Split-cycle internal combustion engine and method of operating a split-cycle internal combustion engine

Abstract

A split-cycle internal combustion engine comprising: a compression cylinder housing a compression piston configured to supply compressed working fluid; a combustion cylinder housing a combustion piston; and a controller, the combustion cylinder coupled to the compression cylinder to receive the compressed working fluid from the compression cylinder, the combustion cylinder comprising (i) an inlet valve configured to control the intake of the compressed working fluid into the combustion cylinder; and (ii) an outlet valve configured to control the exhaust of fluid from the combustion cylinder, the controller configured to vary the position during the engine cycle at which the inlet valve and / or the outlet valve open to switch operation of the engine between an active mode and an engine braking mode, the controller configured to control at least one of the inlet valve opening closer to a bottom dead center (BDC) position when operating in the engine braking mode than when operating in the active mode, and the outlet valve opening closer to a top dead center (TDC) position when operating in the engine braking mode than when operating in the active mode.

Description

[Technical field]

[0001] The present disclosure relates to the field of split-cycle internal combustion engines. [Background technology]

[0002] A four-stroke internal combustion engine uses one cylinder to provide both the compression and combustion strokes of the engine. A split-cycle internal combustion engine uses a different approach. Specifically, a split-cycle engine has separate cylinders for compression and combustion. A working fluid is compressed in the compression cylinder and delivered to the combustion cylinder. Fuel is added to the combustion cylinder such that the fuel is burned in the combustion cylinder and the working fluid expands to drive the movement of a combustion piston in the combustion cylinder. The present disclosure provides an improvement to such split-cycle internal combustion engines. Summary of the Invention [Means for solving the problem]

[0003] Aspects of the disclosure are set out in independent claims and optional features are set out in dependent claims. Aspects of the disclosure may be provided in conjunction with one another and features of one aspect may be applied to other aspects.

[0004] In one aspect, a split-cycle internal combustion engine is provided, the split-cycle internal combustion engine comprising: a compression cylinder housing a compression piston configured to supply compressed working fluid; a combustion cylinder housing a combustion piston; and a controller, the combustion cylinder coupled to the compression cylinder to receive compressed working fluid from the compression cylinder, the combustion cylinder comprising (i) an inlet valve configured to control the intake of the compressed working fluid into the combustion cylinder, and (ii) an outlet valve configured to control the exhaust of fluid from the combustion cylinder, the controller configured to vary the position during the engine cycle at which the inlet valve and / or the outlet valve open to switch operation of the split-cycle internal combustion engine between an active mode and an engine braking mode. The controller is configured to at least one of control the inlet valve to open closer to a bottom dead centre (BDC) position when operating in the engine braking mode than when operating in the active mode, and control the outlet valve to open closer to a top dead centre (TDC) position when operating in the engine braking mode than when operating in the active mode.

[0005] In addition to generating active driving force with the split-cycle internal combustion engine, embodiments may enable the split-cycle internal combustion engine to operate to provide engine braking. The split-cycle internal combustion engine may be provided as part of a vehicle (e.g., a car, a truck, etc.). When such a split-cycle internal combustion engine is used in a vehicle, the engine braking may be used to supplement the deceleration of the vehicle using other means (such as by clamping brake pads to the disk surfaces of the running wheels). In this case, using the split-cycle internal combustion engine to provide the split-cycle engine may reduce wear on other parts of the vehicle (e.g., brake pads or disk rotors). Such engine braking may also be used to make useful energy available from the split-cycle internal combustion engine while it is still operating but not actively driven. For example, engine braking may generate pressurized gas that can be used to provide useful operation, such as by driving the operation of the turbine of the split-cycle internal combustion engine (once the split-cycle internal combustion engine is again in an active mode). This may provide a more energy efficient engine (or vehicle, if a split-cycle internal combustion engine is used as part of that vehicle).

[0006] The controller may be configured to control the inlet valve opening and / or closing positions in the engine braking mode such that the working fluid is further compressed in the combustion cylinder over a majority of the movement of the combustion piston from the BDC position to the TDC position. For example, the internal volume difference of the combustion cylinder between the inlet valve closing position and the outlet valve opening position may be greater than half of the internal volume difference of the combustion cylinder between the BDC position and the TDC position of the combustion piston. In other words, the inlet valve may close at a position closer to BDC and the outlet valve may open at a position closer to TDC.

[0007] The controller may be configured to control the position at which the outlet valve opens and / or closes in the engine braking mode so that further compressed fluid is exhausted from the combustion cylinder. In other words, in the engine braking mode, combustion may not occur in the combustion cylinder and the exhausted fluid may be compressed fluid from the combustion cylinder that has been compressed in the combustion cylinder. Combustion in the combustion cylinder may include oxidation and consumption of fuel that releases energy (e.g., to provide kinetic energy). The controller may be configured to control the outlet valve to open at a position prior to the TDC position in the engine braking mode. For example, this may allow at least a portion of the stroke of the combustion piston from BDC to TDC to act to push further compressed fluid out of the outlet valve. Some of this further compressed fluid exhausted from the combustion cylinder may then be used downstream in the split-cycle internal combustion engine, such as to be stored as a pressurized gas for purposes such as driving a turbine. Opening the outlet valve at or close to TDC may increase the amount of further compression provided in the combustion cylinder (closer to the maximum available compression). The controller may be configured to control the outlet valve to close after the TDC position in an engine braking mode, for example, at least a portion of the stroke of the combustion piston from TDC to BDC may act to return the expelled further compressed fluid through the outlet valve back into the combustion cylinder.

[0008] The controller may be configured to change the position in the engine cycle when the inlet and / or outlet valves close when switching between the active and engine braking modes of operation. The controller may be configured to change the open and closed positions by the same amount when switching between the active and engine braking modes. For example, there may be a fixed, constant position offset between the open and closed positions (when operating in both the active and engine braking modes). The split-cycle internal combustion engine may further comprise a fuel reservoir and may be configured to inject fuel for combustion in the combustion cylinder. The controller may be configured to control the injection of fuel such that no fuel is injected when operating in the engine braking mode.

[0009] The controller may be configured to receive a demand signal for a demand from the split-cycle internal combustion engine. The controller may be configured to control operation of the split-cycle internal combustion engine to be in either an active mode or an engine braking mode based on the demand signal. The controller may be configured to control an open and / or closed position of at least one of an inlet valve and an outlet valve based on the demand signal. For example, the controller may be configured to operate to select an amount of engine braking to be provided and / or to regulate a temperature of the split-cycle internal combustion engine based on the demand signal. The split-cycle internal combustion engine may be for a vehicle (e.g., a car, truck, train, etc.), and the demand signal may include an indication of at least one of (i) that deceleration of the vehicle is desired, and (ii) that further acceleration of the vehicle is not desired.

[0010] The compression cylinder may be coupled to the combustion cylinder via a recuperator. The recuperator may be configured to allow for heat exchange between fluid discharged from the combustion cylinder and compressed working fluid moving from the compression cylinder to the combustion cylinder. The split-cycle internal combustion engine may include a recuperator bypass passage (defining a path for fluid to bypass the recuperator and flow through the split-cycle internal combustion engine, e.g., to reduce the amount of heat exchange that occurs). The controller may be configured to receive a signal indicative of a temperature of the recuperator and control operation of the recuperator bypass passage based on the received signal. The controller may be configured to control a proportion of fluid flowing through the recuperator based on the received signal. The controller may be configured to control operation of the split-cycle internal combustion engine such that, when operating in an engine braking mode, at least a portion of the fluid moves through the recuperator bypass passage.

[0011] For example, selective use of the recuperator bypass passage may allow selective control of the temperature of the split-cycle internal combustion engine (particularly the temperature of the recuperator itself). By keeping the temperature of the recuperator within a selected range (keep it hot), when the split-cycle internal combustion engine returns to active mode, the recuperator may resume operation at a better temperature than it would otherwise be. If the further compressed fluid discharged from the combustion cylinder is too hot, some of this fluid may be directed away from the recuperator to avoid the recuperator getting too hot and / or to avoid overheating the compressed fluid about to be further compressed in the combustion cylinder. If the compressed working fluid is cold (and the recuperator is also too cold), the compressed working fluid may move from the compression cylinder to the combustion cylinder while avoiding the recuperator to avoid overcooling the recuperator. Similarly, this compressed working fluid may be directed to avoid the recuperator if the recuperator is too hot and would overheat this fluid.

[0012] The recuperator bypass passage may comprise at least one of a high-pressure bypass passage arranged to provide a flow path for compressed fluid from the compression cylinder to the combustion cylinder that avoids the recuperator, and a low-pressure bypass passage arranged to provide a flow path for fluid discharged from the combustion cylinder that avoids the recuperator. The controller may be configured to control operation of the split-cycle internal combustion engine such that fluid flows through the high-pressure bypass passage when a temperature associated with the recuperator is below a threshold value. For example, the controller may operate to avoid making the recuperator too cold (or too cold) by reducing an amount of cooling effect provided by cool compressed working fluid flowing between the compression cylinder and the combustion cylinder through the recuperator. The controller may be configured to control operation of the split-cycle internal combustion engine such that fluid flows through the low-pressure bypass passage when a temperature and / or pressure associated with the working fluid is above a threshold value. For example, the controller may operate to prevent the recuperator temperature from becoming too high by reducing the heating effect caused by hot, further compressed fluid being discharged from the combustion cylinder and flowing through the recuperator between the combustion cylinder and the exhaust of the split-cycle internal combustion engine.

