Abstract:
A sensing system for an internal combustion engine having variable compression ratio connecting rods includes a connecting rod sensor which outputs digital signals having characteristic values corresponding to the compression ratio state of the connecting rods.

Description:
This is a companion case to U.S. application Ser. No. 10/707,751, filed on Jan. 9, 2004, which is hereby incorporated by reference into this specification. 

   BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates to a system for determining the compression ratio at which an engine is operating. The present system is particularly adapted for use with a connecting rod for a reciprocating internal combustion engine in which the effective length of the connecting rod may be controllably varied so as to change the compression ratio of the engine. 
   2. Disclosure Information 
   Students of thermodynamics understand that, in general, higher compression ratios yield higher thermal efficiency for piston-type internal combustion engines. Unfortunately, with premixed charge engines, most commonly sold in the form of spark-ignited engines operated on gasoline, higher compression ratios may cause problems arising from pre-ignition. This problem may be exacerbated, moreover, when an engine is turbocharged or super-charged. Therefore, it would be desirable to have an engine which can normally be operated at a higher compression ratio at most operating conditions, so as to yield maximum fuel economy, while still allowing operation at lower compression ratio at the highest power conditions. This would allow the engine to produce maximum power without knock or preignition. The inventor of the present connecting rod and compression ratio measuring system provides a unique solution to problems associated with known variable compression ratio arrangements. Such arrangements as pistons with variable compression height, typically developed by BICERI, as well as a variable plethora of other mechanical devices all suffer from problems relating to controllability, inadequate time response, excessive weight, excessive complexity, and other issues. One of the additional issues deals with the determination, in real time, of the compression ratio at which the engine is operating. U.S. Pat. No. 4,834,031 discloses a pressure sensor for determining the compression ratio of an engine by directly measuring the pressure within the combustion chamber. The system of the &#39;031 patent is an analog device which is excessively expensive and which may suffer from ambiguities arising from the need to factor in many variables to determine the pressure range attributable to various compression ratios. The present compression ratio measuring system, which is mated to a variable length connecting rod, solves the problems associated with prior compression ratio controlling devices by using a robust digital device which produces a signal having a variable duration which is clearly linked to the compression ratio at which the engine is operating. 
   SUMMARY OF INVENTION 
   A variable compression ratio sensing system for an internal combustion engine having a crankshaft and one or more reciprocating pistons includes variable compression ratio connecting rod for attaching said crankshaft to said piston, with said connecting rod having a plurality of discrete compression ratio states, and a digital output sensor for producing a signal having a variable duration corresponding to the particular compression ratio state of the connecting rod. 
   According to an aspect of the present invention, a digital output sensor for a variable compression ratio sensing system may comprise a Hall Effect sensor producing a longer signal when the compression ratio is at one value, and a shorter signal when the compression ratio is at another value. In a preferred embodiment, a Hall Effect sensor is mounted proximate an end of the connecting rod which is attached to the crankshaft of the engine. 
   According to another aspect of the present invention, avariable compression ratio connecting rod has a small end attached to a piston and a large end attached to a crankshaft, with the large end sweeping through a space as the crankshaft rotates, with the space having a boundary which is determined by the compression ratio state of the connecting rod. In effect, the large end of the connecting rod sweeps through an orbit, with the orbit having a center which is closer to the centerline of the crankshaft when the connecting rod is in a first compression ratio state and farther from the centerline of the crankshaft when the connecting rod is in a second compression ratio state. In the particular embodiment described herein the large end sweeps through an orbit having a center which is closer to the centerline of the crankshaft when the connecting rod is in a higher compression ratio state and farther from the centerline of the crankshaft when the connecting rod is in a lower compression ratio state. 
   According to another aspect of the present invention, an engine controller receives inputs from a number of engine operating parameter sensors, including at least a crankshaft position sensor for producing a crankshaft position signal, with the controller using the outputs of the crankshaft position sensor and the compression ratio sensor to determine the compression ratio state of the connecting rod. 
