JP2010149559A - Engine start control device for hybrid vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely generate a slip even when the slip of a second clutch for engine start is disabled because of low input torque of an automatic transmission in starting an engine. <P>SOLUTION: On starting the engine with low transmission input torque, a friction element on the side released in downshifting is used as a second clutch, and its torque capacity tTc2 is reduced at a predetermined gradient. In this process, torque capacity tTon of a friction element on the side engaged in downshifting is increased so that the automatic transmission advances downshifting halfway. Therefore, even if the transmission input torque is low, the second clutch can slip when its torque capacity is lowered. At a slip occurrence time t2, engagement of a first clutch is started by increase in the torque capacity tTc1, and a motor is controlled so that its number of revolutions Nm becomes an engine starting target value. The engine is cranked by the motor rotation speed control and the start of engagement of the first clutch, and the engine start is completed at t3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention includes an engine and a motor as a power source, a first clutch is interposed between the engine and the motor, and a second clutch is interposed between the motor and the drive wheel. The second clutch is provided between the motor and the drive wheel. The present invention relates to an engine start control device for a parallel type hybrid vehicle in which a shift friction element in an automatic transmission is diverted.
In particular, in the electric travel mode in which the first clutch is released and the second clutch is engaged, the first clutch is advanced while the second clutch is slipped, and the engine is started by the power from the motor. This invention relates to an engine start control device capable of reliably generating the slip of the second clutch to compensate for the mode switch (engine start) even when the transmission input torque is small during the mode switch to the hybrid travel mode. It is.

The hybrid drive device used in the hybrid vehicle as described above has already been proposed in Patent Document 1 by the applicant of the present application.
This hybrid drive unit can select the electric travel (EV) mode only by the power from the motor / generator by releasing the first clutch and engaging the second clutch, and both the first clutch and the second clutch are engaged. By doing so, it is possible to select a hybrid running (HEV) mode by power from both the engine and the motor / generator.

Therefore, when switching the mode from the electric drive (EV) mode to the hybrid drive (HEV) mode, it is necessary to start the engine, and conversely, when switching the mode from the hybrid drive (HEV) mode to the electric drive (EV) mode. The engine must be stopped.
When starting the engine at the time of switching the mode from the former EV mode to the HEV mode, the engine is started with the power from the motor / generator by engaging and engaging the first clutch while slipping the second clutch.

By the way, as an engine start control technology at the time of mode switching from the EV mode with the engine start to the HEV mode, Patent Document 1,
An engine start control technique is disclosed as follows when downshifting of an automatic transmission is required at the time of mode switching.

In other words, when the accelerator pedal depression is issued, the EV → HEV mode switching command accompanied by the engine start is issued, and then the automatic transmission downshift command is issued.
First, the first clutch is brought into a state immediately before the start of engagement, and when the set time has elapsed, the motor / generator torque is increased for starting the engine.
As the motor / generator torque increases, the second clutch starts to slip and the motor / generator rotational speed increases, and the slip amount of the second clutch (the increase amount of the motor / generator rotational speed) reaches a predetermined value. Then, the first clutch is started to be engaged and the engine is started by cranking.

At this time, the downshift release side shifting friction element that is changed from the engaged state to the released state at the time of downshift is diverted as the second clutch, and the transmission torque capacity is reduced to the torque capacity for the second clutch,
The downshift engagement side shifting friction element that is brought into the engaged state from the released state during the downshift is brought into a state immediately before the engagement,
When it is determined that the downshift has ended due to the release progress of the release-side shift friction element during downshift and the engagement progress of the engagement-side shift friction element during downshift, the release-side shift element during downshift is completely released. At the same time, the downshift is completed by completely engaging the engagement-side shift friction element during downshifting.
JP 2007-261498 A

However, in the engine start control described in Patent Document 1, when the transmission input torque is small, even if the downshift release side shift friction element as the second clutch is reduced in torque capacity as described above, it does not slip as planned. Sometimes
In this case, the motor / generator cannot be rotated up for starting the engine, and as a result, the cranking rotation speed of the engine is insufficient, which may make it difficult or impossible to start the engine.

  This concern is not only when downshifting of the automatic transmission is required at the same time when EV → HEV mode switching (engine start), but also this shift request does not occur, and EV → HEV mode switching (engine start) is independent. Thus, the same occurs even when the downshift is performed due to a decrease in the torque capacity of the release side shifting friction element (second clutch).

