JP2014125881A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid the shortage of an intake amount at the start or the low speed of an internal combustion engine for which an Atkinson cycle is applied.SOLUTION: A variable valve timing mechanism accompanying an intake valve uses the pressure of working fluid discharged by a hydraulic pump which is operated with the supply of rotation driving force from a crank shaft, for initiating the turn of an intake cam shaft relative to the crank shaft. In the situation that the crank shaft is not rotated and the hydraulic pump does not discharge the working fluid, the rotation phase of the intake cam shaft is in an initial position where it is most advanced, and in the situation that the crank shaft is rotated and the hydraulic pump discharges the working fluid, the rotation phase of the intake cam shaft is changed from the initial position so as to be retarded.

Description

  The present invention relates to an Atkinson cycle internal combustion engine with a variable valve timing mechanism that can control the opening / closing timing of an intake valve.

  2. Description of the Related Art An internal combustion engine mounted on a vehicle or the like is known that includes a variable valve timing mechanism that can variably control intake valve timing. This type of variable valve timing mechanism uses the pressure of the hydraulic fluid discharged from a mechanical hydraulic pump that operates in response to the supply of rotational driving force from the crankshaft to adjust the rotational phase of the intake camshaft relative to the crankshaft. It is something to change.

  One application of the variable valve timing mechanism is to realize an Atkinson cycle (Miller cycle) (see, for example, the following patent document). In other words, by setting the intake valve timing so that it opens at a timing later than the exhaust top dead center and closes at a timing later than the intake bottom dead center, the stroke length of the compression stroke is effectively set to the stroke length of the expansion stroke. Less than. The Atkinson cycle in which the actual expansion ratio is larger than the actual compression ratio is advantageous in that the heat efficiency can be increased by reducing the amount of exhaust heat.

JP 2000-320356 A

  In a variable valve timing mechanism that uses hydraulic fluid discharged from a mechanical hydraulic pump as a drive source, the rotation phase of the intake camshaft is the most retarded when the rotation of the internal combustion engine (crankshaft) is stopped. It is customary to take the initial position.

  In an Atkinson cycle engine using such a variable valve timing mechanism, the opening / closing timing of the intake valve is significantly retarded at the time of start-up and low rotation with low hydraulic fluid pressure. Therefore, if the Atkinson cycle is applied to an internal combustion engine having a relatively small displacement, the amount of intake air charged into the cylinder at the time of start-up or low rotation is extremely small, and the actual compression ratio is also small. For this reason, the startability of the engine may be deteriorated, or the intake negative pressure to be supplied to the brake booster mounted on the vehicle may be insufficient.

  In order to guarantee a reliable start of the engine, it is necessary to increase the discharge pressure of the hydraulic pump by extending the cranking period in which the crankshaft of the internal combustion engine is rotationally driven by the electric motor. However, the extension of the cranking period is not preferable because it directly leads to a delay in starting and causes a reduction in fuel consumption performance due to power consumption.

  The present invention has been made by paying attention to the above-mentioned problem for the first time, and an object of the present invention is to avoid shortage of intake air quantity at the time of starting or low rotation of an internal combustion engine to which the Atkinson cycle is applied.

  According to the present invention, there is an Atkinson cycle internal combustion engine attached with a variable valve timing mechanism that changes the opening / closing timing of the intake valve by changing the rotational phase of the intake camshaft with respect to the crankshaft, wherein the variable valve timing mechanism is a crankshaft. The intake camshaft is rotated relative to the crankshaft by utilizing the pressure of the hydraulic fluid discharged from the hydraulic pump that operates in response to the supply of rotational driving force from the crankshaft. In the situation where the hydraulic pump does not discharge the hydraulic fluid, the intake camshaft is in the initial position where the rotation phase of the intake camshaft is the most advanced, and in the situation where the hydraulic pump discharges the hydraulic fluid as the crankshaft rotates An internal combustion engine capable of changing the rotational phase of the engine from the initial position in the retarding direction. Form was.

