Patent Searching with a Patent Classification System

The USPTO System

Patent classification systems. Ask most professional patent searchers and they will probably tell you that any serious search will have include a through search of one or more of the classification systems.

What does that mean?

Most (maybe all) of the major patent offices around the world have patent classification systems. They are all different but use similar ideas in how they are organized. The bad news is that you couldn't possibly learn all of them. The good news is that you don't have to. Unless you plan to spend more money on your patent search than on your patent you will probably constrain your search to the USPTO patent classification system or the IPC system.

As we discussed earlier you can do a quick and dirty search by using a patent search engine and make skilled use of boolean search terms. That , in fact, is where I often start. But quite frankly, if that is all you do, you may miss some key patents because search engines are inherently dumb - they search only with the terms you give them. And if you hire someone to do a search for you you should insist they do a through search using a patent classification system.

Skilled searchers (and examiners) often know their patent classification system well enough to zero in on the correct class or sub-class quickly. If you don't do this regularly then finding the correct patent classification system may be the most problematic part of your search. You will see why below. I will suggest later a step-by step process for zeroing in on your class or sub-class.

Let's first try to understand a patent classification system. For the remainder of this article I will use the USPTO patent classification system as the example. In another article I will get into the IPC (International Patent Classification) System.

Also I will assume in this article that you are using the search capability of the USPTO website.

For starters - all patents are classified by subject matter. There are hundreds of categories. Each with many sub-categories and sub-sub-categories. To get a taste of this just look at category 475 - PLANETARY GEAR TRANSMISSION SYSTEMS OR COMPONENTS. It can be found here:

http://www.uspto.gov/go/classification/uspc475/sched475.htm

CLASS 475 PLANETARY GEAR TRANSMISSION SYSTEMS OR COMPONENTS

475 PLANETARY GEAR TRANSMISSION SYSTEMS OR COMPONENTS

1 INPUT FROM INDEPENDENT POWER SOURCES

2 .Condition responsive motor control

3 .Including manual input

4 ..And electric motor input

5 .Including electric motor input

6 .Plural outputs

7 .Worm gear in drive train

8 .One-way clutch or brake in drive train

9 .Bevel planet pinion in drive train

10 .Intermeshing planet pinions in drive train

11 ROTARY PLANETATING OUTPUT

12 REVERSAL OF DIRECTION OF POWER FLOW CHANGES POWER TRANSMISSION TO ALTERNATE PATH

13 .Input and output exchange functions

14 CYCLICAL OR INTERMITTENT DRIVE

15 .Plural outputs

16 .With means to adjust cycle or drive during operation

17 .Multilated or noncircular gear in drive train

18 STEERING BY DRIVING

19 .With condition responsive steer control

20 .With cooling or lubrication

21 .With infinitely variable drive

22 ..Variable drive is fluid drive

23 ...Hydrostatic type24 ....Plural pump-motor sets25 ..Belt type

26 ..Variable drive is friction drive

27 .Fluid steer control

28 .With plural power paths to a planetary transmission at each output

29 .With planetary reaction brake steering

30 ..And carrier input to planetary gearing

31 FLUID DRIVE OR CONTROL OF PLANETARY GEARING

32 .Diverse fluid drives

33 .Plural impeller-turbine type fluid circuits

34 ..Fill and empty type

35 .Single impeller-turbine type fluid circuit divides or combines plural power paths