[0013] The controller may be configured to receive a signal indicative of the temperature of the recuperator and to select a position in the engine cycle when the outlet valve closes based on the received signal. The controller may be configured to select a position closer to BDC than TDC to increase the temperature of the recuperator. The controller may be configured to control operation of the split-cycle internal combustion engine such that the temperature of the recuperator exceeds a threshold. The threshold may be selected to provide catalytic action in the recuperator. For example, a coating containing a catalytic material may be provided on the inside of the recuperator. Catalytic action may occur when the recuperator, i.e., the catalyst, is heated above a certain temperature. Such catalytic action may improve engine performance by increasing the efficiency of the catalyst or may reduce the environmental impact of the engine (e.g., the amount of particulates / environmental pollutants generated during operation of the split-cycle internal combustion engine).

[0014] The split-cycle internal combustion engine may further comprise a turbocharger having (i) a turbine configured to be driven by fluid discharged from the combustion cylinder, and (ii) a compressor configured to force additional compressed fluid into the compression cylinder. The split-cycle internal combustion engine may further comprise a turbine bypass passage arranged to provide a flow path for fluid discharged from the combustion cylinder that avoids the turbine. The controller may be configured to control operation of the turbine bypass passage to provide a selected amount of compressed working fluid provided to the compression cylinder. The controller may be configured to control operation of the split-cycle internal combustion engine such that when operating in an engine braking mode, at least a portion of the fluid moves through the turbine bypass passage. The controller may be configured to control a proportion of the fluid that moves through the turbine bypass passage to provide a selected amount of engine braking per engine cycle.

[0015] The split-cycle internal combustion engine may further comprise a compressed gas storage configured to receive gas compressed by the split-cycle internal combustion engine. The compressed gas storage may comprise one or more storages configured to receive compressed gas compressed in the compression cylinder and / or compressed gas further compressed in the combustion cylinder. The controller may be configured to control operation of the split-cycle internal combustion engine to provide compressed gas to the compressed gas storage when operating in an engine braking mode. The controller may be configured to control operation of the compressed gas storage to selectively release gas from the compressed gas storage to increase engine power output. The controller may be configured to control operation of the compressed gas storage to release gas from the compressed gas storage in response to switching from the engine braking mode to the active mode. The split-cycle internal combustion engine may include one or more phase change materials configured to store excess energy from the split-cycle internal combustion engine when operating in an engine braking mode. For example, the phase change material may be provided in a recuperator.

[0016] In one aspect, a method of operating a split-cycle internal combustion engine is provided, the split-cycle internal combustion engine comprising a compression cylinder housing a compression piston configured to supply compressed working fluid, and a combustion cylinder housing a combustion piston, the combustion cylinder being coupled to the compression cylinder to receive the compressed working fluid from the compression cylinder, the combustion cylinder comprising (i) an inlet valve configured to control the intake of the compressed working fluid into the combustion cylinder, and (ii) an outlet valve configured to control the exhaust of the fluid from the combustion cylinder. The method includes varying a position during an engine cycle at which the inlet valve and / or the outlet valve open to switch operation of the split-cycle internal combustion engine between an active mode and an engine braking mode, and controlling at least one of: controlling the inlet valve to open closer to a bottom dead center (BDC) position when operating in the engine braking mode than when operating in the active mode; and controlling the outlet valve to open closer to a top dead center (TDC) position when operating in the engine braking mode than when operating in the active mode.

[0017] An aspect of the present disclosure provides a computer program product including computer program instructions configured to program a processor to control operation of a split-cycle internal combustion engine to perform any of the methods disclosed herein. [Brief description of the drawings]

[0018] Some embodiments of the present disclosure will now be described, by way of example only, with reference to the drawings in which:

[0019] [Figure 1] FIG. 1 is a schematic diagram of a split-cycle internal combustion engine. [Diagram 2] FIG. 2 is a schematic diagram of a split-cycle internal combustion engine. [Figure 3a] FIG. 3a illustrates an exemplary timing diagram for the opening and closing of the inlet and outlet valves of a combustion cylinder of a split-cycle internal combustion engine. [Figure 3b] FIG. 3b illustrates an exemplary timing diagram for the opening and closing of the inlet and outlet valves of a combustion cylinder of a split-cycle internal combustion engine. [Figure 3c] FIG. 3c illustrates an exemplary timing diagram for the opening and closing of the inlet and outlet valves of a combustion cylinder of a split-cycle internal combustion engine. [Figure 3d] FIG. 3d illustrates an exemplary timing diagram for the opening and closing of the inlet and outlet valves of a combustion cylinder of a split-cycle internal combustion engine.

[0020] In the drawings, like numbers are used to indicate like elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present disclosure relates to a split-cycle internal combustion engine that can operate in two different modes. The first mode is an active mode and the second mode is an engine braking mode. In both modes, a working fluid is compressed in a compression cylinder and the working fluid is supplied to a combustion cylinder. In the active mode, fuel is combusted in the combustion cylinder and the combusted working fluid is used to drive the movement of a combustion piston. Instead, in the engine braking mode, the operation of the combustion cylinder is changed such that the combustion cylinder is used to further compress the working fluid. The timing of the opening and / or closing of the inlet valve to the combustion cylinder is changed between the two modes such that in the engine braking mode, the working fluid in the combustion cylinder is further compressed and the compressed fluid is then discharged from the combustion cylinder. A further feature of the present disclosure provides a control mechanism to regulate the operating temperature of one or more components of the split-cycle internal combustion engine when operating in the engine braking mode.

[0022] 1 shows a split-cycle internal combustion engine 100. Engine 100 includes a compression cylinder 110, a combustion cylinder 120, and a crossover passage 130. Compression cylinder 110 includes a compression piston 112, an inlet valve 114, and an outlet valve 116. Combustion cylinder 120 includes a combustion piston 122, an inlet valve 124, and an outlet valve 126. Engine 100 further includes a crankshaft 140.

[0023] The compression cylinder 110 houses a compression piston 112, and the combustion cylinder 120 houses a combustion piston 122. Both the compression piston 112 and the combustion piston 122 are coupled to a crankshaft 140. The compression cylinder 110 is coupled to the combustion cylinder 120 via a crossover passage 130. Specifically, the crossover passage 130 is coupled to an outlet valve 116 of the compression cylinder 110 and an inlet valve 124 of the combustion cylinder 120. The inlet valve 114 of the compression cylinder 110 is coupled to a source of incoming working fluid. The outlet valve 126 of the combustion cylinder 120 is coupled to an exhaust of the engine 100. The crossover passage 130 forms a conduit through which the working fluid travels from the compression cylinder 110 to the combustion cylinder 120.

[0024] The compression cylinder 110 is configured to provide compression of the working fluid. An inlet valve 114 of the compression cylinder 110 is configured to open to allow the working fluid to enter the compression cylinder 110 and close to allow the compression piston 112 to move to compress the working fluid in the compression cylinder 110. The compression piston 112 is arranged to move to lower the volume of the compression cylinder 110 to compress the working fluid in the compression cylinder 110. The compression piston 112 is coupled to a crankshaft 140 such that this movement of the compression piston 112 occurs due to the rotational movement of the crankshaft 140. An outlet valve 116 of the compression cylinder 110 is configured to remain closed to allow compression of the working fluid in the compression cylinder 110 and open to exhaust the compressed fluid from the compression cylinder 110.

[0025] The crossover passage 130 is configured to receive compressed fluid from the compression cylinder 110. The crossover passage 130 may provide heating of the compressed fluid. The inlet valve 124 of the combustion cylinder 120 is configured to open to allow compressed working fluid to enter the combustion cylinder 120 from the crossover passage 130 and close to prevent working fluid from entering the combustion cylinder 120 from the crossover passage 130. The outlet valve 126 of the combustion cylinder 120 is configured to open to exhaust fluid from the combustion cylinder 120 and close to prevent exhaust of fluid from the combustion cylinder 120.

[0026] Although not shown in Figure 1, engine 100 further includes a controller. Engine 100 may further include one or more sensors that provide values ​​of sensed parameters to the controller (e.g., to enable the controller to control operation of engine 100 based on such sensed parameters). This is described in more detail below in connection with engine 100 illustrated in Figure 2.

[0027] The controller is configured to control the engine 100 to operate in two different operating modes: the first operating mode is an active mode, and the second operating mode is an engine braking mode.

[0028] In the active mode, the controller is configured to control the operation of the engine 100 such that compressed working fluid enters the combustion cylinder 120 from the crossover passage 130 and combustion occurs in the combustion cylinder 120. Combustion in the combustion cylinder involves oxidation and consumption of fuel to release energy (e.g., consumption of fuel to provide potential energy in the pressure of the working fluid and kinetic energy of the combustion piston / crankshaft). This combustion may result in an exothermic reaction. This combustion results in an expansion motion of the working fluid to drive the movement of the combustion piston 122 (i.e., movement of the crankshaft 140). The combusted (and expanded) fluid is then exhausted from the combustion cylinder 120.

[0029] In the engine braking mode, the controller is configured to control the operation of the engine 100 such that compressed working fluid enters the combustion cylinder 120 from the crossover passage 130, and the compressed working fluid is then further compressed within the combustion cylinder 120 by the movement of the combustion piston 122. The further compressed fluid is then exhausted from the combustion cylinder 120 (without any combustion occurring).

[0030] The controller is configured to vary the open and / or closed positions of the inlet and / or outlet valves of the combustion cylinders 120 to switch between different operating modes.

[0031] To explain the valve timing / position switching, the operation of the combustion piston 122 will first be described. The combustion piston 122 is configured to move between a bottom dead center ("BDC") position and a top dead center ("TDC") position. When the combustion piston 122 is at the BDC position, the internal volume of the combustion cylinder 120 is at a maximum during a cycle of the engine 100. When the combustion piston 122 is at the BDC position, the combustion piston 122 in the engine 100 of FIG. 1 is at its lowest point within the combustion cylinder 120. That is, the head of the combustion piston 122 (shown as solid black in FIG. 1 ) is toward the bottom end of the combustion cylinder 120, e.g., the position closest to the shaft of the crankshaft 140. When the combustion piston 122 is at the TDC position, the internal volume of the combustion cylinder 120 is at a minimum during a cycle of the engine 100. When the combustion piston 122 is at the TDC position, the combustion piston 122 in the engine 100 of FIG. 1 is at its highest point within the combustion cylinder 120. That is, the head of the combustion piston 122 is toward the top of the combustion cylinder 120 , e.g., further from the shaft of the crankshaft 140 .

