THERMAL MANAGEMENT OF A VEHICLE ENGINE BY PRECISION COOLING WITH A LINE FLOW LIQUID COOLING SYSTEM

Abstract

A liquid cooling system (130) for a vehicle engine (120), wherein the liquid cooling system (130) comprises: a coolant circuit with one or more cooling tubes connected in series in a fluid flow direction to form a channel for the circulation of a coolant for cooling a front cylinder head (122) and a rear cylinder head (126) of the vehicle engine (120), wherein the cooling tubes include a precision cooling tube for the rear cylinder head (132) having a serpentine shape (135) which extends through a gap between a pair of rear exhaust ports (128) of the rear cylinder head (126) to thermally contact one or more heat exchange surfaces of the rear exhaust ports (128).

Description

TECHNICAL FIELD One or more embodiments generally relate to a liquid cooling system for an internal combustion engine (ICE) of a vehicle, a vehicle having such a liquid cooling system, a cooling circuit for such a liquid cooling system, and a method for cooling a vehicle engine. The liquid cooling system includes a cooling circuit configured with a series flow structure that ensures precise cooling of the critical hot zones of the cylinder heads. BACKGROUND Vehicles, such as motorcycles, that contain an internal combustion engine can use air or liquid to cool the cylinder heads of the internal combustion engine. Air cooling relies on airflow over heat transfer surfaces to cool the engine. With liquid cooling, a coolant (e.g., refrigerant, oil, etc.) flows through the engine to absorb heat, and a heat exchanger (e.g., a radiator) transfers the heat absorbed in the coolant to the environment. SHORT SUMMARY According to one or more embodiments, a liquid cooling system for a vehicle engine has a series-flow structural configuration to enable improved thermal management of the internal combustion engine's cylinder heads. Thus, the cooling system enables improved engine performance during vehicle operation. According to one or more embodiments, an exemplary liquid cooling system for a vehicle engine comprises one or more of the following elements: a liquid cooling system having one or more cooling tubes fluidly connected in series to define a channel for circulating a coolant to cool a front cylinder head and a rear cylinder head of the vehicle engine, the cooling tubes comprising a precision rear cylinder cooling tube having a serpentine shape extending through a gap between a pair of rear exhaust ports of the rear cylinder head to thermally contact one or more heat exchange surfaces of the rear exhaust ports. In accordance with the liquid cooling system, the coolant comprises at least one of the following media: water, glycol, oil, and any combination thereof. According to the exemplary liquid cooling system, the coolant comprises a mixture of water and glycol. According to the exemplary liquid cooling system, the coolant comprises a mixture of water and glycol in a 1:1 ratio. According to the exemplary liquid cooling system, the coolant circuit is configured such that the coolant circulates to the rear cylinder head in time before the coolant circulates to the front cylinder head. According to the exemplary liquid cooling system, the serpentine shape of the rear cylinder precision cooling tube includes a first zone configured to thermally contact one or more heat exchange surfaces of a first rear exhaust port of the rear exhaust ports. According to the exemplary liquid cooling system, the serpentine shape of the rear cylinder precision cooling tube includes a second zone oriented opposite to the first zone. According to the exemplary liquid cooling system, the second zone is configured to thermally contact one or more heat exchange surfaces of a second rear exhaust opening of the rear exhaust openings. According to the exemplary liquid cooling system, the serpentine shape of the rear cylinder precision cooling tube includes a third zone extending between the first zone and the second zone and into the gap between the first rear exhaust port and the second rear exhaust port. According to the exemplary liquid cooling system, the third zone is configured to thermally contact one or more heat exchange surfaces of the first rear exhaust opening and the second rear exhaust opening. According to one or more embodiments, an exemplary vehicle includes one or more of the following elements: a vehicle structure; a vehicle engine mounted to the vehicle structure, the vehicle engine having a front cylinder head of a front cylinder and a rear cylinder head of a rear cylinder with a pair of rear exhaust ports; and a liquid cooling system having a coolant circuit including one or more coolant tubes fluidly connected in series to define a channel for circulating a coolant to cool the front cylinder head and the rear cylinder head, the cooling tubes including a precision rear cylinder cooling tube having a serpentine shape extending through a gap between the rear exhaust ports to thermally contact one or more heat exchange surfaces of the rear exhaust ports. In accordance with the exemplary vehicle, the coolant comprises at least one of the following media: water, glycol, oil, and any combination thereof. According to the exemplary vehicle, the coolant circuit is configured such that the coolant circulates to the rear cylinder head prior to the coolant being recirculated to the front cylinder head. According to the exemplary vehicle, the serpentine shape of the rear cylinder precision cooling tube includes a first zone configured to thermally contact one or more heat exchange surfaces