36 ..Planetary gearing divides paths

37 ..Three fluid outputs

38 ...And stator

39 ..Two fluid outputs and stator

40 ...With variable fluid drive control

41 ...And mechanical drive path

42 ..Control of or by fluid drive

43 ..With speed or torque responsive clutch or brake control

44 ..Stator rotatable in reverse direction to provide drive

45 ...Turbine braked, stator provides reverse drive

46 ....And adds torque in forward drive

47 .Impeller-turbine type fluid circuit and mechanical path in parallel

48 ..With control of or by the fluid circuit

49 ...Gearing controlled by fluid circuit condition

50 ...Fill and empty type fluid circuit

51 ..With speed responsive control

52 ..And nonplanetary gearing

53 ..Planetary gearing divides paths

54 ..Sun, orbit and carrier braked

55 ..Sun and orbit braked

56 ..Sun and carrier braked

57 ..Orbit and carrier braked

58 ..Orbits braked

59 .Impeller-turbine type fluid circuit in series with planetary gearing

60 ..And condition responsive control

61 ...Control of or by fluid circuit

62 ....Control responsive to relative impeller and turbine speeds

63 .....System or servo fluid pressure controlled

64 ....Fluid circuit controlled

65 .....By lock-up clutch actuation

66 ..And nonplanetary gearing

67 ..With synchronizing of positive clutch or brake

68 ..With nonratio brake

69 ..Fluid circuit controlled

70 ...Pressure controlled

71 ..And differential in series

72 .Fluid pump and motor in one of plural paths to or from planetary gearing

73 ..Plural fluid power paths to planetary gearing

74 ..Plural outputs

75 ..Three pumps or motors

76 ..Speed responsive control

77 ...Constant speed output

78 ..Interrelated fluid unit and gear control

79 ...With constant speed ratio between input and one fluid unit

80 ..Plural speed ranges

81 ...With constant speed ratio between input and one fluid unit

82 ....Having single planet carrier

83 .Pump and motor in series with planetary gearing

84 .Control of differential planetary gearing

85 ..Special fluid

86 ..By fluid operated mechanical clutch

87 ...Operated by viscous drag

88 ...Operated by a pump responsive to differential action

89 ..Fluid resistance controls relative rotation of outputs

90 ...Fluid pumped by differential gears

91 .Fluid resistance inhibits relative rotation

92 ..Fluid damper for reaction element

93 ..Valve inhibits fluid flow

94 ...Speed or torque responsive valve control

95 ....Centrifugally actuated valve controls fluid clutch

96 .....Clutch connects planet pinion and carrier

97 .....With fluid brake control

98 ....Centrifugally actuated valve controls fluid brake

99 ...Interrelated valve control and mechanical clutch or brake

100 ....Valve control and mechanical clutch

101 .....Pump pressure engages mechanical clutch

102 ...Fluid brake(s) for plural planetary elements

103 ...Plural fluid clutches

104 ...Fluid brake for planetary element

105 ....And fluid clutch

106 ....Bevel gearing

107 ....Sun or orbit braked

108 ...Fluid clutch includes gear type pump

109 ...Planet clutched to carrier

110 ....With reversing means

111 ..Planet clutched to fluid flywheel

112 ..Fluid container connected to planet pinion

113 ..Impeller-turbine type fluid unit used as brake114 .Fluid control of friction planetary gearing

