U.S. patent application number 09/402132 was filed with the patent office on 2001-09-20 for device and method for reducing slip in the control system of a cvt in a motor vehicle.
Invention is credited to BOLZ, MARTIN-PETER, HULSER, HOLGER.
Application Number | 20010023216 09/402132 |
Document ID | / |
Family ID | 7824537 |
Filed Date | 2001-09-20 |
United States Patent
Application |
20010023216 |
Kind Code |
A1 |
BOLZ, MARTIN-PETER ; et
al. |
September 20, 2001 |
DEVICE AND METHOD FOR REDUCING SLIP IN THE CONTROL SYSTEM OF A CVT
IN A MOTOR VEHICLE
Abstract
The invention proceeds from a control of a transmission which is
adjustable continuously with respect to its transmission ratio, for
a motor vehicle. The transmission together with a drive unit is
mounted in the drive train of the motor vehicle and the drive unit
has an adjustable drive torque. The transmission includes a drive
end as well as an output end and operative means for establishing a
mechanical operative connection between the drive end and the
output end. Furthermore, detection means for detecting a slip
quantity is provided. The slip quantity represents the slip between
the operating means and the drive end and/or output end. Pregivable
measures are initiated in response to a pregiven value of the slip
quantity. The essence of the invention is that measures as follows
are initiated: a drive of a clutch mounted in the drive train;
and/or, a change of the transmission ratio; and/or, a change of the
output torque of the drive unit. It is especially intended that
measures are initiated in the sense of a slip reduction.
Inventors: |
BOLZ, MARTIN-PETER;
(OBERSTENFELD, DE) ; HULSER, HOLGER; (STUTTGART,
DE) |
Correspondence
Address: |
WALTER OTTESEN
PO BOX 4026
GAITHERSBURG
MD
208854026
|
Family ID: |
7824537 |
Appl. No.: |
09/402132 |
Filed: |
September 24, 1999 |
PCT Filed: |
February 11, 1998 |
PCT NO: |
PCT/DE98/00374 |
Current U.S.
Class: |
477/44 ; 477/45;
477/46; 477/77 |
Current CPC
Class: |
F16H 61/66272 20130101;
B60W 10/04 20130101; B60W 30/18 20130101; F16H 61/66254 20130101;
F16H 2061/0462 20130101; B60W 30/1819 20130101; B60W 10/101
20130101; F16H 2061/66277 20130101; F16H 2061/6618 20130101; B60W
10/02 20130101; B60W 10/06 20130101; B60W 10/107 20130101; F16H
61/66 20130101 |
Class at
Publication: |
477/44 ; 477/45;
477/46; 477/77 |
International
Class: |
B60K 041/14; B60K
041/22; B60K 041/28 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 25, 1997 |
DE |
197 12 451.8 |
Claims
1. Arrangement for controlling a transmission 4, which is
continuously variable in its transmission ratio, for a motor
vehicle, the transmission together with a drive unit (1; 27) being
mounted in the drive train of the motor vehicle, the drive unit (1;
27) having an adjustable drive torque M.sub.m, the transmission
having a drive end as well as an output end and operative means 9
for producing a mechanical operative connection between the drive
end and the output end; and, detection means 24 for detecting a
slip quantity S, which represents the slip between the operative
means and the drive end and/or output end; and, means 21 by means
of which pregivable measures are introduced in response to a
pregivable value of the slip quantity; characterized in that: as
measures (23, 26, 22): a drive (.DELTA.M.sub.K) of a clutch (28)
mounted in the drive train; and/or, a change (.DELTA.i) of the
transmission ratio (i); and/or, a change (.DELTA.M.sub.m) of the
output torque of the drive unit (27) is pregiven, wherein it is
especially provided that the measures are initiated in the sense of
a slip reduction.
2. Arrangement of claim 1, characterized in that, as a further
measure (25), a change (.DELTA.F) of the contact engaging force
between the drive and/or output end and the operative means,
especially in the sense of a slip reduction, is provided.
