Control device of continuously variable transmission

Details Control device of continuously variable transmission Control device of continuously variable transmission

2001-03-20

2004-04-20

Siconolfi, Robert A. (Department: 3683)

Endless belt power transmission systems or components

Pulley with belt-receiving groove formed by drive faces on...

Load responsive

C474S018000

Reexamination Certificate

active

06723014

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a continuously variable transmission with a V-belt for use in vehicles, etc., and more particularly to an improvement in shift control of the continuously variable transmission.
2. Description of the Prior Art
In recent years, there has been developed a so-called hybrid vehicle, which is a combination of an internal combustion engine (hereinafter referred to as an engine) and an electric motor, in order to protect the environment and improve the fuel economy. Accordingly, a combination of this hybrid vehicle and a V-belt type continuously variable transmission has been proposed.
In the V-belt type continuously variable transmission, a V-belt passes about a primary pulley and a secondary pulley, both of which are variable pulleys. The groove width of the primary pulley is variably controlled by the supply of hydraulic pressure.
More specifically, as shown in
FIG. 5
, a first cylinder chamber
20
and a second cylinder chamber
32
are provided to the primary pulley
16
and the secondary pulley
26
, respectively. Line pressure is continuously supplied to the second cylinder chamber
32
of the secondary pulley
26
. Hydraulic pressure, which is acquired by regulating the line pressure as original pressure with a shift control valve
63
, is supplied to the first cylinder chamber
20
of the primary pulley
16
. The hydraulic pressure supplied to the first cylinder chamber
20
changes the groove width of the primary pulley
16
to change the gear ratio. In the meantime, the line pressure is changed within a predetermined range to control a thrust (pushing pressure) against a V-belt
24
.
To control the hydraulic pressure supplied to the first cylinder chamber
20
, the shift control valve
63
driven by a step motor
64
regulates the line pressure as the original pressure.
More specifically, the shift control valve
63
has a primary port
63
P connected with the first cylinder chamber
20
, a line pressure port
63
L supplied with the line pressure, and a drain port
63
T. The shift control valve
63
also has a spool
63
a
, which slides according to the positions of a moving conical board
22
of the primary pulley
16
and the step motor
64
. The displacement of the spool
63
a
causes the primary port
63
P to selectively connect with the line pressure port
63
L or the drain port
63
T to thereby control the hydraulic pressure supplied to the first cylinder chamber
20
.
Oil supplied to the primary pulley
16
is supplied as control hydraulic pressure to the first cylinder chamber
20
, and is also supplied to a bearing
14
of the primary pulley
16
through an orifice in order to lubricate the bearing
14
.
The continuously variable transmission of this kind is disclosed in, e.g., Japanese Patent Application Laid-Open Publication No. 11-82725.
The hybrid vehicle is equipped with a battery having a large capacity, and it is therefore easy to use the electric motor in various areas of a power system. For this reason, the electric motor preferably drives a hydraulic pump for use in lubricating each part of the engine and operating the continuously variable transmission because this achieves the stable rotation of the pump.
If the electric motor drives the hydraulic pump, however, the hydraulic pump stops functioning and supplying the line pressure when a failure occurs in a power supply system of the electric motor while the vehicle is running.
In this case, an alarm or the like is given to warn of the failure, and the vehicle is stopped to restore the system to a normal operating state. If the vehicle is driven again, however, the shift may not be performed normally.
According to a research, the above problem results from a slip between the variable pulleys and the V-belt.
It is therefore an object of the present invention to provide a continuously variable transmission, which prevents the slip between the variable pulleys and the V-belt even when the supply of the hydraulic pressure is temporarily stopped due to the failure in the power supply system of the electric motor that drives the hydraulic pump.
According to a further research about the slip, if the hydraulic pump stops to cease the supply of the line pressure, the step motor is controlled toward a Lo range (low range gear ratio) with the deceleration of the vehicle. Since the residual hydraulic pressure gradually gets out of a hydraulic circuit, the hydraulic pressure in the second cylinder chamber
32
of the secondary pulley is lowered. Consequently, the vehicle stops while the step motor cannot return to the position corresponding to the lowest gear ratio.
As time passes, the hydraulic pressure in the first cylinder chamber
20
of the primary pulley is further lowered. Moreover, if the oil is also supplied to the bearing
14
, the hydraulic pressure leaks. Consequently, the oil is decreased in the first cylinder chamber
20
.
Therefore, when the vehicle restarts running after the power supply system of the electric motor is restored to a normal operating state following the failure, the shift cannot be started from the lowest range ratio and there is hardly remained the pushing pressure of the pulleys against the V-belt. In addition, the shift is started with only a small amount of hydraulic pressure being supplied. This results in the slip between the pulleys and the V-belt.
SUMMARY OF THE INVENTION
To solve the above-mentioned problems, the present invention provides a control device of a continuously variable transmission which comprises: a transmission mechanism comprising a pair of variable pulleys with groove widths being changed by supply of hydraulic pressure, and a belt passing about the pair of variable pulleys; a hydraulic pump being driven by an electric motor to supply hydraulic pressure; line pressure control means for regulating hydraulic pressure from the hydraulic pump to predetermined line pressure; shift control means for outputting a shift command according to a driving state; and a shift control valve for supplying hydraulic pressure, whose original pressure is line pressure, to the pair of variable pulleys in the transmission mechanism according to the shift command; the control device of the continuously variable transmission further comprising: failure information holding means for holding failure information on a failure of the electric motor; and wherein if, at start of driving, the failure information holding means holds failure information indicating that the electric motor fails in previous driving, the shift control means outputs a predetermined shift command to thereby fill the variable pulleys with hydraulic pressure through the shift control valve.
If the electric motor fails in the previous driving of the vehicle, the variable pulleys are filled with the hydraulic pressure through the shift control valve. Accordingly, if no hydraulic pressure remains in the variable pulleys and it is therefore necessary to prevent the slip, the shift control valve is controlled to fill the variable pulleys with the hydraulic pressure to prevent the slip between the pulleys and the belt.
The present invention also provides a control device of a continuously variable transmission, which comprises: a transmission mechanism comprising a primary pulley and a secondary pulley provided with a first cylinder chamber and a second cylinder chamber, with groove widths being changed by supply of hydraulic pressure respectively, and a belt passing about the primary pulley and the secondary pulley; a hydraulic pump being driven by an electric motor to supply hydraulic pressure; line pressure control means for regulating hydraulic pressure from the hydraulic pump to predetermined line pressure and continuously supplying the line pressure to the second cylinder chamber; a shift control valve being driven by an actuator to supply hydraulic pressure, whose original pressure is line pressure, to the first cylinder chamber; and shift control means for outputting a shift command for controlling the actuator acco

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