JP2006283729A - Piston engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inhibit excess force acting on parts forming a movement system of a piston engine when engine rotation speed is changed in the operation of the piston engine. <P>SOLUTION: The piston engine 1 according to the invention has a piston 3 reciprocating in a cylinder 2. The reciprocating motion of the piston 3 is converted to rotation motion by a crankshaft 5. The crankshaft 5 is disposed in a crankcase 4 and an end of the cylinder 2 is connected to the crankcase 4. As rotation speed of the crankshaft 5 is increased, gas is fed from a pressure supply device 11 into the crank case 4 and pressure in the crankcase 4 is increased. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piston engine in which a piston reciprocates in a cylinder.

  In recent years, Stirling engines with excellent theoretical thermal efficiency have attracted attention in order to recover exhaust heat and factory exhaust heat of internal combustion engines mounted on vehicles such as passenger cars, buses, and trucks. Patent Document 1 discloses a technique for adjusting the pressure in the working chamber so that the fluctuation of the rotational speed of the Stirling engine is within an allowable range when the Stirling engine is stopped.

JP-A-6-264818

  However, in Patent Document 1, pressure adjustment during operation is not taken into consideration, and power is originally taken out to the parts constituting the motion system of the piston engine due to changes in engine speed during operation and other operating condition changes. There is a possibility that an extra force more than the force required above is applied. Therefore, the present invention has been made in view of the above, and when the operating condition of the piston engine changes during the operation of the piston engine, an extra component that acts on the components constituting the motion system of the piston engine. An object of the present invention is to provide a piston engine that can suppress excessive force.

  In order to achieve the above-described object, a piston engine according to the present invention includes a cylinder in which a piston disposed therein reciprocates, a case body to which one end of the cylinder is connected, and when the piston reciprocates. Pressure adjusting means for increasing the internal pressure of the case body as the frequency increases.

  In this piston engine, as the frequency at which the piston reciprocates (in the piston engine that converts the reciprocating motion of the piston into rotational motion by the crankshaft, the engine speed corresponds to this), Increase pressure. Thereby, when there is a change in the operating condition of the piston engine, it is possible to suppress an excessive force acting on the parts constituting the moving system of the piston engine.

  The piston engine according to the present invention is characterized in that, in the piston engine, the pressure inside the case body changes in proportion to the square of the frequency when the piston reciprocates.

  A piston engine according to the next invention is provided in the piston engine, provided in the communication passage, the communication passage capable of communicating the interior of the case body and the working space in the cylinder, and the interior of the case body. And a differential pressure setting means for communicating the inside of the case body and the working space when a differential pressure between the pressure of the working space and the pressure of the working space exceeds a set limit value.

  In the piston engine according to the present invention, an allowable value determination parameter obtained by dividing the internal pressure of the case body by the square of the frequency when the piston reciprocates during operation of the piston engine is set in advance. When it is outside the allowable range, the pressure inside the case body is adjusted so that the allowable value determination parameter falls within the allowable range.

  According to the present invention, when the operating condition of the piston engine is changed during the operation of the piston engine, it is possible to suppress an extra force acting on the parts constituting the moving system of the piston engine.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited to the best mode for carrying out the invention. In addition, constituent elements in the best mode for carrying out the invention include those that can be easily assumed by those skilled in the art or those that are substantially the same.

  In the following, a Stirling engine, which is a heat engine, is taken as an example of a piston engine, but the piston engine to which the present invention can be applied is not limited to this. In the following, an example in which exhaust heat of an internal combustion engine mounted on a vehicle or the like is recovered using a Stirling engine will be described, but the exhaust heat recovery target is not limited to the internal combustion engine. For example, the present invention can also be applied to recovering waste heat from a factory, plant, or power generation facility.

