Driving force transmission control device for vehicle

Abstract

To provide a driving force transmission control device for a vehicle capable of securing traveling stability and driving force when a four-wheel drive vehicle or the like travels on a bad road, as well as, miniaturizing the device by diverting existing components.SOLUTION: A driving force transmission control device for a vehicle comprises: a distribution mechanism 3 for distributing torque output from an engine 2 that is composed of a ring gear R to which torque is input from the engine 2 and which outputs the torque to a rear wheel 5 side, a carrier C which outputs the torque to a front wheel 4 side, and a sun gear S connected with a motor 9, and that limits a differential action of the differential mechanism; a lock mechanism 10 for limiting a differential action of the differential mechanism; and a controller 15. The controller 15 includes a driving force control unit configure to: cause the engine 2 to output a constant driving force of a required driving force required for a vehicle in a state where the differential action is limited; cause the motor 9 to output a remaining driving force other than the driving force output by the engine 2 of the required driving force; and control the remaining driving force so as to maintain a vehicle speed of the vehicle at a target vehicle speed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a driving force transmission control device that distributes and transmits torque output from a driving force source to left and right wheels, front and rear wheels, etc.

Background Art

[0002] In a four-wheel drive vehicle that distributes and transmits the driving torque output from the engine to the rear wheels and the front wheels, the rear wheels and the front wheels are mechanically connected. Therefore, in order to avoid the so-called tight corner braking phenomenon during cornering where a rotational speed difference occurs between the rear wheels and the front wheels, a differential mechanism is provided between the rear wheels and the front wheels to enable differential rotation of these wheels. On the other hand, when a differential mechanism is provided, a state called torque loss occurs where the driving torque of the other wheels decreases when the grip force of one of the wheels decreases, such as when one of the wheels slips. In that case, the driving force of the entire vehicle decreases and the running stability is impaired. In particular, when driving on a road with severe unevenness (rough road), a steep downhill slope, a snowy road, a slippery road surface, etc. (hereinafter, these are collectively referred to as bad roads), it is necessary for all wheels to have driving force. Therefore, usually, when a differential mechanism (center differential mechanism or center diff) that enables differential rotation between the rear wheel side and the front wheel side is provided, a differential limiting mechanism (diff lock mechanism) such as a clutch or a brake for limiting the differential action is provided.

[0003] An example thereof is described in Patent Document 1 and Patent Document 2. The device described in Patent Document 1 distributes the driving torque input from the engine via the transmission to the front wheel side and the rear wheel side by means of a planetary gear mechanism, and torque is transmitted from the planetary gear mechanism to the output shaft on the front wheel side (or propeller shaft) via a transfer composed of a winding transmission mechanism or the like. The planetary gear mechanism has, for example, a sun gear, a ring gear, and a carrier as rotating elements, and a clutch is provided between the ring gear and the output shaft of the transmission, and the ring gear serves as an input element. Further, the output shaft on the rear wheel side (or propeller shaft) is connected to the sun gear, and the sun gear serves as the first output element, and furthermore, the carrier is connected to the transfer and serves as the second output element. And another clutch is provided between the output shaft of the transmission and the sun gear. Therefore, when the two clutches are engaged, the ring gear and the sun gear are connected and the whole planetary gear mechanism is integrated, so that the output shafts on the front wheel side and the rear wheel side are in the same state as being directly connected to the output shaft of the transmission, and a so-called direct four-wheel drive state in which the front wheels and the rear wheels do not perform differential rotation is achieved. In this direct four-wheel drive state, so-called torque loss in which one of the front and rear wheels slips or idles and the torque of the other wheels decreases is avoided, so that the running performance on so-called rough roads is improved.

