HlllllllllllllllllllIlllllllllllllllllllIllllllllllllllllllllllllllllllll
`
`USOOSl49176A
`
`United States Patent
`
`[191
`
`[11] Patent Number:
`
`5,149,176
`
`Eccleston
`
`[54]
`
`[75]
`
`[73]
`
`[21]
`
`[22]
`
`[63]
`
`[51]
`[52]
`
`[53]
`
`[56]
`
`CONTROLLER FOR ELECTRIC BRAKING
`SYSTEMS
`
`Inventor:
`
`Larry Eccleston, Marshall, Mich.
`
`Assignee: Tekonsha Engineering Company,
`Tekonsha, Mich.
`
`App]. No.: 563,505
`
`Filed:
`
`Aug. 7, 1990
`
`Related US. Application Data
`
`Continuation-impart of Ser. No. 390,617, Aug. 7, 1989,
`Pat. No. 5,050,937.
`
`Int. Cl.5 .............................................. B60T 13/72
`US. Cl. ..................................... 303/20; 188/1.11;
`303/7
`Field of Search .................... 303/7, 20, 24.1, 100,
`303/92, 93, 105; 188/112 A, 112 R, 1.11
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`1/1941 Kuiper ............................... 188/111
`2,228,631
`8/1971 Blomenkamp .................. 303/105
`3,601,794
`
`6/1973 Pokrinchak et a1.
`....... 303/20
`3,738,710
`3,780,832 12/1973 Marshall
`............
`3,908,782
`9/1975 Lang et a1.
`.......................... 180/103
`
`
`
`[45] Date of Patent:
`
`Sep. 22, 1992
`
`9/1975 Pittet. Jr. et a1,
`3,909,075
`.................. 303/24.1
`3,953,084 4/1976 Pittet, Jr. et a1.
`...... 303/24.1
`
`3,955,652
`5/1976 Nilsson et a].
`.......
`188/112 R
`3,967,863
`7/1976 Tomecck et al.
`...... 303/24.1
`
`303/24.1
`3,981,542
`9/1976 Abrams et a1.
`.......
`
`.. 303/24.1
`3,981,544 9/1976 Tomecek et a1.
`4,030,756 6/ 1977 Eden .......................... 303/24.1
`
`4,050,550
`9/1977 Grossner et a1.
`188/112 R
`
`4,084,859 4/1978 Bull et a1. ................. 303/ 106
`
`1/1988 Frait et a1. ................ 303/20
`4,721,344
`................. 303/108
`5,032,821
`7/1991 Domanico et a1.
`
`Primary Examiner—Matthew C. Graham
`Attorney, Agent, or Firm—Price, Heneveld, Cooper,
`DeWitt & Litton
`
`[57]
`
`ABSTRACT
`
`A vehicle brake controller includes a variable pulse-
`width modulator operating at a constant frequency and
`with a variable pulse width to provide control pulses to
`a MOSFET element which actuates vehicle braking.
`The controller further includes a visual indicator which
`
`displays different colors to representatively indicate the
`amount of current applied to the brakes, and also to
`indicate whether an operable connection exists between
`the electronic controller and the vehicle brakes.
`
`11 Claims, 3 Drawing Sheets
`
`
`
`Curt - Exhibit 1005 - 1
`
`Curt - Exhibit 1005 - 1
`
`

`

`US. Patent
`
`Sep. 22, 1992
`
`Sheet 1 of 3
`
`5,149,176
`
`
`
`Curt - Exhibit 1005 - 2
`
`Curt - Exhibit 1005 - 2
`
`

`

`US. Patent
`
`Sep. 22; 1992
`
`Sheet 2 of 3
`
`5,149,176
`
`FIG-2
`
`Curt - Exhibit 1005 - 3
`
`Curt - Exhibit 1005 - 3
`
`

