DESC:TECHNICAL FIELD
[0001] The present subject matter relates in general to an engine assembly for a vehicle, in particular but not exclusively to a method and a system of engine cranking from an integrated starter generator.
BACKGROUND
[0002] Conventionally, an internal combustion engine has been the main source for powering a vehicle. In recent years, automobile industry has been investigating alternatives to the internal combustion engine to improve fuel efficiency of the internal combustion engines. To meet the requirement of improving fuel efficiency, an integrated starter-generator (ISG) is used. The ISG replaces conventional starter motor and conventional alternator (generator). The ISG provides a convenient automatic start-stop system for a vehicle which by combining the functions of the starter and the generator. An electronic control system of the vehicle switches off the vehicle during idling or zero load conditions and rapidly automatically restarts the vehicle using ISG when a rider activates the accelerator pedal. The ISG acts as a bi-directional power converter, changing mechanical energy into electrical energy and vice-versa. Functioning as an electric motor or during motoring mode, the ISG rapidly motors the crankshaft. Whereas, when ISG act as a generator or during generator mode, the ISG generates electrical energy for various electrical components of the vehicle from the mechanical energy of the crankshaft. Generally, the ISG is sandwiched between an engine and a transmission system of the vehicle.
[0003] The ISG contributes in start-stop functioning of the vehicle, electricity generation for the vehicle and power assistance for the vehicle. For automatic starting of the vehicle through the ISG, the engine cranking is achieved when ISG provide rotation to the crankshaft using battery power. Once a threshold speed of vehicle is achieved, the ISG drive power is turned off. During braking or retarding force, the ISG regenerate and provide energy back to the battery. For power assistance, the ISG is used to support the engine by supplying additional power for faster acceleration.
[0004] Further, the design of an ISG is a great challenge for professionals because the ISG drive's requirements are quite severe. ISG requires high starting torque at most unfavourable operating conditions. ISG requires wide speed range in generator mode and high efficiency in wide speed range (600-8000 rpm). ISG further requires optimum temperature range to function i.e., within a range of -30°C to 115°C ambient.
SUMMARY
[0005] In one embodiment, a method for cranking of an engine is disclosed. The method being implemented by an electric machine. The electric machine may be a starter motor or an ISG. The method includes receiving of a starting signal from a user for starting operation of said engine. The method further includes initiating a motoring operation of an electrical machine based on said engine starting signal received from said user.
[0006] In another aspect of the present invention, a method of cranking of an engine is disclosed. The method comprising steps of:
receiving of a starting signal from a user for starting operation of the engine,
initiating a motoring operation of an electrical machine based on the engine starting signal received from the user,
detecting, of an operating speed of a crankshaft of the engine, by a speed detection sensor,
sending, a signal of the operating speed of the crankshaft from the speed detection sensor to the electrical machine,
receiving of the signal by the electric machine,
opening of a decompression valve, based on a predetermined operating speed of the crankshaft, to reduce pressure inside a cylinder chamber, during the starting operation of the engine, and
controlling the operating speed, of the crankshaft, below an operating speed threshold value of the crankshaft at which a closure of the decompression valve initiates, by the electric machine, to increase a duration of the opening of the decompression valve during the cranking of the engine.
[0007] In yet another aspect of the present invention, the electrical machine being an integrated starter generator (ISG).
[0008] In another aspect of the present invention, the electrical machine controls a rotation of the crankshaft of the engine.
[0009] In yet another aspect of the present invention, the crankshaft of the engine can be rotated in one of a forward direction and a reverse direction to bring a speed of rotation of the crankshaft within an operating range of the decompression valve.
[00010] In another aspect of the present invention, a control unit determines an operation being performed by said electrical machine.
[00011] In another aspect of the present invention, an engine cranking system comprising an engine drive system and an engine. The engine drive system comprising an electrical machine. The engine comprising a crankshaft and a speed detection sensor, wherein, the electrical machine receives, from a speed detection sensor, a signal indicating an operating speed of a crankshaft of the engine. The electrical machine controls the operating speed of a crankshaft, based on an operation of a decompression valve, to ensure opening of the decompression valve during cranking of the engine.
