Valve driving circuit and air suspension controller

Abstract

The utility model provides a valve driving circuit and an air suspension controller, and the circuit comprises a first driving unit which is connected with a power supply and one end of a valve coil; when the valve works, working current flows to the valve coil from the first driving unit; the second driving unit is connected with the other end of the valve coil and the ground, and when the valve works, the working current flows to the second driving unit from the valve coil; the first follow current unit is respectively connected with one end of the valve coil and the ground, and follow current flows to the valve coil from the first follow current unit when the valve is closed; and the second follow current unit is respectively connected with the power supply and the other end of the valve coil, and the follow current flows to the second follow current unit from the valve coil when the valve is closed. According to the design of the valve driving circuit which is low in cost and fast to turn off, the delay problem of the magnetic valve in the emergency turn-off process is solved.

Description

Technical Field

[0001] This application belongs to the technical field of drive circuits, and relates to a valve drive circuit, in particular to a valve drive circuit and an air suspension controller. Background Art

[0002] Currently, the electronically controlled air suspension system ECAS (Electronic-Controlled Air Suspension) of automobiles consists of components such as an ECAS electronic control unit, a solenoid valve (control valve), a height sensor, and an airbag. The height sensor is responsible for detecting changes in vehicle height. The electronic control unit receives the input information, judges the current vehicle state, and activates the solenoid valve to work. The solenoid valve realizes the charging and discharging adjustment of each airbag. With the improvement of people's requirements for vehicle ride comfort and the development of automotive suspension technology in China, air suspensions are increasingly widely used in various vehicles.

[0003] In the valve drive design of common suspension controllers, there are two ways of drive design for the valve drive circuit: half-bridge drive and full-bridge drive design. (1) For the currently used half-bridge drive valve drive circuit, its architecture block diagram is as shown in the half-bridge drive circuit of Figure 1 When driving the valve load coil through two MOS tubes (Metal-Oxide-Semiconductor Field-Effect Transistor), when controlling the valve to work, the high-side MOS conducts, the low-side MOS conducts, and the current flows from the high-side MOS to the valve; when controlling the valve to turn off, the high-side MOS turns off, the low-side MOS conducts, and the inductive current inside the valve is consumed through the valve itself and the low-side MOS; its turn-on time depends on the turn-on time of the MOS, and the difference is not significant, but when controlling the valve to turn off, its turn-off time is affected by the internal resistance of the valve coil, resulting in a longer turn-off time and valve response hysteresis. (2) For the currently used full-bridge drive valve drive circuit, its architecture block diagram is as shown in the full-bridge drive circuit of Figure 2 When controlling the valve to conduct, the left high-side MOS and the right low-side MOS conduct simultaneously; when controlling the valve to turn off, the left low-side and the right high-side MOS conduct simultaneously; although its turn-off time is shortened, 4 MOS tubes are used in the drive circuit design, making the drive circuit complex, and at the same time, the cost is twice as high as that of the half-bridge drive circuit. In a controller with more than ten valves, this cost is unimaginable. Summary of the Invention

[0004] This application provides a valve drive circuit and an air suspension controller for solving the hysteresis problem of magnetic valves during emergency shutdown.

[0005] In a first aspect, the present application provides a valve drive circuit, the circuit comprising: a first drive unit connected to a power supply and one end of a valve coil respectively; when the valve is operating, the working current flows from the first drive unit to the valve coil; a second drive unit connected to the other end of the valve coil and ground respectively, when the valve is operating, the working current flows from the valve coil to the second drive unit; a first freewheeling unit connected to one end of the valve coil and ground respectively, when the valve is closed, the freewheeling current flows from the first freewheeling unit to the valve coil; a second freewheeling unit connected to the power supply and the other end of the valve coil respectively, when the valve is closed, the freewheeling current flows from the valve coil to the second freewheeling unit.

[0006] In one implementation of the first aspect, the first drive unit includes a first MOS transistor; the drain of the first MOS transistor is connected to the power supply, and the source of the first MOS transistor is connected to one end of the valve coil; when the valve is operating, the working current flows from the first MOS transistor to the valve coil.

