WO2001032484A1

WO2001032484A1 - Braking system for automatic execution of a braking operation in a motor vehicle

Info

Publication number: WO2001032484A1
Application number: PCT/EP2000/010193
Authority: WO
Inventors: Rainer Freitag; Wilfried Huber; Avshalom Suissa
Original assignee: Daimlerchrysler Ag
Priority date: 1999-11-03
Filing date: 2000-10-17
Publication date: 2001-05-10
Also published as: WO2001032484A9; EP1226055A1; JP2003512971A

Abstract

The invention relates to a method and braking system for executing an automatic braking operation in a motor vehicle. In order to increase safety in bends, the actual curvatures of said bends are determined, whereupon it is decided whether the longitudinal speed of the motor vehicle is too high. If said speed is too high, a setpoint speed is determined in order to keep the maximum cross-distance of the vehicle with respect to the middle of the lane to a minimum. The corresponding actuating signals are determined by an adjustment and control device and are used to adjust or control longitudinal acceleration.

Description

Brake system for automatically performing a braking process in a vehicle

The invention relates to a method and a brake system for carrying out an automatic braking process in a vehicle according to the preamble of claim 1.

Nowadays, systems for motor vehicles are known which can trigger a braking process regardless of a driver's braking request. DE 4201142 AI discloses a vehicle speed control device which warns the driver of an impending curve if the current driving speed is greater than the curve limit speed at which the curve can be safely driven through. This is particularly relevant if the driver cannot yet see the upcoming curve. If necessary, an automatic braking operation is carried out in good time before the curve in order to avoid accidents, in order to avoid a critical driving state of the vehicle by entering the curve too quickly beforehand. An upcoming curve can be recognized, for example, by comparing stored road maps with the current position of the vehicle.

On the basis of such safety systems, it is an object of the present invention to provide a method and a device for automatic braking, so that additional safety is ensured when driving through a curve, in particular at excessive vehicle speed.

This object is achieved according to the invention with the features of claims 1 and 11, respectively. If you enter a curve with excessive vehicle speed, the vehicle cannot maintain its desired course and is usually driven out of the curve due to understeering vehicle behavior. The same applies if the driver brakes the vehicle too hard. The invention remedies this by an automatically initiated braking process.

According to the method according to the invention, when entering the curve, the curve curvature of the curve traversed by the vehicle is first determined, it being known that the curve radius can be determined therefrom by generating reciprocal values. The desired target course is formed by the center of the lane, which is identical to the curve radius. The center of the lane indicates, so to speak, the path of the vehicle that could be traveled at an adapted vehicle speed. The aim of the present invention is to prevent, as far as possible, that the vehicle leaves the carriageway due to the excessive vehicle speed. To this end, the invention minimizes the maximum transverse distance between the center of the lane and the position of the vehicle determined by the center of gravity of the vehicle. The transverse distance is measured radially to the center of the lane, regardless of whether the center of the lane has a path with a constant radius or not. The maximum transverse distance occurs when the tangent applied to the center of the lane is aligned parallel to the tangent applied to the actual course of the vehicle.

In order to minimize this maximum transverse distance - so that the maximum course deviation between the desired and actual course is as small as possible - a target longitudinal acceleration is determined using a mathematical optimization process. After an optimal value for the longitudinal acceleration has been found, the actual and Long acceleration of the vehicle generates a control signal, so that the vehicle can be decelerated with the target longitudinal acceleration.

By using the novel method or the novel braking system, attempts are made to minimize the maximum lateral distance by keeping the vehicle on the road when cornering at excessive vehicle speed by optimizing the automatic actuation of the wheel brake devices.

This method or braking system can be used in addition to existing devices that trigger an automatic braking process, such as ESP or ABS. For example, the ESP system generates a yaw moment around the vertical axis of the vehicle in order to stabilize the driving state. The method according to the invention and the device according to the invention set a specific desired longitudinal acceleration of the vehicle, it being irrelevant here the braking force applied to the individual wheels, so that e.g. During an ESP braking process, the wheels can be subjected to different braking forces, and thus a yaw moment and, at the same time, the required longitudinal acceleration can be set.

