JPS6353157A - Braking control device for vehicle - Google Patents

Abstract

PURPOSE:To carry out the optimum braking control regardless of the magnitude of the friction coefficient of a road surface by providing a friction coefficient estimating means for estimating the friction coefficient of a road surface at the next time using the friction coefficient of a road surface up to the present time. CONSTITUTION:Actuators 31-33 control the brake oil pressure of right and left front wheels 1, 2 and right and left rear wheels 3, 4 independently, and are controlled by an ECU 40. Besides signals corresponding to oil pressures from oil pressure sensors 51-53, rotation angular velocity signals from rotation angle sensors 15, 16, 22 and, further, a signal from an accelerator sensor 54, and signals form a brake sensor 25 and a brake switch 26 are inputted into the ECU 40. And, by presuming the friction coefficient at the next time to be nearly the same degree as the present friction coefficient, the friction coefficient at the next time is estimated and, by making it a target brake pressure, the actuators 31-33 are controlled to control the rotation angular velocity omegaof the wheels 1-4.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a device for controlling braking of a vehicle, and particularly to a device for controlling braking of a vehicle, and in particular, a device for controlling braking of a vehicle that uses a friction coefficient estimated from a current road vibration coefficient as a control parameter. Regarding a control device.

[Prior Art] Conventionally, there has been a reduction in safety due to wheel opening distortion during vehicle braking, in other words, the locking of the front wheels of the vehicle, which makes it impossible to steer the vehicle, and the locking of the front wheels of the vehicle, which causes the vehicle to skid. )
In order to prevent this, the slip rate S of each wheel of the vehicle [(vehicle speed - rotational speed to ↑), 7 vehicle speed] is controlled to 20% earlier to maximize the 9 m force between the tires and the road surface. A braking control device for a vehicle is known that controls the rotational speed of a wheel so that
In this type of anti-skid control system π, the following control is carried out so that the Hm force between the tires and the road surface, which tends to occur, is maximized so that the vehicle can stop quickly without locking the wheels when braking the vehicle. Is going. That is, normally.

The rotational speed is detected for each wheel, and the speed determined from the rotational speed (hereinafter referred to as rotational speed) is calculated using the following formula % formula % (1) based on the vehicle body speed Vs (where S is the slimb rate - , 2) By controlling the brake oil pressure to increase or decrease when the reference speed (■) determined by In other words, the brake pressure of the wheel is reduced when the rotational speed of the wheel is less than the reference speed, and then the brake pressure is increased when the rotational speed exceeds the reference speed. By repeatedly reducing the brake pressure, the rotational speed of the wheel is is configured to bring the speed closer to the reference speed.

By the way, braking of wheels is normally performed by controlling brake pressure to drive a wheel cylinder provided on each wheel and transmitting force to a braking member, such as a brake shoe or a disc. Therefore, in a brake control device such as an anti-skid device, the brake pressure is reduced from the mask cylinder that generates pressure in conjunction with the brake pedal to the pressure transmission system connected to the wheel cylinder, etc. that directly controls the brake member. - A brake pressure control device that applies or maintains pressure is installed to control braking force.

In addition, the brake oil pressure, the rotational speed of each wheel, the vehicle body speed, etc. are used as state variable needles, and a control device that constitutes an optimal regulator based on modern control theory, which will be described later, is configured to optimize the above-mentioned slip rate. Brake control devices for vehicles have also been proposed.

[Problem to be Solved by the Invention] Conventional braking control does not take into account the influence of the friction coefficient of the road surface on the slip ratio. That is, the coefficient of friction of the road surface is only considered as a disturbance factor in the braking control system of the vehicle.

Therefore, when the friction coefficient of the road surface suddenly changes, the brake hydraulic pressure command value that causes the brake pressure system to generate the optimal braking force cannot follow the change in the road surface 1 medium pressure coefficient.In other words, when the friction coefficient of the road surface suddenly changes. In some cases, the brake oil pressure is too high and the wheels lock, or conversely, the brake oil pressure is too low and the braking distance becomes longer.

[Means for Solving the Problems] The present invention is configured as follows as a means for solving the above problems.

