WO1990011908A1

WO1990011908A1 - Automatic locking device for a transfer gearbox

Info

Publication number: WO1990011908A1
Application number: PCT/EP1990/000539
Authority: WO
Inventors: Ralf Vorndran; Bernd Robert HÖHN
Original assignee: Zahnradfabrik Friedrichshafen Ag; Audi Ag
Priority date: 1989-04-07
Filing date: 1990-04-06
Publication date: 1990-10-18

Abstract

In a device for automatically locking a transfer gearbox (3) in a motor vehicle fitted with a permanent 4-wheel drive (41, 42; 51, 52) by means of sensors (n1 to n4, 8, 9, 10), the data which characterize the state of motion of the motor vehicle are fed to an electronic unit (6). A signal (61) which actuates the longitudinal locking coupling (33) is produced from data stored in the electronic gearbox control device (6). The locking signal (61) is activated when a threshold value of the acceleration (slim) determined in a driving test is exceeded by one of the two axles. The locking signal is also produced when a given limiting slip (slim) is exceeded by an excessive actual slip (sact).

Description

Device for automatically locking a transfer case

The invention relates to a device for automatically locking a transfer case according to the preamble of claim 1.

Such a device, in which the lock of a transfer case in a motor vehicle is activated automatically, is known from DE-A 35 45 544. The vehicle in which the device for locking the transfer case is arranged also has a drive fault device known per se, in which actions are provided on the wheel brakes of an axle via brake torque controllers and / or on the power actuator of the engine via a torque converter. In this document, an OR element is supplied with the variables characterizing the state of motion of the vehicle and the control signals for the wheel brakes and / or the power actuator, and the output signal acts as a blocking signal for the transfer case. The data characterizing the state of motion of the vehicle is additionally fed to an electronic unit for evaluation. In addition to the speeds of the drive wheels, these data are also the

Steering angle of the front wheels proportional steering angle signal that comes from a steering angle sensor. The electronic unit mentioned in DE-A 35 45 544 is described in more detail in DE-C 35 05 455. It primarily evaluates the speed differences of the front wheels and compares them with the driving speed derived from the front wheel speeds and the limit values assigned to the steering angle. If the limit values are exceeded, an output signal is emitted via which the lock of the transfer case is activated. Such a device may turn the lock of the transfer case on and off in a sensible and self-saturated manner, but the effort required for this is very high.

It is therefore an object of the invention to simplify a device according to the preamble of claim 1 with regard to construction costs, the time until the detection of the locking signal and the reaction time until the locking is closed should also be short no ^" additional sensors, e.g. for determining the steering angle, may be required.

This object is achieved with the characterizing features of claim 1.

While according to the prior art the steering angle signal proportional to the steering angle of the front wheels, which comes from the steering angle sensor, is necessary for determining the locking signal in the electronic unit, the

Invention with information that is generally available in the vehicle. The clever use of the speeds of the drive wheels and the combination of the slip values s-actual, s-target and s-limit as well as the determination of the axis acceleration of one axis each lead to the locking signal in a very simple manner. The computing effort in the electronic transmission control is very low, because primarily easy-to-determine quantities are compared with quantities determined in tests and stored in the electronic transmission control, by linking the equations LW = f (v_) with s-target ^** = f (LW) to the equation s ",, = f (v) there are relationships by which a steering angle sensor on the steering wheel of the vehicle is unnecessary. The total reaction time including the generation of the locking signal is further minimized by the pre-filling of the longitudinal lock clutch, the connection and disconnection quality is ensured via a suitable ramp, which is influenced by the size of the transmission output torque and the current axis acceleration.

The invention is not limited to the feature combination of the claims. For the specialist, there are further useful combinations of claims and individual claim characteristics from the task.

Further details of the invention will be explained with reference to drawings and exemplary embodiments. Show it:

Figure 1 is a block diagram of a motor vehicle with all-wheel drive in connection with an electronic transmission control.