`

`US. Patent
`
`Sep. 22, 1992
`
`Sheet 3 of 3
`
`5,149,176
`
`
`
`Curt - Exhibit 1005 - 4
`
`Curt - Exhibit 1005 - 4
`
`

`

`5,149,176
`
`CONTROLLER FOR ELECTRIC BRAKING
`SYSTEMS
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`This application is a continuation-in-part of prior
`application Ser. No. 390,617 filed Aug. 7, 1989, now
`U.S. Pat. No. 5,050,937.
`
`2
`vehicle braking systems (whether mechanical, electro-
`mechanical or electromagnetic in nature), with the re-
`suit being instability, brake chatter, etc. Indeed, even
`pulse width-modulated (variable-pulse-width) constant-
`frequency systems sometimes utilize operational fre-
`quencies which have such adverse characteristics, and
`are likely to have other disadvantages as well.
`One common incident of practically all state of the
`art electronic brake-system controllers is the fact that
`1 0
`they utilize, and in fact require, interconnection with
`the vehicle brake light circuit. This is conventionally
`This invention relates to controllers for electrically-
`felt to be essential in such systems, because it is widely
`actuated braking systems, such as those used to apply
`thought that the controller must be kept disabled, i.e., in
`the brakes on towed vehicles (i.e., trailers) in response
`15 a condition where it is not capable of providing braking
`to commands from the towing vehicle. More particu-
`excitation, except for the specific instances when either
`larly, the invention relates to electronic controllers for
`braking systems of the general type just noted w厨ch
`the manual control switch is actuated or else the towing
`vehicle brakes are actually being applied, as verified by
`operate in response to inertial sensors and/or manually-
`the presence of the brake light signal. The main reason
`actuated switches or the like to energize the electric
`20
`brake-actuation components of such systems in a partic-
`underlying this conviction is the fact that the stability of
`ular controlled manner.
`prior art inertial sensors and control circuits has not
`In the past, electric brake-system controllers have
`been sufficiently reliable under any and all potential
`progressed from relatively simple and crude circuits
`operating conditions to preclude inadvertent and unde-
`which were little more than manually-variable power
`sired brake actuation under various conditions, for cx-
`
`2 5
`switches, operated directly by the driver, to various
`ample, in response to such extraneous effects as rough
`types of comparatively improved and more sophisti-
`road surfaces, etc.
`cated systems which apply either continuous or pulsing
`While using the tow vehicle brake light signal for the
`drive excitation to the electromagnetic brake shoe actu-
`purpose just noted did prove to be a reasonably effec-
`ators located at the trailer wheels. For example, U.S.
`30 tive measure for coping with the problem of inadvertent
`Pat. No. 3,738,710 shows a series current regulator
`brake actuation, this measure nonetheless created a
`which integrates an actuation signal obtained from the
`number of problems itself, as well as involving at least
`towing vehicle brake light circuit and applies continu-
`some inherent uncertainties. For example, mechanical
`ous braking excitation whose magnitude is basically
`or electrical failure in the brake light circuit entirely
`proportional to the length of time the towing vehicle
`35
`brakes are actuated, or in any event, proportional to the
`extraneous to actual towing vehicle performance could
`length of time the brake lights are energized in the tow-