[0007] In one implementation of the first aspect, the second drive unit includes a second MOS transistor; the drain of the second MOS transistor is connected to the other end of the valve coil, and the source of the second MOS transistor is connected to ground, when the valve is operating, the working current flows from the valve coil to the second MOS transistor.

[0008] In one implementation of the first aspect, the first freewheeling unit includes a first freewheeling diode; the cathode of the first freewheeling diode is connected to one end of the valve coil, and the anode of the first freewheeling diode is connected to ground, when the valve is closed, the freewheeling current flows from the first freewheeling diode to the valve coil.

[0009] In one implementation of the first aspect, the second freewheeling unit includes a second freewheeling diode; the cathode of the second freewheeling diode is connected to the power supply, and the anode of the second freewheeling diode is connected to the other end of the valve coil, when the valve is closed, the freewheeling current flows from the valve coil to the second freewheeling diode.

[0010] In one implementation of the first aspect, the power supply is provided by a storage battery.

[0011] In one implementation of the first aspect, the cathode of the second freewheeling diode is connected to the storage battery; when the valve is closed, the freewheeling current flows through the first freewheeling diode and the second freewheeling diode to the storage battery to charge the storage battery.

[0012] Second aspect, the present application provides an air suspension controller, and the air suspension controller includes: a valve drive circuit; the valve drive circuit includes: a first drive unit, a second drive unit, a first freewheeling unit, and a second freewheeling unit; the first drive unit is respectively connected to a power supply and one end of a valve coil; when the valve is working, the working current flows from the first drive unit to the valve coil; the second drive unit is respectively connected to the other end of the valve coil and the ground, and when the valve is working, the working current flows from the valve coil to the second drive unit; the first freewheeling unit is respectively connected to one end of the valve coil and the ground, and when the valve is closed, the freewheeling current flows from the first freewheeling unit to the valve coil; the second freewheeling unit is respectively connected to the power supply and the other end of the valve coil, and when the valve is closed, the freewheeling current flows from the valve coil to the second freewheeling unit.

[0013] In an implementation manner of the second aspect, the first drive unit includes a first MOS transistor, and the second drive unit includes a second MOS transistor; the drain of the first MOS transistor is connected to the power supply, and the source of the first MOS transistor is connected to one end of the valve coil; when the valve is working, the working current flows from the first MOS transistor to the valve coil; the drain of the second MOS transistor is connected to the other end of the valve coil, and the source of the second MOS transistor is connected to the ground, and when the valve is working, the working current flows from the valve coil to the second MOS transistor.

[0014] In an implementation manner of the second aspect, the first freewheeling unit includes a first freewheeling diode, and the second freewheeling unit includes a second freewheeling diode; the cathode of the first freewheeling diode is connected to one end of the valve coil, and the anode of the first freewheeling diode is connected to the ground, and when the valve is closed, the freewheeling current flows from the first freewheeling diode to the valve coil; the cathode of the second freewheeling diode is connected to the power supply, and the anode of the second freewheeling diode is connected to the other end of the valve coil, and when the valve is closed, the freewheeling current flows from the valve coil to the second freewheeling diode.

[0015] As described above, the valve drive circuit and the air suspension controller of the present application have the following beneficial effects:

[0016] In this application, through the design improvement of the structure of the half-bridge drive circuit for valve drive, compared with the existing half-bridge drive circuit, by changing the external current flow direction of the valve coil at the turn-off moment, the current inside the valve coil remains unchanged at the turn-off moment, and the external current flows to the positive electrode of the storage battery, and the current from the negative electrode of the storage battery flows to the upper end of the coil, thus forming a current loop including the storage battery, so as to have the advantage of quickly turning off the valve; compared with the existing H-bridge valve drive circuit, the external freewheeling circuit only forms a loop through two diodes, eliminating two MOS transistors, reducing the drive cost of a single valve body by half; at the same time, only the working states of two MOS transistors need to be controlled in the drive circuit, reducing the control complexity by half compared with controlling 4 MOS transistors in the H-bridge. Description of the Drawings

[0017] Figure 1 It shows the half-bridge drive circuit diagram in the prior art.

[0018] Figure 2 It shows the full-bridge drive circuit diagram in the prior art.

