Technical Field The present invention relates to the technical field of starters of automotive engines and other engines, in particular to an electromagnetic switch and a starter using same. Background Art

A starter (also referred to as an "initiator") is formed by an electromagnetic switch, a starter motor and a transmission mechanism. When a contact of the electromagnetic switch is closed, on one hand, it is required that a contact piece should be stable and reliable when it is firstly in contact with a contact bolt, the contact resistance should be as small as possible, and the vibration in contact should be as small as possible, such that the risk of electric erosion or immovable welding of the contact is reduced; and all these require a contact spring for the contact piece to be able to provide a sufficient pressure. Further, the contact may get frozen, and a sufficient force from the contact spring for the contact piece may also be required to destroy an ice layer. On the other hand, when the switch is out of operation and the contact is opened, the contact piece is required to be rapidly disengaged from the contact bolt so as to reduce the electric erosion of the contact. Moreover, when the contact piece and the contact bolt are immovably welded, it also needs to be ensured that the contact piece can be rapidly disengaged from the contact bolt, where a sufficient return force from the contact piece return spring is required to timely disengage the contact piece from the contact bolt.

Fig. 1 shows a common electromagnetic switch of a starter in the prior art. As shown in Fig. 1, the electromagnetic switch is formed by a moving iron core 1, a switch winding 2, a contact piece shaft 3, a stationary iron core 4, a switch cover 5, a contact piece 6, a meshing spring 7, a gasket 8, a moving iron core return spring 9, a switch housing 10, a contact spring for the contact piece 11 and a contact piece return spring 12. The moving iron core 1, the switch housing 10 and the stationary iron core 4 form a magnetic circuit. The switch winding 2 generates ampere turns (i.e. magnetomotive force) when the electromagnetic switch operates. The contact piece shaft 3 is driven by the moving iron core 1 to join with the contact piece 6 and a contact bolt (not shown in the figure) . In the prior art, the moving iron core 1 is in contact with one end of the moving iron core return spring 9, and the other end of the moving iron core return spring 9 is in contact with the stationary iron core 4. One end of the contact piece shaft 3 is located in an internal cavity formed by the moving iron core return spring 9, the other end of the contact piece shaft 3 is connected to one end of the contact piece return spring 12 via a blocking piece 13, and the other end of the contact piece return spring 12 is in contact with the switch cover 5. The contact piece shaft 3 passes through the contact piece 6, and the contact spring for the contact piece 11 is provided between the contact piece 6 and a blocking boss of the contact piece shaft. Fig. 2 shows another common electromagnetic switch of a starter in the prior art. It differs from the technical solution as shown in Fig. 1 in the varied position relationship of the moving iron core return spring 9. The moving iron core return spring 9 is located outside the moving iron core 1. One end of the moving iron core return spring 9 is in contact with the blocking piece 14 of the moving iron core, and the other end is in contact with the switch housing 10. The electromagnetic switch in the two common technical solutions mentioned above operates in the following order : First stage: the moving iron core 1 moves until the gasket 8 is in contact with the contact piece shaft 3, and an electromagnetic force generated by the switch winding 2 overcomes a force Fl of the moving iron core return spring 9.

Second stage: The moving iron core 1 pushes the contact piece shaft 3 until the contact piece 6 is in contact with the contact bolt, and an electromagnetic force generated by the switch winding 2 overcomes a force of the moving iron core return spring and a force of the return spring for the contact piece. At this time, the electromagnetic force generated by the switch winding 2 needs to overcome not only two spring forces (i.e. force Fl of the moving iron core return spring and force F2 of the contact piece return spring) , but also a predetermined pressure F2' of the contact piece return spring, which needs a relatively large electromagnetic force. Third stage: The moving iron core 1 pushes the contact piece shaft 3 until the moving iron core 1 is in contact with the stationary iron core 4, and an electromagnetic force overcomes the force Fl of the moving iron core return spring, the force F2 of the contact piece return spring and a force F3 of the contact spring for the contact piece. At this time, the electromagnetic force generated by the switch winding 2 needs to overcome three spring forces at the same time, which also needs a relatively large electromagnetic force.

