DEVICE FOR QUICK RELEASE OF AN ELECTRO-MECHANICAL PARKING BRAKE

Description

[0001] The invention relates to a device for quickly releasing an electromechanical parking brake of a vehicle.

[0002] Many vehicles are equipped with parking brakes that are not manually controlled, including electromechanical brakes. Such brakes are equipped with a mechanical actuator driven by an electric motor. The vehicle driver typically controls them by pressing a button that switches them between application and release states. When a state change command is made by the driver, an engine control unit responsive to this command acts on the brake actuator according to a predefined strategy. And when the brake does not have a sensor that would measure application force or pressure, a common strategy for controlling brake release is to deliver an electrical command to the electric motor whose duration is sufficient to ensure that the brake is fully released at the end of the command, regardless of the initial state of the brake and the circumstances of release.

[0003] But this command duration is excessive in most situations, and felt as significant by the driver.

[0004] The object of the invention is thus to reduce this release time when possible to improve the comfort of use of the vehicle, by still relying on an actuator control strategy ("release strategy") based on delivery of an electrical command, while guaranteeing complete release of the brake.

[0005] The invention applies mainly, but not exclusively, to braking systems in which service braking is provided hydraulically while parking and emergency braking is provided by the electric motor.

[0006] Document US 2016 / 032399 A1 relates to an electromechanical parking brake device for a vehicle, comprising a brake associated with a wheel of the vehicle, an actuator of the brake, an electric motor for moving the actuator, and a motor control unit of the electric motor which comprises: a module for providing commands to the electric motor, including brake release commands; and where the engine control unit further includes: a module for continuously measuring the intensity of the electric current supplied to the electric motor during the release commands; a decision module connected to the modules for continuously measuring the intensity of the electric current and for supplying commands, which operates, during each of the release commands, by evaluating successive values of said intensity of the electric current, by detecting a stabilization of said intensity of the electric current, and by stopping supplying the electric current after having detected the stabilization.

[0007] In this document, an additional opening stroke of the pads is applied after the detection of the stabilization of the current, in order to guarantee an effective release of the brake in all circumstances. It appears, however, that this opening cannot generally be obtained with precision, and that it risks being lower than the value deemed necessary. The inventors have in fact noted that the stabilization of the electric current, supposed to coincide with the start of the release of the pads, often occurs beforehand depending on the state of the brake, and in particular depending on its temperature and the possible application of hydraulic braking carried out by the driver.

[0008] The following documents US 2016 / 032995 A1, JP 2016 124403 and WO 2009 / 053429 A1 may also be cited as prior art.

[0009] The invention is distinguished from the above document in that the control unit, as defined in claim 1, comprises a temperature probe and a hydraulic pressure probe continuously making measurements, respectively, of a temperature and a hydraulic pressure representative of a temperature and a hydraulic pressure present in the brake, the decision module is connected to the temperature probe and the hydraulic pressure probe, and the decision module is arranged to determine a determined duration of extension of supply of the electric current after stabilization has been detected, the determined duration depending on the measurements of the temperature probe and the hydraulic pressure probe.

[0010] The duration of the extended release is then determined with a precision that ensures sufficient, but not excessive, release of the brake. The more rudimentary process of the previous document does not allow this result to be achieved, as it does not take into account the state of the brake at the time of release.

[0011] The accuracy of estimating the extension time required for safe release is further increased if the determined time also depends on a stabilization value of the electric current intensity, obtained during stabilization.

[0012] In practice, the extension duration can be determined to apply an end of release stroke (ΔI) plus a safety release stroke (I 2 + I 3 ) to the brake, the end of release stroke (ΔI) generally being obtained by a linear function of the hydraulic pressure, the safety release stroke (I 2 + I 3 ) being fixed.

[0013] Another aspect of the invention is a parking brake device, as defined in claim 8, electromechanical for a vehicle, comprising said brake, which is associated with a wheel of the vehicle, an actuator of the brake, said electric motor for moving the actuator, and the motor control unit of the electric motor according to the above.

[0014] Another aspect of the invention is a motor vehicle, as defined in claim 9, provided with the parking brake device according to the above.

