Patent Publication Number: US-10767571-B2

Title: Methods and system for operating an engine

Description:
FIELD 
     The present description relates to methods and a system for operating an internal combustion engine. The methods and systems may be particularly useful for reducing the possibility of engine knock. 
     BACKGROUND AND SUMMARY 
     An engine may include an actuator for changing the engine&#39;s compression ratio. By changing the engine&#39;s compression ratio, it may be possible to improve engine efficiency. In one example, a lower compression ratio may be provided in the engine at higher engine speeds and loads to reduce the possibility of engine knock. A higher compression ratio may be provided in the same engine at lower engine loads to increase engine efficiency when the possibility of engine knock is lower. The compression ratio may be set to an intermediate value that is between the high compression ratio and the low compression ratio when the engine is operated at intermediate load levels. However, even with variable compression, the engine may knock during some conditions. Therefore, it may be desirable to provide a way of reducing a possibility of engine knock for a variable compression ratio engine that includes an actuator to adjust the engine&#39;s compression ratio. 
     The inventors herein have recognized the above-mentioned issues and have developed an engine operating method, comprising: adjusting an engine&#39;s compression ratio via a controller responsive to present engine speed and engine load; forecasting a shifting of a transmission from a first gear to a second gear via the controller; and adjusting an engine&#39;s compression ratio via the controller responsive to an engine speed and engine load based on the forecasted shifting of the transmission. 
     By forecasting or predicting when a transmission shift is expected to occur, it may be possible to provide the technical result of reducing the possibility of engine knock that may be related to engine load changing as a result of a transmission gear shift. Specifically, the engine&#39;s compression ratio (CR) may be decreased before the transmission is upshifted so that the engine is at a lower compression ratio when the transmission gear shift completes so that an increase in engine load that results from the transmission gear shift may not cause engine knock. Conversely, the engine&#39;s compression ratio may be maintained at a lower level until a transmission gear shift is completed when the transmission is downshifted since the engine may operate with the lower compression ratio for a short period of time without engine efficiency degrading substantially. 
     The present description may provide several advantages. Specifically, the approach may provide improved engine knock control before and after transmission gear shifts. In addition, the approach forecasts or predicts transmission gear shifting events so that a compression ratio device may be operated to improve engine efficiency and mitigate engine knock. Further, the approach may reduce a possibility of driveline torque disturbances that may be caused by operating a compression ratio changing device while a transmission is shifting between fixed gear ratios. 
     The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages described herein will be more fully understood by reading an example of an embodiment, referred to herein as the Detailed Description, when taken alone or with reference to the drawings, where: 
         FIG. 1  is a schematic diagram of an engine; 
         FIG. 2  is a schematic diagram of a driveline that includes the engine of  FIG. 1 ; 
         FIGS. 3A and 3B  show an engine compression ratio changing linkage in two positions; 
         FIG. 4  shows a plot of an example transmission shift schedule; 
         FIG. 5  shows a plot of an example engine compression ratio map; 
         FIG. 6  shows a plot of an example engine operating sequence according to the method of  FIGS. 7-11 ; and 
         FIGS. 7-11  show a flowchart of an example method for operating a variable compression ratio engine. 
     
    
    
     DETAILED DESCRIPTION 
     The present description is related to operating a variable compression ratio engine and changing a compression ratio of an engine to reduce a possibility of engine knock and to reduce the possibility of driveline torque disturbances. The engine may be of the type shown in  FIG. 1  or it may be a diesel engine. The engine may be incorporated into a driveline with a transmission as shown in  FIG. 2 . The engine may include one or more cylinder compression ratio changing linkages as shown in  FIGS. 3A and 3B . The transmission may be shifted according to a shift schedule as shown in  FIG. 4 . The engine&#39;s compression ratio may be changed as indicated in the compression ratio map of  FIG. 5 . The engine may be operated according to the method of  FIGS. 7-11  to provide the operating sequence shown in  FIG. 6 . 
     Referring to  FIG. 1 , internal combustion engine  10 , comprising a plurality of cylinders, one cylinder of which is shown in  FIG. 1 , is controlled by electronic engine controller  12 . The controller  12  receives signals from the various sensors shown in  FIGS. 1-3B  and employs the actuators shown in  FIGS. 1-3B  to adjust engine and powertrain or driveline operation based on the received signals and instructions stored in memory of controller  12 . 
     Engine  10  is comprised of cylinder head  35  and block  33 , which include combustion chamber  30  and cylinder walls  32 . Piston  36  is positioned therein and it reciprocates with rod  117  via a connection to crankshaft  40 . Flywheel  97  and ring gear  99  are coupled to crankshaft  40 . Starter  96  (e.g., low voltage (operated with less than 30 volts) electric machine) includes pinion shaft  98  and pinion gear  95 . Pinion shaft  98  may selectively advance pinion gear  95  to engage ring gear  99 . Starter  96  may be directly mounted to the front of the engine or the rear of the engine. In some examples, starter  96  may selectively supply torque to crankshaft  40  via a belt or chain. In one example, starter  96  is in a base state when it is not engaged to the engine crankshaft  40 . 
     Combustion chamber  30  is shown communicating with intake manifold  44  and exhaust manifold  48  via respective intake valve  52  and exhaust valve  54 . Each intake and exhaust valve may be operated by an intake cam  51  and an exhaust cam  53 . The position of intake cam  51  may be determined by intake cam sensor  55 . The position of exhaust cam  53  may be determined by exhaust cam sensor  57 . Intake valve  52  may be selectively activated and deactivated by valve activation device  59 . Exhaust valve  54  may be selectively activated and deactivated by valve activation device  58 . Valve activation devices  58  and  59  may be electro-mechanical devices. 
     Fuel injector  66  is shown positioned to inject fuel directly into cylinder  30 , which is known to those skilled in the art as direct injection. Fuel injector  66  delivers liquid fuel in proportion to the pulse width from controller  12 . Fuel is delivered to fuel injector  66  by a fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown). In one example, a high pressure, dual stage, fuel system may be used to generate higher fuel pressures. 
     In addition, intake manifold  44  is shown communicating with turbocharger compressor  162  and engine air intake  42 . In other examples, compressor  162  may be a supercharger compressor. Shaft  161  mechanically couples turbocharger turbine  164  to turbocharger compressor  162 . Optional electronic throttle  62  adjusts a position of throttle plate  64  to control air flow from compressor  162  to intake manifold  44 . Pressure in boost chamber  45  may be referred to a throttle inlet pressure since the inlet of throttle  62  is within boost chamber  45 . The throttle outlet is in intake manifold  44 . In some examples, throttle  62  and throttle plate  64  may be positioned between intake valve  52  and intake manifold  44  such that throttle  62  is a port throttle. Compressor recirculation valve  47  may be selectively adjusted to a plurality of positions between fully open and fully closed. Waste gate  163  may be adjusted via controller  12  to allow exhaust gases to selectively bypass turbine  164  to control the speed of compressor  162 . Air filter  43  cleans air entering engine air intake  42 . 
     Distributorless ignition system  88  provides an ignition spark to combustion chamber  30  via ignition coil  89  and spark plug  92  in response to controller  12  spark timing signals. Universal Exhaust Gas Oxygen (UEGO) sensor  126  is shown coupled to exhaust manifold  48  upstream of catalytic converter  70 . Alternatively, a two-state exhaust gas oxygen sensor may be substituted for UEGO sensor  126 . 
