Position determining method for a parking lock

A method for determining the position of a first actuating element of an electrical parking lock device of a motor vehicle, wherein the first actuating element is mounted on a spindle in an axially mobile manner, where the method includes a step in which the first actuating element is moved in an opening direction to a stop, the spindle is then rotated to move the first actuating element in a closing direction, the current input and the energy consumption of a driver are captured at this point, provision is then made for identifying a first reference point if the current input of the spindle drive increases or decreases by at least a first threshold value, the first reference point is assigned to the energy consumption that has been captured, where the first reference point corresponds to the first actuating element coming into contact with an actuating pawl.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for determining an actuating position of a parking brake in a motor vehicle and to a computer program for performing said method. The invention also relates to a corresponding controller for a parking lock device and the corresponding parking brake system.

2. Description of the Related Art

EP 1 855 033 B1 discloses a transmission lock for a motor vehicle, which serves as a parking lock arrangement. The transmission lock comprises a ratchet wheel that is equipped with teeth in which a pawl engages in a blocked state. The pawl can be actuated by a locking cone that is mounted on a locking element in an axially mobile manner and is pretensioned.

DE 10 2012 205 576 A1 discloses a method for providing a clamping force that is exerted by an auxiliary brake in a motor vehicle. The auxiliary brake has an electric braking motor, by which a brake piston is actuated via a spindle and pushes against a brake disc. In order to determine the clamping force, a motor constant is determined from the voltage and current strength at the braking motor in a no-load phase. A temporal gradient of the current strength at the braking motor is captured to identify the no-load phase. A current strength below followed by a current strength above a first and a second threshold value respectively indicates the start of the no-load phase. The current strength is constant in the no-load phase itself. A subsequent positive gradient in the current strength indicates the end of the no-load phase.

DE 10 2012 206 226 A1 discloses a method for adjusting an auxiliary brake in a vehicle, where a clamping force is exerted on a brake disc via a braking motor. A voltage jump is captured when the braking motor starts up, and a corrected current strength is determined therefrom. The corrected current strength is used as a basis for calculating a motor constant by which the clamping force generated by the auxiliary brake can be determined.

The conventional methods require extensive data relating to the structure of the parking brake or auxiliary brake, and can no longer be used reliably if there is a failure in the vehicle electronics that provide the corresponding data. Moreover, degradation phenomena, such as brake disc wear or slight plastic deformations of parking lock pawl or parking lock wheel, are not sufficiently indicated, and therefore the actuating precision of the parking brake or auxiliary brake decreases during the course of vehicle operation.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the invention to provide a method for operating a parking lock that overcomes the disadvantages of prior art locks, which is resilient in the event of electronic failure and data loss, and which during operation is capable of adapting itself automatically to degradation phenomena in the parking lock, and is executable quickly and without inconvenience to the driver.

These and other objects and advantages are achieved in accordance with the invention by a position identifying method for a parking lock in a motor vehicle in which the method in accordance with the invention is based on determining the position of a first actuating element, which is configured to apply and release the parking lock. The first actuating element is mounted on a spindle in an axially mobile manner, and can be moved in both directions via an electrically operated driver. The first actuating element is configured to activate interlocking of the parking lock by pushing on an actuating pawl. In a first method step, the first actuating element is moved in an opening direction on the spindle until it reaches a stop. The stopping at the stop can be identified by a correspondingly marked increase in the current strength at the driver and is used in the subsequent method steps as a reference level for an energy consumption of the spindle drive motor. Once the first actuation element has reached the stop, it is no longer in mechanical contact with the actuating pawl.

