lllllllllllllllllIllllIllllllllllllllIlillillllllllllllllIllllillllllllllll
`US005615930A
`5,615,930
`[11] Patent Number:
`United States Patent
`McGrath et al.
`[45] Date of Patent:
`Apr. 1, 1997
`
`
`119]
`
`[54] ELECTRONIC TRAHER BRAKE
`CONTROLLER
`
`[75]
`
`Inventors: Michael C. McGrath, Farmington
`-
`.
`-
`-
`Hflls’ MmhaelA'Heddmg’ Cflnmn’
`bOth Of M‘Ch'
`
`[73] ASSigneei Hayes W119?“ International, Inc.,
`Romulus, MICh-
`
`9/1975 Pittet, Jr. et al..
`3,909,075
`7/1976 Tomeceketal..
`3,967,863
`9/1976 Abrams et a1.
`.
`3,981,542
`188/138
`3;i371: goffiecgk at 31-
`-
`23:53::
`a1 ar
`...................................
`,
`,
`4/1978 Bull et a1.
`................................... 303/7
`4,084,859
`4/1980 Snyder.
`4,196,936
`4,295,687 10/1981 Becker et al. .
`4,419,654 12/1983 Funk ....................................... 303/124
`4,721,344
`1/1988 Frait et al.
`.................................. 303/7
`4,856,850
`8/1989 Aichele etal..
`5,050,937
`9/1991 Eccleston .................................... 303/7
`5,149,176
`9/1992 Eccleston,.
`5,333,948
`8/1994 Austin et al.
`5,352,028 10/1994 Eccleston .
`'
`_
`Int. Cl.6 ........................................................ B60T 8/16
`[51]
`_
`Primary Examiner—Matthew 0- Graham
`[52] US. Cl.
`.................................. 303/7; 303/20; 303/124
`[58] Field of Search ............................... 303/7, 20, 3, 15, Mom”) Agent, 0’ F’""*MaCM1“a“’ SObanSkl & TOdd
`303/124, 138
`[57]
`ABSTRACT
`
`[2]] Appl. No]; 572,930
`
`[22]
`
`Filed:
`
`Dec. 15, 1995
`
`.
`
`[56]
`
`References Cited
`
`U-S- PATENT DOCUMENTS
`2/1970 Umpleby .
`3,1970 Broek .
`4/1971 Jacob .......................................... 303/7
`6/1973 Pokrinchak et a1.
`.
`12/1973 Podlewski et a1.
`..................... 303/124
`12/1973 Marshall .
`
`3 497 266
`3:503:652
`3,574,414
`3,738,710
`3,778,118
`3,780,832
`
`An electronic brake controller for actuating electric wheel
`brakes of a towed vehicle in response to braking of an
`associated towing vehicle. The controller includes a micro-
`processor responsive to the braking of the towing vehicle for
`generating an output signal for actuating the towed vehicle
`brakes in accordance with a brake ICSPOIISe CUYVE- The brake
`response curve can include a non—linear portion.
`
`44 Claims, 5 Drawing Sheets
`
`TOWING VEHICLE
`
`TOWED VEHICLE
`
`/—__H
`
`BRAKE
`PEDAL
`
`HYDRAULIC
`BRAKE
`SYSTEM
`
` VEHICAL
`
`7.5
`
`Curt - Exhibit 1013 - 1
`
`Curt - Exhibit 1013 - 1
`
`

`

`US. Patent
`
`Apr. 1, 1997
`
`Sheet 1 of 5
`
`5,615,930
`
`TOWING VEHICLE
`
`TOWED VEHICLE
`
`ABS
`
`45
`
`HYDRAULIC
`BRAKE
`SYSTEM
`
`VEHICAL
`BRAKE
`PEDAL
`
`20
`
`Curt - Exhibit 1013 - 2
`
`Curt - Exhibit 1013 - 2
`
`
`

`

`US. Patent
`
`Apr. 1, 1997
`
`Sheet 2 of 5
`
`5,615,930
`
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`OUTPUT
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`SIGNALDUTYCYCLE
`SIGNALDUTYCYCLE
`OUTPUT
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`Curt - Exhibit 1013 - 3
`
`Curt - Exhibit 1013 - 3
`
`