   According to another aspect of the present invention, a method for determining a compression ratio operating state of a reciprocating internal combustion engine includes the steps of sensing the operating speed of the engine, sensing the duration of a compression ratio state signal, and using the sensed operating speed and the sensed compression ratio state signal duration to determine the compression ratio at which the engine is operating. This method is particularly useful where the engine has a variable compression ratio connecting rod and a Hall Effect sensor associated with the connecting rod, with the Hall Effect sensor being fixedly placed in proximity of the connecting rod&#39;s large end such that the Hall Effect sensor has an output signal with a duration which is dependent upon the compression ratio state of the connecting rod. 
   It is an advantage of the present connecting rod that an engine compression ratio may be measured or determined in a robust manner so as to enable excellent control of the compression ratio of the engine. 
   It is a further advantage of the present invention that the present connecting rod allows provision of compression ratio control with less system weight and less complexity as compared with prior art mechanisms. 
   It is a further advantage of the present invention that the present connecting rod based compression ratio detecting system needs only a digital input, rather than a more costly analog input, for use with an engine control computer. 
   Other advantages, as well as objects and features of the present invention, will become apparent to the reader of this specification. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is an exploded perspective view of a connecting rod which may be used with a compression ratio sensing system according to the present invention. 
       FIG. 2  is a partially schematic representation of the connecting rod shown in  FIG. 1 , shown in a high compression ratio state. 
       FIG. 3  is a partially schematic representation of the connecting rod shown in  FIG. 1 , shown in a low compression ratio state. 
       FIG. 4  illustrates a portion of the orbital trajectories of the large end of the connecting rod of  FIG. 1 , corresponding to low and high compression ratio operating states. 
       FIG. 5  shows a pair of variable compression ratio connecting rods in a low compression ratio operating state. 
       FIG. 6  shows the connecting rods of  FIG. 5  in a high compression ratio operating state. 
       FIG. 7  is a block diagram illustrating one aspect of the present invention. 
       FIG. 8  illustrates a number of unique sensor signals corresponding operation at low, high, and mixed compression ratio states. 
   

   DETAILED DESCRIPTION 
   As shown in  FIG. 1 , connecting rod  10  according to the present invention has large end  22  adapted for attachment to crankshaft  6  (shown in  FIG. 2 ) of an engine, and small end  32  having a wrist pin bore  34  for attaching connecting rod  10  to an engine piston (not shown). Connecting rod cap  24  and screws  26  maintain connecting rod  10  in contact with a crankshaft journal in conventional fashion. 
   Primary link  38  extends between small end  32  and large end  22 . One end of primary link  38  is integral with small end  32 , and the other end  42  comprises a fork with two bores  44  which accept pin  50  so as to allow primary link  38  to be pivotably attached to large end  22 . Primary link  38  comprises one part of a four-bar link system extending between small end  32  and large end  22 . The second portion of the four-bar link is comprised by an adjustable toggle link which is formed by low compression link  56  and high compression link  76 . Beginning now with low compression link  56 , it is seen from  FIG. 1  that link  56  has a primary link engaging bore  58  which allows pivotal mounting upon pivot  46 , which is mounted within primary link  38 . This allows the adjustable toggle link to be pivotably attached to primary link  38 . The second end of low compression link  56  has a bore  62  which permits mounting upon eccentric  92  which is housed within large end  22  of connecting rod  10 . Eccentric  92  is mounted within a bore  96  formed in large end  22 . 
   As shown in  FIG. 1 , large end  22  has two bores,  102  and  104 , which comprise low compression lock pin bore  102  and high compression lock pin bore  104 . Oil arising from a passage in the crankshaft (not shown) and coming through a drilling in the crank journal at the edge of the bearing insert within large end  22  will proceed through passages and into bores  104  and  102 . Pressurized oil will cause the lock pin housed within bore  102  to be retracted, while at the same time the lock pin housed within bore  104  will be extended, so as to engage high compression link  76  (FIG.  1 ). As with low compression link  56 , high compression link  76  is pivotably attached to pivot post  46  on primary link  38  and is also pivotably attached to eccentric  94 , Which is housed within bore  96  in large end  22 . Screws  86  and  98  serve to mount high compression link  76  to low compression link  56 . Screw  98  serves to attach the two eccentric halves  92  and  94 . Details of the oil supply system are shown in U.S. Pat. No. 6,408,804, which is assigned to the assignee of the present invention, and which is hereby incorporated by reference, in its entirety, into this specification. 
