JP7155055B2 - electric parking brake device - Google Patents

Description

The present invention relates to an electric parking brake device for use in vehicles such as automobiles.

For example, Patent Document 1 is known as a conventional technique using an electric parking brake device.

In Patent Document 1, after the energization to the electric motor is interrupted, while the electric motor is operating in a power generation mode in which the electric motor rotates by inertia, a parameter is detected, a motor constant of the electric motor is determined based on the detected parameter, and an electric motor constant is determined. A technique is disclosed that adjusts the tightening force of a parking brake device.

WO2018/046296

In the technique described in Patent Document 1, the parameters of the electric motor are detected when no load is applied to the electric motor. If this occurs, the parameter detected in the no-load state becomes an error, and there is a problem that an appropriate tightening force of the electric parking brake device cannot be secured.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide an electric parking brake device that can operate with an appropriate tightening force according to the load of the electric motor.

In view of the above, in the present invention, an "electric motor having an electric motor, a rotary motion-to-linear motion converting mechanism for converting the rotary motion of the electric motor into a linear motion, and a disk pad that moves by applying current to the electric motor" is proposed. A parking brake device, comprising: a cutoff current calculation unit that calculates a cutoff current that stops current flowing to an electric motor; a torque constant calculation unit that calculates a torque constant required to calculate the cutoff current; and an electric parking brake device having a torque constant correction unit that corrects the torque constant in a state where the electric motor is stopped from being energized after the start."

According to the present invention, it is possible to provide an electric parking brake device that can operate with an appropriate tightening force according to the load of the electric motor.

1 is an overall configuration diagram of an electric parking brake device according to Embodiment 1 of the present invention; FIG. FIG. 2 is a cross-sectional view showing the configuration of the brake caliper shown in FIG. 1; FIG. 4 is a diagram showing the behavior of thrust and electric current when thrust is applied to a piston of a brake caliper that constitutes the electric parking brake device; FIG. 2 is a block diagram of a control model of the electric parking brake device; FIG. 4 is a diagram showing electrical characteristics of a transient current, a voltage between motor terminals, and an inductance voltage drop when an electric motor is started. Control block diagram of model parameters. Waveform diagram of model parameter estimation operation. 4 is a flowchart for explaining the operation of electronic control means; 1 is a diagram showing an electric parking brake device according to Embodiment 1 of the present invention; FIG. The figure which shows the time-series change of a voltage, an electric current, and a thrust. FIG. 4 is a diagram showing time-series changes in voltage, applied torque, and thrust; FIG. 4 is a diagram showing the relationship between the free-running start voltage and the torque constant Kt; FIG. 4 is a diagram showing the relationship between the free-running start current and the torque constant Kt; 4 is a diagram showing the relationship between temperature and torque constant Kt. FIG. FIG. 4 is a diagram showing the relationship between mechanical efficiency and torque constant Kt; 4 is a diagram showing the relationship between pad stiffness D and torque constant Kt. FIG. 4 is a flow showing an example of a series of processing contents in a torque constant Kt corrector; The figure which shows the mode of the motor torque fluctuation of the area which does not generate|occur|produce thrust. 4 is a diagram showing the relationship between temperature and torque constant Kt. FIG. FIG. 4 is a diagram showing the relationship between the free-running start voltage and the torque constant Kt; The figure which shows correspondence by the release side. The control block diagram of the model parameter which concerns on Example 3 of this invention. FIG. 11 is a waveform diagram of a model parameter estimation operation according to the third embodiment of the present invention;

An embodiment of an electric parking brake device according to the present invention will be described below with reference to the drawings. It should be noted that the present invention is not limited to the following examples, and includes various modifications and application examples within the technical concept of the present invention.

The electric parking brake device according to the present invention, which will be described below, obtains an appropriate tightening force according to the load of the electric motor. 1 and a second embodiment in which an appropriate tightening force is determined from information on sections in which thrust is not generated. Moreover, the basic apparatus configuration of the present invention has many parts in common between the first embodiment and the second embodiment.

For this reason, in Embodiment 1, after explaining the basic device configuration of the electric parking brake device according to the present invention and the analysis of events during parking brake control, an appropriate tightening force is determined from information on the thrust generation interval. In the second embodiment, while omitting the explanation of the common basic device configuration while leaving the necessary parts, it will be done in the order of explaining how to determine the appropriate tightening force from the information of the section in which the thrust is not generated. . Further, in Example 3, a further modified example will be described.

Embodiment 1 relates to a method of determining an appropriate tightening force from information on a thrust generation section when obtaining an appropriate tightening force according to the load of an electric motor.

In the following description, the basic device configuration of the electric parking brake system according to the present invention and the analysis of events during parking brake control will be explained using FIGS. The principle of operation and description of Example 1 are provided in FIG. 9 et seq.

First, the basic device configuration of the electric parking brake device according to the present invention will be described with reference to FIGS. 1 to 3. FIG. FIG. 1 is a general configuration diagram of an electric parking brake device according to Embodiment 1 of the present invention, and FIG. 2 is a sectional view showing the configuration of the brake caliper shown in FIG.

An electric parking brake device is composed of an electric motor, a speed reduction mechanism, a rotation/linear conversion mechanism, a piston, a brake pad, and electronic control means.

1 and 2, a brake caliper 10 constituting an electric parking brake device includes a caliper body 11 forming an outer shell and a hydraulic chamber 12 provided inside the caliper body 11 . A piston 13 is arranged in the hydraulic chamber 12 and has a function of driving a first brake pad 14 . A second brake pad 15 is attached to one end of the caliper body 11, and a disk rotor 16 fixed to the axle is arranged between the first brake pad 14 and the second brake pad 15. ing. The disk rotor 16 is sandwiched between the first brake pad 14 and the second brake pad 15 to be braked.

The piston 13 arranged in the hydraulic chamber 12 is driven by the hydraulic pressure from the hydraulic system MB, and is connected to the hydraulic pipe 34 from the booster 33, and the thrust to the piston 13 is also applied by the operation of the brake pedal 17. is a structure in which When the brake pedal 17 is operated during normal running, hydraulic pressure is supplied to the hydraulic chamber 12 to move the piston 13 leftward in FIG. braking operation.

