JP2008062929A - Drive system controller for four-wheel drive vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drive system controller for a four-wheel drive vehicle restraining a drive wheel torque from increasing abruptly, even when an engine output torque increases abruptly due to limitation of engine output control during travel, and restraining a drive slip and a skidding amount of a vehicle while enhancing vehicle stability. <P>SOLUTION: This drive system controller for the four-wheel drive vehicle provided with a front and rear wheel driving force distribution control system and a traction control system is provided with a limit control part for reducing a controlled variable of the engine output control by a driving condition of the vehicle to protect an exhaust system catalyst or for prohibiting the engine output control, in the traction control system, and a limitation control part for outputting a four-wheel driving command to switch a two-wheel drive state to a four-wheel drive state, to an actuator 17 of the front and rear wheel driving force distribution control system, when the slip is generated in the driving wheels, when an automatic transmission is in a range-fixed mode, when a two-wheel drive mode is selected and when the engine output control is impossible. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a traction control system (Traction Control System: TCS) or a vehicle dynamics control in which engine output is controlled by at least one of a fuel cut or an ignition timing change in which the temperature of an exhaust system catalyst is a concern during a high load operation or the like. The present invention belongs to the technical field of a drive system controller for a four-wheel drive vehicle applied to a system (Vehicle Dynamics Control: VDC) or the like.

  A conventional vehicle traction control device is configured such that when a driving wheel is driven slip (accelerated slip), fuel cut (in the case of simply fuel cut, excluding all cylinder fuel cut) or ignition timing retardation (hereinafter referred to as ignition retard). Or, the engine output torque is controlled to be reduced by a combination thereof, or the drive slip is suppressed.

  However, engine output control by fuel cut or ignition retard causes overheating of the exhaust system catalyst. Therefore, in order to protect the exhaust system catalyst from high temperature deterioration, there are restrictions on the accelerator opening, engine speed, control time, etc. Generally, it is provided (see FIG. 3 for details). However, of the engine output control, the all-cylinder fuel cut (emblem state) and the control throttle closing control do not cause the catalyst to overheat.

  On the other hand, in vehicles equipped with automatic transmissions (AT vehicles), the engine output control by fuel cut or ignition retard is made to correspond to the shift control of the automatic transmission, and the engine output control restriction (including prohibition) conditions by shifting up etc. To avoid. More specifically, a shift schedule is set so as to maintain the B · C region → A · B region in FIG. 3, and this is handled by automatic up / down of the gear ratio.

  However, since the conventional catalyst protection measures adjust the engine speed by changing the gear ratio of the automatic transmission and maintain the A and B regions in FIG. 3, the shift position is not changed unless the driver performs a shift operation. In a manual transmission equipped vehicle (MT vehicle) where the gear remains fixed, range position fixed mode (1st speed fixed range, 2nd speed fixed range, etc.) in AT vehicles, and continuously variable transmission mounted vehicles (CVT vehicles) In the range position fixing mode (low range, etc.), since the gear ratio cannot be automatically increased / decreased, it becomes the B / C region in FIG. 3 and the engine output control restriction condition can be avoided. Can not.

  As a result, the engine output control is performed based on the occurrence of slippage of the front wheels or rear wheels that are drive wheels, and the engine output is controlled when the shift shift position of the transmission is fixed as described above. Satisfying the control restriction condition (A / B region → B / C region in FIG. 3) and prohibiting engine output control may cause a drive wheel slip due to a sudden increase in drive wheel torque. There was a problem.

  On the other hand, when the engine output control restriction is started, it is conceivable to shift to the brake control that does not cause the catalyst overheating instead of the engine output control in the two-wheel drive state. Longer time, increased load on powertrain / brake components, and reduced vehicle stability, so that slips are generated due to engine output control restrictions without combining engine output control restrictions and brake control. There is a background to want to suppress.

  The present invention has been made by paying attention to the above-mentioned problems, and its purpose is to suppress a sudden increase in driving wheel torque even if the engine output torque suddenly increases due to the limitation of engine output control during traveling. Another object of the present invention is to provide a drive system control device for a four-wheel drive vehicle capable of suppressing drive slip and vehicle side slip while improving vehicle stability.

  In order to achieve the above object, in the invention according to claim 1, the front and rear wheels are switchable between a two-wheel drive state for driving the rear wheel or the front wheel and a four-wheel drive state for driving the front and rear wheels by a command to the actuator. A driving force distribution control system, an automatic transmission ratio mode for automatically controlling the transmission ratio, a transmission ratio mode switching means for switching between the range fixing modes for fixing the transmission ratio, and a driving slip detection means for detecting slip of the drive wheels A traction control system that controls engine output by performing at least one of fuel cut or ignition timing change when the drive wheels are slipping, and the driving state of the vehicle to protect the exhaust system catalyst Depending on the engine output control limit, the engine output control limit is reduced or the engine output control limit is set to prohibit engine output control. In the fixed range mode, when the drive wheel is slipping and when the two-wheel drive state is selected, the engine output control limit or the engine output control limit is executed. When it is predicted that the four-wheel drive command for switching from the two-wheel drive state to the four-wheel drive state is output to the actuator of the front and rear wheel drive force distribution control system And is provided.

  According to a second aspect of the present invention, in the drive system control apparatus for a four-wheel drive vehicle according to the first aspect, a brake actuator is provided that generates brake hydraulic pressure independently for each of the front and rear wheels independently of the brake operation. The traction control system applies a braking force to the left and / or right driving wheels where the engine output control and / or the slip occurs due to at least one of fuel cut and ignition timing change when the driving wheels are slipping. It is the system which performs brake control to perform.