  The piston engine according to this embodiment stores, for example, a crankshaft as the frequency when the piston reciprocates (hereinafter also referred to as piston frequency) f, that is, the reciprocal of the time t required when the piston reciprocates once is increased. It is characterized in that the pressure inside the case body is increased. Here, in the case of a piston engine that converts the reciprocating motion of the piston by the crankshaft, the crankshaft makes one revolution by one reciprocation of the piston, so the time required for one revolution of the crankshaft is the time required for one reciprocation of the piston. t. Therefore, the piston frequency f corresponds to the rotation speed per unit time of the crankshaft, that is, the engine rotation speed of the piston engine. If n is the engine speed per minute of the piston engine, f = n / 60. In the following, a piston engine that converts the reciprocating motion of the piston into a rotational motion by the crankshaft will be described as an example, and therefore the engine speed of the piston engine is used in the same meaning as the piston frequency f.

  FIG. 1 is a cross-sectional view showing an exhaust heat recovery system including a piston engine according to this embodiment. The piston engine 1 according to this embodiment is a so-called displacer type Stirling engine. The Stirling engine type is not limited to the displacer type, but may be other types such as an α type Stirling engine. The piston engine 1 is a heat engine and is mounted on a vehicle together with the internal combustion engine 14, for example. Then, the exhaust gas of the internal combustion engine 14 is driven as a heat source. That is, in this embodiment, the piston engine 1 is used as an exhaust heat recovery device for the internal combustion engine 14.

  The displacer 7 included in the piston engine 1 includes a displacer cylinder 7T, a displacer piston 7P that reciprocates inside the displacer cylinder 7T, and a heat exchanger 7HE including a heater 7H, a regenerator 7R, and a cooler 7C. The displacer cylinder 7T and the heat exchanger 7HE are filled with the working fluid of the piston engine 1 (in this embodiment, gas and air). The displacer cylinder 7T is partitioned by the displacer piston 7P into a space (high temperature space) on the heater 7H side of the heat exchanger 7HE and a space (low temperature space) on the cooler 7C side. The space on the cooler 7C side and the cylinder 2 are connected by a working fluid passage 8, and the working fluid in the displacer cylinder 7T is guided into the cylinder 2.

  An exhaust passage 15 of the internal combustion engine 14 is connected to the heat exchanger 7HE, and the heater 7H is heated by the exhaust gas of the internal combustion engine 14. The displacer piston 7P is connected to the crankshaft 5 by a displacer connecting rod 7K, and is configured to reciprocate with the piston 3 with a predetermined phase difference.

  The piston engine 1 includes a cylinder (power cylinder) 2, a piston (power piston) 3 that reciprocates in the cylinder 2, a crankshaft 5 that converts the reciprocating motion of the piston 3 into rotational motion, and a piston 3 and a crankshaft 5. Connecting rod 6 and crankcase 4 which is a case body. Here, the space in the cylinder 2 formed between the piston 3 and the cylinder head 2H is the working space 2I.

  The crankcase 4 stores and supports the crankshaft 5 in a rotatable manner. One end of the cylinder 2 is connected to the crankcase 4. In this embodiment, the crankshaft 5 of the piston engine 1 is attached to the output shaft of the internal combustion engine 14. The output generated by the piston engine 1 recovering the exhaust heat of the internal combustion engine 14 is combined with the output of the internal combustion engine 14 and taken out.

  The piston engine 1 according to this embodiment is a piston engine in which the reciprocating motion of the piston 3 is converted into rotational motion by the crankshaft 5, but the reciprocating motion of the piston 3 is directly taken out as an output. . For example, the piston engine according to this embodiment may be a piston engine that takes out the reciprocating motion of the piston 3 by using a linear motor as a generator.

  In the piston engine 1, the inside of the crankcase 4 is pressurized by pressure adjusting means. Here, the pressure in the crankcase is represented by the average pressure of the gas in the crankcase. In this embodiment, the gas that pressurizes the crankcase 4 is the same type of gas as the working fluid of the piston engine 1 (air in this embodiment).

