Variable valve timing device

Abstract: A variable valve timing device for an engine includes a rotatable shaft (12) and a rotation transmitting member (14) rotatably mounted thereon so as to define at least one pressure chamber (38) between the shaft (12) and the member (14). The or each pressure chamber (38) is divided by a vane (52) extending from the shaft (12) or member (14) into a timing advance space (38a) and a timing delay space (38b). A pressure differential between both spaces establishes rotation of the shaft 12 relative to the member (14) which enables an adjustment of timing phase angle between the shaft (12) and the member (14). A retracting bore (40) and a receiving bore (48) are formed in the member (14) and the shaft (12), respectively. A locking member (44) and a piston (60) are fitted in the retracting bore (40) and the receiving bore (48), respectively. A fluid passage (62,62a) is formed communicating with a boundary portion between the piston (60) and the locking member (44), A further fluid passage (50) is formed communicating with the base of the piston (60). When the engine is running either the fluid passage (62,62a) or the further fluid passage (50) is pressurized, preventing the locking member (44) from entering the receiving bore (48). The only time the locking member (44) can enter the receiving bore (48) to lock together the rotatable shaft (12) and the rotation transmitting member (14) is on start-up when there is low fluid pressure. Excessive movement of the locking member (44) into and out of the receiving bore (48) during normal running is therefore avoided.

Description: Background of the Invention 1. Field of the Invention The invention relates to variable valve timing devices for controlling the valve opening and closing timing of intake and exhaust valves of engines. In particular, the invention relates to such timing devices in which at least one pressure chamber is formed between a rotatable shaft and a rotation transmitting member, the or each pressure chamber being divided into a timing advance space and a timing delay space by a vane carried by one or other of the rotatable shaft and rotating transmitting member. The timing is controlled by varying the pressure differential across the vane or vanes. 2. Background of the Invention A known variable valve timing device of the general kind identified above is disclosed in US-A-4858572, and its operation is illustrated herein with reference to Figures 5(A) to 5(C). As illustrated in those Figures, a rotor 2 is fixedly mounted on a rotatable shaft 1, and a rotation transmitting member 3 is rotatably mounted on the rotor 2. A plurality of vanes 4 are connected to an outer periphery of the rotor 2 and are extended into respective pressure chambers 5 defined between an outer periphery of the rotor 2 and an inner side of the rotation transmitting member 3 such that the pressure chambers 5 are arranged along the outer periphery of the rotor 2. Each vane 4 divides its pressure chamber 5 into a timing advance space 5a and a timing delay space 5b. The rotation transmitting member 3 has formed therein a radial retracting bore 6 in which a locking member 8 is accommodated. A spring 7 urges the locking member 8 toward the rotor 2. The rotor 2 has formed therein a receiving bore 9 in which the locking valve 8 can be received when the receiving bore 9 is brought into alignment with the retracting bore 6 as will be explained later. Oil under pressure is supplied selectively to the advance angle space 5a or to the delay angle space 5b via a passage 10b or a passage 10c, respectively. The vanes 4 are moved within their pressure chambers 5 by varying the pressure difference between the timing advance space 5a and the timing delay space 5b, which results in adjustment of the phase angle of the rotor 2 or rotatable shaft 1 relative to the rotation transmitting member 3. A passage 10a communicates with the base of the receiving bore 9 and is in fluid communication with the passage 10b inside the rotatable shaft 1 and fluidly isolated from the passage 10c. When the rotor 2 is at the most advanced timing position relative to the rotation transmitting member 3 as shown in Fig. 5(A), as soon as oil under pressure is supplied to the timing delay space 5b via the passage 10c, the vane 4 is moved counter-clockwise relative to the rotation transmitting member 3 as indicated with an arrow B due to the pressure difference between the timing advance space 5a and the timing delay space 5b. After such rotation of the rotor 2 through a set angle, the rotor 2 is brought into its most delayed position relative to the rotation transmitting member 3 as shown in Fig. 5(B). Immediately upon establishment of such a condition, the receiving bore 9 comes into alignment with the retracting bore 6 and due to the urging force of the spring 7 the locking member 8 partially enters the receiving bore 9, spanning the two bores 6 and 9 and locking together the rotor 2 and rotation transmitting member 3. Thus, the relative rotation between the rotor 2 and the