Valve timing control device

Abstract

A valve timing control device includes a lock member and a push member. The lock member locks a rotor in relation to a case at an approximately intermediate position apart from both of the maximum advanced side position and the maximum retarded side position. At all times, the push member pushes the lock member in a direction-of fitting the lock member in the fitting hole arranged at any one hand of the rotor or the case. A release hydraulic pressure for releasing the fitting state of the lock member in the fitting hole against the push force of the push member is set to be higher than a lock hydraulic pressure for allowing the fitting state of the lock member in the fitting hole.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to a valve timing control device for modifying the opening and closing timing of an intake valve or an exhaust valve making contact with cams fixed on an intake camshaft or an exhaust camshaft of an internal-combustion engine (hereafter, referred as an engine).[0003] 2. Description of the Prior Art[0004] Various types of solutions have been proposed for conventional valve timing control devices. The majority of the proposition includes a housing of rotating in synchronization with a driving force transmitting means transmitting a driving force from a crankshaft of the engine to an intake camshaft and an exhaust camshaft, a case fixed on the housing and having a plurality of shoes which are projected inwardly to form a plurality of hydraulic pressure chambers, and a rotor fixed on an end of the intake camshaft or the exhaust camshaft and having a plurality of vanes to divide the hydraulic pressure chambers into adva...

AI Technical Summary

Benefits of technology

[0014] The lock hydraulic pressure may be set to be nearly equal to or lower than a hydraulic pressure of generating a torque generated in the device, the torque being equal to a cam-torque during internal-combustion. In this way, even under a minimum hydraulic pressure condition such as high temperature oil or idle rotation for example, even in the intermediate retained state, it can obviate the inconvenience of fitting the lock member in the fitting hole or getting trapped therein. As a result, the operation of the lock member can be reliably controlled.

[0015] The present invention may further comprise first and second communication passages, wherein the first communication passage communicates a backward pressure chamber, in which the push member is arranged, to the advance side hydraulic pressure chamber or the retardation side hydraulic pressure chamber as an operational hydraulic pressure chamber of operating the device, and wherein the second communication passage communicates the backward pressure chamber to outside the device. In this way, since a backward pressure can be applied to the lock member in a releasing operation, the release hydraulic pressure can be set to be higher than the lock hydraulic pressure. Since the release operation can be also delayed, discharge of air remaining in each passage and each chamber in the VVT can be ensured through the first and second communication passages to the outside on starting the engine. As a result, release operations, which are not predetermined and result from residual air, can be reliably prevented.

[0016] The first communication passage may be formed at an end of the case in an axial direction of the case. In this way, it is possible to easily process the first communication passage. It is also possible to shorten the length in the minimum cross sectional area of the first communication passage to reduce passage resistance in the first communication passage. It is further possible to perform the release operation of the lock member with stability.

Problems solved by technology

However, the intermediate position lock type of the valve timing control device has typical problems derived from the typical construction, which is different from the conventional valve timing control devices such as the maximum advanced side position lock type or the maximum retarded side position lock type.

A hydraulic pressure in the advance side hydraulic pressure chamber or the retardation side hydraulic pressure chamber and a release hydraulic pressure chamber is therefore substantially reduced to one half of the hydraulic pressure in the OCV and the release hydraulic pressure is not sufficient.

In this case, there is a problem that the lock member and the fitting hole undergo wear which reduces their durability, and that the valve timing control device becomes incapable of operation from the intermediate retained state.

Second, when the lock member is operated beyond the fitting hole as the intermediate lock position and the release hydraulic pressure is reduced associated with the reduction of the hydraulic pressure in the advance side hydraulic pressure chamber or the retardation side hydraulic pressure chamber which is generated by consuming the operating oil used for the operation of the device, the lock member pops up due to the pushing force of the pushing member under operation condition and catches on in the fitting hole to prevent operation.

The operational failure of the device generates when the lock member pops up from the fitting hole due to the pushing force of the pushing member to catch on or engage in the fitting hole.

In this way, even under a minimum hydraulic pressure condition such as high temperature oil or idle rotation for example, even in the intermediate retained state, it can obviate the inconvenience of fitting the lock member in the fitting hole or getting trapped therein.

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