That is, as illustrated in FIG. 1, the present invention includes a slip detection means M1 that detects the slip state of the vehicle at the current time, and a target brake pressure according to the slip state of the vehicle detected by the slip detection means M1. A brake pressure setting means M2 for setting the brake pressure, and a brake pressure adjustment means M3 for adjusting the brake pressure for braking the vehicle to the target brake pressure. Friction coefficient detection means M to detect
4, and friction 1' to estimate the friction coefficient of the road surface at the next time using the friction coefficient of the road surface up to the current time. 7 coefficient estimating means M5, and the brake pressure setting means M2 sets the brake pressure at the next time using the slip state of the vehicle and the coefficient of friction of the road surface at the next time. The main subject of this paper is a braking control system for vehicles.

Here, the slip detection means M1 determines the slip state of the vehicle from the wheel speed, vehicle body speed, etc. as the above-mentioned slip ratio.

Brake pressure: A adjustment means M3 adjusts the actual brake pressure to the brake pressure set by brake pressure setting means M2, and may use a so-called hydraulic servo system.

The friction coefficient detection means M4 detects the road surface friction (thread number μ(k) at the current time 1) from wheel acceleration, brake oil pressure, etc.
For example,

t, t (k>”CI/r・vwd(k>+kt・pr
It is calculated using the relational expression o(k>],'(m4-r).Here, 1 is the moment of inertia of the wheel, r is the radius of the wheel, vwd(k) is the wheel acceleration at the current time k, and k
t is a constant for converting brake pressure and torque determined in advance through experiments, etc., pro(k) is the brake oil pressure at the current time k, rn is the load on the wheels, and g is the gravitational acceleration. The friction coefficient μ(k) of the road surface may be determined by the Ikeg method, for example, by determining the roughness of the road surface using light, ultrasonic waves, or the like.

The friction coefficient estimating means 15 estimates the friction coefficient m(k÷1) of the next road surface from the friction coefficients μ<k) and μ(k-1) of the road surface up to now.

For example, to the next friction coefficient (k+1> is the current friction coefficient μ
<k> is estimated to be the same as <k>, or the current friction 11
A value extrapolated from the i coefficient μ<k> and the previous friction coefficient μ(k-1), that is, estimated as pu(k+1)=2・μ(k>-μ(k-1)), or , calculated from the friction 1 series of H+1 road surfaces μ(k), μ(k-1>-, , 1t (k-m) up to now [value determined from the n-th curve, i.e. n(k+1 )=eo+el・<k+1)+−+em・(
It is estimated that k+1>11. Here, e o and e 1em are coefficients determined from the friction coefficients up to now.

Then, the brake pressure setting means M2 determines the brake oil pressure to ensure that the vehicle is in an appropriate slip state. That is, the target brake oil pressure increases by +1 at the next time ρrsl+s(k÷1)
is calculated from the value prs(k+1) calculated from the pick-pocket knob state of the vehicle obtained as above, and the γ clearance coefficient (k+i) of the road surface which is +1 at the next time obtained as above. Set as the sum with the value.

That is, prshs(k+1)=prs(k+1)+n(k+
i)・m4・r/kt Here, prs(k+1) is a value calculated from a relational expression determined in advance from the slip rate, wheel acceleration, wheel speed, etc.

In addition to utilizing the conventional control circuit used for anti-skid control, the vehicle braking control device of the present invention uses a predetermined R3i1 frequency according to a dynamic model of the vehicle braking system. The brake pressure to be transmitted to the braking members of the wheels is known based on the yield back gain F, and the brake pressure adjusting means M3 adjusts the brake pressure to this brake pressure by means of feed pump control (determining the amount of feed back and controlling it corresponding to this). In other words, this brake control device can also be configured as an additional integral type!3m regulator that determines the optimal amount of feedback from the detected state variable and a predetermined slip ratio. be.

The method for configuring this additively refined optimal regulator can be found, for example, in "Linear System Control Theory" by Katsuhisa Furuta (1976).
It is described in detail in Shoshodo et al.

[The effective coslip ratio is determined by, for example, the friction of the road surface (the number of threads and the force applied to the road surface from the wheels).

Also, the number of stops on the road surface changes continuously to some extent. Therefore, it is possible to estimate the friction coefficient of the road surface at the next time from the friction coefficient up to now. Therefore, by using the estimated friction coefficient at the next time for control, the slip rate at the next time can be made appropriate. In other words, in the present invention, the brake pressure determined from the estimated road surface friction coefficient and the slip state of the vehicle does not disturb the road surface friction coefficient as in the conventional control device. This reflects the condition of the road surface rather than the brake pressure determined as a factor.

