JP2007230477A - Vehicles that are prevented from moving backward during a temporary stop on the uphill - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To hold a vehicle in a stop state on an uphill road preferentially using driving force, coping with a limit of grasping accuracy of friction coefficient between a wheel and a road surface, in order not to make the driving wheel exceed grip margin to the road surface in hill start from the temporary stop on the uphill road. <P>SOLUTION: When the vehicle temporarily stops on the uphill road, in order to deter backward movement of the vehicle, magnitude of the driving force assigned to the driving wheel and braking force assigned to each of the wheels is controlled based on predicted magnitude of the grip limit between the wheel and the road surface, and the magnitude or ratio in an allowance left to the grip margin is made equal to each of the wheels. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control for suppressing the backward movement of a vehicle when the vehicle is temporarily stopped on an uphill.

In a vehicle having a function of holding a braking force, the master cylinder and the A one-way valve and a holding valve are provided between the wheel cylinder and the brake force is held when the holding valve is closed. The vehicle is stopped by the ECU and the engine speed is below a predetermined value. When it is determined that the braking force is maintained, the braking force is maintained by closing the holding valve, and when the vehicle starts running, the holding valve is opened to release the holding of the braking force. Is described in Patent Document 1 below.
JP-A-11-310119

  When the vehicle is temporarily stopped on an uphill and then started, the total weight of the vehicle rises in addition to the inertial force acting on the vehicle's total mass and the force to overcome the static frictional resistance acting on the wheel drive system. Since the force in the reverse direction multiplied by the sine value of the slope angle of the slope must be overcome, a greater driving force is required than when starting on flat ground. In addition, if the release of braking is delayed when starting from a temporary stop on an uphill, the driving wheel tends to exceed the grip limit for the road surface. Once slip occurs beyond the grip limit, the coefficient of friction between the wheel and the road surface is greatly reduced, making slip even more severe. Therefore, when starting from a temporary stop on an uphill, it is important not to cause the drive wheel to exceed the grip limit on the road surface.

  The present invention pays attention to the above situation, and a first problem is to prevent the drive wheels from exceeding the grip limit on the road surface when starting from a temporary stop on an uphill.

  In order to grasp the grip limit of the wheel (tire) against the road surface, it is necessary to grasp the value of the ground contact load of the wheel and the coefficient of friction between the wheel and the road surface, but it is extremely difficult to grasp the latter value with high accuracy. Have difficulty. Therefore, the second object of the present invention is to address the problem of the limit in accuracy in grasping the value of the coefficient of friction between the wheel and the road surface in achieving the first problem. It is said.

  In order to hold the vehicle in the temporarily stopped state on the uphill, the driving force by the driving means and the braking force by the braking means can be used. In this case, if more driving force is used, the required braking force becomes smaller (or only 0), so the timing control for releasing the braking force at the start becomes easier. If the driving force is close to the grip limit of the wheel with respect to the road surface, the grip limit may be exceeded when starting. In view of this point, the third object of the present invention is to use a driving force to hold the vehicle in an uphill state so as not to cause such a grip limit to be exceeded.

  In order to solve the first problem, the present invention provides a pair of front wheels and a pair of rear wheels, a driving means for driving at least one of the front wheels and the rear wheels, and braking the front wheels and the rear wheels. And a control means for controlling the operation of the driving means and the braking means. When the vehicle is temporarily stopped on an uphill, the control means is configured to suppress the backward movement of the vehicle. The driving force applied to the driven wheels of the front wheels and the rear wheels and the magnitude of the braking force applied to the front wheels and the rear wheels are determined by the size of the grip limit between the front wheels and the rear wheels and the road surface. The present invention proposes a vehicle that is controlled based on estimation. Here, the grip limit is primarily a product of the contact load of the wheel and the friction coefficient between the wheel and the road surface, and is a parameter corresponding to the radius of what is generally called a friction circle. However, in ordinary four-wheeled vehicles, etc., the ground contact load of the wheels is not greatly different among the four wheels, and in this case, in particular, this means strictly the product of the ground contact load of the wheels and the friction coefficient between the wheels and the road surface. As well as a value proportional to the friction coefficient between the wheel and the road surface, that is, a value corresponding to the product of the ground contact load of the wheel and the friction coefficient between the wheel and the road surface when the ground contact load of the four wheels is the same. Is also included.

