DE102007044452A1 - Intermittent four-wheel-driven motor vehicle drive moment distribution controlling method, involves distributing torque to wheels of axle by controllable friction clutch, and predetermining reference-coupling moment for friction clutch - Google Patents

Abstract

The method involves distributing a torque to wheels of an axle (1) by a controllable friction clutch (7). A reference-coupling moment is predetermined for the friction clutch by a control device (10). An overload integral is formed as an integral by the difference between the power transferred by the clutch and a transferred continuous power. The power transferred by the clutch is reduced to a smaller power by reduction of the reference-clutch moment, when the overload integral exceeds a preset limiting value. An independent claim is also included for a control device for controlling the distribution of the drive moment of an intermittent four-wheel-driven motor vehicle.

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.

It is therefore an object of the invention, a method and an apparatus indicate that the power transmission capacity of the Clutch fully utilize the powertrain while still providing protection the one to be protected Ensures components.

The solution is that an overload integral as an integral over the difference between the power transmitted by the clutch and a transmittable one Continuous power is formed, and that transmitted from the clutch Performance is reduced by reducing the nominal clutch torque, when the overload integral exceeds a predetermined limit. This is based on the knowledge that the thermal load (For example, the meshing gears) not alone on the size of the transferred Torque, but also from the speed respectively Speed, and thus the transmitted power, depends. Therefore, the power is integrated and the overload integral has the dimension a work.

The transferable Continuous power is the basis of the design of the drive train and is confirmed or determined by tests. The overload integral will only be over the difference, the overload, educated. This reduces the value of the integral when falling below the transferable continuous service again. So the value of the integral is a reflection of the thermal Condition almost in real time. exceeds the overload integral a predetermined limit, then that by the affected Powertrain transmitted Achievement on a for example given value under the transferable Continuous power reduced.

There the power in a torque / speed graph as a hyperbola ("Performance Hyperbola") appears, 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 a further development of the invention, the power transmitted by the clutch power is calculated as the product of the transmitted via the clutch actual torque and speed and with one of the Ge to determine the overload integral speed of the vehicle pending factor corrected (claim 2). This factor is substantially equal to one at standstill and decreases with increasing speed according to a table determined by measurements. Thus, in vehicles whose components to be protected are cooled to a significant extent by the wind, the speed-dependent intensity of this cooling is taken into account.

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 by lowering the target clutch torque without Zeitverzöge tion occurs (claim 7). This further limit represents an emergency fuse in which no regard to the lateral acceleration or the steering angle 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 coupling Lung 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 moves with constant power (which goes along with decreasing speed with increasing torque), the larger as 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 from a control device ( 10 ) a setpoint clutch torque is specified, the latter being limited to the protection of components of the drive train, characterized in that an overload integral (A) as an integral over the difference between that of the clutch ( 7 ) transmitted power (L _k ) and a transmitted continuous power (L _d ) is formed, and that of the clutch ( 7 ) transmissible 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 _torque (M _ksoll ) delayed until a time (t ') occurs when the overload _integral (A) the limit (A _limit ) following a structure of the transmitted torque (M _k ). 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 from a control device ( 10 ) a desired clutch torque (M _soll ) 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 the from the clutch ( 7 ) transmitted power (L _k ) and a transmissible 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.