Valvetrain with rocker arm housing magnetic latch
A valvetrain includes a rocker arm assembly having a rocker arm and an electromagnetic latch assembly. A magnet of the latch assembly is housed within a chamber formed by the rocker arm. The chamber may be a retrofit hydraulic chamber. The magnet may be an electromagnet or a permanent magnet. A flux shifting bi-stable latch provides a sufficiently compact design. Isolation of the magnet within the rocker arm chamber may provide protection from metal particles carried by oil in an operating environment for the rocker arm assembly.
1. A valvetrain for an internal combustion engine of a type that has a combustion chamber, a moveable valve having a seat formed in the combustion chamber, and a camshaft, comprising:
an electromagnetic latch assembly comprising a magnet and a latch pin translatable between a first position and a second position; and
a rocker arm assembly comprising a rocker arm that forms a chamber that houses the magnet and a cam follower configured to engage a cam mounted on a camshaft as the camshaft rotates.
2. A valvetrain according to claim 1 , wherein:
one of the first and second latch pin positions provides a configuration in which the rocker arm assembly is operative to actuate the moveable valve in response to rotation of the cam shaft to produce a first valve lift profile; and
the other of the first and second latch pin positions provides a configuration in which the rocker arm assembly is operative to actuate the moveable valve in response to rotation of the cam shaft to produce a second valve lift profile, which is distinct from the first valve lift profile, or the moveable valve is deactivated.
3. A valvetrain according to claim 1 , wherein the chamber is a retrofit hydraulic chamber.
4. A valvetrain according to claim 1 , wherein the magnet is a coil that provides an electromagnet for the electromagnetic latch assembly.
5. A valvetrain according to claim 4 , further comprising:
a shell surrounding the coil and having an opening through which the latch pin extends;
wherein the latch pin has a non-circular profile where it passes through the opening; and
the shape of the opening cooperates with the latch pin profile to restrict rotation of the latch pin.
6. A valvetrain according to claim 5 , wherein:
the coil is operative to generate magnetic flux;
an operative portion of the magnet flux generated by the coil passes through the shell.
7. A valvetrain according to claim 4 , wherein:
the rocker arm has a first end out of which the latch pin extends, a second end opposite the first end, and a side between the first and second ends; and
a circuit powering the coil includes conductors that run from the coil, out the second end of the rocker arm, and from there to the side of the rocker arm; and
the circuit includes an electrical connection made at the side of the rocker arm.
8. A valvetrain according to claim 7 , wherein one of the conductors runs along the side of the rocker arm and is held by a contact frame that is supported within an opening in the second end of the rocker arm.
9. A valvetrain according to claim 8 , wherein the contact frame is also supported by a fitting against the side of the rocker arm.
10. A valvetrain according to claim 9 , wherein the fitting is, or is an extension of, a contact pin that forms part of the circuit.
11. A valvetrain according to claim 7 , wherein:
the rocker arm has an upper side on which the cam follower engages the cam;
the coil has an axis and is wound about a bobbin providing tie-offs for the conductors; and
ends of the conductors are held by the tie-offs at locations that are displaced to the upper side relative to the location of the coil axis.
12. A valvetrain according to claim 4 , wherein:
the rocker arm has a first end out of which the latch pin extends, a second end opposite the first end, and a side between the first and second ends;
the coil has an axis and comprises a wire wound about a bobbin with tie-off pins to which ends of the wire are attached; and
a portion of each tie-off pin emerges from the rocker arm at the second end of the rocker arm and extends away from the coil axis.
13. A method of manufacturing a valvetrain according to claim 12 , comprising:
winding the wire around the bobbin to form a coil with the ends of the wire attached to the tie-off pins;
placing one side of a can cap on an end of the bobbin with the tie-off pins on an opposite side of the can cap;
sliding the coil, with the can cap attached, into a can; and
installing the can with the coil inside in the chamber formed by the rocker arm;
wherein the tie-off pins extend away from the axis.
14. An internal combustion engine, comprising:
a valvetrain according to claim 4 ; and
circuitry operable to energize the coil with a current in either a first direction or a second direction, which is opposite the first direction.
15. A valvetrain according to claim 4 , wherein the electromagnetic latch assembly provides the latch pin with positional stability independently from the coil when the latch pin is in the first position and when the latch pin is in the second position.
16. A valvetrain according to claim 15 , wherein the magnet is a permanent magnet.
17. A valvetrain according to claim 16 , wherein the permanent magnet is held stationary with respect to the rocker arm.
18. A valvetrain according to claim 17 , wherein the permanent magnet contributes to the positional stability of the latch pin both when the latch pin is in the first position and when the latch pin is in the second position.
19. A valvetrain according to claim 18 , wherein:
the permanent magnet is within the coil; and
the coil is also housed within the chamber.
20. A valvetrain according to claim 18 , wherein:
the electromagnetic latch assembly forms a first magnetic circuit and a second magnetic circuit that is distinct from the first magnetic circuit;
the permanent magnet produces magnetic flux;
an operative portion of the magnetic flux from the permanent magnet follows the first magnetic circuit when the latch pin is in the first position; and
an operative portion of the magnetic flux from the permanent magnet follows the second magnetic circuit when the latch pin is in the second position.
21. A valvetrain according to claim 20 , wherein:
the coil encircles a volume within which a portion of the latch pin comprising low coercivity ferromagnetic material translates;
the electromagnetic latch assembly comprises one or more sections of low coercivity ferromagnetic material outside coil;
both the first and the second magnetic circuits include the portion of the latch pin formed of low coercivity ferromagnetic material;
the second magnetic circuit passes around the coil via the one or more sections of low coercivity ferromagnetic material; and
the first magnetic circuit does not pass around the coil.
22. A valvetrain according to claim 20 , wherein:
the electromagnetic latch assembly further comprises a second permanent housed within the chamber and held stationary with respect to the rocker arm; and
the second permanent magnet also contributes to the positional stability of the latch pin both when the latch pin is in the first position and when the latch pin is in the second position.
23. A valvetrain according to claim 22 , wherein the permanent magnet and the second permanent magnet are arranged with confronting polarities.
24. A valvetrain according to claim 23 , wherein the permanent magnet and the second permanent magnet are separated by a pole piece mounted between them.
25. A valvetrain according to claim 24 , wherein:
the permanent magnet, the second permanent magnet, and the pole piece are arranged about an opening through which the latch pin translates;
the permanent magnet, the second permanent magnet, and the pole piece bound the opening; and
the pole piece bounds the opening more narrowly than the permanent and the second permanent magnet.