JP4894637B2 - Braking assist device for vehicle - Google Patents

Description

  The present invention relates to a vehicle braking support device that supports a driver's braking operation so that a collision with an obstacle ahead of the host vehicle can be avoided.

  Conventionally, as described in Patent Document 1, for example, it is determined that there is a possibility of collision with an obstacle ahead based on the distance and relative speed between the host vehicle and an obstacle ahead such as a preceding vehicle. Then, a device that performs pre-crash brake assist (PBA) control that increases the braking force by the driver's brake pedal operation is known.

In this conventional apparatus, the distance and relative speed between the host vehicle and the obstacle ahead are detected from the measured distance of the distance sensor and the detected vehicle speed of the vehicle speed sensor. Then, the vehicle travels the measurement distance at the relative speed, and calculates the time when the host vehicle and the front obstacle come into contact as the predicted collision time TTC. The predicted collision time TTC decreases as the own vehicle approaches the front obstacle and as the relative speed with respect to the front obstacle increases. When the predicted collision time TTC falls below a reference time set as a time necessary for avoiding a collision, it is determined that a collision with a front obstacle has occurred, and PBA control is started.
JP 2006-218993 A

  In the conventional apparatus, as described above, by comparing the collision prediction time with the reference time, it is determined whether or not a possibility of a collision with a front obstacle has occurred. Here, the reference time is a fixed time of a few seconds or less corresponding to a standard timing at which the driver is expected to step on the brake pedal with the intention of PBA control when a collision is unavoidable. It is set based on experiments and the like.

  However, when the reference time to be compared with the collision prediction time is set to a certain time as in the conventional device, the collision with the front obstacle cannot be avoided only by the driver performing the brake operation, and the steering is also performed. There may be cases where operation is required, and a situation may arise in which the driver is required to perform more advanced operations. That is, as the relative speed between the host vehicle and the front obstacle increases, it is necessary to generate a stronger braking force in order to avoid a collision with the front obstacle. However, when the collision prediction time is compared with a certain reference time, the braking force by the PBA control can be generated only for a time shorter than the reference time. For this reason, when the relative speed is high, a sufficient braking force cannot be generated, and a collision with a front obstacle may not be avoided only by a brake operation.

  The present invention has been made in view of the above points, and even when the relative speed with the front obstacle is high, if the driver performs a braking operation, the collision with the front obstacle can be avoided. An object of the present invention is to provide a vehicular braking assist device.

In order to achieve the above object, the vehicle braking assistance device according to claim 1 is provided.
Distance detection means for detecting the distance between the host vehicle and the front obstacle;
A relative speed detecting means for detecting a relative speed between the host vehicle and a front obstacle;
Collision prediction time calculation means for calculating a collision prediction time until the collision timing between the host vehicle and the front obstacle based on the detected distance and relative speed,
Brake assist means for increasing the braking force by the driver's brake operation when the predicted collision time falls below a predetermined brake assist reference time, and
When the relative speed is greater than or equal to the first predetermined value, the predetermined brake assist reference time increases as the relative speed increases so that a collision with a front obstacle can be avoided by the driver's normal braking operation. Set to
In the range where the relative speed is less than the first predetermined value, the brake assist reference time is the rate of increase of the brake assist reference time in the range greater than or equal to the first predetermined value in the range where the relative speed is from zero to the second predetermined value. Is set to increase at a smaller increase rate than the second predetermined value, and in a range from the second predetermined value to the first predetermined value, at a substantially constant time during which a collision with a front obstacle by a steering operation by the driver can be avoided. It is characterized by being set .

  As described above, depending on the relative speed between the host vehicle and the front obstacle, the braking force required to avoid a collision with the front obstacle greatly changes. In the above-described configuration, the brake assist reference time is changed according to the relative speed. Therefore, the brake assist reference time is set so that the braking force necessary for avoiding a collision with a front obstacle can be generated by the brake assist. Can be set.

