OIL PRESSURE CONTROL SYSTEM FOR A CONTINUOUSLY VARIABLE TRANSMISSION

Abstract: A continuously variable transmission has a torque converter (14) with a lockup clutch (19). A high pressure oil pump (70) is provided for the transmission and a low pressure oil pump (72) provided for the torque converter. A line pressure control valve (100) controls the pressure of oil supplied from the high pressure oil pump (70) to produce a line pressure for operating the transmission, and another control valve (170) is provided for controlling the pressure of oil supplied from the low pressure oil pump (72) to the torque converter (14) and the lockup clutch (19).

Description: The present invention relates to a hydraulic control system for a continuously variable belt-drive automatic transmission for a motor vehicle, and more particularly to a system for controlling pressure of oil in a hydraulic circuit for the transmission as defined in the first part of claim 1 known from US-A- 4478105. A continuously variable transmission with a torque converter having a lockup clutch is known. The transmission is controlled by high line pressure of 30 to 40 kg/cm² at maximum and the torque converter is controlled by lower control pressure of 4 to 6 kg/cm². The transmission is further provided with a multiple-disk friction clutch in a selector device and transfer clutch for a four-wheel drive system. These clutches are independently operated by respective pressures of oil. Accordingly, it is necessary to control the respective pressures with accuracy. The generic US-A-4,478,105 discloses a system in which pressure of oil from an oil pump is adjusted by a line pressure control valve for controlling drive and driven pulleys of the transmission. The line pressure control valve produces a control pressure for controlling a torque converter, a lockup clutch, a lockup control valve, and a clutch for a selector device. However, in such a system, since the oil pump must supply oil to various devices at different pressures, an oil pump having a large discharge capacity is required, as shown in Fig. 3b. Further, since efficiency of the oil pump reduces at high pressure as shown in Fig. 3a, pumping loss is large and life time of a pump driving shaft is shortened. On the other hand, when the transmission is rapidly upshifted, a large amount of oil is fed to a cylinder of a drive pulley. As a result, converter pressure reduces. Further, since it is difficult to adjust converter pressure, the control pressure for the lockup control valve and clutches becomes excessively large, and the control pressure may vary with the variation of the line pressure. Accordingly, it is desirable that a hydraulic system for supplying control pressure for the torque converter is separated from a hydraulic system for supplying the line pressure for the transmission so as to independently produce necessary pressures. WO-A 85 0062 discloses a system in which separate oil pumps are provided for controlling a torque converter and a conventional power shift type transmission, respectively. The present invention seeks to provide a hydraulic control system which is divided into an oil supply system for the transmission and an oil supply system for the torque converter, thereby controlling respective pressures with accuracy and reducing the pumping loss. According to the present invention, there is provided an oil pressure control system for a continuously variable transmission for a vehicle, the control system having a hydraulic circuit including a transmission ratio control valve and a line pressure control valve, and the transmission having a torque converter with a lockup clutch and an associated lock-up control valve, and a selector device for selecting forward and reverse drives, the line pressure control valve being arranged to be operated in accordance with driving conditions of the vehicle, so as to control the pressure of oil supplied for operating the transmission; said other control valves being arranged to operate in accordance with driving conditions of the vehicle, so as to control the pressure of oil supplied to the torque converter and the lockup clutch; the control system being characterised by: a high pressure oil pump arranged to supply oil to the transmission via the line pressure control valve; a low pressure oil gump arranged to supply oil to the torque converter via further control valve means; each of the oil pumps being operatively connected to the engine so as to be driven by the engine; said further control valve means including a reducing valve and said lockup control valve both communicating with the low pressure oil pump, said