Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
1999-04-12
2001-01-23
Louis-Jacques, Jacques H. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C701S110000, C123S339120, C180S170000
Reexamination Certificate
active
06178371
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to vehicle speed control, or cruise control, of a vehicle powered by an internal combustion engine where engine brake torque is controlled to a continuously variable level in both the positive and negative direction.
BACKGROUND OF THE INVENTION
Vehicle speed control systems are utilized to cause the actual vehicle speed to achieve a target vehicle speed set by the vehicle driver. To control vehicle speed, engine torque is adjusted to a value that will cause the actual vehicle speed to achieve the target through manipulation of various parameters that influence engine torque.
A particular situation that has posed considerable challenge in vehicle speed control systems is controlling vehicle speed on a downgrade. In this situation, the engine must be controlled to absorb energy. In an alternate viewpoint, the engine brake torque, which is the torque at the crankshaft available to the vehicle driveline, must be controlled to a negative value.
One method of vehicle speed control controls engine airflow and cylinder deactivation. In this method, a throttle actuator controls engine airflow so that the actual vehicle speed reaches the desired vehicle speed. If an overspeed condition exists, i.e. the actual vehicle speed is greater than the desired vehicle speed and the throttle actuator reaches its lower physical limit, then cylinder deactivation is employed. In this method, the control first employs airflow control. When the airflow reaches its minimum physical value, then cylinder deactivation is used to further decrease the vehicle speed. In other words, airflow control is utilized until the airflow is moved to the minimum physical value (dictated by various air leakage paths), then other methods of reducing engine torque are utilized. One such method is disclosed in U.S. Pat. No. 4,862,367.
The inventors herein have recognized a disadvantage with the above approach. When the engine torque is controlled via airflow, a smooth and continuous engine torque is provided to smoothly control vehicle speed. However, when the airflow reaches its physical minimum value, there is a shock to the vehicle as the torque is further reduced via cylinder deactivation. This disadvantage can be moderated by decreasing the minimum physical airflow value through various mechanical design alternatives and minimization of leakage; however, there will always be some leakage airflow through the engine and thus the minimum airflow will never be zero. Therefore, when practicing the above method, there will always be a shock to the vehicle when it is necessary to deactivate cylinders to maintain the desired vehicle speed.
The inventors herein have recognized another disadvantage with the above approach. Reducing the minimum airflow limit to such low levels increases incidence of engine misfire, causing an increase in regulated emissions. Thus, the shock cannot be reduced to zero due to current emission regulations and problems associated with engine misfire as extremely low airflows.
Another vehicle speed control system attempts to solve this disadvantage by delaying cylinder deactivation for a predetermined time period or allowing vehicle overspeed situations. Such a system is disclosed in U.S. Pat. No. 5,646,851. The inventors herein have recognized a disadvantage with this approach. Using a delay does not eliminate the shock problem, it simply postpones the problem or reduces the frequency at which to problem occurs. Allowing vehicle overspeed is undesirable to a vehicle driver and thus reduces customer satisfaction.
SUMMARY OF THE INVENTION
An object of the invention claimed herein is to provide a vehicle speed control system capable of smoothly controlling vehicle speed on a downgrade without increase in regulated emissions.
The above object is achieved, and problems of prior approaches overcome, by a method for controlling an actual vehicle speed of a vehicle to a desired vehicle speed, the vehicle having an engine with operating parameters that influence an engine torque. The method comprises the steps of calculating a desired engine torque that would cause the actual vehicle speed to approach the desired vehicle speed, determining a required airflow that would generate said desired engine torque, determining a minimum allowable airflow which would allow adjustment of the operating parameters to adjust the engine torque without adversely affecting engine performance, controlling airflow to said required airflow when said required airflow is greater than said minimum airflow, thereby providing said desired engine torque, and controlling airflow to said minimum airflow and adjusting the operating parameters to provide said desired engine torque when said required airflow is less than said minimum airflow.
By going against the teachings of prior art and raising the lower allowable airflow level during torque control to a value greater than the minimum physical airflow, it is possible to smoothly control engine torque to lower levels using a coordinated combination of cylinder deactivation, spark timing, and/or air/fuel ratio. Further the associated problems of operating at a minimum physical airflow, such as engine misfires, are removed. Thus, in the first torque control range, airflow is used to smoothly control engine torque. In the second torque control range where airflow is held at the minimum allowable airflow, the coordination of cylinder deactivation, spark timing, and/or air/fuel ratio are used to smoothly control engine torque without causing engine misfires. Thus, vehicle speed can be smoothly controlled to the desired vehicle speed, even on downgrades where cylinder deactivation is necessary to reduce the engine brake torque to large negative levels.
An advantage of the present invention is the increased customer satisfaction.
Another advantage of the present invention is the ability to reduce regulated emissions.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.
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Cullen Michael John
Hippley Richard John
Light Dennis Allen
Ford Global Technologies Inc.
Louis-Jacques Jacques H.
Russell John D.
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