Specifically, even when the relative speed is increased, so that it can avoid the collision with the front obstacle by normal braking operation by the driver, the relative speed is the first predetermined value or more ranges, predetermined The brake assist reference time is set to increase as the relative speed increases. As a result, the higher the relative speed, the earlier the brake assist is started. Therefore, the driver avoids a collision with a front obstacle by performing a normal brake operation instead of a strong and fast brake operation. It is possible to generate a braking force necessary for the operation. Therefore, the driver can avoid a collision with an obstacle ahead simply by performing a normal braking operation.
On the contrary, in the range where the relative speed is smaller than the first predetermined value, the speed difference between the host vehicle and the front obstacle is relatively small in the first place, so there is little need to start the brake assist control at such an early timing. Therefore, in this case, the brake assist reference time is increased at an increase rate smaller than the increase rate of the brake assist reference time in a range equal to or greater than the first predetermined value, or the brake assist reference time with respect to a change in relative speed. Is set to be substantially constant without changing.

In addition, as described in claim 2 , when the predicted collision time falls below a warning reference time that is substantially constant in a range where the relative speed is equal to or higher than the first predetermined value, the possibility of a collision with a front obstacle is possible. When providing alarm means to warn that there is an alarm, the brake assist reference time should be substantially constant even if the relative speed further increases from the time when the brake reference reference time is increased so as not to exceed the alarm reference time. It is preferably set. When a warning is issued when there is a possibility of a collision with a front obstacle, if the brake assist control for avoiding the collision is started before the warning is given, the driver feels uncomfortable. Because there are things.

According to a third aspect of the present invention , in the case where an automatic brake means for automatically generating a braking force is provided when the predicted time falls below the automatic brake reference time set shorter than the brake assist reference time, the collision predicted time However, when the time is less than the automatic brake reference time, the required deceleration corresponding to the driver's braking operation is calculated, the target deceleration during braking by the automatic braking means is obtained, and the vehicle deceleration is calculated as the required deceleration. The braking force may be generated in the vehicle so as to match the maximum value with the target deceleration.

  When the collision between the host vehicle and the front obstacle is avoided or when the collision cannot be avoided, it is preferable to execute not only the brake assist control but also the automatic brake control in order to reduce the impact caused by the collision as much as possible. When the driver is driving aside or sleeping asleep, there is a possibility that the brake operation may not be performed even though the danger of a collision with a front obstacle is imminent. For this reason, it is because only the brake assist control may not be able to achieve collision avoidance or impact mitigation due to the collision.

  However, if the brake assist control and the automatic brake control are configured to be executable, it is necessary to adjust the control. In this case, by calculating the required deceleration according to the brake operation by the driver and obtaining the target deceleration at the time of braking by the automatic brake control, the contents of both controls can be compared with the same reference. Then, by generating the braking force so that the vehicle deceleration matches the maximum value of the requested deceleration and the target deceleration, it is possible to generate a higher braking force on the vehicle in a situation where the danger of a collision is imminent.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating an overall configuration of a vehicle braking assistance device according to an embodiment.

  In FIG. 1, the vehicle braking assistance device 10 includes various sensors for obtaining information necessary for determining whether or not the own vehicle may collide with a front obstacle such as a preceding vehicle. Specifically, the vehicle braking assistance device 10 includes a radar sensor 1, a yaw rate sensor 2, a vehicle speed sensor 3, and a brake sensor 4.

  As the radar sensor 1, for example, a laser that irradiates a laser beam so as to scan a predetermined angle range in front of the host vehicle and receives a reflected laser beam to detect a distance and direction to a front obstacle. A radar sensor can be used. In addition, as the radar sensor 1, a millimeter wave sensor that can detect the distance and direction to the front obstacle and the relative speed with the front obstacle based on the transmission / reception result of the millimeter wave, a camera, and image processing is used. The apparatus may be configured to recognize a distance from a front obstacle or the like from an image in front of the vehicle imaged by a camera.

  The yaw rate sensor 2 detects a yaw rate (angular velocity about the vertical direction of the host vehicle) generated in the host vehicle when the host vehicle changes its traveling direction. Based on the yaw rate detected by the yaw rate sensor 2, the traveling direction of the host vehicle can be estimated. In the estimated traveling direction, it is determined whether or not a possibility of a collision has occurred with respect to a front obstacle existing at the closest distance.

