JP2008223628A - Control device for free piston engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set a compression ratio to be a desired value by a simple control. <P>SOLUTION: A free piston engine 11 has cylinders 31, 32, and pistons 41, 42 fitted to be capable of reciprocating in the cylinders 31, 32 and receiving combustion pressure in the cylinders 31, 32. A generator 12 has: a permanent magnet 4 displaced according to mechanical displacement of the pistons 41, 42; and a coil 46 for power generation disposed to the circumference of the permanent magnet. When velocities VP of the pistons 41, 42 detected by a piston velocity sensor S5 are a predetermined velocity VC or lower, power generation of the generator 12 is stopped. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control device for a free piston engine.

Recently, a free piston engine has attracted attention from the viewpoint of efficiently extracting thermal energy of combustion gas. Patent Document 1 discloses a technique in which a permanent magnet provided on a piston of a free piston engine generates power by reciprocating in a magnetic field of a linear generator. Patent Document 2 discloses that the generator magnetic field control is performed so as to achieve isobaric expansion while observing the volume change in the cylinder from the viewpoint of improving thermal efficiency.
JP 2005-155345 A JP 2003-343202 A

  By the way, in a free piston engine, it is important how to ensure a predetermined compression ratio. That is, in a free piston engine, there is no member such as a crankshaft or a connecting rod that mechanically regulates the stroke end, so the compression ratio is difficult to be determined uniformly. The compression ratio varies considerably due to differences and the like. On the other hand, it may be required to set the compression ratio as a certain constant value or to variably control it from various viewpoints such as improvement in thermal efficiency and difference in operating environment.

  In a free piston engine, in order to set the compression ratio to a desired size, it is conceivable to use the magnetic field control of the generator, that is, to slightly change and control the power generation load as described in Patent Document 2 described above. . However, in this case, considerably complicated magnetic field control is required, and when the piston speed increases, the magnetic field control may not be able to follow up sufficiently. In particular, when the energy generated by the free piston engine is used for driving a motor for driving an automobile, a considerably large piston speed is required, so the compression ratio is set to a desired value by magnetic field control. It will be very difficult to set.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a control device for a free piston engine that allows a compression ratio to be set to a desired value by simple control.

In order to achieve the above object, the following solution is adopted in the present invention. That is, as described in claim 1 in the claims,
In a control device for a free piston engine comprising a cylinder and a piston that is reciprocally fitted in the cylinder and that receives a combustion pressure in the cylinder,
A generator having a permanent magnet displaced in accordance with a mechanical displacement of the piston and a power generating coil disposed around the permanent magnet;
Piston speed detecting means for detecting a value related to the speed of the piston;
Power generation stop means for stopping power generation by the generator when the piston speed detected by the piston speed detection means becomes a predetermined speed or less;
It is supposed to be equipped with.

  According to the above solution, when the piston is reciprocated, the permanent magnet mechanically interlocked with the piston is displaced, and the generated power is taken out from the power generating coil. Then, the power generation is stopped when the piston speed drops below the predetermined speed, and the compression is performed by the kinetic energy of the piston after the power generation is stopped. The kinetic energy of the piston is expressed as “M · V · V · / 2” where the piston speed is V and the piston mass is M. Since the piston mass M is always a constant value, the kinetic energy of the piston for compression is changed by changing the predetermined piston speed when power generation is stopped, which is a value related to the piston speed V. In other words, the compression ratio can be set to a desired magnitude by executing the power generation stop control using the predetermined speed as a parameter. In order to obtain a desired compression ratio, it is only necessary to look at the piston speed when power generation is stopped. Therefore, the control becomes very simple, and it can be easily handled even when the piston speed is high.

A preferred mode based on the above solution is as described in claim 2 and the following claims. That is,
Comprising a battery charged by the generator;
The predetermined speed is set so that the voltage generated by the generator is larger than the voltage of the battery;
(Corresponding to claim 2). In this case, when the power is generated by the generator, the piston speed becomes higher than the predetermined speed, and the generated voltage becomes higher than the battery voltage. This makes it possible to charge the battery with the generated power from the generator without using a separate booster.