Fig. 2 is a schematic representation of the

Activation of the longitudinal locking clutch;

3 shows a diagram of the slip, recorded over the steering angle LW;

4 shows a diagram of the steering angle, plotted against the vehicle speed v_;

5 shows a diagram of the slip s, plotted against the vehicle speed v_;

Fig. 6 is a diagram for pre-filling the

Longitudinal locking clutch;

Fig. 7 is a diagram showing the initial locking torque; Fig. 8 is a diagram showing the on and off ramp;

Fig. 9 is a flow chart.

In the block diagram according to FIG. 1 of a motor vehicle all-wheel drive in conjunction with an electronic transmission control, 1 denotes the drive motor, 2 the manual transmission and 3 the transfer case. An electronically-hydraulically controlled longitudinal locking clutch 33 is arranged schematically in this. 31 is the drive for the front axle (VA) 4 with the drive wheels 41, 42, which are driven via the front axle differential 44 and the semi-axles 43. 32 is the drive for the rear axle 5, which via the rear axle differential 54 and the semi-axles 53 on the drive wheels 51, 52

Rear axle works. With n 1. to n4. are the speed sensors of the drive wheels 41, 42; 51, 52, wherein these speed sensors are connected to the electronic transmission control 6 via the lines 45, 46 and 55, 56. The motor load is transmitted from the motor system 7 to the electronic transmission control unit 6 via line 71 and the engine speed via line 72. A control signal is sent via line 73 from the motor 7 to the motor to influence it. 8 is the load generator and 9 the

Brake transmitter and 10 of the selector lever, the information of which is forwarded to the electronic transmission control unit 6 via lines 81, 91 and 101. A hydrodynamic torque converter 21 can also be arranged between the engine 1 and the transmission 2.

In Fig. 2, the control of the longitudinal locking clutch is shown schematically, wherein the electronic transmission control 6 is connected via the control line 61 to the electronic pressure control valve 62. The

Pre-control pressure, which via line 66 to the electronic Pressure control valve 62 is supplied, is varied in height via this, depending on the signals from the electronic transmission control 6. The main pressure 65 is fed directly to the safety valve 67 and simultaneously controls this valve for flow. 68 is the clutch valve for the longitudinal locking clutch 33 and is controlled by the pilot pressure. The inner plates of the longitudinal locking clutch 33 are arranged on the hollow shaft 35 and the outer plates on the outer plate carrier 36. At 37 he is

Pressure piston and designated 38 the pressure chamber. The longitudinal locking clutch is used to lock the rear and front wheel drive, z. B. a planetary gear, not shown, is driven via the shaft 34 on the ring gear, while the sun gear, not shown, drives the hollow shaft 35 and the front wheels 41, 42 and the outer disk carrier 36 is provided with the planet carrier for driving the rear wheels 51, 52. Depending on the signal in the control line 61, the main pressure is thus fed into the pressure chamber 38, the piston 37 blocking the outer disk carrier (= planet carrier) and the hollow shaft 35 (= ^* sun gear) via the disks.

To control the automatic longitudinal locking clutch 33 via the control line 61, the wheel speed signals n .. to n4 are first in the electronic transmission control 6. according to the formula

ⁿ l ^{+ n} 2 ^ ^"π 3 ^{+ n} 4 ^ s (%) = 2 -. 100 (1) n_. + n + n, + n.

determined as a slip between the front 4 and the rear wheel axle 5. Criteria as to whether the lock should be closed or not I. impermissibly high slip or differential speeds between the front 4 and the rear wheel axle 5;

II. An inadmissibly high axis loading of one of the two axes.

For a decision as to whether the calculated slip represents an impermissible differential speed or not

^s is ^"S target ^s a G-re - nz ⁽²⁾

apply as equation 2.

The actual slip s _τ . should be the slip that was currently calculated according to equation 1, regardless of whether the lock was open or closed.

