DE102007044452B4 - Method for controlling the distribution of the drive torque of an at least temporarily four-wheel drive motor vehicle and control device - Google Patents

Abstract

Method for controlling the distribution of the drive torque of an at least temporarily four-wheel drive motor vehicle, wherein at least the wheels of an axle (1; 2; 1, 2) are assigned the torque by means of a controllable friction clutch (7), which friction clutch (7) is controlled by a control device (10 ) a desired clutch _torque (M _ksoll ) is specified, the latter being limited to protect components of the drive train, characterized in that an overload integral (A) as an integral over the difference between the of the clutch (7) transmitted power (L _k ) and a transmittable maximum continuous power (L _d ) which can be transmitted by the clutch and drive train, and in that the power (L _k ) transmittable by the clutch (7) is _reduced to a smaller power by reducing the nominal clutch _torque (M _ksoll ). L _k ^* ) is reduced when the overload _integral (A) exceeds a predetermined limit (A _limit ).

Description

The The invention relates to a method for controlling the distribution of Driving torque of an at least temporarily four-wheel drive motor vehicle, at least the wheels an axle torque by means of a controllable friction clutch is assigned, which friction clutch of a control device a desired clutch torque is specified, the latter for protection of components of the drive train can be limited.

It can be both about motor vehicles with permanently driven front axle and over the controllable friction clutch driven rear axle or vice versa as well as to motor vehicles, each with a controllable friction clutch for the front axle and the rear axle act. A clutch can thus in the first Powertrain, be provided in the second output train or in both.

It is uneconomical, each of the two drive trains on the full engine power or the full maximum torque at the gearbox output. That can be in extreme driving situations to overload lead individual components. So it can, for example, in a four-wheel drive vehicle with rigidly driven Front axle and over an integrated in the front axle bevel gear and a controllable Friction clutch driven rear axle with prolonged high load for overheating or excessive wear of the angular gear or the rear axle differential.

One such load case is for Such a vehicle, for example, when driving on a long slope with trailer when the normal clutch control (slip control and / or Feedforward control) by closing the clutch of the rear axle has a large transmittable torque (im called the following target clutch torque). Then the to Rear axle leading Drive train particularly high load. The monitoring by means of temperature sensors is expensive and unsatisfactory.

From the DE 103 33 654 B4 It is known to define three speed ranges (high, normal and low speed) for the protection of components of the drive train and to set for these different limit torques or limit torque curves. The control device comprises a control unit, a component protection unit and a coordination unit in which a minimum selection is made between the output signals of the other two units. The duration of the operation in the individual speed ranges is not considered. It is obvious that with it and with the rough division into three speed ranges, the power transmission capacity of the clutch-containing drive train can not be fully utilized.

From the DE 10 2005 052 359 A1 a generic method is known in which the instantaneous, introduced into a clutch power accumulates and from a clutch temperature is determined, wherein when a temperature value is exceeded, the clutch is disengaged.

The US 2005/0177295 A1 discloses a generic method known in which a controller calculates the loss heat output of the clutch as a difference between the input power and the output power of the clutch. Then, the controller integrates the waste heat output in the period of the execution cycle to determine the thermal energy input to the clutch during the execution cycle. Then, the controller divides the thermal energy input by you thermal mass of the clutch to determine the temperature change. This temperature change is finally compared to a threshold value. If this threshold is exceeded, the clutch is disabled.

Of the Invention is based on the object, a method and a control device to provide the power transmission capacity of the Fully exploited clutch clutch still and clutch the protection of the components to be protected guaranteed.

These The object is achieved by a method having the features of the patent claim 1 solved. Advantageous developments of the method according to the invention are the subject of the claims 2-7. The task is also accomplished by a control device the features of claim 8, which in the claims 9 to 14 is advantageously developed.

The Invention is based on the finding that the thermal load (For example, the meshing gears) not solely on the size of the transferred Torque, but also from the speed respectively Speed, and thus the transmitted Performance, depends. Therefore, the power is integrated and the overload integral has the dimension a work.

The transmissible continuous power is the basis of the design of the drive train and is confirmed or determined by tests. The overload integral is only across the dif renz, the overload. As a result, the value of the integral decreases again when falling below the transmittable continuous power. So the value of the integral is an almost thermal image of the thermal state. If the overload integral exceeds a predetermined limit value, the power transmitted by the affected drive train is reduced to a value, for example, below the transferable continuous power.

There the power in a torque / speed graph appears as a hyperbola ("power hyperbola") means that one "below" the persistent power hyperbola lying hyperbola is approached. This is the moment transmitted by the clutch lowered until an operating point on the "lower" hyperbola is reached words, The lowering of the torque depends on the instantaneous speed (claim 4). This is how the safety controller works gently.

