JPH1178618A - Control device for continuously variable transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress change in the behavior of a vehicle when the acceleration pedal is stamped or brakes are applied while the vehicle is running on a low-μ road surface. SOLUTION: When judgement is passed that the vehicle is running on a low-μ road surface, the maximum Cmax and minimum gear ratios Cmin in the D-range gear ratio region are restricted to the maximum Csmax and minimum gear ratios Csmin in Snow mode so that the extent of the shift region is narrowed, and no fuel cut for engine is performed to be executed when the degree of throttle opening is fully closed. On a low-μ road surface, excessive action of engine brake originating from the gear ratio being controlled to a greater minimum gear ratio Csmin is avoided by generating an engine torque of a certain size in which the fuel cut is prohibited, and a braking effect due to an appropriate engine brake is obtained, and the drawing-in of engine torque at the time of the acceleration pedal of being stamped again can be avoided, so that the frequency of braking operation, etc., on low-μ road surface can be reduced and also a change in the engine torque be suppressed to lead to the suppression of the change in the behavior of vehicle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a continuously variable transmission mounted on a vehicle, and more particularly to a stepping device on a road surface having a low friction coefficient such as an icy snowy road surface or a wet tiled road surface. Alternatively, the present invention relates to a control device for a continuously variable transmission suitable for suppressing a change in vehicle behavior during braking.

[0002]

2. Description of the Related Art Generally, in a conventional continuously variable transmission of a belt type or a toroidal type, a speed change pattern for controlling a speed ratio is, for example, disclosed in Japanese Patent Application Laid-Open No. Hei 4-203665. The speed change pattern is controlled within the speed ratio control region corresponding to the speed change select position, using the valve opening (hereinafter, throttle opening) as a variable. In other words, regarding forward traveling, when a normal traveling range (generally referred to as a D range) is selected as a shift select position, a normal traveling speed ratio control region suitable for normal traveling (that is, a D range speed ratio region). And if the engine brake range (generally L range, S (2) range) is selected,
An engine brake gear ratio control region having a minimum gear ratio larger than the normal traveling gear ratio control region (that is, the L range,
Within S (2) range speed ratio range), the shift pattern of the continuously variable transmission is controlled according to the vehicle speed and the throttle opening.

In general, when the accelerator pedal is open and the vehicle speed is at a certain level, such as during engine braking, the throttle opening is fully closed and the engine speed is low. When it is equal to or more than the predetermined value, it is determined that there is no need to supply fuel to the engine, and a fuel cut for stopping fuel supply to the engine is performed for the purpose of improving fuel efficiency or preventing heating of the catalyst. Has become.

[0004]

However, in the conventional control device for a continuously variable transmission, the friction coefficient of a road surface such as an icy or snowy road surface or a wet asphalt road surface is selected, for example, in a state where a normal traveling range is selected. When traveling on a low, low μ road surface, when the accelerator is operated from the coast running state with the accelerator pedal released, the friction coefficient between the tire and the road surface is low, but it is equivalent to the high μ road surface Is applied, and the driving force tends to be too high, which may cause wheel spin.
In the accelerator pedal released state, the fuel is cut when the vehicle is running at or above a predetermined engine speed, so that the accelerator pedal is depressed from a state in which the negative engine torque is acting due to the fuel cut. Then, since the engine torque is generated after the inertia torque of the engine is accelerated, the fluctuation of the engine torque becomes large and the vehicle behavior becomes unstable.

[0005] Further, even when the accelerator pedal is released to expect a deceleration effect by engine braking when the vehicle shifts from a state of traveling on a high μ road surface to a low μ road surface, it is still a low μ road surface. Since the speed ratio of the continuously variable transmission is controlled to the minimum speed ratio in the normal traveling range speed ratio range, the deceleration effect by the engine brake is small. As a result, the frequency of brake operations and select-downs increases, which leads to unstable vehicle behavior. Especially on low μ road surfaces, unstable vehicle behavior leads to changes in vehicle behavior. It is desirable to be done.

Accordingly, the present invention has been made in view of the above-mentioned conventional problems. In particular, it is possible to suppress a change in the behavior of a vehicle when operating an accelerator pedal or braking on a low μ road surface. It is an object of the present invention to provide a control device for a continuously variable transmission.

[0007]

In order to achieve the above object, a control device for a continuously variable transmission according to a first aspect of the present invention provides a control device for a continuously variable transmission that has a predetermined gear ratio so that the minimum gear ratio is at least when the throttle opening is fully closed. Shift control means for shifting control of the continuously variable transmission in a speed ratio control region, and fuel supply for stopping fuel supply to the engine when the throttle opening is in a fully closed state and the engine speed is equal to or higher than a predetermined value. A control unit for the continuously variable transmission, comprising: a road surface friction coefficient state detection unit that detects a road surface friction coefficient state while the vehicle is traveling; and the road surface friction coefficient state detection unit detects a low friction road surface state. And a low friction road surface adjusting means for prohibiting the fuel supply stop means from stopping the fuel supply and changing the minimum gear ratio in the gear ratio control region to the maximum gear ratio side.

According to the first aspect of the invention, the shift control means controls the speed of the continuously variable transmission within a predetermined gear ratio control range based on the throttle opening, the vehicle speed, and the like, and at least the throttle opening is fully closed. In the state, the speed ratio of the continuously variable transmission is controlled to the minimum speed ratio in the speed ratio control region, and an appropriate speed ratio suitable for the running state of the vehicle according to the throttle opening or the vehicle speed is set. . When the throttle opening is fully closed and the engine speed is equal to or higher than a predetermined value, such as when the engine brake is activated,
When it is determined that there is no need to supply fuel to the engine, fuel supply to the engine is stopped by the fuel supply stopping means, thereby improving fuel efficiency and the like.