`

`US. Patent
`
`Apr. 1, 1997
`
`Sheet 3 of 5
`
`5,615,930
`
`SIGNALDUTYCYCLE
`
`OUTPUT
`
`Curt - Exhibit 1013 - 4
`
`Curt - Exhibit 1013 - 4
`
`

`

`US. Patent
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`Curt - Exhibit 1013 - 6
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`Curt - Exhibit 1013 - 6
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`
`
`
`
`
`

`

`5,615,930
`
`1
`ELECTRONIC TRAILER BRAKE
`CONTROLLER
`
`BACKGROUND OF THE INVENTION
`
`5
`
`2
`Electronic brake controllers further include an output
`stage which is electrically connected to the output of the
`pulse width modulator. The output stage typically has one or
`more power transistors which are connected between the
`towing vehicle power supply and the towed vehicle brake
`electromagnets. The power transistors function as an elec-
`tronic switch for supplying electric current to the towed
`vehicle brakes.
`The output stage is responsive to the pulse width modu-
`lator output signal to switch the power transistors between
`conducting, or "on", and non-conducting, or "oft", states. As
`the output transistors are switched between their on and off
`states in response to the modulator output signal, the brake
`current is divided into a series of pulses. The power supplied
`to the towed vehicle brakes and the resulting level of brake
`application are directly proportional to the duty cycle of the
`modulator generated output signal.
`
`SUMMARY OF THE INVENTION
`
`The present invention relates to an improved electronic
`brake controller for actuating electric wheel brakes of a
`towed vehicle in accordance with a brake response curve.
`The improved electronic trailer brake controller includes
`a detection device for detecting an initiation of a towing
`vehicle braking cycle. The detection device is responsive to
`a braking cycle initiation to generate an input signal. The
`controller also includes a control device connected to the
`detecting device. The control device is operable to generate
`a brake response curve and an output signal for actuating the
`towed vehicle brakes. The brake response curve defines a
`time relationship between the input signal and the output
`signal. The control device is responsive to the input signal
`and the brake response curve to generate the output signal
`with the output signal varying as a function of time in
`accordance with the brake response curve.
`The invention also contemplates that the control device
`can include a microprocessor.
`It is contemplated that the brake controller microproces-
`sor includes a memory having a plurality of brake response
`curves stored therein. The controller has a selector which is
`operative by the towing vehicle operator and causes the
`microprocessor to select one of the stored brake response
`curves.
`Alternately, the brake controller microprocessor is
`adapted to be connected by a data link to a device for
`collecting towing vehicle operating data. The data collection
`device can include a towing vehicle control system which
`has a microprocessor. Ad血tion証ly, the data collection
`device can include a sensor mounted upon the towing
`vehicle. The brake controller microprocessor receives tow-
`ing vehicle operating data over the data link and is respon-
`sive thereto to select one of the brake response curves.
`The invention further contemplates that at least one of the
`brake response curves can include a non-linear portion.
`Another embodiment of the electronic brake controller
`microprocessor has a plurality of brake response curve
`algorithms stored therein. The controller also has a plurality
`of selectors which are operative by the towing vehicle
`operator to input towing vehicle operating data to the
`microprocessor. The microprocessor combines the towing
`vehicle operating data with the algorithms to generate a