The piston 13 is connected to a reduction mechanism 19 via a rotation/linear conversion mechanism 18 . As shown in FIG. 2, the rotation/linear motion conversion mechanism 18 uses a sliding screw, and includes a rotating shaft 20 having a helical threaded surface formed on the outer periphery and a threaded surface of the rotating shaft 20. It is composed of a direct-acting member 21 internally provided with a threaded surface. The direct acting member 21 can be separated from the piston 13 , and the direct acting member 21 can move the piston 13 in the axial direction of the rotating shaft 20 by rotating the rotating shaft 20 .

In this embodiment, the rotation/linear motion converting mechanism 18 is provided with a self-locking function part, and when the rotating shaft 20 is rotated, the linear motion member 21 moves in a linear motion. is stopped, the linear motion member 21 maintains its position even if a force acts on the linear motion member 21 in the linear motion direction. That is, the rotating shaft 20 and the linear motion member 21 have a spiral threaded surface with a lead angle smaller than the friction angle, thereby obtaining a self-locking function. Since this type of rotation/linear conversion mechanism using a threaded surface is well known, detailed description thereof will be omitted.

As shown in FIG. 1 , the rotating shaft 20 is fixed to a large-diameter gear 22 of the speed reduction mechanism 19 , and the large-diameter gear 22 meshes with a small-diameter gear 23 . The small diameter gear 23 is rotated by an electric motor 24, and the rotation of the electric motor 24 is transmitted to the small diameter gear 23 and the large diameter gear 22 to reduce the speed. By rotating the large-diameter gear 22 , the rotational torque of the electric motor 24 is amplified and transmitted to the rotating shaft 20 .

The supply of electric power to the electric motor 24 is controlled by electronic control means 25 having an electric motor control function section, and the electronic control means 25 comprises a well-known microprocessor 29, an output circuit, and the like. As shown in FIG. 1, the electronic control means 25 controls a relay 27 for energizing/interrupting the battery 26, an H-bridge circuit 28 for applying voltage to the electric motor 24, and various circuit elements (not shown). a power supply voltage monitor circuit 37; a current monitor circuit 30 for detecting the current flowing through the electric motor 24; It is composed of a monitor circuit 31 and a voltage monitor circuit 32 of the motor terminal b.

The output signal of the current monitor circuit 30 is input to the microprocessor 29 as a motor current detection value 30S. The voltage detection values 31S and 32S of the voltage monitor circuits 31 and 32 are input to the microprocessor 29, and the differential voltage between the voltage detection values 31S and 32S becomes the voltage V between the terminals of the motor. The voltage V between the terminals of the motor may be obtained by directly detecting a differential voltage between the terminals of the motor.

When the vehicle is parked or stopped, a motor drive stop signal 28S is output from the electronic control means 25 to the H bridge circuit 28, and the electric motor 24 is energized through the H bridge circuit 28 to drive the electric motor 24. rotates the rotary shaft 20 via the gears 23 and 22 of the speed reduction mechanism 19 . When the rotating shaft 20 rotates, the direct acting member 21 and the piston 13 move to the left to press the brake pad 14 against the disk rotor 16 with a predetermined thrust (pressing force) to apply braking (parking brake).

Then, the electronic control means 25 stops energization when the current detection value 30S of the electric motor 24 exceeds a predetermined cutoff current threshold I _CUT (=predetermined thrust). When the electric motor 24 is de-energized, the self-locking function portion between the rotating shaft 20 and the direct-acting member 21 maintains this predetermined thrust, and the disk rotor 16 is continuously braked.

FIG. 3 is a diagram showing the behavior of thrust and current during an operation (hereinafter referred to as "apply operation") that applies thrust to the piston 13 of the brake caliper 10 that constitutes the electric parking brake device. In FIG. 3, timing T1 is the start time of voltage application to the electric motor 24, and the voltage is applied to the windings of the electric motor 24 together with the operation command. However, since the electric motor 24 is in a stopped state immediately after the voltage application, the induced voltage is "0" at this time. After that, an inrush current (IR) is generated in which the current increases rapidly according to the time constant of the electrical resistance and inductance.

Immediately before the inrush current (IR) reaches its maximum value, the electric motor 24 starts to rotate, but since the rotation of the electric motor 24 generates an induced voltage, the current increases and then decreases as indicated by the current (ID). On the other hand, after a while, the current value becomes almost constant as indicated by the current (IC) at the timing T2. The period from timing T1 to T2 is a "current decrease section". At this timing T2, the rotational speed of the electric motor 24 also reaches a substantially constant value.

Next, until timing T6, the piston 13 moves in the direction of clamping the disc rotor 16, but the brake pads 14 and 15 are not yet in contact with the disc rotor 16 and no clamping force is generated. At this time, the thrust force of the piston 13 is "0", and the electric motor load is a relatively small current constant section between timings T2 and T6. Note that this "constant current section" can include a fluctuation state that is allowed for control, and means a section that can be regarded as substantially constant from the control point of view. Therefore, the term "constant current section" is used hereinafter, but it includes a fluctuation state that is allowed from the viewpoint of control. The "decreasing current section" and the "constant current section", that is, the section from timing T1 to T6 are idling sections. This imaginary section fluctuates depending on the piston position of the electric parking brake device and the wear state of the brake pad 14, and there is an operation mode in which there is almost no "constant current section", and the "current decreasing section" immediately shifts to the "current increasing section". It may transition.

Next, when the brake pads 14 and 15 come into contact with the disc rotor 16 and the constant current section ends (timing T6), thrust is generated in the piston 13 . As the thrust increases, the rotation of the electric motor 24 decreases and the current increases (the torque of the electric motor increases). A section in which the current increases is a "current increase section". In order to stop the driving of the electric motor 24 at the target thrust (F ₁ ), the microprocessor 29 calculates the cutoff current threshold (I _CUT ) from the target thrust (F ₁ ), and determines the actual current value flowing through the electric motor 24 ( detected current value) and a cutoff current threshold (I _CUT ) are compared.

At timing T7, the actual current value exceeds the cutoff current threshold value (I _CUT ), and after confirming that it has definitely exceeded, the voltage application to the electric motor 24 is stopped at timing T8 to cut off the current. Therefore, after timing _T8 , the thrust increases by F1 compared to timing T6. The period from timing T6 to T8 is a clamp section. At this time, at timing T8, the terminals of the electric motor 24 are short-circuited (brake operation) in order to prevent the rotor from continuing to rotate due to the inertia of the electric motor 24 .