As a result, if the friction coefficient of the road surface suddenly changes, it will follow the change! & Be able to apply appropriate brake pressure.

[Example code] Next, an embodiment of the present invention will be explained with reference to the drawings.

The following examples are illustrative of the invention.

The present invention also includes a pond aspect, unless it departs from the scope of the invention.

Figure 2 is a schematic configuration diagram showing the overall configuration of a vehicle braking control device mounted on a one-wheeled vehicle as an embodiment of the present invention. The system shown together with the block diagram (this is a wholesale system diagram).

This embodiment uses an additive-integral type optimization method to determine the optimum feed rate from the detected state variable and the target wheel speed calculated from a predetermined pickpocket/knob ratio. A generator is used.

First, the overall configuration and the hydraulic and electrical systems will be explained.

As shown in the figure, each wheel 1.2.3.4 of the vehicle is provided with a hydraulic brake sensor 11.12.13.14, and each of the right and left front wheels 1.2 detects the rotational angular velocity. Electromagnetic pickup type rotational angular velocity sensor 15.1
6 is installed 6 also transmission 18
The rotational angular velocity of the rear wheel 3.4, which rotates by receiving the rotation of the output shaft]9 via the differential gear 2, is determined by the rotational angular velocity sensor 22 provided in the transmission IS.
detected by.

The hydraulic brake devices 11 to 14 provided on each wheel brake the rotation of each of the wheels 1 to 4 using high oil pressure generated by the hydraulic pump 24 as brake oil pressure, but this brake oil pressure is adjusted by the actuator 3L 32.33. be done. The actuators 31, 32, and 33 independently control the brake hydraulic pressure of the front right wheel 1, the front left wheel 2, and the left and right rear wheels 3 and 4, and are connected to the electronic unit (ECU) 4.
Controlled by 0. The structure of the actuators 31 to 33 will be described in detail later, but they function as brake pressure adjusting means 13 for adjusting the brake pressure of each wheel 1 to 4.

The hydraulic pressure of the hydraulic system R1-l5 for brake hydraulic pressure to the right front wheel 1 is determined by the hydraulic pressure sensor 51, and the hydraulic pressure of the hydraulic system LH3 of the left front wheel 2 is determined by the hydraulic pressure sensor 51.
The oil pressure of the rear wheel 3.4 is detected by the oil pressure sensor 52, and the oil pressure of the hydraulic system BH3 of the rear wheels 3.4 is detected by the oil pressure sensor 53.

The ECU 40 controls these hydraulic stations.
In addition to the signal according to the oil pressure from the rotation angular velocity sensor 15
．． 16. Rotational angular velocity signals from 22, signals from the acceleration sensor 54 that detects acceleration (including deceleration) of the vehicle, and signals from the brake sensor 25 and brake switch 26 that detect the amount of operation of the brake pedal 24. etc., and control the actuators 31, 32, and 33, respectively, to control the rotational angular velocity ω of each wheel 1 to 4.

Since the braking forces of the front right wheel 1, the front left wheel 2, and the rear wheels 3 and 4 are controlled independently, control of the right wheel will be explained below. FIG. 3 is a block diagram mainly showing the system for controlling the braking of the right wheel 1.

As shown in the figure, the ECU 40 has an ignition key 56
It is equipped with a power supply section 58 that receives power supply voltage from a battery 57 via a battery 57 and supplies a constant voltage to the entire unit.
7,) CPU61, ROM63. RAM 65'J
Mainly, output port lower, analog input port lower,
The pulse input port door 1, the level manual port door 2, etc. are connected to each other by a bus 73, and are configured as a logic operation circuit. When a predetermined condition is satisfied, the ECU 40 controls the brake hydraulic pressure transmitted from the hydraulic pump 24 to the hydraulic brake device 11, which is a braking member, by driving the spring offset type three-boat three-position valve 75 in the actuator 31. control. When the brake oil pressure increases, the hydraulic brake device 11 rotates the disc 8 that rotates together with the wheel 1.
2 (push the friction pad 83 for 1 inch) and it works to stop the rotation of the wheel 1.