In the present invention, even when the transmission input torque is small during the engine start process for EV → HEV mode switching, when the downshift release side shift friction element as the second clutch is reduced in torque capacity as described above. Surely produced the planned slip,
The motor can be reliably rotated and rotated for starting the engine, and as a result, the above-mentioned concern is made so that the engine is not difficult to start without being deficient in cranking rotational speed. An object of the present invention is to propose an engine start control device for a hybrid vehicle that can wipe out the engine.

For this purpose, the engine start control device for a hybrid vehicle according to the present invention is configured as described in claim 1.
First of all, to explain the prerequisite hybrid vehicle,
With engine and motor as power source,
A first clutch is interposed between the engine and the motor, and a second clutch is interposed between the motor and the drive wheel. The second clutch is responsible for power transmission in the automatic transmission inserted between the motor and the drive wheel. The variable speed friction element is used.

Such a hybrid vehicle can select the electric travel mode only by the power from the motor / generator by releasing the first clutch and engaging the second clutch.
By engaging both the first clutch and the second clutch, it is possible to select a hybrid travel mode based on power from both the engine and the motor.
When switching from electric drive mode to hybrid drive mode,
While the electric travel mode is selected, the first clutch is engaged and advanced while slipping the second clutch, whereby the engine can be started with the power from the motor and the mode can be switched to the hybrid travel mode.

The engine start control device of the present invention is configured such that the following downshift release side shift friction element control means and downshift engagement side shift friction element control means are provided for such a hybrid vehicle.
The former shift friction element control means at the time of downshift is during the downshift when the automatic transmission is shifted from the engaged state to the released state during the downshift of the automatic transmission during the mode switching from the electric travel mode with the engine start to the hybrid travel mode. The disengagement side shift friction element is used as the second clutch to reduce its transmission torque capacity.
The latter downshift engagement side shifting friction element control means includes a downshift engagement side that switches from the released state to the engaged state when the automatic transmission is downshifted while the transmission torque capacity of the downshift release friction component is reduced. The transmission torque capacity of the variable speed friction element is increased.

According to the engine start control device of the hybrid vehicle according to the present invention described above,
In order to increase the transmission torque capacity of the down-side engagement frictional element at the time of downshift, when the transmission torque capacity of the release-side transmission friction element at the time of downshift is used as the second clutch and the transmission torque capacity is reduced for engine start,
The automatic transmission advances half of the downshift by reducing the torque capacity of the release-side shift friction element during downshift and increasing the torque capacity of the engagement-side shift friction element during downshift, and the effective gear ratio is the current gear stage. And an intermediate gear ratio between the lower gear and the lower gear.

For this reason, even when the input torque of the automatic transmission is small during the mode switching (engine start process) from the electric travel mode to the hybrid travel mode,
When the release-side shift friction element at the time of downshift as the second clutch is reduced in torque capacity as described above, it surely causes the planned slip,
The motor can be reliably rotated for starting the engine, and as a result, the cranking rotational speed of the engine is not deficient, and the engine is not made difficult or impossible to start. Can dispel concerns.

Hereinafter, embodiments of the present invention will be described in detail based on examples shown in the drawings.
[Constitution]
FIG. 1 shows a power train of a front engine / rear wheel drive hybrid vehicle including a hybrid drive device incorporating an engine start control device according to an embodiment of the present invention, together with its control system,
1 is an engine as a power source, 2 is an automatic transmission, and 3 is a motor / generator as another power source.

  In the power train of the hybrid vehicle shown in FIG. 1, the automatic transmission 2 is arranged in tandem at the rear of the engine 1 in the vehicle longitudinal direction as in the case of a normal rear wheel drive vehicle, and the engine 1 (specifically, the crankshaft 1a) A motor / generator 3 is connected to a shaft 5 that transmits the rotation to the input shaft 4 of the automatic transmission 2.

The motor / generator 3 includes an annular stator 3a fixed in the housing and a rotor 3b disposed concentrically with a predetermined air gap in the stator 3a.
It acts as a motor (electric motor) or a generator (generator) according to the demand of the operating state, and is arranged between the engine 1 and the automatic transmission 2.
The motor / generator 3 passes through the shaft 5 and is attached to the center of the rotor 3b, and uses the shaft 5 as a motor / generator shaft.

