicle.

[0043] If time or angle control for applying the second torque 40 is omitted, the release force 36, 48 acting on the locking pawl 14 can be regulated. Initially, the release force 36, 48 can be kept very low, for example, 30% to 50% of a nominal force, and then the electric drive can be started. As a result, the parking lock 10 is automatically released as soon as the release force 36, 48 has increased sufficiently that the clamping force present within the clamping area 34 between the second tooth flank 28 and the pawl head 52 of the locking pawl 14 has been reduced sufficiently.

[0044] The method proposed according to the invention also enables a purely time-controlled solution, according to which, after a certain period of time, the release force 36, 48 is increased to such an extent that it is ensured in any case that the parking lock 10 assumes its “unlocked” position 50.

[0045] The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, numerous modifications are possible within the scope of the claims, which are within the scope of one skilled in the art.

Claims

Claims 1 . Method for the quiet disengagement of a parking lock (10) of a vehicle with an electric drive, which is non-rotatably coupled to a rotational axis (30) of a ratchet wheel (18), comprising the following method steps: a) In a "parking" position (12) of the parking lock (10), the vehicle, due to a slope force acting on it, causes a first torque (32), which acts on the parking lock (10) and jams it, b) an electric machine of the electric drive is subjected to a second torque (40), which is directed in the opposite direction to the first torque (32) acting according to method step a), c) during method step b), a pawl (14) of the parking lock (10) is subjected to a first disengagement force (36), which acts on the pawl (14), d) as soon as the second torque (40) exceeds the first torque (32),a jamming of the parking lock (10) within a clamping area (34) is released and a pawl head (52) of the pawl (14) moves almost silently out of a tooth gap (29) of an external toothing (20) of the ratchet wheel (18), e) the parking lock (10) assumes its "unlocked" position (50).

2. Method according to claim 1, characterized in that in method step d) the first release force (36) acting on the pawl (14) according to method step c) is increased to an increased release force (48).

3. Method according to claims 1 and 2, characterized in that the duration of a control of the electric drive for generating the second torque (40) over a fixed, defined period of time or until a defined angle of rotation a (46) is passed through.

4. Method according to claims 1 to 3, characterized in that the duration of the control of the electric drive is carried out depending on the current gradient in which the "parking" position (12) of the vehicle with parking lock (10) is located and / or depending on the load of the vehicle.

5. Method according to claims 1 to 4, characterized in that the degree of the gradient generating the downhill force in the "parking" position (12) of the vehicle is determined on a map-based basis and / or via acceleration sensors installed in the vehicle or via values ​​stored in the drive control unit when the vehicle is stopped.

6. Method according to claim 5, characterized in that the calculation of the gradient is determined from a measured deceleration of the vehicle by the slope force with a known or estimated weight of the vehicle.

7. Method according to claims 1 and 2, characterized in that the release force acting on the pawl (14) is regulated or controlled between the first release force (36) and the increased release force (48).

8. Method according to claim 7, characterized in that at the beginning of the unlocking of the parking lock (10) from the "parking" position (12), the release force is between 30% and 50% of the first release force (36) and the turning of the electric machine to generate the second torque (40) is started.

9. Method according to claims 7 and 8, characterized in that after a defined period of time has elapsed, the disengagement force is increased to a value ensuring the disengagement of the parking lock (10).

10. Use of the method according to one of claims 1 to 9 for the low-noise design of a parking lock (10) of a vehicle provided with a Battery-electric vehicle or hybrid vehicle subjected to downhill force. 11 . Use of the method according to one of claims 1 to 9 for the low-noise design of a parking lock (10) of a vehicle provided with a Electric-powered commercial vehicle subjected to downhill force.

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