[0009] For example, when the driver instructs the snow mode in which the shift control of the continuously variable transmission is performed in the gear ratio control region suitable for traveling on a low friction road surface such as a snowy road, or when the front and rear wheels are instructed. When the road surface friction coefficient state detecting unit detects that the vehicle is traveling on a low friction road surface, for example, when it is detected that the wheel is slipping based on a speed difference between the wheel speeds or the like, the low friction road surface adjusting unit is used. By
The stop of fuel supply to the engine by the fuel supply stop means is prohibited, and the minimum speed ratio in the speed ratio control area is changed to the maximum speed ratio side.

That is, when the accelerator pedal is released for the purpose of applying the engine brake, the minimum speed ratio in the predetermined speed ratio control region is set as the speed ratio of the continuously variable transmission by the speed change control means. It is difficult to obtain the braking effect of the engine brake while the gear ratio is being controlled. As a result, the frequency of the brake operation and the like may be increased and the behavior of the vehicle may be changed.However, in the case of a low friction road surface state, the minimum gear ratio is changed to the maximum gear ratio side, and the fuel supply is stopped. Since the stop of fuel supply to the engine by means is prohibited, the speed ratio of the continuously variable transmission is changed to a speed ratio larger than the minimum speed ratio to obtain the braking effect of the engine brake and stop the fuel supply. The engine braking is prevented from becoming too strong in order to continue the process without performing it. By increasing the speed ratio of the continuously variable transmission while generating a certain amount of engine torque, the deceleration effect due to moderate engine braking is achieved. Is obtained.

In the case where the driver again depresses the vehicle while the engine brake is being applied, the fuel supply is stopped when the throttle opening is fully closed and the engine speed is equal to or higher than a predetermined value. Since the fuel supply to the engine is stopped by the means, the engine torque on the negative side acts, and if the accelerator pedal is depressed from this state, the engine torque is generated after the inertia torque is accelerated Therefore, the fluctuation of the engine torque becomes large, so that the vehicle behavior becomes unstable. However, in the case of a low μ road surface, stopping the supply of fuel to the engine is prohibited, so that the vehicle starts up from a state in which a certain amount of engine torque is generated.
The engine torque rises smoothly in response to the depression of the accelerator pedal, the fluctuation of the engine torque is suppressed, and the vehicle behavior is stabilized.

Further, the control device for a continuously variable transmission according to a second aspect of the present invention includes a vehicle speed detecting means for detecting a vehicle speed, and the low friction road surface adjusting means includes a change width of the minimum speed ratio as the vehicle speed increases. Is characterized by being made smaller.

According to the second aspect of the present invention, since the low friction road surface state is detected by the road friction coefficient state detecting means, the minimum gear ratio in the gear ratio control region is reduced by the low friction road surface adjusting means. When the vehicle speed is changed to the maximum gear ratio side, the vehicle speed is changed so that the change width becomes smaller as the vehicle speed increases. In other words, since the deceleration effect of the engine brake increases as the vehicle speed increases, the minimum gear ratio changes to the maximum gear ratio side as the vehicle speed decreases, and the minimum gear ratio changes so that the change width decreases as the vehicle speed increases. As a result, the minimum gear ratio is changed in accordance with the deceleration effect of the engine brake according to the vehicle speed, so that excessive application of the engine brake is avoided.

Further, in the control device for the continuously variable transmission according to the third aspect, the low friction road surface adjusting means may be arranged such that when the road surface friction coefficient state detecting means detects the low friction road surface state, the speed ratio control region is controlled. Is changed to the minimum gear ratio side.

According to the third aspect of the present invention, when the road surface on which the vehicle is traveling is in a low-friction road surface state, the maximum speed ratio in the speed ratio control area is adjusted by the low-friction road surface adjusting means.
The gear ratio is changed to a smaller value on the minimum gear ratio side.

Therefore, on a low μ road surface, the normal high μ
When the gear ratio is controlled in the same manner as when traveling on a road, for example, when the accelerator is depressed, the same driving force acts on the low μ road as on the high μ road, and the driving force acts. If the vehicle is running on a low μ road surface, the maximum gear ratio is changed to a smaller value for the gear ratio.
Even when an accelerator operation is performed on a low μ road surface, the driving force is suppressed, and the possibility of the vehicle spinning is reduced.

[0017]

According to the control device for a continuously variable transmission according to the first aspect of the present invention, when the low friction road surface state is detected,
The low friction road surface adjusting means prohibits the fuel supply stopping means from stopping the fuel supply to the engine and changes the minimum gear ratio in the gear ratio control region to a larger gear ratio on the maximum gear ratio side. In addition, it is possible to appropriately obtain the deceleration effect by the engine brake, to stabilize the vehicle behavior at the time of re-stepping on, and to suppress the fluctuation of the vehicle behavior on the low friction road surface.

According to the control device for a continuously variable transmission according to the second aspect, when the minimum speed ratio in the speed ratio control region is changed by the low friction road surface adjusting means, the change width increases as the vehicle speed increases. Since it is made smaller, it is possible to obtain a deceleration effect by an appropriate engine brake according to the running state of the vehicle.

Further, according to the control device for a continuously variable transmission according to the third aspect, when a low friction road surface state is detected, the maximum speed ratio in the speed ratio control area is reduced to a smaller speed ratio on the minimum speed ratio side. Therefore, when the accelerator pedal is operated on a low friction road surface, it is possible to prevent the driving force from acting too much, and to prevent the vehicle behavior from becoming unstable.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an example in which the present invention is applied to a toroidal type continuously variable transmission.

