JP2011031698A - Regenerative braking force controller for hybrid four-wheel drive vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a regenerative braking force controller for a hybrid four-wheel drive vehicle capable of improving yaw stability in regenerative braking. <P>SOLUTION: The hybrid four-wheel drive vehicle drives with a first drive source (an engine, for example) a first drive wheel always driven in one of the front and rear wheels; drives with a second drive source (an electric motor, for example) a second drive wheel driven according to need from the other of the front and rear wheels; and can change a mechanical connection state between the first drive wheel and the second drive wheel by a clutch mechanism from an open state to directly connected state. When the clutch mechanism is in an open state in the regenerative braking, braking force of the second drive wheel is set larger than that of ideal braking force distribution. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a regenerative braking force control device for a hybrid four-wheel drive vehicle in which one of front and rear wheels is driven by an engine and the other is driven by an electric motor.

  In recent years, for the purpose of improving fuel efficiency and reducing exhaust gas, on-demand type four-wheel drive, in which one of the front and rear wheels is driven by an engine and the other of the front and rear wheels is driven by a transmission device such as an electronically controlled coupling when necessary. Vehicles are being developed. Some on-demand type four-wheel drive vehicles have a hybrid specification in which an electric motor is mounted on the other of the front and rear wheels. For example, Patent Document 1 discloses in detail a drive mechanism of an on-demand type hybrid four-wheel drive vehicle. Further, for example, FIG. 6B of Patent Document 2 shows that during regenerative braking of an on-demand type hybrid four-wheel drive vehicle, the front and rear wheels are connected and the regenerative braking force is distributed to each axle so that regenerative braking is performed on one axle. A regenerative braking operation for obtaining a greater regenerative braking force than that is disclosed.

JP 2005-231526 A JP 2006-352954 A

  In an on-demand type hybrid four-wheel drive vehicle, as disclosed in Patent Document 2, regenerative braking is performed as a direct-coupled four-wheel drive state, thereby obtaining a greater regenerative braking force than in the two-wheel drive state. Much kinetic energy can be recovered from the vehicle.

  However, in the direct-coupled four-wheel drive state, as shown in FIG. 5 of Patent Document 2, the front-rear braking force distribution moves on the ideal braking force distribution line. In addition, even if the fastening force of the electronically controlled coupling is moderate on the high μ road, the low μ road may be in a direct connection state. For this reason, the maximum braking force can be obtained on the ideal braking force distribution line, but when the wheels are locked, they are simultaneously before and after. If the wheel locks front and back at the same time, yaw stability decreases and the possibility of spinning increases.

  One of the representative aspects of the present invention provides a regenerative braking force control device for a hybrid four-wheel drive vehicle capable of improving yaw stability during regenerative braking.

  Here, in one of the representative aspects of the present invention, the first drive wheel that is always driven on one of the front and rear wheels is driven by a first power source (for example, an engine), and the other front and rear wheels are driven as necessary. The second driving wheel is driven by a second power source (for example, an electric motor), and the mechanical connection state between the first driving wheel and the second driving wheel is changed from the open state to the direct connection state by the clutch mechanism. In the hybrid four-wheel drive vehicle that can be used, the braking force of the second driving wheel is set larger than the ideal braking force distribution when the clutch mechanism is in an open state during regenerative braking.

  According to one of the representative aspects of the present invention, the regenerative braking force can be greater than the normal braking force distribution while improving the yaw stability during regenerative braking.

  The clutch mechanism is in a completely engaged state when the direct-coupled four-wheel drive state is set. In this way, since the front and rear braking force distribution becomes the ideal braking force distribution, the regenerative braking force can be distributed to the front and rear wheels even if the ratio of the regenerative braking force to the total braking force is set large. The regenerative energy can be efficiently recovered within the friction limit, and the maneuverability can be improved.

