GB2500463A

GB2500463A - Traction control device

Info

Publication number: GB2500463A
Application number: GB1301899.9A
Authority: GB
Inventors: Satoshi Ichihashi
Original assignee: Keihin Corp
Current assignee: Keihin Corp
Priority date: 2012-03-12
Filing date: 2013-02-04
Publication date: 2013-09-25
Anticipated expiration: 2033-02-04
Also published as: DE102013002638B4; JP2013185568A; JP5814836B2; GB201301899D0; GB2500463B; DE102013002638A1

Abstract

A traction control device 2 includes a virtual front-wheel-speed calculating unit 22 that calculates a virtual front wheel speed as a front wheel speed after a front wheel has been lifted, by sequentially performing a correction calculation. The front wheel speed, immediately before the front wheel is lifted, is used as an initial value. When a front-wheel lift-state judging unit 21b judges that the front wheel is in the lifted state, a traction-control start determining unit 24 judges a relation between a deviation between the virtual front wheel speed and a rear wheel speed and a predetermined slip rate, and an engine-output control unit 3 controls a drive force of the rear wheel based on the relation between a deviation between the virtual front wheel speed and the rear wheel speed and the predetermined slip rate. The device 2 is particularly useful for a motorbike. It is aimed at addressing a situation with prior systems where engine output might be suppressed unnecessarily promptly, for instance on a dirt road, and coping with an off-road situation where a wheel has to be lifted to negotiate an obstacle.

Description

TITLE OF THE INVENTION

TRACTION CONTROL DEVICE

The present invention relates to a traction control device, and more articulaiiy relates to a traction control device that controls a drive force of a drive wheel according to a gripping state of th.e dr..i ye wheel with respect to a road surfacer of a vehicle such as a motorcycle whose front wheel tends to be 1 ted, In recent years, there has been proposed a traction cant rd device that reduces a drive force of a drive wheel when a drive wheel of-a vehicle slips on a road surface, thereby recovering a gripping force of the drive wheel with respect to the road surface.

Japanese Patent Applcacaon Lai.d-open No, 2010-31845 relates to a vehicle anti-slip control device and proposes a configuration such that a rnonitorino value, which i.savalue corresponding to a difference in rotat ion speed between a front wheel and a rear wheel * i_s det:ec-ted, and when the detected m.onitor.i.n.g value exceeds a predetermined onset threshold, the drive force of the drive wheel is decreased. Furthermore, Japanese Patent Application aia-open No. 201.0-31845 a'roposes a-configuration of changing an onset threshold according to a vehicle speed or speed-change gear position.

Japanese Patent Application Laid-open No. 2008-121595 relates to a vehicle engine control system and proposes a configuration in which when it is judged that a vehicle state is switched from a stopped state to a running state and a clutch is in a half-clutch state or a coupled state, an engine output is restricted to a predetermined output or less regardless of an accelerator operation amount.

Theref ore, Japanese Patent Application Laid-open No. 2008-121595 discloses a technique such that, when it is judged that the vehicle state is switched from the stopped state to the running state and the clutch is in the half-clutch state or the coupled state, the engine output is restricted to a predetermined output or less regardless of the accelerator operation amount, in order to suppress lifting of a front wheel.

However, according to studies by the present inventors, as for Japanese Patent Application Laid-open No. 2010-31845, because it has a configuration of changing the onset threshold to decrease the drive force of the drive wheel, it can handle such a state where traction control is executed according to the running state of the vehicle, although in a state where a driver does not actually feel any slip, thereby decreasing the drive force of the drive wheel to decrease drivability, or a state where the traction control is executed to decrease the drive force in a state where the vehicle can be started more easily with a wheel-slipping feeling, for example, at the time of running on an unpaved road (a dirt road), and thus a acceleration feeling intended by the driver cannot be obtained.

However, at the time of starting in the first gear or at the time of acceleration from an extremely low speed range, the onset threshold is simply made constant. Such traction control is effective at the time of starting on an unpaved road or at the time of acceleration from an extremely low speed range.

However, on a paved road such as an asphalt road, there may be such a tendency that any slip does not occur and a rear wheel as a drive wheel grips the road too much, thereby causing lifting of a front wheel carelessly.

Meanwhile, in Japanese Patent Application Laid-open No. 2008-121595, because it has a configuration such that, when it is judged that the vehicle state is switched from the stopped state to the running state and the clutch is in the half-clutch state or the coupled state, the engine output is restricted to a predetermined output or less regardless of the accelerator operation amount, and thus a state where the front wheel is lifted carelessly can be suppressed.

According to further studies by the present inventors, on an unpaved road, particularly on a so-called scree area where rocks are exposed, a driver may intentionally lift the front wheel to reduce the load on the front wheel at the time of crossing obstacles such as rocks or fallen trees. Furthermore, at the time of running on a stone-paved road or a wavy road, the driver may reduce the load on the front wheel in order to relax an impact on the front wheel.

However, in the configurations described in Japanese Patent Application Laid-open No. 2010-31845 and Japanese Patent Application Laid-open No. 2008-121595, it is determined whether to execute the traction control based on a difference in the rotation speed between the front and rear wheels. Therefore, there can be such a state where although the front wheel is in a lifted state and the rotation speed of the front wheel cannot be detected directly, traction control is executed, and a drive force intended by the driver may not be obtained. Accordingly, there is a room for improvement.