`result in the loss of all trailer braking. Furthermore,
`ing vehicle. Most other control circuits for electric
`with the increasing sophistication of modern-day vehi-
`brakes apply pulsing excitation to the brake-actuating
`dles, the brake light circuit has grown increasingly corn-
`electromagnets, since it is widely thought that such
`plex, since it is now directly intercoupled with such
`40
`pulsing excitation helps obviate lock-up or skidding of
`other systems as electronic cruise controls, anti-skid
`the trailer brakes. Some such controllers utilize a con-
`braking systems, etc., and as a result each such system
`stant pulse-width applied at varying frequencies which
`becomes more interdependent and subject to failure or
`increase in accordance with the amount of braking
`malfunction caused by the others. Furthermore, while
`desired, while others utilize a constant-frequency varia-
`cruise controls, anti-skid braking systems, etc., are usu-
`
`ble-pulse-width form of excitation, for similar reasons. 45
`ally built into the tow vehicle at the factory, this is not
`For example, see prior U.S. Pat. Nos. 3,909,075 and
`true of trailer brake controllers, which are aftermarket
`3,953,084, addressed to the second such type of system,
`devices installed by others. Thus, with the increasing
`together with U.S. Pat. No. 3,967,863, which is directed
`complexity of vehicles and systems related to their
`to the first such type of system, all of which utilize both
`inertial-sensing and manually-actuatable input devices
`50 brakes and brake-light actuation systems, it becomes
`and apply braking excitation as a function of whichever
`increasingly more difficult, as well as more risky and
`such device is controlling.
`potentially damaging, to physically breach the factory-
`While all of the aforementioned state of the art-type
`installed wiring in order to interconnect the brake light
`systems no doubt have their individual advantages and
`circuit with aftermarket devices.
`favorable features, most also involve certain character-
`55
`In addition, prior art electronic controllers for elec-
`istic limitations or undesirable characteristics. For ex-
`tric brake systems have had a number of other disadvan-
`ample, continuous braking excitation is indeed likely to
`tages and limitations, in particular operating inefficien-
`promote trailer brake lock-up, and that is a most unde-
`cies attended by the use of excess power and the pro-
`sirable event since it brings about a marked decrease in
`duction of excess heat. Thus, typical prior art systems
`a
`braking efficiency and loss of operator control. Further,
`utilize resistive-type current-sensors for detecting the
`the mere len夢h of time during which the brake light
`presence of excess braking current and initiating various
`circuit happens to be energized may very well not accu-
`forms of interruptors, for safety purposes, and to pre-
`rately represent the desirable magnitude of braking
`vent controller burn-out. Further, state of the art con-
`force to be applied to the trailer brakes in a given situa-
`trollers utilize inefficient drive components such as
`tion. On the other hand, where pulsating brake excita-
`bi-polar power transistors and the like, thereby using
`tion is utilized, variable-frequency systems usually in-
`dlude some actuation frequencies which unfortunately
`excess power and requiring extensive heat-dissipation
`complement or reinforce resonant frequencies in the
`means, i.e., heat sinks.
`
`BACKGROUND OF THE INVENTION
`
`65
`
`Curt - Exhibit 1005 - 5
`
`

