IMPROVED ENGINE IGNITION STRATEGY

Abstract

Method for automatically starting a motor vehicle engine during a start / stop event, comprising the following: Initiating a starting process by actuating a brushless motor starter, wherein the brushless motor starter is configured to deliver a predetermined maximum starting speed; and after the motor is synchronized and the brushless motor starter has reached its maximum starting speed: Providing an air-fuel mixture with reduced enrichment for the engine; and triggering the ignition of the engine, furthermore, including the expulsion of hot intake gases from the engine after the engine is synchronized and the brushless motor starter has reached maximum starting speed and before the engine is supplied with a reduced enrichment air-fuel mixture, furthermore, comprehensively maintaining the starting of the motor at the maximum starting speed of the brushless motor starter after the brushless motor starter has reached the maximum starting speed, furthermore, encompassing the skipping of all injection events for a first cycle of a first firing cylinder after the engine is synchronized and the brushless engine starter has reached maximum starting speed and before the engine is supplied with a reduced enrichment air-fuel mixture, where providing an air-fuel mixture with reduced enrichment for the engine further includes providing an air-fuel mixture with reduced enrichment for the engine which contains between 10% and 25% more fuel than a stoichiometric air-fuel mixture.

Description

INTRODUCTION

[0001] The present disclosure relates to internal combustion engines and the prevention of pre-ignition and engine knock during a warm start, e.g., during a start-stop operation.

[0002] Many modern automobiles are equipped with start-stop systems. The idea behind the start-stop system is simple. When the engine is switched off briefly, for example when waiting at a traffic light, fuel consumption and emissions are reduced. In this way, the automatic start-stop system helps save fuel and protect the climate. The automatic start-stop system detects when the vehicle is stationary and, with the help of sensors, determines a number of other factors about the vehicle's operating status. In some newer models, the engine even switches off when the speed drops below a certain value. Although the engine, and thus the primary power source for all systems, is switched off, all electrical consumers and auxiliary devices continue to receive power. This power is provided by the vehicle's battery. As soon as the driver releases the brake pedal, the automatic start-stop system restarts the engine.If the vehicle is braked to a stop and the driver's foot remains on the brake pedal, the automatic start-stop system shuts off the engine. When the brake is released, the system restarts the engine.

[0003] One problem that can occur in vehicles with start-stop systems is pre-ignition and engine knocking. When a hot engine is shut down during a start / stop cycle, hot gases become trapped inside the engine. When the system attempts to restart the vehicle's engine, the hot gases inside the engine cause pre-ignition of the fuel in the cylinders, leading to engine knocking.

[0004] One way to prevent pre-ignition and knocking when restarting a hot engine is to provide a rich fuel mixture during the restart. In current vehicles, a rich fuel mixture contains up to 1.45 times more fuel (45% more) than the fuel mixture used in normal, steady-state operation of the running engine. The additional fuel means more fuel must evaporate for combustion. This prevents abnormal combustion (pre-ignition) and ensures stability.

[0005] Unfortunately, a side effect of using a rich fuel mixture is an increase in particulate matter or soot in the exhaust. Given the strict emissions regulations for motor vehicles, this is a problem for car manufacturers.

[0006] While today's motor vehicles with start-stop systems serve their purpose, there is a need for a new and improved system and method to control pre-ignition and engine knock during restart of a hot engine without increasing the level of particulates or soot in the engine exhaust.

[0007] US 2021 / 0 025 364 A1 describes a system for reducing cold-start emissions from a motor vehicle. A brushless DC motor is coupled to an engine to start the engine. Upon receiving a cold-start signal from a cold-start actuator, the engine controller activates the brushless DC motor to start the engine for a cold-start duration and to increase fuel pressure. Upon receiving an auto-start signal from an auto-start actuator, the engine controller activates the brushless DC motor to start the engine for an auto-start duration that is shorter than the cold-start duration. After the cold-start or auto-start duration has elapsed, an engine controller activates the fuel delivery system to supply fuel to the engine. DESCRIPTION

[0008] The object of the invention is to prevent pre-ignition and engine knocking. This object is achieved by the subject matter according to claim 1. Further developments can be found in the subclaims.

[0009] According to several aspects of the present disclosure, a method for automatically starting a motor vehicle engine during a start / stop event includes initiating a starting process by actuating a brushless engine starter and, after the engine is synchronized and the engine starter has reached maximum starting speed, providing a reduced enrichment fuel mixture to the engine and initiating ignition of the engine.