  When starting regenerative braking, the braking force of the front and rear wheels is adjusted after the clutch mechanism is completely engaged. In this way, since the braking force distribution before and after the start of braking becomes the ideal braking force distribution, it is possible to prevent the front wheels from being locked and to ensure yaw stability.

  Further, when the tendency of the wheels to be locked is detected and it is determined from the detection result that the wheels are locked, the regenerative braking force is reduced, and then the clutch mechanism is released. In this way, even if the vehicle enters a low μ road during braking, the rear wheels can be prevented from being locked and yaw stability can be ensured.

  According to one of the representative inventions described above, regenerative energy can be efficiently recovered while suppressing spin.

The block diagram which shows the structure of the drive system of the hybrid vehicle which is an Example of this invention. The block diagram which shows the connection relation between the some control apparatuses mounted in the hybrid vehicle of FIG. 1, and the connection relation between a control apparatus and a some sensor. The figure which shows braking force limit, ideal braking force distribution, normal braking force distribution, and front-rear braking force distribution when the electronic control coupling is opened. The figure which shows the transition of front-and-back braking force distribution at the time of the start of regenerative braking in a direct-coupled four-wheel drive state. The figure which shows two sequence proposals at the time of the start of regenerative braking in a direct-coupled four-wheel drive state. The figure which shows the transition of front-and-back braking force distribution when approaching to a low μ road at the time of regenerative braking in the direct-coupled four-wheel drive state. The figure which shows two sequence proposals after the wheel lock detection at the time of the regenerative braking in a direct-coupled four-wheel drive state. The time chart which shows the sequence after a wheel lock detection from the start of regenerative braking in a direct-coupled four-wheel drive state. The figure which shows the braking force distribution of the sequence after a wheel lock detection after the regenerative braking start in a direct-coupled four-wheel drive state.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows the configuration of a drive system of an on-demand type hybrid four-wheel drive vehicle (hereinafter simply referred to as “vehicle”) 1 to which the present invention is applied.

  On the front side of the vehicle 1, an engine 2 and a transaxle 3 (a transmission, a differential gear (differential gear) and a transfer integrated device) are disposed. A clutch mechanism 15, a motor generator 6, and a rear wheel differential (differential gear) 7 are disposed on the rear side of the vehicle 1. The power of the engine 2 is transmitted to the front wheels 5 via the transaxle 3 and the front wheel drive shaft 4. As a result, the front wheel 5 is driven.

  The power of the motor generator 6 is transmitted to the rear wheel 9 via the rear wheel speed reducer 18, the rear wheel differential 7 and the rear wheel drive shaft 8. As a result, the rear wheel 9 is driven. A clutch 15 is disposed between the motor generator 6 and the rear wheel speed reducer 18. Although the clutch 15 is normally engaged, the transmission of power between the motor generator 6 and the rear wheel differential 7 can be cut off by opening the clutch 15.

  Note that there may be a configuration in which the reduction gear 18 is not provided and the power of the motor generator 6 is directly input to the rear wheel differential device 7 or a configuration in which the clutch 15 is not provided.

  A front wheel mechanical brake 16 is disposed on the front wheel, and a rear wheel mechanical brake 17 is disposed on the rear wheel, and the braking force is adjusted by the brake control device 19.

  A propeller shaft 10 and an electronic control coupling 11 are disposed between the front wheel drive shaft 4 and the front wheel 5 and the rear wheel drive shaft 8 and the rear wheel 9. Power is transmitted to each other. The power transmitted to each other is actively adjusted by the strength of the fastening force of the electronic control coupling 11. In other words, if the electronic control coupling 11 is not fully opened, it is possible to run in a four-wheel drive state with only the power of the engine 2 or only the power of the motor generator 6. The electronic control coupling 11 is a known technique, but may be a device such as a hydraulic multi-plate clutch as long as the fastening force can be adjusted actively.

  The fastening force of the electronic control coupling 11 is adjusted by the electronic control coupling control device 18.

