WO2004031621A1 - Control method for an infinitely variable transmission - Google Patents

Control method for an infinitely variable transmission Download PDF

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Publication number
WO2004031621A1
WO2004031621A1 PCT/NL2003/000578 NL0300578W WO2004031621A1 WO 2004031621 A1 WO2004031621 A1 WO 2004031621A1 NL 0300578 W NL0300578 W NL 0300578W WO 2004031621 A1 WO2004031621 A1 WO 2004031621A1
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WO
WIPO (PCT)
Prior art keywords
drive belt
transmission
torque
output
control method
Prior art date
Application number
PCT/NL2003/000578
Other languages
French (fr)
Inventor
Pieter Abraham Veenhuizen
Original Assignee
Van Doorne's Transmissie B.V.
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Filing date
Publication date
Application filed by Van Doorne's Transmissie B.V. filed Critical Van Doorne's Transmissie B.V.
Publication of WO2004031621A1 publication Critical patent/WO2004031621A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H61/00—Control functions within control units of change-speed- or reversing-gearings for conveying rotary motion ; Control of exclusively fluid gearing, friction gearing, gearings with endless flexible members or other particular types of gearing
    • F16H61/66—Control functions within control units of change-speed- or reversing-gearings for conveying rotary motion ; Control of exclusively fluid gearing, friction gearing, gearings with endless flexible members or other particular types of gearing specially adapted for continuously variable gearings
    • F16H61/662—Control functions within control units of change-speed- or reversing-gearings for conveying rotary motion ; Control of exclusively fluid gearing, friction gearing, gearings with endless flexible members or other particular types of gearing specially adapted for continuously variable gearings with endless flexible members
    • F16H61/66272—Control functions within control units of change-speed- or reversing-gearings for conveying rotary motion ; Control of exclusively fluid gearing, friction gearing, gearings with endless flexible members or other particular types of gearing specially adapted for continuously variable gearings with endless flexible members characterised by means for controlling the torque transmitting capability of the gearing
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H37/00—Combinations of mechanical gearings, not provided for in groups F16H1/00 - F16H35/00
    • F16H37/02—Combinations of mechanical gearings, not provided for in groups F16H1/00 - F16H35/00 comprising essentially only toothed or friction gearings
    • F16H37/06—Combinations of mechanical gearings, not provided for in groups F16H1/00 - F16H35/00 comprising essentially only toothed or friction gearings with a plurality of driving or driven shafts; with arrangements for dividing torque between two or more intermediate shafts
    • F16H37/08—Combinations of mechanical gearings, not provided for in groups F16H1/00 - F16H35/00 comprising essentially only toothed or friction gearings with a plurality of driving or driven shafts; with arrangements for dividing torque between two or more intermediate shafts with differential gearing
    • F16H37/0833—Combinations of mechanical gearings, not provided for in groups F16H1/00 - F16H35/00 comprising essentially only toothed or friction gearings with a plurality of driving or driven shafts; with arrangements for dividing torque between two or more intermediate shafts with differential gearing with arrangements for dividing torque between two or more intermediate shafts, i.e. with two or more internal power paths
    • F16H37/084—Combinations of mechanical gearings, not provided for in groups F16H1/00 - F16H35/00 comprising essentially only toothed or friction gearings with a plurality of driving or driven shafts; with arrangements for dividing torque between two or more intermediate shafts with differential gearing with arrangements for dividing torque between two or more intermediate shafts, i.e. with two or more internal power paths at least one power path being a continuously variable transmission, i.e. CVT
    • F16H37/0846—CVT using endless flexible members
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H37/00—Combinations of mechanical gearings, not provided for in groups F16H1/00 - F16H35/00
    • F16H37/02—Combinations of mechanical gearings, not provided for in groups F16H1/00 - F16H35/00 comprising essentially only toothed or friction gearings
    • F16H37/06—Combinations of mechanical gearings, not provided for in groups F16H1/00 - F16H35/00 comprising essentially only toothed or friction gearings with a plurality of driving or driven shafts; with arrangements for dividing torque between two or more intermediate shafts
    • F16H37/08—Combinations of mechanical gearings, not provided for in groups F16H1/00 - F16H35/00 comprising essentially only toothed or friction gearings with a plurality of driving or driven shafts; with arrangements for dividing torque between two or more intermediate shafts with differential gearing
    • F16H37/0833—Combinations of mechanical gearings, not provided for in groups F16H1/00 - F16H35/00 comprising essentially only toothed or friction gearings with a plurality of driving or driven shafts; with arrangements for dividing torque between two or more intermediate shafts with differential gearing with arrangements for dividing torque between two or more intermediate shafts, i.e. with two or more internal power paths
    • F16H37/084—Combinations of mechanical gearings, not provided for in groups F16H1/00 - F16H35/00 comprising essentially only toothed or friction gearings with a plurality of driving or driven shafts; with arrangements for dividing torque between two or more intermediate shafts with differential gearing with arrangements for dividing torque between two or more intermediate shafts, i.e. with two or more internal power paths at least one power path being a continuously variable transmission, i.e. CVT
    • F16H2037/088—Power split variators with summing differentials, with the input of the CVT connected or connectable to the input shaft