[00012] In another aspect of the present invention, the engine cranking system, wherein the electrical machine maintains an operating speed of a crankshaft below an operating speed threshold at which the decompression valve starts closing.
[00013] Summary provided above explains the basic features of the present subject matter and does not limit the scope of the invention. The nature and further characteristic features of the present subject matter will be made clearer from the following descriptions made with reference to the accompanying drawings.
[00014] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[00015] The detailed description is described with reference to an embodiment of a method and system of engine cranking from an integrated starter generator along with the accompanying figures. The same numbers are used throughout the drawings to reference like features and components.
[00016] Figure 1 illustrates a block drawing of an engine assembly, in accordance with an embodiment of the present subject matter.
[00017] Figure 2 illustrates a block diagram of an integrated starter generator (ISG), in accordance with an embodiment of the present subject matter.
[00018] Figure 3 illustrates a flow chart of a preferred embodiment of the present invention.
DETAILED DESCRIPTION
[00019] Generally, an internal combustion engine is a two-stroke engine or a four-stroke engine. Earlier, two-stroke engines were used in vehicles, but due to low mileage and short life, it was replaced by four-stroke engines. “Four Stroke” means that the cycle of conversion from fuel to mechanical energy is completed in a total of four stages. These steps or strokes are called intake, compression, combustion, and exhaust respectively. A crankshaft makes two revolutions to complete the four strokes.
[00020] In the compression stroke, while starting of the engine, the incoming air or the air stored in cylinder is compressed to assist the rotation of the engine. Further, while cranking the engine, the exhaust valves are also kept open so that the rotation of the engine is easy. After the engine starts rotating with sufficient momentum, the exhaust valve is closed and then normal stroking is allowed to start the engine operation. To start the engine operation and reduce the load on engine while cranking, decompressing the cylinder of the engine is used as a tactic.
[00021] A decompression valve is used inside the engine assembly to release some of the compression from the combustion chamber during engine starting operation thereby making it easier for the engine to start. The purpose of decompression valve is to reduce load from the combustion chamber so that less effort is required to crank the engine while starting operation.
[00022] During compression stroke of the engine cranking operation, the function of decompression valve is to create a bypass path in an exhaust valve when the speed of rotation of crankshaft is less than the idling rpm. A decompression valve is a spring ball mechanism, since spring is an elastic member, it will not close immediately. The spring and ball mechanism of decompression valve will gradually close the decompression valve; hence, the decompression valve will start closing much ahead of a predetermined operating rpm. For instance, if the decompression valve is designed to be closed at 1000 rpm, it will start closing at 800 rpm. This means that the volume of air that was supposed to release during a compression stroke will not be able to release and the enough air will accumulate for compression during a compression stroke. For e.g., if a compression stroke is designed to compress a volume of ‘x’ with ‘y’ power, it will have to compress ‘1.1-1.2x’ with the same ‘y’ power. Since, there is not enough release of air during a compression stroke through the decompression valve, the load increases but the power remains constant during cranking of the engine.
[00023] The above-mentioned problem may be avoided by keeping decompression valve open throughout the cranking of the engine. However, the problem associated by keeping decompression valve open is that the operating ranges will be kept further apart which means that the operating ranges for the decompression valve will be modified as per the operation and the same problem will occur during that situation.
[00024] Another way of solving the above-mentioned problem is to provide an ISG machine with a higher power to compress the air of larger volume during compression stroke. But ISG size and weight increases, while providing the ISG with higher power. Further, more space is required to accommodate ISG in the vehicle. In this case, the more power is required during the engine starting operation only and the addition power consumption is wasted once engine gains momentum.