rotation transmitting member 3 is prevented. When the rotor 2 is desired to advance its timing angle, as shown in Fig. 5(C), oil under pressure is supplied to the timing advance space 5a via the passage 10b and the oil is discharged from the timing delay space 5b via the passage 10c. Simultaneously the oil under pressure is supplied to the passage 10a and the locking member 8 is ejected from the receiving bore 9 into the retracting bore 6. Thus, the vane 4 is permitted to rotate in the clockwise direction as indicated with an arrow A in Fig. 5(C). In the foregoing structure, whenever the rotor 2 takes its most delayed timing position relative to the rotation transmitting member 3 the locking valve 8 is brought into engagement with the receiving bore 9 and whenever an advance of the rotor 2 relative to the rotation transmitting member 3 is required the locking valve 8 is ejected from the receiving bore 9 to be contained wholly within the retracting bore 6. As mentioned above, the passage 10a is in fluid communication with the passage 10b inside the rotating shaft 1. Such a connection is intended for accomplishing two purposes: one is to isolate the passage 10b when the rotor 2 is desired to be transferred toward the delayed position in order to establish a smooth receipt of the locking member 8 into the receiving bore 9 subsequent to the discharge of the oil therefrom immediately when the most delayed position is taken. The other is to establish a quick ejection of the locking member 8 from the receiving bore and a quick subsequent transfer of the rotor 2 toward the most advanced timing position by establishing simultaneous oil supply into the receiving bore 9 and the advance angle space 5a. However, frequent engagements of the locking member 8 with the receiving bore 9, such as occurs whenever the rotor 2 takes the most delayed position relative to the rotation transmitting member 3, leads to the requirement that each of the locking member 8, the receiving bore 9 and the retracting bore 6 have to be of high durability. Thus, the manufacture of these members is difficult and expensive. In addition, the principal purpose for regulating the phase angle between the rotor 2 (or the rotation shaft 1) and the rotation transmitting member 3 is as follows: there may be no oil pressure at all in either of the spaces 5a and 5b when the engine and its associated oil pump are stopped. Even if the engine is re-started, an instantaneous rise in the oil pressure in the spaces 5a or 5b cannot be established, and initially therefore the vane 4 is allowed to move freely in the pressure chamber. The resultant vane movement brings the vane 4 into engagement with a side wall of the pressure chamber 5 and a collision noise generates. To avoid such a noise generation, the movement of the vane 4 is restricted by the locking member 8 which prevents the relative rotation between the rotor 2 and the rotation transmitting member 3 until the pressure in each of the spaces 5a and 5b is raised to a sufficient value. When the engine is running and driving the oil pump, there is sufficient pressure in either the timing advance space 5a or the timing delay space 5b to prevent the free rotation of the vane 4 and therefore the foregoing noise generation fails to occur. In brief, although the locking member 8 is an essential element of the variable valve timing device during start-up, its durability cannot be assured due to frequent engagement and disengagement with the receiving bore 9 during normal running. SUMMARY OF THE INVENTION It is, therefore, a principal object of the present invention to provide a variable valve timing device which is free from the foregoing drawback. It is another object of the present invention to provide a variable valve timing device in which the frequency of the locking member moving into and away from the receiving bore is less than in a conventional device. The invention provides a variable valve timing device for an engine comprising: a rotatable shaft for controlling the valve opening and closing of the engine; a rotation transmitting member rotatably mounted on the rotation shaft; the rotatable shaft and the rotation transmitting member defining therebetween at least one pressure chamber which is divided into a timing advance space and a timing delay space by a vane which is mounted on one of the rotatable shaft and the rotation transmitting member and extending into the pressure chamber; first fluid passage means in fluid communication with the or each timing advance space for supplying a pressurized fluid to and discharging fluid from the respective timing advance space; a second fluid passage means being in fluid communication with the or each timing delay space for supplying the pressurized fluid to and discharging fluid from the respective timing delay space; one of the rotatable shaft and the rotation transmitting member being formed with a retracting bore and the other being formed with a receiving bore; a locking member slidably fitted in the retracting bore; a spring accommodated in the