JP6421210B2 - Torque distribution control device for four-wheel drive vehicle - Google Patents

Description

  The present invention distributes drive torque transmitted to one and the other of the main drive wheel and the sub drive wheel in a four-wheel drive vehicle in which either the front wheel or the rear wheel is the main drive wheel and the other is the sub drive wheel. To distribute the driving torque transmitted to one and the other of the left auxiliary driving wheel and the right auxiliary driving wheel, and the front and rear torque distributing apparatus and the left and right torque distributing apparatus And a torque distribution control device for a four-wheel drive vehicle.

  Conventionally, for example, a vehicle as shown in Patent Document 1 is a four-wheel drive vehicle having a front wheel as a main drive wheel and a rear wheel as an auxiliary drive wheel, and further distributes drive force to the left and right rear wheels. As a device, an electromagnetic torque distribution clutch is provided on each of the driving force transmission paths connected to the left and right rear wheels. By changing the fastening force of the torque distribution clutch, the ratio of torque distributed between the left and right rear wheels can be arbitrarily controlled.

  In such a vehicle, in addition to steering of the steered wheels, the yaw moment of the vehicle is controlled using a difference in driving force between the left and right rear wheels by controlling an electromagnetic clutch. That is, the estimated drive torque output from the transmission is calculated based on the engine speed, intake negative pressure (or intake flow rate), and the like. Based on the calculated estimated driving torque and the lateral acceleration, steering angle, and wheel speed of the vehicle, torque to be distributed to the left and right rear wheels is calculated. For example, if the vehicle slip angle is greater than or equal to a predetermined value, it is determined that the vehicle behavior is unstable, the rear differential gear is controlled to reduce the torque distributed to the left and right rear wheels, and The torque distributed to the turning outer wheel of the rear wheels is reduced. As a result, the vehicle behavior is stabilized.

JP 2011-077942 A

  By the way, when controlling the torque distributed to the left and right rear wheels as described above, if the torque command value (command torque) temporarily becomes zero, there will be a delay in the rise of the actual torque with respect to the subsequent command torque. Thus, there is a problem that it leads to a decrease in torque response. In addition, due to the characteristics of the clutch for distributing torque to the left and right rear wheels, in the region where the command torque is close to zero, the response torque of the actual torque to the command torque becomes non-linear so that the accuracy of the actual torque with respect to the command torque is sufficient. There is also a problem that cannot be secured. For these reasons, in controlling the torque distributed to the left and right rear wheels, it is desirable to avoid the command torque from becoming zero or close to zero as much as possible.

  Therefore, in the conventional control, control is performed such that the command torque is set so as not to fall below a predetermined lower limit (positive value), and the value of the entire command torque is determined based on the lower limit. However, in this method, even when the command value (total value on the left and right) of the drive torque transmitted to the rear wheels (left and right rear wheels), which are auxiliary drive wheels, is below a predetermined lower limit value, the predetermined lower limit value is maintained as it is. If adopted, the driving torque is applied to the rear wheels even when the vehicle is in a driving state (for example, when the accelerator is off) where the command value of the driving torque distributed to the rear wheels is very small or substantially zero. There is a problem that the transmission causes an influence on the fuel consumption (fuel consumption rate) of the vehicle and the durability of the apparatus.

  The present invention has been made in view of the above problems, and its object is to provide a command value for the drive torque distributed to the auxiliary drive wheels (rear wheels) that is very small or substantially zero. A four-wheel vehicle that can improve the fuel consumption (fuel consumption rate) of the vehicle and the durability of the device by preventing the driving torque from being transmitted to the auxiliary drive wheel in a running state of the vehicle. An object is to provide a torque distribution control device for a driving vehicle.

  In order to achieve the above object, a torque distribution control device for a four-wheel drive vehicle according to the present invention uses either a front wheel (WFL, WFR) or a rear wheel (WRL, WRR) as a first drive wheel (of the present invention). In a four-wheel drive vehicle in which the main drive wheel in the embodiment and the other is the second drive wheel (sub drive wheel in the embodiment of the present invention), the drive torque transmitted to the first drive wheel and the second drive wheel is Left / right torque for distributing the drive torque transmitted to the front / rear torque distribution device (14) for distribution, the left second drive wheel (WRL) and the right second drive wheel (WRR) which are the second drive wheels A torque distribution control device comprising a distribution device (16) and a control means (Ua) for controlling drive torque distributed by the front-rear torque distribution device and the left-right torque distribution device, wherein the control means (Ua) Second left drive with distribution device When either the left drive torque command value (LTq) or the right drive torque command value (RTq) distributed to the right second drive wheel falls below a predetermined lower limit value (L1 = LTq1, RTq1), The left drive torque command value (LTq) or the right drive torque command value (RTq) is controlled to be a predetermined lower limit (L1), and the left drive torque command value (LTq) and the right drive torque command value are controlled. The command value (TM = LTq + RTq) of the left-right sum torque that is the sum of (RTq) is calculated, and when the command value (TM) of the left-right sum torque is below the predetermined lower limit value (TM <L1), the predetermined lower limit The value is changed to a command value for the left and right sum torque.

