METHOD FOR DETERMINING A STATE OF A PARKING LOCK OF A VEHICLE

Abstract

Method for determining a state of a parking lock of a vehicle, in which a parking pawl (8) is automatically positively engaged in a parking lock gear (2) by an actuator (6), characterized in that it is determined as a function of a load-dependent actuator current whether the parking lock (1) is securely engaged or a tooth of the parking pawl (8) is on a tooth (5) of the parking lock gear (1).

Description

The invention relates to a method for determining a state of a parking lock of a vehicle, in which a parking pawl is latched in a parking lock wheel in a positive-locking manner in an automated manner by an actuator.Parking locks are used in automated drive trains of vehicles in order to prevent the vehicle from moving in parking operation, in particular on road slopes. The parking lock normally comprises a parking pawl and a parking ratchet wheel. By engaging the parking pawl into a tooth gap of the parking lock wheel, a positive connection is produced between a drive train and a transmission housing. The vehicle is thus secured. By disengaging the parking pawl from the tooth gap of the parking lock wheel, the drive train and thus the vehicle are unlocked.DE 10 2018 203 166 A1 discloses a parking lock in a transmission of a motor vehicle.A parking lock is known from DE 10 2008 000 177 A1, in which the parking lock is actuated by an actuator. In this case, the position of the parking pawl is not detected by a sensor, but the position of the actuating actuator is determined. A disadvantage here is that it is not possible to distinguish between the states of the parking lock "securely engaged" and "tooth on tooth". The state "tooth on tooth" is to be understood below as meaning a state in which a tooth of the parking pawl lies on a tooth of the parking lock wheel. In the "tooth on tooth" state, a reliable engagement of the parking lock is not ensured. Since the parking lock constitutes a safety mechanism, it is of great importance to securely detect the state of the parking lock.The invention is based on the object of specifying a method for determining a state of a parking lock of a vehicle, in which method the state of the parking lock can be detected reliably.According to the invention, the object is achieved in that it is determined as a function of a load-dependent actuator current whether the parking lock is securely engaged or a tooth of the parking pawl is on a tooth of the parking lock wheel. This has the advantage that the current state of the parking lock can be reliably determined without the use of sensors on the mechanical components of the parking lock and thus without additional outlay. It is thus possible to distinguish between the two states of the parking lock "securely engaged" or "tooth on tooth".Advantageously, the measured load-dependent actuator current is compared with a current limit value and, if the current limit value is exceeded by the measured load-dependent actuator current, a reliable engagement of the parking lock is concluded or, if the current limit value is undershot by the measured load-dependent actuator current, a tooth of the parking pawl on a tooth of the parking lock wheel is concluded. Since the actuator current increases with the load of the actuator, it is possible to reliably identify the parking lock state from the actuator current.In one configuration, after the actuator has been moved into a position which is required for engaging the parking lock, the actuator is returned a predefined path and the current load-dependent actuator current is measured, which is compared with the current limit value.By this feedback by the predefined path, the state of the parking lock can be determined simply by measuring the load-dependent actuator current. This is possible because the load on the actuator is at least as high as the force on a biasing spring of the parking pawl when the parking pawl is inserted into a tooth gap of the parking ratchet wheel. However, if the tooth of the parking pawl lies on a tooth of the parking lock gear, no load is transmitted from the parking mechanism to the actuator, since both are decoupled from one another. Thus, an actuator current that is only relatively low as a function of load is measured.In one variant, the current load-dependent actuator current is measured in an actuator travel window of the predefined travel of the actuator, in which no movement of the actuator takes place. This ensures that the actuator current peaks occurring during the acceleration of the actuator do not enter into the measurement and the actuator current is evaluated after the displacement of the actuator by the predefined path in a rest position of the actuator.In one variant, the predefined path by which the actuator is returned is a maximum of 1 to 2 mm. This predefined path is determined as a function of the respective parking lock system and must be selected such that this predefined path does not lead to disengagement of the parking lock.In a further embodiment, after the comparison of the current load-dependent actuator current with the current limit value, the actuator is moved back into the position required for engaging the parking lock. The measurement phase for determining the state of the parking lock is thus ended.The vehicle is advantageously secured by a brake on the vehicle during the measurement of the current load-dependent actuator current. This has the advantage that if the parking lock is not reliably engaged, rolling away of the vehicle, in particular on a mountain, is reliably prevented.The invention permits numerous embodiments. One of these will be explained in more detail with reference to the figures shown in the drawing.The following are shown: FIG. 1 shows an exemplary embodiment of a parking lock for carrying out the method according to the invention, FIG. 2 shows an exemplary embodiment of the parking lock in the "parking lock disengaged" state, FIG. 3 shows an exemplary embodiment of the parking lock in the "Park lock engaged" state, FIG. 4 shows an exemplary embodiment of the parking lock in the "tooth on tooth" state, FIG. 5 shows an exemplary embodiment of the method according to the invention.FIG. 1 shows an exemplary embodiment of a parking lock 1. Such parking locks are advantageously arranged in a transmission. The parking lock 1 comprises a parking lock wheel 2 rotatable about an axis of rotation, wherein the axis of rotation is formed by an intermediate shaft 3 with which the parking lock wheel 2 is directly connected to the drive wheels of the vehicle. The parking lock gear 2 has on its circumference a plurality of teeth 4 which are separated by a tooth gap 5. For actuating the parking lock 2, an actuator 6 is provided, which is actuated by an electric motor, not shown in detail. The electric motor drives a spindle 7 which has a screw drive. A parking pawl 8 is fixed to a housing frame 9 of a transmission, and a return spring 10 is engaged with a fixed end of the parking pawl 8. A locking wedge 11 is connected to the housing frame 9 via a biasing spring 12 and can be operatively connected to the parking pawl 8 and also to the spindle 7 of the actuator 6. In this case, the travel position of the spindle 7 is measured via a position sensor 13, wherein the actuator 6 moves the spindle 7 starting from right to left for actuating the parking lock 1 (arrow P 1). A current sensor 14 is arranged within the actuator 6, with which a change in the actuator current as a function of a changing load on the actuator 6 is detected. Since the actuator current increases with the load, it is possible to identify the parking lock state from the actuator current.FIG. 2 shows the parking lock 1 in the "disengaged" state. In this case, the parking pawl 8 is released from the tooth gap 5 of the parking ratchet wheel 2, wherein the spindle 7 of the actuator 6 bears against the locking wedge 11.The "engaged" state of the parking lock 1 is shown in FIG. 3, in which the parking pawl 8 is pressed into a tooth gap 5 of the parking lock wheel 2 by the locking wedge 11 when the spindle 7 is reset. This allows reliable locking of the parking lock 1.FIG. 4 shows the "tooth on tooth" state of the parking lock 1. In this case, the spindle 7 of the actuator 6 and the locking wedge 11 are decoupled from one another, wherein, however, the locking wedge 11 presses the parking pawl 8 against a tooth 4 of the parking ratchet wheel 1.In order to distinguish the parking lock 1 with regard to the "securely engaged" state or the "tooth-on-tooth" state, the actuator 6 is first moved into a position which is required for engaging the parking lock 1. This is done by the spindle 7 of the actuator 6 traversing a path which is detected by the position sensor 13. After the actuator 6 has reached this position, it travels a predefined small path of approximately 1 mm in the direction of the parking lock 1. This is illustrated in FIG. 5 in the diagrams a and b. The actuator current is then measured.FIGS. 5 cand 5 d show the actuator current I occurring during the movement of the actuator over time t. This is measured in an actuator travel window AWF and compared with a current limit value GW, in which the actuator 6 has traveled in the direction of disengagement of the parking lock 1, but is at a standstill. If the measured actuator current exceeds the current limit value GW, it is concluded from this that the parking lock 1 is securely engaged. This results from the movement of the spindle 7 in the direction of "disengagement", where the load on the actuator 6 is at least as high as the force in the biasing spring 10 of the locking wedge 11 when the parking pawl 8 engages in a tooth gap 5 of the parking ratchet wheel 2. If the vehicle is on a slope, the resulting load on the actuator 6 becomes even higher. Therefore, a relatively high actuator current is measured in the actuator travel window AWF.If, however, as shown in FIG. 5 d, the tooth of the parking pawl 8 now lies on a tooth 4 of the parking ratchet wheel 2, no load is transmitted from the parking mechanism 2, 8, 11 to the actuator 6, because the locking wedge 11 and the spindle 7 are decoupled from one another (FIG. 4 ). This has the consequence that only a relatively low actuator current is measured in the actuator travel window AWF, which lies below the current limit value GW. If the "tooth-on-tooth" state is detected, the vehicle can be briefly set into oscillation so that the parking pawl 8 slides into a tooth gap 5 of the parking lock wheel 2.When the actuator 6 is accelerated, the actuator current exceeds the limit value GW by a multiple, since a large load must be overcome in order to set the actuator 6 in motion. Therefore, the measurement of the load-dependent actuator current must take place within the actuator travel window AWF, in which the acceleration phase of the actuator 6 has already been safely ended and the actuator is at a standstill.After the measurement of the actuator current and the comparison with the current limit value GW, the actuator 6 is moved back again into the predefined position for engaging the parking lock 1. In order to prevent the vehicle from rolling away during the state determination phase, a service brake or a parking brake of the vehicle is engaged in this phase.List of reference characters1 Parking lock 2 Parking lock gear 3 Intermediate shaft 4 Tooth 5 Tooth gap 6 Actuator 7 Spindle 8 Parking pawl 9 Housing frame 10 Return spring 11 Locking wedge 12 Preload spring 13 Position sensor 14 Current sensor