The present invention has been achieved in view of the above problems, and an object of the present invention is to provide a traction control device that can execute appropriate traction control, even under a condition where a front wheel is in a lifted state and a rotation speed of the front wheel cannot be detected directly.

To achieve the above object, a first aspect of the present invention is to provide a traction control device comprising: a front-wheel speed sensor that detects a front wheel speed, which is a rotation speed of a front wheel as a following wheel; a rear-wheel speed sensor that detects a rear wheel speed, which is a rotation speed of a rear wheel as a drive wheel; a traction-control start determining unit that determines start of traction control by judging a relation between a deviation between the front wheel speed and the rear wheel speed and a predetermined slip rate; an engine-output control unit that controls a drive force of the rear wheel based on a determination result obtained by the traction-control start determining unit; a front-wheel lift-state judging unit that judges whether the front wheel is in a lifted state; and a virtual front-wheel-speed calculating unit that calculates a virtual front wheel speed as the front wheel speed after the front wheel has been lifted, by sequentially performing a correction calculation by using a predetermined correction amount, while designating the front wheel speed ittmediately before the front wheel is lifted as an initial value, when the front-wheel lift-state judging unit judges that the front wheel is in the lifted state, wherein when the front-wheel lift-state judging unit judges that the front wheel is in the lifted state, the traction-control start determining unit judges a relation between a deviation between the virtual front wheel speed and the rear wheel speed and a predetermined slip rate, and the engine-output control unit controls the drive force of the rear wheel based on the relation judged by the traction-control start deterrr.iirin unjt According to a second aspect of the present; invention, in addition to the first aspect, the virtual front-wheel--speed calculating unit calculates the predetermined correction amount by taking in ho consideration a rate of change of the front wheel sneed obtained based on the rotation speed o the front wheel before the front wheel is lifted, and the predeterm.ine.d correction amount nas a character; st I c such that it decree see in a damping manner with a passage of Line from a time point; whe a it; has been j udned that the front wheel is lifted.

According to a third aspect of the present invention, in additi on to the first or second asoc;ct, the front-wheel.

itt -udgr Cx nt furtncr ices weLher the irunc noo is in a liftable, state, and the tractiorm-contrcl start deter:mininq unit can freely change. the predetermined slip rate according to thE:Hti fled state of: the front wheel and the liftable state of the front wheel.

According to a fourth aspect of the ore ?en. ion, in additi on to any of the first to third. asnects, the front-wheel lift-state judging unit judges that the front wheel is in the.

lifted state when the front wheel speed is lower than. the rear wneel speed by a first predetermined value or more and the front wheel. speed is decreasing, an engine torque is equal to or larger than a second pre etermined value, the rca.r: wheel, speed is equal b to or larger than a third predetermined value, and a change of speed of the rear wheel is equal to or larger than a fourth predetermined value.

In the traction control device according to the first aspect of the present invention, the traction control device includes the virtual front-wheel-speed calculating unit that calculates a virtual front wheel speed as a front wheel speed after the front wheel has been lifted, by sequentially performing a correction calculation by using a predetermined correction amount, while designating the front wheel speed immediately before the front wheel is lifted as the initial value, when the front-wheel lift-state judging unit judges that the front wheel is in a lifted state, and when the front-wheel lift-state judging unit judges that the front wheel is in the lifted state, the traction-control start determining unit judges a relation between a deviation between the virtual front wheel speed and the rear wheel speed and the predetermined slip rate, and the engine-output control unit controls the drive force of the rear wheel based on the relation between the deviation between the virtual front wheel speed and the rear wheel speed and the predetermined slip rate judged by the traction-control start determining unit. Accordingly, when the front wheel is lifted, because the traction control is executed by using the virtual front wheel speed, even under a condition where the front wheel is in the lifted state and the rotation speed of the front wheel cannot be detected directly, appropriate traction control can be executed.

In the traction control device according to the second aspect of the present invention, the virtual front-wheel-speed calculating unit calculates the predetermined correction amount by taking into consideration a rate of change of the front wheel speed obtained based on the rotation speed of the front wheel before the front wheel is lifted, and the predetermined correction amount has a characteristic such that it decreases in a damping manner with a passage of time from the time point when it has been judged that the front wheel is in the lifted state. Accordingly, the virtual front wheel speed can be obtained more reliably, thereby enabling to execute appropriate traction control.

In the traction control device according to the third aspect of the present invention, the front-wheel lift-state judging unit further judges whether the front wheel is in a liftable state, and the traction-control start determining unit can freely change the predetermined slip rate according to the lifted state of the front wheel and the liftable state of the front wheel. Accordingly, on a road surface having a small friction such as an unpaved road, the ground-covering ability can be improved by allowing a higher slip rate, and on a road surface having a large friction such as a dry asphalt road, it can be suppressed that the front wheel is excessively lifted by suppressing the slip rate.

