JP7491706B2 - Brake system - Google Patents

Description

The present invention relates to a brake device, and in particular to technology that uses an electric parking brake mechanism.

The mainstream foot brake system for automobiles works by using engine vacuum and the power of an electric brake booster to increase brake fluid pressure when the brake pedal is depressed, and then pressing the brake rotor attached to the wheel axle with the brake pads to ensure the vehicle's braking force.
On the other hand, parking brakes (side brakes) have a mechanism in which the driver pulls a side brake lever to press pads directly against the brake rotor via a wire piston, thereby locking the wheels when parking, etc.

Recently, electric parking brakes (EPBs) have also become popular. When the driver presses the EPB button, the EPB motor attached to the brake caliper is activated, and the pads are pressed directly against the brake rotor, locking the wheels.

As is commonly known, there are cases where the foot brake does not work.
The foot brake as described above ensures braking force by utilizing the brake fluid pressure that fills the brake fluid piping. For this reason, for example, if the foot brake is used continuously while going downhill or accelerating and decelerating rapidly, the brake rotor will overheat and the brake fluid will vaporize, making it impossible to ensure hydraulic pressure, and therefore no braking force will be obtained even if the foot brake is applied (vapor lock phenomenon). Also, if the brake booster breaks down or engine negative pressure cannot be secured, sufficient braking force will not be obtained.
It is necessary to be able to brake in such cases, and for example, Patent Document 1 listed below discloses a technology in which, when a hydraulic brake fades, braking is achieved using an electric brake such as an electric parking brake mechanism in accordance with the amount of reduction in braking force.

JP 2008-174114 A

Currently, most EPB systems allow the EPB to be forcibly activated by pressing and holding the EPB button even while the vehicle is moving, allowing the vehicle to be braked as an emergency measure in the event that the foot brake fails to function as described above.
However, the fact that the EPB can be forcibly operated even while the vehicle is moving is not generally recognized, and it is thought that drivers are often unable to use the EPB to brake the vehicle in an emergency when the normal brakes (foot brakes) stop functioning for some reason.
Even if the driver knows that the EPB can secure braking force in an emergency, it is difficult to operate the EPB (press and hold the button) in an instant to apply emergency braking force when the foot brake does not function while driving. In addition, the emergency braking control by the EPB is generally inferior to the braking performance of a normal foot brake, so it is desirable for the driver to repair it as soon as possible.
Therefore, an object of the present invention is to enable braking using the EPB to be properly performed, and to notify the driver that emergency braking using the EPB is in an abnormal state, thereby urging the driver to have it repaired promptly.

A brake device according to one embodiment of the present invention includes a stroke sensor that detects the amount of depression of a brake pedal for a foot brake, a parking brake motor that performs braking by an electric parking brake mechanism, a foot brake abnormality detection unit that detects an abnormality in the foot brake mechanism, a required braking force calculation unit that calculates a required braking force in accordance with the detection value of the stroke sensor when an abnormality is detected by the foot brake abnormality detection unit, a motor torque calculation unit that calculates the torque of the parking brake motor in accordance with the required braking force calculated by the required braking force calculation unit, and a first logic unit that sets a braking force pattern in which the braking force varies while in accordance with the required braking force calculated by the required braking force calculation unit . That is, in the control of the electric parking brake mechanism, when a foot brake abnormality is detected by a hydraulic mechanism, an electric parking brake (EPB) is operated in accordance with the detection value of the stroke sensor of the brake pedal, i.e., the required braking force.
The first logic unit sets either a first braking force pattern or a second braking force pattern different from the first braking force pattern depending on the required braking force calculated by the required braking force calculation unit, and the motor torque calculation unit calculates a torque depending on the braking force pattern set by the first logic unit.
That is, instead of performing EPB control so as to apply a braking force that simply corresponds to the required braking force, braking is applied such that the braking force varies, for example, periodically while corresponding to the required braking force.

Moreover, a brake device according to one embodiment of the present invention includes a stroke sensor that detects the amount of depression of a brake pedal for a foot brake, a parking brake motor that performs braking by an electric parking brake mechanism, a foot brake abnormality detection unit that detects an abnormality in the foot brake mechanism, a required braking force calculation unit that calculates a required braking force in accordance with the detection value of the stroke sensor when an abnormality is detected by the foot brake abnormality detection unit, a motor torque calculation unit that calculates a torque of the parking brake motor in accordance with the required braking force calculated by the required braking force calculation unit, and a first logic unit that sets a braking force pattern in which the braking force varies in accordance with the required braking force calculated by the required braking force calculation unit, wherein the first logic unit sets either a first braking force pattern or a second braking force pattern different from the first braking force pattern in accordance with the required braking force calculated by the required braking force calculation unit, and the motor torque calculation unit calculates a torque in accordance with the braking force pattern set by the first logic unit.

In the above-mentioned brake device, the first braking force pattern is a braking force pattern in which a braking force lower than the required braking force periodically becomes a braking force higher than the required braking force, and the second braking force pattern is a braking force pattern in which a braking force higher than the required braking force periodically becomes a braking force lower than the required braking force, and the first logic unit is considered to set either the first braking force pattern or the second braking force pattern depending on a result of comparing the required braking force calculated by the required braking force calculation unit with a threshold value.
For example, the braking can be applied in such a way that the driver feels a periodic pulsation.