The continuously variable transmission mounted on the vehicle according to this embodiment has at least a normal travel range and an engine brake range for operating an engine brake as shift select positions for forward traveling. D which is the normal driving range in the select position
When the range is selected, it is within a normal traveling speed ratio control region (D range speed ratio region) suitable for normal traveling, and when the S range which is an engine brake range is selected, the normal traveling speed ratio is selected. The engine brake range control region (S
By setting the target input shaft speed in accordance with the vehicle speed and the throttle opening, respectively, within the range gear ratio range),
Controls the gear ratio of the continuously variable transmission.

As shown in FIG. 1, the power transmission mechanism of the continuously variable transmission includes a torque converter 2, a forward / reverse switching mechanism 4, a toroidal-type continuously variable transmission 6, a final reduction gear 8, and the like. The rotation of the output shaft (not shown) of the engine 10 can be transmitted to the left and right drive wheels 9 at a predetermined gear ratio and a predetermined rotation direction. The output side of the torque converter 2 connected to the output shaft of the engine 10 is connected to a rotating shaft (not shown) of the forward / reverse switching mechanism 4. Can be changed to a forward direction for forward movement or a reverse direction for backward movement. Note that a fluid coupling may be used for the torque converter 2.

As shown in FIG. 1, the toroidal type continuously variable transmission 6 has input disks 11 and 12 which rotate integrally with the rotation shaft of the forward / reverse switching mechanism 4, and the input disks 11
, 12, a pair of transmission rollers 15 provided between the input disk 11 and the output disk 13 and transmitting the rotational force therebetween, and a pair of transmission rollers 15 provided between the input disk 12 and the output disk 13. And at least a pair of transmission rollers 16 for transmitting the rotational force therebetween.

Here, the contact surfaces between the input disks 11, 12 and the output disk 13 and the transmission rollers 15, 16 are formed as toroidal surfaces, and the transmission rollers 15, 16 are tilted with respect to the input disks 11, 12 and the output disk 13. By changing the angle, the rotation speed ratio between the input disks 11, 12 and the output disk 13 can be continuously changed.

The tilt angles of the transmission rollers 15, 16 with respect to the input disks 11, 12 and the output disk 13 are controlled by a hydraulic control device 20. As shown in FIG. 2, the hydraulic control device 20 includes a control valve 21 having a spool 21b slidably disposed in a valve body 21a.
A step motor 22 for moving a spool 21b of the control valve 21 via a rack and pinion mechanism;
The hydraulic cylinder 23 includes a hydraulic cylinder 23 connected to a rotation shaft of a support mechanism 17 that rotatably supports the transmission rollers 15 and 16 with one piston rod, and a precess cam surface attached to a tip of the other piston rod of the hydraulic cylinder 23. And a L-shaped link 25 having one end engaged with the cam surface of the precess cam 24 and the other end engaged with a projecting piece 21c formed on the valve body 21a of the control valve 21.

The line pressure PL is supplied to the input port Ps of the control valve 21, and the input / output ports Po1 and Po2
Are respectively connected to the piston 2 of the hydraulic cylinder 23 through the hydraulic piping.
It is connected to the pressure chambers 23b and 23c defined by 3a. Reference numeral 26 denotes a return spring that returns the valve body 21a to the neutral position.

Accordingly, the spool 21b of the control valve 21 moves to the right in response to, for example, clockwise rotation of the step motor 22, so that a predetermined line pressure PL is applied via the input / output port Po1 to the pressure chamber 23b of the hydraulic cylinder 23. is supplied to the pressure oil in the pressure chamber 23c is returned to the tank through the input and output ports Po2 and drain port P _D. Therefore, the piston 23a moves downward, and the support mechanism 17 supporting the transmission roller 15 is moved downward from the neutral position.

As a result, the precess cam 24 is also moved downward, so that the control valve 2 is connected via the L-shaped link 25.
When the first valve body 21a moves to the right, the input / output port P
o1 and Po2 are closed, and at the same time, the transmission roller 1
5 and 16 start tilting, so that the precess cam 2
4 rotates, and the valve body 21a is further moved to the right in response to this, and the line pressure PL is applied to the input / output port Po2 in the opposite manner.
Is supplied, the support mechanism 17 is returned to the neutral position, and the precess cam 24 is raised and the valve body 2
1a moves to the left, the input / output ports Po1 and Po2 are closed, and the tilting angles of the transmission rollers 15 and 16 are
The angle is changed by an angle corresponding to the number of steps of 2.

When the step motor 22 is driven and controlled by the control unit 30, the tilt angles of the transmission rollers 15 and 16 with respect to each input / output disk are changed in accordance with the number of steps of the step motor 22. The number of steps of the motor 22 and the gear ratio uniquely correspond.

On the other hand, the vehicle has a throttle opening T
A throttle opening sensor 41 for detecting VO, an input shaft speed sensor 42 for detecting the speed of the input disk 11 of the toroidal type continuously variable transmission 6, and an output shaft speed sensor 43 for detecting the speed of the output disk 13 When the D range, which is the normal traveling range, is selected by a select lever (not shown), the selector switch 44 outputs the selection signal FD = 1, and the shift in the snow mode traveling pattern for a low friction road surface such as a snowy road or a sandy road. When a snow mode for instructing control is selected, a snow mode switch 45 that outputs a detection signal SW _SNOW = 1, an engine speed sensor 46 that detects the speed of the output shaft of the engine 10, a front wheel speed and a rear wheel side A front wheel speed sensor 47 for detecting the speed,
At least a rear wheel speed sensor 48 is provided, and each is provided at an appropriate position.

