VARIABLE LENGTH CONNECTING ROD

FIELD OF THE INVENTION

The present invention relates to variable compression ratio mechanisms used in engine configurations. In particular, but not exclusively, the present invention relates to a variable length connecting rod suitable for use in homogeneous charge spark ignition engines. However, it will be appreciated that the present invention has broader application and is not limited to that particular use.

BACKGROUND TO THE INVENTION Pressure to reduce energy consumption is increasing. Fuel consumption in vehicles is a major contributor to energy consumption and is also concerning because of the direct use of oil based fossil fuels which are not limitless in supply. Independent of whether the production of Green House Gases (GHGs), in particular, carbon dioxide is a major contributor to global warming, political forces are driving legislative restriction on vehicle GHG emissions. Improving energy conversion efficiency in vehicle engines will directly reduce fuel consumption and carbon dioxide emissions.

Hence, there is a need to improve the efficiency of homogenous charge spark ignition engines, although potential also exists to improve performance characteristics of other engine types such as compression ignition, homogenous charge compression ignition and stratified charge spark ignition and other concepts employing crankshaft/con-rod/piston configurations.

Life Cycle Assessment (LCA) of various options indicates that internal combustion engine powered vehicles compare favourably because of low production cost in spite of only achieving modest energy conversion efficiency in operation. Spark ignition (SI) homogeneous charge engines have dominated as passenger vehicle power plants. SI engines are likely to maintain their prevalence as passenger vehicles power plants into the future, but efficiency improvements are required and are likely to be achievable.

A high Compression Ratio (CR) in conjunction with a reduced compression stroke volume achieved by Late Valve Closing (LVC), an arrangement of the Atkinson cycle, is shown by simulation to produce improved brake efficiency in SI engines. In this fixed configuration, the maximum power produced by the engine is considerably lower than the maximum power that is achieved by the same displacement for a full compression stroke.

To achieve both the improved efficiency at low load using the Atkinson configuration and the power achievable from a full compression stroke, the engine requires a Variable Compression Ratio (VCR). Assessment of VCR concepts from literature and patents suggests that the complexity of continuously variable compression ratio designs prevented their development to production ready configurations. Simulations of fuel consumption over a standard driving cycle shows that a two step VCR arrangement produces the same benefit as a continuously variable CR for physically achievable piston-rod-crank configurations. There have been many attempts to improve efficiency using a variable compression ratio mechanism with an increased compression ratio. For example, US Patent No. 6,394,047 discloses a variable length connecting rod which involves a hydraulic fluid. The variable length connecting rod of US 6,394,047 comprises two locking assemblies which are required to lock the connecting rod at different lengths. The locking assemblies are unlocked by delivering a hydraulic fluid to the respective recesses in each locking member. The hydraulic pressure acts on the surface of each recess to retract a bias spring and unlock the locking assembly to allow an effective length change of the body of the rod.

Australian Patent Application No. 2001277146 discloses a hydraulically adjustable connecting rod comprising a shaft portion which is designed to be slidably received within the opening of an upper elongated portion. The connecting rod comprises a compression spring set between the main body and the shaft to urge the two components together. Fluid flows from a fluid chamber at the base of the main body to a fluid cell in the shaft via a pipe to force the connecting rod into a retracted position. A fluid release means is actuated by rotation of the crankshaft which will release the fluid back to the fluid chamber to return the connecting rod to its original extended position.

However, many of the prior art devices are complex, can have a high degree of friction from additional moving parts and have increased manufacturing costs due to their weight and manufacturing complexity. Furthermore, most prior art devices require additional changes to the existing engine configuration, which generally excludes the option of retrofitting such devices.

In this specification, the terms "comprises", "comprising" or similar terms are intended to mean a non-exclusive inclusion, such that a connecting rod that comprises a list of elements does not include those elements solely, but may well include other elements not listed.