[0004] A so-called differential lock that restricts the differential of the differential mechanism that distributes torque to the front and rear is usually performed when entering rough roads, but it is also preferable to perform differential lock when a slippery road surface such as a snow road appears. On the contrary, after passing such a road surface, it is preferable to release the differential lock in order to avoid the tight corner braking phenomenon. An apparatus configured to automatically perform such differential lock and its release based on data reflecting road surface conditions such as the rotational speeds of the front and rear wheels is described in Patent Document 2. In the inventions of Patent Document 1 and Patent Document 2 described above, the differential of the differential mechanism that distributes torque to the front and rear wheels can be restricted, so that the driving torque of all the front and rear wheels is ensured and the running performance on rough roads is improved.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-260684 [Patent Document 2] Japanese Patent Application Laid-Open No. 62-187623 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] However, when driving on a rough road (especially when driving on a road surface with large unevenness or inclination), due to the unstable sitting posture of the driver, it becomes difficult to operate the accelerator pedal and brake pedal for controlling the driving force and vehicle speed, and there are cases where the driving force and vehicle speed cannot be properly controlled. Therefore, conventionally, a control sometimes called crawl control has been developed. This type of control (hereinafter referred to as crawl control) is a control performed by a start operation by the driver when driving on a rough road, and the output of the engine and the braking force by the brake are automatically controlled so as to maintain the vehicle speed at a low vehicle speed set as a predetermined target. As a result, the burden on the driver when driving on a rough road is reduced.

[0007] However, four-wheel drive vehicles equipped with crawl control usually have an engine to generate a large driving force. Therefore, even if the engine output is controlled by crawl control, in an engine that burns fuel and outputs torque, the control responsiveness is not necessarily high, so there is a possibility that the driving force or vehicle speed when driving on a rough road may not be stabilized at the target value even by crawl control.

[0008] Incidentally, in the apparatus described in Patent Document 2, a first motor is connected to the input side of the transmission in addition to the engine, and a second motor is connected to the output shaft on the front wheel side. Although the torque that the motor can output is smaller than that of the engine, since the control responsiveness is excellent, if these motors are used for driving, it is possible to finely and quickly control the driving force when performing differential lock and driving on a rough road, and stabilize the vehicle speed at the target vehicle speed. However, the first motor and the second motor described in Patent Document 2 are newly provided for additionally controlling the driving force or the regenerative braking force, etc. Therefore, in the configuration of the invention of Patent Document 2, there is a possibility that the number of components of the drive device or the vehicle as a whole increases, the vehicle becomes larger, and the weight increases.

[0009] This invention has been made paying attention to the above technical problems, and aims to provide a driving force transmission control device for a vehicle that ensures driving stability and driving force when a four-wheel drive vehicle or the like drives on a rough road, and enables miniaturization of the device by diverting existing parts.

Means for Solving the Problems

[0010] In order to achieve the above object, the present invention provides a vehicle drive force transmission control device including a distribution mechanism that distributes torque output from a drive force source to a first output side and a second output side, and a rotating machine that changes a torque distribution ratio between the first output side and the second output side by the distribution mechanism. The distribution mechanism includes a differential mechanism that performs a differential action by a first rotating element to which torque is input from the drive force source and that outputs torque to the first output side, a second rotating element that outputs torque to the second output side, and a third rotating element to which the rotating machine is connected. The device further includes a lock mechanism that selectively connects at least two of the first rotating element, the second rotating element, and the third rotating element to limit the differential action of the differential mechanism, and a controller that controls the lock mechanism and controls the drive force source and the rotating machine when the lock mechanism operates to limit the differential action of the differential mechanism. The controller includes a drive force control unit that causes the drive force source to output a certain drive force among the required drive forces required for the vehicle in a state where the differential action of the differential mechanism is limited by the lock mechanism, causes the rotating machine to output the remaining drive force other than the drive force output by the drive force source among the required drive forces, and controls the remaining drive force to maintain the vehicle speed at a predetermined target vehicle speed.

[0011] In the present invention, the vehicle includes a total of four wheels, i.e., front wheels and rear wheels. The distribution mechanism is a center differential that distributes torque to the front wheels and the rear wheels. The controller may further include a bad road determination unit that determines a bad road based on a difference in the number of rotations between the front wheels and the rear wheels, and a lock instruction unit that operates the lock mechanism to limit the differential action of the differential mechanism when the bad road determination unit determines the bad road.