115 ..Stepless ratio change controlled

116 .Fluid controlled mechanical clutch or brake

117 ..Temperature responsive control

118 ..Speed responsive control

119 ...Safety device

120 ...Pressure control

121 ...Ratio change

122 ....Speed responsive valve control

123 .....Electrical control

124 .....Centrifugal control

125 ..Torque responsive control

126 ...Responsive to torque reversal

127 ..Pressure regulation

128 ...Valving controls shift timing

129 ....With fluid accumulator

130 ...Manual regulator

131 ..Manually actuated ratio selector

132 ...Electrical

133 ...With safety valve

134 ...Plural selector valves

135 ...Rotary valve

136 ..With ancillary pump or governor drive

137 ...Plural pumps

138 ..With positive clutch or brake

139 ...And friction synchronizer

140 ..Spring engaged, fluid released clutch or brake device

141 ...Plural devices simultaneously spring engaged

142 ...Single fluid motor engages one device and releases other

143 ..Expanding fluid motor chamber mechanically contracts second motor

144 ..Fluid controlled one-way devices

145 ..Fluid motor controls device through cam or lever

146 ..Fluid motor structure

147 ...Radially expanding motor

148 ...With one-way device

149 ELECTRIC OR MAGNETIC DRIVE OR CONTROL

150 .Differential drive or control

151 .Plural power paths

152 ..With nonplanetary drive to electric or magnetic path

153 .With condition responsive control

154 .With electric or magnetic controlled brake155 ..And manual speed selector

156 ..Electric or magnetic device disengages brake

157 ..Electric or magnetic engaged brake and spring engaged lockup clutch

158 WITH INDICATOR OR ALARM

159 WITH LUBRICATON

160 .For differential planetary gearing

161 WITH TRANSMISSION COOLING OR HEATING MEANS

162 PLANET PERIPHERY SURROUNDS AXIS OF INTERACTING GEAR (E.G., ECCENTRICALLY DRIVEN TRANSMISSON)

163 .Wabbler transmission

164 ..Single member has oppositely axially facing tooth sets

165 .Friction gearing

166 ..Variable speed

167 .Link chain gearing

168 .Gear teeth comprise rolling bodies

169 .Means to change speed ratio between input and output

170 ..Variable eccentricity

171 ..Plural power paths to planetary gearing

172 ..Condition responsive control

173 ..Plural planetary elements braked

174 .Plural outputs

175 .With releasable clutch or brake

176 .Gear has plural circumferential tooth sets

177 ..Internal and external tooth sets

178 .Circumferentially spaced connector pins

179 ..Roller bearing surrounds pin

180 .Particular gear tooth

181 .Particular counterweight

182 PLANET PINION ENGAGES FLEXIBLE BELT OR CHAIN

183 PLANET PINION IS FRICTION GEAR

184 .Plural outputs (e.g., differential)

185 .Variable speed ratio (without slippage)

186 ..Condition responsive ratio change

187 ..Releasably braked element

188 ...Plural elements releasably braked

189 ..Planet pinion is a ball

190 ..Planet pinion rotatable about axis at angle to axis of input or output gear

191 ...Planet pinion is member having axis fixed or adjustable to position perpendicular to axis of input or output gear

192 ....Pinion engages facing concave surfaces (e.g., mounted in torus)

193 ...Conical or frusto-conical planet pinion194 ....Torque responsive means to increase contact pressure

195 .Torque responsive means to increase contact pressure

196 .Planet pinion is ball

197 .Planet pinion rotatable about axis at angle to axis of input or output gear

198 VARIABLE SPEED OR DIRECTION TRANSMISSION COMBINED WITH DIFFERENTIAL

199 .Condition responsive

200 .Differential is beneath prime mover or transmission

201 .Differential is between prime mover and tranmission in the path of power flow

202 .With universal joint in drive train

203 .Plural selectively driveable gears surround differential

204 .Variable speed or direction is planetary transmission

205 ..Plural planetary units combined with differential

206 .Transmission output shaft parallel to differential output shafts

207 NONPLANETARY VARIABLE SPEED OR DIRECTION TRANSMISSION COMBINED WITH PLANETARY TRANSMISSION

208 .Condition repsonsive

209 .Interrelated control of in series transmissions

210 .Nonplanetary transmission is belt or chain gearing

211 ..Plural power paths to planetary gearing

212 ...Nonplanetary transmission is chain gearing

213 ..Nonplanetary transmission is chain gearing

214 .Nonplanetary transmission is friction gearing

215 ..Plural power paths to planetary gearing

216 ...Friction gear engages facing concave surfaces

217 ...Nonplanetary transmission is disc and wheel

218 .Plural power paths to planetary gearing

219 .Plural planetary units

220 DIFFERENTIAL PLANETARY GEARING

221 .Differential or nondifferential planetary combined with differential (e.g., two differentials)

222 .With universal joint in drive train

223 .Including means to selectively apply rotational power to only one output

224 ..By braking other output

225 .With additional gearset between differential output and load

226 .Planet pinion is worm gear

227 ..And spur gear on pinion

228 .Worm drive on input shaft

229 ..And roller bearing supporting worm from casing

230 .Bevel gear differential

231 ..With means to limit overspeed of one output (e.g., lock-up clutch)