When the clamp section ends and no voltage is applied to the electric motor 24, the target thrust _force F1 is maintained. This prevents the electric motor 24 from rotating even if it is pushed from the piston 13 side by using the rotation/linear motion conversion mechanism 18 with reverse action (low reverse efficiency). After this timing T8, it becomes a thrust holding section.

As explained above, it can be understood that the holding thrust (≈target thrust F ₁ ) in the thrust holding section is controlled by the cutoff current threshold (I _CUT ). Here, the relationship between the cut-off current threshold and the holding thrust varies depending on factors such as temperature, individual hardware differences, and voltage. A minimum holding thrust must be guaranteed.

If the holding thrust falls below the minimum guaranteed thrust, the vehicle parked on the slope may start to move on its own. To prevent this, the holding thrust is calculated under many assumed conditions, and the cutoff current threshold is determined so that the minimum value in the dispersion distribution of the holding thrust exceeds the minimum guaranteed thrust. On the other hand, the maximum value may generate more thrust than necessary depending on the individual with good mechanical efficiency and motor characteristics, so excessive stress is applied to the mechanical system of the electric parking brake device, which is a factor in reducing durability.

Therefore, it is necessary to suppress excessive variations in the holding thrust toward the upper limit side while ensuring the minimum guaranteed thrust. In other words, if the thrust can be accurately estimated, the actual thrust can be adjusted between the minimum guaranteed thrust and the allowable upper limit thrust, which is the allowable upper limit. For this purpose, it is important to obtain the model parameters of the thrust estimation model with high accuracy. Moreover, since the relationship between the cut-off current threshold and the holding thrust is affected by temperature and the like, it is important to obtain the model parameters of the thrust estimation model each time.

The basic device configuration of the electric parking brake device according to the present invention has been described above with reference to FIGS. 1 to 3 . Next, using a model to analyze events during parking brake control will be described with reference to FIGS. 4 to 7. FIG.

FIG. 4 is a block diagram of a control model of the electric parking brake system. The control model mainly consists of components such as a battery 26, a master cylinder 35, a microprocessor 29 and an electronic control means 25 including peripheral circuits, a harness 36, an electric motor 24, and a brake caliper 10. FIG. Describing the main connection relationships and input/output signals of these components, the microprocessor 29 controls the switches ( relay, etc.) to turn on/off the voltage output of the battery 26 .

The applied voltage is applied to the electric motor 24 through the harness 36 to drive the electric motor 24 to rotate. Rotational torque generated by the electric motor 24 is input to the brake caliper 10. In the brake caliper 10, the input rotational torque of the electric motor 24 is amplified by the speed reduction mechanism 19, and transmitted through the rotation/linear motion conversion mechanism 18. A thrust force is output to the piston 13 . The brake caliper 10 is also given hydraulic action by the master cylinder 35 .

Then, a motion equation and a voltage equation can be derived for such a control model. Here, based on the main elements expressing the operation of the electric parking brake system described above, the following equations of motion and voltage equations were derived.

First, the equations of motion in the clamped section from timing T6 to timing T8 shown in FIG. 3 are represented by equations (1) and (2).

Here, in the formula (1), "Jdω/dt" is the inertia resistance, "J" is the inertia coefficient, "Kt" is the torque constant, "I" is the current, "η" is the viscosity coefficient, and "ω" is the rotation Speed, “T _frc ” is the total friction torque from the electric motor 24 to the rotation/linear motion conversion mechanism 18 of the power transmission mechanism, and “T _CLP ” is the torque conversion value of the thrust force. At least one of the viscosity coefficient "η", the torque constant "Kt", and the friction torque "T _frc " is a model parameter for estimating the thrust to be obtained in this embodiment.

Further, "K _B " in the formula (1) corresponds to the rotation/linear motion conversion efficiency of the rotation/linear motion conversion mechanism 18, which is caused by the total friction coefficient generated in the rotation/linear motion conversion mechanism 18 in the clamping section. . Note that this "K _B " is set to an arbitrary value from the operation at the time of applying in this embodiment. For example, it can be set using design values. Alternatively, an empirically obtained value may be input. However, as shown below, "T _CLP " corresponding to the thrust is "0" in the idling section, so when estimating the model parameters (viscosity coefficient, torque constant, friction torque) in the idling section, " K _B ” can be ignored.

Also, in the equation (2), "F _CLP " is the thrust applied to the piston 13, and "K" is the torque/thrust force conversion coefficient in rotation/linear motion conversion. Therefore, the torque conversion value "T _CLP " can be obtained by multiplying the thrust "F _CLP " by the torque/thrust conversion coefficient "K". Here, the torque/thrust force conversion coefficient "K" can also be determined from the lead of the structure of the rotation/linear motion conversion unit and the speed reduction ratio of the speed reducer.

Also, the voltage equation of the electric motor is expressed as in Equation (3).

Here, in the equation (3), "V" is the voltage between the motor terminals, "R" is the winding resistance (including harness resistance), and "L" is the inductance.

Next, parameter estimation and thrust calculation based on these motion equations and voltage equations will be described. The equations (1) and (3) of the electric parking brake system described above contain unknown parameters. Then, when the voltage equation of the equation (3) is arranged in this, the right side of the voltage equation consists of three terms: the resistance voltage drop (RI), the inductance voltage drop (LdI/dt), and the induced voltage (Kt·ω). , all of which contain unknown coefficients and unknown variables, it is difficult to solve them strictly.

Here, the electrical characteristics of the transient current when the electric motor 24 is started, the voltage between the motor terminals, and the inductance voltage drop will be described with reference to FIG. FIG. 5 is a diagram for explaining the current, the voltage across the motor terminals, and the inductance voltage drop when the electric motor according to the first embodiment of the present invention is started.

Focusing on the electrical characteristics of the transient current when the electric motor 24 is started, the voltage between the motor terminals, and the inductance voltage drop, it has been found that the inductance voltage drop and the induced voltage can be omitted. As shown in FIG. 5, the inductance voltage reaches a peak at the same time as the electric motor 24 is energized. However, the inductance voltage decreases rapidly within several milliseconds and reaches its maximum value when the inductance voltage reaches its maximum value. It's becoming In addition, since the electric motor gradually increases its rotational speed from a stopped state, the induced voltage (voltage between motor terminals) is relatively small for a period of several milliseconds immediately after starting.