[0010] In another aspect, the method includes providing a reduced enrichment air-fuel mixture to the engine that contains between 10% and 25% more fuel than a stoichiometric air-fuel mixture.

[0011] In another aspect, the method includes expelling hot intake gases from the engine after the engine is synchronized and the brushless engine starter has reached maximum starting speed and before a reduced enrichment air-fuel mixture is supplied to the engine.

[0012] In another aspect, the method includes maintaining cranking of the engine at the maximum cranking speed of the brushless motor starter after the brushless motor starter has reached the maximum cranking speed.

[0013] In another aspect, the method includes skipping all injection events for a first cycle of a first firing cylinder after the engine is synchronized and the brushless engine starter has reached maximum starting speed and before a reduced enrichment air-fuel mixture is supplied to the engine.

[0014] In another aspect, the method includes skipping all injection events for both a first cycle of a first firing cylinder and a first cycle of a second firing cylinder after the engine is synchronized and the engine starter has reached maximum cranking speed and before a reduced enrichment air-fuel mixture is supplied to the engine.

[0015] In another aspect, the method includes initiating the ignition of the engine within less than 400 milliseconds after activation of the start-up process.

[0016] According to several aspects of the present disclosure, an automotive internal combustion engine includes an engine starter configured to start the engine and a controller configured to initiate an automatic start event during a start / stop event by actuating the engine starter, and, after the engine is synchronized and the engine starter has reached maximum starting speed, expel hot intake gases from the engine by skipping a first injection event for one of a first cylinder and both a first cylinder and a second cylinder, supply the engine with a reduced enrichment fuel mixture containing only between 10% and 25% more fuel than a stoichiometric air-fuel mixture, and initiate ignition of the engine less than 400 milliseconds after activation of the start event.

[0017] Further areas of applicability will become apparent from the present description. It should be understood that the description and specific examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE CHARACTERS

[0018] The figures described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way. Fig. 1 is a perspective view of an automotive engine according to an exemplary embodiment; Fig. 2 is a schematic view of a fuel system for the Fig. 1 illustrated motor vehicle engine according to an exemplary embodiment; and Fig. 3 is a flowchart illustrating a method according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION

[0019] The following description is merely exemplary and is not intended to limit the present disclosure, application, or uses.

[0020] Referring to Fig. 1, an automotive engine 10 according to the present disclosure includes an engine starter 12 suitable for starting the engine 10. The engine starter 12 provides input torque to a crankshaft input portion of the engine 10 to facilitate a cold start or restart. The engine starter 12 may be connected to a flywheel portion of the engine 10 via a mechanical geared connection to transmit torque to a crankshaft to start the engine 10. In another example, the engine starter 12 may be connected to a crank pulley via a mechanical timing belt connection to transmit torque to the crankshaft of the engine 10.

[0021] The engine 10 is an internal combustion engine, and the engine starter 12 is a brushless engine starter 12 configured to provide a predetermined maximum starting speed. A conventional brushed engine starter will start the engine 10 at a maximum starting speed appropriate for that engine 10. For example, a large, high-displacement, 8-cylinder engine may be coupled with a conventional brushed starter, providing a maximum starting speed of 140 rpm. A smaller-displacement engine, such as a small 4-cylinder engine, would be coupled with a conventional brushed starter, providing a maximum starting speed much greater than 140 rpm. A predetermined maximum starting speed for a brushless engine starter 12 of the present disclosure has a maximum starting speed that is at least 30% faster than a conventional starter for a particular engine.Referring to the example above, a brushless motor starter 12 for a large displacement 8-cylinder engine may have a maximum starting speed of at least 190 rpm, and a brushless motor starter 12 for a smaller displacement 4-cylinder engine may have a much higher maximum starting speed.

[0022] According to an exemplary embodiment, the motor starter 12 is a brushless permanent magnet DC motor coupled to the engine 10 to generate starting torque for restarting the engine 10. In one example, the motor starter 12 is powered by a high-voltage traction battery via a high-voltage bus. The high-voltage operation of the motor starter 12 provides high cranking speeds to enable rapid engine restart after an engine shutdown, e.g., during a start-stop operation. In other examples, the motor starter 12 may be powered directly from a low-voltage power supply. For example, a conventional drive system with an internal combustion engine and no high-voltage power source may still fall within the scope of the present disclosure.In such cases, engine start-stop functions can operate with improved performance using the motor starter 12 configurations described here. The brushless motor starter 12 is designed so that additional power amplification is not required, even when powered from a low-voltage line. For example, considering 12-volt vehicle electrical systems, a brushless motor starter introduces a voltage drop while drawing current during engine cranking. As previously mentioned, a power amplifier such as an energy storage capacitor or a DC-to-DC boost converter can be used to mitigate the effects of the voltage drop. A brushless motor starter 12 requires less initial current draw to engage the rotor, eliminating the voltage drop during engine cranking and thus reducing the need for additional power amplification.