retracting bore urging the locking member to project from the retracting bore and into the receiving bore when the retracting and receiving bores are in alignment; and the other of the rotatable shaft and the rotation transmitting member being formed with third fluid passage means communicating with the bottom of the receiving bore CHARACTERIZED IN THAT a piston is fitted in the receiving bore; and fourth fluid passage means extend to a boundary portion between the piston and the locking member when the receiving bore is in alignment with the retracting bore. DRAWINGS Fig. 1 is a cross-sectional view of a variable valve timing device according to an embodiment of the present invention; Fig. 2 is a cross-sectional view taken along line A-A in Fig. 1; Fig. 3 is an enlarged view of a principal portion of the variable valve timing device shown in Fig. 1; Fig. 4(A) is a cross-sectional view of the variable valve timing device when a rotatable shaft is at its most delayed timing position relative to the rotation transmitting member, and when an oil pump is at rest; Fig. 4(B) is a cross-sectional view of the variable valve timing device when the rotatable shaft begins to take an advanced position; Fig. 4(C) is a cross-sectional view of the variable valve timing device when the rotatable shaft is at an initial stage of a movement toward the advanced position; Fig. 4(D) is a cross-sectional view of the variable valve timing device when the rotatable shaft is at its most delayed timing position, but when the oil pump is being driven; Fig. 5(A) is a cross-sectional view of a conventional variable valve timing device when a rotor is at its most advanced position relative to a rotation transmitting member; Figure 5(B) is a cross-sectional view of the conventional variable valve timing device when the rotor is at its most delayed position relative to the rotation transmitting member; and Fig. 5(C) is a cross-sectional view of the conventional variable valve timing device when the rotor is in the course of an advance movement. DETAILED DESCRIPTION OF THE INVENTION A preferred embodiment of the present invention will be described hereinafter in detail with reference to Figs. 1 to 4. Referring first to Fig. 1, a cam shaft 12, which will be referred to hereinafter as a rotating shaft, carries a cam (not shown) which opens and closes an intake valve (not shown) provided on a cylinder head (not shown). A variable valve timing device is provided at one end portion of the cam shaft 12. In the variable valve timing device, rotation is transmitted from a crank shaft (not shown) via a belt or chain to a timing pulley 14 mounted on the cam shaft 12. The timing pulley 14, an external rotor 18 and an outer plate 20 are fastened together by bolts 16 so as to prevent the rotation of any one of the members 14, 18 and 20 relative to the other members. Inside the outer rotor 18, which is cylindrical, an inner rotor 22 is fixedly mounted on one end portion of the cam shaft 12 by means of a bolt 17. Thus relative rotation between the outer rotor 18, which acts as the input member of the variable valve timing device, and the inner rotor 22, which acts as the output member driving the cam shaft 12, effects the timing control. In the cam shaft 12, there are formed a timing delay passage 28 and a timing advance passage 30 which are extended in the axial direction. One end of the timing delay passage 28 and one end of the timing advance passage 30 are in fluid communication with outer peripheral ports 35 and 36, respectively. The other end of the timing delay passage 28 and the other end of the timing advance passage 30 are in fluid communication with outer peripheral ports 32 and 34, respectively. A control fluid is in use supplied selectively to either the port 32 or the port 34 via a switching valve 111. The control fluid may be a liquid such as oil supplied from an oil pump (not shown) or a pressurized gas such as air. In the following description the control fluid is described, by way of example only, as oil under pressure from an oil pump. The switching valve 111 is constructed in such a manner that when a solenoid 112 is energized a spool 113 is moved against the bias of a spring 114 in the rightward direction. While the solenoid 112 is de-energized and the spool 114 remains the illustrated condition, the switching valve 111 establishes a fluid communication between a passage 117 and the port 32 as well as establishes a fluid communication between a passage 116 and the port 34. The passage 115 is in fluid communication with a passage 115 to which the oil is supplied from the oil pump. The passage 116 is in fluid communication with a drain 119. Thus, the port 32 and the port 34 are in an oil supply condition and oil drain condition, respectively, which results in the oil being supplied to the timing advance passage 28 while the solenoid 112 is not energized. On the contrary, when the spool 13 is moved to the right by energizing the solenoid 112, the port 32 and the port 34 are in oil drain condition and oil supply condition, respectively, which