In the above-mentioned brake device, the first logic unit may determine switching from the first braking force pattern to the second braking force pattern in response to an increase in the required braking force using a first switching threshold, and may determine switching from the second braking force pattern to the first braking force pattern in response to a decrease in the required braking force using a second switching threshold corresponding to a braking force lower than the first switching threshold.
That is, different threshold values are used when switching the braking force pattern depending on whether the braking force is increasing or decreasing.

The above-mentioned brake device is equipped with a first logic unit that sets a braking force pattern in which the braking force varies in accordance with the required braking force calculated by the required braking force calculation unit, and a second logic unit that sets a braking force pattern for sudden braking, and it is considered that the motor torque calculation unit calculates a motor torque in accordance with the braking force pattern set by either the first logic unit or the second logic unit.
For example, when the driver strongly depresses the brake pedal to apply sudden braking, sudden braking is performed using a braking force pattern determined by the second logic unit, and in other cases, the braking force pattern determined by the first logic unit is used.

In the above-described brake device, it is considered that the electric parking brake mechanism is structured to generate abnormal noise when braking while the vehicle is traveling.
When braking is applied by the EPB, no noise is generated if the vehicle is stopped, but a mechanism is provided that generates an abnormal noise (for example, a sound different from the normal sound caused by friction of pads) when the vehicle is moving.

According to the present invention, by automatically activating the EPB when the foot brake does not operate, it is possible to ensure emergency vehicle braking force and avoid the risk of collisions. In addition, because the EPB is operated to apply braking force according to the braking force required by the driver's operation of the brake pedal, it is possible to generate braking force appropriate to the situation.

1 is an explanatory diagram of a configuration of a brake device according to an embodiment of the present invention; FIG. 4 is an explanatory diagram of a case where the EPB is automatically activated in the brake device according to the embodiment. FIG. 2 is an explanatory diagram of a functional configuration of an EPB control unit according to an embodiment. FIG. 4 is an explanatory diagram of a braking force pattern according to the embodiment. 5 is an explanatory diagram of switching of braking force patterns according to an embodiment. FIG. FIG. 11 is an explanatory diagram of an offset of a braking force pattern according to an embodiment. 4 is a flowchart of a process of an EPB control unit according to an embodiment.

<1. Device configuration>
The brake device according to the embodiment will be described below.
The brake device of the embodiment can be applied to a vehicle that employs an EPB system, and drives the EPB motor in response to brake pedal operation as a fail-safe (F/S) in the event that the foot brake does not work. This ensures emergency braking force.

FIG. 1 shows the configuration of a brake device according to an embodiment of the present invention.
FIG. 1 shows a brake pedal 1, a stroke sensor 2, a brake booster 3, a brake pipe 4, a fluid chamber 5, a brake pad mechanism 6, an EPB motor 7, an EPB pad mechanism 8, a brake rotor 9, an EPB button 10, an EPB control unit 11, and a sensor 12.

The foot brake mechanism of this embodiment includes a brake pedal 1 , a brake booster 3 , brake piping 4 , a hydraulic mechanism having a brake fluid chamber 5 , and a brake pad mechanism 6 that presses a pad 6 a against a brake disc 9 .
In this foot brake mechanism, hydraulic pressure according to the amount of depression of the brake pedal 1 is applied to a brake pad mechanism 6, which presses the pads 6a against a brake disc 9 to apply a braking force. The brake booster 3 acts to increase the hydraulic pressure of the brake fluid.

The stroke sensor 2 is a sensor that detects the amount of depression (stroke amount) of the brake pedal 1 by the driver.
The foot brake mechanism of this embodiment may be a mechanical configuration that applies hydraulic pressure directly corresponding to the amount of depression of the brake pedal 1, or it may be a type in which a controller controls the hydraulic pressure to adjust the braking force according to the stroke amount of the brake pedal 1 detected by the stroke sensor 2.
In either case, however, the present embodiment is provided with a stroke sensor 2 for the brake pedal 1, in order to use it for EPB control, which will be described later.

The EPB mechanism of this embodiment includes an EPB motor 7 and an EPB pad mechanism section 8. The EPB pad mechanism section 8 is driven and controlled by an EPB control unit 11.
The EPB control unit 11 is, for example, a microcomputer, and realizes automatic EPB control as software-based processing. The EPB control unit 11 is basically a controller that drives the EPB motor 7 and causes the EPB pad mechanism 8 to perform braking in response to detection of the operation of the EPB button 10 by the driver.
The EPB pad mechanism 8 is a mechanism that presses the pad 8 a against the brake disc 9 by the EPB motor 7 .

In the illustrated example, the pad 6a of the brake pad mechanism 6 and the pad 8a of the EPB pad mechanism 8 are separate pads, but it is also possible to consider a configuration in which the EPB pad mechanism 8 shares the pad 6a of the brake pad mechanism 6. That is, in addition to the hydraulic control mechanism, the EPB pad mechanism 8 is provided for the pad 6a, and the pad 6a is pressed against the brake disc 9 by the EPB motor 7 as well.

