JP2850452B2 - Automatic transmission for vehicles - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic transmission that is set to a plurality of shift speeds according to the engagement / release state of frictional engagement means such as a clutch and a brake.

2. Description of the Related Art As is well known, a general automatic transmission mounted on an automobile has a gear train formed by a plurality of sets of planetary gear mechanisms, and a clutch determines a connection state and a fixed state of rotating elements by friction such as a brake. It is configured to be changed by the engagement means and set to a plurality of shift speeds. On the other hand, the preferable relationship between the driving force and the vehicle speed is an inversely proportional relationship in which the driving force is larger as the vehicle speed is lower and the driving force is smaller as the vehicle speed is higher. Therefore, the gear ratios of the plurality of gears are set to a geometric series as much as possible. It is well known that a close relationship is preferable.

As described above, in a general stepped automatic transmission, there is a difference between the gear ratios of the respective gears, and a necessary driving force can be obtained by selecting a predetermined gear based on the vehicle speed and the engine load. However, the torque that the tire can bear is limited by the coefficient of friction with the road surface and the load, etc., so if the torque or torque fluctuation given to the tire during gear shifting exceeds the torque that the tire can bear, the tire will slip. Would. That is, if the coefficient of friction is sufficiently high as on a general dry road surface, as described above, a torque is applied to the tire in accordance with the gear position set based on the vehicle speed and the engine load, or slip occurs even when a torque fluctuation occurs. Although there is almost no change, when the coefficient of friction is low, such as on snowy roads or frozen roads, the torque that can be handled by the tires becomes smaller, so the same shifting was performed as when running on dry roads. Then, the tire may slip. Therefore, the applicant of the present invention has proposed a device capable of preventing tire slippage by changing the gear stage of the automatic transmission from a low speed stage to a high speed stage, in place of an engine torque control type device, in Japanese Patent Publication No. 53-4191.

Problems to be Solved by the Invention In the above-described conventional device, the shift stage is switched to the high speed stage based on the slip ratio of the tire, so that the shift is caused by a change in the throttle opening within a range where no shift occurs. When there is a change in the engine output, the amount of change in the torque actually generated in the drive wheels is smaller than when the low-speed gear is set, so that slip can be prevented. However, the shift speed on the low speed side before being switched to the high speed side is set based on the engine load and the vehicle speed, and the required torque in the traveling state can be obtained. If the gear is forcibly changed to the higher gear, the driving force becomes insufficient even if the tire does not slip. Further, in the above-described conventional device, when there is a change in the throttle opening or a change in the vehicle speed,
Since the shift occurs regardless of the road surface condition and the slip state of the tire, the torque based on such shift is large. As a result, on a so-called low μ road such as a frozen road surface, the tire slips and the behavior of the vehicle becomes unstable. Could be.

The present invention has been made in view of the above circumstances, and provides an automatic transmission capable of detecting in advance a situation in which a tire is likely to slip, and reliably performing running without running out of driving force and without slip. It is intended to provide.

Means for Solving the Problems In order to achieve the above object, the present invention provides an automatic transmission that determines a gear position based on at least two factors of an engine load and a vehicle speed. And the difference between the speed ratio of the shift stage after the downshift and the downshift performed when the outside air temperature is equal to or less than the predetermined value is smaller than the downshift performed based on two factors. A control device for setting a shift speed after the downshift is provided.

Effect In the automatic transmission according to the present invention as well, basically, the gear position is selected according to the engine load and the vehicle speed. Further, in the present invention, the difference between the gear ratio of the current gear position and the gear ratio of the gear position after the downshift is set such that the outside air temperature is a predetermined value, In the case of a downshift performed below, the gear is shifted to a gear position having a smaller value. That is, if the outside air temperature is low, there is a high possibility that the road surface freezes, and thus the shift in such a case is performed so that the fluctuation of the torque is reduced.
As a result, the tire is less likely to slip, and stable running can be performed.

Embodiment Next, an embodiment of the present invention will be described with reference to the drawings.

The example shown in FIG. 1 shows an example in which a gear train is composed mainly of three sets of single pinion type planetary gear mechanisms 1, 2, and 3. Each element in the planetary gear mechanisms 1, 2, and 3 is shown. Are concatenated as follows. That is, the carrier 1C of the first planetary gear mechanism 1 and the ring gear 3R of the third planetary gear mechanism 3
And the ring gear 2R of the second planetary gear mechanism 2 and the third planetary gear mechanism 3
And the carrier 3C are connected so as to rotate integrally. The sun gear 1S of the first planetary gear mechanism 1 is connected to the carrier 2C of the second planetary gear mechanism 2 via the second clutch means K2, while the sun gear of the second planetary gear mechanism 2 is connected via the fourth clutch means K4. 2S, and the second carrier 2C of the second planetary gear mechanism is a sun gear of the third planetary gear mechanism 3.
Connected to 3S.