Misfire detection means for detecting a value related to misfire of the free piston engine;
Correction means for correcting the predetermined speed to increase when a misfire is detected by the misfire detection means;
Is further provided (corresponding to claim 3). In this case, when misfire occurs, the compression ratio is increased by correcting the predetermined speed to a large value, and subsequent misfire can be prevented.

Knocking detection means for detecting a value related to knocking of the free piston engine;
Correction means for correcting the predetermined speed to be small when knocking is detected by the knocking detection means;
Is further provided (corresponding to claim 4). In this case, when knocking occurs, the compression ratio is reduced by correcting the predetermined speed to a small value, and subsequent knocking can be prevented.

  According to the present invention, the compression ratio can be set to a desired value by simple control.

  FIG. 1 shows an embodiment in which a free piston engine is used for supplying power to a motor that drives an automobile as a vehicle. In FIG. 1, reference numeral 1 denotes a driving (running) motor, which is an AC motor in the embodiment. Reference numerals 2R and 2L denote left and right driving wheels (front wheels or rear wheels). The driving wheels 2R and 2L are driven by the motor 1 via the differential gear 3.

  Reference numeral 10 denotes a power generation unit, and the power generation unit 10 is configured as a unit body including a free piston engine 11 including a piston and a cylinder and a generator 12. The free piston engine 11 drives the generator 12. The electric power (alternating current) generated by the generator 12 is converted into direct current by the rectifier 20 and then supplied to the motor 1 via the DC-AC converter 21. On the other hand, surplus power is supplied to the battery 22. In addition, power from the battery 22 is supplied to the motor 1 via the DC-AC converter 21. In order to recover regenerative energy during braking, the electric power generated by the motor 1 is converted into direct current by the rectifier 23 and then boosted by the DC-DC converter 24 and supplied to the battery 22 during braking.

The flow of power supply according to the driving state of the automobile is performed, for example, as follows, and the maximum power generation amount by the free piston engine 10 is sufficiently large to ensure the maximum output by the motor 1. .
(1) When the required power generation amount is very small At the time of starting or at an extremely light load, and when the storage amount of the battery 22 is large. At this time, power generation by the generator 12 is not performed (the free piston engine 11 is stopped), and power is supplied to the motor 1 only from the battery 22.
(2) When the required power generation amount is small It is when the battery 22 has a large amount of stored power during light load to medium load. At this time, power is generated by the generator 12 (the free piston engine 11 is operated), and electric power is supplied exclusively from the generator 12 to the motor 1 (a small amount of surplus power is generated to generate surplus power. The battery 22 may be charged).
(3) When the required power generation amount is medium to large When the power storage amount of the battery 22 is small during light load to high load. At this time, the generator 12 generates sufficient electric power more than necessary for traveling (the free piston engine 11 is operated), and the electric power is supplied from the generator 12 to the motor 1 and sufficient surplus power is generated. The battery 22 is charged.
(4) Regenerative braking When the motor 1 functions as a generator driven by the drive wheels 2R, 2L. At this time, the electric power generated by the motor 1 is stored in the battery 22. In addition, although the free piston engine 11 may be stopped, the operation can be continued at an extremely low speed in preparation for the next power generation.

  Next, an example of the power generation unit 10 will be described with reference to FIG. In FIG. 2, the free piston engine 11 has a cylinder member 30 constituted by a cylindrical member closed at both ends. As for the cylinder member 30, the 1st cylinder 31 is comprised in the one end part side, and the 2nd cylinder 32 is comprised in the other edge part side. A first piston 41 is slidably fitted in the first cylinder 31, and a second piston 42 is slidably fitted in the second cylinder 32. The pistons 41 and 42 are connected by a connecting rod 43 and integrated with each other.

  A first combustion chamber 51 is defined by the first cylinder 31 and the first piston 41, and a second combustion chamber 52 is defined by the second cylinder 32 and the second piston 42. In the embodiment, the free piston engine 11 is a self-ignition type two-cycle engine, and a cycle of compression, expansion, exhaust, and scavenging is repeated. The first piston 41 and the second piston 42 are set so that the strokes of the first piston 41 and the second piston 42 are different from each other, and when one piston is at the end of the expansion stroke, the other piston is at the end of the compression stroke. Thereby, the connection unit UT of the pair of pistons 41 and 42 and the connection rod 43 is integrated with each other and reciprocated in the axial direction of the cylinder member 30. In FIG. 2, the intake port, the exhaust port, the scavenging port, and the like are not shown for simplicity.

