JP2014080089A - Traction control unit of four-wheel-drive vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an input load on a clutch mechanism from being excessive due to application of a braking force to two or more wheels through traction control by a traction control unit of a four-wheel-drive vehicle.SOLUTION: When a four-wheel-drive running mode is selected, after an associated initiation condition is established (t3), traction control is immediately initiated for one wheel (RL). For remaining wheels (FL), after the associated initiation condition is established (t3), the traction control is initiated with delay (t3'). As the one wheel (RL), a wheel whose slip ratio is the largest is adopted from among two or more wheels for which the initiation condition is established. Braking forces to be applied to respective wheels are adjusted for fear a sum total of braking forces may exceed a predetermined value THL during implementation of the traction control. The braking forces increase stepwise and thereafter decrease while gradually changing. Therefore, an input load (sum total of braking forces) on a clutch mechanism C/T does not exceed the predetermined value THL at the time t3 and time t3' alike.

Description

  The present invention relates to a traction control device for a four-wheel drive vehicle.

  Conventionally, a transfer including an input shaft, a first output shaft, and a second output shaft is widely known (see, for example, Patent Document 1). The input shaft is connected to the output shaft of a transmission connected to the vehicle engine. The first output shaft is connected to the left and right rear wheels (first left and right wheels) via a rear wheel side propeller shaft (first propeller shaft), and the second output shaft is connected to the front wheel side propeller shaft (second propeller shaft). Via the left and right front wheels (second left and right wheels).

  The transfer includes a clutch mechanism that can adjust a torque (distributed torque) that is a part of the driving torque of the input shaft and is distributed to the second output shaft. The distribution torque adjusted by the clutch mechanism is transmitted to the second output shaft, and the torque obtained by subtracting the distribution torque from the drive torque of the input shaft is transmitted to the first output shaft. Therefore, when the distribution torque is zero, a two-wheel drive state (rear wheel drive state) is obtained. On the other hand, when the distribution torque is greater than zero, a four-wheel drive state is obtained, and the torque distribution of the front and rear wheels can be adjusted by adjusting the distribution torque.

  Such a vehicle is usually provided with a selection switch for selecting one travel mode from a plurality of travel modes including a two-wheel drive travel mode and a four-wheel drive travel mode. When the four-wheel drive traveling mode is selected, the distribution torque is adjusted based on the traveling state of the vehicle such as the slip state of the left and right rear wheels. Thereby, normally, the distribution torque is maintained at zero, and a two-wheel drive state is obtained. On the other hand, the distribution torque is adjusted to a value greater than zero only under predetermined conditions such as when left and right rear wheels slip, and the drive state is automatically switched from the two-wheel drive state to the four-wheel drive state. Such drive control is also called “on-demand type”. On the other hand, when the two-wheel drive travel mode is selected, the distribution torque is maintained at zero. As a result, a two-wheel drive state is obtained.

  On the other hand, traction control is known as a response to a case where a wheel is in a slip state. This traction control is a control for controlling the braking device and applying a braking force to the wheel based on the determination that the execution condition that an excessive slip in the acceleration direction has occurred in the wheel of the vehicle is satisfied. It is. Thereby, the slip of the wheel is suppressed and the traction of the wheel can be recovered. This braking device individually adjusts the braking force applied to each wheel of the vehicle. Therefore, when the four-wheel drive travel mode is selected, control for executing this traction control for each wheel of the vehicle can be considered. This control makes it possible to more reliably cope with the slip state.

Japanese Patent No. 3650255

  Regarding the response to the slip state, the following event may occur in a four-wheel drive vehicle including the above-described control means for “executing traction control individually for each vehicle wheel”. When it is determined that excessive slip has occurred in two or more wheels, traction control is simultaneously performed on the two or more wheels. That is, the braking force is simultaneously applied to the two or more wheels by the braking device. At this time, torque resulting from the braking force of each wheel is simultaneously input to the transfer. As a result, the total torque (load) input to the transfer is based on the total braking force of each wheel and may be excessive.

  For this reason, robustness is required to protect the transfer (related elements such as the above-described clutch mechanism) from damage against an excessive load, resulting in an increase in cost.

  The present invention is for addressing the above problems, and the object thereof is caused by a braking force applied to two or more wheels by traction control in a traction control device for a four-wheel drive vehicle equipped with a transfer. Thus, an object of the present invention is to provide a device capable of suppressing an excessive sum of torques input to the transfer.

  The traction control device for a four-wheel drive vehicle according to the present invention includes a transfer including an input shaft and first and second output shafts, and the same braking device and control means as described above. The feature of the traction control of the four-wheel drive vehicle according to the present invention is that braking force applied to each wheel when the control means determines that the execution condition of the traction control is satisfied for two or more wheels. In other words, the braking force applied to the two or more wheels is adjusted so that the total sum does not exceed a predetermined value (THL).