The target slip should be the slip that is caused by the current vehicle movement, e.g. B. when cornering, arises and the limit slip should be the slip, when the longitudinal lock clutch 33 is to be closed.

The aim of a general slip calculation and detection should be, depending on the parameters tires, steering wheel lock, vehicle speed v_, coefficient of friction μ between the road and the tires and the direction of travel - e.g. B. forwards or backwards - to measure the speed difference between the front 4 and the rear wheel axle 5 according to equation 2, which reveals a spinning axle. Since only for the detection of the target slip

Speed signals n. To n., The vehicle speed v and the direction of travel detection after

Selector lever position 10 is available, it is necessary to measure the driving dynamics of the vehicle as a function of the parameters shown above and to link the measured values determined to the function target slip = f from vehicle speed - s "- = f (v"). To map this function as accurately as possible, it is calculated from the equations target slip = f from the

Steering angle - s "-, = f (LW) - and the steering angle as a target

Function from vehicle speed - LW = f (v) - formed.

3 shows the desired slip as a function of the steering angle on the steering wheel as a function of different tires and friction values (μ), the slip in percent being plotted on the ordinate axis, that from the formula

vm hm s (%) = 2 __-__ — ____ — _-________-___. . 100 v hm

was determined. The abscissa is divided into degrees in the range of the practically possible steering angle on the steering wheel.

For the measurement of s ~,, = f (LW), the vehicle speed v "should be just above the smallest measurable speed v. lie to ensure an almost lateral force-free rolling. Depending on the parameters of the coefficient of friction and tires, the differential speed calculated by the electronic transmission control is directly measured using application devices

Equation 2 measured and displayed. Here, s_ ,, is measured in steering angle steps of 90 ° in the range of 0 ° target

Steering angle up to the maximum steering angle of z. B. 700 °. This measurement is made during forward and reverse travel according to the selector lever position 10. The curves in FIGS. 3, a), b) and c) are measured slip values with different friction values and tires:

a) = s_ _j . with tires of 215/60 and a coefficient of friction of μ 0.9, b) = s _τ with 195/65 tires and a coefficient of friction of μ 0.6,

c) = s_ with 195/65 tires and

• O ^~ m * a coefficient of friction of μ 0.2.

Curve d) is the target slip value, which is obtained from the formula

s _SoU = 0.5. (s _actual (215/60) μ 0.9)

was determined.

The measurement of the steering angle as a function of the vehicle speed LW = f (v_) takes place under the same parameters described above, with the slip s_ being measured at constant steering angle (steering wheel lock) during constant acceleration up to the cornering limit speed at which the lateral acceleration ay reached a maximum or remains constant. This measurement is also carried out when driving forwards and backwards.

The curves e), f), g) shown in FIG. 4 result:

e) ^• = v_ for 215/60 tires with coefficient of friction μ 0.9,

f) = v „for tires 215/60 with coefficient of friction μ 0.6,

g) = v_ for 195/65 tires with coefficient of friction μ 0.6. By linking the functions LW = f (v_) with r the function s „. - = f (LW) is indirect via the

Should

Vehicle speed a statement about the associated maximum differential speed or the maximum steering angle (LW) possible.

5 is about the vehicle speed in the

The abscissa of the slip s is plotted in percent on the ordinate. This slip is determined using the formula

vm hm s (%) = 2 «_______________________-. 100

⁽ⁿ vm ^{+ n} hm ⁾ '