3. Arrangement of claim 1, characterized in that, as a measure: the
drive (.DELTA.M.sub.K) of the clutch (28) takes place in the sense
of an opening of the clutch; and/or, the change (.DELTA.i) of the
transmission ratio (i) takes place in response to a positive slip
quantity in the sense of an increase in the transmission ratio and
in response to a negative slip quantity in the sense of a reduction
of the transmission ratio; and/or, the change (.DELTA.M.sub.m) of
the output torque of the drive unit (27) takes place in response to
a positive slip quantity in the sense of a reduction of the output
torque in response to a negative slip quantity in the sense of an
increase of the output torque.
4. Arrangement of claim 1, characterized in that: the extent of the
drive of the clutch; and/or, the extent of the change of the
transmission ratio; and/or, the extent of the change of the output
torque of the drive unit; and/or, the extent of the change of the
contact engaging force is dependent upon the extent of the detected
slip quantity S.
5. Arrangement of claims 1 or 2, characterized in that the
transmission has a maximum transmissible torque (M.sub.get,max)
and, simultaneously or in time after the drive (.DELTA..sub.K,max)
of the clutch in the sense of an opening of the clutch, a change
(.DELTA.i) of the transmission ratio and/or a change
(.DELTA.M.sub.m) of the instantaneous output torque of the drive
unit and/or, a change of the contact engaging force (.DELTA.F) is
made in such manner that the torque (M.sub.get,max), which is
transmitted maximally by the transmission, becomes greater than the
magnitude (M.sub.m) of the instantaneous output torque of the drive
unit.
6. Arrangement of claim 1, characterized in that the clutch (28)
responds in the sense of a closure opening in response to the
torque (M.sub.get,max), which is the maximum torque transmissible
by the transmission, becomes greater in magnitude than the torque
(M.sub.m) of the instantaneous output torque of the drive unit.
7. Arrangement of claims 1 or 2, characterized in that the change
(.DELTA.M.sub.m) of the output torque of the drive unit is actuated
for slip reduction in support to at least one of the other measures
(clutch drive and/or change of the transmission ratio and/or of the
contact engaging force).
8. Arrangement of claim 1, characterized in that the transmission
(29) is a continuous transmission and the drive end and/or the
output end has at least an axially displaceable element (5, 6)
which has essentially the form of a conical pulley and that as
operative means (9) at least a belt, preferably a thrust element
belt or a belt or a chain is clamped between disc pairs which
define the drive and the output ends.
9. Method of controlling a transmission (4) which is adjustable
continuously with respect to its transmission ratio, for a motor
vehicle; the transmission together with a drive unit (1, 27), which
has an adjustable drive torque (M.sub.m), is mounted in the drive
train of the motor vehicle; the transmission having a drive end as
well as an output end and operative means (9) for producing a
mechanical operative connection between the drive end and the
output end; and a slip quantity (S) is detected which represents
the slip between the operative means and the drive end and/or
output end; and, pregivable measures are initiated in response to a
pregivable value of the slip quantity; characterized in that: as a
measure, especially in the sense of slip reduction, are provided: a
drive (.DELTA.M.sub.K) of a clutch (28) mounted in the drive train;
and/or, a change (.DELTA.i) of the transmission ratio (i); and/or,
a change (.DELTA.M.sub.m) of the output torque of the drive unit
(27).
10. Method of claim 1, characterized in that, as measures: the
drive (.DELTA.M.sub.m) of the clutch (28) takes place in the sense
of an opening of the clutch; and/or, the change (.DELTA.i) of the
transmission ratio (i) in response to a positive slip quantity
takes place in the sense of an increase of the transmission ratio
and, in response to a negative slip quantity, takes place in the
sense of a reduction of the transmission ratio; and/or, the change
of the output torque (.DELTA.M.sub.m) of the drive unit (27) takes
place in response to a positive slip quantity in the sense of a
reduction of the output torque, in response to a negative slip
quantity in the sense of an increase of the output torque; wherein
it is especially provided that: the extent of the drive of the
clutch; and/or, the extent of the change of the transmission ratio;
and/or, the extent of the change of the output torque of the drive
unit is dependent upon the extent of the detected slip quantity
and, as a further measure, a change of the contact engaging force
is provided between the drive and/or output end and the operative
means, especially in the sense of a slip reduction.
