JP4826421B2 - Brake control device for vehicle - Google Patents

Description

  The present invention relates to a vehicular braking control device that performs braking force reduction control when a vehicle shifts to a stop state.

When the vehicle stops due to braking, the vehicle speed becomes zero, so the deceleration becomes zero at a stroke from the predetermined amount. As a result, a nose dive swinging phenomenon occurs in the vehicle, and the passenger receives a stop shock and feels uncomfortable. In order to reduce this stop shock, there is a braking control device that reduces the brake pressure (reducing the braking force) and reduces the deceleration before the vehicle stops. In particular, in the vehicle brake device disclosed in Patent Document 1, the road surface gradient is detected, the control suspension deceleration and the decompression suspension deceleration are obtained based on the road surface gradient, and the vehicle deceleration is larger than the control suspension deceleration. Sometimes the pressure reduction control is performed, and the pressure reduction control is stopped when the vehicle deceleration becomes equal to or lower than the pressure reduction stop deceleration during the pressure reduction control. Furthermore, in this vehicle brake device, the control suspension deceleration and the decompression suspension deceleration are changed according to the magnitude of the road surface gradient.
JP-A-5-270376 JP-A-11-208439 JP-A-5-193474

  When the brake pressure is controlled to be reduced before stopping, after the stop, the pressure increasing control for returning to the brake pressure corresponding to the depression amount of the driver's brake pedal is performed. In particular, when there is a slope on the road surface, if this pressure increase control is not performed, the braking force is insufficient and the vehicle slides down. Therefore, it is necessary to determine with high accuracy when the vehicle has completely stopped. However, the wheel speed sensor generally used for detecting the vehicle speed has a limit in detection accuracy. In particular, the detection accuracy decreases as the vehicle speed approaches 0 km / h. Therefore, when such a wheel speed sensor is used, an error occurs in the vehicle stop determination. Even if the stop timing is estimated from the history such as past vehicle speed changes in this stop determination, it is technically difficult to eliminate this determination error due to a change in road surface gradient or a disturbance such as wind power. In addition, increasing the accuracy of the sensor leads to an increase in cost.

  Therefore, in order to prevent the vehicle from slipping down, it is necessary to quickly return to the brake pressure corresponding to the driver's brake operation. However, if the start of the brake pressure increase control is excessively advanced in order to quickly return the brake pressure, the braking force increases before the stop and induces a stop shock.

  Accordingly, the present invention provides a vehicle brake control device that suppresses vehicle slippage and reduces stop shock even when the road surface has a gradient in a vehicle that performs braking force reduction control to reduce stop shock. The task is to do.

In the vehicular brake control apparatus according to the present invention, after determining the stop of the vehicle to reduce the braking force control have lines, based on the vehicle speed calculated from the detected value of the wheel speed sensors when the vehicle moves to a stopped state A vehicular braking control apparatus that performs an increase control of a braking force, comprising: a control unit that controls a braking force; and a road surface gradient acquisition unit that acquires a road surface gradient. The control unit is acquired by the road surface gradient acquisition unit. The rate of increase of braking force is set based on the road surface gradient, the braking force is increased according to the rate of increase after vehicle stoppage is determined , and a larger value is set as the rate of increase of braking force as the road surface gradient increases. And

