JPH01216153A - Speed change control for automatic transmission - Google Patents

Abstract

PURPOSE:To lighten the work quantity of one frictional engagement device and improve durability by temporarily engaging a frictional engagement device for achieving another speed change stage, added with the frictional engagement device necessary for up-shift, in the up-shift operation. CONSTITUTION:In the shift-up operation from the first speed stage in which a clutch 38, one-way clutches 34 and 36 are fastened to the second speed stage in which clutches 38 and 44 and the one-way clutch 36 are fastened, also the second clutch 40 necessary for achieving the third and fourth speed is engaged temporarily, added with the clutch 44. Therefore, a turning power is inputted from an input shaft 52 into a carrier 16, added with a turning power supplied from a sun gear 20, and the work quantity of the fourth clutch 44 is reduced in accordance. Before the completion of the shift-up, the engagement of the second clutch 40 is released. Therefore, the durability of a frictional engagement device can be improved and the small-sized device can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a speed change control method for an automatic transmission used in a vehicle such as an automobile, and in particular, the present invention relates to a speed change control method for an automatic transmission used in a vehicle such as an automobile. The present invention relates to a method for controlling a shift in an automatic transmission.

C. Prior Art] Automatic transmissions used in vehicles such as six-wheel drive vehicles include sun gears,
It has a planetary gear device constituted by a plurality of rotating elements such as a ring gear, a planetary pinion, and a carrier that rotatably supports the planetary gear, and the plurality of rotating elements of the planetary gear device are connected to a plurality of clutches and brakes. This type of automatic transmission is capable of switching between a plurality of gear stages by interconnecting or fixing them in a predetermined combination by engaging and disengaging frictional engagement devices such as For example, JP-A-54-111050, JP-A-57-101
No. 151 and Japanese Unexamined Patent Publication No. 61-55457.
2-195471.

[Problems to be Solved by the Invention] During gear shifting, the frictional engagement device engages and disengages, and the amount of work of the frictional engagement device at this time is limited to the wide ratio of the gear ratio of the transmission, the planetary gear device, etc. As the speed and output of motors that provide rotational force to motors have increased, the number of rotations has increased, and automatic transmissions have been required to be smaller in order to be able to be mounted on vehicles. In particular, it is difficult to increase the number of friction plates in multi-plate types.

In an automatic transmission that includes a one-way clutch in a planetary gear system to improve speed change control, a brake that selectively operates the one-way clutch and a brake parallel to the one-way clutch and brake are used to selectively operate the one-way clutch. Another brake installed in relation to
That is, it has already been proposed to apply a coast brake and have the two brakes share the work of shifting from engagement to these two brakes. ing.

As mentioned above, temporarily engaging the coast brake, which is provided to obtain an engine braking effect, during gear shifting means that the workload of the frictional engagement device during gear shifting is shared between two brakes, and one brake However, depending on the type of planetary gear system, for example, as in the type of planetary gear system proposed in Japanese Patent Application No. Sho 62-195471, the second speed stage In cases where a clutch for achieving engine braking and a coast brake for obtaining an engine braking effect are provided in series with each other, the amount of work of the clutch does not change at all even when the coast brake is engaged; It is not possible to divide and reduce the workload. Further, there are cases where the above-mentioned engagement of the coast brake does not sufficiently reduce the workload.

In view of the above-mentioned problems, the present invention utilizes an appropriate frictional engagement device other than a coast brake to obtain engine braking, and reduces the workload of the frictional engagement device during gear shifting by engaging the frictional engagement device. The purpose of the present invention is to provide an improved shift control method that reduces the burden of transmission.

[Means for Solving the Problems] According to the present invention, a plurality of rotating elements of a planetary gear device are arranged in a predetermined combination by engagement and disengagement of a plurality of frictional engagement devices. In a method for controlling automatic transmissions that switches between a plurality of gears by interconnecting or fixing the gears, the gears with the above function are achieved when upshifting from one gear to another. In addition to the engagement of the frictional engagement device necessary to achieve a gear shift other than the one described above, a frictional engagement device is engaged to achieve a gear other than the one described above, and the release of the frictional engagement device is caused by This is achieved by a shift control method characterized in that the engagement pressure of the frictional engagement device necessary for achieving the above-mentioned shift stage is increased in conjunction with the release of the gear shift.

