GB2097344A - Self-levelling suspension system - Google Patents
Self-levelling suspension system Download PDFInfo
- Publication number
- GB2097344A GB2097344A GB8208395A GB8208395A GB2097344A GB 2097344 A GB2097344 A GB 2097344A GB 8208395 A GB8208395 A GB 8208395A GB 8208395 A GB8208395 A GB 8208395A GB 2097344 A GB2097344 A GB 2097344A
- Authority
- GB
- United Kingdom
- Prior art keywords
- ride height
- suspension
- vehicle
- height
- ride
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60G—VEHICLE SUSPENSION ARRANGEMENTS
- B60G17/00—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load
- B60G17/015—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements
- B60G17/016—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements characterised by their responsiveness, when the vehicle is travelling, to specific motion, a specific condition, or driver input
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Vehicle Body Suspensions (AREA)
Abstract
A sensor is associated with each suspension unit or coupled pair of units for adjusting the ride height of a vehicle, and each sensor gives an output that varies progressively with ride height. A control circuit, preferably microprocessor based, is arranged to (i) read each of the outputs at least once, preferably in sequence, (ii) select the output which corresponds to the sensed ride height that differs most from the desired ride height, and (iii) apply a correction to the suspension unit(s) associated with the selected output to adjust it/them towards the desired ride height. The control circuit repeats (i) to (iii) until all the sensed ride heights are within acceptable limits of the desired height whereupon the system enters a so-called trim mode. In this mode corrections are based on a calculated ride height at a conceptual centre of height where height variations due to pitch and roll are minimal.
Description
SPECIFICATION
Self-levelling suspension systems
This invention relates to so-called self-levelling suspension systems for vehicles, that is, suspension systems that automatically adjust the ride height between the sprung and unsprung parts of the vehicle to compensate for any alteration or redistribution of load.
The sprung parts of the vehicle, namely the body and its associated components, are supported above the unsprung parts (the wheels, axles etc.) by a number of suspension units of adjustable length.
Generally speaking, known self-levelling suspension systems are based on closed loop control, which involves monitoring the ride height in the vicinity of each suspension unit and adjusting its length until the difference between the actual and desired ride heights is within a certain range. The main problem with this kind of control is that when the vehicle is in motion the actual ride height is constantly varying due to suspension oscillation, cornering, and acceleration or deceleration, so either the system constantly tries to compensate for these variations, or there has to be an in-built delay before correction commences.
What is now proposed is essentially a form of discontinuous closed loop control using open loop increments of correction.
According to the present invention, a selflevelling suspension system for a vehicle comprises a plurality of suspension units for adjusting the ride height between the sprung and unsprung parts of the vehicle, a respective ride height sensor associated with each suspension unit, or coupled pair of suspension units, and adapted to give an output that varies progressively with the ride height in the vicinity of the associated suspension unit(s), and control means for
(i) reading each of the outputs at least once,
(ii) selecting the output which corresponds to the sensed ride height that differs most from the desired ride height, and
(iii) applying a correction to the suspension unit(s) associated with the selected output to adjust it/them towards the desired ride height, the control means being arranged to repeat (i) to (iii) until all the sensed ride heights are within acceptable limits of the desired ride height.
Since the corrections are made one at a time the adjustment rate of the suspension units may be closely defined enabling the magnitude of the necessary corrections to be calculated with considerable accuracy. Furthermore, the capacity of the system will always be directed towards correcting the worst error.
Preferably the control means is arranged to read each of the outputs in sequence. Apart from the cost saving involved in using a single control means sequentially to scan the sensors there is also the advantage that any drift or circuit malfunction will be likely to affect all corrections equally, so such factors will result in an overall alteration in ride height rather than changes in attitude.
Preferably the control means is arranged to read each of the outputs in sequence a plural number of times and calculate for each sensor a computed average value for the readings from that sensor, the computed average values being used in selecting the required output. The computed average value is not necessarily the strict mathematical mean value but may, for example, be weighted in favour of the later readings.