In addition, as a connection structure of the above-described components, a connection structure employed in a general automatic transmission such as a hollow shaft, a solid shaft, or an appropriate connecting drum can be employed.

The input shaft 4 is connected to an engine (not shown) via a power transmission means (not shown) such as a torque converter and a fluid coupling, and the input shaft 4 and the ring gear 1R of the first planetary gear mechanism 1 are connected to each other. In between, the first to selectively connect the two
A clutch means K1 is provided, and a third clutch means K3 for selectively connecting the input shaft 4 and the sun gear 1S of the first planetary gear mechanism 1 is provided between the input shaft 4 and the sun gear 1S.

In practical use, each of the above clutch means K1,
~ K4 can be configured as a multi-plate clutch, a one-way clutch or a combination thereof, and there are restrictions on the arrangement of each component, so that a connecting drum or the like is used as a connecting member for each clutch means K1, ~ K4. It goes without saying that an appropriate intermediate member can be interposed.

The second planetary gear mechanism 2 serves as brake means for preventing the rotation of the rotating members in the planetary gear mechanisms 1, 2, and 3 described above.
Brake means B2 disposed between the carrier 2C of the vehicle and a transmission case (hereinafter simply referred to as a case) 6
And a third brake means B3 disposed between the sun gear 2S of the second planetary gear mechanism 2 and the case 6. As these brake means B2, B3, a multi-plate brake, a band brake, or a configuration in which these are combined with a one-way clutch can be adopted, and these brake means B2, B3 and their brake means B2, B3 It goes without saying that a suitable connecting member can be interposed between the member to be fixed or the case 6.

An output shaft 5 for transmitting rotation to a propeller shaft and a counter gear (not shown) is connected to a ring gear 2R of the second planetary gear mechanism 2 and a carrier 3C of the third planetary gear mechanism 3 which are connected to each other. Have been.

Also in the automatic transmission having the configuration shown in FIG. 1, the clutch means K1 to K4 and the brake means B2, B3 are appropriately engaged and disengaged.
A plurality of shift speeds can be set by releasing the gear, and a hydraulic control device C and an electronic control unit (ECU) E are provided as control devices for performing the control. The electronic control unit E includes a vehicle speed V, a throttle opening θ, a shift position signal, a coolant temperature,
It calculates a gear position to be set based on input data such as the outside air temperature T ° C. and outputs a signal to the hydraulic control device C. A conventional configuration mainly using a microcomputer can be employed. . The hydraulic control device C engages and disengages the clutch means and the brake means with each other.
A conventionally known hydraulic pressure supply / discharge valve for releasing the hydraulic pressure, which includes a pressure regulating valve, a shift control valve, and an electromagnetic valve for operating the shift control valve, can be used.

The shift speeds that can be set based on the output of the above-described control device are the total of the five main forward speeds and the reverse speed, in which the gear ratios are close to geometric series, plus 2.5, 3.2, and 3.5 speeds. Table 8 shows the operation table for setting these and the gear ratio at each gear stage. In Table 1, ○ indicates engagement, blank indicates release, and * indicates that engagement may be performed. The columns with the symbols... Indicate different engagement / disengagement patterns for setting the gear. Further, the gear ratio is obtained by setting the gear ratio of each of the planetary gear mechanisms 1, 2, 3 to ρ1 = 0.450, ρ2 = 0.
405, ρ3 = 0.405.

In the automatic transmission shown in FIG. 1, there are usually five main speeds in which the gear ratio is close to a geometric series, ie, the first gear and the second gear.
The shift is performed in accordance with a gear sequence consisting of a third speed, a third speed, a fourth speed, and a fifth speed, and each speed is selected mainly based on two factors: throttle opening and vehicle speed.
When the outside air temperature T is lower than the predetermined temperature T _C , a shift to a shift different from that, that is, a shift to a shift that has a smaller change in the gear ratio than a shift to a shift determined mainly by the throttle opening and the vehicle speed. Is performed. More specifically, FIG. 2 shows an example of the control routine, and FIG.
When it is determined that the downshift to the first speed is performed (step 1), it is determined whether or not the outside air temperature T ° C. is lower than a predetermined temperature T _C ° C. as a reference value (step 2). The reference temperature TC ° C. is set to a sufficiently low temperature (for example, 0 ° C.). If the determination result is “yes”, the possibility that the road surface is frozen or the possibility of freezing is high. Even if the shift speed determined by the vehicle speed and the vehicle speed is the second speed, the control device executes the shift to the 2.5th speed (step 3). If the result of the determination in step 2 is “NO”, the possibility of the road surface freezing is low, so that the shift to the second speed is performed as in the case of the normal running (step 4).