The first clutch 6 is inserted between the motor / generator 3 and the engine 1, more specifically, between the motor / generator shaft 5 and the engine crankshaft 1a, and the engine 1 and the motor / generator 3 are connected by the first clutch 6. Combine in a detachable manner.
Here, the first clutch 6 is assumed to be capable of continuously changing the transmission torque capacity. For example, the first clutch 6 is a wet type engine that can change the transmission torque capacity by continuously controlling the clutch hydraulic oil flow rate and the clutch hydraulic pressure with a proportional solenoid. It consists of a plate clutch.

The motor / generator 3 and the automatic transmission 2 are directly connected to each other by the direct connection of the motor / generator shaft 5 and the transmission input shaft 4.
The automatic transmission 2 is similar to the well-known planetary gear type automatic transmission in its transmission mechanism, but the torque converter is excluded from this, and the motor / generator 3 is directly connected to the transmission input shaft 4 instead. It shall be combined.

The automatic transmission 2 will be briefly described below.
The automatic transmission 2 includes an output shaft 7 arranged in a coaxial butt relationship with the input shaft 4,
A front planetary gear set Gf, a center planetary gear set Gm, and a rear planetary gear set Gr are sequentially placed on the input / output shafts 4 and 7 from the engine 1 (motor / generator 3) side.
These are the main components of the planetary gear transmission mechanism in the automatic transmission 2.

The front planetary gear set Gf closest to the engine 1 (motor / generator 3) is a simple planetary gear comprising a front sun gear Sf, a front ring gear Rf, a front pinion Pf meshing with the front sun gear Sf, and a front carrier Cf rotatably supporting the front pinion. A gear set.
Next, the center planetary gear set Gm close to the engine 1 (motor / generator 3) includes a center sun gear Sm, a center ring gear Rm, a center pinion Pm meshing with the center sun gear Sm, and a center carrier Cm that rotatably supports the center pinion. A planetary gear set.
The rear planetary gear set Gr farthest from the engine 1 (motor / generator 3) includes a rear sun gear Sr, a rear ring gear Rr, a rear pinion Pr meshing with the rear sun gear Sr, and a rear planetary gear Cr that rotatably supports the rear pinion. Make a pair.

  Front brake Fr / B, input clutch I / C, high-and-low reverse clutch H & LR / C, direct clutch D / C, reverse as the transmission friction elements that determine the transmission path (speed stage) of the planetary gear transmission mechanism A brake R / B and a forward brake FWD / B are provided, and these are correlated with the above-described components of the planetary gear group Gf, Gm, Gr as follows to constitute a planetary gear transmission mechanism of the automatic transmission 2.

The front ring gear Rf is coupled to the input shaft 4, and the center ring gear Rm can be appropriately coupled to the input shaft 4 by the input clutch I / C.
The front sun gear Sf can be appropriately fixed to the transmission case 2a by the front brake Fr / B.
Front carrier Cf and rear ring gear Rr are coupled to each other, and center ring gear Rm and rear carrier Cr are coupled to each other.
The center carrier Cm is coupled to the output shaft 7, and the center sun gear Sm and the rear sun gear Sr can be coupled to each other by a high and low reverse clutch H & LR / C.

The rear sun gear Sr and the rear carrier Cr can be coupled by the direct clutch D / C, and the rear carrier Cr can be appropriately fixed to the transmission case 2a by the reverse brake R / B.
Further, the center sun gear Sm can be appropriately fixed to the transmission case 2a by the forward brake FWD / B.

  The power transmission train of the above planetary gear transmission mechanism is a selective transmission shown by the circles in Fig. 2 for six shift friction elements Fr / B, I / C, H & LR / C, D / C, R / B, and FWD / B. By engaging, it is possible to obtain the forward shift speed and the reverse shift speed of the first forward speed, the second forward speed, the third forward speed, the fourth forward speed, and the fifth forward speed.