  In this embodiment, a case where a gasoline engine is used as the engine 2 will be described as an example. As the engine 2, another engine such as a diesel engine, a hydrogen engine, a gas engine, or a biofuel engine may be used.

  In the present embodiment, the motor generator 6 is a three-phase AC synchronous machine, for example, a permanent magnet field type three-phase AC synchronous machine constituted by a field provided with an armature that generates a rotating magnetic field and a permanent magnet. The case where it is used will be described as an example. As the motor generator 6, a three-phase AC induction machine or a DC machine may be used. In addition, as the three-phase AC synchronous machine, a wound field type three-phase AC synchronous machine constituted by an armature that generates a rotating magnetic field and a field provided with a field winding may be used.

  A power storage device 13 is electrically connected to the armature of the motor generator 6 via the inverter device 12.

  The power storage device 13 is a direct current power source for driving the motor generator 6 and is constituted by a battery having a voltage higher than that of the onboard auxiliary battery, for example, a lithium ion battery or a nickel metal hydride battery.

  In the present embodiment, a case where the power storage device 13 is configured by a high voltage battery will be described as an example. As the power storage device 13, a large capacity capacitor or a capacitor may be used.

  The inverter device 12 is a power converter that performs power conversion from DC power to three-phase AC power and power conversion from three-phase AC power to DC power between the armature of the motor generator 6 and the power storage device 13. A power conversion circuit is provided. In the power conversion circuit, a series circuit for one phase in which two switching semiconductor elements are electrically connected in series is electrically connected in parallel to the DC positive electrode and the negative electrode of the power storage device 8 for three phases. It is constituted by. A winding of a corresponding phase of the armature of the motor generator 6 is electrically connected to the middle point of each series circuit.

  In the present embodiment, an example in which an insulated gate bipolar transistor (IGBT) is used as the six switching semiconductor elements for power conversion will be described. As the switching semiconductor element, a metal oxide semiconductor field effect transistor (MOSFET) may be used.

  The operation of the engine 2 is controlled by an engine control device (not shown). The engine control device outputs a command signal to an engine component device (air throttle valve, intake / exhaust valve, fuel injection valve, etc.) to control the drive of the engine component device, and controls the amount of air supplied to the engine 2 and the fuel Control the amount and so on.

  The operation of the motor generator 6 is controlled by a motor control device 14. The motor control device 14 outputs a drive command signal to the inverter device 12 to control the drive of the inverter device 12, and controls the electric power between the armature of the motor generator 6 and the power storage device 13.

  When the DC power supplied from the power storage device 13 is converted into three-phase AC power by the inverter device 12 and then supplied to the armature of the motor generator 6, the motor generator 6 operates as a power running operation, that is, as an electric motor. Generates rotational power. Driving assist of the front wheels 5 driven by the engine 2 is possible by the power running operation of the motor generator 6.

  On the other hand, when the motor generator 6 is driven by the power from the rear wheel 9 in a state such as braking, the motor generator 6 operates as a regenerative (power generation) operation, that is, as a generator, and the three-phase AC power and the negative rotational power. Is generated. The generated three-phase AC power is converted into DC power by the inverter device 12 and then supplied to the power storage device 13. Thereby, the electrical storage of the electrical storage apparatus 13 and regenerative braking are possible.

  If the electronic control coupling 11 is in the open state, the driving force by the driving assist and the braking force by the regenerative braking are transmitted only to the rear wheel 9. If a fastening force is generated and put into the electronic control coupling 11, driving force and braking force from the front and rear are transmitted to the front wheel 5 and the rear wheel 9 through the propeller shaft 10 in accordance with the fastening force. The

  FIG. 2 shows a connection relationship between a plurality of control devices mounted on the vehicle 1 and a connection relationship between the control device and a plurality of sensors. The motor generator control device (hereinafter simply referred to as “motor control device”). ) 14 is a summary of the signals input to 14.

  A plurality of signals corresponding to a plurality of input information necessary for controlling the motor generator 6 are input to the motor control device 14.

