DE102014005849A1 - A method for automatically detecting damage to a connection of at least one secondary axis in a vehicle - Google Patents

Abstract

The invention relates to methods for automatically detecting a damage of a connection of at least one secondary axis in a vehicle with an at least temporary four-wheel drive and coupled to at least one engine of the vehicle drive axle and at least one further, at least one clutch in the power flow of the motor with the drive axle at least temporarily to be coupled secondary axis, in which when exceeding respective thresholds to be provided in advance by current values of a ratio of slip to wheels of the drive axle and current slip on wheels of the at least one secondary axis and a currently determined lateral acceleration value of the vehicle and a currently determined closing torque of at least a coupling damage to the connection of the at least one secondary axis is reported to a control unit of the vehicle. Furthermore, the invention comprises a corresponding control device and a vehicle with a corresponding control device for carrying out the method according to the invention.

Description

The present invention relates to a method for automatically detecting a damage of a connection of at least one secondary axis in a vehicle with an at least temporary four-wheel drive and a corresponding vehicle and a controller configured for carrying out the method according to the invention.

In particular, powerful vehicles often have a shiftable four-wheel drive, which is also referred to as hang-on or on-demand four-wheel drive. Characteristic of a switchable four-wheel drive is that a secondary axle of a vehicle, d. H. a not directly connected to a respective drive or motor axis both passive, d. H. not driven by a respective motor, as well as actively using a temporary connection to a frictional connection between the motor and primary axis, may be arranged on the vehicle. For connection of secondary axes to a frictional connection between the motor and primary axis, for example, a clutch, in particular a multi-plate clutch, may be provided so that the connection of the secondary axle is activated or deactivated in dependence on a position or a closing torque of the clutch.

As to a powertrain and in particular to the connection, d. H. mechanical parts to force fit between a drive, such as an internal combustion engine and a respective axis, especially in powerful vehicles act considerable forces, it may happen that, for example, occur during cornering damage to the connection, so that a currently delivered by a respective engine Drive torque is no longer divided between the respective axles of a vehicle, but is directed exclusively to a primary axis, whereby a respective vehicle may out of control and cause serious damage.

Methods for protecting drive-relevant components in vehicles are described in the prior art.

The German publication DE 10 20009 022 303 A1 discloses a method in which a torque distribution is controlled individually by means of a torque distribution device of a vehicle as a function of at least one state parameter and a corresponding desired value, if potential damage to a drive train of the vehicle due to changes in the at least one state parameter is to be expected. The German document further provides that the method for protecting drive-relevant components in the torque control unit is implemented on the software side.

The European patent application EP 2 495 123 A1 relates to a method for controlling at least one clutch in a drive train of a motor vehicle in response to a slip on at least one axis. Furthermore, a control signal for actuating the clutch can also take place as a function of further conditions, such as, for example, a detected lateral acceleration.

The German publication DE 37 41 0009 A1 discloses a control system for controlling a distribution of drive torque between front and rear axles of a four-wheel drive vehicle with a sensor for directly or indirectly measuring a lateral acceleration of the vehicle, wherein a torque transmitted to the front axle is continuous and monotonous with an increase of a wheel speed difference with a steep rise rate increases when the lateral acceleration is low and at a gradual increase rate when the lateral acceleration is high.

Against this background, a method for automatically detecting damage to a connection of at least one secondary axis in a vehicle with an at least temporary four-wheel drive and coupled to at least one engine of the vehicle drive axle and the at least one other, at least one clutch in the power flow of the engine with Present at least temporarily to be coupled secondary axis in which when exceeding respective thresholds to be provided by current values of a ratio of slip on wheels of the drive axle and current slip on wheels of at least one secondary axis and a currently determined lateral acceleration value of the vehicle and a currently determined Closing torque of the at least one clutch damage to the connection of the at least one secondary axis is reported to a control unit of the vehicle.

The presented method relates in particular to a control and regulation system for an at least temporarily four-wheel drive motor vehicle with a control unit, the respective wheel speeds of all wheels assigns proportional quantities of the motor vehicle and detected or determined a current lateral acceleration. Furthermore, by means of the control and regulating system a current drive torque of at least one axle of the motor vehicle can be distributed variably, wherein the distribution of the drive torque, the closing torque of the at least one clutch is adjusted by means of a control unit and a connection of electronic Stability Systems is initiated if during an accelerated cornering despite requested clutch torque between a speed of a respective secondary axis and a respective drive axle a negative difference is detected.

In order to influence a lateral force potential of the primary and secondary axes, it is provided that a controllable closing torque of the at least one clutch, which is designed, for example, as a multi-plate clutch, and which is controlled via an actuating mechanism in the form of, for example, an actuator with associated control unit, a current distribution of a current drive torque between the respective axes is affected.