  According to a third aspect of the present invention, in the drive system control device for a four-wheel drive vehicle according to the first or second aspect, the restriction corresponding drive force distribution control means is a control for switching the drive force distribution to four-wheel drive. When the start condition is satisfied, at least one of the engine all-cylinder fuel cut control and the brake control is performed so that the driving wheel speed becomes the same wheel speed as the driven wheel speed or the vehicle body speed. Alternatively, after confirming that the vehicle speed is substantially the same as the vehicle speed, the vehicle is characterized in that it outputs a four-wheel drive command to switch from the two-wheel drive state to the four-wheel drive state.

  In the invention according to claim 4, a front and rear wheel driving force distribution control system capable of switching between a two-wheel drive state for driving the rear wheel or the front wheel and a four-wheel drive state for driving the front and rear wheels by a command to the actuator; Gear ratio mode switching means for switching between an automatic gear ratio mode for automatically controlling the gear ratio and a range fixing mode for fixing the gear ratio, and a target skid that calculates the target skid amount based on the driver's steering operation amount and brake operation amount The vehicle has an amount calculating means and a side slip amount detecting means for detecting a side slip amount of the vehicle, and the wheel is adapted to bring the side slip amount closer to the target side slip amount during traveling in which a deviation occurs between the vehicle side slip amount and the target side slip amount. A vehicle dynamics control system that applies braking force and at least one of fuel cut or ignition timing change to perform engine output control; In order to protect the exhaust system catalyst, an engine output control limiting means for reducing engine output control according to the driving state of the vehicle or prohibiting engine output control to limit engine output control; In this case, a deviation occurs between the side slip amount of the vehicle and the target side slip amount, and when the two-wheel drive state is selected and the engine output control limit or the engine output control limit is executed. A limited corresponding driving force distribution control means for outputting a four-wheel driving command for switching from the two-wheel driving state to the four-wheel driving state to an actuator of the front and rear wheel driving force distribution control system when predicted to be Are provided.

  According to a fifth aspect of the present invention, in the drive system control device for a four-wheel drive vehicle according to the fourth aspect, the restriction corresponding driving force distribution control means satisfies a control start condition for switching the driving force distribution to four-wheel drive. Then, if the side slip amount deviation is large, a 4-wheel drive command for switching from the two-wheel drive state to the four-wheel drive state is output, and at least engine all-cylinder fuel cut control and brake control until the side slip amount deviation decreases. When one side control is performed and the side slip amount deviation is equal to or less than the set deviation, the control unit is a means for outputting a four-wheel drive command for switching from the two-wheel drive state to the four-wheel drive state.

  In the invention according to claim 1, when the drive wheel is slipping, the engine output control is performed in the traction control system by performing at least one of fuel cut or ignition timing change. When the vehicle is in an operating state that causes the catalyst to overheat, the engine output control restriction means reduces the engine output control amount for the protection of the exhaust system catalyst or prohibits the engine output control.

  When engine output control is restricted by this engine output control restriction means or when engine output control restriction is predicted to be executed, when slip occurs on the drive wheels, the shift shift position of the transmission is in a fixed state, In addition, when the condition that the two-wheel drive state is selected in the front and rear wheel drive force distribution control system is satisfied, the two-wheel drive is performed with respect to the actuator of the front and rear wheel drive force distribution control system in the restriction corresponding drive force distribution control means. A four-wheel drive command for switching from the state to the four-wheel drive state is output.

  That is, in the four-wheel drive state, the inertia and friction for the drive system increase compared to the two-wheel drive state, so the total drive torque for the four wheels decreases compared to the two-wheel drive state. Further, since a part of the driving torque to the driving wheel is transmitted to the driven wheel side, the torque transmitted to the driving wheel is reduced, and driving slip due to excessive torque is suppressed. Furthermore, since the driving torque is distributed to the four wheels, the torque that can be transmitted to the road surface per wheel is increased, and the vehicle stability is improved.

  Therefore, even if the engine output torque suddenly rises due to the restriction of the engine output control, it is possible to suppress the sudden increase of the drive wheel torque and to suppress the induction of the drive slip while improving the vehicle stability.

  In the invention according to claim 2, a brake actuator is provided that generates brake fluid pressure independently for each of the front and rear wheels independently of the brake operation, and when the drive wheels are slipping, the traction In the control system, engine output control by at least one of fuel cut and ignition timing change and brake control for applying a braking force to the left and right drive wheels where slip occurs are performed.

  Therefore, when both the left and right drive wheels generate drive slip, in addition to engine output control, brake control that applies braking force to the left and right drive wheels is performed so that the drive slip is more responsive than engine output control alone. A brake that applies braking force only to one slipped wheel even when only one drive wheel slips during split μ road (left and right uneven road surface) or during turning acceleration. Driving slip can be suppressed by performing the control.

  In the invention according to claim 3, when the control start condition for switching the driving force distribution to the four-wheel drive is satisfied in the restriction corresponding driving force distribution control means, the driving wheel speed is the same as the driven wheel speed or the vehicle body speed. At least one of engine all-cylinder fuel cut control and brake control is performed so that the wheel speed is the same, and after confirming that the driving wheel speed is substantially the same as the driven wheel speed or the vehicle body speed, the two-wheel driving state is A 4-wheel drive command for switching to the 4-wheel drive state is output.

  That is, when the engine output control is limited, when switching from the two-wheel drive state to the four-wheel drive state, if the drive wheel slips, there is a large rotational speed difference between the driven wheel speed and 4 A large torque is transmitted to the driven wheel due to the interference of the power train when the transfer for switching to the wheel drive state is concluded. Due to this large torque transmission to the driven wheel, large front and rear G and noise are generated when the transfer is fastened, the transfer is not fastened smoothly and it takes time to fasten, and a heavy load is applied to the powertrain. . Further, on an extremely low μ road such as an icing road surface, in addition to the driving wheel slip, the driven wheel may also slip, resulting in a four-wheel slip state.