  In this vehicle braking control device, when the vehicle shifts to the stop state, the control means reduces the braking force to reduce the braking force from a normal level (for example, a braking force corresponding to the driver's brake operation). . Thereby, when the vehicle stops, the deceleration is suppressed, so that the stop shock is reduced. In the vehicle braking control apparatus, the road surface gradient acquisition means acquires the road surface gradient. The greater the gradient of this road surface, the greater the force in the direction of descending the road surface due to gravity acting on the vehicle. In the vehicle braking control device, the control means sets the increasing rate of the braking force based on the acquired road surface gradient, and after increasing the braking force according to the increasing rate after determining that the vehicle has stopped. Return the braking force to normal. In this way, by changing the rate of increase of the braking force according to the road surface gradient, the braking force once reduced can be controlled against the force of gravity according to the road surface gradient acting on the vehicle. Power can be increased. Therefore, even when the force according to the gradient is large, the braking force of the vehicle increases rapidly. As a result, even when there is an error in the vehicle stop determination (for example, even when the stop determination is delayed from the actual stop of the vehicle), the vehicle slippage can be suppressed or prevented as much as possible. In addition, when the force corresponding to the gradient is small, the braking force of the vehicle gradually increases. As a result, even when there is an error in the vehicle stop determination (for example, even when the stop determination is made earlier than the actual stop of the vehicle), the stop shock can be reduced. Further, even when there is an error in the vehicle stop determination, it is possible to suppress the vehicle sliding down and reduce the stop shock, so that a speed sensor generally used for vehicle stop determination can be applied, and the cost increase due to the sensor can also be suppressed.

  In this vehicle braking control device, the larger the road gradient, the larger the braking force increase rate is set, and the greater the force corresponding to the road gradient acting on the vehicle, the faster the vehicle braking force increases. The braking force of the vehicle can be gradually increased as the force corresponding to the gradient becomes smaller.

  The braking force to be controlled may be generated by any means, for example, means for changing the hydraulic pressure of the wheel cylinder by the brake pressure, means for operating the brake pad by a motor for each wheel. . The road surface gradient acquisition means may be any means as long as the road surface gradient can be acquired. For example, means for estimating the road surface gradient using longitudinal acceleration acting on the vehicle, means for directly detecting with the sensor, road surface gradient information There is a means for holding map data having and acquiring from the map data. An appropriate method may be applied to the vehicle stop determination. For example, when a highly accurate speed sensor is used, the vehicle stop is detected when the vehicle speed is detected as 0 km / h, and the accuracy is not so high. When a speed sensor is used, there are a method for estimating the stop of the vehicle speed after the vehicle speed has fallen to the detection limit of the speed sensor, and a method for acquiring information on the stop of the host vehicle from the outside.

  According to the present invention, by increasing the braking force according to the road surface gradient, the vehicle can be prevented from sliding down as much as possible even when the road surface has a gradient, and the stop shock can be reduced as much as possible.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of a vehicle brake control device according to the present invention will be described with reference to the drawings.

  In the present embodiment, the vehicle brake control device according to the present invention is applied to a brake control device mounted on an automatic vehicle. The braking control device according to the present embodiment controls the braking force by controlling the brake pressure, and has a stop shock reduction function. In the present embodiment, only the stop shock reduction function in the brake control device will be described, but a brake control device having other functions besides the stop shock reduction function may be used.

  With reference to FIGS. 1-4, the braking control apparatus 1 which concerns on this Embodiment is demonstrated. FIG. 1 is a configuration diagram of a braking control device according to the present embodiment. FIG. 2 is a diagram showing the relationship among the driving force, braking force, and gravity (gradient force) acting on the vehicle being braked on a road surface having a predetermined gradient. FIG. 3 is a map showing the increase rate of the brake pressure with respect to the road surface gradient held by the ECU of FIG. FIG. 4 is an example of a time change of the braking force at the end of the stop shock reduction control by the braking control device of FIG.

  The brake control device 1 controls the brake pressure to be reduced when the vehicle shifts to a stop state in order to reduce a shock when the vehicle stops, and a brake corresponding to the driver's brake operation when the vehicle stops. Increase control to pressure. In particular, the brake control device 1 increases the brake pressure increase rate according to the road surface gradient (slope) in order to prevent the vehicle from slipping down as much as possible even when the road surface has a gradient. change. For this purpose, the braking control device 1 includes a longitudinal acceleration sensor 2, a wheel speed sensor 3, a wheel cylinder pressure sensor 4, a master cylinder pressure sensor 5, a brake actuator 6, and an ECU [Electronic Control Unit] 7.

  In the present embodiment, the ECU 7 corresponds to the control means described in the claims, and the sensors 2, 4 and the ECU 7 correspond to the road surface gradient acquisition means described in the claims.