  The vehicle speed sensor 3 detects the traveling speed of the host vehicle. The traveling speed detected by the vehicle speed sensor 3 is used to determine whether or not the control by the vehicle braking assistance device 10 is necessary, or when a laser radar sensor is used as the radar sensor 1, It is used to calculate the relative speed, which is the speed difference with the front obstacle. When the speed of the host vehicle is sufficiently reduced, it is not necessary to support the driver's brake operation in order to avoid a collision with a front obstacle. For this reason, this vehicle braking assistance device executes control only when the traveling speed of the host vehicle is equal to or higher than a predetermined speed (for example, 10 km / h).

  The brake sensor 4 outputs a signal indicating the degree of brake operation by the driver, such as the operation amount and operation speed of the brake pedal by the driver. Based on the output signal of the brake sensor 4, the required deceleration that the driver is trying to achieve by the brake operation is calculated according to a predetermined arithmetic expression. The brake sensor 4 may detect a brake fluid pressure generated by a driver's brake operation.

  Detection signals output by the various sensors 1 to 4 described above are input to the collision mitigation controller 5. The collision mitigation controller determines the possibility of a collision with a forward obstacle based on the input detection signal, and if it determines that there is a possibility of a collision, the collision mitigation controller avoids the collision or at least the shock To alleviate this, pre-crash brake assist control and pre-crash automatic brake control (hereinafter simply referred to as brake assist control and automatic brake control) are executed by outputting a control signal to the brake actuator 6. The brake actuator 6 operates according to a control signal from the collision mitigation controller, and generates a braking force on each wheel of the host vehicle.

  In the brake assist control executed by the collision mitigation controller 5, for example, the required deceleration corresponding to the driver's brake operation is multiplied by a predetermined number greater than 1, thereby amplifying the required deceleration and using the amplified deceleration. A control signal is output to the brake actuator 6 so as to generate a braking force to achieve. Thereby, when the possibility of a collision with a front obstacle arises, a braking force larger than the braking force corresponding to the brake operation which the driver performed can be generated. In addition, automatic brake control is executed when it is difficult to avoid a collision with a front obstacle. Even if no braking operation is performed by the driver, a braking force is automatically generated and at least a collision occurs. It is intended to reduce the impact of time.

  Next, control processing executed in the collision mitigation controller 5 will be described based on the flowchart of FIG.

  First, in step S100, based on detection signals from the radar sensor 1 and the yaw rate sensor 2, a front obstacle that is present at the closest position to the host vehicle in the direction in which the host vehicle travels is selected. Next, in step S110, it is determined whether or not it is necessary to execute brake assist control and / or automatic brake control on the front obstacle selected in step S100, that is, the braking assist device 10 for the vehicle. It is determined whether or not the operation is necessary, and if so, which control should be performed. The operation determination process in step S110 will be described in detail later.

  In step S110, when the operation of the vehicle braking assistance device 10 is necessary and a control to be executed is determined, a control process for performing the determined control is executed in step S120. Specifically, in step S120, a control signal is output to the brake actuator 6 so that the deceleration of the vehicle matches the deceleration to be achieved by the control determined in step S110. In addition, when it is determined in step S110 that processing such as an alarm is necessary, a control signal for executing the alarm is output.

  Next, the operation determination process in step S110 will be described in detail. First, in the vehicle braking assistance device 10, whether or not there is a risk of a collision with a front obstacle and it is necessary to execute control such as brake assist control or automatic brake control, as in the related art. Judgment is made based on a time to collision (TTC). For this reason, the collision prediction time TTC is obtained by dividing the distance to the front obstacle detected by the radar sensor 1 by the relative speed between the front obstacle and the host vehicle.

  A reference time for executing brake assist control, a reference time for executing automatic brake control, and the like are determined in advance for the predicted collision time TTC thus calculated. The calculated collision prediction time TTC is compared with each reference time, and when the collision prediction time TTC falls below those reference times, brake assist control and automatic brake control are started.

  Here, the vehicle braking assistance device 10 is particularly characterized by the setting of a reference time to be compared with the predicted collision time TTC, and this point will be described with reference to the graphs shown in FIGS. 3 and 4. . As shown in FIG. 3, in this vehicle braking assistance device 10, a total of seven types of reference times are set as reference times. Each reference time has a characteristic that changes according to the relative speed between the host vehicle and the front obstacle. In order to show the change characteristics of each reference time, in FIG. 3, each reference time is shown as a line connecting the reference times changed according to the relative speed.

  First, the automatic brake 2 reference time line will be described. The automatic brake 2 reference time line is determined based on a physical limit at which a collision can be avoided by a driver's braking and steering operation.

  Even if the driver depresses the brake pedal most strongly to perform the braking operation, the vehicle can only decelerate at a deceleration of about 0.8G to 1G at the maximum. Thus, there is a physical limit to vehicle deceleration, so as the relative speed increases from zero, the time required to eliminate the relative speed difference and avoid a collision with a front obstacle. Becomes longer. For this reason, the automatic brake 2 reference time line is determined so that the reference time gradually increases from 0 km / h to about 35 km / h.

  However, when the reference time is gradually increased, the collision can be avoided by the steering operation by the driver at the reference time. The collision avoidance by the driver's steering operation can be performed in a substantially constant time regardless of the relative speed. Therefore, the automatic brake 2 reference time line is set to a fixed time in a range where the relative speed is about 35 km / h or more.

  As described above, the automatic brake 2 reference time line is determined based on the physical limit at which collision can be avoided by the driver's braking and steering operations. Therefore, when the calculated predicted collision time TTC is shorter than the reference time determined by the automatic brake 2 reference time line, it is almost maximized in order to avoid the collision or at least reduce the impact caused by the collision. Automatic brake control is executed with a deceleration close to the speed (for example, 0.8 G) as a target deceleration.

  Next, the automatic brake 1 reference time line will be described. As described above, when the predicted collision time TTC falls below the automatic brake 2 reference time line, the vehicle is decelerated at a deceleration close to the maximum deceleration. However, since the automatic brake 2 reference time line is determined based on a physical limit capable of avoiding a collision, the possibility of avoiding a collision is increased by starting automatic braking at an earlier timing. be able to. In addition, when the vehicle is not braked at all, suddenly decelerating at a deceleration close to the maximum deceleration may cause the vehicle deceleration to change too rapidly.

  Therefore, as shown in FIG. 3, in particular, in the range where the relative speed is high (≧ about 35 km / h) in which the automatic brake 2 reference time is set to a fixed time to avoid collision by the driver's steering operation, the automatic brake An automatic brake 1 reference time line having a reference time longer than the 2 reference time line is defined.

  When the remaining collision time TTC falls below the automatic brake 1 reference time line, the automatic brake is decelerated at a smaller deceleration (for example, 0.5 G) than when it falls below the automatic brake 2 reference time line. Control is executed. Thereby, when the relative speed is high, the automatic brake 1 is executed first, and then the automatic brake 2 is executed. For this reason, the possibility of collision avoidance can be increased, and the change in deceleration generated in the vehicle can be mitigated.

  Note that when the driver has already performed a brake operation at the time when the predicted collision time TTC falls below the automatic brake line 1, the process waits without executing the automatic brake control. The automatic brake 1 reference time line is not determined based on the physical limit of collision avoidance like the above-described automatic brake 2 reference time line, and if the driver has already executed a brake operation, This is because it is not necessary to execute the automatic brake control.

  However, when the predicted collision time TTC falls below the automatic brake 2 reference time line, it is preferable to execute the automatic brake control regardless of whether or not the driver performs the brake operation. This is because when the predicted collision time TTC falls below the automatic brake 2 reference time line, the risk of a collision with a front obstacle is very high, so it is preferable to decelerate the vehicle with a high deceleration as much as possible. is there.

  However, when the collision prediction time TTC falls below the automatic brake 2 reference time line and the automatic brake control is executed unconditionally, if the driver is performing a very strong braking operation, the vehicle deceleration will be reduced. There is also a possibility of lowering. Therefore, when the driver is performing a brake operation when the predicted collision time TTC falls below the automatic brake 2 reference time line, the required deceleration amplified by the brake assist control and the target deceleration by the automatic brake control are reduced. It is preferable to compare the speed and generate the braking force so that the deceleration of the vehicle matches the maximum value of the required deceleration and the target deceleration. As a result, it is possible to generate a higher braking force on the vehicle in a situation where the danger of a collision is imminent.

  By executing the automatic brake control based on the automatic brake 1 reference time line and the automatic brake 2 reference time line described above, the vehicle is braked even if the driver does not perform the brake operation. For this reason, prior to the start of the automatic brake control, it is preferable to notify the vehicle driver in advance that the automatic brake control is started. Therefore, as shown in FIG. 3, the automatic brake 1 notification line and the automatic brake 2 notification line are determined by adding a predetermined offset time to the automatic brake 1 reference time line and the automatic brake 2 reference time line, respectively. ing. Therefore, when the predicted collision time TTC falls below the automatic brake 1 notification line and the automatic brake 2 notification line, a notification that the control of the automatic brake 1 and the automatic brake 2 will soon be started to the vehicle driver. Is made by alarm sound or voice.

  Next, the brake assist reference time line will be described. The above-described automatic brake 2 reference time line corresponds to the limit of physical collision avoidance by the driver's braking and steering operation. That is, in a situation corresponding to this automatic brake 2 reference time line, the driver must perform a sudden brake operation or a sudden handle operation in order to avoid a collision with a front obstacle.

  On the other hand, a line that allows the driver to avoid a collision with a front obstacle by performing a normal braking operation or a normal steering operation may be defined above the automatic brake 2 reference line in FIG. it can. Hereinafter, an example of a method for setting a line corresponding to a lower limit at which a collision can be avoided by a driver's normal braking operation or normal steering operation (hereinafter referred to as a collision possibility determination line) will be described with reference to FIG.

  First, as shown in FIG. 4, the line corresponding to the physical limit of collision avoidance by braking is offset so as to increase as a whole by time T (for example, 1 second), so that the driver can perform normal braking operation. Even if it performs, it can be set as the line which shows the reference time which can avoid a collision by the braking operation. Further, the time during which the driver can avoid the collision by the normal steering operation is substantially constant regardless of the relative speed between the host vehicle and the front obstacle as in the case of the automatic brake 2 reference time line. For this reason, the “line where the physical limit of collision avoidance by braking is offset by time T” and the “line where collision can be avoided by normal steering operation” are connected by connecting a line portion indicating a shorter reference time. The collision possibility determination line corresponding to the lower limit at which the collision with the front obstacle can be avoided can be determined by the braking operation or the normal steering operation.

  However, in the range where the relative speed between the host vehicle and the front obstacle is relatively high, the collision possibility determination line is defined by the “collision avoidance line by normal steering operation”. For this reason, even if the brake assist control is performed based on the collision possibility determination line, if the driver only performs the brake operation, it may be difficult to avoid a collision with a front obstacle.

  Therefore, in the vehicle braking assist device 10, a line (brake assist) that can avoid a collision with a front obstacle when the driver performs a normal braking operation and the braking force is amplified by the brake assist control. The brake assist reference time line, which is a reference for starting execution of brake assist control, was set in consideration of the collision avoidance line).

  Specifically, the “collision avoidable line by brake assist” exceeds the “collision avoidable line by normal steering operation” when the relative speed between the host vehicle and the front obstacle is about 40 km / h. . For this reason, the brake assist reference time line was determined in accordance with the “collision avoidance line by brake assist” in the range beyond that. As a result, as the relative speed increases, the brake assist is started at an earlier timing. Therefore, even when the relative speed increases, the collision with the front obstacle can be avoided by the driver's normal brake operation. . As a result, the driver can generate a braking force necessary for avoiding a collision with a front obstacle by the brake assist control only by performing a normal braking operation instead of a strong and rapid braking operation.

  Note that the alarm reference time line shown in FIGS. 3 and 4 is used to warn the driver that the risk of the host vehicle colliding with a front obstacle is increasing. The alarm reference time line is determined by sliding the above-described collision possibility determination line upward by a first predetermined time. When the predicted collision time TTC falls below the warning reference line, a warning sound or sound is informed that the danger of a collision with a front obstacle is increasing.

  Here, when such an alarm reference time line is set, it is not preferable that the brake assist reference time line exceeds the alarm reference time line. In the pre-crash brake assist control, unlike the normal brake assist control, the braking force amplified by the brake assist control is generated only by the driver performing the normal brake operation. Therefore, when brake assist control is started without any notification, the driver may feel uncomfortable.

  Therefore, as shown in FIGS. 3 and 4, the brake assist reference time line is set so as not to exceed the alarm reference time line, that is, the point where the collision avoidable line by the brake assist intersects the alarm reference time line. In a range where the relative speed is higher than the starting point, the brake assist reference time line is set to coincide with the alarm reference time line. Thereby, generation | occurrence | production of the malfunction mentioned above can be prevented.

  Further, in FIG. 3, a warning brake reference time line is further defined. This warning brake reference time line is intended to surely inform the vehicle driver that the danger of a collision with a front obstacle is imminent, and generates a braking force by the alarm brake to decelerate the vehicle. . As the vehicle decelerates, the driver of the vehicle will experience a change in acceleration, so even if the driver is driving aside, the driver is in danger of a collision Can be noticed. The alarm brake reference time line is determined by sliding the collision possibility determination line upward by a second predetermined time, similarly to the alarm reference time line, but the second predetermined time. Is shorter than the first predetermined time.

  When the predicted collision time TTC falls below the warning brake reference time line, the braking force by the warning brake is automatically generated in the vehicle in order to give a warning to the driver. Therefore, it can be said that the alarm brake is a kind of automatic brake. However, the alarm brake is not intended to give the vehicle a braking force for avoiding a collision. Therefore, as shown in FIG. 5, when the alarm brake is operated for a predetermined time, the operation is thereafter terminated. Furthermore, the target deceleration by the alarm brake is set smaller than the target deceleration by the automatic brake 1 and the automatic brake 2.

  Furthermore, since the alarm brake is used to warn the driver of the vehicle that the danger of a collision is imminent, the driver has already noticed a front obstacle and is operating the brake. In some cases, the operation is omitted.

  Thus, the vehicle braking assistance device 10 determines the control to be executed by comparing the predicted collision time TTC with various reference time lines.

1 is a block diagram illustrating an overall configuration of a vehicle braking assistance device according to an embodiment. It is a flowchart which shows the control processing performed in the braking assistance apparatus for vehicles. It is a graph which shows the various reference time lines compared with collision prediction time, in order to determine the control content by the brake assistance apparatus for vehicles. It is explanatory drawing for demonstrating an example of the setting method of a brake assist reference | standard time line. It is explanatory drawing explaining the automatic brake control containing an alarm brake, the automatic brake 1, and the automatic brake 2. FIG.

Explanation of symbols

1 Radar Sensor 2 Yaw Rate Sensor 3 Vehicle Speed Sensor 4 Brake Sensor 5 Collision Mitigation Controller 6 Brake Actuator

Claims (3)

Distance detection means for detecting the distance between the host vehicle and the front obstacle;
A relative speed detecting means for detecting a relative speed between the host vehicle and the front obstacle;
A collision prediction time calculation means for calculating a collision prediction time until the collision timing between the host vehicle and the front obstacle based on the distance and the relative speed;
A brake assist means for increasing a braking force by a driver's brake operation when the predicted collision time falls below a predetermined brake assist reference time;
When the relative speed is greater than or equal to the first predetermined value, the relative speed is increased for the predetermined brake assist reference time so that a collision with the front obstacle can be avoided by a driver's normal brake operation. Is set to grow according to
In the range where the relative speed is less than the first predetermined value, in the range where the relative speed is from zero to the second predetermined value, the brake assist reference time is the brake assist reference in the range equal to or greater than the first predetermined value. Set to increase at a rate that is less than the rate of time increase,
In a range from the second predetermined value to the first predetermined value, the vehicle is set to a substantially constant time during which a collision with the front obstacle by a steering operation by a driver can be avoided. Braking assist device. Warning means for warning that there is a possibility of a collision with the front obstacle when the predicted collision time falls below a warning reference time in which the relative speed is substantially constant within a range of the first predetermined value or more. With
The brake assist reference time is set so as to be substantially constant even when the relative speed is further increased from the time when the brake assist reference time is increased to the alarm reference time so as not to exceed the alarm reference time. The vehicle braking support device according to claim 1. Automatic braking means for automatically generating a braking force when the predicted collision time falls below an automatic brake reference time set shorter than the brake assist reference time;
When the predicted collision time is less than the automatic brake reference time, a required deceleration corresponding to the driver's brake operation is calculated, and a target deceleration during braking by the automatic braking means is obtained to reduce the vehicle speed. The vehicle braking assistance device according to claim 1 or 2, wherein a braking force is generated in the vehicle so that a speed matches a maximum value of the requested deceleration and the target deceleration.

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