of a first rear exhaust port of the rear exhaust ports. According to the exemplary vehicle, the serpentine shape of the rear cylinder precision cooling tube includes a second zone oriented opposite the first zone. According to the exemplary vehicle, the second zone is configured to thermally contact one or more heat exchange surfaces of a second rear exhaust opening of the rear exhaust openings. In the exemplary vehicle, the serpentine shape of the rear cylinder precision cooling tube includes a third zone extending between the first zone and the second zone and into a space between the first rear exhaust port and the second rear exhaust port. In accordance with the exemplary vehicle, the third zone is configured to thermally contact one or more heat exchange surfaces of the first rear exhaust opening and the second rear exhaust opening. In accordance with the exemplary vehicle, a heat exchanger is mounted centrally on the vehicle structure at a predetermined angle (to the vertical) and configured to transfer heat absorbed from the coolant to the environment outside the vehicle. In accordance with the exemplary vehicle, the predetermined angle is 21.1 degrees. According to the exemplary vehicle, a pump is fluidly connected at one end to the heat exchanger and at its opposite end to the rear cylinder precision cooling tube to time-deliver coolant to the rear cylinder head before circulating it to the front cylinder head. According to one or more embodiments, an exemplary coolant circuit for a liquid cooling system for a vehicle engine comprises one or more of the following elements: one or more cooling tubes fluidly connected in series to define a channel for circulating a coolant for cooling a front cylinder head and a rear cylinder head of the vehicle engine, wherein the cooling tubes comprise a precision rear cylinder cooling tube having a serpentine shape extending through a gap between a pair of rear exhaust ports of the rear cylinder head to thermally contact one or more heat exchange surfaces of the rear exhaust ports. According to the example of the coolant circuit, the coolant comprises at least one of the following media: water, glycol, oil and any combination thereof. According to the exemplary coolant circuit, the coolant circuit is configured such that the coolant circulates to the rear cylinder head in time before the coolant circulates to the front cylinder head. According to the coolant circuit example, the serpentine shape of the rear cylinder precision cooling tube includes a first zone configured to thermally contact one or more heat exchange surfaces of a first rear exhaust port of the rear exhaust ports. According to the coolant circuit example, the serpentine shape of the rear cylinder precision cooling pipe includes a second zone oriented opposite to the first zone. According to the coolant circuit example, the second zone is configured to thermally contact one or more heat exchange surfaces of a second rear exhaust opening of the rear exhaust openings. According to the coolant circuit example, the serpentine shape of the rear cylinder precision cooling tube includes a third zone extending between the first zone and the second zone and into the gap between the first rear exhaust port and the second rear exhaust port. According to the coolant circuit example, the third zone is configured to thermally contact one or more heat exchange surfaces of the first rear exhaust port and the second rear exhaust port. According to one or more embodiments, an exemplary method for cooling a vehicle engine includes one or more of the following: disposing an inline flow cooling circuit in a gap between the legs of the rear exhaust port; and circulating (or causing to circulate) a coolant / cooling fluid through the inline flow cooling circuit to capture heat from the rear cylinder head prior to capturing heat from the front cylinder head. According to one or more embodiments, an exemplary method for cooling a vehicle engine includes one or more of the following: disposing a front serpentine portion of an inline flow cooling circuit in a gap between the legs of the front exhaust port and a rear serpentine portion of the inline flow cooling circuit in a gap between the legs of the rear exhaust port; and circulating (or causing to be circulated) a coolant / cooling fluid through the inline flow cooling circuit to absorb heat from the rear cylinder head prior to heat absorption from the front cylinder head. In this manner, the inline flow cooling circuit forms a fluid flow path that thermally contacts one or more heat exchange surfaces of the rear cylinder head in the critical hot zone, which represents the region of the cylinder head where operating temperatures are highest. BRIEF DESCRIPTION OF THE DIFFERENT VIEWS OF THE DRAWINGS The various advantages of embodiments of the present disclosure will become apparent to one skilled in the art upon reading the following description and the appended claims, and upon reference to the following drawings: Fig. 1 shows an exemplary vehicle according to one or more of the embodiments shown, illustrated, and described herein. Fig. 2 shows an exemplary block diagram of the exemplary vehicle of Fig. 1. Fig. 3 shows an exemplary coolant circuit of a liquid cooling system for precision cooling of an internal combustion engine of the exemplary vehicle of Fig. 1. Fig. 4 shows a plan view of the critical hot zone in a gap between the legs of the rear exhaust ports for a rear cylinder head of the internal combustion engine. Fig. 5 shows a plan view of an exemplary arrangement of the liquid cooling system for the