[0032] This process is cyclical, e.g., continues to repeat. In the engine 100 of FIG. 1, the cyclical process includes a reciprocating motion of the combustion piston 122 in the combustion cylinder 120. This cyclical process also includes a rotational motion of the crankshaft 140 with the reciprocating motion of the combustion piston 122. The motion of the combustion piston 122 is such that it repeatedly passes through a TDC position and a BDC position. In other words, the combustion piston 122 reciprocates in the combustion cylinder 120 between the BDC position and the TDC position (e.g., moves backward and forward in the combustion cylinder 120). The BDC position and the TDC position may be expressed as an angle (e.g., a position of the oscillatory motion of the combustion piston 122). In this case, the TDC position is considered to be 0° or 360° (which are the same), and the BDC position is 180°. The piston repeats this action after moving from 0° to over 180° up to 360° (which is the same as 0°).

[0033] The controller is configured to control the positions during the engine cycle when the inlet and / or outlet valves of the combustion cylinder 120 open and / or close. Again, the positions at which these valves open and close may be expressed in degrees to indicate how far into the cycle of the combustion piston 122 the valves are. The valves may be configured to open and / or close using hydraulic and / or pneumatic systems or may be coupled to a camshaft whose rotation controls the opening and closing of the valves. The controller may be configured to adjust the operation of associated components to change the positions at which the valves open and / or close.

[0034] In the active mode, the controller is configured to control the inlet valve 124 of the combustion cylinder 120 to open near the TDC position (e.g., the inlet valve 124 may open for a period between 340° and 20°). The inlet valve 124 of the combustion cylinder 120 is configured to open and close such that after combustion occurs, the working fluid captured in the combustion cylinder 120 may drive the movement of the combustion piston 122 over a majority of the distance between the TDC and BDC positions. For example, the inlet valve 124 of the combustion cylinder 120 may be configured to open at or slightly before TDC, or close at or slightly after TDC.

[0035] In the active mode, the controller is configured to control the outlet valve 126 of the combustion cylinder 120 to open as the engine moves toward the BDC position. The outlet valve 126 of the combustion cylinder 120 is configured to open so that the combusted and expanded fluids are exhausted from the combustion cylinder 120 (e.g., so that the majority of the combustion and / or movement from TDC toward BDC occurs before the outlet valve 126 opens). The controller is configured to control the outlet valve 126 of the combustion cylinder 120 to close as the engine moves toward the TDC position. The outlet valve 126 of the combustion cylinder 120 is configured to close so that the majority of the combusted and expanded fluids are exhausted from the combustion cylinder 120 before the outlet valve 126 of the combustion cylinder 120 closes.

[0036] The controller may be configured to control the operation of engine 100 to minimize (e.g., avoid altogether) the amount of time that the inlet and outlet valves of combustion cylinder 120 are both open. For example, inlet valve 124 of combustion cylinder 120 may open at the same time as, or slightly after, outlet valve 126 of combustion cylinder 120 closes. The delay between when inlet valve 124 of combustion cylinder 120 closes and when outlet valve 126 of combustion cylinder 120 opens is greater (e.g., to allow combustion and expansion to drive combustion piston 122 most of the way from TDC to BDC).

[0037] In the active mode, the engine 100 is configured to inject fuel into the combustion cylinder 120. The fuel is combusted (e.g., oxidized) to mix with the working fluid in the combustion cylinder 120 and cause the working fluid to expand and drive the combustion piston 122 to the BDC position. In the active mode, the controller is configured to control the opening and closing of the inlet and outlet valves of the combustion cylinder 120 such that the fuel is combusted in the combustion cylinder 120 at or slightly after TDC and the compressed working fluid in the combustion cylinder 120 expands and drives the combustion piston 122 to the TDC position. Similarly, in the active mode, the controller is configured to control the opening and closing of the inlet and outlet valves of the cylinder 120 such that the expanded and combusted working fluid is exhausted from the combustion cylinder 120 (e.g., such that a majority of the expanded and combusted working fluid is exhausted from the combustion cylinder 120) before the expanding new compressed working fluid is admitted to the combustion cylinder 120.

[0038] By controlling engine 100 in this active mode, operation of engine 100 may provide a power output (e.g., through rotational movement of crankshaft 140). This output (e.g., driving torque) may be used in many ways, such as to drive movement of a vehicle (e.g., a truck). The controller may be configured to receive a demand signal indicating an amount of demand for engine 100 (e.g., an amount of torque output required). The controller may control operation of engine 100, such as the amount and timing of fuel injection, based on this demand signal.

[0039] During operation of engine 100, the demand for instantaneous power output from engine 100 may vary. For example, if engine 100 is used in a vehicle, the demand for torque output from engine 100 may be reduced when deceleration of the vehicle is desired (e.g., to slow down or when further acceleration is not desired). During such periods, crankshaft 140 may still rotate causing movement of combustion piston 122. To facilitate slowing down of engine 100 (e.g., vehicle deceleration) and / or to extract usable work from operation of engine 100 during this period, the controller is configured to switch operation of engine 100 from an active mode to an engine braking mode. For example, the controller may receive a signal indicating that power output from engine 100 is to be reduced. In response to receiving this signal, the controller may control operation of engine 100 to switch from the active mode to the engine braking mode.

[0040] The controller is configured to vary the open and / or closed positions of the inlet and / or outlet valves of the combustion cylinders 120 to switch between the active mode and the engine braking mode.

[0041] In the engine braking mode, the controller is configured to control the inlet valve 124 of the combustion cylinder 120 to open near the BDC position. The inlet valve 124 of the combustion cylinder 120 may open at or slightly after the BDC. For example, the inlet valve 124 may open near 190°. The controller is configured to control the inlet valve 124 of the combustion cylinder 120 to open and close such that the compressed fluid passes through the crossover passage 130 into the combustion cylinder 120 and is then further compressed in the combustion cylinder 120 as the combustion piston 122 moves toward the BDC position. For example, the working fluid may be compressed in the combustion cylinder 120 for most of the movement of the combustion piston 122 from the BDC position to the TDC position. The open and closed positions of the inlet valve 124 of the combustion cylinder 120 may have a constant offset from one another (e.g., remain constant in both the active mode and the engine braking mode), but the open and closed positions during the engine cycle may vary.

[0042] In other words, in an engine braking mode (e.g., near BDC or slightly behind BDC), the controller is configured to control the inlet valve 124 of the combustion cylinder 120 to open at a position closer to the BDC position of the combustion piston 122 as compared to an active mode (e.g., when the inlet valve 124 opens at a position near TDC). In doing so, a portion of the movement of the combustion piston 122 from its BDC position to its TDC position acts to provide further compression of the compressed working fluid in the combustion cylinder 120 to provide engine braking.

[0043] In the engine braking mode, the controller is configured to control the outlet valve 126 of the combustion cylinder 120 to open at or before the TDC position. The outlet valve 126 of the combustion cylinder 120 may open at a position closer to the TDC than the BDC. For example, the outlet valve 126 of the combustion cylinder 120 may open between about 290° and 300°. The outlet valve 126 of the combustion cylinder 120 may be controlled to open before the TDC so that the combustion piston 122 moves toward the TDC position to allow further compressed fluid (e.g., the working fluid compressed in the compression cylinder 110 and further compressed in the combustion cylinder 120) to be discharged through the outlet valve 126. The outlet valve 126 of the combustion cylinder 120 is controlled to close before the inlet valve 124 opens. The outlet valve 126 of the combustion cylinder 120 may open before the combustion piston 122 reaches the BDC position (e.g., about 140°). As the combustion piston 122 moves toward TDC, the outlet valve 126 may be controlled to open at any position before the inlet valve 124 of the combustion cylinder 120 opens to allow more working fluid to enter the combustion cylinder 120 so that gas remaining in the combustion cylinder 120 can expand.

[0044] The controller may be configured to control operation of the engine 100 to avoid any overlap between the closed position of the inlet valve 124 and the open position of the outlet valve 126 of the combustion cylinder 120 and / or between the closed position of the outlet valve 126 and the open position of the inlet valve 124. The time lag between the closing of the inlet valve 124 and the opening of the outlet valve 126 may be selected to provide a selected amount of compression of the working fluid in the combustion cylinder 120.

[0045] In other words, the controller is configured to control the outlet valve 126 of the combustion cylinder 120 to open closer to the top dead center TDC position (e.g., near TDC or slightly before TDC) when operating in the engine braking mode than when operating in the active mode (e.g., the outlet valve 126 is open near BDC or slightly before BDC). In doing so, a portion of the movement of the combustion piston 122 from the BDC position to the TDC position acts to provide further compression of the compressed working fluid in the combustion cylinder 120 to provide engine braking.

[0046] In engine braking mode, fuel is not injected into the combustion cylinder 120. For example, the controller may be configured to control the operation of both the inlet / outlet valve positioning and the injection of fuel. When the controller is controlling the engine 100 to operate in engine braking mode, the controller may control the fuel injection such that fuel is not injected into the combustion cylinder 120. In this case, the engine 100 may be operated to provide double compression of the working fluid (e.g., as the working fluid is first compressed in the compression cylinder 110 and second compressed in the combustion cylinder 120 without combustion causing expansion of the working fluid). This doubly compressed working fluid is then discharged via the outlet valve 126 of the combustion cylinder 120.