  Here, the “two or more wheels” may be one or more front wheels and one or more rear wheels, only left and right front wheels, or only left and right rear wheels. The “predetermined value” is, for example, a value corresponding to an upper limit value at which the total sum of torques input to the transfer does not become excessive. According to the above configuration, the sum of the torques input to the transfer due to the braking force applied to two or more wheels by traction control can be suppressed.

  Here, “torque input to the transfer due to the braking force applied to the wheel” means that the friction member (brake pad, etc.) presses against the “member that rotates integrally with the wheel” (brake disc, etc.). This is a concept that includes not only the torque (static torque) attributed to the braking force according to the pressing force when being applied, but also the inertia torque (dynamic torque) attributed to the change in the rotational speed of the wheel. . The inertia torque can be represented by the product of the inertia moment related to rotation in the “power transmission system between the wheel and the transfer” and the rotational angular acceleration of the wheel.

  In the traction control device for a four-wheel drive vehicle according to the present invention, it is preferable that the transfer is configured to include the same clutch mechanism (C / T) as described above. This clutch mechanism is inserted in the middle of the power transmission system between the second left and right wheels and the power source (engine and transmission) of the vehicle. Therefore, even if the braking force applied to the second left and right wheels by the traction control may be excessive, a part of the excessive torque input to the transfer due to the excessive braking force is generated by the clutch mechanism. Can be absorbed and consumed by sliding. As a result, the excessive torque is not transmitted to the vehicle power source (engine and transmission), and the vehicle power source (engine and transmission) can be protected.

  Further, in the traction control device for a four-wheel drive vehicle according to the present invention, when it is determined that the execution condition of the traction control is satisfied for two or more wheels, the control means is for one wheel. It is preferable that the traction control is started immediately after the execution condition corresponding only to the start of establishment, and the traction control is started for the remaining wheels with a delay after the corresponding execution condition is established. .

  In this case, the braking force applied by the traction control increases (stepwise immediately (from zero) and then gradually decreases (toward zero)) after the start of the traction control (hereinafter referred to as “step”). It is preferable to make a transition in a pattern called “increase / gradual decrease pattern”.

  It is assumed that the “step increase / gradual decrease pattern” is adopted and the execution conditions of the traction control for two or more wheels start (substantially) simultaneously. In this case, in the configuration in which the traction control is started immediately after the execution condition is satisfied for all the wheels, the traction control is started (substantially) simultaneously for the two or more wheels. Accordingly, particularly when the “step increase / gradual decrease pattern” is employed, the braking force of the two or more wheels increases stepwise (substantially) simultaneously. As a result, the torque input to the transfer tends to be excessive. Note that when the braking force increases stepwise, the change in the rotational speed of the wheel becomes steep, so that the inertia torque (dynamic torque) temporarily increases. Considering this, it can be said that the torque input to the transfer tends to be excessive.

  On the other hand, according to the above configuration, first, traction control is started for only one wheel, and thereafter, traction control is started for other wheels after a delay. Therefore, when the “step increase / gradual decrease pattern” is adopted, the timing at which the braking force increases stepwise for the two or more wheels is shifted, so that the torque input to the transfer is unlikely to become excessive. .

  Further, in the traction control device for a four-wheel drive vehicle according to the present invention, the control means has a slip ratio of a wheel among two or more wheels that satisfy the execution condition of the traction control as the one wheel. Preferably the largest wheel is employed.

  In general, as the slip ratio of the wheel increases from zero, the frictional force (traction) between the wheel and the road surface first increases gradually, reaches a peak, and then gradually decreases. Assume that the slip ratio of two or more wheels is in a region larger than the value corresponding to the peak. In this case, the traction having the smallest traction among the two or more wheels is the wheel having the largest slip rate. Therefore, the braking force is applied to the wheel having the largest slip ratio to reduce the slip ratio of the wheel, and the braking force is applied to the other wheel to reduce the slip ratio of the wheel. In comparison, the vehicle as a whole can obtain better traction. The above configuration is based on such knowledge.