  According to the torque distribution control device for a four-wheel drive vehicle according to the present invention, the command values of the drive torque distributed to the left second drive wheel and the right second drive wheel by the left and right torque distribution device are respectively less than a predetermined lower limit value. In this case, a value that exceeds the limit, such as the command value of the drive torque temporarily becomes zero or becomes a region close to zero, by controlling the command value of the drive torque to a predetermined lower limit value. Can be avoided. As a result, it is possible to prevent a delay in the rise of the actual torque with respect to the command torque, so that the torque response can be improved. Further, since the response waveform of the actual torque with respect to the command torque can be made linear or nearly linear, the accuracy of the actual torque with respect to the command torque can be ensured. By these, it becomes possible to effectively improve the accuracy of the drive torque distributed to the left second drive wheel and the right second drive wheel of the vehicle. Further, compared to the conventional control that determines the value of the entire command torque based on the lower limit value, the command value of the drive torque can be prevented from becoming a large value as a whole. Therefore, it is possible to effectively prevent the driving torque more than necessary from being distributed.

In addition, in the torque distribution control device for a four-wheel drive vehicle according to the present invention, when performing the control with the command value of the drive torque as the predetermined lower limit as described above, When the command value of the left-right sum torque, which is the sum of the command values of the torque distributed to each other, falls below the predetermined lower limit value, the predetermined lower limit value is changed to the command value of the left-right sum torque.
Even when the command value of the left and right sum torque is below the predetermined lower limit value, if the lower limit value is adopted as it is, the command of the drive torque distributed to the second drive wheel between the first drive wheel and the second drive wheel The drive torque is transmitted to the second drive wheels even when the vehicle is in a driving state (for example, when the accelerator is off) where the value (front-rear distribution amount) is very small or substantially zero. According to the present invention, when the command value of the left-right sum torque is lower than a predetermined lower limit, the predetermined lower limit may be affected, which may affect the fuel consumption (fuel consumption rate) of the vehicle and the durability of the device. Is changed to the command value of the left and right sum torque, so that it is possible to prevent the drive torque from being transmitted to the second drive wheel in the traveling state as described above. Therefore, the fuel consumption (fuel consumption rate) of the vehicle and the durability of the device can be improved.

  In this four-wheel drive vehicle torque distribution control device, the control means (Ua) is configured such that the difference (ΔTq) between the left drive torque command value (LTq) and the right drive torque command value (RTq) is a constant value. You may control so that it may become.

  According to this configuration, by controlling the difference between the command values of the drive torque to be a constant value, an appropriate drive torque corresponding to the required value of the drive force between the left second drive wheel and the right second drive wheel Therefore, more appropriate driving force distribution control can be performed.

  In this torque distribution control device for a four-wheel drive vehicle, the control means (Ua) is configured such that one of the left drive torque command value (LTq) and the right drive torque command value (RTq) is a predetermined lower limit value (L1). = LTq1 or RTq1), the left drive torque command value (LTq) or the difference between the command value (RTq) of the right drive torque and the predetermined lower limit value (ΔLTq or ΔRTq) is the command value of the left drive torque ( Control may be performed to add to the other of (LTq) and the command value (RTq) of the right driving torque.

  According to this configuration, the difference between the drive torque command value of the left and right second drive wheels and the predetermined lower limit value is added to the drive torque command value of the other second drive wheel. While avoiding that the command value of the drive torque of the second drive wheel falls below a predetermined lower limit value, the command value of the drive torque of one second drive wheel and the command value of the drive torque of the other second drive wheel The difference can be secured. Accordingly, while avoiding that the command value of the drive torque becomes a small value exceeding the limit, an appropriate drive torque difference according to the required drive force value between the second left drive wheel and the second right drive wheel is set. Therefore, more appropriate driving force distribution control can be performed.

  In addition, the name and code | symbol in said parenthesis show the name and code | symbol of the corresponding component of embodiment mentioned later as an example of this invention.

  According to the torque distribution control device for a four-wheel drive vehicle according to the present invention, the running state of the vehicle such that the command value of the drive torque distributed to the second drive wheel is very small or substantially zero. In this case, since it is possible to avoid transmission of drive torque to the second drive wheel, it is possible to improve the fuel consumption (fuel consumption rate) of the vehicle and the durability of the device.

It is a figure showing the driving force transmission system of vehicles concerning one embodiment of the present invention. It is an enlarged view of a speed increasing device and a rear differential gear. It is a block diagram which shows the structure of 4WD-ECU. It is a block diagram which shows the flow of the process in the torque distribution control of this embodiment. It is a figure which shows the change of the command value of the torque allocated to a right-and-left rear wheel, when a request | requirement right-and-left sum torque is more than a predetermined | prescribed lower limit. It is a figure which shows the change of the command value of the torque allocated to a right-and-left rear wheel, when a request | requirement right-and-left sum torque becomes less than a predetermined lower limit.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a driving force transmission system for a vehicle according to an embodiment of the present invention. FIG. 2 is an enlarged view of the speed increasing device and the rear differential gear. As shown in FIG. 1, the vehicle according to the first embodiment to which the present invention is applied includes left and right front wheels WFL, WFR as main drive wheels (first drive wheels) and sub drive wheels (second drive wheels). Left and right rear wheels WRL and WRR, and the left and right front wheels WFL and WFR are basically always driven when the vehicle is running, and the left and right rear wheels WRL and WRR are in a driving state of the vehicle. It is driven accordingly.

