CVT control system for vehicle drivetrain

• US 5,700,224 A
• Filed: 01/31/1996
• Issued: 12/23/1997
• Est. Priority Date: 02/01/1995
• Status: Expired due to Fees

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Suzuki, Akito, Ochiai, Tatsuo
• Primary Examiner(s): Marmor, Charles A.
• Assistant Examiner(s): Kwon, Peter T.
• Application Number:
  US08/594,992
• Time in Patent Office: 692 Days
• Field of Search: 477/40, 477/44, 477/45, 477/46, 477/92
• US Class Current: 477/45
• CPC Class Codes: F16H 2061/66281 by increasing the line pressure at the occurrence of input torque peak
• CPC Class Codes: F16H 59/54 dependent on signals from the brakes, e.g. parking brakes
• CPC Class Codes: F16H 61/66272 characterised by means for controlling the torque transmitting capability of the gearing

Abstract

A CVT control system for a vehicle drivetrain controls line pressure applied to an output pulley of the CVT to different levels against various CVT ratios in response to operator brake command, causing the output pulley to create force to hold the V-belt.

Claims

1. A CVT control system for a vehicle drivetrain, comprising:

a CVT having an input pulley and an output pulley drivingly connected to the input pulley by a power transmission belt, each of the input and output pulleys having an axially positionable pulley half and an axially stationary pulley half;

a ratio control unit operable to establish various positions of the axially positionable pulley half of the input pulley relative to the axially stationary pulley half of the input pulley to establish various CVT ratios between the input pulley and the output pulley;

a line pressure control unit having an actuator operable in response to a control signal to establish various line pressure levels applied to the output pulley to create force required for the output pulley to hold the power transmission belt between the axially positionable pulley half of the output pulley and the axially stationary pulley half of the output pulley; and

a controller for developing the control signal in response to an operator brake demand for deceleration of the output pulley, wherein the controller;

develops various desired line pressure levels in response to the presence of the operator brake demand,

develops the control signal in a manner determined as a function of the desired line pressure levels, and

applies the control signal to the line pressure control to adjust an actual line pressure toward the desired line pressure level.

2. A CVT control system as claimed in claim 1, wherein the controller stores different data of the desired line pressure level against different CVT ratios within an available range of CVT ratios.

3. A CVT control system as claimed in claim 1, wherein the controller stores data of the desired line pressure level, which decreases as the CVT ratio decreases toward a smallest CVT ratio of an available range of different CVT ratios.

4. A CVT control system as claimed in claim 2, wherein the controller stores data of the desired line pressure level at the largest CVT ratio and the different data of the desired line pressure levels at different CVT ratios are lower than the data of the desired line pressure level at the largest CVT ratio.

5. A CVT control system as claimed in claim 4, wherein the desired line pressure levels are determined so as to adjust the magnitude of force required to hold the power transmission belt to the required minimum over the available range of the CVT ratios.

6. A CVT control system for a vehicle drivetrain, comprising:

a CVT having an input pulley and an output pulley drivingly connected to the input pulley by a power transmission belt, each of the input and output pulleys having an axially positionable pulley half and an axially stationary pulley half;

a ratio control unit operable to establish various positions of the axially positionable pulley half of the input pulley relative to the axially stationary pulley half of the input pulley to establish various CVT ratios between the input pulley and the output pulley;

a line pressure control unit having an actuator operable in response to a control signal to establish various line pressure levels applied to the output pulley to create force required for the output pulley to hold the power transmission belt between the axially positionable pulley half of the output pulley and the axially stationary pulley half of the output pulley; and

a controller for developing the control signal in response to an operator brake demand for deceleration of the output pulley, wherein the controller;

derives an actual CVT ratio between the input and output pulleys based on actual speeds of the input pulley and the output pulley,

develops a desired line pressure level for the actual CVT ratio in response to the operator brake demand,

develops the control signal in a manner determined as a function of the desired line pressure level, and

applies the control signal to the line pressure control unit to adjust an actual line pressure toward the desired line pressure level.

7. A control method for a vehicle drivetrain having a CVT having an input pulley and an output pulley drivingly connected to the input pulley by a power transmission belt, each of the input and output pulleys having an axially positionable pulley half and an axially stationary pulley half, a ratio control unit operable to establish various positions of the axially positionable pulley half of the input pulley relative to the axially stationary pulley half of the input pulley to establish various CVT ratios between the input pulley and the output pulley, a line pressure control unit having an actuator operable in response to a control signal to establish various line pressure levels applied to the output pulley to create force required for the output pulley to hold the power transmission belt between the axially positionable pulley half of the output pulley and the axially stationary pulley half of the output pulley, and a controller for developing the control signal in the presence of an operator brake demand for deceleration of the output pulley, the control method comprising the steps of:

developing various desired line pressure levels in the presence of the operator brake demand;

generating the control signal in a manner determined as a function of the desired line pressure level; and

applying the control signal to the line pressure control unit to adjust an actual line pressure toward the desired line pressure level.