reducing valve producing a constant gressure and said lockup control valve supplying said reduced constant pressure to the torque converter; and solenoid operated valves being provided to operate the transmission ratio control valve, said line pressure control valve, said lockup control valve, respectively, in accordance with the driving conditions of the vehicle. In an aspect of the invention, the control valve means has a reducing valve producing a constant pressure and lockup control valve for supplying oil to the torque converter. One embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figs. 1a and 1b show a sectional view of a continuously variable belt-drive transmission to which the present invention is applied; Figs. 2a and 2b show a hydraulic control circuit according to the present invention; Fig. 3a is a graph showing efficiency of an oil pump; and Fig. 3b is a graph showing a discharge characteristic of the oil pump. Figs. 1a and 1b show a four-wheel drive power transmission system with a continuously variable belt-drive automatic transmission for a motor vehicle, to which the present invention is applied. An engine E is transversely mounted on a motor vehicle at a front portion thereof. The power transmission system comprises a torque converter device 10, a selector device 30, a continuously variable belt-drive transmission 40, a final reduction device 50, and a transfer device 60. The torque converter device 10 is provided in a housing 1. The selector device 30, transmission 40, final reduction device 50 and transfer device 60 are provided in a main housing 2 and a side housing 3. An extension case 4 is secured to the housing 1. The torque converter device 10 has a torque converter 14 with a lockup clutch 19. A drive plate 12 is fixed to a crankshaft 11 of the engine E. A converter cover 13 is secured to the drive plate 12. The torque converter 14 comprises an impeller 14a integral with the converter cover 13 by welding, a turbine 14b fixed to a turbine hub 16 which is splined to an input shaft 15, and a stator 14c connected to a hollow stator shaft 18 through a one-way clutch 17. The lockup clutch 19 is disposed between the converter cover 13 and the torque converter 14, and a facing 20 of the lockup clutch 19 is attached for making a contact with the cover 13. Further, in the torque converter device 10, a release pressure oil chamber 21 is defined adjacent the converter cover 13 for applying release pressure to the lockup clutch 19, and lockup pressure oil chamber 22 is formed adjacent the torque converter 14 for applying lockup pressure to the lockup clutch 19. The selector device 30 comprises a planetary gear 31 having a pair of pinions 33 and 34, and a sun gear 32 mounted on the input shaft 15. Pinions 33 and 34 are supported on a carrier 35. The sun gear 32 is engaged with a ring gear 36 through pinions 33 and 34. A forward clutch 37 is disposed between the sun gear 32 and the ring gear 36. A reverse brake 38 is disposed between the ring gear 36 and the main case 2. At forward driving such as a drive (D) range selection, the forward clutch 37 is engaged to lock the sun gear 32. During reverse operation, the reverse brake 38 is engaged to lock the ring gear 36 so as to reversely rotate the carrier 35. If the number of teeth of the ring gear 36 is set at twice as many as that of the sun gear 32, the gear ratio in reverse drive is equal to that in forward drive. The belt-drive transmission 40 has a main shaft 41 engaged with the carrier 35 and an output shaft 42 provided in parallel with the main shaft 41. A drive pulley (primary pulley) 43 and a driven pulley (secondary pulley) 44 are mounted on the main shaft 41 and output shaft 42, respectively. A fixed conical disc 43a of the drive pulley 43 is integral with main shaft 41 and an axially movable conical disc 43b is axially slidably mounted on the main shaft 41. The movable conical disc 43b also slides in a cylinder 46 formed on the main shaft 41 to provide a servo device. A fixed conical disc 44a of the driven pulley 44 is formed on the output shaft 42 opposite the movable conical disc 43b and a movable conical disc 44b is slidably mounted on the shaft 42 opposite the disc 43a. Movable conical disc 44b has a cylindrical portion which is slidably engaged in a cylinder 47 of the output shaft 42 to form a servo device. A spring 48 is provided to urge the movable conical disc 44b to the fixed conical disc 44a. A drive belt 45 engages with the drive pulley 43 and the driven pulley 44. The cylinder 46 of the drive pulley 43 is so designed that the pressure receiving area thereof is larger than that of the cylinder 