where the values n is the average wheel speed at vm ^

Front 4 and n, the average wheel speed on the rear wheel axle 5. The curves h to 1 shown in FIG. 5 characterize the limit slip according to formula 2, where h means the limit slip in forward travel and z. B. the target slip is + 3%. The curve i is the limit slip when reversing and corresponds to the slip s_ _. _. + 9%. Curves k and 1 contain the limit slip + the target slip when driving forwards (k) and the curve 1 the limit slip + the target slip when reversing. A distinction between forward and reverse travel is essential for the response behavior of the lock in the event of impermissible slip. In position R s is _g., Significantly higher at the same speed, which would cause a deterioration in the response result in equal treatment. s _r (right side of equation 2) is the absolute threshold, when exceeded, the electronic transmission control to the electro-hydraulic control in the transmission, as already described, gives the command to close the lock. s _G characterizes the inaccuracy of the s _ς -.-- detection and thus takes into account all tolerances in the detection of the wheel speeds n, to n .. Since none for the detection of the target slip

Steering angle sensor is available and a statement about the steering angle is therefore not possible, the setpoint slip is stored in a map s _ς _., = F (v) according to FIG. 5 stored in the electronic transmission control and at the same time from a map s G_renz = f (v_F) the limit slip is read out.

The division of the maximum possible slip s ax at a certain speed v, where smax = ss_ol.l, + sG_renz, is described by the equation ~

^s actual max ^(v F ^s actual max ^(v F ⁾

2

^s target ^s limit

s_ is characterized by those tire / roadway friction pairings in which a maximum differential speed occurs for a certain speed v_ (see FIG. 3). When dividing according to equation 3, it is ensured that at half steering angles there is symmetry with regard to the response threshold when the front or rear axle speed is ramping up.

From formula 1 for slip detection, if only the speeds of the front and rear wheel axles are considered, the following formula 1 a can be derived.

⁽ⁿ VA ^"n HA ^} s (%) = 2 100 ^to VA ^{+ n} HA ⁾ The sign of s is always positive if the

Front axle speed is greater than the speed of the

Rear axle. In order to avoid closing the lock in the forward driving state with a maximum steering wheel deflection and an assumed slip of 22%, the

Limit slip can be greater than or equal to 22%. This means that the longitudinal lock is activated as soon as the

Front wheel axle turns slightly faster, i.e. the slip is slightly larger than the assumed limit slip of

22%. If the rear axle rotates in the state shown, the value s _τ actual. - sS "ol, l. less than 22%, g ^~ eht by 0%, and then rises again to 22%. This makes it clear that in the state, the lock is activated when the slip is twice as large as compared to the spinning of the front wheel axle. In order to improve this situation, half the limit slip is added to the target slip and only half the limit slip in formula .2 is used, so that Table 1 shown below is obtained without correction and Table 2 with correction.

1. Without target slip specification with idealized, linear dependency of the actual slip from LH:

LH slip for lock "ON

| ^S is ^S target | > Limit degree VA ϊ HA SI

0 +22 -22 0 0 22

315 +11 -33 +11 0 22

630 +0 -44 +22 0 22

With target slip specification ■ 1/2 limit slip and halved limit slip:

LH slip for blocking-ON "| ^S Isf ^S target> limit degree VA l HA ¹ 1 J

0 +22 -0 0 11 11

315 +11 ^* -11 +11 11 11

630 +0 -22 +22 11 11 In summary, the driving dynamically stable area of the vehicle is through the maps

^S target ^{= ~ (} V sG_renz = f (vF ") when driving forward s" limit - f (v_F) when driving backwards

described in the electronic transmission control.

Another criterion for activating the lock is that an acceleration threshold (s_) of one of the two axles determined and determined in the driving test is exceeded. The axis acceleration s is in the electronic transmission control from the stored target slip and the calculated actual slip during a time 't according to the equation

^ ^(s is ^" ^ oll * _s =. ₍₎

educated. The condition for the response is with s greater than ^s G ~ r ~ -e-. _m nz _r . defined, wherein s "Gre _Λ nz" is a constant value and also takes into account the operation of snow chains and the wheel or axis accelerations which occur.