In a further method step, the driver is activated such that the first actuating element is moved in a closing direction that is opposite to the opening direction. The current input and the energy consumption of the driver are captured during this movement. The current input represents a measure of the mechanical resistance that must be overcome when the first actuating element is moved. In a further method step, a first reference point is identified if the current input of the driving means changes by at least a first threshold value, i.e., increases or decreases. The first reference point comprises the energy consumption between the start of the movement in a closing direction and the change in magnitude in the current input by at least the first threshold value. The first reference point corresponds mechanically to the first actuating element coming into contact with the actuating pawl, at which point a mechanical supporting effect occurs between them. The resistance to be overcome for the movement of the first actuating element and, hence, the current input of the driver, changes accordingly. The method in accordance with the invention provides the first reference value to a controller of the parking lock device such that the energy consumption during the movement of the first actuating element in the region between the stop and the first reference point is the measure for its axial position on the spindle.

The current input and the energy consumption are measured variables that can be measured with a high degree of precision using simple means. Therefore, the position of the first actuating element on the spindle in an axial direction can be determined with a high degree of accuracy. Moreover, the method in accordance with the invention is based on measured variables which are captured by measuring devices arranged at the driver. The measuring devices can therefore be spatially separate from the first actuating element. By virtue of the method in accordance with the invention, it is unnecessary to install costly sensors in the region of the first actuating element and/or the actuating pawl. In summary, the method in accordance with the invention allows a simplified and more economical structure of the parking lock device and ensures significant space savings as a result of the spatial separation of the actuating mechanism and its position capture. As a result, integration of the parking lock device in a motor vehicle is in turn simplified. Moreover, the method in accordance with the invention still allows the position of the first actuating element to be captured accurately if neither position nor reference value are known at the start of the method. The claimed method is therefore robust and offers a high degree of protection against failures or memory resets in the control electronics of the motor vehicle.

In a preferred embodiment of the method in accordance with the invention, an additional step is performed in which a second reference point is identified. In this step, the first actuating element is moved further in the closing direction on the spindle. The identification of the second reference point occurs after the first reference point has been identified. For the purpose of identifying the second reference point, the energy consumption and the current input of the driver are again captured in this case. The presence of the second reference point is identified if the current input of the driver exceeds a second threshold value. Here, the increase in the current input is caused by a second actuating element stopping at an end position. The second actuating element is mounted on the spindle in an axially mobile manner and is also configured to push the actuating pawl in an interlock activating direction. The opening direction of the first actuating element corresponds to the closing direction of the second actuating element. The parking lock pawl also has two functional surfaces accordingly, in order to bring about a closure of the parking lock in each case when the independent actuating elements have opposite directions of movement.

The spindle guide element is arranged between the first and second actuating element on the spindle. The spindle guide element is formed with the spindle as a lead screw, roller screw or ball screw. However, essentially any form of linear actuator which exerts a controlled linear mechanical force along an axial direction is suitable. The axial movement of the spindle guide element occurs as a result of rotation of the spindle or a linear actuator, for example. In this way, the spindle guide element limits the axial movement of the first actuating element along the spindle. The data that forms the basis of the second reference point comprises the energy consumption that occurs from setting off at the stop to reaching the second reference point. The energy consumption is therefore a measure for the axial position of the first actuating element on the spindle. By performing an interpolation between the reference values and the stop, it is possible to determine any position of the first actuating element between the stop and the two reference values. The capture of the energy consumption during the actuation of the spindle drive motor can easily be performed by measuring devices that are already attached to an electric motor or its corresponding control unit. The advantages of the disclosed embodiments of the method in accordance with the invention are consolidated by the use of the second reference value.

In addition to the data for the second reference point, the actuation state of the second actuating element at the beginning of the method is preferably also identified. A released state of the second actuating element at the beginning of the method is identified if the current input between the first and second reference point exhibits, at least to some extent, a positive temporal gradient that corresponds essentially (substantially) to an elastic deformation. As the spindle guide element moves to the second reference point, the second actuating element is pushed out of the released position, where an increasing mechanical resistance must be overcome. Here, the mechanical resistance remains lower than the stopping force that acts on the second actuating element as a result of stopping at the end position.

By contrast, an arrested state of the second actuating element at the beginning of the method is identified if the current input between the first and second reference points (essentially immediately before reaching the stop at the end position) lies in the region of a no-load value of the driving means.

