DE2447182C2 - Method and device for regulating the brake pressure on the wheels of a vehicle - Google Patents

Description

a) until a predetermined first slip threshold is reached (AJ corresponds to the pressure (p ") in the master brake cylinder,

b) after the first slip threshold (A _a ) has been exceeded up to a pressure value (J) Ri ₁ ) assigned to a predetermined second slip threshold (A ₄ ), and

c) after the second slip threshold (A ₄ ) has been exceeded, the value (p _Rb ) assigned to the second slip threshold (A ₄ ) is kept constant or is further reduced.

2. The method according to claim 1, characterized in that the reduction of the pressure (p _R ) in the wheel brake cylinder between the Sidlupfschwellen (A ", A ₄ ) takes place lirearly.

3. The method according to claim 1, characterized in that the first slip threshold (A ₁₁ ) can be changed as a function of the vehicle speed (x) and / or the wheel steering angle (ß {) .

4. The method according to claim 1, characterized in that the second slip threshold (A ₄ ) can be changed as a function of the vehicle speed (x) and / or the wheel steering angle OS ₁ ).

5. The method according to claim 1, characterized in that the second slip threshold (A ₄ ) assigned pressure value (p « ₄ ) as a function of the vehicle speed (ir) and / or the wheel steering angle OSi) and / or the pressure (p _H ) can be changed in the master cylinder (6).

6. Device for carrying out the method according to one or more of the preceding claims, with a master cylinder on which a brake pedal acts and with a wheel brake cylinder assigned to each braked wheel, a pressure sensor being connected to the master cylinder which provides an output signal assigned to the pressure in the master cylinder supplies and wherein the pressure in each wheel brake cylinder is built up, kept constant or reduced depending on the pressure in the master brake cylinder by means of an inlet and an outlet valve, characterized in that an electronic unit (1. \ 20) is provided for each wheel (10) , in which a setpoint value (PR ,,, /,) for the pressure in the wheel brake cylinder (9) is formed from the input variables pressure (p _H ) in the master cylinder (6) and wheel slip (A) according to the characteristic course of the function and that to the electronics -Unit a comparison unit (16) is connected, which the actual value (ρ _{Λι [} ,) and the setpoint ( j> r. ", u) can be supplied and at the output of which a control signal for controlling the brake pressure regulator (17) can be emitted

7. Apparatus according to claim 6, characterized in that the electronics unit comprises (13) from a memory (14), and from a multiplying unit (15), in which each wheel slip (X) associated with output / (A ) from the memory (14 ) is multiplied by the respective pressure ([· #) in the master brake cylinder (S) , and that

ίο the output variable of the multiplier unit is the respective target value (j> _RsB u) for the pressure in the wheel brake cylinder (9)

8. Apparatus according to claim 6, characterized in that a computer is provided as the electronic unit (20), in which from the pressure (p _H ) in the master cylinder (6) and from the wheel slip (A) with variable threshold values (A _a , A ₄ , p _Rb ) the setpoint value (Pr ₃₀ Ii) assigned to the characteristic function curve for the pressure in the wheel brake cylinder (9) is calculated.

9. Device according to one of claims 6 to 8, characterized in that a common central electronics unit (18) is provided for all wheels, which as input variables the pressure (p _H ) in the master cylinder (9), the wheel steering angle (/?] ) and the vehicle speed (x) can be supplied and at which the respective threshold values (A ₀ , A ₄ , p _Rb ) for the computers of the electronic units (20) of each wheel (10) are formed and supplied to them / i .

The invention relates to a method for regulating the brake pressure on the wheels of a vehicle the preamble of claim 1. The invention further relates to a device for implementation this method, as the umbrella term of claim 6 reproduces.

In conventional brake systems, a brake pressure / ^ is generated in the master brake cylinder by pressing the brake pedal, to which a brake pressure p _R corresponds in each wheel brake cylinder. This presses the brake shoes against the brake disc and generates a braking torque M _B :

/ = Brake lining coefficient of friction

k = proportionality factor [cm ³ ]

However, only a limited torque M _{n, which is} dependent on the wheel load G and the adhesion coefficient μ, can be used between the tire and the road surface :

Mr = μ * G ■ R

R ^s dynam. Tire radius

be transmitted.