[00025] Conventionally, the ISG performs motoring of the crankshaft in an opposite direction to that of the direction of rotation of the crankshaft during normal vehicle running conditions. Therefore, during normal vehicle running conditions, the crankshaft rotates in a forward direction whereas during starting through an ISG, the crankshaft is rotated in a reverse direction. In such scenarios, it is imperative that ISG deploys high energy to transmit high torque for causing rotation of the crankshaft for cranking operation of the engine.
[00026] Resultantly, a higher battery power would be necessitated. The present invention aims to avoid a scenario wherein a higher torque is required from the ISG to cause the subsequent rotation of the crankshaft for re-starting of the vehicle through the ISG.
[00027] In a known mechanism, the crankshaft is rotated reverse at end of every engine off condition to optimize the torque required for cranking of the engine during for vehicle-restarting condition. In such a mechanism, the starter motor is designed in a manner that maximum torque delivered by the motor does not exceed sixty percent of the torque required to overcome a compression stroke. Generally, compression stroke is the stroke where very high power is required to start the engine. In a situation where the vehicle is abruptly stopped in during the compression stroke, a high power is required to re-start the vehicle in such condition. The torque required to restart the vehicle to overcome the compression stroke is significantly higher compared to the torque required in any other stroke.
[00028] In another known mechanism, the started motor performs the starting mechanism by controlling the valve movement to a low compression level in the compression stroke and adjusting the valve to a high compression level in an expansion stroke. This necessitates the use of one or more valve actuators which tend to make the assembly complex.
[00029] Therefore, the aim of the present invention is to minimize load during cranking of the engine without making the engine assembly complex.
[00030] The present invention discloses a method and system of cranking an engine. During the starting operation of an engine, the rotational speed of a crankshaft is controlled such that it does not go beyond a threshold value. This threshold value is a function of a decompression valve operation. By doing this, the decompression valve remains open during the compression stroke, while cranking the engine. This will help in releasing the pressure during a compression stroke thereby, reducing the load during engine starting operations.
[00031] In an aspect of the present invention, a method of engine cranking comprising an engine drive system and an engine. The engine comprising a crankshaft and a speed detection sensor. The engine drive system comprising an electrical machine such as an integrated starter generator (ISG). The ISG is receiving, from speed detection sensor, a signal indicating speed of a crankshaft of the engine, after switching on an ignition switch in a vehicle running condition. Thereafter, the ISG determines the operational speed of the crankshaft of the engine and accordingly control the operational speed of the crankshaft while cranking the engine based on the operating rpm for which a decompression valve is designed.
[00032] Exemplary embodiments detailing features of the pedal assembly, in accordance with the present subject matter will be described hereunder with reference to the accompanying drawings. Various aspects of different embodiments of the present subject matter will become discernible from the following description set out hereunder. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the present subject matter. Further, it is to be noted that terms “upper”, “lower”, “right”, “left”, “front”, “forward”, “rearward”, “downward”, “upward”, “top”, “bottom” and like terms are used herein based on the illustrated state or in a standing state of the vehicle with a rider sitting thereon unless otherwise elaborated. Furthermore, a vertical axis refers to a top to bottom axis relative to the vehicle, defining a vehicle vertical direction; while a lateral axis refers to a side to side, or left to right axis relative to said vehicle, defining a vehicle lateral direction. Further, a longitudinal axis refers to a front to rear axis relative to the vehicle, defining the vehicle in a longitudinal direction. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.
[00033] The present subject matter is further described with reference to the accompanying figures. It should be noted that description and figures merely illustrate principles of the present subject matter. Various arrangements may be devised that, although not explicitly described or shown herein, encompass the principles of the present subject matter. Moreover, all statements herein reciting principles, aspects, and examples of the present subject matter, as well as specific examples thereof, are intended to encompass equivalents thereof.
