PRESSURE CONTROL VALVE

Abstract: A pressure control valve (40) has a spool (42) slidably mounted in a valve body (41). The valve body (41) has a chamber (41c) between opposed lands (42b, 42c) of the spool (42). An oil guide (31) is provided in the chamber (41c). The oil guide (31) has a passage (34) arranged to apply oil pressure to the lands (42b, 42c). The passage (34) has a small sectional area so as to reduce pulsation of oil pressure.

Description: The invention relates to a pressure control valve, and more particularly to such a valve for use in the hydraulic control circuit of a continuously variable belt drive automatic transmission for a motor vehicle. A known control system for a continuously variable belt-drive transmission comprises an endless belt running over a drive pulley and a driven pulley. Each pulley comprises a movable conical disc which is axially moved by a fluid operated servo device so as to vary the running diameter of the belt on the pulleys in dependence on driving conditions. The system is provided with a hydraulic circuit including a pump for supplying oil to the servo devices, a line pressure control valve and a transmission ratio control valve. Each valve comprises a spool to control the oil supplied to the servo devices. The transmission ratio control valve operates to decide the transmission ratio in accordance with the opening degree of a throttle valve of an engine and the speed of the engine. The line pressure control valve is adapted to control the line pressure in accordance with the transmission ratio and the engine speed. The line pressure is controlled to prevent the belt from slipping on pulleys in order to transmit the output of the engine. The prior art patent publication US-4 467 674 (with respect to which claim 1 of the present document is characterised) discloses a pressure control valve comprising a body and a spool slidably received in the body. The spool has opposing lands which engage the valve body to define a chamber and a passage communicating through the body with the chamber for the supply of hydraulic liquid thereto. The line pressure control valve disclosed in U.S.Patent 4,467,674 is adapted to be applied with an elastic force of a spring dependent on the transmission ratio at one end of the spool, and with pitot pressure at the other end to generate line pressure. The line pressure is set to a comparatively high value depending on the transmitted torque and changed in a wide range in dependence on the transmission ratio. Accordingly, the line pressure control valve is arranged to directly control the flow of oil from the oil pump so as to control the line pressure. However, fluctuation of the pump oil pressure causes the valve to vibrate, thereby generating noises. The noises become larger when the temperature of the oil is low. One way of reducing the noises is to increase the volume of a passage from the pump to the valve, for example, by providing an accumulator communicated with the passage. However, the volume of the accumulator is limited in order to meet the requirement for a compact valve. Another is to reduce the sectional area of the passage so as to increase the resistance. However, when the valve is manufactured by a metal mould, it is difficult to form a sufficiently small passage, owing to the fragility of a casting pin. Further guidance as to the nature of the prior art may be found by reference to US-4 087 967. US-4 087 967 discloses a valve having a body defining a chamber, a first passage leads into the chamber to supply oil thereto. A guiding insert, in the form of a sleeve, is slidably received into the chamber, and a spool slidably received within the sleeve. Passages are provided in the body to convey hydraulic fluid to and away from the chamber. To pass through the chamber, the fluid must past through further passages provided in the sleeve which serve to attenuate pressure spikes. The present invention aims to provide a pressure control valve wherein noise may be reduced by a simple device. Accordingly the present invention provides a pressure control valve comprising a valve body, a spool slidably mounted in the valve body, the spool having opposed first and second lands which engages the valve body to define an annular chamber between, the spool, the first and second lands and the valve body; a first passage leading to the chamber for the supply of oil under pressure; characterised in that there is provided a guiding insert in said chamber which reduces the volume of said chamber and provides a further passage of a cross-section less than that of the first passage and leading from the first passage to the first and second lands. In an aspect of the invention, the pressure control valve has a spring urging said spool in a direction, and the first land formed to be subjected to the oil pressure on one side thereof in opposition to the spring. In order that the invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of a continuously variable belt-drive transmission; Figure 2 is a schematic diagram of a line pressure control valve; and Fig. 3 is a perspective view of an oil guide according to the present invention. Referring to Fig. 1, a motor vehicle is provided with an 1, an electromagnetic powder clutch 2 for transmitting the power of the engine to a continuously variable belt-drive transmission 4 through a selector mechanism 3. The belt-drive transmission 4 has a main shaft 5 and an output shaft 6 provided in parallel with the main shaft 5. A drive pulley (primary pulley) 7 and a driven pulley (secondary pulley) 8 are mounted on shafts 5 and 6 respectively. A fixed conical disc 7b of the drive pulley 7 is integral with main shaft 5 and an axially movable conical disc 7a is axially slidably mounted on the main shaft 5. The movable conical disc 7a also slides in a cylinder 9a formed on the main shaft 5 to provide a servo device. A fixed conical disc 8b of the driven pulley 8 is formed on the output shaft 6 opposite a movable conical disc 8a. The conical disc 8a has a cylindrical portion which is slidably engaged in a cylinder 6a of the output shaft 6 to form a servo device. A drive belt 11 engages with the drive pulley 7 and the driven pulley 8. Secured to the output shaft 6 is a drive gear 12 which engages with an intermediate reduction gear 13 on an intermediate shaft 14. An intermediate gear 15 on the shaft 14 engages with a final gear 16. The rotation of the final gear 16 is transmitted to axles 18 of vehicle driving wheels 19 through a differential 17. A chamber 9 is formed between the