  As the plurality of input information, for example, an output signal of the accelerator pedal sensor 20 (which may be the opening of the air throttle valve of the engine 2), an output signal of the handle angle sensor 21, and an output signal of the brake pedal switch 22 (even the brake pedal depression amount) Good), wheel speed sensor 23 (for all four wheels), longitudinal acceleration sensor 24, master cylinder pressure sensor 25, shift lever position sensor 26, parking brake switch 27, battery status information 28 output from battery control device of power storage device 13 (For example, charge amount (SOC) information, charge / discharge allowable power information, etc.), current sensor 29 (detects a three-phase alternating current flowing between the motor generator 6 and the inverter device 12), motor rotation position sensor 30 (motor generator 6 Rotation position is detected, eg magnetic pole position sensor such as resolver) A.

  The motor control device 14 is electrically connected to other control devices including the engine control device 31, the electronic control coupling control device 17, and the brake control device 18 via a communication network, and can transmit signals to each other. A plurality of pieces of input information input to the motor control device 14 are directly input from each sensor or signal-transmitted via a communication network.

  The motor control device 14 is configured by mounting a plurality of electronic components including a microcomputer as a semiconductor device and a storage device on an electronic circuit board and electrically connecting them. The microcomputer includes a motor generator controller. Those control units are configured by software.

  The motor generator control unit outputs a drive command signal for turning on and off the switching semiconductor element of the inverter device 12 to the inverter device 12 to control power conversion by the inverter device 12, thereby controlling the operation of the motor generator 6. Based on a plurality of input information including a torque command value for the motor generator 6, a magnetic pole position of the motor generator 6, and a three-phase AC current value between the inverter device 12 and the motor generator 6. A drive command value for turning on and off the switching semiconductor element is calculated, the drive command value is used as output information, and a signal (for example, a PWM (pulse width modulation) signal) corresponding to the drive command value is input to the drive circuit of the inverter device 12. Output.

  The brake control device 19 is configured by mounting a plurality of electronic components including a microcomputer as a semiconductor device and a storage device on an electronic circuit board and electrically connecting them. The microcomputer has a brake control unit. Those control units are configured by software.

  The brake control unit controls, for example, a switching valve, a linear adjustment valve, a pump motor, and the like in order to adjust the hydraulic pressure of the mechanical brake 16 for the front wheels and the mechanical brake 17 for the rear wheels.

  The electronic control coupling control device 18 is configured by mounting a plurality of electronic components including a microcomputer as a semiconductor device and a storage device on an electronic circuit board and electrically connecting them. The microcomputer includes an electronic control coupling control unit. Those control units are configured by software. The electronic control coupling control unit adjusts the fastening force of the electronic control coupling 11 by, for example, current control.

  Next, an advantage of performing regenerative braking in a directly connected four-wheel drive state will be described.

  FIG. 3 shows the braking force limit of the tire and the braking force distribution before and after. The X-axis is the front wheel braking force, the Y-axis is the rear wheel braking force, the line segment pq is the braking force limit line on the front wheel high μ road, and the line qr is the rear wheel braking force limit line on the high μ road. In other words, the braking force distribution between the front wheels and the rear wheels can be distributed inside the square opqr. If the X-axis and Y-axis resolutions are the same, for example, a 45 ° downward-sloping line such as the deceleration α is a constant deceleration line, and the deceleration increases as it goes to the right. The curve (1) is a so-called ideal braking force distribution line, which is obtained by multiplying the front and rear load distribution by a deceleration. As shown in (1), the end point of the ideal braking force distribution line is the intersection point q between the front wheel braking force limit line and the rear wheel braking force limit line, and braking at the maximum deceleration that can be generated by the front and rear tires can be exhibited on this line. However, the wheels are locked at the same time.