[0012] Alternatively, in the present invention, the vehicle includes a total of four wheels, namely front wheels and rear wheels, the distribution mechanism is a center differential that distributes torque to the front wheels and the rear wheels, the vehicle further includes a manual lock operation unit that manually operates the lock mechanism to restrict the differential action of the differential mechanism, the controller further includes a rough road determination unit that determines a rough road based on the difference in rotational speeds between the front wheels and the rear wheels, and a lock notification unit that, when the rough road is determined by the rough road determination unit, operates the lock mechanism to notify the driver of the vehicle to restrict the differential action of the differential mechanism.

[0013] In the present invention, the target vehicle speed may be a predetermined constant vehicle speed.

[0014] In the present invention, the target vehicle speed may be a vehicle speed obtained from the amount of acceleration / deceleration operation by the driver of the vehicle.

[0015] In the present invention, the driving power source is an internal combustion engine, and the rotating machine may be an electric motor having a power generation function.

Advantages of the Invention

[0016] In the driving power transmission control device for a vehicle according to the present invention, the lock mechanism restricts and releases (permits the differential action) of the differential action of the differential mechanism. In a state where the differential action is permitted, the torque distribution ratio by the differential mechanism is controlled by the torque of the rotating machine. For example, by increasing the torque of the rotating machine, the distribution ratio to one output side increases and the distribution ratio to the other output side decreases, and conversely, by decreasing the torque of the rotating machine, the distribution ratio to one output side decreases and the distribution ratio to the other output side increases. On the other hand, when the lock mechanism operates to restrict the differential action of the differential mechanism, the entire differential mechanism rotates integrally, so the torque output by the rotating machine is transmitted as driving force to the first output side and the second output side.

[0017] That is, the rotary machine, together with the driving power source, will generate the driving torque for running. In that case, the driving power source outputs a certain driving force (so-called basic driving force) among the required driving forces, and the rotary machine undertakes and outputs the insufficient driving force (residual driving force). As a result, the rotary machine only needs to output a small driving force, enabling highly responsive driving force control or delicate vehicle speed control. Also, since that rotary machine is an existing component for controlling the torque distribution ratio by the distribution mechanism, it is possible to miniaturize the overall configuration of the device by diverting or sharing components.

[0018] Further, in this invention, if the distribution mechanism is configured as a center differential that distributes torque to the front and rear wheels and allows differential rotation of those wheels, it becomes easy to drive with a stable vehicle speed when running on so-called bad roads such as roads with severe unevenness or steep inclines, and the so-called bad road traversability can be improved.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0020] Embodiments of the present invention will be described with reference to the drawings. Note that the embodiments described below are merely examples of implementing the present invention and do not limit the present invention.

[0021] FIG. 1 schematically shows an example of a vehicle 1 equipped with a driving force transmission control device according to the present invention. The driving force transmission control device according to the present invention includes a distribution mechanism 3 that distributes the torque output by the driving force source 2 to a first output side and a second output side. The first output side and the second output side may be the front wheel 4 side and the rear wheel 5 side, or may be the right wheel and the left wheel. The example shown in FIG. 1 is an example configured to distribute and transmit torque to the front wheel 4 and the rear wheel 5. Therefore, the vehicle 1 shown here is a four-wheel drive vehicle, and the distribution mechanism 3 is a center differential.

[0022] Basically, the driving force source 2 may be a power unit that can output a driving force for traveling by appropriately burning fuel, and may be an internal combustion engine (ENG) using gasoline, light oil, hydrogen, or the like as fuel. Hereinafter, the driving force source 2 will be referred to as the engine 2. The engine 2 is configured to be able to electrically control the intake air amount and the fuel supply amount (injection amount). Therefore, its output can be controlled not only based on the operation by the driver (not shown) of the vehicle 1, but also, if necessary, regardless of the driver's operation.

[0023] The distribution mechanism 3 is constituted by a differential mechanism that performs differential action by three rotating elements. As the differential mechanism, a planetary gear mechanism, a differential gear mechanism configured by meshing a pinion gear held inside the differential case with a pair of left and right side gears, etc. can be adopted. Fig. 1 shows an example in which the distribution mechanism 3 is constituted by a single pinion type planetary gear mechanism. Therefore, the distribution mechanism 3 shown in Fig. 1 includes a sun gear S, a ring gear R which is an internal gear arranged concentrically with respect to the sun gear S, and a carrier C that is arranged between the sun gear S and the ring gear R and rotatably holds a pinion gear meshing with the sun gear S and the ring gear R and rotates, as rotating elements. In the example shown in Fig. 1, torque is transmitted from the engine 2 to the ring gear R. Further, a rear wheel output shaft 6 that outputs torque to the rear wheels 5 is connected to the ring gear R. The ring gear R corresponds to the first rotating element in the embodiment of this invention, and the output of torque toward the rear wheels 5 corresponds to the output to the first output side in the embodiment of this invention.