rear exhaust ports of Fig. 4. Figs. 6 and 77 shows an example of the arrangement of the liquid cooling system for a cylinder head of the internal combustion engine. Fig. 8 shows the liquid cooling system without the liquid coolant pump. Fig. 9 shows a block diagram of the coolant circuit for the liquid cooling system. Figs. 10 and 11 show a schematic diagram of example methods for cooling a vehicle engine according to one or more embodiments illustrated and described herein. DETAILED DESCRIPTION 1 and 2, a vehicle 100 is illustrated having a vehicle structure 110 (e.g., chassis, frame, subframe, body, front / rear forks, etc.) according to one or more embodiments. According to one or more embodiments, a "vehicle" may refer to any form of motorized transportation. In the illustrated embodiment of FIG. 1, the vehicle 100 includes a two-wheeled vehicle, such as a motorcycle. However, the embodiments are not so limited, and therefore, within the scope of this disclosure, the vehicle may include a three-wheeled vehicle, a four-wheeled vehicle, or any other suitable vehicle that falls within the spirit and scope of the principles of this disclosure. In accordance with one or more embodiments, the vehicle 100 may include one or more operating elements. Some of the possible operating elements of the vehicle 100 are illustrated in Fig. 1 and will now be described. It should be understood that the vehicle 100 may not include all of the elements illustrated in Fig. 1 and / or described herein. The vehicle 100 may include any combination of the various elements illustrated in Fig. 1. Furthermore, the vehicle 100 may include additional elements to those illustrated in Fig. 1 or may not include one or more of the elements illustrated in Fig. 1. Although the various operating elements are illustrated as being located within the vehicle 100, the embodiments are not so limited, and thus one or more operating elements may be located external to the vehicle 100 and even separated by large physical distances. In the embodiment illustrated in Figures 1 to 3, the vehicle 100 includes an internal combustion engine 120 connected to the vehicle structure 110. In the direction of travel of the vehicle 100, the internal combustion engine 120 includes a first or front cylinder 121 having a front cylinder head 122 with a pair of intake ports 123 and a pair of exhaust ports 124, and a second or rear cylinder 125 having a rear cylinder head 126 with a pair of intake ports 127 and a pair of exhaust ports 128. The front cylinder 121 and the rear cylinder 125 also include a reciprocating piston (not shown). The front cylinder head 122 includes a front intake valve (not shown) for controlling the intake air flow through the combustion chamber of the front cylinder 121 and a front exhaust valve (not shown) for controlling the exhaust air flow through the combustion chamber of the front cylinder 121.Likewise, the rear cylinder head 126 includes a rear intake valve (not shown) for controlling intake airflow through the combustion chamber of the rear cylinder 125 and a rear exhaust valve (not shown) for controlling exhaust airflow through the combustion chamber of the rear cylinder 125. Due to the structural configuration of the internal combustion engine 120 and its mounting position on the vehicle structure 110, the front cylinder head 122 receives a greater ambient airflow than the rear cylinder head 126. Accordingly, the front cylinder head 122 can be considered both air-cooled (via ambient airflow) and liquid-cooled (via the liquid cooling system 130). Due to its position, the rear cylinder head 126 is heated to a greater extent during operation. In an internal combustion engine with a four-valve head, the critical hot zones of the exhaust port are generally located between the exhaust port legs, and more particularly on the inner surface of the exhaust port legs. To address the technical problem of the heat zones between the exhaust port legs, the vehicle 100 further includes a liquid cooling system 130 that circulates a coolant / cooling fluid to thermally control the internal combustion engine 120 by cooling the internal combustion engine 120 (i.e., reducing its operating temperature) by removing combustion heat from the front cylinder head 122 and the rear cylinder head 126 during operation of the vehicle 100. According to one or more embodiments, the coolant comprises at least one of the following media: water, glycol, oil, and any combination thereof.According to one or more embodiments, the coolant comprises a mixture of water and glycol. According to one or more embodiments, the coolant comprises a mixture of water and glycol in a ratio of 1:1. As shown in Fig. 2, Fig. 3 and Fig. 6, the liquid cooling system 130 includes one or more cooling tubes that are fluidly connected in series. The cooling tubes include a precision cooling tube 131 for the front cylinder, a precision cooling tube 132 for the rear cylinder, and an intermediate transfer hose 133 that fluidly connects the precision cooling tube 131 for the front cylinder and the precision cooling tube 132 for the rear cylinder. The precision cooling tube 131 for the front cylinder includes a length of tubing that forms a channel through which the coolant or cooling liquid flows or circulates. Although the liquid cooling system 130 includes a plurality of cooling tubes in the illustrated examples, the embodiments are not so limited. This disclosure contemplates that the liquid cooling system 130 include any suitable configuration that falls within the spirit and scope of the principles of this disclosure.For example, the