`brake response curve. Alternately, the brake controller
`microprocessor can be connected by a data link to a device
`for collecting operating data for the towing ve血cle. The
`microprocessor receives towing vehicle operating data over
`
`io
`
`15
`
`25
`
`ス5
`
`The present invention relates in general to an electronic
`controller for energizing electric証ly operated brakes in a
`towed vehicle and, in particular, to an electronic brake
`controller w血ch energizes the towed vehicle brakes in
`accordance with a brake response curve.
`Towed vehicles, such as recreational and utility tr証lers
`adapted to be towed by automobiles and small trucks, are
`commonly provided with electric brakes. The electric brakes
`generally include a pair of brake shoes which, when actu-
`ated, frictionally engage a brake drum. An electromagnet is
`mounted on one end of a lever to actuate the brake shoes.
`When an electric current is applied to the electromagnet, the
`electromagnet is drawn against the rotating brake drum
`which pivots the lever to actuate the brakes. Typically, the
`braking force produced by the brake shoes is proportional to 20
`the electric current applied to the electromagnet. This elec-
`tric current can be relatively large. For example, the electric
`brakes on a two wheeled trailer can draw six amperes of
`current when actuated and the electric brakes on a four
`wheeled trailer can draw 12 amperes of current.
`Automotive industry standards require that electrically-
`actuated vehicle brakes be driven against the ground poten-
`tial of the vehicle power supply. Accordingly, one end of
`each of the towed vehicle brake electromaenets is electri-
`c証ly connected to the towed vehicle ground and the towed 30
`vehicle ground is electrically connected to the towing
`vehicle ground. The other end of each of the brake electro-
`magnets is electrically connected through an electric brake
`controller to the towing vehicle power supply.
`Various electric brake controllers for towed vehicle elec-ー
`tric brakes are known in the art. For example, a variable
`resistor, such as a rheostat, can be connected between the
`towing vehicle power supply and the brake electromagnets.
`The towing vehicle operator manually adjusts the variablem
`resistor setting to vary the amount of current supplied to the ~
`brake electromagnets and thereby control the amount of
`braking force developed by the towed vehicle brakes.
`Also known in the art are more sophisticated electric
`brake controllers which include electronics to automatically 45
`supply current to the brake electromagnets when the towing
`vehicle brakes are applied. Such electronic brake controllers
`typically include a sensing unit which generates a brake
`control signal corresponding to the desired braking effort.
`For example, the sensing unit can include a pendulum which
`is displaced from a rest position when the towing vehicle
`decelerates and an electronic circuit which generates a brake
`control signal which is proportional to the pendulum dis-
`placement. One such unit is disclosed in U.S. Pat. No.
`4,721,344. Alternately, the hydraulic pressure in the towing 55
`vehicle's braking system or the pressure applied by the
`driver's foot to the towing vehicle's brake pedal can be
`sensed to generate the brake control signal.
`Known electronic brake controllers also usually include
`an analog pulse width modulator which receives the brake 60
`control signal from the sensing unit. The pulse width modu-
`lator is responsive to the brake control signal for generating
`an output signal comprising a fixed frequency pulse train.
`The pulse width modulator varies the duty cycle of the pulse
`train in proportion to the magnitude of the brake control 65
`signal. Thus, the duty cycle of the pulse train corresponds to
`the amount of braking effort desired.
`
`Curt - Exhibit 1013 - 7
`
`

