Variable expansion-ratio engine

Abstract

A variable expansion-ratio engine includes an expansion-ratio adjuster configured to adjust an expansion ratio; a load detector configured to detect an engine load; and a controller configured to control the expansion-ratio adjuster. The controller controls the expansion ratio such that the expansion ratio at the time when the load is below a predetermined load value is set lower than that at the time when the load is equal to the predetermined load value.

Description

BRIEF DESCRIPTION OF DRAWINGS

While the claims are not limited to the illustrated embodiments, an appreciation of various aspects is best gained through a discussion of various examples thereof. Referring now to the drawings, illustrative embodiments are shown in detail. Although the drawings represent the embodiments, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain an innovative aspect of an embodiment. Further, the embodiments described herein are not intended to be exhaustive or otherwise limiting or restricting to the precise form and configuration shown in the drawings and disclosed in the following detailed description. Exemplary embodiments of the present invention are described in detail by referring to the drawings as follows.

FIG. 1 illustrates a multilink-type variable expansion-ratio engine according to a first exemplary embodiment;

FIGS. 2A to 2C illustrate a method for changing an expansion ratio in the multilink-type variable expansion-ratio engine;

FIG. 3 is a P-V line diagram illustrating an Otto cycle for describing the occurrence of negative work;

FIG. 4 shows the relationship between the load and the expansion ratio (compression ratio) in the multilink-type variable expansion-ratio engine;

FIG. 5 is a flow chart illustrating a variable expansion-ratio control operation;

FIG. 6 is a perspective view showing an example of a valve-timing controlling device for an exhaust valve provided in a multilink-type variable expansion-ratio engine according to a second exemplary embodiment;

FIG. 7 is a partial cross-sectional view of the valve-timing controlling device for the exhaust valve;

FIG. 8 schematically illustrates another example of a valve-timing controlling device, which is for an intake valve;

FIG. 9 schematically illustrates the valve-timing controlling device for the intake valve, as viewed in a direction in which a drive shaft extends;

FIGS. 10A and 10B respectively illustrate a minimum rocking state and a maximum rocking state of the valve-timing controlling device when the lift amount for the intake valve is set low;

FIGS. 11A and 11B respectively illustrate a minimum rocking state and a maximum rocking state of the valve-timing controlling device when the lift amount for the intake valve is set high;

FIG. 12 illustrates the relationship between an operating angle and the lift amount for the intake valve controlled by the valve-timing controlling device;

FIG. 13 illustrates opening and closing timings of the intake and exhaust valves for the second exemplary embodiment;

FIG. 14 is a flow chart illustrating a valve-timing control operation for the exhaust valve;

FIG. 15 is a P-V line diagram illustrating an Otto cycle for describing the occurrence of negative work;

FIGS. 16A to 16C illustrate a piston structure included in a variable expansion-ration engine according to a third exemplary embodiment;

FIGS. 17A and 17B illustrate the piston behavior;

FIG. 18 illustrates opening and closing timings of the intake and exhaust valves for the third embodiment; and

FIG. 19 is a flow chart illustrating a valve-timing control operation for the exhaust valve.

Claims

1. A controlling device for an engine, comprising: an expansion-ratio adjuster configured to adjust an expansion ratio;a load detector configured to detect an engine load; anda controller configured to control the expansion-ratio adjuster on the basis of the engine load detected by the load detector in a manner such that the expansion ratio at the time when the load is below a predetermined load value is set lower than that at the time when the load is equal to the predetermined load value.

2. The controlling device for the engine according to claim 1, wherein the controller is further configured to control the expansion-ratio adjuster in a manner such that the expansion ratio at the time when the load is below the predetermined load value becomes lower as the load decreases.

3. The controlling device for the engine according to claim 1, wherein the predetermined load value is a load value at which a pressure in a cylinder falls below the atmospheric pressure before an exhaust valve opens in a latter half of an expansion process.

4. The controlling device for the engine according to claim 1, wherein the expansion-ratio adjuster includes an exhaust valve opening-timing adjuster configured to adjust an opening timing of an exhaust valve, and wherein when the load is below the predetermined load value, the controller advances the opening timing of the exhaust valve so as to reduce the expansion ratio.

5. The controlling device for the engine according to claim 4, wherein the exhaust valve opening-timing adjuster adjusts only the opening timing of the exhaust valve.

6. The controlling device for the engine according to claim 4, wherein the exhaust valve opening-timing adjuster advances a closing timing of the exhaust valve by the advanced amount of the opening timing of the exhaust valve.

7. The controlling device for the engine according to claim 6, wherein the expansion-ratio adjuster further includes an intake valve opening-timing adjuster configured to adjust an opening timing of an intake valve, and wherein when the load is below the predetermined load value, the controller advances the opening timing of the intake valve together with advancing the opening and closing timings of the exhaust valve.

8. The controlling device for the engine according to claim 1, wherein the expansion-ratio adjuster includes a top-dead-center position adjusting mechanism configured to adjust a top-dead-center position of a piston, and wherein when the load is below the predetermined load value, the controller lowers the top-dead-center position of the piston so as to reduce the expansion ratio.

9. The controlling device for the engine according to claim 8, wherein the top-dead-center position adjusting mechanism comprises a plurality of links that link the piston to a crankshaft, and wherein the expansion ratio is reduced by regulating the movement of at least one of the links.

10. The controlling device for the engine according to claim 9, wherein the plurality of links comprises: a first link connected to the piston by means of a piston pin;a second link rockably connected to the first link and rotatably connected to the crankshaft; anda third link which is rockably connected to the second link and regulates the rocking of the second link.

11. The controlling device for the engine according to claim 8, wherein the piston has stroke characteristics that are substantially a simple harmonic motion.

12. The controlling device for the engine according to claim 8, wherein a stroke amount of the piston is greater than the diameter of the piston.

13. The controlling device for the engine according to claim 4, wherein the expansion-ratio adjuster further includes an intake valve closing-timing adjuster configured to adjust a closing timing of an intake valve, and wherein the controller sets a closing timing of the intake valve prior to a bottom dead center point and advances a closing timing of the intake valve as the load decreases.

14. The controlling device for the engine according to claim 1, wherein the expansion-ratio adjuster includes an exhaust-valve opening-timing adjuster configured to adjust an opening timing of an exhaust valve and a top-dead-center position adjusting mechanism configured to adjust a top-dead-center position of a piston, and wherein when the load is below the predetermined load value, the controller reduces the expansion ratio by means of the exhaust valve opening-timing adjuster.

15. A method for controlling an engine, comprising the steps of: detecting an engine load; andcontrolling an expansion ratio of the engine on the basis of the detecting step in a manner setting lower the expansion ratio at the time when the load is below a predetermined load value than that at the time when the load is at least equal to the predetermined load value.