On the other hand, after confirming that the driving wheel speed is substantially the same as the driven wheel speed or the vehicle body speed, the power train is switched from the two-wheel driving state to the four-wheel driving state. Interference can be prevented, no large back-and-forth G or sound is generated, and the vehicle can be switched to the four-wheel drive state in a short time, so that the load on the power train is suppressed and durability enhancement is not required. Further, since the slip ratio of the drive wheels is reduced (vehicle speed = four-wheel grip state), re-slip after switching to the four-wheel drive state is prevented, which is particularly effective when traveling on an extremely low μ road.
In addition, when the wheel speed of the driving wheel is reduced by using both the all-cylinder fuel cut control and the brake control of the engine, four-wheel drive can be achieved in a shorter time.

  In the invention according to claim 4, the braking force is applied to the wheel so that the side slip amount approaches the target side slip amount in the vehicle dynamics control system during traveling in which a deviation occurs between the side slip amount of the vehicle and the target side slip amount. At the same time, the engine output is controlled by performing at least one of fuel cut and ignition timing change. However, when the vehicle is in an operating state that causes overheating of the exhaust system catalyst, In order to protect the catalyst, the control amount of the engine output is limited or the engine output control is prohibited.

  When the engine output control is restricted by the engine output control restricting means or when it is predicted that the engine output control restriction will be executed, there is a deviation between the side slip amount of the vehicle and the target side slip amount. When the condition that the shift position is fixed and the two-wheel drive state is selected in the front and rear wheel driving force distribution control system is satisfied, the restriction corresponding driving force distribution control means determines whether the front and rear wheel driving force distribution control system A 4-wheel drive command for switching from the 2-wheel drive state to the 4-wheel drive state is output to the actuator.

  That is, in the four-wheel drive state, the inertia and friction for the drive system increase compared to the two-wheel drive state, so the total drive torque for the four wheels decreases compared to the two-wheel drive state. In addition, since a part of the driving torque to the driving wheel is transmitted to the driven wheel side, the torque transmitted to the driving wheel is reduced, and the side slip due to excessive torque is suppressed. Furthermore, since the driving torque is distributed to the four wheels, the torque that can be transmitted to the road surface per wheel is increased, and the vehicle stability is improved.

  Therefore, even if the engine output torque suddenly increases due to the limitation of the engine output control during traveling, the side slip amount of the vehicle can be suppressed while suppressing the rapid increase of the drive wheel torque and improving the vehicle stability.

  In the invention according to claim 5, when the control start condition for switching the driving force distribution to the four-wheel drive is established in the restriction corresponding driving force distribution control means, when the side slip amount deviation is large, the two-wheel driving state is started. A four-wheel drive command for switching to the four-wheel drive state is output and at least one of the engine full cylinder fuel cut control and brake control is performed until the side slip amount deviation decreases, and the side slip amount deviation is less than the set deviation. In this case, a four-wheel drive command for switching from the two-wheel drive state to the four-wheel drive state is output.

  Therefore, the transmission torque to the drive wheels due to the four-wheel drive is reduced until at least one of the engine all-cylinder fuel cut control and the brake control until the side slip amount deviation is reduced, that is, until the vehicle behavior is stabilized. By reducing the vehicle speed by this control, it is possible to perform simple skid prevention control.

  Hereinafter, an embodiment for realizing a drive system control device for a four-wheel drive vehicle according to the present invention will be described based on a first example corresponding to claims 1 to 3.

First embodiment

First, the configuration will be described.
FIG. 1 is a combined system diagram of a VDC, a TCS, and an ABS to which the drive system control device for a four-wheel drive vehicle of the first embodiment is applied.
The VDC system (Vehicle Dynamics Control System) reduces vehicle slippage that occurs during emergency avoidance of slippery road surfaces and obstacles while driving, with four-wheel independent brake control and engine output control, as well as turning performance and braking. This is a vehicle behavior control system that achieves both high performance and improved running stability.
TCS (Traction Control System) is driven by engine output control (closes the electronically controlled throttle valve or cuts fuel) and brake control (increases the brake fluid pressure on the rear wheels) when the slip amount of the drive wheels increases. This system suppresses wheel slip.
ABS (Anti-Rock Brake System) detects wheel speed during braking and controls the braking force by electronic control to prevent locking of the four wheels, improve stability during sudden braking and handle operation It is a system that makes it easier to avoid obstacles.

  In FIG. 1, 1 is an engine, 2 is an automatic transmission, 3 is a transmission output shaft, 4 is a transfer, 5 is a rear propeller shaft, 6 is a rear differential, 7 and 8 are rear drive shafts, 9 is a left rear wheel, 10 is a right rear wheel, 11 is a front propeller shaft, 12 is a front differential, 13 and 14 are front drive shafts, 15 is a front left wheel, 16 is a front right wheel, 17 is an actuator, 18 is a 4WD control unit, and 19 is a mode selection switch. It is.

  That is, in the two-wheel drive state, the rear left and right rear wheels 9 and 10 are drive wheels, and the rear wheel drive base four-wheel drive vehicle distributes the drive torque to the left and right front wheels 15 and 16 that are driven wheels by engaging the clutch in the transfer 4. Yes, 4WD control that outputs a control command to the actuator 17 using as input information an actuator 17 that controls the clutch in the transfer 4 and a mode selection switch 19 that can select a two-wheel drive mode, a four-wheel drive mode, and an auto mode. The unit 18 constitutes a four-wheel driving force distribution control system.

  When the two-wheel drive mode is selected, the drive torque is transmitted only to the left and right rear wheels 9, 10 by releasing the clutch. When the four-wheel drive mode is selected, the drive torque is transmitted to the left and right rear wheels 9, 10 by completely engaging the clutch. It is transmitted to the left and right front wheels 15 and 16 with equal distribution. When the auto mode is selected, the front and rear wheel driving force distribution ratio of the driving torque is variably controlled by the clutch engagement force command proportional to the front and rear wheel rotational speed difference and inversely proportional to the lateral acceleration. Is done.