Preferably the number of readings used in calculating the computed average value for a particular sensor output is varied in accordance with the degree of suspension activity, which may for example be ascertained from the range of readings from that sensor in a predetermined period. The readings are preferably taken at a constant rate but the period over which the readings are taken is varied. The number of readings could be increased in accordance with journey time since rapid corrections are only likely to be required at the commencement of a journey.
The control means is preferably arranged to apply a correction which should be sufficient to reduce the difference between the selected and desired ride heights to less than the next greatest difference between the sensed and desired ride heights. Preferably the control means is arranged to apply a predetermined minimum correction unless the difference between the selected and desired ride heights is less than that predetermined correction.
In a preferred arrangement the control means is arranged to operate in a trim mode when all the sensed heights are within acceptable limits of the desired ride height, in which the control means calculates computed average values for all the sensor readings, uses the computed average values to calculate a central ride height for the vehicle, checks the central ride height to see whether it falls within acceptable limits of a desired central ride height, and re-enters the initial mode if the central ride height is found to be outside the acceptable limits. Preferably the computed average values calculated in the trim mode are based on a larger number of readings than are used in calculating the computed average values in the initial mode.
The control means preferably comprises:
reading means for (i) reading each of the outputs at least once,
selection means for (ii) selecting the output which corresponds to the sensed ride height that differs most from the desired ride height, and
correction signal generating means for (iii) applying a correction to the suspension unit(s) associated with the selected output to adjust it/them towards the desired ride height, the control means being arranged to repeat (i) to (iii) until all the sensed ride heights are within acceptable limits of the desired ride height.
The reading means, the selection means and the correction signal generating means may be in
the form of respective logic circuits or, more
preferably, they may be provided by a
microprocessor.
The invention also includes a method of
adjusting a vehicle suspension system which
comprises a plurality of suspension units for
adjusting the ride height between the sprung and
unsprung parts of the vehicle, the method
comprising:
(a) sensing the ride height in the vicinity of each
suspension unit, or coupled pair of suspension
units,
(b) selecting the sensed ride height that differs
most from the desired ride height,
(c) applying a correction to the corresponding
suspension unit(s) to adjust it/them towards the
desired ride height, and
(d) repeating (a) to (c) if necessary until all the
sensed ride heights are within acceptable limits of
the desired ride height.
The invention will now be further described, by
way of example only, with reference to the
accompanying drawings of which
Figure 1 is a block diagram of a vehicle self
levelling suspension system according to the
invention, and
Figure 2 is a flow diagram that illustrates how
the system operates.
Referring to Figure 1 , four suspension units in the form of struts R1 to R4 support the sprung parts of the vehicle above the unsprung parts. Each strut, R, to R4, is associated with a ride height sensor, S1 to S4 respectively, having an electrical characteristic that varies in proportion to the length of the strut, e.g. resistance or impedance.
(A suitable sensor is described in UK Patent
Specification No. 2 074 736A.)
Struts R, and R2 are mounted at the front of the vehicle, one on each side. The hydraulic height adjustment chambers of the struts are connected via respective solenoid-operated control valves V1, V2, to a common port 6 of a three-way master valve MV, also solenoid-operated. Struts R3 and R4
are mounted at the rear of the vehicle, on opposite
sides, and their hydraulic chambers are both
connected via a single solenoid-operated control valve V3 to the common port 6 of the master valve
MV. The master valve is switchable to connect the control valves V1 to V3 either to a high pressure fluid source, provided by a pump P for supplying fluid at a constant flow rate from a reservoir 7, or to reservoir via a return line 8.
Each sensor Sa to S4 is connected to a
multiplexing circuit MPX for producing a single
multiplexed output 5. This output is connected to a decoding circuit D for converting the multiplex signals into a form which can be handled by a control circuit in the form of a microprocessor
MPU of the type sold under the designation MC 6805. The microprocessor has two output channels 9, 10. One channel 9 controls the valves V1 to V3, and the other channel 10 controls the master valve MV.