It can be seen therefrom, in the two technical solutions mentioned above, that, when the contact of the switch is closed, the contact piece 6 is firstly in contact with the contact bolt, and then the moving iron core 1 will continue to move 1-2 mm to be in contact with the stationary iron core 4; during these two contact processes, vibration of the contact piece 6 may occur and result in poor contact, thereby increasing the risk of electric erosion or immovable welding of the contact, and the contact piece contact spring 11 is required to be able to provide a relatively large contact spring force. In another aspect, when the switch is out of operation and the contact is opened, the contact piece 6 needs to be rapidly disengaged from the contact bolt so as to reduce the electric erosion of the contact, and furthermore, when the contact piece and the contact bolt are immovably welded, it should also be ensured that the contact piece can be rapidly disengaged from the contact bolt, where a relatively large return force from the contact piece return spring is required to open the contact. If the force of the contact piece return spring and the force of the contact spring for the contact piece are enhanced to reduce the risk of electric erosion or immovable welding of the contact, it is necessary to increase the ampere turns (i.e. increasing the amount of copper used of the winding) or increase the volume of the switch (i.e. enhancing the magnetic circuit), which may also result in increased costs and an increased volume of the electromagnetic switch. In view of this, a new technical solution is urgently needed in the prior art, which can significantly enhance the force of the contact spring for the contact piece and the force of the contact piece return spring without increasing the ampere turns (or the volume of the switch) , while also increasing the stability of the contact during closing and reducing the risk of electric erosion or immovable welding of the contact. Summary of the invention

In order to overcome the defects existing in the prior art, a novel electromagnetic switch is provided in the present invention, which can significantly enhance a force of the contact spring for the contact piece and a force of the contact piece return spring without increasing the ampere turns of the switch (or the volume of the switch) .

In order to achieve the purpose of the invention mentioned above, an electromagnetic switch is disclosed, which comprises: a switch winding, a moving iron core, a stationary iron core, a contact piece shaft and a contact, wherein the switch winding generates an electromagnetic force to drive the moving iron core to push the contact piece shaft, and a moving iron core return spring is provided between the moving iron core and the contact piece shaft and is elastically deformed when the electromagnetic force drives the moving iron core.

Furthermore, the moving iron core comprises a gasket, and one end of the moving iron core return spring is in contact with the gasket.

Furthermore, the contact piece shaft comprises a first end and a second end, the inner diameter of the first end is less than the inner diameter of the stationary iron core, the first end further comprises a step, and the moving iron core return spring passes through the first end to be in contact with the step.

Furthermore, a limiting boss is provided between the first end and the second end.

Furthermore, the second end comprises a groove. Furthermore, the gasket comprises a boss, and the boss passes through the moving iron core return spring.

An electromagnetic switch is also disclosed, comprising: a switch winding, a moving iron core, a stationary iron core, a contact piece shaft and a contact, wherein the switch winding generates an electromagnetic force to drive the moving iron core to push the contact piece shaft, the contact piece shaft comprises a first end and a second end, a moving iron core return spring is provided between the moving iron core and the contact piece shaft, the second end of the contact piece shaft is connected to a contact piece return spring, and the moving iron core return spring and the contact piece return spring are connected in series via the contact piece shaft.

Furthermore, one end of the moving iron core return spring is in contact with the gasket of the moving iron core, and the other end passes through the first end of the contact piece shaft and is in contact with the contact piece shaft.

Furthermore, the contact piece shaft further comprises a contact spring for the contact piece, and the contact spring for the contact piece and the contact piece return spring are connected in parallel via the contact piece shaft. Compared with the prior art, the present invention has the following advantages:

Firstly, a force of the contact spring for the contact piece and a force of the contact piece return spring can be significantly enhanced without increasing the ampere turns of the switch (or the volume of the switch) , so as to increase the stability of the contact during closing, thereby reducing the risk of electric erosion or immovable welding of the contact. Secondly, the force of the contact piece return spring can be significantly enhanced to rapidly and reliably open a closed contact (i.e. enabling the contact piece to be rapidly disengaged from the contact) , reduce the electric erosion of the contact or facilitate opening an immovably welded contact.

Finally, significantly enhancing the force of the contact spring for the contact piece can contribute to the destruction of an ice layer at the contact.