In the shift control method for an automatic transmission according to the present invention, the gears other than the above-mentioned functional gears may be higher than the above-mentioned functional gears.

Incidentally, the friction engagement device for achieving a gear position other than the gear position of the above function to be engaged at the time of upshifting from a certain gear position to another gear position is applied with rotational force by the engagement, and the friction engagement device It goes without saying that the friction engagement device is limited to one that rotates in the same direction as the frictional engagement device that is engaged to achieve the above-mentioned gear position when upshifting from one gear position to another gear position.

CJtI! According to the shift control method according to the present invention, when upshifting from a certain gear to another gear, in addition to the friction engagement device necessary for the upshift, the gear shift other than the gear of the above function is required. Since the frictional engagement device to achieve the stage also engages temporarily,
The workload of the frictional engagement device during gear shifting is now shared among these multiple frictional engagement devices, which reduces the workload for a single frictional engagement device and improves the durability of the frictional engagement device. This will lead to improvements in performance or miniaturization. The frictional engagement device for achieving a gear position other than the above-mentioned gear position may be one that is provided in parallel with the frictional engagement device necessary for the upshift in view of the power transmission process; This makes it possible to sufficiently reduce the workload of the frictional engagement device in any type of planetary gear device.

In order to prevent the establishment of a gear position other than the above-mentioned automatic gear position, even if the friction engagement device for achieving a gear position other than the above-mentioned automatic gear position is released prior to the establishment of the other gear position, that is, inertia is prevented. Even if it is released in the phase, the engagement pressure of the frictional engagement device for achieving the other gear is increased due to this release, so that fluctuations in the output torque at this time are avoided, and a large shift is possible. Shocks are avoided.

[Example] The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows one embodiment of a planetary gear type transmission according to the present invention. In the figure, 10 indicates the first sun gear, 1
2 is a first ring gear concentric with the first sun gear 10;
16 is a first carrier rotatably supporting the first planetary pinion 14; 20 is a second sun gear; and 22 is a second planetary pinion. A second ring gear concentric with the sun gear 20, 24 a second planetary binion meshing with the second sun gear 20 and the second ring gear 22, and 26 a second carrier rotatably supporting the second planetary binion 24. Each is shown.

The first ring gear 12 is connected to the second carrier 26 by a connecting element 30, and the first carrier 16 is connected to the second ring gear 22 by a connecting element 32.

Note that the simple planetary gear mechanism constituted by the first sun gear 10, the first ring gear 12, the first planetary pinion 14, and the first carrier 16 will be referred to as a first row planetary gear mechanism, and the second sun gear 20 and A simple planetary gear mechanism constituted by the second ring gear 22, second planetary pinion 24, and second carrier 26 is referred to as a second row planetary gear mechanism.

A first carrier 16 and a second ring gear 22 connected to the first carrier 16 by a connecting element 32 and a housing 5
0, a first one-way clutch 34 and a second one-way clutch 36 are provided in series with each other. In this case, the first one-way clutch 34 is connected to the first carrier 1
6, and a second one-way clutch 36 is provided on the housing 50 side. More specifically, the first one-way clutch 34 is connected to the first carrier 16 through its inner race 34a, and its outer race 34b is connected to the inner race 36a of the second one-way clutch 36 through the connecting member 31. Outer race 36b is connected to housing 50.

The second carrier 26 is connected to the output gear 54 so that it always acts as an output member.

The first one-way clutch 34 is in an engaged state when the outer race 34b is about to rotate beyond the rotational speed of the inner race 34a during engine drive, and is in a slipping state when it is the opposite, and the second one-way clutch 36 is in an engaged state when the inner race 36a is reversed with respect to the outer race 36b during engine drive, and is in a sliding state when the inner race 36a is reversed to the outer race 36b.

A first clutch 38 is provided between the second sun gear 20 and the input shaft 52 to selectively connect the two to each other.

A second clutch 40 is provided between the first carrier 16 and the human power shaft 52 to selectively connect the two to each other.

A third clutch 42 is provided between the first sun gear 10 and the input shaft 52 to selectively connect the two to each other.

A fourth clutch 44 is provided between the first sun gear 10 and the connecting member 31 to selectively connect the two to each other.