[0047] In the engine braking mode, the controller is configured to control the inlet and outlet valves of the combustion cylinder 120 to open and close during a period between the BDC and TDC positions of the combustion piston 122 such that the working fluid in the compression cylinder 110 is compressed as the combustion piston 122 moves toward TDC. Similarly, in the engine braking mode, the controller is configured to control the inlet and outlet valves of the combustion cylinder 120 to open and close such that the further compressed fluid in the combustion cylinder 120 is exhausted through the outlet valve 126 (e.g., without expansion of the working fluid due to combustion in the combustion cylinder 120).

[0048] Thus, operation of engine 100 may be controlled to switch between an active mode and an engine braking mode. The controller may be configured to initiate such a switch in response to receiving a signal indicating that a switch is desired (e.g., in response to an action of the vehicle driver to slow the vehicle or to avoid further acceleration of the vehicle).

[0049] During operation, engine 100 may be controlled to operate in either of two different modes.

[0050] For example, engine 100 may begin operation in an active mode. At this time, inlet valve 114 of compression cylinder 110 opens while outlet valve 116 of compression cylinder 110 is closed to allow working fluid into compression cylinder 110. Inlet valve 114 of compression cylinder 110 then closes. Compression piston 112 moves to compress the working fluid in compression cylinder 110. Outlet valve 116 of compression piston 112 then opens and compressed working fluid passes through compression cylinder 110 and into crossover passage 130. When inlet valve 124 of combustion cylinder 120 opens (near TDC position of combustion piston 122), compressed working fluid enters combustion cylinder 120 from crossover passage 130 and is mixed with fuel. The fuel is combusted (e.g., oxidized), which expands the working fluid and drives combustion piston 122 toward BDC position. The outlet valve 126 of the combustion cylinder 120 then opens (before BDC) and remains open until slightly before the inlet valve 124 of the combustion cylinder 120 opens (before TDC). While the outlet valve 126 is open, the combusted and expanded working fluid is exhausted from the combustion cylinder 120. The driving motion of the combustion piston 122 is transmitted to the crankshaft 140, which may be utilized to extract work from the engine 100.

[0051] The controller may then receive a signal that operation in engine braking mode is desired. At this time, the controller changes the timing of opening and closing of the inlet and / or outlet valves of the combustion cylinder 120. The operation of the compression cylinder 110 may be similar in both modes (i.e., supplying compressed working fluid to the combustion cylinder 120). In the active mode, the inlet valve 124 of the combustion cylinder 120 opens closer to the BDC position (compared to the active mode). The compressed working fluid then enters the combustion cylinder 120 from the crossover passage 130 while the outlet valve 126 is closed and the combustion piston 122 is closer to the BDC position. The inlet valve 124 of the combustion cylinder 120 then closes and the working fluid in the combustion cylinder 120 is compressed as the combustion piston 122 moves toward the TDC position. The outlet valve 126 then opens at or before the TDC position of the combustion piston 122. The working fluid further compressed in the combustion cylinder 120 is then discharged via the outlet valve 126. The work done by further compressing the working fluid in the combustion cylinder 120 provides braking for the engine.

[0052] With reference to FIG. 2, some optional additional features of the present disclosure are described below.

[0053] Figure 2 illustrates a split-cycle internal combustion engine 100. The engine 100 of Figure 2 is similar to the engine of Figure 1, and similar parts of the engine 100 will not be described again.

[0054] 1, the engine 100 may include a turbocharger 150. The turbocharger 150 includes a compressor 151, a turbine 152, and a shaft 153. The engine 100 may further include a turbine bypass passage 154.

[0055] The engine 100 may include a recuperator 160. The recuperator 160 is a heat exchanger having two heat exchange passages, a high pressure heat exchange passage 161 and a low pressure heat exchange passage 162. The recuperator 160 may include one or more bypass passages. Figure 2 illustrates both a high pressure recuperator bypass passage 163 and a low pressure recuperator bypass passage 164.

[0056] The engine 100 may further include an energy storage device. Although not shown, the engine 100 may also include one or more compressed gas storage units. Two exemplary gas recovery locations are illustrated in Figure 2: a first gas recovery location 171 and a second gas recovery location 172.

[0057] 2 indicate the possible directions of flow of working fluid through engine 100. Also illustrated are conduits that contain the working fluid moving through engine 100. It will be understood that these features are not intended to be particularly limiting, but are merely illustrated to aid in the explanation of the function and operation of engine 100.

[0058] The compressor 151 is coupled to the turbine 152 via a shaft 153. The compressor 151 is disposed in fluid communication with the working fluid provided to the inlet valve 114 of the compression cylinder 110. The turbine 152 is disposed in fluid communication with the working fluid discharged from the outlet valve 126 of the combustion cylinder 120. The turbine 152 is located between the outlet valve 126 of the combustion cylinder 120 and the exhaust of the engine 100. A turbine bypass passage 154 is located between the outlet valve 126 of the combustion cylinder 120 and the turbine 152. The turbine bypass passage 154 connects an area upstream of the turbine 152 (e.g., between the outlet valve 126 of the combustion cylinder 120 and the turbine 152) to an area downstream of the turbine 152 (e.g., between the turbine 152 and the exhaust of the engine 100). One or more actuators, such as valves, are provided for selectively opening and closing the turbine bypass passage 154. In FIG. 2, these are illustrated by small black dots and dotted lines extending from these dots.

[0059] The high pressure and low pressure heat exchange passages of the recuperator 160 are located adjacent to one another. For simplicity, these are illustrated in Figure 2 as two passages in contact with one another and extending parallel to one another. However, it will be appreciated that other configurations may be provided (e.g., to increase heat exchange between the two passages).

[0060] The outlet valve 116 of the compression cylinder 110 is connected to the inlet valve 124 of the combustion cylinder 120 via a high-pressure heat exchange passage 161 of the recuperator 160 and a high-pressure recuperator bypass passage 163. In other words, there are two passages between the outlet valve 116 of the compression cylinder 110 and the inlet valve 124 of the combustion cylinder 120. One of these passages (high-pressure heat exchange passage 161) passes through the recuperator 160 to bring the working fluid into close proximity with the exhaust fluid to provide heat exchange between the fluids. The other of these passages (high-pressure recuperator bypass passage 163) provides a flow path that avoids the recuperator 160 (and is located away from the exhaust fluid to reduce heat exchange between the fluids).

[0061] The outlet valve 126 of the combustion cylinder 120 is connected to the exhaust of the engine 100 via a low pressure heat exchange passage 162 of the recuperator 160 and a low pressure recuperator bypass passage 164. Also, in the embodiment of FIG. 2, a turbine 152 and a turbine bypass passage 154 are provided and disposed between the outlet valve 126 of the combustion cylinder 120 and the two low pressure passages (it will be understood that the arrangement could be reversed, e.g., such that the exhaust fluid flows through the low pressure passage before reaching the turbine 152 / turbine bypass passage 154, but this is not required). The low pressure heat exchange passage 162 passes through the recuperator 160 to bring the exhaust fluid from the combustion cylinder 120 into close proximity with the compressed working fluid from the compression cylinder 110 to provide heat exchange between the fluids. The low pressure recuperator bypass passage 164 provides a flow path that avoids the recuperator 160 (located away from the compressed working fluid from the compression cylinder 110 to reduce heat exchange between the fluids).

[0062] The first and second gas recovery points may include valves and / or pumps that allow pressurized gas to flow into the pressurized gas storage. These are illustrated in the high pressure area of ​​the engine 100 in FIG. 2. The first gas recovery point 171 is arranged to receive gas that has just been compressed in the compression cylinder 110. In FIG. 2, the first gas recovery point 171 is illustrated immediately downstream of the compression cylinder 110 (i.e., the first gas recovery point 171 is connected to a conduit extending from the outlet valve 116 and / or the outlet valve 116 of the compression cylinder 110). The second gas recovery point 172 is arranged to receive gas that has just been compressed in the combustion cylinder 120. In FIG. 2, the second gas recovery point 172 is illustrated adjacent to the outlet valve 126 (e.g., located in the high pressure part of the outlet valve 126 or in the outlet valve 126 so that the gas pressure is higher). Each gas recovery point may be connected to a pressurized gas storage tank via a separate conduit. Engine 100 may include one or more pressurized gas storage tanks (eg, both collection points may be connected to the same tank or each collection point may be connected to a separate tank).

[0063] The turbocharger 150 is configured to allow additional work to be extracted by the working fluid discharged from the combustion cylinder 120. The engine 100 is configured to allow this discharged fluid to flow from the combustion cylinder 120 through the turbine 152 to drive the rotation of the turbine 152. The turbocharger 150 is configured such that the rotation of the turbine 152 drives the rotation of the shaft 153. The rotation of the shaft 153 in turn drives the rotation of the compressor 151. The compressor 151 is configured to selectively drive the working fluid towards the inlet valve 114 of the compression cylinder 110. An increase in the rotation of the compressor 151 drives a larger amount of working fluid towards the compression cylinder 110 (e.g., may increase the pressure of the working fluid provided to the compression cylinder 110). In other words, the turbocharger 150 is configured to use energy from the flow of the working fluid discharged from the combustion cylinder 120 through the turbine 152 to increase the compression of the working fluid provided to the compression cylinder 110.

[0064] The turbine bypass passage 154 is arranged to provide an alternative flow path for exhaust fluid from the combustion cylinder 120 that avoids or at least reduces interaction of the exhaust fluid with the turbine 152. In other words, the turbine bypass passage 154 is arranged to provide a path for the exhaust fluid from the combustion cylinder 120 toward the exhaust of the engine 100 while bypassing the turbine 152. The turbocharger 150 may be configured to selectively control whether or not the exhaust fluid flows through the turbine bypass passage 154. The turbocharger 150 may be configured to select (e.g., vary) an amount or percentage of the exhaust fluid that flows through the turbine bypass passage 154. For example, all or a portion of the exhaust fluid may be directed through the turbine bypass passage 154. Or, the exhaust fluid may not be directed through the turbine bypass passage 154. A controller may be configured to control the operation of the turbine bypass passage 154. For example, the controller may be configured to adjust the amount or proportion of working fluid flowing through the turbine bypass passage 154 to provide a selected amount of compression by the compressor 151 (e.g., to adjust the amount of working fluid flowing through the engine 100).