Therefore, in the automatic transmission described above, when the possibility of freezing on the road surface is high, instead of downshifting from the third speed to the second speed, the automatic transmission is downshifted to the 2.5th speed, which is not used in normal running, and its gear ratio Is "0.214", and the amount of change in the gear ratio is smaller than when the gear ratio difference when downshifting to the second speed is "0.632". As a result, the torque fluctuation in the driving wheels is reduced, so that the tire can be prevented from slipping even on a so-called low μ road such as a frozen road surface. Further, since the speed is shifted to a speed near the vehicle speed determined by the throttle opening and the vehicle speed, there is no particular shortage of driving force. 2.5th
Downshifting from first gear to second gear is optional,
Also in this case, there is no possibility of slipping because the torque fluctuation is reduced.

Although the above description has been made by taking a downshift from the third speed as an example, as is known from Table 1, the first shift is performed.
In the automatic transmission shown in the figure, there are a third speed and a third speed between the third speed and the fourth speed, which are not used in normal traveling,
If the shift to the third speed is determined by the change in the throttle opening while driving in the fourth speed, if the outside air temperature is low, the speed is shifted to the third speed or the third speed instead of shifting to the third speed. The speed may be changed.

Further, the present invention can be applied to an automatic transmission having a gear train capable of setting a so-called intermediate stage which is not set in normal traveling, and another example of such a gear train. In the example shown in FIG. 3, the carrier 2C of the second planetary gear mechanism 2 and the third
A fifth clutch means K5 for selectively connecting the sun gear 3C of the planetary gear mechanism 3 to the sun gear 3C and a first brake means capable of fixing the sun gear 3S of the third planetary gear mechanism independently.
B1 and a fourth brake means B4 capable of independently fixing the sun gear 1S of the first planetary gear mechanism are further provided. The operation table is shown in Table 2.

Further, the example shown in FIG. 4 is the second of the configurations shown in FIG.
The ring gear 2R of the planetary gear mechanism 2 is connected to the ring gear 3R instead of the carrier 3C of the third planetary gear mechanism 3, and the fourth brake means B4 is eliminated, and the other configuration is the same as the configuration shown in FIG. Things. Table 3 shows the operation table.

Even in the automatic transmission having the gear train shown in FIG. 3 or FIG. 4, in addition to the five main forward speeds in which the gear ratio is close to a geometric series, the gear ratio value is Since it is possible to set a so-called intermediate speed which is a value between the speed ratios of the shift speeds,
The gear to be set based on the outside air temperature as in the first embodiment described above can be different from that in the case of normal traveling.

Further, as described above, other examples of the gear train capable of shifting using a so-called intermediate speed include, for example, Japanese Patent Application Nos. Hei 1-185151, Hei 1-185152, Japanese Patent Application No. Hei 1-186991, Japanese Patent Application No. 1-1869992, Japanese Patent Application No. Hei 1-20554
No. 78, Japanese Patent Application No. 1-280957, and the like, each of which has a description and drawings.

Effect of the Invention As described above, in the automatic transmission according to the present invention, a shift with a small difference in the gear ratio is performed at a low temperature where there is a high possibility of freezing on the road surface. In this way, stable running can be performed by preventing tire slip beforehand, and shifting to a gear speed close to the gear speed determined by the throttle opening and the vehicle speed is executed. Can be prevented.

[Brief description of the drawings]

FIG. 1 is a skeleton diagram showing an embodiment of the present invention in principle, FIG. 2 is a flowchart showing an example of a control routine, FIG. 3 is a skeleton diagram showing a gear train in another embodiment of the present invention, and FIG. FIG. 4 is a skeleton diagram showing a gear train in still another embodiment of the present invention. 1,2,3 ... Planetary gear mechanism, 1S, 2S, 3S ... Sun gear, 1C, 2
C, 3C carrier, 1R, 2R, 3R ring gear, 4 input shaft, 5 output shaft, C hydraulic control unit, E electronic control unit.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F16H 59/00-61/12 F16H 61 / 15,61 / 24 F16H 63/40-63/48

Claims (1)

(57) [Claims] In an automatic transmission for determining a gear position based on at least two factors of an engine load and a vehicle speed, a difference between a gear ratio of a current gear position and a gear ratio of a gear position after a downshift is determined. Control for setting the shift speed after the downshift so that the downshift performed when the outside air temperature is equal to or less than the predetermined value becomes smaller than the downshift performed based on the above two factors. An automatic transmission for a vehicle, comprising a device.