In Development of the invention is used to determine the overload integral that transmitted from the clutch Performance as a product from the over transmitted the clutch Actual torque and speed calculated and with one of the Speed of the vehicle pending factor corrects (claim 2). At standstill, this factor is essentially equal to one and decreases with increasing speed according to a measurement determined Table off. So is in vehicles whose components to be protected in essential Dimensions of the wind chilled are, the speed-dependent intensity this cooling considered.

Unless No special torque measurement is provided, the value may be of the over transmitted the clutch Actual torque can be supplied from the clutch actuator. Arrives such value is not available, so it can be estimated with reasonable accuracy on the assumption that it does not exceed a certain proportion of the total drive torque (at the transmission output) (Claim 3).

In Further development of the invention, the limitation of the desired clutch torque takes place delayed at one time, when the overload integral exceeds the limit following a buildup of transmitted torque (Claim 5). This will be a smooth transition and in interaction with the traction control achieved a minimization of traction loss.

In A refinement of the invention can be provided that the Limiting the target clutch torque is suppressed if a high lateral acceleration or a large steering angle detected is (claim 6). This allows the driver to drive through one sharp curve (think of a hairpin bend of a pass road) that Accelerate vehicle with minimal slip.

In Another refinement may be one above the limit be given further limit, when exceeded, the transferable Power is achieved by lowering the nominal clutch torque without time delay (Claim 7). This additional limit provides an emergency backup in which on the lateral acceleration or the steering angle no consideration more is taken.

The The invention also relates to a control device which thus obtains is that it carries out the method described above.

in the The invention will be described below with reference to figures and explained. They show:

1 : Drive scheme of a four-wheel drive vehicle as an example of a vehicle equipped according to the invention,

2 : Scheme of the control unit,

3 : Table: speed-dependent factor,

4 : A torque / speed diagram,

5 : A performance / time diagram.

1 shows the drive of a motor vehicle with a front axle 1 and a rear axle 2 , From a motor-transmission block 3 become the Halbach sen 4.1 . 4.2 the front axle 1 permanently driven and via an angle gear 5 (also called "power take-off"), via cardan shafts 6 and a controllable friction clutch 7 a rear axle differential 8th and from this the two half-axes 9.1 . 9.2 one to the left and one to the right wheel of the rear axle. The controllable friction clutch 7 is from a controller 10 by means of an actuator 11 adjusted.

In this arrangement, the two half-axes form 4.1 . 4.2 the front axle 1 the first permanently acting drive train and the elements of the angular gear 5 to the half axes 9.1 . 9.2 the rear axle 2 the second driveline, one of the controllable clutch 7 transmits limited or controllable torque. By means of the coupling 7 is thus the distribution of the drive torque on the two axes 1 . 2 controllable.

The arrangement of 1 serves as an example. The arrangement could also be made such that the wheels of the rear axle 2 permanently driven and the wheels of the front axle 1 are driven via a controllable clutch. Finally, the arrangement could also be made so that the wheels of both axes 1 . 2 each driven via a controllable coupling.

In 2 is the entire control device 10 indicated by a dashed frame. It contains a pilot control unit 20 , An inventively designed and acting protection unit 23 and a vehicle dynamics controller or slip controller 27 ; and a first coordinator 26 who makes a minimum selection and a second coordinator 29 making a maximum selection. The pilot unit 20 and the slip control 27 stand as input signal 21 signals describing the respective operating state of the vehicle. These are, for example, the wheel speeds, the engine speed, the transmission output torque and the accelerator pedal position, as well as possibly the steering angle, the lateral acceleration and more. The protection regulator 23 stand over the signal lines 24 the currently transmitted clutch torque M _k or the transmission output torque and the vehicle speed or the speed n _k available, possibly also further the movement of the vehicle descriptive variables. In the pilot unit 20 will be a setpoint of the clutch 7 transmittable torque (M _soll ) and over the line 22 the coordinator 26 fed.

The protection regulator 23 determined _according to the invention and described below way the setpoint M _ksoll a transferable torque, which ensures the protection of the parts of the drive train from overloading or overheating and performs this via the line 25 the coordinator 26 to. This selects a minimum value - that is, it selects M _ksoll if it is smaller than M _soll - and sets it over the second coordinator 29 the actuator 11 the controllable clutch 7 to disposal. The second coordinator 29 selects if available and / or required by the slip controller 27 emitted signal.