The possibilities of the method in accordance with disclosed embodiments of the invention for identifying the state of the parking lock system, irrespective of previously known information about it, are further extended thereby. The method in accordance with disclosed embodiments of the invention accesses data that has already been measured in this case, and is easy to implement. In particular, the claimed embodiments of the method can be implemented via a software update in the case of an electrical parking lock device.

In addition to the first reference point, the claimed method preferably also identifies the presence of a gap position of the parking brake wheel and the actuating pawl. A gap position is present if, as a pivoting movement of the actuating pawl occurs, the pawl tooth and a space between teeth of the parking brake wheel are facing each other. When the actuating pawl is actuated, these engage in a blocking manner. When the actuating pawl and the parking brake wheel engage, the path of the first actuating element in the closing direction is essentially/substantially free. As a result of the return force of a pawl spring, at least one region of the actuating pawl is pushed laterally against the first actuating element.

The gap position is preferably identified if the current input of the driver remains above the no-load value of the driver essentially/substantially immediately after the first reference point is reached. This corresponds mechanically to a further axial movement of the first actuating element in its closing direction. Here, the first actuating element is in contact with the actuating pawl such that a frictional force occurs between the first actuating element and the actuating pawl. The driver ensures a controlled axial movement of the first actuating element via the spindle guide element. The method in accordance with the invention therefore makes it possible to determine the relative angular position of the parking brake wheel in addition to the position of the first actuating element. The method in accordance with the invention therefore returns detailed information about the mechanical state of the parking lock device, where the information can be made available to a driving assistance system.

Alternatively, the method in accordance with the invention identifies an opposition position of the parking brake wheel and the actuating pawl. An opposition position is present when the pawl tooth and one of the teeth of the parking brake wheel are facing each other, such that any engagement of the actuating pawl and the parking brake wheel is prevented. The opposition position is identified if the current input of the driver decreases to the no-load value of the driver essentially/substantially immediately after the first reference point is reached. In an opposition position, the first actuating element is supported by the actuating pawl in a stable manner, such that the first actuating element is prevented from sliding past the actuating pawl. The spindle guide element is consequently relieved of the first actuating element in an axial direction. The transport of the spindle guide element, now under essentially no mechanical load, in the closing direction of the first actuating element is effected using the no-load power of the driving means. Here, the no-load power is characterized by the no-load value of the current input of the drivers. In summary, the method in accordance with the invention makes it possible to determine the mechanical state of the parking lock device in a detailed manner and make the corresponding information available to a vehicle control system.

The method in accordance with the invention can also have a step in which the actuating pawl is interlocked as a preparatory measure by a second actuating element, which is also mounted on the spindle in an axially mobile manner. The method in accordance with the invention is then performed in an interlocked position of the parking lock device, where the parking lock pawl can be situated in both the gap position and the opposition position. Alternatively, the second actuating element can also be re-released before the stop is reached by the first actuating element. This ensures that the actuating pawl and the parking brake wheel are situated in a gap position after a very short travel distance at most. This results in a first and second reference point being generated with maximal separation. In combination with the precise measurement of the energy consumption until the reference points are reached, a high degree of measurement accuracy for the position of the first actuating element is achieved thereby.

The method in accordance with the invention preferably has an additional step in which provision is made for determining the state of the second actuating element. In the state determining step, the first actuating element is moved in its opening direction on the spindle until the stop is reached. During the movement in the opening direction, the current input and the energy consumption of the driver are measured in this case. The current input and the energy consumption indicate in electrical terms the mechanical resistance of the first actuating element that is to be overcome. In this case, only variations that occur and lie within the hysteresis range of the driver can be ignored. With the state determining step, it is also possible to identify the mechanical state of the parking lock device if no data about the actuating elements is available at the beginning of the method in accordance with the invention. The state of the parking lock device can be accurately and easily derived from the data that is captured when determining the first and/or second reference point and the data that is determined in the state determining step. Additional sensor technology in the parking lock device is rendered unnecessary by the method in accordance with the invention.