A hybrid vehicle having the power train of FIG. 1 composed of the engine 1, the motor / generator 3 and the automatic transmission 2 described above is provided between the motor / generator 3 and a drive wheel coupled to the transmission output shaft 7. A second clutch is required that is detachably coupled,
In this embodiment, among the above-described six shift friction elements Fr / B, I / C, H & LR / C, D / C, R / B, FWD / B existing in the automatic transmission 2, The variable speed friction element responsible for power transmission is used as the second clutch.
Incidentally, the existing transmission friction element in the automatic transmission 2 used as the second clutch is originally capable of continuously changing the transmission torque capacity like the first clutch 6 described above.

In the following, the function for each driving mode of the power train described above with reference to FIG. 1 will be described.
In the power train of FIG. 1, when the electric travel (EV) mode used at low load and low vehicle speed including when starting from a stopped state is required,
The first clutch 6 is released, and the automatic transmission 2 is put into a power transmission state by engaging the second clutch (IC, H & LR / C, D / C, etc.).

When the motor / generator 3 is driven in this state, only the output rotation from the motor / generator 3 reaches the transmission input shaft 4, and the automatic transmission 2 changes the rotation to the input shaft 4 to the selected shift. The speed is changed according to the speed and output from the transmission output shaft 7.
Then, the rotation from the transmission output shaft 4 reaches the left and right drive wheels through a differential gear device (not shown), and the vehicle can be electrically driven (EV traveling) only by the motor / generator 3. (EV mode)

When the hybrid running mode (HEV mode) used when running at high speeds, during heavy loads, or when the battery storage state SOC (carryable power) is low is required.
In addition to engaging the first clutch 6, the automatic transmission 2 is brought into a power transmission state by engaging the second clutch (IC, H & LR / C, D / C, etc.).
In this state, the output rotation from the engine 1 or both the output rotation from the engine 1 and the output rotation from the motor / generator 3 reach the transmission input shaft 4, and the automatic transmission 2 is connected to the input shaft 4 Is rotated according to the currently selected shift speed and output from the transmission output shaft 7.
Thereafter, the rotation from the transmission output shaft 7 passes through a differential gear device (not shown) to reach the left and right drive wheels, and the vehicle can be hybrid-run by both the engine 1 and the motor / generator 3. (HEV mode)

During such HEV traveling, when the engine 1 is operated at the optimum fuel consumption, the energy becomes surplus,
By operating the motor / generator 3 as a generator with this surplus energy, surplus energy is converted into electric power, and this generated power is stored to be used for driving the motor of the motor / generator 3, thereby improving the fuel efficiency of the engine 1. Can be made.

A control system for the engine 1, the motor / generator 3, the first clutch 6, and the second clutch (IC, H & LR / C, D / C, etc.) in the transmission 2 is shown below. An outline will be described based on 1.
This control system comprises an integrated controller 11 for integrated control of the operating point of the power train,
The operating points of the power train are the target engine torque tTe, the target motor / generator torque tTm, the target transmission torque capacity tTc1 of the first clutch 6, and the second clutch (IC, H & LR / C, D / C, etc.). It is defined by the target transmission torque capacity tTc2.

In the integrated controller 11, in order to determine the operating point of the power train,
A signal from the engine rotation sensor 12 for detecting the rotation speed Ne of the engine 1,
A signal from the motor / generator rotation sensor 13 for detecting the rotation speed Nm of the motor / generator 3;
A signal from the input rotation sensor 14 for detecting the transmission input rotation speed Ni;
A signal from the output rotation sensor 15 for detecting the transmission output rotation speed No (from which the vehicle speed VSP can be calculated);
A signal from the accelerator opening sensor 16 for detecting the accelerator pedal depression amount (accelerator opening APO);
A signal from a storage state sensor 17 that detects a storage state SOC of a battery (not shown) that stores electric power for the motor / generator 3 is input.

The integrated controller 11 is based on the accelerator opening APO, the battery storage state SOC, and the transmission output speed No (vehicle speed VSP) among the above input information.
Select the driving mode (EV mode, HEV mode) that can realize the driving force of the vehicle desired by the driver, and target engine torque tTe, target motor / generator torque tTm, first clutch target transmission torque capacity tTc1, And second clutch target transmission torque capacity tTc2 are calculated.

The target engine torque tTe is supplied to the engine controller 21,
This engine controller 21 uses a throttle opening degree control and a fuel injection amount control for realizing the target engine torque tTe based on the engine speed Ne from the engine speed Ne detected by the sensor 12 and the target engine torque tTe. By
The engine 1 is controlled so that the engine torque becomes the target engine torque tTe.