  An automatic transmission T is connected to an engine E mounted horizontally at the front of the vehicle body. The automatic transmission T is connected to the left and right front wheels WFL and WFR via the front differential gear 11 and the left and right front drive shafts 12 and 12. Is done. The front differential gear 11 has left and right via a transfer (not shown), a front propeller shaft 13, a speed increasing device 14, a rear propeller shaft 15, a rear differential gear 16, and left and right rear drive shafts 17L and 17R. It is connected to the rear wheels WRL and WRR.

  As shown in FIG. 2, the speed increasing device 14 includes a planetary gear mechanism 21, a speed increasing clutch 22, and a direct coupling clutch 23.

  The planetary gear mechanism 21 is supported by the input sun gear 24 fixed to the rear end of the front propeller shaft 13, the output sun gear 25 fixed to the front end of the rear propeller shaft 15, the carrier 26, and the carrier 26. A plurality of double pinions 27. Each double pinion 27 is integrally provided with an input side pinion 27a and an output side pinion 27b, and the number of teeth of the output side pinion 27b is set to be larger than the number of teeth of the input side pinion 27a. The number of teeth of the sun gear 25 is set smaller than the number of teeth of the input-side sun gear 24.

  The hydraulic multi-plate type speed increasing clutch 22 is a clutch outer 29 fixed to a housing 28 and a clutch inner 30 positioned inside the clutch outer 29 via a plurality of friction engagement elements 31. When the plurality of friction engagement elements 31 are engaged by the supply of hydraulic pressure, the clutch inner 30 is fastened to the clutch outer 29 and is restrained to the housing 28 so as not to rotate.

  The hydraulic multi-plate direct coupling clutch 23 includes a clutch inner 30 integrated with the clutch inner 30 of the speed increasing clutch 22 and the carrier 26 of the planetary gear mechanism 21, a clutch inner 33 integrated with the front propeller shaft 13, and a clutch outer 32. And a plurality of friction engagement elements 34 disposed between the clutch inner 33 and a one-way clutch 35 disposed between the clutch outer 32 and the clutch inner 33. When the rotational speed of the clutch inner 33 exceeds the rotational speed of the clutch outer 32, the one-way clutch 35 slips and the transmission of the driving force is interrupted. When the plurality of friction engagement elements 34 are engaged by the supply of hydraulic pressure, the clutch outer 32 is fastened to the clutch inner 33 and the front propeller shaft 13 is integrated with the carrier 26 of the planetary gear mechanism 21.

  Therefore, when the speed increasing clutch 22 is engaged and the direct connection clutch 23 is released, the carrier 26 of the planetary gear mechanism 21 is restrained to be non-rotatable by the housing 28. Therefore, the input side sun gear 24, the output side sun gear 25, and the double pinion The rotation speed of the front propeller shaft 13 is increased at a speed increase ratio (for example, 1.05) determined by the number of teeth of 27 and output to the rear propeller shaft 15.

  Conversely, when the speed increasing clutch 22 is released and the direct clutch 23 is engaged, the input side sun gear 24 and the carrier 26 of the planetary gear mechanism 21 are integrated and locked, so that the rotation of the front propeller shaft 13 is prevented. It is output to the rear propeller shaft 15 as it is.

  Since the rear differential gear 16 has a substantially mirror-symmetrical structure with respect to the center plane of the vehicle body, the structure of the left portion of the center plane of the vehicle body will be described as a representative example. Note that symmetrical components are distinguished from each other by adding L and R symbols to the reference numerals in the drawings. Also in the following description, when it is necessary to distinguish between left and right, the reference numerals with L and R symbols are used.

  A driven bevel gear 37 fixed to the intermediate portion of the input shaft 36 disposed coaxially between the opposing ends of the left and right rear drive shafts 17L, 17R is a drive bevel gear 38 fixed to the rear end of the rear propeller shaft 15. To mesh. A planetary gear mechanism 39L and an electromagnetic multi-plate torque distribution clutch 40L are disposed between the input shaft 36 and the left rear drive shaft 17L.

  The planetary gear mechanism 39 includes a ring gear 41, a carrier 42, a sun gear 43, and a plurality of pinions 44 supported by the carrier 42 and simultaneously meshed with the ring gear 41 and the sun gear 43. The ring gear 41 includes the input shaft 36. The carrier 42 is coupled to the right end of the left rear drive shaft 17.

  The torque distribution clutch 40 includes a clutch outer 46 fixed to the housing 45, a clutch inner 47 coupled to the sun gear 43 of the planetary gear mechanism 39, and a plurality of friction engagements disposed between the clutch outer 46 and the clutch inner 47. .. And an electromagnetic actuator 49 (see FIG. 1) for integrally coupling the clutch outer 46 and the clutch inner 47 by engaging the friction engagement elements 48 with each other.

  When the electromagnetic actuator 49 is OFF, the torque distribution clutch 40 is released and the sun gear 43 can freely rotate, so that the driving force of the input shaft 36 is not transmitted to the left rear drive shaft 17. On the other hand, in a state where the electromagnetic actuator 49 is turned on and the torque distribution clutch 40 is engaged, the sun gear 43 is unrotatably restrained by the housing 45, so that the driving force of the input shaft 36 is transmitted to the left rear drive shaft 17. .

  At this time, by changing the current supplied to the electromagnetic actuator 49 to change the slip amount of the torque distribution clutch 40, the torque transmitted from the input shaft 36 to the left rear drive shaft 17 can be continuously changed. it can.