  Further, as a solution to the above second problem, the present invention provides a control device that prevents the vehicle from moving backward when the vehicle is temporarily stopped on an uphill. When controlling the driving force applied to the driven wheel and the braking force applied to the front and rear wheels based on the estimated grip limit between the front wheel and the rear wheel and the road surface The size of the driving force and braking force for preventing the vehicle from moving backward is the amount of margin the sum of which remains with respect to the estimated grip limit, or the ratio of the sum to the estimated grip limit. The vehicle is characterized in that it is controlled so as to be uniform.

  Further, as a solution to the above third problem, the present invention is such that when the vehicle is temporarily stopped on an uphill, the control means is driven among the front wheels and the rear wheels to prevent the vehicle from moving backward. The driving force applied to the front wheel and the braking force applied to the front and rear wheels is controlled based on the estimated size of the grip limit between the front wheel and the rear wheel and the road surface. The present invention proposes a vehicle characterized by being controlled with priority over braking force.

  As described above, the pair of front wheels and the pair of rear wheels, the driving means for driving at least one of the front wheels and the rear wheels, the braking means for braking the front wheels and the rear wheels, and the operations of the driving means and the braking means are performed. In a vehicle having control means for controlling, when the vehicle is temporarily stopped on an uphill, the control means applies to the driven wheel of the front wheels and the rear wheels in order to prevent the vehicle from moving backward. If the force and the amount of braking force applied to the front and rear wheels are controlled based on the estimation of the size of the grip limit between the front and rear wheels, the grip at the ground point of each wheel Since the magnitude of the limit is estimated and grasped in advance and the driving force and the braking force applied to the front and rear wheels are controlled in order to prevent the vehicle from moving backward, the wheel applied with the driving force or braking force is controlled. Carelessly It is possible to avoid the occurrence of a situation that causes beyond lip limit.

  As a method of estimating the friction coefficient between the wheel and the road surface, a method of detecting a slip generated in the wheel with respect to the magnitude of the braking force or driving force acting on the wheel, based on the self-aligning torque (SAT) of the wheel. There are methods (for example, Japanese Patent Application Laid-Open No. 2004-276710), etc., but errors that occur when estimating the size of the grip limit at the ground contact point of a wheel can be broadly divided into disturbance errors due to unstable road surface conditions. And the inherent error based on the accuracy of the means for generating braking force and driving force, the means for detecting slip, and the like, and for the former disturbance error, appropriately determine the size limit of itself. The latter inherent error should be dealt with as the grip limit, which is the target to be estimated, increases proportionally. It is considered to be.

  Therefore, as described above, the magnitude of the driving force applied to the driven wheels of the front wheels and the rear wheels and the braking force applied to the front wheels and the rear wheels in order to suppress the backward movement of the vehicle temporarily stopped on the uphill. Is controlled based on the estimation of the grip limit of the wheel, so that the sum of the driving force and the braking force remains with respect to the estimated grip limit on all wheels. Because of these errors, if controlled or the ratio of the amount of margin left to the estimated grip limit to the estimated grip limit is controlled to be uniform across all wheels Therefore, it is considered that it is possible to avoid the situation that the grip limit is greatly exceeded in any of the wheels.

  Based on the estimation of the slip limit as described above, when controlling the driving force and the braking force for restraining the vehicle from retreating when the vehicle is temporarily stopped on the uphill, this gives priority to the driving force over the braking force. If this is done, the driving force is used as much as possible for the holding force of the vehicle temporarily stopped on the uphill, a large margin can be obtained by the timing of releasing the braking force, and a smooth slope start can be performed.

  FIG. 1 is a schematic diagram showing a state where a vehicle is temporarily stopped on an uphill in an example in which the present invention is implemented in a rear-wheel drive four-wheeled vehicle. The illustrated vehicle is an example of a rear-wheel drive vehicle in which a pair of rear wheels are driven by a hybrid power source device PU formed of an engine or a combination of an engine, a motor generator, and a battery. The braking is performed by a braking device including a wheel cylinder provided for each wheel.

  A grounding load is applied to each of the four wheels, the pair of rear wheels are differentially driven by a power source device PU through a differential device, and the four wheels are individually driven by a wheel cylinder provided to each wheel. The control here involves the estimation of the friction coefficient between the wheels and the road surface, and the friction coefficient of the road surface with respect to the left and right wheels in a general vehicle traveling road. Since it is difficult to estimate the coefficient of friction between the wheel and the road surface with high accuracy as the difference is taken into account, for the sake of simplicity, the ground contact load is a sum of the values for the pair of front wheels and the pair of rear wheels. , Wr, and the braking force is collectively Fbf, Fbr for the pair of front wheels and the pair of rear wheels, the driving force for the pair of rear wheels is collectively Fdr, and a front wheel drive vehicle or a four wheel drive vehicle described later. In the example And Fdf collectively driving force for a pair of front wheels. Further, the wheel ground loads Wf and Wr are detected as loads in the vertical stroke direction of the wheels by the vehicle height sensors HSf and HSr for the pair of left and right front wheels and the pair of left and right rear wheels.