The target motor / generator torque tTm is supplied to the motor / generator controller 22,
The motor / generator controller 22 converts the battery power into DC-AC with an inverter (not shown), and supplies it to the stator 3a of the motor / generator 3 under the control of the inverter.
The motor / generator torque is controlled so that the motor / generator torque matches the target motor / generator torque tTm.

If the target motor / generator torque tTm is such that the motor / generator 3 requires a regenerative braking action,
The motor / generator controller 22 applies a power generation load to the motor / generator 3 through the inverter so that the battery is not overcharged in relation to the battery storage state SOC detected by the sensor 17.
The electric power generated by the motor / generator 3 due to the regenerative braking action is AC-DC converted to charge the battery.

The first clutch target transmission torque capacity tTc1 is supplied to the first clutch controller 23,
This first clutch controller 23 compares the first clutch engagement pressure command value corresponding to the first clutch target transmission torque capacity tTc1 with the actual engagement pressure of the first clutch 6 to determine the actual engagement pressure of the first clutch 6. Control is performed so that the engagement pressure of the first clutch 6 is controlled so as to be the first clutch engagement pressure command value, and the transmission torque capacity of the first clutch 3 becomes the target value tTc1.

The second clutch target transmission torque capacity tTc2 is supplied to the transmission controller 24,
The transmission controller 24 compares the second clutch engagement pressure command value corresponding to the second clutch target transmission torque capacity tTc2 with the actual engagement pressure of the second clutch (IC, H & LR / C, D / C, etc.). The engagement pressure of the second clutch (IC, H & LR / C, D / C, etc.) so that the actual engagement pressure Pc2 of the second clutch (IC, H & LR / C, D / C, etc.) becomes the second clutch engagement pressure command value To control the transmission torque capacity of the second clutch (IC, H & LR / C, D / C, etc.) to the target value tTc2.

The transmission controller 24 basically sets the current driving state based on the planned shift map based on the transmission output rotation speed No (vehicle speed) detected by the sensor 15 and the accelerator opening APO detected by the sensor 16. Find a suitable gear,
It is intended that the transmission 2 is automatically shifted so that this preferred shift speed is selected.

[Engine start control]
The above is an outline of the normal control executed by the control system of FIG.
In this embodiment, the engine when a request to switch to the hybrid travel (HEV) mode occurs due to depression of the accelerator pedal during travel in the electric travel (EV) mode with the first clutch 6 released. Suppose that the control system of FIG. 1 performs the start as shown in FIG. 4 in accordance with the control program shown in FIG.

Therefore, the control program in FIG. 3 starts at the instant t1 in FIG. 4 when the above-described EV → HEV mode switching (engine start) request is generated.
First, in step S11 in FIG. 3, when the automatic transmission 2 is downshifted, the down-shifting release-side shift friction element that switches from the engaged state to the released state (if 4 → 3 downshift, the input is made clear from FIG. Clutch I / C) is used as the second clutch, and its transmission torque capacity tTc2 is reduced at a predetermined time change gradient as illustrated after the instant t1 in FIG.
Therefore, step S11 corresponds to the downshift release side shifting friction element control means in the present invention.

Here, according to the transmission input torque Tin, the predetermined time change gradient is a gentler time change gradient as this is smaller.
When the transmission input torque Tin is equal to or greater than the set value Tins for determining the high acceleration force requirement, it is necessary to make EV-to-HEV mode switching (engine start) abrupt, so that the release-side shift friction during downshifting Reduce the transmission torque capacity tTc2 of the element (second clutch) at once
When the transmission input torque Tin is smaller than the set value Tins (including negative values), the EV → HEV mode switching (engine start) should be performed gently for shock countermeasures. The transmission torque capacity tTc2 of the disengagement side shift friction element (second clutch) is gradually reduced as illustrated after the instant t1 in FIG.

In the next step S12, when the downshift of the automatic transmission 2 is performed, the downshift engagement side shifting friction element that switches from the released state to the engaged state (if the 4 → 3 downshift, the front brake Fr The transmission torque capacity tTon of / B) is controlled as follows.
Therefore, step S12 corresponds to the downshift engagement side frictional element control means in the present invention.