  The connecting rod 43 is integrally formed with a magnet holder 44 serving as a mass pair. A large number of permanent magnets 45 are fixed to the magnet holder 44 along the axial direction of the connecting rod 43. Corresponding to the permanent magnet 45, a power generation coil 46 for three-phase alternating current is fixedly arranged outside the cylinder 30. As a result, when the coupling unit UT is reciprocated in a state where a magnetic field is applied to the power generation coil 46, the permanent magnet 45 moves in the immediate vicinity of the power generation coil 46, and a change in the magnetic field occurs. Inductive electromotive force is generated in (generation of generated power). Thus, in the embodiment, the linear generator 12 is configured by the permanent magnet 45 and the power generation coil 46 in cooperation.

  FIG. 3 is a block diagram showing a control system for performing fuel injection control and power generation control. In FIG. 3, U is a controller (control unit) configured using a microcomputer. Signals from various sensors S1 to S6 are input to the controller U. The controller U performs fuel injection control from the fuel injection valve 51 and power generation control of the generator 12 based on input signals from the various sensors S1 to S6.

  The sensor S1 is a vehicle speed sensor that detects the vehicle speed. The sensor S2 is an accelerator opening sensor that detects the accelerator opening. The sensor S3 is a knocking sensor that detects knocking (level). The sensor S4 is a misfire sensor that detects misfire. The sensor S5 is a piston speed sensor that detects the degree of piston speed. The sensor S6 is a piston position sensor that detects the piston position.

  As the knocking sensor S3, an appropriate sensor that detects a value related to knocking can be used. As the misfire sensor S4, for example, an appropriate sensor that detects a value related to misfire, such as a sensor that outputs a signal according to a generation mode of ions generated by combustion, can be used. The piston speed sensor S5 can detect an appropriate value related to the speed of the unit body UT. For example, a linear encoder can be used as a sensor that can be detected most accurately. (It corresponds to the change speed of the magnetic field which changes according to the moving speed of the permanent magnet 45) or the piston speed may be detected indirectly by looking at the change in the phase of the generated AC voltage.

  The power generation by the generator 12 is executed only when the piston speed (speed of the connecting unit body UT) is higher than the predetermined speed, and the power generation is stopped below the predetermined speed. When the power generation is stopped when the piston speed becomes equal to or lower than the predetermined speed, an example in which the piston speed is changed is shown in FIG. 4, and when the piston speed is changed in the manner shown in FIG. FIG. 5 shows how the generated voltage changes. In FIG. 5, the voltage value indicated by BV corresponds to the voltage value (output voltage value) of the battery 22, and the predetermined speed is within a range in which the power generation voltage at the generator 12 is greater than BV. Is set.

  As described above, since the predetermined speed when stopping power generation is set in a range larger than the battery voltage, as long as power generation is performed by the power generator 12, the power generation voltage at the power generator 12 is the battery. It becomes a state larger than the voltage. This makes it possible to supply the power generated by the generator 12 for charging the battery 22 without using a separate voltage booster. The waveform of the generated voltage is almost rectangular.

  In FIG. 6, the excess air ratio λ of the air-fuel mixture supplied to the combustion chambers 51 and 52 is set to a constant value of 2, and the generator load G (N / (m / s)) is set to a constant value of 2000. In this state, the relationship between the piston movement amount (movement position), the piston speed, and the compression ratio when the predetermined speed VC when power generation is stopped is changed is shown. In FIG. 6, the piston movement amount is shown as the movement amount of the connecting unit UT, and the upper part is the combustion pressure in one combustion chamber (for example, the combustion chamber 51) with the piston speed being zero. And the lower part of the lower part receives the combustion pressure in the other combustion chamber (for example, the combustion chamber 52) and returns. The solid line indicates when the predetermined speed VC for stopping power generation is set to 8.0 m / s, the broken line indicates when the predetermined speed VC is set at 7.0 m / s, and the alternate long and short dash line indicates the predetermined speed VC of 6 When set to 0.0 m / s.

