JP2007237828A - Hill start controller for electric motor type four-wheel-drive-vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To propose hill start control for early eliminating the roll back of an electric motor type four-wheel-drive-vehicle in hill start. <P>SOLUTION: In hill start performed by releasing a brake pedal at t1, and pressing on a gas pedal at t2, the delay control of the increase in an engine output is performed so that the increase in the driving force of front wheels being engine driven wheels can be delayed against the pressing-on of the gas pedal as shown by Tf in the roll back when a speed VSP is generated in a backward direction. When the front wheel driving force (engine torque) is tried to increase as a dashed line Tfo according to the pressing-on of the gas pedal, the front wheel driving force is decreased as shown by a real line Tfo due to the driving slip of the front wheels, and the roll back is not eliminated until t4. The delay control of the engine output increase is performed to prevent the driving slip of the front wheels so that the front wheel driving force can be maintained so as to be large as shown by Tf, and that the roll back can be eliminated earlier at t3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric motor type four-wheel drive vehicle in which one of front and rear wheels is driven by a main power source such as an internal combustion engine (engine) and the other wheel is driven by power from an electric motor, and in particular, the vehicle is driven on a slope. The present invention relates to a hill start control technology for quickly converging that a vehicle rolls back in a direction opposite to the start direction when starting.

  In addition to main drive wheels driven by power from a main power source such as an internal combustion engine (engine), an electric motor responding to power generated by a generator coupled to the main power source and a drive system between the main drive wheels Conventionally, as an electric motor type four-wheel drive vehicle including an electric motor drive wheel driven by the motive power of, for example, the one described in Patent Document 1 is known.

In this vehicle, the front two wheels (or the rear two wheels) are driven by an engine, the rear two wheels (or the front two wheels) can be driven by an electric motor via a clutch, and the vehicle is dedicated to four-wheel drive power generation coupled to the engine. The electric motor is directly driven by the power from the machine.
Briefly described, the main drive wheel driven by the engine is likely to drive slip, or the generator is loaded with the surplus torque of the engine when the drive slip occurs, and the electric motor is driven with the generated power, By transmitting the power from the electric motor to the electric motor drive wheels through the clutch fastened at this time, motor four-wheel drive is enabled.

Note that the clutch is basically released when it is not driven by four wheels, so that the electric motor drive wheels do not drag the electric motor to avoid deterioration of fuel consumption. Since the drive wheels are likely to cause drive slip and are preferably in the four-wheel drive state, the clutch is kept in the engaged state.
When starting, a load corresponding to the amount of depression of the accelerator pedal is applied to the generator to generate power, and the electric motor is driven by the electric power to start in a four-wheel drive state.

As a starting control technique for such an electric motor type four-wheel drive vehicle, as described in Patent Document 2, the transmission between the engine and the main drive wheel can generate the rotational speed of the generator driven by the engine. There has also been proposed a technique in which an electric motor-driven wheel is driven by electric power from a generator to achieve a four-wheel drive state only when the low-side gear ratio is high.
JP 2002-218605 A JP 2000-318473 A

  The above-mentioned start control of the electric motor type four-wheel drive vehicle uses the driving force of the main drive wheel to the maximum while driving the electric motor drive wheel with the motor under the condition that it cannot start only by driving the main drive wheel. The main purpose is to enable the vehicle to start under the driving conditions.

  By the way, when starting on a slope, especially when starting on a low μ road where the level of the main drive wheel is higher than that of the electric motor drive wheel in a direction in which the main drive wheel is forward in the traveling direction, the wheel of the electric motor drive wheel. As the load increases, the wheel load of the main drive wheel decreases, the road surface μ is small, the grip force of the main drive wheel decreases, and a drive slip occurs.

  This slip significantly reduces the driving force of the main drive wheels, and when the vehicle rolls back in the direction opposite to the starting direction during the starting operation of releasing the brake pedal and then depressing the accelerator pedal when starting on a slope, Even with the driving force assist, this rollback cannot be quickly eliminated.

