METHOD FOR CONTROLLING AN ELECTRONICALLY SLIP-CONTROLLABLE POWER BRAKING SYSTEM OF A MOTOR VEHICLE, ELECTRONICALLY SLIP-CONTROLLABLE POWER BRAKING SYSTEM, AND ELECTRONIC CONTROL UNIT

Abstract

A method for controlling an electronically slip-controllable power braking system, an electronically slip-controllable power braking system, and an electronic control unit of an electronically slip-controllable power braking system. The power braking system has a friction braking device, a generator braking device, and an electronic control unit for controlling the braking devices adapted to need. The friction braking device includes an electronically activatable brake pressure generator including a displacer which is actuatable by an activatable drive unit and conveys pressure medium to a wheel brake of the power braking system. After a change of the power braking system from generating a generator braking torque to generating a friction braking torque, the activation of the drive unit of the displacer is carried out by the electronic control unit in such a way that a velocity of the actuated displacer changes strictly monotonously.

Claims

1. A method for controlling an electronically slip-controllable power braking system of a motor vehicle, the power braking system being equipped with a friction braking device configured to generate a friction braking torque, a generator braking device configured to generate a generator braking torque, and an electronic control unit configured to control the friction braking device and the generator braking device in a manner adapted to need, the friction braking device including a brake pressure generator, using which a pressure medium may be conveyed to a wheel brake of the power braking system, and the brake pressure generator including a displacer actuatable by an electronically activatable drive unit for the pressure medium conveyance, the method comprising the following steps: after a change of the power braking system from generating a generator braking torque to generating a friction braking torque, activating the drive unit of the displacer by the electronic control unit in such a way that a velocity of the actuated displacer changes strictly monotonously.

2. The method as recited in claim 1, wherein the activation of the drive unit is carried out by the electronic control unit in such a way that the velocity of the displacer increases strictly monotonously from a beginning of the actuation up to a maximum velocity of the displacer, and the velocity of the displacer decreases strictly monotonously from the maximum velocity until an end of the actuation.

3. An electronically slip-controllable power braking system for a motor vehicle, comprising: a friction braking device configured to generate a friction braking torque; a generator braking device configured to generate a generator braking torque; and an electronic control unit configured to control the friction braking device and the generator braking device in a manner adapted to need; wherein the friction braking device including a brake pressure generator, using which a pressure medium may be conveyed to a wheel brake of the power braking system; wherein the brake pressure generator includes a displacer actuatable by an electronically activatable drive unit for the pressure medium conveyance; and wherein the electronic control unit is configured to: after a change of the power braking system from generating a generator braking torque to generating a friction braking torque, activate the drive unit of the displacer by the electronic control unit in such a way that a velocity of the actuated displacer changes strictly monotonously.

4. The electronically slip-controllable power braking system as recited in claim 3, wherein the displacer is a piston movably accommodated in a cylinder, which is actuatable by the drive unit to carry out a translation movement for the pressure medium conveyance.

5. An electronic control unit for controlling an electronically slip-controllable power braking system of a motor vehicle, the power braking system being equipped with a friction braking device configured to generate a friction braking torque, a generator braking device configured to generate a generator braking torque, the friction braking device including a brake pressure generator, using which a pressure medium may be conveyed to a wheel brake of the power braking system, and the brake pressure generator including a displacer actuatable by an electronically activatable drive unit for the pressure medium conveyance, the electronic control unit configured to: after a change of the power braking system from generating a generator braking torque to generating a friction braking torque, activate the drive unit of the displacer by the electronic control unit in such a way that a velocity of the actuated displacer changes strictly monotonously.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention is illustrated with reference to the Figures and explained in greater detail hereinafter.

[0021] FIG. 1 shows, schematically heavily simplified, the version of a power braking system explained above and refined by the integration of an additional generator braking device.

[0022] FIGS. 2 through 5 show, on the basis of diagrams, the travel, the velocity, and the acceleration of the displacer of a brake pressure generator of the friction braking device and the pulses originating from the movement of this displacer over the time of a braking process and after a change of the power braking system from the generator braking operation into the friction braking operation has taken place. The diagrams are each recorded synchronized in time with one another.

[0023] Two characteristic curves are depicted in each diagram, of which one characteristic curve illustrates the curve in the event of an activation of the piston drive according to the related art and the particular other characteristic curve illustrates, in direct comparison thereto, the curve of the particular variable in the case of an activation method according to the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0024] The diagram shown in FIG. 2 indicates the curve of travel s covered by displacer 32 or piston of brake pressure generator 30 over time t of a braking process taking place, after a change has taken place of power braking system 10 from generator braking operation to friction braking operation. Two characteristic curves A, B are shown, of which characteristic curve A continuously rises from a starting point t1, at which covered travel s is zero, at constant slope up to an end point t2, at which maximum travel s(max) has been covered. This characteristic curve corresponds to the activation method known from the related art for drive unit 40 of brake pressure generator 30. In this activation method, displacer 32 moves between the endpoints at constant velocity (see FIG. 3).