  The operation of the power source device PU and the braking device while the vehicle is temporarily stopped on the uphill is controlled by an electronic control unit ECU having a microcomputer. The electronic control unit is supplied with signals indicating the values of Wf and Wr from the vehicle height sensors HSf, HSr, etc., and a signal indicating the slope angle θ of the slope from the G sensor GS, which is not shown in the figure. A signal indicating the vehicle speed (or wheel speed) and various signals indicating the operation state of other vehicles are supplied from the vehicle speed sensor.

  (A) and (B) of FIG. 2 mean a friction circle corresponding to the grip limit at the contact point of the four wheels on the front, rear, left and right sides of the four-wheeled vehicle and a braking / driving force corresponding thereto (here, braking force or driving force or both). 2 is a schematic plan view of a vehicle showing two ways of taking a margin distribution. As described above, for the convenience of handling the pair of front wheels and the pair of rear wheels together, the radius of the friction circle for each of the front wheels and the rear wheels is compared with values Rf and Rr, which are treated as grip limits for the front wheels and the rear wheels below. Rf / 2 and Rr / 2, and a later-described uniform grip limit margin ΔR is ΔR / 2 for each wheel. Also, the braking / driving force and Ftf and Ftr for the pair of front wheels and the pair of rear wheels are Ftf / 2 and Ftr / 2 for each wheel.

  With reference to the flowchart of FIG. 3, one embodiment of the reverse restraining control at the time of temporary stop on the uphill will be described for the rear wheel drive vehicle shown in FIG. 1. The control according to the flowchart is performed according to a control program incorporated therein by the microcomputer of the electronic control unit ECU, and may be repeated at a cycle of several tens to several hundreds of milliseconds during operation of the vehicle.

  When the control is started at the same time as the operation of the vehicle is started, it is determined in step 10 whether or not the vehicle is on the uphill and the vehicle has moved backward. If the driver does not fully depress the brake pedal from the beginning of the temporary stop, the vehicle will not reverse, and if the answer is no (N), the control according to the present invention is not required. Control ends here. If the answer is yes (Y), control proceeds to step 20.

  In step 20, grounding loads Wf and Wr in the vertical stroke direction of the front and rear wheels are detected based on signals from the vehicle height sensors HSf and HSr.

  Next, at step 30, the value of the force Ft required to suppress the reverse of the vehicle is determined as (Wf + Wr) tan θ based on Wf and Wr. This corresponds to a component along the slope of the force Wt due to gravity acting on the center of gravity of the vehicle.

  Control then proceeds to step 40 where the coefficient of friction μ between the wheel and the road surface is estimated. As an example, this can be obtained by starting a subroutine operation according to the flowchart shown in FIG. 9 at the same time as the start of the control according to the flowchart of FIG. 3 and with a period of about several tens to several hundred milliseconds. It may come to be. FIG. 9 will be described later.

  Control then proceeds to step 50, where the grip limits at the front and rear wheel contact points, i.e., the friction circle radii Rf and Rr, are estimated. These are values obtained by multiplying the ground contact loads Wf and Wr perpendicular to the road surface of the front and rear wheels detected at step 20 by the friction coefficient μ with the road surface obtained at step 40, respectively.

Next, the control proceeds to step 60, and as shown in FIG. 2A, the magnitude of ΔR when the braking / driving force on all the front, rear, left and right wheels is to leave a uniform margin ΔR with respect to the friction circle. Saga
ΔR = (Rf + Rr-Ft) / 2
As required.

Next, the control proceeds to step 70, and braking / driving forces Ftf and Ftr of the front wheels and the rear wheels are obtained as follows.
Ftf = Rf−ΔR
Ftr = Rr-ΔR

  Next, the control proceeds to step 80, and in this case, since it is a rear wheel drive vehicle, the rear wheel drive force is controlled to Ftr, and then the control proceeds to step 90, where the front wheel braking force is controlled to Ftf. To be done.

FIG. 4 is a flowchart similar to FIG. 3 showing another embodiment of the reverse restraining control at the time of temporary stop on the uphill in the case of the rear wheel drive vehicle shown in FIG. In this flowchart, the same steps as those in the flowchart of FIG. 3 are indicated by the same step numbers as in FIG. 3, and the embodiment shown in FIG. 4 is the same as the embodiment shown in FIG. Compared to the configuration, only the steps 65 and 75 are different. In this case, in step 65, as shown in FIG. 2 (B), when the braking / driving force at all the front, rear, left and right wheels has a uniform margin α with respect to the friction circle, value,
α = Ft / (Rf + Rr)
As required.