232 ...Centrifugal actuator

233 ...Lock-up clutch between pinion and pinion carrier

234 ...By axial movement of output gear

235 ....With spring bias on gear or clutch

236 ...Particular gear shape or tooth interaction limits overspeed

237 ...Manual actuator

238 ....Friction clutch

239 .....Plate clutch

240 ...Spring bias on overspeed limiting means

241 ....Helically coiled spring

242 ..Separate planet pinions or separate tooth set on same pinion for each output

243 ..Output gear rotatable relative to axial support shaft

244 ...Support shaft coupled to other output gear

245 ...With roller bearing between output gear and shaft

246 ..With roller bearing between gear and its support

247 ...Ball bearing

248 .Spur gear differential

249 ..With means to limit overspeed of one output

250 ...Manual actuator

251 ..Pinion axis at angle intersecting axis of output

252 ..Intermeshing planet pinions

253 ..With roller bearing between gear and its support

254 CONDITION RESPONSIVE CONTROL

255 .Eccentrically weighted planet

256 .Downshift responsive to high speed limit

257 .Speed responsive control adjusted or opposed by torque

258 .Centrifugally controlled clutch or brake

259 ..One-way clutch or brake

260 ..Centrifugal brake control

261 ..Positive clutc

262 ..Axially engaged friction clutch

263 .Overload release

264 ..Spring applied friction drive establishing means

265 ...Drive establishing means is friction brake

266 .Stepped, torque responsive ratio change

267 .With flywheel or centrifugal weight control

268 ..With planet pinion axis at angle to axis of mating gear (e.g., bevel gears)

269 WITH MEANS TO VARY DRIVE RATIO OR DISCONNECT DRIVE (E.G., BRAKE OR CLUTCH)

270 .Manual force provides reaction during drive

271 .Plural elements selectively braked

272 ..With preselection

273 ..Axis of planet pinion at angle to axis of mating gear (e.g., bevel gears)

274 ...And additional planetary gearset having axis of pinion parallel to axis of mating gear

275 ..Transmission includes three relatively rotatable sun gears

276 ...With brake for sun, carrier and orbit

277 ...With brake for plural sun gears

278 ....And brake for carrier

279 ...With brake for plural orbits

280 ..Brake for sun, carrier and orbit

281 ...Including one-way clutch or brake282 ..Brake for sun and orbit

283 ...Including one-way clutch or brake

284 ..Brake for sun and carrier

285 ...Including one-way clutch or brake

286 ..Brake for orbit and carrier

287 ...Including one-way clutch or brake

288 ..Plural suns braked

289 ...Including one-way clutch or brake

290 ..Plural orbits braked

291 ...Including one-way clutch or brake

292 ..Including one-way clutch or brake

293 .Speed responsive clutch or brake

294 .Ratio shift initiated by reverse rotation of input shaft

295 .Plural outputs

296 .Plural drive ratios other than unity

297 ..Including one-way clutch or brake

298 .Gear shiftable axially to disconnect or vary ratio

299 ..Orbit shiftable relative to sun and carrier

300 ..Sun shiftable relative to orbit and carrier

301 .Brake or clutch on surface of helically coiled member

302 .Nonplanetary gearing combined with planetary

303 .With synchronizing clutch or brake

304 .Planet pinion is worm gear

305 .Including releasable clutch directly between planet pinion and carrier

306 .Brake for planetary transmission having axis of planet pinion at angle to axis of mating gear (e.g., bevel gears)

307 ..Including one-way clutch or brake

308 ..And lock-up clutch

309 ...Friction clutch

310 ....Plate clutch

311 .Sun braked

312 ..Including one-way clutch or brake

313 ..Intermeshing planet pinions on single carrier

314 ..And lock-up clutch

315 ...Friction clutch

316 ....Plate clutch

317 .Orbit braked

318 ..Including one-way clutch or brake

319 ..Intermeshing planet pinions on single carrier

320 ..And lock-up clutch

321 ...Friction clutch

322 ....Plate clutch

323 .Carrier braked

324 ..Including one-way clutch or brake

325 ..Intermeshing planet pinions on single carrier

326 ..And lock-up clutch

327 ...Friction clutch

328 ....Plate clutch

329 PLURAL POWER PATHS TO PLANETARY GEARING

330 .Plural planetary units

331 PLANETARY GEARING OR ELEMENT

332 .Plural outputs

333 .Planet pinion is worm gear

334 .Floating support annulus in rolling contact with planet pinion

335 .Toothed planet pinion has smooth bearing surface engaging raceway on sun or orbit gear