  Therefore, by changing the fastening force of the left and right torque distribution clutches 40L, 40R of the rear differential gear 16, the ratio of the torque distributed between the front wheels WFL, WFR and the rear wheels WRL, WRR is arbitrarily controlled, and the left and right The ratio of torque distributed between the rear wheels WRL, WRR can be arbitrarily controlled.

  Next, the configuration of the 4WD electronic control unit (4WD-ECU) Ua that controls the operation of the speed increasing device 14 and the rear differential gear 16 will be described with reference to FIG.

  The input unit 51 of the 4WD electronic control unit Ua includes a FI / AT electronic control unit Ub that controls the operation of the engine E and the automatic transmission T, and an ESC electronic control unit Uc that controls the operation of the vehicle behavior stabilization system. For example, a vehicle speed sensor 52a for detecting the vehicle speed from the rotation speed of the gear of the automatic transmission T and a steering angle sensor 52b for detecting the steering angle of the steering wheel are connected.

  The signal input to the input unit 51 from the FI / AT electronic control unit Ub includes the engine speed, the intake negative pressure, the main shaft and counter shaft speeds of the automatic transmission T, the shift position of the automatic transmission T, and the like. . The signals input from the ESC electronic control unit Uc to the input unit 51 include wheel speeds of the front wheels WFL, WFR and rear wheels WRL, WRR, vehicle lateral acceleration, vehicle longitudinal acceleration, and the like.

  The estimated drive torque calculation unit 53 includes an engine speed input from the input unit 51, a negative intake pressure (or intake flow rate), a gear ratio estimated from the rotation speeds of the main shaft and the counter shaft, a speed ratio of the torque converter, The estimated driving torque output from the transmission T is calculated based on the efficiency at the gear stage. Instead of estimating the gear ratio from the rotation speeds of the main shaft and the counter shaft, the gear ratio of the shift position detected by the shift position sensor may be used.

  The steering control unit 54 distributes the left and right rear wheels WRL and WRR based on the estimated driving torque calculated by the estimated driving torque calculating unit 53 and the lateral acceleration, steering angle and wheel speed input from the input unit 51. The steering control torque to be calculated is calculated. For example, when the slip angle of the vehicle is greater than or equal to a predetermined value, it is determined that the vehicle behavior is in an unstable state, and the torque distributed to the left and right rear wheels WRL and WRR is reduced by controlling the rear differential gear 16. In addition, the vehicle behavior is stabilized by reducing the torque distributed to the turning outer wheel of the left and right rear wheels WRL, WRR.

  The speed increase control unit 55 engages the speed increasing clutch 22 of the speed increasing device 14 when the vehicle body speed is medium speed and the lateral acceleration is large, and the rotational speed of the rear propeller shaft 15 with respect to the rotational speed of the front propeller shaft 13. And the rear differential gear 16 distributes torque to the turning outer wheels of the left and right rear wheels WRL and WRR, thereby improving turning performance while avoiding understeering of the vehicle. When the vehicle body speed is low or high and the lateral acceleration is small, the direct clutch 23 of the speed increasing device 14 is engaged and the speed increase of the rear propeller shaft 15 with respect to the speed of the front propeller shaft 13 is stopped. Thus, by distributing the torque to the turning outer wheel of the left and right rear wheels WRL, WRR by the rear differential gear 16, stable turning performance is ensured.

  Further, if the speed increase is executed, the vehicle behavior may be disturbed, and the operation of the speed increase device 14 is prohibited when the operation control unit 54 outputs a speed increase prohibition request.

  The LSD control unit 56 compares the wheel speeds of the left and right front wheels WFL and WFR with the wheel speeds of the left and right rear wheels WRL and WRR, and the friction coefficient of the road surface that the front wheels WFL and WFR step on when the vehicle starts is determined by the rear wheel WRL. When the front wheels WFL and WFR slip because they are smaller than the friction coefficient of the road surface on which the WRR steps, or even if the friction coefficient of the road surface on which the four wheels step is equal, the main driving force of the front wheels WFL and WFR is the rear wheel WRL. When the front wheel WFL, WFR slips because it is larger than the auxiliary driving force of WRR, the LSD torque distributed to the rear wheels WRL, WRR is calculated according to the differential rotation between the front and rear wheels. When the LSD torque is distributed to the rear wheels WRL and WRR by the rear differential gear 16, the slippage of the front wheels WFL and WFR is eliminated accordingly, and the vehicle can start smoothly.

  The uphill controller 58 compares the actual longitudinal acceleration detected by the longitudinal acceleration sensor with the estimated longitudinal acceleration obtained by differentiating the vehicle speed, thereby calculating the vehicle uphill angle (inclination angle of the road uphill). Then, in order to increase the climbing force at the start of the vehicle on the uphill, the uphill starting torque distributed to the rear wheels WRL, WRR is calculated by the rear differential gear 16 according to the uphill angle.

  The torque adding unit 57 adds the steering control torque calculated by the steering control unit 54, the LSD torque calculated by the LSD control unit 56, and the uphill starting torque calculated by the uphill control unit 58.

  The clutch torque limiting unit 60 prevents the rear differential gear 16 from being applied to the rear wheels WRL and WRR in order to prevent an excessive load from acting on the rear differential gear 16 when the vehicle is reverse-backed and forward-backed. Limit the upper limit of the target torque to be transmitted.