Description
STATE OF THE ART
[0001] The invention relates to an arrangement and a method for
controlling a transmission in a motor vehicle having the features
of the preamble of claims 1 and 9. The transmission is continuously
adjustable with respect to its transmission ratio.
[0002] In motor vehicles having a known continuously variable
transmission (CVT) with a continuous element (for example, a thrust
element belt or chain), the contact engaging force of the conical
pulleys against the thrust element belt must be so adjusted via
suitable measures that the torque, which is to be transmitted, can
be transmitted. A high slippage between the continuous element and
the pulleys occurs when the contact engaging force is too low and
this can lead to damage. If the contact engaging force is, however,
greater than absolutely necessary to avoid slippage, then the
efficiency of the transmission drops which leads to an
unnecessarily high consumption of fuel. For this reason, it is
advantageous to so select the contact engaging force that the
maximum tranmissible torque for this contact engaging force is only
slightly greater than the torque to be transmitted at the
particular time. If a high slippage of the continuous element
nonetheless occurs, then measures must be taken in order to
stabilize or stop the relative movement of the continuous element
so that damage is avoided.
[0003] Conventional continuously variable transmission controls,
such as disclosed in EP,A1, 0 451 887, determine the transmission
input torque from the torque, which is outputted by the engine, and
the converter amplification. A belt tension is computed from this
torque from which belt tension a contact engaging force results
which makes possible a reliable transmission of this torque. Here,
as a rule, a considerable reserve of reliability is considered
which causes a higher fuel consumption. If an impermissibly high
slippage nonetheless occurs, then, in general, the contact engaging
force and therefore the belt tension is increased. The speed with
which a reaction can be had to excessive slippage is, however,
limited by the time constants of the hydraulic and of the
mechanical system of the belt tensioning adjustment.
[0004] A system is known from EP,B1,0 446 497 (corresponding to
U.S. Pat. No. 5,098,345) for protecting against exceeding a maximum
slippage of the belt. Here, a clutch is so controlled that this
clutch always starts slipping at lower drive torques than the band.
A reaction to a possible slippage of the band is not described
here.
[0005] The detection of belt slippage is known in many
configurations. Thus, and for example in accordance with DE-OS 44
11 628, it is suggested to detect the speed of the continuous
element. Furthermore, the belt slippage can be detected by a sensor
which simultaneously detects the axial displacement of
conical-pulley pair and the rpm of this pair. From earlier German
patent application 196 38 277.7, it is known to provide at least
two sensor units for slippage detection which are mounted in the
region of the continuous means and between the drive end and the
output end.
[0006] The object of the present invention is to provide effective
measures for excessive slippage in order to reliably avoid damage
to the transmission.
[0007] This object is achieved with the features of claims 1 and
9.
ADVANTAGES OF THE INVENTION
[0008] As mentioned, the invention proceeds from a control of a
transmission, which is continuously adjustable with respect to its
transmission ratio, for a motor vehicle. The transmission is
mounted in the drive train of the motor vehicle together with a
drive unit having an adjustable drive torque. The transmission has
a drive end and an output end and operative means for establishing
a mechanical operative connection between the drive end and the
output end. Furthermore, detecting means for detecting a slippage
quantity is provided which represents the slippage between the
operative means and the drive end and/or output end. Pregivable
measures are initiated in response to a pregivable value of the
slip quantity. The essence of the invention is seen in that the
following are provided as measures:
[0009] a control of a clutch mounted in the drive train;
and/or,
[0010] a change of the transmission ratio; and/or,
[0011] a change of the output torque of the drive unit.
[0012] It is especially intended here that the measures are
initiated in the sense of avoiding slip.
[0013] In an advantageous embodiment of the invention, a further
measure is a change of the contact engaging force between the drive
end and/or the output end and the operative means, especially in
the sense of avoiding slip.