[0023] A battery 14 supplies power to the engine starter 12. An operator can selectively actuate the engine starter 12 via an ignition switch 16 to start the engine 10. A control unit 18 connected to the vehicle engine 10 controls the operation of the engine 10, including the engine starter 12, a fuel system 20, the spark plugs, etc. As shown in Fig. 2, the fuel system 20 includes a fuel pump 22 that draws fuel from a fuel tank 24. The fuel pump 22 feeds fuel into fuel lines 26, which in turn supply fuel to a plurality of fuel injectors 28. Each of a plurality of cylinders of the engine 10 is associated with a fuel injector 28. As shown, the fuel system 20 includes eight injectors 28. A fuel injector 28 is configured to supply fuel to each of the eight cylinders in the engine 10. In a gasoline internal combustion engine, the control unit 18 may also control the firing of the spark plugs in the engine 10.

[0024] It should be understood that the controller 18 may be any programmable electronic control unit or a dedicated electronic control unit. Similarly, the processes, methods, or algorithms disclosed herein may be stored as data and instructions executable by a controller or computer in many forms, including, but not limited to, information permanently stored on non-writable storage media such as read-only memory devices and information modifiably stored on writable storage media such as floppy disks, magnetic tapes, compact discs, RAM devices, and other magnetic and optical media. The processes, methods, or algorithms may also be implemented in an executable software object.Alternatively, the processes, methods, or algorithms may be embodied in whole or in part by suitable hardware components such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), state machines, controllers, or other hardware components or devices, or a combination of hardware, software, and firmware components.

[0025] The control unit 18 is designed to initiate an automatic starting process during a start / stop process by actuating the engine starter 12. After the engine 10 is synchronized and the engine starter 12 has reached maximum starting speed, the control unit 18 can supply a reduced-enrichment fuel mixture to the engine 10 and initiate the ignition of the engine 10. During normal engine operation, a stoichiometric air-fuel mixture, or a mixture close to it, is supplied to the cylinders in the engine. A stoichiometric air-fuel mixture is the air-fuel ratio at which exactly all of the available oxygen is used to completely, or at least optimally, combust the fuel. The stoichiometric air-fuel mixture depends on many characteristics of the engine and is different for each engine.In an exemplary embodiment, the reduced enrichment fuel mixture contains between 10% and 25% more fuel than the stoichiometric fuel mixture for that engine.

[0026] In an exemplary embodiment, the controller 18 is configured to exhaust hot intake gases from the engine 10 after the engine has been synchronized and the engine starter 12 has reached maximum starting speed and before an enriched fuel mixture is supplied to the engine 10.

[0027] In another exemplary embodiment, the controller 18 is configured to maintain engine cranking after the engine starter 12 has reached maximum cranking speed to expel the hot intake gases from the engine 10 before supplying the reduced enrichment fuel mixture to the engine 10.

[0028] In another exemplary embodiment, the controller 18 is configured to exhaust hot intake gases from the engine 10 by skipping all injection events for a first cycle of a first fuel injector 28A after the engine 10 is synchronized and the engine starter 12 has reached maximum cranking speed and before a reduced enrichment fuel mixture is supplied to the engine 10.

[0029] In another exemplary embodiment, the controller 18 is configured to exhaust hot intake gases from the engine 10 by skipping all injection events for a first cycle for both a first fuel injector 28A and a second fuel injector 28B after the engine 10 is synchronized and the engine starter 12 has reached maximum starting speed and before supplying a reduced enrichment fuel mixture to the engine 10.

[0030] To ensure smooth vehicle operation during a start / stop process without any noticeable delay for the driver, it is important that the engine 10 restarts quickly. During a start / stop process, the engine 10 restart (start process) is triggered, for example, when the driver releases the brake pedal. In an exemplary embodiment, the control unit 18 is configured to initiate the ignition of the engine 10 within 400 milliseconds of initiating the start process.