  The quadrangle opqr becomes smaller as the quadrangle op′q′r ′, for example, when the road surface μ decreases. Below the ideal braking force distribution line of (1), the braking force limit line of the front wheel is reached before the braking force limit line of the rear wheel, so that the front wheel is locked first. On the other hand, the ideal braking force distribution line of (1) reaches the braking force limit line of the rear wheel before the braking force limit line of the front wheel above the braking force limit line, so that the wheel is locked before the rear wheel.

  When the rear wheel is locked, the lateral force of the rear wheel becomes extremely small, so the yaw stability is lowered and a spin tendency tends to occur, which is very dangerous. In some cases, it is possible to deviate from the road. Therefore, a general vehicle usually employs a braking force distribution line as shown in (2) below the ideal braking force distribution line of (1) so as not to have a spin tendency during braking.

  Here, in the vehicle 1 of FIG. 1, the motor generator 6 is disposed on the rear wheel side downstream of the electronic control coupling 11 when viewed from the engine 2. Assuming that braking with the deceleration rate α is performed with the braking force distribution of (2), which is a normal braking force distribution line when the electronic control coupling 11 is in the open state, the braking force distribution is point A.

Here, assuming that the total braking force at the deceleration α in FIG. 3 is 100, the front-rear braking force distribution at point A is the front wheel braking force: rear wheel braking force = 70: 30 (1) )
And

Since it is not possible to obtain a regenerative braking force greater than the rear wheel braking force on this distribution line,
Maximum regenerative braking force by rear wheels at point A = 30 (2)
It is.

  If the motor generator 6 is disposed on the front wheel side upstream of the electronic control coupling 11, a maximum of 70 regenerative braking forces can be obtained. That is, the regenerative energy can be recovered more when the motor generator 6 is disposed on the front wheel side.

  However, configuring the vehicle 1 of FIG. 1 by arranging the motor generator 6 on the rear wheel side of the front-wheel drive vehicle has a great advantage that a hybrid with a few modifications can be realized.

  Here, in the vehicle 1 in FIG. 1, if it is desired to obtain a larger regenerative braking force at the same deceleration α as described above, for example, the braking force distribution at point B in FIG.

Here, the front / rear braking force distribution at point B is determined as follows: front wheel braking force: rear wheel braking force = 45: 55 (3)
And

That is, the maximum regenerative braking force by the rear wheels at point B = 55 (4)
It is.

  Therefore, the regenerative braking force can be obtained at the point B greater than the point A in the braking force distribution from the equations (2) and (4). In other words, larger regenerative energy can be recovered.

  However, since the braking force distribution at the point B is located above the ideal braking force distribution line of (1) as described above, the road surface μ is lowered and the braking force limit becomes, for example, a square op′q′r ′. The wheel lock occurs first on the rear wheel, which is not good from the viewpoint of vehicle yaw stability.

  Therefore, the electronically controlled coupling 11 is completely fastened at the time of regenerative braking, and a direct-coupled four-wheel drive state is brought about. In the direct-coupled four-wheel drive state, as described above, the front wheel braking force and the rear wheel braking force are respectively distributed forward and backward by the longitudinal load distribution at the deceleration α, so the braking force distribution is a point on the ideal braking force distribution line. Go to C.

  This is verified by calculation.

Since the ideal braking force distribution is the same as the front / rear load distribution, the front / rear load distribution at the deceleration α, that is, the braking force distribution is the front wheel load distribution: rear wheel load distribution = front wheel braking force distribution: rear wheel braking force distribution.
= 65 [%]: 35 [%] (5)
It becomes.

Since the front wheel braking force 45 at the point B is distributed back and forth at the distribution rate of the expression (5) in the direct-coupled four-wheel drive state,
Front wheel distribution 45 x 65 [%] = 29.25 (6)
Rear wheel distribution 45 × 35 [%] = 15.75 (7) and distributed back and forth.

