Machine element or mechanism – Gearing – Interchangeably locked
Reexamination Certificate
2001-06-29
2002-10-15
Marmor, Charles A. (Department: 3681)
Machine element or mechanism
Gearing
Interchangeably locked
C074S331000, C074S336001, C477S174000, C477S175000, C477S176000, C192S1030FA, C192S1030FA
Reexamination Certificate
active
06463821
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally pertains to motor vehicles. More particular, the present invention pertains to a method of controlling a transmission. More specifically, but without restriction to the particular embodiment and/or use which is shown and described for purposes of illustration, the present invention relates to a method for controlling a transmission having a dual clutch system during vehicle launch.
BACKGROUND OF THE INVENTION
There are presently two typical power transmissions in use on the conventional automobile. The first, and oldest, type of powertrain is the manually operated powertrain. These powertrains are characterized by having manual transmissions including a clutch pedal to the left of a brake pedal and a gear shift lever which is usually mounted at the center of the vehicle just behind the dashboard. To operate the manual transmission, the driver must coordinate depression of the clutch and accelerator pedals with the position of the shift lever in order to select the desired gear. Proper operation of a manual transmission is well known to those skilled in the art, and will not be described further herein.
In a vehicle having an automatic transmission, no clutch pedal is necessary. The standard H configuration of the shift lever is replaced by a shift lever which typically moves back and forth. The driver need only select between park, reverse, neutral, drive, and one or two low gears. As is commonly known in the art, the shift lever is placed in one of several positions having the designator P, R, N, D,
2
, and maybe
1
which correspond to Park, Reverse, Neutral, Drive, and one or two low gears, respectively. Vehicle operation when the gear shift lever is placed in one of these positions is well known in the art. In particular, when in the drive mode, the transmission automatically selects between the available forward gears. As is well known, older systems typically included first, second and third gears, while newer systems include first through third gears as well as a fourth and possibly a fifth and a sixth overdrive gears. The overdrive gears provide an improved fuel economy at higher speeds. As is well known, early transmissions were almost exclusively manually operated transmissions.
With a steady development of automatic transmissions, drivers increasingly gravitated toward the easy operation of automatic transmissions. However, in the mid 1970s, rising concerns about present and future fossil fuel shortages resulted in an implementation of corporation average fuel economy (CAFÉ) regulations propagated in several countries. These fuel economy requirements necessitated the investigation of increasing the fuel economy of motor vehicles in order to meet government regulations. These government regulations prompted a gradual return to manual transmissions which are typically more efficient than automatic transmissions.
In the ensuring years, many mechanically operated vehicle systems were replaced or at least controlled by electronic control systems. These electronic control systems greatly increased the fuel efficiency of vehicle engines and enabled a gradual return to the convenience of automatic transmissions. In addition, electronic controls used with automatic transmissions, greatly improved the shift schedule and shift feel of automatic transmissions and also enabled implementation of fourth and fifth overdrive gears thereby increasing fuel economy. Thus, automatic transmissions have once again become increasingly popular.
Automatic and manual transmissions offer various competing advantages and disadvantages. As mentioned previously, a primary advantage of a manual transmission is improved fuel economy. Conversely, automatic transmissions first and foremost offer easy operation, so that the driver need not burden both hands, one for the steering wheel and one for the gear shifter, and both feet, one for the clutch and one for the accelerator and brake pedal, while driving. When operating an automatic transmission, the driver may have both one hand and one foot free. In addition, an automatic transmission provides extreme convenience in stop and go situations, as the driver need not worry about continuously shifting gears to adjust to the ever-changing speed of traffic.
The primary reason for the superior efficiency of the manual transmission over the automatic transmission lies in the basic operation of the automatic transmission. In most automatic transmissions, the output of the engine connects to the input of the transmission through a torque converter. Most torque converters have an input impeller that is connected to the output shaft of the engine and an input turbine that is connected to the input shaft of the transmission. Movement of the impeller at the input side results in a hydraulic fluid flow which causes a corresponding movement of the hydraulic turbine connected to the input shaft of the transmission. While torque converters provide a smooth coupling between the engine and the transmission, the slippage of the torque converter results in a parasitic loss, thereby decreasing the efficiency of the powertrain. Further, the shift operation in an automatic transmission requires a hydraulic pump which pressurizes a fluid for clutch engagement. The power required to pressurize the fluid introduces additional parasitic losses of efficiency in the powertrain.
Before a shift between the gear ratios of a manual transmission can occur, it is necessary to synchronize the rotational speed of the driveshaft with the rotational speed of the driven shaft. Typically, synchronization is obtained in a manual transmission by way of a synchronizing mechanism such as a mechanical synchronizer which is well known in the art. The mechanical synchronizer varies the speed of the driveshaft to match the speed of the driven shaft to enable smooth engagement of the selected gear set. For example, during an upshift, the mechanical synchronizer utilizes frictional forces to decrease the rate of rotation of the driveshaft so that the desired gear of the driveshaft is engaged smoothly to drive the desired gear of the driven shaft. Conversely, during a downshift, the mechanical synchronizer increases the rate of rotation of the driveshaft so that the desired gear is engaged smoothly to drive the desired gear on the driven shaft.
Typically, with a manual transmission, there is a delay period between disengagement of the currently engaged gear and the subsequent synchronization and engagement of the desired transmission gear. Also, during this process, the clutch connection between the engine output shaft and the transmission input shaft needs to be disengaged prior to the gear shifting process and reengaged upon synchronization. These delays and periods of clutch disengagement create periods of torque interruption that are generally undesirable and usually result in a noticeable jolt as the gears are shifted. Such a jolt is particularly noticeable in the shift between first and second gears as the vehicle accelerates.
In order to reduce these jolts and to still take advantage of the benefits of manual transmissions, as well as to provide an automated shifting system, various designs have been proposed. In particular, various dual clutch manual transmissions have been proposed that include automated electromechanical shifting mechanisms and methods. For example, U.S. Pat. Nos. 6,044,719 and 6,012,561, which are incorporated herein by reference, each disclose a dual clutch electo-mechanical automatic transmission.
In general, these dual clutch type systems attempt to reduce the jolt associated with torque interruption as gears are shifted by starting to engage the next gear with one clutch while the current gear is disengaged with the other clutch. To further reduce the jolt associated with gear shifts in these types of transmissions, methods to control dual clutch transmissions have also been proposed.
For example, U.S. Pat. Nos. 5,950,781 and 5,915,512 each disclose a twin-clutch transmission having two input shafts and a method for
Cherry Jeffrey P
Reed, Jr. Richard G.
Calcaterra Mark P.
DaimlerChrysler Corporation
Le David D.
Marmor Charles A.
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