A connecting member 31 is provided between the connecting member 31 and the housing 50.
A first brake 46 is provided for selectively securing the housing 50 to the housing 50.

A second brake 48 is provided between the second ring gear 22 and the housing 50 to selectively fix the second ring gear 22 to the housing 50.

The manner in which the first gear, second gear, third gear (directly coupled gear), fourth gear (increasing gear), and reverse gear are achieved by the planetary gear type transmission configured as described above is as follows. As shown in Table 1. In this table, the O mark indicates that the relevant clutch, brake, or one-way clutch is engaged in the engine drive state, and (0) indicates that the relevant clutch or brake is engaged, the gear shift is This indicates that engine braking can be applied during this stage.

When the ratio of the number of teeth of the first sun gear 10 to the number of teeth of the first ring gear 12 is ρ1, and the ratio of the number of teeth of the second sun gear 20 to the number of teeth of the second ring gear 22 is ρ2, the gear ratio of each gear is shown in Table 2.

Second speed in Table 2 ((1+ρ2)/ρ2)-(1/In an automatic transmission having a planetary gear device having the structure as described above, the speed change control method according to the present invention applies to This is executed by engaging the second clutch 22 in addition to the fourth clutch 44 when upshifting to the second gear.The engagement of the fourth clutch 44 achieves the second gear, which is an upshift gear. This is an essential engagement for the second clutch 40
This engagement is necessary to achieve the third and fourth gears, which are higher gears than the first gear.

When the second clutch 40 is engaged in addition to the fourth clutch 44 during an upshift from the first gear to the second gear, rotational power is manually applied from the input shaft 52 to the carrier 16 in addition to the sun gear 20. Accordingly, the fourth clutch 4
4 workload will be reduced.

If the total input torque is Tln and the transmission torque capacity of the second clutch 40 is Tc2, then the sun gear 20 has Tln-
Tc2 is input, and the torque equation at the time of upshifting from the first gear to the second gear in this case is shown by the following equation.

That is, in FIG. 2, Tc 4 (1+ (
1/ρ+ ))-(1/ρ2) (Tln-Tc 2
) +Tc 2-0...■ holds true. Note that Tc4 is the transmission torque capacity of the fourth clutch 44.

■From the formula, Tln-(1+-p2)Te 2 + (ρ 2 / ρ I ) (1+ ρ ) Tc
４・・・・・・■ Also, during gear shifting, T 1n= T t + T +
--@TI-finω1n
・・・・・・■ holds true. In addition, 1 is the turbine torque, TI is the inertia torque, 11n is the input inertia,
uln is the angular acceleration of the input shaft 52.

Therefore, assuming that uln is constant during gear shifting, fin=
((1+ρ2) Tc 2 + (+1)2 /ρ+
)(1+ρ+)Tc 4 Tt)/fin...
・・■ Also, Tout −−(Te 4 /ly+ ) +(Tln
-Tc2) (1+ (1/ρ2))...
...■ holds true. Note that T out is the output torque.

When the second clutch 40 is released, Tc2 in equations (1) and 0 becomes 0, the input torque after the release of the second clutch 40 is T1n', the output torque is Tout', and the fourth clutch 44 is transmitted. If the torque capacity is Tc4°, T1n' = (ρ2 /p+) (1+ρ
+) Tca.

・・・・・・■ Tout' --(Tc a ° /p+)
+ (1+ (1/ρ2)) T In
' ・・・・・・■.

Therefore, the difference in the output torque before and after the release of the second clutch 40 is expressed by the equation 0 and the equation below from the equation 0.

Tout −Tout'−−(1//)l ) (T
e a Tc4 ° ) + (1+1/ρ2
) (Tln-Tln'-'rcz)...
・・■ ■If Tln and T in' are eliminated from the formula 0 and 0, Tout −Tout' −(ρ 1 ρ 2 +
ρ weight + ρ 2 ) /ρ1 (Tc 4
-Te s ° )+ (1+ρ2)Te2...
... [phase] becomes.

In order for the output torque to not fluctuate before and after the second clutch 40 is released, it is sufficient that Tout - Tout'=0.

Tout − Tout'm O is satisfied by the following formula.