liquid cooling system 130 may include a single, monolithic cooling tube that defines the coolant circuit for the circulation or flow of coolant / cooling liquid to cool the internal combustion engine 120. In the embodiment shown in Fig. 2, the cold region CR of the liquid cooling system 130 is located downstream of the radiator 150 (i.e., shown to the right of the coolant circuit in Fig. 2) and merges into the hot region upstream of the radiator 150 (i.e., shown to the left of the coolant circuit in Fig. 2). Counterclockwise, the flow of coolant / cooling liquid is driven by the liquid coolant pump 160 through the rear cylinder precision cooling pipe 132, which provides precision cooling to the rear cylinder 125. The coolant or cooling liquid then flows from the rear cylinder precision cooling pipe 132 via the intermediate hose 133 to the front cylinder precision cooling pipe 131, which provides precision cooling to the front cylinder 121.The coolant / coolant fluid then flows from the front cylinder precision cooling pipe 131 into the radiator 150, which is configured to be in thermal contact with the hot coolant / coolant fluid to lower the temperature of the coolant / coolant fluid (water). The front cylinder precision cooling tube 131 and the rear cylinder precision cooling tube 132 each comprise a piece of tubing that defines a channel through which the coolant or cooling liquid is to flow. A section of the front cylinder precision cooling tube 131 and the rear cylinder precision cooling tube 132 comprises an S-core section 134, 135 configured in a serpentine fashion and extending between the exhaust port legs to provide precision cooling. The serpentine shape of the S-core sections 134, 135 is advantageous in that it allows the liquid cooling system 130 to selectively extend into the critical hot zones (i.e., between the exhaust port legs) of the internal combustion engine 120 and provide precise cooling there. As shown in Figs. 4 and 5, to ensure optimal thermal management for the critical hot zones of the front cylinder 121 and the rear cylinder 125, the S-core sections 134, 135 extend into the critical hot zone between the legs of the front exhaust ports 124 (of the front cylinder 121) and the rear exhaust ports 128 (of the rear cylinder 125). In this way, the structural configuration of the S-core sections 134, 135 provides precise cooling of the critical hot zones of the internal combustion engine 120 by extracting heat therefrom. In particular, the S-core sections 134, 135 each form a fluid flow path that is in thermal contact with one or more heat exchange surfaces of the front cylinder 121 and the rear cylinder 125 in the critical hot zone.The S-core sections 134, 135 are also located near the spark plugs and thus serve to thermally contact the spark plugs to remove heat from them. This results in greater NOx resistance of the internal combustion engine 120. As used herein, "thermal contact" means that at least one surface of a structure or component absorbs heat dissipated by at least one surface of another structure or component, either through thermal radiation, conduction, and / or convection. The S-core section 134 of the front cylinder precision cooling tube 131 includes three regions or zones 134a, 134b, and 134c that help reduce the operating temperature of the internal combustion engine 120 and remove heat from the critical hot zone of the front cylinder 121. The first zone 134a has an inner manifold that is generally concave and defines a flow channel that is in thermal contact with one or more heat exchange surfaces of one of the front exhaust ports 124. The second zone 134b has an inner manifold oriented in the opposite direction to the inner manifold of the first zone 134a, thus redirecting the flow of coolant / coolant fluid. The inner manifold of the second zone 134b is generally concave and defines a flow channel that is in thermal contact with one or more heat exchange surfaces of the other of the front exhaust ports 124. The third zone 134c extends between or otherwise between the first zone 134a and the second zone 134b in a space or gap between the exhaust port legs of the front exhaust ports 124. In this manner, the third zone 134c defines a flow channel that provides precise cooling of the critical hot zone of the front cylinder 121 by making thermal contact with one or more heat exchange surfaces of the front exhaust ports 124. The S-core section 135 of the rear cylinder precision cooling tube 132 includes three regions or zones 135a, 135b and 135c, which also contribute to lowering the operating temperature of the internal combustion engine 120. The first zone 135a has an inner manifold that is generally concave and defines a flow channel that is in thermal contact with one or more heat exchange surfaces of one of the rear exhaust openings 128. The second zone 135b has an inner manifold oriented in the opposite direction to the inner manifold of the first zone 135a, thus redirecting the flow of coolant / coolant fluid. The inner manifold of the second zone 135b is generally concave and defines a flow channel that is in thermal contact with one or more heat exchange surfaces of the other of the rear exhaust ports 128. The third zone 135c extends between or otherwise between the first zone 135a and the second zone 135b in a space or gap between the exhaust port legs of the rear exhaust ports 128. In this manner, the third zone 135c defines a flow channel that provides precise cooling of the critical hot zone of the rear cylinder 125 by making thermal contact with one or more heat exchange surfaces of the