336 .Axis of planet pinion at angle intersecting rotational axis of mating gear (e.g., bevel gears)

337 .Plural planet carriers in series move at different speeds

338 .Coaxial teeth around planet pinion engage axially spaced relatively rotatable gears

339 ..Engage plural relatively rotatable sun gears

340 ...And orbit gear

341 ..Engage plural relatively rotatable orbit gears

342 ...And sun gear

343 .Nonplanetary gearing combined with planetary

344 .Particular gear tooth feature

345 ..Nonmetallic or resilient

346 .Floating or flexible coupling or support

347 ..Resilient member

348 .Planet pinion supported by roller bearings

349 .With manual input

This class - one of many in the US patent classification system, is clearly focused on planetary gear transmissions systems. But broken up into many classes, sub classes, and yes sub-sub classes.

You may have noticed the dots in front of the definitions for the various classes and sub-classes. These dots indicate additional hierarchy levels in the class/subclass structure of the patent classification system. In this example, the class (475) is at the highest level; everything else falls under class 475. But only some of the subclasses are directly under class 475. All of the all-cap definitions with no dot in front of them are directly in 475. You know this because they have no dots in front of their definitions which would indicate additional steps down in the hierarchy structure. So class 331 (written as CCL/475/331 is directly in 475. Subclass 338 on the other hand, is not directly under class 475. It is actually under subclass 331. Note that 339 has two dots and is thus a subclass of 338 and 340 is a subclass of 339.

Calling all of these as subs and sub-subs, etc would get quickly confusing, so they distinguish the different levels with dots - the more dots, the lower it is in the hierarchy. If you are trying to figure out what class or subclass a given category falls under, go up the listing from the category of interest to the first class or subclass with one less dot.

It works just like an outline, but dots are used in place of Roman numerals, and other traditional outline level designations.

It is extremely important to understand this hierarchical system. If you do not understand the patent classification system, it is absolutely impossible to know if you are looking in right places when you do a search.

As you look through that example you will quickly see that depending on the details of your invention it becomes difficult to see it in just one category. And in fact there is no way to know under which class/subclass the USPTO examiners decided to file an invention. And, a single invention can be filed under more than one class/subclass (in fact, most inventions are filed in several classes/subclasses).

You may now have an Excedrin headache. The patent classification system can have that effect.

This is one of the most important challenges of patent searching: Thoroughly understanding the patent classification system, and wisely choosing which classes/subclasses appear to be most relevant to the search you are performing. If you choose poorly, there may be another class/subclass filled with dozens of patents relevant to your search, and you may miss them.

Frankly - unless you do this fairly often using the patent classification system will be very tedious for you. But it can be a very comprehensive way of doing a search. Let's assume that you have done this though and zoomed in on a few classes and sub-classes that correspond well to the invention you are searching. Then from the USPTO website you can quickly move into lists of patents in your chosen subclasses.

Let's assume that you are convinced that your invention is a planetary gear transmission system steered by driving with an infinitely variable fluid drive of the hydrostatic type. Setting Class 475 to display all indent levels revels CCL/475/23, which fits your criteria, and is a 3 dot sub-level. You can then click on "A" to see the published applications in that sub-class , which will show about 3 applications. Clicking on "P" to see patents will reveal about 78 patents.

Now comes the hard part - you have to read them. Although the first level of effort is to read the abstracts. This will usually enable you to eliminate many of the patents and applications as to relevance.

All of this may sound complicated - because it is.

I have suggested that searching the patent classification categories is the way the pros do it. But frankly good patent searching is more of an art than a science. In other articles I will suggest what I consider practical approaches to doing good searches that will eventually lead you to probable patent classification categories to search. In other words I view patent classification searching as one of the tools to use but not the final answer.


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Mike Ervin
Mike Ervin - Cost Effective Small Business Patent Protection.

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