[0019] Figure 3 It shows the structural schematic diagram of the valve drive circuit described in the embodiment of this application.

[0020] Figure 4 It shows the principle logic schematic diagram of the valve drive circuit described in the embodiment of this application.

[0021] Figure 5 It shows the circuit diagram of the valve drive circuit described in the embodiment of this application.

[0022] Figure 6 It shows the schematic diagram of the working current flow direction of the valve drive circuit described in the embodiment of this application.

[0023] Figure 7 It shows the schematic diagram of the freewheeling current flow direction of the valve drive circuit described in the embodiment of this application.

[0024] Figure 8 It shows the structural principle schematic diagram of the air suspension controller described in the embodiment of this application.

[0025] Description of Component Labels

[0026] 1 Valve drive circuit

[0027] 11 First drive unit

[0028] 12 Second drive unit

[0029] 13 First freewheeling unit

[0030] 14 Second freewheeling unit Detailed Description of the Invention

[0031] The following uses specific specific examples to illustrate the implementation manners of the present application. Those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in this specification. The present application can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0032] It should be noted that the diagrams provided in the following embodiments only illustrate the basic concept of the present application in a schematic manner. Therefore, only the components related to the present application are shown in the diagrams, rather than being drawn according to the number, shape, and size of the components in actual implementation. The types, quantities, and proportions of the components in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0033] The present application is a design for an air suspension controller valve drive circuit. The improvement is that through an innovative valve drive circuit design, the drive circuit can quickly turn off the valve, and at the same time, compared with the H-bridge drive design, it has the advantage of low cost.

[0034] Next, the technical solutions in the embodiments of the present application will be described in detail with reference to the accompanying drawings in the embodiments of the present application.

[0035] Please refer to Figure 3 , which shows the structural schematic diagram of the valve drive circuit described in the embodiment of the present application. As Figure 3 shown, the embodiment of the present application provides a valve drive circuit 1, which specifically includes: a first drive unit 11, a second drive unit 12, a first freewheeling unit 13, and a second freewheeling unit 14.

[0036] The first drive unit 11 is respectively connected to the power supply and one end of the valve coil; when the valve works, the working current flows from the first drive unit 11 to the valve coil.

[0037] The second drive unit 12 is respectively connected to the other end of the valve coil and the ground. When the valve works, the working current flows from the valve coil to the second drive unit 12.

[0038] The first freewheeling unit 13 is respectively connected to one end of the valve coil and the ground. When the valve is closed, the freewheeling current flows from the first freewheeling unit 13 to the valve coil.

[0039] The second freewheeling unit 14 is respectively connected to the power supply and the other end of the valve coil. When the valve is closed, the freewheeling current flows from the valve coil to the second freewheeling unit 14.

[0040] Please refer to Figure 4 , which shows the principle logic schematic diagram of the valve drive circuit described in the embodiments of the present application. As Figure 4 shown, the positive and negative electrodes of the battery BATTERY are respectively connected to the drive circuit of the valve. When the valve works, the drive circuit forms a loop with the coil load through both the high side and the low side. In addition, when the valve is closed, the coil load discharges energy through the freewheeling circuit, where the arrow direction is the current flow direction.

[0041] In one embodiment, the first drive unit includes a first MOS transistor.

[0042] The drain of the first MOS transistor is connected to the power supply, and the source of the first MOS transistor is connected to one end of the valve coil; when the valve works, the working current flows from the first MOS transistor to the valve coil.

[0043] Please refer to Figure 5 , which shows the circuit diagram of the valve drive circuit described in the embodiments of the present application. As Figure 5 shown, the first drive unit includes a first MOS transistor a. The drain of the first MOS transistor a is connected to the power supply VDD, and the source of the first MOS transistor a is connected to one end of the valve coil; when the valve works, the working current flows from the first MOS transistor a to the valve coil.

[0044] In one embodiment, the second drive unit includes a second MOS transistor.

[0045] The drain of the second MOS transistor is connected to the other end of the valve coil, and the source of the second MOS transistor is connected to the ground. When the valve works, the working current flows from the valve coil to the second MOS transistor.