In this step S12, if the transmission input torque Tin is less than the set value Tins, the transmission torque capacity tTon of the downshift engagement side shifting friction element at a predetermined time change gradient as illustrated after the instant t1 in FIG. Increase,
If the transmission input torque Tin is equal to or greater than the set value Tins, the transmission torque capacity tTon of the engaging gearshift friction element at the time of downshift is not increased and is kept at 0.

  Here, Tin <Tins means that even if the transmission torque capacity tTc2 of the release side shifting friction element (second clutch) during the downshift is reduced as described above, the release side shifting friction element (second clutch) during the downshift slips. When the transmission torque capacity tTc2 of the small transmission input torque range that does not cause the gearshift and the disengagement side shift friction element (second clutch) at the time of downshift is reduced as described above, the transmission input rotational speed decreases and the engine starts. It means the negative transmission input torque range that becomes impossible.

During this small (including negative value) transmission input torque range, the transmission torque capacity tTon of the down-shift engagement frictional element at the time of downshift is a predetermined time-varying gradient as illustrated after the instant t1 in FIG. 4 in step S12. If you increase it,
Coupled with the decrease in the transmission torque capacity tTc2 of the release side shifting friction element (second clutch) executed in step S11, the automatic transmission 2 is advanced by half the downshift, and the effective gear ratio is the same as the current gear. An intermediate gear ratio is set between the lower gear and the lower gear.
For this reason, even in a small (including negative value) transmission input torque range, the down-shifting release-side shift friction element (second clutch) can reliably perform as planned when the transmission torque capacity tTc2 is reduced as described above. Causes slip.

In step S13, it is checked whether or not the release side shifting friction element (second clutch) at the time of downshift has slipped,
Until the instant t2 in FIG. 4 when the slip occurs, the control is returned to step S11 and step S12, and the above-mentioned in steps S11 and S12 until the release side shifting friction element (second clutch) during downshift slips. Repeat the process.

After the instant t2 in FIG. 4 where it is determined that the disengagement side shifting friction element (second clutch) during the downshift has slipped in step S13,
In step S14, the transmission torque capacity tTc2 of the disengagement side shifting friction element (second clutch) at the time of downshift is controlled as follows,
In step S15, the transmission torque capacity tTon of the downshift engagement side shifting friction element is controlled as follows.
Therefore, step S14 corresponds to the downshift release side frictional element control means in the present invention,
Step S15 corresponds to the downshift engagement side shift friction element control means in the present invention.

First, the control of the transmission torque capacity tTc2 related to the downshifting release side frictional element (second clutch) performed in step S14 will be described.
If the transmission input torque Tin is equal to or greater than the set value Tins, the transmission torque capacity tTc2 of the downshifting release side frictional element (second clutch) is set to the target driving torque equivalent value at the time of engine start.
If the transmission input torque Tin is less than the set value Tins (including negative values), the transmission torque capacity tTc2 of the downshift release side frictional element (second clutch) is shown as shown after the instant t2 in FIG. Set to virtually zero.

In order to explain the control of the transmission torque capacity tTon related to the downshift engagement side shifting friction element at the next step S15,
If the transmission input torque Tin is equal to or greater than the set value Tins, the transmission torque capacity tTon of the engagement gear shift friction element during downshift is set to 0,
If the transmission input torque Tin is less than the set value Tins (including a negative value), the transmission torque capacity tTon of the engaging gearshift friction element during downshift is the target drive torque at engine start as shown after the instant t2 in FIG. Equivalent value.

Therefore, when the transmission input torque Tin is less than the set value Tins (including negative values), after the second clutch slip occurrence instant t2 in FIG.
The transmission torque capacity (tTc2) of the release side shifting friction element (second clutch) at the time of downshift is substantially zero as shown in step S14,
In step S15, the transmission torque capacity (tTon) of the down-shift engagement side shifting friction element is set to a target driving torque equivalent value at the time of engine start as shown in the figure.

In this way, by controlling the transmission torque capacity (tTon) of the engaging side shifting friction element at the time of downshift to a value equivalent to the target driving torque at the time of engine start, while compensating the vehicle driving force to become the target driving torque at the time of engine start ,
As described above, the transmission torque capacity (tTc2) of the release-side shift friction element (second clutch) during downshifting is substantially zero as described above, so that the following engine start process can be performed for the shift friction element (second clutch). Can be made to slip.