  In FIG. 1, 20 is a brake pedal, 21 is a master cylinder, 22 is a steering angle sensor, 23 is a yaw rate / lateral G sensor, 24 is a left front wheel rotation sensor, 25 is a right front wheel rotation sensor, 26 is a left rear wheel rotation sensor, 27 is a right rear wheel rotation sensor, 28 is a pressure sensor, 29 is a VDC / TCS / ABS control unit, 30 is an engine control unit, 31 is an automatic transmission control unit, 32 is an electronic control throttle, 33 is a precharge pump, 34 Is a VDC / TCS / ABS actuator, 35 is an ABS warning lamp, 36 is a VDC-OFF indicator lamp, and 37 is a SLIP indicator lamp.

  Sensor signals from the steering angle sensor 22, the yaw rate / lateral G sensor 23, the left front wheel rotation sensor 24, the right front wheel rotation sensor 25, the left rear wheel rotation sensor 26, the right rear wheel rotation sensor 27, and the pressure sensor 28 are VDC / It is output to the TCS / ABS control unit 29.

  The VDC / TCS / ABS control unit 29 receives various sensor signals, information on the engine 1 and the automatic transmission 2, and determines the running state of the vehicle. Then, the target brake fluid pressure necessary for VDC / TCS / ABS control is calculated, the brake actuator drive signal is output, and the target engine torque is calculated.

  The engine control unit 30 receives a command from the VDC / TCS / ABS control unit 29 and performs throttle opening control for the throttle motor of the electronic control throttle 32 and fuel cut control for the injector of the engine 1.

  The precharge pump 33 draws in brake fluid for increasing pressure from the reservoir tank during VDC / TCS operation, and generates brake operation fluid pressure. The VDC / TCS / ABS actuator 34 is connected to the VDC / TCS / ABS control unit 29. In response to the actuator drive signal from, the brake fluid pressure to the wheel cylinder of each wheel is adjusted.

  The VDC / TCS / ABS control unit 29, the engine control unit 30, the automatic transmission control unit 31, and the steering angle sensor 22 are connected to each other by a CAN communication line (multiplex communication line).

Next, the operation will be described.
[TCS control operation processing]
FIG. 2 is a flowchart showing a flow of TCS control operation processing executed by the TCS control unit of the VDC / TCS / ABS control unit 29. Each step will be described below.
In step S1, it is determined whether or not a four-wheel drive flag 4WDF indicating whether or not four-wheel drive control is being performed is 4WDF = 0 (during non-control of four-wheel drive). If YES, the process proceeds to step S2, and NO is determined. In this case, the process proceeds to step S17.

  In step S2, whether or not slip has occurred in the drive wheels (left and right rear wheels 9 and 10) is determined based on whether or not the calculated values such as the slip ratio and the slip ratio are equal to or greater than a set threshold value. Advances to step S3, and if NO, advances to return.

  In step S3, based on the range position information from the automatic transmission control unit 31, it is determined whether or not the automatic transmission 2 is in the range fixing mode (first speed fixed range or second speed fixed range). The process proceeds to step S4, and if NO, the process proceeds to step S11.

  In step S4, based on the switch signal from the mode selection switch 19, it is determined whether or not the two-wheel drive mode is selected. If YES, the process proceeds to step S5, and if NO, the process proceeds to step S11.

  In step S5, it is determined whether engine output control by fuel cut and ignition retard is impossible based on the engine speed detection value, the accelerator opening detection value, and the fuel cut controllable region characteristic shown in FIG. If so, the process proceeds to step S6. If NO, the process proceeds to step S11.

  That is, if the vehicle operating state based on the engine speed and the accelerator opening is in the A region (unrestricted region), the process proceeds to step S11, and if it is in the B region (restricted region) and the C region (prohibited region), the process proceeds to step S6. move on. Here, in the B region, engine output control by fuel cut and ignition retard is possible until a predetermined time, but when the predetermined time has elapsed, all cylinder cut or full recover (all cylinder fuel cut prohibited = all cylinder injection) Can be switched to. Further, in the C region, only full cylinder cut or full recover is permitted, and engine output control by partial cylinder fuel cut and ignition retard is prohibited. The region D is a region where the engine speed is equal to or lower than the engine stall limiter (1000 rpm), and is a region where TCS control is not performed in the first place.

  When processing is performed by predicting whether or not the engine output control restriction is likely to be executed, it is determined whether or not the region B is approaching the region B or C as time elapses in the region A, or the region B Whether or not the vehicle is approaching the C region is determined based on the detected engine speed value, the detected accelerator opening value, and the fuel cut controllable region characteristic shown in FIG. 3, and the A or B region is approaching the B or C region. In this case, or in the case of the B area approaching the C area, the process proceeds to step S6, and if not, the process proceeds to step S11.

In step S6, a target drive torque is calculated as follows: driven wheel speed (left and right front wheel speed average value) = drive wheel speed (left and right rear wheel speed average value).
In step S7, the engine drive torque is controlled by the combined use of all-cylinder fuel cut and brake control in order to obtain the target drive torque calculated in step S6.
In step S8, it is determined whether driven wheel speed = drive wheel speed. If YES, the process proceeds to step S9, and if NO, the process proceeds to return.

In step S 9, a 4-wheel drive command is output from the 4WD control unit 18 to the actuator 17 of the transfer 4 based on a command to the 4WD control unit 18.
In step S10, the four-wheel drive flag 4WDF is rewritten to 4WDF = 1 (indicating that four-wheel drive control is being performed).