`

`BRIEF DESCRIPTION AND FEATURES OF THE
`PRESENT INVENTION
`
`5,149,176
`
`4
`considered with and in light of the accompanying draw-
`ings.
`
`BRIEF DESCRIPTION OF THE DRAWING
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`In the accompanying drawings:
`FIG. 1 is a schematic circuit diagram showing a first
`embodiment of an electronic controller in accordance
`with the invention.
`FIG. 2 is a schematic circuit diagram showing a sec-
`ond embodiment of an electronic controller in accor-
`dance with the invention.
`FIG. 3 is a schematic circuit diagram showing a fur-
`ther embodiment of an electronic controller in accor-
`dance with the invention.
`
`The present invention effectively resolves many,
`indeed most, of the problems described above which 5
`characterize prior art controllers. In accordance with
`the invention, new and more effective controllers are
`provided through the combined effect of a number of
`distinct features which vary in both concept and imple-
`mentation from those found in prior art devices, and 10
`which combine synergistically to provide electronic
`brake controllers which are both more effective and
`more efficient than those utilized heretofore.
`More particularly, the controllers of the present in-
`vention are both more stable and more responsive to 15
`important braking system criteria than prior controllers, ・
`and at the same time they are far more energy-efficient
`Referring now to drawings, and the illustrative em-
`and cooler in operation, while also providing opera-
`tion誠 characteristics which avoid undesirable interac-
`bodiments depicted therein, a first controller circuit is
`shown in FIG. 1, the upper portion of the circuit, desig-
`tion with tow vehicle braking systems. More specifi- 20
`nated generally by the numeral 10, comprises the brak-
`cally considered, some of the more salient attributes of
`ing current control portion of the circuit, while the
`the present controllers include an optional new form of
`lower portion, generally designated by the numeral 12,
`interface for interconnecting with the tow vehicle brake
`comprises the novel braking current display-generation
`light circuit, new and novel variable-pulse-width fixed
`means, Referring first to the braking current control
`repetition rate circuits which operate at high efficiency, 25
`portion of the circuit 10, the control circuit generally
`effectiveness, and stability, and a new form of braking
`includes a detection and control portion 14 shown at the
`current controller output driver (pass element) of high
`left and, proceeding toward the right, includes a dual-
`efficiency, coupled with new concepts in braking cur-
`slope integrator section 16, a variable-pulse-width mod-
`rent detection and display, for increased operator
`ulator 18 which includes an integrated circuit 20 and
`awareness, effectiveness, and operational flexibility.
`30
`logic switch means 22 (both described in more deねil
`In a still more particular sense, the present invention
`provides a new form of electronic controller for electric
`hereinafter), and an output stage 24 comprising the
`aforementioned MOSFET elements, which may be
`braking systems which features a constant-frequency,
`single or double in form as described hereinafter. As
`variable-pulse-width modulator which interacts with
`shown, the output stage 24 has an output conductor 26
`the vehicle braking system through an N-channel 35
`which comprises the connection to the towed vehicle
`power MOSFET, which is the control element for the
`(trailer) brake actuators, here symbolized by the large
`braking current supplied to the electromagnets that
`inductive winding labeled "Li," it being understood
`actuate the brakes. The operational frequency for the
`that in actual practice there will be a number of individ-
`controller is such as to avoid resonance problems in the
`ual such inductances in parallel, each comprising the
`braking assemblies of the trailer previously encountered 40
`electromagnet which actuates one set of brakes at one
`in other systems, while at the same time facilitating
`wheel, all wheels usually being controlled simulta-
`efficient and effective component operation. The N-
`neously and in a substantially identical fashion.
`channel power MOSFET acting as the pass element has
`With first reference to the detection and control por-
`extremely low forward or "on" resistance, and im-
`tion 14 of the circuit 10, elements Dl and Qi symbolize
`proves the efficiency of the output stage by on the order 45
`the signal-generating portions of the inertial sensor
`of about ten times, in comparison to prior art systems,
`noted above, which is most preferably in accordance
`and circuit efficiency is further augmented by the imple-
`mentation of a novel braking current-sensing technique,
`with that described in copending application Ser. No.
`07/390,280, filed May 24, 1989. While an appropriate
`in which the voltage drop across the power MOSFET
`
`during conduction is sensed and used as a control signal, 50 signal could, of course, be provided by other than dlcc-
`tro-optical elements, the latter do provide a preferred
`thereby eliminating the lossy and heat-producing series
`embodiment of the invention, particularly in combina-
`resistances utilized heretofore.
`tion with the inertial sensor of the copending applica-
`In accomplishing the foregoing goals, a novel power
`supply is utilized for driving the N-channel MOSFET,
`tion just described. Thus, in a preferred embodiment,
`element Dl comprises an infrared light-emitting diode,
`which constitutes a distinct departure from prior art 55
`electric brake controller concepts.
`and element Qi comprises a corresponding phototran-
`Furthermore, the controller in accordance herewith
`sistor (both of which may desirably be implemented by
`may optionally feature in combination with the afore-
`use of Motorola components MLED 71 and MRD 701,
`respectively). As will be understood, the basic purpose
`mentioned constant-frequency variable-pulse-width
`circuit operation, a new and novel MOSFET interface 60
`of circuit portion 14 is to provide an analog control
`signal corresponding in magnitude to the extent of
`for interconnecting with the towing vehicle brake-light
`actuation circuit to avoid some of the significant prob-
`trailer braking desired, and thus an integral portion of
`circuit 14 is a manual switch Si, by which the towing
`lems and potential problems encountered by users and
`vehicle operator may manually initiate measured brak-
`manufacturers in interfacing with the towing vehicle
`ing effects on the trailer whenever desired, apart from
`65
`brake light circuitry.
`The foregoing features and attributes of the invention
`the operation of the towing vehicle brakes and the cor-
`responding inertial effects. In the most preferred em-
`will become more apparent after contemplation of the
`bodiment in accordance herewith, switch Si comprises
`ensuing more detailed description, particularly when
`
`Curt - Exhibit 1005 - 6
`
`