It is the figure which showed typically the power transmission system of the vehicle carrying the traction control apparatus of the four-wheel drive vehicle which concerns on embodiment of this invention. It is a schematic diagram which shows an example of the specific structure of the multi-plate clutch mechanism shown in FIG. It is a graph which shows the relationship between the clutch drive current and distributed torque about the multi-plate clutch mechanism shown in FIG. FIG. 3 is a flowchart showing a routine for controlling distributed torque in a four-wheel drive running mode (H4Auto), which is executed by the ECU shown in FIG. 1. FIG. 3 is a flowchart showing a routine for performing traction control in a four-wheel drive travel mode (H4Auto and H4Lock), which is executed by the ECU shown in FIG. 1. It is the time chart which showed an example in case the traction control (normal control) in 4 wheel drive travel mode is performed. FIG. 6 is a time chart showing an example when traction control (special control) is performed in a four-wheel drive travel mode based on the routines shown in FIGS. 4 and 5. FIG. It is the time chart which showed an example in case traction control (special control) in four-wheel drive travel mode is performed by ECU with which the traction control apparatus of the four-wheel drive vehicle which concerns on the modification of embodiment of this invention is equipped. It is the figure which showed typically the power transmission system of the vehicle carrying the traction control apparatus of the four-wheel drive vehicle which concerns on the other modification of embodiment of this invention.

  Hereinafter, a traction control device (hereinafter also referred to as “the present device”) for a four-wheel drive vehicle according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a power transmission system of a vehicle drive system equipped with the present apparatus. This drive system includes a transfer T / F, a rear wheel side differential D / Fr, a front wheel side differential D / Ff, a switching mechanism M, a braking device BRK, wheel speed sensors Vfr, Vfl, Vrr, Vrl, A front wheel side propeller shaft rotational speed sensor Vfp, a longitudinal acceleration sensor Gx, a 2WD / 4WD selector switch S, and an electronic control unit ECU are provided.

  The transfer T / F includes an input shaft A1, a first output shaft A2, and a second output shaft A3. The input shaft A1 is connected to the output shaft of the automatic transmission A / T connected to the engine E / G, and a power transmission system is formed between the input shaft A1 and the engine E / G. The first output shaft A2 is connected to the rear wheel side differential D / Fr via the rear wheel side propeller shaft Arp, and a power transmission system is formed between the first output shaft A2 and the rear wheel side differential D / Fr. ing. The second output shaft A3 is connected to the front wheel side differential D / Ff via the front wheel side propeller shaft Afp, and a power transmission system is formed between the second output shaft A3 and the front wheel side differential D / Ff.

  Further, the transfer T / F includes an auxiliary transmission mechanism Z and a multi-plate clutch mechanism C / T. The sub-transmission mechanism Z has one of the well-known configurations, and the same ratio is “1” in the HIGH mode in which the ratio of the rotation speed of the first output shaft A2 to the rotation speed of the input shaft A1 is “1”. The LOW mode, which is a constant value less than “,” can be selectively switched.

  As shown in FIG. 2, the multi-plate clutch mechanism C / T is configured by a multi-plate clutch electronic control coupling having a known configuration. C / T is a part of the “driving torque of the input shaft A1”, and the torque distributed to the second output shaft A3 (hereinafter referred to as “distributed torque Tc”) can be adjusted. The distribution torque Tc adjusted by C / T is transmitted to the second output shaft A3, and the torque obtained by subtracting the distribution torque Tc from the “driving torque of the input shaft A1” is transmitted to the first output shaft A2. .

  Therefore, when the distribution torque Tc is zero, a two-wheel drive state (rear wheel drive state) is obtained. On the other hand, when Tc is larger than zero, a four-wheel drive state is obtained, and the torque distribution of the front and rear wheels can be adjusted by adjusting Tc.

  The distribution torque Tc can be adjusted by adjusting a current (hereinafter referred to as “clutch drive current I”) for driving an actuator (not shown) in the multi-plate clutch mechanism C / T. Specifically, as shown in FIG. 3, Tc is adjusted to increase from “0” as I increases from “0”.

  The rear wheel side differential D / Fr has one of known configurations, and the torque of the rear wheel side propeller shaft Arp is applied to the left and right rear wheels via the right rear wheel axle Arr and the left rear wheel axle Arl. It comes to distribute. Similarly, the front wheel side differential D / Ff has one of known configurations, and distributes the torque of the front wheel side propeller shaft Afp to the left and right front wheels via the right front wheel axle Afr and the left front wheel axle Afl. It is like that.

  The switching mechanism M is interposed on the axle Afr of the right front wheel, and a “connected state” in which a power transmission system is formed between the right front wheel and the front wheel side differential D / Ff, and the right front wheel and the front wheel side differential D. The “non-connected state” in which no power transmission system is formed with / Ff can be selectively realized. Hereinafter, in the right front wheel axle Afr, a portion between the switching mechanism M and the right front wheel is particularly referred to as “first shaft Afr1”, and a portion between the switching mechanism M and the front wheel side differential D / Ff is particularly referred to as “first”. This is called “2-axis Afr2”. The switching mechanism M may or may not be provided with a rotation synchronizer (synchronizer) for bringing the rotation speeds of the first and second shafts Afr1 and Afr2 close to each other. Further, the switching mechanism M may be interposed on the axle Afl of the left front wheel.