In step S11, it is determined in step S2 that slip has occurred in the drive wheel, and if it is determined NO in at least one of the determination steps S3, S4, and S5, VDC / TCS control is started. The
In step S12, the target drive wheel torque is calculated according to the drive wheel slip level.
In step S13, the target engine torque shared by the engine output control is calculated among the target drive wheel torques calculated in step S12.

In step S14, the target brake torque is calculated by subtracting the target engine torque calculated in step S13 from the target drive wheel torque calculated in step S12.
In step S15, engine output control is performed by fuel cut and ignition retard.
In step S16, brake control for obtaining the target brake torque calculated in step S14 is performed.

  In step S17, when 4WDF = 1 (during four-wheel drive control) and NO is determined in step S1, the engine speed detection value, the accelerator opening detection value, and the fuel cut control possible region characteristics shown in FIG. Based on this, it is determined whether engine output control by fuel cut and ignition retard is possible. If YES, the process proceeds to step S18, and if NO, the process proceeds to return.

In step S18, it is determined whether the detected yaw rate value is equal to or less than the threshold value. If YES, the process proceeds to step S19, and if NO, the process proceeds to return.
In step S19, it is determined whether or not the wheel slips of all the front and rear wheels have converged. If YES, the process proceeds to step S20, and if NO, the process proceeds to return.

In step S20, when all of the four-wheel drive control end conditions in steps S17, S18, and S19 are satisfied, two-wheel drive is performed from the 4WD control unit 18 to the actuator 17 of the transfer 4 based on a command to the 4WD control unit 18. A command is output.
In step S21, the four-wheel drive flag 4WDF is rewritten from 4WDF = 1 to 4WDF = 0 (indicating non-control of four-wheel drive).

[During normal TCS control]
At the time of normal TCS control that suppresses the drive slip of the left and right rear wheels 9 and 10 that are drive wheels during driving in the two-wheel drive mode, in the flowchart of FIG. 2, step S1, step S2, step S3 (→ step S4, Step S5) → Step S11 → Step S12 → Step S13 → Step S14 → Step S15 → Step S16. When it is determined in step S1 that the left and right rear wheels 9 and 10 have slipped, If any of the determination steps S3, S4, and S5 of the four-wheel drive control start condition is not satisfied, the process proceeds to step S11, where TCS control is started, and engine output control is performed by fuel cut and ignition retard. And a brake for applying a braking force to the left and right rear wheels 9 and 10 where slip occurs. Slip of the drive wheels is suppressed by combination with the control.

  For example, in the time chart of FIG. 5, normal TCS control is performed from time t0 when drive wheel slip occurs until time t1 when the engine output control by the fuel cut and ignition retard becomes impossible. That is, in step S12, the target drive wheel torque is calculated as shown in the target drive wheel torque characteristic, and in step 15, the fuel cut while changing the number of fuel cut cylinders as shown in the fuel cut control characteristic by the VDC / TCS control. In step S16, the brake control (intervention amount) for obtaining the target brake torque is performed in step S16.

  Therefore, when both the left and right rear wheels 9 and 10 cause a drive slip, in addition to the engine output control by fuel cut and ignition retard, the brake control for applying a braking force to the left and right rear wheels 9 and 10 is performed, thereby Drive slip can be suppressed more responsively than output control only, and when only one rear wheel 9 or rear wheel 10 slips during split μ road (left / right uneven road surface) or turning acceleration, etc. However, it is possible to suppress the drive slip by performing a brake control in which a braking force is applied only to one wheel that has slipped.

[Driving wheel speed control]
While driving in the two-wheel drive mode, the left and right rear wheels 9 and 10 that are drive wheels generate drive slips. In FIG. 3, when the driving state enters the B region or the C region, , Step S1 → step S2 → step S3 → step S4 → step S5 → step S6 → step S7. In step S7, the range fixing mode condition in step S3 and the two-wheel drive mode selection condition in step S4. If the four-wheel drive control start condition is satisfied, that is, the engine output control restriction region (B region) or the prohibition region (C region) in step S5, the drive wheel speed = subordinate prior to the four-wheel drive control. Engine output control and brake control for reducing the wheel speeds of the left and right rear wheels 9 and 10 are performed so as to achieve the moving wheel speed.
In the limiting means, the control amount of the engine output is limited or the engine output control is prohibited to protect the exhaust system catalyst.

  For example, in the time chart of FIG. 5, the target drive wheel torque characteristics from time t1 when the engine output control by the fuel cut and ignition retard becomes impossible until time t2 when the drive wheel speed becomes the driven wheel speed. As shown in FIG. 5, the drive wheel speed control is performed in which the target drive wheel torque is set to the minimum torque, and the drive wheel speed is reduced in a short time with good response. That is, in step S7, as shown in the brake control characteristics, the brake control is performed with the substantially maximum intervention amount, and the engine control that alternately repeats all cylinder cuts and full recovery as shown in the fuel cut control characteristics is performed. To be implemented.

  That is, when the engine output control is restricted, if the vehicle is immediately switched from the two-wheel drive state to the four-wheel drive state, the left and right rear wheels 9 and 10 are slipping, resulting in a large gap between the left and right front wheels 15 and 16. Since there is a difference in rotational speed, a large torque is transmitted to the left and right front wheels 15 and 16 due to power train interference when the clutch in the transfer 4 is switched to the four-wheel drive state.

  Due to the large torque transmission to the left and right front wheels 15 and 16, a large front and rear G and sound are generated when the clutch in the transfer 4 is engaged, or the clutch in the transfer 4 is not engaged and the engagement takes time. In addition, a heavy load is applied to the power train. Further, on an extremely low μ road such as an icy road surface, the driven wheels of the left and right front wheels 15 and 16 may slip in addition to the drive wheel slip of the left and right rear wheels 9 and 10, and a four-wheel slip state may occur.