[0065] Additionally or alternatively, the engine 100 may include one or more exhausts selectively operable to exhaust compressed gases to regulate the pressure (and temperature of the engine 100). For example, an exhaust may be provided for intake gases (e.g., upstream of the inlet valve 114 of the compression cylinder 110). This exhaust may be used to reduce the pressure of the gases flowing through the engine. For example, by increasing the amount of exhaust gas, the pressure of the gases flowing through the engine may be reduced. Any gases removed from the gases flowing through the engine may be used within the engine, for example, to cool the intake air.

[0066] The recuperator 160 is configured to allow heat exchange between the exhaust fluid from the combustion cylinder 120 and the compressed fluid between the compression cylinder 110 and the combustion cylinder 120. For example, the exhaust fluid flowing through the low pressure heat exchange passage 162 is typically at a higher temperature than the compressed fluid flowing through the high pressure heat exchange passage 161. The recuperator 160 is configured to allow heat transfer between the hot exhaust fluid in the low pressure heat exchange passage 162 and the cold compressed fluid in the high pressure heat exchange passage 161.

[0067] The recuperator bypass passages are configured to provide a fluid flow path that avoids the recuperator 160 (e.g., to reduce the amount of heat exchange provided between the exhaust fluid and the compressed fluid). In other words, each recuperator bypass passage may provide an alternative flow path for the fluid that avoids the recuperator 160. The engine 100 may be controlled to select the amount or proportion of fluid that flows through each recuperator bypass passage. It will be understood in view of the present disclosure that only recuperator bypass passages may be provided.

[0068] The engine 100 may be configured to select (e.g., vary) the amount or percentage of compressed fluid from the compression cylinder 110 that flows through the high-pressure recuperator bypass passage 163. For example, all or a portion of this compressed fluid may be directed through the high-pressure recuperator bypass passage 163. Or, this compressed fluid may not be directed through the high-pressure recuperator bypass passage 163. A controller may be configured to control the operation of the high-pressure recuperator bypass passage 163. For example, the controller may be configured to adjust the amount or percentage of working fluid that flows through the high-pressure bypass passage to provide a selected amount of heating of the compressed working fluid and / or a selected amount of cooling (and / or exhaust fluid) provided to the recuperator 160.

[0069] The engine 100 may be configured to select (e.g., vary) the amount or percentage of exhaust fluid from the combustion cylinder 120 that flows through the low-pressure recuperator bypass passage 164. For example, all or a portion of this exhaust fluid may be directed through the low-pressure recuperator bypass passage 164. Or, this exhaust fluid may not be directed through the low-pressure recuperator bypass passage 164. A controller may be configured to control the operation of the low-pressure recuperator bypass passage 164. For example, the controller may be configured to adjust the amount or percentage of working fluid that flows through the low-pressure bypass passage to provide a selected amount of heating of the compressed working fluid and / or a selected amount of cooling (and / or exhaust fluid) provided to the recuperator 160.

[0070] The gas recovery points may be positioned to allow compressed gas to be fed to a pressurized gas storage of the engine 100. The gas recovery points may be located such that pressurized gas is recovered from an area of ​​the engine where gas pressure is high. The pressurized gas storage may be configured to store the pressurized gas and allow the pressurized gas to be returned to the engine 100. For example, the engine 100 may have a gas intake point for feeding gas to the storage and a gas return point for returning gas from the storage to the engine 100. The gas recovery points may include both such intake and return points. Alternatively, one or more gas return points may be provided in areas of the engine where gas pressure is low, such as downstream of the outlet valve of the combustion cylinder 120. For example, the engine 100 may be configured to allow pressurized gas to be removed from any location during its flow through the engine 100 (e.g., such that the gas is under pressure due to compression in the compression cylinder 110 and / or the combustion cylinder 120) and stored in the storage. Engine 100 may be configured to return the pressurized gas to engine 100 for further use during operation of engine 100. For example, engine 100 may be configured to allow the pressurized gas to return to drive turbine 152. In other words, engine 100 may be configured to store the gas in gas storage when engine demand is low (e.g., when the compressed gas flowing through engine 100 is not needed to obtain meaningful power output from engine 100). Engine 100 may be configured to return the gas to engine 100 for use in conversion to meaningful power output when demand is higher (e.g., to provide more compressed gas flowing through engine 100).

[0071] Similar to engine 100 of FIG. 1, engine 100 includes a controller, not shown. Engine 100 may further include one or more sensors. For example, sensors may be provided to obtain indications of temperature and / or pressure for one or more components of engine 100. For example, the controller may be configured to receive an indication of the temperature of recuperator 160 and / or the pressure of the working fluid flowing through engine 100. The controller may be configured to control operation of engine 100 based on such received indications.

[0072] The controller may be configured to control one or more components of the engine 100 to achieve selected operating characteristics of the engine 100. Similar to the engine 100 of FIG. 1, the controller may be configured to control switching of the engine 100 between an active mode and an engine braking mode. Additionally, the controller may be configured to control operation of one or more different components of the engine 100 to achieve selected operating characteristics of the engine 100 in one or both of these operating modes. Specifically, the controller may be configured to control operation of the engine 100 in the engine braking mode to regulate the temperature of the recuperator 160. For example, it may be beneficial to keep the recuperator 160 within a selected temperature range (e.g., to keep the recuperator 160 hot and / or not to overheat the recuperator 160) so that the recuperator 160 is at a desired temperature to resume operation in the active mode (e.g., so that the recuperator 160 does not need time to warm up before it functions optimally once the engine 100 returns to the active mode).

[0073] Described below are examples of feedback loops that control the operation of engine 100. In particular, some of these examples relate to mechanisms that control the operation of engine 100 during engine braking modes. Before a description of the control loops is given, a description will first be given of the various components of engine 100 and how their operation may affect the operating conditions of engine 100.

[0074] The amount of heating provided to the various engine components varies based on the amount of compressed working fluid flowing through the engine. As the amount of fluid compressed per cycle increases (e.g., as the gas pressure in the engine increases), this may increase the heating effect on the engine components. For example, if a larger amount of working fluid is compressed in the compression cylinder 110, this will increase the temperature of this working fluid flowing through the recuperator 160 (and thus the temperature of the recuperator 160 itself). Similarly, the more hot fluid flowing through the recuperator, the higher the temperature of the recuperator (and vice versa). The engine components may be manipulated to adjust their characteristics to control the temperature of the engine 100, as desired.

[0075] The turbocharger 150 is configured to affect the amount of working fluid flowing through the engine 100 during one engine cycle. The turbocharger 150 is configured to regulate the amount of working fluid forced into the compression cylinder 110. By increasing the amount of air flowing through the turbine 152, the compressor 151 forces more air into the compression cylinder 110 (and vice versa). Increasing the amount of air compressed in the compression cylinder 110 may increase the temperature of this working fluid and / or its ability to heat the recuperator 160. Thus, by controlling the amount of air flowing through the turbine bypass passage 154, the amount and heating capacity of the working fluid may be controlled. In other words, the operation of the turbine bypass passage 154 may be controlled to control the heating effect of the working fluid flowing through the engine (e.g., to control the temperature of the recuperator 160). For example, to increase the temperature of the recuperator 160, the engine 100 may be configured to increase the amount of working fluid flowing through the turbine 152 (i.e., to decrease the amount of fluid flowing through the turbine bypass passage 154).

[0076] The high pressure section of the recuperator 160 may be controlled to affect the amount of compressed working fluid from the compression cylinder 110 that flows through the high pressure recuperator heat exchange passage 161. If the working fluid flowing through the high pressure section 161 of the recuperator 160 is cooler than the recuperator 160, this may have a cooling effect on the recuperator 160. If the exhaust fluid flowing through the low pressure section 162 of the recuperator 160 is hotter than the recuperator 160, this may have a heating effect on the recuperator 160. The engine 100 may be configured to vary these two characteristics (e.g., to balance heating and cooling to the recuperator 160) to achieve a desired recuperator temperature.

[0077] At the high pressure section 161 of the recuperator, where the compressed working fluid may have a cooling effect on the recuperator, directing more of this compressed working fluid through the high pressure recuperator bypass passage 163 may act to make the recuperator 160 hotter (e.g., to avoid as much of a drop in the temperature of the recuperator as possible). At the low pressure section 162 of the recuperator 160, where the discharged working fluid may have a heating effect on the recuperator 160, directing this hot working fluid through the low pressure recuperator bypass passage 164 may have a cooling effect on the recuperator 160.

[0078] The low pressure portion of the recuperator 160 may be controlled to affect the amount of hot exhaust fluid from the combustion cylinder 120 that flows through the low pressure recuperator heat exchange passage 162. As a larger volume of hotter exhaust fluid passes through the recuperator 160 and exchanges heat with the cooler compressed working fluid, the temperature of the recuperator 160 may increase (or decrease less). Directing a larger volume of compressed working fluid through the low pressure recuperator bypass passage 164 may act to cool the recuperator 160 (e.g., to minimize recuperator temperature increases).

[0079] Controlling the opening and closing times of the inlet and / or outlet valves of the combustion cylinder 120 can affect the temperature of the recuperator 160. It will be appreciated in light of the present disclosure that by varying the amount of compression in the combustion cylinder 120, the amount of temperature rise will vary (e.g., the more compression the greater the temperature rise). The opening and closing of the inlet and outlet valves may be controlled to result in a selected amount of temperature rise caused by the compression. Additionally or alternatively, controlling the position at which the outlet valve 126 opens and closes may affect the amount of hot fluid that is exhausted from the combustion cylinder 120 and drawn back into the combustion cylinder 120 for further compression (and further heating). As the combustion piston 122 moves toward the BDC position with the outlet valve 126 open, a portion of the exhaust fluid is drawn back into the combustion cylinder 120. As the exhaust fluid repeatedly flows in for further compression, the temperature of the exhaust fluid increases. By controlling the amount of this recompression (and reheating), the temperature of the recuperator 160 is varied (the temperature of the exhaust fluid, i.e., the low pressure part of the recuperator 160, can be increased due to the further recompression of the exhaust fluid occurring within the combustion cylinder 120).