In the traction control device according to the fourth aspect of the present invention, the front-wheel lift-state judging unit judges that the front wheel is in the liftable state, when the front wheel speed is lower than the rear wheel speed by the first predetermined value or more and the front wheel speed is decreasing, the engine torque is equal to or larger than the second predetermined value, the rear wheel speed is equal to or larger than the third predetermined value, and a change of speed of the rear wheel is equal to or larger than the fourth predetermined value. Accordingly, it can be suppressed that a state where the rear wheel speed is suddenly changing because the rear wheel bounces on a stone pavement or the like is erroneously judged as a state where the front wheel is lifted, and traction control when the front wheel is lifted can be accurately executed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. is a block diagram showing a configuration of an electronic control device to which a traction control device according to an embodiment of the present invention is applied; FIG. 2 is a flowchart showing a flow of a traction control process of the traction control device according to the embodiment; FIG. 3 is a flowchart showing a flow of a front-wheel lift predicting process during the traction control process in the embodiment; FIGS. 4A to 4C are flowcharts showing flows of a front-wheel lift judging process during the traction control process in the embodiment; FIG. S is a flowchart showing a flow of a virtual front-wheel-speed calculating process during the traction control process in the embodiment; FIG. 6 is a flowchart showing a flow of a traction-control start determining process during the traction control process in the embodiment; and FIG. 7 is a timing chart showing an example of the traction control process in the embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of a traction control device according to the present invention will be explained below in detail with reference to the drawings.

[Configuration of electronic control device] First, a configuration of an electronic control device to which a traction control device according to the present embodiment is applied is explained in detail with ref erence to FIG. 1.

FIG. 1 is a block diagram showing a configuration of an electronic control device to which the traction control device according to the embodiment of the present invention is applied.

As shown in FIG. 1, an electronic control device 1 to which the traction control device according to the present embodiment is applied is mounted on a vehicle (not shown), typically on a motorcycle, and operates by using power supplied from a battery mounted on the vehicle and can freely control various components of the vehicle. The electronic control device 1 includes a memory (not shown) or the like. The electronic control device 1 also includes a traction control unit 2 and an engine-output control unit 3. The traction control unit 2 includes a front-wheel lift-state judging unit 21, a virtual front-wheel-speed calculating unit 22, a slip-rate calculating unit 23, and a traction-control start determining unit 244 The front-wheel lift-state judging unit 21 includes a front-wheel lift predicting unit 21a, and a front-wheel lift judging unit 2lb. The traction control unit 2, the front-wheel lift-state judging unit 21, the front-wheel lift predicting unit 21a, the front-wheel lift judging unit 21b, the virtual front-wheel-speed calculating unit 22, the slip rate calculating unit 23, the traction-control start determining unit 24, and the engine-output control unit 3 are shown as functional blocks. The traction control device according to the present embodiment corresponds to portions of the traction control unit 2 and the engine-output control unit 3 of the electronic control device 1.

The front-wheel lift predicting unit 21a is connected to a crank sensor 41 that detects an engine speed of the vehicle, a gear position sensor 42 that detects a speed-change gear position of the vehicle, and an accelerator position sensor 43 that detects an opening degree of an accelerator grip of the vehicle. The front-wheel lift predicting unit 21a performs a front-wheel lift predicting process described later to judge whether the front wheel is in a liftable state.

The front-wheel lift judging unit 21b is connected to the accelerator position sensor 43, a front-wheel speed sensor 44 that detects a front wheel speed, which is a rotation speed of the front wheel as a following wheel of the vehicle, and a rear-wheel speed sensor 45 that detects a rear wheel speed, which is a rotation speed of the rear wheel as a drive wheel of the vehicle. The front-wheel lift judging unit 21b performs a front-wheel lift judging process described later to judge whether the front wheel is lifted.

When the front-wheel lift judging unit 21b judges that the front wheel is lifted, the virtual front-wheel-speed calculaLi.ng unit 22 corrects the front who-el speed. immediately before the front wheel is lifted by a. predetermined value to calculate the virtual front wheel speed.

The slip rat.e calculating unit 23 is connected to the front-wheel speed sensor 44, tte rear--wheel sueed sensor 15, and the virtual front-whee.i---speed calculating unit 22. The slip-rate calculating unit 23 calculates a deviation between th ront wheel speed detected ty the. front---whee.l speed sensor 44 or the virtual front wneei 5pnJ calculated by the virtual front-wheel---spe.ed calculat.r:ig unit 22 and the rear wheel speed detected by the rear-wheel speed sensor 45 to read out a slip rate corresponding to the dcvi a Lion calculated based on table data indicating a correspondence rd a Lion between the deviation and the slip rate.

The traction--control start detenin.in unit 24 compares a rate calculate d. by the slip-rats calculating unit 23 with a predetermined slip-rate (a traction-control start slip rate.) to judge the ecessity of t..h-c traction control based on a comparison result..

The engine-output cortrol unit 3 controls an injector 51, an ignition svstem52, and a throttle, valve. 52 based on a jucicinent i-a,ui L obtained cy t raJ ion-c ncr t cit t eel ermirincl..rit 2.4 to control the drive fc-rce of the rear wheel.

[Traction control process I 1 3 In the electronic control device 1 having the configuration described above, even under such a condition where the front wheel is in the lifted state and the rotation speed of the front wheel cannot be detected directly, appropriate traction control is executed by performing the traction control process described below. An operation of the electronic control device 1 at the time of performing the traction control process is explained below in detail with reference to a flowchart shown in FIG. 2.

FIG. 2 is a flowchart showing a flow of the traction control process of the traction control device according to the present embodiment.

The flowchart shown in FIG. 2 is started at a timing when an ignition switch of the vehicle is switched from an ON state to an OFF state, and the traction control process proceeds to a process in Step Si. While the ignition switch is in the ON state, the traction control process is repeatedly performed in each predetermined control cycle.

