DE2447182A1 - METHOD AND DEVICE FOR REGULATING THE BRAKING FORCE ON THE WHEELS OF VEHICLES - Google Patents

Description

Daimler-Benz Aktiengesellschaft Daim 9721 / fr

Stuttgart _{2 # loe}

Method and device for regulating the braking force on the wheels of vehicles

The invention relates to a method for regulating the braking force on the wheels of vehicles. The invention relates to furthermore a device for carrying out this method.

In conventional brake systems, when the brake pedal is actuated, a brake pressure p ″ is generated in the master brake cylinder, 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 Mq ^:

M ₅ = k. f. p _R

f = brake lining tire value

k = proportionality factor

However, between the tire and the road there is only a limited amount that depends on the wheel load G and the coefficient of adhesion / c Torque M »:

M _n « ^ . G. R.

R = dynara. Tire radius

be transmitted.

The adhesion coefficient yU required for a desired vehicle deceleration χ. is through

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Zc = x / g

g = acceleration due to gravity

certainly. The physically possible adhesion coefficient Lc. however changes with the brake slip \:

λ.

χ = vehicle speed y = angular speed of the wheel

and with the road conditions.

The course of the possible adhesion coefficient / ^ or the vom Wheel torque ML that can still be transmitted to the road

the slip λ is zero for most road surfaces increasing up to a maximum value and then again up to λ = 1 slightly sloping. If the introduced braking torques Mj, Also entered in this diagram, the result is a straight line with a constant M "over the slip, since the braking torques M_ does not depend on the slip Λ.

When braking, there is either a stable or an unstable one State of equilibrium

™ B = ^M R

on or «if Mg is greater than the maximum value of the M _R curve associated with the current road condition over the slip, the wheel runs into the locked state with λ =» 1 ·

A stable state of equilibrium exists at a point M "= M" if, with a constant braking torque M_uisd increasing slip λ, the transmittable torque ML is greater, an unstable state of equilibrium, however, - if the transmittable torque M _{R is} smaller under the same conditions. If ML> Μ .., the wheel runs into the locked state.

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With previous normal brake systems as well as with brake control systems, the braking torque is controlled or regulated by parallel shifting of the braking torque line parallel to the abscissa of this diagram assigned to the slip Λ, whereby the braking torque M _n or the pressure p "
increases in the wheel brake cylinder by moving it downwards
on the other hand, it drops »In normal braking systems, a stable or unstable state of equilibrium or the
Blocked state of the R ^ des, in the case of brake control systems, commutes
the state that is established in each case, according to the design of the brake control system, is more or less far around the torque equilibrium state associated with the optimal deceleration of the vehicle. This is a disadvantage of such braking systems.
Further disadvantages are correspondingly non-optimal braking distances, rattling noises and vibrations as a result of high valve control frequencies and, as a result, high mechanical stress and
Valve wear, etc.

The object of the invention is to provide a method which avoids the disadvantages mentioned, in which the wheels cannot lock, in which a stable state of equilibrium is established even in the previously unstable range, with a new stable state of equilibrium if possible when the external conditions change is reached quickly and the
installed braking force distribution automatically to the ua
sets the ideal braking force distribution depending on the road gradient and load condition.

This object is achieved in that the acting on the wheel Braking torque according to a function that is dependent on the wheel slip and the pressure in the master brake cylinder, at least in a specific one Slip range, is changed, the following regulation is met:

At each intersection of the braking torque curve over the slip with the curve of the torque over the slip that can be transmitted by the wheel to every possible road surface, the first derivative dMg / dA of the braking torque is negative and more negative than
the first derivative dMp / dλ of the transmittable torque

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With a brake control system that works according to this method, it is possible to achieve stable torque equilibrium states in the entire slip range and to safely prevent the strife from being blocked.

An embodiment of this method preferred by the invention is that of the respective pressure in the master brake cylinder assigned braking torque is fully transferred to the wheel until a first slip threshold is reached, that it is exceeded after it has been exceeded this first slip threshold is lowered to a predetermined braking torque value at a second slip threshold and that it remains constant or is further reduced after the second slip threshold is exceeded.