rear exhaust ports 128. As shown in Figs. 3 and 6, the liquid cooling system 130 further includes a heat exchanger such as a radiator 150 that transfers the heat absorbed by the coolant / cooling liquid to the environment outside the vehicle 100. The radiator 150 is centrally mounted on the front of the vehicle structure 110 and oriented at a predetermined angle relative to the vertical to further contribute to the improved thermal management of the internal combustion engine 120 provided by the liquid cooling system 130. In accordance with one or more embodiments, the predetermined angle is 21.1 degrees. As shown in Figs. 3 and 7, a liquid coolant pump 160 is fluidly connected at one end to the radiator 150 and at its opposite end to the rear precision cooling tube 132 for driving or otherwise circulating the coolant counterclockwise to absorb heat from the rear cylinder head 125 ahead of the heat from the front cylinder head 121. A coolant bottle overflow device 140 is fluidly connected to the radiator 150 via a coolant fill hose 141.The coolant bottle overflow device 140 includes a pressurized portion in fluid communication with the pressurized liquid cooling system 130 and a non-pressurized portion operable to facilitate the collection and discharge of the overflowing coolant / cooling liquid during operation due to normal expansion / contraction of the coolant / cooling liquid in the pressurized liquid cooling system 130. In the direction of travel of the vehicle 100, the rear cylinder head 126 is shielded at least by the front cylinder head 122. The liquid cooling system 130 is therefore configured, as shown in Fig. 9, so that the coolant exiting the radiator 150 reaches the rear cylinder heads 126 before the front cylinder heads 122. Due to its installation position, the front cylinder head 122 is subjected to a greater amount of ambient air flow during operation of the vehicle 100 (compared to the rear cylinder head 126). The temporal circulation of the coolant / cooling liquid to the rear cylinder head 126 achieves additional heat transfer via the coolant / cooling liquid. This effect is particularly noticeable at very low operating speeds of the vehicle 100 when the ambient air flow is minimal.Thus, the liquid cooling system 130 cools the rear cylinder head 126 before the front cylinder head 122 because the rear cylinder head 126 generates the most heat (compared to the front cylinder head 122) since it is less exposed to airflow during operation of the vehicle 100. In the examples of Fig. 10 and Fig. 11, a flowchart of the methods 1000 and 1100 for cooling a vehicle engine is shown. In the example method 1000 shown in Fig. 10, the illustrated process block 1002 includes disposing a series flow cooling circuit in a gap between the legs of the rear exhaust opening. Method 1000 may then proceed to the illustrated method block 1004, which includes circulating (or causing to circulate) a coolant / cooling fluid through the inline flow cooling circuit to capture heat from the rear cylinder head prior to heat absorption from the front cylinder head. In this way, the inline flow cooling circuit forms a fluid flow path that thermally contacts one or more heat exchange surfaces of the rear cylinder head in the critical hot zone. In the illustrated example method 1100 of Fig. 11, the illustrated process block 1102 includes disposing a front serpentine portion of a series flow cooling circuit in a gap between the legs of the front exhaust opening and a rear serpentine portion of the series flow cooling circuit in a gap between the legs of the rear exhaust opening. Method 1100 may then proceed to the illustrated method block 1104, which includes circulating (or causing to circulate) a coolant / cooling fluid through the inline cooling circuit to capture heat from the rear cylinder head prior to heat absorption from the front cylinder head. In this way, the inline cooling circuit forms a fluid flow path that thermally contacts one or more heat exchange surfaces of the rear cylinder head in the critical hot zone. The terms "coupled," "attached," or "connected" may be used herein to refer to any type of direct or indirect relationship between the components in question, and may refer to electrical, mechanical, fluid, optical, electromagnetic, electromechanical, or other connections. Furthermore, the terms "first," "second," etc., are used herein only for convenience of discussion and have no particular temporal or chronological significance unless otherwise noted. The terms "cause" or "effect" mean to effect, compel, compel, direct, command, direct, and / or enable an event or action, or at least to bring about a condition in which such an event or action may occur, either directly or indirectly. Those skilled in the art will appreciate from the foregoing description that the broad techniques of the embodiments of the present disclosure may be embodied in a variety of forms. Although the embodiments have been described in connection with specific examples, the true scope of the embodiments should not be so limited, since other modifications will become apparent to those skilled in the art upon study of the drawings, the specification, and the following claims. EXAMPLES The disclosure also includes additional guidance and examples as set out in the following sections. Section 1. A coolant circuit for a vehicle engine having a front cylinder head of a front cylinder and a rear cylinder head of a rear cylinder, the cooling structure comprising: a coolant circuit defined at least partially by a front cylinder precision cooling tube through which a coolant / cooling fluid flows to precisely cool the front cylinder head, and a rear cylinder precision cooling tube fluidly connected to the front cylinder precision cooling tube and through which a coolant / cooling fluid flows to precisely cool the rear cylinder head, the front cylinder precision cooling tube and the rear cylinder precision cooling tube being fluidly connected in series, the front cylinder precision cooling tube being arranged downstream of the rear cylinder precision cooling tube in a flow direction of the fluid circuit,that the cooling medium / coolant fluid first circulates to the rear cylinder head before flowing to the front cylinder head. Section 2. A coolant circuit for a vehicle engine having a front cylinder head of a front cylinder and a rear cylinder head of a rear cylinder, the cooling structure comprising: a fluid circuit defined at least partially by a front cylinder precision cooling tube through which a coolant / cooling fluid flows to precisely cool the front cylinder head, and a rear cylinder precision cooling tube fluidly connected to the front cylinder precision cooling tube and through which a coolant / cooling fluid flows to precisely cool the rear cylinder head, the front cylinder precision cooling tube and the rear cylinder precision cooling tube being fluidly connected in series, a portion of the front cylinder precision cooling tube having a serpentine shape extending between the exhaust port legs of the front cylinder,to provide precision cooling thereat, wherein the rear cylinder precision cooling pipe has a portion having a serpentine shape extending between the rear cylinder exhaust port legs to provide precision cooling thereat. Section 3. A coolant circuit for a vehicle engine having a front cylinder head of a front cylinder and a rear cylinder head of a rear cylinder, the cooling structure comprising: a fluid circuit defined at least partially by a front cylinder precision cooling tube through which a coolant / cooling fluid flows to provide precision cooling to the front cylinder head, and a rear cylinder precision cooling tube fluidly connected to the front cylinder precision cooling tube through which a coolant / cooling fluid flows to provide precision cooling to the rear cylinder head, the front cylinder precision cooling tube and the rear cylinder precision cooling tube being fluidly connected in series, the front cylinder precision cooling tube having a portion formed with a serpentine shape,which extends between the exhaust port legs of the front cylinder to provide precision cooling. Section 4. A coolant circuit for a vehicle engine having a front cylinder head of a front cylinder and a rear cylinder head of a rear cylinder, the cooling structure comprising: a fluid circuit defined at least partially by a front cylinder precision cooling tube through which a coolant / cooling fluid flows to provide precision cooling to the front cylinder head, and a rear cylinder precision cooling tube fluidly connected to the front cylinder precision cooling tube and through which a coolant / cooling fluid flows to provide precision cooling to the rear cylinder head, the front cylinder precision cooling tube and the rear cylinder precision cooling tube being fluidly connected in series, a portion of the rear cylinder precision cooling tube having a serpentine shape,which extends between the legs of the exhaust port of the rear cylinder to provide precision cooling. Section 5. A liquid cooling system for a vehicle engine having a front cylinder head of a front cylinder and a rear cylinder head of a rear cylinder, the liquid cooling system comprising: a plurality of cooling tubes fluidly connected in series and defining a channel through which a coolant / cooling liquid is to flow, the cooling tubes comprising a front cylinder precision cooling tube, a rear cylinder precision cooling tube, and an intermediate transfer hose for fluidly connecting the front cylinder precision cooling tube and the rear cylinder precision cooling tube, wherein a portion of the front cylinder precision cooling tube has a serpentine shape extending between the exhaust port legs of the front cylinder to provide precision cooling thereat,and a portion of the rear cylinder precision cooling tube has a serpentine shape extending between the rear cylinder exhaust port legs to provide precision cooling thereat. Section 6. A liquid cooling system for a vehicle engine having a front cylinder head of a front cylinder and a rear cylinder head of a rear cylinder, the liquid cooling system comprising: a fluid circuit comprising a plurality of cooling tubes fluidly connected in series and defining a channel through which a coolant / cooling liquid is to flow, a radiator operable to cool the coolant, and a pump for driving the coolant through the fluid circuit, the cooling tubes comprising a precision front cylinder head cooling tube operable to provide precision cooling to the front cylinder head and a precision rear cylinder cooling tube fluidly connected to the precision front cylinder head cooling tube to provide precision cooling to the rear cylinder head,wherein the precision cooling pipe for the front cylinder is arranged downstream of the precision cooling pipe for the rear cylinder head in a flow direction of the fluid circuit such that the coolant first circulates to the rear cylinder head before flowing to the front cylinder head., Section 7. A liquid cooling system for a vehicle engine having a front cylinder head of a front cylinder and a rear cylinder head of a rear cylinder, the liquid cooling system comprising: a front cylinder