[0046] As Figure 5 shown, the second drive unit includes a second MOS transistor b. The drain of the second MOS transistor b is connected to the other end of the valve coil, and the source of the second MOS transistor b is connected to the ground. When the valve works, the working current flows from the valve coil to the second MOS transistor b.

[0047] In one embodiment, the first freewheeling unit includes a first freewheeling diode.

[0048] The cathode of the first freewheeling diode is connected to one end of the valve coil, and the anode of the first freewheeling diode is connected to the ground. When the valve is closed, the freewheeling current flows from the first freewheeling diode to the valve coil.

[0049] As Figure 5As shown, the first freewheeling unit includes a first freewheeling diode c. The cathode of the first freewheeling diode c is connected to one end of the valve coil, and the anode of the first freewheeling diode c is connected to the ground. When the valve is closed, the freewheeling current flows from the first freewheeling diode c to the valve coil.

[0050] In one embodiment, the second freewheeling unit includes a second freewheeling diode.

[0051] The cathode of the second freewheeling diode is connected to the power supply, and the anode of the second freewheeling diode is connected to the other end of the valve coil. When the valve is closed, the freewheeling current flows from the valve coil to the second freewheeling diode.

[0052] As Figure 5 shown, the second freewheeling unit includes a second freewheeling diode d. The cathode of the second freewheeling diode d is connected to the power supply VDD, and the anode of the second freewheeling diode d is connected to the other end of the valve coil. When the valve is closed, the freewheeling current flows from the valve coil to the second freewheeling diode d.

[0053] In one embodiment, the power supply is provided by a storage battery.

[0054] In one embodiment, the cathode of the second freewheeling diode is connected to the storage battery.

[0055] When the valve is closed, the freewheeling current flows through the first freewheeling diode and the second freewheeling diode to the storage battery to charge the storage battery.

[0056] As Figure 5 shown, the cathode of the second freewheeling diode d is connected to the storage battery. When the valve is closed, the freewheeling current flows through the first freewheeling diode c and the second freewheeling diode d to the storage battery to charge the storage battery.

[0057] Please refer to Figure 6 , which shows a schematic diagram of the working current flow of the valve drive circuit according to the embodiment of the present application. As Figure 6 shown, when controlling the valve to work, as Figure 6 shown by the arrow direction, the high-side MOS transistor a is turned on, and the low-side MOS transistor b is turned on. The current flows from the high side MOS to the valve coil. The freewheeling diodes c and d are in the reverse cut-off state at this time and do not participate in the work of controlling the valve to conduct.

[0058] Please refer to Figure 7 , which shows a schematic diagram of the freewheeling current flow of the valve drive circuit according to the embodiment of the present application. As Figure 7As shown, when the control valve is closed, the high-side MOS transistor a and the low-side MOS transistor b are both turned off. At this time, the valve responds to the control of the high-side MOS transistor a and the low-side MOS transistor b and enters the off state (for example, at time t0). At the moment t0 when the valve is turned off, due to its own characteristics, the inductive coil in the valve will still continuously generate current. At this time, the current passes through two freewheeling diodes c and d, and the freewheeling current flows to the VDD power supply to charge the battery, so as to quickly consume the current and achieve a quick turn-off, that is, a loop is formed for quickly consuming the positive current generated by the inductive coil in the valve. The flowing direction of this loop is: inductive coil in the valve - freewheeling diode d - VDD - freewheeling diode c - inductive coil; due to the formation of this loop, the current in the inductive coil of the valve can be quickly consumed, thereby accelerating the valve turn-off time.

[0059] Therefore, through the drive circuit design of discrete components, the architecture position of the driven valve in the original half-bridge circuit is changed, and the architecture design of the half-bridge valve drive circuit is changed. On the basis of the original components of the half-bridge valve drive, two freewheeling diode devices c and d are added; two MOS transistors are used to drive the valve, and at the same time, two freewheeling diodes are used for freewheeling design. When the valve is at the moment t0 of turn-off, the current in the inductive coil of the valve passes through two freewheeling diodes c and d, and the freewheeling current flows to the VDD power supply to achieve the effect of quick closing.

[0060] Combined with Figures 3 to 7 the circuit shown, in another embodiment, the present application can also achieve quick freewheeling through two diodes c and d at the moment t0 of quick turn-off of the valve by omitting one of the two MOS transistors in the actual circuit application, that is, removing one of the a tube or the b tube in the fast turn-off half-bridge drive circuit.