  The longitudinal acceleration sensor 2 is a sensor that detects the longitudinal acceleration of the vehicle. The longitudinal acceleration sensor 2 detects the longitudinal acceleration of the vehicle and transmits the detected value to the ECU 7 as a longitudinal acceleration signal.

  The wheel speed sensor 3 is a sensor that is provided on each wheel and detects the rotational speed of the wheel. The wheel speed sensor 3 detects the rotational speed of the wheel and transmits the detected value to the ECU 7 as a wheel speed signal. For each wheel, the ECU 7 calculates the wheel speed of each wheel from this rotational speed, and calculates the vehicle speed from the wheel speed of each wheel. The wheel speed sensor 3 includes a pickup coil in which a copper wire is wound around a permanent magnet, and generates a voltage when the projection of the gear pulser that rotates with the wheel crosses the magnetic flux generated by the permanent magnet. It changes according to the rotation speed of the wheel. Therefore, as the vehicle speed decreases, the frequency decreases, and the accuracy of the wheel speed calculated by the ECU 7 decreases. Therefore, the vehicle speed detection based on the detection value of the wheel speed sensor 3 cannot accurately detect 0 km / h when the vehicle is actually stopped.

  The wheel cylinder pressure sensor 4 is a sensor that is provided on each wheel and detects the hydraulic pressure of the wheel cylinder. The wheel cylinder pressure sensor 4 detects the wheel cylinder pressure and transmits the detected value to the ECU 7 as a wheel cylinder pressure signal.

  The master cylinder pressure sensor 5 is a sensor that is provided in the master cylinder and detects the hydraulic pressure of the master cylinder. The master cylinder pressure sensor 5 detects the master cylinder pressure and transmits the detected value to the ECU 7 as a master cylinder pressure signal. The master cylinder pressure indicates the amount of brake operation by the driver because the pedal effort of the brake pedal is amplified by the brake booster and the amplified pedal effort is converted by the master cylinder. Usually, since the braking force according to the master cylinder pressure is generated, the braking force according to the driver's brake operation is generated.

  The brake actuator 6 is an actuator that is provided on each of two systems of hydraulic pipes that connect the master cylinder and the wheel cylinders of each wheel, and that adjusts the brake pressure that is output from the master cylinder and output to the wheel cylinder. . The brake actuator 6 includes a pressure regulating valve provided in the hydraulic piping and a motor for changing the opening of the pressure regulating valve. Normally, this pressure regulating valve is fully opened, and the wheel cylinder pressure is a hydraulic pressure corresponding to the driver's brake operation. In each brake actuator 6, the motor is driven to rotate in accordance with the control current from the ECU 7 to operate the pressure regulating valve, the opening degree is adjusted, and the wheel cylinder has a predetermined hydraulic pressure (lower than the hydraulic pressure corresponding to the driver's brake operation). Hydraulic pressure). Note that the brake actuator may adjust the hydraulic pressure of the master cylinder or the hydraulic pressure of each wheel cylinder.

  The ECU 7 is an electronic control unit that includes a CPU [Central Processing Unit], a ROM [Read Only Memory], a RAM [Random Access Memory], and the like, and performs overall control of the braking control device 1. In the ECU 7, detection signals are received from the sensors 2, 3, 4, 5 at regular intervals. Then, the ECU 7 controls the brake actuator 6 based on each detection signal by the stop shock reduction function. The ECU 7 performs vehicle stop determination, road surface gradient estimation, and the like in order to perform a stop shock reduction function.

  The vehicle stop determination will be described. The ECU 7 calculates the wheel speed of each wheel from the detected value indicated by the wheel speed signal of each wheel. Further, the ECU 7 calculates the vehicle speed (vehicle speed) from the wheel speed of each wheel. As described above, the calculated vehicle speed includes an error corresponding to the detection accuracy of the wheel speed sensor 3, and particularly when the vehicle is actually stopped, it cannot be detected as 0 km / h. Therefore, when the vehicle speed calculated from the wheel speed of each wheel falls to the detection limit vehicle speed, the ECU 7 estimates the stop of the vehicle based on the driving force (creep force), braking force, road surface gradient, and the like at that time. The estimated stop time may be earlier than the time when the vehicle actually stops, but may be later.