Definitions

  • the present invention relates to a control method for an infinitely variable transmission, as can be used, for example, in motor vehicles for passenger transport for transmitting engine power between engine and driven wheels with a variable transmission ratio between the rotational speed of an input shaft of the transmission, which is coupled to the engine, and an output shaft of the transmission, which is coupled to the wheels.
  • a transmission of this type is known, for example, from European Patent EP-A-0 232 979 and the later German Patent Application DE-A 19 631 216 and comprises a continuously variable transmission of the known drive belt-and-pulley type (known as the drive belt CVT) and a fixed transmission with a fixed transmission ratio which can be shifted in parallel in a mechanical sense in order to transmit power between the input shaft and the output shaft of the transmission, the drive belt
  • CVT drive belt-and-pulley type
  • This transmission has the particular and advantageous property that the rotational speed and the direction of rotation of the output shaft with an input shaft rotating within a defined range can be controlled by varying the transmission ratio of the drive belt CVT.
  • the rotational speed of the output shaft itself is equal to zero. This makes it possible, inter alia, to avoid the use of a moving- off clutch for stopping the wheels or accelerating the wheels from a standstill when the engine is running.
  • the transmission ratio of the drive belt CVT is controlled as a function of the difference between a desired rotation, i.e. a desired rotational speed and associated direction of rotation, and an actual rotation of the output shaft of the transmission by controlling this difference towards zero.
  • a desired rotation i.e. a desired rotational speed and associated direction of rotation
  • an actual rotation of the output shaft of the transmission by controlling this difference towards zero.
  • the transmission ratio of the drive belt CVT is controlled as a function of the difference between a desired torque on the output shaft of the transmission, i.e. a desired absolute level and a desired direction of rotation for this torque, and an actual torque by controlling this difference towards zero.
  • this improved control method has the drawback that there are no available sensors which can detect the actual torque on the said shaft with such an accuracy and robustness, or at least not without incurring relatively high costs .
  • the torque of the output shaft on the transmission is controlled by adjusting the slip across a frictional element in the transmission, such as a clutch or a drive belt CVT, having an input component and an output component, the slip being defined as the difference between the input speed of the frictional element and an output speed of the frictional element of the frictional element, to a desired value and by controlling the normal force in the frictional contact.
  • a frictional element in the transmission such as a clutch or a drive belt CVT
  • the slip being defined as the difference between the input speed of the frictional element and an output speed of the frictional element of the frictional element, to a desired value and by controlling the normal force in the frictional contact.
  • the invention exploits the insight that ther.e is a known relationship between the abovementioned slip, a normal force which is applied in frictional contact between the output component and the input component, and a torque on the output component, and this relationship is in turn related to the torque on the output shaft of the transmission.
  • FIG. 1 diagrammatically depicts the known infinitely variable transmission
  • Figure 2 shows a simplified illustration of a typical traction curve of a drive belt CVT having a drive belt in accordance with the VDT design
  • Figure 3 shows a block diagram illustrating the control method according to the invention
  • Figure 4 shows a simplified illustration of a typical traction curve of a standard wet disc clutch.
  • the infinitely variable transmission 10 shown in Figure 1 comprises an input shaft 2, which is coupled to an engine 1, and an output shaft 3, which is coupled to driven wheels 4, between which a drive belt CVT 11 with a variable transmission ratio, which is provided with an input pulley 111 and an output component 112, in this case an output pulley 112 surrounded by an input component 113, in this case a drive belt 113, and a fixed transmission 12 with a fixed transmission ratio, which is provided with an input gearwheel 121 and an output gearwheel 122 surrounded by a chain 123, are accommodated, the transmissions 11 and 12 being connected in parallel in a mechanical sense and the drive belt CVT 11, the fixed transmission 12 and one of the said shafts 3 of the transmission 10 each being separately coupled to one shaft 131, 132, 133 of a three-shaft epicyclic gearwheel set 13.
  • a gearwheel set 13 of this type is generally known and comprises, for example, a sun gear 134, which is positioned centrally and is coupled to a first shaft 131, and a hollow ring gear 135, which is coupled to a second shaft, between which there is a number of planetary gears 137 which can rotatable freely about their own axis and are secured to planet carrier 136 which is coupled to a third shaft 133.
  • an output pulley 112 of the drive belt CVT 11 is coupled to the first shaft 131 of the gearwheel set 13
  • the output gearwheel 132 of the fixed transmission 12 is coupled to the third shaft 133 of the gearwheel set 13
  • the output shaft 3 of the transmission 10 is connected to the second shaft 132 of the gearwheel set 13.
  • the transmission 10 also comprises two clutches 14 and
  • Figure 1 shows that a final reduction gearwheel set 5 is accommodated between the output shaft 3 of the transmission 10 and the driven wheels 4.
  • the drive belt CVT 11 is of a type which is generally known per se .
  • each pulley 111, 112 requires a clamping force, by which they clamp in the drive belt 113 in order to transmit a rotation between the pulleys 111, 112.
  • this clamping force is determined as a function of frictional force required between the pulley 111, 112 and the drive belt 113 and by realizing a desired transmission ratio icvr between the rotational speed of the input pulley G> IN and that of the output pulley ⁇ C v ⁇ -ou ⁇ - It should be noted that the clamping forces are often generated with the aid of a hydraulic pressure.
  • the relationship between the said output torque Tv ⁇ -ou ⁇ and the torque T 0 u on the output shaft 3 of the transmission 10 itself is substantially advantageously linear, and the output torque T C v ⁇ -ou ⁇ of the drive belt CVT 11 can in principle be calculated by dividing the torque T 0 u on the output shaft 3 of the transmission 10 by the ratio of the geometric radius of the hollow ring gear 135 and that of the sun gear 134.
  • a first clamping force Fcl as a function of the desired value for the output torque T CVT - DV of the drive belt CVT 11, i.e. in such a manner that the friction between pulley 111, 112 and drive belt is sufficient to transmit the desired value for the output torque T CVT - DV -