The throttle opening sensor 41 includes:
The throttle opening of the engine 10 is detected as a voltage signal. The amount of depression of the accelerator pedal is divided stepwise, and the amount of depression of the accelerator pedal is "0", that is, the equivalent throttle opening. Is the minimum value TVO _MIN when the vehicle is fully closed, and the maximum value TVO _MAX when the accelerator pedal is fully depressed, that is, when the equivalent throttle opening is fully open.
As an analog signal TV corresponding to the throttle opening.
O is output.

The control unit 30
Are a microcomputer 31 for performing arithmetic processing for speed ratio control and other shift function control described later, and a motor drive circuit 3 for driving the step motor 22.
And 2. The microcomputer 31
Is an input interface circuit 31a having an A / D conversion function for reading signals from the sensors, an arithmetic processing unit 31b including a microprocessor unit MPU and the like, and a storage device including a ROM, a RAM, and the like. 31c and an output interface circuit 31d having a D / A conversion function and the like.

Then, the microcomputer 31
Is a calculation process for a gear ratio control described later, for example.
Therefore, the throttle opening from the throttle opening sensor 41 is
Degree TVO and output shaft speed from output speed sensor 43
Vehicle speed V calculated based on No _SP, D range is selected
Or if the S range is selected
Continuously variable transmission based on whether or not
Calculate the input rotation speed to be achieved by
Calculation of gear ratio C to be achieved by idal type continuously variable transmission mechanism 6
And the steps required to achieve this gear ratio C.
Motor control signal S for driving the motor 22_MRaw
Output to the motor drive circuit 32 and the engine
A snow mode flag F to be described later_SNOW
Is output.

The motor drive circuit 32 converts the input motor control signal S _M into a drive signal for the step motor 22 and outputs it. Next, a gear ratio control process executed by the arithmetic processing unit 31b of the microcomputer 31 will be described with reference to a flowchart shown in FIG. This calculation process is executed by a timer interrupt every sampling period of, for example, about 10 msec. It should be noted that although no particular communication step is provided in this flowchart, maps, programs, or predetermined arithmetic expressions required for arithmetic processing are stored in the ROM of the storage device 31c.
, And the calculated value and each information value obtained by the calculation are stored in the RAM of the storage device 31c at any time.

In this gear ratio control process, first, in step S1, the throttle opening TVO from the throttle opening sensor 41, the engine speed Ne from the engine speed sensor 46, and the input shaft from the input shaft speed sensor 42. Rotation speed Nt, output shaft rotation speed N from output shaft rotation sensor 43
o, detection signal S from snow mode switch 45
W read _SNOW, selector position signal FD from the selector switch 44, a front wheel rotational speed N _F and the rear wheel rotational speed N _R of the rotational speed sensor 47, 48 of the front wheel side and rear wheel side.
Next, the routine proceeds to step S2, where the vehicle speed _VSP is calculated from the output shaft speed No based on the following equation (1). Note that A in the equation is a conversion coefficient.

V _SP = No × A (1) Further, based on the engine speed Ne and the throttle opening TVO, the engine speed Ne and the engine torque Te are shown in FIG. 4 using the throttle opening TVO as a parameter. The engine torque Te is calculated from a control map representing the correspondence between Then, the estimated input torque Tin of the continuously variable transmission 6 is calculated from the engine torque Te and the torque converter ratio t (e) according to the following equation (2). The torque converter ratio t (e) is calculated from the input shaft speed Nt and the engine speed Ne according to the following equation (3).

Tin = Te × t (e) (2) t (e) = Nt / Ne (3) Next, the process shifts to step S3 to execute a snow mode determination process. In the snow mode determination process, as shown in the flowchart of FIG. 5, first, the detection signal SW _SNOW from the snow mode switch 45 is SW _SNOW = 1, that is, the driver performs traveling in the snow mode traveling pattern. It is determined whether or not an instruction has been given (step S11). And when SW _SNOW = 1,
The process proceeds to step S12, and the snow mode flag F _{SNOW
Is set} to F _SNOW = 1, and the processing ends, and the process returns to the main program.

On the other hand, if not SW _SNOW = 1 in step S11, the process proceeds to step S13, whether or not slipping based on the difference between the front wheel-side rotation speed N _F and the rear wheel-side rotation speed N _R Or it is determined whether or not the vehicle is in the automatic snow mode suitable for traveling in the snow mode traveling pattern based on a change in the wheel speed of the drive wheel, that is, whether or not the vehicle is traveling on a low μ road surface. If the mode is the automatic snow mode, the process proceeds to step S12. On the other hand, if the mode is not the automatic snow mode, the process proceeds to step S14, the snow mode flag F _{SNOW is set} to F _SNOW = 0, the processing is terminated, and the process returns to the main program.

Returning to the flowchart of FIG. 3, when the snow mode determination processing is completed in the processing of step S3, the process proceeds to step S4 to execute a shift determination processing. In this shift determination process, it is determined whether or not the D range, which is the normal traveling range, is selected based on whether or not the selector position signal FD from the selector switch 44 is FD = 1, and the D range is selected. If not, for example, if the S range has been selected, the target gear ratio Ct according to the gear select position is set in the same manner as in the normal processing for setting the target gear ratio.

On the other hand, if the D range has been selected, the flowchart of FIG.
At 21, based on the vehicle speed _VSP and the throttle opening TVO,
The target input shaft speed TNt is set in the control map of FIG.