The operation of the system is best understood with reference to Figure 2. When no levelling is taking place the control valves V1 to V3 are all closed so that hydraulic fluid is trapped in the struts and the ride height of the vehicle remains constant. "Switch On" occurs when the vehicle ignition key is turned, whereupon an "Initialise" command is generated to start a levelling program.
The levelling program commences by commanding the microprocessor to read all the output signals from the sensors in a predetermined sequence. At this stage it is assumed that the vehicle is stationary and only one set of readings is taken. The readings are stored in the memory of the microprocessor. Next, the readings are analysed to check that they include only valid errors. In this context an error is a difference between the actual reading and the reading corresponding to a desired ride height An example of a valid error is one that is due to uneven load distribution causing the vehicle to tilt, whereas an example of an invalid error would be one produced when the vehicle was parked with one wheel on the pavement.
If the errors are not valid it is assumed that no height adjustment is required and the system goes into standby until the readings change. But if the errors are valid the worst error is selected and analysed to see whether it falls within acceptable limits of the desired ride height (the so-called dead band). If the error falls outside the dead band a correction is immediately applied to the corresponding strut to bring the vehicle closer to a level condition. This is achieved by generating a signal on output channel 10 to set the master valve according to whether the strut is to be lengthened or shortened, and then applying a pulse on output channel 9 to open the appropriate control valve for a calculated period corresponding to the desired degree of correction.
After this preliminary correction, sequential reading of the sensor outputs recommences and continues until several readings have been obtained for each strut. The sensour output signals are filtered to remove any transient variations and stored. The stored readings are then checked to see how much the readings from each strut differ in a predetermined period. If the readings are quiet (little difference), as might be the case when the vehicle is stationary, the worst error is again selected (which may be the reading from the same strut as before or a different one), checked to see whether it is out of band, and a further correction is applied. This sequence of operations constitutes a so-called fast mode of correction. On the other hand, if there is a substantial difference in the readings, such as might occur when the vehicle is in motion, the length of time over which readings are taken is increased in proportion to the degree of variation ("Take More Readings") so that although the rate at which readings are taken remains constant, the number of readings for any given strut increases. These further readings are stored along with those previously stored. This enables a computed average error to be accurately calculated for each strut from the stored readings, the computed average values being used as the basis for the next selection of the worst error. This latter sequence of operations constitutes a socalled slow mode of correction which the system enters when the vehicle is moving.
The rate at which the struts increase in length is defined due to the fact that the pump is arranged to produce a predictable flow, and the number of struts, of known support area, being adjusted at any given time is known. Of course, the support areas of different struts may differ and this is taken into account in the computation. Similarly the rate at which they decrease in length is also defined.
The length of time which the control valves V1 to
V3 need be opened for a given change in strut length can therefore be calculated to a reasonable degree of accuracy. The amount of correction applied to each strut is calculated to be at least sufficient to reduce the error below that of the strut with the next largest error, although in practice there is a degree of interaction between the struts and the actual change in strut length will not necessarily be the same as that which the adjustment was intended to produce. For this reason it is preferred not to apply a full correction to a strut or over-compensation may result.In order to ensure that a reasonable degree of correction is applied, a predetermined minimum correction of, say, 6 mm is always applied to each strut unless the actual ride height is within 6 mm of the desired ride height in which case a smaller correction is applied. In this example the dead band is 2 mm wide.
The program moves around the loop formed between "Select Worst Error" and "Are Readings
Quiet?", optionally via "Take More Readings", applying a correction on each occasion. This constitutes an initial mode pf relatively rapid correction which embraces the fast and slow modes. After a suitable number of corrections have been made a condition is eventually reached in which the last worst error falls within the dead band, or in other words, all the struts are within acceptable limits of the desired ride height. The system then enters the so-called trim mode which is intended to overcome the tendency for the struts to be continually readjusted in response to statistical errors in the analysis of the normal oscillatory movements between the sprung and unsprung parts.
