JP2019182034A - Vehicular brake control apparatus - Google Patents

Abstract

An object of the present invention is to reliably hold a vehicle on a slope during execution of hill hold control regardless of the angle formed by the direction of the longitudinal axis of the vehicle and the "inclination direction of the slope" and the steering angle of the steering wheel.
A hill hold braking force is determined based on a first inclination angle θs and a second inclination angle θ specified by an angle parameter acquisition means, and a steering angle θf detected by a steering angle sensor. Thereby, even when the steering angle θf of the steered wheel is changed during the hill hold control, the vehicle can be prevented from moving in the downhill direction.
[Selection] Figure 7

Description

  The present invention provides a braking force for stopping a vehicle on a slope when the driver releases the brake pedal after the driver has operated the brake pedal and the vehicle has stopped on the slope. The present invention relates to a braking control device that executes hill hold control that continues to be applied to the vehicle.

  One of the conventional braking control devices (hereinafter referred to as “conventional device”) is designed to quickly increase the braking force so that the vehicle can start when the driver operates the accelerator pedal during the hill hold control. (For example, refer patent document 1).

JP 2007-112294 A

  By the way, the braking force (hill hold braking force) applied to each wheel during the hill hold control is set to a smaller value as the angle of the longitudinal axis of the vehicle stopping on the slope with respect to the horizontal plane is smaller. It is desirable. This is because when the accelerator pedal is depressed during the hill hold control and the hill hold control is terminated, the braking force is quickly reduced so that the vehicle can start smoothly. Therefore, the hill hold braking force is preferably determined based on the inclination of the longitudinal axis of the vehicle with respect to the horizontal plane.

  However, when the vehicle is stopped on the slope and the hill hold control is being executed, the direction of the longitudinal axis of the vehicle and the direction of the “component along the slope of gravity” acting on the vehicle (hereinafter referred to as “the slope The hill hold braking force determined as described above may be excessively small depending on the angle between the angle and the direction of the steering wheel (steering angle). As a result, the vehicle may move in the downhill direction from the stop position.

  For example, when the longitudinal axis of the vehicle stopped on the slope and the slope direction of the slope do not match, if the direction of the steering wheel of the vehicle is in the direction that matches the `` slope slope direction '' The lateral force of the steering wheel that contributes to the holding of the steering wheel is reduced. As a result, when the hill hold control is executed, the force for holding each wheel is insufficient, and the vehicle moves in the downhill direction.

  The present invention has been made to address the above-described problems. That is, one of the objects of the present invention is to ensure that the vehicle is placed on the slope when the hill hold control is executed, regardless of the angle formed by the direction of the longitudinal axis of the vehicle and the “slope inclination direction” and the steering angle of the steering wheel. An object of the present invention is to provide a braking control device for a vehicle that can be held.

Therefore, the vehicle braking control device of the present invention (hereinafter also referred to as “the present invention device”)
A braking device (40) for applying a braking force to each of the plurality of wheels (W) and a steering device (50) capable of changing the steering angle (θf) of the steering wheel (WF) of the plurality of wheels are provided. Applies to vehicle (12).

  The device according to the present invention releases the operation of the brake pedal after the vehicle stops on the slope (S) by applying a braking force according to the operation of the brake pedal (41) to the plurality of wheels by the braking device. And a control unit (70) that applies a hill hold braking force equal to or greater than a braking force required to keep the vehicle stopped when the vehicle is stopped (step 750).

The device of the present invention further comprises
Obtaining angle parameters for specifying a first inclination angle (θs) which is an angle formed by the slope and a horizontal plane (H) and a second inclination angle (θ) which is an angle representing the front-rear direction of the vehicle on the slope. Means (71, 70);
A steering angle sensor (73) for detecting the steering angle of the steering wheel.

  When the vehicle is stopped on the slope with the front-rear direction of the vehicle not parallel to the slope direction of the slope, if the steering wheel is operated in such a direction that the direction of the steering wheel approaches the slope direction of the slope, Lateral force decreases. As a result, the force (holding braking force) for holding each wheel calculated based on the first inclination angle (θs) and the second inclination angle (θ) is insufficient and the wheels rotate, and the vehicle moves in the downhill direction. The problem of moving to can occur.

  Therefore, in order to solve the above problem, the control unit is based on at least the first inclination angle and the second inclination angle specified by the angle parameter acquisition unit, and the steering angle detected by the steering angle sensor. The hill hold braking force is determined (step 720, step 730, step 790).

  Therefore, according to the device of the present invention, the vehicle is reliably held on the slope when the hill hold control is executed, regardless of the angle formed by the direction of the longitudinal axis of the vehicle and the “inclination direction of the slope” and the steering angle of the steering wheel. In addition, the vehicle can be prevented from moving in the downhill direction.

  In the above description, in order to help understanding of the present invention, names and / or symbols used in the embodiment are attached to the configuration of the invention corresponding to the embodiment described later in parentheses. However, each component of the present invention is not limited to the embodiment defined by the names and / or symbols.