The reference to any prior art or prior art techniques in this specification is not, and should not be taken as an acknowledgement or any suggestion that these references form part of the common general knowledge of persons skilled in the relevant field of technology of the invention.

OBJECT OF THE INVENTION It is a preferred object of the present invention to provide a variable length connecting rod that addresses or at least ameliorates one or more of the aforementioned problems of the prior art.

It is a preferred object of the present invention to provide a variable length connecting rod which improves the efficiency of homogeneous charge spark ignition engines.

SUMMARY OF THE INVENTION

Generally, embodiments of the present invention relate to a variable length connecting rod and methods of varying the length of a connecting rod.

According to one aspect, although not necessarily the broadest aspect, the present invention resides in a variable length connecting rod comprising:

a body having a floating bush slidably mounted within the body; a pair of chambers on opposing sides of the bush; and

at least one channel to transfer hydraulic fluid between the pair of chambers to move the bush between a first position and a second position to vary the length of the connecting rod.

Preferably, the body has an upper elongated portion and a lower portion.

Preferably, the upper elongated portion has an aperture for coupling to a piston and the lower portion has an opening formed to accommodate a crank of a crankshaft.

Preferably, the lower portion comprises an upper cap and a lower cap fastened together.

Preferably, the floating bush is positioned between the upper cap and the lower cap of the lower portion of the body.

Preferably, the floating bush comprises an upper half and a lower half.

Preferably, the connecting rod further comprises a pair of alignment sleeves positioned between the upper half and lower half of the floating bush to facilitate the alignment of the upper half and the lower half of the floating bush.

Preferably, the pair of chambers are formed in a space between an outer surface of the floating bush and the adjacent upper and lower caps.

Preferably, the connecting rod further comprises a control device mounted between the upper chamber and the lower chamber of the lower portion of the connecting rod to control the direction of fluid flow therebetween.

Preferably, the control device is in the form of a control lever.

Preferably, the control device uses one or more valves to control the direction of fluid flow between the pair of chambers to control the length of the connecting rod.

Preferably the valve comprises a ball and a seat.

Preferably, the connecting rod comprises at least one one-way valve within the floating bush.

Preferably, the upper half and the lower half of the floating bush comprise a port to allow fluid from a standard hydrodynamic lubrication system to recharge the chambers.

According to another aspect, although again not necessarily the broadest aspect, the present invention resides in a combustion engine comprising the aforementioned variable length connecting rod.

According to a further aspect, although again not necessarily the broadest aspect, the present invention resides in a method of varying a length of a connecting rod for a combustion engine, the connecting rod comprising a floating bush slidably mounted within a body of the connecting rod, the method comprising transferring hydraulic fluid between a first chamber and a second chamber on opposing sides of the floating bush to move the floating bush between a first and second position to vary the length of the connecting rod. According to a further aspect, although not necessarily the broadest aspect, the present invention resides in a variable length connecting rod for a combustion engine, the connecting rod comprising:

a body having a floating bush slidably mounted within the body; a pair of chambers on opposing sides of the floating bush formed by spaces between outer surfaces of the floating bush and upper and lower caps of the body;

at least one channel coupled to the pair of chambers; and a control device coupled to the at least one channel to control transfer of hydraulic fluid between the pair of chambers via the at least one channel to move the bush between a first position and a second position to vary the length of the connecting rod.

Further features and forms of the present invention will become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be readily understood and put into practical effect, reference will now be made to embodiments of the present invention with . reference to the accompanying drawings, wherein like reference numbers refer to identical elements. The drawings are provided by way of example only, wherein:

FIG 1 is a front cross-sectional view of a variable length connecting rod; and FIG 2 is an exploded front cross-section view of a floating bush of the variable length connecting rod of FIG 1 ;

FIG 3 is a perspective view of the floating bush of FIG 2 mounted within a body of the variable length connecting rod of FIG 1 ;

FIG 4 shows perspective views of a control device of the variable length connecting rod of FIG 1 ;

FIG 5 shows a front view of the variable length connecting rod of FIG 1 in a first "short" length position and a second "long" length position; and

FIG 6 shows a perspective view of a one way valve and a port in the floating bush.