[0080] Increasing the amount of compressed gas moving into the compressed gas storage may decrease the amount of compressed working fluid flowing through the engine 100. The temperature of the recuperator 160 may change accordingly (e.g., less fluid flows through the system as cooler compressed fluid from the compression cylinder 110 is instead diverted into the gas storage). As compressed gas is released from the gas storage to the engine 100, this may increase engine power output (and increase engine temperature).

[0081] Engine 100 may include other features to regulate temperature. For example, engine 100 may include a cooling system (e.g., configured to inject coolant into compression cylinder 110). Increasing the amount of coolant injected may reduce the temperature of engine 100. Engine 100 may include one or more phase change materials configured to store heat by changing phase. The phase change materials may be used to allow heat stored during operation in an active mode to be released during operation in an engine braking mode (or vice versa, depending on which mode results in a higher temperature).

[0082] Several example feedback loops and control methods will now be described to illustrate potential functionality of engine 100.

[0083] The controller is configured to receive a signal indicative of the temperature of the recuperator 160 and control operation of the engine 100 based on the received signal. The controller may control operation of the engine 100 to be in an engine braking mode. In the engine braking mode, the controller may control operation of the engine 100 to maintain the temperature of the recuperator 160 within a selected range. For example, the controller may be configured to maintain the temperature of the recuperator above a minimum threshold temperature and / or to maintain the temperature of the recuperator below a maximum threshold temperature. The controller (and the sensor) may be configured to provide a dynamic feedback loop for operation of the engine 100. In other words, the controller may be configured to continue to receive a signal indicative of the temperature of the recuperator and continue to control operation of the engine 100, thereby maintaining the temperature of the recuperator within a selected range.

[0084] When operating in an engine braking mode, if the controller receives a signal indicating that the recuperator temperature is outside a selected range, the controller is configured to control operation of the engine 100 to regulate the flow of working fluid through the recuperator 160. To this end, the controller may be configured to control operation of the recuperator bypass passage. The controller may control operation to regulate the proportion of hot and / or cold fluid flowing through the recuperator bypass passage based on an indication of the recuperator temperature. For example, the controller may control operation of the engine to balance the heating effect of the hot fluid on the recuperator 160 and the cooling effect of the cold fluid on the recuperator 160.

[0085] If the temperature of the recuperator is too low, the controller is configured to increase the amount of hot fluid flowing through the recuperator 160 and / or decrease the amount of cold fluid flowing through the recuperator 160. For example, the controller may be configured to operate such that operation of the engine provides a greater heating effect and / or a lesser cooling effect on the recuperator 160. In some cases, the controller may control operation of the engine 100 to increase the amount of hot exhaust fluid flowing through the low-pressure recuperator heat exchange passage 162 or decrease the amount of cold compressed fluid flowing through the high-pressure recuperator heat exchange passage 161 to increase the temperature of the recuperator. To this end, the controller is configured to selectively decrease usage of the low-pressure recuperator bypass passage 164 and / or increase usage of the high-pressure recuperator bypass passage 163.

[0086] The controller may be configured to vary the proportion of fluid passing through the recuperator bypass passage (e.g., use more or less of the recuperator bypass passage if more or less temperature is required) based on the difference between the indication of the recuperator temperature and a threshold temperature. For example, the controller may control operation of engine 100 such that at least some fluid passes through the recuperator bypass passage when operating in an engine braking mode. If the recuperator temperature is too low, the low pressure bypass passage may be used, and / or if the recuperator temperature is too high, the high pressure recuperator bypass passage 163 may be used.

[0087] When operating in engine braking mode, if the controller receives a signal indicating that the recuperator temperature is outside a selected range, the controller is configured to control operation of the engine 100 to regulate the amount of hot exhaust fluid from the combustion cylinder 120 that is drawn back to the combustion cylinder 120 for further compression (and heating). To this end, the controller may be configured to control an open and / or closed position of the outlet valve 126 of the combustion cylinder 120. The control may select an open and / or closed position of the outlet valve 126 of the combustion cylinder 120 to regulate the amount of hot exhaust fluid drawn back to the combustion cylinder 120 for further compression within the combustion cylinder 120. For example, the controller may control the open and / or closed position based on the indicated temperature. If the recuperator temperature is too low, the outlet valve 126 of the combustion cylinder 120 may be open for a longer period of time as the combustion piston 122 moves (from the TDC position) toward the BDC position. For example, the controller may be configured to select a position closer to BDC than TDC (or vice versa) to increase the temperature of the recuperator 160. The controller may dynamically adjust the open and / or closed positions in response to the temperature of the recuperator (e.g., such that the position changes by a selected amount based on the temperature difference between the recuperator temperature and a threshold temperature).

[0088] If the controller receives a signal indicating that the recuperator temperature is outside a selected range when operating in engine braking mode, the controller is configured to control operation of the engine 100 to adjust the flow of working fluid to drive the turbine 152. To this end, the controller may be configured to control operation of the turbine bypass passage 154. The controller may control operation to adjust the proportion of fluid flowing through the turbine bypass passage 154 based on an indication of the recuperator temperature. If the recuperator temperature is too low, the controller is configured to control operation of the turbine bypass passage 154 to increase the heating effect. The controller is configured to decrease the amount of exhaust fluid flowing through the turbine bypass passage 154 (e.g., to increase the amount of fluid flowing through the turbine 152). Thus, the turbine 152 drives more work for the compressor 151, which increases the amount of working fluid compressed in the compression cylinder 110 to provide a greater heating effect.

[0089] The controller may be configured to vary the percentage of exhaust fluid passing through turbine bypass passage 154 (e.g., to increase or decrease usage of turbine bypass passage 154 if more or less temperature is required) based on the difference between the indication of the recuperator temperature and a threshold temperature. For example, the controller may control operation of engine 100 such that at least a portion of the fluid passes through turbine bypass passage 154 when operating in an engine braking mode.

[0090] If the controller receives a signal indicating that the recuperator temperature is outside a selected range when operating in engine braking mode, the controller may be configured to control operation of engine 100 to adjust the amount of coolant supplied to engine 100 and / or to adjust the amount of working fluid flowing through engine 100. To this end, the controller may be configured to control operation of the cooling system (e.g., to increase or decrease the amount of coolant supplied to increase or decrease the temperature, respectively). The controller may be configured to control the amount of working fluid stored in the compressed gas reservoir to control the amount of working fluid flowing through engine 100 (e.g., to store more compressed fluid to increase the temperature).

[0091] In the exemplary feedback loop described above, the controller is configured to receive an indication of the temperature of the engine 100. For example, this may be the temperature of the recuperator 160. The controller is configured to adjust the operation of the engine 100 to control this temperature (e.g., according to the embodiments described above). For example, the controller may control the operation of the engine 100 such that the temperature of the recuperator falls within a threshold range. This control of the recuperator 160 may be to keep the recuperator 160 at a temperature selected based on desired operating conditions for the temperature of the recuperator 160 in the active mode. For example, the controller may adjust the temperature of the recuperator above a threshold value to keep the recuperator 160 warm enough to provide efficient operating conditions for the engine 100 when the engine 100 returns to operation in the active mode.

[0092] Additionally or alternatively, the controller may be configured to control the operation of the engine 100 to regulate the temperature of the engine 100 for different reasons. For example, the operation of the engine 100 may be controlled to provide maintenance of the engine 100 when operating in an engine braking mode. The catalyst may be provided as part of the recuperator 160 (e.g., inside the recuperator 160). In the engine braking mode, the controller may control the operation to provide a catalytic reaction in the recuperator 160 (e.g., a reaction that aids the performance of the catalyst during engine operation). For example, the temperature may be regulated within a threshold range to provide this reaction (e.g., the temperature of the recuperator 160 may be controlled to exceed a threshold temperature to provide a catalytic reaction). For example, such an operation may act to burn off any undesirable material from the catalytic coating of the recuperator 160. During engine operation, particulates may accumulate on the catalytic coating. For example, heating the temperature of the recuperator (e.g., during engine braking mode) may act to de-soot the engine 100 (e.g., to remove undesirable particulate matter from the catalytic coating, thereby improving future engine performance upon return to active mode). The controller may be able to control operation of the engine 100 in active mode to achieve such maintenance of the recuperator 160 (e.g., to achieve de-sooting / catalysis). To this end, the controller may be configured to, for example, control the delay of fuel injection to allow some combustion to occur later in the engine cycle, thereby expelling hot fluids from the combustion cylinder 120.

[0093] In addition to or instead of controlling operation of engine 100 in an engine braking mode to provide a selected temperature to recuperator 160, the controller may be configured to control operation of engine 100 to provide a desired amount of engine braking. For example, the controller may be configured to receive a signal indicative of the pressure of the working fluid and / or the amount of engine braking to be provided. The controller may be configured to control operation of engine 100 based on this received signal to increase or decrease the amount of engine braking accordingly. While this operation may be controlled using the functions described above, it will be understood in view of the present disclosure that variable engine braking is provided. For example, the controller may adjust the opening and / or closing positions of inlet and / or outlet valves of combustion cylinder 120 to control the amount of compression work performed in combustion cylinder 120 (e.g., to increase compression work to provide more engine braking).