  The driving force is a value based on the engine torque and the vehicle speed, and the information is acquired from the ECU that controls the engine. The braking force is a total value of the braking force of each wheel. The braking force of each wheel is a value based on the wheel cylinder pressure of each wheel. The ECU 7 calculates the braking force acting on the vehicle from the wheel cylinder pressure of each wheel at regular intervals during braking. Further, the ECU 7 estimates the road surface gradient θ at regular intervals during braking.

  The road gradient estimation will be described. As shown in FIG. 2, during braking, a driving force (creep force) Fe in the traveling direction of the vehicle and a braking force Fb in a direction opposite to the traveling direction of the vehicle are applied to the vehicle. Further, since the gravitational acceleration g acts on the vehicle, when the road surface has a gradient θ, a force (hereinafter referred to as a gradient force) Fg in a downward direction corresponding to the gradient θ acts on the vehicle. To do. This gradient force Fg acts in the direction opposite to the traveling direction of the vehicle when the vehicle is going up the slope, and acts in the traveling direction of the vehicle when the vehicle is going down the slope. Therefore, assuming that the vehicle is going up a slope, the relationship of Expression (1) is established during braking.

  M is the weight of the vehicle, and a is the longitudinal acceleration (deceleration) of the vehicle. “a” is expressed by a plus / minus value, and is a plus value during acceleration and a minus value during deceleration. Here, since the gradient force Fg is Mgsin θ, Equation (1) can be converted to Equation (2). Note that when the vehicle is going down a slope, the gradient force Fg (Mgsin θ) acts in the traveling direction of the vehicle, so Fg (Mgsin θ) is added to the equation. Further, when there is no gradient on the road surface, the gradient force Fg (Mgsin θ) is zero.

  Equation (2) is converted to Equation (3). The ECU 7 can estimate the gradient θ during braking by calculating the gradient θ from the equation (3). Further, when the vehicle stops, the longitudinal acceleration a (deceleration) becomes 0, and therefore equation (3) becomes equation (4). The ECU 7 can estimate the gradient θ during stoppage by calculating the gradient θ from the equation (4).

  In the equations (3) and (4), the longitudinal acceleration a is the value detected by the longitudinal acceleration sensor 2, the driving force Fe is the value from the engine ECU as described above, and the braking force Fb is the ECU 7 described above. The calculated value at is used.

  The stop shock reduction function will be described. When the ECU 7 detects a driver's brake operation based on a change in the master cylinder pressure, the ECU 7 determines whether or not a stop shock reduction control start condition is satisfied at regular intervals. The stop shock reduction control start condition is that the calculated vehicle speed is equal to or less than the vehicle speed threshold. The vehicle speed threshold is a low vehicle speed when the vehicle shifts to the stop state, and is a vehicle speed that is at least higher than the vehicle speed at the detection limit by the wheel speed sensor 3. The vehicle speed threshold is set in advance by experiments or the like. FIG. 4 shows the time change of the braking force during braking, and the time indicated by t1 is the time when the vehicle speed becomes equal to or lower than the vehicle speed threshold. The braking force up to t1 is the braking force Fb1 corresponding to the driver's braking operation.

  When it is determined that the vehicle speed is equal to or less than the vehicle speed threshold, first, the ECU 7 calculates a reduction lower limit braking force. The reduction lower limit braking force is a minimum braking force required for the vehicle. In particular, when the road surface has a gradient, the lower limit braking force is a braking force necessary for the vehicle not to slide down. Therefore, it is necessary for the lower limit reduction braking force to consider the driving force, the braking force, and the gradient, as well as the target deceleration for reducing the stop shock. The target deceleration is a small deceleration that can suppress the swing-back due to the nose dive to such an extent that the occupant does not feel uncomfortable when the vehicle stops (when the deceleration becomes zero). The target deceleration is set in advance by experiments or the like. The ECU 7 calculates a braking force Fb that satisfies the relationship of the expression (2) when the longitudinal acceleration a is set as the target deceleration, and uses this calculated value as a reduction lower limit braking force. At this time, in Equation (2), the driving force Fe is a value from the engine ECU described above, and the gradient θ is an estimated value from the ECU 7 described above.