[0024] The carrier C corresponds to the second rotating element in the embodiment of this invention, and is configured to distribute and output torque from the carrier C to the front wheels 4 side corresponding to the second output side. A transfer 8 for transmitting torque from the carrier C to the front wheel output shaft 7 is provided. The transfer 8 in the example shown in Fig. 1 is constituted by a winding transmission mechanism that transmits torque by a chain, a belt, etc. For example, a sprocket is attached to the carrier C, and a transmission member wound around this is wound around another sprocket attached to the front wheel output shaft 7. Note that the front wheel output shaft 7 is arranged parallel to the rotation center axis of the distribution mechanism 3.

[0025] The torque input to the ring gear R is distributed to the carrier C. A rotary machine 9 that controls the distribution ratio between the torque distributed to the front wheel output shaft 7 side via the carrier C and the torque distributed from the ring gear R to the rear wheel output shaft 6 side is connected to the sun gear S. The rotary machine 9 is specifically an electric motor (motor) or an electric motor (motor - generator) with a power generation function, and hereinafter, the rotary machine 9 is referred to as the motor 9. This motor 9 is, as an example, a permanent magnet type synchronous motor, connected to a power storage device (battery) (not shown in each case) via an inverter, and its rotational speed and torque are controlled by the inverter and the like.

[0026] Furthermore, the differential mechanism 3 is provided with a lock mechanism 10 that selectively restricts its differential action. The lock mechanism 10 is a mechanism that connects at least two rotating elements in the planetary gear mechanism constituting the differential mechanism 3 to restrict differential rotation, and a friction clutch is an example thereof. In the example shown in FIG. 1, it is configured to selectively connect the ring gear R and the carrier C. Also, the lock mechanism 10 is switched between an engaged state (locked state) and a released state (unlocked state) by hydraulic pressure or electromagnetic force, and its control can be performed electrically.

[0027] Note that the vehicle 1 is provided with an accelerator pedal 11 for performing acceleration and deceleration operations, a brake pedal 12 for braking operations, a mechanism for steering (not shown), etc., in the same manner as a normal vehicle. Further, a manual switch 13 is provided as a manual lock operation unit for switching the above - mentioned lock mechanism 10 between an engaged state (locked state) and a released state (unlocked state). Furthermore, although not particularly shown, various sensors for detecting the depression amount of the accelerator pedal 11 representing the required driving force, the depression amount or depression force of the brake pedal 12, and the rotational speeds of the front wheels 4 and the rear wheels 5 are provided on the vehicle 1. And also, a notification means 14 for notifying the driver of the driving state of the vehicle 1, such as the need to operate the lock mechanism 10 or that the road surface is rough, by an image or sound is provided on the vehicle 1.

[0028] Here, the torque distribution function by the above-described distribution mechanism 3 and the control of the torque distribution ratio by the motor 9 will be described. FIG. 2 shows a collinear diagram of the planetary gear mechanism that constitutes the distribution mechanism 3. The collinear diagram is drawn with three straight lines, a straight line indicating the sun gear S, a straight line indicating the carrier C, and a straight line indicating the ring gear R, parallel to each other. The distance between the straight line indicating the sun gear S and the straight line indicating the carrier C is set to "1", and the distance between the straight line indicating the carrier C and the straight line indicating the ring gear R is set to the gear ratio of the planetary gear mechanism (the ratio of the number of teeth of the sun gear S to the number of teeth of the ring gear R). At the positions on these three straight lines, the positions from the baseline orthogonal to these three straight lines indicate the rotational speeds of the respective rotating elements.