To activate the braking system, the entrance to a curve is first detected when a curve curvature is determined. It is then determined whether the vehicle's longitudinal speed is too high. For this purpose, in an expedient embodiment, the actual yaw rate is determined by sensors and compared with a determined target yaw rate, with the current vehicle longitudinal speed being too high when the actual yaw rate deviates m from the target yaw rate in an impermissible manner, for example when the difference between the actual values - Yaw rate and target yaw rate exceeds a certain amount. The The desired yaw rate is expediently derived from the driver's request, in particular from the steering wheel angle specified by the driver, which is related to the yaw rate via the steering ratio, the vehicle speed, the wheelbase of the vehicle and the self-steering gradient of the vehicle ,

The current curve curvature can be estimated from the ratio of the given target yaw rate to the vehicle's longitudinal speed. The middle of the lane is equated with the curve radius, which results from the curve curvature through the creation of reciprocal values. This estimate is justified insofar as it can be assumed that the driver stops the vehicle at the specified curve radius at least at the beginning of the curve. This embodiment is characterized by a simple mode of operation with sufficient accuracy.

In a further embodiment, however, it can also be advantageous to determine the current curvature from a measurement. Such measurements can be carried out, for example, with the aid of optical detection devices such as Cameras are carried out, the actual yaw angle of the vehicle preferably being determined in relation to the edge of the lane or the center of the lane. This version is characterized by a high degree of accuracy, which means that the vehicle limit range can be determined more precisely and thus a higher degree of safety when driving through curves.

The curvature of the curve can also be determined by determining the exact vehicle position and comparing it with the current route profile, which can be stored, for example, as an electronic map. The position of the vehicle can be determined with the aid of a location system, for example GPS. Further advantages and expedient embodiments can be found in the further claims, the description of the figures and the drawings. Show it:

1 is a schematic representation of several trajectories of vehicles entering a curve or passing through the curve,

2 shows a flowchart with the method steps for carrying out an automatic braking process in curves,

3 shows a schematic illustration of a first exemplary embodiment of a brake system and

4 shows a schematic illustration of a second exemplary embodiment of a brake system.

FIG. 1 shows a number of vehicles 1, 1 ', l ¹ ' which are shown schematically by their centers of gravity and which after entering m move a curve 2 along different tracks 3, 4, 4 '. A first vehicle 1 moves at a vehicle longitudinal speed v that does not exceed a physically determined curve-dependent limit speed, ideally along the center 3 of the lane shown with a dashed line, which lies, for example, on the curve radius R of the curve 2 to be traveled.

A conventional, second vehicle 1 ', in which an automatic braking process according to the invention does not take place and which enters the curve at a vehicle speed above the limit speed v' m, moves, for example, along the path 4 shown in broken lines. This vehicle 1 'can make the curve due to the vehicle speed v 'being too high, do not drive through and is driven in deviation from the ideal track 3 m in the direction of the outside of the curve, which, for example, leads to the vehicle 1' leaving the paved track. Finally, FIG. 1 shows a third vehicle 1A in which an automatic braking operation can be carried out according to the present invention. The vehicle 1 ″ also travels into the curve em at a vehicle longitudinal speed v ¹ ′ that is above the limit speed. In this situation, an automatic braking process is carried out with the aim of keeping the vehicle 1 ″ as far as possible on the road.

The method for carrying out the automatic braking process is explained in more detail using the flowchart in FIG.

If the vehicle 1 ″ drives into a curve, the curve curvature p is first determined in a first method step 5. This can be done, for example, using an estimate for the curve curve

mation pm Dependence of the target yaw rate Ψ _s „// and the vehicle's longitudinal speed v '' according to the relationship

respectively. As an alternative to this, there is also the possibility of determining the curve curvature p in such a way that the position of the vehicle with the aid of a location system, e.g. GPS, is determined and the curvature p is determined by evaluating a stored road map as a function of the current vehicle position. The curve curvature p can also be measured directly, e.g. with an optical detection device (not shown) on the vehicle 1'A, for example a camera.