  • ⁇ is an angle between the contact surfaces of the drive belt 113 and a pulley 111, 112
  • R 0 u ⁇ is a radius with which the drive belt 113 runs over the output pulley 112
  • ⁇ (ds) is a coefficient of friction between the drive belt 113 and the output pulley 112, which is defined as a function of the difference in speed between them, known as the drive belt slip.
  • the said coefficient of friction ⁇ (ds), for a fixed value of the clamping force Fc and the running radius R OUT * can be defined in what is known as a traction curve, in which t-he output torque T CVT - DV is plotted against the drive belt slip ds, which drive belt slip ds can be defined as follows: .
  • FIG. 2 diagrammatically reproduces a traction curve for a metal drive belt 113 in accordance with the Van Doorne's Transmissie (VDT) design in oil-lubricated contact with metal pulleys 111, 112.
  • VDT Van Doorne's Transmissie
  • a drive belt of the VDT design is described in EP-A-0 014 013 and comprises at least one continuous carrier in ribbon form, over which a large number of so-called transverse elements in plate form can move, the carrier being accommodated in a recess in the transverse elements.
  • the line MA represents the limit beneath which the drive belt slip ds is still acceptable according to this criterion.
  • the line MI represents the limit beneath which the drive belt slip ds has a considerable influence on the transmitted output torque T C VT-DV-
  • Allowing the drive belt 113 to slip in a controlled manner up to a defined level of the drive belt slip ds between the two lines MI and MA in the traction curve presented in Figure 2 therefore allows the output torque T C T - DV of the drive belt CVT 11 to be controlled relatively accurately irrespective of minor variations in the drive belt slip ⁇ ds .
  • this factor is exploited by determining a second clamping force Fc2 as a function of the difference between a desired value for the drive belt slip ds DV and the actual value of the drive belt ds RV , in such a manner that this second clamping force Fc2 is proportional to the said difference.
  • the transmission 10 has to be provided with additional measurement means, for example means which measure the longitudinal speed of the drive belt 113 and compare it with the rotational speed com, ⁇ C v ⁇ -ou ⁇ of a pulley 111, 112 or which measure the actual running radius of the drive belt 113 on a pulley 111, 112 and compare it with a value for this radius which has been calculated from the pulley rotational speeds ⁇ N , ⁇ C v ⁇ our-
  • a pulley 111, 112 then exerts the first clamping force Fcl on the drive belt 113, and another pulley 111, 112 exerts the sum of the two abovementioned clamping forces Fcl and Fc2 on the drive belt 113.
  • the drive belt slip ds is therefore in fact controlled by using the second clamping force Fc2 to adjust the transmission ratio of the drive belt CVT i ⁇ / while the first clamping force Fcl ensures a sufficiently high frictional force between the pulleys 111, 112 and the drive belt 113 to transmit a desired torque through the transmission.
  • the transmission ratio of the drive belt CVT i C v ⁇ has to be increased or reduced depending on the sign of the said difference between the desired value for the drive belt slip ds DV and the actual value ds RV .
  • the control method according to the invention is summarized once again in the block diagram presented in Figure 3.
  • the output torque T CVT - DV for the drive belt CVT is calculated from the desired torque T OU for the output shaft 2.
  • the first clamping force Fcl required for this purpose is calculated, for example in accordance with equation 1.
  • the sign of the desired drive belt slip ds D v is defined as a function of the sign of the desired output torque T CVT - DV
  • the difference ⁇ ds between the desired value and sign ds DV for the drive belt slip ds RV and the measured value for this slip is determined.
  • the required second clamping force Fc2 is calculated on the basis of the absolute value of the latter difference
  • the said clamping forces Fcl and Fc2 are added.
  • the sign of the latter difference ⁇ ds is determined, and on the basis of this block VIII determines to which of the two pulleys 111, 112 the first clamping force Fcl applies and to which of the two pulleys 111, 112 the added clamping forces Fcl and Fc2 apply.
  • the desired value for the torque T 0 u ⁇ can be determined, for example, as a function of the extent to which an accelerator pedal is depressed.
  • the said extent to which an accelerator pedal is depressed can be representative of a speed or acceleration of the vehicle, from which the desired value for the torque TOUT can then be determined.
  • the two clutches 14 and 15 shown in Figure 1 are, incidentally, not required for the infinitely variable transmission 10 to function, but they do enable the transmission 10 also to be used as a conventional drive belt CVT 11 with a continuously variable transmission ratio and an associated generally known control method. It should be noted that it is also possible in this case, in which the transmission 10 is used as a conventional drive belt CVT 11, for it to be controlled using the control method according to the invention.
  • Opening the first clutch 14 means that the fixed transmission 12 no longer transmits any mechanical power, while closing the second clutch 15 brings about a direct one-on-one connection between the drive belt CVT 11 and the output shaft 3. All this has the advantage that part of the range of transmission ratios of the drive belt CVT 11 can be passed through again after the first clutch 14 has been opened and/or the second clutch 15 has been closed, on account of the fact that the transmission ratio of the drive belt CVT 11 during the closure of the second clutch 15 has to be reduced in order to synchronize the rotational speed fOcv-ou of the output pulley 112 with the rotational speed ⁇ 0 u ⁇ of the output shaft 3.
  • the use of the first clutch 14 in this case allows an alternative control method for the infinitely variable transmission. This is because, according to the invention, there is a fixed and substantially advantageous linear relationship between the torque T CL output to the fixed transmission by the first clutch 14, as well as between the torque T 0 u ⁇ on the output shaft 3 and the torque T C v ⁇ -ou ⁇ which is output by the drive belt CVT to the epicyclic gearwheel set.
  • the torque T C is in this case adjusted to the desired level by corresponding activation of the clutch 14, for example, in the case of a standard wet disc clutch, by pressing the friction discs, which in this case form the output and input components according to the invention, onto one another with the aid of a hydraulically applied pressure P C where:
  • the abovementioneds is not required.
  • the said desired value for the clutch slip S CL - DV across the first clutch 14 should not be selected to be too small, in order to limit the possible error T ERROR in the torque T CL output to the fixed transmission 12 as a result of variations in the clutch slip ⁇ S CL -
  • this desired value S CL - DV should also not be selected to be too high, so that the power dissipated by the clutch 14 remains below a maximum acceptable limit.