The engine start process after the second clutch slip occurrence instant t2 in FIG. 4 will be described below.
At the instant t2, the transmission torque capacity tTc1 of the first clutch 6 is set to such a value that the engagement of the first clutch 6 is started, and the motor / generator 3 is switched from torque control to rotational speed control to rotate the motor / generator. The motor / generator torque tTm is increased from the instant t2 as shown in the figure so that the number Nm becomes the target engine start speed.

With the start of engagement of the first clutch 6 and the rotational speed control of the motor / generator 3, the engine 1 is cranked as is apparent from the change over time of the engine rotational speed Ne,
At the instant t3, the engine 3 can be operated independently (after the engine has been started), the engine speed Ne coincides with the motor / generator speed Nm, and the first clutch 6 has its front-rear rotational difference reduced to zero. The rotation is synchronized.
The rotation synchronization of the first clutch 6 is checked in step S16 of FIG. 3, and the control is returned to step S14 until this rotation synchronization state is reached, thereby completing the rotation synchronization of the first clutch 6.

In step S16, the rotation synchronization of the first clutch 6 is detected. After the instant t3 in FIG. 4, although not shown in FIG. 3, the transmission torque capacity tTc1 is set so that the first clutch 6 is completely engaged as shown in FIG. Is the maximum value.
After detecting the rotation synchronization of the first clutch 6 in step S16, in step S17, the depression of the accelerator pedal (vehicle request) in which the EV → HEV mode switching (engine start) is accompanied by the downshift request of the automatic transmission 2 is performed. Whether it was based on an increase in load).
Therefore, step S17 corresponds to the required load increase detecting means in the present invention.

When it is determined in step S17 that the accelerator operation is accompanied by a downshift request, in order to complete the downshift in step S18, the downshift engagement side shift friction element is completely engaged and the downshift release side shift is performed. Fully release the friction element (second clutch).
The downshift process in step S18 is performed at the instant t4 in FIG. 4 where the release side shifting friction element (second clutch) during the downshift is in a rotationally synchronized state in which the forward / backward rotational difference is set to 0, but FIG. Since it is an operation time chart when no shift request is generated, the downshift process in step S18 is not shown in FIG.

However, if it is determined in step S17 that the accelerator operation is not accompanied by a downshift request, the gear position (effective gear ratio) is returned to the original gear position in step S19, so that the second clutch rotation synchronization instant t4 in FIG. As shown in this figure, the downshift engagement frictional friction element is completely released and the downshift release friction element (second clutch) is completely engaged.
Therefore, step S19 corresponds to the downshift release side shift friction element control means and the downshift engagement side shift friction element control means in the present invention.

[Effect]
According to the engine start control device of the present embodiment described above,
During EV → HEV mode switching (engine start), when the downshift release friction element is used as the second clutch and its transmission torque capacity tTc2 is reduced for engine start (step S11, instant t1 to t2 in FIG. 4) ) In order to increase the transmission torque capacity tTon of the engagement side shifting friction element at the time of downshift (step S12, instants t1 to t2 in FIG. 4),
By reducing the torque capacity of the disengagement side shifting friction element (second clutch) during downshift and increasing the torque capacity of the engagement side shifting friction element during downshifting, the automatic transmission 2 proceeds halfway through the downshift, and its effective The gear ratio is set to an intermediate gear ratio between the current shift speed and the lower gear position immediately below.

For this reason, during EV → HEV mode switching (engine start), the input torque Tin of the automatic transmission 2 is a small value less than the set value Tins, and only the torque capacity reduction of the downshift disengagement side shift friction element (second clutch) Then, even if it is difficult to cause the slip of this speed change friction element (second clutch) and it is difficult to start the engine due to the rotation increase of the motor / generator 3,
When the release side shifting friction element (second clutch) at the time of downshift is reduced in torque capacity as described above, it is possible to surely generate a slip as planned (instantaneous t2 in FIG. 4).
The motor / generator 3 can be reliably rotated for starting the engine, and as a result, the engine cranking speed is not insufficient, and the engine start is not difficult or impossible. be able to.

Since the engine start control for achieving the operation and effect is executed when the transmission input torque Tin is smaller than the set value Tins,
Even when the driver performs the operation of repeatedly turning the accelerator ON and OFF without performing the positive / negative determination of the transmission input torque Tin, the above-described effects can be achieved.