  ADVANTAGE OF THE INVENTION According to this invention, the shortage of the intake air quantity at the time of the start of the internal combustion engine to which an Atkinson cycle is applied, or low rotation can be avoided.

The figure which shows schematic structure of the internal combustion engine in one Embodiment of this invention. The figure which shows the variable valve timing mechanism incidental to the internal combustion engine. The figure which shows the control range of the intake valve timing by the variable valve timing mechanism. The perspective view which shows the principal part of the variable valve timing mechanism. The figure which shows the relationship between the driving | operation area | region in the internal combustion engine, and the intake valve timing which should be set.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle in the present embodiment. The internal combustion engine in the present embodiment is a spark ignition type four-stroke engine and includes a plurality of cylinders 1 (one of which is shown in FIG. 1). In the vicinity of the intake port of each cylinder 1, an injector 11 for injecting fuel is provided. A spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The spark plug 12 receives spark voltage generated by the ignition coil and causes spark discharge between the center electrode and the ground electrode. The ignition coil is integrally incorporated in a coil case together with an igniter that is a semiconductor switching element.

  The intake passage 3 for supplying intake air takes in air from the outside and guides it to the intake port of each cylinder 1. On the intake passage 3, an air cleaner 31, a compressor 51 of the exhaust turbo supercharger 5, an intercooler 35, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from the upstream.

  The exhaust passage 4 for discharging the exhaust guides the exhaust generated as a result of burning the fuel in the cylinder 1 from the exhaust port of each cylinder 1 to the outside. An exhaust manifold 42, a drive turbine 52 of the exhaust turbocharger 5, and an exhaust purification three-way catalyst 41 are disposed on the exhaust passage 4. In addition, an exhaust bypass passage 43 that bypasses the turbine 52 and a waste gate valve 44 that is a bypass valve that opens and closes the inlet of the bypass passage 43 are provided. The waste gate valve 44 is an electric waste gate valve that can be opened and closed by inputting a control signal n to the actuator, and a DC servo motor is used as the actuator.

  The exhaust turbocharger 5 is configured such that the drive turbine 52 and the compressor 51 are connected and linked in a coaxial manner. Then, the driving turbine 52 is rotationally driven by using the energy of the exhaust gas, and the compressor 51 is pumped by using the rotational force, whereby the intake air is pressurized and compressed (supercharged) and sent to the cylinder 1.

  As shown in FIG. 2, in the internal combustion engine in the present embodiment, a timing chain 74 is wound around a crank sprocket 71, an intake side sprocket 72 and an exhaust side sprocket 73, and the rotational driving force provided from the crankshaft by this timing chain 74. Is transmitted to the intake camshaft via the intake side sprocket 72 and to the exhaust camshaft via the exhaust side sprocket 73.

  In addition, a variable valve timing mechanism 6 is interposed between the intake side sprocket 72 and the intake camshaft. The variable valve timing mechanism 6 in the present embodiment changes the opening / closing timing of the intake valve by changing the rotational phase of the intake camshaft with respect to the crankshaft.

  The housing 61 of the variable valve timing mechanism 6 is fixed to the intake side sprocket 72, and the intake side sprocket 72 and the housing 61 are integrally rotated in synchronization with the crankshaft. On the other hand, the rotor 62 fixed to one end portion of the intake camshaft is housed in the housing 61 and can rotate relative to the intake-side sprocket 72 and the housing 61. A plurality of fluid chambers into which hydraulic fluid (hydraulic oil) flows in and out are formed inside the housing 61, and each fluid chamber is formed by an advance chamber 612 and a retard chamber by a vane 621 formed on the outer periphery of the rotor 62. 611.