Hydraulic pressure is transmitted to the actuator 31 from the hydraulic pump 24 . The hydraulic pressure is guided to the hydraulic brake device 11 via the three-boat three-position valve 75. Pond actuator 32
．． The same applies to 33. Hydraulic pressure is pumped through a check valve 24a and discharge is made to a reservoir 24b.

The spring offset type 3-boat 3-position valve 75 is in position a (hereinafter referred to as 1st position) in Fig. 3 when the solenoid is not supplied with power.
When power is supplied to the right solenoid, it switches to the right switching position b (hereinafter referred to as the second position) in Figure 3.
When the left solenoid is supplied with power, it is located at the left-hand cut-off position C (hereinafter referred to as the third position) in FIG. 3.

Since the actuator 31 operates as described above, the oil pressure is maintained at the position a of the valve 75, increases at the position b, and decreases at the position C.

The 41'7I is the tn configuration and friction coefficient of the control system described above,
It is a figure which shows the physical relationship with each state deafness amount, such as the rotational speed of a wheel.

That is, first, the resistance force Ft applied to the wheels from the road surface is the current friction f of the road surface μ(k) and the aforementioned m and g.

r (Sl); On the other hand, the force Fs applied to the wheel by the brake is the aforementioned pro(k)
and kt (S2). Therefore, the force Fr applied from the wheels to the road surface, which is the difference between the resistance force Ft applied to the wheels from the road surface and the force Fs applied to the wheels by the brake, and the force Fr of the wheels The wheel acceleration Vvd (k) is determined from the inertia ff1I/r (S3). This wheel acceleration vwd (k) is integrated to obtain the wheel speed vw (k).
(S4). The target wheel speed VW (k'l) and the wheel speed vw (k'l) set separately from the optimum slip ratio etc.
The value Ierr(k) is determined by integrating the difference between > (S5)
. This integral value Ierr(k) and the wheel acceleration Vνd
(k), the wheel speed vw(k), and the output of the feed bank determination unit F, which will be described later, to the feedback amount determination unit E.
By inputting into
S6), +1 friction coefficient n (k+1) at the next time determined from the friction coefficient up to the current time, and the aforementioned m・g・r,
/kt, the brake pressure P'5p(k+1), which depends on the 1'61m coefficient of the road surface, is determined (S7).This prsp
By adding the brake pressure prs (k+1) that depends on the slip state of the vehicle to (k+1), the target brake pressure pr
Define shs(k+1). This target brake pressure prs
When hs (k+1) is input as a target value to the hydraulic servo system, the brake oil pressure becomes pro (kt1) (S8)
. Since the control system shown in FIG. 4 constitutes an additive integral type optimal regulator, the above-mentioned target brake oil pressure prshs(k+]) determined by this control system is determined by the wheel speed vw(
1<) is a value that quickly matches the target wheel speed V-(k).

Next, the processing executed by the ECU 40 in the above-described configuration is shown in FIG. 5 and explained.

Step 100: Various variables and flags are initialized.

Step 110: It is determined whether the brake switch 1+26 is on or not. If it is on, the vehicle is being braked, so the process moves to step 120. On the other hand, if it is not on, the process moves to step 230, which will be described later.

Step 12Q: Input the wheel speed vv(k) at the current time from the rotational angular velocity sensor 15, 16, 22.

Step 130: Differentiate wheel speed vw(k) to calculate wheel acceleration vwd(k) at the current time.

Step 140: Input the brake oil pressure pro(k) at the current time 1 from the oil pressure sensors 51, 52, and 53.

Step 150: Calculate the road surface friction coefficient μ(k) at the current time using the following equation.

μ (k) (I/r・vwd(k)+kt−pro(k
)]/(m-g・r) where ■ is the moment of inertia of the wheel, 1- is the radius of one wheel, kt is a constant for converting brake pressure and torque determined in advance through experiments, etc., and m is the load on the wheel. .

Each g represents gravitational acceleration.

Step 160: Input the vehicle body acceleration ννdl(k) at the current time from the acceleration sensor 54.

Step 170: Integrate the m-body acceleration vvdHk),
9 steps 180 for calculating the vehicle body speed vwl(k) at the current time: Calculate the drifting wheel speed vwl(k) using the following equation.

VW book=vwl (k) −S ・vwl (k) Here, S represents the target slip rate, and is usually 2.
All you have to do is 0°.