According to another aspect, the invention relates to an electromagnetic switch comprising:

- a stationary iron core,

- a moving iron core able to move between an inactive position and an active position with regard to the stationary iron core, the moving iron core comprising a recess ,

- a shaft comprising a portion located within the recess of the moving iron core,

- a meshing spring mounted around said portion of the shaft,

Wherein, in a rest position, the shaft abuts a bottom wall of the recess by the pushing force of the meshing spring,

characterized in that the bottom wall is formed in one- piece with the moving iron core. This arrangement allows to limit the risk that water penetrates into the connecting chamber comprising the contact piece and the contact bolds . This also limits the total number of parts of the switch assembly with regard to a standard assembly.

According to a particular embodiment, the electromagnetic switch comprises a locking washer positioned around the shaft, the locking washer being fixed to the moving iron core on the side of an opening of the recess.

According to a particular embodiment, in the rest position, the meshing spring is mounted prestressed in the recess between an internal border of the locking washer and a shoulder of the shaft.

According to a particular embodiment, the internal border of the locking washer is crimped at the periphery of the recess.

According to a particular embodiment, the locking washer comprises an external border having a diameter superior to an external diameter of the moving iron core, a moving iron core return spring being mounted between said external border of the locking washer and a fixed element of the electromagnetic switch with regard to the stationary iron core, in particular the switch housing.

According to a particular embodiment, it further comprises a contact piece shaft and a moving iron core return spring mounted between a step of the contact piece shaft and the bottom wall of the moving iron core .

Furthermore, the invention is directed to a starter, comprising a starter motor, a transmission motor and either electromagnetic switch mentioned above, wherein the electromagnetic switch is used to control the starter motor to switch on or off, and the transmission mechanism is used to transfer a torque to an engine.

Description of the Drawings The advantages of the present invention can be further learnt from the following description of the present invention and the accompanying drawings. Fig. 1, already disclosed, is a first structural schematic view of an electromagnetic switch of a starter involved in the prior art;

Fig. 2, already disclosed, is a second structural schematic view of an electromagnetic switch of a starter involved in the prior art;

Fig. 3 is a structural schematic view of an electromagnetic switch of a starter involved in the present invention; and

Fig. 4 is a simulation schematic diagram of the technical effect of an electromagnetic switch of a starter involved in the present invention;

Fig. 5 is a structural schematic view of an electromagnetic switch according to the invention;

Fig. 6 is a view of the assembly of the moving iron core, the shaft, the meshing spring, and the locking washer belonging to the electromagnetic switch according to the invention;

Fig. 7 is a cross-sectional view of the moving iron core of the electromagnetic switch according to the invention;

Fig. 8a and 8b are perspective views of the assembly of the moving iron core and the locking washer of the electromagnetic switch according to the invention; Fig. 9 is a structural schematic view of the electromagnetic switch according to an alternative embodiment of the invention. Detailed Description

The particular embodiments of the present invention are provided in conjunction with the accompanying drawings.

The purpose of the present invention is to provide an electromagnetic switch, which can significantly enhance a force of the contact spring for the contact piece and a force of the contact piece return spring without increasing the ampere turns of the switch (or the volume of the switch) , while increasing the stability of the contact during closing, thereby reducing the risk of electric erosion or immovable welding of the contact .

In order to achieve the purpose of the invention mentioned above, an electromagnetic switch is disclosed, which comprises: a switch winding, a moving iron core, a stationary iron core, a contact piece shaft and a contact, wherein the switch winding generates an electromagnetic force to drive the moving iron core to push the contact piece shaft, and a moving iron core return spring is provided between the moving iron core and the contact piece shaft and is elastically deformed when the electromagnetic force drives the moving iron core.