  In order to improve the engine efficiency of the piston engine 1, the piston engine 1 according to this embodiment receives components constituting the motion system of the piston engine 1 such as the connecting rod 6 and the crankshaft 5 from the net load of the piston engine 1. Designed to withstand a certain amount of force. For this purpose, it is necessary to reduce the load applied to the parts constituting the motion system of the piston engine 1 such as the connecting rod 6 and the crankshaft 5 to the level of the force received from the net load of the piston engine 1.

  In order to solve such a problem, the inventors of the present application have made extensive studies and, as a result, by maintaining the pressure in the crankcase 4 and the engine speed of the piston engine 1 (that is, the piston frequency) in a specific relationship, The force received from the pressure of the working fluid in the working space 2 </ b> I during the operation of 3 and the force received from the acceleration generated by the operation of the piston 3 are offset. And even if it is a case where the engine speed of piston engine 1 changes, the pressure in crankcase 4 is changed and the said specific relationship is maintained.

  The pressure adjusting means provided in the piston engine 1 according to this embodiment includes a pressure supply device 11 and a pressure adjusting mechanism 12. The pressure adjustment mechanism 12 includes a switching valve 12V and a valve operating device 12C. The valve operating device 12C is controlled by a pressure control device 30 incorporated in an ECU (Electronic Control Unit) 40. The ECU 40 controls the internal combustion engine 14.

For the pressure supply device 11, for example, a compressor, a pressure accumulation cylinder storing high-pressure gas, or the like can be used. Switching valve 12V is provided with a gas inlet 12i, a gas inlet and outlet 12o _1, and a gas outlet 12o _2. Then, it is possible to switch the valve operation device 12C, communication between the gas inlet 12i and the gas inlet and outlet 12o _1, and the communication between the gas inlet and outlet 12o ₁ and the gas outlet 12o _2. Here, the gas inlet / outlet port 12 o ₁ of the switching valve 12 </ b> V and the crankcase 4 are connected by a pressurized gas passage 10. Further, the pressure supply device 11 is connected to the gas inlet 12i of the switching valve 12V, supplies gas into the crankcase 4 via the switching valve 12V, and pressurizes the crankcase 4.

When it is desired to increase the pressure in the crankcase 4, the valve operating device 12C causes the gas inlet 12i and the gas inlet / outlet 12o ₁ to communicate with each other. Then, gas is supplied from the pressure supply device 11 into the crankcase 4 through the gas inlet 12 i, the gas inlet / outlet 12 o ₁ , and the pressurized gas passage 10. As a result, the pressure in the crankcase 4 increases. When it is desired to lower the pressure in the crank case 4, a valve operating device 12C is to communicate the gas inlet and outlet 12o ₁ and the gas outlet 12o _2. Then, the gas in the crankcase 4 is released into the atmosphere through the pressurized gas passage 10, the gas inlet / outlet 12 o ₁ , and the gas outlet 12 o ₂ . As a result, the pressure in the crankcase 4 decreases.

  With such a configuration, the pressure in the crankcase 4 and the engine speed of the piston engine 1 can be maintained in a specific relationship. As a result, even when the operating conditions of the piston engine 1 change, the force received from the pressure of the working fluid in the working space 2I when the piston 3 is operated cancels the force received from the acceleration generated by the operation of the piston 3. Can do.

  In the piston engine 1, the working space 2 </ b> I and the inside of the crankcase 4 are connected by a communication passage 9. The communication passage 9 is provided with a safety valve 13 which is a limit differential pressure setting means. The safety valve 13 opens when a differential pressure exceeding a preset limit value is applied, and closes when the differential pressure applied to the safety valve 13 falls below the limit value. The safety valve 13 is composed of, for example, a bidirectional pressure relief valve.