[0025] In contrast thereto, characteristic curve B shows an s-shaped curve between endpoints t1 and t2. Characteristic curve B indicates the movement of displacer 32 which results when brake pressure generator 30 is activated according to the method according to the present invention. Displacer 32 also begins its travel at starting point in time t1, but this travel initially only increases extremely slowly thereafter and remains significantly behind in relation to the travel according to characteristic curve A within the first half-wave of the s-shaped curve. Up to a point in time t3, the travel difference increases up to a maximum and only gradually decreases again in a range between point in time t3 and a point in time t4. At point in time t4, the piston, independently of the activation method, has covered the same travel, so that the two characteristic curves A, B intersect. Displacer 32 driven according to the method according to the present invention only thereafter covers more travel than according to the known method. The covered additional travel increases up to a point in time t5 and then gradually decreases. At point in time t2, the end of the movement is reached or travel s(max) has been covered by displacer 32.

[0026] FIG. 3 also shows, on the basis of two characteristic curves C and D, the curve of velocity v of displacer 32 moving between the two endpoints according to FIG. 2.

[0027] In the activation method according to the related art (characteristic curve C), velocity v increases at point in time t1 nearly vertically or without delay up to maximum velocity v1 and then remains constant until shortly before reaching point in time t2. At point in time t2, velocity v of displacer 32 also decreases nearly without delay to zero. A nearly rectangular velocity curve accordingly results.

[0028] The velocity curve in the case of activation according to the present invention of displacer 32 (characteristic curve D) is arc-shaped in contrast and increases strictly monotonously up to a maximum velocity v2 at point in time t4 and then decreases falling strictly monotonously to zero. Up to a point in time t7 and from a point in time t8, velocity v is lower than in the case of the related art; it is higher in between.

[0029] FIG. 4 shows characteristic curves E and F, which depict the curve of acceleration a occurring at displacer 32.

[0030] In the activation method according to the related art (characteristic curve E), a relatively pointed acceleration peak directed in the positive in the diagram occurs at the beginning and a pointed deceleration peak directed in the negative occurs at the end of the movement of displacer 32. The acceleration is zero between these peaks, since displacer 32 moves at constant velocity here (see FIG. 3).

[0031] In contrast, the acceleration in the activation method according to the present invention has the curve of an extremely flat wave (characteristic curve F). Wave peaks, i.e., maximum acceleration values, occur shortly after the beginning of the movement of displacer 32, i.e., in the area around point in time t1. Wave valleys, i.e., ranges of maximum decelerations of displacer 32, result at the end of the movement of displacer 32 (area around point in time t2). It may be inferred from the amplitude and the shape of the wave peaks and valleys that the occurring accelerations and decelerations are significantly less than those according to the known activation method (characteristic curve E). Moreover, the wavy curve shows that the acceleration in the present invention, in contrast to the related art, changes more continuously or uniformly than in the related art and does not display “jump behavior,”, i.e., no pronounced peaks.

[0032] Characteristic curves G and H of FIG. 5 illustrate the force pulses emitted by actuated displacer 32 on the hydraulic circuit of power braking system 10. Pulses having a relatively high amplitude in both directions, i.e., in the acceleration direction and also in the deceleration direction of displacer 32, each occur in the related art at the beginning (around point in time t1) and at the end of the movement of displacer 32 (around point in time t2). Peaks in the current signal for drive unit 40 and thus peaks in the drive force given to displacer 32 of brake pressure generator 30 correlate with these pulses. The latter peaks are the cause of the noises and vibrations occurring in the related art.

[0033] In the activation method according to the present invention (characteristic curve H), force pulses only occur in the acceleration direction of displacer 32. These resulting force pulses are significantly less in direct comparison in their amplitude than in the related art and moreover dissipate (around point in time t1) or build up (around point in time t2) over a longer period of time. Characteristic curve H is overall distinguished by a smooth, continuous curve. The drive force given to displacer 32 of brake pressure generator 30 by drive unit 40 behaves accordingly and as a result the drive of brake pressure generator 30 thus causes less noise and vibrations.

[0034] The provided activation method may always be used, as already described at the outset, when power braking system 10 of the vehicle is transferred or switched from a generator mode into a friction braking operation, i.e., in spite of an existing braking intention, a sufficiently high generator braking torque for decelerating the vehicle is no longer present.

[0035] In addition, it is to be noted that the present invention has only been described by way of example on the basis of a brake pressure generator 30 which is equipped with a piston/cylinder unit for pressure medium conveyance. Alternatively, it would be conceivable to use a displacer pump, for example, instead of such a brake pressure generator, for example a gearwheel pump which continuously conveys the pressure medium.

[0036] Further changes or additions to the statements in the description are possible without departing from the explained basic concept of the present invention.