In subsequent step 6 of the method, it is determined whether the current vehicle speed v ″ is greater than a curve-dependent limit speed.

By way of example, a comparison between the factual and

are actual yaw rate Ψ “, which is determined, for example, by sensors, and a target yaw rate

Ψ _i0 ιι be carried out. The target yaw rate Ψ “// represents the driver's request and can be taken from context, for example

Depending on the steering ratio 1, the wheelbase L of the vehicle, the steering wheel angle δ, the vehicle's longitudinal speed v '' and the self-steering gradient EG of the vehicle

be communicated. If the actual yaw rate Ψ, _* , beyond a predeterminable difference from the target

Yaw rate Ψ __ // deviates, it can be concluded that cornering at excessive vehicle speed v '', i.e. The vehicle's longitudinal speed v '' is above the limit speed which enables the vehicle to negotiate the curve. As a rule, motor vehicles are designed to understeer so that the actual actual

Yaw rate Ψ, _s when the vehicle's longitudinal speed is too high

speed v ¹ 'is lower than the target yaw rate Ψ ₄ _ //.

If it is determined in method step 6 that the vehicle is not moving the curve at an excessive vehicle longitudinal speed m, a branch is made to step 5 (branching "neg" m FIG. 2). Otherwise, step 7 is carried out (branch "pos" in FIG. 2), in which a target Long deceleration a, _ _{: 1 is} determined, with which the vehicle 1 '' is then decelerated by an automatic braking process.

The target longitudinal acceleration a _{X; Jüll} is determined in such a way that the transverse distance Δy between the lane center 3 and the actual movement path 4 of the vehicle 1 ″ ′ radially to the lane center 3 is measured at the point at which it reaches its maximum Δy _{ma ^} In other words, the maximum deviation Λy "between the desired path along the lane center 3 and the actually driven lane 4 is minimized in order to be able to drive the vehicle 1" through the curve as close as possible to the lane center 3 and to make an agreement to prevent as far as possible from the paved road.

The initial equations for the transverse distance Δy and the course angle A <9 are as follows:

Δy = smΔ <v "(1)

Δ _l 9 = - ^ ₇ -v "cosΔ. P (2)

wherein A indicates the Kurswmkel, ie the angle between the current actual direction of the vehicle ¹ l 'along the web 4 and represents the desired Bewegungsπchtung along the lane center. 3 The course angle Δι thus results from the angle between the tangent to the lane center 3 and the tangent to the path 4 (FIG. 1); a _y represents the acceleration of the vehicle 1 ″ transversely to the direction of travel (y direction).

The determination of the target longitudinal acceleration a _x , _S oiι is an optimization problem that can be solved using various methods. In a first method, one simplifies assuming that the target longitudinal acceleration a _x , _JolJ = a _x , _{j ll # 1} . is constant, which results in a simple and robust control or regulation of the actual longitudinal acceleration a _{X; 1} .

Deriving from equation (1):

Δy = v "sιn (Δ, 9) + v" cos (Δ,) A3 (3:

For small course angles A3, the equation (3;

Ay = v "A Θ = a _v - v" ² p (:

Because of the target longitudinal acceleration a _x , _so ιι = a _x , _S oiι, equation (4) can be integrated from this because:

This equation is derived in part from the time t and the acceleration a _x , _k and is set equal to zero, which results in:

From these equations (6), (7) one obtains: " ^l v * k +. a ~ _v v _k k + 'k" ^• a "vk ^, + l

k = (µg) ² 10;

The 3rd order equation (8) is

^l y toll kz + j ^* with ^> --- i 12 ^'

Where z = s + w: i3)

s = H - ^ + D: i)

w ^■ V _- -V_>; i5:

Discriminant D; i6:

The result is as follows:

The time t _e when the maximum of the transverse distance Δy _ma is reached is given by

2 Λ

3 {μ g) 3 v 0 19: ^l x, soll, k P ^V 0 ^a y, oll k J and the target longitudinal acceleration

where in these two solution equations (19), (20) equations (12) to (18) are to be used.