[0014] The present invention describes how through slipping of the
continuous element can be stopped and stabilized to a tolerable
slip with three or four possible interventions when through slip of
the continuous element is detected. The invention offers the
possibility to undertake the introduced measures individually or
with a coordinated strategy. Depending upon the particular
situation, which led to a through slip of the continuous element, a
response is provided in accordance with a previously determined
strategy having a selection of the measures according to the
invention simultaneously or in a tight time-dependent sequence.
This always takes place with the objective to suppress a detected
slip as quickly as possible and not to confuse the driver with
effects of the measures. Depending upon the equipped variation of
the vehicle, it is possible that not all of these measures can be
carried out.
[0015] It is especially provided that:
[0016] the drive of the clutch takes place in the sense of an
opening of the clutch; and/or,
[0017] the change of the transmission ratio takes place in response
to a positive slip quantity in the sense of an increase of the
transmission ratio and in response to a negative slip quantity in
the sense of a reduction of the transmission ratio; and/or,
[0018] the change of the output torque of the drive unit takes
place in response to a positive slip quantity in the sense of a
reduction of the output torque and in response to a negative slip
quantity in the sense of an increase of the output torque.
[0019] Furthermore, it is especially advantageous that the
following is dependent upon the extent of the detected slip
quantity:
[0020] the extent of the drive of the clutch; and/or,
[0021] the extent of the change of the transmission ratio;
and/or,
[0022] the extent of the change of the output torque of the drive
unit; and/or,
[0023] the extent of the change of the contact engaging force.
[0024] In a further advantageous embodiment of the invention it is
provided that, simultaneously or in time after the drive of the
clutch in the sense of an opening of the clutch, the following is
provided: a change of the transmission ratio; and/or, a change of
the instantaneous output torque of the drive unit; and/or, a change
of the contact engaging force in such a manner that the maximum
transmissible torque by the transmission becomes again greater in
magnitude than the magnitude of the instantaneous output torque of
the drive unit. In this way, the clutch slip can again be reduced
by an increase of the maximum transmissible torque of the clutch
(closing of the clutch).
[0025] It is especially provided that the change of the output
torque of the drive unit for slip reduction is actuated as support
to at least one of the other measures (clutch drive and/or change
of the transmission ratio and/or contact engaging force).
[0026] As already described, the transmission can be a continuous
transmission. The drive end and/or the output end can have at least
an axially displaceable element which has essentially the form of a
conical pulley. As operative means, at least a belt (preferably a
thrust element belt) or a belt or a chain is tensioned between
pulley pairs which define the drive end and the output end.
[0027] Further advantageous configurations of the invention can be
taken from the dependent claims and the embodiments described
hereinafter.
DRAWING
[0028] FIG. 1 shows schematically a continuously variable
transmission having a known control of the contact engaging force;
whereas, FIG. 2 shows an embodiment with reference to a block
circuit diagram.
EMBODIMENTS
[0029] The invention will now be described in detail in the
following with respect to the embodiments.
[0030] In FIG. 1, a known configuration of a continuously variable
transmission is shown in section. The internal combustion engine 1
can be influenced by the throttle flap 2 with respect to its
outputted torque M.sub.m. The throttle flap 2 is, for example,
coupled mechanically or electrically to the accelerator pedal (not
shown). The engine 1 is coupled mostly by means of a clutch and/or
a converter 3 to the drive end (primary end) of the CVT
transmission 4. The output end (secondary end) of the CVT
transmission 4 is connected via a downstream transmission (not
shown) to the wheels of the vehicle. The CVT transmission has an
axially displaceable conical pulley on each of the primary and
secondary ends. To adjust the transmission ratio, a corresponding
primary pressure P.sub.p or a secondary pressure P.sub.s is built
up in the oil chambers 7 and 8, respectively.
[0031] With a suitable selection of the actuating quantities of
primary pressure P.sub.p and secondary pressure P.sub.s, the
following must be ensured:
[0032] 1. the transmission ratio i corresponds to the desired ratio
of primary rpm N.sub.p and secondary rpm N.sub.s; and,
[0033] 2. the force transmitting thrust element belt 9 (for
example, chain, belt) is pressed against the pulleys with
sufficient force in order to prevent a through slippage of the
thrust element 9.
