Method for ascertaining a future wheel brake pressure of a hydraulic vehicle braking system

Abstract

For ascertaining a future wheel brake pressure, pressure generator pressures of an external power brake pressure generator are continuously measured at measurement time intervals, the wheel brake pressure changes are ascertained therefrom, and the sum of the wheel brake pressure changes ascertained during a time period prior to the measurement is added to the last measured pressure generator pressure. The wheel brake pressure thus ascertained is considered to be the wheel brake pressure that will prevail after the time period following the measurement of the pressure generator pressure in a wheel brake.

Claims

1. A method for ascertaining a future wheel brake pressure of a hydraulic vehicle braking system including a brake pressure generator, to which a pressure sensor is connected, and to which a hydraulic wheel brake is connected via a valve, the method comprising: ascertaining a future wheel brake pressure, which will prevail in the wheel brake after a response time period following an actuation of the vehicle braking system using the brake pressure generator, the ascertaining including: during the response time period, measuring a pressure generator pressure a plurality of times using the pressure sensor, a period of time between each two of the measurements of the pressure generator pressure being a measurement time interval; for each respective measurement of the measurements of the pressure generator pressure, ascertaining a wheel brake pressure change in the wheel brake during the measurement time interval following the respective measurement of the pressure generator pressure, wherein a sum of those of the wheel brake pressure changes that were ascertained within the response time period and prior to a last measurement of the pressure generator pressure of the response time period, is added to the pressure generator pressure measured last in the response time period, to ascertain the future wheel brake pressure, the response time period being a sum of a response time of the pressure sensor and a closing time of the valve, and the response time period being longer than the measurement time interval.

2. The method as recited in claim 1, wherein the wheel brake pressure changes ascertained during the response time period are written into a ring memory, an oldest wheel brake pressure change being overwritten by a most recent wheel brake pressure change and the sum of the wheel brake pressure changes stored in the ring memory being added to the pressure generator pressure measured last in the response period.

3. The method as recited in claim 1, wherein the wheel brake pressure changes are computed using a flow equation or are experimentally ascertained.

4. The method as recited in claim 1, further comprising closing the valve when the ascertained future wheel brake pressure reaches or exceeds a setpoint pressure.

5. The method as recited in claim 1, wherein the future wheel brake pressure is computed only if the valve is open.

6. The method as recited in claim 1, wherein the future wheel brake pressure is computed only if the pressure generator pressure increases and/or if there is a possibility that the valve is to be closed.

7. The method as recited in claim 1, wherein the valve is an inlet valve, which is assigned to the wheel brake, of a slip control of the vehicle braking system.

8. The method as recited in claim 1, wherein the vehicle braking system includes an external power brake pressure generator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is explained in greater detail below on the basis of one specific example embodiment illustrated in the FIGURE.

(2) FIG. 1 shows a schematic illustration of a hydraulic muscular power and external power vehicle braking system for the purpose of elucidating a method according to an example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(3) The hydraulic vehicle braking system illustrated in a simplified manner in FIG. 1 is a muscular power and external power vehicle braking system. It includes a brake master cylinder 1 that may be in general understood to mean a muscular power brake pressure generator 2. One or preferably multiple brake circuits having one or multiple hydraulic wheel brakes 3 in each case is/are connected to brake master cylinder 1. A single circuit brake master cylinder 1, to which a brake circuit is connected, is shown in the drawing. The vehicle braking system preferably includes a dual circuit brake master cylinder 1, to which two brake circuits are connected, each having one or multiple wheel brake(s) 3. The vehicle braking system includes two wheel brakes 3 in each brake circuit, for example. Brake master cylinder 1 is actuatable using muscular power with the aid of a brake pedal 4 or a hand brake lever (not shown) and may include a brake booster (not illustrated).

(4) As a further brake pressure generator, the vehicle braking system includes an external power brake pressure generator 5 having a piston cylinder unit 6, whose piston 7 is displaceable with the aid of an electric motor 8 via a screw drive (not illustrated) in a cylinder 9 for the purpose of generating a brake pressure in the vehicle braking system. Each brake circuit is connected through an external power valve 10 to cylinder 9 of piston cylinder unit 6 of external power brake pressure generator 5.

(5) To actuate the vehicle braking system, a brake pressure is generated with the aid of external power brake pressure generator 5 and the brake pressure is applied to wheel brake(s) 3 by opening external power valve(s) 10. Brake master cylinder 1 is hydraulically separated from the vehicle braking system by closing a separating valve 11, each brake circuit being connected via a separating valve 11 in each case to brake master cylinder 1, which forms a muscular power brake pressure generator 2 as already described above.

(6) In the case of the external power actuation, brake master cylinder 1 is used as a setpoint generator for the brake pressure that is to be generated by external power brake pressure generator 5 and that is controlled by an electronic control unit 12 as a function of the pedal force, the pedal travel and/or the brake master cylinder pressure. For this purpose, a pressure sensor 13 is connected to brake master cylinder 1 and brake pedal 4 includes a pedal travel sensor 14.

(7) A pressure sensor 15 is also connected to cylinders 9 of external power brake pressure generator 5. Pressure sensors 13, 15 and pedal travel sensor 14 are connected to electronic control unit 12.