results in the supply of oil under pressure to the timing delay passage 30 while the solenoid 113 is being energized. As best shown in Fig. 2, around the inner circumference surface of the outer rotor 18 there are formed five pressure chambers 38 each of which is defined between two facing radial partition walls 33, and a single retracting bore 40. Each pressure chamber 38 is divided into a timing advance space 38a and a timing delay space 38b by a vane 52. The vane 52 is connected to the inner rotor 22 such that the vane extends radially outwardly from the inner rotor 22, and is received in the pressure chamber 38. The vane 52 is urged outwardly by a spring 49 (Fig. 1) so as to be in sliding engagement with a radially outermost wall of the pressure chamber 38. The timing advance space 38a is in fluid communication with a port 35 of the timing advance passage 28 through an intermediate passage 54 formed in the inner rotor 22. The timing delay space 38b is in fluid communication with a port 36 of the timing delay passage 30 through an intermediate passage 56 formed in the inner rotor 22. As shown in Fig. 3, the retracting bore 40 formed in the outer rotor 18 is covered with or sealed by a plug 42 having at the outer portion thereof an air bleeder passage (not shown). The plug 42 supports a spring 46 which urges a locking member 44 radially inwardly against the inner rotor 22. In the outer peripheral surface of the inner rotor 22, there is formed a receiving bore 48 whose diameter is equal to that of the retracting bore 40. At a central portion of the base of the receiving bore 48 there is formed a passage 50 which extends into a central portion of the inner rotor 22 so as to be in fluid communication with the outer peripheral port 36. Thus, the passage 50 is in fluid communication with the timing delay passage 30 and the intermediate passage 56 via the outer peripheral port 36. In addition, in the receiving bore 48, a piston 60 is slidably fitted so as to oppose the locking member 44. The piston 60 acts to eject or exclude the locking member 44 from the receiving bore 48 against the urging force of the spring 46 when the piston 60 is urged radially outwardly by oil under pressure supplied to the receiving bore 48 via the timing delay passage and the passage 50. The most delayed timing condition is established when the receiving bore 48 and the retracting bore 40 are in register. This occurs as shown in Fig. 3, when each vane 52 minimizes the volume of its timing advance space 38a. As is clear from Fig. 2, of the five intermediate passages 54 for charging the oil under pressure into the respective timing advance spaces 38a, only one, the intermediate passage 54a immediately adjacent to receiving bore 48, is in fluid communication with both the corresponding timing advance space 38a and a branch passage 62 which communicates with a radially outer portion of the receiving bore 48. In particular, an opening of an end 62a of the passage 62 opening into the receiving bore 48 is enlarged for enabling oil supply concurrently to a contact portion between a top end of the locking member 40 and a top end of the piston 60. Such oil supply becomes effective by rounding the mutually facing ends of the locking valve 40 and the piston 60. The variable valve timing device thus constructed operates as follows. While an engine (not shown) is at rest, its oil pump is also at rest, so that there is low pressure oil in the timing delay passage 28, the timing advance passage 30, the timing advance spaces 38a, the timing delay spaces 38b, the passage 50, the intermediate passage 54, and intermediate passage 56. Thus, the locking member 44 is acted upon only by the spring 46 and is moved into the receiving bore 48, as shown in Fig. 4(A). Such an insertion of the locking member 44 into the receiving bore 48 prevents the relative rotation between the inner rotor 22 and the outer rotor 18. Even though the receiving bore 48 and the retracting bore 40 may initially be out of phase when the engine is at rest, the desired insertion is rapidly established. The reason is that the vane 52 begins to rotate toward the delayed timing side immediately the engine starts, while the oil pressure in the spaces 38a and 38b is at a low level, and as soon as the vanes 52 reach their most delayed timing positions relative to the pressure chambers 38, the receiving bore 48 and the retracting bore 40 become in register. If an advance of the timing is desired while the rotor 22 is at its most delayed position as shown in Fig. 4(A) the solenoid 112 of the switching valve 111 is energized and oil under pressure is supplied into the timing advance passage 28 and is introduced via the intermediate passage 54 to the timing advance space 38a. Until then due to the insertion of the locking member 44 into the receiving bore 48 as shown in Fig. 4(A) relative rotation is prevented between the inner rotor 22 and the outer rotor 18. However, as shown in Fig. 4(B), some oil under pressure enters between the piston 60 and the locking member 44 