In a preferred embodiment of the claimed method, an unretained state of the second actuating element is identified both during the identification of the first and/or second reference point and during the state determining step. In such an unretained state, the second actuating element abuts the spindle guide element before and after the state determining step and is guided first in its closing direction and then in its opening direction. The opening direction of the second actuating element corresponds to the closing direction of the first actuating element and the closing direction of the second actuating element corresponds to the opening direction of the first actuating element. The second actuating element is preferably pretensioned in an axial direction by a spring, such that the force exerted on the spindle guide element when identifying the first and/or second reference point increases in a largely continuous manner at least partially in the region between the first and second reference point, and decreases in a largely continuous manner in the state determining step. The force exerted by the second actuating element corresponds to the current input, and therefore the current input when identifying the first and/or second reference point corresponds essentially/substantially to the current input when determining the state. A correspondence here is understood to mean having equal magnitude while discounting variations due to hysteresis losses.

In an alternative embodiment of the method in accordance with the invention, a retained state of the second actuating element is identified during the determination of the first and/or second reference point and the state determining step. In such a retained state, the second actuating element is prevented from moving along the axial direction before and after the state determining step by an arrester. The respective current inputs when identifying the first and/or second reference point and during the state determining step correspond to each other and are therefore essentially/substantially equal. The spindle guide element comes up against the second actuating element in the region of the second reference point, such that an essentially stepped or sudden increase in the current input occurs. When the state determining step is initiated, a tightening torque between the spindle guide element and the second actuating element is released, such that the current input decreases in an essentially stepped or sudden manner. The method in accordance with the invention therefore identifies from the stepped increase or decrease of the current input that the second actuating element is in a retained state at the beginning and end of the method. In this context, a decrease or increase of the current input is understood to signify a change whose magnitude substantially exceeds the variations caused by hysteresis losses of the driver.

Alternatively, it is possible to identify the presence of an unretained state when determining the first and/or second reference point and a retained state when determining the state. In this case, the second actuating element is moved during the determination of the first and/or second reference point, and caught by the arrester. Here, the force exerted in an axial direction by the second actuating element must be overcome by the spindle actuating element. The force thus exerted forms a mechanical resistance that corresponds to a corresponding energy consumption. When the state determining step is initiated, the second actuating element remains in its arrested position, such that the spindle guide element is not subjected to any forces by the second actuating element. Consequently, the energy consumption during the state determining step is lower than the energy consumption when determining the first and/or second reference point. When comparing the energy consumptions in terms of magnitude, variations due to hysteresis losses should be ignored.

Similarly, the method in accordance with the invention can identify the presence of a retained state when determining the first and/or second reference point and an unretained state when determining the state. Here, the second actuating element is situated in its arrested position and does not move during the determination of the first and/or second reference point. When the state determining step is initiated, the force exerted in an axial direction by the second actuating element must be overcome by the spindle actuating element. The force thus exerted forms a mechanical resistance which corresponds to a corresponding energy consumption. Consequently, the energy consumption when determining the first and/or second reference point is lower than the energy consumption during the state determining step. When comparing the energy consumptions in terms of magnitude, variations due to hysteresis losses should be ignored.

In summary, the method in accordance with the invention makes it possible to identify the mechanical state of the second actuating element without additional sensors. As a result, the parking lock device has resilience against data loss in a supervisory control unit, e.g., following a memory reset. Moreover, the state of the parking lock device can be identified automatically and reliably to allow correct actuation following exposure to interference. In particular, it is possible to dispense with expensive adjustment of the controller of the driver in the event of a repair to the parking lock device. The resilience and economic efficiency of the parking lock device are further increased thereby. The method in accordance with the invention is suitable for monitoring its own proper service condition, where the monitoring can be integrated into the standard use of the parking lock device. Such self-monitoring avoids inconveniences to the driver and allows the parking lock device to be actuated in a constantly precise manner.

