DE102010014563B4 - Device and method for controlling starting processes of vehicles with multiple drive axles - Google Patents

Abstract

Device for controlling starting processes of vehicles with multiple drive axles, which include a main drive axle and a four-wheel drive axle, with: a first control device (R1) for regulating a slip (S) of the main drive axle to a predetermined slip (S(µopt)) by appropriately adjusting a Clutch value of a main clutch (20); a second control device (R2) for regulating an engine speed (n) to a predetermined engine speed (n*), which corresponds to a specific engine torque (MdMot*), by correspondingly adjusting a clutch ratio value (MdVA/MdVH). Drive torque (MdVA) of the all-wheel drive axle and a drive torque (MdHA) of the main drive axle of an all-wheel drive clutch (40) and wherein the predetermined engine speed (n*) corresponds to a maximum engine torque (MdMot*), wherein a limiting device (50) for limiting the clutch ratio value (MdVA/ MdVH) is provided to a range which corresponds to a range of the drive torque (MdVA) of the all-wheel drive axle between a predetermined lower value (Mdmin) and a predetermined upper value (Mdmax).

Description

The present invention relates to a device and a method for controlling starting processes of vehicles with multiple drive axles.

Although applicable to any vehicle with multiple drive axles, the present invention and the underlying problem are described with reference to four-wheeled vehicles with a front and a rear drive axle.

Four-wheel drive or all-wheel drive is a type of drive in which the driving force or driving torque is sent to all wheels in contact with the ground.

In all-wheel drive vehicles with very high engine power, optimal acceleration is expected when starting off under full load. Sporty vehicles often use a control method for traction control known as “launch control”, which is used to accelerate a vehicle with an automated manual transmission, automatic transmission or dual clutch transmission to the maximum speed with an optimized acceleration value.

In the simplest case, the automatic gearshift system is controlled in such a way that when starting off, the speed at which the vehicle accelerates fastest from a standstill without spinning the wheels is applied. Depending on the software implementation, the automatic gearshift system then fully extends the gears and only shifts to the next gear at the highest possible speed until the maximum speed is reached.

The traction control is usually controlled or regulated via the clutch torque, so that optimal slip occurs on the wheels. When starting at full load without launch control, however, tire slip occurs automatically on each axle due to the torque balance.

In high-performance vehicles with all-wheel drive systems, it was found that even when using launch control, the acceleration values vary and optimal acceleration cannot always be achieved when starting off.

There are essentially two reasons for this that prevent optimal acceleration.

The first cause is the pressure of the engine, especially with high friction values, such as. B. on dry roads and good tire friction values, the engine torque is not sufficient to operate all four wheels at the slip limit. Without controlling the torque on the front axle, too much torque is applied to the front axle wheels. The engine speed is reduced and the engine torque is also reduced due to the lower engine speed. So the acceleration is not optimal.

A second reason is that when the coefficient of friction is low, for example in wet conditions or poor tire friction, the torque that can be transmitted to the front and rear axles is lower than the torque delivered by the engine. The wheels spin and the engine speed increases as the wheels spin. As the engine speed increases, the engine torque decreases. The acceleration is also not optimal.

From the DE 196 53 855 C1 a device for controlling a starting process is known, wherein an automated friction clutch provided between an engine and a transmission is controlled by a corresponding control device.

When the starting time is detected, the friction clutch is briefly closed completely or almost completely to transmit a high torque to produce slipping of the drive wheels. If a slip condition is established, the slip is regulated by actuating the friction clutch. Only part of the torque introduced by the engine is then transmitted to the drive wheels via the friction clutch.

The part of the excess torque that is not converted into heat in the friction clutch increases the engine speed. If the vehicle speed is below a predetermined driving speed limit, a constant speed of the drive wheels or a constant transmission output shaft speed is preferably controlled by means of the control device. When an upper speed limit is exceeded, the friction clutch is completely closed, completing launch control.

The DE 103 05 297 A1 discloses a device for controlling a starting process, whereby when the starting process is selected, the speed of the internal combustion engine is first set to a predetermined engine speed value with the clutch open and the clutch torque is then regulated in areas of a maximum possible vehicle acceleration.

The DE 10 2005 051 154 A1 discloses a method for operating a drive train of a motor vehicle, wherein the wheel slip value is adjusted to an optimal coefficient of friction, with a coefficient of friction between the drive wheels and the road being in the range of its maximum value.

From the DE 10 2005 035 302 A1 a method for controlling a starting process of a motor vehicle that can be selected by the driver is known, wherein for optimal acceleration the wheel torque is maximized at the beginning of the acceleration phase and during the following acceleration phase a defined threshold value curve for an increased maximum permissible wheel slip is specified.