  The switching mechanism M has, for example, a dog type (spline fitting type) configuration. In this case, the switching mechanism M includes, for example, a hub (outer spline or inner spline) integral with one of the first and second shafts Afr1 and Afr2, and a sleeve (inner spline or outer spline) that is spline-fitted with the hub. , A piece (outer spline or inner spline) integral with the other of the first and second shafts Afr1 and Afr2, and a fork for adjusting the position of the sleeve. Then, when the sleeve is in the first position, the piece and the sleeve are spline-fitted to obtain a “connected state”, and when the sleeve is in the second position, the piece and the sleeve are not spline-fitted. A “disconnected state” is obtained.

  The braking device BRK is an actuator having one of well-known configurations provided to adjust the brake fluid pressure that applies a braking force to the wheels of the vehicle. The control device BRK is configured to adjust the brake fluid pressure based on an operation amount (stroke) of a brake pedal (not shown) by a driver of the vehicle when traction control described later is not executed. As a result, the pressing force is adjusted to the “member that rotates integrally with the wheel” (brake disc, etc.) of the friction member (brake pad, etc.) according to the driver's brake operation, and each wheel is adjusted according to the driver's brake operation. Each braking force is applied.

  On the other hand, when the traction control is being executed, the control device BRK adjusts the brake fluid pressure independently for each wheel regardless of the brake pedal operation amount (even if the brake pedal operation amount is zero). Configured to do. As a result, the braking force applied to each wheel is individually adjusted without depending on the driver's brake operation.

  The wheel speed sensors Vfr, Vfl, Vrr, and Vrl detect the wheel speeds of the corresponding wheels, respectively. The front wheel side propeller shaft rotational speed sensor Vfp detects the rotational speed of the front wheel side propeller shaft Afp. The longitudinal acceleration sensor Gx detects the longitudinal acceleration (longitudinal acceleration) of the vehicle. The two-wheel drive / four-wheel drive changeover switch S is operated by a vehicle occupant by operating a “two-wheel drive travel (H2) mode”, a “four-wheel drive travel (H4Lock) mode”, and an “on-demand four-wheel drive travel (H4Auto). ) ”Is selectable.

  The electronic control unit ECU is a microcomputer having one of known configurations. The electronic control unit ECU controls the states of the engine E / G and the automatic transmission A / T according to the state of the vehicle. In addition, the electronic control unit ECU is an actuator for controlling the state (HIGH mode or LOW mode) of the auxiliary transmission mechanism Z based on the state (position) of an operating member (not shown) operated by the driver. (Not shown) is controlled. Further, the electronic control unit ECU controls the braking device BRK in accordance with the amount of operation of the brake pedal operated by the driver and the state of the vehicle (rotation speed of each wheel, slip rate, vehicle speed, etc.). Yes.

  In addition, the electronic control unit ECU determines the multi-plate clutch mechanism C / T according to the state of the 2WD / 4WD switch S and the traveling state of the vehicle (rotational speed of each wheel, longitudinal acceleration of the vehicle, etc.). An actuator (not shown) for controlling the distribution torque Tc of the switch S is controlled, and the state of the switching mechanism M (“connected state” or “non-connected state”) is controlled according to the state of the switch S. An actuator (not shown) for controlling is controlled.

  Specifically, when the switch S is set to the “H2 mode”, the switching mechanism M is maintained in the “disconnected state” and the distribution torque Tc is maintained at zero. As a result, the two-wheel (rear wheel) driving state is always obtained, and the rotation of the front-wheel side propeller shaft Afp is (almost) stopped by the action of the front-wheel differential D / Ff while the vehicle is running, Occurrence can be prevented (suppressed). Therefore, driving energy for idling Afp having a relatively large moment of inertia becomes unnecessary. As a result, the fuel efficiency of the vehicle can be improved as compared with a vehicle in which the switching mechanism M is not mounted (that is, a vehicle in which the front wheel side propeller shaft is idling in the two-wheel drive state).

  When the switch S is set to the “H4Lock mode”, the switching mechanism M is maintained in the “connected state” and the distribution torque Tc is maintained at the maximum. As a result, a four-wheel drive state is always obtained.

  When the switch S is set to the “H4Auto mode”, the switching mechanism M is maintained in the “connected state”, and the distribution torque Tc is adjusted based on the traveling state of the vehicle. Specifically, normally, Tc is maintained at zero, and a two-wheel drive state is obtained. On the other hand, when it is determined that the left and right rear wheel slip actually occurred, or when it is determined that the left and right rear wheel slip is likely to occur, only based on the traveling state of the vehicle. Thus, Tc is adjusted to a value larger than zero, and the driving state is automatically switched from the two-wheel driving state to the four-wheel driving state. In this way, when the “H4Auto mode” is set, an “on-demand” drive state control device is obtained. The control of Tc when “H4Auto mode” is set will be described later.