Tc 4'-Tea + ((ρ
+ 11)2 + ρ 1 ) /(ρlρ2+
ρ+ρ, 2)lTc2...■ Therefore, in synchronization with the release of the second clutch 40, the transmission torque capacity of the fourth clutch 44 becomes ((ρrichρ2+ρt)/(ρ1ρ2+ρ1+ρ)
2) It is only necessary to increase the torque by lTc2, so that the output torque does not fluctuate before and after the second clutch 40 is released.

FIG. 3 shows the change in output torque when shifting up from 1 to 2. The solid line shows the output torque characteristic when the transmission torque capacity of the fourth clutch 44 is not increased when the second clutch 40 is disengaged, and the broken line shows the output torque characteristic when the second clutch 40 is released. The output torque characteristics are shown when the transmission torque capacity of the fourth clutch 44 is increased as described above when the second clutch 40 is disengaged according to the control method according to the invention, and in this case, the output torque is gradually increased in the inertia phase region. There is no change in speed, and no large shift shock occurs.

FIG. 4 shows an example of a hydraulic circuit device for speed change control used to implement the speed change control method according to the present invention. In FIG. 4, 40a indicates the hydraulic servo chamber of the second clutch 40,
Reference numeral 44a indicates a hydraulic servo chamber of the fourth clutch 44. When hydraulic pressure is supplied to the hydraulic servo chamber 40a, the second clutch 40 is engaged, and when hydraulic pressure is supplied to the hydraulic servo chamber 44a, the second clutch 40 is engaged. Four clutches 44 are engaged.

Line hydraulic pressure is selectively supplied to the hydraulic servo chamber 40a from an oil passage 62 by switching the shift valve 60. The shift valve 60 is operated to switch by opening and closing the solenoid valve 64, and when the solenoid valve 64 is in the on state, the shift valve 60 is switched to the line hydraulic pressure supply position as shown in the figure in response to the opening of the solenoid valve 64; When 64 is in the OFF state, it is switched to the oil drain position in response to the valve closing.

Therefore, when the solenoid valve 60 is in the on state, the second clutch 40 is engaged by supplying line hydraulic pressure to the hydraulic servo chamber 40a thereof, whereas when the solenoid valve 64 is in the off state, the second clutch 40 is engaged. The hydraulic pressure of 40a is discharged and the state is released.

Line hydraulic pressure is selectively supplied to the hydraulic servo chamber 44a from the oil passage 62 by switching the shift valve 66. The shift valve 66 is switched by opening and closing the solenoid valve 68, and when the solenoid valve 68 is in the on state, when the solenoid valve 68 is opened, the shift valve 66 is switched to the line oil pressure supply position as shown in the figure. When the valve is in the OFF state, it is switched to the oil drain position in response to the valve closing.

Therefore, when the solenoid valve 68 is in the on state, the fourth clutch 44 is engaged by being supplied with the line hydraulic pressure from the hydraulic servo chamber 44a, whereas when the solenoid valve 68 is in the off state, the fourth clutch 44 is engaged by the line hydraulic pressure in the hydraulic servo chamber 44a. is ejected and becomes free.

A hydraulic delay circuit 70 and an accumulator 72 are provided in the middle of the oil path leading from the shift valve 60 to the hydraulic servo chamber 40a. Further, a hydraulic delay circuit 74 and an accumulator 76 are provided in the middle of the oil path leading from the shift valve 66 to the hydraulic servo chamber 44a.

The accumulators 72 and 76 have back pressure chambers 72B and 76, respectively.
The accumulator functions with characteristics corresponding to the oil pressure applied to a, and the transmission torque capacities of the second clutch 40 and the fourth clutch 44 during gear shifting are each optimized.

Hydraulic pressure regulated by an accumulator control valve 78 is supplied to a back pressure chamber 72a of an accumulator 72 for the second clutch 40, and a discharge pressure chamber of an accumulator 76 for the fourth clutch 44 is supplied. Hydraulic pressure regulated by an Aquiemulator control valve 80 is supplied to 76a. The pressure regulation value of the achievator control valve 78 is determined by the pressure regulation value by the duty solenoid valve 82, and this pressure regulation value is determined by the duty ratio of the pulse signal given to the duty solenoid valve 82. The pressure regulation value of the other Akiemulator control valve 80 is determined by the pressure regulation value by the duty solenoid valve 84, and the pressure regulation value of the duty solenoid valve 84 is determined by the duty ratio of the pulse signal given to it. .

