WO2016193999A2

WO2016193999A2 - Starting system for internal combustion engine and method thereof

Info

Publication number: WO2016193999A2
Application number: PCT/IN2016/000146
Authority: WO
Inventors: Dixit AMIT; Vinjamoor HARSH
Original assignee: Sedemac Mechatronics Pvt Ltd
Priority date: 2015-06-05
Filing date: 2016-06-06
Publication date: 2016-12-08
Also published as: WO2016193999A3

Abstract

Based on the presence of start command and motion of crankshaft of an IC engine, a motor coupled to the crankshaft is energized or de-energized by a control unit. If the crankshaft stops moving in a forward direction or starts moving in a reverse direction the motor is de-energized allowing the crankshaft to move in reverse direction, and if crankshaft stops moving in reverse direction or starts moving in forward direction, the motor is energized causing the crankshaft to move in forward direction with an increasing kinetic energy to overcome starting resistance of the motor. Various sensor means may be implemented to detect the motion of the crankshaft.

Description

TITLE OF THE INVENTION

Starting System for Internal Combustion Engine and Method Thereof FIELD OF THE INVENTION

[001] The present invention relates to starting system for internal combustion engine and a method thereof.

BACKGROUND OF THE INVENTION

[002] Internal combustion engines are widely used in applications such as automobiles, small generator sets, snowmobiles and lawn mowers. Most internal combustion engines have an electric starter arrangement, which consists of an electric motor coupled to the crankshaft of the engine, which is powered by a battery through controlling means. The starter motor rotates the crankshaft to attain speed at which the combustion process can begin thereby starting the engine.

[003] During the engine starting process, the starting system experiences a resistance, which is a function of the crankshaft angle. A typical pattern of the resistance experienced by the starter motor as a function of crankshaft angle for an internal combustion engine is shown in Figure 3. As shown in Figure 3, the resistance has sharp peaks at certain crankshaft angles, and the average value of the resistance is substantially lower than the peak value. [004] Traditionally, the starter motors are sized according to the peak value of the starting resistance. Thus, the conventional starter motors are oversized as compared to the average value of the starting resistance. Further, any degradation in conditions such as a weak battery or increased engine friction leads to the conventional starter motor being unable to start the engine although the starter motor torque is much higher than the average starting resistance.

[005] Methods of starting an engine using a starter motor having maximum torque value lesser than the peak starting resistance of the engine have been mentioned in literature (see US Patents 5458098, 5713320). These methods involve positioning the crankshaft to a pre-defined position by reversely rotating the crankshaft, thereby enabling the crankshaft to gather enough momentum to overcome the higher starting resistance through a combined effect of motor torque and kinetic energy of crankshaft inertia. These methods require means for energizing the starter motor in two opposite directions.

SUMMARY OF THE INVENTION

[006] Accordingly, the present invention in one aspect provides a method of starting an internal combustion engine, the method comprising: receiving a start command; energizing a motor coupled to a crankshaft in response to the start command causing the crank shaft to move in a forward direction; detecting the motion of the crankshaft in the forward direction and a reverse direction through motion detection means; and energizing or de-energizing the motor depending upon the start command and the motion of the crank shaft whereby if the crankshaft stops moving in the forward direction or starts moving in the reverse direction the motor is de-energized allowing the crankshaft to move in the reverse direction, movement of the crankshaft in the reverse direction imparts energy to the crankshaft, and if the crankshaft stops moving in reverse direction or starts moving in the forward direction, the motor is energized causing the crankshaft to move in the forward direction with an increasing kinetic energy to overcome starting resistance of the motor.

[007] In another embodiment the invention provides a starting system for an internal combustion engine, the system comprising of: a motor coupled to a crankshaft causing the crank shaft to move in a forward direction when the motor is energized in response to a start command; a motion sensor for detecting the motion of the crankshaft; and a control unit for energizing or de-energizing the motor depending upon the start command and the motion of the crank shaft whereby if the crankshaft stops moving in the forward direction or starts moving in the reverse direction the motor is de-energized allowing the crankshaft to move in the reverse direction, movement of the crankshaft in the reverse direction imparts energy to the crankshaft, and if the crankshaft stops moving in reverse direction or starts moving in the forward direction, the motor is energized causing the crank shaft to move in the forward direction with an increasing kinetic energy to overcome starting resistance of the motor.