In order to shorten the reaction time between the output of the signal 61 from the electronic transmission control 6 to the control hydraulics, which closes the lock, and the reaction in the disk pack, the piston becomes the

The longitudinal locking clutch has already been pressurized to reduce the play in the disk pack. The start of the pre-filling is tied to an engine speed threshold n "_ which is above the idling speed of the engine n _M. _, lies - see Fig. 6 -. Since the longitudinal locking clutch rotates, the pre-filling pressure p "vor is a function of the speed or the vehicle speed v "controlled. If ⁿ MotGrenz ^is exceeded ^{, p is} built up ^{by a} chord filling, therefore a rectangular control current signal ^is output by the electronic transmission control 6 for a time t to the electro-hydraulic control of the transmission, which builds up the pressure with a corresponding delay on the longitudinal locking clutch 33, such as it can be seen from Fig. 6. From the time the signal is sent via the line 61 from the electronic transmission control 6, rapid filling is achieved for a short time, as already described. The duration of this is adjusted in such a way that the output pressure and thus the initial locking torque - point A- in FIG. 7 - is reached very quickly, from which the actual modulation of the pressure ramp to the synchronization point takes place. With this steep increase in pressure, without

Loss of comfort counteracted at the time of the slip detection of the dynamics of the away axis - see Fig. 7 -. The modulation of the switch-on pressure ramp A, B begins at point A. The instantaneous magnitude of the transmission output torque M or the instantaneous value are used as control variables

Axis acceleration s used. The level of the transmission output torque M present at this point in time is determined from the engine load signal and the gear recognition and shifts the characteristic curve upwards to higher locking torques by means of an additive pressure component. The

The characteristic curve itself is p = function (t) in the electronic through time and pressure support points

Transmission control filed. The measured in point A ..

Axial acceleration s modulates the pressure ramp in its steepness, hence fp: t = f (s). The limit value s limit defines the maximum slope of the ramp - see B in FIG. 8. These parameters are adjusted so that the synchronization of the axes in area A is completed in all operating states. In region B the holding pressure of the clutch is reached - Fig. 8 -. The course of the barrier pressure build-up in areas A and B is crucial for comfort and the impact on driving behavior.

The slip detection and the pressure ramp control are operated in parallel by the electronic transmission control 6, regardless of whether the lock is open or closed. This makes it possible to start up the switch-on pressure ramp again from the same pressure level at the point of the switch-off pressure ramp at which slip is measured again. In this case, the rapid filling is suppressed so that the longitudinal locking clutch 33 abuts. The pressure reduction from

Holding pressure p „,. to the pre-filling pressure P _v takes place in two phases, the area D and the area E according to FIG. This gradient is coordinated so that it is not a so-called

Discharge comes. The area E characterizes the pressure range in which there are corresponding differences in the coefficient of friction between the front 4 and the rear wheel axle 5 when the locking torque is reduced, so that the axles diverge again, and thus again

Closing the lock via the switch-on ramp described, comes. The coordination of the pressure gradient depends on the program runtime and the axis acceleration that can be achieved at maximum output torque. The gradient Jp / / t is adjusted so that the acceleration of the axle within a program run and thus the differential speed between the front 4 and the rear wheel axle 5 remains so small that when the pressure is increased, the switching work for renewed synchronization in accordance with the switch-on pressure ramp the axes remain as low as possible.

In .flg. 9 shows a flowchart for the engagement and disengagement of the longitudinal locking clutch 33. After the detection of the wheel speeds n. To n ,, the selector lever position 10, the

Brake, switch (brake sensor 9) and the engine speed The parameters, which are immediate, are queried via line 72 or vehicle speed v_

- black and white - open the longitudinal lock. This

Parameters are N or P from the selector lever position 10, the throttle valve angle 82, z. B. greater than 5 ° from the