From these facts, when the electric motor 24 is started, that is, when the apply operation is started, in the voltage equation shown in the equation (3), the inductance voltage drop (LdI/dt) and the induced voltage (Kt·ω) If the term can be ignored, the electrical resistance (R) can be approximated as shown in the following equation (4).

Next, a model parameter estimation method will be described with reference to FIGS. 6 and 7. FIG. FIG. 6 is a control block diagram of the model parameters, and FIG. 7 is a waveform diagram of the estimation operation of the model parameters. The same reference numerals as in FIG. 1 indicate the same operations.

A control block 100 implemented in the microprocessor 29 includes a model parameter estimator 110 , a drive controller 130 for controlling motor drive signals, and a motor stop determiner 120 .

When a voltage is applied to the windings of the electric motor 24 by the electric motor 24 operation command (T1), an inrush current (IR) is generated in which the current increases rapidly according to the time constant of the electric resistance and the inductance. The model parameter estimator 110 detects and holds the motor current I(T2) at an arbitrary timing (T2) when the current of the electric motor 24 increases in the idling section. The no-load current _INL holds the current value immediately before the timing (T6) when the current increases. After that, the motor stop determiner 120 outputs a free-run request FRcmd to stop energization of the electric motor to the drive controller 130, and the drive controller 130 outputs a motor drive stop signal 28S to the H bridge circuit 28 to stop the electric motor. inertia rotation. In the free-running section, the back electromotive force E of the motor is generated in the terminal voltage of the motor, so the back electromotive force E (T3) of the motor is detected at T3.

Here, the potential difference between the motor terminal voltage V(T2) at timing T2 and the back electromotive force E(T3) at timing T3 is the voltage drop (V(T2)- E(T3)), and by dividing by the motor current I(T2) at timing T2, the motor winding resistance R can be derived and used for parameter calculation.

Timing T4 is an arbitrary timing during the inertial rotation of the electric motor, and derives the torque constant Kt and the like. After deriving the model parameters, energization of the motor is resumed at timing T5. The time interval from timing T2 to T5 can be set arbitrarily. In the inertia rotation of the electric motor, the motor rotation speed is reduced by the amount of speed reduction due to the viscosity coefficient η of the electric motor 24 and the speed reduction mechanism 19, the friction torque T _frc , and the motor load. After the energization of the electric motor 24 is stopped, the back electromotive force E (T4) of the motor is also detected at a timing (T4) after a predetermined time has elapsed. It is preferable to set the number of times of sampling in consideration of the filter circuit time constants of the voltage monitor circuits 31 and 32 and the like.

Here, the current of the electric motor 24 is detected at least at the timing (T2) before coasting when the current is increasing, and the timing at which the back electromotive force E is generated during coasting when the energization of the electric motor 24 is stopped. At (T3), the terminal voltage of the electric motor 24 is detected at an arbitrary timing (T4) when the rotation speed of the electric motor 24 decreases. These terminal voltages of the electric motor 24 are detected during normal parking brake operation (the electric motor 24 drives the piston and the brake pad presses the disk rotor).

Here, the model parameter estimation calculation formula is obtained by multiplying both sides of the formula (1) by the torque constant Kt to obtain the formula (6). The suffixes of the back electromotive force E, the motor current I, and the motor rotation speed ω indicate the respective held values at each timing. In order to obtain the formula (6), the motor load T _L is expressed by the formula (5) by combining the load torque T _load (KB·T _CLP ), the friction torque T _frc and the viscous torque _ηω (t).

Also, the formula (7) is obtained from the formulas (1) and (5).

Since the change in the rotation speed of the electric motor 24 during the coasting period is relatively monotonic, the torque constant Kt of equation (8) is obtained. In order to obtain the equation (8), in order to express the speed ω with the back electromotive force E, both sides of the equation (7) are multiplied by the torque constant _KT to replace the equation (6). E(t1)/tz indicates the voltage slope average value.

When the electric motor is inertially rotating, the change in back electromotive force is negative, and the difference in the back electromotive force at each timing is generally equal because the deceleration rate of the motor is assumed to be substantially constant.

A cut-off current threshold _ICUT is calculated from the equation (9) using each model parameter derived using the free-run period and the target torque _Tcmd converted into _a torque value from the target thrust force F1. Note that the motor rotational speed ω is calculated using the result obtained by setting Ldi/dt≈0 in the equation (3), and the cutoff current threshold _ICUT is repeatedly calculated until the application is completed.

Model parameters that can be finally estimated include the torque constant Kt and the loss torque (viscosity coefficient η, friction torque T _frc ), which increases the estimation accuracy.

After that, the clamping force is generated at timing T6, the detected current value of the electric motor 24 increases, and the current value reaches the cut-off current threshold _ICUT calculated at timing T7. When the detected current value of the electric motor 24 exceeds the cut-off current threshold _ICUT (T8), the current is cut off. In the first embodiment, the series of operations described above are executed each time the electric parking brake device operates.

According to the results of event analysis during parking brake control using the model described with reference to FIGS. 4 to 7, the electronic control means 25 of FIG. 1 should operate as follows.

Next, the operation of the electronic control means 25 will be collectively described with reference to FIG. FIG. 8 is a flow chart for explaining the operation of the electronic control means reflecting the above analysis results. Here, an example is shown in which it is determined whether the terminal voltage of the electric motor 24 has crossed zero at timing T4. In addition, in the present invention, it is proposed that the torque coefficient should be further corrected because the correspondence shown in FIG. 8 is insufficient.

In FIG. 8, when the electronic control means 25 is activated (started), it is determined whether or not there is an operation command for the electric parking brake device (PB) (processing step S101).

This operation is repeated when the electric parking brake device is not operating. If there is an operation command for the electric parking brake device, the electric motor 24 is started to be energized (S102).

After a predetermined period of time has passed since the start of energization of the electric motor 24, it is determined whether or not a predetermined current value (for example, 4 A to 11 A) has been reached (processing step S103). If the current has not reached the predetermined current, this operation is repeated.

The terminal voltage/current of the electric motor 24 is detected at the timing T2 when the rotation speed of the electric motor 24 is stabilized (S104).