One design goal of four-wheel-drive systems is to distribute drive torque to increase a settleable circumferential force while reducing traction on tires of respective axles. A corresponding distribution of drive torque usually also leads to an increase in a maximum transferable lateral force of respective wheels. By increasing the maximum transferable lateral force or deductible circumferential force while simultaneously reducing a current traction slip, an acceleration capacity during cornering can be improved without impairing an actual driving stability. As soon as a driving situation with increased traction slip of the drive axle during accelerated cornering is detected despite a sufficiently high closing torque of the at least one clutch provided for connecting the secondary axle, damage to the drive train can be assumed.

In order to identify damage to the drive train, in particular the connection of the secondary axle to the force flow between the engine and the primary axle, and to initiate corresponding countermeasures or preventive measures for alleviating this by damaging possibly arising driving conditions, the method according to the invention provides detection by means of values of differential slip between primary and Secondary axis, lateral acceleration and actual Asked actual closing torque of the provided for connecting the secondary axle coupling.

In order to identify a cornering safely, it is provided to determine a current lateral acceleration. The current lateral acceleration can be determined, for example, directly via a lateral acceleration sensor or indirectly, for example, via a current speed in conjunction with a current steering angle.

wobei ΔS für den Differenzschlupf, ν_wheel für eine aktuelle Raddrehgeschwindigkeit und ν_wheelcenter für eine aktuelle Radmittelpunktsgeschwindigkeit steht.The differential slip provided for detecting problems or damage in the distribution of torque between the drive and secondary axes can be calculated according to equation (1).

wherein .DELTA.S represents the differential slip, ν _wheel for a current wheel speed and ν _{wheel center} for a current Radmittelpunktsgeschwindigkeit.

When the torque distribution between the drive and secondary axes is correct, the respective wheel center speeds of the respective wheels at the drive and secondary axes are identical, so that equation (2) applies: ν _{wheelcenter, 1} = ν _{wheelcenter, 2} (2)

In an error case, ie, for example, in case of damage to the connection of the secondary axis, the secondary axis is usually no longer driven or only reduced and the Raddrehgeschwindigkeit the secondary axis decreases approximately to the Radmittelpunktsgeschwindigkeit the secondary axis, so that further equation (3) applies: ν _{wheel, 2} ≈ ν _{wheelcenter, 2} (3)

Taking into account these assumptions according to equation (2) and equation (3), the following simplification can be made to measurable quantities:

The relationships set forth above in equation (4) can be transferred from wheel to axle plane in a temporary four-wheel system, such as a hang-on four-wheel system, which means that axle rather than wheel slips can be considered, so that equations (5 ) and (6) are as follows:

Crossing lateral acceleration, current closing torque, d. H. Actual closing torque and differential speed, d. H. Differential slip predefined, for example, provided by a technician or calculated by a calculation method thresholds or thresholds, can be assumed by a decoupling of the connection of the secondary axis to the adhesion between the engine and the primary axis of the vehicle.

When establishing thresholds, i. H. Triggering thresholds, which are exceeded by lateral acceleration, actual closing torque and / or differential slip from decoupling or damage to the connection of the secondary axis, results in a conflict of objectives between reliable detection of decoupling or damage to the secondary axis and avoidance of unnecessary connections For example, electronic auxiliary systems, such as stability systems.

Since, in particular, the differential slip under unfavorable circumstances can also briefly exceed a respective triggering threshold in normal operation, it is provided that damage to the connection of the secondary axis is detected by means of a suitable detection algorithm, so that misrecognition or incorrect regulation by differential slip, for example, in sporty driving situations, is avoided becomes.

In a further possible embodiment of the method according to the invention, it is provided that at least one value from the values lateral acceleration, differential slip, d. H. a ratio of actual slip on wheels of the drive axle to actual slip on wheels of the at least one secondary axle, and a value of the current closing torque is determined directly.

In order to identify respective values for the automatic detection of damage at the connection of the at least one secondary axis as accurately as possible, it is provided that the respective values directly, d. H. For example, via corresponding sensors, are determined.

In a further possible embodiment of the method according to the invention, it is provided that the respective values for the automatic detection of damage to the connection of the at least one secondary axis are determined indirectly. In order to determine respective values indirectly and thus, for example, to dispense with a respective sensor system, it may be provided that the respective values of lateral acceleration, differential slip and actual closing torque of the at least one clutch via further values, depending on, for example, a current speed and / or a current steering angle are calculated.

In a further embodiment of the method according to the invention, it is provided that the respective threshold values, beyond which it is assumed that the connection of the at least one secondary axis is damaged, are automatically provided.