47 of the driven pulley 44. Thus, the running diameter of the belt 45 on the pulleys is varied dependent on driving conditions. Secured to the output shaft 42 is a drive gear 51a of the final reduction device 50 which engages with an intermediate reduction gear 51 on an intermediate shaft 52. An intermediate gear 53 on the shaft 52 engages with a final reduction gear 54. The rotation of the final reduction gear 54 is transmitted to axles 56 of front driving wheels through a differential 55. The transfer device 60 comprises a transfer gear 61 engaged with the final reduction gear 54 and rotatably mounted on a transfer shaft 62 which is transversely disposed and rotatably supported by bearings, and a transfer clutch 63 in the form of a fluid operated multiple-disk friction clutch. The transfer clutch 63 operates to couple the gear 61 with the shaft 62, so that the rotation of the gear 61 is transferred to rear drive wheels through shaft 62, bevel gear 64a secured to the shaft 62, bevel gear 64 engaged with the bevel gear 64a and rear drive shaft 65. In the side housing 3, an oil pump 70 is provided for supplying a high pressure of oil for the transmission. The main shaft 41 has an axial passage in which an oil pump driving shaft 71 connected to the crankshaft 11 is rotatably mounted. An oil pump 72 for the torque converter device 10 is housed in a pump housing 73 and a cover 74 at the rear end of the housing 1. A pump drive shaft 75 is connected to the impeller 14a and is operatively connected with a rotor of the oil pump 72. Thus, the oil pump 70 is disposed adjacent the transmission 40, and oil pump 72 is disposed adjacent the torque converter device 10. Referring to Figs. 2a and 2b, showing a hydraulic control circuit, oil in an oil reservoir 80 is supplied to a line pressure control valve 110 through a line pressure passage 81 by the pump 70. An oil passage 82 connected to the passage 81 is communicated with the cylinder 47 of the driven pulley 44. The passage 81 is further communicated with a transmission ratio control valve 110 through a passage 83. The cylinder 46 of drive pulley 43 is applied with pressurized oil passing through the passage 81, passage 83, transmission ratio control valve 110, and a passage 84. A passage 140 connected to the oil pump 72 is communicated with a passage 85. The pressure of oil supplied to the passage 85 is regulated by a pair of relief valves 150 and 160 to produce a low control pressure. The passage 85 is connected to a drain port of the line pressure control valve 100. A part of the oil in the passage 85 is supplied to the drive pulley 44 from a nozzle 87 passing through a passage 86 to lubricate the pulley device. The passage 86 is further communicated with a passage 89 through a check valve 88. The passage 89 is communicated with a lubricating oil tube on which a transmission ratio sensing shoe 90 is slidably mounted. The passage 85 is communicated with a reducing valve 120 for providing a constant reducing pressure of oil. A conduit 91a is communicated with the line pressure control valve 100 through a passage 107. The conduit 91a is also communicated with a solenoid operated on-off valve 109 and with an accumulator 108. Further, a conduit 91 is communicated with the transmission ratio control valve 110 through a passage 92 and with a solenoid operated on-off valve 119. The solenoid operated valve 109 is adapted to be operated by duty signals for producing control pressure in the form of pulses and the control pressure is applied to the line pressure control valve 100. Further, the line pressure control valve 100 is applied with signals dependent on the transmission ratio from the sensor shoe 90 and on oil pressure through a passage 93 in accordance with conditions of the torque converter, so that the line pressure is controlled in accordance with the transmission ratio, engine torque, and torque increasing factor of the torque converter. The solenoid operated valve 119 is also operated by duty signals and produces reducing pressure which is applied to the transmission ratio control valve 110 for shifting a spool of the valve 110 to an oil supply position and an oil drain position by the degree of duty cycle. Thus, the flow rate of oil supplied to or drained from the cylinder 46 of drive pulley 43 is controlled to provided optimum transmission ratio. A drain passage 118 is communicated with the oil reservoir 80 through a check valve 117. A prefill passage 116 is provided between the passage 85 and a position upstream of the check valve 117. Thus, oil is supplied to the cylinder 46, even if the transmission ratio control valve 110 is in the