`

`5,615,930
`
`3
`the data link and is responsive thereto to combine the
`operating data with the 司gorithms to generate the brake
`response curve.
`The invention 組so contemplates that the detection device
`can be a sensor. The sensor can be adapted to be connected
`to the towing vehicle brake light circuit. The sensor gener-
`ates an input sign司 which includes a br水e trigger signal
`while the towing vehicle brakes are actuated and discontin-
`ues generation of the brake trigger signal upon release of the
`towing vehicle brakes.
`Alternately, the sensor can be an inertial sensor which is
`operable to generate an input signal which includes a series
`of brake trigger signals upon deceleration of the towing
`vehicle. The microprocessor receives the brake trigger sig-
`nals and averages the brake trigger signals over a predeter-
`mined period of time to generate an average brake trigger
`signal. The microprocessor initiates a braking cycle only
`when the average brake trigger signal exceeds a predeter-
`mined threshold value. The controller can 加rther include a
`selector which is operable by the towing vehicle operator to
`adjust the predetermined averaging time period.
`The invention further contemplates that the sensor gen-
`erates an input signal which includes a brake control signal.
`The microprocessor is responsive to the brake control signal
`to generate an output signal which varies in accordance with
`the brake control signal and the brake response curve.
`Similarly, the microprocessor can average the brake control
`signal over a predetermined time period to determine an
`average brake control sign証. The microprocessor then gen-
`crates an output signal which is a function of the average
`brake control signal and the brake response curve.
`Other objects and advantages of the invention will
`become apparent from the following det血ed description of
`the invention and the accompanying drawings.
`35
`
`25
`
`10
`
`15
`
`20
`
`30
`
`4
`current through line 12 to energize electric brakes 13 and 14
`which brake the wheels of the towed vehicle (not shown).
`The electric brakes 13 and 14 each include a pair of brake
`shoes 15 and 16 which, when actuated by a lever 17, are
`5 expanded into contact with a brake drum 18 for braking the
`wheels of the towed vehicle. A separate electromagnet 19 is
`mounted on an end of each of the brake actuating levers 17.
`Each electromagnet 19 is positioned to abut the generally
`flat side of the brake drum 18. As an electric current is
`passed through each of the electromagnets 19, the electro-
`magnets 19 are drawn into contact with the brake drums 18
`and the resulting drag pivots the levers 17 to engage the
`brake shoes 15 and 16 in a conventional manner. It will be
`appreciated that, while FIG. 1 shows two sets of brakes 13
`and 14, the invention also can be applied to towed vehicles
`having more than two sets of brakes.
`The towing vehicle typically includes a conventional
`hydraulic brake system 20 which is actuated when a brake
`pedal 21 is depressed by a vehicle driver. The brake pedal 21
`is coupled to a brake light switch 22. When the brake pedal
`21 is depressed, the switch 22 is closed and power from a
`vehicle power supply 23, shown as a storage battery in FIG.
`1, is supplied to one or more towing vehicle brake lights 24
`and one or more towed vehicle brake lights 25. The vehicle
`power supply 23 is also connected by a first line 26 through
`a circuit breaker 27 to the controller 11. Power is continu-
`ously supplied to the controller 11 through the first line 27.
`It will be appreciated that, while a circuit breaker 27 is
`shown in FIG. 1, a fuse or other overcurrent protection
`device can be used. A second line 28 connects the brake light
`side of the brake light switch 22 to the controller 11. The
`second line 28 supplies power to the controller 11 when the
`brake light switch 22 is closed upon actuation of the towed
`vehicle brakes.
`The brake controller 11, which is described in detail in
`co-pending patent application Ser. No. 08/313,703, filed on
`Sep. 27, 1994, senses the braking force applied to the towing
`vehicle and generates a brake control signal. In the preferred
`embodiment, a pendulum device senses the braking force
`and generates the brake control sign証, however, it will be
`appreciated that other devices can be used to generate the
`brake control signal. For example, the hydraulic brake fluid
`pressure can be sensed and used to generate the brake
`control sign証. A device for sensing the brake fluid pressure
`(not shown) is described in U.S. Pat. No. 4,295,687, which
`is hereby incorporated by reference. Similarly, the force
`applied to the brake pedal 21 can be sensed by a pressure
`sensitive pad (not shown) attached thereto. The pad, which
`generates a brake control signal proportional to the applied
`force, is described in U.S. Pat. No. 5,115,162, which is
`hereby incorporated by reference. The brake control signal
`also can be generated by microprocessors used to control
`anti-lock and traction control systems. Alternately, wheel
`speed sensor signals for the towing vehicle wheels can be
`used to generate the brake control signal. Additionally,
`electromagnetic sensors using magnetically actuated poten-
`tiometers can be used to generate the brake control signal.
`Various commercially available accelerometers, including
`ones which incorporate a mercury switch, can generate the
`brake control signal.
`The controller 11 further includes a microprocessor (not
`shown) which, in the preferred embodiment, is a prepro-
`grammed eight bit device. The microprocessor is responsive
`to the brake control signal to generate an output sign誠 The
`output signal is a pulse train which is transmitted through
`line 12 to actuate the electric brakes 13 and 14. The output
`signal is related to the brake control signal by an adjustable
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`40
`
`45
`
`FIG. 1 is a schematic diagram illustrating an electric brake
`system which includes an electronic brake controller.
`FIG. 2 is a graph illustrating response curves for the brake
`controller shown in FIG. 1.
`FIG. 3 is a graph illustrating the time response of a linear
`brake controller in accordance with the invention.
`FIG. 4 is graph illustrating the time response of a non-
`linear brake controller in accordance with the invention.
`FIG. 5 shows an alternate embo山ment of a non-linear
`brake controller in accordance with the invention.
`FIG. 6 is a graph illustrating response curves for the
`non-linear controller shown in FIG. 5.
`FIG. 7 is a block diagram for the non-linear controller
`shown in FIG. 5.
`FIG. 8 is a block diagram for an alternate embodiment of
`the non-linear controller shown in FIG. 7.
`55
`
`50
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`
`Referring now to the drawings, there is shown in FIG. 1
`60
`a schematic diagram illustrating an electric brake system for
`a towed vehicle (not shown), shown generally at 10, which
`utilizes an electronic brake controller 11 embodying the
`principles of the present invention. The brake controller 11
`is typically located in a towing vehicle (not shown), usually
`65
`being mounted beneath the towing vehicle dashboard. When
`actuated, the controller 11 functions to supply an electric
`
`Curt - Exhibit 1013 - 8
`
`