Once the system enters the trim mode the microprocessor proceeds to take sequential reading from the sensors over an extended period of time. The readings are again stored and the computed average error of the readings for each strut is calculated. These computed average values are then weighted according to the characteristics of the particular vehicle and the weighted values are used to calculate the central ride height, that is, the ride height at a conceptual "centre of height" point of the vehicle. The location of this point is determined by the vehicle track, wheelbase, and the location of the struts and height sensors. The ride height at this point is disturbed only to a minor degree by pitch and roll due to vehicle motion. Similarly, if the total load remains constant, but is redistributed, the central ride height will be unaffected.However, if the total load changes, for example through gradual use of fuel, the central ride height will tend to change throughout the journey. The central ride height is checked to see whether it falls within acceptable limits of a desired central ride height ("Central
Ride Height In Error?") and if not the program returns to the initial mode and any necessary corrections are made to the struts, these corrections being made in the fast or slow mode as appropriate.If the central ride height does fall within the limits the microprocessor continues to take readings over an even longer period and store them, before recalculating the computed averages and returning to the initial anode. Since in this latter stage of the trim mode the readings are taken over an extremely long period any variation due to normal oscillatory movements, or transient effects such as cornering or braking, will have relatively little effect on the final average. Only prolonged effects due to genuine variations in vehicle load will be likely to affect the final computed averages such as to result in compensatory adjustment of the struts.
A further feature of the system, which is not apparent from Figure 2, is that, if a sensor develops a fault, the microprocessor uses the readings from the remaining sensors to calculate a reading for the faulty sensor. This reading is then substituted for the incorrect reading so that the vehicle level remains largely unaffected. Such fault conditions may be ascertained by a general comparison of the readings from the different sensors, a lack of variation in the readings from a particular sensor or a reading which is outside the usual range being interpreted as indicative of a fault.
The desired ride heights at which the system aims are determined by desired height parameters for the individual struts and a demand value of the central ride height. By varying the appropriate constants it is possible to modify the overall ride height and/or the attitude of the vehicle according to the speed of the vehicle, as measured by an independent transducer, or by the degree of suspension activity. Thus it might for example be arranged that the front of the vehicle dips when travelling at high speed and/or the overall ride height is reduced. Similarly the overall ride height may be increased when travelling over a deeply undulating surface, e.g. a field, to accommodate the increased degree of suspension activity.
Although all the struts may be adjusted independently, in practice it is usually acceptable to adjust the two rear struts R3, R4, together as in the manner shown. Although each of these struts has its own ride height sensor S3, S4, the signals derived from these sensors are combined to produce an average reading for the ride height in the region of the rear axle, or they may be combined in the output channel 9.
Instead of providing an individual sensor for each strut as shown, in some cases it may be sufficient to provide only a single sensor for a pair of struts, at the front or the rear of the vehicle. For example, the sensor may be arranged to detect displacement of an anti-roll bar associated with a pair of wheels.
It will be apparent from the foregoing description that the microprocessor comprises, in effect, reading means for reading each of the sensor output corresponding to the sensed ride
height that differs most from the desired ride height, and correction signal generating means for applying a correction to the suspension unit or units associated with the selected output to adjust the unit or units towards the desired ride height. It will be appreciated that all the functions of the microprocessor could be performed by separate logic circuits, or even analogue circuits, using discreet components or integrated circuits.
Claims (16)
1. A self-levelling suspension system for a vehicle comprising a plurality of suspension units for adjusting the ride height between the sprung and unsprung parts of the vehicle, a respective ride height sensor associated with each suspension unit, or coupled pair of suspension units, and adapted to give an output that varies progressively with the ride height in the vicinity of the associated suspension unit(s), and control means for
(i) reading each of the outputs at least once,
(ii) selecting the output which corresponds to the sensed ride height that differs most from the desired ride height, and
(iii) applying a correction to the suspension units associated with the selected output to adjust it/them towards the desired ride height, the control means being arranged to repeat (i) to (iii) until all the sensed ride heights are within acceptable limits of the desired ride height.