Here, the control map shown in FIG.
_This is equivalent to a general control map of a normal shift pattern using _SP as the horizontal axis, target input shaft speed TNt as the vertical axis, and throttle opening TVO as parameters. A straight line passing through the origin and having a constant slope has a constant speed ratio. I think. For example, a straight line having the largest slope in the entire region of the shift pattern has the largest reduction ratio of the entire vehicle, that is, the maximum speed ratio C
Represents _MAX, most slope small straight reduction ratio smallest reversed, that is, represents the minimum speed ratio C _MIN. Then, even at the same vehicle speed V _SP , the fact that the depression amount of the accelerator pedal is large and the throttle opening TVO is large is that
For example, it is necessary to increase the engine rotation speed to increase the output torque because the load required for the engine is large due to the need for acceleration force or the running load such as uphill road or head wind resistance. Using the throttle opening TVO detected by the throttle opening sensor 41 as a parameter, the larger the throttle opening TVO, the larger the target input shaft rotation speed TNt is set. In a region where the vehicle speed _VSP is smaller than a certain speed ratio control start threshold, the speed ratio is equal to the maximum speed ratio C.
Set to _MAX .

Then, within the D range speed ratio range from the minimum speed ratio C _MIN to the maximum speed ratio C _MAX , the target input shaft speed TN according to the throttle opening TVO and the vehicle speed V _SP.
t is set.

Next, the process proceeds to step S22, and based on whether or not the snow mode flag F _SNOW = 1, the target input shaft rotational speeds TNt _MAX and TNt according to the maximum and minimum values of the available gear ratio. _MIN is set from the control map of FIG. That is, when a snow mode flag F _SNOW = 0, the maximum speed ratio C _MAX and the minimum speed ratio C _{MI N}
Sets the maximum value and the minimum value of the speed ratio in the D range speed ratio region as the maximum speed ratio and the minimum speed ratio as shown by the solid line in the control map of FIG.

On the other hand, if the snow mode flag F _SNOW = 1, the maximum gear ratio C _MAX is set to the minimum gear ratio C _MIN , as shown by the broken line in the control map of FIG. of limited to smaller snow mode at the maximum speed ratio C _SMAX gear ratios, also the minimum speed ratio larger snow mode at the minimum transmission ratio C _SMIN of C _MIN this maximum speed ratio side C _MAX side speed ratio than The maximum speed ratio C _{SMAX in the} snow mode and the minimum speed ratio C in the snow mode
_SMIN is _set as the maximum gear ratio and the minimum gear ratio. That is, when the snow mode flag F _SNOW = 1, the low μ is set.
When it can be considered that the vehicle is traveling on a road surface, and when the accelerator pedal is depressed while traveling on this low μ road surface, a driving force equivalent to that on a high μ road surface is generated on a low μ road surface May have too strong a driving force. Therefore, in order to avoid this, the maximum gear ratio C _MAX is limited to the maximum gear ratio C _SMAX in the snow mode having a smaller gear ratio, thereby suppressing the driving force.

When the engine brake is applied, that is, when the throttle opening is fully closed, the speed ratio is controlled to the minimum speed ratio C _MIN .
It is difficult to obtain the braking effect of the engine brake. In order to avoid this, the minimum gear ratio C _MIN is limited to the minimum gear ratio C _SMIN in the snow mode having a larger gear ratio to improve the braking effect by the engine brake.

Next, the process proceeds to step S23, in which the target input shaft speed TNt obtained in step S21 is changed to the maximum value TNt _MAX and the minimum value TNt _MAX of the target input shaft speed corresponding to the maximum and minimum speed ratios obtained in step S22. The target rotation speed TNt ^* is set to a value within the range of the value TNt _MIN and set. That is, when the target input shaft speed TNt exceeds the maximum value TNt _MAX of the target input shaft speed (TNt> TNt)
_MAX ), the target rotation speed TNt ^* = TNt _MAX , and if the target input shaft rotation speed TNt is smaller than the minimum value TNt _MIN of the target input shaft rotation speed (TNt <TNt _MIN ), the target rotation speed TNt is reached. ^* = TNt _MIN , and the target input shaft speed TNt is the maximum value TNt of the target input shaft speed.
When it is within the range of _MAX and the minimum value TNt _MIN , the target rotation speed TNt ^* is set to TNt.

Next, the process proceeds to step S24, where a time constant Kr is set according to, for example, vehicle characteristics. The time constant Kr is a weighting factor indicating how much the first-order lag target rotation speed Nt (k-1) described later is reflected on the attained target rotation speed TNt ^* , and is set to a value satisfying 0 <Kr <1. .
Incidentally, the time constant Kr be a fixed value, may be reduced to "1" to "0" in response to an increase in the vehicle speed when the vehicle speed V _SP is equal to or larger than a predetermined vehicle speed.

Next, the routine proceeds to step S25, where the first-order lag target rotation speed Nt (k) is calculated based on the following equation (4). Nt (k) = [TNt ^* + Nt (k−1) × Kr] / (Kr + 1) (4) where Nt (k−1) is stored in a predetermined storage area at the time of previous execution of the shift control process. This is the primary delay target rotation speed at the time of the previous calculation.

Next, the routine proceeds to step S26, where the target speed ratio Ct is calculated according to the following equation (5) based on the primary delay target rotational speed Nt (k) and the output shaft rotational speed No calculated in step S25. Is calculated. Then, the processing ends and the process returns to the main program.

Ct = Nt (k) / No (5) Returning to FIG. 3, when the shift determination process is completed in the process of step S4, the process proceeds to step S5 to execute a shift process. In this shift processing, the control speed is defined because the step motor 22 cannot instantaneously achieve the target position. As shown in the flowchart of FIG. 8, first, in step S31, the control map of FIG. Based on the target speed ratio Ct and the estimated input torque Tin set in the process of step S4, an actual target speed ratio C ^* is set in consideration of torque shift compensation. Next, the process proceeds to step S32, and corresponds to the actual target gear ratio C ^* .
The actual target step number STP ^* , which is the number of steps of the step motor 22, is obtained from the control map shown in FIG. 10 which shows the correspondence between the actual target gear ratio C ^* and the step number STP of the step motor 22.

