CAM MOUNTED ACCUMULATOR

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The invention pertains to the field of accumulators. More particularly, the invention pertains to cam mounted accumulator.

DESCRIPTION OF RELATED ART

Many phasers require a source of supply oil to move the vane or aid in moving the vane of the phaser. The oil supplied to the phaser must be maintained at a relative constant pressure in order to achieve maximum shift rates. One problem with phasers in the prior art is that as the phaser shifts the oil pressure between the chambers on either side of the vanes, oil pressure may drop to a low level and even zero. In some cases, the force from the rotor and vane can cause the pressure to create a partial vacuum in the chambers and supply line. The partial vacuum leads to air being drawn in to the phaser, resulting in poor performance and NVH concerns.

In the prior art, one solution to the partial vacuum that may result is to provide a leak path from the source oil to the advance and retard inlet oil passages leading to the chambers on either side of the vane. However by adding the leak path, the overall oil usage of the system increases, as well as the parasitic losses of the engine.

Accumulators are used when an additional oil supply is necessary, for example as the engine starts. In U.S. Patent No. 5,707,317, a method of operating a hydraulically controlled/regulated camshaft adjuster is disclosed, where when the engine starts, the pressure medium is supplied to the piston from an essentially full accumulator as a function of a start signal under valve control in order to advance the camshaft using the adjusting device. The accumulator is present in the engine and is connected to a hydraulic circuit that includes the valve controlling the position of the hydraulic actuating device, a pump, the feed line, and the return line from the hydraulic actuating device.

Accumulators are also present in various parts of the engine. For example, in U.S. Patent No. 6,227,154, an accumulator piston is present in a valve gear for the engine and arranged within an accumulator chamber. The accumulator chamber includes a piston spring. The piston is moved against the force of the spring by pressure acting in the accumulator chamber. The accumulator chamber is connected to an actuating chamber of the valve through a solenoid.

In US Publication No. 2005/0274344, a phaser has a volume accumulator disposed a) in the hydraulic fluid circuit, between the phaser and the hydraulic valve; b) in the vane; or c) as a separate unit or integrated into the locking element/locking pin. The volume accumulator may be a compression spring controlled piston accumulator, a diaphragm accumulator, or a bladed accumulator. The volume of the accumulator is variable and solely determined by the pressure in the hydraulic fluid circuit. If the pressure in the hydraulic fluid circuit then increases abruptly, the volume available for the hydraulic fluid is increased by the volume accumulator. The volume accumulator can also reduce the volume available for the hydraulic fluid in the hydraulic fluid circuit. If the inertia of the volume accumulator is low, it can also act as an oscillating circuit damper and counteract a pulsation generated by a pressure peak.

U.S. Patent No. 6,782,856 discloses an accumulator provided in the camshaft. The accumulator may be in the rearward end, the middle, or the front end of the camshaft. A phaser is connected to the camshaft. An external solenoid valve controls the fluid to and from the phaser. The accumulator has a rearward internal cavity provided by the internal cavity of the camshaft. A stop within the cavity provides a limit for the piston. The piston is biased by a coil spring. The tension of the spring may be adjusted by a core screw. The accumulator is used to specifically provide fluid to the solenoid valve and subsequently the VCT system when engine rotational speed is low and therefore the pressure of the oil delivered to the main oil pump will not be sufficiently high to operate the solenoid valve external from the phaser itself. The accumulator provides additional volume when short duration, high volume pressurized oil is needed by the VCT phaser. In another words, an auxiliary supply from the accumulator is necessary so that the phaser can function at all.

U.S. Patent No. 5,158,049 discloses deactivatable cams that are axially and slidably arranged on a camshaft. The cams are axially slidable to couple with claw clutches arranged on each cam by increasing the pressure of a pressure medium of pressure chambers adjacent to the cams. When the claws of the claw clutches are not in relative rotation positions that are necessary for coupling, pressure accumulators, forced by spring are arranged in the pressure chambers for pressure accumulation.