In the process in Step Si, the front-wheel lift predicting unit 21a judges whether the front wheel is in the liftable state (the front-wheel lift predicting process). Details of the front-wheel lift predicting process are described later with reference to a flowchart shown in FIG. 3. With this operation, the process in Step SI is complete, and the traction control process proceeds to a process in Step 52.

In the process in Step S2, the front-wheel lift judging unit 21b judges whether the front wheel is lifted. When the front-wheel lift judging unit 21b judges that the front wheel is lifted, the virtual front-wheel-speed calculating unit 22 corrects the front wheel speed immediately before the front wheel is lifted by a predetermined value to calculate a virtual front wheel speed (the front-wheel lift judging process).

Details of the front-wheel lift judging process are described later with reference to flowcharts shown in FIGS. 4A to 4C and FIG. 5. With this operation, the process in Step 82 is complete, and the traction control process proceeds to a process in Step 33.

In the process in Step 83, the slip-rate calculating unit 23 calculates a deviation between the front wheel speed detected by the front-wheel speed sensor 44 or the virtual front wheel speed calculated by the virtual front-wheel-speed calculating unit 22 and the rear wheel speed detected by the rear-wheel speed sensor 45. The slip-rate calculating unit 23 reads out a slip rate corresponding to the deviation calculated based on the table data indicating the correspondence relation between the deviation and the slip rate. With this operation, the process in Step 83 is complete, and the traction control process proceeds to a process in Step 54, In the process in Step 54, the traction-control start determining unit 24 compares the slip rate calculated by the process in Step 83 with a predetermined slip rate (a traction-control start slip rate) to judge the necessity of the traction control based on the comparison result (a traction-start determining process). Details of the traction-start determining process are described later with reference to a flowchart shown in FIG. 6. with this operation, the process in Step 34 is complete, and the traction control process proceeds to a process in Step 35.

In the process in Step 35, the engine-output control unit 3 controls the injector 51, the ignition system 52, and the throttle valve 53 based on a processing result in Step 34 to control the drive force of the rear wheel (an engine-output control process). With this operation, the process in Step S5 is complete to finish a series of the traction control.

[Front-wheel lift predicting process] FIG. 3 is a flowchart showing a flow of the front-wheel lift predicting process during the traction control process in the present embodiment.

The flowchart shown in FIG. 3 is started at a timing when the traction control process is started, and the front-wheel lift predicting process proceeds to a process in Step $11.

In the process in Step Sit, the front-wheel lift predicting unit 21a judges whether the engine speed is equal to or larger than a predetermined value (for example, 1800 rpm) based on an output signal from the crank sensor 41. As a result of judgment, when the engine speed is equal to or larger than the predetermined value, the front-wheel lift predicting unit 21a brings the front-wheel lift predicting process forward to a process in Step 512. On the other hand, when the engine speed is lower than the predetermined value, the front-wheel lift predicting unit 21a brings the front-wheel lift predicting process forward to a process in Step 315.

In the process in Step S12, the front-wheel lift predicting unit 21a judges whether the speed-change gear position is equal to or lower than a predetermined value (for example, the first gear) based on an output signal from the gear position sensor 42. As a result of judgment, when the speed-change gear position is equal to or lower than the predetermined value, the front-wheel lift predicting unit 21a brings the front-wheel lift predicting process forward to a process in Step $13. On the other hand, when the speed-change gear position is higher than the predetermined value, the front-wheel lift predicting unit 21a brings the front-wheel lift predicting process forward to a process in Step 515.

In the process in Step 313, the front-wheel lift predicting unit 21a judges whether an accelerator opening degree (driver' s request torque) has increased by a predetermined value or more within a predetermined time (for example, 350 ms) based on an output signal from the accelerator position sensor 43. As a result of judgment, if the accelerator opening degree has increased by the predetermined value or more within the predetermined time, the front-wheel lift predicting unit 21a brings the front-wheel lift predicting process forward to a process in Step SN. On the other hand, if the accelerator opening degree has not increased by the predetermined value or more within the predetermined time, the front-wheel lift predicting unit 21a brings the front-wheel lift predicting process forward to a process in Step 315.

In the process in Step 314, the front-wheel lift predicting unit 21a sets a value of a front-wheel lift prediction flag indicating whether the front wheel is in the liftable state to 1 (the front wheel is in the liftable state). With this operation, the process in Step 314 is complete to finish a series of the front-wheel lift predicting process.

In the process in Step 315, the front-wheel lift predicting unit 21a sets the value of the front-wheel lift prediction flag indicating whether the front wheel is in the liftable state to O (the front wheel is not in the liftable state). With this operation, the process in Step 315 is complete to finish a series of the front-wheel lift predicting process.

In the front-wheel lift predicting process described above, when such a condition is satisfied that the engine speed is equal to or larger than the predetermined value, the speed-change gear position is equal to or lower than the predetermined position, and the driver' s request torque has changed by the predetermi.ned value or more within the predetermined time, the front-wheel lift-state judging unit judges that the front wheel is in the liftable state. Accordingly, it can be predicted that the front wheel will be lifted if the speed-change gear position is low and the driver's request torque changes suddenly, thereby enabling to control the traction appropriately.

[Front-wheel lift judging process] FIGS. 4 to 4C are flowcharts showing flows of the front-wheel lift judging process during the traction control process in the present embodiment.