Next, the process proceeds to step S33 to determine whether or not the actual target step number STP ^* obtained in step S32 is smaller than the current step number STP _NOW of the step motor 22. And the current step number STP
_{If the} actual target step number STP ^* is not smaller than _NOW (STP ^* ≧ STP _NOW ), the process proceeds to step S34, and the unit step amount ΔSTP is changed to the current step number STP ^.
The temporary target step number STP 'is calculated by adding to TP _NOW .

[0052] Then, the processing proceeds to step S35, 'determines whether is greater than the actual target step number STP ^*, temporary target step number STP' temporary target step number STP than the actual target step number STP ^* If larger, the process proceeds to step S36, sets the actual target step number STP ^* as a motor control signal S _M. Then, the process ends and returns to the main program.

On the other hand, if the provisional target step number STP 'is not larger than the actual target step number STP ^* (STP'≤STP ^* ) in the process of step S35, the process proceeds to step S35.
38 and proceeds to set the temporary target step number STP 'as a motor control signal S _M. Then, the process ends and returns to the main program.

In step S33, the current step is executed.
STP_NOWIs the actual target number of steps STP^*Larger than
If not, the process proceeds to step S39 and the current step number S
TP _NOWFrom the unit step amount ΔSTP
The target step number STP 'is calculated. Then, step S
40, and the number of temporary target steps STP 'is
Step number STP^*Is smaller than ST
P '<STP^*If not, proceed to step S41.
Then, the provisional target step number STP 'is set to the motor control signal S_M
Set as Then, terminate the process and
Return to Lamb.

On the other hand, if the provisional target step number STP 'is smaller than the actual target step number STP ^* (STP'<STP ^* ) in the process of step S40, step S36 is performed.
Move to

[0056] Thus, the speed change process in FIG. 6, that is, the process of step S5 in FIG. 3 is terminated, and then proceeds to step S6, a motor control signal S _M set by shifting the processing of FIG. 6 motor The output to the drive circuit 32 and the snow mode flag F _SNOW set in the processing of FIG. Then, the shift control process is terminated, and thereafter, the above process is repeatedly executed at a predetermined sampling cycle.

The engine control device 50 controls, for example, the fuel injection amount, ignition timing, and the like according to the engine load, the vehicle speed, and the like, and controls the rotational state of the engine 10 to an optimum state according to the running state of the vehicle. In addition, when the engine brake is operated, the throttle opening is in a fully closed state, and the engine speed is a predetermined value determined by the engine coolant temperature or the vehicle speed, for example, a fuel return speed indicated by a dashed line in FIG. when it is greater fuel cutoff engine speed higher than the N _FC, it is determined that there is no need to perform the combustion supply to the engine 10 until the engine speed falls below the fuel return rotational speed N _FC, the supply of fuel to the engine 10 The deceleration-time fuel cut process for stopping the engine is performed. At this time, when the snow mode flag F _SNOW input from the control unit 30 is F _SNOW = 1, the deceleration fuel cut process is not performed. That is, as shown in the flowchart of FIG. 11, first, it is determined whether or not the snow mode flag F _SNOW = 0 (step S51). If F _SNOW = 0, it is determined that the mode is not the snow mode. Then, deceleration fuel cut processing is executed based on the throttle opening and the engine speed, etc.
When the predetermined condition is satisfied, the fuel supply to the engine 10 is stopped (step S52).

On the other hand, when the snow mode flag is F _SNOW = 1, that is, when the snow mode is set, even if the predetermined condition in the fuel cut processing at the time of deceleration is satisfied, the engine 1
The fuel supply to 0 is not stopped (step S53).

Next, the operation of the above embodiment will be described.
Now, on a high μ road surface such as a dry asphalt road surface or a concrete road surface where a sufficient coefficient of friction between the tires is maintained, the accelerator pedal is depressed and the vehicle normally travels in a constant speed state or acceleration state It is assumed that a D range suitable for normal traveling is selected as the shift select position.

In the control unit 30, as shown in FIG.
Is executed at a predetermined sampling cycle, and
The detection values from various sensors are read (step S
1) Based on these, the vehicle speed V _SP and the estimated input torque T
in is calculated (step S2).

Then, first, a snow mode determination process is executed (step S3). At this time, since the vehicle is traveling on a high μ road surface, the driver instructs traveling in a snow mode traveling pattern for a low friction road surface. If not, the detection signal SW _SNOW of the snow mode switch 45 = 0.
Becomes Since the vehicle is traveling on a high μ road surface and the wheels are not slipping, the snow mode flag F _SNOW is set to F
_SNOW = 0 is set. Next, a shift determination process in step S4 is performed. In this case, since the D range is selected, in the control map of FIG. 7, based on the vehicle speed V _SP and the throttle opening TVO, the D range gear ratio region The target input shaft rotational speed TNt is set from within, and the target gear ratio Ct is set based on this. Then, a shift process is executed based on the target speed ratio Ct (step S).
5) The motor control signal S _M thus calculated and set is output to the motor drive circuit 32. By driving signal corresponding to the motor drive circuit 32 second motor control signal S _M is supplied to the step motor 22, step motor 22 moves the control valve 21 is operated according to the moving direction of the step motor 22 , Whereby the transmission rollers 15,
As the gear 16 moves, the gear ratio is controlled to a predetermined gear ratio.

Next, it is assumed that the vehicle shifts from this state to a coasting state in which both the depression of the brake pedal and the depression of the accelerator pedal are released without changing the shift select position on the high μ road surface. . In this coast running state, since the accelerator pedal is released, the shift control is performed so that the minimum speed ratio C _{MIN in} the D range speed ratio area of the control map of FIG. 7 is obtained.