[0031] In Fig. 3, a method for automatically starting a motor vehicle engine 10 during a start-stop event is illustrated generally at 100. Starting at block 102, the control unit 18 begins a starting process by actuating a brushless engine starter 12 whose maximum starter speed is at least 30% higher than the maximum starter speed of a conventional brush starter.

[0032] In block 104, the control unit 18 monitors the engine 10, including the position of the pistons within the engine 10, to determine when the engine 10 is synchronized. The control unit 18 uses sensors within the engine 10 to monitor the positions of the pistons in the cylinders of the engine 10. For proper combustion in the cylinders of the engine 10, the fuel must be injected into the cylinders and ignited when the piston is in the correct position in the cylinder. For a gasoline engine, the control unit 18 monitors the position of the pistons in the cylinders and precisely controls when the fuel injectors 28 inject fuel into a cylinder and when a spark plug is actuated to initiate ignition. For a diesel engine, the control unit 18 monitors the position of the pistons in the cylinders and precisely controls when the fuel injectors 28 inject fuel into a cylinder.The engine 10 is synchronized when the control unit 18 detects that the pistons are in the correct position in the cylinders.

[0033] After the engine 10 is synchronized and the engine starter 12 has reached the maximum starting speed, the control unit 18 controls the fuel system 20 in block 106 to supply the engine 10 with a less enriched air-fuel mixture and triggers the ignition of the engine 10 in block 108.

[0034] In an exemplary embodiment, the reduced enriched air-fuel mixture contains between 10% and 25% more fuel than a stoichiometric base fuel air-fuel mixture. When the engine 10 is running under normal operating conditions, a stoichiometric base fuel mixture is delivered to the cylinders. As previously mentioned, to avoid pre-ignition and knock during a warm start, an enriched fuel mixture containing more than 45% more fuel than the base stoichiometric fuel mixture is often used. The use of a brushless engine starter 12 enables the use of a fuel mixture enriched with only 10% to 25% more fuel than the base stoichiometric mixture. A brushless engine starter has a maximum cranking speed at least 30% higher than a conventional brush starter.The high power density of the brushless starter 12 enables a faster restart with a shortened ignition delay time (the time between the end of the injection timing and the ignition timing), resulting in approximately 30% faster ignition of the engine 10 than with a conventional starter. This reduces the likelihood of pre-ignition (or knocking) during the restart of the engine 10.

[0035] As previously mentioned, when the engine 10 is shut down during a start-stop operation, hot gases become trapped within the engine 10. During the restart of the engine 10, the hot gases in the cylinders increase the likelihood of pre-ignition and knock in the engine. At block 110, in an exemplary embodiment, the method includes expelling hot intake gases from the engine 10 after the engine 10 has been synchronized and the engine starter 12 has reached maximum starting speed and before a reduced-enriched air-fuel mixture is supplied to the engine 10.

[0036] In an exemplary embodiment, in block 112, venting hot intake gases from the engine 10 includes cranking the engine at the maximum cranking speed of the brushless motor starter 12 after the brushless motor starter 12 has reached the maximum cranking speed and before a reduced enrichment fuel mixture is supplied to the engine 10.

[0037] The cylinders in the engine are controlled by the control unit so that they fire in a specific order. As in Fig.As shown, each of the eight fuel injectors 28 is assigned to one of eight cylinders in the engine 10. Each of the eight fuel injectors 28 is identified by a number from 1 to 8. Once the engine 10 is synchronized and the engine starter 12 has reached maximum cranking speed, a rich fuel mixture is supplied to the cylinders in this order: first to a first fuel injector 28A and a first cylinder, then to a second fuel injector 28B and a second cylinder, and so on. The cylinders always fire in this order.

[0038] At block 114, in an exemplary embodiment, the hot intake gases are expelled from the engine by skipping all injection events for a first cycle of the first fuel injector 28A and the first cylinder. Once the engine 10 is synchronized and the engine starter 12 reaches maximum cranking speed, cranking of the engine 10 is maintained while the engine 10 is allowed to complete one piston stroke, or one cycle of the first cylinder, without any fuel mixture being delivered to the first cylinder. This cycling of pistons, intake, and exhaust valves within the engine 10 allows some of the hot intake gases trapped within the engine 10 to be vented from the engine 10 before combustion occurs, reducing the likelihood of pre-ignition and engine knock.

