Control apparatus for continuously variable transmission mounted in automotive vehicle

• US 5,672,137 A
• Filed: 04/24/1996
• Issued: 09/30/1997
• Est. Priority Date: 04/24/1995
• Status: Expired due to Term

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Ishii, Shigeru, Adachi, Kazutaka, Sudo, Hideki
• Primary Examiner(s): Marmor, Charles A.
• Assistant Examiner(s): Kwon, Peter T.
• Application Number:
  US08/637,069
• Time in Patent Office: 524 Days
• Field of Search: 477/45, 477/43, 477/46, 477/48, 477/49, 364/424.08, 364/424.082, 364/424.094
• US Class Current: 477/45
• CPC Class Codes: F16H 59/46 dependent on a comparison between speeds
• CPC Class Codes: F16H 59/72 dependent on oil characteristics, e.g. temperature, viscosity
• CPC Class Codes: F16H 61/66227 controlling shifting exclusively as a function of speed and torque
• CPC Class Codes: F16H 61/66254 controlling of shifting being influenced by a signal derived from the engine and the main coupling

Abstract

In a control apparatus for controlling a gear shift ratio of a continuously variable transmission mounted in an automotive vehicle as an automatic power transmission, a gear shift ratio command value is calculated using a control constant corresponding to a dynamic characteristic determined for each instantaneous gear shift ratio of the continuously variable transmission so as to achieve a target gear shift ratio response characteristic. In addition, a disturbance compensator (robust compensator) of a robust type filter is used against a disturbance such as a parameter variation to achieve a gear shift ratio control characteristic that a designer of the control apparatus has desired to achieve in cases where the parameter variation occurs due to a load variation, a change in an environment temperature or deterioration of an oil viscosity in a hydraulic pressure mechanism which creates a pressing force on each of drive and driven pulleys of the continuously variable transmission and where an individual difference in the dynamic characteristic of the continuously variable transmission due to a working and/or assembly accuracy of a power transmission part of the continuously variable transmission occurs.

Claims

1. A control apparatus for an automotive vehicle, comprising:

a) a continuously variable transmission, including a gear shift ratio varying mechanism and whose gear shift ratio is continuously controlled according to an operating variable of said gear shift ratio varying mechanism, said gear shift ratio varying mechanism being so arranged and constructed as to continuously vary the gear shift ratio of the continuously variable transmission according to a gear shift ratio command value;

b) a first sensor which is so arranged and constructed as to detect a vehicle driving condition of the vehicle in which the continuously variable transmission is mounted;

c) a second sensor which is so arranged and constructed as to detect an actual gear shift ratio of the continuously variable transmission; and

d) a control unit having;

e) a target gear shift ratio calculating block for calculating a target gear shift ratio on the basis of the detected vehicle driving condition;

f) a dynamic characteristic estimating block for estimating a predetermined dynamic characteristic for each instantaneous gear shift ratio of the continuously variable transmission;

g) a disturbance compensator which is so arranged and constructed as to calculate a disturbance compensation output as functions of the actual gear shift ratio and of either the gear shift ratio command value or the operating variable of the gear shift ratio varying mechanism;

h) a gear shift ratio control constant calculating block for calculating a control constant of each instantaneous gear shift ratio of the continuously variable transmission so as to achieve a target dynamic characteristic using the estimated dynamic characteristic;

i) a first gear shift ratio command calculating block for calculating a first gear shift ratio command value from the target gear shift ratio, the actual gear shift ratio, and the control constant of the corresponding instantaneous gear shift ratio; and

j) a second gear shift ratio command calculating block for subtracting the disturbance compensation output of the disturbance compensator from the first gear shift ratio command value so as to derive and output the gear shift ratio command value,

and the control apparatus further comprising;

k) a gear shift ratio control block for adjustably controlling the operating variable of the gear shift ratio varying mechanism as the function of the output gear shift ratio command value.

2. A control apparatus for an automotive vehicle as claimed in claim 1, wherein said disturbance compensator comprises a first disturbance compensator, having a transfer function of a previously set low pass filter, for receiving the gear shift ratio command value of the gear shift command value calculating block and calculating a first disturbance compensation output as the function of the received gear shift command value;

a second disturbance compensator, having a transfer function of another low pass filter which is a multiplication of the transfer function of the first disturbance compensator by an inverse of a transfer function of a still another low pass filter in which the estimated value of the dynamic characteristic is used, for receiving the actual gear shift ratio and calculating a second disturbance compensator as the function of the actual gear shift ratio of the continuously variable transmission; and

a disturbance compensation output block for subtracting an output of the first disturbance compensator from an output of the second disturbance compensator to derive the disturbance compensation output.

3. A control apparatus for an automotive vehicle as claimed in claim 2, wherein the disturbance compensation output i_pD (t) of the disturbance compensator is expressed as:

space="preserve" listing-type="equation">i.sub.pD (t)={T.sub.H (i.sub.p)s+1}/{T.sub.p (i.sub.p)s+1}·

i .sub.pR (t) -exp.sup.-Ls /{T.sub.H (i.sub.p)s+1}·

Si .sub.p (t),

wherein t denotes a time, T_H (i_p) denotes a cut-off frequency of the low pass filter of the first disturbance compensator, i_pR (t) denotes the actual gear shift ratio, s denotes a differential operator (s=σ

+jω and

corresponds to a Laplace transform operator), T_p (i_p) denotes a time constant of the continuously variable transmission and determined for each instantaneous gear shift ratio and a varying direction of the gear shift ratio, L denotes a dead time, exp denotes an exponential function, and Si_p (t) denotes the gear shift ratio command value.