When the accelerator pedal is depressed from this state, the throttle opening increases, so that, for example, the maximum speed ratio _CMAX is set as the speed ratio, and the speed change control is performed accordingly. As a result, an appropriate acceleration force is given, and acceleration is favorably performed.

On the other hand, when the vehicle shifts from a state in which the vehicle is traveling on a high μ road surface to a low μ road surface, it is detected that the vehicle is in the automatic snow mode from a slip state based on a difference in rotation speed between the front wheel side and the rear wheel side. The snow mode flag is set to F _SNOW =
Set to 1. Alternatively, since the vehicle travels on a low μ road surface, the driver instructs to travel in the snow mode traveling pattern, whereby the snow mode flag is set to F _SNOW = 1. Therefore, in the control map of FIG. 7, the possible range of the gear ratio is from C _MAX to C
From _MIN D-range speed ratio region in the range of, it is limited to a range of snow mode at the maximum speed ratio C _{SM AX} and the minimum speed ratio C _SMIN.

When the accelerator pedal is opened in this state in order to expect the deceleration effect of the engine brake, the throttle opening is fully closed.
In the control map of FIG.
_SMIN will be set as the gear ratio. The minimum speed ratio at the time of snow mode C _SMIN usually minimum speed ratio of C _{MI N}
Since the gear ratio is set to be larger, the continuously variable transmission is controlled to have a larger gear ratio.

[0066] When the engine speed at this time becomes the fuel cut-off rotation speed or more, and a state of not less than the fuel return rotational speed N _FC, when the throttle opening is fully closed, the engine control device 50, The fuel cut for the engine 10 is performed. In this case, since the snow mode flag F _SNOW is F _SNOW = 1, the fuel cut is prohibited, and the fuel cut is not performed.

Therefore, when the engine brake is in operation, a certain amount of engine torque is generated without performing fuel cut, thereby avoiding the tendency that the engine brake tends to operate excessively with an increase in the speed ratio. On a low μ road surface, a braking effect by an appropriate engine brake can be obtained.

Accordingly, an appropriate braking effect by the engine brake can be obtained even on a low μ road surface, so that the frequency of performing the brake operation or the select-down operation is reduced, and the change in the behavior accompanying the operation is suppressed. In particular, since a change in behavior on a low μ road surface is suppressed, running stability on a low μ road surface can be improved.

When the accelerator pedal is depressed from the state where the vehicle is coasting on this low μ road surface, for example, when the throttle opening is maximized, the snow mode flag F _SNOW is F _SNOW = 1. , FIG.
In this control map, the maximum value of the speed ratio is the maximum speed ratio _{CSMAX in the} snow mode, and the speed ratio of the continuously variable transmission is controlled so as to become the maximum speed ratio _CSMAX . At this time, the maximum gear ratio C _SMAX is smaller than the maximum gear ratio C _MAX in the normal D range gear ratio region,
The driving force generated as compared with the road surface is suppressed. Therefore, a smaller driving force is generated on a low μ road surface than on a high μ road surface, and the vehicle behavior does not become unstable due to an excessively large driving force.

Further, at this time, the fuel cut is not performed when the vehicle is in the coast running state. Therefore, even when the state shifts from the coast running state to the acceleration state, the fluctuation of the engine torque is small. That is, as shown in FIG. 12, the engine torque Te with respect to the engine speed Ne is smaller than the engine torque Te indicated by the broken line compared with the engine torque Te when the throttle opening indicated by the solid line is in the fully closed state and the fuel cut is performed. The engine torque Te when the opening is in the fully closed state and the fuel cut is not performed is larger.

Therefore, when the accelerator pedal is depressed from the coast running state and the fuel is cut, the negative engine torque Te acts in the coast running state as shown in FIG. 13 (a). When the accelerator pedal is depressed in this state, the inertia torque must be accelerated, and the engine torque Te is temporarily reduced. After that, the engine torque Te corresponding to the depression of the accelerator pedal is generated,
A step ΔTe will occur.

On the other hand, when the fuel cut is not performed, the accelerator pedal is depressed because the engine torque Te is positive even in the coast running state as shown in FIG. 13B. Even in this case, no pull-in occurs, and the step ΔTe ′ of the engine torque Te is reduced.

Therefore, such an engine torque T
When the fuel cut is performed, the driving torque generated in the propeller shaft when the fuel gas e is generated is shown in FIG.
As shown in (1), the pull-in similarly occurs in proportion to the engine torque Te, and thereafter, the driving torque increases. On the other hand, when the fuel cut is not performed, since the engine torque Te is not drawn, a certain amount of drive torque is output even in the coast state as shown in FIG. The speed is smoothly increased in response to the depression of the pedal, and the maximum gear ratio is changed to a smaller value, so that the step in the driving torque is suppressed and the vehicle is accelerated in a state where the vehicle behavior is stable. Will be. Also,
It can be seen that the engine brake torque, which is the difference between the driving torque and the road surface rotation driving force, which is the driving force that causes the road surface to rotate the wheels, indicated by the broken line in the figure, can be obtained to some extent.

Therefore, when the accelerator pedal is depressed from coasting on a low μ road surface, the retraction by the inertia torque is reduced, and the maximum gear ratio is changed to a smaller value so that an appropriate driving force can be obtained. , The fluctuation of the driving force is suppressed, and the change in the behavior of the vehicle accompanying this is suppressed. In particular, the change in the behavior of the vehicle on a low μ road surface can be suppressed, and the running stability of the vehicle can be suppressed. Performance can be improved.