As shown in Fig. 5, the brake pedal is released at the instant t1, and the accelerator pedal is depressed at the instant t2 to start the vehicle forward in the direction in which the main drive wheels (front wheels) are ahead in the traveling direction. As will be apparent, the following is added when the vehicle rolls back after instant t1.
If the main driving wheel (front wheel) does not slip, the driving force Tfo of the main driving wheel (front wheel) rises as indicated by the alternate long and short dash line from the moment when the accelerator pedal is depressed t2, and the driving force Tro of the electric motor driving wheel (rear wheel) While being able to quickly resolve the rollback,
When the drive slip occurs on the main drive wheel (front wheel), the driving force Tfo of the main drive wheel (front wheel) generated from the instant t2 when the accelerator pedal is depressed becomes small as shown by the solid line, and it is resolved if the rollback does not reach instant t4. Can not do it.

Even if the vehicle is equipped with a trunk control device that reduces the driving force to the wheel and suppresses the driving slip during the driving slip of the wheel, the trunk that reduces the engine output for suppressing the driving slip of the main driving wheel. The control of the main drive wheel is performed after the drive slip of the main drive wheel occurs. During the initial drive slip of the main drive wheel before the start of the trunk control, the recovery of the drive force of the main drive wheel is I can't hope.
Therefore, even in a car equipped with a trunk control device, there arises a problem that the above-described rollback elimination delay occurs.

  The present invention is based on the fact that the rollback cancellation delay is caused by the drive slip of the main drive wheel, so that the drive slip including the initial drive slip of the main drive wheel does not occur. An object of the present invention is to propose a slope start control device for an electric motor type four-wheel drive vehicle capable of solving the above-mentioned problem relating to the rollback elimination delay.

For this purpose, the slope start control device for an electric motor type four-wheel drive vehicle according to the present invention has the following configuration as described in claim 1.
First of all, the premise of the electric motor type four-wheel drive vehicle is
A main drive wheel driven by power from a main power source;
An electric motor drive wheel driven by power from an electric motor that responds to the generated power of a generator coupled to a drive system between the main power source and main drive wheels.

The present invention, in such an electric motor type four-wheel drive vehicle,
A configuration in which an increase in the output of the main power source is delayed with respect to the depression of the accelerator pedal while the vehicle rolls back in a direction opposite to the starting direction when the accelerator pedal is depressed after releasing the brake pedal of the vehicle. It is characterized by that.

According to such a slope start control device of the present invention, during the rollback, the increase in the output of the main power source is delayed with respect to the depression of the accelerator pedal. Therefore, during this time, the main drive wheels driven by the power from the main power source Drive slip is suppressed,
Rollback can be quickly eliminated by effectively utilizing the driving force of the main drive wheels during rollback and by cooperating with the drive force of the motor drive wheels as necessary.

Hereinafter, embodiments of the present invention will be described in detail based on examples shown in the drawings.
FIG. 1 schematically shows a drive system of an electric motor type four-wheel drive vehicle having a slope start control device according to an embodiment of the present invention. In this embodiment, the vehicle is driven by left and right front wheels 1L and 1R as main power. A front engine / front wheel drive vehicle (F / F vehicle) driven by the engine (internal combustion engine) 2 as a base vehicle is used as a base vehicle, and the left and right rear wheels 3L, 3R are electric motors as required. This is a so-called electric motor type four-wheel drive vehicle that can be driven by the vehicle.

  The engine 2 is drive-coupled to the left and right front wheels (main drive wheels) 1L and 1R via a transaxle in which the automatic transmission 5 and the differential gear device 6 are configured as an integrated unit, and the output torque of the engine 2 is connected to the automatic transmission 5 and the differential. It is assumed that the vehicle is transmitted to the left and right front wheels 1L and 1R via the gear device 6 and used for traveling of the vehicle.

Next, the rear wheel drive system by the electric motor 4 will be described. This is basically the same as that in the electric motor type four-wheel drive vehicle described in Patent Document 1.
In other words, it has a dedicated generator 8 driven via an endless belt 7 by a part of the output torque of the engine 2, and this generator 8 is rotated at a rotational speed obtained by multiplying the rotational speed of the engine 2 by the belt pulley ratio. The power generation load corresponding to the field current Ifh adjusted by the four-wheel drive controller 9 is applied to the engine 2 to generate electric power corresponding to the load torque.