The flowcharts shown in FIGS. 4A to 4C are started at a timing when the front-wheel lift predicting process is complete, and the front-wheel lift judging process proceeds to a process in Step 321.

In the process in Step 521, the front-wheel lift judging unit 21b judges whether the rear wheel speed is equal to or larger than a predetermined value (for example, 8 km/h) based on an output signal from the rear-wheel speed sensor 45. As a result of judgment, if the rear wheel speed is equal to or larger than the predetermined value, the frontt--whe. itt judging unit 2lh brings the ftc)rtheP judging process forward to a process i.r Step 322. On the other hand, if the rear wheel speed is lower ti-an the predetermined value, the front -whee lift udging unit 21b brings the.. :i.itt j udging process forward to a r:rocess in Step 328.

In the process in Step 322, the front -wheei. lift judging unit 21b judges whether the rear wheel speed has increased by a predetermined value or more within a predetermined time (whether there is a sudden increase rear wheel speed) based on the output slums 1 from the rear-wheel speedS sensor 45.

As a result of jud.ament, if the rear wheel speed has not incres.sed ny tue or edetermined va.lu.e or more within the time (there. is no sudden.nc.rease of the rear whee.I speed) , the front-wheel lift j. udging unit 21b brings th:e tront.wheel Ii ft judoing process forward to a process in Sten 323. On the other hand, if the rear wheel speed has increased by the predetermined value or more; within the predetermined time (there is a sudden ijcrease of the rear wheel speed') , the front-wheel lift judging unit 21b brings the front-wheel lift judging process forward to the process in 31cc 328 In the-process in Step 523, the front--wheel lift judging unit 2lb judges whether the front wheel speed Is lower than the rear wheel speed by a predetermined value (f-or example, 3 km/h) or more, based on output signals of the front-wheel speed sensor 44 and the rear-wheel speed sensor 45. As a result of judgment, if the front wheel speed is lower than the rear wheel speed by the predetermined value, the front-wheel lift judging unit 21b brings the front-wheel lift judging process forward to a process in Step 824. On the other hand, if the front wheel speed is not lower than the rear wheel speed by the predetermined value, the front-wheel lift judging unit 21b brings the front-wheel lift judging process forward to the process in Step 328.

In the process in Step S24, the front-wheel lift judging unit 21b judges whether the output torque of the engine is equal to or larger than a predetermined value based on the output signal from the accelerator position sensor 43. As a result of judgment, if the output torque of the engine is equal to or larger than the predetermined value, the front-wheel lift judging unit 21b brings the front-wheel lift judging process forward to a process in Step 325. On the other hand, if the output torque of the engine is not equal to or larger than the predetermined value, the front-wheel lift judging unit 21b brings the front-wheel lift judging process forward to a process in Step 529.

In the process in Step S25, the front-wheel lift judging unit 2lb judges whether the front wheel speed has decreased by a predetermined value or more within a predetermined time based on the output signal from the front-wheel speed sensor 44. As a result of judgment, if the front wheel speed has decreased by the predetermined value or more within the predetermined time, the front-wheel lift judging unit 21b brings the front-wheel lift judging process forward to a process in Step 526. On the other hand, if the front wheel speed has not decreased by the predetermined value or more within the predetermined time, the front-wheel lift judging unit 21b brings the front-wheel lift judging process forward to the process in Step 529.

In the process in Step 526, the virtual front-wheel-speed calculating unit 22 corrects the front wheel speed detected by the front-wheel speed sensor 44 by a predetermined correction value to calculate a virtual front wheel speed (a virtual front-wheel-speed calculating process). Details of the virtual front-wheel-speed calculating process are described later with reference to a flowchart shown in FIG. 5. With this operation, the process in Step S26 is complete, and the front-wheel lift judging process proceeds to a process in Step S27.

In the process in Step 527, the front-wheel lift judging unit 21b sets a value of a front-wheel lift flag indicating whether the front wheel has been lifted to 1 (the front wheel is in the lifted state). With this operation, the process in Step 527 is complete to finish a series of the front-wheel lift judging process.

In the process in Step 528, the front--wheel lift judging unit 21b sets the value of tihe front-wheel lift flag indicating whetl.ier: the front wheel has been lifted to 0 (the front wheel is not in the lifted state) With this oneration, the nrocess inSten 328 is complete to finish, a series of: the front-wheel 1. itt. udging process In the process in Step 52.9, the front--wheel lift. judging unit SIb judges whether the front. wheel. speed has decreased by the predetermined value or more wi thin the predetermined time based c)n. the output signal from the frorit---w}ee.i speed sensor 44 Asaresu.l t of 4udgraent, if the front whee. sceed has decreaseuby the predetermined value or more within the redetermrned time, the front-wheel lift judging unit 21b finishes a series the front wheel 1. itt udgiri process. On the other hand, if the front. wheel sneed has not decreased by the predetermined value, or more within the redete.rmrned time, the front --wheel lift i udging unit 2lb brings the front-wheel.

lift judging process; forward to a process in Step 530 In the: process in Step 530, the front-wheel lift, judging unit Sib judges whether a state where the front wheel speed is not decreasing continues for a predeterminect time (for example, mc) based. on the oi.; trut signal fx:om the front-whee-l speed sensor 4 4\s a result of judgment, if the state where the front wheel speed is not decreasing has not continued for the predetermined time, the front-wheel lift judging unit 21b finishes a series of the front-wheel lift judging process. On the other hand, if the state where the front wheel speed is not decreasing has continued for the predetermined time, the front-wheel lift judging unit 21b brings the front-wheel lift judging process forward to a process in Step 331.

