phân phối khí thông minh VTEC

061463 RESOURCE VTEC System C & F RESOURCE VTEC System Construction and Function Table of Contents „ Introduction „ Types of VTECs „ SOHC VTEC Construction „ SOHC VTEC Operation „ DOHC VTEC Construction „ DOHC VTEC Operation „ New VTEC Construction „ New VTEC Operation „ 3-stage VTEC Construction „ VTEC-E Construction RT 1/26 061463 RESOURCE VTEC System C & F RT 2/26 „ Introduction The Variable Valve Timing and Lift Electronic Control (VTEC) system is engineering features to change valve timing and lift parameters in response to engine speed characteristics Its action allows combustion properties to match as perfectly as possible to the demands of current engine operating conditions, hence delivering both high performance and high efficiency Put simply, each valve in an engine employing the VTEC system is assigned a number of individually shaped cam lobes These are all formed on the same camshaft and, through the implementation of electronic control, are switched in response to engine conditions using hydraulic pressure, thus enabling the above mentioned features to be realized „ Types of VTECs Currently there are five types of VTEC systems as follows: DOHC VTEC This application of VTEC technology sees high-speed and low-speed cams with differing profiles provided on both the intake and exhaust camshafts In the low- and mid-range engine speeds, the intake and exhaust valves are operated by the low-speed cams Above this range, the high-speed cams take over The combination of these actions allows the engine to offer ample torque and flexibility at moderate speeds and deliver both the sharp response and high power output at higher operating speeds SOHC VTEC High-speed and low-speed cams with differing profiles are provided on the intake camshaft in the SOHC VTEC engine As is the case with the DOHC implementation, the low-speed cam operates valves in the low- and mid-speed range, and the high-speed cam operates in the high-speed range – although this is only true for the intake valve in this case This technique allows the engine to offer the best possible combination of ease-of-driving in the practical speed range, high power output, and fuel efficiency 061463 RESOURCE VTEC System C & F RT 3/26 New VTEC As in the SOHC VTEC, high-speed and low-speed cams with differing profiles are provided on the intake camshaft, the former taking control of the high-speed range whereas the former is active at low- and mid-range speeds In this implementation, secondary intake valves are kept almost stationary at low vehicle speeds while the primary intake valves allow air to be supplied to the cylinders In combination with refinement of the shapes of combustion chambers and ports, this action creates a swirl in each chamber to ensure that combustion is carried out more efficiently The new VTEC engine can deliver substantial power and torque while still boasting excellent fuel economy 3-stage VTEC The three different stages of this VTEC unit correspond to low-speeds (one valve operated by the low-speed cam), mid-range speeds (both valves operated by the low-speed cam), and high-speeds (both valves operated by the high-speed cam) This design allows the realization of an engine with excellent fuel efficiency in the low-speed range, excellent torque output at mid-range speeds, and excellent power output in the high-speed range VTEC-E The intake valve camshaft is provided with independently profiled low-speed and mid-speed cams At low-speeds, the secondary valve is operated by the low-speed cam (although in reality it is almost motionless); both valves are operated by the mid-speed cam at mid-range speeds As a result, this engine delivers exceptional fuel efficiency while at the same time maintaining a high-level of driveability Each of these implementations of VTEC is described in detail below 061463 RESOURCE VTEC System C & F RT 4/26 „ SOHC VTEC Construction This is the most basic type of VTEC System and comprises the following components: • • • • • Camshaft Rocker arms Lost motion mechanisms Spool valve Control system (ECM) Synchronizing piston A Lost motion assembly Synchronizing piston B Mid rocker arm Primary rocker arm Secondary rocker arm Intake valve Camshaft 061463 RESOURCE VTEC System C & F RT 5/26 Camshaft The intake camshaft for the SOHC VTEC engine has three types of cams, namely primary, mid, and secondary These cams have independent profiles to provide different valve timing and lift A: Secondary cam B: Mid cam C: Primary cam Rocker Arms The primary, mid, and secondary rocker arms are incorporated into one mechanism The primary and secondary rocker arms make contact with the valves Each rocker arm consists of synchronizing pistons, a stopper piston, and a spring It is through the action of these components that the motion of the individual rocker arms can be