  When the actual deceleration is smaller than the target deceleration or when the master cylinder pressure (that is, the driver's brake operation amount) is smaller than the predetermined pressure, the brake pressure reduction control is performed without calculating the reduction lower limit braking force. Not performed. Further, the reduction lower limit braking force may be obtained by another method, for example, may be obtained based on a master cylinder pressure or the like, or may be a predetermined constant value.

  The ECU 7 calculates a brake pressure for achieving a target reduction rate at regular time intervals, and sets a target opening of the pressure regulating valve for achieving the brake pressure. Then, the ECU 7 generates a control current necessary for achieving the target opening degree of the pressure regulating valve, supplies the control current to the motor of each brake actuator 6, and controls the brake pressure to be reduced. The target reduction rate is a constant value, and is set to a reduction rate that does not give the passenger a sense of incongruity due to a reduction in brake pressure. The target reduction rate is set in advance by experiments or the like. Note that the target reduction rate may be a variable value. For example, the target reduction rate may be set so that the braking force becomes the reduction lower limit braking force when the vehicle stops every time stop shock reduction control is performed.

  After the start of the brake pressure reduction control, the ECU 7 determines whether or not the braking force has become the reduction lower limit braking force at regular time intervals. The ECU 7 continues the above-described pressure reduction control of the brake pressure until the braking force is reduced to the reduction lower limit braking force. When it is determined that the braking force has become the lower limit braking force, the ECU 7 stops the above-described brake pressure reduction control and holds the opening of the pressure regulating valve (and thus holds the braking force at the lower limit braking force). . As shown in FIG. 4, after t1, the braking force is reduced at the target reduction rate until the lower limit braking force Fb2 is reached. When the braking force is reduced to the lower limit lower braking force Fb2, the vehicle deceleration is about the target deceleration, and no swing back by nose dive that causes discomfort to the occupant when the vehicle stops is not generated.

  Further, after starting the brake pressure reduction control, the ECU 7 determines whether or not the stop shock reduction control end condition is satisfied at regular intervals. The stop shock reduction control end condition is a condition that the vehicle has stopped, and is determined by the vehicle stop determination described above. In FIG. 4, the time indicated by t2 is the time when the ECU 7 determines that the vehicle has stopped. However, the time point when the vehicle actually stops is a time point indicated by t2 ', which is earlier than the time point t2 when the ECU 7 determines the vehicle stop. When the stop shock reduction control termination condition is satisfied (when it is determined that the vehicle is stopped), the braking force usually decreases to the lower limit braking force, but the amount of depression of the brake pedal by the driver is large. When the braking force at the time of starting the brake pressure reduction control is large, the braking force may not be reduced to the lower limit braking force.

  If it is determined that the vehicle has stopped, the ECU 7 first calculates the road surface gradient θ at that time. Specifically, since the vehicle is stopped at this time, the longitudinal acceleration (deceleration) of the vehicle becomes 0, and the ECU 7 controls the driving force (creep force) at that time and the wheel cylinder pressure of each wheel (and hence the control). The road surface gradient θ is calculated from the above equation (4).

  Then, the ECU 7 refers to the brake pressure increase rate map and extracts the pressure increase rate corresponding to the calculated road surface gradient θ. The brake pressure increase rate map is a map showing the increase rate of the brake pressure at the end of the stop shock reduction control with respect to the road gradient. As shown in FIG. 3, in the brake pressure increase rate map, a default increase rate is set when the road gradient is 0 (that is, a horizontal plane), and the increase increases linearly as the gradient increases from the default value. The rate is set. The brake pressure increase rate map is set in advance by experiments or the like.

