Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
2002-05-02
2004-03-02
Marc-Coleman, Marthe Y. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C701S084000, C701S082000, C303S141000
Reexamination Certificate
active
06701243
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to vehicle brakes, and more particularly relates to a method and a device for controlling traction slip.
BACKGROUND OF THE INVENTION
When driving on very rough or slippery road surfaces, high traction slip values may occur at the wheels of a vehicle even if the driver accelerates only slightly, that means, the engine has only a low excess torque or traction torque. On rough surfaces this is due to the fact that single wheels will lose ground contact at least temporarily in part or in total. On slippery surfaces, the coefficient of friction between the roadway and one or more wheels may be so low that even a low engine torque will cause spinning of the wheels.
When traction control intervenes in such situations, i.e., the control of tractive force which acts by way of an active pressure increase at the wheel brake circuits (BTCS=Brake Traction Control System), stalling of the engine may be caused when the vehicle is equipped with a manually operated transmission and the driver has engaged the clutch. Such a style of driving is conventional even at low vehicle speeds when the driver recognizes that the wheels generally tend to spin. More particularly, full engagement of the clutch is appropriate in offroad driving when the vehicle has a countershaft transmission and there is an extreme gearing-down in a low off-highway gear.
In general, brake-induced ‘stalling situations’ can be avoided because a permanent monitoring of the engine speed, for example, is carried out during traction control. When e.g. the engine speed falls below a critical threshold (‘stalling speed’), the risk of stalling of the engine is detected. In the case of such a stalling risk, the active brake pressure increase on the wheels will be stopped, and pressure decrease can be effected with the maximum possible decrease gradient in order to relieve the engine.
Pressure decrease is usually stopped when the engine speed has reached values again which confirm a stabilization of the engine run.
A measure of this type prevents direct stalling of the engine in the majority of cases. It is disadvantageous that the entire control mostly acts very abruptly and causes frequent stuttering of the engine. On difficult off-road tracks, a driver may become disconcerted by such an abrupt intervention and may be induced to even reduce opening of the throttle, which may further impair the performance of the control. The less the throttle is opened, the greater the risk of stalling the engine in the case of an active braking. In addition, complete brake evacuation may lead to unexpected vehicle reactions, such as a sudden rolling back on a hill.
FIG. 1
shows a conventional BTCS control with the example of a spinning wheel.
In this illustration, reference numeral
10
designates the speed variation of the wheel that tends to spin, reference numeral
11
designates the vehicle speed or a substitute value estimated within the controller, reference numeral
12
is assigned to the engine speed,
13
to a speed threshold, and
14
designates the variation of the pressure which the BTCS delivers into the associated wheel brake circuit. Signals
15
and
16
show two speed thresholds which are calculated during the BTCS control on the basis of slip values (in percent) and determine the change-over between different control states.
The control starts with a pressure increase at the point of time T
1
when the speed
10
of the spinning wheel has exceeded the higher speed threshold
15
. The subsequent pulsed pressure increase ends at the point of time T
2
when the wheel speed
10
has fallen below a lower threshold
16
. Then a normally pulsed pressure decrease will start. Directly afterwards (point of time T
3
) the engine speed drops below the speed threshold
13
in the embodiment shown which triggers a pressure decrease with the maximum gradient (unpulsed) according to the conventional control strategy. This steep pressure decrease is required to prevent ‘stalling’ of the engine in time.
After the engine speed has increased again, the pressure increase after the point of time T
4
will be dictated by the slip of the greatly spinning wheel again and will be performed in a relatively steep fashion which, in turn, causes a strong load on the engine and decrease of the rotational speed with a new instability at the point of time T
5
.
According to the greatly simplified concept in
FIG. 1
, the change-over between the control states ‘pressure increase’ and ‘pressure decrease’ depends on thresholds which, for reasons of clarity, are calculated equidistantly to the (estimated) vehicle speed.
However, the shortcoming of the conventional control is generally seen in that a reaction to the engine in the form of a wheel pressure decrease typically occurs only when the engine speed has dropped below a critical speed threshold. In all other respects, the control and the pressure modulation are only dictated by the behavior of the spinning wheels.
In view of the above, an object of the present invention is to provide a method and a device for controlling traction slip which permit greater engine stability.
According to the present invention, this object is achieved in that a generic method is performed so that at least one further variable which represents a running stability of the engine, is included in the control of the control states and/or the switch-over between the control states.
This renders it possible to make fine adjustments to the traction slip while taking into account the engine situation. The control is dictated by the engine situation which is taken into consideration in each phase of controlling the traction slip. Beside the traction slip (wheel speed and/or wheel acceleration), the running stability of the engine or an engine stability reserve derived therefrom is a controlled variable which is taken into consideration when the correcting variable is formed.
Another object of the present invention is to design a generic device for controlling the traction slip so that a first determination device determines a variable which determines a wheel behavior (speed and/or acceleration) on at least one of the driven wheels and, in dependence on this variable, controls control states such as increase brake pressure, reduce brake pressure, or maintain brake pressure, and regulates the change-over between the control states such a increase brake pressure, reduce brake pressure, or maintain brake pressure, or switch on or off traction slip control, and a second determination device determines at least one further variable which represents a running stability of the engine and makes the first determination device become involved in the control of the control states and/or the change-over between the control states.
To further improve the control behavior, the second variable is continuously considered in the control and/or change-over.
The running stability of the engine is calculated from the difference between an engine speed
F-E-S
and a dynamic instability threshold of the engine, preferably according to the following relation:
ENGINE_STABILITY_RESERVE=
K
1
•(FILTERED_ENGINE_SPEED−ENGINE_STALLING_THR),
with ENGINE_STABILITY_RESERVE=running stability of the engine, K
1
=a constant dependent on the engine characteristic and on the average vehicle weight, FILTERED_ENGINE_SPEED=the filtered engine speed, and ENGINE_STALLING_THR is the instability threshold.
The running stability of the engine or the engine stability reserve is formed by the difference between the current (filtered) engine speed and a dynamic instability threshold according to the relation mentioned hereinabove in that the dynamic instability threshold was calculated by that a portion is subtracted from a vehicle-related base value which is determined proportionally to the gradient of the engine speed.
The second variable is used for switching over between the pressure-increase and pressure-decrease control phases of the BTCS by initiating a pressure decrease when the sec
Haller Frank
Roll Georg
Continental Teves AG & Co. oHG
Marc-Coleman Marthe Y.
Rader & Fishman & Grauer, PLLC
LandOfFree
Method and device for controlling traction slip does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for controlling traction slip, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for controlling traction slip will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3262466