Dual-vehicle operating system
This is a division of application Ser. No. 812,179 filed July 1, 1977 now U.S. Pat. No. 4,119,166. 
    
    
     This invention relates to vehicle operating systems and more particularly relates to systems for operating two vehicles simultaneously. 
     The dual-car system was primarily developed to allow one driver to simultaneously operate two test vehicles. The system consists of a lead vehicle with driver, a servo-operated driverless trailing vehicle, and a zero-force mechanical connecting link. An electronic controller, coupled with throttle, brake, and steer servo motors, drives the trail vehicle to mimic the lead vehicle and its driver. The nominal zero-force link, which is approximately one car length or six meters long, uses transducers to provide information for the servo operation of the trailing vehicle, and allows safe management of the system in the event of a vehicle or system malfunction. 
     The dual-car system makes available a safe, accurate and economic means by which two vehicles may be subjected to the same test schedule by a single driver. This system is primarily for use in mileage accumulation type durability testing. The primary objects and advantages of dual-car system vehicle test programs are improved safety, economics, and correlation of test results when comparison of two vehicles is desired. The safety aspect is a direct result of the fact that fewer drivers on the test roads at a given time will automatically reduce the likelihood of driver-caused accidents. Similarly from an economic consideration, the number of drivers needed to operate a given number of test vehicles, will be reduced by one-half. Technical support personnel will, of course, be required, but the net result is a significant reduction in manpower for the conducting of a multiple-vehicle test program. A higher density of vehicles can also occupy a given road system because the trailing vehicle is approximately one car length behind the leading vehicle for all speeds. It is often desirable to study the behavior of two different vehicles when driven on an identical road test schedule. Assurance that the test conditions are in fact similar is obviously enhanced with the dual-car system. 
     An important consideration in the conduct of valid test programs is that modification to the vehicle itself be held to a minimum in order to produce as nearly as possible a real-world simulation of operating conditions. A great deal of effort is spent in automotive testing to achieve this end. Equipment mass, power demand, and interface techniques have been carefully considered to reduce unrealistic effects on the vehicles during testing. A principle feature of the dual-car system is that the vehicles may be readily separated from the system and driven independently in a normal manner. 
     All control and safety features are fully automatic, freeing the test driver to operate in essentially the same manner he would while operating a single vehicle. There are no routine adjustments or calibrations necessary in the operation of the system, so driver training is reduced to a familiarization period primarily concerned with adapting to driving a single vehicle with a long trailer attached. The long trailer effect is in itself reduced to a steering consideration, as the zero-force connecting link removes all force inputs to the driven vehicle which are normally experienced with trailer driving. The operation of the trail vehicle and the control system are constantly monitored so that impending or actual malfunctions are signaled to the driver, through an alarm system, and automatic shutdown of the trail vehicle is initiated. 
    
    
     These and other objects and advantages of the dual-car test system will be more apparent from the following description and drawings in which: 
     FIG. 1 is a side view of the dual-vehicle system; 
     FIG. 2 is a perspective view of a portion of the dual-vehicle system; 
     FIG. 3 is an elevational view of the steering, brake, and throttle servo-systems in the vehicles; 
     FIG. 4 is a view taken along line 4--4 of FIG. 3; 
     FIG. 5 is a top view of the rear pivot of the connecting link; 
     FIG. 5a is a top view of a portion of the latching mechanism; 
     FIG. 6 is a side view of the rear pivot of the connecting link; 
     FIG. 7 is a view taken along line 7--7 of FIG. 5; 
     FIG. 8 is a view taken along line 8--8 of FIG. 7; 
     FIG. 9 is a side view partly in section of a portion of the front hitch; 
     FIG. 10 is a top view of a portion of the front hitch taken along line 10--10 of FIG. 9; 
     FIG. 11 is a side view partly in section of a portion of the front hitch; 
     FIG. 12 is a view taken along line 12--12 of FIG. 11; 
     FIG. 13 is a view taken along line 13--13 of FIG. 11; 
     FIG. 14 is a view taken along line 14--14 of FIG. 13; 
     FIG. 15 is a diagrammatic representation of the dual-car test system in another mode of operation; 
     FIG. 16 is a perspective view of the readouts provided for the driver of the lead vehicle; 
     FIG. 17 is a schematic diagram of the steer control system for the dual-car system; and 
     FIG. 18 is a schematic view of the brake and throttle pedal controls used in the dual-car test system. 
    