drain state, thereby improving starting characteristic. The passage 85 is communicated with the transfer control valve 130, and a solenoid operated valve 139 for the transfer control valve 130 is communicated with the reducing valve 120 through a passage 94. The solenoid operated valve 139 actuates the transfer control valve 130 to produce clutch pressure which is supplied to the transfer clutch 63 through a passage 138 for controlling clutch torque dependent on driving conditions. The passage 140 is communicated with the lockup control valve 170. The lockup control valve 170 is communicated with the torque converter 14 through a passage 141 and the release side oil chamber 21 of the lockup clutch 19 through a passage 142. A relief valve 143 is provided on the passage 141 for preventing increase of pressure in the torque converter 14 when the torque converter is locked up. A drain passage 144 of the lockup control valve 170 is communicated with the oil reservoir 80 through a check valve 145 and an oil cooler 146. The lockup control valve 170 is communicated with the reducing valve 120 through passages 95, 92 and 91 for supplying with the reducing pressure. The reducing pressure is also supplied to the passage 93 communicated with the line pressure control valve 100 and to a solenoid operated on-off valve 179. The solenoid operated valve 179 operates the lockup control valve 170 to communicate the passage 140 with the passage 141 or the passage 142, and to produce converter condition pressure in the passage 93. The passage 140 is further communicated with a safety lock valve 180 which is connected to a selector valve 190 through a passage 147. The selector valve 190 is provided for selectively connecting passages in accordance with operations of a selector lever for selecting operational ranges such as a parking range (P), reverse range (R), neutral range (N), and drive range (D). The selector valve 190 is communicated with the forward clutch 37 through a passage 148 and with the reverse brake 38 through a passage 149. The safety lock valve 180 has a solenoid operated on-off valve 189 which is supplied with the reducing pressure of the reducing valve 120 through passage 95 to forcibly drain the oil in the forward clutch 37 or the reverse brake 38 to disengage the transmission. Describing operation of the system, the system supplies pulse signals to the solenoid operated valves 109, 119, 139, 179 and 189 to operate them at duty cycles dependent on driving conditions. When the engine starts, the oil pumps 70 and 72 are driven to supply oil to the system. The high line pressure is supplied by the oil pump 70 to the passage 81 and controlled by the line pressure control valve 100. The cylinder 47 of the driven pulley 44 is supplied with the line pressure adjusted by the line pressure control valve 100 through the passages 81, 82. Thus, the continuously variable transmission 40 provides the largest transmission ratio at low engine speed stage. Low pressure control oil adjusted by the relief valves 150 and 160 is supplied to passages 140 and 85. From the low control pressure, the reducing valve 120 produces a further reduced level of pressure which is applied to solenoid operated valves 109, 119, 139, 179 and 189. The low control pressure is supplied to the transfer control valve 130 through the passage 85 to produce the clutch pressure which is supplied to the transfer clutch 63. The control pressure is also supplied to the lockup control valve 170 through the passage 140. At starting of the vehicle, the passage 140 is communicated with the passage 142 by the operation of the solenoid operated valve 179. Thus, the pressure of oil is applied to the torque converter 14 through the release side oil chamber 21 and drained to the oil reservoir 80 through the passages 141 and 144. The lockup clutch 19 is disengaged and the torque converter 14 is in operating state. In a normal state, the safety lock valve 180 operates to communicate the passage 140 with the passage 147 by the solenoid operated valve 189, so that the selector valve 190 is supplied with the control pressure. When the P or N range is selected at starting, oil in the forward clutch 37 and the reverse brake 38 are drained. Thus, the planetary gear 31 is released to disengage the transmission 40. When the D range is selected, the control pressure is applied to the forward clutch 37 to lock the planetary gear 31, so that the input shaft 15 is engaged with the main shaft 41. Thus, the torque converter 14 operates to transmit the power of the engine to the automatic transmission 40. The power of the engine is transmitted to the output shaft 