     Engine torque may be adjusted via adjusting spark timing, fuel amount supplied via the fuel injectors, fuel timing, throttle plate position, intake and exhaust valve timing, boost pressure, spark energy, and the amount of air supplied to the engine. Thus, engine torque may be adjusted via adjusting operation of actuators such as ignition coil  89 , a position of throttle  62 , a position of waste gate  163 , a position of compressor recirculation valve  47 , intake valve activation device  59 , and exhaust valve activation device  58 . 
     Converter  70  can include multiple catalyst bricks, in one example. In another example, multiple emission control devices, each with multiple bricks, can be used. Converter  70  can be a three-way type catalyst in one example. 
     Controller  12  is shown in  FIG. 1  as a conventional microcomputer including: microprocessor unit  102 , input/output ports  104 , read-only memory  106  (e.g., non-transitory memory), random access memory  108 , keep alive memory  110 , and a conventional data bus. Controller  12  is shown receiving various signals from sensors coupled to engine  10 , in addition to those signals previously discussed, including: engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling sleeve  114 ; a position sensor  134  coupled to an accelerator pedal  130  for sensing force applied by human foot  132 ; a position sensor  154  coupled to brake pedal  150  for sensing force applied by human foot  132 , a measurement of engine manifold pressure (MAP) from pressure sensor  122  coupled to intake manifold  44 ; an engine position sensor from a Hall effect sensor  118  sensing crankshaft  40  position; a measurement of air mass entering the engine from sensor  120 ; and a measurement of throttle position from sensor  68 . Barometric pressure may also be sensed (sensor not shown) for processing by controller  12 . In a preferred aspect of the present description, engine position sensor  118  produces a predetermined number of equally spaced pulses every revolution of the crankshaft from which engine speed (RPM) can be determined. Further, controller  12  may communicate with human/machine interface  91  to indicate status of diagnostics and provide feedback to vehicle occupants. 
     During operation, each cylinder within engine  10  typically undergoes a four stroke cycle: the cycle includes the intake stroke, compression stroke, expansion stroke, and exhaust stroke. During the intake stroke, generally, the exhaust valve  54  closes and intake valve  52  opens. Air is introduced into combustion chamber  30  via intake manifold  44 , and piston  36  moves to the bottom of the cylinder so as to increase the volume within combustion chamber  30 . The position at which piston  36  is near the bottom of the cylinder and at the end of its stroke (e.g. when combustion chamber  30  is at its largest volume) is typically referred to by those of skill in the art as bottom dead center (BDC). 
     During the compression stroke, intake valve  52  and exhaust valve  54  are closed. Piston  36  moves toward the cylinder head so as to compress the air within combustion chamber  30 . The point at which piston  36  is at the end of its stroke and closest to the cylinder head (e.g. when combustion chamber  30  is at its smallest volume) is typically referred to by those of skill in the art as top dead center (TDC). In a process hereinafter referred to as injection, fuel is introduced into the combustion chamber. In a process hereinafter referred to as ignition, the injected fuel is ignited by known ignition means such as spark plug  92 , resulting in combustion. 
     During the expansion stroke, the expanding gases push piston  36  back to BDC. Crankshaft  40  converts piston movement into a rotational torque of the rotary shaft. Finally, during the exhaust stroke, the exhaust valve  54  opens to release the combusted air-fuel mixture to exhaust manifold  48  and the piston returns to TDC. Note that the above is shown merely as an example, and that intake and exhaust valve opening and/or closing timings may vary, such as to provide positive or negative valve overlap, late intake valve closing, or various other examples. 
       FIG. 2  is a block diagram of a vehicle  225  including a powertrain or driveline  200 . The powertrain of  FIG. 2  includes engine  10  shown in  FIG. 1 . Powertrain  200  is shown including vehicle system controller  255 , engine controller  12 , transmission controller  254 , and brake controller  250 . The controllers may communicate over controller area network (CAN)  299 . Each of the controllers may provide information to other controllers such as torque output limits (e.g., torque output of the device or component being controlled not to be exceeded), torque input limits (e.g., torque input of the device or component being controlled not to be exceeded), torque output of the device being controlled, sensor and actuator data, diagnostic information (e.g., information regarding a degraded transmission, information regarding a degraded engine, information regarding degraded brakes). Further, the vehicle system controller  255  may provide commands to engine controller  12 , transmission controller  254 , and brake controller  250  to achieve driver input requests and other requests that are based on vehicle operating conditions. 
     For example, in response to a driver releasing an accelerator pedal and vehicle speed, vehicle system controller  255  may request a desired wheel torque or a wheel power level to provide a desired rate of vehicle deceleration. The desired wheel torque may be provided by vehicle system controller  255  requesting a braking torque from brake controller  250 . 
     In other examples, the partitioning of controlling powertrain devices may be partitioned differently than is shown in  FIG. 2 . For example, a single controller may take the place of vehicle system controller  255 , engine controller  12 , transmission controller  254 , and brake controller  250 . Alternatively, the vehicle system controller  255  and the engine controller  12  may be a single unit while the transmission controller  254  and the brake controller  250  are standalone controllers. 
     In this example, powertrain  200  may be powered by engine  10 . Engine  10  may be started with an engine starting system shown in  FIG. 1 . Further, torque of engine  10  may be adjusted via torque actuator  204 , such as a fuel injector, throttle, etc. 
     An engine output torque may be transmitted to torque converter  206 . Torque converter  206  includes a turbine  286  to output torque to input shaft  270 . Transmission input shaft  270  mechanically couples torque converter  206  to automatic transmission  208 . Torque converter  206  also includes a torque converter bypass lock-up clutch  212  (TCC). Torque is directly transferred from impeller  285  to turbine  286  when TCC is locked. TCC is electrically operated by controller  254 . Alternatively, TCC may be hydraulically locked. In one example, the torque converter may be referred to as a component of the transmission. 
     When torque converter lock-up clutch  212  is fully disengaged, torque converter  206  transmits engine torque to automatic transmission  208  via fluid transfer between the torque converter turbine  286  and torque converter impeller  285 , thereby enabling torque multiplication. In contrast, when torque converter lock-up clutch  212  is fully engaged, the engine output torque is directly transferred via the torque converter clutch to an input shaft  270  of automatic transmission  208 . Alternatively, the torque converter lock-up clutch  212  may be partially engaged, thereby enabling the amount of torque that is relayed to the transmission to be adjusted. The transmission controller  254  may be configured to adjust the amount of torque transmitted by torque converter  212  by adjusting the torque converter lock-up clutch in response to various engine operating conditions, or based on a driver-based engine operation request. Torque converter  206  also includes mechanically driven pump  283  that pressurizes fluid to operate gear clutches  211 . Pump  283  is driven via impeller  285 , which rotates at a same speed as engine  10 . 
     Automatic transmission  208  includes gear clutches (e.g., gears  1 - 10 )  211  and forward clutch  210 . Automatic transmission  208  is a fixed step ratio transmission. The gear clutches  211  and the forward clutch  210  may be selectively engaged to change a ratio of an actual total number of turns of input shaft  270  to an actual total number of turns of wheels  216 . Gear clutches  211  may be engaged or disengaged via adjusting fluid supplied to the gear clutches via shift control solenoid valves  209 . Torque output from the automatic transmission  208  may also be relayed to wheels  216  to propel the vehicle via output shaft  260 . Specifically, automatic transmission  208  may transfer an input driving torque at the input shaft  270  responsive to a vehicle traveling condition before transmitting an output driving torque to the wheels  216 . Transmission controller  254  selectively activates or engages TCC  212 , gear clutches  211 , and forward clutch  210 . Transmission controller also selectively deactivates or disengages TCC  212 , gear clutches  211 , and forward clutch  210 . Transmission controller  254  removes pressurized fluid from gear clutches  211  when transmission  208  is engaged in park. Further, transmission controller  254  engages parking pawl  268  to reduce transmission shaft movement and vehicle movement when transmission shifter  213  is in a park position. A position of shifter (e.g., Park, neutral, or drive) may be indicated via shifter position sensor  214 . Parking pawl  268  may engage output shaft  260  or a gear within transmission  208  when transmission  208  is commanded to park. Actuator  267  may engage or disengage parking pawl  268  via commands sent via controller  12 . 