If the transmission input torque Tin is less than the set value Tins (including negative values) after the start of the second clutch slip t2 in FIG. 4, the engine start is performed on the transmission torque capacity tTon of the engagement gear shift friction element during downshift. In order to obtain a target driving torque equivalent value (step S15, instant t2 to t4 in FIG. 4),
Further, during this time, coupled with the fact that the transmission torque capacity (tTc2) of the release side shifting friction element (second clutch) during the downshift is substantially zero (step S14, instants t2 to t4 in FIG. 4),
The shift friction element (second clutch) can be slipped so that the engine start process can be performed while compensating for the driving force of the vehicle to be the target drive torque at the time of engine start.

Further, when it is determined that the EV → HEV mode switching (engine start) request is not accompanied by the downshift of the automatic transmission 2 (step S17), the engagement side shifting friction element is completely released during the downshift and the downshift is performed. In order to fully engage the release-side shift friction element (second clutch) (step S19, after instant t4 in FIG. 4),
After the engine is started, the shift stage (effective gear ratio) of the automatic transmission 2 can be returned to the original shift stage, and sacrifice of the original drivability can be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a power train of a front engine / rear wheel drive hybrid vehicle including a hybrid drive device incorporating an engine start control device according to an embodiment of the present invention, together with its control system. FIG. 2 is an engagement logic diagram showing a relationship between a selected shift stage of the automatic transmission in FIG. 1 and a combination of engagement of shift friction elements. 2 is a flowchart showing an engine start control program executed by a power train control system in FIG. FIG. 4 is an operation time chart of engine start control during low load traveling without downshifting executed by the engine start control program of FIG. 3. FIG.

Explanation of symbols

1 Engine (Power source)
2 Automatic transmission 3 Motor / generator (power source)
4 Transmission input shaft 6 First clutch 7 Transmission output shaft
I / C input clutch (shifting friction element)
H & LR / C high and low reverse clutch
D / C direct clutch (shifting friction element)
11 Integrated controller
12 Engine rotation sensor
13 Motor / generator rotation sensor
14 Transmission input rotation sensor
15 Transmission output rotation sensor
16 Accelerator position sensor
17 Storage state sensor
21 Engine controller
22 Motor / generator controller
23 1st clutch controller
24 Transmission controller

Claims (3)

With engine and motor as power source,
A first clutch is interposed between the engine and the motor, and a second clutch is interposed between the motor and the drive wheel. The second clutch is responsible for power transmission in the automatic transmission inserted between the motor and the drive wheel. Diverting the variable speed friction element
By releasing the first clutch and engaging the second clutch, it is possible to select the electric travel mode using only the power from the motor. By engaging both the first and second clutches, the power from both the engine and the motor can be selected. Hybrid driving mode can be selected,
In the hybrid vehicle capable of switching the mode to the hybrid driving mode by starting the engine with the power from the motor by making the first clutch engage and advance while slipping the second clutch while the electric driving mode is selected.
During the mode switching from the electric travel mode with engine start to the hybrid travel mode, the downshift release side frictional element that switches from the engagement state to the release state when the automatic transmission is downshifted is used as the second clutch. Downshift-side release friction element control means for reducing the transmission torque capacity of the friction element;
Downshift that increases the transmission torque capacity of the engagement-side transmission friction element during downshift when the automatic transmission is downshifted from the release state to the engagement state while the transmission torque capacity of the release-side transmission friction element is reduced by the means An engine start control device for a hybrid vehicle, comprising: an hour engagement side shift friction element control means. In the engine start control device of the hybrid vehicle according to claim 1,
The downshift engagement side shift friction element control means increases the transmission torque capacity of the downshift engagement side shift friction element to a value corresponding to a target drive torque at engine start. Start control device. In the engine start control device of the hybrid vehicle according to claim 1 or 2,
A required load increase detection means for detecting an increase in the vehicle required load is provided,
The downshift release side frictional element control means increases the transmission torque capacity of the downshift release side frictional element when the increase in vehicle required load is detected by the required load increase detection means.
The downshift engagement side shift friction element control means reduces the transmission torque capacity of the downshift engagement side shift friction element when the increase in vehicle required load is detected by the required load increase detection means. An engine start control device for a hybrid vehicle.

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