[0034] The above-mentioned point 1 is utilized via an
electro-hydraulic transmission ratio or primary rpm control 10. For
point 2, a belt tension control 11 is used.
[0035] Rpm sensors 12, 13 and 14 are provided on the engine 1 and
on the CVT transmission 4 for the transmission ratio and belt
tension control. The rpm sensors 12, 13 and 14 detect the engine
rpm M.sub.m, the primary rpm N.sub.p, and the secondary rpm
N.sub.s.
[0036] The master-slave principle is shown in FIG. 1 and is mostly
utilized. In this master-slave principle, the secondary pressure
P.sub.s serves to adjust the belt tension and the primary pressure
P.sub.p serves to adjust the transmission ratio rpm or the primary
rpm. For the alternative partner principle, the belt tension
control influences the primary pressure as well as the secondary
pressure.
[0037] Generally, one can state that a position signal in the form
of a pressure quantity P.sub.B is available for the belt tension
control. From the literature, several methods for controlling the
belt tension are known, which however all work in a similar
manner.
[0038] In FIG. 1, a sensor is identified by reference numeral 18
which detects the speed V.sub.b of the belt 9. In block 24, the
actual belt slip S is determined from the belt speed V.sub.b, the
primary rpm N.sub.p and the secondary rpm N.sub.s as described in
the initially-mentioned DE-OS 44 11 628. It is here noted that the
slip determination can also be obtained differently without
departing from the concept of the invention.
[0039] In FIG. 2, the four possible interventions for slip
reduction are shown. With reference numerals 27, 28 and 29, the
drive motor 27 with the corresponding engine control 22, the clutch
28 with the corresponding clutch control 23 as well as the CVT
transmission 29 with the already-described slip detection 24, the
belt tensioning control 25 and the transmission ratio control 26
are shown.
[0040] The individual actions for reducing the through slip of the
continuous element are matched by the block 21 "slip intervention"
in response to a detected excessive slip S of the continuous
element in order to stop the slip or to stabilize the slip to an
acceptable slip. In dependence upon the particular situation which
led to a through slip of the continuous element 9, a response is
provided in accordance with a previously determined strategy with a
selection of measures (here described) simultaneously or in a tight
time sequence. These measures are undertaken with the object of
suppressing a detected slip as quickly as possible and not to
confuse the driver by the effects of the measures.
[0041] Not all of these measures can be carried depending upon the
equipment variation of the vehicle.
[0042] Increase of the Belt Tension (Block 25):
[0043] If the slip detection 21 detects an increased slip S, then
the tension of the continuous element 9 is increased in order to
reduce the slip S to a tolerable amount via an increased contact
engaging force. The increase .DELTA.F takes place independently of
the sign of the detected slip S.
[0044] It is especially advantageous to select the quantity
.DELTA.F of the additional tension of the continuous element 9 in
dependence upon the amount of the detected slip S. Here, it must
considered that the contact engaging force must be greatly
increased because of the transition from static friction to sliding
friction between the continuous element and the pulley in order to
reduce slip. It is therefore advantageous when the additional belt
tension .DELTA.F is not linearly dependent upon the detected slip
S. As already mentioned, the speed with which a response can be
made is limited by the time constants of the hydraulic system and
of the mechanical system.
[0045] Transmission Ratio Adjustment (Block 26):
[0046] If the slip detection 24 detects an increased slip S, then
the transmission ratio i of the continuous transmission is so
adjusted that the geometric transmission ratio corresponds again to
the rpm transmission ratio.
[0047] For a known positive slip, this means that the slip
intervention requires a positive additional transmission ratio
.DELTA.i, that is, a larger transmission ratio is required than
without intervention. On the other hand, for a detected negative
slip S, a negative additional transmission ratio .DELTA.I is
required which reduces the transmission ratio i of the
transmission.
[0048] It is especially advantageous to select the magnitude of the
additional transmission ratio .DELTA.i in dependence upon the
detected slip S.