When the number of revolutions of the electric motor 24 is stabilized, the energization of the electric motor 24 is stopped, and the terminal voltage of the electric motor 24 is detected at the stop timing T3 (processing step S105). The electric motor 24 coasts.

After a predetermined time has elapsed, the terminal voltage of the electric motor 24 is detected at timing T4, and it is determined whether or not the voltage has crossed zero (processing step S106). This operation is repeated when the voltage does not cross zero. When the voltage crosses zero, the electric motor 24 is re-energized (processing step S107).

On the other hand, the winding resistance R of the electric motor 24 can also be calculated from the terminal voltage/current of the electric motor 24 detected at timings T2 and T3 (processing step S201). Also, model parameters of torque constant Kt and loss torque (viscosity coefficient η, friction torque T _frc ) are calculated from the terminal voltage of the electric motor 24 at timing T4 (processing step S202).

A cutoff current threshold is calculated from the electric resistance R and model parameters and set (processing step S203).

After restarting the energization of the electric motor 24 (processing step S107), it is determined whether or not the detected current value has reached the cutoff current threshold set in processing step S203 (processing step S108). If the detected current value has not reached the cutoff current threshold, this operation is repeated.

When the detected current value reaches the cutoff current threshold, the energization of the electric motor 24 is stopped (processing step S109).

In this way, the electric parking brake system estimates the model parameters during normal operation and calculates the cutoff current threshold.

In the above example, a cut-off current threshold calculation model for controlling the thrust force of the piston is provided, a free-run section is provided in a section where the load torque T _load of the electric motor increases, and at least a voltage value and a current value applied to the electric motor are provided. is detected a plurality of times, a predetermined estimation operation is performed using the plurality of voltage values and current values, a model parameter used in the cutoff current threshold calculation unit is estimated, and the model parameter is used to cut The configuration is such that the OFF current threshold value is calculated. Moreover, these operations are executed each time the electric parking brake device operates.

According to the above example, the free run section is provided in the section where the load torque T _load is generated, and the model parameters of the cutoff current threshold calculation section can be reliably estimated and calculated. An accurate cutoff current threshold estimate can be made.

In the above example, the model parameters can be reliably estimated and calculated even in a section in which the load torque T _load is generated and the motor current increases. Since the back electromotive force E (T4) of the motor is detected even at the timing (T4) after a predetermined time has elapsed after stopping, the torque constant Kt, the viscosity coefficient η, and the friction torque T _frc are calculated based on the detection results. , the cut-off current threshold is set, it is possible to provide an electric parking brake device that can be operated with an appropriate tightening force. In addition, since the rotation speed information from the rotation sensor is not used for estimating these model parameters, the rotation sensor can be omitted. Furthermore, since the estimation of these model parameters is executed each time the electric parking brake device is operated, the wear of the brake pads, aging of the rotation/linear motion conversion mechanism, speed reduction mechanism, etc., temperature changes, etc. It is possible to provide an electric parking brake device that can accurately detect a change in torque constant and that can operate with an appropriate tightening force.

In the above description, a case has been described in which the motor energization stop (free run) state is generated once in the interval in which the load torque T _load is generated after the motor is driven and the motor current increases. It can also be generated multiple times and repeatedly detected to improve detection accuracy.

In the above, the premises of the present invention have been generally explained. However, in the present invention, it is considered that only estimating the model parameters is insufficient, so the reason for this will be explained below.

First, the operation of the electric parking brake device is very simple as described above. When the motor is energized, rotational torque is generated, the torque is increased by the reduction gear, and the rotational torque is converted into thrust by the rotary linear motion mechanism. When the piston pushes the pad to generate thrust, and when the current threshold is reached, the motor is turned off, the thrust is maintained by the self-locking function of rotation, and when the voltage is reversed, the thrust is released. In this case, there is a problem that the thrust varies.

In mechanical systems, the causes of thrust force variation are individual differences, viscous resistance due to temperature, frictional resistance, etc. In electrical systems, magnetic flux (torque constant), motor resistance due to temperature, etc. are thought to be the causes, and even if the current threshold is the same, thrust differs.

However, in the electric parking brake system, the minimum guaranteed thrust increases, which increases the range of variation in the thrust and generates an excessive thrust. A more accurate estimation of thrust is desired because this thrust causes excessive force on the brake mechanism components, requires a durability margin, and increases cost.

These parameters need to be estimated in order to reduce costs and reduce thrust variations, and the present invention focused on estimating the torque constant. Note that the cited document does not pay attention to the problem that the torque constant estimation accuracy decreases when the motor load torque fluctuates in the de-energization section for estimating the model parameters such as the torque constant. Merely installing the model parameter estimator 110 shown in FIG. 6 cannot cope with thrust variations.

FIG. 9 is a diagram showing an electric parking brake device 25 according to Embodiment 1 of the present invention. Compared to the basic configuration of FIG. 6, the only difference is that a torque constant Kt corrector 150 is added. Therefore, in the following description, the concept and operation of the added torque constant Kt corrector 150 will be described.

The model parameter estimator 110 shown in FIGS. 6 and 9 performs analysis focusing on the equation of motion in the clamped interval from timing T6 to timing T8 shown in FIG. On the other hand, the torque constant Kt corrector 150 in FIG. 9 focuses on the equation of motion of the motor when the disc pad is in contact. However, piston sliding resistance and O-ring resistance are ignored.

FIG. 10 shows time-series changes in voltage, current, and thrust from the top. Solving the equation of motion of the motor will be described using this diagram. In FIG. 10, note that the voltage value E1 at time t0 immediately before free-running, the voltage value E2 at time t1 immediately after free-running, and the current I(t1) at time t1 immediately after free-running are zero. In FIG. 10, the thrust after coasting is equal to or higher than the minimum guaranteed thrust, and although it is desired to be stable, it actually fluctuates.

An equation of motion of the motor can be expressed by Equation (10) using load torque TLoad, friction torque Tfirc, viscous torque λω (λ: viscosity coefficient, ω: motor rotation speed), and motor friction torque Tm. In addition, explanation may be omitted about the already explained symbol.

In equation (10), if the sum of load torque TLoad, friction torque Tfirc, viscous torque λω (λ: viscosity coefficient, ω: motor rotation speed), and motor friction torque Tm is total torque TL, equation (11) can be obtained. .