  The current control unit 61 converts the clutch torque command value calculated by the clutch torque limiting unit 60 into a current value (PWM value) supplied to the electromagnetic actuators 49L and 49R of the torque distribution clutches 40L and 40R of the rear differential gear 16.

  Thus, the drive circuit unit 62 controls the operation of the speed increasing device 14 based on the speed increasing command output from the speed increasing control unit 55, and the rear differential gear 16 based on the current value output from the current control unit 61. Control the operation of

  Here, drive torque distribution control for the left rear wheel WRL and the right rear wheel WRR when the vehicle turns will be described. During the turning of the vehicle, the magnitude of the torque of the left and right rear wheels WRL, WRR is usually the sum of the left rear wheel torque and the right rear wheel torque (hereinafter sometimes referred to as a first relationship). Control is performed based on the torque request in the front-rear direction and the difference between the left rear wheel torque and the right rear wheel torque (hereinafter also referred to as a second relationship), that is, the torque request in the turning direction.

  The torque distribution control in this case will be described using mathematical expressions. The target torque of the left rear wheel WRL is TT1, the target torque of the right rear wheel WRR is TT2, the total target torque of the left and right rear wheels WRL and WRR (the sum of the left rear wheel torque and the right rear wheel torque) is TRT, and the left and right rear wheels When the target torque difference between WRL and WRR (the difference between the left rear wheel torque and the right rear wheel torque) is ΔTT, the following equation (1) is established from the first relationship, and the following equation (2) is established from the second relationship.

TT1 + TT2 = TRT (1)
TT1-TT2 = ΔTT (2)

ΔTT is expressed by the following equation (3) where YMT is the target yam moment (clockwise is positive), Y is the wheel radius, r is the red width (distance between the left and right rear wheels WRL, WRR) Tr.
ΔTT = 2 · r · YMT / Tr (3)

  Therefore, the target torques TT1 and TT2 for the left and right rear wheels WRL and WRR are uniquely determined from the above equations (1) and (2).

  Thus, the torque requirement in the front-rear direction and the torque requirement in the turning direction can be satisfied from the first relationship and the second relationship, and the running performance of the vehicle is emphasized.

  FIG. 4 is a block diagram for explaining the flow of processing in the torque distribution control of this embodiment. In this torque distribution control, the requested left and right sum torque (rear wheel shaft torque) TM (71) and the requested left and right differential torque TS (72) are input, and the values restricted by the restriction blocks 81 and 82 (here, whichever Is also 0.5 times (1/2 times the value). Thereafter, a difference calculation block 83 calculates a difference value between the required left-right sum torque TM and the required left-right difference torque TS, and a sum calculation block 84 calculates a sum value of the requested left-right sum torque TM and the requested left-right difference torque TS. Calculated.

  Further, in the lower limit calculation block 95, the lower limit value (lower limit value per wheel) L1 (described later) of the required left-right sum torque TM restricted by the restriction block 81 and the left and right rear wheels WRL, WRR. The lower limit values LTq1 and RTq1 shown in FIGS. 5 and 6 correspond to each other), and the lower one of these values is output. That is, when the lower limit value L1 is smaller than the requested left-right sum torque TM, the lower limit value L1 is output as the output value of the lower limit value calculation block 95, and the requested left-right sum torque TM is smaller than the lower limit value L1. When this is the case, the required left-right sum torque TM is output as the output value of the lower limit calculation block 95.

  That is, in the lower limit value calculation block 95, when the value of the required left-right sum torque TM decreases, the lower limit value L1 (LTq1, RTq1) of the preset required torque in the left and right rear wheels WRL, WRR is calculated as the required left-right sum torque (rear). Control to change to the value of the wheel shaft torque TM is performed.

  Thereafter, in the first lower limit processing block 85, the difference value calculated in the previous difference calculation block 83 is compared with the output value of the lower limit calculation block 95 to select the larger value ( Lower limit processing) is performed. That is, when the difference value between the requested left-right sum torque TM and the requested left-right difference torque TS is larger than the output value of the lower limit value calculation block 95, the difference value is selected, and the requested left-right sum torque TM and the requested left-right difference When the difference value of the torque TS is equal to or less than the output value of the lower limit value calculation block 95, the output value of the lower limit value calculation block 95 is selected. Thereafter, in the first deficient amount calculation block 87, the value of the difference between the required left / right sum torque TM and the required left / right difference torque TS calculated in the previous difference calculation block 83, and the value selected in the first lower limit processing block 85, The difference value is calculated.

  On the other hand, the second lower limit processing block 86 compares the sum value calculated in the previous sum calculation block 84 with the output value of the lower limit calculation block 95 and selects the larger value (lower limit). Limit processing) is performed. That is, when the sum value of the requested left-right sum torque TM and the requested left-right difference torque TS is larger than the output value of the lower limit calculation block 95, the sum value is selected, and the requested left-right sum torque TM and the requested left-right torque TM When the value of the sum of the differential torque TS is less than or equal to the output value of the lower limit value calculation block 95, the output value of the lower limit value calculation block 95 is selected. Thereafter, in the second deficient amount calculation block 88, the sum of the required left / right sum torque TM and the required left / right difference torque TS calculated in the previous sum calculation block 84, and the value selected in the second lower limit processing block 86, The difference is calculated.