[0015] Another aspect of the invention is a method of controlling, as defined in claim 10, an electromechanical vehicle brake by commands of electric current for applying and releasing the brake supplied to an electric motor for controlling a brake actuator, comprising continuous measurements of values of intensity of the electric current during the release commands of a temperature representative of a temperature in the brake and of a hydraulic pressure representative of a hydraulic pressure in the brake, and an interruption of the release commands after a determined duration as soon as a stabilization of said values is observed, the determined duration depending on the measurements of the temperature, the hydraulic pressure and a stabilization value of the electric current.

[0016] According to certain optional but advantageous characteristics of the invention: the motor control unit is designed to calculate a time derivative of said intensity of the electric current; the motor control unit is designed to detect stabilization by detecting a crossing of a determined threshold, by a function obtained using the measurement module; the function is an absolute value of said time derivative; the function is the intensity of the electric current.

[0017] The invention will now be described in its various aspects, characteristics and advantages by means of the detailed description of the following figures, which illustrate a particular embodiment given purely for illustrative purposes: there Figure 1 schematically represents a motor vehicle; the Figure 2 illustrates an exploded view of an electromechanical brake; Figure 3 illustrates the motor control unit of said brake; the Figure 4 illustrates the steps of releasing the brake; Figure 5 illustrates a control of the electric current for controlling the brake; the Figure 6 illustrates how the duration of brake release is adjusted; Figure 7 is a process diagram; and the Figure 8 illustrates strategy correction functions based on brake status.

[0018] There figure 1 represents an automobile 1 equipped with two front wheels 2 driven and steered on a front axle 3, and two rear wheels 4 non-driven and non-steered on a rear axle 5. Each of the front wheels 2 is equipped with a main service brake actuated directly by the driver, and each of the rear wheels 4 is equipped with a brake 7 described below in detail, and which is associated with an actuator 8 capable of making it work as a parking and emergency brake. The actuators 8 of the two brakes 7 are controlled by the same engine control unit 9 based on various information relating to certain parameters of the vehicle 1 and its driving state. The engine control unit 9 is active when emergency braking becomes necessary or when parking is requested.

[0019] There figure 2 schematically illustrates a known and non-limiting embodiment of the brake 7, according to an exploded view. The brake 7 comprises a caliper 11 joined to a cylindrical housing 12. It also comprises a geared motor 60, a flange 61 of which is joined to a flange 62 on the rear face of the housing 12 by screws (not shown here). The geared motor 60 contains an electric motor 18 and gears for reducing the rotation speed of said electric motor 18. The housing 12 comprises a hydraulic cavity 13 called a cylinder, open towards the front (on the right at figure 2 ) and in which slides a piston 14 carrying a movable pad (not shown). Braking is achieved by sliding the piston 14 forward, to bring the movable pad closer to a fixed pad located at the front end of the caliper 11 and to grip a disc of the rear wheel 4 between these pads. This movement of the piston 14 is obtained, when the brake 7 is working as a service brake, by the application of hydraulic pressure in the hydraulic cavity 13 while the vehicle is driving: this pressure is exerted on the rear face of the piston 41 and pushes it forward. If, however, the brake 7 is controlled as a parking brake or as an emergency brake, braking is achieved by using the electric motor 18 according to strategies imposed by the engine control unit 9. The electric motor 18 sets the gears of the geared motor 60 in motion, which turns a screw 15 which extends into the hydraulic cavity 13.The screw 15 is engaged with a nut 16 on which a rear face of the piston 14 is then in abutment. The rotations of the screw 15 are converted into translations of the nut 16 and of the piston 14, which moves according to the duration of actuation of the electric motor 18. The actuator 8 considered here notably comprises the geared motor 60 and therefore its electric motor 18, and the system 17 composed of the screw 15 and the nut 16.

[0020] The invention could be implemented on other vehicles and other brakes than these.