4. A control apparatus for an automotive vehicle, as claimed in claim 3, wherein the dynamic characteristic Gp(s) for each gear shift ratio of the continuously variable transmission which is estimated by the dynamic characteristic estimating block is expressed as:

Gp(s)=Kp(i_p)·

exp^-Ls /{Tp(i_p)s+1}, wherein Kp(i_p) denotes a gain of the continuously variable transmission.

5. A control apparatus for an automotive vehicle, as claimed in claim 4, wherein the target dynamic characteristic G_T (s) which a designer of the control apparatus is desired to achieve is expressed as:

G_T (s)=exp^-Ls /(T_T s+1) wherein T_T denotes a time constant corresponding to a designed target gear shift ratio response.

6. A control apparatus for an automotive vehicle, as claimed in claim 5, wherein the gear ratio command value is expressed as:

Sip(t)=C₂ (i_p){C₁ (i_p (t)-i_PR (t)}-i_pD (t), wherein C₁ (i_p)=Tp(i_p)-T_T } and C₂ (i_p)={T_T /T_p (i_p)}-1, i_pT denotes the target gear shift ratio at the time of t, and i_pR (t) denotes the actual gear shift ratio at the time of t.

7. A control apparatus for an automotive vehicle, as claimed in claim 6, wherein said gear ratio varying mechanism comprises:

a gear shift ratio control valve which is so arranged and constructed as to variably control a hydraulic pressure supplied to the continuously variable transmission so as to continuously vary the gear shift ratio of the continuously variable transmission; and

a stepping motor associated with the gear shift ratio control valve and which is so arranged and constructed as to control an opening angle of the gear shift ratio control valve according to its angular position approximately corresponding to the gear shift ratio command value and which further comprises conversion determination means for determining a conversion quantity from the gear shift ratio command value into the corresponding angular position of the stepping motor using the following equations;

space="preserve" listing-type="equation">r.sub.i ={Ds/2tan(β

)}+r.sub.io,

space="preserve" listing-type="equation">r.sub.o = 2r.sub.i -π

Dc+{(2r.sub.i -π

Dc).sup.2 -4(r.sub.i.sup.2 +D.sub.c r.sub.i +Dc(2Dc-L.sub.B))}.sup.l/2 !/2,

space="preserve" listing-type="equation">i.sub.p =r.sub.o /r.sub.i,

wherein r_i denotes a radius of a belt contacting part of a drive pulley of the continuously variable transmission, Ds denotes a displacement of a belt within an spatial interval of the drive pulley and corresponds to the angular position of the stepping motor, r_io denotes a minimum radius of the drive pulley, r_o denotes a radius of a belt contacting part of a driven pulley of the continuously variable transmission, Dc denotes an interaxial distance between the drive pulley and the driven pulley, L_B denotes a circumferential length of the belt, and β

denotes a sheave angle of the pulleys, i_p denotes the gear shift ratio which has a proportional relationship to the gear shift command value.

8. A control apparatus for an automotive vehicle, as claimed in claim 7, wherein said conversion quantity determining means comprises a map representing the relationship between the gear shift ratio command value and the angular position of the stepping motor and which has already determined according to an experiment.

9. A control apparatus for an automotive vehicle, as claimed in claim 1, wherein said disturbance compensator comprises:

a first disturbance compensator, having a transfer function of a low pass filter using the estimated value of the dynamic characteristic, for calculating and outputting a first disturbance compensation output as a function of the gear shift ratio command value, a subtractor for subtracting the first disturbance compensation output from the actual gear shift ratio, and a second disturbance compensator, having a transfer function of another low pass filter which is a multiplication of the transfer function of the first disturbance compensator by an inverse of a transfer function of a still another low pass filter previously set, for calculating and outputting a second disturbance compensation output as the function of the subtracted result of the subtractor, said second disturbance compensation output serving as the disturbance compensation output of the disturbance compensator.

10. A control apparatus for an automotive vehicle, as claimed in claim 9, wherein said disturbance compensation output of the disturbance compensator is expressed as:

space="preserve" listing-type="equation">i.sub.pD (t)={T.sub.H (i.sub.p)s+1}/{Tp(i.sub.p)s+1}·

i.sub.pR (t) -exp.sup.-Ls /{T.sub.H (i.sub.p)s+1},

wherein t denotes a time, T_H (i_p) denotes a cut-off frequency of the low-pass filter in each of the first and second disturbance compensators and is determined so that the dynamic characteristic of the continuously variable transmission and a stability of the control apparatus are satisfied, Tp(i_p) denotes a time constant of the continuously variable transmission which is determined for each gear shift ratio and each direction of the gear shift ratio, i_pR (t) denotes the actual gear shift ratio at the time of t, L denotes a dead time, s denotes a differential operator, and exp denotes an exponential function.