[0061] Please refer to Figure 8 , which shows the schematic structural principle of the air suspension controller described in the embodiment of the present application. As Figure 8 shown, the embodiment of the present application provides an air suspension controller, and the air suspension controller includes: a valve drive circuit; the valve drive circuit includes: a first drive unit, a second drive unit, a first freewheeling unit, and a second freewheeling unit.

[0062] The first drive unit is respectively connected to the power supply and one end of the valve coil; when the valve works, the working current flows from the first drive unit to the valve coil.

[0063] The second drive unit is respectively connected to the other end of the valve coil and the ground. When the valve works, the working current flows from the valve coil to the second drive unit.

[0064] The first freewheeling unit is respectively connected to one end of the valve coil and the ground. When the valve is closed, the freewheeling current flows from the first freewheeling unit to the valve coil.

[0065] The second freewheeling unit is respectively connected to the power supply and the other end of the valve coil. When the valve is closed, the freewheeling current flows from the valve coil to the second freewheeling unit.

[0066] In one embodiment, the first driving unit includes a first MOS transistor, and the second driving unit includes a second MOS transistor.

[0067] The drain of the first MOS transistor is connected to the power supply, and the source of the first MOS transistor is connected to one end of the valve coil. When the valve is operating, the working current flows from the first MOS transistor to the valve coil.

[0068] The drain of the second MOS transistor is connected to the other end of the valve coil, and the source of the second MOS transistor is connected to the ground. When the valve is operating, the working current flows from the valve coil to the second MOS transistor.

[0069] In one embodiment, the first freewheeling unit includes a first freewheeling diode, and the second freewheeling unit includes a second freewheeling diode.

[0070] The cathode of the first freewheeling diode is connected to one end of the valve coil, and the anode of the first freewheeling diode is connected to the ground. When the valve is closed, the freewheeling current flows from the first freewheeling diode to the valve coil.

[0071] The cathode of the second freewheeling diode is connected to the power supply, and the anode of the second freewheeling diode is connected to the other end of the valve coil. When the valve is closed, the freewheeling current flows from the valve coil to the second freewheeling diode.

[0072] Such as Figure 5As shown, the first driving unit includes a first MOS transistor a. The drain of the first MOS transistor a is connected to the power supply VDD, and the source of the first MOS transistor a is connected to one end of the valve coil; when the valve works, the working current flows from the first MOS transistor a to the valve coil. The second driving unit includes a second MOS transistor b. The drain of the second MOS transistor b is connected to the other end of the valve coil, and the source of the second MOS transistor b is connected to the ground. When the valve works, the working current flows from the valve coil to the second MOS transistor b. The first freewheeling unit includes a first freewheeling diode c. The cathode of the first freewheeling diode c is connected to one end of the valve coil, and the anode of the first freewheeling diode c is connected to the ground. When the valve is closed, the freewheeling current flows from the first freewheeling diode c to the valve coil. The second freewheeling unit includes a second freewheeling diode d. The cathode of the second freewheeling diode d is connected to the power supply VDD, and the anode of the second freewheeling diode d is connected to the other end of the valve coil. When the valve is closed, the freewheeling current flows from the valve coil to the second freewheeling diode d.

[0073] In several embodiments provided in the present application, it should be understood that the disclosed circuit or controller device can be implemented in other ways. For example, the circuit embodiments described above are only illustrative. For example, the division of units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed mutual coupling or direct coupling or communication connection can be through some interfaces. The indirect coupling or communication connection of devices or units can be in electrical, mechanical or other forms.

[0074] The units described as separate components may or may not be physically separated. The components displayed as units may or may not be physical modules, that is, they can be located in one place or distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the embodiments of the present application. For example, in each embodiment of the present application, the functional units can be integrated into one functional unit, or each unit can exist physically alone, or two or more units can be integrated into the same unit.

[0075] The descriptions of the corresponding processes or structures in the above respective drawings have their own emphases. For parts not detailed in a certain process or structure, reference can be made to the relevant descriptions of other processes or structures.