  On the other hand, after confirming that the driving wheel speed is the same as the driven wheel speed (the vehicle speed may be used instead of the driven wheel speed), the two-wheel driving state is switched to the four-wheel driving state. Interference of the power train can be prevented when switching to the wheel drive state, no large front and rear G or sound is generated, and it can be switched to the four wheel drive state in a short time, and the load of the power train can be suppressed. Powertrain durability is no longer required.

  Further, since the slip ratio of the drive wheels is reduced (vehicle speed = four-wheel grip state), re-slip after switching to the four-wheel drive state is prevented, which is particularly effective when traveling on an extremely low μ road.

  Moreover, since the wheel speeds of the left and right rear wheels 9, 10 are reduced by the combined use of the all cylinder fuel cut control and the brake control of the engine 1, the left and right rear wheels 9, 10 are controlled by one of the all cylinder fuel cut control and the brake control. Compared to a case where the wheel speed of 10 is reduced, four-wheel drive can be achieved in a short time.

[4-wheel drive control]
When the wheel speeds of the left and right rear wheels 9, 10 are reduced by the driving wheel speed control and the driven wheel speed is equal to the driving wheel speed, the process proceeds from step S7 to step S8 to step S9. In step S9, the four-wheel drive control is performed. In step S10, the four-wheel drive flag 4WDF is rewritten to 4WDF = 1.

  For example, in the time chart of FIG. 5, as shown in the target drive wheel torque characteristics from time t2 when the drive wheel speed = driven wheel speed to time t3 when the four-wheel drive control termination condition is satisfied, The torque is returned to the driver's required torque, the brake control and the fuel cut control are stopped, and the clutch in the transfer 4 is completely engaged, so that the front and rear wheel driving force distribution is driven to the rear wheels 9 and 10 only. The distribution state is switched to the four-wheel drive distribution state in which distribution is made to the front and rear wheels 9, 10, 15, and 16.

  That is, in the four-wheel drive state, the inertia and friction for the drive system increase compared to the two-wheel drive state, so the total drive torque for the four wheels decreases compared to the two-wheel drive state. Further, since a part of the driving torque to the left and right rear wheels 9, 10 is transmitted to the left and right front wheels 15, 16, the torque transmitted to the left and right rear wheels 9, 10 is reduced, and the driving slip due to excessive torque is suppressed. It is done. Furthermore, since the driving torque is distributed to the four wheels, the torque that can be transmitted to the road surface per wheel is increased, and the vehicle stability is improved.

  That is, as shown in the μ (driving force) -S (slip rate) characteristic of the tire in FIG. 4, the driving force μ is low in the slip state, but the driving force μ is increased by reducing the slip rate. This driving force μ can be paraphrased as road grip force or road surface transmission torque, so that the torque that can be transmitted to the road surface per wheel increases due to suppression of driving slip due to the dispersion of the driving torque to the four wheels, and vehicle stability Will be enhanced.

  Therefore, as shown in the wheel speed characteristics between t2 and t3 in FIG. 5, even if the engine output torque suddenly increases due to the limitation of the engine output control, the rapid increase in drive wheel torque is suppressed and the vehicle stability is improved. The driving wheel speed changes in the vicinity of the vehicle body speed, and the induction of driving slip can be suppressed.

Here, when the engine output control restriction is started, it is conceivable to shift to the brake control that does not cause the catalyst overheating instead of the engine output control in the two-wheel drive state.
However, the difference between "control with 2WD" and "4WD" is in (1) TCS control time, (2) load on powertrain / brake parts, and (3) vehicle stability. The details are described below.

  As for (1) and (2), in the case of “control while keeping 2WD”, as a result, the TCS control is continued only by the brake. Therefore, since the surplus torque is received by the two drive wheels, the load on the brake unit (durability such as heat and wear) and the load on the powertrain (differential and drive shaft durability) continue to be large. In this case, it is necessary to strengthen each unit (cost increase) if the brake control is prohibited or not desired to be prohibited.

  By “4WD”, surplus torque can be received by the two drive wheels only during the 4WD transition period (short time), so the load on the powertrain / brake parts is low (conventional product) Further, there is no need to perform processing such as prohibiting brake control. In particular, in the brake-only TCS control, a large load is applied to the differential.

  Regarding (3), the vehicle is more stable in the 4WD that effectively uses four wheels than in the 2WD + TCS. In particular, in the case of the present invention, it corresponds to a rapid recovery of engine torque, and 4WD is more effective. In this case, it can be considered that “always 4WD” should be used, but since the driver has selected 2WD intentionally, it is set back to 2WD when it is not necessary to convert to 4WD.

  Therefore, there is a background that it is desired to suppress the occurrence of slip due to the limitation of the engine output control without combining the limitation of the engine output control and the brake TCS control.

[Transition from 4-wheel drive to 2-wheel drive]
When the four-wheel drive flag 4WDF is rewritten to 4WDF = 1 by the four-wheel drive control, the flow proceeds from step S1 to step S17 in the flowchart of FIG. 2, and engine output control is possible in step S17. When it is determined that the vehicle has entered the region, the flow proceeds from step S17 to step S18 → step S19 → step S20 → step S21. In step S20, the yaw rate condition indicating the stable state of the vehicle behavior in step S18, and step S19. When the four-wheel drive control termination condition of the wheel slip convergence condition is satisfied, the four-wheel drive state is returned to the two-wheel drive state, and the four-wheel drive flag 4WDF is rewritten to 4WDF = 0 in step S21. Return to normal control.

  For example, in the time chart of FIG. 5, when engine output control is enabled by the accelerator OFF operation at time t3 ′, the process waits until time t3 when the four-wheel drive control termination condition based on the yaw rate condition and the wheel slip convergence condition is satisfied. At t3, by releasing the clutch in the transfer 4, the four-wheel drive distribution state in which the drive torque is distributed to the front and rear wheels 9, 10, 15, 16 is changed to the two-wheel drive distribution state in which the drive torque is distributed only to the rear wheels 9, 10. Is returned.