FIG. 1 is a schematic configuration diagram of a vehicle to which a vehicle braking control device according to an embodiment of the present invention is applied. 2 is an explanatory view showing a state where the vehicle shown in FIG. 1 is stopped on a slope, FIG. 2 (A) is a perspective view of the vehicle stopped on the slope, and FIG. 2 (B) is a side view of the slope. FIGS. (1-1 cross-sectional view) and FIG. 2 (C) are top views (2-2 cross-sectional views) of the slope as seen from the normal direction of the slope. FIG. 3 is a model for explaining the operation of the vehicle braking control apparatus shown in FIG. 1, and is a view when the front portion of the vehicle is directed downward and the steering angle is zero. FIG. 4 is a diagram when the steering angle is a positive value in the model shown in FIG. 3. FIG. 5 is a diagram when the steering angle is a negative value in the model shown in FIG. 3. FIG. 6 is a model for explaining the operation of the vehicle braking control apparatus shown in FIG. 1, and is a view when the front portion of the vehicle faces upward. 6A is a diagram in which the steering angle is zero, FIG. 6B is a diagram in which the steering angle is a positive value, and FIG. 6C is a diagram in which the steering angle is a negative value. FIG. 7 is a flowchart showing a “hill hold control routine” executed by the CPU of the ECU shown in FIG.

(Constitution)
A vehicle braking control device according to an embodiment of the present invention (hereinafter also referred to as “the present control device”) is applied to a vehicle 10 as shown in FIG. The vehicle 10 includes a driving device 20, a driving force transmission mechanism 30, a hydraulic friction braking device 40, a steering device 50, an ECU 60, wheels W (WFL, WFR, WRL, and WRR) and the like.

  The drive device 20 includes an engine body, a transmission, and the like (not shown). The driving device 20 generates a driving force for driving the front wheels (the left front wheel WFL and the right front wheel WFR) of the vehicle 10 via the driving force transmission mechanism 30.

  The driving force transmission mechanism 30 includes a propeller shaft 31, a differential gear 32, a left front wheel axle 33L, a right front wheel axle 33R, and the like. The driving force generated by the driving device 20 is transmitted to the propeller shaft 31. The driving force of the propeller shaft 31 is transmitted to the left front wheel axle 33L and the right front wheel axle 33R via the differential gear 32, whereby the left front wheel WFL and the right front wheel WFR are rotationally driven.

  Hereinafter, for the elements provided for each wheel, a suffix FL representing the left front wheel, a suffix FR representing the right front wheel, a suffix RL representing the left rear wheel, and a suffix RR representing the right rear wheel are respectively attached to the end of the reference numerals. However, if the wheel position is not specified for the elements provided for each wheel, the suffixes are omitted.

  The hydraulic friction braking device 40 includes a brake pedal 41, a master cylinder 42, a hydraulic circuit 43, a wheel cylinder 44, and the like.

  The braking force of the wheel W is the pressure of hydraulic oil supplied to the wheel cylinder 44 corresponding to the wheel W by the hydraulic circuit 43 of the hydraulic friction braking device 40 (hydraulic pressure, hereinafter also referred to as “braking pressure”). It is controlled by controlling. That is, the braking force of the left front wheel WFL, the right front wheel WFR, the left rear wheel WRL, and the right rear wheel WRR is controlled by controlling the braking pressures of the wheel cylinders 44FL, 44FR, 44RL, and 44RR. The hydraulic circuit 43 includes a reservoir, an oil pump, various valve devices and the like (not shown) and functions as a brake actuator.

  The braking pressure of the wheel cylinder 44 is controlled by the ECU 60 based on the pressure Pm of the master cylinder 42 (hereinafter also referred to as “master cylinder pressure”) that changes in response to the driver's depression operation of the brake pedal 41 in the normal state. Or individually controlled as needed.

  The hydraulic circuit 43 is a well-known circuit provided with a holding valve and a pressure reducing valve (not shown) corresponding to each wheel cylinder 44 for individually controlling the braking pressure of each wheel cylinder 44 as a valve device. The holding valve and the pressure reducing valve are well-known two-position solenoid valves that selectively select one of the communication position and the shut-off position.

  The steering device 50 includes a steering wheel 51, a steering shaft 52, a rack shaft 53, a rack and pinion mechanism 54, and the like. The steering wheel 51 and the steering shaft 52 are connected coaxially and integrally rotatable. The steering shaft 52 and the rack shaft 53 are connected by a known rack and pinion mechanism 54. The left front wheel WFL and the right front wheel WFR are connected to both ends of the rack shaft 53 via knuckle arms 55L and 55R, respectively.