`

`5,149,176
`
`6
`5
`sion, by a four-part analog switch, e.g., the commercial-
`a membrane-type "touch pad" switch of an appropriate
`commercially-available type, the use of which in such a
`ly-available element designated by the identifier
`braking controller is believed to constitute a novel and
`"CD4066," the four operational components of which
`desirable feature in and of itself. Apart from this, how-
`are illustrated separately for convenience in FIG. 1 and
`designated "U2a, U2b, Uた," etc. Basically, this corn-
`ever, it will be observed that both the inertial sensor 5
`components and the manually-actuated components are
`pound switch operates in conjunction with the output
`effectively coupled between mutually-shared supply
`from the pulse-width modulator (pin 7 of Ui) to control
`and ground conductors 28 and 30, respectively, through
`conduction of the MOSFET output transistor Q2 (and,
`potentiometers R2 and R3, respectively, with an inter-
`where higher levels of current are needed, a second
`connecting line 31 extending between the lower-voltage 10
`such MOSFET designated here as Q3, which is to be
`side of each such potentiometer. As will be understood,
`understood as being optional, depending upon the level
`potentiometer R2 is merely for the purpose of adjusting
`of current output needed).
`the operation司 range of the phototransistor Qi, to
`As indicated previously, the output stages Q2 and Q3
`avoid circuit performance variation as a function of
`are preferably N -channel devices, whose use in this
`manufacturing tolerances in the optical components. 15
`environment is accomplished, in the embodiment under
`Potentiometer R3, on the other hand, comprises a gain
`consideration, by use of a floating-ground "flying"
`control for the entire control circuit 10, since it acts to
`power supply which, in effect, doubles the available
`set the level at which signals from the detection portion
`power level, so as to m泳e it possible to use N-channel
`14 are provided to the integrator portion 16.
`MOSFET devices as output stages Q2 and Q3 (for ex-
`The dual-slope integrator 16 comprises basic司ly ca- 20
`ample, by use of the commercially-available N-channel
`pacitor Cl, resistors R4 and R5, and diode D2; also, this
`devices identified as #SMP50NOS). Logic switch 22
`integrating section works in conjunction with another
`thus functions as an integral part of this "flying" power
`integrating section comprising capacitor C3 and resistor
`supply by performing the・ necessary switching, in con-
`R7, in a manner described more fully hereinafter. More
`junction with a "pull-up" circuit comprising capacitor
`particularly, the signal from the detection and control 25
`CS and diode D7. As illustrated, these components are
`section 14 of the circuit is coupled from the movable
`connected across output stages Q2 and Q3, and between
`contact of potentiometer R3 to the first integrating
`twelve volt supply conductor 28 and the floating
`section just noted and, due to the polarity of diode D2,
`ground conductor 30, the latter in fact providing the
`together with the operational characteristics of inte-
`excitation appearing on output conductor 26 noted pre-
`grated circuit Ui, this results in a comparatively slow 30
`viously, leading to the brake-actuation electromagnets
`and gradual increase in control voltage (determined in
`Li.
`essence by the time constant established by both resis-
`Somewhat more particularly, the operation of con-
`tors R4 and R5, together with capacitor Cl), but with a
`trol circuit 10 is as follows. Internally, the non-inverting
`much faster discharge time (established, in essence, by
`input of the operational amp in integrated circuit Ui is