  The hydraulic fluid stored in the oil pan 81 is supplied from the hydraulic pump 82 to the hydraulic pressure (hydraulic pressure) circuit of the variable valve timing mechanism 6. The hydraulic pump 82 is a mechanical type driven by power from an internal combustion engine. An OCV (Oil Control Valve) 9 that is a switching control valve is provided between the hydraulic pump 82 and the variable valve timing mechanism 6. By operating the flow rate and direction of the hydraulic fluid via the OCV 9, the hydraulic fluid pumped from the oil pan 81 can be selectively supplied to the advance chamber 612 or the retard chamber 611. Then, the housing 61 rotates relative to the rotor 62, and the opening / closing timing of the intake valve can be advanced or retarded.

  The OCV 9 is a so-called electromagnetic four-way spool valve. As shown in FIG. 2, the OCV 9 has a supply port 91 connected to the discharge port of the hydraulic pump 82, an A port 92 connected to the advance chamber 612 of the housing 61, and a B port connected to the retard chamber 611 of the housing 61. 93 and drain ports 94 and 95 connected to the oil pan 81. The spool of the OCV 9 switches the internal particle path by an advancing and retreating operation, and connects the A port 92 and the B port 93 to one of the supply port 91 and the drain ports 94 and 95, respectively. Further, when the spool 96 is in the neutral position, the internal fluid path is interrupted, and the A port 92 and the B port 93 are not communicated with the supply port 91 and the drain ports 94 and 95. FIG. 2 shows a state where the spool 96 is in the neutral position.

  The spool 96 is driven by a solenoid 97. That is, the advance / retreat distance of the spool 96 changes according to the duty ratio of the pulse current (or voltage) input to the solenoid 97 as the control signal m.

  When the duty ratio of the control signal m is relatively large, the hydraulic fluid pressure discharged from the hydraulic pump 82 is supplied to the advance chamber 612 through the A port 92, while already stored in the retard chamber 611. The hydraulic fluid flows down toward the oil pan 81 through the B port 93, and the vane 621 and the rotor 62 are rotated so that the volume of the advance chamber 612 is enlarged and the volume of the retard chamber 611 is reduced. As a result, the rotational phase of the intake camshaft, in other words, the displacement angle of the intake camshaft with respect to the crankshaft is advanced, and the valve timing of the intake valve is advanced.

  On the contrary, when the duty ratio of the control signal m is relatively small, the hydraulic fluid pressure discharged from the hydraulic pump 82 is supplied to the retard chamber 611 through the B port 93, while already stored in the advance chamber 612. The working fluid that has flown down flows toward the oil pan 81 through the A port 92, and the vane 621 and the rotor 62 rotate so that the volume of the retard chamber 611 is expanded and the volume of the advance chamber 612 is decreased. . As a result, the displacement angle of the intake camshaft with respect to the crankshaft is retarded, and the valve timing of the intake valve is retarded.

  Generally speaking, the valve timing of the intake valve is advanced faster as the duty ratio of the control signal m is larger than neutral, and the valve timing of the intake valve is retarded faster as the duty ratio is smaller than neutral.

  An ECU (Electronic Control Unit) 0 that controls operation of the internal combustion engine is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like.

  The input interface includes a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal (N signal) b output from an engine rotation sensor that detects the rotation angle of the crankshaft and the engine speed, An accelerator opening signal c output from a sensor that detects the amount of depression of the accelerator pedal or the opening of the throttle valve 32 as an accelerator opening (so-called required load), and a brake that is output from a sensor that detects the amount of depression of the brake pedal Stepping amount signal d, intake air temperature / intake pressure signal e output from a temperature / pressure sensor for detecting intake air temperature and intake pressure in intake passage 3 (especially surge tank 33), water temperature sensor for detecting engine cooling water temperature Output from the cam angle sensor at a plurality of cam angles of the cooling water temperature signal f output from the intake camshaft or exhaust camshaft. Is the cam angle signal (G signal) g, a knock signal h or the like to be output from the knock sensor for detecting the presence or absence of occurrence of knocking in the cylinder 1 is input.

  From the output interface, an ignition signal i for the igniter of the spark plug 12, a fuel injection signal j for the injector 11, an opening operation signal k for the throttle valve 32, a control signal m for the OCV 9, and a waste gate valve An opening operation signal n or the like is output to 44.