In the next step 75, braking / driving forces Ftf and Ftr at the front wheels and the rear wheels are calculated as follows.
Ftf = αRf
Ftr = αRr

  FIG. 5 is a flowchart similar to FIG. 3 showing one embodiment of the reverse restraining control during a temporary stop on an uphill in the case of a front wheel drive vehicle. In this flowchart, the same steps as those in the flowchart of FIG. 3 are indicated by the same step numbers as in FIG. 3, and the embodiment shown in FIG. 5 is the same as the embodiment shown in FIG. Compared to the configuration, only the steps 85 and 95 are different. In this case, since the vehicle is front wheel drive, the driving force of the front wheels is controlled to Ftf in step 85, and the braking force of the rear wheels is controlled to Ftr in step 95.

  FIG. 6 is a flowchart similar to FIG. 4 showing another embodiment of the reverse restraining control during a temporary stop on an uphill in the case of a front wheel drive vehicle. In this flowchart, the same steps as those in the flowchart of FIG. 4 are indicated by the same step numbers as in FIG. 4, and the embodiment shown in FIG. 6 is the same as the embodiment shown in FIG. Compared to the configuration, only the steps 85 and 95 are different. In this case, since the vehicle is front wheel drive, the driving force of the front wheels is controlled to Ftf in step 85, and the braking force of the rear wheels is controlled to Ftr in step 95.

  FIG. 7 is a flowchart similar to FIG. 3 or FIG. 5 showing one embodiment of the reverse restraining control at the time of a temporary stop on an uphill in the case of a four-wheel drive vehicle. In this flowchart, the same steps as those in the flowchart of FIG. 3 or 5 are indicated by the same step numbers as in FIG. 3 or FIG. 5, and the embodiment shown in FIG. Compared to the embodiment shown in FIG. 3 or FIG. In this case, in step 100, the ratio (front / rear ratio) is calculated as Sfr = Ftf / Ftr from the braking / driving forces of the front wheels and the rear wheels calculated in step 70.

Next, the control proceeds to step 110, and it is determined whether or not the front / rear ratio Sfr of the braking / driving force calculated above is larger than the front / rear ratio Scfr of the center differential of the four-wheel drive. If the answer is yes, control proceeds to step 120 where the driving forces Fdf and Fdr for the front and rear wheels are calculated as follows.
Fdf = FtrScfr
Fdr = Ftr
In the next step 130, braking forces Fbf and Fbr for the front wheels and the rear wheels are calculated as follows.
Fbf = Ftf-Fdf
Fbr = 0

If the answer to step 110 is no, the control proceeds to step 140, and the driving forces Fdf and Fdr for the front wheels and the rear wheels are calculated as follows.
Fdf = Ftf
Fdr = FtfScfr
Then, in the next step 150, braking forces Fbf and Fbr for the front wheels and the rear wheels are calculated as follows.
Fbf = 0
Fbr = Ftr-Fdr

  In any case, control then proceeds to step 160 where the driving forces of the front and rear wheels are controlled to Fdf and Fdr, respectively, based on Fdf and Fdr calculated above. Further, the control proceeds to step 170, and based on Fbf and Fbr calculated above, the braking forces of the front wheels and the rear wheels are controlled to Fbf and Fbr, respectively.

  FIG. 8 is a flowchart similar to FIG. 7 showing another embodiment of the reverse restraining control during a temporary stop on an uphill for a four-wheel drive vehicle. In this flowchart, the same steps as those in the flowchart of FIG. 7 are indicated by the same step numbers as in FIG. 7, and the embodiment shown in FIG. 8 is the same as the embodiment shown in FIG. Compared to the configuration, steps 60 and 70 in FIG. 7 differ only in that they are steps 65 and 75 in FIG. In this case, the difference between steps 65 and 75 compared to steps 60 and 70 has already been described with reference to FIG. 4, so further redundant description of the embodiment of FIG. 8 avoids redundant description. Omitted.

  FIG. 9 is a flowchart showing an example of a subroutine for estimating the friction coefficient μ between the road surface and the wheels performed in step 40 of FIGS. 3 to 8. However, while the control according to the flowcharts of FIGS. 3 to 8 is executed when the vehicle is temporarily stopped on an uphill, the estimation of the friction coefficient between the road surface and the wheels is performed while the vehicle is running. Therefore, as described above with reference to step 40 in FIG. 3, the estimation of the coefficient of friction between the road surface and the wheel by such a subroutine is started simultaneously with the start of the control according to the flowcharts in FIGS. Similar to the control according to these flowcharts, it is always performed at a cycle of about several tens to several hundreds of milliseconds.