(Traction control)
In this device, traction control for controlling the braking device BRK to apply braking force to the wheels is executed individually for each wheel of the vehicle. The traction control is executed when it is determined that the execution condition that an excessive slip in the acceleration direction occurs on the wheel is satisfied.

  For example, the traction control start condition is that a predetermined slip ratio TH1 is passed while the slip ratio in the wheel driving direction increases, and the traction control end condition is that the slip ratio decreases while the slip ratio decreases. It has passed TH2 (<TH1). That is, the traction control execution condition is established for the wheel from when the slip ratio of the wheel becomes equal to or higher than TH1 to when it becomes equal to or lower than TH2, during which the traction control is executed for the wheel. This makes it possible to maintain good traction for the wheel.

  Here, the slip ratio of the wheel is a value obtained by dividing the deviation (absolute value) between the estimated vehicle speed and the wheel speed of the wheel by the estimated vehicle speed. The wheel speed is obtained based on the detection result of the wheel speed sensor described above for the corresponding wheel. The estimated vehicle body speed can be calculated using one of well-known calculation methods based on the detection result of the four-wheel wheel speed sensor described above.

  A braking force is applied to the wheel determined to satisfy the execution condition of the traction control by the brake fluid pressure of the control device BRK without depending on the driver's brake operation. As a mode of applying the braking force, after the start of the traction control, a pattern “increases immediately (from zero) stepwise and then gradually decreases (towards zero)” (described above “step increase / gradual increase”). And a pattern that changes according to the change of the slip ratio after the start of the traction control.

  In this apparatus, when the switch S is set to the “H2 mode” (when the vehicle is in a two-wheel (rear wheel) drive state), immediately after the traction control start condition is established for each wheel. Traction control is started. The control in which the application of the braking force is started immediately after the traction control start condition is satisfied is specifically referred to as “normal control”. When the switch S is set to either “H4Auto mode or H4Lock mode” (when the vehicle is in an “on-demand” state or a four-wheel drive state) This control will be described later (see FIG. 5).

(Control of distribution torque in H4Auto mode)
In the present apparatus, when the “H4Auto mode” is set, the distribution torque Tc is adjusted using a map described later. Hereinafter, the flow of processing relating to the control of Tc in the H4Auto mode will be described with reference to FIG.

  As understood from FIG. 4, the control of Tc in the H4Auto mode is executed on condition that “H4Auto mode” is selected and the switching mechanism M is in the “connected state” (“Yes” in step 405). Determined). In a state where this condition is satisfied, first, a target value of the distribution torque Tc is determined based on the traveling state of the vehicle (step 410).

  Specifically, for example, when it is not determined that the left and right rear wheel slip actually occurred and it is not determined that the left and right rear wheel slip is likely to occur, the target value of Tc is Maintained at zero. On the other hand, if it is determined that the left and right rear wheel slip has actually occurred, or if it is determined that the left and right rear wheel slip is likely to occur, the target value of Tc is zero according to the running state of the vehicle. A larger value is determined. The determination as to whether the left and right rear wheels have actually slipped can be achieved based on information such as the rotational speed of each wheel and the longitudinal acceleration of the vehicle, for example. The determination as to whether or not there is a high possibility that the left and right rear wheels will slip can be achieved based on, for example, whether or not a sudden increase in the amount of depression of an accelerator pedal (not shown) has occurred.

  When the target value of the distribution torque Tc is determined, the current I is determined by substituting the target value into the map (step 415). This map defines the relationship between the target value of Tc and the current I. This relationship is such that the current I is determined to be larger as the target value of Tc is larger, and when the target value of Tc is zero, the current I is determined to be zero (see FIG. 3).

  When the current I is determined, the current I is supplied to the multi-plate clutch mechanism C / T (step 420). Thereby, the distribution torque Tc is adjusted based on the running state of the vehicle. Thus, in the H4Auto mode, Tc is adjusted using the map.

(Operation example)
Next, traction control in the H4Auto mode and the H4Lock mode executed by the present apparatus will be described with reference to FIGS. The flowchart shown in FIG. 5 represents the flow of processing related to the traction control. The time charts shown in FIGS. 6 to 8 show an example of changes with time of various variables when the vehicle travels.