linked or unlinked during operation of the engine 10 Secondary rocker arm Primary rocker arm Mid rocker arm Camshaft Stopper piston Secondary rocker arm Mid rocker arm Primary rocker arm Synchronizing piston B 10 Synchronizing piston A 061463 VTEC System C & F RESOURCE RT 6/26 Lost Motion Mechanism The lost motion assembly includes a lost motion piston, a lost motion guide, and lost motion springs A and B It is in constant contact with the mid rocker-arm At low speeds, the lost motion mechanism suppresses unnecessary movement of this rocker arm; it functions as an auxiliary spring at high speeds to ensure smooth valve operation Lost motion assembly Mid rocker arm Lost motion spring A Lost motion guide Lost motion piston Lost motion spring B Camshaft 061463 RESOURCE VTEC System C & F RT 7/26 Spool Valve A spool valve assembly is mounted at the side of cylinder head It consists of a screen, a solenoid, and the spool valve The function of this valve is to control the oil passage between the oil pump and the synchronizing pistons When the solenoid is activated, the spool valve opens the oil passage and hydraulic pressure is applied to the synchronizing pistons, thus activating the VTEC system A pressure switch is located at the rear of the spool valve It senses the pressure in the synchronizing piston’s oil passage and provides feedback to the ECM should rocker arm switching not occur as intended 1 Screen Solenoid Pressure switch Spool valve Cylinder head 061463 RESOURCE VTEC System C & F RT 8/26 Control System (ECM) The VTEC system is controlled by the PGM-FI ECM Using a lot of sensors, the ECM monitors engine speed, the degree of engine loading, vehicle speed, engine coolant temperature, and many other factors Then, in reference to this data, the ECM determines the current engine operating condition and activates the solenoid valve accordingly (The solenoid valve in turn controls the hydraulic pressure supplied to the spool valve.) VTEC pressure switch Oil flow VTEC solenoid valve From oil pump Engine speed Engine control module (ECM) Engine load Vehicle speed Engine coolant temperature 061463 VTEC System C & F RESOURCE RT 9/26 „ SOHC VTEC Operation At Low Engine Speeds (System Not Activated) The VTEC system is not active at low engine speeds (Actually, many different factors are involved in determining whether the system operates To keep the explanation simple, they will be overlooked here.) The spool valve is closed and no hydraulic pressure is applied to the synchronizing pistons inside the rocker arms Accordingly, each of the rocker arms is free to move independently and are operated by the primary, mid, and secondary cams respectively In this condition, the primary and secondary valves open and close following the timing and lift determined by the profiles of the primary and secondary cams Naturally, the mid rocker-arm is being operated by the mid cam at this time, but it causes no further operation and is suppressed by the lost motion assembly to prevent rattling Synchronizing piston A Synchronizing piston B Stopper piston Secondary rocker arm 5 Mid rocker arm Primary rocker arm 061463 RESOURCE VTEC System C & F RT 10/26 At High Engine Speeds (System Activated) Once the engine speed exceeds a predetermined limit, the ECM outputs a signal to the spool valve solenoid causing it to open Hydraulic pressure from the oil pump can now pass through the oil passage inside the camshaft to the rocker arms, where it acts on the synchronizing pistons pushing them sideways If, however, any of the rocker arms are in contact with cams at the moment, all of the pistons will not be lined up together Consequently, the rocker arms will continue to move even though the hydraulic pressure is acting on the pistons When all three rocker arms left the cam simultaneously, the pistons will slide and the arms will be secured together In this condition, both primary and secondary valves will be operated by the mid cam – profiled for high-speeds – through the action of the mid rocker arm Hydraulic pressure 061463 VTEC System C & F RESOURCE RT 12/26 „ DOHC VTEC Construction Whereas in the SOHC VTEC system the intake camshaft alone was fitted with VTEC components, the DOHC VTEC sees this technology applied to both the intake and exhaust camshafts This enables both intake and exhaust characteristics to be controlled in response to engine speed 2 10 11 Camshaft Low speed cam High speed cam Primary rocker arm 12 Mid rocker arm Secondary rocker arm Synchronizing piston A Synchronizing piston B Stopper piston 10 Lost motion spring 11 Exhaust valve 12 Intake valve 061463 RESOURCE VTEC System C & F RT 13/26 „ DOHC VTEC Operation Apart from the fact that DOHC VTEC has two independent VTEC systems as opposed to one in SOHC VTEC, the modes of operation of these two systems are essentially the same Camshaft Exhaust valve