The electric power generated by the generator 8 is supplied to the rear wheel drive motor 4 through the relay 11 through the power line 10.
Relay 11 can also be used to shut off the power line 10 when the generator 8 is out of control by a command from the controller 9 or when the controller 9 does not apply a load to the generator 8 because rear wheel drive is not required. Since there is some power generation by the permanent magnet, the power line 10 is cut off so as not to be supplied to the motor 4.

  The drive shaft of the rear wheel drive motor 4 is coupled to the differential gear device 14 of the rear wheels (electric motor drive wheels) 3L and 3R via the speed reducer 12 and the clutch 13 incorporated therein, and the output torque of the motor 4 is If the gear 13 is increased by the reduction gear 12 and the clutch 13 is engaged, this increased torque is distributed and output to the left and right rear wheels 3L, 3R by the differential gear device 14.

The four-wheel drive controller 9 also controls the engagement / disengagement of the clutch 13 and the rotation direction / drive torque of the electric motor 4.
In controlling the electric motor 4, the controller 9 controls the motor driving torque by adjusting the field current Ifm to the electric motor 4, and controls the motor rotation direction by the direction of the field current Ifm.

In addition to inputting the signal from the four-wheel drive switch 21 to the four-wheel drive controller 9 for performing the above-described control of the motor 4, the generator 8, the relay 11, and the clutch 13,
Signals from the wheel speed sensor group 22 for individually detecting the wheel speeds (front wheel speeds) V _WFL and V _WFR of the left and right front wheels 1L and 1R and the wheel speeds (rear wheel speeds) V _WRL and V _WRR of the left and right rear wheels 3L and 3R When,
A signal from the motor rotation sensor 23 for detecting the rotational speed Nm of the rear wheel drive motor 4,
A signal from the inhibitor switch 24 that detects whether the selection range RNG (travel direction by the driver, start direction command) of the automatic transmission 5 is the forward (D) range or the reverse (R) range;
A signal from the accelerator opening sensor 25 that detects the accelerator pedal depression amount APO is input.

The four-wheel drive controller 9 determines whether the four-wheel drive is necessary and automatically performs the motor four-wheel drive while the driver is turning on the four-wheel drive switch 21 as described later.
While the driver is turning off the four-wheel drive switch 21, the two-wheel drive by only the engine drive of the front two wheels is continuously performed.
The four-wheel drive controller 9 further obtains a target engine torque tTe for later-described slope start control targeted by the present invention, and the output torque of the engine 2 matches the target engine torque tTe by throttle opening control or the like. It is assumed that control is also performed.

Hereinafter, basic four-wheel drive control performed by the controller 9 will be described.
First, by the process shown in FIG. 2, surplus torque of the engine 2 that causes the driving (acceleration) slip of the front wheels 1L and 1R that are the main driving wheels (engine driving wheels) is calculated.
In step S1, from the average front wheel speed Vwf that can be obtained from the front wheel speeds V _WFL and V _WFR detected by the wheel speed sensor group 22, the average after that that can be obtained from the rear wheel speeds V _WRL and V _WRR that are also detected by the wheel speed sensor group 22 By subtracting the wheel speed Vwr, the acceleration slip amount ΔVf of the left and right front wheels 1L and 1R which are the main drive wheels is obtained.

In the next step S2, it is determined whether or not an acceleration slip has occurred depending on whether or not the acceleration slip amount ΔVf of the left and right front wheels 1L and 1R is a predetermined value, for example, 3 km / h or more.
When it is determined that the acceleration slip amount ΔVf is less than 3 km / h, the control is terminated as it is because no acceleration slip has occurred and there is no surplus of engine output.