It is provided that the braking torque is reduced linearly between the slip thresholds.

Since the coefficient of adhesion and thus the transferable Torque as well as the transferable braking force and the cornering force i.a. changes with the wheel steering angle above the slip, it is provided that the first slip threshold and / or the second slip threshold and / or the specified braking torque value as a function of the vehicle speed and / or the wheel steering angle and / or the pressure in the master brake cylinder is changeable.

In known brake control systems there are sensors on the wheels to determine their rotational state wr seen their signals too Output signals are linked, which control the pressure in the wheel brake cylinders with the help of valves so that this rises, remains constant or falls »

In a device for carrying out the method according to the invention, there is also an electronic unit for each wheel provided, in which from the input variables pressure in the master cylinder and wheel slip according to the characteristic funcion v «srli% uf © in setpoint for the Pressure is formed in the wheel brake cylinder and where to the

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Electronics unit a comparison unit "is included, which the actual value and the setpoint can be supplied and to the output of which is a control signal for activating the brake pressure regulator is deliverable.

The braking torque acting on the wheel is proportional to it Pressure in the wheel brake cylinder determined.

In a simple embodiment according to the invention it is provided that the electronics unit from a memory, in which the characteristic curve is stored as a function of the slip, and from a multiplier unit consists in which the output variable assigned to the respective wheel slip with the respective pressure in the master brake cylinder multiplies x * ird, and that the output of the multiplier unit is the respective setpoint for the pressure in the wheel brake cylinder.

With this device, the slip thresholds are unchangeable and constantly changing along with the course of the function external conditions such as vehicle speed, wheel steering angle, etc. cannot be influenced. If the storage capacity is large enough can possibly have several characteristic function processes saved according to various conditions and selected when necessary.

In an exemplary embodiment preferred by the invention, a computer is therefore provided as the electronic unit, in which from the pressure in the master brake cylinder and the wheel slip with variable threshold values of the characteristic Functional characteristic assigned setpoint for the pressure in the wheel brake cylinder is calculated.

For this purpose there is a common central electronic unit for all wheels provided, which as input variables the pressure in the brake master cylinder, the wheel steering angle and the vehicle speed can be supplied and in which from these the respective threshold values for the computers of the electronic unit each wheel are formed and fed to them. It is without

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further möglieb various devices within the scope of the invention to create, which work in analog or digital technology according to the specified method.

The mode of operation and structure of the invention are shown below Description of the method and two exemplary embodiments. Show in the drawing;

Fig. 1: a diagram with the course of the respective Torques above the slip,

Fig. 2: a diagram with the desired braking torque curve,

Fig. 3 ^: a first embodiment with fixed slip thresholds,

Fig. K: two diagrams of the torque and lateral force curves taking into account the wheel steering angle and

Fig. 5 ^; a second embodiment with variable slip swell «,

In Fig. 1, to discuss the processes in known unregulated and regulated brake systems, three Ic- _{dependent torques ML ·, to M R,} which can be transmitted from the wheel to the roadway, _{and three different braking torques Mw 1} to Mg., Which can be introduced via the brake pedal, are shown in a diagram above applied to the Bretnsschlupf Λ. Since the introduced braking torques Mj. do not depend on the brake slip λ, result for this parallel straight line, which depends on the current soil conditions, transferable torque curve M ", z. B. M "with Ll. ~ 1.0 corresponding to a dry, non-slip concrete surface, cut at points 1, 2 and 3. At these points there is a stable equilibrium M "= JL. etc., accordingly, there is an assigned BrOmSSChIuPfA ₁ to λ ^ and a certain vehicle deceleration χ on the wheel. to x_ a.

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If the initiated Dremsmomfint M is increased while J ^ x 1.0 BUf Mj ₃₂ remains the same, then at intersection 2 with greater brake _{slip λ o} a sinhilic equilibrium state M_ = M " ₂ is again established. With a constant ground condition Jbu- 1,0, the equilibrium condition> Lj s M _R can be fulfilled up to a maximum braking torque Mj> „and can therefore be braked normally.