In the process in Step S31, the front-wheel lift judging unit 21b judges whether an increase of the front wheel speed has been converged (whether the front wheel is in no accelerating state) due to grounding of the front wheel based on the output signal from the front-wheel speed sensor 44. As a result of judgment, if the increase of the front wheel speed has been converged (the front wheel is in no accelerating state), the front-wheel lift judging unit 21b brings the front-wheel lift judging process forward to a process in Step 532. On the other hand, if the increase of the front wheel speed has not been converged(the front wheel is in an accelerating state), the front-wheel lift judging unit 21b finishes a series of front-wheel lift judging process.

In the process in Step 532, the front-wheel lift judging unit 21b sets the value of the front-wheel lift flag indicating whether the front wheel has been lifted to 0 (the front wheel is not in the lifted state). With this operation, the process in Step S32 is complete to finish a series of the front-wheel lift judging process.

(Virtual front-wheel-speed calculating process] FIG. 5 is a flowchart showing a flow of the virtual front-wheel-speed calculating process during the traction control process in the present embodiment.

The flowchart shown in FIG. 5 is started at a timing when it is judged that the front wheel speed has decreased by the predetermined value or more within the predetermined time in the process in Step S25, and the virtual front-wheel-speed calculating process proceeds to a process in Step 541.

In Step S41, the virtual front-wheel-speed calculating unit 22 judges whether a front-wheel-speed additional-value acquisition flag indicating whether front-wheel-speed additional value data used at the time of calculating the virtual front wheel speed has been acquired is 1 (the data has been acquired), thereby judging whether the front-wheel-speed additional value data has been acquired. As a result of judgment, if the front-wheel-speed additional value data has been acquired, the virtual front-wheel-speed calculating unit 22 brings the virtual front-wheel-speed calculating process forward to a process in Step 544. On the other hand, if the front-wheel-speed additional value data has not been acquired, the virtual front-wheel-speed calculating unit 22 brings the virtual front-wheel-speed calculating process forward to a proc3siu' Step 542..

In the process in Step S'12, the virtual front-wheel-speed calculating unit 22 calculates a difference value between the front wheel speed detected in. the previous process and the front wheel. speed detected in th.e current process as a front--wheel--speed additior:.al value (a rate of change of the front wheel speed) The front-wheel--speed additional value becomes an initial value of the predetermined correction amount used at the time of calculating the virtual front wheel speed.

With this operation, the process in Step S42 is complete, and virtual front-wheel--speed calculating process proceeds to a process in Step 543, In-the process in Step 543, the virtual front--wheel-speed calculating unit 22 sets the value of the front--wheel-speed additional-value acquisition flao to 1 (the data has been acquired) With this operation, the process in Step 343 is complete, and the virtual front--wheel--speed calculating process proceeds to a process in-Step 543 in the process in Step 544, the virtual front-wheel-speed calculating urn.. t 22 judges whether a predetermined time has passed since acquisition of the-front-wheel-speed additional value data by the process in Step 542., thereby j tinging whether it is an update timing of the-front--wheel-speed addition-al value. / r;

As a result of judgment, when the predetermined time has passed since acquisition of the front-wheel-speed additional value data, the virtual front--wheel--speed calculating unit 22 j udqes that it is the update. timing of the front-wheel-speed additional value, s.nd brings the virtual front-wheel-speed cal culatirig process forward to a process in Step 545. On the other hand, if the predetermined tix-ae has not passed since acquisition-, of the front iheel-speed additional value data, the virtual front-wheel---speeci calculating unit 22 judges that. it is not the update timing of the front-wheel--speed additional value, and :O.riflCS the virtual front-wheel-speed calculatinq-process forward to a process in Step 548.

In the process in Step 345, the virtual front--wheel-speed cal oul.ating unit 22 calculates a value by subtract.in. a oredererni ad alc fro t° t rout -who ii -sped dd value used in the previous process as a new front-wheel--speed .Ldd1tILonaJ. value. The front-whee speed addition-al value: becomes the predetermined correction amount at the time of.

calculatinq the virtual front-wheel, speed second time an-d thereafter in a processing loop, an--d the predetermined correcuion amount has a characteristic such that it dec:eases in a darnoing manner with a passag of time from a t. true point when it is,udged that the front. wheel has been lifted The predetermined value is preferably acquired from the engine.

speed when the front wheel is lifted. With this operation, the process in Step 345 is complete, and the virtual front-wheel-speed calculating process proceeds to a process in Step 546.

In the process in Step 846, the virtual front-wheel-speed calculating unit 22 judges whether the new front-wheel-speed additional value calculated in the process in Step S45 is equal to or lower than 0. As a result of judgment, if the new front-wheel-speed additional value is not equal to or lower than 0, the virtual front-wheel-speed calculating unit 22 brings the virtual front-wheel-speed calculating process forward to the process in Step 848. On the other hand, if the new front-wheel-speed additional value is equal to or lower than 0, the virtual front-wheel-speed calculating unit 22 brings the virtual front-wheel-speed calculating process forward to a process in Step 547.