SUMMARY OF THE INVENTION

A phaser for an internal combustion engine with at least one camshaft with a housing, a rotor, a control valve, and an accumulator. The housing has an outer circumference for accepting a drive force. The rotor is connected to the camshaft coaxially located within the housing, The housing and the rotor define a vane separating a chamber in the housing, the vane being capable of rotation to shift the relative angular position of the housing and the rotor. A control valve is received by the rotor for directing fluid to the chambers. The accumulator is located within a hollow of the camshaft adjacent to the control valve. When the relative angular position of the housing and the rotor shifts, fluid from the accumulator is provided to the chamber in the housing, preventing fluid pressure within the chambers from dropping to a low level and creating a partial vacuum within the chambers.

BRIEF DESCRIPTION OF THE DRAWING

Fig. 1 shows a cross-section of phaser mounted to a camshaft with an accumulator without oil pressure present.

Fig. 2 shows a cross-section of a phaser mounted to a camshaft with an accumulator with oil pressure present.

DETAILED DESCRIPTION OF THE INVENTION

Internal combustion engines have employed various mechanisms to vary the angle between the camshaft and the crankshaft for improved engine performance or reduced emissions. The phasers may also be used to change the timing of the valves or vary the

duration of the vale depending on the cam and lifter arrangement of the engine. The majority of these variable camshaft timing (VCT) mechanisms use one or more "vane phasers" on the engine camshaft (or camshafts, in a multiple-camshaft engine). In most cases, the phasers 122 have a rotor 103 with one or more vanes (not shown), mounted to the end of the camshaft 108, surrounded by a housing 104 with the vane chambers into which the vanes fit, dividing the vane chambers into advance chambers and retard chambers 124, 126. It is possible to have the vanes mounted to the housing, and the chambers in the rotor, as well. The housing's outer circumference 104a forms the sprocket, pulley or gear accepting drive force through a chain, belt, or gears, usually from the crankshaft, or possible from another camshaft in a multiple-cam engine.

In the phaser 122 of the present invention, an accumulator 120 is mounted within the camshaft 108 adjacent to the phaser. The accumulator 120 may be a spring and plunger as shown in Figures 1 and 2 or a bladder type accumulator.

Figure 1 shows a sectional view of the variable cam timing system without oil in the accumulator 120. Figure 2 shows a sectional view of the variable cam timing system with fluid in the accumulator 120. The phaser 122 has a rotor 103 with one or more vanes mounted to the end of the camshaft 108, surrounded by a housing 104 with vane chambers into which the vanes fit, dividing the vane chambers into advance and retard chambers. It is possible to have the vanes mounted to the housing 104, and the chambers in the rotor 103, as well. The housing 104 of the phaser has an outer circumference 104a for accepting drive force through a chain, usually from the crankshaft (not shown), or possibly from another camshaft in a multiple-cam engine. A control valve 106 is present in the rotor 103. The control valve includes a spool with plurality of lands slidably received in a bore of the rotor. The spool is biased in one direction by a spring and in an opposite direction by an actuator 102. The control valve 106 aids in moving the vane and thus altering the timing of the engine.

The camshaft 108 is at least partially hollow 108 a to accommodate an accumulator 120. The accumulator 120 comprises a piston 116 within the hollow 108a of the camshaft 108 with a head 115 at one end. The piston 116 is biased towards the phaser 122 by a spring 114. A reservoir 117 is formed within the hollow 108a of the camshaft 108 between

the stops 113 and head 115 of the piston 116 and the control valve 106 of the phaser 122. Extension of the spring 114 towards the phaser 122 within the reservoir 117 formed in the hollow 108a of the camshaft 108 is limited by contact of the head 115 of the piston 116 with stops 113. The spring 114 provides compliance to pressurize accumulated oil within the reservoir 117. A vent 107 is provided at the end of the hollow 108a of the camshaft 108 to allow any fluid between the head 115 of the piston 116 and the end of the hollow near the spring 114 to exit the camshaft 108.

Supply fluid is provided to the phaser 122 and the accumulator 120 through a supply line 110 in a bearing 105 adjacent to the phaser 122. An inlet check 118 valve may be present in the supply line 110 to help maintain oil pressure during short periods of low pressure and to prevent any backflow to supply. The accumulator 120 regulates oil pressure at the input of the oil supply to the chambers 124, 126 of the phaser 122. In other words, the accumulator 120 provides a constant pressure on the spool of the control valve 106.