Step 185: Integral value of the difference between vν book and Vν 1err
Calculate.

Step 190: Brake pressure prs(k+1)f that depends on the slip state of the vehicle! :prs(
k+1) =A1・prs(k)+A2・vwd(k>÷A3・v
Ii (k > 10 to 4- Ierr where Al, A2.
, 83. A4 is each element of the optimum feedback gain obtained off-line by computer simulation.

Step 200: From the friction coefficient up to the current time, estimate a +1 friction coefficient a<k+] at the next time. This estimation method will be described later.

Step 210; +1 target brake pressure prs at next time
hs(k+1> is calculated by the following formula prshs
(k+1>=prs(k+1)+n (k+1)・m4
・r,'kt Step 220: Current brake oil pressure Pr
o(k,) and the target brake oil pressure ρrs of +l at the next time
hs(k+1).

If pro(k) > prshs(k+l), proceed to step 230; if pro(k>= prshs(k+1), proceed to step 240; if p, ro(k)<prshs(k+1), proceed to step 240. The process moves to step 250.

Step 230: Power is supplied to the left solenoid of the spring offset type 3 boat 3 suspension valve 75 shown in Fig. 3 to set the valve position to C. Through these two steps, the hydraulic pressure of the hydraulic brake device 11 decreases, and the braking force becomes small. Become.

Step 240: Set the valve position to a without supplying power to the solenoid of the spring offset type 3-boat 3-position valve 75 shown in FIG. As a result, the oil pressure of the hydraulic brake device 11 remains constant, and the braking force does not change.

Step 250: Spring offset I type 3 in Figure 3
Power is supplied to the right solenoid of the boat 3 position valve 75 to set the valve position to b. As a result, the oil pressure of the hydraulic brake device 11 increases, and the braking force increases.

When the valve position manipulation is completed in this way, the processing from step 110 is executed again.

Note that even if it is determined in step 110 that the brake switch 26 is off, the valve position becomes C in step 240.

Next, Fig. 6(a) shows an example of a method for estimating the friction coefficient (k+1) of the following road surface in the steering wheel 200.
This will be explained in detail using (b) and (c). 1. FIG. 6(a) is a flowchart when estimating that the next friction coefficient a (k+1) is the same as the current friction coefficient μ(k).

That is, the friction coefficient of the road surface changes continuously. Therefore, the friction coefficient at the next time is estimated on the assumption that the friction coefficient at the next time is approximately the same as the current friction coefficient. A brake control device using this estimation method is similar to a conventional brake control device that uses a friction coefficient as a disturbance. However, in the conventional case, the control amount (target brake oil pressure) was determined by the slip ratio etc. determined from the rotation speed, and the friction coefficient of the road surface did not directly determine the control amount. In other words, conventionally, the friction coefficient was only used to correct the control amount obtained from the slip ratio,
The friction coefficient was not reflected in the controlled variable.

In contrast, in the present invention, OF! The estimated friction coefficient at the next time is reflected in the brake oil pressure.

Therefore, the target brake oil pressure reflects the road surface condition more than the conventional one.

When the process starts, 8(k+1
) is substituted with μ(k) and the process ends.

Figure 6(b) shows that the first-order friction coefficient (1:+1) is estimated to be a value extrapolated from the current friction coefficient μ(k) and the previous friction coefficient μ(k-1). This is a flowchart of the case.

When the process starts, the following equation is executed in step 310 and the process ends.

Xi (k+1) = 2・μ(k>−μ(k−1)) Figure 6(c) shows that the following friction 1 series common <k+1) is m+1f[! Friction coefficient u(k), u of the road surface of il
(k-1) This is a flowchart for estimating the error value to be obtained from the m-dimensional curve obtained from μ(k-+++).

When processing starts, the following steps are executed.

Step 320: Calculate the following matrix G.

Ru.

Step 340: The above coefficients eO1e1...eIll
is calculated using the following formula.

E = K -1・S Here, matrices E and S are expressed as follows.

Step 350: Find the friction coefficient (k+1) at the next time using the following equation.

fi(k+1)=eo+el ・<k+1)+--
+em·(k+1)' Here, eo and el-em are coefficients obtained by the above processing.