  Then, the ECU 7 calculates a brake pressure for achieving the extracted increase rate at regular time intervals, and sets a target opening of the pressure regulating valve for achieving the brake pressure. Then, the ECU 7 generates a control current necessary for achieving the target opening of the pressure regulating valve, supplies the control current to the motor of each brake actuator 6, and controls the brake pressure to increase. After the start of the brake pressure increase control, the ECU 7 determines whether or not the pressure regulating valve of the brake actuator 6 is fully opened at regular time intervals (that is, whether the braking force is a braking force corresponding to the driver's braking operation). Or not). The ECU 7 continues the above-described brake pressure increase control until the braking force increases to a braking force corresponding to the driver's braking operation.

  FIG. 4 shows the time change of the braking force due to the brake pressure increase control at the end of the stop shock reduction control when the road surface has a predetermined gradient and when the gradient is 0. A case where the gradient is 0 is indicated by reference numeral I2. When it has a predetermined gradient, the braking force increases more quickly to the braking force Fb1 corresponding to the driver's braking operation than when the gradient is zero. Thus, the braking force increases at a large increase rate as the road surface becomes steep, so even if the vehicle stop determination time t2 is slightly delayed from the actual stop time t2 ′, the braking force is rapidly increased. Since the braking force returns to the braking operation, the vehicle can be suppressed or prevented from slipping down even on a steep slope. On the other hand, the braking force increases at a small increase rate as the slope of the road becomes gentler, so even if the vehicle stop judgment time is a little earlier than the actual stop time, the braking force slowly responds to the driver's brake operation. Since it returns to the braking force, it does not induce a stop shock of the vehicle.

  With reference to FIG. 1, the operation | movement of the stop shock reduction function in the braking control apparatus 1 is demonstrated. In particular, processing in the ECU 7 will be described along the flowchart of FIG. FIG. 5 is a flowchart showing a flow of processing of the stop shock reduction function in the ECU of FIG.

  The longitudinal acceleration sensor 2 detects the longitudinal acceleration of the vehicle and transmits a longitudinal acceleration signal to the ECU 7. Each wheel speed sensor 3 detects the rotational speed of each wheel and transmits each wheel speed signal to the ECU 7. Each wheel cylinder pressure sensor 4 detects the hydraulic pressure of the wheel cylinder of each wheel and transmits each wheel cylinder pressure signal to the ECU 7. The master cylinder pressure sensor 5 detects the oil pressure of the master cylinder and transmits a master cylinder pressure signal to the ECU 7.

  The ECU 7 receives signals from the sensors 2, 3, 4, 5 at regular intervals. Then, the ECU 7 calculates the wheel speed based on the wheel speed signal of each wheel, and further calculates the vehicle speed from the wheel speed of each wheel. Further, the ECU 7 determines whether or not the driver is operating a brake based on the master cylinder pressure signal. When the brake is being operated, since the pressure regulating valve of the brake actuator 6 is normally fully open, a brake pressure corresponding to the driver's brake operation is generated in the wheel cylinder of each wheel. Therefore, a braking force according to the driver's braking operation acts on the vehicle, and the vehicle decelerates.

  When it is determined that the brake is being operated, the ECU 7 determines whether or not the calculated vehicle speed is equal to or less than the vehicle speed threshold at regular time intervals, and determines whether or not the stop shock reduction control start condition is satisfied (S1). If it is determined in S1 that the stop shock reduction control start condition is not satisfied, the ECU 7 waits until a predetermined time elapses and performs the stop shock reduction control start condition determination again. At this time, the fully open state of the pressure regulating valve of the brake actuator 6 is maintained, and a braking force according to the driver's braking operation is applied to the vehicle.