Changes with smaller initiated Bremsiiiomenten, z. B. at Mrj _n , during the braking process, the soil condition, z. D. from ώ. = 1.0 to pu = 0.6, corresponding for example to a dry, smooth asphalt pavement, a new moment equilibrium state M " ₂ - M" arises with a greater brake slip λ ₂ '.

"Does the soil condition worsen with constant braking torque M _Q o>'- · ⁿ " from / i. = 0.6 to jLl- 0.2, or with constant ^ = 0.6 the braking torque, for example, from M ^ _{2 increased} to M _--, the initiated! Braking torque of the transferable torque can no longer be transferred to the road surface and the wheel locks.

If the current ground condition improves from X ^ = 0.2 atif., A- = 0.6 with the braking torque Jl ₃ remaining the same during the approach to blocking, the braking torque Mn introduced can “at point 'i show the course of the transmissible torque M ₀₀ Although cut and re-establish a state of equilibrium, but a slight increase in the brake slip X1 enough to the wheel block to let * In point h so there is an unstable Momentengleichgewichtszustnnd.

The method according to the invention consists in regulating the braking torque Hn as a function of the brake slip Λ in such a way that the above-mentioned stability criterion is also fulfilled in points with a previously unstable moment equilibrium. This is the case if the first derivative d> U / d λ is negative and more negative than the first derivative dM ^ / d λ in the point under consideration. In FIG. 1, the straight line G fulfills this condition for the point k. 609816/0504 _ ₈ _

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For the application of the method in practice, FIG. 2 shows a diagram with the desired curve of the braking torque over the slip and with the torque curves ML to M _R _ from FIG. 1 that can be transmitted by the wheel.

The desired braking torque curve M_ over the slip is determined by two slip thresholds A and \. divided into three areas:

1. 0 - λί λ: In this area there is no regulation of the

Braking torque instead. The braking torque introduced is fully transferred to the wheel.

2. λ - λ "^ a.: In this area the braking torque is released

away

speaking of the desired function from the full value at λ to a predetermined value M. at the second slip threshold Λ. lowered.

3 λ, £ \ ^ 1 : In this area the braking torque M.

kept constant or further reduced.

As long as a certain slip Λ is not exceeded during braking, the device does not intervene in the control process. The braking torque introduced, e.g. B. M "" M _n .

corresponds to the pressure p " ₂ in the master brake cylinder and can determine the transmittable torque curve, e.g. B. _{Cut Mn 1} * at point 2.

If the road surface is different, ie A- * 0.6, the _{brakes are applied at a higher pressure p "" (* M n} . »Mg ti *), then the wheel runs to higher slip values at the first moment. However, as soon as the first slip threshold A is exceeded , the pressure in the wheel brake cylinder, which until then was proportional to the pressure p "~, is lowered in accordance with the desired function, so that a stable torque equilibrium is leveled off at point 3 '. If the road condition improves to A. = I ₁ O, a new stable state of equilibrium is established at point 3. If, on the other hand, the second threshold value X- is exceeded, which with a corresponding design only happens temporarily when overshooting, then P ₁₃ = M _n ..

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to a value p _R. = M, lowered, which is below all M "values occurring in this range.

A first exemplary embodiment according to the invention is equipped with fixed, predetermined slip thresholds λ and λ as well as with a fixed predetermined value M. of the braking torque in the third slip range. The actual and setpoint values Mp .. and Mg _{8011 of} the braking torque are the actual and setpoint values p ". . and p_ ... proportional to the pressure in the wheel brake cylinder, the actual values M _n are in the first slip range up to λ. . and p ". . also proportional to the pressure p "in the master brake cylinder.

KlSt »1

3 shows schematically the structure of the first exemplary embodiment for a wheel. The driver uses a brake pedal 5 to generate 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 in a known manner on the brake disc of the wheel via brake shoes. A sensor 11 which determines the angular velocity ψ of the wheel is arranged on the wheel. The vehicle speed χ is determined via a device (not shown) and, together with the angular velocity) ^ of the wheel 10, is fed to a circuit 12 which determines the slip λ of the wheel therefrom in a known manner. The value of the wheel slip determined in this way is fed to an electronic unit 13, which consists of a memory lk and a multiplier unit 15.