When an acceleration slip is determined in step S2 that the acceleration slip amount ΔVf is 3 km / h or more, it is necessary to suppress the surplus torque of the engine that generates the acceleration slip of the front wheels 1L and 1R, that is, the acceleration slip in step S3. The absorption torque T (ΔVf) is calculated by T (ΔVf) = K1 × ΔVf.
K1 is a gain obtained through experiments or the like.

In the next step S4, the current load torque Tg of the generator 8 is obtained. In step S5, the current generator load torque Tg and the surplus torque T (ΔVf) are added together to obtain the target power generation load of the generator 8. Find the torque Th.
In step S 6, the motor overspeed vehicle speed (for example, the vehicle speed VSP that can be obtained from the wheel speeds V _WFL , V _WFR , V _WRL , V _WRR is the lower limit value of the vehicle speed range in which the motor 4 is over-rotated when the clutch 13 is engaged) Check if it is less than 30km / h).

If the vehicle speed VSP is equal to or higher than the motor overspeed vehicle speed, the motor 4 is overrotated and its durability is lowered. Therefore, the control is terminated as it is so that the four-wheel drive is not performed, but the vehicle speed VSP is less than the motor overspeed vehicle speed. Then, in step S7, the maximum load torque Thmax of the generator 8 is obtained.
Next, in step S8, it is checked whether or not the target power generation load torque Th of the generator 8 is equal to or greater than the maximum load torque Thmax. If so, in step S9, Th = Thmax is set to Thmax, which is a limit that can achieve the target power generation load torque Th. If Th <Thmax, the control is terminated and the target power generation load torque Th is set to the value obtained in step S5.

In FIG. 2, the method of obtaining the target power generation load torque Th of the generator 8 only when the engine drive wheels 1L and 1R generate an acceleration slip has been described.
Even if the engine drive wheels 1L and 1R may be accelerated and slipped, or when the engine drive wheels 1L and 1R are in a low speed state below a predetermined level, the target power generation load torque Th of the generator 8 is driven in order to realize the four-wheel drive of the electric motor. According to

The controller 9 controls the generator 8 and the motor 4 by the control program of FIG. 3 based on the target power generation load torque Th of the generator 8 obtained as described above.
In step S11, it is checked whether or not there is a power generation request depending on whether or not the target power generation load torque Th of the generator 8 is positive.
If there is no power generation request, the control is terminated so that the power generation load of the generator 8 is not applied to the engine 2 and the clutch 13 is in a released state.
If there is a power generation request, in step S12, the target motor field current Ifm is calculated from the motor rotation speed Nm based on the planned map, and this is commanded to the motor 4.
Although not shown, at the same time, when the input / output rotational speeds of the clutch 13 coincide with each other, the clutch 13 is engaged so that the rotation of the motor 4 can be transmitted to the rear wheels 3L and 3R.

Here, as shown in step S12, the target motor field current Ifm with respect to the rotational speed Nm of the motor 4 is set to a constant predetermined current value when the motor rotational speed Nm is equal to or smaller than the predetermined rotational speed, and the motor rotational speed beyond that is determined. When the number is reached, the field current Ifm of the motor 4 is reduced by a known field weakening control method.
The reason for this is that when the motor 4 rotates at a high speed, the motor torque decreases due to the increase of the motor back electromotive force E. Therefore, when the motor rotation speed Nm exceeds a predetermined value, the field current Ifm of the motor 4 is decreased and reversed. This is because the current flowing through the motor 4 is increased by reducing the electromotive voltage E so that the required motor torque Tm can be obtained.

Next, in step S13, the back electromotive force E of the motor 4 is calculated from the target motor field current Ifm obtained as described above and the rotational speed Nm of the motor 4 based on a predetermined map.
Further, in step S14, a corresponding target motor torque Tm is calculated based on the power generation load torque Th described above,
In step S15, a target armature current Ia that is a function of the target motor torque Tm and the target motor field current Ifm is calculated.
Thereafter, in step S16, the target voltage V of the generator 8 is obtained from the target armature current Ia, the total resistance R, and the counter electromotive voltage E by calculation of V = Ia × R + E.
The controller 9 feedback-controls the field current Ifh of the generator 8 so that the generated voltage of the generator 8 becomes the target voltage V thus obtained.