  Therefore, when the four-wheel drive control that suppresses the generation of the drive slip due to the engine output control restriction is started, the vehicle state in which the engine output control restriction is released, the vehicle behavior is stable, and the wheel slip is prevented. Under the condition that there is no occurrence, the vehicle is restored from the four-wheel drive state to the two-wheel drive state, so that the stability of the vehicle behavior is maintained even if the drive force distribution is changed, and the two-wheel drive state There is no re-slip immediately after the change to.

Next, the effect will be described.
(1) In a drive system controller for a four-wheel drive vehicle equipped with a front / rear wheel drive force distribution control system and a traction control system, the traction control system controls engine output according to the characteristics shown in FIG. 3 to protect the exhaust system catalyst. When the automatic transmission 2 is in the range fixed mode and when the two-wheel drive mode is selected, when the drive wheel is slipping, together with the limit control unit that reduces the control amount of the engine or prohibits the engine output control When the engine output control cannot be restricted, a restriction corresponding control unit that outputs a four-wheel drive command for switching from the two-wheel drive state to the four-wheel drive state to the actuator 17 of the front and rear wheel drive force distribution control system. Therefore, even if the engine output torque suddenly rises due to the restriction of engine output control, while suppressing the sudden increase in drive wheel torque and improving vehicle stability, Induction of driving slip can be suppressed.

  (2) The traction control system applies a braking force to the left and / or one drive wheel where the engine output is controlled by at least one of fuel cut or ignition timing change and when the slip occurs on the drive wheel. Since the brake control system is applied, when both the left and right drive wheels generate a drive slip, only engine output control can be performed by applying brake control to the left and right drive wheels in addition to engine output control. The drive slip can be suppressed more responsively than when the split wheel is on the split μ road (left and right uneven road surface) or during turning acceleration. Driving slip can be suppressed by performing brake control that applies braking force only to the vehicle.

  (3) When the control start condition for switching the driving force distribution to the four-wheel drive is satisfied, the restriction handling control unit performs all-cylinder fuel cut control of the engine so that the driving wheel speed becomes the same wheel speed as the driven wheel speed. After performing brake control and confirming that the driving wheel speed is the same as the driven wheel speed, a four-wheel driving command for switching from the two-wheel driving state to the four-wheel driving state is output. Interference of the power train can be prevented at the time of switching, and there is no large front and rear G or sound, and it can be switched to the four-wheel drive state in a short time, the power train load is suppressed and durability is enhanced Is no longer necessary.

Further, since the slip ratio of the drive wheels is reduced (vehicle speed = four-wheel grip state), re-slip after switching to the four-wheel drive state is prevented, which is particularly effective when traveling on an extremely low μ road.
In addition, since the wheel speed of the drive wheel is reduced by the combined use of the all-cylinder fuel cut control and the brake control of the engine, the wheel speed of the drive wheel is reduced by one of the all-cylinder fuel cut control and the brake control. Compared to, four-wheel drive can be achieved in a short time.

(Other examples)
As mentioned above, although the drive system control apparatus of the four-wheel drive vehicle of this invention was demonstrated based on 1st Example, about a specific structure, it is not restricted to this 1st Example, Claim of Claim Design changes and additions are allowed without departing from the spirit of the invention according to each claim.

  For example, in the first embodiment, an example of application to a traction control system has been shown, but during traveling in which a deviation occurs between the side slip amount of the vehicle and the target side slip amount, the wheels are controlled so that the side slip amount approaches the target side slip amount. The present invention can also be applied to a vehicle dynamics control system that applies engine power and controls engine output by performing at least one of fuel cut and ignition timing change.

  In this case, when engine output control is restricted or when engine output control restriction is predicted to be executed, the shift shift position of the transmission is fixed while the vehicle is traveling with a deviation between the side slip amount and the target side slip amount. And when the two-wheel drive state is selected in the front and rear wheel drive force distribution control system, the two-wheel drive state to the four-wheel drive state are applied to the actuator of the front and rear wheel drive force distribution control system. Because the 4-wheel drive command to switch to is output, even if the engine output torque suddenly rises due to the restriction of engine output control while driving, while suppressing the sudden increase in drive wheel torque and improving vehicle stability, The amount of side slip of the vehicle can be suppressed (corresponding to the invention according to claim 4).

  When the control start condition for switching the driving force distribution to the four-wheel drive is satisfied, if the side slip amount deviation is large, a four-wheel drive command for switching from the two-wheel drive state to the four-wheel drive state is output and the side slip amount is output. The engine is controlled by all-cylinder fuel cut control and brake control until the deviation becomes small. If the skid deviation is less than the set deviation, the four-wheel drive is switched from the two-wheel drive state to the four-wheel drive state. A command may be output. In this case, the transmission torque to the drive wheels due to the four-wheel drive is reduced until the side slip amount deviation is reduced, that is, until the vehicle behavior is stabilized, and the engine all-cylinder fuel cut control and brake control are performed. When the vehicle speed is reduced by at least one of the controls, a simple skid prevention control is possible (corresponding to the invention according to claim 5).

  In the first embodiment, an example of application to a four-wheel drive vehicle based on a rear wheel drive is shown, but the present invention can be similarly applied to a four-wheel drive vehicle based on a front wheel drive base. Further, even if the transfer changes the front and rear wheel driving force distribution ratio steplessly from the two-wheel drive state to the complete four-wheel drive state as in the first embodiment, the two-wheel drive state and the four-wheel drive are used. The state may be switched ON / OFF.

