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.

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 Mm. 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 Pp or a secondary pressure Ps is built up in the oil chambers 7 and 8, respectively.

[0031] With a suitable selection of the actuating quantities of primary pressure Pp and secondary pressure Ps, the following must be ensured:

[0032] 1. the transmission ratio i corresponds to the desired ratio of primary rpm Np and secondary rpm Ns; 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 Mm, the primary rpm Np, and the secondary rpm Ns.

[0036] The master-slave principle is shown in FIG. 1 and is mostly utilized. In this master-slave principle, the secondary pressure Ps serves to adjust the belt tension and the primary pressure Pp 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 PB 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 Vb of the belt 9. In block 24, the actual belt slip S is determined from the belt speed Vb, the primary rpm Np and the secondary rpm Ns 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 &Dgr;F takes place independently of the sign of the detected slip S.

[0044] It is especially advantageous to select the quantity &Dgr;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 &Dgr;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 &Dgr;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 &Dgr;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 &Dgr;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 Mm can no longer be transmitted, the engine rpm increases greatly. The additional transmission ratio &Dgr;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 Mm, 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 Mmax and to thereby reduce the slip to a tolerable amount.

[0052] For positive slip (that is, when the transmission input rpm Np is greater than it should be in accordance with the geometric transmission ratio), the torque Mm, which is outputted by the engine 27, must be reduced (the additional torque &Dgr;Mm 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 &Dgr;Mm requires a negative additional torque.

[0053] If the drag torque of the engine 27 with respect to magnitude is greater than the torque Mmax, which is maximally transmissible by the transmission, then the transmission input rpm Np 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 &Dgr;Mm for a negative slip.

[0054] It is especially advantageous in both cases to select the magnitude of the additional torque &Dgr;Mm 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 MKmax 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 MK,max is reduced at the clutch 28 by a clutch intervention &Dgr;MK, then the torque at the transmission input cannot be greater in magnitude than the maximum transmissible torque MK,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 Mget,max of the transmission 29 and to so limit the slip at the transmission to a noncritical value.

[0058] As long as the torque Mm 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 Mget,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 MK,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.

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 Mm, 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 (&Dgr;MK) of a clutch (28) mounted in the drive train; and/or,

a change (&Dgr;i) of the transmission ratio (i); and/or,

a change (&Dgr;Mm) 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 (&Dgr;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 (&Dgr;MK) of the clutch (28) takes place in the sense of an opening of the clutch; and/or,

the change (&Dgr;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 (&Dgr;Mm) 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 (Mget,max) and, simultaneously or in time after the drive (&Dgr;K,max) of the clutch in the sense of an opening of the clutch, a change (&Dgr;i) of the transmission ratio and/or a change (&Dgr;Mm) of the instantaneous output torque of the drive unit and/or, a change of the contact engaging force (&Dgr;F) is made in such manner that the torque (Mget,max), which is transmitted maximally by the transmission, becomes greater than the magnitude (Mm) 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 (Mget,max), which is the maximum torque transmissible by the transmission, becomes greater in magnitude than the torque (Mm) of the instantaneous output torque of the drive unit.

7. Arrangement of claims 1 or 2, characterized in that the change (&Dgr;Mm) 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 (Mm), 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 (&Dgr;MK) of a clutch (28) mounted in the drive train; and/or,

a change (&Dgr;i) of the transmission ratio (i); and/or,

a change (&Dgr;Mm) of the output torque of the drive unit (27).

10. Method of

claim 1, characterized in that, as measures:

the drive (&Dgr;Mm) of the clutch (28) takes place in the sense of an opening of the clutch; and/or,

the change (&Dgr;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 (&Dgr;Mm) 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.