The accumulator 120 present within the hollow 108a of the camshaft 108 also provides pressure to the phaser 122 when the oil pressure drops during the phaser's shifting from one position to another position. The drop in oil pressure in the main oil gallery may occur in oil pressure actuated (OPA) phasers and torsion assist (TA) phasers when a torque pulse occurs. The torsion assist (TA) phasers may be as disclosed in U.S. Patent No. 6,883,481, issued April 26, 2005, entitled "TORSIONAL ASSISTED MULTI- POSITION CAM INDEXER HAVING CONTROLS LOCATED IN ROTOR" with a single check valve TA, and is herein incorporated by reference and/or U.S. Patent No. 6,763,791, issued July 20, 2004, entitled "CAM PHASER FOR ENGINES HAVING TWO CHECK VALVES IN ROTOR BETWEEN CHAMBERS AND SPOOL VALVE" which discloses two check valve TA, and is herein incorporated by reference. The accumulator 120 is sized such that enough oil is stored within the reservoir 117 to maximize the shift rate of the phaser 122.

When the engine first starts, fluid is supplied to the phaser and reservoir 117 in the camshaft from supply line 110 as shown in Figure 1. Prior to the phaser altering the timing between the rotor 103 and the housing 104, the reservoir 117 is filled, such that the

pressure of the fluid in the reservoir 117 against the head 115 of the piston 116 is greater than the force of spring 114, moving the piston 116 to the position shown in Figure 2. A constant pressure is now present on the spool of the control valve 106.

It should be noted that the phaser 122 may operate without the accumulator 120, but, as stated earlier the force from the rotor 103 and vane during shifting of the phaser 122when the pressure drops to a low level may cause the pressure to create a partial vacuum in the chambers 124, 126 and the supply line 110 leading air to be drawn into the phaser 122, resulting in poor performance.

Unlike in the prior art, fluid from the accumulator 120 of the present invention is used to provide additional fluid to the advance and retard chambers 124, 126 on opposite sides of the vanes to prevent oil pressure from dropping to a low level when the fluid is shifted from the advance chamber 124 to the retard chamber 126 or vice versa. The accumulator 120 is located within the camshaft 108 such that it is integral to the phaser 122, providing a constant pressure to the spool and regulating oil pressure at the input from the oil supply 110 to the chambers 124, 126 of the phaser.

Again, the accumulator in U.S. Patent No. 6,782,856 provides fluid to an external solenoid valve when the engine rotational speed is low and the oil pressure from the main oil pump is insufficient to operate the external solenoid valve and the phaser itself. It should also be noted that engine rotational speed is not directly related to oil pressure. The engine rotational speed may be low and the oil pressure may be engineered to be high or the engine rotational speed may be low and the oil pressure may be engineered to be low. Furthermore, in U.S. Patent No. 6,782,856, pressure is regulated at the oil supply far down within the hydraulic circuit input at the VCT check valve or a significant distance from the phaser itself. In order for fluid from the accumulator to reach the chambers of the phaser, oil travels from the accumulator through a pressurized oil line in the camshaft bearing to a line with a T connection. Pressurized oil from the T connection moves into a line leading through a VCT oil filter to other VCTs or to an external solenoid valve. From the external solenoid valve, fluid is delivered into the camshaft through multiple lines. One of the lines connects a first passage that includes a cross bore, an axial cross bore, a VCT fastener bore, and fastener cross bore leading to a retard chamber. Another line connects to a

second passage that includes a longitudinal bore which connects to the advance chamber. The fluid path from the accumulator to the advance and retard chambers must run through two cam bearings, an external solenoid valve, and multiple passages, increasing the amount of leakage of fluid that occurs during travel between the accumulator and chambers. In other words, the oil supply is not regulated by the chambers of the phaser, but near the inlet check valve and the oil filter leading to the external solenoid valve. By having the pressure regulated near the inlet check valve, the fluid is subjected to numerous passages and crossing of the cam bearing leading to significant oil leakage.

Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.