The detection value of the stroke sensor 2 is input to the EPB control unit 11. Using the detection value of the stroke sensor 2, the EPB control unit 11 can detect the braking force (required braking force) required by the driver when the driver operates the brake pedal 1.
In addition, detection values of various sensors are input to the EPB control unit 11 as a sensor 12. Examples of the sensor 12 include a gradient sensor, a speed sensor, and an acceleration sensor provided on the vehicle. In addition, detection values of a motor angle sensor attached to the EPB motor 7 are input to the EPB control unit 11.

In the brake device of this embodiment, when an abnormality occurs in the foot brake mechanism, the EPB control unit 11 detects this and automatically applies braking by the EPB pad mechanism 8 in response to the driver's operation of the brake pedal 1.
FIG. 1 shows a schematic state in which a pad 6a of a brake pad mechanism 6 is pressed against a brake disc 9 (arrow BK1) by the action of a hydraulic mechanism according to the amount of depression of a brake pedal 1 by a driver (arrow BK0).
In contrast, Figure 2 shows a schematic diagram of a state in which, when sufficient braking force cannot be obtained due to an abnormality such as vapor lock in the foot brake mechanism or a failure of the brake booster, the pad 8a of the EPB pad mechanism 8 is pressed against the brake disc 9 (arrow BK2) by the EPB control unit 11 controlling the drive of the EPB motor 7 in accordance with the amount of depression of the brake pedal 1 by the driver (arrow BK0).

FIG. 3 shows a case where the foot brake mechanism 30 (in this case, the foot brake mechanism 30 refers to the brake booster 3, brake piping 4, fluid chamber 5, brake pad mechanism 6, etc.) functions in response to the operation of the brake pedal 1 as shown in FIG. 1, and also shows a case where the EPB control unit 11 drives and controls the EPB motor 7 in response to the stroke amount of the brake pedal 1 detected by the stroke sensor 2 as shown in FIG.
In order to realize the operation as shown in Fig. 2, the EPB control unit 11 has the functions shown in Fig. 3, which are a foot brake abnormality detection section 21, a required braking force calculation section 22, an F/S transition recognition logic section 23, a sudden braking logic section 24, and a motor torque calculation section 25. These functions are realized by software processing in the EPB control unit 11, which is a microcomputer.

The foot brake abnormality detection unit 21 performs processing to detect an abnormality in the foot brake mechanism.
A means for detecting an event in which braking cannot be applied by the foot brake mechanism may be based on the angle of the brake pedal 1, the gradient value, the deceleration, the EPB motor angle, and the like.

Examples of detection methods for different factors are given below.
When vapor lock occurs In this case, air bubbles form inside the brake fluid pipe 4 near the wheel axle, allowing the brake pedal 1 to be depressed to a greater angle with less force. Therefore, an abnormality caused by vapor lock can be detected by the fact that the brake pedal 1 is depressed faster than normal and the maximum pedal angle is outside the normal range of use.

When the brake fluid pressure is abnormal If the cause is a malfunction of the negative pressure system or the brake booster 3, the abnormality can be detected because the value of the negative pressure sensor or the stroke sensor inside the brake booster 3 does not change even though the angle of the brake pedal 1 is changing (the brake pedal is being depressed).

It should be noted that the detection method is not limited to the above, and various other detection methods are possible. It is also possible to improve the detection accuracy by using detection values from various sensors.
For example, when it is possible to detect that the vehicle is on a downhill slope based on the gradient value obtained by a gradient sensor, it is possible to determine whether the current operation of the brake pedal 1 is appropriate for a downhill slope. If the stroke amount of the brake pedal 1 is large even when the vehicle is on a gentle downhill slope, this can be considered to be an abnormality in the foot brake mechanism.
When referring to the deceleration, if the deceleration does not correspond to the stroke amount of the brake pedal 1, it can also be considered that there is an abnormality in the foot brake mechanism.

The required braking force calculation unit 22 in the EPB control unit 11 is a function that calculates the required braking force according to the detection value of the stroke sensor 2 when an abnormality in the foot brake mechanism is detected by the foot brake abnormality detection unit 21.

The motor torque calculation unit 25 performs a process of calculating the torque of the EPB motor 7 according to the required braking force calculated by the required braking force calculation unit 22. The EPB motor 7 is driven by the torque calculated by this motor torque calculation unit 25, so that the EPB applies a braking force according to the required braking force.

The motor torque calculation unit 25 may calculate a motor torque that directly corresponds to the required braking force calculated by the required braking force calculation unit 22 and control the EPB motor 7, but in the case of FIG. 3, the motor torque is calculated according to a braking force pattern that corresponds to the required braking force, which is set by the F/S transition recognition logic unit 23 or the sudden braking logic unit 24.

The F/S transition cognitive logic unit 23 sets a braking force pattern in which the braking force varies in accordance with the required braking force calculated by the required braking force calculation unit 22 .
The sudden braking logic unit 24 sets a braking force pattern when sudden braking is required. For example, the sudden braking logic unit 24 sets a braking force pattern so as to perform brake control that applies intermittent braking force similar to an ABS (Anti-lock Braking System).

In the example of FIG. 3, the foot brake abnormality detection unit 21, the required braking force calculation unit 22, the F/S transition recognition logic unit 23, the sudden braking logic unit 24, and the motor torque calculation unit 25 are provided within the EPB control unit 11, but this is just one example. For example, the foot brake mechanism 30 may be controlled by a control unit separate from the EPB mechanism, and the foot brake abnormality detection unit 21 that detects abnormalities in the foot brake mechanism 30 may be provided in the foot brake control unit (e.g., a VDC (Vehicle Dynamics Control) unit, an ABS unit). The same applies to other functions such as the F/S transition recognition logic unit 23 and the sudden braking logic unit 24.