     Further, a frictional force may be applied to wheels  216  by engaging friction wheel brakes  218 . In one example, friction wheel brakes  218  may be engaged in response to the driver pressing their foot on a brake pedal (not shown) and/or in response to instructions within brake controller  250 . Further, brake controller  250  may apply brakes  218  in response to information and/or requests made by vehicle system controller  255 . In the same way, a frictional force may be reduced to wheels  216  by disengaging wheel brakes  218  in response to the driver releasing his foot from a brake pedal, brake controller instructions, and/or vehicle system controller instructions and/or information. For example, vehicle brakes may apply a frictional force to wheels  216  via controller  250  as part of an automated engine stopping procedure. 
     In response to a request to accelerate vehicle  225 , vehicle system controller may obtain a driver demand torque or power request from an accelerator pedal or other device. Vehicle system controller  255  then commands engine  10  in response to the driver demand torque. Vehicle system controller  255  requests the engine torque from engine controller  12 . If engine torque is less than a transmission input torque limit (e.g., a threshold value not to be exceeded), the torque is delivered to torque converter  206 , which then relays at least a fraction of the requested torque to transmission input shaft  270 . Transmission controller  254  selectively locks torque converter clutch  212  and engages gears via gear clutches  211  in response to shift schedules and TCC lockup schedules that may be based on input shaft torque and vehicle speed. 
     Accordingly, torque control of the various powertrain components may be supervised by vehicle system controller  255  with local torque control for the engine  10 , transmission  208 , and brakes  218  provided via engine controller  12 , transmission controller  254 , and brake controller  250 . 
     As one example, an engine torque output may be controlled by adjusting a combination of spark timing, fuel pulse width, fuel pulse timing, and/or air charge, by controlling throttle opening and/or valve timing, valve lift and boost for turbo- or super-charged engines. In the case of a diesel engine, controller  12  may control the engine torque output by controlling a combination of fuel pulse width, fuel pulse timing, and air charge. In all cases, engine control may be performed on a cylinder-by-cylinder basis to control the engine torque output. 
     Transmission controller  254  receives transmission input shaft position via position sensor  271 . Transmission controller  254  may convert transmission input shaft position into input shaft speed via differentiating a signal from position sensor  271  or counting a number of known angular distance pulses over a predetermined time interval. Transmission controller  254  may receive transmission output shaft torque from torque sensor  272 . Alternatively, sensor  272  may be a position sensor or torque and position sensors. If sensor  272  is a position sensor, controller  254  may count shaft position pulses over a predetermined time interval to determine transmission output shaft velocity. Transmission controller  254  may also differentiate transmission output shaft velocity to determine transmission output shaft acceleration. Transmission controller  254 , engine controller  12 , and vehicle system controller  255 , may also receive addition transmission information from sensors  277 , which may include but are not limited to pump output line pressure sensors, transmission hydraulic pressure sensors (e.g., gear clutch fluid pressure sensors), and ambient temperature sensors. 
     Brake controller  250  receives wheel speed information via wheel speed sensor  223  and braking requests from vehicle system controller  255 . Brake controller  250  may also receive brake pedal position information from brake pedal sensor  154  shown in  FIG. 1  directly or over CAN  299 . Brake controller  250  may provide braking responsive to a wheel torque command from vehicle system controller  255 . Brake controller  250  may also provide anti-skid and vehicle stability braking to improve vehicle braking and stability. As such, brake controller  250  may provide a wheel torque limit (e.g., a threshold negative wheel torque not to be exceeded) to the vehicle system controller  255 . 
       FIGS. 3A and 3B  show a cylinder compression ratio changing linkage that changes a compression ratio of an engine  10 .  FIG. 3A  shows compression ratio changing linkage  300  in a first position that increases a compression ratio of cylinder  30 .  FIG. 3B  shows compression ratio changing linkage  300  in a second position that decreases a compression ratio of cylinder  30 . Controller  12  may include non-transitory executable instructions to operate the cylinder compression ratio changing linkage at the positions shown and other positions to adjust the engine&#39;s compression ratio. 
     Connecting rod  117  is shown mechanically coupled to upper link  303  via connecting pin  302 . Upper link  303  is coupled to crankpin  304  and crankpin  304  is part of crankshaft  40 . Crank journal  318  is supported via engine block  33  and crankpin  304  is offset from crank journal  318 . Upper link  303  is mechanically coupled to lower link  315  via connecting pin  306 . Lower link  315  is mechanically coupled to control link  316  via connecting pin  308 . Motor  312  is mechanically coupled to control link  316  via connecting pin  309 . Shaft  310  of motor  312  may selectively rotate clockwise or counter clockwise to advance or retract control link  316 . Controller  12  may selectively supply electric current to motor  312  and electric current may be monitored via current sensor  350   c . Current that is supplied to motor  312  to maintain a position of control link  316  may be indicative of force applied to rod  117  since rod  117  is mechanically coupled to control link  316 . Thus, motor  312  may be applied as a force sensor coupled to control link  316 . In some examples, strain gauge  350   b  may be mechanically coupled to lower control line  315  to determine force applied to rod  117 . Alternatively, strain gauge  350   a  may be mechanically coupled to control link  316  to determine force applied to rod  117 . 
       FIG. 3A  shows control link  316  in an extended state via motor shaft  310  rotating counter clockwise, which causes upper link  303  to rotate, thereby changing an angle between rod  117  and upper link  303 .  FIG. 3B  shows control link  316  in a retracted state via motor shaft  310  rotating clockwise, which causes upper link  303  to rotate and change the angle between rod  117  and upper link  303 .  FIG. 3A  shows compression ratio changing linkage  300  in a high compression state (e.g., 14:1 compression ratio) and  FIG. 3B  shows compression ratio changing linkage  300  in a low compression state (e.g., 8:1 compression ratio). 
     Thus, the system of  FIGS. 1-3B  provides for a vehicle system, comprising: an engine including a compression ratio adjustment linkage; an automatic transmission coupled to the engine; and a controller including executable instructions stored in non-transitory memory to change the engine&#39;s compression ratio via the compression ratio adjustment linkage according to an increasing or decreasing accelerator pedal position and a forecast gear shifting of the automatic transmission from a first gear to a second gear. The system further comprises additional instructions to change the engine&#39;s compression ratio before shifting the automatic transmission from the first gear to the second gear. The system includes where changing the engine&#39;s compression ratio includes decreasing the engine&#39;s compression ratio. The system further comprises additional instructions to change the engine&#39;s compression ratio immediately after shifting the automatic transmission from the first gear to the second gear. The system includes where changing the engine&#39;s compression ratio includes increasing the engine&#39;s compression ratio. The system includes where forecasting the shifting of the transmission includes anticipating an accelerator pedal position and anticipating a vehicle speed. 