Although the equation (11) is expressed by the motor rotation speed ω, it can be expressed by the equation (12) using the voltage value E1 at the time t0 immediately before the coasting.

Further, since I(t1)=0 at time t1 immediately after the free run, equation (11) can be expressed by equation (13).

Furthermore, since the total torques TL(t0) and TL(t1) at times t0 and t1 are the same in equations (12) and (13), the torque constant Kt can be obtained by equation (14).

The torque constant Kt can be obtained by executing the formula (14) according to the above idea, but as a practical matter, the voltage When the torque constant Kt is calculated using the variation ΔE(t1), the pad still operates with respect to the voltage variation dE(t1)/dt in the theoretical formula, so the thrust force variation ΔF occurs. The thrust force fluctuation ΔF acts on the motor shaft via the rotation/linear motion conversion mechanism and the speed reducer.

When calculating the estimated value K _t ^e and the true value K _t ^r of the torque constant Kt in this case, the equation (15) is obtained by substituting the equation (13) into the equation (10). Note that Tl is the total torque of the load torque due to the thrust force, the viscosity torque due to the viscosity of the oil, and the friction torque. Further, when calculating with the voltage variation ΔE(t1), the equation (16) is obtained.

From the relationship between the estimated value _Kt ^e and the true value _Ktr of the torque constant ^Kt , the following can be said. First, the main factors of the torque constant Kt estimation error in the thrust generation section are: A: Thrust torque change due to free-run start voltage/current difference, B: Viscous torque change due to temperature change, C: Thrust torque change due to mechanical efficiency change, D: Change in thrust torque due to pad stiffness.

Further, the relationship between each torque constant Kt estimation error factor and the error is as follows.

Free-running start voltage A1: As the free-running start voltage increases, the motor rotation speed increases and the advance amount of the pad increases, so the thrust force fluctuation ΔF increases and the load torque fluctuation ΔTL also increases. As a result, the torque constant Kt is estimated to be large from the equation (16). FIG. 12 shows the relationship between the free-run start voltage and the torque constant Kt.

Free-run start current A2: As the free-run start current increases, the motor rotation speed decreases and the advance amount of the pad decreases, so the thrust force fluctuation ΔF and the load torque fluctuation ΔTL also decrease. As a result, the torque constant Kt is estimated to be small from the equation (16). FIG. 13 shows the relationship between the free-run start current and the torque constant Kt.

Temperature B: The lower the temperature, the higher the viscous torque. Since the motor rotation speed is reduced and the advance amount of the pad is also reduced, the thrust force fluctuation ΔF is reduced and the load torque fluctuation ΔTL is also reduced. As a result, the torque constant Kt is estimated to be small from the equation (16). FIG. 14 shows the relationship between temperature and torque constant Kt.

Mechanical efficiency C: As the mechanical efficiency decreases, the thrust decreases, so the thrust fluctuation ΔF also decreases. As a result, the motor load torque fluctuation .DELTA.TL is reduced, and the torque constant Kt is estimated to be small. FIG. 15 shows the relationship between mechanical efficiency and torque constant Kt.

Pad Rigidity D: As the pad stiffness decreases, the motor rotation speed at the start of free running increases, and the thrust force fluctuation ΔF increases. As a result, the motor load torque variation .DELTA.TL increases, and Kt is estimated to be large. FIG. 16 shows the relationship between pad stiffness D and torque constant Kt.

Next, a specific example of correction in the thrust generation section will be described. In simple terms, it is preferable to multiply the inverse function so that the torque constant Kt is constant regardless of the free-running start voltage, as shown in FIG. 12, for example.

Concretely, for example, in the case of correcting for free-run start voltage/current and temperature, for example, for the correcting method for voltage/current, the correction coefficient is calculated by the ratio of the torque constant Kt true value and the estimated value under each condition. , a two-dimensional correction map is created using correction coefficients for each condition corresponding to the free-run start voltage and current, and the torque constant Kt is corrected using the voltage/current correction map.

Regarding the temperature correction, the temperature equivalent value is calculated from the current slope di/dt/V for each condition, the temperature change rate (relative temperature) is calculated from the ratio between the current temperature and the previous temperature, and the torque constant Kt is calculated under each condition. It is preferable to calculate a correction coefficient from the ratio of the value and the estimated value after voltage/current correction, create a correction map from the current temperature and temperature change rate, and correct the torque constant Kt with the temperature correction map. Regarding temperature correction, both temperature and relative temperature were used this time due to repeatability errors. Relative temperature alone can also be corrected if there is no repeat error.

Although the correction of the mechanical efficiency and pad stiffness is not mentioned, if the mechanical efficiency and pad stiffness can be calculated, they can be corrected by the same method.

From the above, the torque constant Kt corrector 150 in FIG. 9 receives the terminal voltage from the voltage monitor circuits 31 and 32 and the current from the current monitor circuit 30, and the built-in characteristics ( It is preferable to calculate the correction coefficient with reference to the current, voltage-torque constant (Kt) and reflect it in the estimation result of the model parameter estimator. Similarly, it is preferable to measure the temperature, calculate the characteristic (temperature-torque constant Kt) in FIG. 14, and reflect it in the estimation result of the model parameter estimator.

FIG. 17 is a flow showing an example of a series of processing contents in the torque constant Kt corrector 150. As shown in FIG. In the flow of FIG. 17, the resistance estimated value is held in the first processing step S301. This means that the calculation result in processing step S201 of FIG. 8 is held. In processing step S302, the temperature is estimated from the current after the occurrence of the rush current.

In processing step S303, completion of the free-run request flag is confirmed, and accordingly, voltage changes (ΔE0/Δt, ΔE1/Δt) immediately before and after the start of free-running are measured and calculated in processing steps S304 and S305. .

In processing step S306, the torque coefficient Kt is calculated, then in processing step S307 a correction coefficient for voltage and current is calculated, in processing step S308 a correction coefficient for temperature is calculated, and finally the torque coefficient Kt is corrected by the correction coefficient. .

When performing correction from multiple viewpoints of the free-running voltage, current, and temperature, there are three methods of correction: correction from individual viewpoints, correction with a representative value that has a large influence, and correction from multiple viewpoints. It is conceivable to perform correction as one value integrating the corrections of , and the present invention may adopt any of them.