  Further, in the requested right rear wheel torque calculation block 89, the requested right rear wheel, which is the sum of the value selected in the previous first lower limit processing block 85 and the value calculated in the second insufficient amount calculating block 88. Torque 91 is calculated. Further, in the requested left rear wheel torque calculation block 90, the requested left rear wheel, which is the sum of the value selected in the previous second lower limit processing block 86 and the value calculated in the first deficient amount calculation block 87. Torque 92 is calculated. These requested right rear wheel torque 91 and requested left rear wheel torque 92 are command values (hereinafter simply referred to as “torque”) of drive torque distributed to the left and right rear wheels WRL and WRR in the torque distribution control of the present embodiment. Command torque).

  5 and 6 are diagrams showing changes (changes with respect to the elapsed time T) of command values (command torques) distributed to the left and right rear wheels WRL, WRR in the torque distribution control of the present embodiment. 6 (a) is the steering angle of the vehicle (steering wheel steering angle), (b) is the torque command value LTq [Nm] distributed to the left rear wheel WRL, and (c) is the torque distributed to the right rear wheel WRR. Command value RTq [Nm]. FIG. 5 shows that the required left-right sum torque TM (= LTq + RTq) is equal to or greater than the lower limit value L1 (= LTq1, RTq1) of the preset required torque in the left and right rear wheels WRL, WRR (required left-right sum torque TM ≧ lower limit value L1) This is a case where the lower limit value L1 (= LTq1, RTq1) of the torque distributed to the left and right rear wheels WRL, WRR is not changed (changed). On the other hand, FIG. 6 shows a case where the requested left-right sum torque TM is less than the lower limit value L1 (required left-right sum torque TM <lower limit value L1). This is a case where (= LTq1, RTq1) is changed (held).

  First, when the required left-right sum torque TM shown in FIG. 5 is equal to or greater than a predetermined lower limit value L1, as shown in FIG. 5, the left rear wheel WRL command is issued when the vehicle starts turning right at time t1. The torque LTq gradually increases from LTq = 100 [Nm]. On the other hand, the command torque RTq for the right rear wheel WRR gradually decreases from RTq = 100 [Nm]. Then, the command torque RTq of the right rear wheel WRR becomes a lower limit value RTq1 = 50 [Nm] at time t2, and thereafter, a constant value of RTq = lower limit value RTq1 = 50 [Nm] until time t3. Maintained. That is, from time t2 to time t3, the basic value (value indicated by the alternate long and short dash line) of the command torque of the right rear wheel WRR is lower than the lower limit value RTq1 = 50 [Nm]. The lower limit value RTq1 = 50 [Nm] is selected as the torque RTq without selecting the basic value (value indicated by the one-dot chain line). On the other hand, the command torque LTq of the left rear wheel WRL is a value obtained by adding a predetermined addition value ΔLTq (≦ 150 [Nm]) to the basic value of the command torque LTq from time t2 to time t3. Become. The added value ΔLTq added here corresponds to a difference ΔRTq between the basic value of the command torque RTq in the right rear wheel WRR and the lower limit torque RTq1.

  Further, when the vehicle is switched from a right turn to a left turn at time t4, the command torque LTq of the left rear wheel WRL thereafter decreases from LTq = 100 [Nm]. On the other hand, the command torque RTq of the right rear wheel WRR falls from RTq = 100 [Nm]. Then, the command torque LTq for the left rear wheel WRL becomes the lower limit value LTq1 = 50 [Nm] at time t5, and thereafter is maintained at a constant value of the lower limit value LTq1 = 50 [Nm] until time t6. That is, from time t5 to time t6, the basic value (one-dot chain line) of the command torque LTq of the left rear wheel WRL is lower than the lower limit value LTq1 = 50 [Nm]. The lower limit LTq1 = 50 [Nm] is selected without selecting the basic value (value indicated by the alternate long and short dash line). On the other hand, the command torque RTq of the right rear wheel WRR is a value obtained by adding a predetermined addition value ΔRTq (≦ 150 Nm) to the basic command value RTq from time t5 to time t6. The added value ΔRTq to be added corresponds to a difference ΔLTq between the basic value of the command torque LTq and the lower limit torque LTq1 in the left rear wheel WRL.

  Next, when the requested left-right sum torque TM shown in FIG. 6 is less than the lower limit value L1, as shown in the figure, the command torque of the left rear wheel WRL is started by the vehicle starting to turn right at time t1. LTq gradually increases from LTq = 100 [Nm]. On the other hand, the command torque RTq for the right rear wheel WRR gradually decreases from RTq = 100 [Nm]. Then, the command torque RTq of the right rear wheel WRR becomes a lower limit value RTq1 = 50 [Nm] at time t2, and thereafter, a constant value of RTq = lower limit value RTq1 = 50 [Nm] until time t3. Maintained. That is, from time t2 to time t3, the basic value (value indicated by the alternate long and short dash line) of the command torque of the right rear wheel WRR is lower than the lower limit value RTq1 = 50 [Nm]. The lower limit value RTq1 = 50 [Nm] is selected as the torque RTq without selecting the basic value (value indicated by the one-dot chain line). On the other hand, the command torque LTq of the left rear wheel WRL is a value obtained by adding a predetermined addition value ΔLTq (≦ 150 [Nm]) to the basic value of the command torque LTq from time t2 to time t3. Become. The added value ΔLTq added here corresponds to a difference ΔRTq between the basic value of the command torque RTq in the right rear wheel WRR and the lower limit torque RTq1.