  When the steering wheel 51 is operated by the driver, the rotational motion of the steering shaft 52 is converted into the axial linear motion of the rack shaft 53 by the rack and pinion mechanism 54, whereby the left front wheel WFL and the right front wheel WFR are steered. To do. Furthermore, the steering device 50 is provided with a power steering mechanism (not shown) for assisting the driver's steering operation.

  The ECU 60 is electrically connected to an inclination sensor 71, a wheel speed sensor 72 for each wheel, a steering angle sensor 73, a master cylinder pressure sensor 74, and the like, and receives output signals from these sensors. The ECU is an abbreviation for an electronic control unit, and is an electronic control circuit having a microcomputer including a CPU, a ROM, a RAM, a backup RAM (or nonvolatile memory), an interface I / F, and the like as main components. The CPU implements various functions to be described later by executing instructions (routines) stored in a memory (ROM).

  The tilt sensor 71 is a sensor that can detect acceleration along the directions of two axes (x-axis and y-axis) orthogonal to each other. The tilt sensor 71 is attached to the vehicle 10 such that the x axis coincides with the front-rear direction of the vehicle 10 and the y axis coincides with the lateral direction of the vehicle 10. The inclination sensor 71 generates an output signal representing the longitudinal acceleration Gx with a value detected when the front part of the stopped vehicle 10 is located at a position lower than the rear part. The tilt sensor 71 generates an output signal representing the lateral acceleration Gy with a value detected when the right side of the stopped vehicle 10 is lower than the left side being positive.

  The wheel speed sensor 72 generates a signal NP corresponding to the rotational speed of the wheel W. The ECU 60 detects the vehicle speed based on the signal from the wheel speed sensor 72. The steering angle sensor 73 is attached to the steering shaft 52 and generates an output signal representing the steering angle θf of the steering wheel 51. The steering angle sensor 73 detects the steering angle θf with a value detected when the vehicle 10 turns left as a positive value. The master cylinder pressure sensor 74 generates an output signal representing the master cylinder pressure Pm.

(Operation)
The hill hold control execution (start) condition described above is satisfied when all of the following conditions are satisfied.
<Hill hold control execution conditions>
-The brake pedal 41 is operated.
-The vehicle speed is below a predetermined speed Vth.
The magnitude | θx | of the longitudinal inclination θx of the vehicle 10 is equal to or greater than a predetermined angle θxth.

The longitudinal tilt θx of the vehicle 10 is acquired based on a signal representing the longitudinal acceleration Gx detected by the tilt sensor 71. When the gravitational acceleration is expressed as g (m / s ² ), the detected longitudinal acceleration Gx and the tilt θx in the longitudinal direction have a relationship of Gx = g · sin θx.

  The hill hold control is canceled when an accelerator pedal (not shown) is operated by the driver. More specifically, when the driver operates the accelerator pedal during the hill hold control, the hydraulic circuit 43 starts to reduce the braking pressure.

  This control device is based on the minimum value of the braking force that can reliably hold the vehicle 10 on the slope in consideration of not only the direction in which the vehicle 10 is stopped with respect to the slope but also the steering angle θf. Thus, the braking force during the hill hold control (hereinafter referred to as “hill hold braking force”) is determined. The minimum value of the braking force that can reliably hold the vehicle 10 on the slope is referred to as “minimum holding braking force”. Accordingly, the hill hold braking force is equal to or greater than the minimum holding braking force.

  Hereinafter, the minimum holding braking force will be examined. As shown in FIG. 2A, it is assumed that the vehicle 10 is stopped on the slope S with the front portion of the vehicle 10 facing the lower side of the slope S (that is, the vehicle 10 is in a downhill state). The slope S is flat, and as can be understood from FIG. 2B which is a cross-sectional view taken along the line 1-1 in FIG. 2A, the angle between the slope S and the horizontal plane H (hereinafter referred to as “slope gradient” Or it is called “slope slope”) is θs.

When the weight of the vehicle 10 is expressed as m (kg) and the acceleration of gravity is expressed as g (m / s ² ), the gravity acting on the vehicle 10 is m · g. Therefore, as shown in FIG. 2B, the “component in the direction D along the slope S of gravity m · g” acting on the vehicle 10 is m · g · sin θs. Hereinafter, the direction in which the gravity component m · g · sin θs in the direction along the slope S acts on the vehicle 10 is referred to as “slope inclination direction D”. The vertical direction Z of the vehicle 10 coincides with the direction of the normal line N of the slope S.

  Further, as shown in FIG. 2C, which is a 2-2 cross-sectional view of FIG. 2A, a straight line that is orthogonal to the inclined direction D of the slope and is on the slope S is referred to as a straight line L1, and A straight line representing the front-rear direction is called a straight line X1, and an angle formed by the straight line L1 and the straight line X1 is called a stop angle θ. The stop angle θ is an angle representing the front-rear direction of the vehicle 10 on the slope S.