The coefficient of adhesion required for a desired vehicle deceleration χ is given by

μ = x / g

g = acceleration due to gravity

certainly. The physically possible coefficient of adhesion However, μ changes with the brake slip:

λ -

x-R

χ = vehicle speed?
φ = angular speed of the wheel

and with the road conditions

The course of the possible adhesion coefficient α or the torque M _R that can still be transmitted from the wheel to the road over the slip λ increases for most road surfaces from zero to a maximum value and then decreases again slightly until A = I. If the introduced braking torques M _{B are} also entered in this diagram, the result is straight lines with a constant M _B over the slip, since the braking torques M ₈ do not depend on the slip λ.

When braking, either a stable equilibrium is established

M _B = M _R

on or, if M _{B is} greater than the maximum value of the M _R curve associated with the current road condition over the slip, an unstable condition, the wheel runs into the locked condition with λ = I.

A stable state of equilibrium exists at a point M _B = M _R when the transmittable torque M _R increases with a constant braking torque Mβ and increasing slip λ , whereas an unstable state exists when the transmittable torque Mg decreases under the same conditions. But if M ₈ > Mk "" ,, then the wheel runs into the locked state.

In previous normal brake systems as well as brake force regulating systems, the braking torque is controlled or regulated by shifting the braking torque straight line parallel to the abscissa of this diagram assigned to the slip λ , whereby the braking torque M ₈ or the pressure p _R in the wheel brake cylinder increases by shifting upwards however, it drops downwards. In normal brake systems, a stable or unstable state of equilibrium or the locked state of the wheel is established; in brake control systems, the respective state that occurs, depending on the design of the brake control system, fluctuates to a greater or lesser extent around the torque equilibrium state assigned to the optimal deceleration of the vehicle. This is a disadvantage of such braking systems. Further disadvantages are accordingly non-optimal braking distances, rattling noises and vibrations due to high valve control frequencies and the resulting high mechanical stress and wear on the valves, etc.

From DE-OS 21 17 052 such a brake control system is known by comparing the brake pressures in the master cylinder and in the wheel brake cylinder or according to the signs of the time derivative of braking pressure and braking resistance around the point the maximum braking resistance is controlled.

The US-PS 35 08 795 describes a brake control system, which according to the signs of the time Ableitunßf / n of braking force and slip and the sign of the derivation of the 3: emskrait after the slip also regulates to the point of maximum braking resistance.

It is the object of the invention to provide a method which avoids the disadvantages mentioned, in which locking of the wheels is not possible, in which a stable state of equilibrium is established even in the previously unstable area, with a change the external conditions a new stable state of equilibrium is reached as quickly as possible and the installed braking force distribution automatically based on the road gradient and load condition, among other things dependent ideal braking force distribution.

According to the invention, this object is achieved by the features mentioned in the characterizing part of claim 1.
With a brake control system that works according to this method, it is possible to maintain stable torque equilibrium states in the entire slip range and to reliably prevent the wheels from locking.

A preferred solution of the invention provides that the lowering of the braking torque between the Slip threshold takes place linearly.

Since the coefficient of adhesion and thus the transferable Torque as well as the transferable braking force and the cornering force, among other things. with the wheel steering angle changes above the slip, it is provided that the first slip threshold and / or the second Slip threshold and / or the specified brake pressure value as a function of the vehicle speed and / or from the wheel steering angle and / or from the pressure in the master brake cylinder can be changed.