  Hereinafter, the switch S is set to the “H4Auto mode”, and the rear wheel drive state at time t1 on the road surface (so-called split road surface) where the vehicle left side is a low road surface friction coefficient and the vehicle right side is a high road surface friction coefficient. It is assumed that the vehicle starts suddenly and the vehicle speed increases from zero. It is assumed that the braking force applied to all the wheels at time t1 is zero. The braking force is detected by a brake fluid pressure sensor (not shown). Further, it is assumed that the above-described “step increase / gradual decrease pattern” is adopted as a braking force application pattern by traction control.

  It is assumed that the slip ratio of the left rear wheel (RL) increases from zero while the slip ratio of the right rear wheel (RR) is maintained at zero after the time t1 when the vehicle starts suddenly. For this reason, it is determined that slip has occurred in the left rear wheel (RL), and Tc also increases from zero after time t1 by the above-described distribution torque Tc control (see FIG. 4). As a result, after time t1, driving of the left and right front wheels is started and executed. Thereafter, after time t2, the slip ratio of the left front wheel (FL) increases from zero, while the slip ratio of the right front wheel (FR) is maintained at zero (see FIGS. 6 to 8).

  As can be understood from FIG. 5, first, the slip ratio in the driving direction of each wheel is calculated (step 505). The calculation method of the slip ratio is the same as that in the traction control in the H2 mode described above. That is, the slip ratios corresponding to the wheel speed sensors Vfr, Vfl, Vrr, Vrl are calculated for each of the left and right rear wheels and the left and right front wheels.

  Next, it is determined whether or not there is a wheel that satisfies the traction control start condition (step 510). The traction control start condition is the same as the condition based on the slip ratio described above, and is determined for each of the left and right rear wheels and the left and right front wheels. More specifically, the starting condition for the left and right rear wheels (RL, RR) is that the calculated slip ratio corresponding to the left and right rear wheels (corresponding to Vrl, Vrr) is equal to or greater than a predetermined slip ratio THr. . The starting condition for the left and right front wheels (FL, FR) is that the calculated slip ratio corresponding to the left and right front wheels (corresponding to Vfl, Vfr) is greater than or equal to a predetermined slip ratio THf (<THr) greater than zero. That is, THr and THf correspond to the predetermined slip ratio TH1.

  It is assumed that the slip ratios of the left rear wheel (RL) and the left front wheel (FL) reach THr and THf, respectively, at time t3 after time t2. For this reason, before time t3, the slip rates of the left and right rear wheels and the left and right front wheels are smaller than THr and THf. Accordingly, since the traction control start condition is not satisfied for all the wheels, it is determined as “No” in Step 510. As a result, before the time t3, no braking force is applied as traction control to any wheel, and the braking force applied to all the wheels is maintained at zero.

  On the other hand, since the traction control start condition is satisfied for the left rear wheel (RL) and the left front wheel (FL) at time t3, it is determined as “Yes” in step 510, and the wheel for which the start condition is satisfied It is determined whether or not there are two or more wheels (step 515). If the number of wheels is not two or more, “No” is determined in step 515, and the “normal control” described above is executed. On the other hand, when there are two or more wheels, it is determined as “Yes” in Step 525, and “Special Control” is executed. In this example, at time t3, the start condition is established for the two wheels, the left rear wheel (RL) and the left front wheel (FL), so that “special control” is executed (step 525). ). The execution of this “special control” will be described later.

  In order to explain the operation and effect of this device, let us consider a case where the above-mentioned “normal control” is executed at time t3 when the start condition is established for the two wheels (proceed from step 515 to step 520). Assumed). In this case, as shown in the time chart of FIG. 6, immediately after time t3, each braking force increases stepwise from zero to the left rear wheel (RL) and the left front wheel (FL), and then gradually changes. Each braking force becomes smaller. Immediately before the time t4, the braking force is applied at the time t4 as the traction control termination condition similar to the above is satisfied for the left rear wheel (RL) and the left front wheel (FL). Has ended.

  Here, attention is focused on the input load to the clutch mechanism C / T due to the braking force. Torque resulting from the braking force of the wheel is input to the transfer T / F via the first and second output shafts A2 and A3. This torque (load) is based on the sum of the braking forces of the wheels and is collected by the clutch mechanism C / T. For this reason, at time t3, the load also increases stepwise due to a stepwise increase in braking force applied to the left rear wheel (RL) and the left front wheel (FL). The degree of increase in load is excessive, and the load exceeds a predetermined value THL.

  Therefore, if the “normal control” described above is executed at time t3 (step 520), robustness is required to protect the clutch mechanism C / T from damage against the excessive load. The As a result, problems such as an increase in cost occur.