Since the rear wheel braking force 55 of the point B is also distributed back and forth at the distribution rate of the equation (5) in the direct-coupled four-wheel drive state,
Front wheel distribution 55 x 65 [%] = 35.75 (8)
Rear wheel distribution 55 x 35 [%] = 19.25 (9)
And distributed back and forth.

Therefore, the front / rear braking force distribution is the front wheel braking force 29.25 + 35.75 = 65 (10)
Rear wheel braking force 15.75 + 19.25 = 35 (11)
It becomes.

That is, front wheel braking force: rear wheel braking force = 65: 35 (12)
Which is consistent with Equation (5).

  From the above, in order for the motor generator 6 disposed on the rear wheel to sufficiently exert the regenerative braking force, the front and rear braking force distribution is made dominant over the ideal braking force distribution, and the direct-coupled four-wheel drive state is set. It's fine.

  Since the braking force is 0 before the start of braking, it is point o. That is, when braking is started at the deceleration α, the braking force is adjusted and the driving state is changed to the direct-coupled four-wheel drive, and the transition from the point o to the point C may be performed. However, since the point C has the front and rear wheels simultaneously locked on the ideal braking force distribution line, the yaw stability is not better than the normal braking force distribution. Therefore, if the wheel tends to lock, the braking force is adjusted and the front and rear wheels are opened, and the point C is shifted to the point A on the normal braking force distribution line (2).

  Next, a specific method of regenerative braking in the directly connected four-wheel drive state will be described.

  First, a method for starting regenerative braking will be described.

  When the driver's braking start request is detected, the front wheels are braked with a mechanical brake according to the driver's required braking force, and the rear wheels are regeneratively braked with the motor generator 6. Here, the mechanical brake is a known technique such as a disc brake or a drum brake. Since it is desired to increase the rear wheel regenerative braking force at this time, the distribution of the front wheel mechanical brake braking force and the rear braking regenerative braking force is set within the range above the ideal braking force distribution line, for example, the point B described above. Since this is the characteristic of the rear wheel tip lock as it is, the electronically controlled coupling is completely fastened and the point is shifted to the point C on the ideal braking force distribution line, so that the front / rear simultaneous locking characteristic is obtained. It is necessary to instantaneously perform this operation, that is, braking and fastening of the electronic control coupling 11.

  Here, as a first proposal for instantaneously engaging the brake and the electronic control coupling 11, as shown in FIG. 5 (a), the front wheel mechanical braking force and the rear wheel regenerative braking force are first generated, Next, consider a sequence for fastening the electronic control coupling 11. In this sequence, the braking force distribution point changes from point o → point B → point C.

  Specifically, there are the following two stages.

  (1) Since the front wheel mechanical brake braking force and the rear wheel regenerative braking force are increased simultaneously, the transition from point o to point B is made.

  (2) Since the electronic control coupling 11 is fastened, the point B changes to the point C.

  At the stage of (1), at point B, the rear wheel braking force is generated to near the braking force limit of the rear wheel even on a high μ road, so that the lateral force of the rear wheel is reduced, and an oversteer tendency occurs. Stability deteriorates.

  Further, for example, when the road surface μ becomes small and the square opqr becomes the square op′q′r ′, the braking force of the rear wheel is outside the rear wheel braking force limit line, so the rear wheel is locked. As a result, the yaw stability deteriorates, and the possibility of spin, and thus off-road departure increases.

  Next, as a second method of instantaneously increasing the braking force and opening the electronic control coupling 11, as shown in FIG. 5B, the electronic control coupling 11 is first completely fastened, and then Consider a sequence that increases the braking force. In this sequence, the braking force distribution point changes from point o to point C.

  Specifically, there are the following two stages.

  (1) The electronically controlled coupling 11 is fastened to the direct-coupled four-wheel drive state. However, since the braking force is 0, the point o remains.

  (2) Since the front-wheel mechanical brake braking force and the rear-wheel regenerative braking force are increased simultaneously, the movement point o changes to the point C on the ideal braking force distribution line.

