Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication
Reexamination Certificate
2002-02-20
2004-03-02
Camby, Richard M. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
C701S036000, C701S051000
Reexamination Certificate
active
06701224
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to a method for determining the descending/ascending status of a moving vehicle.
BACKGROUND OF THE INVENTION
Modern motor vehicles are equipped with different electronic systems for controlling and regulating the driving performance. Examples are brake force control systems (ABS), driving stability programs (ESP) and traction slip control systems (TCS, BTCS or TSC). Depending on their design, the control programs integrated in the electronics of these systems evaluate a varying number of sensors provided in the motor vehicle. These are, for example, wheel speed, longitudinal acceleration, transversal acceleration and engine torque sensors. The electronics in a traction slip control system ensure that the wheels accelerating the vehicle do not spin when the vehicle is accelerated strongly. This can be achieved by braking the spinning wheel and/or by throttling the propulsion power (engine torque reduction).
DE-A 3809101 discloses a method and a circuit arrangement for controlling a TCS by means of brake and engine intervention. According to this method, the wheel brake is used for controlling the traction slip and/or the system intervenes in the control of the driving engine. For this purpose, the traction slip control, amongst others, uses the components usually found in anti-lock systems (ABS), which are provided in any case. The communication with the required vehicle components (for example the engine) can occur through a vehicle databus (CAN). For the purpose of executing the method, sensors for determining the rotational wheel behavior are evaluated by electric circuits in order to process signals, and actuating signals for generating electromagnetic hydraulic valves are generated, thus making control of the braking force possible. The electronics of the system need the so-called vehicle reference speed V
ref
for calculating the required actuating value. As a rule, this value is determined on the basis of the wheel speeds of the individual wheels. In special driving situations, one or several wheels may no longer provide the current vehicle speed since one of the wheels is spinning. In this case, the spinning wheel is not used for calculating the vehicle reference speed V
ref
.
The control algorithms of the ABS use the vehicle reference speed V
ref
as an essential input variable. When the vehicle reference speed deviates from the actual vehicle speed V
t
, this may cause an unjustified activation of the anti-lock system, which leads to a decrease in braking pressure for a certain time. Due to the dangers connected to this, a deviation between V
ref
and the actual speed V
t
should, if at all, prevail for as short a time period as possible.
In the electronic systems for controlling the driving performance described above, the effects of driving uphill or downhill, which are especially important in all-wheel vehicles, are not taken into consideration at all or not sufficiently. If, for example, a traction slip control determines that the driving wheels are spinning, the vehicle reference speed while driving uphill would be too high because of an erroneous interpretation of the longitudinal sensor. As a result the traction slip control would not respond adequately to the traction slip, e.g. by reducing the engine torque. On the other hand, the ABS control would be too sensitive when driving downhill.
BRIEF SUMMARY OF THE INVENTION
Hence, it is the object of the present invention to provide the electronic systems customarily used today for controlling the driving performance with an improved method for determining that the motor vehicle is driving uphill or downhill, so that the vehicle reference speed V
ref
can be approximated more quickly to V
t
, meaning that the electronic systems for controlling the driving stability, etc. which use the vehicle reference speed as an input variable, can be applied more reliably.
According to the present invention, this object is solved by a method for determining that a motor vehicle (
1
) moving at the speed V
t
is climbing or descending a slope, including the following steps:
determining a vehicle reference speed V
ref
by means of wheel speed sensors (
2
), wherein V
ref
can, if necessary, be corrected through extrapolation of acceleration data, engine torque data and/or information on the gear level that is engaged, especially when wheels (
3
) are spinning exclusively;
determining a vehicle acceleration a
ref
from V
ref
by means of differentiation (
4
);
comparing a
ref
with a vehicle longitudinal acceleration a
L
(
5
) determined by sensors,
a) checking whether there is deviation from normal driving by monitoring whether the value of the difference a
L
−a
ref
is greater than a threshold value SL, with SL being greater than zero (
6
),
b) determining a deviation time t within which the determined deviation from normal driving prevails uninterruptedly (
7
),
c) monitoring whether the deviation time t exceeds a minimum time value T
M
, with T
M
being greater than zero, and
d) concluding that the vehicle is driving uphill or downhill when t is greater than T
M
.
According to the present invention, the fact that the motor vehicle is descending or climbing a slope can be determined by means of vehicle data given in the motor vehicle in any case, e.g. longitudinal acceleration, engine torque or wheel speed. For this purpose, a vehicle reference speed V
ref
is determined first on the basis of the wheel sensor signals in a manner known from the prior art. For example, the wheel speed of the slowest rotating wheel can be used for this purpose. By means of differentiation, which, for example, can be numerical, a vehicle acceleration A
ref
can be calculated or generated based on this vehicle reference speed. According to the present invention, this vehicle acceleration is then related to a vehicle acceleration of other sensors. If it seems necessary, a plausibility evaluation of the vehicle acceleration determined on the basis of the wheel speeds may be carried out. When it is plausible that the current vehicle reference speed does not correspond to the actual vehicle speed, this can be extrapolated on the basis of the determined vehicle acceleration (for example, directly from the derived vehicle reference speed or from the acceleration detected by the sensors). For this purpose, for example, a vehicle acceleration is estimated as accurately as possible corresponding to the methods described in P 98938709.7 (P9071) and the unpublished patent application P 19939979.4 (P9584). However, this extrapolation can only be executed without corrections if driving uphill or downhill is not determined at the same time.
P 98938709.7 (P9071) already proposes that driving uphill or downhill be taken into consideration when correcting or extrapolating the vehicle reference speed. This is done according to the method known from the prior art in that spinning of the wheels is detected only if the angular speeds and/or angular acceleration of the wheels differ from one another by certain minimum amounts, or to put it differently, if the above-mentioned values do not lie within a certain value range. In this connection, the knowledge based on past experience is used, i.e. that the wheels do not spin symmetrically, but rather in an uncoordinated fashion; and this means that marked differences in values occur.
According to the present invention, however, wheels spinning equally occur in today's all-wheel vehicles, especially such vehicles that are equipped with an essentially rigid all-wheel clutch (e.g. Haldex clutch), meaning that the method known from the prior art no longer works.
In a motor vehicle with all-wheel drive it may happen that the vehicle reference speed determined over a long period of time on the basis of the wheel speed signals does not correspond to the actual vehicle speed, since all wheels that can be used for this purpose spin on a slippery surface. In the case of spinning wheels, the vehicle acceleration essentially depends on the friction coefficient &mgr; of
Camby Richard M.
Continental Teves AG & Co. oHG
Rader & Fishman & Grauer, PLLC
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