Method for activating a parking lock system and parking lock system

Abstract

Systems and methods related to activating a parking lock system in the drive train of a vehicle having at least one electrical machine comprising a transmission which is connected to driven wheels. The method includes comparing a rotational speed n.sub.E of the at least one electrical machine with the transmission to a predetermined threshold value for a limiting speed n.sub.G, triggering, in the event that the rotational speed n.sub.E is below the threshold value for the limiting speed n.sub.G, a command for the actuation of an actuator system for activating the parking lock system, triggering, in the event that the rotational speed n.sub.E exceeds the threshold value for the limiting speed n.sub.G, a command for preventing an actuation of an actuator system for activating the parking lock system, and miming through a second comparison stage so long as n.sub.E≥n.sub.G.

Claims

1. A method for activating a parking lock system (20) in a drive train (18) of a vehicle (10) with at least one electric motor (24), with a transmission, which is connected to driven wheels (16), the method comprising: a) comparing a speed n.sub.E of the at least one electric motor (24) with the transmission with a preset limit speed n.sub.G which represents a threshold value, b) when the speed n.sub.E falls below the limit speed n.sub.G, triggering a control command to actuate an actuating mechanism for activating the parking lock system (20), c) when the speed nE exceeds the limit speed n.sub.G, preventing triggering of the control command to actuate the actuating mechanism for activating the parking lock system (20), and d) performing a second comparison step (44) as long as n.sub.E>n.sub.G and, if n.sub.E<n.sub.G, branching to method step b) wherein if the speed n.sub.Eof the at least one electric motor (24) with the transmission exceeds the limit speed n.sub.G, the triggering of a control command for actuating the actuating mechanism for activating the parking lock system (20) is delayed by a period of time Δt.

2. The method as claimed in claim 1, wherein there is a fixed correlation between the speed nE of the at least one electric motor (24) with the transmission and a speed v.sub.F of the vehicle (10).

3. The method as claimed in claim 1, wherein the speed nE of the at least one electric motor (24) with the transmission is calculated in an evaluation unit (22) using the vehicle speed v.sub.F or a speed of the transmission.

4. The method as claimed in claim 1, wherein the duration of the period of time Δt is dependent on a degree by which the limit speed n.sub.G is exceeded by the calculated speed n.sub.E of the at least one electric motor (24) with a transmission.

5. The method as claimed in claim 1, wherein the control command is triggered to actuate the actuating mechanism for activating the parking lock system (20) in such a way that a front axle (12), a rear axle (14), or the drive train (18) is immobilized.

6. The parking lock system (20) for a vehicle (10) with at least one electric motor (24), with a transmission, which is connected to the wheels (16) of the vehicle (10), wherein the parking lock system (20) is operated according to the method as claimed in claim 1, wherein the parking lock system (20) comprises a switchable positive-fit lock.

7. The parking lock system (20) as claimed in claim 6, wherein the parking lock system (20) is associated with a front axle (12), a rear axle (14), or a drive train (18) of the vehicle (10).

8. The parking lock system (20) as claimed in claim 6, wherein the parking lock system comprises a mechanical prohibiting mechanism which prevents the switchable positive-fit lock from engaging at a higher vehicle speed v.sub.F.Math.s.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described in greater detail below with the aid of the drawings, in which:

(2) FIG. 1 shows a vehicle with a partially electrified drive train, and

(3) FIG. 2 shows a signal flow diagram which essentially illustrates the method proposed according to the invention.

DETAILED DESCRIPTION

(4) A vehicle 10 with a partially electrified drive train 18 can be seen schematically in the view in FIG. 1.

(5) The vehicle 10 comprises a front axle 12 and a rear axle 14. The front axle 12 has respectively two wheels 16, the rear axle 14 has two wheels 16 which are connected to an electric motor 24, with a transmission, integrated into the rear axle 14. The at least one electric motor 24 with a transmission is connected to an evaluation unit 22; a parking lock system 20 is moreover associated with the at least one electric motor 24 with a transmission. It is important that the electric motor 24 is not disconnected from the transmission when the parking lock system 20 is engaged or otherwise the speed n.sub.E of the electric motor 24 with a transmission would not provide any information about the vehicle speed v.sub.F which actually exists.