Intake valve Mid cam Exhaust Valve timing Primary + secondary cams Valve lift Primary + secondary cams Time Intake 061463 VTEC System C & F RESOURCE RT 14/26 „ New VTEC Construction The New VTEC system was realized through further development of SOHC VTEC This development added the following components • Timing plate • Timing piston Timing plate Mid rocker arm Secondary rocker arm Synchronizing piston B Synchronizing piston A Timing piston Intake valve Primary rocker arm Camshaft Primary cam Exhaust Mid cam Intake Secondary cam 061463 VTEC System C & F RESOURCE RT 15/26 Timing Plate and Timing Piston A timing plate and timing piston are mounted on the primary rocker arm in the New VTEC system The timing plate is positioned on the outside of the rocker arm and both of these components move in unison The timing piston is mounted in line with the synchronizing piston A A section of the timing plate passes through an opening in the primary rocker arm and engages with a channel in the timing piston 10 Timing plate Synchronizing piston A Timing piston Primary rocker arm Mid rocker arm Secondary rocker arm Synchronizing piston B Synchronizing piston A Timing plate 10 Timing piston 061463 RESOURCE VTEC System C & F RT 16/26 „ New VTEC Operation Although the operating principles of the New and SOHC implementations of VTEC technology are essentially the same, they exhibit differences with respect to the following two items: • Secondary valve opening • Timing mechanism Valve Opening At low engine speeds, the primary and secondary valves in SOHC VTEC exhibit almost the same amount of lift However, the cam profile employed in New VTEC ensures that the secondary valve opens only slightly when the primary valve is opened Primary cam Exhaust Mid cam Intake Secondary cam This ensures that a swirl* is created in the combustion chamber due to supply of the air/fuel mixture via one valve only Flame propagation speed is, therefore, increased and the burning of lean mixtures is stabilized If the secondary valve were to be completely closed at this time, a certain amount of fuel would accumulate at the intake port It is to prevent this situation that the valve is opened slightly At high engine speeds, both valves are activated by the high speed cam (i.e., the mid cam) *: The shape of intake ports, combustion chambers, and other similar components have also been modified to improve swirl characteristics 061463 RESOURCE VTEC System C & F RT 17/26 Timing Mechanism The main purpose of the timing mechanism is to secure the synchronizing piston in place when the VTEC system is operational Operation of the VTEC system occurs at lower speeds in the New VTEC implementation than in DOHC or SOHC (This is also true for the other systems which employ timing mechanisms such as the VTEC-E or 3-stage VTEC.) As a direct consequence of this, the hydraulic pressure available for securing the synchronizing piston during operation of the system is lower than in the cases mentioned previously This low hydraulic pressure may fluctuate and could conceivably result in unintentional motion of the synchronizing piston In order to prevent this from occurring, the timing piston is held securely in place by the timing plate whenever the pistons are in a condition where sliding would be possible Timing plate Synchronizing piston A Stopper piston Timing piston * Synchronizing piston B is omitted The timing plate, mounted on the primary rocker arm, moves in unison with the rocker arm However, the degree of this motion is limited by the stopper fitted to the camshaft holder Thus, whenever the rocker arm is lifted, the timing plate slips out of the channel in the timing piston, releasing the piston lock condition If switching pressure is acting on the timing piston at this time, it will slide sideways by a small amount 061463 RESOURCE VTEC System C & F RT 18/26 (Cont’d.) Cam rotation will continue and when the amount of cam lift subsequently approaches zero, the timing plate will try to return to its original position However, due to the fact that the timing piston has moved a small distance from its original position, these two components will not now engage When the lift reaches zero, the timing piston, and also the synchronizing pistons will be slid by the hydraulic pressure, securing the rocker arms together When the timing piston reaches a certain position, the timing plate will once again engage to another groove of timing piston and further sliding will be prevented When hydraulic pressure drops as a result of the operation of the VTEC system being terminated, a weak internal spring will push the timing piston back to its original position during the period of time in which the timing plate is pulled away by lifting of the rocker arm The piston will then be secured in place once again by the timing plate 061463 RESOURCE VTEC System