As an alternative to this first determination method with constant target longitudinal acceleration a _x , _so n, _k , a dynamic optimization problem can be solved with a further method.

The problem to be solved is:

te. th

J = JΔ v Λ ≡ jV 'Δ? dt = Ay (t _e ) (21)

0 0

where J is the good functional and is a secondary condition:

A3 = - ^ - v "cos A3 p. (22) v"

This determination method is based on a 2-point boundary value problem, with a first point at time t _. when entering m, curve 2 and a second point when the end time t _{e has been reached} at which the automatic braking process is ended (hypothetical end point of the curve). First of all, the initial speed v ₀ ″ at which the vehicle 1 ″ is entering the curve is recorded and stored for further calculation. The end time t _e is reached when the vehicle 1 ″ takes the maximum transverse distance Δy _max from the lane center 3. Because of the automatic braking process, it then has a final speed V _e '' which is lower than V _o '. At this end time t_, the automatic braking process gear ended and the vehicle 1 '' can continue to be driven on a track with a radius that corresponds at least to the curve radius R. By way of example, the final speed V ″ is so low that a track with a smaller radius than the radius R can also be driven, so that the vehicle 1 ″ can again be steered in the direction of the center of the lane 3 (see FIG. 1).

From the formulation of the optimization criterion that the maximum transverse distance Λy _m between the vehicle 1 ″ and the lane center 3 should be minimized, and the solution of the resulting system of equations, the target longitudinal acceleration av , ₃ __ι can be determined. However, additional boundary conditions are expediently taken into account. In particular, the condition is formulated that the course angle Δ <is equal to zero both at the beginning of the corner entry (time t ₀ ) and at the hypothetical end point of the curve (time t_).

The target longitudinal acceleration a, _jl can then be determined as a function of the initial speed v 'of the current vehicle speed v'', the usable friction coefficient μ and the curve curvature p.

M ² -) ² A3 ^'

with the lateral acceleration of the vehicle 1 ''

a = fetf (24)

where λ is the current distance of the vehicle from the hypothetical curve end point (which is reached at time A) poses.

An analytical solution to the problem is given here

A3

Case omitted and an approximation for the quotient

set .

Since the course angle A3 is zero at the beginning but λ is not equal to zero, the quotient at time t _t (entry m, curve 2) is zero. At the time t _e (hypothetical curve end point when the maximum transverse distance is reached), the course angle Δι and distance λ are equal to zero. The quotient is determined by the assumption that the lateral acceleration a _v am

End point is maximum (a _ma _ = // g). This gives the quotient at the end point:

e e

Between the start and end point is linearly interpolated via the driving speed:

The following relationship is used for the top speed

v is the cornering speed.

The target longitudinal acceleration a _{x so} _ι is determined by using equations (24) to (27) m equation (23).

The target longitudinal acceleration a _x , _so ιι has now been determined in step 7 of the method of Figure 2. In a last method step 8, an actuating signal 13 is then generated which is used for Control or regulation of the actual longitudinal acceleration a _λ , is used.

The entire process is continuously repeated cyclically during the journey, so that step 8 follows step 5 again.

It goes without saying that the sequence shown can be used in a modification of the representation according to FIG. 1 even with non-constant curve curvatures, that is to say with curve paths which have no circular shape.

3 and 4, two embodiments of a brake system 10 according to the present invention are shown schematically with the aid of a block diagram.

According to FIG. 3, the brake system 10 has a regulating and control unit 11, to which the variables necessary for calculating the desired longitudinal acceleration a _x , _Sü n are fed via several inputs 12. On the output side, the regulating and control unit 11 generates an actuating signal 13, which can be present in a conventional hydraulic braking device, for example in the form of the braking pressure P _{B to be set} or a braking force F _B (FIG. 3). The control signal 13 is compared with the driver brake pressure specified by the driver on an operating element 14, for example the brake pedal, and the signal 15 determined therefrom is forwarded to an driving dynamics control or control device 16 (for example ESP controller or ABS controller). This then regulates or controls the actuators of the individual wheel brake devices 17 to 20 of the vehicle, which are not shown in more detail, as a function of the signal 15. If the driver wishes to brake, the deceleration is greater than that which is achieved by the desired longitudinal acceleration a _y , _S oiι , the driver's braking request can be given priority and, for example, a deceleration required according to the driver's braking request is initiated or controlled by the vehicle dynamics control unit 16. adjusted.