Note that dampers 86 and 88 are installed to absorb hydraulic pulsations caused by the repeated opening and closing of duty solenoid valves 82 and 84.
and is provided. Further, in order to prevent the oil pressure control state by the duty ratio control of the duty solenoid valves 82 and 84 from changing due to a change in the line oil pressure, a modulating valve 9 is provided for these duty solenoid valves 82 and 84.
0, a constant oil pressure is supplied.

According to the above configuration, the duty solenoid valve 82
and 84 by controlling the duty ratio of the pulse signal applied to each of the accumulators 72 and 76.
The back pressure of each of the accumulators of the second clutch 40 and the fourth clutch 44 during gear shifting is controlled accordingly.
The transmission torque capacity of can now be set arbitrarily.

The fourth clutch 44 in the control device as described above is a wet multi-disc clutch, and its transmission torque capacity is equal to the engagement pressure P.
Since it is proportional to c4, if the proportionality constant is α, then Te4−αPc4 ・・・・・・
Becomes a [stock].

When accumulator back pressure control is performed using an accumulator as shown in FIG. 5, the engagement pressure Pc4 is expressed by the following formula.

Pca = ((A+ -A2)/A+] Pe
4 bp+(F/A+)...0 where A is the large diameter chamber area of the accumulator, A2 is the small diameter chamber area, F is the accumulator spring force, and PCa bp is the accumulator back pressure.

Therefore, if the back pressure Pe4bp of the accumulator 76 of the fourth clutch 44 is increased by ΔPe4''bp shown in the equation [phase] below at the same time as the second clutch 40 is released, the engagement pressure Pc4 of the fourth clutch 44 will increase. Accordingly, the transmission torque capacity JiTc4 increases, and stepwise changes in the output torque are avoided.

ΔPc 4 bp= (A+ a/ (A+ −A2
) ) ((ρ ρ 2 + ρ I ) /
(ρ ρ 2 + ρ weight + ρ 2 ) )T
c2...■ Next, one embodiment of the speed change control method according to the present invention will be described with reference to FIGS. 6 and 7.

The flowchart shown in FIG. 6 shows a routine when starting an upshift from the first gear to the second gear. In the first step 100, the throttle opening θ of the prime mover, for example, the internal combustion engine It is determined whether or not is greater than or equal to a predetermined value θset. When θ≧θset is not the normal 1→
2-shift up control is performed, whereas θ≧θset
If so, the process advances to step 110, and in step 110, control is performed to optimize the back pressures of the accumulators 76 and 72 of the fourth clutch 44 and the second clutch 40. This control is performed based on the duty ratio applied to duty solenoid valves 84 and 82 in the hydraulic control circuit shown in FIG. Step 110 is followed by step 12
0, and in step 120, the solenoid valve 68
and 64 are both turned on.

As a result, the line hydraulic pressure is supplied to the hydraulic servo chamber 40a of the second clutch 40 in addition to the hydraulic servo chamber 44a of the fourth clutch 44, whereby both the fourth clutch 44 and the second clutch 40 are engaged. I come to do it.

After step 120, the process proceeds to step 130, in which the flag F1 is set to 1. Flag F is a flag indicating that the second clutch 40 is engaged during a 1→2 shift up.

After step 130, the process proceeds to step 140, where the timer T is cleared and the C2 simultaneous engagement time Tset is set according to the throttle opening, vehicle speed, etc. This timer T is incremented for a predetermined time by interrupt processing.

Figure 7 shows the second clutch 4 when shifting up from 1 to 2.
0 shows the release control routine. In step 200, it is determined whether flag F is 1 or not. When the flag is F1-1, the process advances to step 210, and in step 210, it is determined whether the timer value T of the timer is less than or equal to a predetermined value T set. T≦
When it is T set, the process advances to step 220, and in step 220, it is determined whether the flag F2 is 1 or not. The flag F2 is a flag indicating that the second clutch is released, and if the flag is not F2-1, the process proceeds to step 230.

In step 230, control is performed to turn off the solenoid valve 64 and to optimize the back pressure of the accumulator 76 of the fourth clutch 44.

At this time, the hydraulic pressure in the servo hydraulic chamber 40a of the second clutch 40 is discharged, thereby releasing the second clutch 40 and engaging the fourth clutch 44 to achieve the second gear.