  In FIG. 6, the position where the piston movement amount is 0 mm is one compression stroke end position, and the position where 140 mm is the other compression stroke end position. Therefore, when the piston speed is 0, the compression ratio becomes smaller as the piston moves away from the position of 0 mm (or 140 mm). It is understood that the kinetic energy of the unit body UT used exclusively for compression increases and the compression ratio increases as the predetermined speed VC at which power generation is stopped increases.

  FIG. 7 is a diagram corresponding to FIG. 6, but when the predetermined speed VC at which power generation is stopped is set to a constant value of 7.0 m / s, the excess air ratio λ and the generator load G are changed. The state is shown. That is, the solid line shows the case of λ = 5 and the generator load G = 2500, the one-dot chain line shows the case of λ = 5 and the generator load G = 2000, the broken line shows λ = 2 and the generator load G = 2500. In this case, the two-dot chain line is λ = 2 and the generator load G = 2000. As can be seen from FIG. 7, if the predetermined speed VC at which power generation is stopped is a constant value, the compression ratio is constant regardless of the change in the excess air ratio λ or the change in the power generation load G.

  Next, a control example for stopping power generation (power generation cut) when the piston speed becomes equal to or lower than the predetermined speed VC will be described with reference to the flowcharts of FIGS. In the following description, Q indicates a step.

  In FIG. 8, which is the main flowchart, first, in Q1, after signals from various sensors and the like are input, in Q2, the required power generation amount is determined. This required amount of power generation can be determined based on, for example, the vehicle speed and the accelerator opening. Thereafter, after the fuel injection amount corresponding to the power generation request amount is determined in Q3, fuel injection is executed in Q4 (since it is intake port injection, the degree of freedom in setting the injection timing becomes high, In the combustion chambers 51 and 52, uniform combustion is performed).

  After Q4, at Q5, it is determined whether or not the current combustion is knocking based on the output from the knocking sensor S3. If the determination in Q5 is YES, the predetermined speed VC when power generation is stopped is corrected to a value smaller than the current value. The degree of correction increases as the level of knocking increases.

  When the determination in Q5 is NO, it is determined in Q6 whether or not the current combustion is misfiring based on the output from the misfire sensor S4. If YES in Q6, the predetermined speed VC when power generation is stopped is corrected to a value greater than the current value in Q8. The degree of correction increases as the misfire level increases.

  When the determination at Q6 is NO, knocking or misfiring has not occurred even at the current predetermined speed VC. At this time, at Q9, the current predetermined speed VC is maintained as it is. After Q7, Q8 or Q9, the process shifts to Q10 and is stored (updated) at the set predetermined speed VC. The processing at Q10 is, for example, an update of a stored value to a map showing a correspondence relationship between a required compression ratio and a predetermined speed VC at which power generation is stopped, and the correction at Q8 and Q9 is the map value. Correction.

  The flowchart in FIG. 9 is interrupted at predetermined time intervals with respect to the flowchart in FIG. 8. First, in Q21, signals from various sensors are read. Thereafter, at Q22, the required compression ratio is determined. That is, for example, the excess air ratio λ is determined based on the current operating state of the free piston engine 11 (for example, the fuel injection amount and the piston speed) (for example, determined in the range of λ = 2 to 5). Further, the required compression ratio is determined based on the excess air ratio λ (for example, collation with a map).

  After Q22, at Q23, a predetermined speed VC for stopping power generation is determined based on the required compression ratio. The predetermined speed VC is determined by collating with the map described in Q10 described above (the correction in Q7 and Q8 may be performed).

  After Q23, in S24, it is determined whether or not the actual piston speed VP detected by the piston speed sensor S5 is equal to or lower than the predetermined speed VC set in Q23. When the answer is NO in Q24, the process returns to Q24 after performing a process of continuously executing power generation in Q25. If YES in Q24, power generation is stopped in Q26.