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  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Control Of Transmission Device (AREA)

Abstract

Control method for an infinitely variable transmission (10) having an input shaft (2) and an output shaft (3) which is at least provided with a drive belt CVT 11 having a continuously variable transmission ratio and a friction element (11, 14) such a clutch (14) or the drive belt CVT (11), having an input component (113) and an output component (112) which are in frictional contact with one another and between which a normal force can be applied, wherein a torque TOUT on the output shaft (3) of the transmission (10) is adjusted towards a desired value for this torque by controlling the said normal force, characterized in that a difference between an actual input speed ωIN of the frictional element (11, 14) and an actual output speed ωCVT-OUT, ωVO-IN of the frictional element- (11, 14) is adjusted towards a desired value for this. difference by controlling the transmission ratio of the drive belt CVT (11).

Description

CONTROL METHOD FOR AN INFINITELY VARIABLE TRANSMISSION
The present invention relates to a control method for an infinitely variable transmission, as can be used, for example, in motor vehicles for passenger transport for transmitting engine power between engine and driven wheels with a variable transmission ratio between the rotational speed of an input shaft of the transmission, which is coupled to the engine, and an output shaft of the transmission, which is coupled to the wheels.
A transmission of this type is known, for example, from European Patent EP-A-0 232 979 and the later German Patent Application DE-A 19 631 216 and comprises a continuously variable transmission of the known drive belt-and-pulley type (known as the drive belt CVT) and a fixed transmission with a fixed transmission ratio which can be shifted in parallel in a mechanical sense in order to transmit power between the input shaft and the output shaft of the transmission, the drive belt
CVT, the fixed transmission and one of the said shafts of the transmission each being separately coupled to one shaft of a three-shaft epicyclic gearwheel set.
This transmission has the particular and advantageous property that the rotational speed and the direction of rotation of the output shaft with an input shaft rotating within a defined range can be controlled by varying the transmission ratio of the drive belt CVT. At a certain transmission ratio of the drive belt CVT, known as the geared neutral ratio, the rotational speed of the output shaft itself is equal to zero. This makes it possible, inter alia, to avoid the use of a moving- off clutch for stopping the wheels or accelerating the wheels from a standstill when the engine is running.
In a known control method for the infinitely variable transmission, the transmission ratio of the drive belt CVT is controlled as a function of the difference between a desired rotation, i.e. a desired rotational speed and associated direction of rotation, and an actual rotation of the output shaft of the transmission by controlling this difference towards zero. Although this control method in theory functions appropriately, it has the significant inherent drawback that for a desired rotation of the output shaft which is equal to zero, the actual rotation of this shaft will always vary slightly around the zero mark. It will be clear that, especially if the transmission is used in a motor vehicle for passenger transport, this constant rotation of the output shaft and therefore also the driven wheels forwards and backwards is extremely undesirable.
In a known improvement to the control method for the infinitely variable transmission, in which rotational oscillations of this type do not occur or at least occur to a significantly reduced extent, the transmission ratio of the drive belt CVT is controlled as a function of the difference between a desired torque on the output shaft of the transmission, i.e. a desired absolute level and a desired direction of rotation for this torque, and an actual torque by controlling this difference towards zero. However, this improved control method has the drawback that there are no available sensors which can detect the actual torque on the said shaft with such an accuracy and robustness, or at least not without incurring relatively high costs .
It is an object of the present invention to provide an alternative control method for the infinitely variable transmission, which makes it possible to avoid the abovementioned shortcomings of the known control methods. According to the invention, this object is achieved by the control method according to Claim 1.
In the control method according to the invention, the torque of the output shaft on the transmission is controlled by adjusting the slip across a frictional element in the transmission, such as a clutch or a drive belt CVT, having an input component and an output component, the slip being defined as the difference between the input speed of the frictional element and an output speed of the frictional element of the frictional element, to a desired value and by controlling the normal force in the frictional contact. In this context, the invention exploits the insight that ther.e is a known relationship between the abovementioned slip, a normal force which is applied in frictional contact between the output component and the input component, and a torque on the output component, and this relationship is in turn related to the torque on the output shaft of the transmission.