Skilled addressees will appreciate that elements in the drawings are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the relative dimensions of some of the elements in the drawings may be distorted to help improve understanding of embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described with reference to a variable length connecting rod which improves the efficiency of homogenous charge spark ignition engines. The present invention is suited for any crank/con-rod/piston machine including engines and compressors. It is envisaged that the technology can also be applied to any engine that requires a broad operating power range and can be expanded to manufacturing equipment, industrial machines and farm machinery. Referring to FIG 1 , the variable length connecting rod 100 according to embodiments of the present invention is made of a metal, such as steel or the like. Preferably, the components of the connecting rod are machined using 1020 steel and/or 4140 steel material. However, other materials can be used. -

Referring to FIG 1 , the variable length connecting rod 100 comprises a body 200 having an upper elongated portion 210 and a lower portion 220. The upper elongated portion 210 has an aperture 211 for coupling to a piston (not illustrated). The lower portion 220 has an opening 221 formed to accommodate a crank of a crankshaft (not illustrated). The lower portion 220 comprises an upper cap 222 and a lower cap 223 which are fastened together. The opening 221 shape in the upper cap 222 and the lower cap 223 is substantially semi-circular in side elevation and both the upper and lower caps 222, 223 each comprise recesses 224 at both ends of the semi- circular portion for receiving a fastening aid in the form of a pin 225 to enable the caps 222, 223 to be fastened together. In this embodiment, the pin 225 is a cylindrical rod-like pin. However, it is envisaged that other suitable fastening aids could be used.

Referring now to FIG 2, the body of the connecting rod 100 comprises a floating bush 300 slidably mounted within the body 200. Preferably, the floating bush is positioned within an opening formed between the upper cap 222 and the lower cap 223 of the lower portion 220 of the body 200. The floating bush 300 comprises an upper half 310 and a lower half 320 which are fixed together via retaining screws or any other suitable fasteners. Suitable retaining screws provide the necessary fastening load for the floating bush 300. A pair of alignment sleeves 301 is positioned between the upper half 310 and the lower half 320 of the floating bush 300 to facilitate the alignment of the floating bush 300.

Referring to FIG 3 and 5, a pair of chambers 330 are located on opposing sides of the floating bush 300. A first chamber 330a is located above the floating bush 300 between the upper cap 222 of the lower portion 220 of the body 200 and the upper half 310 of the floating bush 300. A second chamber 330b is located below the floating bush 300 between the lower cap 223 of the lower portion 220 of the body 200 and the lower half 320 of the floating bush 300. The chambers 330a, 330b receive a hydraulic fluid (not illustrated) such as oil therein. In alternative embodiments, any other suitable hydraulic fluid can be used.

In the embodiment shown in FIGS 3 and 5, the pair of chambers 330 are formed above and below the floating bush 300 and the floating bush 300 is movable within a restricted range within the connecting rod 100. The pair of chambers 330 are formed by the space between an outer surface 302 of the floating bush 300 and the adjacent caps 222, 223. The connecting rod further comprises a control device 350 mounted between an upper chamber 330a and a lower chamber 330b of the lower portion 220 of the connecting rod 100 to control the direction of fluid flow therebetween.

At least one channel 355 is coupled to and connects the pair of chambers 330 so that the hydraulic fluid can flow in either direction between the upper and lower chambers 330a, 330b of the connecting rod 100 depending on the position of a control device 350 coupled to the channel 355. The upper half 310 and the lower half 320 of the floating bush 300 each comprise a port 360 and at least one valve 340 (shown in FIG 6) to allow the ingress of hydraulic fluid, such as oil from a standard hydrodynamic lubrication system, to charge the chambers 330 and/or recharge the chambers 330 after leakage.