As is clear from the above description, the torque constant Kt corrector 150 corrects the torque constant based on the amount of variation of the load torque of the electric motor with respect to time. The load torque variation amount corrects the torque constant based on the voltage and current applied to the motor when the disc pad is in contact.

As is clear from the above description, the torque constant Kt corrector 150 corrects the torque constant based on the amount of variation of the load torque of the electric motor with respect to time. As a result, it is possible to ensure an appropriate tightening force of the electric parking brake device reflecting the state at each time.

The amount of load torque fluctuation is determined based on any one or a combination of the voltage and current applied to the motor, temperature information, pad rigidity, and mechanical efficiency of the speed reducer and rotation mechanism when the disk pad is in contact. , corrected for the torque constant. According to these corrections, it is possible to solve the fluctuation factors that each viewpoint gives to the tightening force of the electric parking brake device for each factor.

According to the electric parking brake device of the first embodiment described above, it is possible to provide an electric parking brake device that can operate with an appropriate tightening force according to the load of the electric motor based on the information on the thrust generation section.

Example 2 corrects the torque coefficient Kt when using the method described in Patent Document 1. FIG. It should be noted that many of the premises of Example 2 are described in Patent Document 1 and are the same as the contents already explained in Example 1, or are within a range that can be easily analogized, so they are not described here. A detailed explanation is omitted.

The configuration of the electric parking brake device is basically the same as the configuration shown in FIG. 9 of the first embodiment. In addition, in the second embodiment, the torque coefficient Kt is obtained by the model parameter estimator 110 from the voltage, current, etc. at this time, in which the power supply to the motor is stopped in a section in which no thrust force is generated. 1 or by applying the method described in Example 1.

In short, including omitted content, Patent Document 1 states that "in a section in which a braking thrust is not generated, energization of the motor is interrupted, an induced voltage is detected, and a torque constant is derived." The torque constant at this time is obtained by the model parameter estimator 110 in FIG.

On the other hand, the torque constant Kt corrector 150 of FIG. 9 for the second embodiment is configured and functions as follows.

FIG. 18 shows how the motor torque fluctuates in a section in which no thrust is generated, and from the top shows the voltage drop, torque, and thrust caused by stopping power supply. In this case, the calculation formula considering the torque change during coasting is expressed by the same formula (16) as described above.

The following can be said from the relationship between the estimated value _Kt ^e of the torque constant ^Kt obtained from the motor torque variation in the section where no thrust is generated and the true value _Ktr . First, the main causes of the torque constant Kt estimation error in the section where thrust is not generated are: E: Viscous torque change due to temperature change, F: Viscous torque change due to motor rotation speed difference (voltage difference) at the start of coasting. .

The relationship between each torque constant Kt estimation error factor and the error in this case is as follows.

Temperature E: The lower the temperature, the greater the viscous torque of the speed reducer. As a result, the motor load torque fluctuation .DELTA.TL increases, and as a result, the torque constant Kt is estimated to be small according to the equation (16). FIG. 19 shows the relationship between temperature and torque constant Kt.

Free-run start voltage F: As the free-run start voltage increases, the motor rotation speed at the start of free-run increases, so the viscous torque increases. As a result, the motor load torque fluctuation .DELTA.TL increases, and as a result, the torque constant Kt is estimated to be small according to the equation (16). FIG. 20 shows the relationship between the free-run start voltage and the torque constant Kt.

In FIG. 18, the apply side is used as the section in which no thrust is generated, and the information at the time of the voltage drop due to the stoppage of energization is used. As a further application of the second embodiment, the release side shown in FIG. is also possible.

Note that the concept of the correction method in the case of the second embodiment can be applied as it is described in the first embodiment, so the description is omitted here.

In embodiment 3, further modifications and embodiments of the present invention will be described with reference to FIGS. 22 and 23. FIG. FIG. 22 is a model parameter control block diagram according to the third embodiment of the present invention, and FIG. 23 is a waveform diagram of the model parameter estimation operation according to the third embodiment of the present invention. In FIGS. 22 and 23, the same reference numerals as in FIGS. 6 and 7 indicate the same operations.

The control block 101 in FIG. 22 further includes a transient model parameter estimator 111 for estimating model parameters in a section in which the current decreases before reaching a constant current section in which the current becomes substantially constant after the electric motor 24 starts to be energized. ing. In the third embodiment, the transient model parameter estimator 111 and the model parameter estimator 110 estimate model parameters such as a torque constant under different operating conditions, and use a plurality of estimated results under different operating conditions to improve the model parameter estimation accuracy. High precision. This point is different from the first embodiment.

The transient model parameter estimator 111 in FIG. 22 detects the voltage and current applied to the electric motor 24 multiple times (sampling Sp1, Sp2, Sp3) in the current decrease section in FIG. is used to obtain the electric resistance (R) at the start of the electric motor 24 from the voltage (V) and the current (I). Further, the induced voltage (ωKt=V−RI) is calculated from the equation (3) when Ldi/dt≈0. Since this induced voltage (ωKt) is estimated in consideration of the influence of temperature change, it is possible to compensate for the change in thrust of the electric motor 24 due to the temperature.

Since the no-load loss torque T _Loss corresponding to the mechanical parameter can be expressed as the sum of the viscous torque (ηω) and the friction torque (T _frc ), the equation (17) is obtained.

When the change in the minute time change is small, the no-load loss torque T _Loss is eliminated by obtaining the difference of two or more samplings Sp1, Sp2, Sp3 (current decrease section) in the equation (17), and the torque constant Kt1 is calculated. Calculate. Here, it may be assumed that the inertia coefficient "J" does not vary, and is input as a known value.

Next, using the model parameter estimator 110 in the constant current section of the idling section, the free running section described with reference to FIG. 23 can be generated to obtain the torque constant Kt2. The motor stop determiner 121 obtains the torque constant Kt with high accuracy by averaging the torque constant Kt1 and the torque constant Kt2, and obtains the target cutoff current threshold (I _CUT ) based on the equation (9). The cut-off current threshold (I _CUT ) is compared with the actual current value to determine that the actual current value exceeds the cut-off current threshold (I _CUT ), and cut off the drive signal 120S that is transmitted to the drive controller 130. demand. In this manner, the electronic control means 25 cuts off the current supplied to the electric motor 24 when the actual current value actually flowing through the electric motor 24 reaches the cutoff current threshold (I _CUT ) to generate thrust. It will shift to the holding section.