To elucidate the invention, the control method will be explained in more detail on the basis of an exemplary embodiment and with reference to the figures, in which:
Figure 1 diagrammatically depicts the known infinitely variable transmission;
Figure 2 shows a simplified illustration of a typical traction curve of a drive belt CVT having a drive belt in accordance with the VDT design;
Figure 3 shows a block diagram illustrating the control method according to the invention;
Figure 4 shows a simplified illustration of a typical traction curve of a standard wet disc clutch.
The infinitely variable transmission 10 shown in Figure 1 comprises an input shaft 2, which is coupled to an engine 1, and an output shaft 3, which is coupled to driven wheels 4, between which a drive belt CVT 11 with a variable transmission ratio, which is provided with an input pulley 111 and an output component 112, in this case an output pulley 112 surrounded by an input component 113, in this case a drive belt 113, and a fixed transmission 12 with a fixed transmission ratio, which is provided with an input gearwheel 121 and an output gearwheel 122 surrounded by a chain 123, are accommodated, the transmissions 11 and 12 being connected in parallel in a mechanical sense and the drive belt CVT 11, the fixed transmission 12 and one of the said shafts 3 of the transmission 10 each being separately coupled to one shaft 131, 132, 133 of a three-shaft epicyclic gearwheel set 13. A gearwheel set 13 of this type is generally known and comprises, for example, a sun gear 134, which is positioned centrally and is coupled to a first shaft 131, and a hollow ring gear 135, which is coupled to a second shaft, between which there is a number of planetary gears 137 which can rotatable freely about their own axis and are secured to planet carrier 136 which is coupled to a third shaft 133. In this exemplary embodiment, an output pulley 112 of the drive belt CVT 11 is coupled to the first shaft 131 of the gearwheel set 13, the output gearwheel 132 of the fixed transmission 12 is coupled to the third shaft 133 of the gearwheel set 13, and the output shaft 3 of the transmission 10 is connected to the second shaft 132 of the gearwheel set 13.
The transmission 10 also comprises two clutches 14 and
15, of which, at least in an infinitely variable transmission mode, the first clutch 14 transmits at least some of the engine power and, of which, the second clutch 15 is open. Moreover, Figure 1 shows that a final reduction gearwheel set 5 is accommodated between the output shaft 3 of the transmission 10 and the driven wheels 4.
The drive belt CVT 11 is of a type which is generally known per se . In this type of transmissions, which are based on friction, each pulley 111, 112 requires a clamping force, by which they clamp in the drive belt 113 in order to transmit a rotation between the pulleys 111, 112. For each pulley 111, 112, this clamping force is determined as a function of frictional force required between the pulley 111, 112 and the drive belt 113 and by realizing a desired transmission ratio icvr between the rotational speed of the input pulley G>IN and that of the output pulley ωCvτ-ouτ- It should be noted that the clamping forces are often generated with the aid of a hydraulic pressure.
As has been stated, at a specific transmission ratio of the drive belt CVT known as the geared neutral ratio icvτ-GN/ the rotational speed of the output shaft ω0uτ is equal to zero, irrespective of the rotational speed of the input shaft cθιN. A very accurate and stable control of drive belt CVT 11 at least in the geared neutral ratio icvτ-GN is extremely desirable, but is also difficult to achieve with the aid of the known control methods. However, according to the invention it is possible to indirectly control the torque T0uτ on the output shaft 3 of the transmission 10 by controlling the output torque TCvτ-ouτ which is actually output by the drive belt CVT 11 to the epicyclic gearwheel set 13 towards a desired value TCV -DV for this output torque. In this case, the relationship between the said output torque Tvτ-ouτ and the torque T0u on the output shaft 3 of the transmission 10 itself is substantially advantageously linear, and the output torque TCvτ-ouτ of the drive belt CVT 11 can in principle be calculated by dividing the torque T0u on the output shaft 3 of the transmission 10 by the ratio of the geometric radius of the hollow ring gear 135 and that of the sun gear 134.
In the control method according to the invention, a first clamping force Fcl as a function of the desired value for the output torque TCVT-DV of the drive belt CVT 11, i.e. in such a manner that the friction between pulley 111, 112 and drive belt is sufficient to transmit the desired value for the output torque TCVT-DV-
To do this, it is possible, for example, to make use of the following equation:
Fc = {Tcvτ-Dvcos(λ) }/{2-Rouτ-μ(s) } (1)