In known brake force control systems there are sensors on the wheels to determine their state of rotation provided, from which the respective slip of the wheels relative to the vehicle speed can be determined is and where these slip values by comparison with fixed predetermined slip thresholds to output signals which control the pressure in the wheel brake cylinders with the help of valves in such a way that that it rises, remains constant or falls. In a device for performing the invention In addition, an electronic unit is provided for each wheel, in which from the input variables pressure in the master cylinder and wheel slip according to the characteristic Functional curve a setpoint for the pressure in the wheel brake cylinder is formed and a comparison unit is connected to the electronics unit, which the actual value and the setpoint value of the wheel brake pressure can be supplied and at their output Control signal for controlling the brake pressure regulator can be emitted.

The braking torque acting on the wheel is averaged via the pressure in the wheel brake cylinder that is proportional to it.
In an embodiment according to the invention it is provided that the electronic unit consists of a memory in which the characteristic curve is stored as a function of the slip, and of a multiplier unit in which the output variable assigned to the respective wheel slip with the respective pressure in the brake master cylinder is multiplied, and that the output variable of the multiplying unit is the respective setpoint value for the pressure in the wheel brake cylinder.
In this device are with the functional progression.

6f also the slack thresholds are unchangeable and self-sufficient changing external conditions such as vehicle speed, wheel steering angle etc. cannot be influenced. If the storage capacity is large enough, it may be possible to

several characteristic function courses according to different conditions are stored and at Can be selected as required.

In an embodiment preferred by the invention, there is therefore an electronic unit Computer provided, in which the pressure in the master cylinder and the wheel slip can be changed Threshold values of the setpoint for the pressure assigned to the characteristic function curve is calculated in the wheel brake cylinder.

For this purpose, a common central electronic unit is provided for all wheels, which is used as input variables the pressure in the master cylinder, the wheel steering angle and the vehicle speed can be supplied and in which therefrom the respective quick values for the computers of the electronics unit each wheel are formed and fed to them. It is readily possible to use various devices to create, which work in analog or digital technology according to the specified method.

Operation and structure of the invention are based on the following description; of the procedure and two exemplary embodiments. In the drawing show:

1 shows a diagram with the course of the respective torques over the slip,

2 shows a diagram with the desired braking torque curve,

3 shows a first exemplary embodiment with fixed slip thresholds,

4 shows two diagrams of the torque and lateral force curves taking into account the wheel steering angle and

F i g. 5 shows a second exemplary embodiment with variable slip thresholds.

In Fig. i, three of α-dependent torques M _Rl to M _Ri that can be transmitted from the wheel to the roadway and three different braking torques M ₈₁ to M _8i that can be introduced via the brake pedal are shown in a diagram above the Brake slip X applied. Since the introduced braking torques M ₈ do not depend on the brake slip X , this parallel straight line results in the transmittable torque curve M _R , z. B. M _R > with -j. = 1.0 corresponding to a dry, non-slip concrete surface, cut in points 1, 2 and 3. At these points there is a stable equilibrium M _Bl = M _R \ etc .. accordingly an assigned brake slip X] to Xi and a certain vehicle deceleration .ti to Jc ₃ are established on the wheel.

If the introduced braking torque M _{Bi is} increased to Af ^ while μ = 1.0 remains constant, a stable state of equilibrium M ₈₂ = M _R 2 is again established at intersection 2 with greater brake slip X ₂ . With a constant soil condition μ = 1.0, the equilibrium condition M _B = M _R can thus be met up to a maximum braking torque M _B y and can thus be braked normally.

Changes with smaller braking torques introduced, e.g. B. at M ₈₇ , during the braking process, the soil condition, z. B. from μ = 1.0 to μ = 0.6, corresponding to a dry, smooth Asphalibclag, a new moment equilibrium state AZg ₂ = M _R2 , with a larger brake slip X ₂ a.

If the condition of the ground worsens if the braking torque M ₈₂ remains the same, e.g. B. from μ = 0.6 to μ = 0.2, or if the μ = 0.6 remains the same, the braking torque z. B. won M ₈₂ to M _B } increased, so ib | nn the braking torque introduced by the transferable torque is no longer transferred to the road and the wheel is blocked.