  As described above, the piston engine 1 according to this embodiment can withstand the force of receiving the components such as the connecting rod 6 and the crankshaft 5 constituting the motion system of the piston engine 1 from the net load of the piston engine 1. Design as follows. Therefore, when the differential pressure between the pressure in the working space 2I and the pressure in the crankcase 4 increases, an unexpected force may act on the parts constituting the motion system of the piston engine 1.

  In the piston engine 1 according to this embodiment, when the pressure difference between the pressure in the working space 2I and the pressure in the crankcase 4 exceeds a preset limit value, the safety valve 13 opens. Thereby, the inside of the working space 2I and the inside of the crankcase 4 communicate with each other, and the pressure inside the working space 2I and the pressure inside the crankcase 4 become substantially equal. As described above, the safety valve 13 generates an unexpected force that acts on the connecting rod 6 and the crankshaft 5 due to an increase in the differential pressure between the pressure in the working space 2I and the pressure in the crankcase 4. Can be suppressed. As a result, the connecting rod 6 and the like can be protected. Here, the case where the differential pressure between the pressure in the working space 2I and the pressure in the crankcase 4 exceeds a preset limit value is, for example, the piston frequency f of the piston engine 1, that is, the engine rotation of the piston engine 1. This is the case when the number is changed rapidly.

  Next, a pressure control apparatus according to this embodiment will be described. FIG. 2 is an explanatory view showing a pressure control device according to this embodiment. The piston engine 1 according to this embodiment is controlled by the pressure control device 30 according to this embodiment. As shown in FIG. 2, the pressure control device 30 is configured to be incorporated in the ECU 40. The ECU 40 includes a CPU (Central Processing Unit) 40p, a storage unit 40m, input and output ports 36 and 37, and input and output interfaces 38 and 39.

  A pressure control device 30 according to this embodiment may be prepared separately from the ECU 40 and connected to the ECU 40. And in order to implement | achieve the crankcase pressure control of the piston engine 1 which concerns on this Example, you may comprise so that the said pressure control apparatus 30 can utilize the control function of the piston engine 1 with which ECU40 is provided.

  The pressure control device 30 includes a control parameter calculation unit 31 and a pressure adjustment unit 32. These are the parts that control the pressure in the crankcase 4 of the piston engine 1 according to this embodiment. In this embodiment, the pressure control device 30 is configured as a part of the CPU 40 p that constitutes the ECU 40. In addition, the CPU 40 p includes an engine control unit 40 c that controls the operation of the internal combustion engine 14 and the piston engine 1.

And CPU40p, a storage unit 40 m, are connected together by a bus 35 _3. Further, the control parameter calculation unit 31, the pressure adjustment unit 32, and the engine control unit 40c of the CPU 40p are provided via the buses 35 ₁ and 35 ₂ , the input port 36, and the output port 37. Connected. Thereby, the control parameter calculation part 31 and the pressure adjustment part 32 which comprise the pressure control apparatus 30 are comprised so that a control data can be mutually exchanged and a command can be issued to one side. Further, the pressure control device 30 can interrupt the control of the pressure in the crankcase 4 of the piston engine 1 according to this embodiment into an operation control routine provided in advance in the ECU 40.

  An input interface 38 is connected to the input port 36. Sensors that acquire information necessary for controlling the pressure in the crankcase of the piston engine 1, such as the pressure sensor 41, the engine speed sensor 42, and the like are connected to the input interface 38. Signals output from these sensors are converted into signals that can be used by the CPU 40 p by the A / D converter 38 a and the digital buffer 38 d in the input interface 38 and sent to the input port 36. Thereby, CPU40p can acquire information required for operation control of internal-combustion engine 14, and control of pressure in crankcase 4 of piston engine 1 concerning this example.

An output interface 39 is connected to the output port 37. The output interface 39 is connected to a valve operating device 12 </ b> C included in the pressure adjustment mechanism 12. The output interface 39 includes control circuits 39 ₁ , 39 _{2 and the} like, and operates the control target based on a control signal calculated by the CPU 40p. With this configuration, based on the output signals from the sensors, the pressure control device 30 according to this embodiment can control the pressure in the crankcase 4 of the piston engine 1 according to this embodiment. .