    
     MAJOR SYSTEM COMPONENTS 
     Trail Car 
     The basic concept of the dual-car system, shown in FIGS. 1 and 2, is that of a totally automatic driverless trail vehicle 10 which accurately mimics a driver-operated lead vehicle 12. The lead and trail vehicles are connected by a mechanical headway link or zero-force 14. Steering wheel, accelerator pedal, and brake pedal actuations necessary to accomplish this are provided by three independent closed-loop servo systems. These servo systems form an integrated actuator assembly which is mounted on the steering column 16 of the trail vehicle 10 as shown in FIGS. 3 and 4. All three servo motors are 12-volt DC permanent magnet gear motors. The steer servo motor 18 is connected to the steering wheel 20 through a gear train 21, an electromagnetic clutch 22 and a gear belt 24. Rotation of the steering wheel is sensed by a steer transducer or potentiometer 25. The accelerator and brake servo motors 26, 27 actuate their respective pedals 28, 29 through cable arrangements 30, 31, respectively, allowing maximum flexibility of installation for different vehicle pedal locations. A conventional linear displacement transducer 32 senses throttle movement, while a conventional force transducer 33 senses the brake apply force. The servo loop feedback transducers associated with each function are: steer angle, mounted within the steer actuator gearbox; accelerator pedal angle, mounted on the upper pedal arm; and brake pedal force, a strain gauge transducer mounted on the brake pedal. Each servo function includes a separate control loop using conventional pulse width modulated (PWM) motor drivers which can respond to command voltage signals originating from a conventional electronic control unit. The lead vehicle 12 has similar transducers on the accelerator pedal and brake pedal, not shown, for initiating acceleration and brake signals to the trail vehicle. 
     The force and rate capabilities of each servo mechanism, listed in Table 1 below, are consistent with the normal steering and pedal efforts required for the mileage accumulation type driving schedules on which the system was designed to operate. Table 1 also includes the approximate power drain on the vehicle electrical system during the maximum servo effort levels listed. Under normal operation, the electrical load of the servos approximates the average vehicle accessory load. Both manual and power assist steer and brake functions are included within these ranges. The general mechanical configuration of the actuator assembly allows normal operation of the vehicle by a driver when it is disconnected from the lead car. 
     
                       Table 1                                                     
______________________________________                                    
Servo Mechanism Specifications                                            
______________________________________                                    
Steer Rate:      1 rps                                                    
Steer Torque:    28 N m      at 240 W                                     
Brake Pedal Rate:                                                         
                 100 mm/s                                                 
Brake Pedal Force:                                                        
                 450 N       at 72 W                                      
Accelerator Pedal Rate:                                                   
                 200 mm/s                                                 
Accelerator Pedal Force:                                                  
                 90 N        at 48 W                                      
______________________________________                                    
 