If the current ground condition improves from μ = 0.2 to μ = 0.6 with the braking torque M ₈ J remaining the same during the approach to blocking, the braking torque M _{82 introduced} in point 4 can indeed intersect the course of the transmittable torque M _{R2 and thus} restore a state of equilibrium, but a slight increase in brake slip Ai is sufficient to lock the wheel. In point 4, there is an unstable moment equilibrium.

The method consists in regulating the braking torque M ₈ as a function of the brake slip X in such a way that the stability criterion mentioned above is also fulfilled in points with a previously unstable torque equilibrium. This is the case if the first derivative dM _B / d X is negative and more negative than the first derivative dM _R / d X in the point under consideration. In Fig. 1, the straight line G for point 4 fulfills this condition.

For the application of the method in practice, FIG. FIG. 2 shows a diagram with the desired course of the Bremsmcoientes over the slip and with the torque courses M _R \ to M _R) from FIG. 1 that can be transmitted by the wheel.

The desired braking torque curve M ₈₃₀ H over the slip is divided into three areas by two slip thresholds X _a and X _b:

1. 0 <X <X _a :

There is no regulation of the braking torque in this area. The applied braking torque is fully transferred to the bike.

2. X _a <X <X _b :

In this area, the braking torque is reduced in accordance with the desired function from the full value at X ₀ to a predetermined value M _b at the second slip threshold X _b .

In this area, the braking torque M _{b is} kept constant or further reduced.

As long as a certain slip X _{11 is} not exceeded during braking, the device does not intervene in the control process. The braking torque introduced, e.g. B. M _B2 = M ₈₃₀ It ₂ corresponds to the pressure p _H2 in the master cylinder and can determine the transmittable torque curve, e.g. B. M _R 1, cut at point 2.

_{If the road surface is different, i.e.} μ = 0.6, with a higher pressure p _Hi {= M ₈₃ = M Bsoin) , the wheel initially runs to higher slip values. As soon as the first slip threshold X _{a is} exceeded, however, the pressure in the wheel brake cylinder, which was previously proportional to the pressure phz , is lowered according to the desired function, so that a stable moment equilibrium settles in at point 3 'If the road conditions improve to u = 1 , 0, a new stable state of equilibrium is established at point 3. Will however

the second fast _{value A 4 is} exceeded, which with the corresponding design only happens temporarily in the event of overshoot, then p _R ~ M _B , _{oll is} reduced to a value p _Rh = M _h , which maintains all / l / _λ values occurring in this range lies.

A first exemplary embodiment according to the invention is with <est predetermined slip thresholds A "and k _h as well as with a fixed predetermined value M _{h of} the braking torque in the third Sch! .power area equipped. The actual and nominal values M _Bi., R zw. _Μ Β, _οΊ the braking torque are the actual and target values p _Risl and p _{R, o} the pressure n in the wheel cylinder in proportion, in the first slip region to A ₀ are the actual values of M _BI " and p _Rls , also proportional to the pressure p _H in the master brake cylinder.

F i g. 3 shows schematically the structure of the first exemplary embodiment for a wheel. Using a brake pedal 5, the driver generates a pressure in the master brake cylinder 6 which, via the brake pressure line 7, reaches the wheel brake cylinders 8 of the individual wheels and thus also to the wheel brake cylinder 9 of the wheel 10 under consideration, where it acts on the brake disc of the wheel via brake shoes. A sensor 11 which determines the angular speed φ of the wheel is arranged on the wheel. The vehicle speed χ is determined via a device (not shown) and, together with the angular speed φ of the dog 10, is fed to a circuit 12 which uses this to determine the slip A of the wheel. The wheel slip value determined in this way is fed to an electronic unit 13, which consists of a memory 14 and an multiplier unit 15.