via the branch passage 62 from the intermediate passage 54a which neighbours the receiving bore 48, and the pressure of that oil pushes the locking member 44 from the receiving bore 48 by overcoming the urging force of the spring 46. Thus, the relative rotation of the inner rotor 22 and the outer rotor 18 becomes possible, and the rotor 22 begins to advance clockwise relative to the outer rotor 18 as shown in Fig. 4(C). On the other hand, when the relative rotation between the outer rotor 18 and the inner rotor 22 is desired to be in a delayed timing condition, the oil under pressure is supplied to the timing delay space 38b through the timing delay passage 30 and the intermediate passage 50 by de-energizing the switching valve 111. Because the intermediate passage 56 and the intermediate passage 50 are in fluid communication with each other, the oil under pressure is also passed to the receiving bore 48 beneath the piston 60. Thus, when the relative position between the inner rotor 22 and the outer rotor 18 has become the most delayed timing condition as shown in Fig. 4(D), the oil under pressure in the receiving bore 48 has moved the piston 60 to the radially outer end of the receiving bore 48, which prevents the entrance into the receiving bore 48 of the locking member 44. Thus the locking member 44 is prevented from entering the receiving bore 48 whenever there is a working oil pressure, both when the oil is supplied to the intermediate passage 54a and when the oil is supplied to the intermediate passage 56. Thus, whenever the engine is in rotation and driving the oil pump, the locking member 44 is kept in its rest condition, out of engagement with the receiving bore 48, which results in an increase of the life or durability of the locking member 44 as well as avoiding unnecessary movement thereof.

Claims: A variable valve timing device for an engine comprising: a rotatable shaft (12) for controlling the valve opening and closing of the engine; a rotation transmitting member (14) rotatably mounted on the rotation shaft; the rotatable shaft (12) and the rotation transmitting member (14) defining therebetween at least one pressure chamber (38) which is divided into a timing advance space (38a) and a timing delay space (38b) by a vane (52) which is mounted on one of the rotatable shaft (12) and the rotation transmitting member (14) and extending into the pressure chamber (38); first fluid passage means (54) in fluid communication with the or each timing advance space (38a) for supplying a pressurized fluid to and discharging fluid from the respective timing advance space (38a) a second fluid passage means (56) being in fluid communication with the or each timing delay space (38b) for supplying the pressurized fluid to and discharging fluid from the respective timing delay space (38b); one of the rotatable shaft (12) and the rotation transmitting member (14) being formed with a retracting bore (40) and the other being formed with a receiving bore (48); a locking member (44) slidably fitted in the retracting bore (40); a spring (46) accommodated in the retracting bore (40) urging the locking member (44) to project from the retracting bore (40) and into the receiving bore (48) when the retracting and receiving bores are in alignment; and the other of the rotatable shaft (12) and the rotation transmitting member (14) being formed with third fluid passage means (50) communicating with the bottom of the receiving bore (48); CHARACTERIZED IN THAT a piston (60) is fitted in the receiving bore (48); and and fourth fluid passage means (62,62a) extend to a boundary portion'between the piston (60) and the locking member (44) when the receiving bore (48) is in alignment with the retracting bore (40). A variable valve timing device according to claim 1, wherein the alignment between the rotatable shaft (12) and the rotation transmitting member (14) is established when the rotatable shaft (12) is at its most delayed timing position relative to the rotation transmission member (14) A variable valve timing device according to claim 1 or claim 4, wherein the first fluid passage means (54) is in fluid communication with the fourth fluid passage means (62,62a) and the second fluid passage means (56) is in fluid communication with the third fluid passage means (50). A variable valve timing device according to any of claims 1 to 3, wherein the fourth fluid passage means (62,62a) is formed at a sliding boundary between the rotatable shaft (12) and the rotation transmitting member (14). A variable valve timing device according to claim 4, wherein the fourth fluid passage means (62,62a) has an outwardly flared mouth (62a) communicating with the receiving bore (48). A variable valve timing device according to any of claims 1 to 5 wherein the piston (60) has a rounded end facing the locking member (44).

Inventors: AOKI KONGO, EGUCHI KATSUHIKO, NOGUCHI YUJI, AOKI, KONGO, EGUCHI, KATSUHIKO, NOGUCHI, YUJI
Applicants: AISIN SEIKI, AISIN SEIKI KABUSHIKI KAISHA
Application year: 1997
Main classification: F01L1
IPC codes: F01L1