[0021] There figure 3 illustrates in more detail the engine control unit 9. It comprises: a command supply module 19 which supplies commands to the electric motor 18 by being connected to a battery or another energy source present in the vehicle 1; a measurement module 20; and a decision module 23 which connects the command supply modules 19 and measurement 20, and which uses the output signal of the measurement module 20 to adjust the duration of the commands. The measurement module 20 and the decision module 23 are features of the invention. The measurement module 20 measures the intensity of the current in the electrical circuit on which the electric motor 18 and said energy source are installed. The device further comprises means for continuously measuring a temperature of the brake 7 by a temperature probe 21, and a hydraulic pressure 22.The temperature probe 21 is advantageously placed as close as possible to one of the brake pads 7 in order to attenuate their temperature as much as possible, and the hydraulic pressure probe 22 can directly measure the pressure in the hydraulic cavity 13 or, as shown here, estimate the hydraulic pressure in the brake 7 by measuring the pressure in another portion of the hydraulic circuit 10 subjected to the action on a brake pedal 6, such as the master cylinder. The temperature and hydraulic pressure probes 21 and 22 provide, like the measurement module 20, their measurements to the decision module 23.

[0022] There figure 4 is a diagram which illustrates the steps of the release of the brake 7 from a tightened state as a function of the translational movement of the nut 16 of the screw-nut system 17, according to the known strategy. This movement can be broken down into three deflections: a first deflection, of length l 1 , corresponds to the useful stroke of the screw-nut system 17 and is assumed to result in the start of the release of the portions; a second deflection, of length l 2 , must be added although it is theoretically useless for the release of the brake, but it corresponds to an idle stroke of the screw-nut system 17 which serves to release the disc clamped between the pads of the brake 7; and a third deflection I 3 must also be added to ensure that the desired idle stroke is actually obtained despite the uncertainties of construction and operation of the brake 7.According to a real example, the deflections have values I 1 =0.94mm, I 2 =0.35mm and I 3 =0.05mm respectively, the total deflection then being equal to 1.34mm. All these deflections are invariable in a known strategy. We see that the deflections I 2 and I 3 imposed for reasons of safety or subsequent good operation of the brake 7 have a significant part in the total deflection; it must be added that the deflection necessary for the release of the pads of the brake 7 is in reality almost always less than I 1 , and that it is often much less, because I 1 is a value calculated from an extreme tightening of the brake 7 which is not necessarily present at the beginning of the release. The commands of the known processes however have, for the most part, a uniform duration and calculated to impose this total deflection (I 1 +I 2 +I 3 ).

[0023] The experimental form of an electrical control for releasing the brake 7 from a applied state is shown in the upper part of the figure 5 , which represents the intensity I of the current passing through the electrical circuit comprising the electric motor 18 as a function of time t; the lower part of this figure 5 represents the corresponding deflection obtained for the actuator 8. The control successively comprises a starting peak 24, a decreasing portion 25 and a flat portion 26 where the current is uniform at a low intensity ("idle current"). The starting peak 24 at high current intensity corresponds to a transient state mainly due to play compensation in the mechanisms, the decreasing portion 25 corresponds to the progressive release of the brake 7, and the flat portion 26 to a stroke with residual force, or idle stroke of the actuator 8 when the brake 7 is completely released. In the decreasing portion 25 and the flat portion 26, the intensity I is proportional to the force applied by the electric motor 18 and which is necessary to move the actuator 8.

[0024] According to the invention, the total deflection of the brake actuator 7 (or the translation of the nut 16) during a release must become equal to (I 1 '+I 2 +I 3 ) ( figure 6 ), where I 1 ' corresponds to the deflection strictly necessary for loosening the pads, and therefore I 1 ' ≤ I 1 , while I 2 and I 3 remain unchanged. It should be noted that I' 1 can be much lower than I 1 , for example close to 0.6mm in the example mentioned.

[0025] This is achieved by adding the measuring module 20, which measures the intensity I of the current supplied to the electric motor 18 and whose output signal, supplied to the decision module 23, is a function conforming to the figure 5 . When the flat portion 26 is reached, the decision module 23 calculates an extension duration Δt of application of the current allowing only the total necessary stroke to be completed (I' 1 + I 2 + I 3 ). The detection of the flat portion 26 amounts to a detection of stabilization of the electric current. The detection criterion can advantageously be the crossing towards zero of a threshold determined by the absolute value of the time derivative of the intensity I of the current (dl / dt); other stabilization criteria could be envisaged, such as the crossing towards zero of a threshold of the value of the intensity I of the electric current.