     Referring now to  FIG. 4 , a plot of an example transmission gear shifting schedule is shown. The vertical axis represents accelerator pedal position and the accelerator pedal position increases (e.g., is further applied or depressed) in the direction of the vertical axis arrow. The horizontal axis represents vehicle speed and vehicle speed increases in the direction of the horizontal axis arrow. 
     Solid lines  402 ,  404 ,  406 ,  409 , and  410  are transmission gear upshift lines and dot-dot-dash lines  401 ,  403 ,  405 ,  407 , and  408  are transmission gear downshift lines. Specifically, line  402  is an upshift curve for a 1&gt;2 gear shift. Line  404  is an upshift curve for a 2&gt;3 gear shift. Line  406  is an upshift line for a 3&gt;4 gear shift. Line  409  is an upshift curve for a 4&gt;5 gear shift. Line  410  is an upshift curve for a 5&gt;6 gear shift. Line  401  is a downshift curve for a 2&gt;1 gear shift. Line  403  is a downshift curve for a 3&gt;2 gear shift. Line  405  is a downshift curve for a 4&gt;3 gear shift. Line  407  is a downshift curve for a 5&gt;4 gear shift. Line  408  is a downshift curve for a 6&gt;5 gear shift. 
     The transmission is upshifted if the intersection of accelerator pedal position and vehicle speed at the present time intersects an upshift curve. The transmission is downshifted if the intersection of accelerator pedal position and vehicle speed at the present time intersects with a downshift curve. 
       FIG. 4  shows how a change in accelerator pedal position and vehicle speed may be used to forecast, anticipate, or predict a gear shift. In particular, if accelerator pedal position and vehicle speed intersect at point  450  at a first time and a short time later accelerator pedal position and vehicle speed intersect at  451 , then the rate of change of accelerator pedal position and vehicle speed may be used to predict that accelerator pedal position and vehicle speed will be at point  453  at a future time. Line  452  is an extension of the line between points  450  and  451 , which allows a prediction of vehicle speed and accelerator pedal position reaching point  453 . The time that line  452  intersects with line  405  is a time when the transmission is expected, predicted, or anticipated to downshift in response to accelerator pedal position and vehicle speed. Thus, if a gear shift prediction is based on the accelerator pedal moving from point  450  to  451 , then a downshift from 4&gt;3 is predicted. The method of  FIG. 7  explains the gear shift prediction in greater detail. 
     Referring now to  FIG. 5 , an example engine compression ratio map is shown. In this example, the engine compression ratio is adjusted based on engine load and engine speed. However, in other examples, the engine compression ratio may be adjusted responsive to other engine parameters (e.g., engine torque and engine speed). 
     The vertical axis represents engine load (e.g., the actual air mass flowing through the engine divided by the theoretical maximum air mass flowing through the engine) and engine load increases in the direction of the vertical axis arrow. The horizontal axis represents engine speed and engine speed increases in the direction of the horizontal axis arrow. 
     At lower engine speeds and loads the engine (e.g., region  501 ) the engine is operated with a higher compression ratio (e.g., 14:1). At higher engine speeds and loads the engine (e.g., region  503 ) the engine is operated with a lower compression ratio (e.g., 8:1). At medium engine speeds and loads the engine (e.g., region  505 ) the engine is operated with an intermediate compression ratio (e.g., between 14:1 and 8:1). 
     Referring now to  FIG. 6 , plot showing a prophetic engine operating sequence is shown. The sequence of  FIG. 6  may be provided via the system of  FIGS. 1-3B  in cooperation with the method of  FIGS. 7-11 . The plots of  FIG. 6  are time aligned and they occur at the same time. Vertical lines at time t 0 -t 10  represent times of interest in the sequence. Controller  12  may include non-transitory executable instructions to operate the engine at the conditions shown and discussed in the description of  FIG. 6 . 
     The first plot of  FIG. 6  is a plot of accelerator pedal position versus time. The vertical axis represents accelerator pedal position and the accelerator pedal position increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Curve  602  represents accelerator pedal position. 
     The second plot of  FIG. 6  is a plot of engine load versus time. The vertical axis represents engine load and engine load increases in the direction of the vertical axis arrow. Trace  604  represents engine load. Engine load may be represented as a value that ranges from 0 to 1, where 0 is no engine load and 1 is full engine load. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The third plot of  FIG. 6  is a plot of forecasted, predicted, or anticipated transmission gear method versus time. The vertical axis represents forecasted, predicted, or anticipated transmission gear and the forecasted, predicted, or anticipated transmission gear are indicated along the vertical axis. Trace  606  represents forecasted, predicted, or anticipated transmission gear. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fourth plot of  FIG. 6  is a plot of engaged transmission gear versus time. The vertical axis represents engaged transmission and the engaged transmission is indicated along the vertical axis. Trace  608  represents engaged transmission. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fifth plot of  FIG. 6  is a plot of engine compression ratio (CR) versus time. The vertical axis represents engine compression ratio and engine compression ratio increases in the direction of the vertical axis arrow. Trace  610  represents engine compression ratio. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     At time t 0 , the accelerator pedal is depressed a large amount and the engine load is high. The forecast transmission gear ratio is 4 th  gear and the engaged transmission gear is 4 th  gear. The engine compression ratio is set to a low value to reduce the possibility of engine knock. 
     At time t 1 , the human driver (not shown) begins to release the accelerator pedal (e.g., a tip-out condition) and the engine load begins to decline as the engine&#39;s throttle (not shown) is closed in response to the accelerator pedal position. The forecast transmission gear and engaged transmission gear remain unchanged and the engine compression ratio remains low. 
     At time t 2 , the forecast transmission gear changes from 4 th  gear to 6 th  gear indicating that an upshift is expected. The transmission gear change is forecast as described in greater detail in the description of method  700 . The accelerator pedal position and the engine load continue to decline and the transmission is still engaged in 4 th  gear. The engine compression ratio is unchanged. 
     At time t 3 , the engaged transmission gear changes from 4 th  gear to 6 th  gear. The forecast transmission gear remains 6 th  gear and the engine compression ratio is maintained at a low level even though engine load is decreasing so that no change in compression ratio is made during the transmission gear shift. This may reduce the possibility of driveline torque disturbances. The engine load is increased briefly since the gear change causes a reduction in engine speed and an increase in engine load to maintain engine torque. The compression ratio begins to change to a high compression ratio after the gear shift is complete so that engine efficiency may be increased. 
     Between time t 3  and time t 4 , the engine compression ratio is changed from the low compression ratio to the high compression ratio. The accelerator pedal position and engine load finish declining and then remain at a low level. The transmission remains engaged in 6 th  gear and the forecast transmission gear remains 6 th  gear. 
     At time t 4 , the vehicle speed is declining (not shown) so the transmission is forecast to downshift to 5 th  gear. The accelerator pedal remains not applied and engine load remains low. The transmission remains engaged in 6 th  gear and the engine compression ratio remains high. 
     At time t 5 , the transmission engaged gear changes from 6 th  to 5 th  and gear change decreases the engine load by a small amount since engine speed is increased and engine torque (not shown) is maintained. The accelerator pedal position remains unchanged and the forecast transmission gear remains 5 th  gear. The engine compression ratio remains high. 
     At time t 6 , the vehicle speed continues declining (not shown) so the transmission is forecast to downshift to 4 th  gear. The accelerator pedal remains not applied and engine load remains low. The transmission remains engaged in 5 th  gear and the engine compression ratio remains high. 