  The storage unit 40m stores a computer program, a control map, and the like including processing procedures for controlling the crankcase pressure of the piston engine 1 according to this embodiment. Here, the storage unit 40m can be configured by a volatile memory such as a RAM (Random Access Memory), a nonvolatile memory such as a flash memory, or a combination thereof.

  The computer program may be capable of realizing a processing procedure for controlling the crankcase internal pressure of the piston engine 1 according to this embodiment, in combination with a computer program already recorded in the CPU 40p. Moreover, this pressure control apparatus 30 may implement | achieve the function of the control parameter calculating part 31 and the pressure adjustment part 32 using a dedicated hardware instead of the said computer program. Next, a procedure for controlling the pressure in the crankcase of the piston engine 1 according to this embodiment using the pressure control device 30 will be described. In the following description, please refer to FIGS. 1 and 2 as appropriate.

  FIG. 3 is a flowchart showing a procedure for controlling the pressure in the crankcase according to this embodiment. First, the control parameter calculation unit 31 of the pressure control device 30 acquires the target load Wm of the piston engine 1 (step S101). The target load Wm is determined, for example, by the engine control unit 40c of the ECU 40 based on a drive request and operating conditions for the internal combustion engine 14. The control parameter calculation unit 31 acquires the target load Wm determined by the engine control unit 40c.

  Next, the control parameter calculation unit 31 calculates a target engine speed (target engine speed) Nm from the acquired target load Wm (step S102). In this embodiment, the engine speed N of the piston engine 1 is changed in proportion to the 1/3 power of the load W of the piston engine 1. For this reason, if the target load Wm of the piston engine 1 is determined, the target engine speed Nm can be determined based on the target load Wm. Here, the reason why the engine speed N of the piston engine 1 is changed in proportion to the 1/3 power of the load W of the piston engine 1 will be described.

  The piston engine 1 according to this embodiment maintains the crankcase pressure Pc and the engine speed N in a specific relationship, thereby receiving a force received from the pressure of the working fluid in the working space 2I when the piston 3 is actuated, The force received from the acceleration generated by the operation of the piston 3 is offset. Therefore, as will be described later, the crankcase internal pressure Pc is changed in proportion to the square of the engine speed N. Here, the load W of the piston engine 1 changes in proportion to the pressure of the working fluid existing in the working space 2I. Note that the pressure of the working fluid has a strong correlation with the crankcase pressure Pc. Further, the load W of the piston engine 1 changes in proportion to the engine speed N.

  In the piston engine 1 according to this embodiment, for example, when the engine speed N is doubled, the crankcase pressure Pc is changed in proportion to the square of the engine speed, so that it is four times the original pressure. Increase to. As a result, the pressure of the working fluid existing in the working space 2I also becomes four times the original pressure. Accordingly, the load W of the piston engine 1 at that time is eight times the original load W. Thus, in the piston engine 1 according to this embodiment, since the load W changes in proportion to the cube of the engine speed N, the engine speed N of the piston engine 1 is equal to the load W of the piston engine 1. It is changed in proportion to the 1/3 power.

  After calculating the target engine speed Nm, the control parameter calculation unit 31 calculates a target average pressure (target crankcase pressure) Pm in the crankcase 4 (step S103). In this embodiment, the engine speed of the piston engine 1 increases and the pressure in the crankcase 4 is increased. Therefore, if the target engine speed Nm of the piston engine 1 is determined, the target average pressure Pm in the crankcase 4 can be calculated. The target engine speed N and the target average pressure Pm are control parameters for realizing the crankcase pressure control of the piston engine 1 according to this embodiment.