  Since it is on the ideal braking force distribution line in the direct-coupled four-wheel drive state immediately after the start of braking, the lateral force of the rear wheels can be secured more than plan 1, and the operability is good.

  For example, when the road surface μ becomes small and the quadrangle opqr becomes a quadrangle op ″ q ″ r ″, the front wheel and the rear wheel are simultaneously locked at the point q ″.

  If these two plans are compared, it is clear that the second plan with good maneuverability is selected.

  Next, consider a case where the vehicle enters a low μ road during regenerative braking in a directly connected four-wheel drive state.

  It is assumed that the vehicle enters a low μ road in a braking state at point C. As described above, the braking force limit on the low μ road is as small as a square op "q" r "as shown in Fig. 6. At this point, the wheel is locked simultaneously in the front and rear. Even if the lock is avoided, if the road surface μ is further lowered, it will fall into the simultaneous forward and backward lock again.

  In other words, when the wheel locking tendency is detected, the total braking force is reduced and the electronic control coupling 11 is instantaneously released, and a transition is made to the braking force distribution line in (2) normal braking. As a result, since the transition from the point C to the point D is made, the front wheel braking force can be understood by comparing the point B which is the distribution of the rear wheel regenerative braking force and the point D after the transition, before the wheel lock is detected. Is increased and the rear wheel regenerative braking force is decreased. At this time, the deceleration is reduced from α to β.

  Here, as a first method of instantaneously reducing the braking force and opening the electronic control coupling 11, the electronic control coupling 11 is first opened as shown in FIG. Consider a sequence that reduces power. In this sequence, the braking force distribution changes from point C → point B → point D.

  Specifically, there are the following two stages.

  (1) Since the dispersion of the braking force due to the coupling fastening force is eliminated by opening the electronic control coupling 11, the transition from the point C to the point B is made.

  (2) Since the front wheel braking force and the rear wheel regenerative braking force are increased simultaneously, the transition from point B to point D is made.

  This (1) results in a longer time outside the square op ″ q ″ r ″, which is the low μ braking force limit.If disturbance is applied to the vehicle during this time, it is difficult to maintain yaw stability. In the worst case, it is very dangerous that a departure from the road can occur.

  Next, as a second method of instantaneously reducing the braking force and opening the electronic control coupling 11, the braking force is first reduced as shown in FIG. Consider a sequence that releases. In this sequence, the braking force distribution point changes from point C → point E → point D.

  Specifically, there are the following two stages.

  (1) Since the front wheel braking force and the rear wheel regenerative braking force are increased simultaneously, the transition from point C to point E is made.

  (2) Since the dispersion of the braking force due to the coupling fastening force is eliminated by opening the electronic control coupling 11, the transition from the point E to the point D is made.

  That is, since it remains in the square op "q" r "which is the low μ braking force limit, it is easy to maintain yaw stability and the operability is good.

  If these two plans are compared, it is clear that the second plan is selected.

  From the above, in the sequence for increasing the braking force as regenerative braking in the direct-coupled four-wheel drive state at the start of braking, the second proposal, “First, electronically coupled coupling and then adjust braking force” select.

  In addition, in the sequence for reducing the braking force when entering a low μ road by regenerative braking in the state of direct-coupled four-wheel drive, the second plan is “First adjust braking force, then electronic control. It is assumed that “sequence for releasing coupling” is selected.

  The specific braking force adjustment and the operation of the electronic control coupling 11 selected from the above two plans will be described with reference to FIGS.

  FIG. 8 is a time chart of the above results from the start of braking on the high μ road to the entry and stop of the low μ road. Also, the braking force distribution at that time is shown in FIG.

  First, the braking start is detected in (1) of FIG. The start of braking can be detected, for example, by measuring a brake switch signal or master cylinder pressure.