     At time t 7 , the transmission engaged gear changes from 5 th  to 4 th  and gear change decreases the engine load by a small amount since engine speed is increased and engine torque (not shown) is maintained. The accelerator pedal position remains unchanged and the forecast transmission gear remains 4 th  gear. The engine compression ratio remains high. 
     Between time t 7  and time t 8 , the forecast transmission gear changes from 4 th  gear to 3 rd  gear, but 3 rd  gear is not engaged in the transmission. The accelerator pedal position remains unchanged and the engine load remains low after it changed due to the gear shift at time t 7 . 
     At time t 8 , the human driver begins to apply the accelerator pedal and the engine load begins to increase. The forecast transmission gear changes from 3 rd  gear to 4 th  gear and the transmission remains engaged in 4 th  gear. The engine compression ratio remains high, but it is adjusted to a lower level based on engine speed (not shown) and load. 
     At time t 9 , the accelerator pedal position continues to increase and the engine load continues to increase. The transmission is forecast to upshift to 5 th  gear and the transmission remains engaged in 4 th  gear. The engine compression ratio begins to be adjusted to a lowest level based on the forecasted transmission gear and the accelerator pedal position. The forecasted transmission gear is an upshift so that the upshift will result in a low engine speed and a higher engine load to maintain a level of engine torque before the upshift. Lowering the engine compression ratio may reduce the possibility of engine knock that may occur due to the transmission gear shift. The engine compression ratio is lowered before the forecast transmission gear is engaged so that the engine may not knock as a result of the transmission gear change. 
     At time t 10 , 5 th  gear is engaged in the transmission and the engine load is increased due to the transmission being upshifted while the accelerator pedal position is increasing. The engine is operating with a low compression ratio and the forecast transmission gear remains 5 th  gear. 
     In this way, the engine compression ratio may be changed after a gear shift when the gear shift is expected to increase engine load and the engine is operating with a low compression ratio before the gear shift. Alternatively, the engine compression ratio may be changed before the gear shift when the gear shift is expected to increase engine load and the engine is operating with a high compression ratio before the gear change so that the possibility of engine knock may be avoided. 
     Referring now to  FIG. 7 , a flowchart for operating an engine is shown. At least portions of the method of  FIG. 7  may be incorporated as executable instructions stored in non-transitory memory of the system shown in  FIGS. 1-3B . Additionally, portions of the method of  FIG. 7  may take place in the physical world as operations or actions performed by a controller to transform an operating state of one or more devices. Some of the control parameters described herein may be determined via receiving input from the sensors and actuators described herein. The method of  FIG. 7  may also provide the operating sequence shown in  FIG. 6 . Further, the engine may be operated at the conditions mentioned in method  700 . The engine controller may also include executable instructions stored in non-transitory memory to operate the engine at the conditions mentioned in method  700 . 
     At  702 , method  700  determines vehicle operating conditions including but not limited to vehicle speed, accelerator pedal position, engine speed, engine load, and engine temperature. The various vehicle operating conditions may be determined via sensors. Method  700  proceeds to  704 . 
     At  704 , method  700  judges whether or not accelerator pedal position is increasing (e.g., is being applied further). In one example, method  700  may compute a derivative of accelerator pedal position from accelerator pedal sensor output taken at two different times. If the sign of the derivative is positive, method  700  may determine that the accelerator pedal position is increasing. If method  700  determines that accelerator pedal position is increasing, the answer is yes and method  700  proceeds to  720  of  FIG. 8 . Otherwise, method  700  proceeds to  706 . 
     At  706 , method  700  judges whether or not accelerator pedal position is decreasing (e.g., is being at least partially released). If the sign of the derivative of accelerator pedal position determined at  704  is negative, method  700  may determine that the accelerator pedal position is decreasing. If method  700  determines that accelerator pedal position is decreasing, the answer is yes and method  700  proceeds to  740  of  FIG. 9 . Otherwise, method  700  proceeds to  708 . 
     At  708 , method forecasts, predicts, or anticipates a next gear to be engaged by the transmission. In one example, accelerator pedal position and vehicle speed are measured at a first time (e.g., accelerator pedal position=200 counts and vehicle speed=30 Kph). Further, method  700  measures accelerator pedal position and vehicle speed at a second time (e.g., accelerator pedal position=300 counts and vehicle speed=32 Kph). Then, method  700  determines the rate of change of accelerator pedal position and the rate of vehicle speed change between the two points. In this example, the rate of change of accelerator position is 100 counts/second (e.g., (300−200 counts)/1 second) when the time between samples is 1 second. The rate of vehicle acceleration change is 2 Kph/second (32−30 Kph/1 second). 
     The next transmission gear may be forecast at a predetermined time in the future (e.g., 2 seconds from the present time). In one example, the predetermined amount of time is an amount of time it takes for the compression ratio actuator to change the engine&#39;s compression ratio by a specified amount (e.g., the full range of authority 8:1 to 14:1 or a partial range of authority 8:1 to 12:1, or vice-versa). Consequently, if it takes the compression ratio two seconds to fully advance, then method  700  forecasts a transmission gear ratio two seconds into the future by extending the line between the two presently measured points (e.g., 200 counts/30 Kph and 300 counts/32 Kph) two seconds into the future. Since it is been determined that the accelerator pedal position is changing by 100 counts/second, the accelerator pedal position two seconds in the future is 300 counts+2 seconds(100 counts/second)=500 counts. Similarly, the vehicle speed two seconds into the future is 32 Kph+2(2 Kph/sec)=36 Kph. If the intersection of the forecasted accelerator pedal position and the forecasted vehicle speed in the shift schedule crosses an upshift curve or downshift curve, then the forecast transmission gear is the gear described by the upshift curve or the downshift curve. If the intersection of the forecasted accelerator pedal position and the forecasted vehicle speed crosses more than one upshift curve or one downshift curve, then the forecast transmission gear is the gear described by the upshift curve or downshift curve that is closest to the forecasted accelerator pedal position and the forecasted vehicle speed at the predetermined amount of time in the future. For example, if the transmission is engaged in fourth gear and the forecast accelerator pedal position and vehicle acceleration passes through a boundary of the 4&gt;3 downshift curve, then the transmission gear forecast by method  700  is 3 rd  gear. Conversely, if the transmission is engaged in fourth gear and the forecast accelerator pedal position and vehicle acceleration passes through a boundary of the 4&gt;5 upshift curve, then the transmission gear forecast by method  700  is 5 th  gear.  FIG. 4  shows this concept graphically via points  450 ,  451 , and  453 . If the transmission is engaged in fourth gear and the forecast accelerator pedal position and vehicle acceleration do not pass through a boundary of an upshift curve or a downshift curve, then the transmission gear forecast by method  700  remains the presently engaged gear. Method  700  proceeds to  710  after forecasting the transmission gear. 
     At  710 , method  700  judges whether or not a transmission gear downshift is forecast within a predetermined amount of time (e.g., the predetermined amount of time described at  708 ). If so, the answer is yes and method  700  proceeds to  750  of  FIG. 10 . Otherwise, method  700  proceeds to  712 . 
     At  712 , method  700  judges whether or not a transmission gear upshift is forecast within a predetermined amount of time (e.g., the predetermined amount of time described at  708 ). If so, the answer is yes and method  700  proceeds to  770  of  FIG. 11 . Otherwise, method  700  proceeds to  714 . 