In addition, from the DE 195 13 516 A1 , the DE 43 27 507 A1 and the DE 102 50 734 A1 multi-axis controllable drive arrangements are known.

The object of the present invention is to create a device and a method for controlling starting processes of vehicles with multiple drive axles, through which further improved acceleration values can be achieved.

ADVANTAGES OF THE INVENTION

The device according to the invention for controlling starting processes of vehicles with multiple drive axles according to claim 1 and the corresponding method according to claim 6 have the advantage over the known approaches that optimal acceleration times can be achieved when driving off in a sporty manner.

The idea on which the present invention is based is that during the acceleration process, the motor rotates during a certain phase in the speed range of the maximum engine torque that is as constant as possible and, in addition, at least one axle is operated in the slip range of the optimal tire friction value.

Modern powershift transmissions and all-wheel drive systems have precise clutch torque control. During the slip phase, the corresponding clutch torques can be set precisely, regulated in closed control loops or quickly readjusted. If a motor delivers sufficient motor torque to operate at least one axis in the optimal slip range, the starting process can be optimized. For optimal acceleration in vehicles with high engine power and an adjustable all-wheel drive system, it is advisable to operate the higher-loaded axle in the optimal slip range and the lower-loaded axle to operate in such a way that the engine speed is adjusted to the optimal speed via the drive torque of the axle.

According to the invention, it is proposed to divide the control into two separate control loops. The controller on the higher-loaded axle controls wheel slip, and the controller on the lower-loaded axle controls engine speed. Target values for the full values are the optimized wheel slip and the optimized engine speed for the maximum engine torque. The inertial mass of the engine is not accelerated. This means that the delivered engine torque remains constant at the highest possible level. Here, a limiting device is provided for limiting the clutch ratio value to a range which corresponds to a range of the drive torque of the all-wheel drive axle between a predetermined lower value and a predetermined upper value.

Advantageous developments and improvements of the respective subject matter of the invention can be found in the subclaims.

According to a preferred development, the predetermined engine speed corresponds to a maximum engine torque.

According to a further preferred development, the specified slip is in the range between 10% and 20%.

According to a further preferred development, the first control device is designed in such a way that it keeps the corresponding clutch value or the clutch torque constant after the predetermined slip has been reached.

According to a further preferred development, the second control device is designed such that, before the start of control, it sets the clutch ratio value to a predetermined value corresponding to a predetermined lower value of the drive torque of the all-wheel drive axle.

According to a further preferred development, the second control device is designed in such a way that it adjusts the clutch ratio value linearly, non-linearly or in a ramp to the predetermined value before the control begins

DRAWINGS

Exemplary embodiments of the invention are shown in the drawings and explained in more detail in the following description.

• 1 ein Blockdiagramm einer Ausführungsform einer Vorrichtung zum Steuern von Anfahrvorgängen von Fahrzeugen mit mehreren Antriebsachsen gemäß der vorliegenden Erfindung;
• 2 ein Zeitablaufdiagramm zum Erläutern einer Ausführungsform eines Verfahrens zum Steuern von Anfahrvorgängen von Fahrzeugen mit mehreren Antriebsachsen gemäß der vorliegenden Erfindung;
• 3 ein Flussdiagramm zum Erläutern der Ausführungsform des Verfahrens zum Steuern von Anfahrvorgängen von Fahrzeugen mit mehreren Antriebsachsen gemäß 2; und
• 4 ein Diagramm, welches die Abhängigkeit des Reifenreibwertes von dem Schlupf darstellt.

Illustrate it:

• 1 a block diagram of an embodiment of an apparatus for controlling vehicle starts with multiple drive axles according to the present invention;
• 2 a timing chart for explaining an embodiment of a method for controlling starts of vehicles having multiple drive axles according to the present invention;
• 3 a flowchart for explaining the embodiment of the method for controlling starting processes of vehicles with multiple drive axles according to 2 ; and
• 4 a diagram showing the dependence of the tire friction coefficient on the slip.

DESCRIPTION OF THE EMBODIMENTS

In the figures, the same reference numerals designate the same or functionally identical components.

1 shows a block diagram of an embodiment of a device for controlling starting processes of vehicles with multiple drive axles according to the present invention.

In 1 Reference numeral 10 denotes an internal combustion engine or an engine of a motor vehicle, which is connected via a controllable main clutch 20 to an automatic transmission 30, which can be switched to a desired gear via a gear shift signal GS.