`the value of only resistor R5 and capacitor Cl, resistor 35
`tied to a 3.75 volt reference and, as noted above, the
`R4 having been shunted out of operation by diode D2).
`dual-slope integrator 16 connected between the detec-
`Preferably, the value of resistor R5 is on the order of
`tor and control section 14 and the PWM section 18 is
`only about fifteen percent of that of resistor R4, such
`connected to the inverting input of IC UI, i.e., on pin 3.
`that the charging time constant of the integrator is
`4OThus, in response to control voltages from circuit 14
`about 1.5 seconds, whereas the discharge time is about
`calling for the application of braking current, the collec-
`0.1 second.
`tor of the internal op amp in IC Ui is pulled down and
`Integrated circuit Ui is utilized as a comparatively
`divided by potentiometer R3, current being applied
`simple pulse-width modulator, and may be implemented
`through resistors R5 and R4 at a rate determined by the
`by use of the commercial IC No. 5561, which basically
`longer time constant of the dual-slope integrator 16.
`includes an internal operational amplifier, comparator, 45
`The output of the internal op amp in IC Ut appears on
`and sawtooth wave generator. As utilized in the present
`pin 4 thereof, which is thus affected by the time con-
`application, the inverting input of the internal operation
`amplifier いin 3) is coupled to integrator 16, in particular
`stant of the network including capacitor C3 and resistor
`R7, which forms a second integrator. Thus, initially,
`to the "low" side of capacitor Cl, and to the common
`current is drawn Out of the summing point represented
`junction of resistor R7 and capacitor C3. The output of 50
`by the inverting terminal of the internal op amp, whose
`such internal "op amp" appears on pin 4, and is con-
`output thus responds accordingly. The op amp output
`nected to the opposite common junction of capacitor
`appearing on pin 4 is applied internally to a comparator
`C3 and resistor R7. It will be observed that positive
`which conducts a continuing comparison of that signal
`operating voltage ("B+") for the entire control circuit
`55 to a standard sawtooth wave form, so as to continually
`10 is provided on the aforementioned supply conductor
`change the proportion of conduction. In accordance
`28 which, among other connections, is coupled to pin 1
`with the present application, a pulse-repetition rate of
`of integrated circuit Ui. As will be explained subse-
`appro血mately 300 Hz is chosen, to best complement the
`quently in more detail, control circuit 10 utilizes a "fly-
`braking systems being actuated (i.e., to best accommo-
`ing" power supply concept, in which conductor 30
`60 date brake magnet performance with maximal isolation
`functions as a floating ground, and it will be noted that
`from natural mechanical resonances typically encoun-
`the latter is coupled to pin 8 of IC Ui through conduc-
`tered). Accordingly, the output from the PWM (IC
`tor 34. The primary output from integrated circuit Ui
`Ui), appearing on pin 7, constitutes a repetitive pulse
`appears on pin 7 thereof, and this is coupled to the logic
`whose width is a function of the control signal from
`switch means 22 by conductors 32 (and its interconnect-
`
`ing branches 32a, 32b, 3た, which are also connected to 65 circuit portion 14, as a function of the internal compari-
`son with the aforementioned sawtooth wave. This out-
`the B+ supply line 28 through resistor R12).
`The loがc switch means 22 may be implemented, in
`put from pin 7 is inverted through the analog switch
`accordance with the embodiment here under discus-
`stage 22 and applied to the gate of output MOSFET Q2
`
`Curt - Exhibit 1005 - 7
`
`