  In contrast, in the present apparatus, at time t3, “special control” is executed instead of “normal control” described above (step 525). The “special control” will be described below. “Special control” differs from “normal control” only in the following points. In “special control”, traction control is started immediately after the start condition corresponding to “one wheel” is satisfied, and is started after the corresponding start condition is satisfied for “remaining wheels”. The As the “one wheel”, a wheel having the largest slip ratio among two or more wheels satisfying the start condition is employed. Then, the braking force applied to each wheel is adjusted so that the total braking force does not exceed the predetermined value THL during execution of the traction control. The points described above are different from “normal control” in which traction control is started immediately after the start condition is established for any wheel and the braking force applied to each wheel is not limited.

  As shown in FIG. 7, at time t3, the traction control start condition is satisfied for the two wheels, the left rear wheel (RL) and the left front wheel (FL). At this time, the slip ratio of the left rear wheel (RL) is larger than that of the left front wheel (FL). For this reason, the left rear wheel (RL) is adopted as the “one wheel”. Then, for the left rear wheel (RL) only, the braking force increases stepwise from zero immediately after reaching time t3, and then the braking force decreases in a diminishing manner. At time t4, the left rear wheel (RL) The application of braking force to is completed. For the left front wheel (FL), the braking force increases stepwise from zero at a time t3 ′ after the elapse of a predetermined time from the time t3, and then the braking force decreases in a diminishing manner after the time t4. At time t4 ′, the application of the braking force to the left front wheel (FL) is completed.

  The interval (time t3 to t3 ′) between the start points of traction control for each of the “one wheel (left rear wheel (RL))” and the “remaining wheel (left front wheel (FL))” is predetermined. It will be time. This predetermined time may be constant or may be adjusted according to the total braking force. In addition, after the traction control start time (time t3) for the “one wheel (left rear wheel (RL))”, the load on the clutch mechanism C / T that decreases after stepwise increase (total braking force) ) May become a predetermined time (<THL) or less as a start time (time t3 ′) of applying braking force to the “remaining wheel (left front wheel (FL))”.

  At time t3, the load on C / T that increases stepwise is based on the braking force of the left rear wheel (RL) only, based on the total braking force. The stepwise increase in the braking force of the left rear wheel (RL) is adjusted so that the total braking force (in this case, only the braking force for the left rear wheel (RL)) does not exceed the predetermined value THL. Therefore, the load does not exceed the predetermined value THL.

  Also at time t3 ', the load on C / T increases stepwise. This degree of increase is also based on the total braking force (in this case, the sum of the braking forces for the left rear wheel (RL) and the left front wheel (FL)), and the stepwise increase in the braking force for the left front wheel (FL) is also The total is adjusted so as not to exceed a predetermined value THL. Therefore, the load does not exceed the predetermined value THL. As a result, an excessive load on the C / T is suppressed from the start to the end of the traction control (between times t3 and t4 ').

  As described above, according to this device, in the traction control device for a four-wheel drive vehicle equipped with the transfer T / F (equipped with the clutch mechanism C / T), the control applied to two or more wheels by the traction control. Due to the power, an excessive load input to the clutch mechanism C / T can be suppressed. As a result, the clutch mechanism C / T can be protected against load input.

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention. For example, in the above-described embodiment, as the “special control”, the traction control is started immediately after the start condition corresponding only to “one wheel” is satisfied, and the corresponding start condition for “remaining wheels”. It is started after the establishment of Instead, the traction control is started immediately after the corresponding start condition is established for each wheel, and the total braking force does not exceed the predetermined value THL during execution of the traction control. The braking force applied to each may be adjusted.

  According to this, as shown in FIG. 8, at the time t3, the traction control start condition is established for the left rear wheel (RL) and the left front wheel (FL). For the left rear wheel (RL) and the left front wheel (FL), the braking force increases stepwise from zero immediately after reaching time t3, and thereafter the braking force decreases in a divergent manner. These stepwise increases in braking force are adjusted so that the sum of the braking forces (in this case, the sum of the braking forces for the left rear wheel (RL) and the left front wheel (FL)) does not exceed a predetermined value THL. Therefore, the load on C / T that increases stepwise does not exceed the predetermined value THL. As described above, it is possible to suppress an excessive load input to the clutch mechanism C / T even with the above-described configuration.

  In the above embodiment, as the “special control”, the braking force applied to each wheel is adjusted while monitoring the total braking force so as not to exceed the predetermined value THL during execution of the traction control. . Instead of this, it is not necessary to perform monitoring related to the sum of the braking forces. If it is previously known that the sum of the braking forces cannot exceed the predetermined value THL unless stepwise increases in braking force for two or more wheels are made at the same time, by adopting this configuration, The calculation load on the ECU accompanying the monitoring burden can be reduced. In this case, it is preferable that the traction control for the “remaining wheels” is started after the traction control end condition for the “one wheel” is satisfied. According to this, since the load input to the clutch mechanism C / T can be a braking force for one wheel at the maximum, it may exceed the predetermined value THL until the traction control for all the wheels is completed. It can be further suppressed.