  In the subroutine of FIG. 9, first, when braking force or driving force is applied to the wheel in step 210, the friction between the road surface and the wheel detected based on the slip between the vehicle speed and the wheel speed. The coefficient is detected and stored as μtrac. In this case, as the friction coefficient, an average vehicle speed within a certain appropriate minute period including the vicinity of each time point detected by the vehicle speed sensor is used as the vehicle speed, and each moment of the rotational speed of one wheel appropriately selected for this is used. May be detected by contrasting the values of.

  Control then proceeds to step 220 where the coefficient of friction by a method based on the wheel self-aligning torque (SAT) (eg, Japanese Patent Application Laid-Open No. 2004-276710) is detected and stored as μsat.

  Next, in step 230, it is determined whether any of the antilock brake system (ABS), the traction control system (TRC), or the vehicle stability control system (VSC) is operating. If the answer is yes, there is a high possibility that a large error is included in the estimation of the friction coefficient by the above SAT. Therefore, the control proceeds to 240, and the final estimated value μ of the friction coefficient is based on the braking / driving force. The detection value μtrac is used. On the other hand, if the answer to step 230 is no, the larger of μtrac and μsat detected above in step 250 is used as the μ estimated value μn + 1 in the current flow, and then In step 260, the larger one of the μ estimated value μn + 1 in the current flow and the μ estimated value μn in the previous flow is adopted and stored as the final estimated value of μ. In any of the above, finally, in step 270, the final estimated value of μ adopted this time is stored as the next μ value μn.

  While the present invention has been described in detail with respect to several embodiments thereof, it will be apparent to those skilled in the art that various modifications can be made to these embodiments within the scope of the present invention. .

1 is a schematic diagram showing a state where a vehicle is temporarily stopped on an uphill in an example in which the present invention is implemented in a rear-wheel drive four-wheel vehicle. (A) And (B) is a schematic plan view of a vehicle showing two ways of taking a friction circle corresponding to a grip limit at a grounding point of four wheels on the front, rear, left and right of a four-wheeled vehicle and a marginal distribution of braking / driving force thereto. The flowchart which shows one embodiment of the reverse suppression control at the time of the temporary stop on an uphill about the case of a rear-wheel drive vehicle. The flowchart which shows another one Embodiment of the reverse suppression control at the time of the temporary stop on an uphill about the case of a rear-wheel drive vehicle. The flowchart which shows one embodiment of the reverse suppression control at the time of the temporary stop on an uphill about the case of a front-wheel drive vehicle. The flowchart which shows another one Embodiment of the reverse suppression control at the time of the temporary stop on an uphill about the case of a front-wheel drive vehicle. The flowchart which shows one embodiment of the reverse suppression control at the time of the temporary stop on an uphill about the case of a four-wheel drive vehicle. The flowchart which shows another one Embodiment of the reverse suppression control at the time of the temporary stop on an uphill about the case of a four-wheel drive vehicle. The flowchart which shows an example of the subroutine for estimation of the friction coefficient (mu) between a road surface and a wheel.

Explanation of symbols

  PU ... Power source device, HSf, HSr ... Vehicle height sensor, ECU ... Electronic control device, GS ... G sensor

Claims (4)

  A pair of front wheels and a pair of rear wheels, driving means for driving at least one of the front wheels and the rear wheels, braking means for braking the front wheels and the rear wheels, and controlling the operation of the driving means and the braking means And when the vehicle is temporarily stopped on an uphill, the control means applies driving to the driven wheels of the front wheels and the rear wheels to prevent the vehicle from moving backward. The vehicle is configured to control the magnitude of the force and the braking force applied to the front wheel and the rear wheel based on the estimation of the grip limit between the front wheel and the rear wheel and the road surface. .   The magnitudes of the driving force and the braking force for restraining the vehicle from moving backward are controlled so that the sum of the margins for the estimated grip limit is uniform for all the wheels. The vehicle according to claim 1.   The magnitude of the driving force and the braking force for restraining the vehicle from moving backward is the ratio of the sum of the remaining amount with respect to the estimated grip limit to the estimated grip limit for all wheels. The vehicle according to claim 1, wherein the vehicle is controlled to be The vehicle according to any one of claims 1 to 3, wherein the control of the magnitude of the driving force and the braking force for preventing the vehicle from moving backward is performed with priority given to the driving force over the braking force.

Images