C & F RT 19/26 (Cont’d.) When lift reaches zero, the synchronizing pistons are pushed back to their original positions by a return spring, thus disengaging the rocker arms Valve Timing Change Condition Engine speed: Vehicle speed: Engine coolant temperature: Engine load: 2,300 to 3,200 min-1 (Depending on manifold pressure) Over 10 km/h Over 10 degrees Celsius Determined from manifold vacuum 061463 VTEC System C & F RESOURCE RT 20/26 „ 3-stage VTEC Construction Further development of New VTEC technology has resulted in the 3-stage VTEC system which controls the intake valves in three different stages Although most components are the same as those used in New VTEC, there are two switching pressure systems, and two spool valves are also employed Synchronizing piston Primary rocker arm Lost motion assembly Timing plate Stopper piston Low-/mid-range-speed switchover Secondary rocker arm Mid-/high-range-speed switchover Mid rocker arm 061463 RESOURCE VTEC System C & F RT 21/26 Rocker Arms The rocker arms are connected to the two following independent switching systems – each one of these hydraulic systems is controlled by one of the spool valves • A low-speed to mid-range speed switching system which comprises a timing piston and a stopper piston for connecting the primary and secondary rocker arms • A mid-range speed to high-speed switching system which comprises a stopper piston, synchronizing piston A, and synchronizing piston B for connecting the primary, mid, and secondary rocker arms The timing plate engages with the low-speed to mid-range speed switching system’s timing piston Engine speed Throttle opening angle Vehicle speed Engine coolant temperature Hydraulic circuit #1 Hydraulic circuit #2 Solenoid valve Hydraulic pressure Mid rocker arm Secondary rocker arm Mid rocker arm Primary rocker arm High speed cam Low speed cam 061463 RESOURCE VTEC System C & F RT 22/26 Operation Although the operation of all systems is very similar, three stage valve control is implemented in the 3-stage VTEC At Low Engine Speeds All rocker arms operate independently The primary valve is opened by the mid-range speed primary cam The secondary valve, following the secondary cam, is opened by a very small amount only (identical to New VTEC low-speed operation) Secondary rocker arm Primary rocker arm Mid rocker arm 061463 RESOURCE VTEC System C & F RT 23/26 (Cont’d.) At Mid-range Engine Speeds One of the spool valves opens and hydraulic pressure is introduced into the low-speed to mid-range speed switching system This causes the timing piston to slide and connect the primary and secondary rocker arms Thus, both the primary and secondary valves are subsequently activated by the primary cam Hydraulic pressure for low-/mid-range speed switchover 061463 RESOURCE VTEC System C & F RT 24/26 At High Engine Speeds The second spool valve opens and hydraulic pressure is introduced into the mid-range speed to high-speed switching system This causes the synchronizing pistons to slide and connect the primary and secondary cams to the mid cam This cam, profiled for high speed situations, will subsequently activate the primary and secondary valves Timing piston Synchronizing piston B Synchronizing piston A At mid-range speeds At low speeds At high speeds Camshaft Stationary Crank angle (deg.) 2-valve operation with high speed cam Lift (mm) 2-valve operation with low speed cam Lift (mm) Lift (mm) 1-valve operation Crank angle (deg.) Crank angle (deg.) 061463 VTEC System C & F RESOURCE RT 25/26 Valve Timing Change Condition Engine speed: Low to mid range 3,000 min-1 Mid to high range 6,000 min-1 M/T Over 15 km/h A/T Over 10 km/h Low to mid range Over 40 degrees Celsius Mid to high range Over 60 degrees Celsius Determined from throttle opening angle Vehicle speed: Engine coolant temperature: Engine load: „ VTEC-E Construction Although incorporating a timing plate in the same way as the New VTEC system, VTEC-E does not have a mid cam or a mid rocker arm Accordingly, there is no lost motion assembly either The switching system is comprised of a timing piston, a synchronizing piston, and a stopper piston 3 Timing plate Primary rocker arm Secondary rocker arm Synchronizing piston Timing piston Intake valves Camshaft Stopper piston 061463 RESOURCE VTEC System C & F RT 26/26 Operation At Lower Engine Speeds The primary and secondary valves are activated independently by the primary and secondary cams respectively The secondary valve is opened only very slightly in this condition At Higher Engine Speeds Hydraulic pressure causes the timing and synchronizing pistons to slide, thus connecting the primary and secondary rocker arms As a result, the primary and secondary valves are subsequently activated by the primary cam Primary cam Secondary cam Lift Exhaust Intake Time Valve Timing Change Condition Engine speed: Vehicle speed: Engine coolant temperature: Engine load: Over 2,500 min-1 Over km/h Over -5.3 degrees Celsius Determined from intake manifold vacuum [...]