Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Reexamination Certificate
1999-12-23
2001-06-05
Nguyen, Tan (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C701S055000, C474S018000, C477S045000
Reexamination Certificate
active
06243638
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic transmission control system for an automotive vehicle employing a belt-type continuously variable automatic transmission (often abbreviated to “CVT”) which uses a drive belt running in a pair of variable-width pulleys to provide varying gear ratios (transmission ratios or pulley ratios), and specifically to techniques for directly efficiently controlling working pressures of adjustable flanges (or axially-slidable flanged pistons) of both primary and secondary pulleys of the CVT by the use of two motor-driven oil pumps.
2. Description of the Prior Art
Japanese Patent Provisional Publication No. 7-259941 has disclosed a transmission control system for a belt-type continuously variable automatic transmission (CVT). Generally, the V groove of a primary pulley of the belt-type CVT is constructed by a stationary flange and an adjustable flange axially slidable on linear ball bearing splines for varying the width of the V groove of the primary pulley by hydraulic pressure (often called a “primary pulley pressure” or a “speed-change control pressure”), whereas the V groove of a secondary pulley is constructed by a stationary flange and an adjustable flange axially slidable on linear ball bearing splines for varying the width of the V groove of the secondary pulley by at least hydraulic pressure (often called a “secondary pulley pressure” or a “regulated line pressure”). The CVT has a hydraulic modulator or a hydraulic control unit for controlling the working pressure of the adjustable flange (the flanged piston) of each of the primary and secondary-driving and driven-pulleys. The hydraulic control unit includes a line pressure control valve which regulates the hydraulic pressure of working fluid discharged from a sole oil pump and then produces the regulated line pressure (the secondary pulley pressure P
sec
) applied to a secondary pulley actuation cylinder, and a speed-change control valve which further regulates the line pressure and then generates the speed-change control pressure (the primary pulley pressure P
pri
) applied to a primary pulley actuation cylinder. The sole oil pump is commonly driven by an engine. The line pressure is regulated so that there is no slippage of a drive belt (usually a single segmented steel belt) running in the primary and secondary pulleys.
SUMMARY OF THE INVENTION
In the conventional transmission control system, however, the working pressures of the adjustable flanges of the primary and secondary pulleys are produced by modulating or regulating the hydraulic pressure of working oil discharged from the engine-driven sole oil pump (a sole hydraulic pressure source) by way of the hydraulic control unit. Thus, there are the following several drawbacks.
(i) The conventional system requires complicated hydraulic circuits and control valves, and therefore there are increased tendencies for oil leakage from each of control valves and/or hydraulic circuits to occur. This increases energy loss.
(ii) In case of the use of an engine-driven oil pump, if a specified discharge from the oil pump is designed to insure a discharge of working fluid at low engine speeds, there is a tendency of excessive supply of working oil discharged from the pump at high engine speeds. In such a case, superfluous oil must be drained, thus resulting in wasteful energy consumption.
(iii) Additionally, in case of the use of an engine-driven oil pump, there is no hydraulic pressure produced by the pump while the engine is not running. Thus, the conventional system, which uses an engine-driven oil pump, cannot be used for a so-called idle-stop control according to which the engine is also stopped during the vehicle standstill state.
To eliminate the previously-discussed drawbacks, it is desirable to directly control the working pressures of the adjustable flanges of the primary and secondary pulleys by the use of two electric-motor-driven oil pumps. However, when the working pressures of the adjustable flanges of the primary and secondary pulleys are controlled independently of each other with the use of the two motor-driven oil pumps, a considerably large energy may be consumed by the two oil pumps for working-oil transfer between the primary and secondary pulleys during speed-change control action, especially in a system that a desired primary pulley pressure is supplied as a differential pressure from atmospheric pressure by a first motor-driven pump and a desired secondary pulley pressure is also supplied as a differential pressure from atmospheric pressure by a second motor-driven pump. This undesiredly increases a maximum required output from each of the motor-driven oil pumps, thus requiring a large-size motor-driven pump. To avoid this, that is, to solve the problem of large-sizing of the two motor-driven pumps, a control system can be constructed so that a motor-driven oil pump mainly associated with a secondary pulley serves as a pressure hold pump, whereas a motor-driven oil pump mainly associated with a primary pulley serves as a speed-change pump, and so that the working oil comes and goes between the primary pulley actuation cylinder (or the primary pulley actuation chamber) and the secondary pulley actuation cylinder (or the secondary pulley actuation chamber) through the previously-noted speed-change pump. In controlling the speed-change pump by adjusting a required flow rate (which will be hereinafter referred to as a “speed-change flow rate” and is needed for speed-change control action) or a “speed-change velocity” being defined as the time rate of change of the transmission ratio (the pulley ratio) during shifting from an actual transmission ratio (an actual pulley ratio) to a desired transmission ratio (a target pulley ratio), so that the actual pulley ratio is adjusted to the desired pulley ratio, especially during downshifting action where the working oil is released from the primary pulley actuation chamber, there is another problem. That is to say, there is a possibility that the amount of stroke (axial sliding motion) of the adjustable flange of each of the pulleys cannot follow up satisfactorily in comparison with a flow rate of working fluid obtained by the speed-change pump control, in presence of output of an excessive command signal value for the speed-change flow rate (or an excessive command signal value for the speed-change velocity). As a result, the actual primary pulley pressure reduces to below a lowest primary pulley pressure below which there is a possibility of slippage of the drive belt. In such a case, assuming that the excessive speed-change flow rate command signal value or the excessive speed-change velocity command signal value retains unchanged, there may result a lack of a so-called belt capacity (that is, a lack of a drive-belt. slippage preventable capacity) in the primary pulley side. In other words, there is a possibility of slippage of the drive belt (the segmented steel belt) running in the primary and secondary pulleys.
Accordingly, it is an object of the invention to provide an electronic transmission control system for an automotive vehicle with a belt-type continuously variable automatic transmission which avoids the aforementioned disadvantages of the prior art.
It is another object of the invention to provide an electronic transmission control system for an automotive vehicle with a belt-type continuously variable automatic transmission (CVT), which is capable of reducing fuel consumption of each of oil pumps employed in the control system, and of performing a so-called idle-stop control, and of preventing undesired slippage of a drive belt running in a pair of pulleys of the CVT by ensuring a so-called belt capacity (corresponding to a drive-belt slippage preventable capacity) in the primary pulley side (the speed-change-control-action side pulley) even during downshifting action.
In order to accomplish the aforementioned and other objects of the present invention, an electronic transmission control system for an automotive
Abo Keiju
Sato Osamu
Suzuki Hideaki
Yamamoto Masahiro
Foley & Lardner
Nguyen Tan
Nissan Motor Co,. Ltd.
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