  FIG. 4 is an explanatory view showing a load due to acceleration applied to the piston and a change in pressure of the working fluid due to the operation of the piston. The piston engine 1 according to this embodiment maintains a specific relationship between the pressure in the crankcase 4 (crankcase pressure) Pc and the engine speed N (that is, corresponding to the piston frequency of the piston engine 1). Thereby, the force Ps received from the pressure of the working fluid when the piston 3 is operated and the force F received from the acceleration generated by the operation of the piston 3 (that is, the differential value of the piston speed) can be canceled.

  Here, it is preferable to reduce the internal friction of the piston engine 1 as much as possible in order to offset the Ps and F by maintaining the crankcase pressure and the engine speed of the piston engine 1 in a specific relationship. For example, the internal friction of the piston engine 1 can be reduced by supporting the piston 3 with an air bearing or by reciprocating the piston 3 with a linear approximation mechanism.

As shown in FIG. 4, for example, when the engine speed of the piston engine 1 is N ₁ , if the crankcase internal pressure is set to Pc ₁ , a force Ps ₁ received from the pressure of the working fluid when the piston 3 is operated, The force F ₁ received from the acceleration generated by the operation of the piston 3 is canceled out. Here, if the crankcase pressure remains Pc ₁ when the engine speed changes to N ₂ (N ₁ <N ₂ ), the force (Ps ₁ ) received from the pressure of the working fluid during the operation of the piston 3 However, since the force (F ₂ ) received from the acceleration generated by the operation of the piston 3 becomes larger, they are not canceled out.

Therefore, as shown in FIG. 4, when the engine speed changes to N ₂ (N ₁ <N ₂ ), the crankcase pressure is changed to Pc _{2 accordingly} , and when the piston 3 operates, the force received from the pressure and Ps _2. Thereby, the force F ₂ received from the acceleration generated by the operation of the piston 3 can be canceled with the force Ps ₂ received from the pressure of the working fluid when the piston 3 is operated. As a result, when there is a change in the engine speed N of the piston engine 1, it is possible to suppress an extra force that acts on the parts that constitute the motion system of the piston engine 1.

  Here, the force F received from the acceleration generated by the operation of the piston 3 is proportional to the square of the piston frequency, that is, the square of the engine speed. Therefore, when the crankcase pressure Pc is changed by changing the piston frequency, that is, by changing the engine speed, the crankcase pressure Pc is changed in proportion to the square of the engine speed N.

  Here, when the reciprocating motion of the piston 3 is converted to a rotational motion by the crankshaft 5, the acceleration change of the piston 3 does not accurately indicate a sin wave. For this reason, in consideration of such variation factors, the crankcase pressure is changed in proportion to approximately the square of the piston frequency, that is, approximately the square of the engine speed. In the present invention, when “the crankcase pressure is changed in proportion to the square of the engine speed (equivalent to the piston frequency)”, not only the square of the engine speed but also the approximate square of the engine speed. Including. It should be noted that the relationship between the engine speed and the crankcase pressure is obtained in advance through experiments or the like, and this is mapped and stored in the storage unit 40m of the ECU 40, and the crankcase pressure is obtained from the engine speed with reference to the map. May be.

  Thus, the piston engine 1 according to this embodiment maintains the crankcase internal pressure and the engine speed of the piston engine 1 (corresponding to the piston frequency) in a specific relationship even when the engine speed changes. Thus, the force received from the pressure of the working fluid when the piston 3 is operated cancels the force received from the acceleration generated by the operation of the piston 3. As a result, the load applied to the components constituting the motion system of the piston engine 1 such as the connecting rod 6 and the crankshaft 5 can be reduced to the level of the force received from the net load of the piston engine 1. For this reason, the components constituting the motion system of the piston engine 1 such as the connecting rod 6 and the crankshaft 5 can be designed to withstand the force received from the net load of the piston engine 1.