`

`5,615,930
`
`5
`
`10
`
`40
`
`5
`6
`controller g証n. In the preferred embodiment, the output
`signal and the microprocessor gain is illustrated by the graph
`sign証 has a constant frequency and a variable duty cycle
`shown in FIG. 2. The horizontal axis in FIG. 2 represents the
`which is proportional to the brake control sign誠
`brake control signal magnitude while the vertical axis rep-
`resents the output signal duty cycle. Accordingly, the scale
`A gain control push-button 32 is mounted on the front of
`the controller 11 and is operative to select the controller g証n
`on the horizontal axis varies from zero, representing no
`setting. The controller 11 租so includes a plurality of Light
`towing vehicle brake application to five volts, representing
`the maximum magnitude of the brake control signal. The
`Emitting Diodes (LED's) 33 which provide visual feedback
`scale on the horizontal axis varies from a zero duty cycle,
`to the towing vehicle operator. When the gain control
`push-button is depressed, selected LED'S 33 are illuminated
`representing no output signal from the microprocessor and
`to indicate the present v租ue of the controller g証n. Succes-
`no towed vehicle brake application, to a 100 percent duty
`sive operation of the push-button 32 sequences the micro-
`cycle, representing a continuous output signal and maximum
`processor through the available gain values while the cor-
`towed vehicle brake application.
`responding value appears on the display 35. When the
`The graph in FIG. 2 includes three straight lines which are
`desired gain value is displayed, the operator stops operating
`labeled G1, G2 and G3 and represent brake controller
`the push-button 32 and the controller adapts the displayed
`15 response curves. These straight lines illustrate typical micro-
`gain setting.
`processor responses for three brake controller gains where
`A manu証 switch 40 is provided on the electro血c con-
`the gain for G3 is greater than the gain for G2 and the gain
`troller 11 to allow the vehicle driver to actuate the towed
`for G2 is greater than the gain for G1. While three gains are
`vehicle brakes 13 and 14 without applying the towing
`illustrated, it will be appreciated that more or less gain
`vehicle brakes. Pressing the manual switch 40 causes the
`20 settings can be programmed into the brake controller 11.
`microprocessor to generate the output signal. The controller
`As shown in FIG. 2, the duty cycle of the microprocessor
`11 also is provided with a hand held manual remote switch
`output signal corresponding to a specific brake control signal
`41. The manu証 remote switch 41 includes a push-button
`is a function of the brake controller gain. For example, the
`which can be used to actuate the controller 11. When either
`vehicle operator can depress the towing vehicle brake pedal
`the manual switch 40 or the manual remote switch 41 are
`25 21 at a time t1 to cause the brake control signal generator to
`pressed, the towing vehicle and towed vehicle brake lights
`generate a first brake signal voltage, V1, which is shown on
`24 and 25 are illuminated.
`the horizontal axis in FIG. 2. When the brake controller gain
`In the preferred embodiment, the controller 11 is electri-
`setting is G1, the microprocessor output signal duty cycle
`cally coupled to an anti-lock brake system 45 (ABS), which
`corresponding to the first brake control signal V1 is D1, or
`is included in the towing vehicle, by a data link 46. While
`30 approximately 30 percent. Similarly, with a gain setting of
`a single line is shown for the data link 46 in FIG. 1, it will
`G2, the duty cycle corresponding to V1 is D2, which, in the
`be appreciated that the data link 46 may be a multi-
`example illustrated, is about 50 percent; and, with a gain
`conductor cable or a portion of a data highway. While the