[0094] Additionally or alternatively, engine 100 may be controlled to extract compressed gas and store it in a compressed gas storage when operating in engine braking mode. The amount of compressed gas extracted and / or stored may be selected depending on the operating conditions of engine 100 and / or how full the storage is. For example, when the controller switches to operating in engine braking mode, the controller may control operation of one or more gas recovery points to begin directing a portion of the compressed working fluid to a gas storage of engine 100. The controller may continue to extract gas until active mode is enabled or the gas storage is full, and / or if a different amount of engine braking and / or heating is required for engine 100 when in engine braking mode.

[0095] The controller may be configured to selectively release compressed gas from the gas storage during operation of the engine 100 in an active mode. The compressed gas may be released to support the flow of working fluid through the engine 100 (e.g., to supplement the engine 100). For example, the controller may be configured to control the gas storage to provide compressed gas to increase the energy output of the engine 100 (e.g., in response to an engine demand signal indicating that additional power is desired, such as in response to switching back to an active mode and / or acceleration of the engine 100). The engine 100 may be configured such that compressed gas may be released from the gas storage to drive the turbine 152 of the turbocharger 150. Additionally or alternatively, compressed fluid may be released from the gas storage toward the combustion cylinder 120.

[0096] It will be appreciated in light of the foregoing disclosure that the features described in connection with FIG. 2 are optional and not all of the illustrated features need to be provided in combination. For example, an engine of the present disclosure may include some but not all of the features illustrated in FIG. 2. For example, only one recuperator bypass passage may be used. As another example, a turbocharger may not be provided or the turbine bypass passage 154 may not be provided. It will be appreciated that when an engine includes multiple components as described above, the operation of any or all of the different components may be controlled together (such that the operation of one or more components may be controlled based on the operation of one or more other components, such as the high pressure recuperator bypass passage 163 may be used more in combination with a delayed closing of the outlet valve 126 of the combustion cylinder 120 to increase the temperature of the recuperator 160). The controller may be configured to control the operation of the engine based on one or more signals indicative of engine parameters. It will be appreciated that any suitable representation of the engine parameters may be used. For example, if the indication is the temperature of the recuperator, this indication may be obtained using a temperature sensor connected to the recuperator 160, but may also be obtained using other means based on an indication of the change in temperature of the working fluid flowing through the recuperator 160, the working fluid after passing through the recuperator 160, etc.

[0097] It will also be understood that a respective plurality of cylinders may be provided. For example, a split-cycle engine may include a plurality of compression and / or combustion cylinders. The controller may be configured to control the operation of all the different cylinders together. For example, in an active mode, the operation of the combustion cylinders may be staggered such that each combustion piston moves toward its respective BDC position at a staggered time from the other combustion pistons. Similarly, when controlling the timing of the outlet valves 126 of the combustion cylinders to switch to an engine braking mode, these timings may be staggered from each other (e.g., such that each combustion cylinder provides engine braking at a different time than the other combustion cylinders). The number of compression and combustion cylinders also need not be the same. For example, the crossover passage 130 may have multiple inlets (from each compression cylinder) and multiple outlets (to each combustion cylinder). Each inlet or outlet may have a respective valve to control the flow of fluid therethrough. The number of inlets and outlets may be different, such that there may be, for example, five compression cylinders and three combustion cylinders.

[0098] 3a-d show exemplary timing diagrams illustrating example operation of engine 100 in each mode. These timing diagrams show the cycle of combustion piston 122 from 0° (top dead center position) to 180° (bottom dead center position) and back to 360° / 0°. Lines extending radially outward from the circle indicate the opening and closing times of inlet valve 124 and outlet valve 126. Reference numerals 1241 and 1261 are used generally to indicate the opening of the inlet and outlet valves, respectively, and reference numerals 1242 and 1262 are used generally to indicate the closing of the inlet and outlet valves, respectively. Arrows link the opening and closing times of each valve to indicate when the valve is open (i.e., when fluid can flow through that valve).

[0099] FIG. 3a illustrates the valve timing in an active mode of operation. The inlet valve 124 opens at 1241 (e.g., anywhere between 0° and 20° before TDC), which is slightly before TDC. The inlet valve 124 then closes at 1242 (e.g., somewhere between 0° and 20° after TDC), which is slightly after TDC. The outlet valve 126 then opens at 1261, which is between BDC and TDC, typically closer to BDC than TDC. In FIG. 3a, this is illustrated at about 140° to 150°. The outlet valve 126 then stays open for a longer period of time than the inlet valve 124. The outlet valve 126 then closes slightly before the inlet valve 124 opens. In FIG. 3a, the outlet valve closes at 1262 (e.g., 10° to 40° before TDC), which is just before the inlet valve 124 opens at 1241. Thus, compressed fluid enters the combustion cylinder 120 between 1241 and 1242. Combustion then occurs, which expands the working fluid and moves the combustion piston 122 toward the TDC position. The exhaust valve 126 then opens between 1261 and 1262. The movement of the combustion piston 122 from TDC to BDC acts to push out any remaining combustion fluid in the combustion cylinder 120 (e.g., such that most of the combustion fluid is expelled from the combustion cylinder 120 before the cycle repeats and new working fluid is drawn into the combustion cylinder 120).

[0100] FIG 3b illustrates a first set of example valve timings for engine braking mode operation. In FIG 3b, the open / close positions vary, but their fixed offsets remain the same. For example, the opening and closing of each valve may be actuated by camshaft rotation (e.g., such that the opening and closing occur at selected rotation phases). Thus, the combustion piston 122 travels the same angle of crank rotation between the opening and closing of the valve. However, the positions at which the opening and closing occur vary.

[0101] In FIG. 3b, the inlet valve 124 opens at 1241a, a little after BDC (e.g., anywhere between 0° and 40° after BDC). The inlet valve 124 then closes at 1242a, a position between TDC and BDC, typically closer to BDC than TDC. FIG. 3a illustrates this to be anywhere between 20° and 40° after TDC. The outlet valve 126 then opens at 1261a, a position between TDC and BDC, typically closer to TDC than BDC. In FIG. 3b, this is illustrated to be about 50° to 70° before TDC. The outlet valve 126 then stays open longer than the inlet valve 124 (the opening duration is the same as in the active mode, but the position is different). The outlet valve 126 then closes at 1262a, between TDC and BDC (e.g., 20° to 60° before TDC). Thus, compressed fluid enters the combustion cylinder 120 between 1241a and 1242a. This working fluid is further compressed by the movement of the combustion piston 122 towards TDC. The exhaust valve 126 then opens between 1261a and 1262a. The movement of the combustion piston 122 towards TDC acts to push a portion of the further compressed fluid out of the combustion cylinder 120 through the outlet valve 126. The movement of the combustion piston 122 back to BDC after passing TDC, with the outlet valve 126 still open, then acts to draw back into the combustion cylinder 120 a portion of the further compressed fluid that was exhausted from the combustion cylinder 120. This drawn back portion of the further compressed fluid may then be further compressed again within the combustion cylinder 120.

[0102] Figures 3c and 3d illustrate open / closed positions that are slightly different from those of Figure 3b. For example, the valves may open and close independently and the timing of this opening and closing may be freely varied (e.g., no fixed offset is required). For example, hydraulically / pneumatically actuated valves may be used. In both Figures 3c and 3d, the differences from the open and closed positions of the valves of Figure 3b (1241a, 1242a, 1261a, 1262a) are shown.

[0103] In FIG. 3c, the only difference is that the outlet valve closes at 1262b (instead of 1262a). Position 1262b is closer to the open position 1261a. This closed position is therefore closer to TDC than the closed position of FIG. 3b. For example, the controller may control the operation of the engine to switch from the position of FIG. 3b to the position of FIG. 3c in order to reduce the amount of further compressed fluid that is discharged from the combustion cylinder and drawn back into the combustion cylinder. This may be done to regulate the temperature of the recuperator (e.g., because the more such fluid drawn back, the higher the temperature of the discharged fluid, which is hotter for further compression). For example, the controller may be configured to select the closed position in order to regulate the temperature of the recuperator.

[0104] In FIG. 3d, all four positions are changed. The inlet valve opens at 1241c and closes at 1242c, both of which are closer to BDC than the respective positions (1241a and 1242a) in FIG. 3b. The outlet valve opens at 1261c and closes at 1262c, both of which are further back than the corresponding positions (1261a and 1262a) in FIG. 3b. For example, the controller may select such positions to increase the amount of compression provided to the combustion cylinder 120 (e.g., to maximize the difference in position between the inlet valve closing 1242c and the outlet valve opening 1261c). For example, the controller may select such positions to increase the temperature of the engine (e.g., recuperator) by drawing more hot exhaust fluid back into the combustion cylinder 120 (e.g., to maximize the difference between the position of the outlet valve opening TDC and the position of the outlet valve closing 1262c).

[0105] It will be understood that the relative positions illustrated in Figures 3a and 3d are examples to illustrate the underlying concepts, but are not intended to be limiting, and the exact open and closed positions may vary and be selected based on the desired operating conditions of the engine.

[0106] It will be understood that the engines described herein are with reference to engines in which there is reciprocating motion of the piston within the cylinder between TDC and BDC positions. In these examples, the combustion piston effectively moves in one dimension (forward and backward). However, it will be understood that this should not be limiting. For example, a Wankel engine may be provided in which the piston moves in a rotational fashion between the BDC and TDC positions.

[0107] From the foregoing description, it will be understood that the illustrated examples are merely illustrative and include features that may be generalized, omitted, or replaced as described herein and in the claims. With reference to the drawings in general, it will be apparent that schematic functional block diagrams are used to illustrate the functionality of the systems and devices described herein. As will be understood by those skilled in the art in light of the present disclosure, each of the examples described herein may be implemented in a variety of different ways. Features of any aspect of the present disclosure may be combined with any other aspect of the present disclosure. For example, method aspects may be combined with device aspects, and features described with reference to the operation of specific pieces of equipment may be provided in a manner that does not use those specific types of equipment. Furthermore, each feature of each example is intended to be separable from the features with which it is described in combination, unless some other feature is expressly stated as essential to its operation. Each of these separable features may, of course, be combined with any other feature of the described example, or with any other feature or combination of features of the other examples described herein. Furthermore, equivalents and modifications not described above may also be employed without departing from the present invention.