     At  714 , method  700  adjusts the engine compression ratio responsive to engine speed and load. In one example, method  700  adjusts the engine compression ratio to a compression ratio that is defined in a map as shown in  FIG. 5 . The engine compression ratio may be adjusted via an actuator as shown in  FIGS. 3A and 3B  and controller  12 . Thus, as engine speed and load vary, the engine compression ratio may be increased or decreased to improve engine efficiency. Method  700  proceeds to exit. 
     At  720 , method  700  forecasts, predicts, or anticipates a next gear to be engaged by the transmission. In one example, forecasts a next transmission gear as described at  708 . Method  700  proceeds to  721  after forecasting the transmission gear. 
     At  721 , method  700  judges whether or not a transmission gear upshift is forecast within a predetermined amount of time (e.g., the predetermined amount of time described at  708 ). If so, the answer is yes and method  700  proceeds to  722 . Otherwise, method  700  proceeds to  730 . 
     At  722 , method  700  estimates what the engine load and engine speed will be immediately following the forecasted upshift. In one example, method  700  estimates the engine speed immediately following the forecasted upshift by dividing the vehicle speed that is forecasted immediately following the upshift (e.g., the vehicle speed forecast at  720 ) by the combined ratio of the forecasted gear and the vehicle&#39;s axle. The result is then divided by the distance the tire travels in a single rotation. The forecast engine load may be determined via a lookup table that is referenced by engine speed and engine torque immediately before the gear shift. The engine load output from the table is modified for engine air-fuel ratio and spark timing. For example, forecast engine load=ƒ(forecast_engine_speed, engine_torque), where ƒ is a function that outputs empirically determined values of engine torque, forecast_engine_speed is forecasted engine speed (e.g., engine speed immediately following the shift), and engine_torque is engine torque immediately before the shift). In one example, the values in the function ƒ may be determined via operating the engine connected to a dynamometer and monitoring engine speed, engine load, and engine torque. Method  700  proceeds to  723  after determining the forecasted engine speed and load values. 
     At  723 , method  700  determines forecast engine compression ratio at the predetermined time in the future. The forecast engine compression ratio is based on the forecast engine load and speed that were determined at  722 . In one example, the forecast engine load and speed are applied as indexes or reference values into an engine compression ratio map (e.g., as shown in  FIG. 5 ) and the engine compression ratio map outputs an engine compression ratio value. The operation may be expressed as engine CR=ENG_CR(forecast engine speed, forecast engine load), where CR is the forecast engine compression ratio, ENG_CR is an engine compression ratio map, and forecast engine speed and load are arguments for referencing the function or table ENG_CR. Method  700  proceeds to  724 . 
     At  724 , method  700  estimates an amount of time it will take to move the engine&#39;s compression ratio from its present value to the forecast engine compression ratio at the predetermined time in the future. In one example, a function describing movement of the engine compression ratio is referenced by the change in the engine compression ratio from its present value to its forecasted value. For example, if the present engine compression ratio is 8:1 and the forecasted engine compression ratio is 10:1, the function describing movement of the engine compression ratio is referenced or indexed via a value of 2:1 (e.g., 10:1−8:1=2:1). The operation may be described as amount of time to change engine compression ratio=CR_time (CR_Δ), where CR_time is a function that outputs an amount of time to change the engine compression ratio and CR_Δ is the change in compression ratio (e.g., 2:1). The values in the function CR_time may be determined via operating the engine, demanding a compression ratio change, and recording an amount of time it takes for the compression ratio changing device to change the engine&#39;s compression ratio from its initial value to its demanded value. Method  700  proceeds to  725  after the time to change the engine&#39;s compression ratio is estimated. 
     At  725 , method  700  begins to change the engine&#39;s compression ratio from its present value to the forecasted value when the amount of time to the beginning of the forecasted transmission shift is equal to the time it takes to move the engine compression ratio from its present value to the forecasted engine compression ratio (e.g., the engine compression ratio based on engine speed and load immediately following the upshift) plus a threshold amount of time. For example, if it takes 0.5 seconds to move the engine&#39;s compression ratio from its present value of 14:1 to the forecasted engine compression ratio of 8:1 (e.g., the engine compression ratio that is based on engine speed and load that immediately follows the present upshift), and the forecasted transmission upshift is 2 seconds in the future, then the engine compression ratio begins to change 1.5 seconds in the future minus the threshold amount of time (e.g., an amount of time to ensure that the compression ratio change is complete (e.g., 0.1 second)). Thus, if the transmission is forecast to shift 2 seconds in the future from the present time, it takes 0.5 seconds to change the engine compression ratio, and the threshold amount of time is 0.1 seconds, then the compression ratio begins to change to the forecast value 1.4 seconds in the future. The compression ratio change is completed before the transmission upshifts to reduce the possibility of engine knock. Method  700  proceeds to  726 . 
     At  726 , method  700  shifts the transmission to the forecasted or new gear when the engine speed and accelerator pedal position intersect a shift curve in the transmission shift schedule. Method  700  proceeds to exit after upshifting the transmission. 
     At  730 , method  700  judges whether or not a transmission gear downshift is forecast within a predetermined amount of time (e.g., the predetermined amount of time described at  708 ). If so, the answer is yes and method  700  proceeds to  731 . Otherwise, method  700  proceeds to  736 . 
     At  731 , method  700  estimates what the engine load and engine speed will be immediately following the forecasted downshift. In one example, method  700  estimates the engine speed immediately following the forecasted upshift by dividing the vehicle speed that is forecasted immediately following the upshift (e.g., the vehicle speed forecast at  720 ) by the combined ratio of the forecasted gear and the vehicle&#39;s axle. The result is then divided by the distance the tire travels in a single rotation. The forecast engine load may be determined via a lookup table that is referenced by engine speed and engine torque immediately before the gear shift. The engine load output from the table is modified for engine air-fuel ratio and spark timing. For example, forecast engine load=ƒ(forecast_engine_speed, engine_torque), where ƒ is a function that outputs empirically determined values of engine torque, forecast_engine_speed is forecasted engine speed (e.g., engine speed immediately following the shift), and engine_torque is engine torque immediately before the shift). In one example, the values in the function ƒ may be determined via operating the engine connected to a dynamometer and monitoring engine speed, engine load, and engine torque. Method  700  proceeds to  732  after determining the forecasted engine speed and load values. 
     At  732 , method  700  determines forecast engine compression ratio at the predetermined time in the future. The forecast engine compression ratio is based on the forecast engine load and speed that were determined at  731 . In one example, the forecast engine load and speed are applied as indexes or reference values into an engine compression ratio map (e.g., as shown in  FIG. 5 ) and the engine compression ratio map outputs an engine compression ratio value. The operation may be expressed as engine CR=ENG_CR(forecast engine speed, forecast engine load), where CR is the forecast engine compression ratio, ENG_CR is an engine compression ratio map, and forecast engine speed and load are arguments for referencing the function or table ENG_CR. Method  700  proceeds to  733 . 
     At  733 , method  700  estimates an amount of time it will take to move the engine&#39;s compression ratio from its present value to the forecast engine compression ratio at the predetermined time in the future. In one example, a function describing movement of the engine compression ratio is referenced as previously described by the change in the engine compression ratio from its present value to its forecasted value. Method  700  proceeds to  734  after the time to change the engine&#39;s compression ratio is estimated. 