  As a result, the parts constituting the motion system of the piston engine 1 can be reduced in weight and size. Further, since the load applied to the components constituting the motion system of the piston engine 1 can be reduced to the level of the force received from the net load, the counterweight provided on the crankshaft 5 can be reduced. Thereby, the energy which drives the piston engine 1 can be reduced. Further, since the parts constituting the motion system of the piston engine 1 can be reduced in size, the sliding portion of the parts constituting the motion system of the piston engine 1 is also reduced. Thereby, since the internal friction of the piston engine 1 can be reduced, the internal loss of the piston engine 1 can be reduced.

  Furthermore, the manufacturing cost of the piston engine 1 can also be reduced by reducing the weight and size of the parts constituting the motion system of the piston engine 1. In particular, in a Stirling engine used to recover exhaust heat from an internal combustion engine or the like, the internal friction needs to be reduced to the minimum in order to recover the heat energy from the lower heat energy. For this reason, the piston engine 1 which concerns on this Example is preferable for the Stirling engine used in order to collect | recover waste heat.

  When the control parameter calculator 31 calculates the target average pressure Pm in the crankcase 4 (step S103), the control parameter calculator 31 calculates the allowable value determination parameter PN (step S104). As described above, the piston engine 1 according to this embodiment maintains the crankcase pressure and the engine speed of the piston engine 1 (corresponding to the piston frequency) in a specific relationship, and operates the working fluid when the piston 3 is operated. The force received from the pressure and the force received from the acceleration generated by the operation of the piston 3 are offset.

  However, if the specified relationship between the crankcase pressure and the engine speed of the piston engine 1 cannot be maintained due to disturbances or other factors, it is not expected for the components that make up the motion system of the piston engine 1. There is a risk that the power of. For this reason, at the target average pressure Pm set in step S103, the force received from the pressure of the working fluid when the piston 3 is operated and the force received from the acceleration generated by the operation of the piston 3 It is determined whether or not it is canceled within an allowable range such as a load.

The permissible value determination parameter PN is determined from the viewpoint of protecting the parts constituting the motion system of the piston engine 1, and the crankcase internal pressure (at this stage, the set target average pressure Pm corresponds to this). The value divided by the square of the piston frequency f (Pm / f ² ). Since the engine speed N of the piston engine 1 corresponds to the piston frequency f, the allowable value determination parameter PN is a value obtained by dividing the set target average pressure Pm by the square of the engine speed N (Pm / N ² ) may be used.

  The control parameter calculation unit 31 determines whether or not the calculated allowable value determination parameter PN is within a preset allowable range, that is, within a range that is larger than the first threshold A and smaller than the second threshold B (step S105). . Here, the first threshold value A and the second threshold value B that define the permissible range are determined based on the load resistance of the components (for example, the connecting rod 6) constituting the motion system of the piston engine 1. When B> PN> A, the pressure adjusting unit 32 sends a control signal to the valve operating device 12C of the pressure adjusting mechanism 12 to operate the switching valve 12V.

  Then, the pressure adjusting unit 32 changes the crankcase internal pressure Pc to the set target average pressure Pm (step S106). Further, the engine control unit 40c changes the engine speed N of the piston engine 1 to the target engine speed Nm (step S106). At this time, the control parameter calculation unit 31 acquires the crankcase internal pressure Pc from the pressure sensor 41, acquires the engine speed N of the piston engine 1 from the engine speed sensor 42, and uses the information as the pressure control unit. 32 and feedback to the engine control unit 40c. The pressure control unit 32 and the engine control unit 40c control the crankcase internal pressure Pc and the engine speed N based on the fed back information.

  When B> PN> A is not satisfied, that is, when PN ≦ A or B ≦ PN, the control parameter calculation unit 31 corrects the target average pressure Pm (step S107). Then, the control parameter calculation unit 31 calculates the allowable value determination parameter PN again based on the corrected target average pressure Pm, and determines whether this is within the allowable range (step S105). When the allowable value determination parameter is not within the allowable range, the control parameter calculator 31 corrects the target average pressure Pm until the allowable value determination parameter enters the allowable range.