[008] In an embodiment of the invention, the starter motor can be a conventional brushed DC motor, brushless DC motor, permanent magnet AC synchronous motor or a switched reluctance motor.

[009] In some embodiments, the motion sensor can be a hall-effect based crankshaft position sensor or a variable reluctance sensor or a sensor using back-emf voltage or a sensor based on battery or stator current and battery voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[010] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.

Figure 1 shows a starting system in accordance with an embodiment of the invention.

Figure 2 shows a flowchart of a method for starting an internal combustion engine in accordance with an embodiment of the invention.

Figure 3 shows a graphical representation of starting resistance as a function of crank angle in accordance with an embodiment of the invention.

Figure 4 shows a starting resistance for crankshaft motion in forward direction in accordance with an embodiment of the invention.

Figure 5 shows a crankshaft speed in forward direction for constant starter motor torque in accordance with an embodiment of the invention.

Figure 6 shows a crankshaft motion near recoverable region of starting resistance in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[01 1] The present invention is drawn towards a system and a method of starting an internal combustion engine using a motor, wherein the motor has a maximum torque which is less than the peak value of starting resistance without requiring means for reversing the direction of motor energization.

[012] Figure 1 shows a starting system 100 for an internal combustion engine 200 in accordance with an embodiment of the invention. The system comprises a battery 1 10, a motor 120, a control unit 130, and a motion sensor 140.

[013] As shown, the staring system is connected to an engine of the vehicle. More particularly, the motor is connected to a crankshaft of the engine.

[014] The motor can either be a conventional ^' brushed DC motor, or it could be a different type of electric motor such as a brushless DC motor, permanent magnet AC synchronous motor or a switched reluctance motor.

[015] The motion sensor monitors movement/position of the crankshaft and provides this information to the control unit. Based on the information received from the sensor, the control unit energizes/de-energizes the motor to start the engine accordingly. The motion sensor could either be a hall-effect based crankshaft position sensor or it could be a variable reluctance type of sensor, or a sensor using the back-emf voltage generated due to crankshaft motion or a sensor based on battery or stator current and battery voltage or any other suitable sensor.

[016] The starting system attains a substantially continuous motion of the crankshaft at speeds large enough for the combustion process to begin. Due to the uneven nature of the starting resistance (as illustrated in Figure 3), it is inevitable that the crankshaft speed during the starting process does not remain constant, but varies depending on the starting resistance. Typically, the crankshaft speed drops in the region where the starting resistance is high, and recovers back when the high resistance region is passed. This is illustrated in Figure 5. From Figure 5, it is conceivable that once a certain crankshaft speed is attained, it is possible to perform a continuous motion of the crankshaft while applying a torque equal to only the average starting resistance. If the crankshaft speed when entering the region where the resistance is more than the applied force is high enough, it is ensured that while the crankshaft speed reduces during the region of high starting resistance, the crankshaft does not come to a standstill. Subsequently, when the high resistance region is passed, the crankshaft speed recovers back to the original value. Thus, if it is ensured through appropriate means that the crankshaft attains a specific speed (speed ooentry in Figure 5), it will keep rotating without coming to a standstill even if the torque applied by the starter motor is lesser than the peak starting resistance.

[017] The operation of the system is illustrated through a method flowchart shown in Figure 2. As shown, the method starts at step 2A, where a start command is received by the system to start the engine. On receiving the start command, at step 2B the motor is energized in a forward direction i.e. direction along which engine normally operates. Energizing the motor causes the crankshaft to move in a forward direction. At 2C, the method determines motion of the crankshaft to detect whether the crankshaft is moving in the forward direction or a reverse direction. The method also verifies status of the start command. Thereafter, at step 2D, the motor is energized or de-energized depending upon the start command and the motion of the crank shaft. If it is detected that the start command is withdrawn, motor power is removed. If it is detected that the start command is present, and the crankshaft stops moving in the forward direction or starts moving in the reverse direction, the motor is de-energized allowing the crankshaft to move in the reverse direction. Movement of the crankshaft in the reverse direction imparts energy to the crankshaft. [018] If it is detected the start command is present and the crank shaft stops moving in reverse direction or start moving in the forward direction, the motor is energized causing the crank shaft to move in the forward direction with an increasing kinetic energy to overcome starting resistance of the engine.

