Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Reexamination Certificate
1998-12-14
2001-07-31
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C701S054000, C701S064000, C074S732100, C477S109000
Reexamination Certificate
active
06269293
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention generally relates to transmission control systems and, more particularly, to an interactive engine and automatic transmission control system for improving vehicle drivability during coast down gear shifts and accelerations.
2. Discussion
When an automotive vehicle changes speeds from a cruising rate to a stop or near stop condition, the transmission shifts from a high forward gear down to a low forward gear. This event is known in the art as a coast down shift. In terms of shift quality and driver expectation, the points where the shifts occur are critical.
Shift points are chosen so that the torque on the transmission either remains entirely positive or entirely negative before, during, and after the shift. Because of the wide range of engine speeds that can exist during a coast down event, the shift points are confined to very narrow ranges. Shifting anywhere outside of these ranges has the potential to cause a torque reversal of the drive train which is detectable to the driver as a bump or knock.
Also, when braking moderately from a high speed, a driver expects the deceleration rate of the vehicle to remain constant. However, if a down shift occurs at a relatively high speed, it is possible for the turbine speed to increase substantially above the engine speed. The difference in speed between the engine and turbine will produce a negative torque which will tend to decelerate the vehicle. This torque will add to the driver's braking and cause an objectionable change in the deceleration rate of the vehicle.
For the above reasons, coast down shift points have been traditionally confined to low speed ranges. However, in terms of vehicle performance, low shift speeds can be undesirable. For example, when turning a corner a vehicle should optimally be in a down shifted gear just after entering the corner so that a better engine response and acceleration is provided out of the corner when the driver steps back into the throttle. If a vehicle is in a high gear when exiting the corner, time must be taken to perform a down shift and the desired vehicle response is delayed.
In addition, after braking to a near stop, a driver may tip back into the throttle to accelerate. This often happens when braking for a stop light and then accelerating when the light turns green before a complete stop is achieved. By placing the transmission in the appropriate gear prior to the driver pressing the accelerator pedal, vehicle performance is improved. Unfortunately, to date no effective control system has been provided for adequately down shifting the transmission.
In view of the foregoing, it would be desirable to provide a transmission controller which interacts with the engine controller to increase engine speed above turbine speed during a coast down shift with spark and air flow control so as to improve drivability.
SUMMARY OF THE INVENTION
The above and other objects are provided by an interactive engine and automatic transmission control system wherein spark and air control is used to control engine speed under high speed conditions to maintain a small positive torque on the transmission before and after coast down shifts. More particularly, a transmission controller is electrically coupled to an engine controller in a motor vehicle such that information can be passed therebetween. Such information includes a start of shift signal, a phase of the shift signal (i.e., clutch release phase, speed change phase, or clutch application phase), and a shift complete signal. In addition, the transmission controller identifies the type of shift that is occurring (i.e., fourth gear to third, third to second, or second to first), transmission oil temperature and the acceleration (braking) rate of the vehicle to the engine controller. During the three phases of a coast down shift, air flow control is used to supply an appropriate amount of air to the engine so that closed loop spark control can be used to adjust the speed of the engine. The amount of air supplied during a coast down shift is dependant on the acceleration rate of the vehicle and transmission oil temperature. Spark control is used in conjunction with the air flow control to change the speed of the engine to a level just above or at that of the turbine. By maintaining the engine speed slightly above the turbine speed just before and just after a coast down shift, very little torque is transmitted to the input of the transmission during the shift. As such, very little torque is transmitted through the transmission to the output shaft. Thus, the coast down shift is practically imperceivable to the driver.
As a further feature of the present invention, the capability of performing coast down shifts at higher speed enables shift points to be selected based on a particular vehicle driver's driving habits. For example, a person who is aggressive at braking and accelerating may have coast down shift points selected at a higher speed than a person who is less aggressive. As such, the aggressive driver is provided with good vehicle performance (acceleration and deceleration) while the less aggressive driver is provided with a smooth and quiet drive (e.g., less busy shift schedule).
REFERENCES:
patent: 5211080 (1993-05-01), Leising et al.
patent: 5450828 (1995-09-01), Sakamoto et al.
patent: 5468198 (1995-11-01), Holbrook et al.
patent: 5596495 (1997-01-01), Brown et al.
Correa Colt R.
Huff Shean P.
Leising Maurice B.
Calcaterra Mark P.
Cuchlinski Jr. William A.
DaimlerChrysler Corporation
Donnelly Arthur D.
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