During the operation of the piston engine 1, the following control may be performed. That is, the control parameter calculation unit 31 of the pressure control device 30 acquires the crankcase internal pressure Pc from the pressure sensor 41, acquires the engine speed N of the piston engine 1 from the engine speed sensor 42, and operates the piston engine. The permissible value determination parameter PN_D = Pc / N ² (corresponding to Pc / f ² ) during operation 1 is calculated. Then, the control parameter calculation unit 31 determines whether or not the allowable value determination parameter PN_D during the operation of the piston engine 1 is within the allowable range.

  When the allowable value determination parameter PN_D is out of the allowable range, control is performed so as to correct the crankcase internal pressure Pc so that the allowable value determination parameter PN_D falls within the allowable range. Thereby, during operation of the piston engine 1, the possibility of unexpected force acting on the parts constituting the motion system of the piston engine 1 can be greatly reduced, so that the piston engine 1 can be operated safely.

  As described above, the piston engine according to this embodiment sets the crankcase internal pressure and the engine speed (corresponding to the piston frequency) to a specific relationship, and increases the crankcase internal pressure as the engine speed increases. . As a result, even when a change occurs in the engine speed of the piston engine, the specific relationship between the crankcase internal pressure and the engine speed is maintained, and the force received from the pressure of the working fluid during the operation of the piston, The force received from the acceleration generated by the operation can be offset. Thereby, the piston engine which concerns on this Example can suppress that excessive force acts on the components which comprise the moving system of a piston engine, when there exists a change in engine speed (equivalent to the frequency of a piston). .

  In the above description, the configuration, operation, and effect have been described using an example in which the piston engine 1 is a Stirling engine. However, the piston engine according to this embodiment is used in a heat engine or device other than a Stirling engine. It can be easily applied to this. And when applied, it has the same utility as the above.

  As described above, the piston engine according to the present invention is useful for a heat engine, and is particularly suitable for suppressing an excessive force from acting on components constituting a moving system of the piston engine.

It is sectional drawing which shows the waste heat recovery system containing the piston engine which concerns on this Example. It is explanatory drawing which shows the pressure control apparatus which concerns on this Example. It is a flowchart which shows the procedure for controlling the pressure in the crankcase which concerns on this Example. It is explanatory drawing which shows the pressure change of the working fluid by the load by the acceleration added to a piston, and the action | operation of a piston.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piston engine 2 Cylinder 2H Cylinder head 2I Working space 3 Piston 4 Crankcase 5 Crankshaft 6 Connecting rod 9 Communication passage 10 Pressurized gas passage 11 Pressure supply device 12 Pressure adjustment mechanism 12V Switching valve 12C Valve operation device 13 Safety valve 14 Internal combustion engine DESCRIPTION OF SYMBOLS 30 Pressure control apparatus 31 Control parameter calculating part 32 Pressure adjusting part 40 ECU
40c Engine control unit 40m Storage unit 41 Pressure sensor 42 Engine speed sensor

Claims (4)

A cylinder in which a piston disposed inside reciprocates;
A case body to which one end of the cylinder is connected;
Pressure adjusting means for increasing the pressure inside the case body as the frequency when the piston reciprocates increases;
A piston engine comprising:   2. The piston engine according to claim 1, wherein the pressure inside the case body changes in proportion to a square of a frequency when the piston reciprocates. A communication passage capable of communicating the inside of the case body and the working space in the cylinder;
Provided in the communication passage, when a differential pressure between the pressure inside the case body and the pressure in the working space exceeds a set limit value, a limit differential pressure that causes the inside of the case body to communicate with the working space Setting means;
The piston engine according to claim 1, further comprising: During the operation of the piston engine, if the allowable value determination parameter obtained by dividing the pressure inside the case body by the square of the frequency when the piston reciprocates is outside a preset allowable range, The piston engine according to any one of claims 1 to 3, wherein a pressure inside the case body is adjusted so that an allowable value determination parameter falls within the allowable range.

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