The transmission 30 is connected to the rear axle HA of the motor vehicle via a first drive train A1 and connected to a front axle VA of the vehicle via a second drive train A2. In the present case, the rear axle HA is also called the main drive axle of the all-wheel drive system, whereas the front axle VA is also called the all-wheel axle of the motor vehicle. In front-engine vehicles, the front axle is the main axle and the four-wheel axle is at the rear. A controllable all-wheel clutch 40 is designed such that it distributes the output torque of the transmission 30 to the drive train A2. If the four-wheel clutch 40 is open, the entire output torque of the transmission 30 reaches the rear axle HA as the main drive axle. With increasing closing of the all-wheel drive clutch 40, an increasing proportion MdVA of the output torque MdMot of the transmission 30 or the engine 10 reaches the front axle HA as the all-wheel drive axle, with a limiting device 50 ensuring that the torque applied to the front axle VA, i.e. the all-wheel drive axle, is between a lower value Md _min and an upper value Md _max . To a corresponding extent, as the four-wheel clutch 40 is increasingly closed, a decreasing proportion MdHA of the output torque of the transmission 30 reaches the rear axle HA as the main drive axle. The following applies: MdMot + i _gear = (MdHA + MdVA), where i _gear is the ratio of the transmission that determines the behavior between the engine torque and the output torque.

In the 1 The device shown for controlling starting processes has a first controller device R1 and a second controller device R2.

The first control device R1 is designed to adjust the grinding of the main clutch 20 during a launch control to an optimal slip S (µ _opt ) of the wheels of the main drive axle, where µ _opt is an optimal tire friction coefficient (see also 4 ).

The first control device R1 receives the current slip S of the main drive axle, i.e. the rear axle HA, as an actual value signal S. This actual value signal S can be obtained, for example, based on the difference between the vehicle speed and the wheel speed.

The second control device R2 is designed in such a way that it regulates the speed n of the internal combustion engine 10 to an optimal value n*, at which the output engine torque corresponds to the maximum engine torque MdMot*, in that the proportion MdVA of the output torque of the transmission 30 on the front axle HA as All-wheel drive axle and correspondingly at the same time the proportion MdHA of the output torque of the transmission 30 to the rear axle HA as the main drive axle is varied as a manipulated variable via the all-wheel drive clutch 40 or in other words a clutch ratio value MdVA / MdVH of the drive torque MdVA of the all-wheel drive axle and the drive torque MdHA of the main drive axle of the all-wheel drive clutch 40 is varied .

2 shows a timing diagram for explaining an embodiment of a method for controlling starting operations of vehicles with multiple drive axles according to the present invention, and 3 shows a flowchart for explaining the embodiment of the method for controlling starting processes of vehicles with multiple drive axles 2 .

In 2 the time t is shown on the x-axis. The lower area of the y-axis shows the engine speed n, the vehicle speed v and the wheel speed V _R. In the upper area of the y-axis, the torque of the vehicle MdVA on the all-wheel axle (here front axle VA) is shown.

The launch control according to the present embodiment can be divided into four phases, which are referred to as phase 1 (preparation phase), phase 2 (slip build-up phase), phase 3 (control phase) and phase 4 (driving phase).

Phase 1 runs from time t0 to time t1, phase 2 runs from time t1 to time t2, phase 3 runs from time t2 to time t3, and phase 4 begins from time t3.

Phase 1 is the preparation phase in which the drive is prepared for the acceleration process. The beginning of phase 1 at time t0 is initiated, for example, by completely depressing the accelerator pedal or exceeding a certain accelerator pedal actuation speed at time t0. Following time t0, the engine speed n is increased from the idle speed n _L to the maximum speed n _max after a certain reaction time Δt and adjusted. In order to minimize losses, the pressure in the all-wheel drive clutch 40 of the drive is largely reduced to a minimum clutch torque Md0 in order to largely open the all-wheel drive system.

Phase 1 is in 3 referred to as steps S1 and S5.

At time t1, the slip build-up phase begins as phase 2, in which the engine 10, which is under full load, is pulled down by the main clutch 20 with excessive clutch torque. The clutch torque is supported on the engine inertia mass and thereby transmits a very high drive torque. This causes the main drive axle to start spinning. Phase 2 ends at time t2 when an optimal initial slip is built up on the main drive axle.

In order to facilitate the slip build-up, in this exemplary embodiment the all-wheel drive axle is kept as open as possible at the beginning of phase 2 and the all-wheel drive torque MdVA is increased linearly, non-linearly, in a ramp or in another suitable manner from the minimum torque Md0 to a minimum torque Md _min . This means that the torque on the all-wheel drive axle is built up smoothly and continuously without disturbing the build-up of slip.