`setting of G3, the duty cycle corresponding to V1 is D3, or
`controller 11 is illustrated and described as being coupled to
`approximately 80 percent.
`an ABS, it will be appreciated that the controller 11 also can
`If, at a later time t2, the vehicle operator further depresses
`be utilized in a vehicle which is not ABS equipped
`the brake pedal 21, the brake control signal generator
`The ABS 45 is of a conventional design and is responsive
`generates a second brake control signal, V2. which is greater
`to data concerning the operation of the towing vehicle to
`than the first brake control signal, V1. As shown in FIG. 2,
`control the hydraulic brake system 20 during impending
`the corresponding output signal duty cycles, D1', D2', and
`D3「 for each of the response curves G1, G2 and G3 are greater
`wheel brake lock-up conditions. The ABS 45 sends data over
`the data link 46 to the controller 11. The controller 11 is
`than the duty cycles D1, D2, and D3 corresponding to the first
`responsive to the data to control the towed vehicle brakes 13
`brake control signal VI.
`and 14 as a 釦nction thereof. For example, actuation of the
`The duty cycle of the microprocessor output signal also is
`ABS 45 due to an impending wheel lock-up condition of the
`a function of time. The variation of the duty cycle of the
`towing vehicle brakes could cause the brake controller 11 to
`microprocessor output signal with time is shown in FIG. 3
`decrease the braking intensity of the towed vehicle. Other
`where a typical braking cycle is illustrated. In FIG. 3, the
`horizontal axis represents time while the vertical 砥is again
`examples of data which can be transmitted from the ABS 45
`represents the output signal duty cycle. For simplici以 the
`to the controller 11 include vehicle speed, vehicle decelera-
`tion, brake failure, brake application, and changes in road
`microprocessor response is shown in FIG. 3 for only one
`surface conditions.
`gain setting, G1; however, similar responses would occur for
`The communication over the data link 46 is hi-directional,
`other gain settings.
`with the controller 11 also sending data to the ABS 45. For
`The solid line labeled R1 in FIG. 3 represents the micro-
`example, the controller 11 could transmit the controller gain,
`processor response to the brake control signal which was
`which is indicative of the towed vehicle load, to the ABS 45.
`described above. At t1, the microprocessor is responsive to
`55
`The ABS 45 would accordingly adjust the magnitude of the
`the first brake control signal V1 to generate an output signal
`towing vehicle braking. However, it will be appreciated that
`having the duty cycle D1. At t2, when the vehicle operator
`the communication over the data link 45 also can be uni-
`further depresses the brake pedal 21, the brake control signal
`direction証
`increases to V2 and the microprocessor begins generating an
`While the controller 11 has been illustrated as being
`output signal with the duty cycle D1'. At tR, the operator
`connected to an ABS 45 in FIG. 1, it will be appreciated that
`releases the brake pedal 21 causing the microprocessor to
`the controller 11 also can be connected to and commu血cat-
`stop generating an output signal.
`ing with other vehicle control systems. Examples of such
`As shown by R1 in FIG. 3, the microprocessor output
`systems include traction control systems, engine control
`signal instantaneously switches at t1 from zero to a signal
`computers and vehicle diagnostic computers.
`65 having the duty cycle D1. Similarly, at t2, the duty cycle of
`The relationship between the duty cycle of the micropro-
`the output signal instantaneously increases from D1 to D1'.
`cessor output signal, the magnitude of the brake control
`As described in the co-pending application described above,
`
`3 5
`
`45
`
`S0
`
`60
`
`Curt - Exhibit 1013 - 9
`
`