In the above embodiment, the case where the minimum speed ratio is uniformly changed to the maximum speed ratio side C _SMIN when the snow mode flag is F _SNOW = 1 has been described. For example, as shown in FIG. 15, the change width may be made smaller as the vehicle speed increases. In other words, as the vehicle speed increases speed ratio C _{MI N}
May be set to a gear ratio having a small difference from the gear ratio. By doing so, the deceleration effect of the normal engine brake increases as the vehicle speed increases, so that by changing the change ratio of the gear ratio in accordance with the vehicle speed, a more appropriate engine brake appropriate for the running state of the vehicle can be used. A great braking effect can be obtained.

In the above embodiment, the case where the half toroidal type continuously variable transmission 6 is applied as the continuously variable transmission has been described. However, the present invention is not limited to this, and the full toroidal type continuously variable transmission is not limited thereto. The present invention is also applicable to a belt-type continuously variable transmission in which a V-belt is stretched between a primary pulley and a secondary pulley.

In the above embodiment, the case where the valve body 21a and the spool 21b of the transmission control valve 21 are relatively moved has been described. However, the present invention is not limited to this. By displacing the sleeve with the precess cam 24, the same effect as described above can be obtained.

In the above embodiment, the case where the control unit is constructed by a microcomputer has been described. However, the present invention is not limited to this, and it is needless to say that an electronic circuit such as an arithmetic circuit may be combined. No.

In the above embodiment, the case where the torque shift compensation is performed in step S31 has been described, but this can be omitted. 8, the open-loop control process is performed. For example, the input shaft rotation speed Nt from the input shaft rotation speed sensor 42 and the output shaft rotation speed No. , The current actual gear ratio Cp (= Nt / No) may be calculated, and the feedback control processing may be performed based on the calculated actual gear ratio Cp (= Nt / No).

Here, the D-range gear ratio area corresponds to the gear ratio control area, the gear shift determination processing in step S4 in FIG. 3 corresponds to gear shift control means, and the engine control device 50 corresponds to fuel supply stop means. The snow mode determination processing in step S3 in FIG. 3 corresponds to the road friction coefficient state detecting means, and the processing in steps S22 and S23 in FIG. 6 and the step S53 when the snow mode flag F _SNOW = 1 in step S51 in FIG. Corresponds to the low friction road surface adjusting means, and the processing for detecting the vehicle speed in step S2 in FIG. 3 corresponds to the vehicle speed detecting means.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an example of a control device for a continuously variable transmission according to the present invention.

FIG. 2 is an explanatory diagram showing a schematic configuration of a hydraulic control device.

FIG. 3 is a flowchart illustrating an example of a processing procedure of a shift control process.

FIG. 4 is a control map showing a correspondence between an engine speed Ne and an engine torque Te using a throttle opening TVO as a parameter.

FIG. 5 is a flowchart illustrating an example of a processing procedure of a snow mode determination process.

FIG. 6 is a flowchart illustrating an example of a processing procedure of a shift determination process.

7 is a control map representing a correspondence between the vehicle speed V _SP and the target input shaft rotational speed TNt the throttle opening TVO as a parameter.

FIG. 8 is a flowchart illustrating an example of a processing procedure of a shift process.

FIG. 9 is a control map showing a correspondence between a target gear ratio Ct and an actual target gear ratio C ^{* using an} input torque Tin as a parameter.

FIG. 10 is a control map showing a correspondence between an actual target gear ratio C ^* and a step number STP of a step motor.

FIG. 11 is a flowchart illustrating an example of a processing procedure of a fuel cut-off process during deceleration in the engine control device.

FIG. 12 is an engine torque map when the fuel is cut and when the fuel is not cut.

FIG. 13 is an explanatory diagram illustrating a state of change in engine torque when the accelerator pedal is operated from a coasting state.

FIG. 14 is an explanatory diagram illustrating a change in drive torque of the propeller shaft when the accelerator pedal is operated from a coasting state.

FIG. 15 is another example of the control map of FIG. 7;

[Explanation of symbols]

 Reference Signs List 6 toroidal-type continuously variable transmission 9 wheels 10 engine 11, 12 input disk 13 output disk 15, 16 transmission roller 20 hydraulic control device 21 control valve 22 step motor 23 hydraulic cylinder 24 precess cam 25 L-shaped link 30 control unit 32 motor drive Circuit 41 Throttle opening sensor 42 Input shaft speed sensor 43 Output shaft speed sensor 45 Snow mode switch 46 Engine speed sensor 50 Engine control device

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI // F16H 59:24 59:66

Claims (3)

[Claims] 1. A shift control means for controlling a shift of a continuously variable transmission in a predetermined gear ratio control region so that a minimum gear ratio is at least when the throttle opening is fully closed, and the throttle opening is fully closed. And a fuel supply stopping means for stopping the fuel supply to the engine when the engine speed is equal to or higher than a predetermined value. Road surface friction coefficient state detecting means for detecting, and when the road friction coefficient state detecting means detects a low friction road surface state, stopping the fuel supply by the fuel supply stopping means is prohibited, and the minimum gear ratio in the gear ratio control region. And a low-friction road surface adjusting means for changing the gear ratio to a maximum gear ratio side. 2. The vehicle according to claim 1, further comprising a vehicle speed detecting unit configured to detect a vehicle speed, wherein the low friction road surface adjusting unit decreases a change width of the minimum speed ratio as the vehicle speed increases. Item 2. The control device for a continuously variable transmission according to Item 1. 3. The low friction road surface adjusting means changes a maximum gear ratio in the gear ratio control region to a minimum gear ratio side when the road friction coefficient state detecting means detects a low friction road surface state. 3. The control device for a continuously variable transmission according to claim 1, wherein