<2. F/S recognition due to changes in braking force>
In this embodiment, safety is improved by automatically applying braking by the EPB when an abnormality occurs in the foot brake mechanism, but it is desirable to make the driver aware of this situation.
Braking by the EPB in the situation shown in FIG. 2 is initiated in response to the driver's operation of the brake pedal 1, similar to the foot brake mechanism.
In this way, if braking force is ensured by the intervention of the EPB system instead of the foot brake mechanism, the driver may continue driving without noticing a malfunction in the foot brake mechanism, which may result in the driver being unable to apply the brakes properly when sudden braking is required, or in unstable braking when cornering, creating a dangerous situation.

Therefore, when braking force is ensured by the EPB, the brakes are applied in a way that makes the driver aware that the vehicle is transitioning to a fail-safe (F/S) state, creating a sense of discomfort for the driver and encouraging them to take evacuating action.

In order to make the driver aware that the system is shifting to F/S (braking by EPB), it is conceivable to intentionally vary the strength of the braking or to generate an abnormal noise.
Here, we will explain techniques for varying the strength of braking.

When the foot brake mechanism fails and the driver depresses the brake pedal, the EPB control unit 11 calculates the pedal angle (the braking force required by the driver) based on the detection value of the stroke sensor 2 .
Here, instead of driving the EPB motor directly according to the braking force requested by the driver, the braking force is increased or decreased at regular intervals to let the driver know that the required braking force is being secured while transitioning to F/S.

The specific method of varying the braking force is determined by the F/S transition recognition logic unit 23. That is, the F/S transition recognition logic unit 23 sets the braking force pattern PA shown in FIG. 4A or the braking force pattern PB shown in FIG. 4B so as to vary the braking force. The motor torque calculation unit 25 controls the EPB motor 7 according to this braking force pattern PA or braking force pattern PB.

The braking force pattern PA in FIG. 4A is a braking force pattern that is set when the required braking force is smaller than a threshold value f1.
For example, while driving, a traffic light a short distance ahead turns red, and the driver lightly applies the brakes to slowly slow down and come to a stop.
In such a case, when the required braking force is small, the vehicle deceleration is not so great (the change in vehicle speed is small), so the braking force pattern PA is set so that the moment when the braking force is increased occurs periodically, as shown in the figure. For example, the braking force is increased by a fluctuation amount Δf every period T.

Generally, the greater the change in braking force (the rate of change in deceleration; the slope of the braking force line in the waveform in Figure 4A) [m/ ^s3 ], the greater the perceived acceleration, making it easier for a person to notice the vehicle behavior and feeling uncomfortable. Therefore, when the braking force changes from small to large, the rate of change (the slope of the braking force line in the figure) is made large to ensure that the driver can sense it, and conversely, when the braking force changes from large to small, the rate of change (the slope of the line in the figure) is made small to allow the braking force to gradually converge to the original required braking force.

The braking force pattern PB in FIG. 4B is a braking force pattern that is set when the required braking force is greater than the threshold value f1.
For example, consider a situation where the vehicle is driving on a straight road and then entering a sharp curve (without sudden braking).
In such a case, when the required braking force is large, the braking force pattern PB is set so that the braking force is periodically reduced as shown in the figure. For example, the braking force is reduced by a fluctuation amount Δf every period T.
In this case, the driver wants to reduce the speed significantly, so the vehicle is experiencing a large deceleration. If the braking force is suddenly released (the deceleration sensation is released for just a moment) while a large braking force is being requested (or generated), the driver feels a sense of danger due to the sudden loss of braking force, and immediately feels uncomfortable.

As described above, by selectively using the braking force patterns PA and PB depending on the magnitude of the required braking force, the driver is likely to feel uncomfortable, and this allows the driver to sense that the F/S transition is occurring.
The threshold value f1 for this purpose will be described.

Which of the two braking force patterns PA or PB is used for control when braking is determined based on the magnitude of the required braking force, and the threshold (switching point) is set to threshold value f1 as a constant that satisfies the following two conditions.

- If braking force pattern PA is applied when the absolute value of the required braking force is large (the driver applies the brakes strongly), an additional braking force fluctuation Δf (a fluctuation that the driver can definitely sense) will be added to the driver's required braking force, which could cause the tires to lock, disrupting the vehicle's behavior and creating a dangerous situation, or the driver could be subjected to sudden braking and receive a shock such as whiplash. For this reason, an upper limit is set for the required braking force when braking force pattern PA is applied.

-If braking force pattern PB is not applied when the required braking force is relatively large, it is believed that the driver will not easily notice the fluctuation in braking force. For example, if the absolute value of the braking force applied to the vehicle is small, the driver may not notice even if there is a slight loss of braking force. For this reason, braking force pattern PB is applied when the required braking force exceeds the braking force fluctuation amount Δf that the driver can definitely sense.

By using the threshold value f1 that is set so as to satisfy the above conditions, the F/S transition logic unit 23 can select either the braking force pattern PA or PB in accordance with the required braking force.
However, when the driver first operates the brake pedal 1, the selection using the threshold value f1 may be sufficient, but the driver may increase or decrease the brake pressure while depressing the brake pedal 1. For this reason, it may be necessary to switch the braking force patterns PA and PB.

In this case, it is also possible to switch the braking force patterns PA, PB based on the threshold value f1. However, if the required braking force changes as the driver changes the amount of depression of the brake pedal 1, a sudden switch in the waveform shape may result in the driver being unable to adapt to the sudden change in vehicle behavior or feeling uncomfortable.
Therefore, when the required braking force changes, the threshold value f2 shown in FIG. 5A or the threshold value f3 shown in FIG. 5B is used as the threshold value for the switching determination (switching threshold value) to avoid a sudden change in behavior.

Figure 5A shows a case where the braking force pattern PA was applied because the required braking force was initially lower than the threshold value f1, but then the required braking force changed to a higher value as shown by line RQB1. In this case, the switching decision is made using threshold value f2, which corresponds to a braking force higher than threshold value f1. In other words, when the required braking force becomes higher than threshold value f2, the braking force pattern PB is switched to.

Figure 5B shows a case where the braking force pattern PB was applied because the required braking force was initially higher than the threshold value f1, but then the required braking force changed to a lower value as shown by line RQB2. In this case, the switching decision is made using threshold value f3, which corresponds to a braking force lower than threshold value f1. In other words, when the required braking force becomes lower than threshold value f3, the braking force pattern is switched to PA.

In this way, by determining the timing to switch between braking force patterns PA and PB using different thresholds f2 and f3 when the required braking force increases and decreases, sudden changes in vehicle behavior are prevented.

Next, the setting of the waveforms of the braking force patterns PA and PB will be described.
First, the period T will be described.
The period of the strength of the braking force (period T in Figs. 4A and 4B) is set to a time period that allows the driver to feel the change in deceleration.
It is assumed that if the period is too short, it will be difficult for the driver to perceive it.
Conversely, if the cycle is too long, for example when a car cuts in front of you and you brake for only a few seconds, you may not feel any change in braking force during that time.
Therefore, the period T should be set in a range that allows the user to feel the intensity of the sound but is not too long. Specifically, the period T may be between about 0.5 and 2 seconds. However, the period T is not limited to this range.

Next, the offset amount of the braking force patterns PA and PB will be described.
If the braking force has periodic strength and weakness (pulsation), the average braking force will not match the braking force required by the driver. In other words, the braking force may be applied more than the driver expected, or may not be applied as expected. For this reason, as shown in Figures 6A and 6B, the offset amount OF is determined so that the average braking force matches the braking force required by the driver's operation of the brake pedal 1.

6A and 6B show the braking force patterns PA and PB, respectively, and also show the required braking force RQB calculated by the required braking force calculation unit 22.
When the required braking force RQB is lower than the threshold value f1 and the braking force pattern PA is applied, the braking force pattern PA is a pattern in which the braking force periodically exceeds the required braking force RQB from a state in which the braking force is lower than the required braking force RQB by the offset amount OF, as shown in Figure 6A.
When the required braking force RQB is higher than the threshold value f1 and the braking force pattern PB is applied, the braking force pattern PB is a pattern in which the braking force periodically falls below the required braking force RQB from a state in which the braking force is higher than the required braking force RQB by the offset amount OF, as shown in Figure 6B.

In either case, the average braking force during the period T is set to match the required braking force RQB. In other words, the integrated value of the braking force during one period of the braking force patterns PA and PB is set to match the integrated value during one period when the required braking force RQB is a constant value.
In this way, braking control according to the required braking force can be performed even with a pulsating pattern.

The above is an explanation of examples of the braking force patterns PA, PB that are set by the processing of the F/S transition logic unit 24. However, controlling the strength of the braking force must not pose any danger to the occupants.
When the driver operates the brake pedal 1 to suddenly apply braking force, it is considered that the braking force provided by the EPB motor 7 controlled by the braking force patterns PA and PB is insufficient.
In such a case, the sudden braking logic unit 24 sets a braking force pattern with a strong braking force, and the motor torque calculation unit 25 drives the EPB motor 7 for sudden braking.

Specifically, when braking suddenly (when the driver is requesting maximum braking force) or when braking on a low μ road, there is a possibility that the vehicle's tires may lock or slip, so the ABS normally activates to prevent the tires from locking.
Therefore, in a situation where sudden braking is required, the logic of the F/S transition logic unit 24 is not entered, but the sudden braking logic 25 is intervened to enter control similar to that of the ABS, thereby preventing tire lock and slippage and ensuring the safety of the occupants.

<3. Example of processing by EPB control unit>
An example of the processing performed by the EPB control unit 11 for the above-mentioned operation is shown in FIG.
FIG. 7 shows an example of a process executed when the EPB control unit 11 detects an abnormality in the foot brake mechanism.
This process is repeatedly performed by the EPB control unit 11 at each sampling period of the detection value of the stroke sensor 2 as long as the brake pedal 1 is being operated by the driver.

In step S101, the EPB control unit 11 acquires the detection value of the stroke sensor 2 and calculates the required braking force from the detected stroke amount.

In step S102, the EPB control unit 11 determines whether or not the braking force requested by the driver is intended for emergency avoidance of a collision or the like.
In this case, for example, it is determined whether or not there is a sudden and large change in the stroke amount. Whether or not the brake operation is for sudden braking may be determined not only based on the detection value of the stroke sensor 2, but also based on the detection value of other sensors such as a G sensor and a steering angle sensor, or by using them in combination.

If it is determined that sudden braking is occurring, the EPB control unit 11 proceeds to step S111 and activates the sudden braking logic unit 24 to perform EPB control for sudden braking.

If it is determined that the braking is not sudden, the EPB control unit 11 proceeds to step S103, and activates the F/S transition logic section 24 to perform EPB control.
In this case, first, in step S103, the EPB control unit 11 determines whether or not the previous required braking force is 0. That is, it determines whether or not the current time is the first time that depression of the brake pedal 1 has been detected and the process proceeds to step S103.

If it is the first time point (previous required braking force=0), the EPB control unit 11 proceeds to step S104 and compares the currently calculated required braking force with the threshold value f1.
If the required braking force is smaller than the threshold value f1, the EPB control unit 11 proceeds to step S108 and applies the braking force pattern PA.
If the required braking force is not smaller than the threshold value f1, the EPB control unit 11 proceeds to step S109 and applies the braking force pattern PB.
By applying the braking force pattern PA or the braking force pattern PB, the EPB control unit 11 calculates a corresponding motor torque, and the EPB motor 7 is driven to apply braking.

After the processing of step S108 or step S109, the EPB control unit 11 proceeds to step S110 and checks whether the brake pedal 1 is being operated. If the driver is continuing to operate (press) the brake pedal 1, the process returns to step S101, and if the driver is not continuing to operate the brake pedal 1, the process of FIG. 7 ends.

If the driver continues to operate the brake pedal 1, the next time the process proceeds to step S103, the previous requested braking force is not 0, so the process proceeds to step S105. In step S105, the EPB control unit 11 branches the process depending on whether the braking force pattern PA is currently being applied or not.
If the braking force pattern PA is being applied, the EPB control unit 11 proceeds to step S106, where it compares the current required braking force with the threshold value f2, and if the required braking force is less than the threshold value f2, it proceeds to step S108, where it continues to apply the braking force pattern PA.

When the process repeatedly proceeds to step S108, the waveform is the braking force pattern PA, but the braking force level is set according to the required braking force at that time.
The required braking force varies from moment to moment in response to the driver's operation of the brake pedal 1. In step S108, the braking force is specified by setting the offset amount OF described in Fig. 6A based on the most recent required braking force detected in step S101.
That is, the braking force pattern PA shown by the waveform in FIG. 6A shifts up and down in response to changes in the required braking force.

If it is determined in step S106 that the current requested braking force exceeds the threshold value f2, the EPB control unit 11 proceeds to step S109 and switches to applying the braking force pattern PB.

Also, if the braking force pattern PB is being applied at the time of step S105, the EPB control unit 11 proceeds to step S107, compares the current required braking force with the threshold value f3, and if the required braking force is not less than the threshold value f3, proceeds to step S109, and continues to apply the braking force pattern PB.

When the process repeatedly proceeds to step S109, the waveform is the braking force pattern PB, but the braking force level is set according to the required braking force at that time, just like the braking force pattern PA described above. In other words, the braking force pattern PB shown by the waveform in Figure 6B shifts up and down according to changes in the required braking force.

If it is determined in step S107 that the current requested braking force is smaller than threshold value f3, the EPB control unit 11 proceeds to step S108 and switches to applying the braking force pattern PA.

When the foot brake abnormality detection unit 21 detects an abnormality in the foot brake mechanism, EPB control is performed by the functions of the required braking force calculation unit 22, F/S transition logic unit 23, sudden braking logic unit 24, and motor torque calculation unit 25 through the processing shown in Figure 7 above.

<4. F/S recognition due to abnormal noise>
As mentioned above, other than the braking strength pattern, an abnormal sound may be generated to make the driver aware of the fail-safe state.
For example, one possible method for achieving this is to use the pad 8a of the EPB pad mechanism 8 to generate abnormal noise.

In other words, as shown in Figure 1, in the case of a vehicle that has a dedicated EPB pad 8a installed in addition to the foot brake mechanism pad 6a, the pad 8a is made special so that it makes a sound when braking by the EPB, and a special sound is generated when the F/S function is activated. This makes it possible for the driver to notice something is wrong and encourages him to take refuge.

More specifically, the use of a so-called pad wear indicator is envisaged.
As is well known, pad wear indicators are embedded in the brake pads, become visible as the pads wear, and come into contact with the brake disc, generating abnormal noise.

In this embodiment, the EPB pad 8a is designed so that the pad wear indicator is exposed from the beginning (when the pad 8a is new and unworn). More specifically, the pad wear indicator is designed to come into contact with the brake disc 9 when the unworn pad 8a is pressed against the brake disc 9.
Since the EPB is originally designed to apply a braking force while the vehicle is stopped, even if the pad wear indicator is exposed and in contact with the brake disc 9, the brake disc 9 does not rotate and no abnormal noise is generated.
On the other hand, when the EPB control is automatically performed as the F/S, since the vehicle is moving, the pad wear indicator rubs against the brake disc 9, generating an abnormal noise (metallic noise).
This allows the driver to recognize the state in which braking is being applied by EPB control when the brake pedal 1 is operated (the foot brake mechanism is in an abnormal state).

5. Summary and Modifications
The effects of the above embodiment will be described.
The brake device of the embodiment includes a stroke sensor 2 that detects the amount of depression of the brake pedal for the foot brake, an EPB motor 7 that performs braking by the EPB mechanism, a foot brake abnormality detection unit 21 that detects an abnormality in the foot brake mechanism, a required braking force calculation unit 22 that calculates a required braking force in accordance with the detection value of the stroke sensor 2 when an abnormality is detected by the foot brake abnormality detection unit 21, and a motor torque calculation unit 25 that calculates the torque of the EPB motor 7 in accordance with the required braking force calculated by the required braking force calculation unit 22.

That is, when an abnormality in the foot brake caused by the hydraulic mechanism is detected, the EPB is operated in accordance with the detection value of the stroke sensor of the brake pedal.
By automatically activating the EPB when an abnormality occurs in the foot brake mechanism, the vehicle's braking force can be secured in an emergency, and the risk of a collision or the like can be avoided, thereby significantly improving safety.
In addition, since the EPB is operated to apply braking force according to the detection value of the stroke sensor 2, i.e., the required braking force due to the driver's operation of the brake pedal 1, it is possible to generate an appropriate braking force according to the situation, i.e., the amount of depression of the brake pedal 1 by the driver, rather than a uniform braking force.

The brake device of the embodiment is equipped with an F/S transition logic unit 24 (first logic unit) that sets braking force patterns PA, PB in which the braking force varies in accordance with the required braking force calculated by the required braking force calculation unit 22, and an example is given in which the motor torque calculation unit 25 calculates the motor torque in accordance with the braking force pattern set by the F/S transition logic unit 24.
The braking force patterns PA, PB set by the F/S transition recognition logic 23 cause the driver to feel a sense of discomfort as if the braking force is changing when the driver is depressing the brake pedal 1. This makes the driver realize that a transition has been made to the fail-safe state. The driver recognizes the abnormality in the foot brake mechanism by sensing the fail-safe transition and can take appropriate action.
In other words, the driver can be prevented from continuing to drive with the foot brake mechanism not functioning (prompting the driver to drive to an evacuation site), thereby ensuring the safety of passengers.
In particular, the fact that the EPB has automatically applied the brakes when an abnormality occurs in the foot brake mechanism may be displayed on a display panel in front of the driver's seat, but the driver does not always look at the display panel while driving, and some drivers rarely look at it. Therefore, giving a sense of discomfort is useful in making the driver recognize the fail-safe transition.
In order to obtain a braking force corresponding to the required braking force while the braking force is changing, for example, by changing the braking force in a period of about 0.5 to 2 seconds and performing control so that a braking force equivalent to the required braking force is integrally applied in one period. For example, the braking force patterns PA and PB may be set as shown in Figures 6A and 6B. Of course, other patterns may also be used.

In the embodiment, the F/S transition logic unit 24 is configured to set either a braking force pattern PA (first braking force pattern) in which a braking force lower than the required braking force periodically becomes higher than the required braking force, or a braking force pattern PB (second braking force pattern) in which a braking force higher than the required braking force periodically becomes lower than the required braking force, depending on the result of comparing the required braking force calculated by the required braking force calculation unit 22 with the threshold value f1.
By using the braking force pattern PA when the required braking force is low, the driver feels a periodically large braking force while lightly depressing the brake pedal 1.
Moreover, by using the braking force pattern PB when the required braking force is low, the driver feels that the braking force is periodically released while the driver is strongly depressing the brake pedal 1.
In either case, it is easy to create a sense of discomfort, and the F/S transition becomes easier to perceive.

In addition, the braking force pattern PA when the required braking force is relatively low can obtain a braking force equivalent to the required braking force by periodically changing from a braking force lower than the required braking force to a braking force higher than the required braking force.
Similarly, the braking force pattern PB when the required braking force is relatively high can obtain a braking force equivalent to the required braking force by changing from a braking force higher than the required braking force to a braking force lower than the required braking force periodically.
In these braking force patterns PA and PB, the pulsation period, offset amount, peak/bottom levels, and gradient (rate of change in braking force) may be appropriately set.

In the embodiment, the F/S transition logic unit 24 determines whether to switch from the braking force pattern PA to the braking force pattern PB in response to an increase in the required braking force using a threshold value f2 (first switching threshold), and whether to switch from the braking force pattern PB to the braking force pattern PA in response to a decrease in the required braking force using a threshold value f3 (second switching threshold) corresponding to a braking force lower than the threshold value f2.
As a result, hysteresis control is performed in switching between the braking force patterns PA and PB, and it is possible to prevent the driver from feeling any unnecessary sudden change in braking behavior when operating the brakes while driving.
In the embodiment, the threshold values are set to f3<f1<f2. By using the threshold value f2 higher than the threshold value f1 and the threshold value f3 lower than the threshold value f1, it is possible to prevent the braking force pattern from being immediately switched after the braking force patterns PA and PB are initially set.