  In the case shown in FIG. 6, the required left-right sum torque TM is lower than the lower limit (lower limit torque) LTq1 = 50 [Nm] until time t4, so that the lower limit LTq1 = 50 [Nm]. On the other hand, after the time t4, the required left-right sum torque TM becomes less than the lower limit (lower limit torque) LTq1, so that the lower limit LTq1 ′ = 20 [Nm]. That is, the lower limit LTq1 ′ after time t4 is the value of the requested left-right sum torque TM after time t4. In other words, after time t4, the requested left-right sum torque TM falls below the original lower limit value LTq1 = 50 [Nm], so that the original lower limit value LTq1 is changed to the value of the requested left-right sum torque TM (new lower limit value LTq1 ′). Like to do.

  Then, when the vehicle switches from the right turn to the left turn at time t4, the command torque LTq of the left rear wheel WRL decreases thereafter. On the other hand, the command torque RTq for the right rear wheel WRR rises and falls. Then, the command torque LTq of the left rear wheel WRL becomes a new lower limit value LTq1 ′ = 20 [Nm] at time t5, and thereafter reaches a constant value of the lower limit value LTq1 ′ = 20 [Nm] until time t6. Maintained. That is, from time t5 to time t6, the basic value (one-dot chain line) of the command torque LTq of the left rear wheel WRL is lower than the lower limit value LTq1 ′ = 20 [Nm]. The lower limit value LTq1 ′ = 20 [Nm] is selected without selecting a basic value (value indicated by a one-dot chain line) as LTq. On the other hand, the command torque RTq of the right rear wheel WRR is a value obtained by adding a predetermined addition value ΔRTq ′ (≦ 120 Nm) to the basic command value RTq from time t5 to time t6. This added value ΔRTq ′ is equivalent to the difference ΔLTq ′ between the basic value of the command torque LTq and the lower limit torque LTq1 ′ in the left rear wheel WRL.

  In this way, the torque that is lower than the lower limit torque LTq1 (LTq1 ′) or RTq1 in the left rear wheel WRL or the right rear wheel WRR is added to the command torque RTq or LTq of the opposite right rear wheel WRR or left rear wheel WRL. By doing so, the command torque of the left rear wheel WRL and the right rear wheel can be prevented while preventing the command torque of the left rear wheel WRL or the right rear wheel WRR from falling below a preset lower limit torque LTq1 (LTq1 ′) or RTq1. The difference from the command torque of the wheel WRR can always be maintained constant or above a certain level.

  That is, in the torque distribution control of the left and right rear wheels WRL and WRR of the present embodiment, when the torque vectoring of the left and right rear wheels (sub driving wheels) WRL and WRR is performed in a system including the two-clutch type rear differential gear 16. The lower limit (lower limit values LTq1, RTq1) is provided for the command value of the drive torque so that the drive force of the left and right wheels does not become zero or a value close to zero due to the request for the left / right difference of the drive force. Further, by performing control to add the command torque that is below the predetermined lower limit values LTq1, RTq1 to the command torque of the opposite rear wheel, the difference between the command torques of the left and right rear wheels WRL, WRR is maintained. ing.

  In addition, when performing control to set the drive torque command values LTq, RTq to the predetermined lower limit value L1 (LTq1, RTq1) as described above, the command value of the torque distributed to the left rear wheel WRL and the right rear wheel WRR. When the left and right sum torque command value TM is less than the predetermined lower limit value L1, the predetermined lower limit value L1 is changed to the left and right sum torque command value TM (the lower limit value L1 is set as the left and right sum torque command value TM). )

  When the left and right sum torque command value TM is below the lower limit value L1, if the lower limit value L1 is adopted as it is, the command value of the drive torque distributed to the left and right rear wheels WRL and WRR is very small or substantially zero. The driving torque is transmitted to the left and right rear wheels WRL, WRR even when the vehicle is in a running state (for example, when the accelerator is off), which affects the fuel consumption (fuel consumption rate) of the vehicle and the durability of the device. However, according to the control of the present embodiment, when the left-right sum torque command value TM falls below the predetermined lower limit value L1, the predetermined lower limit value L1 is changed to the left-right sum torque command value TM. Thus, it is possible to prevent the driving torque from being transmitted to the left and right rear wheels WRL and WRR in the traveling state as described above. Therefore, the fuel consumption (fuel consumption rate) of the vehicle and the durability of the device can be improved.

  In this four-wheel drive vehicle torque distribution control device, the drive torque command value LTq distributed to the left rear wheel WRL by the left clutch 40L and the drive torque command distributed to the right rear wheel WRR by the right clutch 40R. Control is performed so that the difference ΔTq from the value RTq becomes a constant value.

  According to this configuration, by controlling the difference ΔTq in the drive torque command value to be a constant value, an appropriate drive torque difference according to the required drive force value for the left and right rear wheels WRL, WRR is provided. Therefore, more appropriate driving force distribution control can be performed.