[0029] FIG. 2(a) shows a state in which the lock mechanism 10 is released to unlock the distribution mechanism 3 and the vehicle is running with the driving force output from the engine 2. Torque Teg transmitted from the engine 2 acts on the ring gear R in the positive rotation direction. When the motor 9 functions as a motor and outputs torque in the positive rotation direction in this state, torque Ts in the positive rotation direction acts on the sun gear S. FIG. 2(a) shows a state in which the rotational speeds of the ring gear R and the sun gear S are the same. The point where the straight line L1 connecting these rotational speed points intersects the vertical line indicating the carrier C indicates the rotational speed of the carrier C, and that rotational speed is the same as the rotational speeds of the ring gear R and the sun gear S.

[0030] The relationship of the torque can be explained by regarding the above-mentioned straight line L1 as a lever with the sun gear S as the effort point, the ring gear R as the fulcrum, and the carrier C as the point of application. On the carrier C, a torque Tc appears, which is obtained by increasing the torque Ts of the sun gear S according to the gear ratio of the planetary gear mechanism. This becomes the driving force of the front wheels 4. On the other hand, a reaction force TRr against the torque Tc for rotating the carrier C in the forward rotation direction acts on the ring gear R. Therefore, the torque Tr of the ring gear R is the torque obtained by adding the torque Teg of the engine 2 and the above-mentioned reaction force TRr, and this becomes the driving force of the rear wheels 5. Therefore, by increasing or decreasing the torque of the motor 9, the torque Tc of the carrier C, which is the torque for driving the front wheels 4, the torque of the ring gear Tr, and their ratio (i.e., the distribution ratio) change.

[0031] Figure 2(b) shows the rotational speeds of the sun gear S, the ring gear R, and the carrier C when differential rotation occurs between the front wheels 4 and the rear wheels 5 while driving on a rough road. Note that the straight line L1 indicates the state where the front wheels 4 and the rear wheels 5 maintain a grip state and no differential rotation occurs. When driving on a rough road, for example, if the rear wheels 5 tend to slip or lock, as shown by the dashed line L2 in Figure 2(b), the rotational speed of the ring gear R increases or decreases with respect to the rotational speed when no differential rotation occurs. Accordingly, the rotational speeds of the motor 9 and the sun gear S decrease or increase. Also, for example, if the front wheels 4 tend to slip or lock, as shown by the broken line L3 in Figure 2(b), the rotational speed of the carrier C increases or decreases with respect to the rotational speed when no differential rotation occurs. Accordingly, the rotational speeds of the motor 9 and the sun gear S increase or decrease. Therefore, when driving on a rough road with the differential action of the distribution mechanism 3 allowed, in order to maintain a constant vehicle speed, it is necessary to finely and frequently control the rotational speed or torque of the engine 2 or the motor 9.

[0032] Figure 2(c) shows the state in which the above-described lock mechanism 10 is operated to perform differential restriction of the distribution mechanism 3. In this state, since the entire planetary gear mechanism constituting the distribution mechanism 3 rotates integrally, its operating state is represented by the straight line L1. In this state, the distribution ratio of the torque cannot be changed (controlled) by the motor 9, but the motor 9 can be operated as a driving force source for traveling. Therefore, the torques Tmg and Teg of the engine 2 and the motor 9 are evenly distributed to the carrier C and the ring gear R (on the front wheel 4 side and the rear wheel 5 side), and the total torque of these becomes the torque Tc of the carrier C and the torque Tr of the ring gear R.

[0033] The embodiment of this invention is configured to control the vehicle speed or the driving torque when traveling on a rough road by effectively using the above-described functions of the distribution mechanism 3 and the motor 9. The control during rough road travel includes determination of a rough road, notification of a rough road, differential restriction by the lock mechanism 10, output control of the engine 2 and the motor 9 for outputting a required driving force, etc., and an electronic control unit (ECU) 15 for performing such control is provided. The ECU 15 corresponds to the controller in the embodiment of this invention, and is mainly composed of a microcomputer including an arithmetic element (CPU), a storage element (RAM, ROM), an interface, etc., and performs arithmetic operations according to a preset program using the data obtained by the above-described various sensors and the data stored in advance, and is configured to output the result of the arithmetic operation as a control command signal.