In a modification of FIG. 3, the brake system 10 according to FIG. 4 is designed in the manner of a so-called "brake-by-wire" brake system, for example as an electrohydraulic brake system (EMS) or electromechanical brake system (EMB). The driver's braking request is output directly via a specification device 21 as the driver acceleration signal 22 corresponding to the desired driver longitudinal acceleration. The regulating and control unit 11 can therefore also directly output the calculated target longitudinal deceleration a _IrS0 u as a control signal 13, so that the signal 15 for the driving dynamics control or control device 16 is also present in the form of a signal corresponding to the acceleration value to be set, this acceleration value can then be adjusted or controlled. As already mentioned in connection with FIG. 3, the driver's braking request can also be treated with priority in this embodiment, before the braking request of the regulating and control unit 11, for example if the driver's longitudinal acceleration is greater in magnitude than the desired longitudinal acceleration av, ₃₀ n.

Claims

claims

1. A method for performing an automatic braking process in a vehicle, characterized in that when entering a curve (2) its current curve curvature (p) is determined, that it is determined whether the current vehicle speed (v, v ¹ , v 'for driving through) of the curve with the curve curvature determined (p) is too great that the target longitudinal acceleration (a, __ n) m is determined in such a way that the maximum transverse distance (Δy _ma ,) between the vehicle (1 '') and the center of the lane (3) - Measured radially to the center of the lane (3) - it is minimized that when the vehicle's longitudinal speed (V ') is too high, an actuating signal (13) is generated so that the desired longitudinal acceleration (a, ₃ _ιι) can be controlled or regulated

2. The method according to claim 1, d a d u r c h g e k e n n z e i c h n e t,

that the actual yaw rate (Ψ, ₅ ,) of the vehicle is determined by a sensor and the excessive vehicle longitudinal speed (V ') can be determined in that a determinable

Target yaw rate (Ψ__ «) m inadmissible from the

Actual yaw rate (Ψ «.) Differs.

3. The method of claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the current curvature (p) by the ratio of a

given target yaw rate (Ψ ", //) to the vehicle longitudinal speed (v") according to the relationship

p = (Ψ _-0 «) / v"

is appreciated.

4. The method of claim 1 or 2, so that the current curvature (p) is determined with the aid of an optical detection device.

5. The method of claim 1 or 2, so that the current curve curvature (p) is determined by a position determination by means of a location system and an electronically stored map.

6. The method according to any one of claims 1 to 5, d a d u r c h g e k e n n z e i c h n e t,

that the target yaw rate (Ψ _i0 _) from the steering wheel angle (δ) according to the relationship

Ψ? O! L A i -AL l + EG-v " ² it is determined where

1 the steering ratio,

L the wheelbase of the vehicle and

EG denote the self-steering gradient of the vehicle.

7. The method according to any one of claims 1 to 6, characterized in that the target longitudinal acceleration (a _XfS0 n) at least from the initial speed (v ₀ '') of the vehicle (1 '') when cornering, the friction coefficient used (μ) Curve curvature (p) and the gravitational acceleration g is determined.

8. The method according to claim 7, characterized in that the target longitudinal acceleration (a _{/ 30l} ι) is additionally determined as a function of the current vehicle _speed (v '').

9. The method according to claim 7, characterized in that the vehicle (1 '') experiences a constant longitudinal acceleration (a _y ,) during the automatic braking process.

10. The method according to any one of claims 1 to 9, d a d u r c h g e k e n n z e i c h n e t that the transverse distance (Δy) between the vehicle (1 '') and lane center (3) depending on the course angle (Δθ) according to