The control device 350 allows the hydraulic fluid to flow between the chambers in one direction to shift the length of the connecting rod between a first position, e.g. a "short" length and a second position, e.g. a "long" length. Preferably, the control device 350 is in the form of a control lever. An actuating device can be provided to move the control device 350. For example, the actuating device can be a control cam mounted on the engine. The dynamics of the motion of the connecting rod 100 and piston create forces that tend to extend or contract the length of the rod 100. Such forces generate pressure in the hydraulic chambers 330 of the connecting rod 100. By porting the pressure directionally from one chamber to the other, the length of the connecting rod 100 can be changed. In this embodiment, valving is arranged so that hydraulic fluid is controlled to flow in one direction only for each of the two positions of the control device 350. In a first position, the hydraulic fluid can only flow from an upper chamber 330a to a lower chamber 330b. In a second position, the hydraulic fluid can only flow from the lower chamber 330b to the upper chamber 330a. In both cases, the flow is through the control lever 350.

At least one one-way valve 340 in the floating bush 300 ports hydraulic fluid, such as oil, from a conventional crank journal hydrodynamic lubrication system at a conventional pressure to recharge hydraulic fluid lost due to leakage from the chambers 330. A directional one-way hydraulic valve 351 is incorporated in the control device 350. Together, the combination of valves allows flow of hydraulic fluid from one chamber to the other when the compliant pressure exists. When the other chamber is pressurised at other parts of the crank motion, the valves prevent hydraulic fluid flow. The result is incremental changes in the rod length in one direction over several crank revolutions until the full extent of the change in length of the rod 100 is achieved.

In some embodiments, the valves 340, 351 are ball and seat valves. FIG 4 shows two views of the valve 351 of the control device 350 in the same orientation in the body 200. The views show that the upper valve ball seats 341 whereas the lower valve ball 343 in unable to seat. One or more indents 344 allow the lever to switch to a second position by rotating 15 degrees counter-clockwise where the action is reversed when the lower valve can seat and the upper valve ball is unable to seat. The control lever has a small through hole that vents leakage pressure that may accumulate behind the control lever. In some embodiments, the balls 341 , 343 are 3 mm hardened bearing balls and rely on an initial flow of the hydraulic fluid to seat or unseat the valves 351. The seats 342 are machined directly into the 1020 steel for the floating bush and 4140 steel for the control device 350.

The control device 350 is retained in the body 200 with a pair of spring loaded balls 352 acting in the indents 344 in the control device 350. The pressure held by the one-way valve 351 at the control device 350 is the same as the chamber pressure supporting the connecting rod 100. That pressure will force hydraulic fluid past the clearance between the control device 350 and the body 200 increasing the leakage losses from the chamber 330 under pressure. The pressure will also vent to the volume behind the control lever device boss (not illustrated) and potentially force the control lever device 350 out of rod 100. The control device 350 comprises a hole (not illustrated) to port any pressure vented to the volume behind the control lever boss which could potentially force the control lever 350 out of the rod 100. The control device 350 is controlled by a rotating cam (control cam) (not illustrated) mounted through an engine block. The control cam contacts the control lever 350 at approximately 65 degrees of crankshaft rotation. Rotation of the control cam is limited by adjustable stops to enable deflection of the control lever 350 within the indents 344.

In practice, the hydraulic chambers 330 are not completely sealed, therefore hydraulic fluid leaks from the chamber 330 under pressure when the one-way control valve 340 is preventing flow from that chamber 330. The motion acts in a damped fashion. The leakage reduces the volume of the pressurised chamber and increases the volume of the other chamber. The one way valves 340 in the floating bush 300 then port hydraulic fluid to the chamber which is increasing in volume without being supplied by fluid from the pressurised chamber. Flow control of the hydraulic fluid is reversible by creating directional one-way valves 351 in the control device 350 dependent on its position, thereby controlling the direction in which the length of the connecting rod 100 is changed.