[0076] The above embodiments are only illustrative of the principles and effects of the present application and are not intended to limit the present application. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present application should still be covered by the claims of the present application.

Claims

1. A valve drive circuit, characterized in that The circuit includes: A first driving unit, which is respectively connected to a power supply and one end of a valve coil; when the valve works, the working current flows from the first driving unit to the valve coil; A second driving unit, which is respectively connected to the other end of the valve coil and the ground; when the valve works, the working current flows from the valve coil to the second driving unit; A first freewheeling unit, which is respectively connected to one end of the valve coil and the ground; when the valve is closed, the freewheeling current flows from the first freewheeling unit to the valve coil; A second freewheeling unit, which is respectively connected to the power supply and the other end of the valve coil; when the valve is closed, the freewheeling current flows from the valve coil to the second freewheeling unit.

2. The circuit according to claim 1, wherein The first driving unit includes a first MOS transistor; The drain of the first MOS transistor is connected to the power supply, and the source of the first MOS transistor is connected to one end of the valve coil; when the valve works, the working current flows from the first MOS transistor to the valve coil.

3. The circuit according to claim 1, wherein The second driving unit includes a second MOS transistor; The drain of the second MOS transistor is connected to the other end of the valve coil, and the source of the second MOS transistor is connected to the ground; when the valve works, the working current flows from the valve coil to the second MOS transistor.

4. The circuit according to claim 1, characterized in that, The first freewheeling unit includes a first freewheeling diode; The cathode of the first freewheeling diode is connected to one end of the valve coil, and the anode of the first freewheeling diode is connected to the ground; when the valve is closed, the freewheeling current flows from the first freewheeling diode to the valve coil.

5. The circuit according to claim 4, wherein The second freewheeling unit includes a second freewheeling diode; The cathode of the second freewheeling diode is connected to the power supply, and the anode of the second freewheeling diode is connected to the other end of the valve coil; when the valve is closed, the freewheeling current flows from the valve coil to the second freewheeling diode.

6. The circuit according to claim 5, characterized in that, The power supply is provided by a storage battery.

7. The circuit according to claim 6, characterized in that, The cathode of the second freewheeling diode is connected to the storage battery; When the valve is closed, the freewheeling current flows through the first freewheeling diode and the second freewheeling diode to the storage battery to charge the storage battery.

8. An air suspension controller, characterized in that, The air suspension controller includes: a valve driving circuit; the valve driving circuit includes: a first driving unit, a second driving unit, a first freewheeling unit and a second freewheeling unit; The first driving unit is respectively connected to a power supply and one end of a valve coil; when the valve works, the working current flows from the first driving unit to the valve coil; The second driving unit is respectively connected to the other end of the valve coil and the ground; when the valve works, the working current flows from the valve coil to the second driving unit; The first freewheeling unit is respectively connected to one end of the valve coil and the ground; when the valve is closed, the freewheeling current flows from the first freewheeling unit to the valve coil; The second freewheeling unit is respectively connected to the power supply and the other end of the valve coil; when the valve is closed, the freewheeling current flows from the valve coil to the second freewheeling unit.

9. The air suspension controller according to claim 8, wherein The first driving unit includes a first MOS transistor, and the second driving unit includes a second MOS transistor; The drain of the first MOS transistor is connected to the power supply, and the source of the first MOS transistor is connected to one end of the valve coil; when the valve is working, the working current flows from the first MOS transistor to the valve coil. The drain of the second MOS transistor is connected to the other end of the valve coil, and the source of the second MOS transistor is connected to the ground. When the valve is working, the working current flows from the valve coil to the second MOS transistor.

10. The air suspension controller according to claim 8, characterized in that, The first freewheeling unit includes a first freewheeling diode, and the second freewheeling unit includes a second freewheeling diode. The cathode of the first freewheeling diode is connected to one end of the valve coil, and the anode of the first freewheeling diode is connected to the ground. When the valve is closed, the freewheeling current flows from the first freewheeling diode to the valve coil. The cathode of the second freewheeling diode is connected to the power supply, and the anode of the second freewheeling diode is connected to the other end of the valve coil. When the valve is closed, the freewheeling current flows from the valve coil to the second freewheeling diode.

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