(6) The vehicle 10 moves at a vehicle speed v.sub.F, the speed of the at least one electric motor 24 with a transmission is designated by n.sub.E, and a wheel speed of the wheels 16 is designated by n.sub.R.

(7) Although not shown explicitly in FIG. 1, the at least one electric motor 24 with a transmission, as well as the parking lock system 20, can also be provided on the front axle 12. In vehicles 10 with a partially electrified drive train 18, an electric motor 24 with a transmission can be provided both on the front axle 12 and on the rear axle 14, respectively.

(8) FIG. 2 shows a signal flow diagram, the purpose of which is to illustrate the essential components of the method proposed according to the invention.

(9) In order to reduce the abovedescribed critical elevated torques, the parking lock system 20 should be engaged only at vehicle speeds v.sub.F≤2 km/h. First, the speed n.sub.E of the at least one electric motor 24 with a transmission is calculated 34. In the case of the transmissions described here, there is a fixed correlation between the speed n.sub.E of the at least one electric motor 24 with a transmission and the vehicle speed v.sub.F of the vehicle 10, as indicated in FIG. 1. In a first comparison step 36, the calculated speed n.sub.E of the at least one electric motor 24 with a transmission is compared with a threshold value, a limit speed n.sub.G. The first comparison step 36 takes place in an evaluation unit 22 which is connected to the at least one electric motor 24 with a transmission. If the calculated speed n.sub.E of the at least one electric motor is above a preset threshold value 32 for the limit speed n.sub.G, the activation of the parking lock system 20 is prevented or delayed by a period of time Δt.

(10) In this case, the triggering of a control command for the actuating system for activating the parking lock system 20 is prevented 42 or delayed.

(11) Otherwise, i.e. when the calculated speed n.sub.E of the at least one electric motor 24 with a transmission falls below the predefined limit speed n.sub.G set as a threshold value, the intention to apply the parking lock from the by wire system is transformed into a control command to activate the parking lock system 20. The threshold value is ideally checked in the evaluation unit 22 which coordinates the parking lock system 20 but could also be implemented in a different control system such as, for example, in a separate parking lock control system.

(12) An activated parking lock system 20 is indicated by the reference numeral 40. In this case, it is ensured that the parking lock system 20 is activated in a gentle fashion for the mechanical components of the parking lock system 20 below a vehicle speed v.sub.F≤2 km/h.

(13) When it occurs in the first comparison step 36 that the speed n.sub.E of the at least one electric motor is above the limit speed n.sub.G which serves as a threshold value, the triggering of the control commands for the actuating system of the parking lock system 20 is prevented 42. It remains deactivated. The second comparison step 44 runs for as long as n.sub.E≤n.sub.G and then a control command to actuate the actuating system of the parking lock system 20 takes place so that the latter is activated.

(14) After a period of time Δt has expired, it is also alternatively possible in a second comparison step 44 for a comparison to be made again between the calculated speed n.sub.E of the at least one electric motor 24 with a transmission and the limit speed n.sub.G which serves as a threshold value. The period of time Δt can be chosen depending on the degree by which the speed n.sub.E exceeds the limit speed n.sub.G. The period of time Δt can be short when the limit speed n.sub.G is exceeded by a relatively small amount but can be longer when the amount by which the calculated speed n.sub.E of the at least one electric motor 24 with a transmission exceeds the limit speed n.sub.G is greater.

(15) In this alternative embodiment, a control command for the actuating system to actuate the parking lock system 20 is then also triggered 38. This is activated at position 40, wherein the criterion for applying the parking lock system 20, that the vehicle speed v.sub.F is below 2 km/h, is taken into account.

(16) By virtue of the method proposed according to the invention, the abovementioned load cases which damage the mechanical components are eliminated both for the mechanical components of the transmission and the mechanical prohibiting system for preventing the application of the parking lock system 20. The parking lock system 20, which can be associated with the rear axle 14, the partially electrified drive train 18, and the front axle 12 is designed without taking account of these load cases. The prohibiting mechanism can also be designed more simply. The demands on the parking lock mechanism can consequently also be correspondingly reduced so that a more favorable and affordable design of said components, i.e. of the parking lock system 20 and the transmission associated with the electric motor 24, results.

(17) The invention is not limited to the exemplary embodiments described here and the aspects highlighted therein. Instead, numerous variations known to a person skilled in the art are possible within the scope defined by the claims.