  The minimum holding braking force when the vehicle 10 is stopped as shown in FIGS. 2A to 2C will be examined using the model (two-wheel model) of the vehicle 10 shown in FIGS. 3 and 4 show views of the two-wheel model viewed from the normal N direction of the slope S. FIG. In these drawings, the distance between the ground contact point Pf of the front wheel WF and the ground contact point Pr of the rear wheel WR (ie, the wheel base) is L, and the distance between the center of gravity G and the ground contact point Pr of the rear wheel WR is Lr. .

As described above, the gravity component m · g · sin θs acts on the vehicle 10 in the inclination direction D of the slope. As shown in FIG. 3, when the steering angle θf is “0”, the minimum holding braking force of the front wheel WF is Fbf0, the rolling resistance of the front wheel WF is Rf, the lateral force of the front wheel WF is Kf0, and the minimum of the rear wheel WR is The holding braking force is represented by Fbr0, the rolling resistance of the rear wheel WR is represented by Rr, and the lateral force of the rear wheel WR is represented by Kr. At this time, the equation of balance of force in the inclination direction D of the slope is as shown in the following equation (1).

m ・ g ・ sinθs ＝ Kf0 ・ cosθ + (Fbf0 + Rf) ・ sinθ
+ Kr ・ cosθ + (Fbr0 + Rr) ・ sinθ (1)

On the other hand, the balance equation of the moment of force with the contact point Pr of the rear wheel WR as the center of rotation is as shown in the following equation (2).

Kf0 · L = (m · g · sinθs) · cosθ · Lr (2)

On the other hand, as shown in FIG. 4, when the steering angle θf is larger than 0 °, the minimum holding braking force of the front wheel WF is Fbf1, the lateral force of the front wheel WF is Kf1, and the minimum holding braking force of the rear wheel WR is Fbr1. When the lateral force of the rear wheel WR is expressed as Kr, the balance equation in the slope inclination direction D is expressed by the following equation (3).

m ・ g ・ sinθs ＝ Kf1 ・ cos (θ + θf) + (Fbf1 + Rf) ・ sin (θ + θf)
+ Kr · cosθ + (Fbr1 + Rr) · sinθ (3)

Further, in this case, the balance of the moment of force with the contact point Pr of the rear wheel WR as the center of rotation is expressed by the following equation (4).

Kf1 · cosθf + (Fbf1 + Rf) · sinθf) · L = m · g · sinθs · cosθ · Lr (4)

The following equation (5) is derived from the above equations (1) to (4).

(Fbf1−Fbf0) + (Fbr1−Fbr0) ・ cosθf
= (Lr / L) · m · g · sinθs · cosθ · sinθf + (Fbf0 + Rf) · (cosθf-1) (5)

  By the way, as understood from FIGS. 3 and 4, the lateral force Kf1 of the front wheel WF when the steering angle θf of the front wheel WF is a positive value is the lateral force when the steering angle θf of the front wheel WF is 0 °. The force is smaller than Kf0 (that is, Kf1 <Kf0). Further, when considering the range of the stop angle θ and the steering angle θf, cos (θ + θf) is smaller than cosθ. As a result, the component Kf1 · cos (θ + θf) of the “slope tilt direction D” of the lateral force of the front wheel WF when the steering angle θf is a positive value is the lateral force when the steering angle θf is 0 °. It is smaller than the component Kf0 · cos θ of the “slope inclination direction D”. That is, the component in the “slope inclination direction D” of the lateral force of the front wheel WF decreases from Kf0 · cos θ to Kf1 · cos (θ + θf). Therefore, the minimum holding braking force of the front wheel WF and the rear wheel WR when the steering angle θf of the front wheel WF is a positive value is the minimum holding braking force of the front wheel WF and the rear wheel WR when the steering angle θf is 0 °. Bigger than. That is, when the steering angle θf is larger than 0 °, in order to keep the vehicle 10 on the slope S, in addition to the minimum holding braking force when the steering angle θf is 0 °, “the lateral force of the front wheel WF” It is necessary to apply a “braking force to compensate for the decrease”. The value (Fbf1−Fbf0) and the value (Fbr1−Fbr0) seen on the left side of the above equation (5) are “braking force to compensate for the decrease in lateral force” to be applied to the front wheel WF and the rear wheel WR, respectively. It is.

  Therefore, it is considered to calculate the value (Fbf1-Fbf0) and the value (Fbr1-Fbr0) using the above equation (5). On the right side of the equation (5), there is a term for the minimum holding braking force Fbf0 of the front wheel WF when the steering angle θf is 0 °. As will be described later, the minimum holding braking force Fbf0 of the front wheel WF is uniquely calculated as a function of the slope gradient θs and the stop angle θ (see the following formula (11) and the following formula (12)). Therefore, the right side of the above equation (5) is a value that can be calculated as a function of the slope gradient θs, the stop angle θ, and the steering angle θf.