precision cooling tube through which a coolant / cooling liquid flows to precisely cool the front cylinder head; a rear cylinder precision cooling tube fluidly connected to the front cylinder precision cooling tube and through which a coolant / cooling liquid flows to precisely cool the rear cylinder head; a radiator operable to cool the coolant; and a pump for driving the coolant through a fluid circuit defined by the front cylinder precision cooling tube, the rear cylinder precision cooling tube, and the radiator. Section 8. A liquid cooling system for a vehicle engine having a front cylinder head of a front cylinder and a rear cylinder head of a rear cylinder, the liquid cooling system comprising: a precision cooling pipe for the front cylinder head through which a coolant / cooling liquid flows to precisely cool the front cylinder head; a precision cooling pipe for the rear cylinder fluidly connected to the precision cooling pipe for the front cylinder head and through which a coolant / cooling liquid flows to precisely cool the rear cylinder head, the precision cooling pipe for the front cylinder head and the precision cooling pipe for the rear cylinder head being connected in series; a radiator capable of cooling the coolant;and a pump for driving the coolant through a fluid circuit defined by the front cylinder precision cooling tube, the rear cylinder precision cooling tube, and the radiator, wherein the front cylinder precision cooling tube has a portion formed with a serpentine shape extending between exhaust port legs of the front cylinder to provide precision cooling thereto, wherein the rear cylinder precision cooling tube has a portion formed with a serpentine shape extending between exhaust port legs of the rear cylinder to provide precision cooling thereto; Section 9. A liquid cooling system for a vehicle engine having a front cylinder head of a front cylinder and a rear cylinder head of a rear cylinder, the liquid cooling system comprising: a front cylinder precision cooling tube through which a coolant / cooling liquid flows to precisely cool the front cylinder head; a rear cylinder precision cooling tube fluidly connected to the front cylinder precision cooling tube and through which a coolant / cooling liquid flows to precisely cool the rear cylinder head, the front cylinder precision cooling tube and the rear cylinder precision cooling tube being connected in series; a radiator operable to cool the coolant;and a pump for driving the coolant through a fluid circuit defined by the front precision cooling pipe, the rear precision cooling pipe, and the radiator, wherein the front precision cooling pipe is arranged downstream of the rear precision cooling pipe in a flow direction of the fluid circuit such that the coolant is first circulated to the rear cylinder head before flowing to the front cylinder head.; Section 10. A method of cooling a vehicle engine having a front cylinder head of a front cylinder and a rear cylinder head of a rear cylinder, the method comprising: providing a fluid circuit defined at least in part by a front cylinder precision cooling tube and a rear cylinder precision cooling tube such that a coolant / cooling fluid is circulated to the rear cylinder head first in time. Section 11. A method of cooling a vehicle engine having a front cylinder head of a front cylinder and a rear cylinder head of a rear cylinder, the method comprising: circulating a coolant / cooling fluid through a fluid circuit defined at least in part by a precision cooling tube of the front cylinder and a precision cooling tube of the rear cylinder in a manner such that the coolant / cooling fluid is circulated to the rear cylinder head first in time. Section 12. A method of cooling a vehicle engine having a front cylinder head of a front cylinder and a rear cylinder head of a rear cylinder, the method comprising:fluidically connecting a front cylinder precision cooling tube and a rear cylinder precision cooling tube in series, wherein a portion of the front cylinder precision cooling tube has a serpentine shape extending between the front cylinder exhaust port legs and a portion of the rear cylinder precision cooling tube has a serpentine shape extending between the rear cylinder exhaust port legs to provide precision cooling thereat,circulating a coolant / cooling fluid through the rear cylinder precision cooling tube to provide precision cooling of the rear cylinder exhaust port legs. The terms "coupled," "attached," or "connected" may be used herein to refer to any type of direct or indirect relationship between the components in question, and may refer to electrical, mechanical, fluid, optical, electromagnetic, electromechanical, or other connections. Furthermore, the terms "first," "second," etc., are used herein only for convenience of discussion and have no particular temporal or chronological significance unless otherwise noted. The terms "cause" or "effect" mean to effect, compel, compel, direct, command, direct, and / or enable an event or action, or at least to bring about a condition in which such an event or action may occur, either directly or indirectly. Those skilled in the art will appreciate from the foregoing description that the broad techniques of the embodiments of the present disclosure may be embodied in a variety of forms. Although the embodiments have been described in connection with specific examples, the true scope of the embodiments should not be so limited, since other modifications will become apparent to those skilled in the art upon study of the drawings, the specification, and the following claims.