where λ is an angle between the contact surfaces of the drive belt 113 and a pulley 111, 112, R0uτ is a radius with which the drive belt 113 runs over the output pulley 112 and μ(ds) is a coefficient of friction between the drive belt 113 and the output pulley 112, which is defined as a function of the difference in speed between them, known as the drive belt slip. The said coefficient of friction μ(ds), for a fixed value of the clamping force Fc and the running radius ROUT* can be defined in what is known as a traction curve, in which t-he output torque TCVT-DV is plotted against the drive belt slip ds, which drive belt slip ds can be defined as follows: .
ds = { (icvτ/icvτ-o) -1} (2)
where iCvτ is the actual instantaneous transmission ratio of the drive belt CVT 11 and icvτ=o is the transmission ratio of the drive belt CVT 11 if the output torque TCVT-DV of the drive belt CVT 11 were to be equal to zero .
Figure 2 diagrammatically reproduces a traction curve for a metal drive belt 113 in accordance with the Van Doorne's Transmissie (VDT) design in oil-lubricated contact with metal pulleys 111, 112. A drive belt of the VDT design is described in EP-A-0 014 013 and comprises at least one continuous carrier in ribbon form, over which a large number of so-called transverse elements in plate form can move, the carrier being accommodated in a recess in the transverse elements. It has been found that at least this type of drive belt 113 can be subjected to a certain degree of long-term drive belt slip ds without suffering fatal damage, i.e. without adversely affecting the functioning of the transmission 10. In Figure 2, the line MA represents the limit beneath which the drive belt slip ds is still acceptable according to this criterion. The line MI represents the limit beneath which the drive belt slip ds has a considerable influence on the transmitted output torque TCVT-DV-
Allowing the drive belt 113 to slip in a controlled manner up to a defined level of the drive belt slip ds between the two lines MI and MA in the traction curve presented in Figure 2 therefore allows the output torque TC T-DV of the drive belt CVT 11 to be controlled relatively accurately irrespective of minor variations in the drive belt slip Δds . In the control method according to the invention, this factor is exploited by determining a second clamping force Fc2 as a function of the difference between a desired value for the drive belt slip dsDV and the actual value of the drive belt dsRV, in such a manner that this second clamping force Fc2 is proportional to the said difference.
It should be noted that it is not readily possible to measure the actual value of the drive belt slip dsRV. To do this, the transmission 10 has to be provided with additional measurement means, for example means which measure the longitudinal speed of the drive belt 113 and compare it with the rotational speed com, ωCvτ-ouτ of a pulley 111, 112 or which measure the actual running radius of the drive belt 113 on a pulley 111, 112 and compare it with a value for this radius which has been calculated from the pulley rotational speeds ωιN, ωCvτ~ our-
In the control method according to the invention, a pulley 111, 112 then exerts the first clamping force Fcl on the drive belt 113, and another pulley 111, 112 exerts the sum of the two abovementioned clamping forces Fcl and Fc2 on the drive belt 113. As a result of the control method selected, the drive belt slip ds is therefore in fact controlled by using the second clamping force Fc2 to adjust the transmission ratio of the drive belt CVT i τ/ while the first clamping force Fcl ensures a sufficiently high frictional force between the pulleys 111, 112 and the drive belt 113 to transmit a desired torque through the transmission. The transmission ratio of the drive belt CVT iCvτ has to be increased or reduced depending on the sign of the said difference between the desired value for the drive belt slip dsDV and the actual value dsRV. This means that the sum of the said clamping forces Fcl and Fc2 relates to the input pulley 111 if the transmission ratio icv / which in this context is defined as COCVT-OUT/GIN has to increase, and on the output pulley 112 in the opposite scenario, while the first clamping force Fcl in each case relates to the respective other pulley 111, 112.
The control method according to the invention is summarized once again in the block diagram presented in Figure 3. In block I, the output torque TCVT-DV for the drive belt CVT is calculated from the desired torque TOU for the output shaft 2. Then, in block II, the first clamping force Fcl required for this purpose is calculated, for example in accordance with equation 1. In block III, the sign of the desired drive belt slip dsDv is defined as a function of the sign of the desired output torque TCVT-DV, and then in block IV the difference Δds between the desired value and sign dsDV for the drive belt slip dsRV and the measured value for this slip is determined. In block V, the required second clamping force Fc2 is calculated on the basis of the absolute value of the latter difference |Δds|, for example using a proportional amplifier P. In block VI, the said clamping forces Fcl and Fc2 are added. Finally, in block VII, the sign of the latter difference Δds is determined, and on the basis of this block VIII determines to which of the two pulleys 111, 112 the first clamping force Fcl applies and to which of the two pulleys 111, 112 the added clamping forces Fcl and Fc2 apply.