  In the above embodiment, the clutch mechanism is provided in the transfer T / F. Instead, as shown in FIG. 9, a center differential D / Fc is provided in the transfer T / F. May be. In this case, a target to which a load is input by the transfer T / F due to the application of the braking force by the traction control is the center differential D / Fc instead of the clutch mechanism C / T. Therefore, in this embodiment, the center differential D / Fc can be protected against the input of the load.

  Moreover, in the said embodiment, the rear-wheel drive state is employ | adopted as a two-wheel drive state. On the other hand, the front wheel drive state may be adopted as the two-wheel drive state. In this case, the first output shaft A2 of the transfer T / F is connected to the front-wheel-side propeller shaft Afp, the second output shaft A3 of the transfer T / F is connected to the rear-wheel-side propeller shaft Afp, and the switching mechanism M is rear-left and right. What is necessary is just to comprise so that it may be interposed in one of the axles Arl and Arr of a wheel.

  In addition, in the above embodiment, the auxiliary transmission mechanism Z is provided in the transfer T / F, but the auxiliary transmission mechanism may not be provided.

  E / G ... engine, A / T ... automatic transmission, T / F ... transfer, C / T ... multi-plate clutch mechanism, D / Fc ... center differential, A1 ... input shaft, A2 ... first output shaft, A3 ... Second output shaft, BRK: braking device, Vfr, Vfl, Vrr, Vrl ... wheel speed sensor, ECU ... electronic control unit

Claims (5)

An input shaft (A1) connected to an output shaft of a transmission (A / T) connected to a power source (E / G) of the vehicle, a front wheel side propeller shaft (Afp) and a rear wheel side propeller shaft of the vehicle The first output shaft (A2) connected to the first propeller shaft which is one of (Arp), and the second propeller shaft which is the other of the front wheel side propeller shaft and the rear wheel side propeller shaft. A transfer output (T / F) configured to distribute and transmit the drive torque of the input shaft to the first output shaft and the second output shaft. )When,
The first propeller shaft is connected to the first propeller shaft via the respective axles of the first left and right wheels, which are one of the left and right front wheels and the left and right rear wheels. A first differential (D / Fr) distributed to the first left and right wheels while allowing,
The second propeller shaft is connected to the second propeller shaft, and the torque of the second propeller shaft is determined through the respective axles of the second left and right wheels which are the other of the left and right front wheels and the left and right rear wheels. A second differential (D / Ff) distributed to the second left and right wheels while allowing,
A braking device (BRK) for individually adjusting the braking force applied to each wheel of the vehicle;
Applied to a four-wheel drive vehicle with
Traction control for controlling the braking device and applying braking force to the wheel based on the determination that an execution condition that excessive slip in the acceleration direction has occurred in the wheel of the vehicle is established, In a traction control device for a four-wheel drive vehicle provided with a control means (ECU) executed individually for each wheel of the vehicle,
The control means includes
When it is determined that the execution condition of the traction control is satisfied for two or more wheels, the total of the braking force applied to each wheel is set so as not to exceed a predetermined value (THL). A traction control device for a four-wheel drive vehicle configured to adjust a braking force applied to each wheel. In the traction control device for a four-wheel drive vehicle according to claim 1,
The transfer is
A clutch mechanism (C / T) capable of adjusting a distribution torque (Tc) that is a part of the driving torque of the input shaft and is distributed to the second output shaft is provided, and the second output shaft includes The four-wheel drive configured to transmit the distribution torque adjusted by the clutch mechanism and transmit the torque obtained by subtracting the distribution torque from the drive torque of the input shaft to the first output shaft. Vehicle traction control device. In the traction control device for a four-wheel drive vehicle according to claim 1 or 2,
The control means includes
When it is determined that the execution condition of the traction control is satisfied for two or more wheels, the traction control is started immediately after the execution condition corresponding to only one wheel is satisfied, and the remaining A traction control device for a four-wheel drive vehicle configured to start the traction control for a wheel after a start of establishment of the corresponding execution condition. In the traction control device for a four-wheel drive vehicle according to claim 3,
The control means includes
A traction control device for a four-wheel drive vehicle, wherein a wheel having the largest wheel slip ratio among two or more wheels satisfying the traction control execution condition is adopted as the one wheel. In the traction control device for a four-wheel drive vehicle according to any one of claims 1 to 4,
The first and second propeller shafts are the rear wheel side and front wheel side propeller shafts, respectively.
The traction control device for a four-wheel drive vehicle, wherein the first and second left and right wheels are the left and right rear wheels and the left and right front wheels, respectively.

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