     At  734 , method  700  begins to change the engine&#39;s compression ratio from its present value to the forecasted value when the amount of time to the beginning of the forecasted transmission downshift is equal to the time it takes to move the engine compression ratio from its present value to the forecasted engine compression ratio (e.g., the engine compression ratio based on engine speed and load immediately following the upshift) plus a threshold amount of time. Thus, if the transmission is forecast to shift 2 seconds in the future from the present time, it takes 0.5 seconds to change the engine compression ratio, and the threshold amount of time is 0.1 seconds, then the compression ratio begins to change to the forecast value 1.4 seconds in the future. The compression ratio change is completed before the transmission downshifts to reduce the possibility of engine knock. Method  700  proceeds to  735 . 
     At  735 , method  700  shifts the transmission to the forecasted or new gear when the engine speed and accelerator pedal position intersect a shift curve in the transmission shift schedule. Method  700  proceeds to exit after downshifting the transmission. 
     At  736 , method  700  adjusts the engine compression ratio responsive to engine speed and load. In one example, method  700  adjusts the engine compression ratio to a compression ratio that is defined in a map as shown in  FIG. 5 . The engine compression ratio may be adjusted via an actuator as shown in  FIGS. 3A and 3B  and controller  12 . Thus, as engine speed and load vary, the engine compression ratio may be increased or decreased to improve engine efficiency. Method  700  proceeds to exit. 
     At  740 , method  700  forecasts, predicts, or anticipates a next gear to be engaged by the transmission. In one example, forecasts a next transmission gear as described at  708 . Method  700  proceeds to  741  after forecasting the transmission gear. 
     At  741 , method  700  judges whether or not a transmission gear upshift is forecast within a predetermined amount of time (e.g., the predetermined amount of time described at  708 ). If so, the answer is yes and method  700  proceeds to  742 . Otherwise, method  700  proceeds to  747 . 
     At  742 , method  700  estimates what the engine load and engine speed will be immediately following the forecasted upshift. In one example, method  700  estimates the engine speed immediately following the forecasted upshift by dividing the vehicle speed that is forecasted immediately following the upshift (e.g., the vehicle speed forecast at  720 ) by the combined ratio of the forecasted gear and the vehicle&#39;s axle. The result is then divided by the distance the tire travels in a single rotation. The forecast engine load may be determined via converting accelerator pedal position into an engine torque via a function of accelerator pedal position and vehicle speed at the predetermined time in the future. Once the forecast engine torque is determined, forecast engine load may be determined via a function or table that describes forecast engine load as a function of forecast engine speed and forecast engine torque. Method  700  proceeds to  743  after determining the forecasted engine speed and load values. 
     At  743 , method  700  determines forecast engine compression ratio at the predetermined time in the future. The forecast engine compression ratio is based on the forecast engine load and speed that were determined at  742 . In one example, the forecast engine load and speed are applied as indexes or reference values into an engine compression ratio map (e.g., as shown in  FIG. 5 ) and the engine compression ratio map outputs an engine compression ratio value. Method  700  proceeds to  744 . 
     At  744 , method  700  prevents the engine compression ratio from changing beginning a predetermined amount of time before the forecast transmission gear shift. For example, if the forecast transmission gear shift is in 2 seconds, the engine compression ratio may not be adjusted within 0.5 seconds of the forecasted transmission gear shift. This may reduce the possibility of driveline torque disturbances during the gear shift. Method  700  proceeds to  745 . 
     At  745 , method  700  shifts the transmission to the forecasted or new gear when the engine speed and accelerator pedal position intersect a shift curve in the transmission shift schedule. Method  700  proceeds to  746  after upshifting the transmission. 
     At  746 , method  700  begins to change the engine&#39;s compression ratio from its present value based on the present engine speed and engine load after the forecasted transmission upshift. Method  700  proceeds to exit after adjusting the engine compression ratio. 
     At  747 , method  700  adjusts the engine compression ratio responsive to engine speed and load. In one example, method  700  adjusts the engine compression ratio to a compression ratio that is defined in a map as shown in  FIG. 5 . The engine compression ratio may be adjusted via an actuator as shown in  FIGS. 3A and 3B  and controller  12 . Thus, as engine speed and load vary, the engine compression ratio may be increased or decreased to improve engine efficiency. Method  700  proceeds to exit. 
     At  750 , method  700  judges whether or not engine load is less than a threshold engine load. If so, the answer is yes and method  700  proceeds to  751 . Otherwise, method  700  proceeds to  760 . 
     At  751 , method  700  prevents the engine compression ratio from changing beginning a predetermined amount of time before the forecast transmission gear shift. For example, if the forecast transmission gear shift is in 2 seconds, the engine compression ratio may not be adjusted within 0.5 seconds of the forecasted transmission gear shift. This may reduce the possibility of driveline torque disturbances during the gear shift. Method  700  proceeds to  752 . 
     At  752 , method  700  shifts the transmission to the forecasted or new gear when the engine speed and accelerator pedal position intersect a shift curve in the transmission shift schedule. Method  700  proceeds to  753  after downshifting the transmission. 
     At  753 , method  700  begins to change the engine&#39;s compression ratio from its present value based on the present engine speed and engine load after the forecasted transmission downshift. Method  700  proceeds to exit after adjusting the engine compression ratio. 
     At  760 , method  700  estimates what the engine load and engine speed will be immediately following the forecasted downshift. In one example, method  700  estimates the engine speed immediately following the forecasted upshift by dividing the vehicle speed that is forecasted immediately following the upshift (e.g., the vehicle speed forecast at  720 ) by the combined ratio of the forecasted gear and the vehicle&#39;s axle. The result is then divided by the distance the tire travels in a single rotation. The forecast engine load may be determined via converting accelerator pedal position into an engine torque via a function of accelerator pedal position and vehicle speed at the predetermined time in the future. Once the forecast engine torque is determined, forecast engine load may be determined via a function or table that describes forecast engine load as a function of forecast engine speed and forecast engine torque. Method  700  proceeds to  761  after determining the forecasted engine speed and load values. 
     At  761 , method  700  determines forecast engine compression ratio at the predetermined time in the future. The forecast engine compression ratio is based on the forecast engine load and speed that were determined at  760 . In one example, the forecast engine load and speed are applied as indexes or reference values into an engine compression ratio map (e.g., as shown in  FIG. 5 ) and the engine compression ratio map outputs an engine compression ratio value. Method  700  proceeds to  762 . 
     At  762 , method  700  estimates an amount of time it will take to move the engine&#39;s compression ratio from its present value to the forecast engine compression ratio at the predetermined time in the future. In one example, a function describing movement of the engine compression ratio is referenced by the change in the engine compression ratio from its present value to its forecasted value. The operation may be described as amount of time to change engine compression ratio=CR_time (CR_Δ), where CR_time is a function that outputs an amount of time to change the engine compression ratio and CR_Δ is the change in compression ratio (e.g., 2:1). The values in the function CR_time may be determined via operating the engine, demanding a compression ratio change, and recording an amount of time it takes for the compression ratio changing device to change the engine&#39;s compression ratio from its initial value to its demanded value. Method  700  proceeds to  763  after the time to change the engine&#39;s compression ratio is estimated. 
     At  763 , method  700  begins to change the engine&#39;s compression ratio from its present value to the forecasted value when the amount of time to the beginning of the forecasted transmission shift is equal to the time it takes to move the engine compression ratio from its present value to the forecasted engine compression ratio (e.g., the engine compression ratio based on engine speed and load immediately following the downshift) plus a threshold amount of time. Thus, if the transmission is forecast to shift 2 seconds in the future from the present time, it takes 0.5 seconds to change the engine compression ratio, and the threshold amount of time is 0.1 seconds, then the compression ratio begins to change to the forecast value 1.4 seconds in the future. The compression ratio change is completed before the transmission downshifts to reduce the possibility of engine knock. Method  700  proceeds to  764 . 