[00034] Figure 1 illustrates a block drawing of engine assembly 101, in accordance with an implementation of the present invention. The engine assembly 101 include an engine 102 and an engine drive system 106. The crankshaft 104 is mechanically coupled to other components of the engine such as a piston (not shown) through a connecting rod (not shown). The movement of the piston from a TDC position to a BDC position cause rotational movement of the crankshaft 103. The engine drive system 106 include an integrated starter generator (ISG) 103. The ISG 103 is connected to the speed detection sensor 105. The ISG 103 receives a signal from the speed detection sensor 105. The speed detection sensor 105 detects the speed of a crankshaft 104. The ISG 103 controls the operational speed of a crankshaft 104. In the present invention, the speed of the crankshaft 104 is kept below a threshold speed of at which the decompression valve starts closing. This helps in reducing compression pressure and operating torque of starter motor and ensures an effective starting of the system.
[00035] Figure 2 illustrates a block diagram of the ISG 103. The ISG 103 includes a starter-generated 202 and a control unit 201. The starter generator 103 may include various components such as a rotor, a stator, an armature, etc. The control unit 201 act as an intelligence unit for the ISG 103. The control unit 201 controls the operation of ISG 103. The control unit 201 receives signals from various sensors like a speed detection sensor 105, position detection sensor (not shown) etc., and accordingly commands the starter generator 103. The control unit 201 include programs, objects, data structures, machine readable instructions and the likes incorporated in a hardware. The control unit 201 is also electrically connected to the starter generator 103.
[00036] The control unit 201 controls bi-direction operation of the ISG 103 as per the operating mode. During the motoring mode when the engine 102 is switched off and the engine 102 is to be started with the ISG 103, a torque is transmitted to the crankshaft 104 through the ISG 103 for cranking of the engine. As described above, conventionally, the crankshaft 104 rotates in a reverse direction through an activation of an ISG 103.
[00037] Figure 3 illustrates a flow chart of a preferred embodiment of the present invention. As per the present invention, the engine starts (step 301) by action of switching on the ignition switch. The ISG 103 is activated. The activation of the ISG 103 is determined by an ISG control unit 201 based on an engine start request generated when the ignition key is switched on (step 302). The present invention provides a speed detection sensor 105 which detects the speed of the crankshaft 104 of the engine 102. The detection of the speed 205 is imperative for proper operation of ISG 103 during subsequent restarting of the engine 102.
[00038] The determination of speed of crankshaft 104 by a control unit 201 is done with the help of the speed detection sensor 105. When the crankshaft speed is greater than minimum required cranking speed (step 303), the control unit 201 checks whether the speed of crankshaft 104 is less than the speed of crankshaft 104 at which the decompression valve starts closing (step 304). If the speed of crankshaft 104 is not less than the speed of crankshaft 104 at which the decompression valve starts closing, the control unit 201 commands a starter generator 202 to bring the speed of the crankshaft 104 within an operating range of decompression valve. This is done to ensure that a decompression valve remains open during the cranking of the engine 102. Once the engine is cranked and has gained momentum i.e., the speed of crankshaft reaches a speed more than a cranking cut off speed (step 305), then, the cranking of engine 102 is stopped (step 306) and the vehicle starts.
[00039] In an embodiment of present invention, a starter motor or any other electrical machine that controls the rotation of the crankshaft, may be used in place of an ISG. Hence, the present invention is not limited to an ISG.
[00040] In the present invention, a reliable starting functionality of an engine is achieved without any compromise on the dynamic performance of the vehicle. Further, a complex engine assembly or any electrical machine with higher power is not required to ensure an effective cranking of the engine. Hence, in an embodiment of the present invention, an optimal low power starter motor can be used for successful start of high capacity engine with high compression pressure.
[00041] Specifically, the technical problem being solved by the present disclosure is that generally in a particular system with starter motor, it rotates the crankshaft only in the forward direction. Due to this in a four-stroke engine, maximum load is faced by the starter motor during compression stroke, in which both inlet and exhaust valve is closed and the gases having air, fuel mixture is compressed before ignition for optimal combustion. Though the compressed air, fuel mixture delivers an optimal operation of engine, on a cranking state of engine where engine hasn’t started and motor is motoring the crankshaft to a certain speed depending on the characteristics of the motor, compressed air acts as an additional load which can result in unsuccessful start and poor life of starter motor. Further, by swinging back and forth based on the load detected will lead to increase in time required to perform electric start thereby causes inconvenience to the customer.