Load encoder position 8, and brake released from the

Brake transmitter 9 or the brake light switch. After asking the

Engine speed 72 is exceeded if n M _M ot. "Limit

= 800 1 / min the pre-filling of the clutch is initiated. The lock is opened via a pressure ramp either when a speed of 100 km / h is exceeded when overrun is detected or after 2 s after the lock has been activated. A query as to whether R or D is engaged makes it possible to determine the limit slip according to the direction of travel as a function of the speed. The target slip is specified as a function of the vehicle speed. If the lock is not yet switched on, the slip s _χ is calculated. and the slip change s. After querying the s and s thresholds, it is decided whether the lock is closed or not. The pressure ramp itself is modulated by the engine torque and the axis acceleration s - during rapid filling. After switching on, a time step is started which opens the lock via the pressure ramp after 2 s.

reference numeral

1 drive motor

2 gears

21 torque converters

3 transfer case

31 Front axle drive

32 Rear axle drive

33 Locking clutch

34 shaft drive, e.g. B. ring gear

35 Hollow shaft with inner plate carrier for the sun gear drive for the front wheel axle

36 outer disk carrier = planet carrier - - drive for

Rear axle

37 pressure pistons

38 pressure chamber

4 front axle VA

41 VR drive wheel

42 drive wheel VL

43 semi-axis

44 front axle differential

45 line

46 line

5 rear wheel axle HA

51 HR drive wheel

52 drive wheel HL

53 semi-axis

54 rear axle differential

55 line

56 line

6 electronic transmission control

61 control line

62 electric pressure control valve

65 High pressure line

66 Pilot pressure line

67 Safety valves 1 68 clutch valve

69 pressure line

7 Motronic

71 Engine load line 72 Engine speed line

73 Control signal line

8 load sensors

81 line

82 throttle valve bracket 9 brake sensor (brake light switch)

91 line

10 selector lever

101 line

Table 1 without target slip specification with idealized, linear dependence of the actual slip on the steering angle

Table 2 with target slip specification = half and halved limit slip

a curve s_ with 215/60 tires, coefficient of friction 0.9 b curve s _* LsX- with 195/65 tires, coefficient of friction 0.6 c curve s_ with 195/65 tires, coefficient of friction 0.2 d curve ss „ol.l. = 0.5. (s_ist.) 215/60, coefficient of friction 0.9 e curve v_ r for 250/60, coefficient of friction 0.9 f curve v_ for 215/60, coefficient of friction 0.6 g curve v for 195/65, coefficient of friction 0.6 h Curve s _limit in D = B _SO11 + 3% i Curve s _limit in R = s _SoU + 9% k Curve s _limit + s _target in D

1 curve s _limit + β _goll in R

s Axis acceleration ⁿ Mot limit engine speed n M _« O_ti- _π l engine idling speed Priming pressure

^ Ago

Holding pressure

^P stop

Initial locking torque

^A l A first area of the switch-on ramp

B second area of the switch-on ramp

C Area in which the longitudinal locking clutch is closed

D first area of the switch-off ramp

E second area of the switch-off ramp

M. Transmission output torque from ^s Actual slip

^S Desired slip

Limit limit slip s Maximum slip max ⁿ l Display speed sensor VR / speeds on VR ⁿ 2 Speed sensor VL / speeds on VL ⁿ 3 Speed sensor HR / speeds on HR ⁿ 4 Speed sensor HL / speeds on HL

Maabl transmission output torque LW steering angle

^V I vehicle speed v

Fmin vehicle speed (smallest measurable) f function μ coefficient of friction t time

Claims

Expectations

1. Device for automatically locking a transfer case (3) in a permanent

Four-wheel drive (41, 42; 51, 52) equipped motor vehicle, with sensors (n_, to n., 8, 9, 10) for detecting information characterizing the state of motion of the motor vehicle, which are supplied to an electronic unit (6), these Information in connection with information stored in the electronic unit (6) is processed into a signal which triggers the actuation of the lock (33), characterized in that only the axis acceleration (5) of one of the two

Drive axes (4, 5) or the slip (s) or the differential speeds between these two axes in connection with the data stored in the electronic transmission control (6) to form the locking signal (61) in the electronic

Lead transmission control (6) and that only information from this electronic transmission control (6) is supplied that is already available in a modern vehicle with ABS and traction control and with an electro-hydraulically controlled automatic transmission for automatic finding of a gear and for automatic driving.