2. A system according to Claim 1, in which the control means is arranged to read each of the -outputs in sequence.
3. A system according to Claim 2, in which the control means is arranged to read each of the outputs in sequence a plural number of times and calculate for each sensor a computed average value for the readings from that sensor, the computed average values being used in selecting the required output.
4. A system according to Claim 3, in which the
number of readings used in calculating the
computed average value for a particular sensor
output is varied in accordance with the degree of
suspension activity.
5. A system according to Claim 4, in which the
degree of suspension activity is ascertained from
the range of readings in a predetermined period from the respective sensor.
6. A system according to Claim 4 or 5, in which
the readings used in calculating the computed
average value are taken at a constant rate but the
period over which the readings are taken is varied.
7. A system according to any preceding claim,
in which the control means is arranged to apply a correction which should be sufficient to reduce the difference between the selected and desired ride heights to less than the next greatest difference between the sensed and desired ride heights.
8. A system according to any preceding claim, in which the control means is arranged to apply a predetermined minimum correction unless the difference between the selected and desired ride heights is less than that predetermined correction.
9. A system according to any preceding claim, in which the control means is arranged to operate in a trim mode when all the sensed heights are within acceptable limits of the desired ride height, in which the control means calculates computed average values for all the sensor readings, uses the computed average values to calculate a central ride height for the vehicle, checks the central ride height to see whether it falls within acceptable limits of a desired central ride height, and re-enters the initial mode if the central ride height is found to be outside the acceptable limits.
10. A system according to Claims 3 and 9, in which the computed average value calculated in the trim mode are based on a larger number of reading than are used in calculating the computed average values in the initial mode.
11. A self-levelling suspension system for a vehicle comprising a plurality of suspension units for adjusting the ride height between the sprung and unsprung parts of the vehicle, a respective ride height sensor associated with each suspension unit, or coupled pair of suspension units, and adapted to give an output that varies progressively with the ride height in the vicinity of the associated suspension unit(s), and control means comprising::
reading means for (i) reading each of the outputs at least once,
selection means for (ii) selecting the output which corresponds to the sensed ride height that differs most from the desired ride height, and
correction signal generating means for (iii) applying a correction to the suspension unit(s) associated with the selected output to adjust it/them towards the desired ride height, the control means being arranged to repeat (i) to (iii) until all the sensed ride heights are within acceptable limits of the desired ride height.
12. A system according to Claim 1 in which the reading means, the selection means and the correction signal generating means are in the form of respective logic circuits.
13. A system according to Claim 11, in which the reading means, the selection means and the correction signal generating means are provided by a microprocessor.
14. A self-levelling suspension system for a vehicle, which is substantially as described with reference to the drawings.
1 5. A method of adjusting a vehicle suspension system which comprises a plurality of suspension units for adjusting the ride height between the sprung and unsprung parts of the vehicle, the method comprising:
(a) sensing the ride height in the vicinity of each suspension unit, or coupled pair of suspension units,
(b) selecting the sensed ride height that differs most from the desired ride height,
(c) applying a correction to the corresponding suspension unit(s) to adjust it/them towards the
desired ride height, and
(d) repeating (a) to (c) if necessary until all the sensed ride heights are within acceptable limits of the desired ride height.