  When it is determined in S1 that the stop shock reduction control start condition is satisfied (when the vehicle is at a low speed before the stop), the ECU 7 uses the road surface gradient and driving force at that time to determine the longitudinal acceleration a as the target deceleration. A reduction lower limit braking force that satisfies the relationship of the equation (2) is calculated (S2). At this time, the ECU 7 calculates the gradient of the road surface from Equation (3). Then, at regular intervals, the ECU 7 generates a control current necessary for achieving the target reduction rate, and supplies the control current to the motor of each brake actuator 6 (S2). The motor is driven to rotate according to this control current. The pressure regulating valve is gradually closed by the rotational driving force of the motor. The hydraulic pressure generated in the wheel cylinder of each wheel is gradually reduced by the opening by the pressure regulating valve. Therefore, a braking force smaller than the braking force corresponding to the driver's braking operation is applied to the vehicle, and the braking force gradually decreases.

  After starting the brake pressure reduction control, the ECU 7 determines whether or not the braking force has decreased to the reduction lower limit braking force (S2). When it is determined that the braking force has not decreased to the lower limit lowering braking force, the ECU 7 waits until a predetermined time elapses and performs motor control in accordance with the target reduction rate (S2). On the other hand, when it is determined that the braking force has decreased to the lower limit braking force, the ECU 7 ends the brake pressure reduction control. Thereafter, the brake pressure is maintained, and the reduction lower limit braking force continues to act on the vehicle.

  After starting the brake pressure reduction control, the ECU 7 determines whether or not the vehicle has stopped at regular intervals, and determines whether or not the stop shock reduction control end condition is satisfied (S3). When it is determined that the stop shock reduction control termination condition is not satisfied, the ECU 7 waits until a predetermined time elapses and performs the above-described brake pressure reduction control (S2).

  When the vehicle actually stops, the deceleration of the vehicle becomes zero. However, since the deceleration that has been acting on the vehicle just before is a small deceleration corresponding to the target deceleration, the vehicle does not generate a large nose dive and its swing back is suppressed as much as possible. Therefore, the vehicle occupant receives almost no stop shock and hardly feels discomfort.

  When it is determined that the stop shock reduction control end condition is satisfied, the ECU 7 calculates the road surface gradient θ by using the driving force and braking force at that time according to the above equation (4) (S4). Then, the ECU 7 refers to the brake pressure increase rate map, and sets the brake pressure increase rate according to the calculated road surface gradient θ (S5). Further, the ECU 7 generates a control current necessary for achieving the increase rate at regular intervals, and supplies the control current to the motors of the brake actuators 6 (S6). The motor is driven to rotate according to this control current. The pressure regulating valve is opened by the rotational driving force of the motor. The hydraulic pressure generated in the wheel cylinder of each wheel increases by the opening degree of the pressure regulating valve. Therefore, the braking force increases until the braking force according to the driver's braking operation is reached. At this time, as the road surface gradient increases, the brake pressure (and thus the braking force) increases rapidly.

  After the brake pressure increase control is started, the ECU 7 determines whether or not the braking force has become a braking force corresponding to the driver's braking operation. When it is determined that the braking force has not increased to the braking force corresponding to the driver's braking operation, the ECU 7 waits until a predetermined time elapses and performs motor control according to the above-described increase rate (S6). On the other hand, when it is determined that the braking force has increased to the braking force corresponding to the driver's brake operation, the ECU 7 ends the brake pressure increase control.

  Until the vehicle stop determination is made, a braking force smaller than the braking force corresponding to the brake operation by the driver is applied to the vehicle by the low pressure control of the brake pressure. When the gradient of the road surface is steep, a large gradient force is applied to the vehicle in a downward direction corresponding to the gradient. After the vehicle is judged to stop, the vehicle tends to slide down due to the large gradient force, but the braking force is controlled from the small braking force to the braking operation by the driver by the brake pressure increase control according to the large gradient. Increase rapidly. Therefore, the vehicle will slide down little or not at all. On the other hand, when the road surface has a gentle gradient (including a case where the gradient is zero), a small gradient force (including a case where the gradient force is zero) in the downward direction according to the gradient is applied to the vehicle. After the stop of the vehicle is determined, the braking force is gradually increased from a small braking force to a braking force corresponding to the brake operation by the driver by increasing the brake pressure according to the small gradient. For this reason, even if the vehicle stop determination is earlier than the actual time, the vehicle is hardly shaken back due to the nose dive.