[0034] Examples of the input data include the rotational speed of the front wheels 4, the rotational speed of the rear wheels 5, the accelerator opening which is the amount of depression of the accelerator pedal 11 or the required driving force based thereon, the on / off signal of the manual switch 13, and the like. Also, the pre-stored data includes a reference value for determining a rough road from the differential rotational speed between the front wheels 4 and the rear wheels 5 and the occurrence frequency of the differential rotational speed, a determination value for determining whether the determined rough road requires differential limitation by the lock mechanism 10, and the like. Further, examples of the control command signal to be output include a signal for operating the lock mechanism 10, a signal for controlling the output torque of the engine 2 and the motor 9, a signal for instructing the content to be notified by the notification means 14, and the like.

[0035] The ECU 15 makes a determination of a rough road using the above-described input data and pre-stored data. When the determination is established, the ECU 15 performs differential limitation of the distribution mechanism 3 by the lock mechanism 10 or notifies that the lock mechanism 10 should be operated, and is configured to control the rotational speed or output torque of the engine 2 and the motor 9 required to maintain the target vehicle speed when differential limitation is performed by the distribution mechanism 3. That is, as shown in FIG. 3, the ECU 15 includes, as a functional configuration, a rough road determination unit 15a, a lock instruction unit 15b, a lock notification unit 15c, and a driving force control unit 15d.

[0036] The rough road determination unit 15a determines whether the road surface on which the vehicle is currently traveling is a rough road based on the differential rotational speed between the front wheels 4 and the rear wheels 5 and the occurrence frequency of the differential rotational speed. When the difference (absolute value) between the rotational speeds of the front wheels 4 and the rear wheels 5 exceeds a predetermined value, it is determined that differential rotation has occurred, and the number of times the determination is established within a predetermined unit time is defined as the occurrence frequency. As described above, the determination of a rough road can be made by comparing the detected value with a reference value prepared in advance.

[0037] When the determined bad road is a bad road to a certain extent where it is necessary to limit the differential action of the distribution mechanism 3, the lock instruction unit 15b is configured to output a control command signal to the lock mechanism 10 to operate the lock mechanism 10. This lock instruction unit 15b is a control unit that operates the lock mechanism 10 regardless of the driver's instruction to perform differential limit of the distribution mechanism 3, while the lock notification unit 15c is a control unit that, when the determination of the bad road is established, gives a notification to prompt the driver to operate the lock mechanism 10 to perform differential limit of the distribution mechanism 3. Therefore, the lock notification unit 15c may be provided together with the lock instruction unit 15b, or may be provided in place of the lock instruction unit 15b.

[0038] The driving force control unit 15d is configured to control the outputs of the engine 2 and the motor 9 during traveling on a bad road where the differential of the distribution mechanism 3 is limited by operating the lock mechanism 10. An example of such control may be control to maintain the vehicle speed at a predetermined target vehicle speed, similar to the crawl control described above, or may be control to maintain the target vehicle speed obtained from the accelerator opening. In particular, the driving force control unit 15d limits the driving force that is sequentially changed to maintain the target vehicle speed to the torque of the motor 9, and maintains the driving force output by the engine 2 at a predetermined torque determined in control, and thus controls the driving torque of the entire vehicle 1.

[0039] That is, as shown in (c) of FIG. 2 described above, when the engine 2 and the motor 9 output driving torque in a state where the differential of the distribution mechanism 3 is limited, the torque on the front wheel 4 side and the torque on the rear wheel 5 side are respectively torques obtained by adding the torque by the engine 2 and the torque by the motor 9. Therefore, the torque by the engine 2 is set to a torque of a predetermined ratio among the required driving forces obtained from the accelerator opening or the target vehicle speed, etc., and the torque that is insufficient or excessive to make the vehicle speed the target vehicle speed is taken over by the motor 9 and its output torque is controlled by feedback control or the like.

[0040] An example of the control executed by the above ECU 15 will be described with reference to FIG. 4. FIG. 4 is a flowchart for explaining the control executed in the embodiment of the present invention, and the routine shown here is repeatedly executed when the vehicle 1 is running. First, the differential rotation of the front and rear wheels is determined (step S1). When the vehicle is traveling straight ahead without being steered, there is almost no difference in the rotational speed between the front wheels 4 and the rear wheels 5. When the vehicle is turning, a difference in rotational speed corresponding to the turning radius occurs between the front wheels 4 and the rear wheels 5. Therefore, the determination in step S1 can be made by comparing a threshold value corresponding to the steering angle and the turning radius with the rotational speed difference between the front and rear wheels.