16. A method of adjusting a vehicle suspension system which is substantially as described with reference to the drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8208395A GB2097344B (en) | 1981-04-08 | 1982-03-23 | Self-leveling suspension system |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8110972 | 1981-04-08 | ||
| GB8208395A GB2097344B (en) | 1981-04-08 | 1982-03-23 | Self-leveling suspension system |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2097344A true GB2097344A (en) | 1982-11-03 |
| GB2097344B GB2097344B (en) | 1984-05-16 |
Family
ID=26279070
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8208395A Expired GB2097344B (en) | 1981-04-08 | 1982-03-23 | Self-leveling suspension system |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2097344B (en) |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2546112A1 (en) * | 1983-05-20 | 1984-11-23 | Mitsubishi Motors Corp | SYSTEM FOR ADJUSTING THE HEIGHT OF A VEHICLE |
| FR2550737A1 (en) * | 1983-08-19 | 1985-02-22 | Mitsubishi Motors Corp | ELECTRONICALLY CONTROLLED SUSPENSION SYSTEM |
| EP0143984A2 (en) * | 1983-10-27 | 1985-06-12 | Nippondenso Co., Ltd. | Vehicle height control system |
| EP0157576A2 (en) * | 1984-03-27 | 1985-10-09 | Mitsubishi Jidosha Kogyo Kabushiki Kaisha | Automobile suspension system |
| EP0159833A2 (en) * | 1984-04-19 | 1985-10-30 | General Motors Corporation | Vehicle level control system |
| GB2204286A (en) * | 1987-04-30 | 1988-11-09 | Williams Grand Prix Eng | Active fluid suspension system |
| EP0315163A2 (en) * | 1987-11-06 | 1989-05-10 | Pfister GmbH | Method for optimizing the driving characteristics of a vehicle |
-
1982
- 1982-03-23 GB GB8208395A patent/GB2097344B/en not_active Expired
Cited By (17)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2546112A1 (en) * | 1983-05-20 | 1984-11-23 | Mitsubishi Motors Corp | SYSTEM FOR ADJUSTING THE HEIGHT OF A VEHICLE |
| FR2550737A1 (en) * | 1983-08-19 | 1985-02-22 | Mitsubishi Motors Corp | ELECTRONICALLY CONTROLLED SUSPENSION SYSTEM |
| DE3428397A1 (en) * | 1983-08-19 | 1985-03-07 | Mitsubishi Jidosha Kogyo K.K., Tokio/Tokyo | ELECTRONICALLY CONTROLLED SUSPENSION SYSTEM |
| JPS6034910U (en) * | 1983-08-19 | 1985-03-09 | 三菱自動車工業株式会社 | electronically controlled suspension |
| JPH0338005Y2 (en) * | 1983-08-19 | 1991-08-12 | ||
| EP0143984A2 (en) * | 1983-10-27 | 1985-06-12 | Nippondenso Co., Ltd. | Vehicle height control system |
| EP0143984A3 (en) * | 1983-10-27 | 1985-12-27 | Nippondenso Co., Ltd. | Vehicle height control system |
| EP0157576A3 (en) * | 1984-03-27 | 1987-11-25 | Mitsubishi Jidosha Kogyo Kabushiki Kaisha | Automobile suspension system |
| EP0157576A2 (en) * | 1984-03-27 | 1985-10-09 | Mitsubishi Jidosha Kogyo Kabushiki Kaisha | Automobile suspension system |
| EP0159833A3 (en) * | 1984-04-19 | 1986-05-28 | General Motors Corporation | Vehicle level control system |
| EP0159833A2 (en) * | 1984-04-19 | 1985-10-30 | General Motors Corporation | Vehicle level control system |
| GB2204286A (en) * | 1987-04-30 | 1988-11-09 | Williams Grand Prix Eng | Active fluid suspension system |
| US4861066A (en) * | 1987-04-30 | 1989-08-29 | Williams Grand Prix Engineering Limited | Vehicle suspension systems |
| GB2204286B (en) * | 1987-04-30 | 1991-02-06 | Williams Grand Prix Eng | Vehicle suspension systems |
| EP0315163A2 (en) * | 1987-11-06 | 1989-05-10 | Pfister GmbH | Method for optimizing the driving characteristics of a vehicle |
| US4913457A (en) * | 1987-11-06 | 1990-04-03 | Pfister GmbH and Bayrische Motoren Werke AG | Method and apparatus for optimizing the driving characteristics of a vehicle |
| EP0315163A3 (en) * | 1987-11-06 | 1990-05-30 | Pfister Gmbh | Method for optimizing the driving characteristics of a vehicle |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2097344B (en) | 1984-05-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |