Automobile starter control circuit and its control method and diagnosis method

Abstract

The present invention relates to the field of automotive control technology, and more specifically to an automotive starter control circuit and its control and diagnostic methods. The circuit comprises a first relay K1, a second relay K2, and an engine control unit. The contact terminals of the first relay K1 and the second relay K2 are sequentially connected in series between a battery and a starter. The coil terminals of the first relay K1 are electrically connected to the battery and a first control signal output terminal of the engine control unit, respectively. The coil terminals of the second relay K2 are electrically connected to the battery and a second control signal output terminal of the engine control unit, respectively. A sampling node A is provided between the second relay K2 and the starter, and the sampling node A is electrically connected to a sampling signal input terminal of the engine control unit. By providing a starter control circuit and a control method for the circuit, the number of times the relay contacts operate under load is reduced, thereby increasing the service life of the relays and, consequently, the service life of the starter control circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile control, and in particular to an automobile starter control circuit and a control method and a diagnosis method thereof. Background Art

[0002] As the country continues to enact increasingly stringent fuel consumption regulations, more and more vehicles are equipped with automatic engine start-stop systems. Automatic engine start-stop automatically shuts down the vehicle when it stops temporarily (for example, at a red light). When it's time to continue driving, the system automatically restarts the engine. This system integrates an enhanced starter with idle start-stop functionality into a conventional engine. This allows the engine to completely shut down when the idle stop conditions are met. When the vehicle needs to start again, the enhanced idle start-stop system quickly responds to the driver's start command, quickly starting the engine and instantly connecting, significantly reducing fuel consumption and exhaust emissions. Because the enhanced starter needs to be started frequently during vehicle operation, its service life is required to be longer, necessitating a simultaneous increase in the service life of the starter control circuit. Summary of the Invention

[0003] The purpose of the present invention is to address the defects of the prior art and provide an automobile starter control circuit and its control method and diagnosis method. By providing a starter control circuit and a circuit control method to reduce the number of load operations of the relay contacts, the service life of the relay is increased, thereby increasing the service life of the starter control circuit.

[0004] The present invention provides an automobile starter control circuit, comprising a first relay K1, a second relay K2, and an engine control unit. Contact ends of the first relay K1 and the second relay K2 are sequentially connected in series between a battery and a starter. A coil end of the first relay K1 is electrically connected to a first control signal output end of the battery and the engine control unit, respectively. A coil end of the second relay K2 is electrically connected to a second control signal output end of the battery and the engine control unit, respectively. A sampling node A is provided between the second relay K2 and the starter, and the sampling node A is electrically connected to a sampling signal input end of the engine control unit.

[0005] The present invention also provides a control method for an automobile starter control circuit, comprising:

[0006] The engine control unit controls the starter motor by alternating the on-off timing of the first relay and the on-off timing of the second relay;

[0007] The first relay on-off timing sequence includes:

[0008] When starting the starter, the first relay K1 is first closed, and after the set time interval is reached, the second relay K2 is closed to complete the power supply to the starter;

[0009] When the starter starts to drive the engine and the engine reaches the target speed, the first relay K1 is turned off first, and then the second relay K2 is turned off after the set time interval is reached;

[0010] The second relay on-off timing sequence includes:

[0011] When starting the starter, the second relay K2 is first energized, and after the set time interval is reached, the first relay K1 is energized to complete the power supply to the starter.

[0012] When the starter starts to drive the engine to run and the engine reaches the target speed, the second relay K2 is turned off first, and then the first relay K1 is turned off after the set time interval is reached.

[0013] More preferably, the set time interval is 100ms to 200ms.

[0014] The present invention also provides a method for diagnosing an automobile starter control circuit, comprising:

[0015] When the engine control unit issues a closure command for the first relay K1 and issues a closure command for the second relay K2 after the set time interval, the starter does not work. If the voltage collected by the sampling signal input terminal of the engine control unit is always a low-level voltage, or

[0016] When the engine control unit issues a closure command for the second relay K2 and then issues a closure command for the first relay K1 after the set time interval, the starter does not work. If the voltage collected by the sampling signal input terminal of the engine control unit is always a low-level voltage;

[0017] It is diagnosed that the first relay K1 and / or the second relay K2 has a normally-off fault.

[0018] More preferably, it also includes:

[0019] When the starter is in the working state before the first relay K1 or the second relay K2 is energized, if the voltage collected by the sampling signal input terminal of the engine control unit is always a high-level voltage, it is diagnosed that both the first relay K1 and the second relay K2 have a normally closed fault.

[0020] More preferably, it also includes:

[0021] When the engine control unit issues a closure command for the first relay K1, and then issues a closure command for the second relay K2 after the set time interval, the starter works, and the voltage collected by the sampling signal input terminal of the engine control unit is a high-level voltage, and after the engine reaches the target speed, the first relay K1 is turned off, the starter does not stop working, and the voltage collected by the sampling signal input terminal of the engine control unit is still a high-level voltage, or

[0022] When the engine control unit issues a closure command for the second relay K2, the starter works and the voltage collected by the sampling signal input terminal of the engine control unit is a high-level voltage, after the set time interval is reached, the first relay K1 is issued a closure command, and after the engine reaches the target speed, the second relay K2 is issued a shutdown command, the starter stops working, and the voltage collected by the sampling signal input terminal of the engine control unit is a low-level voltage;

[0023] The diagnosis is that the first relay K1 has a normally closed fault and the second relay K2 is normal.

[0024] More preferably, it also includes:

[0025] When the engine control unit issues a closure command for the first relay K1, the starter works, and the voltage collected by the sampling signal input terminal of the engine control unit is a high-level voltage, after the set time interval is reached, the second relay K2 is issued a closure command, and after the engine reaches the target speed, the first relay K1 is issued a closure command, the starter stops working, and the voltage collected by the sampling signal input terminal of the engine control unit is a low-level voltage, or

[0026] When the engine control unit issues a closure command for the second relay K2, and after a set time interval has elapsed, it issues a closure command for the first relay K1, the starter operates, and the voltage collected at the sampling signal input terminal of the engine control unit is a high-level voltage. After the engine reaches the target speed, it issues a closure command for the second relay K2, the starter continues to operate, and the voltage collected at the sampling signal input terminal of the engine control unit is still a high-level voltage. After a set time interval has elapsed, it issues a closure command for the first relay K1, and the voltage collected at the sampling signal input terminal of the engine control unit is a low-level voltage;

[0027] The diagnosis is that the first relay K1 is normal, and the second relay K2 has a normally closed fault.

[0028] The beneficial effects of the present invention are:

[0029] 1. The present invention provides a starter control circuit that integrates the logic control of the engine control unit and subsequent circuit diagnosis through two series-connected electromagnetic relays combined with a voltage sampling circuit. Its circuit design is reasonable and conducive to the implementation of software control logic, providing a basis for the life of the relay.

[0030] 2. The circuit control method provided by the present invention employs two relays that alternately engage and disengage. Each time the starter starts and stops, both relays operate only once with load. This doubles the electrical life of the control circuit comprised of two relays compared to a single-relay control circuit. By reducing the number of times the relay contacts operate with load, this method extends the service life of the relays, thereby extending the service life of the starter control circuit.

[0031] 3. By controlling the on and off of the two relays and sampling the voltage at sampling node A, the relay control circuit can be diagnosed, effectively distinguishing between normally-off and normally-closed faults of the two relays, which is beneficial for troubleshooting and further improves the service life of the starter control circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of an automobile starter control circuit of the present invention;

[0033] Figure 2 This is a timing diagram of the starter start-stop for the first time under normal circumstances of the present invention;

[0034] Figure 3 This is a timing diagram of the second starter start-stop under normal circumstances of the present invention;

[0035] Figure 4 、 5 This is a start-stop timing diagram of two starters when the K1 relay is normally off and / or the K2 relay is normally off;

[0036] Figure 6 、 7 This is a starter start-stop timing diagram when the K1 relay and the K2 relay of the present invention are both normally closed;

[0037] Figure 8 、 9 This is a starter start-stop timing diagram when the K1 relay of the present invention is normally closed and the K2 relay is normal;

[0038] Figure 10 、 Figure 11 This is the starter start-stop timing diagram when the K2 relay of the present invention is normally closed and the K1 relay is normal. DETAILED DESCRIPTION

[0039] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, this application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0040] In the following description, specific details such as specific system structures and techniques are provided for purposes of illustration rather than limitation to facilitate a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid obscuring the description of the present application with unnecessary detail.

[0041] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or collections thereof.

[0042] It will also be understood that the term "and / or" used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0043] As used in this specification and the appended claims, the term "if" can be interpreted as "when" or "upon" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "upon determination" or "in response to determining" or "upon detection of [described condition or event]" or "in response to detecting [described condition or event]," depending on the context.

[0044] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0045] References to "one embodiment" or "some embodiments" in this specification mean that one or more embodiments of the present application include a particular feature, structure, or characteristic described in conjunction with that embodiment. Thus, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in other embodiments" appearing in various places in this specification do not necessarily refer to the same embodiment, but rather mean "one or more but not all embodiments," unless otherwise specifically emphasized. The terms "including," "comprising," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized. "Multiple" means "two or more."

[0046] Generally, the starter power supply of a car engine is controlled by an electromagnetic relay. The starting current of the starter can be greater than 300A. When the contacts of the electromagnetic relay are closed and opened, there will be spark erosion and wear. Therefore, reducing the number of times the relay contacts operate under load can increase the electrical life of the relay.

[0047] Example 1

[0048] Figure 1 The present invention shows an automobile starter control circuit, comprising a first relay K1, a second relay K2, and an engine control unit (ECU). The contact ends of the first relay K1 and the second relay K2 are sequentially connected in series between a battery and a starter. The coil end of the first relay K1 is electrically connected to the battery and a first control signal output terminal PIN1 of the ECU, respectively. The coil end of the second relay K2 is electrically connected to the battery and a second control signal output terminal PIN2 of the ECU, respectively. A sampling node A is provided between the second relay K2 and the starter, and the sampling node A is electrically connected to a sampling signal input terminal PIN3 of the ECU.

[0049] The present invention also provides a control method for an automobile starter control circuit, comprising:

[0050] The engine control unit controls the starter motor by alternating the on-off timing of the first relay and the on-off timing of the second relay;

[0051] The first relay on-off timing sequence includes:

[0052] When starting the starter, the first relay K1 is first closed, and after the set time interval is reached, the second relay K2 is closed to complete the power supply to the starter;

[0053] When the starter starts to drive the engine and the engine reaches the target speed, the first relay K1 is turned off first, and then the second relay K2 is turned off after the set time interval is reached;

[0054] The second relay on-off timing sequence includes:

[0055] When starting the starter, the second relay K2 is first energized, and after the set time interval is reached, the first relay K1 is energized to complete the power supply to the starter.

[0056] When the starter starts to drive the engine to run and the engine reaches the target speed, the second relay K2 is turned off first, and then the first relay K1 is turned off after the set time interval is reached.

[0057] In one embodiment, the set time interval is 100ms to 200ms.

[0058] The following takes the process of starting the starter twice as an example to illustrate:

[0059] When the starter is started for the first time, the first relay is energized first, and the second relay is energized 100ms-200ms later, completing the power supply to the starter so that the starter can work and drive the engine to run. When the engine reaches the target speed, the first relay is turned off first, stopping the power supply to the starter and disengaging the engine. The second relay is turned off 100ms-200ms later.

[0060] When starting the starter for the second time, the second relay is energized first, and then the first relay is energized after 100ms-200ms, completing the power supply to the starter so that the starter can work and drive the engine to run. When the engine reaches the target speed, the second relay is turned off first, stopping the power supply to the starter and disengaging the engine, and then the first relay is turned off after 100ms-200ms.

[0061] This sequence repeats the next time the starter is activated. The advantage of this control circuit is that it completes a complete starter start-stop process, equivalent to the K1 relay energizing with no load, the K2 relay energizing with load, then the K1 relay deenergizing with load, and the K2 relay deenergizing with no load. The next starter start-stop process is equivalent to the K2 relay energizing with no load, the K1 relay energizing with load, then the K2 relay deenergizing with load, and the K1 relay deenergizing with no load. Each time the starter is started or stopped, both relays operate only once, each with load. This two-relay control circuit doubles the electrical life of a single-relay control circuit. Simultaneously, the voltage at point A between the relay and the starter is sampled by the engine electronic control unit (ECU) on pin 3 to complete relay control circuit diagnosis.

[0062] The present invention also provides a method for diagnosing an automobile starter control circuit, comprising:

[0063] When the engine control unit issues a closure command for the first relay K1 and issues a closure command for the second relay K2 after the set time interval, the starter does not work. If the voltage collected by the sampling signal input terminal of the engine control unit is always a low-level voltage, or

[0064] When the engine control unit issues a closure command for the second relay K2 and then issues a closure command for the first relay K1 after the set time interval, the starter does not work. If the voltage collected by the sampling signal input terminal of the engine control unit is always a low-level voltage;

[0065] It is diagnosed that the first relay K1 and / or the second relay K2 has a normally-off fault.

[0066] In one embodiment, the diagnostic method further comprises:

[0067] When the starter is in the working state before the first relay K1 or the second relay K2 is energized, if the voltage collected by the sampling signal input terminal of the engine control unit is always a high-level voltage, it is diagnosed that both the first relay K1 and the second relay K2 have a normally closed fault.

[0068] In one embodiment, the diagnostic method further comprises:

[0069] When the engine control unit issues a closure command for the first relay K1, and then issues a closure command for the second relay K2 after the set time interval, the starter works, and the voltage collected by the sampling signal input terminal of the engine control unit is a high-level voltage, and after the engine reaches the target speed, the first relay K1 is turned off, the starter does not stop working, and the voltage collected by the sampling signal input terminal of the engine control unit is still a high-level voltage, or

[0070] When the engine control unit issues a closure command for the second relay K2, the starter works and the voltage collected by the sampling signal input terminal of the engine control unit is a high-level voltage, after the set time interval is reached, the first relay K1 is issued a closure command, and after the engine reaches the target speed, the second relay K2 is issued a shutdown command, the starter stops working, and the voltage collected by the sampling signal input terminal of the engine control unit is a low-level voltage;

[0071] The diagnosis is that the first relay K1 has a normally closed fault and the second relay K2 is normal.

[0072] In one embodiment, the diagnostic method further comprises:

[0073] When the engine control unit issues a closure command for the first relay K1, the starter works, and the voltage collected by the sampling signal input terminal of the engine control unit is a high-level voltage, after the set time interval is reached, the second relay K2 is issued a closure command, and after the engine reaches the target speed, the first relay K1 is issued a closure command, the starter stops working, and the voltage collected by the sampling signal input terminal of the engine control unit is a low-level voltage, or

[0074] When the engine control unit issues a closure command for the second relay K2, and after a set time interval has elapsed, it issues a closure command for the first relay K1, the starter operates, and the voltage collected at the sampling signal input terminal of the engine control unit is a high-level voltage. After the engine reaches the target speed, it issues a closure command for the second relay K2, the starter continues to operate, and the voltage collected at the sampling signal input terminal of the engine control unit is still a high-level voltage. After a set time interval has elapsed, it issues a closure command for the first relay K1, and the voltage collected at the sampling signal input terminal of the engine control unit is a low-level voltage;

[0075] The diagnosis is that the first relay K1 is normal, and the second relay K2 has a normally closed fault.

[0076] Example 2

[0077] This embodiment illustrates the diagnostic method of this solution in conjunction with the starter start-stop timing sequence under normal conditions and various faults.

[0078] 100-200ms after ECU PIN1 issues K1 relay energizing command, ECU PIN2 issues K2 relay energizing command. At this time, the starter power supply circuit is connected to the battery voltage, and the starter works. ECU PIN3 collects the voltage at point A, which is 12V. After the engine reaches the target speed, ECU PIN1 issues K1 relay energizing command, cutting off the battery voltage supply to the starter, and the starter stops working. At this time, the voltage collected by ECU PIN3 becomes 0. 100-200ms later, ECU PIN2 issues K2 relay energizing command. Figure 2 As shown:

[0079] Line ① represents the ECU PIN1 K1 relay control command, 0 means off, 1 means on

[0080] Line ② represents the ECU PIN2 K2 relay control command, 0 means off, 1 means on

[0081] Line ③ represents the sampling voltage value of point A of ECU PIN3 circuit

[0082] like Figure 3As shown, 100-200ms after ECU PIN2 issues the K2 relay energizing command, ECU PIN1 issues the K1 relay energizing command. At this point, the starter power supply circuit is connected to the battery voltage, and the starter operates. ECU PIN3 samples the voltage at point A, which is 12V. After the engine reaches the target speed, ECU PIN2 issues the K2 relay energizing command, disconnecting the battery voltage supply to the starter, and the starter stops operating. At this point, the voltage sampled by ECU PIN3 becomes 0, and 100-200ms later, ECU PIN1 issues the K1 relay energizing command. Repeat step 1 the next time you start the starter.

[0083] like Figure 4 As shown in the figure, when ECU PIN1 issues the K1 relay energizing command and 100-200ms later ECU PIN2 issues the K2 relay energizing command, the starter does not work. If the voltage at point A collected by ECU PIN3 is always 0V, it is diagnosed that the K1 relay and / or K2 relay has a normally-off fault.

[0084] like Figure 5 As shown in the figure, when ECU PIN2 issues the K2 relay energizing command 100-200ms later, ECU PIN1 issues the K1 relay energizing command, and the starter does not work, if the voltage at point A collected by ECU PIN3 is always 0V, it is diagnosed that the K1 relay and / or K2 relay has a normally-off fault.

[0085] like Figure 6 As shown in the figure, the starter has been working before the K1 relay and the K2 relay are energized. If the voltage at point A collected by the ECU PIN3 is always 12V, it is diagnosed that the K1 relay and the K2 relay have a normally closed fault at the same time.

[0086] like Figure 7 As shown in the figure, the starter has been working before the K1 relay and the K2 relay are energized. If the voltage at point A collected by the ECU PIN3 is always 12V, it is diagnosed that the K1 relay and the K2 relay have a normally closed fault at the same time.

[0087] like Figure 8As shown, 100-200ms after ECU PIN1 issues the K1 relay energize command, ECU PIN2 issues the K2 relay energize command. At this point, the starter power supply circuit is connected to the battery voltage, and the starter operates. ECU PIN3 collects the voltage at point A, which is 12V. After the engine reaches the target speed, ECU PIN1 issues the K1 relay OFF command, but the starter does not stop operating. Since the K1 relay is normally closed, the voltage collected by ECU PIN3 remains at 12V, indicating a K1 relay normally closed fault. 100-200ms later, ECU PIN2 issues the K2 relay OFF command, and the voltage collected by ECU PIN3 drops to 0. This diagnoses a K1 relay normally closed fault, and the K2 relay is normal.

[0088] like Figure 9 As shown, ECU PIN2 issues a command to close the K2 relay. Since the K1 relay is normally closed, the starter power supply circuit is connected to the battery voltage, and the starter is operating. The voltage at point A collected by ECU PIN3 is 12V, and a K1 relay fault is diagnosed. 100-200ms later, ECU PIN1 issues a command to close the K1 relay. After the engine reaches the target speed, ECU PIN2 issues a command to close the K2 relay, cutting off the battery voltage supply to the starter and causing the starter to stop operating. At this time, the voltage collected by ECU PIN3 becomes 0. 100-200ms later, ECU PIN1 issues a command to close the K1 relay. In other words, the K1 relay fault can be diagnosed as normally closed, and the K2 relay is normal.

[0089] like Figure 10 As shown, ECU PIN1 issues a command to close the K1 relay. Since the K2 relay is normally closed, the starter power supply circuit is connected to the battery voltage, causing the starter to operate. The voltage at point A measured by ECU PIN3 is 12V, indicating a normally closed K2 relay fault. 100-200ms later, ECU PIN2 issues a command to close the K2 relay. After the engine reaches the target speed, ECU PIN1 issues a command to close the K1 relay, cutting off the battery voltage supply to the starter and causing the starter to stop operating. At this point, the voltage measured by ECU PIN3 drops to 0. 100-200ms later, ECU PIN2 issues a command to close the K2 relay. In this case, the K2 relay is diagnosed as normally closed, and the K1 relay is normal.

[0090] like Figure 11As shown, ECU PIN2 issues a K2 relay energization command. 100-200ms later, ECU PIN1 issues a K1 relay energization command. At this point, the starter power supply circuit is connected to the battery voltage, and the starter operates. ECU PIN3 collects a voltage of 12V at point A. After the engine reaches the target speed, ECU PIN2 issues a K2 relay energization command, but the starter continues to operate. Since the K2 relay is normally closed, the voltage collected by ECU PIN3 remains at 12V, indicating a K2 relay normally closed fault. 100-200ms later, ECU PIN1 issues a K1 relay energization command, and the voltage collected by ECU PIN3 drops to 0. In this case, the K2 relay is diagnosed as normally closed, and the K1 relay is operating normally.

[0091] It should be understood that the specific order or hierarchy of steps in the disclosed processes is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process can be rearranged without departing from the scope of the present disclosure. The accompanying method claims present elements of the various steps in an exemplary order and are not intended to be limited to the specific order or hierarchy described.

[0092] In the foregoing detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that embodiments of the claimed subject matter require more features than are expressly recited in each claim. On the contrary, as reflected in the appended claims, the invention comprises less than all the features of any individual disclosed embodiment. The appended claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0093] The above description of the disclosed embodiments is intended to enable any person skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments without departing from the spirit and scope of the present disclosure. Therefore, the present disclosure is not limited to the embodiments presented herein but is intended to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0094] The foregoing description includes examples of one or more embodiments. Of course, it is not possible to describe all possible combinations of components or methods for the purposes of describing the above embodiments, but one of ordinary skill in the art will recognize that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to encompass all such changes, modifications and variations that fall within the scope of the appended claims. Furthermore, to the extent the term "comprising" is used in the specification or claims, the term is intended to be encompassed in a manner similar to the term "including," as explained in terms of "including," used as a transitional word in the claims. Furthermore, any use of the term "or" in the specification of the claims is intended to mean a "non-exclusive or."

[0095] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A control method for an automobile starter control circuit, characterized in that: Applicable to an automobile starter control circuit, the automobile starter control circuit includes a first relay K1, a second relay K2, and an engine control unit, wherein contact ends of the first relay K1 and the second relay K2 are sequentially arranged in series between a battery and a starter, a coil end of the first relay K1 is electrically connected to a first control signal output end of the battery and the engine control unit, respectively, a coil end of the second relay K2 is electrically connected to a second control signal output end of the battery and the engine control unit, a sampling node A is provided between the second relay K2 and the starter, and the sampling node A is electrically connected to a sampling signal input end of the engine control unit; The method comprises: The engine control unit controls the starter motor by alternating the on-off timing of the first relay and the on-off timing of the second relay; The first relay on-off timing sequence includes: When starting the starter, the first relay K1 is first closed, and after the set time interval is reached, the second relay K2 is closed to complete the power supply to the starter; When the starter starts to drive the engine and the engine reaches the target speed, the first relay K1 is turned off first, and then the second relay K2 is turned off after the set time interval is reached; The second relay on-off timing sequence includes: When starting the starter, the second relay K2 is first energized, and after the set time interval is reached, the first relay K1 is energized to complete the power supply to the starter. When the starter starts to drive the engine and the engine reaches the target speed, the second relay K2 is turned off first, and then the first relay K1 is turned off after the set time interval is reached; The set time interval is 100ms~200ms; When the engine control unit issues a closure command for the first relay K1 and issues a closure command for the second relay K2 after the set time interval, the starter does not work. If the voltage collected by the sampling signal input terminal of the engine control unit is always a low-level voltage, or When the engine control unit issues a closure command for the second relay K2 and then issues a closure command for the first relay K1 after the set time interval, the starter does not work. If the voltage collected by the sampling signal input terminal of the engine control unit is always a low-level voltage; The diagnosis is that the first relay K1 and / or the second relay K2 has a normally-off fault; When the starter is in the working state before the first relay K1 or the second relay K2 is energized, if the voltage collected by the sampling signal input terminal of the engine control unit is always high, it is diagnosed that both the first relay K1 and the second relay K2 have a normally closed fault; When the engine control unit issues a closure command for the first relay K1, and then issues a closure command for the second relay K2 after the set time interval, the starter works, and the voltage collected by the sampling signal input terminal of the engine control unit is a high-level voltage, and after the engine reaches the target speed, the first relay K1 is turned off, the starter does not stop working, and the voltage collected by the sampling signal input terminal of the engine control unit is still a high-level voltage, or When the engine control unit issues a closure command for the second relay K2, the starter works and the voltage collected by the sampling signal input terminal of the engine control unit is a high-level voltage, after the set time interval is reached, the first relay K1 is issued a closure command, and after the engine reaches the target speed, the second relay K2 is issued a shutdown command, the starter stops working, and the voltage collected by the sampling signal input terminal of the engine control unit is a low-level voltage; The diagnosis is that the first relay K1 has a normally closed fault, and the second relay K2 is normal; When the engine control unit issues a closure command for the first relay K1, the starter works, and the voltage collected by the sampling signal input terminal of the engine control unit is a high-level voltage, after the set time interval is reached, the second relay K2 is issued a closure command, and after the engine reaches the target speed, the first relay K1 is issued a closure command, the starter stops working, and the voltage collected by the sampling signal input terminal of the engine control unit is a low-level voltage, or When the engine control unit issues a closure command for the second relay K2, and after a set time interval has elapsed, it issues a closure command for the first relay K1, the starter operates, and the voltage collected at the sampling signal input terminal of the engine control unit is a high-level voltage. After the engine reaches the target speed, it issues a closure command for the second relay K2, the starter continues to operate, and the voltage collected at the sampling signal input terminal of the engine control unit is still a high-level voltage. After a set time interval has elapsed, it issues a closure command for the first relay K1, and the voltage collected at the sampling signal input terminal of the engine control unit is a low-level voltage; The diagnosis is that the first relay K1 is normal, and the second relay K2 has a normally closed fault.

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