It should be noted that the desired value for the torque T0uτ can be determined, for example, as a function of the extent to which an accelerator pedal is depressed. Alternatively, it is possible for the said extent to which an accelerator pedal is depressed to be representative of a speed or acceleration of the vehicle, from which the desired value for the torque TOUT can then be determined.
It should also be noted that in practice it may be difficult or even impossible to adjust the desired a drive belt slip dsDv given a low desired value for the torque -T0uτ (for example a torque level equal to zero) may be difficult. In such a situation, it is possible, for example, to define a minimum achievable lower limit for this torque T0UT-MIN/ at which, for example, the brakes of the vehicle are activated in order to dissipate the power which is then supplied, i.e. to allow the wheels to stop despite the presence of the said torque TOUT-MIN on the output shaft 3 of the transmission 10.
It should furthermore be noted that in the geared neutral ratio icvτ-GN of the transmission 10 no power is released to the output shaft 3, so that the engine 1 is subject to load only from power losses in the drive train 1, 11, 12, 13, 14, 15 to the output shaft 3, such as frictional losses in the drive belt CVT 11. If the engine power is then increased, for example by more fuel being supplied to the engine as a result of the accelerator pedal being depressed, the torque can easily exceed a critical value. According to the invention, it may therefore be important to provide independent control of the engine speed and/or the rotational speed ωιN of the input shaft 2 of the transmission 10 in the control method according to the invention.
The two clutches 14 and 15 shown in Figure 1 are, incidentally, not required for the infinitely variable transmission 10 to function, but they do enable the transmission 10 also to be used as a conventional drive belt CVT 11 with a continuously variable transmission ratio and an associated generally known control method. It should be noted that it is also possible in this case, in which the transmission 10 is used as a conventional drive belt CVT 11, for it to be controlled using the control method according to the invention.
Opening the first clutch 14 means that the fixed transmission 12 no longer transmits any mechanical power, while closing the second clutch 15 brings about a direct one-on-one connection between the drive belt CVT 11 and the output shaft 3. All this has the advantage that part of the range of transmission ratios of the drive belt CVT 11 can be passed through again after the first clutch 14 has been opened and/or the second clutch 15 has been closed, on account of the fact that the transmission ratio of the drive belt CVT 11 during the closure of the second clutch 15 has to be reduced in order to synchronize the rotational speed fOcv-ou of the output pulley 112 with the rotational speed ω0uτ of the output shaft 3.
The use of the first clutch 14 in this case allows an alternative control method for the infinitely variable transmission. This is because, according to the invention, there is a fixed and substantially advantageous linear relationship between the torque TCL output to the fixed transmission by the first clutch 14, as well as between the torque T0uτ on the output shaft 3 and the torque TCvτ-ouτ which is output by the drive belt CVT to the epicyclic gearwheel set. The torque TC is in this case adjusted to the desired level by corresponding activation of the clutch 14, for example, in the case of a standard wet disc clutch, by pressing the friction discs, which in this case form the output and input components according to the invention, onto one another with the aid of a hydraulically applied pressure PC where:
TC = μdyn * C * PCL (3)
where C is a constant which takes account of the clutch geometry and μayn is the coefficient of friction in a dynamic contact between the friction discs.
At the same time, a clutch slip SCL-RV across the first clutch 14, i.e. a difference between the rotational speed ωΪN of the input pulley 111 of the transmission 10 and the rotational speed ωo-iN of the input gearwheel 121 the fixed transmission 12, is controlled to a defined desired value for this slip SCL-DV by controlling the transmission ratio of the drive belt CVT 11 as a function of the difference between this desired value Sc-D and the actual value of the clutch slip SCL-RV across the first clutch 14. In this case, of course, the abovementioned drive belt slip ds is not required. As illustrated in Figure 4, which presents a typical traction curve of a standard wet disc clutch, the said desired value for the clutch slip SCL-DV across the first clutch 14 should not be selected to be too small, in order to limit the possible error TERROR in the torque TCL output to the fixed transmission 12 as a result of variations in the clutch slip ΔSCL- However, this desired value SCL-DV should also not be selected to be too high, so that the power dissipated by the clutch 14 remains below a maximum acceptable limit.
In addition to what has been described above, the invention also relates to all the details in the figures and everything which is described in the claims which follow.