  In this four-wheel drive vehicle torque distribution control device, the command value LTq or RTq of the drive torque distributed to the left or right rear wheel WRL or WRR by the left or right clutch 40L or 40R is a predetermined lower limit value LTq1 or RTq1. Is less than the difference ΔLTq or ΔRTq between the drive torque command value LTq or RTq and the predetermined lower limit value LTq1 or RTq1, and the other (right or left) rear wheel WRR with the other (right or left) clutch 40R or 40L. Alternatively, control for adding to the command value RTq or LTq of the drive torque distributed to WRL is performed.

  According to this configuration, the difference ΔLTq or ΔRTq between the drive torque command value LTq or RTq of the left or right clutch 40L or 40R and the lower limit value LTq1 or RTq1 is used as the drive torque command value RTq or LTq of the other clutch 40R, 40L. Is added to the command value of the drive torque of one clutch 40L or 40R while avoiding the command value LTq or RTq of the drive torque of one clutch 40L or 40R being lower than the lower limit value LTq1 or RTq1. A difference between the value LTq or RTq and the command value RTq1 or LTq1 of the driving torque of the other clutch 40R or 40L can be secured. Therefore, while avoiding that the drive torque command values LTq and RTq become a small value exceeding the limit, appropriate drive torque command values LTq and RTq corresponding to the required drive force values for the left and right rear wheels WRL and WRR. Therefore, more appropriate driving force distribution control can be performed.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the technical idea described in the claims and the specification and drawings. Is possible. For example, the specific numerical values of the drive torque command values shown in the above-described embodiments are examples, and the specific values are other numerical values as long as the drive torque command values are values within the scope of the present invention. There may be.

  Further, the specific configuration of the driving force transmission system shown in the present embodiment is an example, and the configuration of the driving force transmission system for carrying out the driving force distribution control according to the present invention is either a front wheel or a rear wheel. In a four-wheel drive vehicle in which one is a main drive wheel and the other is a sub drive wheel, a front and rear torque distribution device for distributing drive torque transmitted to one and the other of the main drive wheel and the sub drive wheel; As long as the configuration includes a left-right torque distribution device for distributing the drive torque transmitted to one and the other of the drive wheel and the right auxiliary drive wheel, the specific configuration is the one shown in the above embodiment. Different configurations may be used.

11 Front differential gears 12, 12 Front drive shaft 13 Front propeller shaft 14 Speed increasing device (front / rear torque distribution device)
15 Rear propeller shaft 16 Rear differential gear (left and right torque distribution device)
17L, 17R Rear drive shaft 21 Planetary gear mechanism 22 Speed increasing clutch 23 Direct coupling clutch 24 Input side sun gear 25 Output side sun gear 26 Carrier 27 Dual pinion 27a Input side pinion 27b Output side pinion 28 Housing 29 Clutch outer 30 Clutch inner 31 Friction engagement Coupling element 32 Clutch outer 33 Clutch inner 34 Friction engagement element 35 One-way clutch 36 Input shaft 37 Driven bevel gear 38 Drive bevel gear 39 Planetary gear mechanisms 40L, 40R Torque distribution clutch (torque distribution device)
41 Ring gear 42 Carrier 43 Sun gear 44 Pinion 45 Housing 46 Clutch outer 47 Clutch inner 48 Friction engagement element 49 Electromagnetic actuator 51 Input section 52a Vehicle speed sensor 52b Steering angle sensor 53 Estimated drive torque calculation section 54 Stabilization control section 55 Speed increase control Unit 56 LSD control unit 57 torque addition unit 58 climbing control unit 60 clutch torque limiting unit 61 current control unit 62 drive circuit unit T automatic transmission Ua electronic control unit (4WD-ECU, control means)
WFL, WFR Front wheel WRL, WRR Rear wheel LTq, RTq Drive torque command value (command torque)
LTq1, RTq1 lower limit (lower limit torque)

Claims (3)

In a four-wheel drive vehicle in which one of the front wheels and the rear wheels is the first drive wheel and the other is the second drive wheel,
Front and rear torque distribution devices for distributing drive torque transmitted to the first drive wheel and the second drive wheel;
A left and right torque distribution device for distributing drive torque transmitted to the left second drive wheel and the right second drive wheel, which are the second drive wheels;
A torque distribution control device comprising: control means for controlling drive torque distributed by the front-rear torque distribution device and the left-right torque distribution device;
The control means has one of a left drive torque command value and a right drive torque command value distributed to the left second drive wheel and the right second drive wheel by the left and right torque distribution device having a predetermined lower limit value. When the value is lower, while performing control to set the command value of the left drive torque or the command value of the right drive torque as the predetermined lower limit,
A left-right sum torque command value, which is the sum of the left drive torque command value and the right drive torque command value, is calculated;
A torque distribution control device for a four-wheel drive vehicle, wherein the predetermined lower limit value is changed to the left / right sum torque command value when the left / right sum torque command value falls below the predetermined lower limit value. 2. The torque distribution of a four-wheel drive vehicle according to claim 1, wherein the control unit controls the difference between the command value of the left drive torque and the command value of the right drive torque to be a constant value. Control device. When one of the command value for the left drive torque and the command value for the right drive torque falls below the predetermined lower limit value, the control means determines the command value for the left drive torque or the command value for the right drive torque and the predetermined value. 3. The torque distribution control of a four-wheel drive vehicle according to claim 2, wherein a control for adding a difference from a lower limit value to the other of the left drive torque command value and the right drive torque command value is performed. apparatus.

Images