     FIGS. 2 and 3  show the manner in which the configuration of connecting rod  10  changes as the connecting rod moves from a higher compression state to a lower compression state. In  FIG. 2 , primary link  38  is positioned such that the distance between the center of bore  8  (the large end bore) and the center of bore  34  (the small end bore) is at a maximum. In  FIG. 3 , however, primary link  38  is rotated with respect to large end  22  such that the distance between bores  8  and  34  is at a minimum. Thus, the resulting compression ratio is at a minimum. These compression ratio changes are accompanied by rotation of large end  22  about crankpin  6 , and this rotation can be used in conjunction with Hall Effect sensor  140  to determine the phase shift resulting from the compression ratio state change. 
   The geometry of connecting rod  10  is such that the boundary of the space through which large end  22  sweeps as crankshaft  6  rotates changes as the compression ratio is adjusted. This is shown in FIG.  4 . Thus, when connecting rod  10  is operating at a high compression ratio state, large end  22  sweeps through an orbit having a radius which is greater than the radius associated with the lower compression ratio state. As shown in  FIG. 4 , this geometrical change causes the pulse width of the output of sensor  140  to change. Thus, the pulse width indicates whether connecting rod  10  is operating in a higher compression state or a lower compression state. This is particularly useful for the case in which a single connecting rod  10  is attached to a single crankshaft journal. Those skilled in the art will appreciate in view of this disclosure that as an alternative, controller  500  ( FIG. 7 ) may measure the phase shift of the sensor&#39;s output with respect to the crankshaft&#39;s position. This may be accomplished, for example, by positioning Hall Effect sensor  140  such that the sensor will be triggered by one of the tabs  35  shown in FIG.  5 . By marking the location of the crankshaft whenever the Hall Effect sensor is triggered, the change in phase between the crankshaft position and the Hall Effect signal will readily disclose the compression ratio operating state. Thus, the timing of the Hall Effect pulse, and not its duration, may be used to determine the compression ratio operating state.  FIG. 8  shows the signal generated by a single sensor observing two connecting rods side by side. The falling edge phase tracks one rod&#39;s position, while the phase of the rising edge tracks the other rod&#39;s position. The pulse duration may also be used to determine if both rods are in the high compression state, or the low compression state, or if the rods are in opposite states. 
   The case of multiple connecting rods  10  attached to crankshaft  6  is shown in  FIGS. 5 and 6 . The connecting rods of  FIG. 5  are operating in a lower compression state, and this means that tabs  35 , which depend from large ends  22 , are in a converged configuration. The pulse from sensor  140  therefore has the shape shown in  FIG. 8  as trace “LCR”. In  FIG. 6 , connecting rods  10  are in the high compression state, and tabs  35  are splayed apart. The resultant pulse is labeled in Fig. as “HCR”. The traces labeled “MIX  1 ” and “MIX  2 ” correspond to cases in which one of connecting rods  10  is in the HCR mode and the other rod is in the LCR mode. In either case, engine controller  500  ( FIG. 7 ) will set a malfunction flag and attempt to use connecting rod actuator  506  to set connecting rods  10  to a default lower compression ratio state. It is easily seen from  FIG. 8  that connecting rod sensor  140  produces a unique signal for each of the possible connecting rod compression ratio states. This is important for the purpose of on board diagnostic (OBD) routines. 
   Engine controller  500  receives inputs from a number of sensors, shown at  502  in  FIG. 7 , including such sensors as those relating to crankshaft position, engine speed, camshaft position, engine coolant and ambient temperatures, throttle position, intake manifold pressure, and other engine operating parameters. The output of these sensors allows controller  500  to sense both the operating speed of the engine and the duration and phasing of the compression ratio state signal. These sensed values will be used to determine the compression ratio operating state of the engine, which may be controlled by means of connecting rod actuator  506 . In the case illustrated herein, connecting rod actuator  506  comprises the four-bar link system described herein and the valving and associated hardware described in U.S. Pat. No. 6,408,804, which has been incorporated by reference into this specification. 
   Although the present invention has been described in connection with particular embodiments thereof, it is to be understood that various modifications, alterations, and adaptations may be made by those skilled in the art without departing from the spirit and scope of the invention set forth in the following claims.