In the process in Step S47, the virtual front-wheel-speed calculating unit 22 sets the new front-wheel-speed additional value to 0. With this operation, the process in Step 547 is complete, and the virtual front-wheel-speed calculating process proceeds to the process in Step 348.

In the process in Step 548, the virtual front-wheel-speed calculating unit 22 calculates a value by adding the front-wheel-speed additional value to the front wheel speed detected by the. front-wheel speed sensor 44 as the value of the vrtuai. front wheel speed. With this operation, the urocess in Step 518:s compiete to finish a series of the virtual.

front--wheel---speed calculating process.

[Traction---controlt start determining process] FIG. S is a flowchart showing a flow of a traction-control start determirii n.cx process in the e.mbocnment: of the present: invention. Tie flowchart shown in FiG, 6 is started at a timing when a slip--rate calculating process is complete, and t.he tractior control start determining process proceeds to a rtces s in Step 551.

In the cr00055 in Step 351, the traction-control start: determining unit 24 judges whether the value of the front-wheel lift prediction flag is 1. As a result of judgment, when the value of the front-wheel lift prediction flag is 1, the traction-control start deteninin ing unit 24 brings the traction-control. start determining process forward to a process in Step 3.53. On the other hand, when the value of the front-wheel lift prediction flag is 0, the traction-control start determining unit. 24 brings the traction---control start determining process forward to a process in Step 352., In the process in Step 552. the traction-control, start determining unit 2] judges whether the value of the front-wheel lift, flag is I. As a result of jud.gment, when the value of the C) 0 front-wheel lift flag is 1, the traction-control start determining unit 24 brings the traction-control start determining process forward to the process in Step 553. On the other hand, when the value of the front-wheel lift flag is 0, the traction-control start determining unit 24 brings the traction-control start determining process forward to a process in Step S54.

In the process in Step 553, the traction-control start determining unit 24 acquires information of the traction-control start slip rate and a target slip rate when the front wheel is in the liftable state or in the lifted state.

The traction-control start slip rate and the target slip rate when the front wheel is in the liftable state can be different from those when the front wheel is lifted, and for example, can be set to a higher value. With this operation, the process in Step 553 is complete, and the traction-control start determining process proceeds to the process in Step 554.

In the process in Step S54, the traction-control start determining unit 24 judges whether the slip rate calculated in the slip-rate calculating process is equal to or higher than the traction-control start slip rate acquired by the process in Step 553. As a result of judgment, if the slip rate is equal to or higher than the traction-control start slip rate, the traction-control start determining unit 24 brings the traction-control start determining process forward to a process in Step 355. On the other hand, if the slip rate is lower than the traction-control start slip rate, the traction-control start determining unit 24 brings the traction-control start determining process forward to a process in Step $56.

In the process in Step S55, the traction-control start determining unit 24 controls the engine-output control unit 3 to start execution of the traction control so that the slip rate becomes the target slip rate acquired by the process in Step S53. With this operation, the process in Step 555 is complete to finish a series of the traction-control start determining process.

In the process in Step 556, the traction-control start determining unit 24 controls the engine-output control unit 3 to finish the traction control. With this operation, the process in Step S56 is complete to finish a series of the traction-control start determining process.

[Specific example]

Lastly, a specific example of the traction control process is explained in detail with reference to FIG. 7.

FIG. 7 is a timing chart showing an example of the traction control process in the present embodiment.

In the traction control process shown in FIG. 7, if the speed-change gear pos±tion is shifted to the first gear when a time t is at ti, and when the time t is at t2, if the engine speed is equal to or larger than a predetermined value, the speed-change gear position is in the first gear, and the engine torque becomes equal to or larger than a predetermined value, it is judged that the front wheel is in the liftable state, and the value of the front-wheel lift prediction flag is set to 1.

The traction-control start slip rate indicated by a one-dot chain line Li is set to a value matched with the front-wheel

liftable state.

When the time t is at t3, if a front wheel speed Vi is lower than a rear wheel speed V2 by the predetermined value or more and decreasing, the engine torque is equal to or larger than the predetermined value, the rear wheel speed V2 is equal to or larger than a predetermined value, and a change of speed of the rear wheel is equal to or larger than a predetermined value, it is judged that the front wheel is lifted, and the value of the front-wheel lift flag is set to 1. With this operation, the traction-control start slip rate indicated by the one-dot chain line LI is set to a value matched with the lifted state of the front wheel.

When the time t is at t4, if the slip rate obtained from a virtual front wheel speed V3 becomes the traction-control start slip rate or higher, the traction control for suppressing the engine torque is executed. As a result, the engine torque indicated by a curved line L2 decreases with respect to the driver's request torque (a straight line L3).

When the time t is at tS, if the slip rate obtained from the virtual front wheel speed VS becomes lower than the traction-control start slip rate, the traction control for suppressing the engine torque finishes. As a result, the engine torque indicated by the curved line L2 returns to the driver's request torque (the straight line L3).

At time t is at t6, when it is judged that an increase of the front wheel speed has been converged, it is judged that the front wheel is not lifted, and the value of the front-wheel lift flag is set to 0. With this operation, the traction-control start slip rate indicated by the one-dot chain line Li returns to the value matched with the front-wheel liftable state.