Here, if the value (Fbf1-Fbf0) is set as ΔFbf, the value (Fbr1-Fbr0) is set as ΔFbr, cos θf is set as C1, and the right side of the formula (5) is set as C2, the above formula (5) is It is represented by the following formula (6).

ΔFbf + ΔFbr · C1 = C2 (6)

Although the difference ΔFbf and the difference ΔFbr are not uniquely determined only by the equation (6), if ΔFbr / ΔFbf = K1 is set, the difference ΔFbf and the difference ΔFbr from the equation (6) are expressed by the following equations (7) and (8), respectively. ) Is calculated as follows:

ΔFbf = C2 / (1 + K1 · C1) (7)
ΔFbr = K1 · ΔFbf = K1 · C2 / (1 + K1 · C1) (8)

  From the above, if the “braking force for compensating for the decrease in lateral force” is calculated based on the slope gradient θs, the stop angle θ, and the steering angle θf, the minimum holding braking force Fbf1 of the front wheel WF is calculated based on the result. And the minimum holding braking force Fbr1 of the rear wheel WR can be calculated. However, it is necessary to calculate the minimum holding braking force Fbf0 of the front wheel WF when the steering angle θf is 0 °. This minimum holding braking force Fbf0 is calculated as follows.

The minimum holding braking force Fre of the entire vehicle 10 when the steering angle θf is 0 ° is equal to the product of “acceleration gx representing the forward / backward inclination of the vehicle 10” and the weight of the vehicle 10. The “acceleration gx representing the vehicle longitudinal inclination” is a component of the gravitational acceleration g in the longitudinal direction of the vehicle 10, and the “acceleration gx representing the vehicle longitudinal inclination” is calculated based on the longitudinal acceleration Gx. (Gx = g · sinθs · sinθ). The minimum holding braking force Fre of the entire vehicle 10 is expressed by the following equation (9).

Fre = m · gx (9)

By predetermining a ratio (front / rear distribution ratio) Fbf0 / Fbr0 between the minimum holding braking force Fbf0 of the front wheel WF and the minimum holding braking force Fbr0 of the rear wheel WR, the minimum holding control of the entire vehicle 10 calculated by the equation (9). The power Fre can be distributed to the front wheel WF and the rear wheel WR. Assuming that the front / rear distribution ratio Fbr0 / Fbf0 = K0, the equation (9) is expressed by the following equation (10).

Fre = Fbf0 + Fbr0 = (1 + K0) Fbf0 = m · gx (10)

Accordingly, the minimum holding braking force Fbf0 of the front wheel WF and the minimum holding braking force Fbr0 of the rear wheel WR are expressed by the following equations (11) and (12), respectively.

Fbf0 = gx / (1 + K0) (11)
Fbr0 = K0.Fbf0 = m.gx.K0 / (1 + K0) (12)

  Incidentally, when the steering angle θf of the front wheel WF is a negative value, as shown in FIG. 5, the lateral force Kf2 of the front wheel WF is greater than the lateral force Kf0 when the steering angle θf of the front wheel WF is 0 °. growing. Further, when considering the range of the stop angle θ and the steering angle θf, cos (θ + θf) is larger than cosθ. As a result, the component Kfi · cos (θ + θf) in the inclination direction D of the slope increases. That is, the component in the inclination direction D of the lateral force of the front wheel WF changes from Kf0 · cos θ to Kf2 · cos (θ + θf). Accordingly, the braking force Fbf2 required for the front wheel WF in this case is smaller than the braking force Fbf0 required when the steering angle θf is 0 °.

  When the vehicle 10 is stopped on the slope S in an uphill state, when the steering angle θf of the front wheel WF is 0 °, as shown in FIG. 6A, the slope of the lateral force Kf of the front wheel WF is increased. The component in the inclination direction D is Kf3 · cos θf.

  On the other hand, when the steering angle θf of the front wheel WF is a positive value, as shown in FIG. 6B, the lateral force Kf4 of the front wheel WF is obtained when the steering angle θf of the front wheel WF is 0 °. It becomes smaller than the lateral force Kf3. As a result, the component Kf · cos (θ + θf) in the inclination direction D of the slope also decreases. That is, the component in the inclination direction D of the lateral force of the front wheel WF changes from Kf3 · cos θ to Kf4 · cos (θ + θf). Accordingly, the braking force Fbf4 required for the front wheel WF in this case is larger than the braking force Fbf3 required when the steering angle θf is 0 °.

  On the other hand, when the steering angle θf of the front wheel WF is a negative value, as shown in FIG. 6C, the lateral force Kf5 of the front wheel WF is the lateral force when the steering angle θf of the front wheel WF is 0 °. It becomes larger than Kf3. As a result, the component Kf · (θ + θf) in the inclination direction D of the slope also increases. In other words, the component of the “slope inclination direction D” of the lateral force of the front wheel WF changes from Kf3 · cos θ to Kf5 · cos (θ + θf). Accordingly, the braking force Fbf5 required for the front wheel WF in this case is smaller than the braking force Fbf3 required when the steering angle θf is 0 °.