The memory 14 consists, for example, of an analog function generator implemented by a diode matrix, in which the desired course can be approximated piece by piece. Each slip value A between 0 and 1.0 appearing at the entrance is assigned a dimensionless variable / (A) between 1.0 and 0 with fixed slip thresholds, e.g. B. A ₀ = 0.1 and X _b = 0.25, as in FIG. 3 is indicated in a rectangle 14 representing the memory. The variable / (A) is supplied from the memory 14 to one input of an analog multiplier unit 15, at the other input of which an electrical variable corresponding to the respective pressure p _H in the master brake cylinder 6 arrives. The two variables are multiplied with one another in the multiplying unit 15; the result is the setpoint value p _R , "ii" for the pressure in the wheel brake cylinder.

The electronics unit 13 is followed by a comparison unit 16, which compares the pressure p _Rh in the wheel brake cylinder with the setpoint value p _Rso i and, corresponding to this comparison, sends a control signal to one in the brake pressure line 7 between the master brake cylinder 6 and the wheel brake cylinder 9 arranged brake pressure _regulator 17 for adapting p Rls to p _Rso " generated.

_{In this exemplary embodiment} , the electronics unit 13 is provided with a circuit, not shown, which switches off the multiplier unit 15 when the second slip threshold X _{b is} exceeded and forwards a predetermined fixed value p RsoU to the comparison unit 16 as long as λ> Ä _b .

It is known that the coefficient of adhesion μ and thus also the transmittable torque M _R as well as the transmittable braking force P _R and the cornering force P _{s change} with the wheel steering angle! JS ₁ over the slip. 4 shows these relationships in two diagrams lying one above the other. The upper diagram shows the change in the transmittable torque M _R when the road surface condition remains the same when the wheel steering angle jS increases from 0 ° to 8 °. The lower diagram shows the course of the available cornering force P _s at different wheel steering angles.

The desired target value curve of the braking torque is also entered in the upper diagram. The diagram above shows that the wheel slip increases from Ai to A _2. The diagram below shows that the available cornering force is P ₅₂ when the wheel steering angle has changed from 0 ° to 8 ° during the braking process. In order to increase the available lateral force in such a driving situation, the preferred method provides a shift in the slip thresholds that is at least dependent on the wheel steering angle. B., / ?, = 8 ° results in the increased available lateral guidance force of the size P _sl. Another relationship, not shown, also arises for the dependence of these variables on the vehicle speed x.

The embodiment example shown schematically in FIG. 5 is identical to the first embodiment example shown in FIG. 3, with the exception of the electronics unit. The brake pedal 5, master cylinder 6, the brake pressure line 7 to the wheel brake cylinders 8 and 9 act as described via the brake pressure regulator 17 on the wheel 10, the sensor U of which supplies an electrical variable proportional to the angular speed φ of the wheel to the circuit 12 for calculating the wheel slip A.

In this embodiment there is a central electronic unit 18 in which the respective slip thresholds λ _α and A ₄ and the predefinable value p _Rb for the pressure in the wheel brake cylinder after the second slip threshold A _{6 has been} exceeded according to the relationships determined for each vehicle type F i g. 4 can be calculated. These values are supplied with the pressure p _H in the master brake cylinder, the electronics unit 20 of the wheel under consideration and, indicated by the lines 19, to the electronics units (not shown) of the other wheels. The electronics unit 20 in this embodiment is composed of a calculator which according to the desired setpoint value profile of FIG. 4 with the variable quantities A _a, X _b, p _Rb and / // the wheel of each slip Ades respective 10 associated desired value for the pressure p _Rsoll in the wheel brake cylinder is calculated and supplied to the comparison unit 6 , which, as already described, forwards a control signal to the brake pressure regulator 17 after comparing it with the actual value p _Rh.

For this purpose 3 sheets of drawings

Claims (1)

Patent claims: 1. A method for regulating the braking force on the wheels of a vehicle, in particular a motor vehicle, wherein the pressure applied by the driver in the master brake cylinder of the brake system is measured and processed with at least one other variable to a setpoint for the pressure in the wheel brake cylinder of each wheel to be braked, characterized that the slip (A) of the wheel to be braked is determined and that the pressure (p _R ) in the wheel brake cylinder is controlled in accordance with a predetermined function of the pressure (j> _H ) in the master brake cylinder that is dependent on the slip (A)