... valve 061463 RESOURCE VTEC System C & F RT 13/26 „ DOHC VTEC Operation Apart from the fact that DOHC VTEC has two independent VTEC systems as opposed to one in SOHC VTEC, the modes of operation of these two systems are essentially the same Camshaft Exhaust valve Intake valve Mid cam Exhaust Valve timing Primary + secondary cams Valve lift Primary + secondary cams Time Intake 061463 VTEC System C & F RESOURCE... 061463 RESOURCE VTEC System C & F RT 17/26 Timing Mechanism The main purpose of the timing mechanism is to secure the synchronizing piston in place when the VTEC system is operational Operation of the VTEC system occurs at lower speeds in the New VTEC implementation than in DOHC or SOHC (This is also true for the other systems which employ timing mechanisms such as the VTEC- E or 3-stage VTEC. ) As a direct... start to operate independently Exhaust valve Intake valve Camshaft Mid cam Primary + secondary cams Exhaust Intake 061463 VTEC System C & F RESOURCE RT 12/26 „ DOHC VTEC Construction Whereas in the SOHC VTEC system the intake camshaft alone was fitted with VTEC components, the DOHC VTEC sees this technology applied to both the intake and exhaust camshafts This enables both intake and exhaust characteristics... km/h Over 10 degrees Celsius Determined from manifold vacuum 061463 VTEC System C & F RESOURCE RT 20/26 „ 3-stage VTEC Construction Further development of New VTEC technology has resulted in the 3-stage VTEC system which controls the intake valves in three different stages Although most components are the same as those used in New VTEC, there are two switching pressure systems, and two spool valves... piston 7 061463 RESOURCE VTEC System C & F RT 16/26 „ New VTEC Operation Although the operating principles of the New and SOHC implementations of VTEC technology are essentially the same, they do exhibit differences with respect to the following two items: • Secondary valve opening • Timing mechanism Valve Opening At low engine speeds, the primary and secondary valves in SOHC VTEC exhibit almost the... valve Mid cam Exhaust Valve timing Primary + secondary cams Valve lift Primary + secondary cams Time Intake 061463 VTEC System C & F RESOURCE RT 14/26 „ New VTEC Construction The New VTEC system was realized through further development of SOHC VTEC This development added the following components • Timing plate • Timing piston 1 2 3 4 1 Timing plate 5 6 2 Mid rocker arm 7 3 Secondary rocker arm 4 Synchronizing... 061463 RESOURCE VTEC System C & F RT 22/26 Operation Although the operation of all systems is very similar, three stage valve control is implemented in the 3-stage VTEC At Low Engine Speeds All rocker arms operate independently The primary valve is opened by the mid-range speed primary cam The secondary valve, following the secondary cam, is opened by a very small amount only (identical to New VTEC low-speed... New VTEC system, VTEC- E does not have a mid cam or a mid rocker arm Accordingly, there is no lost motion assembly either The switching system is comprised of a timing piston, a synchronizing piston, and a stopper piston 2 3 1 2 3 5 4 8 4 5 7 6 1 Timing plate 2 Primary rocker arm 3 Secondary rocker arm 4 Synchronizing piston 5 Timing piston 6 Intake valves 7 Camshaft 8 Stopper piston 061463 RESOURCE VTEC. .. hydraulic pressure drops as a result of the operation of the VTEC system being terminated, a weak internal spring will push the timing piston back to its original position during the period of time in which the timing plate is pulled away by lifting of the rocker arm The piston will then be secured in place once again by the timing plate 061463 RESOURCE VTEC System C & F RT 19/26 (Cont’d.) When lift reaches... Crank angle (deg.) 061463 VTEC System C & F RESOURCE RT 25/26 Valve Timing Change Condition Engine speed: Low to mid range 3,000 min-1 Mid to high range 6,000 min-1 M/T Over 15 km/h A/T Over 10 km/h Low to mid range Over 40 degrees Celsius Mid to high range Over 60 degrees Celsius Determined from throttle opening angle Vehicle speed: Engine coolant temperature: Engine load: „ VTEC- E Construction Although ... Exhaust Intake 061463 VTEC System C & F RESOURCE RT 12/26 „ DOHC VTEC Construction Whereas in the SOHC VTEC system the intake camshaft alone was fitted with VTEC components, the DOHC VTEC sees this... Intake valve 061463 RESOURCE VTEC System C & F RT 13/26 „ DOHC VTEC Operation Apart from the fact that DOHC VTEC has two independent VTEC systems as opposed to one in SOHC VTEC, the modes of operation... above mentioned features to be realized „ Types of VTECs Currently there are five types of VTEC systems as follows: DOHC VTEC This application of VTEC technology sees high-speed and low-speed cams