[00042] Therefore , the aforementioned technical problem is solved by the present invention and thereby leading to technical advantages such as reliable starting functionality of the engine is achieved without compromise on the dynamic performance of the vehicle. Furthermore, an optimal low power starter motor can be used for successful start of engine with high compression pressure and high capacity engine.
[00043] In light of the above-mentioned advantages and the technical advancements provided by the disclosed method and system, the claimed steps as discussed above are not routine, conventional, or well understood in the art, as the claimed steps enable the following solutions to the existing problems in conventional technologies. Further, the claimed steps clearly bring an improvement in the functioning of the device itself as the claimed steps provide a technical solution to a technical problem.
[00044] Although the subject matter has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. It is to be understood that the appended claims are not necessarily limited to the features described herein. Rather, the features are disclosed as embodiments of the present subject matter.
LIST OF REFERENCE SIGNS

100: Engine Cranking System
101: Engine Assembly
102: Engine
103: Electrical Machine / ISG
104: Crankshaft
105: Speed Detection Sensor
106: Engine Drive System
201: Control Unit
202: Starter generator
300-307: A method comprising steps of cranking of an engine

,CLAIMS:I/We claim:
1. A method (300) of cranking of an engine (102), said method comprising steps of:
receiving, by a control unit (201), of a starting signal from a user for starting operation of said engine (102);
Initiating, by said control unit (201), a motoring operation of an electrical machine (103) based on said engine starting signal received from said user,
detecting, by a speed detection sensor (105), an operating speed of a crankshaft (104) of said engine (102),
sending, by said control unit (201), a signal of said operating speed of said crankshaft from said speed detection sensor (105) to said electrical machine (103),
receiving of said signal by said electric machine (103),
opening of a decompression valve, based on a predetermined operating speed of said crankshaft (104), to reduce pressure inside a cylinder chamber, during said starting operation of said engine (102), and
controlling said operating speed, of said crankshaft (104), below an operating speed threshold value of said crankshaft (104) at which a closure of said decompression valve initiates, by said electric machine (203), to increase a duration of said opening of said decompression valve during said cranking of said engine (102).
2. The method as claimed in claim 1, wherein said electrical machine (103) being an integrated starter generator (ISG) (103).
3. The method as claimed in claim 1, wherein said electrical machine (103) controls a rotation of said crankshaft (104) of said engine (102).
4. The method as claimed in claim 1, wherein said crankshaft (104) of said engine (102) can be rotated in one of a forward direction or a reverse direction to bring a speed of rotation of said crankshaft (104) within an operating range of said decompression valve.
5. The method as claimed in claim 1, wherein a control unit (201) determines an operation being performed by said electrical machine (202).
6. An engine cranking system (100) comprising:
an engine drive system (106), said engine drive system (106) comprising an electrical machine (103), and
an engine (102); said engine (102) comprising a crankshaft (104) and a speed detection sensor (105),
wherein
said electrical machine (103) being configured to:
receive from a speed detection sensor (105), a signal indicating an operating speed of a crankshaft (104) of said engine (102),
control said operating speed of a crankshaft (104), based on an operation of a decompression valve, to ensure opening of said decompression valve during cranking of said engine (102).
7. The engine cranking system (100) as claimed in claim 6, wherein said electrical machine (103) maintains an operating speed of a crankshaft (104) below an operating speed threshold at which said decompression valve starts closing.
8. The engine cranking system (100) as claimed in claim 6, wherein said electrical machine (103) being an integrated starter generator (ISG) (103).
9. The engine cranking system (100) as claimed in claim 6, wherein said crankshaft (104) of said engine (102) can be rotated in one of a forward direction and a reverse direction to bring a speed of rotation of said crankshaft (104) within an operating range of said decompression valve.