  The processor of the ECU 0 interprets and executes a program stored in the memory in advance, calculates operation parameters, and controls the operation of the internal combustion engine. The ECU 0 acquires various information a, b, c, d, e, f, g, and h necessary for operation control of the internal combustion engine via the input interface, knows the engine speed, and is filled in the cylinder 1. Estimate the intake volume. Various operating parameters such as required fuel injection amount, fuel injection timing (including the number of fuel injections per combustion), fuel injection pressure, ignition timing, intake valve timing, etc. To decide. As the operation parameter determination method itself, a known method can be adopted. The ECU 0 applies various control signals i, j, k, m, and n corresponding to the operation parameters via the output interface.

  The internal combustion engine of the present embodiment can implement an Atkinson cycle by controlling the opening / closing timing of the intake valve via the variable valve timing mechanism 6. FIG. 3 shows the intake valve timing of the internal combustion engine of the present embodiment. In FIG. 3, the solid line represents the valve opening period of the intake valve when the intake valve timing is most advanced, and the broken line represents the valve opening period of the intake valve when the intake valve timing is most retarded. A one-dot chain line represents a valve opening period of the exhaust valve.

  When the intake valve timing is set to the most advanced angle, the intake valve opens at an earlier timing than the exhaust top dead center (for example, 10 ° CA (crank angle) before the top dead center) and later than the intake bottom dead center (for example, Close at 30 ° CA after bottom dead center. At this time, the actual compression ratio of the internal combustion engine, in other words, the length of the period from the closing of the intake valve to the compression top dead center, and the actual expansion ratio, in other words, the period from the compression top dead center to the opening of the exhaust valve Is almost equal to the length of. In other words, it becomes an Otto cycle organization. The valve overlap period in which both the intake valve and the exhaust valve are open is not so long (about 15 ° CA).

  If the intake valve timing is retarded, the intake valve opens at a timing later than the exhaust top dead center, and the intake valve closes at a timing considerably delayed from the intake bottom dead center. As a result, an Atkinson cycle engine in which the actual expansion ratio of the internal combustion engine exceeds the actual compression ratio is obtained.

  Therefore, in this embodiment, the variable valve timing mechanism 6 associated with the intake valve is in a state in which the intake valve timing is most advanced in a situation where the crankshaft does not rotate and the hydraulic pump 82 does not discharge the hydraulic fluid. In addition, the variable valve timing mechanism 6 is configured.

  FIG. 4 shows a state where the intake valve timing is most advanced, that is, a state where the variable valve timing mechanism 6 and the intake camshaft are in the initial positions. In this initial position, the volume of the advance chamber 612 is the maximum, and the volume of the retard chamber 611 is the minimum (almost 0).

  The variable valve timing mechanism 6 in this embodiment is provided with an advance assist spring (not shown). By this assist spring, the rotor 62 and the intake camshaft are elastically biased in the direction in which the intake valve timing advances (the clockwise direction in FIGS. 2 and 4).

  As shown in FIG. 4, the variable valve timing mechanism 6 includes a lock pin 63 for holding the rotor 62 at the initial position. The lock pin 63 is elastically biased in a direction protruding from the vane 621 by a biasing spring (not shown). On the other hand, when receiving the pressure of the hydraulic fluid supplied to the advance chamber 612 or the retard chamber 611, the lock pin 63 is immersed in the vane 621.

  When the hydraulic pump 82 does not discharge the hydraulic fluid or when the discharge pressure is low, the rotor 62 and the intake camshaft rotate relative to the housing 61 and the intake-side sprocket 72 in the advance direction, and ultimately Return to the initial position shown in FIG. Further, the lock pin 63 immersed in the vane 621 protrudes outside the vane 621, and the rotor 62 returned to the initial position is held at the initial position.