The configuration of the present embodiment includes the virtual front-wheel-speed calculating unit 22 that uses the front wheel speed immediately before the front wheel is lifted as an initial value to sequentially perform a correction calculation by using the predetermined correction value, when the front-wheel lift-state judging unit 21 judges that the front wheel is in the lifted state, thereby calculating the virtual front wheel speed as the front wheel speed after the front wheel is lifted. When the front-wheel lift-state judging unit judges that the front wheel is in the lifted state, the traction-control start determining unit 24 judges the relation between the deviation between the virtual front wheel speed and the rear wheel speed and the predeteritined slip rate, and the engine-output control unit 3 controls the drive force of the rear wheel based on the relation between the deviation between the virtual front wheel speed and the rear wheel speed and the predetermined slip rate judged by the traction-control start determining unit. Accordingly, when the front wheel is lifted, the traction control is executed by using the virtual front wheel speed, and thus even under a condition where the front wheel is in the lifted state and the rotation speed of the front wheel cannot be detected directly, appropriate traction control can be executed.

The virtual front-wheel-speed calculating unit 22 calculates a predetermined correction amount by taking into consideration the rate of change of the front wheel speed obtained based on the rotation speed of the front wheel before the front wheel is lifted, and the predetermined correction amount has a characteristic such that it decreases in a damping manner with a passage of time from a time point when it is judged that the front wheel has been lifted. Accordingly, the virtual front wheel speed can be obtained more reliably, thereby enabling to execute appropriate traction control.

The front-wheel lift-state judging unit 21 further judges whether the front wheel is in the liftable state, and the traction-control start determining unit 24 can freely change the predetermined slip rate according to the lifted state of the front wheel and the liftable state of the front wheel.

Accordingly, on a road surface having a small friction such as an unpaved road, the ground-covering ability is improved by allowing a higher slip rate, and on a road surface having a large friction such as a dry asphalt road, it can be suppressed that the front wheel is excessively lifted by suppressing the slip rate.

The front-wheel lift-state judging unit 21 judges that the front wheel is in the lifted state, when the front wheel speed is lower than the rear wheel speed by the first predetermined value or more and the front wheel speed is decreasing, the engine torque is equal to or larger than a second predetermined value, the rear wheel speed is equal to or larger than the third predetermined value, and the change of speed of the rear wheel is equal to or larger than the fourth predetermined value.

Accordingly, it can be suppressed that a state where the rear wheel speed is suddenly changing because the rear wheel bounces on a stone pavement or the like is erroneously judged as a state where the front wheel is lifted, and traction control when the front wheel is lifted can be accurately executed.

The present embodiment described above adopts a configuration in which a virtual front wheel speed after a front wheel is lifted is calculated when the front-wheel lift-state judging unit 21 judges that the front wheel is in a lifted state.

However, such a configuration can be adopted independently or in addition thereto that when the front-wheel lift-state judging unit 21 judges that the front wheel is in a liftable state, the virtual front wheel speed after it is judged that the front wheel is in the liftable state until it is judged that the front wheel is lifted is calculated.

In the present invention, the types, arrangements, and numbers of constituent elements are not limited to those described in the above embodiment, and it is needless to mention that changes can be appropriately made without departing from the scope of the invention, such as replacing these constituent elements with other elements having equivalent operational effects.

Claims

What is claimed is: 1. A traction control device comprising: a front-wheel speed sensor that detects a front wheel speed, which is a rotation speed of a front wheel as a following wheel; a rear-wheel speed sensor that detects a rear wheel speed, which is a rotation speed of a rear wheel as a drive wheel; a traction-control start determining unit that determines start of traction control by judging a relation between a deviation between the front wheel speed and the rear wheel speed and a predetermined slip rate; an engine-output control unit that controls a drive force of the rear wheel based on a determination result obtained by the traction-control start determining unit; a front-wheel lift-state judging unit that judges whether the front wheel is in a lifted state; and a virtual front-wheel-speed calculating unit that calculates a virtual front wheel speed as the front wheel speed after the front wheel has been lifted, by sequentially performing a correction calculation by using a predetermined correction amount, while designating the front wheel speed immediately before the front wheel is lifted as an initial value, when the front-wheel lift-state judging unit judges that the front wheel is in the lifted state, wherein when the front-wheel lift-state judging unit judges that the front wheel is in the lifted state, the traction-control start determining unit judges a relation between a deviation between the virtual front wheel speed and the rear wheel speed and a predetermined slip rate, and the engine-output control unit controls the drive force of the rear wheel based on the relation judged by the traction-control start determining unit.
2. The traction control device according to claim 1, wherein the virtual front-wheel-speed calculating unit calculates the predetermined correction amount by taking into consideration a rate of change of the front wheel speed obtained based on the rotation speed of the front wheel before the front wheel is lifted, arid the predetermined correction amount has a characteristic such that it decreases in a damping manner with a passage of time from a time point when it has been judged that the front wheel is lifted.
3. The traction control device according to claim 1, wherein the front-wheel lift-state judging unit further judges whether the front wheel is in a liftable state, and the traction-control start determining unit can freely change the predetermined slip rate according to the lifted state of the front wheel and the liftable state of the front wheel.
4. The traction control device according to any of claims 1 to 3, wherein the front-wheel lift-state judging unit judges that the front wheel is in the lifted state, when the front wheel speed is lower than the rear wheel speed by a first predetermined value or more and the front wheel speed is decreasing, an engine torque is equal to or larger than a second predetermined value, the rear wheel speed is equal to or larger than a third predetermined value, and a change of speed of the rear wheel is equal to or larger than a fourth predetermined value.