Fig. 3 is a structural schematic view of the electromagnetic switch of the starter involved in the present invention. As shown in Fig. 3, the electromagnetic switch comprises a moving iron core 10, a switch winding 20, a contact piece shaft 30, a stationary iron core 40, a switch cover 50, a contact bolt 60, a contact piece return spring 70, a contact piece 80, a contact bolt 90, a contact piece contact spring 100, a switch housing 110, a moving iron core return spring 120, a boss gasket 130 and a meshing spring 140. As shown in Fig. 3, one end of the moving iron core return spring 120 is in contact with the moving iron core 10, preferably in contact with the gasket of the moving iron core 10. In order to reduce the swinging of the spring in operation, the gasket is designed as a boss gasket 130, and in a further preferred embodiment, the boss gasket 130 can be designed as a cylindrical solid shaft. The other end of the moving iron core return spring 120 is in contact with the contact piece shaft 30. Preferably, the contact piece shaft 30 partially passes through the moving iron core return spring 120, and is in contact with the moving iron core return spring 120 via a step. This is also for reducing the swinging of the spring in operation. In addition to the connection of the contact piece shaft and the moving iron core return spring 120, the other end of the contact piece shaft is further connected to the contact piece return spring 70, the moving iron core return spring 120 and the contact piece return spring 70 are both mounted on the contact piece shaft 30, which means that the moving iron core return spring 120 and the contact piece return spring 70 are connected in series; the moving iron core return spring 120 and the contact piece return spring 70 are connected in series via the contact piece shaft 30; and the contact piece return spring 70 and the contact spring for the contact piece 100 are connected in parallel via the contact piece shaft 30. The electromagnetic switch provided by the present invention operates in the following order: First stage: An electromagnetic force generated by the switch winding 20 drives the moving iron core 10 to move, and the moving iron core return spring is deformed until the boss gasket 130 is in contact with the contact piece shaft 30. In the first stage, the electromagnetic force overcomes a force Fl of the moving iron core return spring. Since the moving iron core return spring 120 and the contact piece return spring 70 are connected in series, the moving iron core return spring 120 gradually offsets a predetermined pressure of the contact piece return spring 70 during compression, however, the predetermined pressure of the contact piece return spring 70 is slightly greater than the force when the moving iron core return spring is completely compressed, and the contact piece return spring in this process is deformed, that is, the contact piece cannot move.

Second stage: The moving iron core 10 pushes the contact piece shaft 30 until a contact piece 80 is in contact with a contact bolt 60, 90, and in this stage, an electromagnetic force overcomes a force F2 of the contact piece return spring force. Since the moving iron core return spring 120 cannot be further compressed, the force thereof becomes an internal force, the electromagnetic force only overcomes the force of the contact piece return spring, and the predetermined pressure is offset in the previous .stage and no additional electromagnetic force is needed to overcome the force F2 of the contact piece return spring .

Third stage: The moving iron core 10 pushes the contact piece shaft 30 until the moving iron core 10 is in contact with the stationary iron core 40, the force of the moving iron core return spring becomes an internal force, and an electromagnetic force only overcomes the force F2 of the contact piece return spring and a force F3 of the contact spring for the contact piece.

Since the moving iron core return spring 120 and the contact piece return spring 70 are connected in series, three situations may occur when one force presses two springs at the same time: in the first situation, the moving iron core return spring 120 is deformed, and the contact piece return spring 70 is not deformed; in the second situation, the moving iron core return spring 120 is not deformed, and the contact piece return spring 70 is deformed; and in the third situation, the moving iron core return spring 120 and the contact piece return spring 70 are deformed at the same time. That is, one force can be used to achieve the deformations of two springs, and a pressing force generated due to the elastic deformation of the spring in the prior art is converted into a pushing force required by the deformation of another spring.

In the second stage, the electromagnetic force only needs to be able to overcome the force Fl of the moving iron core return spring rather than increasing by the force F2 of the contact piece return spring as in the prior art, and when in contact with the boss gasket, the force Fl of the moving iron core return spring has offset the predetermined pressure F2 ' of the force of the contact piece return spring, and therefore, in the second stage of the technical solution of the present invention, there is no need to overcome the predetermined pressure F2' of the contact piece return spring (see table 1) .

In the third stage, the electromagnetic force only needs to overcome the force F2 of the contact piece return spring and the force F3 of the contact spring for the contact piece, and needs neither to overcome the predetermined pressure F2' (which has been offset in the second stage) of the contact piece return spring as in the prior art, nor overcome the force Fl of the moving iron core return spring (which has become an internal force) as in conventional designs.

Therefore, the spring force required to be overcome by the electromagnetic switch decreases. Fig. 4 is a simulation schematic diagram of the technical effect of an electromagnetic switch of a starter involved in the present invention. The length of an air gap of the electromagnetic switch means an air portion between a moving iron core and a stationary iron core, and when the switch is closed, the length of the air gap is gradually reduced. It can be seen from the simulation diagram that in the first stage, in which the distance between the moving iron core and the stationary i on core is decreased from 10 mm o 6 mm, the spring forces required in the present invention and in the prior art are the same. In the second stage, in which the distance between the moving iron core and the stationary iron core is decreased from 6 mm to 2 mm, the spring force required in the present invention is far less than the spring force required in the prior art. In the third stage, the spring force required in the present invention is slightly less than the spring force required in the prior art. Compared with the prior art, the present invention has the following advantages: Firstly, a force of the contact spring for the contact piece and a force of the contact piece return spring can be significantly enhanced without increasing the ampere turns of the switch (or the volume of the switch), so as to increase the stability of the contact during closing, thereby reducing the risk of electric erosion or immovable welding of the contact.