The memory lk 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 λ between ¹ B "and 1.0 appearing at the input is assigned a dimensionless quantity f (λ.) Between 1.0 and ©" with fixed slip thresholds, ζ. Β.λ »0.1 and λ,« 0.25 »as indicated in FIG. 3 in the rectangle 1A representing the memory. The variable f (A) is transferred from the memory lk to one input of an analog multiplier unit

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delivered, & n whose other input an electrical variable corresponding to the respective pressure pjj in the master brake cylinder 6 arrives ο In the multiplier unit 15, the two variables are multiplied with one another, the result is the setpoint p _R .. for the pressure in the wheel brake cylinder.

The electronics unit 13 is followed by a comparison unit l6, which determines the pressure p_. in the wheel brake cylinder with the setpoint P-JIg ₀ Ii and, corresponding to this comparison, a control signal to a brake pressure regulator 17 arranged in the brake pressure line 7 between the master cylinder 6 and the wheel brake cylinder 9 to adapt p_. , at p ".., generated.

In this exemplary embodiment, the electronic unit 13 is provided with a circuit (not shown) which is used in Exceeding the second slip threshold A - the multiplier unit 15 turns off and a predetermined fixed value p ",.,

passes to the comparison unit l6 as long as X ^ A-.

It is known that the coefficient of adhesion jU.va.xd also changes the transmittable torque H as well as the transmittable braking force P "and the cornering force P_ with the wheel steering angle / 3 .. above the slip λ. FIG. K shows these relationships in two diagrams lying one above the other. In the upper diagram, the change in the transferable torque M ₁ , when the wheel steering angle / 3., Increases from 0 ° to 8 °, is shown with the road surface remaining the same. The lower diagram shows the course of the available cornering force P _c at different wheel steering angles.

The desired setpoint curve for the braking torque is also entered in the upper diagram. The diagram above shows that the slip of the wheel increases from A _{Λ to A.} The diagram below shows that the available cornering force is P ₅₂ if during the braking process® ;; the wheel steering angle changed from 0 ° to 8 °. To with © ira © r such a Pahrsituation

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to increase the available lateral force sees the vosi the invention preferred method at least a wheel steering angle is dependent on the displacement of the slip thresholds before _{bringing the setpoint curve shown in Fig. 4 with broken lines for z. B./S = 8 ° the increased available cornering force of the size P_ . results. Another relationship, not shown, also arises for the dependence of these variables on the vehicle speed x.

The exemplary embodiment preferred by the invention, shown schematically in FIG. 5, is identical to the first exemplary embodiment shown in FIG. 3, with the exception of the electronics unit. Brake pedal 5i master brake cylinder 6, the brake pressure line 7 act on the wheel brake cylinders 8 and 9 as described "uf the wheel 10, the sensor 11 provides via the brake pressure regulator 17 * one of the angular velocity of ^ the wheel proportional electrical parameter to the circuit 12 to calculate the wheel slip Λ .

In this exemplary embodiment there is a central electronic unit l8 in which the respective slip thresholds λ and h, as well as the predeterminable value p _R, for all wheels. for the pressure in the wheel brake cylinder after the second slip threshold λ has been exceeded. can be calculated according to the relationships determined for each vehicle type according to FIG. 4. These values are supplied with the pressure p "in the master brake cylinder, the electronics unit 20 of the wheel in question and, indicated by the lines 19", to the electronics units (not shown) of the other wheels. The electronics unit 20 in this exemplary embodiment consists of a computer which in accordance with the variable sizes K, λ the desired setpoint value profile in accordance with Fig. 4., Pm ₃ wnd Pj ₁ to the respective slip K of the respective wheel p 10 associated desired value for the pressure _R calculated ,, in the wheel brake cylinder and to the Comparison unit 16 supplies which, as already described, forwards a control signal to brake pressure regulator 17 _{after comparison with actual value P Rist.}