In order to avoid false identifications and corresponding faulty regulations of the vehicle, it can be provided that the respective threshold values are determined and provided automatically by the vehicle itself, for example as a function of current driving situations, so that respective threshold values of a current driving situation are adapted and a recognition algorithm to detect the damage of the Connection of the at least one secondary axis can distinguish a normal operation of the vehicle from a potentially dangerous or defective operation.

In a further possible embodiment of the method according to the invention, it is provided that at least one state variable of the following list of state variables is used to automatically detect the damage to the connection of the at least one secondary axis: engine torque, yaw rate, pitch angle and steering angle as well as any further technically suitable state variable for detecting a current state of a drive train of an at least temporarily four-wheel drive vehicle.

In order to reliably detect current damage to the drive train or the connection of the at least one secondary axis and to avoid potential incorrect interventions, it is conceivable that, in addition to the state variables actual closing torque of the clutch, differential slip and lateral acceleration, further state variables are detected, for example, by suitable sensors and corresponding thresholds or to calculate an index value, i. H. a value for interpreting a current state of the secondary axis interface. On the basis of the calculated index value, for example, in potentially unclear situations, reliable information about a current state of the connection or the drive train can be determined.

Furthermore, the present invention relates to a control device in a vehicle, which is configured to carry out the method according to the invention. The control unit according to the invention is used in particular for carrying out the method according to the invention in a vehicle by providing or activating hardware requirements, such as, for example, a processor and / or sensor system.

Furthermore, the control unit according to the invention is used for interacting with the vehicle in order, for example, to activate a further control unit and / or at least one driver assistance system in the event of detected or detected damage to the connection of the at least one secondary axle, thereby protecting the vehicle against an uncontrollable situation.

Furthermore, the present invention relates to a vehicle with an at least temporary four-wheel drive and at least one control unit according to the invention.

It is envisaged that the vehicle according to the invention comprises the control device according to the invention for carrying out the method according to the invention, so that the vehicle according to the invention can be used even if the drive train is damaged, ie. H. the connection of the secondary axis, not out of control device, for example, by reducing a torque of an engine or drive of the vehicle or another technically suitable control is performed to stabilize the vehicle.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is schematically illustrated by means of embodiments in the drawing and will be described schematically and in detail with reference to the drawings.

1 shows a schematic overview of a possible embodiment of a drive with a connection of a secondary axis via a so-called hang-on coupling.

2 Figure 11 is a graph illustrating dependency of settable circumferential and lateral force on circumferential slippage.

3 shows a schematic representation of possible threshold values for triggering a case of damage according to an embodiment of the method according to the invention.

An in 1 illustrated construction of a temporary four-wheel drive comprises a primary axis 1 that is constant from a motor 3 is driven and coupled with this directly and permanently. Furthermore, the drive concept comprises a secondary axis 2 , which have a multi-plate clutch 5 at least temporarily to a frictional connection between the engine 3 and primary axis 1 can be coupled, so that the engine 3 the secondary axis 2 via the multi-plate clutch 5 also supplied with torque and the secondary axis 2 thereby drives. Depending on the location of the engine 3 in a given vehicle, the primary axis, in the case of an open multi-plate clutch 5 act as a front-wheel drive or rear-wheel drive.

As with accelerated cornering with closed multi-plate clutch 5 considerable forces on the multi-plate clutch 5 or a complete powertrain 7 It can happen that there is damage in a part of the drive train 7 comes to supply the secondary axis 2 with torque through the engine 3 serves. By such damage, the torque of the engine 3 no longer as intended to the secondary axis 2 be transferred, thereby automatically applying an applied torque to the primary axis 1 increased suddenly and the respective vehicle is destabilized if necessary.

To damage the drive train 7 and in particular a connection 4 the secondary axis 2 to the engine 3 or the primary axis 1 to recognize and possibly counteract destabilization of the respective vehicle, it is provided that the connection 4 , in particular during cornering, which is detected, for example. Via a centrifugal force sensor, a closing torque of the multi-plate clutch 5 and a current differential slip between wheels of primary axis 1 and secondary axis 2 constant, eg. Is monitored by suitable sensors, so that in the case of unexpected differential slip in a closed multi-plate clutch 5 or high closing torque of the multi-plate clutch 5 from damage to the drive train 7 is to be assumed and, for example, respective brakes of primary axis 1 and / or secondary axis 2 can be controlled by a controller so that the respective vehicle remains stable and controllable.

This in 2 The diagram shown serves to illustrate forces acting on a tire of a vehicle. On the abscissa 21 a circumferential slip is plotted in [%] and on the ordinate 22 an applied force in [N]. A deductible, ie acting on a roadway to stop a respective vehicle or tire side force 23 decreases with increasing circumferential slip. This means that a respective tire that develops slippage along a longitudinal axis also slips along a side axis. Accordingly, an increase in applied torque that results in increase in slip along a longitudinal axis of a respective tire also adversely affects a lateral force of the respective tire, such that a vehicle turns during cornering with an increase in torque at least one Tire may lose grip and be carried out of a curve.