Secondly, the force of the contact piece return spring can be significantly enhanced to rapidly and reliably open a closed contact (i.e. enabling the contact piece to be rapidly disengaged from the contact), reduce the electric erosion of the contact or facilitate opening an immovably welded contact.

Finally, significantly enhancing the force of the contact spring for the contact piece can contribute to the destruction of an ice layer at the contact. Figure 5 is a structural schematic view of the electromagnetic switch of the starter according to the present invention. The electromagnetic switch comprises a moving iron core 10, a switch winding 20, a contact piece shaft 30, a stationary iron core 40, a switch cover 50, a contact bolt 60, a contact piece return spring 70, a contact piece 80, a contact bolt 90, a contact piece contact spring 100, a switch housing 110, a moving iron core return spring 120, and a meshing spring 140.

The moving iron core 10 is able to move between a inactive position and an active position with regard to the stationary iron core 40. In the inactive position, no electromagnetic force is generated by the switch winding 20, so that the moving iron core 10 is away from the stationary iron core 40. In the active position, the electromagnetic force generated by the switch winding 20 overcome the force of the moving iron core return spring 120, so that the moving iron core 10 abuts the stationary iron core 40.

Furthermore, a shaft 150 comprises a portion located within a recess 151 of the moving iron core 10. A meshing spring 140 is mounted around said portion of the shaft 150. This meshing spring 140 allows the moving iron core 10 to continue its displacement when the gear of the starter does not properly meshes with the ring gear of the combustion engine but interfere with the teeth of the ring gear. In that case, the meshing spring 140 compresses while the moving iron core 10 continues to move towards the stationary iron core 40.

In a rest position, i.e when the gear of the starter does not interfere with the ring gear of the engine, the shaft 150 abuts a bottom wall 152 of the recess 151 by the pushing force of the meshing spring 140.

As illustrated by figure 7, the bottom wall 152 is formed in one-piece with the moving iron core 10. For example, the piece comprising the moving iron core 10 and the bottom wall 152 can be obtained by moulding.

This arrangement allows to limit the rls thai water penetrates, via the shaft 150, into the connecting chamber comprising the contact piece 80 and the contact bolds 60, 90. This also limits the total number of parts of the switch assembly with regard to a standard assembly .

As shown in figures 5, 6, and 8b, a second recess 156 opened in direction of the stationary iron core 40 is aimed to receive an end of the shaft 30. The bottom wall 152 forms a separation between the recess 151 and the recess 156. As it can be seen on figures 5, 6, 8a and 9, a locking washer 153 is positioned around the shaft 150. The locking washer 153 is fixed to the moving iron core 10 on the side of an opening of the recess 151.

In the rest position, the meshing spring 140 is mounted prestressed in the recess 151 between an internal border of the locking washer 153 and a shoulder 154 of the shaft 150.

As it can be clearly seen in figures 6 and 8a, the internal border of the locking washer 153 is crimped at the periphery of the recess 151. The locking washer 153 comprises also an external border having a diameter superior to an external diameter of the moving iron core 40. The moving iron core return spring 120 is mounted between said external border of the locking washer 153 and a fixed element of the electromagnetic switch with regard to the stationary iron core 40, in particular the switch housing 110.

In an alternative embodiment showed at figure 9, the moving iron core 10 comprising an integrated bottom wall 152 is used in the arrangement of figure 3.

Therefore, the moving iron core return spring 120 is mounted between a step of the contact piece shaft 30 and the bottom wall 152 of the moving iron core 10.

The bottom wall 152 may comprise a cylindrical portion inserted into the moving iron return spring 120 in order to guide said spring 120.

The description only illustrates preferred particular embodiments of the present invention, and the above- mentioned embodiments are merely used to describe the technical solution of the present invention rather than limit the present invention. Any technical solution which would be obtained by a person skilled in the art via logical analysis, reasoning or limited experiments according to the present invention should be included within the range of the present invention.