  After detecting the start of braking, first, the electronic control coupling 11 is fastened. Then, in order to start braking in (2) of FIG. 8, it raises according to a driver | operator's request | requirement deceleration or request | requirement braking force. As a method for setting the required deceleration or the required braking force, for example, there is a method of setting by a map corresponding to the master cylinder pressure. The distribution of the front-wheel mechanical brake and the rear-wheel regenerative braking force is, for example, higher than the ideal braking force distribution when the electronically controlled coupling 11 is in an open state as indicated by point B in FIG. It is set to fall within the range below the wheel braking force limit line. At this time, since the electronic control coupling 11 is engaged and is in a direct-coupled four-wheel drive state, the actual braking force distribution before and after is point C.

  The reason is that it is better to set the regenerative braking force of the rear wheel so that it does not exceed the braking force limit line on the high μ road surface when the electronic control coupling 11 is in the open state. is there. If, for example, the point X is exceeded that exceeds the braking force limit line on the high μ road surface, if the electronically controlled coupling 11 breaks down and suddenly opens, the transition from point C to point X causes the rear of the high μ road surface. The wheel locks. This is because if the rear wheel is locked as described above, the yaw stability deteriorates, and in the worst case, there may be a deviation from the road.

  Next, for example, as a result of entering a low μ road, a wheel lock tendency is detected in (3) of FIG. The wheel lock tendency can be detected from, for example, the difference between the pseudo vehicle speed and the wheel speed obtained from the wheel speed and acceleration, the wheel slip ratio, the wheel acceleration, and the like. Since various methods are already known, they are omitted here.

  Detection of the wheel lock tendency in (3) of FIG. 8 is point C in FIG. From point C, point D, which is the intersection of the front wheel braking force limit line at that time and the normal braking force distribution line, is found. As an example of how to obtain the point D, a map may be prepared in advance.

  If the point D is obtained, the deceleration at the point D is obtained. The braking force of the front wheels is increased while the deceleration feedback is performed with the obtained deceleration as a target, and the regenerative braking force of the rear wheels is decreased.

  Since the road surface μ is not constant, there is a possibility that even if the road surface μ transitions to the point D, the road surface μ tends to be further locked. In that case, what is called ABS control may be performed.

  In the above description, the rear wheel braking force when the point B, that is, the electronically controlled coupling 11 is opened, is all regenerative braking force. However, a part of the rear wheel braking force may be borne by the braking force of the mechanical brake. .

Claims (4)

A first drive wheel that is one of the front and rear wheels and is always driven; a second drive wheel that is the other of the front and rear wheels and is driven as necessary;
A first power source for supplying power to the first drive wheel;
A second power source that supplies power to the second drive wheel and regenerates by receiving power supplied from the second drive wheel;
A clutch mechanism provided between the first drive wheel and the second drive wheel and capable of changing a mechanical connection state between the first drive wheel and the second drive wheel from an open state to a fully engaged state; In a regenerative braking force control device for a hybrid four-wheel drive vehicle equipped with
During regenerative braking, when the clutch mechanism is in an open state, the braking force of the second drive wheel is set larger than the ideal braking force distribution.
A regenerative braking force control device for a hybrid four-wheel drive vehicle. In the regenerative braking force control device for a hybrid four-wheel drive vehicle according to claim 1,
To start regenerative braking, the clutch mechanism is in a fully engaged state and is in a directly connected four wheel drive state.
A regenerative braking force control device for a hybrid four-wheel drive vehicle. The regenerative braking force control device for a hybrid four-wheel drive vehicle according to claim 2,
When regenerative braking is started, the clutch mechanism is fastened and the four-wheel drive state is set, and the braking force of the first and second drive wheels is adjusted.
A regenerative braking force control device for a hybrid four-wheel drive vehicle. The regenerative braking force control device for a hybrid four-wheel drive vehicle according to claim 2,
During regenerative braking, the tendency of the wheels to lock is detected. If it is determined that the wheels are locked, the clutch mechanism is released after adjusting the braking force of the first and second drive wheels. State
A regenerative braking force control device for a hybrid four-wheel drive vehicle.

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