[0049] This intervention for positive slip is especially suitable
for the present-day conventional constructions of the CVTs. For
positive slip, for which the engine torque M.sub.m can no longer be
transmitted, the engine rpm increases greatly. The additional
transmission ratio .DELTA.i can be realized by releasing oil from
the primary pulley without an additional pumping capacity for
hydraulically increasing the contact engaging force. This measure
should, however, be combined with a reducing engine torque
intervention (block 22) which is yet to be described.
[0050] Torque Intervention at the Engine (Block 22, 27):
[0051] If the slip detection 21 detects an increased slip S, then
the torque M.sub.m, which is outputted by the engine 27, can be
changed in order to adapt the torque, which is to be transmitted by
the transmission, to the maximum transmissible torque M.sub.max and
to thereby reduce the slip to a tolerable amount.
[0052] For positive slip (that is, when the transmission input rpm
N.sub.p is greater than it should be in accordance with the
geometric transmission ratio), the torque M.sub.m, which is
outputted by the engine 27, must be reduced (the additional torque
.DELTA.M.sub.m is negative). For this purpose, all interventions
can be used which are applicable to a known output slip control
(ASR). These interventions include, for example, an ignition angle
intervention for a spark-ignition engine not having electronic
engine power control (E-gas). For engines having electronic engine
power control (E-gas or EDC), simply a reduced torque is required.
In each case, the slip intervention .DELTA.M.sub.m requires a
negative additional torque.
[0053] If the drag torque of the engine 27 with respect to
magnitude is greater than the torque M.sub.max, which is maximally
transmissible by the transmission, then the transmission input rpm
N.sub.p is less than it should be in accordance with the geometric
transmission ratio. In this case, a negative belt slippage is
present and the drag torque of the engine 27 should be reduced. All
interventions can serve for this purpose which are used at the
present time for a known engine drag torque control (MSR). For
engines having electronic engine power control (E-gas or EDC),
simply a higher torque is required. This means that the slip
intervention requires a positive additional torque .DELTA.M.sub.m
for a negative slip.
[0054] It is especially advantageous in both cases to select the
magnitude of the additional torque .DELTA.M.sub.m at the engine 27
in dependence upon the amount S of the detected slip. These
interventions are characterized by their relatively short time
constants and should therefore always be applied supportive to the
other interventions presented in this application.
[0055] Clutch Intervention (Block 23, 28):
[0056] If the vehicle has, for example, an electronically
influenceable clutch 28, then, when slip S of the continuous
element 9 in the transmission is detected, the maximum
transmissible torque M.sub.Kmax of the clutch 28 can also be
reduced so that the slip occurs at the clutch 28 in lieu of at the
continuous element 9. This is advantageous because the clutch 28 is
so configured in its construction that it can withstand a higher
slip for a certain time without damage.
[0057] If the maximum transmissible torque M.sub.K,max is reduced
at the clutch 28 by a clutch intervention .DELTA.M.sub.K, then the
torque at the transmission input cannot be greater in magnitude
than the maximum transmissible torque M.sub.K,max of the clutch. In
this way, it is possible to make the torque of the transmission 29,
which is to be transmitted, less in magnitude than the maximum
transmissible torque M.sub.get,max of the transmission 29 and to so
limit the slip at the transmission to a noncritical value.
[0058] As long as the torque M.sub.m at the engine output, the
contact engaging of the continuous element 9 and the transmission
ratio i of the transmission do not change, the slip then occurs at
the clutch 28 instead of at the transmission 29. This is
advantageous for the above-mentioned reasons.
[0059] It is especially advantageous to ensure, via one of the
other three described measures, that the torque M.sub.get,max,
which is the maximum torque transmissible by the transmission 29,
becomes greater again in magnitude than the magnitude of the engine
output torque in order to be able to reduce the slip at the clutch
28 via an increase (closure of the clutch) of the maximum
transmissible torque M.sub.K,max of the clutch.
[0060] In summary, it can be stated that the described
possibilities can be applied individually or in combination.
Especially, in dependence upon the situation, combined
interventions should always be carried out so that the driver does
not notice the interventions on the slip control. Within a few
milliseconds (50 to 590 ms), the condition wanted by the driver
should again be applicable in the drive train of the vehicle so
that the vehicle does not unexpectedly accelerate or
decelerate.
* * * * *