  In addition to the control of the generator 8, the four-wheel drive controller 9 commands the target engine torque tTe determined by the control program shown in FIG. 4 to the engine 2 when starting on a slope, and the engine 2 is controlled by, for example, throttle opening control. The engine 2 is controlled so that the torque becomes the target engine torque tTe.

  The control program shown in FIG. 4 is started when the vehicle is ready to start on a hill. First, in step S21, it is checked whether or not the brake pedal is released as shown in the instant t1 in FIG. It is checked whether or not the vehicle has started to roll back when the pedal is released. In step S3, it is checked whether or not the accelerator pedal has been depressed as at the instant t2 in FIG.

In the rollback start determination in step S22, it is detected from the signal from the inhibitor switch 24 whether it is a front start command or a rear start command, and then the wheel speed (front wheel speed) V _WFL , V of the left and right front wheels 1L, 1R. _{Based on} the wheel speed (rear wheel speed) V _WRL and V _WRR of the left and right rear wheels 3L and 3R, the actual movement start and the actual movement direction of the vehicle are detected, and the actual movement direction is determined by a signal from the inhibitor switch 24. It can be determined that the rollback has started when the reverse of the possible start direction command.

  While it is determined in step S21 that the brake pedal has not yet been released, rollback does not occur, and the slope start control (engine output increase delay control) according to the present invention for eliminating this early is unnecessary. From step S25, the control proceeds to step S25 to cancel the engine output increase delay control, so that the normal engine output control corresponding to the accelerator opening APO is performed to obtain the target engine torque tTe. To

If it is determined in step S21 that the brake pedal has been released (instant t1 in FIG. 5), it is checked in step S22 whether or not rollback has been started.
If the rollback is not started, the slope start control (engine output increase delay control) according to the present invention is not required to eliminate this early, so the control proceeds to step S25 and the target engine is controlled by normal engine output control. Torque tTe is obtained and commanded to engine 2 in step S27.

If it is determined in step S22 that the rollback has started, it is checked in step S23 whether or not the accelerator pedal has been depressed as at the instant t2 in FIG.
While the accelerator pedal is not depressed, the engine output torque is at the minimum value, and there is no room for the slope start control (engine output increase delay control) according to the present invention. Wait until you have stepped on.

If it is determined in step S23 that the accelerator pedal has been depressed (instant t2 in FIG. 5), the control proceeds to step S24, where it is checked whether the rollback is immediately before the end.
Immediately before the end of the rollback, it can be determined when the electric motor 4 is about to rotate in the starting direction commanded by the driver from the state where the electric motor 4 is rotating in the rollback direction. It is good to judge this from the rotation speed change of 4.

Until it is determined in step S24 that the rollback has just ended, that is, during the rollback, the control proceeds to step S26, and the hill start control (engine output increase delay control) according to the present invention for eliminating the rollback early is performed. Do the following:
That is, as shown by Tf in FIG. 5, the target engine torque tTe is determined so as to be as large as possible within a range where no driving (acceleration) slip occurs, and this is commanded to the engine 2 in step S27. Thus, the engine output torque is matched with this target value tTe.

It should be noted that the front wheel driving force Tf as large as possible within the range in which the driving (acceleration) slip of the front wheels 1L and 1R does not occur is the braking operation force, the front wheel speeds V _WFL and V _WFR, and the rear wheel speeds V _WRL and V just before the vehicle stops. _The road surface μ can be obtained from the tendency of the _WRR to decrease, and can be easily estimated by calculating the maximum front wheel driving force Tf obtained under this road surface μ at the time of starting.

According to the engine output control in step S26 and step S27, the engine output is not uniquely determined by the accelerator opening APO, and is limited to a value that does not cause the front wheels 1L and 1R to slip, resulting in the engine output. Is delayed with respect to the depression operation of the accelerator pedal after the instant t2 in FIG.
Due to the delay in the engine output increase, the front wheels 1L and 1R, which are the main drive wheels, do not cause a drive slip when starting on a slope, and the driving force of the front wheels 1L and 1R is kept at the maximum value as indicated by Tf in FIG. By cooperating with the rear wheel driving force Tr (same as Tro) by the electric motor 4, the rollback of the vehicle can be eliminated at an early stage (at instant t3 in FIG. 5).