In the protection regulator 23 is the difference between the instantaneous power L _k and that of the clutch 7 containing powertrain sustainable continuous power L _d formed and these continuously integrated over time. The power L _k transmitted by the clutch is the product of the momentarily transmitted torque M _k and the instantaneous speed n _k or speed and is corrected with an influencing factor k _v , which takes into account the speed-dependent heat dissipation by the driving wind. This is the easiest one in 3 taken from the reproduced table. The vehicle speed is plotted on the ordinate and the value K _v on the abscissa. This value is between 0 and 1 and is substantially equal to 1 even at travel speed 0, and decreases with increasing speed. The corresponding curve is with 29 designated.

The overload integral A thus formed, and according to the equation given below, has the dimension of a work. As a result of the fact that the integral is formed continuously, it increases when the instantaneous power L _k lies above the sustainable continuous power L _d and decreases again when it lies below (L _k ).

When the overload _integral A thus formed reaches a predetermined limit A limit, the protection _{controller operates} 23 a lowering of the transmitted power from L _k to L _k *, a given lower power. This is determined according to vehicle-typical sizes, whereby also in refinement of the method different values can be determined. The reduced power L _k * corresponds to a power hyperbola on which the new operating point can adjust accordingly. By specifying a lower power level (and not a smaller transmittable torque), the protection device comes into effect without interfering or even surprisingly intervene in the prevailing driving state. This is a considerable advantage in a difficult driving situation.

In 4 this is shown in a diagram on whose ordinate the speed or travel speed and on the abscissa of which the transmitted torque in the drive train with the clutch M _{k is} plotted. The current operating point is with 30 means that during normal travel it constantly shifts in both horizontal and vertical directions. If the accelerator pedal position or the transmitted power is con stant, it moves on the Leistungshyperbel L _k . About the performance in this variable operating point 30 is continuously integrated according to the following equation: A = ∫ [(M k · n k · K v ) - Ld] dt

A

Überlastintegral,

A_grenz

Grenzwert des Überlassintegrals,

M_k

das Momentan über die Kupplung 7 übertragene Drehmoment,

n_k

einen der Fahrgeschwindigkeit proportionalen Wert, eine Dreh zahl,

K_v

einen die Wärmeabfuhr durch den Fahrtwind berücksichtigender Einflussfaktor gemäß der Tabelle in 3,

L_d

die von dem Antriebsstrang bzw der Kupplung maximal übertragbare Dauerleistung.

In it means:

A

Integral overload,

A _border

Limit value of the transfer integral,

M _k

the momentary about the clutch 7 transmitted torque,

n _k

a value proportional to the driving speed, a rotational speed,

K _v

an influencing factor taking into account the heat dissipation by the wind, in accordance with the table in 3 .

L _d

the maximum transferable from the drive train or the clutch continuous power.

Which of the the clutch 7 containing powertrain transmissible continuous power is in 4 entered as Leistungshyperbel L _d . If the overload _integral A exceeds the predetermined limit A limit, is in the protection controller 23 a new operating state is set starting from a performance hyperbola L _k * corresponding to a smaller power. This is somewhere on the reduced Leistungshyperbel L _k *, which is in 4 through the dots 31 (practically unavailable) respectively 32 is indicated with the associated rotational speeds n ₁ *, n ₂ * and the associated adjusted torque M _k1 *, M _k2 *. In this case, the latter are the target values, depending on the currently prevailing driving condition on the controllable clutch 7 from the actuator 11 be set.

5 shows in the upper diagram the work and in the associated diagram below the power as abscissa over time as ordinate. In the first period 35 the vehicle is moving at a constant power (which is associated with increasing torque at decreasing speed) which is greater than the transmissible continuous power L _d . The working integral A is thereby continuously by integration over the positive distance between the instantaneous power L _k and the transmissible continuous power L _d (reference numeral 38 ) integrated. If the working _integral A, the border work A _limit (reference _numeral 39 in the upper diagram), the power is withdrawn.

Specifically, when the transmitted torque was increasing at this time, a dead time timer starts in the control device 10 to run. During this time t '(reference numeral 36 ) is further integrated until after the time t ', the power is reduced to the reduced level L _k *. Thereby, depending on the current driving state of the vehicle and the speed of the withdrawal, an operating point on the lower Leistungshyperbel L _k * reached, for example point 31 (only theotetic) or a point 32 in 5 (see also 4 ).

In the upper of the two diagrams can be seen that from the point 40 the working integral A decreases again. The withdrawal of the power L _k can also be completely inhibited when the vehicle is in a critical driving state (tight curve), which is not shown in the diagram. It is not specifically shown that a further limit value (A _limit ^* ) lying above the limit value (A _limit ) can be predetermined, at which point the transmittable power (L _k ) is exceeded by lowering the setpoint clutch _torque (M _ksoll ) without time delay and Consideration has been given to lateral acceleration or steering angle. The course is then analogous to that described with regard to the limit value (A _grenz ).