[0041] If the determination result in step S1 is "No", the routine in FIG. 4 is temporarily terminated without performing any particular control. On the contrary, if the determination result in step S1 is "Yes", it is determined whether the differential frequency (occurrence frequency) of a predetermined differential amount (differential rotational speed) or more is greater than a predetermined reference value (step S2). Since differential rotation of the front and rear wheels also occurs when the vehicle 1 is turning, in step S2, a determination is made considering such a running state of the vehicle 1, or a reference value is adopted.

[0042] If the determination result in step S2 is "No", the routine in FIG. 4 is temporarily terminated without performing any particular control. On the contrary, if the determination result in step S2 is "Yes", a determination of a rough road is made (step S3). As described above, a rough road is a road with severe unevenness (rough road), a steep downhill slope, a snowy road, a slippery road surface, etc. Even if the determination of a rough road is established in step S3, since the degree of unevenness, the degree of inclination, and further the duration or distance thereof vary, the necessity of switching to a state where the differential of the distribution mechanism 3 is restricted (CDL switching) is determined (step S4).

[0043] If the result of the determination in step S4 is "Yes", the locking mechanism 10 is operated to switch to the state (CDL) in which the differential restriction of the distribution mechanism 3 is performed (step S5). Subsequently, the driving force control (driving force control during CDL) when traveling with the differential restriction of the distribution mechanism 3 is executed (step S6). This control is the control by the driving force control unit 15d described above. While maintaining the output of the engine 2 at a constant value, the so-called residual driving force that is insufficient to satisfy the required driving force is output from the motor 9, and in order to maintain the target vehicle speed, the residual driving force by the motor 9 is changed in magnitude. That is, the vehicle speed is controlled by the motor 9.

[0044] The maximum torque that can be output by the motor 9 is smaller than that of the engine 2, but since the control responsiveness is superior to that of the engine 2, by controlling the driving force for maintaining the vehicle speed by the motor 9, it becomes possible to finely adjust the vehicle speed and control the vehicle speed as desired. In other words, the burden on the driver for maintaining the vehicle speed on a rough road can be reduced. Further, the motor 9 is an existing component provided for controlling the torque distribution ratio by the distribution mechanism 3, and since the driving force control during rough road driving is performed using this, there is no need to add new components for performing the control according to this invention, and thus the overall configuration of the device can be downsized.

[0045] Subsequently, it is determined whether or not the driver has selected to release the differential restriction (CDL OFF) of the distribution mechanism 3 (step S7). This operation can be performed, for example, by the manual switch 13 described above. If the result of the determination in this step S7 is "No", the process returns to step S6 and the driving force control during differential restriction is continued. On the contrary, if the determination result of step S7 is "Yes", the routine shown in FIG. 4 is temporarily terminated.

[0046] On the other hand, when the result of the determination in step S4 above is "No", it is determined whether the driver has been instructed to switch the distribution mechanism 3 to the differential limit state (CDL) (step S8). Considering the road surface condition where the differential limit of the distribution mechanism 3 must always be executed even on a rough road and the driving skills of the driver, there may be a road surface condition where it is preferable to perform the differential limit of the distribution mechanism 3 and the associated driving force control. In the latter case, the determination in step S4 is "No", and the determination in step S8 is "Yes".

[0047] When the result of the determination in step S8 is "Yes", the driver is informed by the notification means 14 to operate the lock mechanism 10 to perform the differential limit of the distribution mechanism 3. Accordingly, the driver operates the manual switch 13 (step S9), and the lock mechanism 10 switches to the engaged state (locked state) (step S5). Thereafter, the process proceeds to step S6 and then step S7 in sequence, and the control as described above is performed. That is, in the embodiment of the present invention, in addition to the configuration in which the differential limit of the distribution mechanism 3 and the associated driving force control are automatically performed when the determination of a rough road is established, it is possible to adopt a configuration in which the differential limit of the distribution mechanism 3 and the associated driving force control are performed by the driver's manual operation. When the determination result in step S8 is "No", the routine in FIG. 4 is terminated once without performing any particular control.

