Multi-mode control system for variable camshaft timing devices

Abstract

A variable camshaft timing apparatus (10) includes a pulse actuating circuit (24A, 50, 44, 56, 60, 24R and 24R, 52, 46, 54, 58, 24A) for oscillating the variable camshaft timing apparatus in reaction to fluid under pulsation, and includes a pressure actuating circuit (30, 34, 36, 40, 44, 50, 24A, 24R, 52, 46, 66, 80 / 180, 32 and 30, 34, 38, 42, 46, 52, 24R, 24A, 50, 44, 64, 80 / 180, 32) for oscillating the variable camshaft timing device in reaction to fluid under pressure. Advance and retard valves (44, 46) are interconnected with the pulse and pressure actuating circuits for independently and simultaneously activating the pulse and pressure actuating circuits. Finally, an exhaust valve (80, 180, 280) is positioned in fluid communication with the pulse and pressure actuating circuits, such that the variable camshaft timing device may be oscillated using one or both of the pulse actuating and pressure actuating circuits, and may be maintained in position using one or both of the pulse actuating and pressure actuating circuits.

Description

[0001] This application is based, in part, on co-pending provisional U.S. Patent application No. 60 / 260,039 (attorney docket DKT00011), which was filed on Jan. 8, 2001.[0002] 1. Field of the Invention[0003] The present invention generally relates to an internal combustion engine having a control system for controlling the operation of a variable camshaft timing mechanism (VCT) of the type in which the position of a camshaft is circumferentially varied relative to the position of a crankshaft. More specifically, this invention relates to control systems for operating VCT devices in response to fluid under continuous pressure and fluid under pulsation to selectively advance, retard, or maintain the position of the camshaft.[0004] 2. Description of the Prior Art[0005] It is known that the performance of an internal combustion engine can be improved by the use of dual overhead camshafts, one to operate the intake valves of the various cylinders of the engine and the other to operate the...

AI Technical Summary

Benefits of technology

[0021] It is yet another object to provide a multi-mode variable camshaft timing device that is capable of maintaining position anywhere between a fully advanced and fully retarded position over the full range of engine speed, and does not necessarily require use of a spool valve, but may as an option.

Problems solved by technology

First, there are shortcomings to using only the CTA powered VCT. The CTA device has a significantly lower frequency response than the OPA device, even though the potential actuation rate of the CTA device is substantially higher than the OPA device due to the larger amount of energy in the cam torque inputs. For example, inline four cylinder engines typically operate at relatively high speeds and therefore generate very high frequency torque pulses to which CTA systems do not respond quickly enough to cause actuation of the VCT. Thus, the relatively low frequency response of the CTA system results in a dramatic drop in CTA performance at the higher engine speeds of the inline four cylinder engines. Similarly, inline six cylinder engines typically exhibit low amplitude camshaft torque pulses that are also inadequate to actuate the VCT.

In contrast, the OPA systems have nearly the opposite problem.

At lower engine speeds, however, particularly when the engine is running hot, the performance suffers because the oil pump is producing relatively little oil pressure.

For example, the system is two-position only and is not capable of maintaining position between fully advanced and fully retarded positions.

Additionally, the system uses a relatively complicated hydraulic circuit and spool valve system.

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