8. A control method for a vehicle drivetrain including a CVT having an input pulley and an output pulley drivingly connected to the input pulley by a power transmission belt, each of the input and output pulleys having an axially positionable pulley half and an axially stationary pulley half, a ratio control unit operable to establish various positions of the axially positionable pulley half of the input pulley relative to the axially stationary pulley half of the input pulley to establish various CVT ratios between the input pulley and the output pulley, a line pressure control unit having an actuator operable in response to a control signal to establish various line pressure levels applied to the output pulley to create force required for the output pulley to hold the power transmission belt between the axially positionable pulley half of the output pulley and the axially stationary pulley half of the output pulley, and a controller for developing the control signal in response to an operator brake demand for deceleration of the output pulley, the control method comprising the steps of:

deriving an actual CVT ratio between the input and output pulleys based on actual speeds of the input pulley and the output pulley;

developing a desired line pressure level for the actual CVT ratio in response to the operator brake demand;

developing the control signal in a manner determined as a function of the desired line pressure level; and

applying the control signal to the line pressure control unit to adjust an actual line pressure toward the desired line pressure level.

9. A vehicle drivetrain control system, comprising:

an engine having a positional throttle;

a hydraulic torque converter;

a CVT having an input pulley and an output pulley drivingly connected to the input pulley by a power transmission belt, each of the input and output pulleys having an axially positionable pulley half and an axially stationary pulley half;

a ratio control unit operable to establish various positions of the axially positionable pulley half of the input pulley relative to the axially stationary pulley half of the input pulley to establish various CVT ratios between the input pulley and the output pulley;

a line pressure control unit having an actuator operable in response to a control signal to establish various line pressure levels applied to the output pulley to create force required for the output pulley to hold the power transmission belt between the axially positionable pulley half of the output pulley and the axially stationary pulley half of the output pulley; and

a controller for developing the control signal in response to an operator brake demand for deceleration of the output pulley, wherein the controller;

derives an actual engine torque based on an actual engine speed and an actual throttle position,

derives an actual torque multiplication ratio provided by the torque converter based on a torque converter ratio, which is based on the actual engine speed and an actual speed of the input pulley,

derives an actual input torque applied to the input pulley based on the derived actual torque ratio and the derived engine torque,

derives an actual CVT ratio based on the actual speed of the input pulley and an actual speed of the output pulley,

develops a desired line pressure level based on the derived actual CVT ratio and the derived input torque in the absence of the operator brake demand and a different desired line pressure level based on the derived input torque in the presence of the operator brake demand, and

develops the control signal in a manner determined as a function of the desired line pressure level in the absence of the operator brake demand.

10. A CVT control system for a vehicle drivetrain, comprising:

a CVT having an input pulley and an output pulley drivingly connected to the input pulley by a power transmission belt, each of the input and output pulleys having an axially positionable pulley half and an axially stationary pulley half;

a ratio control unit operable to establish various positions of the axially positionable pulley half of the input pulley relative to the axially stationary pulley half of the input pulley to establish various CVT ratios between the input pulley and the output pulley;

a line pressure control unit having an actuator operable in response to a control signal to establish various line pressure levels applied to the output pulley to create force required for the output pulley to hold the power transmission belt between the axially positionable pulley half of the output pulley and the axially stationary pulley half of the output pulley; and

a controller for developing the control signal in response to an operator brake demand for deceleration of the output pulley, wherein the controller;

develops various first desired line pressure levels in the absence of the operator brake demand,

develops various second desired line pressure levels, which are different from the various first desired line pressure levels, in the presence of the operator brake demand,

develops the control signal in a manner determined as a function of the second desired line pressure level in the presence of the operator brake demand, and

applies the control signal to the line pressure control unit to adjust an actual line pressure toward the second desired line pressure level.

11. A CVT control system for a vehicle drivetrain, comprising:

a CVT having an input pulley and an output pulley drivingly connected to the input pulley by a power transmission belt, each of the input and output pulleys having an axially positionable pulley half and an axially stationary pulley half;

a ratio control unit operable to establish various positions of the axially positionable pulley half of the input pulley relative to the axially stationary pulley half of the input pulley to establish various CVT ratios between the input pulley and the output pulley;

a line pressure control unit having an actuator operable in response to a control signal to establish various line pressure levels applied to the output pulley to create force required for the output pulley to hold the power transmission belt between the axially positionable pulley half of the output pulley and the axially stationary pulley half of the output pulley; and

a controller for developing the control signal, wherein the controller;

develops various first desired line pressure levels based on operative conditions of the vehicle in the absence of an operator brake demand,

develops various second desired line pressure levels based on the CVT ratios prevailing at the time when the operator brake demand is present, which levels are different from the various first desired line pressure levels,

develops the control signal in a manner determined as a function of the second desired line pressure level in the presence of the operator brake demand, and

applies the control signal to the line pressure control unit to adjust actual line pressure toward the desired line pressure level.

12. A CVT control system as claimed in claim 11, wherein the second desired line pressure levels are related to the CVT ratios such that the higher the CVT ratio, the higher the second desired line pressure.