In the third embodiment, the accuracy of the torque constant is improved by averaging the torque constant Kt1 and the torque constant Kt2. It is also possible to increase the reliability of the parameter estimation calculation by using any one of the torque constants within the range preset using the torque constant Kt2.

As described above, in the third embodiment, the cut-off current threshold calculation model for controlling the thrust of the piston is provided, and the constant current section in which the current after the inrush current generated when the electric motor is started to be energized is substantially constant. In the current decrease section before reaching , at least the voltage value and current value applied to the electric motor are detected a plurality of times, and a predetermined estimation calculation is performed using the plurality of voltage values and current values. Furthermore, the average value of the results of predetermined estimation calculations in the free run section is obtained, the model parameters used for the cutoff current threshold calculation are estimated, and the cutoff current threshold is calculated using the model parameters. . Moreover, these operations are executed each time the electric parking brake device operates.

According to the third embodiment, it is possible to perform highly accurate model parameter estimation calculations from two operating states, i.e., in the current decreasing section before reaching the constant current section and in the constant current section of the constant current section. It is possible to improve thrust control accuracy based on the off-current threshold. In addition, since the rotation speed information from the rotation sensor is not used for estimating these model parameters, the rotation sensor can be omitted.

Furthermore, since the estimation of these model parameters is executed each time the electric parking brake device is operated, the wear of the brake pads, aging of the rotation/linear motion conversion mechanism, speed reduction mechanism, etc., temperature changes, etc. It is possible to provide an electric parking brake device that can accurately detect a change in torque constant and that can operate with an appropriate tightening force.

According to the present invention described above, it has "an electric motor, a rotation-to-linear motion conversion mechanism that converts the rotary motion of the electric motor into a linear motion, and a disc pad that moves by applying current to the electric motor. A control device for an electric brake, comprising: a cutoff current calculation section for calculating a cutoff current for stopping current to an electric motor; a torque constant calculation section for calculating a torque constant required for calculation of the cutoff current; and an electric motor and a torque constant correction unit that corrects the torque constant in a state in which the electric motor is stopped from being energized after the start of driving." It is possible to provide an electric parking brake device that can operate with an appropriate tightening force according to the load.) can be achieved.

It should be noted that the present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the described configurations. In addition, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Moreover, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

DESCRIPTION OF SYMBOLS 10... Brake caliper 11... Caliper main body 12... Hydraulic chamber 13... Piston 14, 15... Brake pad 16... Disk rotor 17... Brake pedal 18... Rotation/linear motion conversion mechanism 19... Reduction mechanism, 20... Rotating shaft 21... Linear motion member 22... Large gear 23... Small gear 24... Electric motor 25... Electronic control means 26... Battery 27... Relay 28... H bridge circuit 30... Current Monitor circuit 31 Voltage monitor circuit for motor terminal a 32 Voltage monitor circuit for second motor terminal b 35 Master cylinder 36 Harness 37 Power supply voltage monitor circuit 100, 101 Control block 110 Model Parameter estimator 111 Transient model parameter estimator 120 Motor stop determiner 130 Drive controller 150 Torque constant Kt corrector

Claims (13)

An electric parking brake device comprising: an electric motor; a rotation-to-linear motion converting mechanism for converting rotary motion of the electric motor into a linear motion; and a disk pad that moves when current is applied to the electric motor,
a cutoff current calculation unit that calculates a cutoff current that stops the current to the electric motor;
a torque constant calculation unit that calculates a torque constant necessary for calculating the cutoff current;
an electric parking brake device comprising: a torque constant correction unit that corrects the torque constant in a state where the electric motor is stopped from being energized after the electric motor starts to drive. The electric parking brake device according to claim 1,
The torque constant correcting unit corrects the torque constant based on a variation amount of the load torque of the electric motor with respect to time. The electric parking brake device according to claim 2,
The torque constant correction unit corrects the torque constant based on the voltage and current applied to the motor when the disc pad is in contact. The electric parking brake device according to claim 2,
The torque constant correcting unit corrects the torque constant based on temperature information when the disc pad is in contact with the electric parking brake. The electric parking brake device according to claim 2,
The torque constant correcting unit corrects the torque constant based on pad rigidity when the disc pad is in contact with the electric parking brake device. The electric parking brake device according to claim 2,
The torque constant correction unit corrects the torque constant based on the mechanical efficiency of the speed reducer and the rotation mechanism when the disc pad is in contact with the electric parking brake device. The electric parking brake device according to claim 2 ,
The torque constant correction unit corrects the torque constant based on a combination of voltage and current applied to the motor, pad rigidity, and mechanical efficiency of the speed reducer and the rotation mechanism when the disc pad is in contact with the electric parking brake. Device. The electric parking brake device according to claim 2,
The electric parking brake device, wherein the torque constant correction unit corrects the torque constant based on information on temperature and voltage applied to the motor, or a combination thereof, before the disc pad contacts. The electric parking brake device according to claim 2,
The torque constant correcting unit corrects the torque constant after the disc pad is separated based on information on temperature and voltage applied to the motor, or a combination thereof. The electric parking brake device according to claim 2,
A cutoff current threshold of the electric motor is set using the corrected torque constant, and energization of the electric motor is stopped when the current of the electric motor exceeds the cutoff current threshold. electric parking brake device. The electric parking brake device according to claim 1 ,
An electric parking brake device according to claim 1, wherein a state in which the electric motor is de-energized after the electric motor starts driving is within a period in which no thrust is generated to the disc pad. The electric parking brake device according to claim 1 ,
An electric parking brake device according to claim 1, wherein after the electric motor starts to be driven, a state in which the electric motor is de-energized is within a period in which a thrust to the disc pad is generated. An electric parking brake device comprising: an electric motor; a rotation-to-linear motion converting mechanism for converting rotary motion of the electric motor into a linear motion; and a disk pad that moves when current is applied to the electric motor,
The torque constant determined from the equation of motion of the energized section of the electric motor is corrected by the torque constant determined from the equation of motion of the motor when the disk pad is in contact, and the torque constant after correction is used to stop the current to the electric motor. An electric parking brake device that calculates an off current.

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