`

`5,149,176
`
`5
`
`8
`7
`and, under the circumstances present in the use of the
`(and, where used, the second MOSFET Q3), to provide
`circuit under discussion, the logically-switched "float-
`brakeactuating excitation on output conductor 26
`ing" supply concept works well for the intended pur-
`As noted above, previous systems have used PNP
`pose.
`transistors with the emitter connected to battery posi-
`In order to preclude capacitor C4 from fully dis-
`tive and the collector to the brake magnets, which in
`charging, and thereby losing drive, the duty cycle
`turn connect to ground. The base drive is applied by
`should be set to a level slightly less than full-cycle, to
`pulling base current from the transistor to ground. The
`ensure time for capacitor recharge during the output
`base current out of the base causes collector current to
`transistor "off" time. Accordingly, it will be observed
`flow, thereby energizing the brake magnets. It would be
`somewhat an誠ogous to this to use a P-channel MOS-
`10 that capacitor C4, which serves to boost the operating
`level of the entire control circuit to a level essentially
`FET in such circumstances, since one could configure
`twice that of the B + actually supplied, recharges
`the circuit much the same as with the PNP transistor,
`through the tow vehicle ground circuit, i.e., through
`with the source connected to battery positive and the
`the brake magnets, since when the brake-energizing line
`drain connected to the brake magnets, which in turn
`15 26 is driven in a negative direction, a current pulse is
`connect to ground. However, P-channel MOSFETs of
`supplied to capacitor C4 through conductor 34 from
`sufficiently low "on" resistance and current-handling
`floating ground conductor 30. When this is completed,
`capacity are simply not available as of this point in time.
`i.e., when the cycle ends, the polarity of diode D6
`Paralleling higher-resistance devices would work, but
`causes the supply level to continue to increase. Accord-
`the cost would be prohibitive. Accordingly, the present
`20 ingly, the inductive load comprising the brake-actuation
`invention utilizes an N-channel MOSFET, even though
`electromagnet coils functions to provide a constant
`this requires a substantially different and more involved
`current flow through them which is a function of the
`circuit configuration. The configuration required is that
`"duty cycle" of the applied pulse, i.e., the pulse-width.
`of a source-follower, but this configuration requires that
`The duty cycle control, in turn, is set up through resis-
`the MOSFET gate always be driven positive with re-
`25 tor Ri! and diode D5, plus resistor R6 and diode D3,
`spect to the source in order to cause conduction. Be-
`which are coupled between pins 2 and 3 of the PWM IC
`cause the source rises to very near battery positive
`Ui and the logic switch 22, the output from the PWM
`when the MOSFET is turned on, it is necessary that the
`IC, on pin 7, being applied through logic switch 22 to
`gate be driven to a potential greater than battery poten-
`ti誠. That is, an N-channel MOSFET requires that the
`the output transistors in stage 24. Thus, the circuit oper-
`gate be driven positive with respect to the source to 30 ates to inject current into pin 3 of the pulse-width modu-
`
`lator Ui when the duty cycle exceeds the selected level,
`cause conduction of the MOSFET. In a normal ground-
`and this reduces the pulse-width from the PWM stage.
`ed-source configuration, gate drive is simply applied
`It is, in effect, negative feedback, which establishes the
`from a normal five to twenty volt source. The load
`maximum duty cycle of circuit Ui.
`would then be connected between the drain and the
`positive supply, and power would be delivered any time
`Circuit duty cycle as a function of output current is
`35
`the gate was above threshold. In the present case, it is
`an important function played by the logic switch 22.
`Thus, when gate drive of output transistors Q2 and Q3
`required that the brake magnets operate against ground,
`is applied using section Uk of logic switch 22, section
`mostly because of tradition in the automotive industry.
`U2b is turned off as a clamp and section U2d is turned
`The high end must therefore be driven positive with
`40 on as a voltage sensor, being connected to brake actua-