Using the method in accordance with the invention, it is also possible to capture a first rotor position of the spindle when the stop is reached. The first rotor position comprises an angular value between 0° and 360°, which is measured by the rotor position sensor of the drive motor, and does not state how many complete rotations have already been made. Once captured, the first rotor position is stored. This is followed by the state determining step, in which the first actuating element is again moved to the stop, where the change in the rotor position is determined via integration. A second rotor position is then captured, which like the first rotor position comprises an angular value between 0° and 360° and does not state how many complete rotations have already been made. A warning is then output if the difference between the first and second rotor position exceeds a tolerance value. Here, the tolerance value can correspond essentially to a play of the spindle and the spindle guide element, where the play allows the axial movement on the spindle. One important aspect of the invention is the fact that any drift of the ends of travel due to wear does not occur suddenly but rather is incremental, and that it is therefore not necessary to re-store the end of travel positions at every actuation cycle of the parking lock. Recalibration of the values stored in the control device is performed as required. The warning is then likewise output as an optical, acoustic or haptic warning to the driver, a controller or a driving assistance system. The method in accordance with the invention offers a high degree of precision when determining the position of the first actuating element. A high degree of actuating precision is thereby achieved for the parking lock device.

The first and/or second actuating element are each preferably pretensioned in an axial direction along the spindle by at least one spring. As a result of this pretensioning, the first or second actuating element is pushed in its respective closing direction. The first and second actuating element are most preferably installed so as to form a reciprocally opposing arrangement, such that the opening direction of the first actuating element corresponds to the closing direction of the second actuating element. The at least one spring is preferably formed as a helical spring, a disc spring, or a combination of both. Springs can easily be manufactured in practically any spring strength, and are both reliable and economical. Pretensioning by at least one spring allows an axial force to be exerted constantly on the first and/or second actuating element.

Furthermore, using the method in accordance with the invention, it is preferably possible to move the first and/or second actuating element via a largely constant rotational speed of the driver. A constant rotational speed reduces the number of changeable variables in the claimed method and results in further simplification. In particular, the current consumption and the energy consumption between the stop, the first reference point and optionally the second reference point at a constant rotational speed are an immediate measure for the mechanical variables of the first actuating element. Such immediately meaningful variables allow rapid analysis and make it possible to output reliably valid warnings. Moreover, a constant rotational speed results in a largely constant frictional force between the first actuating element and the actuating pawl, thereby simplifying the data analysis and hence the identification of the first and/or second reference point. As a result of the method in accordance with the invention, the efficiency of the electrical parking lock device is increased for the driver.

It is also the object of the invention to provide a program, which is designed to be stored and executed in a memory of a controller of the driver, where the controller includes a computing unit or processor. The controller is connected to the driver of the electrical parking lock device. The program is suitable for executing at least one of the methods described above, and thereby determine the position of the first actuating element of the parking lock device.

It is a further object of the invention to provide the controller. The controller in accordance with the invention is configured to control the driver of the electrical parking lock device, and comprises a computing unit or processor and a memory. The memory and the computing unit or processor are configure to store and execute the program described above.

It is yet a further the invention to provide a parking lock device having a first actuating element that is mounted in an axially mobile manner on a spindle along which it can be moved by a driver. The driver can be connected to and controlled by the controller in accordance with the invention which is equipped with a program that is suitable for implementing at least one of the above-described methods.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1schematically illustrates the structure of an electrical parking lock device10in which the position of the first actuating element16can be determined via the method100in accordance with the invention. The parking lock device10comprises a driver20, this taking the form of a spindle drive motor20that is controlled via a control unit70by the program80, which implements at least one embodiment of the method in accordance with the invention100. The driver20causes a spindle14to rotate in either a clockwise or counterclockwise direction. The spindle14is equipped with a thread, by which a spindle guide element24is moved in a controlled manner along an axial direction34. Depending on the direction of rotation of the spindle14, the spindle guide element is moved in the closing direction36or the opening direction38of the first actuating element16. The first actuating element16is essentially configured as a cone or truncated cone, wherein the end face17is supported by the spindle guide element14and points in the closing direction38of the first actuating element16. The actuation path of the first actuating element16is limited in a closing direction38by a stop44, to which the first actuating element16is brought in a method step. The first actuating element16is pretensioned by a first spring26, such that the associated pretension force27pushes the first actuating element16in its closing direction36.