Claims (14)

Method for controlling the distribution of the drive torque of an at least temporarily four-wheel drive motor vehicle, wherein at least the wheels of one axle ( 1 ; 2 ; 1 . 2 ) the torque by means of a controllable friction clutch ( 7 ), which friction clutch ( 7 ) from a control device ( 10 ) a desired clutch _torque (M _ksoll ) is specified, wherein the latter can be limited to protect components of the drive train, characterized in that an overload integral (A) as an integral over the difference between the of the clutch ( 7 ) transmitted power (L _k ) and a transmissible, sustainable for clutch and drivetrain, maximum continuous power (L _d ) is formed, and that of the clutch ( 7 ) transmittable power (L _k ) by reducing the target clutch _torque (M _ksoll ) is reduced to a smaller power (L _k ^* ) when the overload _integral (A) exceeds a predetermined limit (A _limit ). A method according to claim 1, characterized in that for determining the overload integral (A) from the clutch ( 7 ) transmitted power (L _k ) is calculated as the product of the torque transmitted via the clutch (M _k ) and the speed (n _k ) or another variable proportional to the speed of the vehicle and at a factor dependent on the speed of the vehicle ( k _v ) is corrected. Method according to claim 2, characterized in that via the coupling ( 7 Transmitted) actual torque (M _k) is estimated on the assumption that it (not exceed a certain proportion of the total drive torque at the transmission output). A method according to claim 1, characterized in that the reduction of the desired clutch _torque (M _ksoll ) is speed-dependent, wherein the instantaneous operating point ( 31 . 32 ) lies on a power hyperbola (L _k *), which power hyperbola (L _k *) corresponds to a smaller power than the transmissible continuous power (L _d ). A method according to claim 1, characterized in that the limitation of the desired clutch Momentes (M _ksoll ) delayed by a time (t ') takes place when the overload _integral (A) the limit (A _limit ) following a structure of the transmitted torque (M _k ) overshoots. A method according to claim 1, characterized in that the limitation of the target clutch _torque (M _ksoll ) is suppressed when a high lateral acceleration or a large steering angle is detected. A method according to claim 1, characterized in that a further above the limit (A _cross) lying limit _(cross A ^*) is determined which, if exceeded, the transmittable power (L _k) by lowering the target clutch torque (M _{K desired)} without any time delay he follows. Control device for controlling the distribution of the drive torque of an at least temporarily four-wheel drive motor vehicle, wherein at least the wheels of one axle ( 1 ; 2 ; 1 . 2 ) the torque by means of a controllable friction clutch ( 7 ), which friction clutch ( 7 ) from a control device ( 10 ) a desired clutch _torque (M _ksoll ) is specified, the latter being limited to the protection of components of the drive train, characterized in that the control device ( 10 ) is equipped such that the of the clutch ( 7 ) transmitted power (L _k ) by reduction of the desired clutch _torque (M _ksoll ) is limited, if one as an integral on the difference between that of the clutch ( 7 ) transmissible power (L _k ) and a transferable, for the clutch and drive train sustainable, maximum continuous power (L _d ) formed overload _integral (A) exceeds a limit (A _limit ). Control device according to Claim 8, characterized in that, to determine the overload integral (A), that of the clutch ( 7 ) transmitted power (L _k ) as a product of the transmitted over the clutch actual torque (M _k ) and the rotational speed (n _k ) or another of the speed of the vehicle proportional size determined and with a dependent on the speed of the vehicle factor ( k _v ) is corrected. Control device according to claim 9, characterized in that via the coupling ( 7 Transmitted) actual torque (M _k) is estimated on the assumption that it (not exceed a certain proportion of the total drive torque at the transmission output). Control device according to claim 8, characterized in that the reduction of the desired clutch torque is speed-dependent, wherein the instantaneous operating point ( 31 . 32 ) lies on a power hyperbola (L _k *), which power hyperbola corresponds to a power smaller than the transmissible continuous power (L _d ). _{Control device} according to Claim 8, characterized in that the limitation of the setpoint clutch _torque (M _ksoll ) does not take place until a time (t) when the overload integral (A) _exceeds the limit value (A _limit ) following a build-up of the transmitted torque (M _k ). _{Control device} according to claim 8, characterized in that the limitation of the target clutch _torque to (M _ksoll ) is suppressed when a high lateral acceleration or a large steering angle is detected. _{Control device} according to Claim 8, characterized in that a further limit value (A _limit ^* ) lying above the limit value (A limit) is predetermined, at which point the transmittable power (L _k ) is exceeded by lowering the setpoint clutch _torque (M _ksoll ) without a time delay he follows.