Claims

CLAIM
Control method for an infinitely variable transmission (10) having an input shaft (2) and an output shaft (3) which is at least provided with a drive belt CVT (11) having a continuously variable transmission ratio and a friction element (11, 14) such as a clutch (14) or the drive belt CVT (11) , having an input component (113) and an output component (112) which are in frictional contact with one another and between which a normal force can be applied, wherein a torque (T0uτ) on the output shaft (3) of the transmission (10) is adjusted towards a desired value for this torque by controlling the said normal force, characterized in that a difference between an actual input speed (com) of the frictional element (11, 14) and an actual output speed (COCVT-OUT- G>VO-IN) of the frictional element (11, 14) is adjusted towards a desired value (dsDV, SCL-DV) for this difference by controlling the transmission ratio of the drive belt CVT (11) .
PCT/NL2003/000578 2002-10-03 2003-08-12 Control method for an infinitely variable transmission WO2004031621A1 (en)

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NL1021578A NL1021578C2 (en) 2002-10-03 2002-10-03 Control method for an infinitely variable transmission.
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101688607A (en) * 2007-07-11 2010-03-31 罗伯特·博世有限公司 Method for controlling a friction-type continuously variable transmission and a transmission equipped with means for carrying out the method

Citations (5)

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Publication number Priority date Publication date Assignee Title
EP0014013A1 (en) 1979-01-19 1980-08-06 Van Doorne's Transmissie B.V. A composite driving belt with transverse elements provided with mutual coupling means
EP0232979A2 (en) 1986-02-03 1987-08-19 General Motors Corporation Geared-neutral continuously variable transmission
EP0497038A1 (en) * 1991-01-30 1992-08-05 Borg-Warner Automotive, Inc. Control strategies for a dual range infinitely variable transmission
US5462492A (en) * 1993-10-06 1995-10-31 Bando Chemical Industries, Ltd. Continuous speed-shifting device
DE19631216A1 (en) 1995-08-23 1997-03-20 Luk Getriebe Systeme Gmbh Transmission unit esp. for motor vehicle with cone and pulley belt drive

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0014013A1 (en) 1979-01-19 1980-08-06 Van Doorne's Transmissie B.V. A composite driving belt with transverse elements provided with mutual coupling means
EP0232979A2 (en) 1986-02-03 1987-08-19 General Motors Corporation Geared-neutral continuously variable transmission
EP0497038A1 (en) * 1991-01-30 1992-08-05 Borg-Warner Automotive, Inc. Control strategies for a dual range infinitely variable transmission
US5462492A (en) * 1993-10-06 1995-10-31 Bando Chemical Industries, Ltd. Continuous speed-shifting device
DE19631216A1 (en) 1995-08-23 1997-03-20 Luk Getriebe Systeme Gmbh Transmission unit esp. for motor vehicle with cone and pulley belt drive

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101688607A (en) * 2007-07-11 2010-03-31 罗伯特·博世有限公司 Method for controlling a friction-type continuously variable transmission and a transmission equipped with means for carrying out the method

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