[0039] At block 116, in another exemplary embodiment, the hot intake gases are expelled from the engine by skipping all injection events for both the first fuel injector 28A and the first cylinder, and a second fuel injector 28B and a second cylinder. Once the engine 10 is synchronized and the engine starter 12 reaches maximum cranking speed, cranking of the engine 10 is maintained while the engine 10 is allowed to complete one piston stroke or cycle of both the first fuel injector 28A and the first cylinder, and the second fuel injector 28B and the second cylinder, without any fuel mixture being delivered to either the first or second cylinder.This allows a greater portion of the hot intake gases trapped within the engine 10 to be removed from the engine 10 before combustion occurs, further reducing the likelihood of pre-ignition and engine knock.

[0040] As described above, it is desirable for the ignition of the engine 10 to occur within 400 milliseconds of the activation of the start event. Skipping injection events, as described above in blocks 114 and 116, is enabled by the brushless engine starter 12. While skipping injection events increases the engine cranking time, the high power density of the brushless engine starter 12 enables a faster restart with a reduced ignition delay time. This enables the use of intentional ignition delay by skipping ignition events, as described in blocks 114 and 116, while still allowing the ignition of the engine 10 to occur within 400 milliseconds of the activation of the start event.

[0041] An automotive engine 10 and the method of the present disclosure provide several advantages. The use of a brushless engine starter 12 with a maximum cranking speed at least 30% higher than conventional brush starters allows for the use of a fuel mixture enriched with only 10% to 25% more fuel than a stoichiometric fuel mixture used during normal operation. The high power density of the brushless engine starter 12 enables a faster restart with a reduced ignition delay time, thereby reducing the likelihood of pre-ignition (or knock) during a restart of the engine 10. This also has the advantage of producing less particulate matter or soot in the engine exhaust compared to other methods that use higher fuel enrichment fuel mixtures.The use of a brushless engine starter 12 further enables intentional delay by maintaining engine cranking and skipping pre-ignition injections to remove some of the hot intake gases trapped within the engine 10, further reducing the likelihood of pre-ignition and engine knock. The brushless engine starter 12 enables this while ensuring ignition of the engine 10 within 400 milliseconds of initiating the start-up sequence.

[0042] The description of the present disclosure is merely exemplary, and variations that do not depart from the gist of the present disclosure are intended to be within the scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure. The features of various embodiments disclosed herein may be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments have been described as being advantageous or preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those skilled in the art will recognize that one or more characteristics or features may be compromised to achieve desired overall system characteristics, depending on the specific application and implementation.These characteristics may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, maintainability, weight, manufacturability, ease of assembly, etc. Therefore, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more features are not outside the scope of the disclosure and may be desirable for certain applications.

Claims

[1] A method for automatically starting a motor vehicle engine during a start / stop event, comprising: Initiating a starting operation by actuating a brushless motor starter, the brushless motor starter being configured to provide a predetermined maximum starting speed; and after the motor is synchronized and the brushless motor starter has reached the maximum starting speed: Providing a reduced enrichment air-fuel mixture to the engine; and triggering the engine ignition, further comprising expelling hot intake gases from the engine after the engine is synchronized and the brushless engine starter has reached maximum starting speed and before a reduced enrichment air-fuel mixture is supplied to the engine, further comprising maintaining the starting of the motor at the maximum starting speed of the brushless motor starter after the brushless motor starter has reached the maximum starting speed, further comprising skipping all injection events for a first cycle of a first firing cylinder after the engine is synchronized and the brushless engine starter has reached maximum starting speed and before a reduced enrichment air-fuel mixture is supplied to the engine, wherein providing a reduced enrichment air-fuel mixture to the engine further comprises providing a reduced enrichment air-fuel mixture to the engine containing between 10% and 25% more fuel than a stoichiometric air-fuel mixture. [2] The method of claim 1, further comprising skipping all injection events for both a first cycle of a first firing cylinder and a first cycle of a second firing cylinder after the engine is synchronized and the brushless engine starter has reached maximum cranking speed and before a reduced enrichment air-fuel mixture is supplied to the engine. [3] The method of claim 1, further comprising skipping all injection events for a first cycle of a first firing cylinder after the engine is synchronized and the brushless engine starter has reached maximum cranking speed and before a reduced enrichment air-fuel mixture is supplied to the engine. [4] The method of claim 3, further comprising skipping all injection events for both a first cycle of a first firing cylinder and a first cycle of a second firing cylinder after the engine is synchronized and the brushless motor starter has reached maximum starting speed and before a reduced enrichment air-fuel mixture is supplied to the engine.

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