axially movable disc 7a and the cylinder 9a of the drive pulley 7. The chamber 9 is supplied with pressurized oil by an oil pump 21 from an oil reservoir 26 passing through a line pressure passage 22, a line pressure control valve 40, passage 23', transmission ratio control valve 50, and passage 23. A chamber 10 formed between the movable disc 8a and cylinder 6a of driven pulley 8 is applied with pressurized oil through a passage 24 without passing through transmission ratio control valve 50. The movable conical disc 7a of the drive pulley 7 is so designed that the pressure receiving area thereof is larger than that of movable conical disc 8a of the driven pulley 8. Oil flows back to the oil reservoir 26 through drain passages 25 and 27 which are in communication with the valves 40 and 50, respectively. The drive pulley 7 has an annular groove 7c and a rotation speed sensor 28 in the form of a pitot tube is provided for detecting the pressure of the oil in the groove that is the speed of the main shaft 5 which varies dependent on the engine speed. The pitot pressure produced by the rotation speed sensor 28 is applied to an end of each of valves 40 and 50 through a passage 29. Referring to Fig. 2, the line pressure control valve 40 comprises a valve body 41, a spool 42, a spring 44 provided between a spring retainer 43 and one end of the spool 42 for urging the spool 42 to the left. The spring retainer 43 is axially slidably mounted in the valve body 41. A sensor shoe 45, one end of which is slidably engaged with the movable disc 7a is provided for detecting the actual transmission ratio. The sensor shoe 45 has a bolt 45a which engages with an end of a bolt 43a secured to the spring retainer 43. Thus, the position of the movable disc 7a which means the transmission ratio during the operation is transmitted to the spool 42 through the spring 44. The spool 42 has a pressure regulating land 42a and a balancing land 42b. The land 42a is arranged to control the communication between chambers 41a and 41b. Adjacent the land 42b and opposite to the chamber 41a, a balance chamber 41c is formed in the valve body 41. The chambers 41a and 41c are supplied with the pressurized oil from the pump 21 through passage 22. An orifice 30 is provided in the passage 22 at an inlet of the chamber 41c. At the end of the valve body 41, opposite to the spring 44, pitot pressure is applied to an end chamber 41d through the oil passage 29. The chamber 41b and a chamber 41e, which is provided between the chambers 41d and 41c for receiving the leakage of the oil from chambers 41c and 41a, are communicated with the oil reservoir 26 through drain passage 25. Thus, the spool 42 is applied with the pitot pressure and pump oil pressure so as to be moved in the direction to communicate the chamber 41a with the chamber 41b, whereas the elastic force of the spring corresponding to the transmission ratio detected by the sensor shoe 45 urges the spool 42 in the direction to close the chamber 41a. Accordingly, high line pressure generates in the chamber 41a at a low engine speed with a large transmission ratio. The sensor shoe 45 is moved to the right in Figure 2 as the transmission ratio decreases, reducing the force of the spring 44 to lower the line pressure. The line pressure exerts on the belt 11 at a proper force dependent on the transmission ratio so as not to cause the belt to slip on the pulleys. The land 42b has a side 42b having a larger pressure receiving area than that of a land 42c opposite the land 42b. Thus, the line pressure applied to the balance chamber 41c causes the spool 42 to move to the right against spring 44, so that extreme increase of the line pressure is prevented. According to the present invention, in order to reduce the noise from the line pressure control valve 40, an oil guide 31 is embedded in the balance chamber 41c. As shown in Figure 3, the oil guide 31, which is made of plastics material, such as resin, has a degree of elasticity and comprises a guide body 32 so shaped as to snugly fit in the chamber 41c. The guide body 32 has a hole 33 in which land 42b of the spool 42 is slidably engaged. Narrow radial oil passages 34 and 35 are formed on either side of the body 32. The passages 34 and 35 are communicated with each other at the lower ends by a groove 36. Thus, the space in the chamber 41c is almost entirely occupied by the oil guide 32. The line pressure is applied to the side 42d of the land 42b through groove 36, passages 34 and 35 and the hole 33. Since sectional areas of the passages for the oil to the land 42b are reduced to increase the resistance thereof, pulsation of oil pressure decreases. Accordingly, noises as well as vibration of the valve 40 reduces. The present invention may be applied to other pressure regulator valves and pressure reducing valves in the automatic transmission control system. From the foregoing, it will be understood that the present invention provides a valve for regulating the pump oil pressure wherein noises and vibration of the valve can be easily diminished by a simple device, thereby increasing the reliability of the valve.

Claims: A pressure control valve comprising a valve body (41), a spool (42) slidably mounted in the valve body the spool (42) having opposed first and second lands (42b, 42c) which engage the valve body (41) to define an annular chamber (41c) between, the spool (42), the first and second lands (42b, 42c) and the valve body; a first passage (22) leading to the annular chamber (41c) for the supply of oil under pressure; characterised in that a guide insert (31) is provided in the annular chamber (41c) which reduces the volume of said chamber (41c) and provides a further passage (34, 35) of a cross-section less than that of the first passage (22) and leading from the first passage (22) to the first and second lands (42b, 42c). A pressure control valve as claimed in claim 1 characterised in that the spool is biased in one direction of movement by a spring (44). A pressure control valve as claimed in claim 2, characterised in that said first land (42b) has a greater cross-sectional area than said second land (42c) and force applied to said spool by oil pressure in the chamber acting on the first land is opposed by the action of the spring (44). A pressure control valve as claimed in any of the preceding claims, characterised in that said guide insert is of plastics material.

Inventors: TAKAHASHI, MASAHIKO
Applicants: FUJI JUKOGYO KABUSHIKI KAISHA
Application year: 1987
Main classification: F16K11
IPC codes: F16H61, F16K47, F16K11