  As described above, the minimum holding braking force when the steering angle θf of the front wheel WF is a positive value regardless of whether the vehicle 10 is stopped in the uphill state or the downhill state with respect to the slope S is as follows. This is larger than the minimum holding braking force when the steering angle θf is 0 °. On the other hand, the minimum holding braking force when the steering angle θf of the front wheel WF is a negative value is smaller than the minimum holding braking force when the steering angle θf is 0 °.

  As can be understood from the above description, the minimum holding braking force varies depending on the slope gradient θs, the stop angle θ, and the steering angle θf. Therefore, the present control device obtains the minimum holding braking force in consideration of the slope gradient θs, the stop angle θ, and the steering angle θf, and determines the hill hold braking force based on the minimum holding braking force.

The control device obtains the gradient θs of the slope S based on the detected value (longitudinal acceleration Gx) of the x-axis sensor of the tilt sensor 71 and the detected value (lateral acceleration Gy) of the y-axis sensor of the tilt sensor 71. . That is, the slope gradient θs is calculated by the following equation (13).

θs = arcsin ((Gx ² + Gy ² ) ^1/2 / g) (13)

On the other hand, the component m · g · sinθs in the inclination direction D of the slope of gravity is, as can be understood from FIG. 2C, the force in the longitudinal direction X1 of the vehicle 10 and the force in the lateral direction of the vehicle 10. Disassembled. That is, since the gravitational acceleration component gx = Gx in the longitudinal direction X1 of the vehicle 10 is (g · sin θs) · sin θ, the stop angle θ is obtained based on the following equation (14). Further, since the gravitational acceleration component gy = Gy in the lateral direction of the vehicle 10 is (g · sin θs) · cos θ, the stop angle θ can also be obtained based on the following equation (15).

θ = arcsin (gx / (g · sinθs)) (14)
θ = arccos (gy / (g · sin θs)) (15)

(Actual operation)
Next, the actual operation of the present control device will be described. The CPU of the ECU 60 (hereinafter simply referred to as “CPU”) executes a hill hold control routine shown by a flowchart in FIG. 7 every time a predetermined time elapses.

  At a predetermined timing, the CPU starts processing from step 700 and proceeds to step 710 to determine whether or not the above-described hill hold control execution condition is satisfied. If the hill hold control execution condition is satisfied, the CPU makes a “Yes” determination at step 710 to proceed to step 720, in accordance with the longitudinal acceleration Gx, the lateral acceleration Gy, the steering angle θf, and the rotational speed of each wheel. The signal NP is acquired. Further, the CPU applies the acquired longitudinal acceleration Gx and lateral acceleration Gy to the equation (13) to calculate the slope gradient θs, and the obtained longitudinal acceleration Gx and the calculated slope gradient θs to the equation (14). Apply the stop angle θ to calculate.

  Next, the CPU proceeds to step 730, and acquires the holding braking force Fbhf0 of the front wheel WF and the holding braking force Fbhr0 of the rear wheel WR when the steering angle θf is 0 ° according to the following procedure. The holding braking force Fbhf0 of the front wheel WF is greater than or equal to the minimum holding braking force Fbf0. The holding braking force Fbhr0 of the rear wheel WR is greater than or equal to the minimum holding braking force Fbr0.

(1) First, the CPU calculates the holding braking force Fbhf0 of the front wheel WF when the steering angle θf is 0 ° based on the slope gradient θs and the stop angle θ acquired in step 720. More specifically, the CPU determines the acquired slope gradient θs in a lookup table MapFbhf0 (θs, θ) that defines the relationship between the slope gradient θs and the stopping angle θ and the holding braking force Fbhf0 of the front wheel WF. And the holding braking force Fbhf0 of the front wheel WF is calculated by applying the stop angle θ. The table MapFbhf0 (θs, θ) and the following lookup tables are obtained in advance from simulations and experiments and stored in the ROM in the ECU 60.

(2) Next, the holding braking force Fbhr0 of the rear wheel WR is calculated based on the calculated holding braking force Fbhf0 of the front wheel WF. More specifically, the CPU holds the holding braking force Fbhf0 of the front wheel WF calculated by a look-up table MapFbhr0 (Fbhf0) that defines the relationship between the holding braking force Fbhf0 of the front wheel WF and the holding braking force Fbhr0 of the rear wheel WR. Is applied to calculate the holding braking force Fbhr0 of the rear wheel WR. This table MapFbhr0 (Fbhf0) is a table for multiplying the holding braking force Fbhf0 of the front wheels WF by a constant (K0 times) (see equation (12)).

  Next, the CPU determines whether or not the actual (acquired) steering angle θf is 0 °. When the actual steering angle θf is 0 °, the CPU makes a “Yes” determination at step 740 to proceed to step 750, and uses the obtained holding braking force Fbhf0 of the front wheel WF and holding braking force Fbhr0 of the rear wheel WR. Give to each wheel.