`respect to battery potential.
`tion line 26 through conductor 36 to the common con-
`Accordingly, where the preferred N-channel MOS-
`FET devices are utilized, so as to provide maximum
`nection node of output transistors Q2, Q3, and conduc-
`tor 26. This in effect senses the voltage across output
`circuit efficiency and minimum losses, the operational
`parameters encountered in typical vehicle-trailer envi-
`transistors Q2 (and, where used, Q3), and applies the
`
`ronments, involving a positive-ground twelve volt 45 sensed voltage back as a signal to pin 6 of the PWM (i.e.,
`integrated circuit UI). That voltage level is propor-
`power supply, requires a pull-up, "flying" supply which
`in effect doubles the available voltage level to provide
`tional to the current flow through the vehicle brakes,
`with a typical "on" resistance of an extremely low level.
`above-rail drive to the MOSFET gate. In the circuit
`configuration shown in FIG. 1, the MOSFET gate
`The sensed voltage drop across Q2 and Q3 should be
`50 referenced to the MOSFET source, and therefore both
`supply is referenced to the voltage applied to supply
`conductor 28, but at a level which is effectively in-
`UI and U3 are operated from the same flying supply,
`creased through the operation of capacitor C4 and
`with their negative terminals common to the source.
`diode D6, which is series-connected in supply line 28.
`Because U2 is driven from Ui, it also is referenced to
`Thus, when output transistor Q2 (and Q3, where used)
`the flying source. Accordingly, the pulse-width modu-
`
`is non-conducting, capacitor C4 charges to the level 55 lator 41 will turn off if current exceeds a pre-set limit,
`present on conductor 28 through diode D6, through a
`thereby establishing a selected duty cycle which corre-
`charge path which includes the brake magnet coils Li.
`sponds directly to the level of current flow through the
`When the output transistors are turned on and conduct
`trailer brake electromagnets. Furthermore, such turnoff
`the supply effectively rises with the source because
`provides an effective short-circuit protection for the
`
`diode D6 then allows the positive terminal of capacitor 60 brake magnet actuation line. Accordingly, if the output
`C4 to "boo協trap" up to a value of twice the applied
`transistors for any reason overheat and their conducting
`B +. Since the gate drive for output MOSFETs Q2 and
`resistance rises accordingly, the current limit for excita-
`Q3 is supplied from conductor 28, through resistors R13
`tion to the brake magnets will be cut back correspond-
`ingly, to maintain circuit performance.
`and R14, the foregoing charge state of capacitor C4
`causes a corresponding supply condition to be present 65 The same voltage sensed and applied to the pulse-
`
`as gate drive. Of course, other voltage-doubling circuits
`width modulator Ui as a measure of output current, as
`are known and could be used, but most others utilize
`just described, is also applied to the display circuit 12,
`more expensive components,. e.g., transformers, etc.,
`which preferably comprises an LED bar-graph driver
`
`Curt - Exhibit 1005 - 8
`
`

`

`5,149,176
`
`10
`9
`deliberately avoids interconnection with such brake
`U3, for example of the type known as an LM3914,
`light circuit. The slower, initial slope of the dual-slope
`which includes an internal voltage divider and a set of
`integrator 16 helps obviate the need for any intercon-
`ten comparators. The resulting function is that as the
`nection to the towing vehicle brake light circuit for
`voltage across output transistor Q2 increases during its
`5 safety purposes, since even though the preferred inertial
`operating cycle, in proportion to the current through
`sensor identified hereinabove (i.e., that which is the
`the brakes, the bar-graph driver will progressively ener-
`subject of copending application Ser. No. 07/390,2 80) is
`gize one after another of the LEDs which it controls
`(identified in FIG. 1 as LD1, LD2, etc.). Accordingly,
`substantially immune to erratic operation and inadver-
`the operator of the towing vehicle will have available a
`tent braking signal commands in response to merely
`rough roads and the like, the comparatively slow ramp-
`direct display of the magnitude of braking current actu- 10
`up and rapi