42 at the largest transmission ratio by the driving belt 45 and pulleys 43, 44, and further transmitted to axles of the driving wheels through the final reduction device 50. Thus, the vehicle is started. In this state, converter pressure is supplied to the line pressure control valve 100 by the operation of the lockup solenoid 179 through the passage 93 to increase the line pressure. The torque converter 14 increases the torque in accordance with the speed, and the increased torque is transmitted through the transmission 40 without slipping of the belt 45 due to the high line pressure. After starting, when the torque converter 14 becomes a condition for a lockup range, and the solenoid operated valve 179 is turned off, the oil in the release side chamber 21 is drained through the passage 142 so that lockup clutch 19 is pushed by the oil pressure in the apply side chamber 22. Thus, the facing 20 comes in contact with the converter cover 13 to lock the crankshaft 11 and the lockup clutch 19, which means locking of the torque converter 14. Therefore, the engine power can be transmitted to the input shaft 15 through the lockup clutch 19. In this state, converter pressure in the passage 93 becomes zero, so that the line pressure is controlled by the line pressure control valve 100 without the torque increasing factor, thereby preventing the line pressure supplied to the pulleys from exceeding. The transmission ratio control valve 110 is operated by solenoid valve 119, for controlling the pressure applied to the cylinder 46 of the drive pulley 43. Thus, the transmission ratio is controlled at a predetermined transmission ratio changing speed. When the R range is selected, the reverse brake 38 is supplied with the pressure of oil to reversely rotate the carrier 35 for providing a reverse driving. In accordance with the present invention, since the system provides two oil pumps for supplying high pressure and low pressure to the transmission and the torque converter respectively, pumping loss is reduced. Since, one of the oil pumps is disposed adjacent the transmission and one is adjacent the torque converter, the oil is efficiently supplied to the desired element, and the system is simplified in construction. By having an exclusive oil pump, the application of high line pressure is ensured upon rapid transmission ratio change whilst reducing the control pressure of the torque converter.

Claims: 1. An oil pressure control system for a continuously variable transmission (40) for a vehicle, the control system having a hydraulic circuit including a transmission ratio control valve (110) and a line pressure control valve (100), and the transmission having a torque converter (14) with a lockup clutch (19) and an associated lock-up control valve (170), and a selector device (30) for selecting forward and reverse drives, the line pressure control valve (100) being arranged to be operated in accordance with driving conditions of the vehicle, so as to control the pressure of oil supplied for operating the transmission (40); said other control valves being arranged to operate in accordance with driving conditions of the vehicle, so as to control the pressure of oil supplied to the torque converter (14) and the lockup clutch (19); the control system being characterised by: a high pressure oil pump (70) arranged to supply oil to the transmission (40) via the line pressure control valve (100); a low pressure oil pump (72) arranged to supply oil to the torque converter (14) via further control valve means; each of the oil pumps (70, 72) being operatively connected to the engine (E) so as to be driven by the engine (E); further control valve means including a reducing valve (120) and said lockup control valve (170) both communicating with the low pressure oil pump (72), said reducing valve (120) producing a constant pressure and said lockup control valve (170) supplying said reduced constant pressure to the torque converter (14); and solenoid operated valves being provided to operate the transmission ratio control valve (110), said line pressure control valve (100), said lockup control valve (170), respectively, in accordance with tne driving conditions of the vehicle. 2. A system according to claim 1 wherein the constant pressure is applied to the solenoid operated valves, so as to operate the corresponding valves and the lockup clutch. 3. A system according to claim 1 wherein the low pressure oil pump communicates with a lubrication system of the transmission.

Inventors: SAKAI, YASUHITO
Applicants: FUJI JUKOGYO KABUSHIKI KAISHA
Application year: 1988
Main classification: F16H59
IPC codes: F16H47, F16H61