The method shown in FIG. 6(a) is easy to process and requires short calculation time. On the other hand, the method No. 611(c) is based on a large amount of data up to the present, so the estimated next time friction coefficient a (k+1) and the actual next time friction coefficient μ(k
The method shown in FIG. 6(b), which has a small difference from the actual friction coefficient μ(
k+1) is relatively small. However, whichever method is used, the vehicle stability during braking increases compared to conventional braking control that does not use the number of R scratches as a parameter for braking control.

FIG. 7 shows the experimental results of the vehicle braking control system of this embodiment, and shows the relationship between the time from the start of braking and the target wheel speed, wheel speed, and target oil pressure. The vehicle braking control device of this embodiment used in this experiment uses the following friction coefficient D (k+
1) is the same as the current friction coefficient μ(k) (6th method)
(see figure (a)).

In this experiment, a vehicle traveling at 60 mph on an artificial resin road (which has a lower coefficient of friction than wet asphalt) plunges into wet asphalt one second after the start of braking. For comparison, a conventional braking control system for a vehicle, which is configured as an additive integral type optimal regulator as in this example, but processes the friction coefficient of the road surface as a disturbance factor, is used as an example, and the experimental results are also shown. In Figure 0, the solid line shows the target wheel speed, the broken line shows the wheel speed, and the -dotted chain line shows the target oil pressure.The thick white line shows the results of this example, and the thin line shows the results of the conventional example.

The following was found from the above experiment.

■ The rotational speed of the wheels suddenly decreases t1 seconds after the start of braking. However, in this embodiment, since the coefficient of friction of the road surface is estimated, the wheel does not roll and the speed quickly reaches a value close to the obstructing wheel speed. It should be noted that since the conventional example is also configured as an additive integral type optimal regulator, the difference between the wheel speed and the target wheel speed is very small compared to a brake control device using feedback of classical control theory.

However, the vehicle braking control device of this embodiment performs control more quickly than that.

(2) As mentioned above, this experiment uses a road surface where the friction coefficient of the road surface increases one second after the start of braking. The vehicle braking control device of this embodiment can increase the gate brake hydraulic pressure according to the change, and can stop the vehicle in a shorter time than the conventional example.

[Effects of the Invention] The vehicle braking control device of the present invention also uses the road surface friction coefficient at the next time as a parameter when determining the brake oil pressure command value that generates the optimum braking force for the brake pressure control device that brakes the vehicle. . Therefore, even if the friction coefficient of the road surface suddenly changes, the optimal brake oil pressure command value can always be calculated.

Therefore, the vehicle braking control device of the present invention can perform optimal braking control regardless of the magnitude of the friction coefficient of the road surface.

[Brief explanation of drawings]

FIG. 1 is a block diagram illustrating the configuration of the present invention, FIG. FIG. 4 is a control block diagram showing the physical relationship between the configuration of the control system and each state quantity such as the friction coefficient and the rotational speed of the wheels. FIG. 5 explains the processing in the electronic unit. Flowcharts, Figures 6(a), (b), and (c) are all flowcharts explaining the process of estimating the friction (number of threads) at the next time, and Figure 7 is a flowchart for explaining the process of estimating the friction (number of threads) at the next time. It is a diagram showing the experimental results.Ml...Slip detection means M2...Brake pressure setting means M3...Brake pressure adjustment means M4...Friction coefficient detection means M5...Friction coefficient estimation means 1 .2.3.4...Wheel 11.12.13.14...Hydraulic brake device 15.16.22...Rotation angular velocity sensor 24...Hydraulic pump 31.32.33...Actuator 40 ...Electronic unit (ECU) 51.52.53...Oil pressure sensor 54...Acceleration sensor 75...

Claims (1)

[Scope of Claims] 1. Slip detection means for detecting the slip state of the vehicle at the current time; Brake pressure setting means for setting a target brake pressure according to the slip state of the vehicle detected by the slip detection means; Brake pressure adjusting means for adjusting the brake pressure for braking to the target brake pressure; further comprising: a friction coefficient detecting means for detecting a coefficient of friction of a road surface at the current time; friction coefficient estimating means for estimating a friction coefficient of the road surface at the next time using the friction coefficient of the road surface, the brake pressure setting means using the slip state of the vehicle and the friction coefficient of the road surface at the next time. A braking control device for a vehicle, characterized in that a target brake pressure for the next time is set based on the timing.