1. Spherical ferrite nanoparticles obtained by a process comprising particle growth in a first aqueous solution comprising a disaccharide, an alkaline, an oxidation agent, seed particles and divalent iron ions,
wherein the disaccharide is selected from the group consisting of cellobiose, maltose, lactose and trehalose.
2. The spherical ferrite nanoparticles of claim 1, wherein the first aqueous solution is prepared by adding the seed particles and the divalent iron ions to a second aqueous solution comprising the disaccharide, the alkaline and the oxidation agent.
3. The spherical ferrite nanoparticles of claim 1, wherein the first aqueous solution is prepared by adding the alkaline and the seed particles to a third aqueous solution comprising the divalent iron ions and the disaccharide to obtain a fourth aqueous solution, and adding the oxidation agent to the fourth aqueous solution.
4. The spherical ferrite nanoparticles of claim 1, having a number-averaged particle size in a range of 30 nm to 250 nm, wherein 95% or more of the spherical ferrite nanoparticles have a particle size within a range of \xb140% of the number-averaged particle size.
5. Surface-modified ferrite nanoparticles, comprising:
the spherical ferrite nanoparticles of claim 1, and
at least one surface modification agent selected from the group consisting of a surface-active agent, a hydroxyl acid and a sugar alcohol,
wherein the surface modification agent modifies a surface of the spherical ferrite nanoparticles.
6. Composite ferrite nanoparticles, comprising:
the spherical ferrite nanoparticles of claim 1, and
at least one surface covering agent selected from the group consisting of a polystyrene, a polyethylene, a polyacrylic acid ester, a polymethacrylic acid ester, a polyethylene glycol (PEG), a polyglycidyl methacrylate, a silica, and a silane coupling agent,
wherein the surface covering agent covers a surface of the spherical ferrite nanoparticles.
7. Composite ferrite nanoparticles, comprising:
the surface-modified ferrite nanoparticles of claim 5, and
at least one surface covering agent selected from the group consisting of a polystyrene, a polyethylene, a polyacrylic acid ester, a polymethacrylic acid ester, a polyethylene glycol (PEG), a polyglycidyl methacrylate, a silica, and a silane coupling agent,
wherein the surface covering agent covers a modified surface of the surface-modified ferrite nanoparticles.
8. The spherical ferrite nanoparticles of claim 1, wherein the oxidation agent is at least one selected from the group consisting of a nitric acid, a nitrous acid, a nitrate and a nitrite.
9. The spherical ferrite nanoparticles of claim 1, having a sphericity of 0.3 or less.
10. The spherical ferrite nanoparticles of claim 1, wherein the seed particles have an average particle diameter of about 8 nm.
11. The spherical ferrite nanoparticles of claim 1, wherein the first aqueous solution further comprises trivalent iron ions.
12. The spherical ferrite nanoparticles of claim 1, wherein a concentration of the disaccharide in the first aqueous solution is 0.1M to 5M.
13. The spherical ferrite nanoparticles of claim 1, wherein a ratio of a concentration of the divalent iron ions to a concentration of the disaccharide in the first aqueous solution is in a range of 0.002 to 50.
14. The spherical ferrite nanoparticles of claim 12, wherein a ratio of a concentration of the divalent iron ions to the concentration of the disaccharide in the first aqueous solution is in a range of 0.002 to 50.
15. The surface-modified ferrite nanoparticles of claim 5, wherein the surface modification agent is at least one surface-active agent selected from the group consisting of a fatty acid, an alkylbenzene sulfonic acid and an alkyl phosphoric acid.
16. The surface-modified ferrite nanoparticles of claim 5, wherein the surface modification agent is at least one hydroxyl acid selected from the group consisting of a citric acid, a tartaric acid and a malic acid.
17. The surface-modified ferrite nanoparticles of claim 5, wherein the surface modification agent is at least one sugar alcohol selected from the group consisting of a sorbitol and a xylitol.
18. The spherical ferrite nanoparticles of claim 2, wherein the seed particles are added in a concentration range of 2.7 mg40 ml to 13.5 mg40 ml.
19. The spherical ferrite nanoparticles of claim 1, wherein the first aqueous solution comprises no monosaccharide.
20. The spherical ferrite nanoparticles of claim 1, wherein the disaccharide is trehalose.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. An electric power steering system comprising:
a steering force assist device that provides assist force for assisting a steering operation, to a steering system, using a motor as a driving source; and
a controller that controls the operation of the steering force assist device, wherein
the controller includes
a control signal generator that generates a motor control signal so as to produce a motor torque corresponding to the assist force, and
a driving circuit that supplies driving electric power based on the motor control signal, to the motor, wherein
the control signal generator calculates a current command value corresponding to a target assist force, based on a detected steering torque, and performs a current feedback computation so as to create the motor control signal, wherein
the motor is a non-connected brushless motor in which motor coils of three phases are not connected to each other, wherein
the controller includes three systems provided independently of one another with respect to each phase of the motor, each of the systems having the driving circuit and the control signal generator, wherein
each of the control signal generators of the three systems converts a current command value of a two-phase coordinate system corresponding to the target assist force, into a phase current command value of each phase, so as to perform phase current feedback control with respect to the corresponding phase, and executes an abnormality determination based on a deviation of a phase current value from the phase current command value, with respect to each of the two phases other than the corresponding phase, and wherein
when the control signal generators of two of the three phases determine that an abnormality occurs in the remaining one phase, the controller confirms the determination.
2. The electric power steering system according to claim 1, wherein
when the controller confirms a determination that an abnormality occurs in one of the three phases, the controller stops only application of electric current to the phase in which the abnormality occurs, and continues to apply current to the remaining two phases.
3. The electric power steering system according to claim 2, wherein
each of the control signal generators generates results of abnormality determinations concerning two phases other than the corresponding phase, as status signals, and wherein
the controller has a status evaluator and a stopper for each phase, the status evaluator generating a confirmed status signal indicative of an abnormality in the phase in question when the status evaluator receives the two status signals concerning the phase in question, both of which indicate that the phase in question is in an abnormal condition, the stopper being operable to stop application of current to the phase in question when the confirmed status signal indicates the abnormality in the phase in question.
4. The electric power steering system according to claim 3, wherein
each of the driving circuits applies current to the motor coil of the corresponding phase when gate voltages based on the motor control signal are applied to the driving circuit, and wherein
the controller has a pre-driver provided for each phase, for applying the gate voltages to the driving circuit of the corresponding phase when the confirmed status signal indicates that the corresponding phase is in a normal condition.