2 further shows that the side force 23 in relation to a circumferential or longitudinal force 25 responds more strongly to occurring circumferential slip, since the lateral force 23 falls more than the longitudinal force 25 , This means that a vehicle, in particular when cornering sensitive to torque changes or circumferential slip and increased circumferential slip should be avoided when cornering.

Furthermore, in 2 longitudinal force 25 and lateral force 23 for different steering angles α from 0 ° to 15 °, at intervals of 3 °. Based on a history of lateral force 23 at a steering angle of 0 °, as by line 27 shown, it can be seen that the circumferential slip in a straight-ahead driving only a little on the side force 23 effect. Unlike line 27 , makes line 29 a cornering with a steering angle of 15 °, in which already a circumferential slip of about 40% to a halving of the deductible side force 25 and thus leads to a significantly lower driving stability of the respective vehicle. In the 2 For example, these forces refer to a vehicle with 205/50 R 15 tires on a dry road with a 4000 Newton wheel load, 0 ° camber, and 2.0 bar air pressure.

In the 3 illustrated visualization of tripping thresholds for detecting damage to the connection 4 the secondary axis 2 based on a current lateral acceleration 31 , which is plotted on the abscissa and on an actual closing moment 33 the multi-plate clutch 5 , which is plotted on the ordinate. If a current lateral acceleration 31 and a current actual closing moment 33 the clutch within a range 32 lie, ie the multi-plate clutch 5 is closed and the vehicle is cornering, is at an exceeding of a threshold, not shown by an actual differential slip of the vehicle from an error case 37 ie damage to the drive train 7 go out. line 35 borders the area 32 compared to a non-critical state of the vehicle, in which an exceeding of the threshold, not shown, by the current differential slip as normal driving 39 , for example, without activated four-wheel drive and with a correspondingly low actual closing torque 33 the multi-plate clutch 5 , is interpreted.

To go on a normal trip 39 occurring differential slip of differential slip due to damage to the drive train 7 To differentiate, a recognition algorithm is executed by a control unit of the vehicle, which knows, for example, characteristic differential slip characteristics for normal driving and damage cases and classified currently determined values in normal driving or damage case. For this purpose, the recognition algorithm may in particular comprise a neural network or another suitable classifier.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 1020009022303 A1 [0005]
• EP 2495123 A1 [0006]
• DE 37410009 A1 [0007]

Claims (11)

A method for automatically detecting damage to a connection of at least one secondary axis in a vehicle with an at least temporary four-wheel drive and at least one coupled to at least one engine of the vehicle drive axle and the at least one further, at least one clutch in the power flow of the motor with the drive axle at least temporarily coupling secondary axis, in which when exceeding respective thresholds to be provided in advance by current values of a ratio of slip at wheels of the drive axle and current slip on wheels of the at least one secondary axis and a currently determined lateral acceleration value of the vehicle and a currently determined closing torque of the at least one clutch Damage to the connection of the at least one secondary axis is reported to a control unit of the vehicle. Method according to Claim 1, in which at least one state variable is used to automatically detect the damage to the connection of the at least one secondary axis. The method of claim 2, wherein the at least one state quantity is selected from the following list of state quantities of the vehicle: engine torque, yaw rate, pitch angle, and steering angle. Method according to one of the preceding claims, in which at least one of the values of lateral acceleration, the ratio of actual slip on wheels of the drive axle to actual slip on wheels of the at least one secondary axle and the current closing torque is determined directly. Method according to one of the preceding claims, in which at least one of the values of lateral acceleration, the ratio of current slip on wheels of the drive axle to actual slip on wheels of the at least one secondary axle and the current closing torque is determined indirectly. Method according to one of the preceding claims, in which at least one driver assistance system of the vehicle is activated as a function of a detected damage to the connection of the at least one secondary axle. Method according to one of the preceding claims, in which the detection of the damage to the connection of the at least one secondary axis is effected by means of a recognition algorithm executed by a control device. The method of claim 7, wherein the detection algorithm is selected such that short-term exceedance of respective threshold values in a normal operation are not considered as damage to the connection of the at least one secondary axis. Method according to one of the preceding claims, in which the respective threshold values are calculated automatically by a control unit as a function of a current driving situation. A controller in a vehicle configured to perform a method of detecting damage to a connection of at least one secondary axle of the vehicle according to any one of the preceding claims. Vehicle with at least temporary four-wheel drive and at least one control device according to claim 10.

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