  According to this braking control device 1, by controlling to increase the brake pressure in accordance with the road surface gradient, even when a stop determination is made later than the actual stop of the vehicle, the slippage of the vehicle is suppressed or prevented as much as possible. Even when the stop determination is made earlier than the actual stop of the vehicle, the stop shock can be reduced. Thus, in the braking control device 1, even if there is an error in the vehicle stop determination, it is possible to suppress the vehicle sliding down and reduce the stop shock, so that it is possible to apply a wheel speed sensor generally used for vehicle stop determination, Cost increase due to sensors can be suppressed.

  In this braking control device 1, by setting a larger value as an increase rate of the brake pressure as the road surface gradient is larger, the braking force of the vehicle can be rapidly increased as the gradient force acting on the vehicle becomes larger. As the force decreases, the braking force of the vehicle can be increased gradually.

  As mentioned above, although embodiment which concerns on this invention was described, this invention is implemented in various forms, without being limited to the said embodiment.

  For example, although the present embodiment is applied to an automatic vehicle, it can also be applied to other vehicles such as a manual vehicle and a CVT vehicle. In the case of a vehicle having no creep force, it is necessary to obtain a lower limit braking force and a road surface gradient by setting the driving force to zero.

  In the present embodiment, the road surface gradient is estimated using the longitudinal acceleration detected by the sensor. However, the road surface gradient may be acquired by other methods, for example, a configuration in which the road surface gradient is directly detected by the sensor. It is good also as a structure which hold | maintains the map data which has road surface gradient information, and acquires from map data.

  Further, in the present embodiment, the braking force is changed by the brake pressure, and the stop shock is reduced by reducing the brake pressure. However, other means may be used as a means for changing the braking force, for example, a wheel. A brake pad may be driven by a motor every time to change the braking force.

  In this embodiment, the brake pressure increase rate is set immediately after the stop shock reduction control end condition is satisfied. However, immediately after the stop shock reduction control start condition is satisfied or during the reduction control, the brake pressure increase rate is set. The rate of increase may be set. In this case, since the deceleration of the vehicle is not 0, the road surface gradient is obtained from Expression (3).

  In this embodiment, the map is used to extract the increase rate of the brake pressure according to the road surface gradient. However, another method may be used to obtain the increase rate, for example, based on the road surface gradient. It is good also as a structure which calculates the increase rate of brake pressure. Further, in the present embodiment, the increase rate is linearly increased according to the road surface gradient, but the relationship between the road surface gradient and the increase rate takes into account vehicle braking characteristics, vehicle weight, creep force, etc. You may set suitably.

It is a block diagram of the braking control apparatus which concerns on this Embodiment. It is a figure which shows the relationship of the driving force, braking force, and gravity (gradient force) which act on the vehicle currently braked on the road surface which has a predetermined gradient. It is a map which shows the increase rate of the brake pressure with respect to the road surface gradient hold | maintained by ECU of FIG. It is an example of the time change of the braking force at the time of completion | finish of the stop shock reduction control by the braking control apparatus of FIG. It is a flowchart which shows the flow of a process of the stop shock reduction function in ECU of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Brake control apparatus, 2 ... Longitudinal acceleration sensor, 3 ... Wheel speed sensor, 4 ... Wheel cylinder pressure sensor, 5 ... Master cylinder pressure sensor, 6 ... Brake actuator, 7 ... ECU

Claims (1)

There rows reduction control of the braking force when the vehicle shifts to the stop state, the vehicle brake control for increasing the braking force control after determining the stop of the vehicle based on the vehicle speed calculated from the detected value of the wheel speed sensor A device,
Control means for controlling the braking force;
Road surface gradient acquisition means for acquiring the road surface gradient,
The control means, the set rate of increase of the braking force based on the road surface gradient obtained in the road surface gradient obtaining means, in accordance with the increase rate after judging the vehicle is stopped to increase the braking force, the braking as road surface gradient is larger A braking control apparatus for a vehicle, wherein a large value is set as an increase rate of power .

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