[0108] Certain functions of the methods described herein may be implemented in hardware, and one or more functions of an apparatus may be implemented in method steps. It will also be understood in view of the present disclosure that the methods described herein need not be performed in the order described. Thus, aspects of the present disclosure described with reference to a product or apparatus are also intended to be performed as a method, and vice versa. Aspects of the control methods described herein may be performed in a computer program, or in hardware, or in any combination thereof. Computer programs include software, middleware, firmware, and any combination thereof. Such programs may be provided as signals or network messages, or may be recorded on a computer-readable medium, such as a tangible computer-readable medium that stores a computer program in a non-transitory form. Hardware includes computers, portable devices, programmable processors, general-purpose processors, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), and arrays of logic gates. For example, a controller as described herein may be provided by any control device, such as a general purpose processor having a computer program product configured to program the processor to operate according to any one of the methods described herein. Additionally, the functionality of the controller may be provided by an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), an arrangement of logic gates, or any other control device.

[0109] In some examples, one or more memory elements can store data and / or program instructions used to perform the operations described herein.Embodiments of the present disclosure provide a tangible, non-transitory storage medium including program instructions operable to program a processor to perform one or more of the methods described herein and / or provide a data processing apparatus described herein and / or.

[0110] Other examples and modifications of the present disclosure will be apparent to those of ordinary skill in the art in light of the present disclosure.

Claims

1. 1. A split-cycle internal combustion engine, comprising: a compression cylinder containing a compression piston configured to supply compressed working fluid; a combustion cylinder containing a combustion piston; A controller; and the combustion cylinder is coupled to the compression cylinder to receive compressed working fluid from the compression cylinder; The combustion cylinder comprises: (i) an inlet valve configured to control the intake of compressed working fluid into the combustion cylinder; (ii) an outlet valve configured to control the discharge of fluid from the combustion cylinder; With the controller is configured to vary the open position during an engine cycle at which the inlet valve and / or the outlet valve open to switch operation of the split-cycle internal combustion engine between an active mode and an engine braking mode; The controller controlling the inlet valve to open closer to a bottom dead center (BDC) position when operating in the engine braking mode than when operating in the active mode; controlling the outlet valve to open closer to a top dead center (TDC) position when operating in the engine braking mode than when operating in the active mode; configured to perform at least one of the following controls: A split-cycle internal combustion engine characterized by:

2. the controller is configured to control the open and / or closed positions of the inlet valve in the engine braking mode to further compress working fluid within the combustion cylinder over a majority of the movement of the combustion piston from the BDC position to the TDC position.

2. The split-cycle internal combustion engine of claim 1.

3. the controller is configured to control the open and / or closed positions of the outlet valve in the engine braking mode to allow further compressed working fluid to be discharged from the combustion cylinder. A split-cycle internal combustion engine according to any one of claims 1 to 2.

4. the controller is configured to control the outlet valve to open at a position prior to the TDC position in the engine braking mode.

4. The split-cycle internal combustion engine of claim 3.

5. the controller is configured to change the closed position during the engine cycle at which the inlet valve and / or the outlet valve are closed when switching between the active mode and the engine braking mode of operation; Optionally, the controller is configured to change the open and closed positions by the same amount when switching between the active mode and the engine braking mode. A split-cycle internal combustion engine according to any one of claims 1 to 2.

6. The split-cycle internal combustion engine comprises: fuel storage, and The split-cycle internal combustion engine is configured to inject fuel for combustion into the combustion cylinders, the controller is configured to control injection of fuel such that no fuel is injected when operating in the engine braking mode. A split-cycle internal combustion engine according to any one of claims 1 to 2.

7. the controller is configured to receive a demand signal from the split-cycle internal combustion engine; the controller is configured to control operation of the split-cycle internal combustion engine to be in either the active mode or the engine braking mode based on the demand signal. A split-cycle internal combustion engine according to any one of claims 1 to 2.

8. the controller is configured to control the open and / or closed positions of at least one of the inlet valve and the outlet valve based on the demand signal; Optionally, said split-cycle internal combustion engine is for use in a vehicle; The request signal is (i) a desire to decelerate the vehicle; and (ii) further acceleration of the vehicle is not desired; and including at least one of the following:

8. The split-cycle internal combustion engine of claim 7.

9. The compression cylinder is connected to the combustion cylinder via a recuperator, the recuperator is configured to allow heat exchange between fluid discharged from the combustion cylinder and compressed working fluid traveling from the compression cylinder to the combustion cylinder. A split-cycle internal combustion engine according to any one of claims 1 to 2.

10. Recuperator bypass passage, consisting of 10. The split-cycle internal combustion engine of claim 9.

11. the controller is configured to receive a signal indicative of the temperature of the recuperator and to control operation of the recuperator bypass passage based on the received signal; Optionally, the controller is configured to control a rate of working fluid flowing through the recuperator based on the received signal; Optionally, configured to control operation of the split-cycle internal combustion engine such that, when operating in the engine braking mode, at least a portion of the working fluid is transferred through the recuperator bypass passage.

11. The split-cycle internal combustion engine of claim 10.

12. The recuperator bypass passage is a high pressure bypass passage configured to provide a flow path for compressed working fluid from the compression cylinder to the combustion cylinder that avoids the recuperator; a low pressure bypass passage configured to provide a flow path for fluid discharged from the combustion cylinder that avoids the recuperator; At least one of 11. The split-cycle internal combustion engine of claim 10.

13. the controller is configured to control operation of the split-cycle internal combustion engine to allow fluid to flow through the high-pressure bypass passage when a temperature associated with the recuperator is below a threshold; the controller is configured to control operation of the split-cycle internal combustion engine such that when a temperature and / or pressure associated with a working fluid exceeds a threshold, the fluid flows through the low-pressure bypass passage.

13. The split-cycle internal combustion engine of claim 12.

14. the controller is configured to receive a signal indicative of a temperature of the recuperator and to select the closed position during the engine cycle in which the outlet valve is closed based on the received signal; Optionally, the controller is configured to select a position closer to the BDC position than the TDC position to increase the temperature of the recuperator.

10. The split-cycle internal combustion engine of claim 9.

15. the controller is configured to control operation of the split-cycle internal combustion engine such that the temperature of the recuperator exceeds a threshold; Optionally, the threshold is selected to provide a catalytic effect in the recuperator.

10. The split-cycle internal combustion engine of claim 9.

16. The split-cycle internal combustion engine comprises: turbocharger, and The turbocharger is (i) a turbine configured to be driven by fluid discharged from said combustion cylinder; (ii) a compressor configured to force additional compressed working fluid into the compression cylinder; Equipped with 10. The split-cycle internal combustion engine of claim 1.

17. The split-cycle internal combustion engine comprises: a turbine bypass passage configured to provide a flow path for fluid discharged from the combustion cylinder that avoids the turbine; and the controller is configured to control operation of the turbine bypass passage to provide a selected amount of compressed working fluid delivered to the compression cylinder.

17. The split-cycle internal combustion engine of claim 16.

18. the controller is configured to control operation of the split-cycle internal combustion engine such that, when operating in the engine braking mode, at least a portion of fluid is transferred through the turbine bypass passage; Optionally, the controller is configured to control a rate of fluid moving through the turbine bypass passage to provide a selected amount of engine braking per engine cycle.

18. The split-cycle internal combustion engine of claim 17.

19. a compressed gas reservoir configured to receive gas compressed by the split-cycle internal combustion engine; consisting of A split-cycle internal combustion engine according to any one of claims 1 to 2.

20. The compressed gas storage unit one or more reservoirs configured to receive compressed gas compressed in the compression cylinder and / or compressed gas further compressed in the combustion cylinder; Equipped with 20. The split-cycle internal combustion engine of claim 19.

21. the controller is configured to control operation of the split-cycle internal combustion engine to supply compressed gas to the compressed gas storage when operating in the engine braking mode.

20. The split-cycle internal combustion engine of claim 19.

22. the controller is configured to control operation of the compressed gas storage to selectively release gas from the compressed gas storage to increase engine power; Optionally, the controller is configured to control operation of the compressed gas storage to release gas from the compressed gas storage in response to switching from the engine braking mode to the active mode.

20. The split-cycle internal combustion engine of claim 19.

23. one or more phase change materials configured to store excess energy from the split-cycle internal combustion engine when operating in the engine braking mode; consisting of A split-cycle internal combustion engine according to any one of claims 1 to 2.

24. 1. A method of operating a split-cycle internal combustion engine, comprising: The split-cycle internal combustion engine comprises: a compression cylinder containing a compression piston configured to supply compressed working fluid; (ii) a combustion cylinder containing a combustion piston; With the combustion cylinder is coupled to the compression cylinder to receive compressed working fluid from the compression cylinder; The combustion cylinder comprises: (i) an inlet valve configured to control the intake of compressed working fluid into the combustion cylinder; (ii) an outlet valve configured to control the discharge of fluid from the combustion cylinder; With The method comprises: Varying the open positions during an engine cycle at which the inlet valve and / or the outlet valve open to switch operation of the split-cycle internal combustion engine between an active mode and an engine braking mode; controlling the inlet valve to open closer to a bottom dead center (BDC) position when operating in the engine braking mode than when operating in the active mode; controlling the outlet valve to open closer to a top dead center (TDC) position when operating in the engine braking mode than when operating in the active mode; a step of executing at least one of the following controls; consisting of 1. A method of operating a split-cycle internal combustion engine, comprising:

25. 25. Computer program instructions configured to program a processor to control operation of a split-cycle internal combustion engine to perform the method of claim 24. consisting of 1. A computer program product comprising:

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