  In the first embodiment, an example of application to an automatic transmission vehicle (AT vehicle) has been shown. However, a manual transmission vehicle (MT vehicle), a V belt type or toroidal type continuously variable transmission vehicle (CVT). It can also be applied to cars.

It is a VDC / TCS / ABS control system diagram to which the drive system control device of the four-wheel drive vehicle of the first embodiment is applied. It is a flowchart which shows the flow of the TCS control operation process performed in the TCS control part of the VDC / TCS / ABS control unit of 1st Example. FIG. 5 is a characteristic diagram of fuel cut controllability used in the first embodiment device. FIG. 5 is a characteristic diagram of a tire (μ (driving force) −S (slip ratio)). It is a figure which shows the time chart in the case of transfering from normal TCS control to driving wheel speed control → 4WD control → normal control (2WD) in the first embodiment apparatus.

Explanation of symbols

1 Engine 2 Automatic transmission 3 Transmission output shaft 4 Transfer 5 Rear propeller shaft 6 Rear differential 7, 8 Rear drive shaft 9 Left rear wheel 10 Right rear wheel 11 Front propeller shaft 12 Front differential 13, 14 Front drive shaft 15 Left front wheel 16 Right front wheel 17 Actuator 18 4WD control unit 19 Mode selection switch 20 Brake pedal 21 Master cylinder 22 Steering angle sensor 23 Yaw rate / lateral G sensor 24 Left front wheel rotation sensor 25 Right front wheel rotation sensor 26 Left rear wheel rotation sensor 27 Right rear wheel rotation Sensor 28 Pressure sensor 29 VDC / TCS / ABS control unit 30 Engine control unit 31 Automatic transmission control unit 32 Electronic control throttle 33 Precharge Pump 34 VDC / TCS / ABS actuator 35 ABS warning light 36 VDC-OFF indicator 37 SLIP indicator

Claims (5)

A front and rear wheel driving force distribution control system capable of switching between a two-wheel drive state for driving the rear wheel or the front wheel and a four-wheel drive state for driving the front and rear wheels by a command to the actuator;
Gear ratio mode switching means for switching between an automatic gear ratio mode for automatically controlling the gear ratio and a range fixing mode for fixing the gear ratio;
A traction control system that has drive slip detection means for detecting slip of the drive wheel, and performs engine output control by performing at least one of fuel cut or ignition timing change when slip occurs in the drive wheel;
Engine output control limiting means for reducing engine output control according to the operating state of the vehicle for protecting the exhaust system catalyst, or for limiting engine output control for prohibiting engine output control;
In the fixed range mode, when the drive wheel is slipping, when the two-wheel drive state is selected, and when the engine output control limit or the engine output control limit is executed A limited corresponding driving force distribution control means for outputting a four-wheel driving command for switching from the two-wheel driving state to the four-wheel driving state to an actuator of the front and rear wheel driving force distribution control system,
A drive system control apparatus for a four-wheel drive vehicle. The drive system controller for a four-wheel drive vehicle according to claim 1,
A brake actuator is provided to generate brake fluid pressure independently for each of the front and rear wheels regardless of the brake operation.
The traction control system applies a braking force to the left and right drive wheels where the engine output control and the slip are generated by at least one of fuel cut or ignition timing change when the drive wheels are slipping. A drive system control device for a four-wheel drive vehicle, characterized in that the system performs brake control. In the drive system control device for a four-wheel drive vehicle according to claim 1 or 2,
When the control start condition for switching the driving force distribution to the four-wheel drive is satisfied, the restriction-corresponding driving force distribution control unit is configured so that the driving wheel speed becomes the same wheel speed as the driven wheel speed or the vehicle body speed. Perform at least one of fuel cut control and brake control, confirm that the driving wheel speed is almost the same as the driven wheel speed or the vehicle body speed, and then switch from the two-wheel driving state to the four-wheel driving state. A drive system control device for a four-wheel drive vehicle, characterized in that it is means for outputting commands. A front and rear wheel driving force distribution control system capable of switching between a two-wheel drive state for driving the rear wheel or the front wheel and a four-wheel drive state for driving the front and rear wheels by a command to the actuator;
Gear ratio mode switching means for switching between an automatic gear ratio mode for automatically controlling the gear ratio and a range fixing mode for fixing the gear ratio;
There is a target side slip amount calculating means for calculating a target side slip amount based on a steering operation amount and a brake operation amount of the driver, and a side slip amount detecting means for detecting a side slip amount of the vehicle, and between the side slip amount of the vehicle and the target side slip amount. A vehicle dynamics control system that applies a braking force to the wheel so that the side slip amount approaches the target side slip amount during running, and performs engine output control by performing at least one of fuel cut or ignition timing change, and
Engine output control limiting means for reducing engine output control according to the operating state of the vehicle for protecting the exhaust system catalyst, or for limiting engine output control for prohibiting engine output control;
In the fixed range mode, when the vehicle is running with a deviation between the side slip amount and the target side slip amount, and when the two-wheel drive state is selected, and when the engine output control is limited or the engine output When the control restriction is predicted to be executed, the restriction corresponding drive that outputs the four-wheel drive command for switching from the two-wheel drive state to the four-wheel drive state to the actuator of the front and rear wheel drive force distribution control system Power distribution control means;
A drive system control apparatus for a four-wheel drive vehicle. The drive system controller for a four-wheel drive vehicle according to claim 4,
When the control start condition for switching the driving force distribution to the four-wheel drive is satisfied, the restriction-corresponding driving force distribution control means switches the two-wheel drive state to the four-wheel drive state when the side slip amount deviation is large. When the side slip amount deviation is less than the set deviation, at least one of the engine all-cylinder fuel cut control and the brake control is performed until the side slip amount deviation is reduced. A drive system control device for a four-wheel drive vehicle, characterized in that it is means for outputting a four-wheel drive command for switching to a state.

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