At the end of phase 2, the clutch torque Md _min of the all-wheel drive axle is, and the engine speed n approaches the speed with the maximum engine torque MdMot*, this speed being referred to as n*. At time t* 1, the minimum torque Md i _{gear n} is reached.

Phase 2 is in 3 designated by steps S10 and S15.

In the control phase, which is referred to as phase 3 and begins at time t2, the wheel slip S is regulated to the optimal value S(µ _opt ) by the first control device R1 for the clutch torque of the main clutch 20. As in 4 , which is a diagram that shows the dependence of the tire friction coefficient on the slip, this value for modern tires is approx. 10 - 15% wheel slip with tire friction coefficients between approx. 1.1 and 1.2. Thanks to the optimal tire friction coefficient µ _opt , a maximum of torque is transmitted and thus the highest possible acceleration is achieved. According to the invention, it is proposed to keep the setting of the first control device R1 constant in control phase 3 after the optimal value S(µ _opt ) has been reached in order to avoid interference with the second control device R2. After the slip build-up phase, phase 2, the first control device R1 therefore stops regulating and keeps the engine torque of the main clutch 20 constant at a value corresponding to the maximum engine torque, at which the input torque of the main clutch 20 is kept constant at the maximum value.

In order to operate the motor 10 in the optimal torque range MdMot*, as in the upper part of 2 shown, a suitable engine speed n* is regulated in phase 3 by the second control device R2.

In the control phase, phase 3, the engine speed n is adjusted to the optimal speed n* using the manipulated variable of the torque MdVA on the all-wheel drive axle, i.e. the front axle VA, at which the maximum engine torque MdMot* is present. In other words, the torque ratio MdVA/MdHA acts as a manipulated variable and the engine speed n as a reference variable.

For example, if the tire friction coefficient is low, the engine speed n increases because the main drive axle, i.e. the rear axle HA, builds up too much slip S. This reduces the tire coefficient on the one hand and the crankshaft torque delivered on the other. As the engine speed n increases, the acceleration decreases. In this case, the torque MdVA of the all-wheel drive axle is increased by the second control device R2. This reduces the torque MdHA on the main drive axle and thus the slip S of the main drive axle, while the all-wheel drive axle transmits more torque. The delivered maximum engine torque MdMot* and the optimal slip S(µ _opt ) are retained and the acceleration is therefore maximum.

For example, if the tire friction coefficient is high, the engine speed n drops because the main drive Saxony can no longer maintain the slippage. This reduces the tire coefficient and the engine speed n and thus the output crankshaft torque. As the engine speed n falls, the acceleration decreases. In this case, the torque on the all-wheel drive axle MdVA is reduced by the second control device R2. This increases the torque MdHA and thus the slip of the main drive axle, while the all-wheel drive axle transmits less torque. As the all-wheel drive torque falls, the engine speed can be kept constant and thus the maximum engine torque MdMot* and the optimal acceleration can be adjusted.

The limiting device 50 ensures that the all-wheel drive system is not overloaded.

The division into the first control device R1 and the second control device R2 enables a reliable elimination of disturbance variables, such as fluctuations in the coefficient of friction on the road, and a guarantee of the maximum possible acceleration. Since the engine speed n can be measured and controlled very precisely by digital speed detection, the device described for controlling launch control processes works extremely quickly and accurately.

The control phase is in 3 characterized by steps S20 and S25.

In the entire area of phase 2 and phase 3 there is a controlled wheel slip S, which is characterized by the area designated by reference symbol K, which lies between the vehicle speed curve v and the wheel speed curve V _R.

At time t2* at the end of the control phase, on the one hand, there is a reduction in clutch engagement of the clutch torque MdVA and, on the other hand, an increase in the speed of speed n, with the reduction in clutch engagement being indicated by the reference symbol AS and the increase in speed by reference symbol EH.

At time t3 at the end of phase 3 and at the beginning of phase 4, coupling occurs, that is, the clutch torque MdVA is increased to the maximum clutch torque Md _max . The difference in speed between the input shaft and the output shaft at the main clutch 20 becomes zero and the transmission input shaft reaches the engine speed n.

With optimal control, the clutch could be engaged at the speed n* regulated in phase 3, which corresponds to the maximum engine torque MdMot*. However, since the engine's inertial mass is accelerated in addition to the vehicle mass when the clutch is engaged, a change in torque occurs at the transmission input. Therefore, the present embodiment uses the aforementioned clutch reduction AS of the clutch torque to Md _min and the speed increase EH in order to avoid a noticeable clutch engagement jerk.