(8) Wheel brake 3 or wheel brakes 3 is/are actuated with the aid of brake master cylinder 1 in the case of an interference or a failure of external power brake pressure generator 5.

(9) Each wheel brake 3 is assigned an inlet valve 16 and an outlet valve 17, with the aid of which slip controls, such as anti-lock systems, traction control systems and/or vehicle dynamics control systems or anti-skid control systems are possible in a conventional manner. The abbreviations ABS, TCS, VDC and ESP are commonly used for these slip control systems. The brake pressure control takes place with the aid of external power brake pressure generator 5 and/or inlet valves 16 and outlet valves 17.

(10) Separating valve(s) 11 and inlet valves 16 are currentless open and external power valve(s) 10 and outlet valves 17 are currentless closed 2/2-way solenoid valves, which is not absolutely necessary for the present invention, however.

(11) According to the present invention, a pressure that prevails in cylinder 9 of external power brake pressure generator 5 upon actuation of the vehicle braking system with the aid of external power brake pressure generator 5 and that is referred to here as pressure generator pressure p.sub.Vor, is measured with the aid of pressure sensor 15. The measurements take place in preferably constant measurement time intervals t.sub.clock.

(12) Wheel brake pressure changes p.sub.Inc i in wheel brakes 3 are ascertained for measured pressure generator pressures p.sub.Vor, i.e., wheel brake pressure changes p.sub.Inc i are ascertained during measurement time interval t.sub.clock until the next measurement of pressure generator pressure p.sub.Vor. The sum of measured pressure generator pressure p.sub.Vor and wheel brake pressure change p.sub.Inc i is wheel brake pressure p.sub.wheel, which will prevail in wheel brakes 3 after measurement time intervals t.sub.clock.

(13) The ascertainment of wheel brake pressure change p.sub.Inc i may be a computation using a flow equation, such as the Bernoulli equation, for example. A volume flow of brake fluid from cylinder 9 of piston cylinder unit 6 of external power brake pressure generator 5 into wheel brake(s) 3 and wheel brake pressure changes p.sub.Inc i resulting therefrom are computed, for example. Another possibility is an ascertainment of wheel brake pressure change p.sub.Inc i from a characteristic diagram that is experimentally ascertained, for example, and stored. Other types of ascertaining wheel brake pressure change p.sub.Inc i are also possible. The sum of measured pressure generator pressure p.sub.Vor and wheel brake pressure change p.sub.Inc i during measurement time interval t.sub.clock until the next measurement yields the wheel brake pressure in wheel brake(s) 3 at the next measurement of pressure generator pressure p.sub.Vor.

(14) According to the present invention, however, not only one wheel brake pressure change P.sub.Inc i is added to the pressure generator pressure, but multiple wheel brake pressure changes P.sub.Inc i are added to last measured pressure generator pressure p.sub.Vor. Those wheel brake pressure changes P.sub.Inc I are added that were ascertained during a time period t.sub.Response that is as long as a response time of pressure sensor 15 and a closing time of/of one of inlet valve(s) 16 and that ends with the last measurement of pressure generator pressure p.sub.Vor. The measurement time intervals t.sub.clock are shorter than time period t.sub.response, so that multiple wheel brake pressure changes p.sub.Inc i are taken into consideration or added. The sum of last measured pressure generator pressure p.sub.Vor and ascertained wheel brake pressure changes p.sub.Inc i during time period t.sub.response or until the measurement is considered to be wheel brake pressures p.sub.wheel prevailing in wheel brakes 3 after the same time period t.sub.response following the measurement of pressure generator pressure p.sub.Vor. This thus means that those wheel brake pressures p.sub.wheel are ascertained that will theoretically prevail around the response time of pressure sensor 15 and the closing time of/of one of inlet valve(s) 16 after the last measurement of pressure generator pressure p.sub.Vor in wheel brakes 3.

(15) Wheel brake pressure changes p.sub.Inc i ascertained for each measured pressure generator pressure p.sub.Vor are written into a ring memory, this being a first in first out memory, in the case of which the oldest value is overwritten by the most recent value. The ring memory has as many memory locations as there are measurements of pressure generator pressure p.sub.Vor during time period t.sub.response. The sum of wheel brake pressure changes p.sub.Inc i stored in the ring memory is added to last measured pressure generator pressure p.sub.Vor and forms the theoretical wheel brake pressure in wheel brakes 3 around time period t.sub.response following the measurement.

(16) Inlet valve(s) 16 is/are closed if ascertained future wheel brake pressure p.sub.wheel has reached or exceeded setpoint pressure p.sub.setpoint after time period t.sub.response, setpoint pressure p.sub.setpoint being predefined by the driver with the aid of brake master cylinder 1 and/or another vehicle dynamics control function, such as for example ABS, TCS and/or VDC or ESP. Here, setpoint pressure p.sub.setpoint may be equal to or different from the brake master cylinder pressure.

(17) Future wheel brake pressure p.sub.wheel is only ascertained in particular if inlet valve(s) 16 is/are open, pressure generator pressure p.sub.Vor increases and/or inlet valve(s) 16 is/are to be closed for a wheel brake pressure control and/or a slip control.

(18) The method according to the present invention is also possible in the case of a muscular power or assisted power actuation of the vehicle braking system with the aid of brake master cylinder 1, which forms muscular power brake pressure generator 2.