Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
2000-01-27
2001-07-24
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C701S074000, C701S071000, C701S082000, C180S197000
Reexamination Certificate
active
06266603
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to automatic transmissions for land vehicles equipped with gearboxes with discrete gear ratios or constantly varying transmission ratios. It relates more specifically to a method for detecting slippery ground on which the driving wheels of a vehicle have a tendency either to spin or to lock up.
DESCRIPTION OF THE INVENTION
A number of methods of controlling automatic transmissions, having a greater or lesser ability to take particular running conditions into consideration, are already known in the state of the art.
Thus, document FR 83/07277 describes a control method intended to eliminate inopportune up-shifting from a ratio N−1 to a higher ratio N in a phase when the driver has lifted off. However, this document does not tackle the problems associated with the spinning or locking of the driving wheels.
Another prior document, EP-A-0,638,742, describes the control of an automatic transmission using variables associated with the load of the vehicle, with the driver's more or less sporty driving style, and with the advisability of a change in gear ratio. These variables are obtained using fuzzy logic, as a function of a number of input parameters including conditions of the spinning of the driving wheels. However, the way in which the wheelspin or wheel lock-up conditions are taken into account, and the detection of the existence of slippery ground, are not described.
Furthermore, in most of the known methods for managing gear changes (continuous or discrete) in automatic mode, the driver has the option of manually selecting, using a switch, a particular driving mode tailored to slippery ground, and generally known as the “winter” or “snow” mode.
SUMMARY OF THE INVENTION
An object of the invention is to assist the driver in the particular situations mentioned previously, so as to guarantee optimum safety and the best possible driving comfort.
To this end, the invention proposes a method comprising steps consisting in:
detecting the instantaneous running conditions, with the aid of at least one parameter that represents the existence or otherwise of slippery ground;
on the basis of this detection, generating, by counting, a value that represents the change in running conditions as a function of time;
comparing the said value with reference conditions;
as a function of the result of the said comparison, deciding whether or not the instantaneous running conditions correspond to slippery ground,
characterized in that in order to generate, by counting, a value that represents the change in running conditions as a function of time, a current value is decremented by a first step (&Dgr;x_&Dgr;B) each time locking of the driving wheels is detected, the said current value is decremented by a second step (&Dgr;x_&Dgr;E) each time the spinning of the driving wheels is detected, and the said current value is incremented by a third step (&Dgr;x_out) when the wheels are not locked or spinning.
According to other features of the method:
the said reference conditions with which the value representing the change in running conditions is compared consist of a lower threshold (S
1
) and an upper threshold (S
2
), and it is decided that the ground is slippery when the said value becomes higher than the lower threshold (S
1
), and it is decided that the ground is not slippery when the said value becomes lower than the upper threshold (S
2
).
advantageously, the lower threshold (S
1
) and the upper threshold (S
2
) are variable over time and are set as a function of the driver's driving style.
as a preference, the incrementation step (&Dgr;x_out) is set as a function of the driver's driving style.
The invention makes provision, when slippery ground is detected, for at least one of the following actions to be taken:
the automatic transmission is switched into a safety operating mode, particularly the so-called “snow” mode to provide drive to the vehicle;
an indicator alerting the driver to the fact that the safety mode has been adopted is activated;
the function of down-shifting early under braking is cancelled so as not to down-shift if the wheels are locked.
In order to obtain the intended results, the invention therefore relies firstly on a principle of detecting slippery ground, this principle being based essentially on analysing the gradient of a parameter that represents the speed of the driving wheels. This analysis makes it possible automatically to activate a special mode for managing the transmission ratios, this mode being tailored to low adhesion, and this, on the one hand, provides the driver with greater safety and, on the other hand, affords driving comfort that is optimized with respect to the specific running conditions.
Automatic switching to “snow” mode allows the driver to obtain optimized management of the automatic transmission ratios for the running conditions encountered on slippery ground.
This makes it possible, for example, when pulling way with wheelspin, to be in a transmission ratio which provides the vehicle with drive and which, when the wheels lock up, makes it possible not to engage low ratios at high speed, as this would be ill advised from the safety point of view.
Furthermore, in order to detect a condition in which the driving wheels are locked up, the derivative of a characteristic variable of the rotation of the driving wheels is analysed under braking, and a locking of wheels is detected if the brake is active and if the said derivative is negative and below a threshold (Sb) representative of locking.
Furthermore, to detect the end of a condition of locking, the method according to the invention comprises the following steps:
(C1): testing whether the brake is released and whether the vehicle speed is below a first threshold (Svv1) and, if these conditions are satisfied, starting a first time delay (T1);
(C2): testing whether the vehicle speed is above a second threshold (Svv2) or whether the selected transmission ratio is higher than or equal to the current ratio and, if one of these conditions is satisfied, starting a second time delay (T2);
(C3): testing whether one of the said time delays (T1,T2) has elapsed, whether the automatic transmission is in the P, R or N position, or whether the “kick-down” is activated,
and if one of these conditions (C1,C2,C3) is satisfied, detecting the end of a condition in which the driving wheels are locked.
The invention also relates to an automatic transmission employing the above control methods and to a motor vehicle with an automatic gear box with discrete gear ratios equipped with such an automatic transmission.
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Arbona Jean-Pierre
Taffin Christian
Cuchlinski Jr. William A.
Hernandez Olga
Renault
Young & Thompson
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