[0026] There figure 5 further illustrates, in dotted lines, the effects of the known strategy: the electrical control continues after Δt, as does the empty stroke, so as to finally obtain the deflection (I 1 +I 2 +I 3 ).

[0027] The method of determining the extension duration Δt is an essential aspect of the invention, and it will be detailed below: the stabilization of the electric current at a stabilization value I 0 does not in reality generally coincide with the start of the loosening of the pads.

[0028] There figure 7 illustrates the main steps of the method. Step E1 consists of the application of a brake release command by the driver. In step E2, the motor control unit 9 becomes active, the command supply module 19 supplies a command to the electric motor 18, and the measurement module 20 begins to measure the intensity I of the current of the command. The decision unit 23 continuously observes the evolution of the intensity I, or of a time function correlated thereto and which it calculates, in step E3. If it concludes that this function has stabilized (step E4), in particular if the function crosses a determined threshold (for example dl / dt < 5 A / s), it orders that the electric command be extended only for a determined duration Δt and that the command then stops (step E9); otherwise, the program returns to step E3.

[0029] Here is how the extension duration Δt is estimated during steps E5, E6, E7 and E8 taking place between steps E4 and E9, simultaneously or successively for E5, E6 and E7: the temperature θ in the brake 7 is measured by means of the temperature probe 21 (step E5); the hydraulic pressure P in the brake 7 is measured by means of the hydraulic pressure probe 22 (step E6); and the stabilization value I 0 of the electric current is also measured (step E7).

[0030] As already mentioned, the temperature and pressure measurements can be made directly in the brake 7, or in the vicinity of it, and then possibly be subject to corrections. Alternatively, in E5 the value of the temperature θ is estimated.

[0031] The inventors have found that the stabilization of the electric current of the electric motor 18 actually occurs a little before the actual release of the pads when the brake 7 is hot, or when hydraulic pressure is applied to it by the driver pressing the brake pedal 6. This means that the deflection I' 1 is not completed at the instant of stabilization of the electric current (at the start of the flat portion 26) in these circumstances, and that it is still necessary to apply, in addition to the safety strokes I 2 and I 3 , an end of release stroke ΔI, which can be known in advance by prior tests on the brake 7 and measurements of the temperature θ and the hydraulic pressure P.In other words, the duration of extension Δt of the operation of the electric motor 18 after the stabilization of its supply current becomes adaptive or variable in the invention, as well as the corresponding spacing stroke of the brake pads 7, in order to maintain the safety stroke (I 2 +I 3 ) after the release of the pads at an invariable value.

[0032] The decision module 23 therefore contains functions such as those of the figure 8 , which express the end of release travel ΔI as a function of the hydraulic pressure P and the temperature θ (here L 100 , L 200 and L 300 for temperatures of 100°C, 200°C and 300°C respectively for brake 7). The hydraulic pressure P is expressed in bars, and the end of release travel ΔI in millimeters. These functions are, at equal temperature, approximately linear (ΔI = a P + b, where a and b are fixed coefficients) as soon as moderate braking is applied, and tend towards zero in the absence of braking (ΔI ≈ 0 for P ≈ 0).

[0033] Finally, the extension time Δt generally depends not only on the end of travel (ΔI + I 2 + I 3 ) to be applied, but on the rotation speed of the electric motor 18 when the stabilization value I 0 has been reached. This speed as a function of the intensity can also be determined by preliminary tests.

[0034] The invention therefore allows for a shorter duration of releases (approximately a third less than with known methods, under ordinary conditions), a saving of material and energy consumed, and also faster re-tightening of the brake thanks to the shortening of the free stroke, which is very appreciated if the parking brake must also serve as an auxiliary brake in certain emergency circumstances during driving: this becomes safer. Nomenclature

[0035] 1 Automobile 2 Front wheels 3 Front axle 4 Rear wheels 5 Rear axle 6 Brake pedal 7 Brake 8 Actuator 9 Engine control unit 10 Hydraulic circuit 11 Caliper 12 Housing 13 Hydraulic cavity 14 Piston 15 Screw 16 Nut 17 Screw-nut system 18 Electric motor 19 Control supply module 21 Temperature sensor 22 Hydraulic pressure sensor 20 Measurement module 23 Decision module 24 Starting peak 25 Decreasing portion 26 Flat portion 60 Geared motor 61 Flange 62 Flange I Current intensity I 0 Current stabilization value t Time dl / dt Derivative of current I1 Imposed brake release deflection I1' Useful brake release deflection I2 First additional actuator deflection I3 Second additional actuator deflection ΔI End of pad release stroke θ Temperature P Hydraulic pressure Δt Current control extension time E1 Driver control E2 Supply ofcontrol and intensity measurement E3 Intensity evolution function E4 Stabilization E5 Temperature measurement E6 Hydraulic pressure measurement E7 Measurement of stabilized intensity E8 Determination of the extension duration E9 Extension determined then stopping of the control L 100, L 200, L 300 Release limit switch functions

Claims

1. Motor control unit (9) intended to control an electric motor (18) of an electromechanical actuator of a brake (7) of a vehicle (1), which comprises: - a module (19) supplying commands of an electric current to the electric motor (18), including commands to release the brake (7); - a module (20) for continuous measurement of the intensity (I) of the electric current supplied to the electric motor during the release commands; - a decision module (23) connected to the modules for continuously measuring the intensity of the electric current (20) and for supplying commands (19), which is designed, during each of the release commands, to evaluate successive values of said intensity of the electric current, to note a stabilisation of said intensity of the electric current, and to stop supplying the electric current after having noted the stabilisation, - the control unit being characterised in that it comprises a temperature sensor (21) and a hydraulic-pressure sensor (22) continuously making measurements, respectively, of a temperature and of a hydraulic pressure representing a temperature (θ) and a hydraulic pressure (P) present in the brake (7), - the decision module (23) is connected to the temperature sensor (21) and to the hydraulic-pressure sensor (22), - and the decision module is arranged to determine a given duration (Δt) of prolongation of supply of the electric current after the stabilisation has been noted, the given duration (Δt) being dependent on the measurements of the temperature sensor (21) and of the hydraulic-pressure sensor (22).

2. Motor control unit according to claim 1, characterised in that the given duration (Δt) also depends on a degree of stabilisation (I0) of the intensity of the electric current, obtained during stabilisation.

3. Motor control unit according to claim 1 or 2, characterised in that the given duration (Δt) is determined for applying an end-of-release travel (ΔI) plus a safety release travel (I2 + I3) to the brake, the end-of-release travel (ΔI) being obtained by a linear function (L100, L200, L300) of the hydraulic pressure (P), the safety release travel (I2 + I3) being fixed.

4. Motor control unit according to any one of claims 1 to 3, characterised in that it is designed to calculate a temporal drift of said intensity of the electric current.

5. Motor control unit according to any one of claims 1 to 4, characterised in that it is designed to note the stabilisation by detecting that a given threshold has been crossed, by a function of intensity of the electric current obtained by means of the measuring module.

6. Motor control unit according to claims 4 and 5, characterised in that the function of intensity of the electric current is an absolute value of said temporal drift.

7. Motor control unit according to claim 5, characterised in that the function of intensity of the electric current is the intensity of the electric current.

8. Electromechanical parking brake device for a vehicle, comprising said brake (7), which is associated with a wheel (4) of the vehicle, an actuator (8) of the brake, said electric motor (18) for moving the actuator, and the motor control unit (9) of the electric motor in accordance with any one of the preceding claims.

9. Motor vehicle, characterised in that it comprises a parking brake device according to claim 8.

10. Method for controlling an electromechanical vehicle brake by electric-current commands for clamping and releasing the brake supplied to an electric motor controlling an actuator of the brake, comprising continuous measurements of intensity values of the electric current during the release commands, of a temperature representing a temperature (θ) in the brake and of a hydraulic pressure representing a hydraulic pressure (P) in the brake, and an interruption of the release commands after a given duration (Δt) as soon as a stabilisation of said values is noted, the given duration (Δt) being dependent on the measurements of the temperature, of the hydraulic pressure and of an electric-current stabilisation value (I0).