[0048] As described above, one embodiment of the present invention has been described. However, the present invention is not limited to the above-described embodiment and can be appropriately modified. For example, the distribution mechanism may be configured as a mechanism for torque vectoring that distributes and transmits torque to the left and right wheels and appropriately controls the distribution ratio. Also, road information from the navigation system or road information obtained by VICS may be added to the determination of a rough road or the determination of the necessity to perform the differential limit of the distribution mechanism.

Explanation of Reference Numerals

[0049] 1 Vehicle 2 Driving force source (engine) 3 Distribution mechanism 4 Front wheels 5 Rear wheels 6 Rear wheel output shaft 7 Front wheel output shaft 8 Transfer 9 Rotator (motor) 10 Lock mechanism 11 Accelerator pedal 12 Brake pedal 13 Manual switch 14 Notification means 15 Electronic control unit (ECU, controller) 15a Rough road determination unit 15b Lock instruction unit 15c Lock notification unit 15d Driving force control unit C Carrier R Ring gear S Sun gear

Claims

1. A driving force transmission control device for a vehicle, comprising: a distribution mechanism that distributes torque output from a driving force source to a first output side and a second output side; and a rotating machine that changes a distribution ratio of the torque to the first output side and the second output side by the distribution mechanism, the distribution mechanism is composed of a differential mechanism that performs a differential action using a first rotating element that receives torque from the driving force source and outputs the torque to the first output side, a second rotating element that outputs torque to the second output side, and a third rotating element to which the rotating machine is connected, a lock mechanism that selectively connects at least two of the first rotary element, the second rotary element, and the third rotary element to limit a differential action of the differential mechanism; a controller that controls the locking mechanism and controls the driving force source and the rotating machine when the locking mechanism operates to limit the differential action of the differential mechanism, The controller: a driving force control unit that causes a driving force source to output a certain driving force of a required driving force required for the vehicle in a state in which the differential action of the differential mechanism is restricted by the lock mechanism, causes the rotating machine to output a residual driving force of the required driving force other than the driving force output by the driving force source, and controls the residual driving force so as to maintain a vehicle speed of the vehicle at a predetermined target vehicle speed. A vehicle driving force transmission control device comprising:

2. 2. A vehicle driving force transmission control device according to claim 1, The vehicle has a total of four wheels, including front wheels and rear wheels, the distribution mechanism is a center differential that distributes torque to the front wheels and the rear wheels, The controller: a rough road determination unit that determines a rough road based on a difference between the rotation speeds of the front wheels and the rear wheels; and a lock instruction unit that operates the lock mechanism to limit the differential action of the differential mechanism when the bad road is determined by the bad road determination unit. A vehicle driving force transmission control device comprising:

3. 2. A vehicle driving force transmission control device according to claim 1, The vehicle has a total of four wheels, including front wheels and rear wheels, the distribution mechanism is a center differential that distributes torque to the front wheels and the rear wheels, The vehicle further includes a manual lock operation unit that is manually operated to operate the lock mechanism so as to limit the differential action of the differential mechanism, The controller: a rough road determination unit that determines a rough road based on a difference between the rotation speeds of the front wheels and the rear wheels; and a lock notification unit that notifies a driver of the vehicle to operate the lock mechanism to limit the differential action of the differential mechanism when the bad road is determined by the bad road determination unit. A vehicle driving force transmission control device comprising:

4. 4. A vehicle driving force transmission control device according to claim 1, The target vehicle speed is a predetermined constant vehicle speed. A vehicle driving force transmission control device comprising:

5. 4. A vehicle driving force transmission control device according to claim 1, The target vehicle speed is a vehicle speed calculated from an amount of acceleration or deceleration operation by a driver of the vehicle. A vehicle driving force transmission control device comprising:

6. 4. A vehicle driving force transmission control device according to claim 1, the driving force source is an internal combustion engine, The rotating machine is an electric motor having a power generating function. A vehicle driving force transmission control device comprising:

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