2. Device according to claim 1, characterized g e k e n n z e i c h n e t that the electronic

Transmission control (6) the wheel speed signals (n. To n.) From the drive wheels (41, 42; 51, 52), the

Selector lever position (10), the brake actuation (brake transmitter 9), the load specification via the accelerator pedal (8) and the throttle valve, the engine speed (line 72), the engine load (line 71) are fed from the motor system (7).

3. Apparatus according to claim 2, characterized g e k e n n z e i c h n e t that the actual slip (s..) From the wheel speeds (n. To n.) Using the formula

(n ₁ + n ₂ ) - (n ₃ + n ₄ ) s (%) = 2. 100 (1) n _χ + n ₂ + n ₃ + n ₄

is determined and the blocking signal (61) is formed after a slip limit value has been exceeded in the electronic transmission control (6) and is fed to the transfer case (3) to activate the longitudinal blocking clutch (33).

4. The device according to claim 3, characterized in that the slip limit value according to the formula

^s is ^"s target ^s limit ⁽²⁾

is calculated, the slip target value based on the current vehicle movement, z. B. cornering, which can be derived from the speeds of the front wheels, is determined.

5. The device according to claim 4, characterized g e k e n n z e i c h n e t that the slip setpoint (sS-, o, ll_,) as a function of

Vehicle speed

^S target ^{= ~ (} V is represented by the equations ^s soiι ^{= ~ (L) and}

LW = f (v _p )

is formed, both s, _, = f (LW) and LW = f (v_r) being determined by means of measurement tests using driving tests.

6. The device according to claim 1, characterized in that a signal (61) in the electronic transmission control (6) is formed by one of the two drive axles when an acceleration threshold (s_) defined in the driving test is exceeded and to the electro-hydraulic transmission control for closing the longitudinal locking clutch (33) in the transfer case (3) is passed.

7. The device according to claim 6, characterized in that in the electronic transmission control (6) the axial acceleration (s) from the stored target slip (s _ς ,,) and the calculated actual slip (s_) during a defined time Λ t according to the formula

^ ^(s is ^"S Soll ^} s = - • (4) 4 t

is formed and if the condition s greater than s _G the lock is activated.

8. The device according to claim 1, characterized in that the transfer case (3) is a planetary differential with a multi-plate clutch (33).

9. The device according to claim 1, characterized g e k e n n z e i c h n e t that to shorten the

Response time of the longitudinal locking clutch (33) of the

Transfer case (3) is filled when a motor speed threshold (n M. "" Limit) is exceeded and that the

Pressure of the pre-filling (p) is controlled as a function of the speed or the vehicle speed (v).

10. The device according to claim 9, characterized g e k e n n z e i c h n e t that when the

Engine speed threshold (n M..G limit) for a time t in one

Rapid filling of the pre-filling pressure () via a signal from the electronic transmission control (6).

11. The device according to claim 10, characterized in that the filling of the longitudinal locking clutch (33) up to the holding pressure (p ".) Via a switch-on ramp ^* (A, B) and the emptying via a switch-off ramp (D, E).

12. The apparatus of claim 11, characterized g e k e n n z e i c h n e t that the size of the transmission output torque (M,) and the current axis acceleration (s) are used as control variables for the shape of the switch-on ramp (A, B), the

Transmission output torque (M,) shifts the characteristic curve, which is determined by time and pressure points in its

Course (p's = function t) in the electronic

Transmission control (6) is stored and the steepness of the pressure ramp is modulated by the axis acceleration (s) (4p: it = function s).