`

`5,615,930
`
`40
`
`7
`the microprocessor output signal is applied to a br水e driver
`which controls a brake switching circuit. The brake switch-
`ing circuit energizes the electric brake coils 19 to actuate the
`towed vehicle brakes. While the inductance of the brake
`coils 19 will prevent an instantaneous actuation of the towed 5
`vehicle br水es, the towed vehicle brakes are applied very
`rapidly, which can cause the brakes to grab. As a result, the
`towed vehicle can decelerate more rapidly than the towing
`ve血cle, thereby strai血ng the towing connection.
`The present invention contemplates programming the 10
`microprocessor to change the output signal duty cycle in
`response to a change in the brake control signal as a function
`of time. The dashed line labeled R2 in FIG. 3 illustrates a
`preprogrammed linear relationship between the output sig-
`nal duty cycle and time. Thus, at t1, the duty cycle begins to 15
`increase at a constant rate until D1 is reached at ta. The
`constant rate defines a ramp function. In response to the
`ramp function, the brake driver and brake switching circuit
`gradually increase the electric current supplied to energize
`the br水e coils 19 to smoothly actuate the towed vehicle 20
`brakes.
`Similarly, at t2, the brake control signal changes from V1
`to V2 and the microprocessor begins a ramp increase of the
`output signal duty cycle from D1 to D1. The increased duty
`25
`cycle D1' is reached at time tb. In the preferred embodiment,
`the ramp from t2 to tb has the same slope as the ramp from
`t1 to ta, however, the ramps may have different slopes.
`The output signal duty cycle remains at D1I until the brake
`ped司21 is released 証time 与，at w血ch time the microproー
`30
`cessor decreases the duty cycle of the output signal to zero,
`which is reached at time tc. As shown in FIG. 3 the slope,
`from tR to tc is greater than the slopes from t1 to ta and from
`t2 to tb. Because the brakes are being released, inclusion of
`a ramp response at the end of the brake cycle is optional.
`35
`The present invention also contemplates that a plurality of
`slopes of the ramp are programmed into the microprocessor.
`A particular slope is selected by the towing vehicle operator
`to match the towed vehicle and/or towed vehicle load. Thus,
`a gentle slope is selected when the towed vehicle is empty
`and a steeper slope is selected to apply the brakes more
`quickly when the towed ve血cle is loaded. Slopes could also
`be selected to match road conditions with gentler slopes
`used on slippery road surfaces.
`In the preferred embodiment, the slope is selected by
`manual operation of the gain push-button 32. The gain
`push-button 32 is depressed for a predetermined time period
`to signal the microprocessor that the response slope is to be
`changed. The microprocessor illuminates selected LED's 33
`to indicate receipt of the signal to change the slope. Then the
`specific slope is:selected by depressing the gain control
`button 32 a correspon山ng number of times. The micropro-
`cessor again illuminates the LED's to indicate the slope
`selected. Alternately, a separate slope selection push-button
`(not shown) or slope selector knob (not shown) could be
`added to the brake controller 11.
`The present invention further contemplates that the micro-
`processor can be programmed to generate an output signal
`having a duty cycle which is a non-linear function of time,
`as illustrated in FIG. 4. In FIG. 4, the duty cycle is increased 60
`with an increasing rate from t1 to t' and from t2 to tbI. Thus,
`the intensity of the towed vehicle brake application increases
`with an increasing rate with the passage of time. As
`described above, the duty cycle remains constant once the
`desired value is reached. As also described above, it is 65
`contemplated than a plurality of non-linear relationships
`would be stored in the microprocessor with a specific one of
`
`8
`the non-linear relationships being selected by the towing
`vehicle operator to correspond to the specific towed vehicle
`and/or road conditions.
`In the preferred embodiment illustrated in FIG. 4, the
`braking cycle is terminated at a cycle end time, te, which
`occurs before the brake pedal is released at tR. The cycle end
`time te is calculated by adding the maximum stopping time
`for the towing and towed vehicles to the time at which the
`last change in duty cycle occurs, which is tb' in FIG. 4.
`Typically, the maximum stopping time is less than two
`minutes. When the brake application time exceeds the cycle
`end time, te, the brake controller 11 releases the towed
`vehicle brakes. This precludes overheating the towed
`vehicle brakes while halted in stopped traffic. As shown in
`FIG. 4, the output signal duty cycle is reduced from t , to tc'
`in accordance with a non-linear function of time. Because
`the brakes are being released, inclusion of a non-linear
`response at the end of the brake cycle is optional.
`Alternately, the microprocessor can be programmed to
`continue to generate an output signal once the final duty
`cycleD1 is reached until the brake pedal 21 is released at TR.
`At tR, the duty cycle of the output signal can be instanta-
`neously reduced to zero or ramped to zero as illustrated at
`the end of the braking cycle in FIG. 3.
`Additionally, the microprocessor can be programmed to
`reduce the duty cycle of the output signal by a predetermined
`amount at te and continue at that level until tR (not shown).
`For example, atte , the duty cycle could be reduced to 20
`percent of D1' and remain at that level until tR. Thus, a light
`application of the towed vehicle brakes would continue until
`the end of the braking cycle. This could be desirable for
`holding the towing and towed vehicles stationary on an
`incline.
`As described above, the brake controller 11 can be con-
`nected by a data link 46 to a microcomputer or control
`system carried on the towing vehicle. For example, as shown
`in FIG. 1, the brake controller 11 can be connected to the
`ABS of the towing vehicle. When a data link 46 is available,
`the invention contemplates that the microprocessor continu-
`ously monitors the speed of the towing vehicle. The micro-
`processor uses the towing vehicle speed to calculate the
`maximum stopping time tm required to stop the towing and
`towed vehicles. The microprocessor then calculates te as:
`
`'=Ib4ら‘
`
`The maximum stopping time tm and cycle end time t would
`be continuously updated by the microprocessor.
`Additionally, the ABS sensor data could be used to
`determine when the towing