Interrelated power delivery controls – including engine control – Transmission control – Continuously variable friction transmission
Reexamination Certificate
2001-02-12
2003-04-15
Wright, Dirk (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Continuously variable friction transmission
Reexamination Certificate
active
06547692
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a system for adjusting the tension of the belt of a continuously variable transmission.
BACKGROUND OF THE INVENTION
Such a system is described in FIG.
1
and is known, for example, from EP-A-0 451 887. This publication too relates to the adjustment of the tension of a belt means
1
, usually a belt, in a continuous belt transmission
2
comprising belt means
1
, a drive pulley
3
and an output pulley
4
which is driven by an engine
11
.
To adjust the transmission ratio of a continuously variable belt transmission and the tension of the belt means
1
, the drive pulley
3
comprises an axially stationary conical pulley half
7
and an axially movable conical pulley half
9
and the output pulley
4
comprises an axially stationary conical pulley half
8
and an axially movable conical pulley half
10
. The drive pulley
3
is also known as the primary pulley and the output pulley
4
is also known as the secondary pulley. Pressing of the axially movable conical pulley halves
9
and
10
against the belt means
1
takes place in response to the build-up of a hydraulic pressure in the respective oil chambers
5
and
6
. The desired transmission ratio of the continuously variable belt transmission and the required tension of the belt means
1
can be adjusted by a suitable selection of the applied pressures P
prim
and P
sec
in the oil chambers
5
and
6
. For the force transmission from the engine
11
to the drive pulley
3
, for example, a torque converter
12
and a planetary assembly
13
can be provided with clutches for forward and rearward travel. The engine
11
can also drive the pump
14
of the continuously variable belt transmission. A transmission control
18
comprises the electrical and hydraulic components for driving the continuously variable belt transmission. The transmission control
18
includes means for adjusting the pressure in the oil chamber
6
or in the oil chambers
5
and
6
.
The tension of the belt means
1
is adjusted in one embodiment of the transmission control
18
utilizing the pressure P
sec
in the output end oil chamber
6
.
The tension of the transmission means
1
is to be so adjusted that the efficiency of the continuously variable belt transmission is a maximum. On the one hand, it is to be prevented that the belt means
1
slips because of too low a tension and, on the other hand, the tension of the belt means
1
should not be too high in order to avoid high losses in the continuously variable belt transmission. To reconcile the two requirements, the torque transmitted from the drive pulley
3
to the output pulley
4
must be known as precisely as possible. The torque to be transmitted on the drive pulley
3
is determined primarily by the torque of the engine
11
and the torque amplification factor of the torque converter
12
.
In U.S. Pat. No. 5,337,628 a method for adjusting the pressure P
sec
in the output end oil chamber
6
is described. In this method, the rotational angle &agr;
Dk
of the throttle flap
15
of the engine
11
is detected by a sensor
16
. Furthermore, the rpm N
mot
of the engine
11
, the rpm N
prim
of the primary pulley
3
and the rpm N
sec
of the secondary pulley
4
are measured with rpm sensors
19
,
20
and
21
and conducted as corresponding signals to the transmission control
18
. The angle position &agr;
Dk
of the throttle flap is measured by the sensor
16
. The angle position &agr;
Dk
, the engine rpm N
mot
, the primary rpm N
prim
, and the secondary rpm N
sec
are utilized in the transmission control
18
to adjust the tension of the belt means
1
by adjusting the pressure in the oil chamber
6
.
To adjust the tension of the belt means
1
, the engine torque to be expected is estimated with a characteristic field of the throttle flap angle and the engine rpm. The engine torque to be expected is converted into an expected primary torque in a characteristic field with the formed quotient of the primary rpm and the engine rpm. Thereafter, the computation of the required pressure P
sec
takes place in the output end oil chamber to adjust the tension of the belt element
1
.
The use of the throttle flap angle &agr;
Dk
to estimate the torque has the disadvantage that the calibration of the throttle flap potentiometer must take place very precisely. Even a small deviation of the measured throttle flap angle from the actual throttle flap angle can, in the above method, lead to a considerable deviation between the expected engine torque and the actual engine torque. It is difficult to guarantee that the throttle flap angle will always be measured correctly. For this reason, the belt tension must be held above the required level with a higher safety reserve in that a pressure higher about the reserve pressure is adjusted in the output end oil chamber. This leads to higher losses in the transmission and in the pump. Furthermore, problems can occur for the estimate of the engine torque during dynamic driving conditions with greater time-dependent changes of the engine rpm.
U.S. Pat. No. 6,050,913 improves the above-mentioned adjustment of the belt tension in that, for example, a torque value, which is computed in the engine control apparatus, is applied to adjust the belt tension. Embodiments for determining the safety reserve are not be found.
In modern-day engine control systems, a detection of combustion misfires of one or several cylinders of the vehicle is mostly in use which computes an engine rough running value from fluctuations of the engine rpm. This value is compared to the applied threshold values. A combustion misfire is detected when the engine rough running exceeds the threshold value. For this purpose, reference is made to German patent publication 4,138,765. Problems can be caused in this context by various disturbance quantities on the engine rpm signal. Such disturbance quantities are, for example, mechanical defects of the transducer wheel in detecting engine rpm, charge differences of the individual cylinders (differences because of the combustion process) and torsion vibrations. These disturbance influences are adapted in normal operation for precise misfire detection which is described in German patent publication 196 22 448 and in European patent publication 0,733,890. This means that, after a completed adaptation, corrective values are available which are considered for a precise detection of the engine rpm.
Furthermore, distance control systems are known from the state of the art, for example, from the publication mot, no. 15, Jun. 11, 1998. These distance control systems detect the distance of a vehicle to a vehicle traveling ahead. In general, this takes place via a radar sensor. If the distance becomes too little, then these systems provide for brake interventions independent of the driver.
SUMMARY OF THE INVENTION
The task of the present invention comprises optimizing the belt tension and especially determining the safety reserve.
As already mentioned, the invention proceeds from a system for adjusting the tension of the belt part (for example, the band) of a belt transmission mounted downstream of the vehicle engine and preferably a belt transmission which is continuously adjustable in its transmission ratio. First means for controlling (open loop and/or closed loop) the vehicle engine and second means for controlling (open loop and/or closed loop) of the continuously variable transmission are provided. With the first means, a first signal is determined which represents the engine torque of the vehicle engine and is supplied by the first means to the second means. With the second means, the tension is then adjusted in dependence upon the first signal and a safety reserve.
The essence of the invention comprises that this safety reserve is not fixedly pregiven; instead, this safety reserve is determined in dependence upon various conditions. For this reason, one reaches a reduction of the lump-sum reserve pressure of the belt tension control and thereby an improved transmission efficiency and thereby a reduced c
Dressler Norbert
Luh Joachim
Ries-Mueller Klaus
Ottesen Walter
Robert & Bosch GmbH
Wright Dirk
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