Method for controlling a brake

Abstract

The present invention relates to a method for controlling the brakes of a motor vehicle using an estimated clamping force applied by a brake, the value of which is obtained from the current consumed by the brake, the method comprising: a) monitoring the voltage at the terminals of the brake, b) detecting voltage variations that may cause errors in the estimated clamping force, and c) calculating a corrected estimated clamping force by at least partially eliminating the voltage variations.

Description

Technical fields and existing technologies

[0001] The present invention relates to a method for controlling a brake to provide increased safety, and to a braking system that provides increased operational safety.

[0002] Motor vehicles are equipped with brakes at each wheel. These can be disc brakes or drum brakes.

[0003] The brake can be a hydraulic brake or an electromechanical brake known as an EMB.

[0004] Furthermore, parking brakes are increasingly being electrically actuated. For example, an electric motor-driven screw-nut system applies brake pads against the brake disc in the case of disc brakes, and applies brake linings against the brake drum in the case of drum brakes.

[0005] The clamping force applied by the pads or shims is not measured, but is estimated specifically based on the value of the current consumed by the motor. This estimation eliminates the need for a force sensor, which in particular simplifies the braking system. Motor actuation is interrupted when the clamping force reaches a preset threshold.

[0006] This operating mode is satisfactory.

[0007] The inventors observed that the estimation of the clamping force applied by the parking brake may be incorrect, especially significantly lower than the actual value, resulting in premature stopping of the parking brake motor.

[0008] This estimation error is caused by the measurement of the current consumed by the motor. In fact, the inventors discovered that rapid voltage changes, particularly voltage increases, in the electrical system of a vehicle cause current spikes. The electric brake controller converts these current spikes into a clamping force exceeding a set threshold and commands the motor to stop. Therefore, even though this is not actually the case, the electric brake is assumed to be fully clamped.

[0009] Voltage changes are caused by external phenomena that occur simultaneously with the actuation of the parking brake. These phenomena include, for example, starting the internal combustion engine, stopping the heater, and stopping the parking brake. In practice, both parking brakes are actuated in a time-shifted manner to prevent overloading of the vehicle's electrical system; when the first actuated parking brake stops at its clamped position, the voltage in the vehicle's circuitry increases, which affects the current to the second parking brake.

[0010] The premature stopping of the parking brake's electric motor results in lower clamping force, which in turn makes securing the vehicle (especially on slopes) less effective. Disclosure of the invention

[0011] Therefore, the object of the present invention is to provide a method for controlling at least one brake to provide improved operation, and a braking system with improved operational safety.

[0012] The above objective is achieved by a method for controlling a brake, the method comprising the steps of monitoring voltage changes at at least one parking brake during the actuation phase of the brake, and taking into account the voltage changes in the control of the brake.

[0013] The monitoring steps include, for example, determining the voltage gradient, comparing the gradient with a high value, and establishing a disturbance period (if applicable), during which the method used to estimate the clamping force is modified to at least partially compensate for the effect of voltage variations on the clamping force estimation.

[0014] In one embodiment, the step of considering voltage variations includes estimating the clamping force during the disturbance period by not using the current consumed by the parking brake.

[0015] In another embodiment, the step of considering voltage changes includes estimating the clamping force by estimating the clamping force gradient using at least one value prior to the start of the estimation period during the disturbance period.

[0016] In the event of a sudden increase in voltage, the clamping force may be overestimated, leading to premature termination of the parking brake actuation. In the event of a sudden decrease in voltage, the clamping force may be underestimated, potentially resulting in over-clamping that could damage the brake.

[0017] This invention reduces or even eliminates the risk of estimating the clamping force of electric brakes, a risk that could lead to a decrease in safety levels or damage to the brakes. It improves the operational safety of electric brakes and, more generally, braking systems.

[0018] In other words, the method for controlling the electric brake determines the time period during which the estimated clamping force may be erroneous due to voltage variations, and takes corrective measures during that time period.