  Although the embodiment has been described above, the present invention is not limited to the embodiment, and can be appropriately changed within the scope described in the scope of claims. For example, the invention includes the following cases. . The piston is not limited to a pair of structures integrated with each other, but may be a single piston, or may be a structure in which a plurality of pistons having the structure shown in FIG. For example, when three stages of the structure shown in FIG. 2 are juxtaposed (the number of pistons or combustion chambers is 6 in total) and the displacement of one combustion chamber is 330 cc, the total displacement of 1980 cc is free. A piston engine will be obtained. In the case where the piston is not adopted as a pair structure as shown in FIG. 2, for example, a return spring that urges the piston in the compression direction may be separately provided (piston motion when power generation is stopped at a predetermined speed VC). With the energy, the energy for the next compression is stored in the return spring).

  The permanent magnet 45 is not provided integrally with the unit body UT, that is, the pistons 51 and 52, but is provided with, for example, a magnet holder linked to the pistons 51 and 52 via a gear or the like. What is necessary is just to make it hold the permanent magnet 45. In particular, when the permanent magnet is interlocked with the piston via a gear, the permanent magnet (magnet holder) can be configured to rotate forward and backward in accordance with the reciprocating motion of the piston. As this, a rotary type with higher power generation efficiency can be used. The specification range of the free piston engine is not limited, such as being used not only for automobiles but also for stationary power generation. The free piston engine may be a spark ignition type or may adopt an appropriate type such as a four-cycle type. The required compression ratio may be basically a constant value without being variable, and in the case of a constant value, the required compression ratio is corrected according to the difference in operating environment such as atmospheric pressure and intake air temperature. You can also. Of course, the object of the present invention is not limited to what is explicitly stated, but also implicitly includes providing what is substantially preferred or expressed as an advantage.

The whole system diagram which shows embodiment at the time of utilizing a free piston engine for the electric power feeding to the motor for driving | running | working a motor vehicle. 1 is a partially sectional plan view showing an example of a free piston engine according to the present invention. The figure which shows the control system of this invention in a block diagram. The time chart which shows a mode that a piston speed changes, when a power generation stops when a piston speed becomes below a predetermined speed. The time chart which shows the mode of the change of the generated voltage which arose by the change of the piston speed of FIG. FIG. 5 is a characteristic diagram showing a piston movement amount, a compression ratio, and a piston speed when a predetermined speed VC when power generation is stopped is changed with the excess air ratio λ and the generator load G as constant values. FIG. 6 is a characteristic diagram showing a piston movement amount, a compression ratio, and a piston speed when an excess air ratio λ and a generator load G are changed with a predetermined speed VC when power generation is stopped as a constant value. The flowchart which shows the example of control of this invention. The flowchart which shows the example of control of this invention.

10: power generation unit 11: free piston engine 12: generator 22: battery 30 cylinder member 31: first cylinder 32: second cylinder 41: first piston 42: second piston 43: connecting rod 44: magnet holder 45: Permanent magnet 46: Coil for power generation 51: First combustion chamber 52: Second combustion chamber U: Controller S3: Knocking sensor S4: Misfire sensor S5: Piston speed sensor

Claims (4)

In a control device for a free piston engine comprising a cylinder and a piston that is reciprocally fitted in the cylinder and that receives a combustion pressure in the cylinder,
A generator having a permanent magnet displaced in accordance with a mechanical displacement of the piston and a power generating coil disposed around the permanent magnet;
Piston speed detecting means for detecting a value related to the speed of the piston;
Power generation stop means for stopping power generation by the generator when the piston speed detected by the piston speed detection means becomes a predetermined speed or less;
A control device for a free piston engine. In claim 1,
Comprising a battery charged by the generator;
The predetermined speed is set so that the voltage generated by the generator is larger than the voltage of the battery;
A control device for a free piston engine. In claim 1 or claim 2,
Misfire detection means for detecting a value related to misfire of the free piston engine;
Correction means for correcting the predetermined speed to increase when a misfire is detected by the misfire detection means;
A control device for a free piston engine, further comprising: In any one of Claims 1 thru | or 3,
Knocking detection means for detecting a value related to knocking of the free piston engine;
Correction means for correcting the predetermined speed to be small when knocking is detected by the knocking detection means;
A control device for a free piston engine, further comprising:

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