A second actuating element18is also arranged on the spindle14, and can likewise move along the axial direction34of the spindle14. The second actuating element18is subjected to a pretension force29from a second spring28. According toFIG. 1, the second actuating element18is held in its position by an axially displaceable straight pin40. The second actuating element18is likewise essentially configured as a cone or truncated cone, its end face19facing the end face17of the first actuating element16. Both the first and the second actuating element16,18are contained in an essentially cylindrical sleeve42that ensures a linear movement in an axial direction34.

The parking lock device10inFIG. 1further comprises an actuating pawl12, which is pretensioned in an interlock deactivating direction15by a pawl spring13. A pawl tooth32that is formed at the end of the actuating pawl12is configured to engage in the teeth30of an opposing parking brake wheel11. An actuating section33is formed on that side of the actuating pawl11that faces away from the pawl tooth32, and comes into contact with the first and/or second actuating element16,18when the parking lock device10is actuated. The actuating section33includes a contact region31that is configured by virtue of its orientation to support a contact edge35of the first actuating element16.

FIG. 2shows a section of the parking lock device10as perFIG. 1in a start position in the method in accordance with the invention100. The reference signs inFIG. 2consequently designate the same features as inFIG. 1. In the start position, the spindle guide element24is situated in a position at which the first actuating element16pushes against the stop44. In order to achieve this, the spindle guide element24exerts a pressure force22on the end face17of the first actuating element16. In this case, the spring force27exerted by the first spring26reaches a maximum. In the start position shown inFIG. 2, the arrival at the stop44is identified by the controller70of the driver20(neither of which is illustrated in greater detail) by the presence of a marked increase in the current input of the driver20. The start position shown inFIG. 2describes the point in the method at which the first actuating element16assumes a zero position on the spindle14.

With reference toFIG. 2, the actuating pawl12with the pawl tooth32, as pretensioned in the interlock deactivating direction15by the pawl spring13, is situated in a non-interlocked position. The opposing parking brake wheel ills free of forces in this position, and therefore the motor vehicle can move. The pawl tooth32is in a gap position relative to the teeth30of the parking brake wheel11. The actuating section33of the actuating pawl12rests against the second actuating element18in the region of the end face19thereof. An air gap is present in the region of the contact edge35between the contact region31of the actuating pawl12and the first actuating element16. The second actuating element18is pretensioned by the second spring28, but is held in an open position within the cylindrical sleeve42by the straight pin40. The closing direction36of the first actuating element16corresponds to the opening direction of the second actuating element18. Accordingly, the closing direction38of the first actuating element16corresponds to a closing direction of the second actuating element18.

FIG. 3shows an intermediate stage of the method in accordance with the invention100, where the stage follows the start position inFIG. 2. The reference signs inFIG. 3designate the same features as inFIG. 1andFIG. 2. InFIG. 3, the actuating pawl12in the parking lock device10continues to be pushed in an interlock deactivating direction15by the pawl spring13. The spindle guide element24abuts the end face17of the first actuating element16, which is pushed in the closing direction26by the first spring26. By rotating the spindle14, the spindle guide element24with its thread is moved in the closing direction36, such that the first actuating element16does not abut the stop44. As a result of the spring force27of the first spring26acting on the first actuating element16, the region of the contact edge35of the first actuating element16is pushed against the contact region31of the actuating pawl12. By virtue of the conical form of the first actuating element16and the obliquely aligned contact region31, a supporting force23occurs when they come into contact in the opening direction38, and acts in the opening direction38. A frictional force22also occurs when the first actuating element16slides on the actuating pawl12, and also acts in the opening direction38. The interaction of the spring force27, the supporting force23and the effective frictional force22brings about a change in the mechanical load on the spindle guide element24. The load on the spindle guide element24is transferred via its thread to the spindle14, such that the current input64(not shown in greater detail) changes for the spindle driver20as shown inFIG. 1. In the intermediate stage as perFIG. 3, provision is made for identifying the energy consumption66(not shown in greater detail) of the driver20for the movement from the stop44until the change in the current input64. The energy consumption66until the change in the current input64corresponds to the first actuating element16coming into contact with the actuating pawl12and forms the first reference point45.

FIG. 4shows an intermediate stage of the method in accordance with the invention100, where the stage follows the start position inFIG. 3. The reference signs inFIG. 3designate the same features as perFIG. 1toFIG. 3. In the intermediate stage shown inFIG. 4, the first actuating element16is moved further in the closing direction34. Here, the spring force27of the first spring26pushes the first actuating element in a closing direction36. The first actuating element16is supported at its end face17by the spindle guide element24, which is guided via its thread on the spindle14. The contact edge35of the first actuating element16, this having the shape of a cone or a truncated cone, comes into contact with the actuating section33. As a result of the frictional force22caused by the contact between the contact edge35and the actuating section33, the current input64(not shown in greater detail) of the driver20is essentially constant. During the intermediate stage as perFIG. 4, the current input64and the energy consumption66(not illustrated in greater detail) of the driver20are captured. As the contact edge35slides along the actuating section33of the actuating pawl12, the actuating pawl12is pushed in an interlock activating direction25, such that the pawl tooth32engages in the teeth30of the parking brake wheel11. Here, the movement of the spindle guide element24is effected at an essentially/substantially constant rotational speed.

FIG. 5shows an intermediate stage of the method in accordance with the invention100, where the stage follows the start position inFIG. 4. The reference signs inFIG. 5designate the same features as perFIG. 1toFIG. 4. InFIG. 5, the pawl tooth32of the actuating pawl12engages in the teeth30of the parking brake wheel11, thereby causing the associated motor vehicle to stop. The actuating pawl12is held in place by the first actuating element16which, in the region of its contact edge35, is in contact with the actuating section33of the actuating pawl12. The first spring26is essentially without tension and exerts a minimal spring force27in the closing direction36. It is countered by a frictional force22from the contact with the actuating pawl12, this being caused by static friction. The minimal remainder of the spring force27of the first spring26and the frictional force22are indicated inFIG. 5by broken-line arrows. The spindle guide element24is moreover in contact with the end face19of the second actuating element18. In comparison with the intermediate stage shown inFIG. 4, the contact of the spindle guide element24with the first actuating element16is released. Between being released from the end face17of the first actuating element16and arriving at the end face19of the second actuating element18, the spindle guide element24is only under minimal mechanical load. In this case, current input64(not shown in greater detail) of the driver20reaches a no-load value67. The second actuating element18inFIG. 5is retained in its end position by the arresting means40. When the spindle guide element24arrives at the second actuating element18, an essentially sudden increase (not illustrated in greater detail) occurs in the current input64of the driving means20. As a result, the second reference value46, which is not shown inFIG. 5, is captured. The second reference value46assigns the location of the second actuating element18in its arrested end position to the energy consumption66from the start of the axial movement of the spindle guide means24in the closing direction36of the first actuating element16. By performing an interpolation between the second reference point46and the stop44and/or the first reference point45, the energy consumption66(not shown in greater detail) represents a measure for the axial position of the spindle guide element24.