[0019] The present invention then aims to provide a method for controlling an electric brake of a motor vehicle using an estimated clamping force applied by a brake, the value of which is obtained from the current consumed by the brake, the method comprising: a) Monitor the voltage at the brake terminals. b) Detect voltage changes that may introduce errors into the estimated clamping force. c) The corrected estimated clamping force is calculated by at least partially eliminating voltage variations. d) Use the corrected estimated clamping force instead of the estimated clamping force to control the brake.

[0020] Preferably, during step b), the absolute value of the voltage gradient is compared with a high threshold UH, and if >UH, it is considered that there is an error in the value of the estimated clamping force.

[0021] For example, after step b), the absolute value of the voltage gradient is compared with a low value UL, and if within a given time t <UL, the value of the estimated clamping force is obtained from the current consumed by the brake.

[0022] In one embodiment, step c) implements Hooke's law to determine the estimated clamping force, and the stiffness of the brake has been previously determined, for example, on a test bench.

[0023] In another embodiment, step c) implements Hooke's law to determine the estimated clamping force, and the stiffness of the brake is determined according to the estimated clamping force before >UH.

[0024] In another embodiment, step c) uses the clamping force gradient at time t0 when <UH. In the case where the brake includes an electric motor, step c) calculates the clamping force gradient at time t, and also uses the ratio between the rotational speed of the electric motor at time t and the rotational speed of the electric motor at time t0.

[0025] The object of the present invention also lies in an electric brake microcontroller for a motor vehicle, which electric brake microcontroller is configured to control the brake, the microcontroller controls the electric brake based on the clamping force, and the microcontroller is configured to: Estimate the clamping force according to the current consumed by the brake, Monitor the voltage at the terminals of the brake, Detect voltage changes that may cause an error in the estimated clamping force, Calculate the corrected estimated clamping force by at least partially eliminating the voltage changes.

[0026] The object of the present invention also lies in a braking system, which braking system includes at least one electric brake and a microcontroller according to the present invention.

[0027] The brake advantageously includes an electric motor.

[0028] The electric brake is, for example, a parking brake. Brief description of the drawings

[0029] With the aid of the accompanying drawings, the following description will be better understood, wherein: Figure 1 This is a schematic diagram illustrating an example of a parking brake system to which the present invention can be applied. Figure 2 A flowchart of a method for controlling a parking brake according to the present invention is shown. Figure 3 It represents the change in brake stiffness (in kN / m) as a function of stroke (in mm), as measured on a test bench. Figure 4 The following are graphical representations: voltage variation over time, actual clamping force Fr, estimated clamping force, and corrected estimated clamping force obtained according to the first example of the first embodiment. Figure 5 The following are graphical representations: the sinusoidal change of voltage over time, the actual clamping force Fr, the estimated clamping force, and the corrected estimated clamping force obtained according to the first example of the first embodiment. Figure 6 The following are graphical representations: voltage variation over time, actual clamping force Fr, estimated clamping force, and corrected estimated clamping force obtained according to the first example of the first embodiment. Figure 7 The following are graphical representations: the sinusoidal change of voltage over time, the actual clamping force Fr, the estimated clamping force, and the corrected estimated clamping force obtained according to the first example of the first embodiment. Figure 8 The following are graphical representations: voltage variation over time, actual clamping force gradient Fr, and the estimated clamping force gradient according to the first example of the second embodiment. Figure 9 The following are graphical representations: voltage change over time, actual clamping force Fr, estimated clamping force, and voltage variation from... Figure 8 The estimated clamping force obtained from the estimated force gradient is shown. Figure 10 The following are graphical representations: the sinusoidal change of voltage over time, the actual clamping force Fr, the estimated clamping force, and the value derived from... Figure 8 The estimated clamping force obtained from the estimated force gradient is shown. Figure 11 The following are graphical representations: voltage variation over time, actual clamping force gradient Fr, estimated clamping force gradient, and corrected estimated force gradient obtained according to the second example of the second embodiment. Figure 12 The following are graphical representations: voltage change over time, actual clamping force Fr, estimated clamping force, and voltage variation from... Figure 11 The estimated clamping force obtained from the estimated force gradient is shown. Figure 13 The following are graphical representations: the sinusoidal change of voltage over time, the actual clamping force Fr, the estimated clamping force, and the value derived from... Figure 11 The estimated clamping force is obtained by estimating the force gradient shown. Detailed Implementation

[0030] exist Figure 1 In the diagram, a vehicle V is schematically shown, which includes a braking system S, which includes brakes F mounted to the wheels.

[0031] Service braking is achieved through hydraulic brakes or electric brakes.

[0032] The braking system also includes a parking brake device, which includes at least a first parking brake FP1 at the left rear wheel and a second parking brake FP2 at the right rear wheel.

[0033] Parking brakes FP1 and FP2 are electric parking brakes.

[0034] Advantageously, the parking brake is integrated into the service brake.

[0035] Each electric parking brake includes an actuator equipped with an electric motor and means for converting the rotational motion of the electric motor into translational motion, which applies brake pads against a brake disc or applies brake linings against a brake drum.

[0036] The braking system advantageously includes an electronic control unit for the anti-lock braking system (ABS) and / or the vehicle stability system (ESP).

[0037] The braking system includes an electronic control unit, or ECU, also known as a microcontroller (MC), with integrated software for controlling the parking brakes FP1 and FP2. For example, control of the parking brakes is achieved by actuating button B located in the passenger compartment.

[0038] Motor vehicles include electrical circuits, also known as onboard circuits, which include at least one battery and various power-consuming systems connected to the circuits. Examples of these power-consuming systems include the vehicle's temperature control system, internal combustion engine starting system, and two electric brakes FP1 and FP2.

[0039] The microcontroller includes an estimation device 2 for estimating the clamping force applied by each electric brake.

[0040] In the following description, we will describe the microcontroller’s control of electric brake FP1, but it should be understood that the microcontroller controls both electric brakes in a similar manner.

[0041] The estimation device 2 is configured to estimate the clamping force exerted by the brake FP1 based on the current consumed by the motor of the brake FP1.

[0042] According to the invention, the microcontroller is configured to: Detect a voltage change that may generate a current peak that causes an error in the estimation of the clamping force, Establish a correction period during which the clamping force is corrected with respect to the estimated force, and this value is referred to as the corrected estimated force.

[0043] Determine the corrected estimated clamping force during this correction period.

[0044] For this purpose, the microcontroller is associated with a detection device 4, which is configured to determine the voltage change or voltage gradient at the terminals of the parking brake and to detect whether the voltage change may cause a current peak at the motor of the motor FP1.

[0045] This determination and this detection are carried out during the stage of applying the parking brake, particularly at the end of the stage of applying the parking brake (as will be explained below).

[0046] The voltage used is the voltage applied at the terminals of the motor of the parking brake or the supply voltage of the microcontroller. These two voltages undergo the same change. They will be referred to as the "voltage at the terminals of the parking brake" hereinafter.

[0047] Determining the voltage change includes calculating a voltage gradient GradU, for example, in V / s. This calculation is carried out, for example, every 10 ms based on the voltage value provided by the control unit at the terminals of the brake.

[0048] The aim is to detect a sudden voltage increase that may cause an overestimation of the clamping force or a sudden voltage decrease that may cause an underestimation of the clamping force.

[0049] For this purpose, the absolute value of the gradient GradU is compared with a high threshold UH, and when this high threshold UH is exceeded, the voltage change is considered likely to cause the occurrence of a current peak. For example, UH is equal to 20 V / s. When the gradient <UH, the microcontroller switches to the correction phase Tc; when the value of Tc increases, the correction is activated.

[0050] Then, the control unit establishes a correction period Tc for estimating the clamping force.

[0051] If becomes lower than the low threshold UL, the voltage change is considered unlikely to cause the occurrence of a current peak. Preferably, it is verified that Maintain below UL for a long enough time to ensure that current peaks are no longer possible. If within a given time t (e.g., a few tens of ms (e.g., 20 ms)) <UL, the correction period is considered to have ended, and the clamping force can be estimated in a conventional manner by device 2.

[0052] In addition, the microcontroller is configured to provide a value of the corrected estimated clamping force.

[0053] The method of controlling the parking brake by the microcontroller is shown by the flowchart in Figure 2 A command to activate the parking brake is issued.

[0054] During step 100, the voltage gradient at the terminals of the parking brake is determined

[0055] .

[0056]

[0056] During step 200, it is checked whether >UH; if the answer is "N" (negative), proceed to step 300, during which the clamping force is estimated based on the current consumed by the motor of the parking brake. If the answer is "Y" (positive), proceed to step 600.

[0057] After step 300, proceed to step 400 to check whether the clamping force has reached the clamping force value from which the parking brake is considered to ensure secure fixation. If the answer is "Y" (positive), proceed to step 500, during which a command to stop the motor is issued. If the answer is "N" (negative), return to step 100.

[0058] During step 600, the correction phase Tc starts, during which the corrected estimated clamping force is calculated. During step 700, it is checked whether the corrected estimated clamping force has reached the clamping force value from which the parking brake is considered to ensure secure fixation. If the answer is "Y" (positive), proceed to step 800, during which a command to stop the motor is issued. If the answer is "N" (negative), proceed to step 900, during which the voltage gradient GradU at the terminals of the parking brake is measured.

[0059] During step 1000, it is checked whether <UL and whether it remains below UL within a given time t. If the answer is "Y" (positive), proceed to step 300; if the answer is "N" (negative), return to step 600.

[0060] According to the first embodiment, the microcontroller is configured to estimate the clamping force at time t without using the current consumed by the motor at time t.

[0061] In this first embodiment, the microcontroller uses a so-called spring model to estimate the clamping force. To do this, the increase in clamping force ΔFc is estimated according to Hooke's law by equating the brake to a spring.

[0062] Hooke's Law states the following: ΔF = k × ΔStr (I) Where k is the restoring constant or stiffness of the brake, and ΔStr is the stroke of the moving element (e.g., the piston in a disc brake), which is estimated based on the rotation of the motor. The motor speed can be measured by means of a sensor, or estimated using voltage and current measurements along with estimates of motor parameters (R: resistance, K: motor constant, and L: motor inductance). Advantageously, estimating the motor speed allows for the elimination of sensors and thus simplifies the brake.

[0063] In a first example of the implementation, the value of k is predetermined, for example, on a test bench and stored in the microcontroller. In one example, k is a curve stored in the microcontroller. In practice, k changes with the deformation of the brake, and the value of k is selected based on the stroke value. Figure 3 The example shows how the stiffness k (in kN / mm) varies with the stroke (in mm), obtained on a test bench. In another example, k is a constant, the value of which is preferably chosen to avoid overestimating the clamping force. For example, k is chosen to be equal to 30 kN / mm.

[0064] exist Figure 4 The graph shows the following: the change in voltage U (in V) at the brake terminals over time (in seconds); the estimated clamping force Fe (in N) as a function of time (in seconds); and the corrected estimated clamping force Fec (in N) as a function of time (in seconds). The actual clamping force Fr, for example, measured using a sensor, is also shown. The actual value was obtained, for example, using a test bench.

[0065] A strong change in the estimated clamping force Fe was observed after the voltage change, and then... Greater than UH.

[0066] With the present invention, the value of the estimated clamping force Fec corrected by Hooke's law with a constant stiffness is relatively close to Fr and is hardly disturbed by voltage variations. When a strong voltage variation occurs, the actual clamping force is less than Fe and greater than Fec, so a safety margin is ensured by controlling the parking brake using the force Fec.

[0067] In Figure 5 it is possible to see another graphical representation of the corrected estimate of the clamping force in the case where the voltage U varies in a sinusoidal form. Note that the corrected estimated clamping force is less than the actual clamping force, which makes the control of the parking brake safer.

[0068] In a second exemplary embodiment according to the first embodiment, the stiffness value k used in the model is not constant but is calculated in real time using estimated values of the clamping force and the stroke variation.

[0069] In fact, according to formula (I) k = ΔF / ΔStr As long as <UH, the clamping force is estimated based on the value of the current consumed and the stroke is estimated based on the rotation of the motor. Then, as long as <UH, ΔFe can be calculated, which makes it possible to calculate the value of k. For example, a value is calculated and stored every calculation period (i.e., every 10 ms).

[0070] Once >UH, the last calculated value of k (referred to as k') is stored and used to calculate the corrected estimated clamping force according to formula (I). ΔFer’ = k’ × ΔStr (I) In Figure 6 it is possible to see a graphical representation of the corrected estimated clamping force Fec’ as a function of time in the case of a step voltage variation. When a strong voltage variation occurs, the actual clamping force is less than Fe and greater than Fec’. Thus, a safety margin is ensured by controlling the parking brake using the force Fec’.

[0071] In Figure 7 it is possible to see a graphical representation of the corrected estimated clamping force Fec’ as a function of time in the case where the voltage varies in a sinusoidal form.

[0072] According to another embodiment, the microcontroller is configured to calculate the corrected estimated clamping force based on the estimated clamping force gradient GradFe(t) at time t.

[0073] The gradient GradFe(t) is calculated, for example, every calculation cycle (i.e., every 10 ms), based on the value of the clamping force estimated for each calculation cycle (i.e., every 10 ms).

[0074] Once >UH, the value of GradFe is fixed at the last calculated value, which is referred to as GradFe(t0).

[0075] Using the value GradFec(t0), the corrected estimated clamping force Fec(t) can be reconstructed.

[0076] In Figure 8 it is possible to observe the variation of the following terms: GradFe(t), GradFe(t0), GradFr(t), and the voltage U at the motor terminals. Note that when the voltage variation detection is activated, the value of GradFe(t0) takes the value of GradFe from the previous cycle. It should be noted that in this representation, in order to compare GradFe(t0) with GradFr, when <UH, the value of GadFe(t0) does not follow the value of GradFe(t).

[0077] Note that when GradU>UH, the value of GradFec(t) is closer to the actual value compared to the estimated value.

[0078] In Figure 9 it is possible to observe the variation of the following terms: Fe(t), Fec(t) calculated based on GradFe(t0), Fr(t), and the voltage U at the motor terminals.

[0079] In Figure 10 it is possible to observe the variations of Fe(t), Fec(t) calculated based on GradFe(t0), and Fr(t) when the voltage U varies sinusoidally.

[0080] According to another exemplary implementation of the second embodiment, an estimated clamping force gradient is used, which is corrected for t≥t0 by the following formula: GradFec(t) = GradFe(t0) × ω(t) / ω(t0) (II) where ω(t) is the rotational speed of the motor at time t.

[0081] It should be noted that the motor rotational speed ω(t) is estimated using the following formula: ω(t) = (U(t)-R×i(t)) / K (III) where U(t) is the voltage at the motor terminals, R is the motor resistance, i(t) is the current consumed by the motor at time t, and K is the motor constant.

[0082] However, due to the subtraction U(t) - R×i(t), the influence of the voltage variation is significantly reduced.

[0083] Based on the knowledge of GradFec(t), the corrected estimated clamping force Fec(t) can be reconstructed.

[0084] At Figure 11 one can see the variations of the following terms: GradFe(t), GradFec(t), the measured Gradf(t), and the voltage at the motor terminals. Note that when the voltage variation detection is activated, the value of GradFe(t0) takes the value of GradFe from the previous cycle. It should be noted that in this representation, in order to compare GradFe(t0) with GradFr, when <UH, the value of GadFe(t0) does not follow the value of GradFe(t).

[0085] Note that when >UH, the value of GradFec(t) is closer to the actual value compared to the estimated value.

[0086] At Figure 12 one can see the variations of the following terms: Fe(t), Fec(t) calculated according to GradFec(t), Fr(t), and the voltage U at the motor terminals.

[0087] At Figure 13 one can see the variations of Fe(t), Fec(t) calculated according to GradFec(t), and Fr(t) when the voltage U varies sinusoidally.

[0088] When the voltage variation occurs near the end of the actuation phase of the parking brake, the implementation of determining the corrected estimated clamping force is more effective. In fact, if the voltage variation occurs at the beginning of the actuation phase, the current peak is less likely to cause the estimated result of the clamping force to be greater than the clamping force threshold to stop the actuation of the parking brake. On the contrary, if the voltage variation occurs at the end of the braking phase, the estimated clamping force has a higher value, and the overestimation caused by the current peak is more likely to result in premature stopping of the motor.

[0089] In the example described in detail above, the present invention makes it possible to reduce the risk of overestimated clamping force. The present invention is also applicable to underestimated clamping force, which makes it possible to reduce the risk of damaging the brake.

[0090] The present invention is applicable to controlling an electric service brake and a parking brake, and more generally to controlling any brake in which the control of the braking force uses an estimation of the clamping force. <00​​2: A device for estimating clamping force 4: Devices used to detect voltage changes 100, 200, 300, 600, 400, 500, 700, 800, 900, 1000: Steps of the control method S: Braking system F: Brake FP1: First parking brake P2: Second parking brake B: Button GradU: Voltage gradient The absolute value of the voltage gradient UH: High threshold TC: Correction Phase UL: Low threshold N: Negative response Y: Affirmative response Fe: Estimated clamping force Fec: Corrected estimated clamping force Fec': Corrected estimated clamping force Fr: Actual clamping force R: Motor V: Means of transportation.

Claims

1. A method for controlling an electric brake of a motor vehicle using an estimated clamping force applied by a brake, the value of the estimated clamping force being obtained from an electric current consumed by the brake, the method comprising: a) Monitor the voltage at the terminals of the brake. b) Detect voltage changes that may cause errors in the estimated clamping force. c) Calculate the corrected estimated clamping force by at least partially eliminating the voltage variation. d) Use the corrected estimated clamping force instead of the estimated clamping force to control the brake. During step b), the absolute value of the voltage gradient is... Compared with the high threshold UH, if If the value is >UH, then the estimated clamping force is considered to have an error.

2. The control method according to claim 1, wherein, After step b), the absolute value of the voltage gradient is compared with a low value UL, and if within a given time t < UL, the value of the estimated clamping force is obtained from the current consumed by the brake.

3. The control method according to claim 1 or 2, wherein, Step c) Apply Hooke's law to determine the estimated clamping force, wherein the stiffness of the brake is predetermined, for example, on a test bench.

4. The control method according to claim 1 or 2, wherein, Step c) Apply Hooke's Law to determine the estimated clamping force, and wherein, in The stiffness of the brake is determined based on the estimated clamping force before UH.

5. The control method according to claim 1 or 2, wherein, Step c) uses the clamping force gradient at time t0 determined when <UH.

6. The control method according to claim 5, wherein the brake includes an electric motor, wherein, Step c) Calculate the clamping force gradient at time t, and also use the ratio between the rotational speed of the motor at time t and the rotational speed of the motor at time t0.

7. A microcontroller for an electric brake in a motor vehicle, the microcontroller being configured to control the brake, the microcontroller controlling the electric brake based on clamping force, the microcontroller being configured to: The clamping force is estimated based on the current consumed by the brake. Monitor the voltage at the terminals of the brake. Detecting voltage variations that could introduce errors into the estimated clamping force. The corrected estimated clamping force is calculated by at least partially eliminating the voltage variation.

8. A braking system comprising at least one electric brake and a microcontroller according to claim 7.

9. The braking system according to the preceding claim, wherein, The brake is a brake that includes an electric motor.

10. The braking system according to claim 8 or 9, wherein, The electric brake is a parking brake.

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