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Claims (1)

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Stuttgart Expectations l. \ method for regulating the braking force on the wheels of ι J vehicles, in particular motor vehicles, characterized by that the acting on the wheel torque (M ") after a the wheel slip (λ) and the pressure (p «) in the master brake cylinder (6) dependent function, at least in a certain slip range, is changed, the following rule Fulfills: At each intersection of the braking torque curve over the slip with the curve of the torque that can be transmitted by the wheel to every possible road surface over the slip, the first derivative (dMg / dX) of the braking torque is negative and more negative than the first derivative (dM _R / dM of the transmittable torque. 2. The method according to claim 1, characterized in that the respective pressure (p ") in the brake master cylinder (6) associated Bfemsmoment (Mg) until reaching a first slip threshold (λ) is fully transmitted to the wheel (10) that it after this first slip threshold is exceeded, it is lowered to a predetermined braking torque value (M.) at a second slip threshold (X _fe ) and that it remains constant or is further reduced after the second slip threshold is exceeded. 3. The method according to claim 2, characterized in that the Lowering of the braking point (Mg) between the slip threshold · !! (A? Ai) takes place linearly » - 13 - ' 609816/0504 Daim 9721/4 k · Method according to claim 2, characterized in that the first slip threshold (λ) can be changed as a function of the vehicle speed (x) and / or the wheel steering angle (/ 6,) and / or the pressure (p ") in the master brake cylinder (6) is. 5. The method according to claim 2, characterized in that the second slip threshold (λ.) as a function of the Vehicle speed (x) and / or the wheel steering angle (/ &,) and / or the pressure (ρ «) in the master brake cylinder (6) is changeable. 6. The method according to claim 2, characterized in that the predetermined braking torque value (M ^ ₂ ) as a function of the vehicle speed (x) and / or the wheel steering angle (/ B. And / or the pressure (p «) in the master cylinder ( 6) is changeable. 7. Device for performing the method according to one or more of the preceding claims, wherein sensors are provided on the wheels to determine their rotational state, the signals of which are linked to output signals that control the pressure in the wheel brake cylinders with the help of valves in such a way that it increases , remains constant or falls, characterized in that an electronic unit (13, 20) is provided for each wheel (10), in which from the input variables pressure (ρ *,) in »master brake cylinder (6) and wheel slip (K) _{a setpoint (Pn so} ji) for the pressure in the wheel brake cylinder (9) is formed in accordance with the characteristic course of the function and that a comparison unit (l6) is connected to the electronics unit, which compares the actual value (p _R · +) and the setpoint (p “ _1Ί ) can be supplied and at their output a KSO λ. JL Control signal for activating the brake pressure regulator »(17) is deliverable. 609816/0504 ORIGINAL BATHROOM Since in 9721/4 8. Apparatus according to claim 7 _8, characterized in that the electronics unit (13) consists of a memory (lk) in which the characteristic curve is stored as a function of the slip "and" consists of a multiplier unit (15) in which the the output variable f (X) assigned to the respective wheel slip (λ) is multiplied by the respective pressure (pjj) in the master brake cylinder (6), and that the output variable of the multiplier unit is the respective nominal value (p ",,) for the pressure in the wheel brake cylinder ( 9) is. 9. The device according to claim 7 »characterized in that a computer is provided as the electronic unit (20), in which from the pressure (p _H ) ina master cylinder (6) and the wheel slip (A) with variable threshold values (X , X,, p ".) the setpoint value (p_ _.) assigned to the characteristic function curve for the pressure in the wheel brake cylinder KSO JL JL (9) is calculated. 10. The device according to Anspriich 9 »characterized in that a common central electronics unit (l8) is provided for all wheels, which as input variables dsr pressure (p.?) In the master cylinder (9)? ^ r wheel steering angle (föi) ^{un <} ^ the vehicle speed (x) can be supplied and in which from this the respective threshold values ^ λ »Χ. , pp.) for the computers of the electronic units (20) of each wheel (10) are formed and supplied to them » 609816/0 504
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