The brake device of the embodiment is equipped with a sudden braking logic unit 24 (second logic unit) that sets a braking force pattern for sudden braking, and the motor torque calculation unit 25 calculates the motor torque according to the braking force pattern set in either the F/S transition logic unit 24 or the sudden braking logic unit 24.
When sudden braking is required, the sudden braking logic unit 24 performs braking control using a braking force pattern similar to that of ABS, for example, thereby enabling the vehicle to cope with sudden braking and improving safety.

In this embodiment, the EPB mechanism is structured to generate abnormal noise by applying the brakes while the vehicle is running.
For example, by making a part such as a pad wear indicator in contact with the brake disc 9 from the beginning, an abnormal noise (e.g., a metallic sound) is generated when driving with braking applied by the EPB. As a result, no abnormal noise is generated when the EPB is used during normal stopping, but when braking is automatically applied by the EPB when an abnormality occurs in the foot brake mechanism as in this embodiment, the driver can recognize the condition by the abnormal sound. This is also suitable for making a driver who does not look at the display panel recognize the fail-safe transition.
Of course, both of the above-mentioned braking force patterns PA and PB that cause discomfort and the generation of abnormal noise may be used.

The present invention is not limited to the processes and structures described in the embodiments, and various modifications are contemplated.
Although the pads 6a of the foot brake mechanism and 8a of the EPB mechanism are shown to have a structure in which they press against the brake disc 9 from both sides, they may also be of a type in which they press against the brake disc 9 from one side.
Additionally, the EPB may have a braking structure other than a disc brake structure.
There is no limitation on the vehicle to which the brake device of the present invention can be applied. For example, the brake device of the present invention can be applied to any vehicle, regardless of whether it is a gasoline vehicle, a hybrid vehicle, or an electric vehicle. The present invention can be applied to any vehicle that is equipped with at least an EPB and has a stroke sensor 2 that detects the amount of operation of the brake pedal 1.

REFERENCE SIGNS LIST 1 Brake pedal 2 Stroke sensor 3 Brake booster 4 Brake piping 5 Fluid chamber 6 Brake pad mechanism 6a Pad 7 EPB motor 8 EPB pad mechanism 8a Pad 9 Brake rotor 10 EPB button 11 EPB control unit 12 Sensor 21 Foot brake abnormality detection unit 22 Required braking force calculation unit 23 F/S transition recognition logic unit 24 Sudden braking logic unit 25 Motor torque calculation unit

Claims (6)

a stroke sensor for detecting the amount of depression of a brake pedal for a foot brake;
a parking brake motor that applies braking using an electric parking brake mechanism;
A foot brake abnormality detection unit that detects an abnormality in a foot brake mechanism;
a required braking force calculation unit that calculates a required braking force in accordance with the detection value of the stroke sensor when an abnormality is detected by the foot brake abnormality detection unit;
a motor torque calculation unit that calculates a torque of the parking brake motor in accordance with the required braking force calculated by the required braking force calculation unit;
a first logic unit that sets a braking force pattern in which the braking force varies in accordance with the required braking force calculated by the required braking force calculation unit;
Equipped with
the first logic unit sets a braking force pattern that is a periodic variation having a first section in which the braking force is increased or decreased, and a second section in which the braking force increased in the first section is decreased, or the braking force decreased in the first section is increased, and an absolute value of a braking force change rate per unit time in the first section is greater than an absolute value of a braking force change rate per unit time in the second section;
The motor torque calculation unit calculates a torque according to a braking force pattern set by the first logic unit. a stroke sensor for detecting the amount of depression of a brake pedal for a foot brake;
a parking brake motor that applies braking using an electric parking brake mechanism;
A foot brake abnormality detection unit that detects an abnormality in a foot brake mechanism;
a required braking force calculation unit that calculates a required braking force in accordance with the detection value of the stroke sensor when an abnormality is detected by the foot brake abnormality detection unit;
a motor torque calculation unit that calculates a torque of the parking brake motor in accordance with the required braking force calculated by the required braking force calculation unit;
a first logic unit that sets a braking force pattern in which the braking force varies in accordance with the required braking force calculated by the required braking force calculation unit;
Equipped with
the first logic unit sets either a first braking force pattern or a second braking force pattern different from the first braking force pattern according to the required braking force calculated by the required braking force calculation unit,
The motor torque calculation unit calculates a torque according to a braking force pattern set by the first logic unit. the first braking force pattern is a braking force pattern in which a braking force lower than a required braking force periodically becomes a braking force higher than the required braking force,
the second braking force pattern is a braking force pattern in which a braking force higher than a required braking force periodically becomes a braking force lower than the required braking force,
3. The brake device according to claim 2, wherein the first logic unit sets either the first braking force pattern or the second braking force pattern depending on a result of comparing the required braking force calculated by the required braking force calculation unit with a threshold value. The first logic unit is
The switching from the first braking force pattern to the second braking force pattern in response to an increase in the required braking force is determined using a first switching threshold value;
The brake device according to claim 3 , wherein switching from the second braking force pattern to the first braking force pattern in response to a decrease in the required braking force is determined using a second switching threshold value corresponding to a braking force lower than the first switching threshold value. a second logic unit that sets a braking force pattern for sudden braking;
The brake device according to claim 1 , wherein the motor torque calculation unit calculates a torque according to a braking force pattern set by either the first logic unit or the second logic unit. The brake device according to any one of claims 1 to 5, wherein the electric parking brake mechanism is structured to generate abnormal noise when braking while the vehicle is moving.

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