A method for controlling the timing of a camshaft in an internal combustion engine comprising a variable cam timing phaser arrangement comprising
- a rotor having at least one vane, the rotor arranged to be connected to a camshaft;
- a stator co-axially surrounding the rotor, having at least one recess for receiving the at least one vane of the rotor and allowing rotational movement of the rotor with respect to the stator, the stator having an outer circumference arranged for accepting drive force;
- wherein the at least one vane divides the at least one recess into a first chamber and a second chamber, the first chamber and the second chamber being arranged to receive hydraulic fluid under pressure, wherein the introduction of hydraulic fluid into the first chamber causes the rotor to move in a first rotational direction relative to the stator and the introduction of hydraulic fluid into the second chamber causes the rotor to move in a second rotational direction relative to the stator, the second rotational direction being opposite the first rotational direction;
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- a control assembly for regulating hydraulic fluid flow from the first chamber to the second chamber or vice-versa, wherein the control assembly comprises:
- a cam torque actuation control valve located centrally within the rotor and/or camshaft, the CTA control valve comprising a valve body having a first port arranged in fluid communication with the first chamber, a second port arranged in fluid communication with the second chamber, and a hydraulic shuttle element arranged in the valve body;
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- a blocking device arranged in conjunction with the valve body;
- wherein the hydraulic shuttle element is configured to be moved in a first direction to a first closed position by overpressure in the first chamber and moved in the second direction to a second closed position by overpressure in the second chamber;
- whereby in the first closed position the hydraulic shuttle element forms a seal together with an inner wall of the valve body or a valve seat located in the valve body, thereby preventing fluid flow from the first chamber to the second chamber;
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- whereby in the second closed position the hydraulic shuttle element forms a seal together with an inner wall of the valve body or a valve seat located in the valve body, thereby preventing fluid flow from the second chamber to the first chamber;
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- wherein the blocking device comprises at least one blocking element that is deployable between a disengaged position and an engaged position, wherein the at least one blocking element is in the engaged position configured to prevent the hydraulic shuttle element from moving to the first closed position or the second closed position depending on the position of the hydraulic shuttle element when the blocking device is deployed, whereby the hydraulic shuttle element is configured to move either between the first closed position in response to overpressure in the first chamber and a second open position in response to overpressure in the second chamber, or between the second closed position in response to overpressure in the second chamber and a first open position in response to overpressure in the first chamber;
- whereby in the second open position the hydraulic shuttle element allows fluid flow from the second chamber to the first chamber;
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- whereby in the first open position the hydraulic shuttle element allows fluid flow from the first chamber to the second chamber,
- the method comprising the steps:
- i. providing the variable cam timing phaser arrangement having the blocking device in a disengaged position, thereby preventing fluid communication between the first chamber and the second chamber;
- ii. deploying the blocking device at a time to coincide with the hydraulic shuttle element being in the first position thereby engaging the at least one blocking element to block the second position;
- or deploying the blocking device at a time to coincide with the hydraulic shuttle element being in the second position thereby engaging the at least one blocking element to block the first position;
- iii. maintaining the deployment of the blocking device thereby allowing fluid to periodically flow in a single direction between the first chamber and the second chamber due to camshaft torque, and preventing fluid flow in the opposite direction, thus rotating the rotor relative to the stator in a chosen direction;
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- iv. once the desired rotation of the rotor relative to the stator is obtained, disengaging the blocking device, thereby preventing further fluid communication between the first chamber and the second chamber.