The sequence of a second embodiment of the method100in accordance with the invention is schematically shown inFIG. 6in a time-value diagram. In this diagram, the horizontal axis is the time axis50and the vertical axis is the value axis60, from which it is possible to “read off” the path of travel62parameter of the spindle guide element24and/or the first actuating element16as perFIG. 1toFIG. 5. Here, the path of travel62corresponds to a position along the axial direction34as perFIG. 1toFIG. 5. Likewise, the current input64and the energy consumption66of the associated driver20(not shown in greater detail) and corresponding limit values47,48and no-load values67can be read off from the value axis60. At a start time point61, the first actuating element16abuts the stop44. At the start time point61, no movement occurs and the current input64and energy consumption66are set to the value zero when they are captured. Following the start time point61, the current input64of the driver20increases and reaches a largely constant value. The corresponding energy consumption66increases in an essentially linear manner during this activity. In the region of the first reference point45, the first actuating element16and the actuating pawl12come into contact, as perFIG. 2. As a result of the effective mechanical interaction between the first actuating element16and the actuating pawl12, a change in the current input64occurs. The magnitude of the change exceeds a first threshold value41, which serves as a measure for an acceptable variation in the current input64. The first threshold value41is selectable and ensures that incorrect diagnoses of the parking lock device10are avoided according to the field of use. The energy consumption66that occurs before reaching the first reference point45is higher than a first limit value47. The first limit value47being exceeded indicates that the first spring26as perFIG. 1toFIG. 5is intact or that there is no jamming of the first actuating element16at the stop44. The change in the current input64effectively allows the identification of the first reference point45. The energy consumption66between the start time point61and the first reference point45can be interpolated, such that the position of the spindle guide element24along the path of travel62can be identified during subsequent actuations of the parking lock device10. As a result of the change in the current input64in the region of the first reference point45, the characteristic curve of the energy consumption63exhibits a point of discontinuity63, i.e., essentially a bend.

In the region between the first reference point45and the second reference point46, the current input64is essentially constant and the energy consumption66increases in an essentially linear manner in the corresponding region. When the second reference point46is reached, the current input64decreases to the no-load value6of the driver20. The course of the energy consumption66exhibits a point of discontinuity63, i.e., essentially a bend, at the intermediate point49in the same way as it does at the first reference point45. At the intermediate point49, the spindle drive element24releases itself from the first actuating element24and moves with essentially no load towards the second actuating element18as shown inFIG. 4andFIG. 5. The energy consumption66exceeds the second limit value48in the region between the first reference point45and the intermediate point49. The exceeding of the second limit value48indicates that the first actuating element24is being moved in its interlock activating direction25while in contact with the actuating pawl12, as illustrated inFIG. 3andFIG. 4. Any sticking of the first actuating element24on the actuating pawl12is reliably excluded thereby. The energy consumption66between the first reference point45and the intermediate point49can easily be interpolated, such that the position of the spindle guide element24and the first actuating element16can be determined.

After the intermediate point49has been passed and until the end face19of the second actuating element18is reached, only minimal current input64occurs, i.e. in the region of the no-load value67of the driver20and, hence, only minimally increasing energy consumption66. Contact with and axial movement of the second actuating element18is accompanied by an essentially linear increase in the current input64in the region before the second reference point46. In this case, the second actuating element18, against which the second spring28(not illustrated in greater detail inFIG. 6) presses, is pushed in the direction of its end position. At the second reference point46, the second actuating element18reaches its end position and stops. As a result of stopping at the end position, an essentially stepped increase in the current input64occurs at the second reference point46, such that the second threshold value66is exceeded. A point of discontinuity63, i.e., a bend, occurs in the curve of the energy consumption66at the second reference point46.

The method in accordance with the invention100returns an increasing energy consumption66between the start point61and the end point49, where the first and second reference points45,46correspond to mechanical processes in the parking lock device10. By interpolating the energy consumption66, it is therefore possible to calculate the position of the spindle drive element24and, provided the parking lock device10is functioning correctly, the position of the first actuating element24. It is moreover possible to identify mechanical faults based on deviations from the first and/or second limit value47,48.