Claims

Method for determining a state of a parking lock of a vehicle, in which a parking pawl (8) is latched in a parking lock wheel (2) in a positively locking manner in an automated manner by an actuator (6), characterized in that it is determined, as a function of a load-dependent actuator current, whether the parking lock (1) is securely engaged or a tooth of the parking pawl (8) is located on a tooth (5) of the parking lock wheel (1).Method according to Claim 1, characterized in that the measured load-dependent actuator current is compared with a current limit value (GW) and, if the current limit value (GW) is exceeded by the measured load-dependent actuator current, a reliable engagement of the parking lock (1) or, if the current limit value (GW) is undershot by the measured load-dependent actuator current, a tooth of the parking pawl (8) is stopped on a tooth (4) of the parking lock wheel (2) is concluded.Method according to Claim 1 or 2, characterized in that, after the actuator (6) has been moved into a position which is required for engaging the parking lock (1), the actuator (6) returns a predefined path and the current load-dependent actuator current is then measured, which is compared with the current limit value (GW).Method according to Claim 3, characterized in that the current load-dependent actuator current is measured in an actuator travel window (AWF) of the predefined travel of the actuator (6), in which no movement of the actuator (6) takes place.Method according to either of Claims 3 and 4, characterized in that the predefined path by which the actuator (6) is returned is at most 1 to 2 mm.Method according to at least one of the preceding claims, characterized in that, after the comparison of the current load-dependent actuator current with the current limit value (GW), the actuator (6) is moved back into the position which is required for engaging the parking lock (1).Method according to at least one of the preceding claims, characterized in that the vehicle is secured by a brake on board the vehicle during the measurement of the current load-dependent actuator current.

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