  When it is determined in step S24 that the rollback is about to end (instant t3 in FIG. 5), the control is sequentially advanced to step S25 and step S27 to return to normal engine output control.

According to this embodiment, when the vehicle is rolled back in the direction opposite to the starting direction when the accelerator pedal is depressed after releasing the brake pedal (momentary t2 to t3 in FIG. 5), the output increase of the engine 2 is increased. To delay the accelerator pedal depression,
During this time, the driving slip of the front wheels 1L, 1R driven by the power from the engine 2 is suppressed, and the driving force Tf of the front wheels 1L, 1R is effectively used to the maximum during rollback, and if necessary, by the motor 4 By cooperating with the driving force Tr of the driven rear wheels 3L and 3R, the rollback can be quickly eliminated.

Further, when the electric motor 4 is rotating in the rollback direction, it is determined that the time immediately before the end of the rollback is reached when it is going to rotate in the starting direction commanded by the driver. Since the output rise delay control was canceled and returned to the normal control,
The output increase delay control of the engine 2 is continued even after the end of the rollback, and a situation in which the driving performance of the vehicle is hindered can be avoided.

Furthermore, it is better to predict the timing at which the electric motor 4 is going to rotate in the start direction commanded by the driver from the state in which the electric motor 4 is rotating in the rollback direction from the change in the rotational speed of the electric motor 4,
In this case, it is possible to cope with a change in rollback acceleration due to a change in slope of the slope after starting, which is very advantageous.

It is a basic diagram which shows the drive control system of the electric motor type | mold four-wheel drive vehicle provided with the slope start control apparatus which becomes one Example of this invention. It is a flowchart which shows the engine surplus torque calculation program which the four-wheel drive controller in the drive control system of the motor four-wheel drive vehicle performs. It is a flowchart which shows the generator control program which the four-wheel drive controller performs. It is a flowchart which shows the target engine torque calculation program for the slope start which the same 4 wheel drive controller performs. It is an operation | movement time chart of the Example.

Explanation of symbols

1L front left wheel (main drive wheel)
1R right front wheel (main drive wheel)
2 Engine (Main power source)
3L left rear wheel (electric motor drive wheel)
3R right rear wheel (electric motor drive wheel)
4 Rear wheel drive motor (electric motor)
5 Automatic transmission 6 Differential gear device 7 Endless belt 8 Generator 9 Four-wheel drive controller
10 Power line
11 Relay
12 Reducer
13 Clutch
14 Differential gear unit
21 Four-wheel drive switch
22 Wheel speed sensors
23 Motor rotation sensor
24 Inhibitor switch
25 Accelerator position sensor

Claims (3)

A main drive wheel driven by power from a main power source;
In an electric motor type four-wheel drive vehicle comprising an electric motor drive wheel driven by power from an electric motor that responds to power generated by a generator coupled to a drive system between the main power source and the main drive wheel,
While starting the vehicle by releasing the brake pedal of the vehicle and then depressing the accelerator pedal, while the vehicle rolls back in the direction opposite to the starting direction, the output increase of the main power source is delayed with respect to the depression of the accelerator pedal. A hill start control device for an electric motor type four-wheel drive vehicle, characterized in that it is configured. In the slope start control device for an electric motor type four-wheel drive vehicle according to claim 1,
The electric motor is configured to stop the output increase delay control of the main power source when the electric motor is going to rotate in the starting direction from the state rotating in the rollback direction. A four-wheel drive vehicle slope start control device. The slope start control device for an electric motor type four-wheel drive vehicle according to claim 2,
An electric motor type four-wheel drive configured to predict a timing at which the electric motor starts to rotate in the starting direction from a state in which the electric motor rotates in the rollback direction from a change in the rotational speed of the electric motor. Vehicle slope start control device.

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