A known hydraulic pressure control apparatus for an automatic transmission is disclosed in JP2001-248724A (hereinafter referred to as Patent reference 1). The known hydraulic pressure control apparatus disclosed in Patent reference 1 includes five frictional engagement elements including a brake B2 (i.e., refereed to as a low and reverse brake) shared by a first speed stage of a forward drive range (D range) and a reverse drive range (R range) (reverse shift stage). According to the hydraulic pressure control apparatus disclosed in Patent reference 1, four low pressure type linear solenoid valves and a pressure regulating valve are arranged for the five frictional engagement elements, and the linear solenoid valves and the pressure regulating valve are controlled for controlling a line pressure. Thus, hydraulic pressure control apparatus of Patent reference 1 is configured to achieve a gear skip shift with the reduced number of linear solenoid valves relative to the number of the frictional engagement elements by one.
JP2004-116734A (i.e., hereinafter referred to as Patent reference 2) discloses a known hydraulic pressure control apparatus for an automatic transmission which includes a brake B2 (i.e., refereed to as a low and reverse brake) shared by a first speed stage of a forward drive range (D range) and a reverse drive range (R range) (reverse shift stage). Further, according to the hydraulic pressure control apparatus disclosed in Patent reference 2, a linear solenoid valve is connected to the low and reverse brake via a shift valve which is controlled to switch by an on-off solenoid valve. The shift valve is configured to supply a hydraulic pressure from the linear solenoid valve to other frictional engagement elements other than the low and reverse brake.
JP2008-144941A (i.e., referred to as Patent reference 3) discloses a known hydraulic pressure control apparatus for an automatic transmission in which a linear solenoid valve for an engagement of a second clutch C2, which is another frictional engagement element, is connectable to a brake (low and reverse brake) B2, which is applied when selecting a first speed stage of a forward drive range (D range) and a reverse drive range (R range), to engage the low and reverse brake B2 when a park position (P position) or a neutral range (N range) is selected so that the brake (low and reverse brake) B2 does not have to be additionally engaged when the gear stage (gear selector position) is shifted from the P position or N range to the D range or R range (i.e., when a “garage shift” is executed).
According to the hydraulic pressure control apparatus disclosed in Patent reference 1, at a “garage shift” in which selected gear stage is shifted from a P position or a neutral range (N range) to the D range or the R range, it is required to newly establish engagements of two frictional engagement elements in order to establish the first speed stage of the D range and the R range. Thus, according to the construction disclosed in Patent reference 1, a time required for shifting is increased. Further, according to the construction disclosed in Patent reference 1, because it is required to increase a volume of an oil pump, which is a source of the hydraulic pressure, a loss of torque of the oil pump is increased and fuel economy is deteriorated.
According to the construction disclosed in Patent reference 2, because the hydraulic pressure is supplied to the low and reverse brake B2 via the shift valve which is controlled to switch by the on-off solenoid valve, structures of a hydraulic pressure circuit and controls of the apparatus is complicated.
According to the hydraulic pressure control apparatus disclosed in Patent reference 3, because the “garage shift” is required to be detected and the linear solenoid valve for the C2 clutch engagement is required to be controlled synchronizing to the garage shift, control logics are complicated.
A need thus exists for a hydraulic pressure control apparatus for an automatic transmission which is not susceptible to the drawback mentioned above.
USPTO Backgrounds
USPTO Backgrounds