In some embodiments, hydraulic seals (not illustrated) could be placed between the floating bush 300 and the lower portion 220, reducing leakage of the hydraulic fluid.

The chambers 330 pressurised by the hydraulic fluid are used as the means to support the connecting rod 100 in its extended "long" position. The hydraulic fluid pressure fluctuates with load during each cycle in the engine, but for all four stroke engines, forces exist at various stages of the cycle that tend to extend or retract the length of the connecting rod 100. Arrangement of the valves 351 allow the exchange of hydraulic fluid between the chambers 330 above and below the floating bush 300 which can slide in the connecting rod 100 while being rotatably connected to the crankshaft. This results in the connecting rod 100 progressively increasing or decreasing in length depending on the direction of flow through the valves. For example, the connecting rod 100 can change from the short length to the long length in about twenty revolutions (half a second) while being exposed on every second revolution to engine combustion pressure similar to that which would produce low load power when the appropriate valve settings are applied. The connecting rod 100 changes from the long to the short length when the appropriate valve settings are applied in about four revolutions while operating under the same combustion pressures.

It is envisaged that other control devices and/or valve types and configurations can be used in production models of the connecting rod.

FIG 5 illustrates the rod 100 in the first "short" position and the second "long" position. In the first "short" length position, the majority of the hydraulic fluid resides in the lower chamber 330b. In the second "long" length position, the majority of the hydraulic fluid resides in the upper chamber 330a. The present invention enables an engine of fixed configuration to run in one of two operating conditions:

a) . The engine operates with the variable compression ratio connecting rod 100 in the first "short" length position resulting in the engine configuration being essentially the same as currently manufactured spark ignition engine; or b) The engine operates with the variable compression rod connecting rod 100 in the second "long" length position in combination with late valve closing to reduce the volume of the compression stroke (a version of the Atkinson Cycle) resulting in an effective compression ratio that optimizes efficiency through optimum temperature at combustion and increased work from the cycle via an increased relative expansion ratio.

The ability to change compression ratio allows the engine to operate as the majority of automotive spark ignition engines currently do, but also enables the engine to switch to a high efficiency mode for low load operation. The high efficiency mode requires that the engine cannot produce the maximum power available from the displacement of the engine piston, but switching to the full inducted stroke with the short connecting rod length allows the engine to then produce the full power available from the displacement of the engine piston.

Hence, the connecting rod 100 of the present invention thus provides a solution to the aforementioned problems of the prior art by providing a connecting rod 100 for achieving variable compression by changing the length of the connecting rod utilising a floating bush. The efficiency advantage is achieved from a step compression ratio between two defined positions and allows for improved fuel efficiency over the majority of the operating power range with best advantage at low loads, which is the power used for most general driving. The present invention makes homogeneous charge engines (petrol, ethanol, gas) more efficient and increases their competitive advantage against diesel and electric cars. The present invention lends itself to application in existing engine configurations and thus can be readily integrated into existing systems having little effect on already established and proven design and manufacture principles. The connecting rod of the present invention is simpler in its design and construction leading to reduced manufacturing costs. The design of the rod and use of the floating bush also results in less friction between the components relative to other variable compression ratio devices.

The connecting rod employs a new technique for variable compression that allows the engine to be made in essentially the same way, which is a big advantage for engine manufacturers on a cost basis. The advantage for manufacturers is that the improved efficiency allows vehicles to operate inside legislative restrictions for emissions. It improves the competitive advantage that spark ignition internal combustion powered vehicles currently have over diesel powered vehicle and electric vehicles because the production cost of the engine/vehicle would be substantially less than the competitors.

Throughout the specification the aim has been to describe the invention without limiting the invention to any one embodiment or specific collection of features. Persons skilled in the relevant art may realize variations from the specific embodiments that will nonetheless fall within the scope of the invention.