  Next, the CPU proceeds to step 760 to determine whether hill hold control is being executed. At present, the hill hold control is being executed. Accordingly, the CPU makes a “Yes” determination at step 760 to proceed to step 770 to determine whether or not the hill hold control cancellation condition is satisfied. As described above, the hill hold control cancellation condition is that the accelerator pedal is operated during the execution of the hill hold control.

  If the hill hold control cancellation condition is not satisfied, the CPU makes a “No” determination at step 770 to directly proceed to step 795 to end the present routine tentatively. That is, in this case, the holding braking force applied in step 750 is maintained. On the other hand, if the hill hold cancellation condition is satisfied, the CPU makes a “Yes” determination at step 770 to proceed to step 780. In step 780, the CPU reduces the braking pressure at a predetermined rate, and proceeds to step 795 to end the present routine tentatively. Note that the CPU determines that the hill hold control is finished (the hill hold control is not in progress) when the braking pressure reaches a predetermined braking pressure (for example, zero).

  On the other hand, when the steering angle θf is not 0 °, the CPU makes a “No” determination at step 740 to proceed to step 790, and the holding braking force Fbhf1 of the front wheel WF when the steering angle θf is not 0 ° is performed according to the following procedure. And the holding braking force Fbhr1 of the rear wheel WR is acquired.

(3) The CPU calculates “steering based on the“ holding braking force Fbhf0 of the front wheel WF when the steering angle θf is 0 ° ”, the stop angle θ, the slope gradient θs, and the steering angle θf calculated in step 730. The difference between the holding braking force Fbhf1 of the front wheel WF when the angle θf is not 0 ° and the holding braking force Fbhf0 of the front wheel WF when the steering angle θf is 0 ° (hereinafter referred to as the “difference of the front wheel holding braking force”). ) ΔFbhf is calculated. More specifically, the CPU looks up a table Map (Fbhf0, Fbhf0, which defines the relationship between the holding braking force Fbhf0 of the front wheel WF when the steering angle θf is 0 ° and the difference ΔFbhf of the front wheel holding braking force. Front wheel holding by applying the actual "holding braking force Fbhf0 of the front wheel WF when the steering angle θf is 0 °", the actual stop angle θ, the slope gradient θs, and the steering angle θf to θ, θs, θf) The braking force difference ΔFbhf is calculated.

(4) Next, based on the calculated difference ΔFbhf of the front wheel holding braking force, “after the holding brake force Fbhr1 of the rear wheel WR when the steering angle θf is not 0 ° and the steering angle θf is 0 °. ΔFbhr is calculated as “difference from holding braking force Fbhr0 of wheel WR” (hereinafter referred to as “difference of rear wheel holding braking force”). More specifically, the CPU calculates the difference of the calculated front wheel holding braking force in a lookup table MapΔFbhr (ΔFbhf) that defines the relationship between the difference ΔFbhf of the front wheel holding braking force and the difference ΔFbhf of the rear wheel holding braking force. By applying ΔFbhf, the difference ΔFbhr of the rear wheel holding braking force is calculated. This table MapΔFbhr (ΔFbhf) is a table for multiplying the difference ΔFbhf of the front wheel holding braking force by a constant (K1 times) (see the equation (8)).

(5) Next, the CPU holds the front wheel WF when the steering angle θf calculated in step 730 is 0 ° to the calculated difference ΔFbhf of the front wheel holding braking force and the difference ΔFbhr of the rear wheel holding braking force. By applying the braking force Fbhf0 and the holding braking force Fbhr0 of the rear wheel WR, the holding braking force when the steering angle θf is not 0 ° is obtained. That is, the holding braking force Fbhf1 of the front wheel WF and the holding braking force Fbhr1 of the rear wheel WR when the steering angle θf is not 0 ° are expressed by the following equations (16) and (17), respectively.

Fbhf1 = Fbhf0 + ΔFbhf (16)
Fbhr1 = Fbhr0 + ΔFbhr (17)

  Next, the CPU proceeds to step 750, applies a holding braking force to each wheel, and proceeds to step 760. When the hill hold control is being executed and the hill hold control release condition is not satisfied, the CPU proceeds to step 760, step 770, and step 795 in this order to end the present routine tentatively. When the hill hold control execution condition is not satisfied, the CPU makes a “No” determination at step 710 to directly proceed to step 760. When the hill hold control is not being executed, the CPU makes a “No” determination at step 760 to directly proceed to step 795 to end the present routine tentatively.

  As described above, the present control device is an angle representing the first inclination angle (slope gradient) θs that is an angle formed between the slope S and the horizontal plane H and the direction of the longitudinal axis X1 of the vehicle 10 on the slope S. An angle parameter obtaining unit (tilt sensor) 71 for specifying the second tilt angle (stop angle) θ, a steering angle sensor 73 for detecting the steering angle θf of the steered wheels, and a control unit (ECU) 60 are provided.