At this time, control to optimize the back pressure of the accumulator 76 is performed according to the above-mentioned [phase] formula, and as a result, the fourth clutch 4
4 increases, and its transmission torque capacity increases.

This back pressure optimization control may be performed in accordance with a control characteristic determined in advance based on the transmission torque reduction characteristic when the second clutch 40 is disengaged, which is measured in advance through experiments, etc., or by monitoring the engagement pressure of the second clutch 40. However, it may be carried out accordingly.

After step 230, the process proceeds to step 240, in which flag F2 is set to 1.

Note that the flag F and flag F2 may be cleared in the 1-2 shift up completion determination routine.

In the embodiment described above, the second clutch 40 is engaged from the start of the shift until a predetermined time period determined by a predetermined timer set value T set has elapsed, and shares the work of the fourth clutch 44. It becomes like this.

When the second clutch 40 is engaged during upshifting from the first gear to the second gear from the start of the gear shift until the rotational speed of the input shaft 52 reaches a predetermined value, FIG. Control may be performed according to a flowchart as shown in FIG.

In step 210 in FIG. 9, it is determined whether the rotational speed Nin of the input shaft 52 is less than or equal to a predetermined value Nset.

The speed change control method according to the present invention is not limited to the automatic transmission having the planetary gear device shown in FIG. 1, but can of course be applied to automatic transmissions having various types of planetary gear devices. That's true.

Furthermore, the speed change control method according to the present invention can be applied not only when upshifting from the first gear to the second gear, but also when upshifting from the second gear to the third gear or from the third gear to the second gear. It may be performed as necessary when upshifting to fourth gear.

Although the present invention has been described in detail above with reference to specific embodiments, it is understood that the present invention is not limited thereto and that various embodiments are possible within the scope of the present invention. It's obvious for business owners.

[Brief explanation of the drawing]

FIG. 1 is a skeleton diagram showing, in particular, the planetary gear unit of an automatic transmission suitable for implementing the speed change control method according to the present invention, and FIG. 2 is a first speed stage of the planetary gear unit shown in FIG. A skeleton diagram showing the balance of torque when upshifting to the second gear, FIG. 3 is a graph showing the change in output torque when upshifting from 1 to 2, and FIG. 4 is a control method according to the present invention. FIG. 5 is a schematic configuration diagram showing an example of an accumulator used in the hydraulic circuit device, and FIGS. 6 to 9 each illustrate the present invention. 2 is a flowchart showing an embodiment of a speed change control method according to the present invention. 10...first sangya, 12...first ring gear. 14... First planetary pinion, 16... First carrier, 20... Second sun gear, 22... Second ring gear, 24... Second planetary pinion, 26...
・Second carrier, 30.31.32...Connection element, 3
4...First one-way clutch, 36...Second one-way clutch, 38...First clutch, 40...
Second clutch, 42...Third clutch, 44...Fourth clutch. 46...first brake, 48...second brake, 5
0... Housing, 52... Output shaft, 54... Output gear. 60... Shift valve, 62... Oil path, 64... Solenoid valve, 66... Shift valve, 68... Solenoid valve, 70... Hydraulic delay valve, 72... Accumulator, 74 ...Hydraulic delay valve, 76...Accumulator,
78.80...Accumulator control valve, 82.84.
...Duty solenoid valve, 86.88...Damper, 90...Modulation valve Patent applicant: Toyota Motor Corporation representative
Attorney Masatake AkashiFigure 1Figure 2 (1+(1/p2)XTin-Tax)Figure 3C2 engagementFigure 5Figure 6Figure 7Figure 8

Claims (1)

[Claims] An automatic transmission in which a plurality of rotating elements of a planetary gear device are interconnected or fixed in a predetermined combination by engagement and release of a plurality of frictional engagement devices, thereby switching between a plurality of gear stages. In the speed change control method, in addition to the engagement of a frictional engagement device necessary for achieving the other gear when upshifting from a certain gear to another gear, upshifting other than the other gear is performed. engaging a frictional engagement device to achieve a gear stage;
The frictional engagement device is released prior to establishing the other gear, and the engagement pressure of the frictional engagement device required to achieve the other gear is increased in conjunction with this release. transmission control method.