  When the internal combustion engine is stopped, the hydraulic pressure supplied from the hydraulic pump 82 to the variable valve timing mechanism 6 becomes 0, the rotor 62 and the intake camshaft take the initial positions, and the intake valve timing is in the most advanced state. . Therefore, an Otto cycle occurs when the internal combustion engine is started, and a sufficient amount of intake air necessary for the start can be charged into the cylinder 1 to improve startability.

  In addition, even during idling when the engine speed is low, the intake negative pressure downstream of the throttle valve 32 can be increased while the amount of intake air charged in the cylinder 1 is secured, and the capacity of the brake booster is improved (the brake is improved). Effectiveness is improved).

  The ECU 0 determines the amount by which the intake valve timing is retarded from the most advanced angle state, which is the initial position, in accordance with the current operating region of the internal combustion engine, and controls the variable valve timing mechanism 6. FIG. 5 illustrates the relationship between the operation region and the intake valve timing to be set in the internal combustion engine of the present embodiment. The intake valve timing becomes the most retarded state in the operation range of medium-medium-load rotation, and advances from there as the engine speed and / or load deviates. When the accelerator opening is close to full close and the required load is low, or when the accelerator opening is close to full open and the required load is high, the intake valve timing is in the most advanced angle state.

  The present embodiment is an Atkinson cycle internal combustion engine with a variable valve timing mechanism 6 that changes the opening / closing timing of the intake valve by changing the rotational phase of the intake camshaft with respect to the crankshaft, and is a variable valve associated with the intake valve. The timing mechanism 6 causes the relative rotation of the intake camshaft with respect to the crankshaft by using the pressure of the hydraulic fluid discharged from the hydraulic pump 82 that operates by receiving the rotational driving force from the crankshaft. In the situation where the crankshaft does not rotate and the hydraulic pump 82 does not discharge the hydraulic fluid, the rotational phase of the intake camshaft is at the most advanced initial position, and the hydraulic pump 82 is operated by rotating the crankshaft. In the situation where liquid is discharged, the rotational phase of the intake camshaft is retarded from the initial position. And configure the internal combustion engine can be varied.

  According to the present embodiment, although it is an Atkinson cycle engine, it becomes an Otto cycle engine or something close to it at the time of start-up or at a low speed, and it is possible to avoid a shortage of the intake air amount and the compression pressure of the intake air. There is no need to extend the cranking period when starting the engine.

  In addition, the small valve overlap amount at the time of engine start contributes to further improvement of engine startability.

  In an operation range of about a medium load, the intake valve timing is retarded from the initial position and the Atkinson cycle is performed, so that fuel efficiency can be improved.

  If a sufficient hydraulic pressure cannot be supplied to the variable valve timing mechanism 6 due to a failure of the hydraulic system (hydraulic pressure), etc., the intake valve timing naturally returns to the most advanced state. This functions as a fail safe against a failure of the hydraulic system.

  Incidentally, as the variable valve timing mechanism 6 having the most advanced angle state as the initial position, an existing exhaust valve variable valve timing mechanism can be used and can be mounted at low cost.

  The present invention is not limited to the embodiment described in detail above. The specific configuration of each part can be variously modified without departing from the spirit of the present invention.

  The present invention can be used as an internal combustion engine mounted on a vehicle or the like.

6 ... Variable valve timing mechanism 82 ... Hydraulic pump

Claims (1)

An Atkinson cycle internal combustion engine with a variable valve timing mechanism that changes the opening / closing timing of the intake valve by changing the rotational phase of the intake camshaft relative to the crankshaft,
The variable valve timing mechanism induces relative rotation of the intake camshaft with respect to the crankshaft by utilizing the pressure of hydraulic fluid discharged from a hydraulic pump that operates by receiving rotational driving force from the crankshaft. Is,
In a situation where the crankshaft does not rotate and the hydraulic pump does not discharge hydraulic fluid, the intake camshaft is in the initial position where the rotational phase of the intake camshaft has advanced most, and the hydraulic pump discharges hydraulic fluid as the crankshaft rotates Then, an internal combustion engine capable of changing the rotational phase of the intake camshaft from the initial position in the retarding direction.

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