Claims

A liquid cooling system for a vehicle engine, the liquid cooling system comprising:a coolant circuit having one or more cooling tubes fluidly connected in series to form a channel for circulating coolant to cool a front cylinder head and a rear cylinder head of the vehicle engine, the cooling tubes comprising a precision rear cylinder head cooling tube having a serpentine shape extending through a gap between a pair of rear exhaust ports of the rear cylinder head to thermally contact one or more heat exchange surfaces of the rear exhaust ports. The liquid cooling system according to claim 1, wherein the coolant circuit is arranged such that the coolant circulates to the rear cylinder head in time before the coolant circulates to the front cylinder head. The liquid cooling system of claim 1, wherein the serpentine shape of the rear cylinder precision cooling tube includes a first zone configured to thermally contact one or more heat exchange surfaces of a first rear exhaust port of the rear exhaust ports. The liquid cooling system of claim 3, wherein the serpentine shape of the rear cylinder precision cooling tube includes a second zone oriented in a different direction than the first zone. The liquid cooling system of claim 4, wherein the second zone is configured to thermally contact one or more heat exchange surfaces of a second rear exhaust opening of the rear exhaust openings. The liquid cooling system of claim 5, wherein the serpentine shape of the rear cylinder precision cooling tube includes a third zone extending between the first zone and the second zone and into the gap between the first rear exhaust port and the second rear exhaust port. The liquid cooling system of claim 6, wherein the third zone is configured to thermally contact one or more heat exchange surfaces of the first rear exhaust port and the second rear exhaust port. A vehicle comprising:a vehicle structure;a vehicle engine mounted on the vehicle structure, the vehicle engine having a front cylinder head of a front cylinder and a rear cylinder head of a rear cylinder with a pair of rear exhaust ports; anda liquid cooling system having a coolant circuit including one or more coolant tubes fluidly connected in series to form a channel for circulating a coolant to cool the front cylinder head and the rear cylinder head, the cooling tubes including a precision rear cylinder head cooling tube having a serpentine shape extending through a gap between the rear exhaust ports to thermally contact one or more heat exchange surfaces of the rear exhaust ports. The vehicle according to claim 8, wherein the coolant circuit is arranged such that the coolant circulates to the rear cylinder head in time before the coolant circulates to the front cylinder head. The vehicle of claim 8, wherein the serpentine shape of the rear cylinder precision cooling tube includes a first zone configured to thermally contact one or more heat exchange surfaces of a first rear exhaust port of the rear exhaust ports. The vehicle of claim 10, wherein the serpentine shape of the rear cylinder precision cooling tube includes a second zone oriented in a different direction than the first zone. The vehicle of claim 11, wherein the second zone is configured to thermally contact one or more heat exchange surfaces of a second rear exhaust opening of the rear exhaust openings. The vehicle of claim 12, wherein the serpentine shape of the rear cylinder precision cooling tube includes a third zone extending between the first zone and the second zone and into a gap between the first rear exhaust port and the second rear exhaust port. The vehicle of claim 13, wherein the third zone is configured to thermally contact one or more heat exchange surfaces of the first rear exhaust opening and the second rear exhaust opening. The vehicle according to claim 8 further comprises a heat exchanger mounted in the center of the vehicle structure at a predetermined angle and configured to dissipate the heat absorbed by the coolant to the environment outside the vehicle. The vehicle of claim 15, wherein the predetermined angle is 21.1 degrees. The vehicle of claim 15, further comprising a pump fluidly connected at one end to the heat exchanger and at an opposite end to the rear cylinder precision cooling tube for temporarily supplying the coolant to the rear cylinder head before circulating it to the front cylinder head. A coolant circuit for a liquid cooling system for a vehicle engine, the coolant circuit comprising:one or more cooling tubes fluidly connected in series to form a channel for circulating coolant for cooling a front cylinder head and a rear cylinder head of the vehicle engine, the cooling tubes comprising a precision rear cylinder head cooling tube having a serpentine shape extending through a gap between a pair of rear exhaust ports of the rear cylinder head to thermally contact one or more heat exchange surfaces of the rear exhaust ports. The coolant circuit of claim 18, wherein the serpentine shape of the rear cylinder precision cooling tube comprises:a first zone configured to thermally contact one or more heat exchange surfaces of a first rear exhaust port of the rear exhaust ports,a second zone oriented in a direction opposite the first zone, anda third zone extending between the first zone and the second zone and into the gap between the first rear exhaust port and the second rear exhaust port. The coolant circuit of claim 19, wherein:the second zone is configured to thermally contact one or more heat exchange surfaces of a second rear exhaust port of the rear exhaust ports, andthe third zone is configured to thermally contact one or more heat exchange surfaces of the first rear exhaust port and the second rear exhaust port.