  When the braking force corresponding to the operation of the brake pedal 41 is applied to the plurality of wheels W by the braking device 40 and the operation of the brake pedal 41 is released after the vehicle 10 stops on the slope S, A hill hold braking force equal to or greater than a braking force (minimum holding braking force) necessary to keep the vehicle 10 stopped is applied to each of the plurality of wheels W using the braking device 40.

  At this time, the control unit 60 is detected by at least the first inclination angle (slope gradient) θs and the second inclination angle (stop angle) θ specified by the angle parameter acquisition means (inclination sensor) 71, and the steering angle sensor 73. The hill hold braking force is determined based on the steering angle θf.

  According to this configuration, the vehicle 10 is reliably held on the slope S when the hill hold control is executed regardless of the angle formed by the longitudinal axis X1 of the vehicle 10 and the slope inclination direction D and the steering angle θf of the steering wheel. Can do. As a result, the vehicle 10 can be prevented from moving in the downhill direction.

<Modification>
The present invention is not limited to the above embodiment, and various modifications can be adopted within the scope of the present invention as described below.

  In the above embodiment, “the holding braking force Fbhf0 of the front wheel WF when the steering angle θf is 0 °”, “the holding braking force Fbhr0 of the rear wheel WR when the steering angle θf is 0 °”, and “the front wheel holding” The braking force difference ΔFbhf ”and the“ rear wheel holding braking force difference ΔFbhr ”were calculated based on a predetermined look-up table. However, these values may be calculated by calculating Expressions (11), (12), (7), and (8) without using a lookup table.

  In the above embodiment, the calculation of the holding braking force when the steering angle θf is 0 ° is performed before the determination (step 740) of whether or not the steering angle θf is 0 ° (step 740). Step 730). On the other hand, after determining whether or not the steering angle θf is 0 °, when the steering angle θf is 0 °, the above-described calculation procedures (1) and (2) of the holding braking force are executed. When the steering angle θf is not 0 °, the holding braking force calculation procedures (1) to (5) may be executed.

  Although the braking device of the present embodiment is a hydraulic friction braking device that generates a frictional force by hydraulic pressure, an electric friction braking device that generates a frictional force by the torque of an electric motor may be used. Furthermore, a braking device in which a regenerative braking device that generates a regenerative force by an in-wheel motor is combined with a hydraulic friction braking device or an electric friction braking device may be used.

  Although the driving device 20 and the driving force transmission mechanism 30 of the present embodiment are configured to drive only the front wheels, the control device includes a driving device and a driving force transmission mechanism configured to drive the rear wheels. You may apply to the vehicle provided. Furthermore, the present control device may be applied to a vehicle including a driving device and a driving force transmission mechanism configured to drive all four wheels.

  The drive device 20 of the present embodiment uses an engine as a drive source, but the present control device is applied to a drive device using a combination of an engine and an electric motor as a drive source or a vehicle equipped with a drive device using an electric motor. May be.

  Although the tilt sensor 71 of the present embodiment is a biaxial tilt sensor, a triaxial tilt sensor capable of detecting the vertical acceleration Gz of the vehicle (vehicle body) in addition to the longitudinal acceleration Gx and the lateral acceleration Gy is used. May be. In this case, the slope gradient θs is calculated as θs = arccos (Gz / g).

DESCRIPTION OF SYMBOLS 10 ... Vehicle, 20 ... Driving device, 30 ... Driving force transmission mechanism, 40 ... Braking device, 41 ... Brake pedal, 50 ... Steering device, 60 ... Electronic control unit (ECU), 71 ... Inclination sensor, 73 ... Steering angle sensor , H ... horizontal plane, S ... slope, WF ... front wheel, WR ... rear wheel, X1 ... longitudinal axis, θf ... steering angle, θs ... slope slope (first slope angle), θ ... stop angle (second slope angle) .

Claims (1)

Applied to a vehicle equipped with a braking device for applying a braking force to each of a plurality of wheels and a steering device capable of changing a steering angle of a steering wheel among the plurality of wheels;
When the braking force is applied to the plurality of wheels by the braking device according to the operation of the brake pedal, the vehicle is stopped when the operation of the brake pedal is released after the vehicle stops on the slope. A control unit that applies a hill hold braking force that is greater than or equal to a braking force required for the plurality of wheels using the braking device,
A vehicle braking control device comprising:
Angle parameter acquisition means for specifying a first inclination angle that is an angle between the slope and a horizontal plane, and a second inclination angle that is an angle representing the direction of the longitudinal axis of the vehicle on the slope;
A steering angle sensor for detecting the steering angle of the steering wheel;
With
The controller is
The hill hold braking force is determined based on at least the first inclination angle and the second inclination angle specified by the angle parameter acquisition means and the steering angle detected by the steering angle sensor. The
Braking control device.

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