[019] The rationale behind the above operations will now be explained. It has been shown in Figure 3 that the starting resistance as a function of crank angle consists of distinct peaks. The starting resistance can be thought to be composed of two elements: a dissipative element and a recoverable element. The dissipative element, which largely constitutes the engine friction, dissipates the energy from the starter motor as heat. On the other, hand, the energy imparted to the starter motor to move against the recoverable element is recovered back in the starter motor as an assisting force when a certain crank angle is reached. This is illustrated in Figure 4, which shows that while a resistance is faced when moving the crankshaft through region 1 , a portion of the energy imparted in the starter motor is recovered back as an assisting force when the crankshaft moves through region 2. The recoverable element in the starting resistance arises due to the spring loading while opening the intake valve and the exhaust valve, and due to the gas compression process during the compression stroke. When the crankshaft is moving through a recoverable resistance, a part of the energy being imparted in the crankshaft is being stored in the recoverable element, and is returned to the crankshaft if the crankshaft moves along the direction of the recoverable resistance.

[020] Figure 6 shows behavior pattern of the crankshaft motion near the recoverable element of the starting resistance. It is assumed that the crankshaft starts from standstill from the position A, and a constant starter motor torque of a value less than the peak starting resistance but more than twice of the average dissipative starting resistance is applied. As shown in Figure 6, in region from position A to position B, value of starting resistance is less than the motor torque, whereas from position B to position C, the value of starting resistance is more than the motor torque. If it is assumed that the crankshaft comes to a standstill at position D, then the energy stored in the recoverable element of the starting resistance is (Fm-Ff)^*x, where x is the distance from point A to point D. If it is assumed that the motor torque is thereby removed, the crankshaft will rotate in the reverse direction due to the force exerted by the recoverable element. For this reverse motion, since the only opposing force is the dissipative element of starting resistance (which will oppose the reverse motion), the distance to which the reverse motion will occur will be given by y = (Fm-Ff)^*x/Ff. If the motor torque is more than twice the dissipative starting resistance, then it can be seen that magnitude of y is greater than that of x, that is, the crankshaft will move to a point E farther from point D as compared to point A. If, when the crankshaft comes to rest after the reverse motion, the motor torque is re-applied, it is easy to see that point F to which the crankshaft will be able to travel before coming to standstill will be farther than point D. Thus, by repeating this maneuver multiple times if required, it is possible to go past point C. Once the crankshaft moves past point C, the recoverable element will assist the forward motion of the crankshaft, and energy that was stored in the recoverable element in moving from point B to point C will be imparted back to the crankshaft. Thus, by suitably detecting the crankshaft motion and energizing/de-energizing the starter motor, it is possible to move past the region where the instantaneous starting resistance is more than the motor torque without net loss of kinetic energy while energizing the starter motor in only one direction. By following this procedure, it follows that the crankshaft kinetic energy will keep on increasing till it comes to a value where the crankshaft motion will continue, without coming to standstill, even in regions where instantaneous starting resistance is more than the starter motor torque.

[021 ] While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.

Claims

CLAIMS:

1 . A method of starting an internal combustion engine, the method comprising: receiving a start command;

energizing a motor coupled to a crankshaft in response to the start command causing the crank shaft to move in a forward direction;

detecting the motion of the crankshaft in the forward direction and a reverse direction through motion detection means; and

energizing or de-energizing the motor depending upon the start command and the motion of the crankshaft whereby

if the crankshaft stops moving in the forward direction or starts moving in the reverse direction the motor is de-energized allowing the crankshaft to move in the reverse direction, movement of the crankshaft in the reverse direction imparts energy to the crankshaft, and

if the crankshaft stops moving in reverse direction or starts moving in the forward direction, the motor is energized causing the crank shaft to move in the forward direction with an increasing kinetic energy to overcome starting resistance of the motor.

2. A starting system for an internal combustion engine, the system comprising of: a motor coupled to a crankshaft causing the crank shaft to move in a forward direction when the motor is energized in response to a start command;

a motion sensor for detecting the motion of the crankshaft; and a control unit for energizing or de-energizing the motor depending upon the start command and the motion of the crank shaft whereby

3. The system as claimed in claim 2, wherein the starter motor can be a conventional brushed DC motor, brushless DC motor, permanent magnet AC synchronous motor or a switched reluctance motor.

4. The system as claimed in claim 2, wherein the motion sensor can be a hall-effect based crankshaft position sensor or a variable reluctance sensor or a sensor using back-emf voltage or a sensor based on battery or stator current and battery voltage.