Finally, when the clutch is engaged, the moments MdVA, MdHA on both axles can be adjusted as required (via pressure in the clutch) in order to avoid slippage rebuilding.

Phase 4 is in 3 denoted by steps S30 and S35, respectively, whereby in step S35 the all-wheel drive system is in the normal control range.

Although the present invention has been explained above using preferred exemplary embodiments, it is not limited to this but can also be implemented in other ways.

Although in the present embodiment the rear axle is the main drive axle and the front axle is the four-wheel drive axle, the invention is not limited thereto.

Advantageously, the clutch control of the main drive axle can also be protected against overload. During the engagement phase, heating can be calculated by suitable calculation of the friction power minus a calculated cooling power, which in the limit case influences the manipulated variable of the first control device R1 by torque limitation (minimum torque/maximum torque) (analogous to the second control device).

Of course, the launch control phases can also be further varied and, for example, additional phases can be added.

Claims (11)

Device for controlling starting processes of vehicles with multiple drive axles, which include a main drive axle and a four-wheel drive axle, with: a first control device (R1) for regulating a slip (S) of the main drive axle to a predetermined slip (S (µ _opt )) by appropriate adjustment a clutch value of a main clutch (20); a second controller device (R2) for regulating an engine speed (n) to a predetermined engine speed (n*), which corresponds to a specific engine torque (MdMot*), by ent speaking adjustment of a clutch ratio value (MdVA/MdVH) of a drive torque (MdVA) of the all-wheel drive axle and a drive torque (MdHA) of the main drive axle of an all-wheel drive clutch (40) and wherein the predetermined engine speed (n*) corresponds to a maximum engine torque (MdMot*), wherein a limiting device (50) is provided for limiting the clutch ratio value (MdVA/MdVH) to a range corresponding to a range of the drive torque (MdVA) of the all-wheel drive axle between a predetermined lower value (Md _min ) and a predetermined upper value (Md _max ). Device according to Claim 1 , whereby the specified slip (S(µ _opt )) is in the range between 10% and 20%. Device according to Claim 1 or 2 , wherein the first control device (R1) is designed in such a way that it keeps the corresponding clutch value constant after reaching the predetermined slip (S(µ _opt )). Device according to one of the preceding claims, wherein the second control device (R2) is designed such that, before the start of control, it sets the clutch ratio value (MdVA/MdVH) to a predetermined value corresponding to a predetermined lower value (Md _min ) of the drive torque (MdVA). All-wheel axle adjusted. Device according to Claim 4 , wherein the second control device (R2) is designed in such a way that it sets the clutch ratio value (MdVA/MdVH) linearly, non-linearly or in a ramp to the predetermined value before the control begins. Method for controlling starting processes of vehicles with multiple drive axles, which include a main drive axle and an all-wheel drive axle, with the following steps: regulating a slip (S) of the main drive axle to a predetermined slip (S(µ _opt )) by appropriately adjusting a clutch value of a main clutch ( 20) by means of a first control device (R1) in a slip build-up phase; Controlling an engine speed (n) to a predetermined engine speed (n*), which corresponds to a specific engine torque (MdMot*), by correspondingly adjusting a clutch ratio value (MdVA/MdVH), a drive torque (MdVA) of the all-wheel drive axle and a drive torque (MdHA) of the main drive axle a four-wheel clutch (40) by means of a second control device (R2) in a subsequent control phase, wherein the second control device (R2) before the start of control in the control phase, the clutch ratio value (MdVA / MdVH) in the slip build-up phase to a predetermined value corresponding to a predetermined lower value (Md _min ) of the drive torque (MdVA) of the all-wheel drive axle. Procedure according to Claim 6 , whereby the first control device (R1) keeps the corresponding clutch value constant in the control phase after the predetermined slip (S(µ _opt )) has been reached. Procedure according to Claim 6 or 7 , wherein the second control device (R2) sets the clutch ratio value (MdVA/MdVH) in the slip build-up phase linearly, non-linearly or in a ramp to the predetermined value before the start of the control in the control phase. Procedure according to one of the Claims 6 until 8th , wherein the second control device (R1) at the end of the control phase before the start of a subsequent clutch engagement phase (AS) of the clutch ratio value (MdVA / MdVH) to a predetermined value corresponding to a predetermined lower value (Md _min ) of the drive torque (MdVA) of the all-wheel drive axle with a speed increase (EH). Procedure according to one of the Claims 6 until 9 , where the specified engine speed (n*) corresponds to a maximum engine torque (MdMot*). Procedure according to one of the Claims 6 until 10 , whereby the specified slip (S(µ _opt )) is in the range between 10% and 20%.

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