     At  764 , method  700  shifts the transmission to the forecasted or new gear when the engine speed and accelerator pedal position intersect a shift curve in the transmission shift schedule. Method  700  proceeds to exit after downshifting the transmission. 
     At  770 , method  700  judges whether or not engine load is less than a threshold engine load. If so, the answer is yes and method  700  proceeds to  771 . Otherwise, method  700  proceeds to  780 . 
     At  771 , method  700  prevents the engine compression ratio from changing beginning a predetermined amount of time before the forecast transmission gear shift. For example, if the forecast transmission gear shift is in 2 seconds, the engine compression ratio may not be adjusted within 0.5 seconds of the forecasted transmission gear shift. This may reduce the possibility of driveline torque disturbances during the gear shift. Method  700  proceeds to  772 . 
     At  772 , method  700  shifts the transmission to the forecasted or new gear when the engine speed and accelerator pedal position intersect a shift curve in the transmission shift schedule. Method  700  proceeds to  773  after upshifting the transmission. 
     At  773 , method  700  begins to change the engine&#39;s compression ratio from its present value based on the present engine speed and engine load after the forecasted transmission upshift. Method  700  proceeds to exit after adjusting the engine compression ratio. 
     At  780 , method  700  estimates what the engine load and engine speed will be immediately following the forecasted upshift. In one example, method  700  estimates the engine speed immediately following the forecasted upshift by dividing the vehicle speed that is forecasted immediately following the upshift (e.g., the vehicle speed forecast at  720 ) by the combined ratio of the forecasted gear and the vehicle&#39;s axle. The result is then divided by the distance the tire travels in a single rotation. The forecast engine load may be determined via converting accelerator pedal position into an engine torque via a function of accelerator pedal position and vehicle speed at the predetermined time in the future. Once the forecast engine torque is determined, forecast engine load may be determined via a function or table that describes forecast engine load as a function of forecast engine speed and forecast engine torque. Method  700  proceeds to  781  after determining the forecasted engine speed and load values. 
     At  781 , method  700  determines forecast engine compression ratio at the predetermined time in the future. The forecast engine compression ratio is based on the forecast engine load and speed that were determined at  780 . In one example, the forecast engine load and speed are applied as indexes or reference values into an engine compression ratio map (e.g., as shown in  FIG. 5 ) and the engine compression ratio map outputs an engine compression ratio value. Method  700  proceeds to  782 . 
     At  782 , method  700  estimates an amount of time it will take to move the engine&#39;s compression ratio from its present value to the forecast engine compression ratio at the predetermined time in the future. In one example, a function describing movement of the engine compression ratio is referenced by the change in the engine compression ratio from its present value to its forecasted value. The operation may be described as amount of time to change engine compression ratio=CR_time (CR_Δ), where CR_time is a function that outputs an amount of time to change the engine compression ratio and CR_Δ is the change in compression ratio (e.g., 2:1). The values in the function CR_time may be determined via operating the engine, demanding a compression ratio change, and recording an amount of time it takes for the compression ratio changing device to change the engine&#39;s compression ratio from its initial value to its demanded value. Method  700  proceeds to  783  after the time to change the engine&#39;s compression ratio is estimated. 
     At  783 , method  700  begins to change the engine&#39;s compression ratio from its present value to the forecasted value when the amount of time to the beginning of the forecasted transmission shift is equal to the time it takes to move the engine compression ratio from its present value to the forecasted engine compression ratio (e.g., the engine compression ratio based on engine speed and load immediately following the upshift) plus a threshold amount of time. Thus, if the transmission is forecast to shift 2 seconds in the future from the present time, it takes 0.5 seconds to change the engine compression ratio, and the threshold amount of time is 0.1 seconds, then the compression ratio begins to change to the forecast value 1.4 seconds in the future. The compression ratio change is completed before the transmission downshifts to reduce the possibility of engine knock. Method  700  proceeds to  784 . 
     At  784 , method  700  shifts the transmission to the forecasted or new gear when the engine speed and accelerator pedal position intersect a shift curve in the transmission shift schedule. Method  700  proceeds to exit after upshifting the transmission. 
     In this way, the compression ratio may be changed immediately before a gear shift to reduce the possibility of engine knock immediately following the gear shift. Further, during conditions where the engine compression ratio is low before a gear shift, the compression ratio may not be changed until immediately following the gear shift so that the possibility of driveline torque disturbances during the transmission gear shift may be avoided. 
     Thus, the method of  FIGS. 7-11  provides for an engine operating method, comprising: adjusting an engine&#39;s compression ratio via a controller responsive to present engine speed and engine load; forecasting a shifting of a transmission from a first gear to a second gear via the controller; and adjusting an engine&#39;s compression ratio via the controller responsive to an engine speed and engine load based on the forecasted shifting of the transmission. The method includes where the engine&#39;s compression ratio is adjusted before the shifting of the transmission from the first gear to the second gear. The method includes where adjusting the engine&#39;s compression ratio before the shifting of the transmission from the first gear to the second gear includes beginning to change the engine&#39;s compression ratio beginning at a time before the shifting of the transmission from the first gear to the second gear begins, the time being a time the shifting of the transmission from the first gear to the second gear begins minus a time for a compression ratio changing actuator to change the engine from its present compression ratio to a compression ratio based on engine speed and engine load after shifting the transmission from the first gear to the second gear. The method includes where the first gear is a higher gear than the second gear so that the shifting of the transmission from the first gear to the second gear is a downshift. The method includes where the first gear is a lower gear than the second gear so that the shifting of the transmission from the first gear to the second gear is an upshift. The method further comprises delaying adjusting of the engine&#39;s compression ratio to a time immediately following the shifting of the transmission from the first gear to the second gear. 
     The method also provides for an engine operating method, comprising: adjusting an engine&#39;s compression ratio via a controller responsive to present engine speed and engine load; forecasting a shifting of a transmission from a first gear to a second gear while an accelerator pedal is being released or immediately after the accelerator pedal is released via the controller; and maintaining an engine&#39;s compression ratio from a time when the shifting of the transmission from the first gear to the second gear begins to a time when shifting of the transmission from the first gear to the second gear ends via the controller. The method includes where the time when the shifting of the transmission from the first gear to the second gear begins is a time when an on-coming clutch begins to be applied. The method includes where the time when the shifting of the transmission from the first gear to the second gear ends is a time when an on-coming clutch is fully applied. The method further comprises changing the engine&#39;s compression ratio immediately following shifting of the transmission from the first gear to the second gear. The method includes where the first gear is a higher gear than the second gear so that the shifting of the transmission from the first gear to the second gear is a downshift. The method includes where the first gear is a lower gear than the second gear so that the shifting of the transmission from the first gear to the second gear is an upshift. The method further comprises shifting the transmission from the first gear to the second gear when engine speed and engine load equal engine speed and engine load of a transmission shift schedule curve. The method includes where forecasting shifting of the transmission includes anticipating an engine accelerator pedal position and anticipating a vehicle speed. 
     Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, at least a portion of the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the control system. The control actions may also transform the operating state of one or more sensors or actuators in the physical world when the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with one or more controllers. 
     This concludes the description. The reading of it by those skilled in the art would bring to mind many alterations and modifications without departing from the spirit and the scope of the description. For example, I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas, gasoline, diesel, or alternative fuel configurations could use the present description to advantage.