    
     Connecting Link 
     The headway link 14 maintains a fixed distance, six meters, between the lead and trail vehicles while permitting the required turning maneuvers. The headway link 14 serves as the source of some control signals and a medium for information transmitted between the lead car 12 and the trail car 10. 
     The length of the headway link 14 is a compromise between acceptable drafting loads, cooling air-flow restriction, and overall manageability of the system under normal test driving conditions. 
     A twenty-degree articulation point or rear pivot 34, FIG. 5, at the rear of the link 14 permits lateral freedom within this range, and the articulation point 34, through latch arms 35, also limits offset tracking between the two vehicles to one meter which is approximately an angle of ten degrees between the longitudinal axes of the link 14 and trail vehicle 10, as shown in FIG. 15, in the event that the trail vehicle 10 doesn&#39;t track correctly. When this limit is reached, the rear pivot 34 is automatically latched, FIG. 5a, to prevent further swaying of the trail car, and the steer servo clutch 22 is simultaneously disengaged to allow the front wheels of the trail vehicle 10 to castor normally. The link 14 is connected to the lead vehicle 12 through a front pivot 36. This places the system in a conventional towing mode. In this mode, the system is driveable at speeds up to 110 km/h, allowing the driver to bring the system to a safe stop. 
     The primary steer control signal for the trail vehicle&#39;s steer servo is produced by an angle transducer potentiometer 38, FIG. 9, located at the lead pivot 36 end of the link 14. This information is summed with angle information derived from a second angle transducer potentiometer 40, FIG. 7, located at the rear pivot point 34. These signals comprise a command input to the steer servo to complete an open-loop servo control, discussed later, which maintains the trail car in alignment with the longitudinal axis of link 14 at all times. 
     Normal performance variations between two vehicles will cause axial forces to be generated in the link 14 and reflected back to both vehicles. Since a primary use of this system is vehicle drive-train testing, these forces cannot be tolerated. A force transducer 42, positioned to detect force transmission between the link 14 and a hitch assembly 44 at the front pivot 36 of the link 14, measures these forces for inclusion in the accelerator and brake pedal control loops. The force transducer 42, having a measurement range of ±2000 N, consists of a parallelogram mounted, spring-loaded ball hitch 46 and a conventional linear variable displacement transducer 48. The parallelogram mounting permits fore and aft movement between the ball hitch 46 and the link 14. 
     The rear pivot 34 has a base member 50 secured to the headway link 14 and a pivotable frame member 52 which is secured via support members 54 to a frame member 56 which is secured to the trailing vehicle 10. The member 52 is pivotally connected to the member 50 such that relative angular movement is possible between the headway link 14 and the trail vehicle 10. The pivotal connection is made via a pin 58 which is secured to the member 50 and is pivotally supported in a bushing, not shown, in the member 52. The angle transducer 40 is mounted in a housing 60 which is secured to the member 52 such that the housing 60 will pivot with the trail vehicle 10. The transducer 40 is connected through a belt drive 62 to a pulley 64 which is rotatably mounted on the pin 58. Thus, as the relative angle between the trail vehicle 10 and the headway link 14 is changed, the transducer 40 will be rotated. For extension of useful range and life considerations, there is an 8:1 ratio between the pulley 64 and a pulley 66 which is secured to the angle transducer 40. 
     Also mounted on the member 52 are a pair of limit switches 68 and 70 which are set to be actuated when the member 52 is rotated to an angle of 10° relative to the headway link 14. The switches 68 and 70 are operable to disconnect the steer clutch 22 of the trail vehicle steer system to permit the trail vehicle wheels to castor normally. Also when the angle of 10° is reached between the headway link 14 and the trail vehicle 10, one or the other of the latch arms 35 which are pivotally connected to member 52 will latch onto the member 50 as shown in FIG. 5a. This prevents the relative angle between the trail vehicle 10 and the headway link 14 from changing so that the position of the trail vehicle, as shown in FIG. 15, will be maintained. The latch arms 35 are spring-loaded by compression springs 72 such that during normal operation the latch arms 35 are spring-loaded against the member 50. The latch arms must be movably disengaged to permit normal operation. 
     The trailing pivot 34 has an upper pivot portion 74 which is comprised of a U-shaped bracket 76 which is rotatably connected to the headway link 14 through a tongue-bracket 78. The members 76 and 78 are connected by a pin member 80 which permits pivotal relationship between the brackets. The bracket 76 is secured by a support or structure member 82 which in turn is secured to the frame member 56. 
     The lead pivot 36 includes the hitch assembly 44 and the force transducer 42. The hitch assembly 44 is connected to a housing 84 by four rod members or links 86. The links 86 are pivotally connected by pins 88 to the housing 84 and by pins 90 to the ball hitch 46. This four-bar linkage or parallelogram mounting permits free longitudinal movement of the ball hitch 46 relative to the housing 84 and therefor the headway link 14. The ball hitch 46 is inhibited from longitudinal movement by a pair of compression springs 92 and 94 which are trapped between the ball hitch 46 and the housing 84 by a pin member 96 and the rear of the housing 84. Thus a predetermined force between the headway link and the lead vehicle is necessary to provide the longitudinal movement. The longitudinal movement is measured by the conventional linear variable displacement transducer 48. Since the springs 92 and 94 provide a predetermined force reaction to achieve the longitudinal movement, the transducer 48 will effectively measure the force determined between the lead vehicle and the headway link which is, of course, the force between the lead vehicle and the trail vehicle. The output of the transducer is proportional to the longitudinal force exerted on the connecting link 14. Also, secured in the ball hitch 46 is a block 98 which has a V-groove 100 formed therein. 
     As seen in FIG. 9, the angle transducer 38 of the lead pivot is mounted in a housing 102. The transducer 38 is connected to a bar 104 which is pivotally connected by a pin 106 to a bar 108. The pin connection 106 permits vertical pivoting of the bar 108 relative to the bar 104. A tension spring 110 provides a force to pivot the bar 108 relative to the bar 104. Secured to the bar 108 is a follower arm 112 which has a ball or sphere 114 at its distal end. The sphere 114 is held in engagement with the V-groove through the action of the spring 110. The V-groove 100 and pin 106 permit limited vertical angular displacements between the headway link 14 and the lead vehicle caused by road surface imperfections without affecting the transducer 38. However, longitudinal angular displacement between the lead vehicle and the headway link is sensed by the arm 112 and transmitted to the lead angle transducer 38 such that a signal proportional to the angle between the longitudinal axes of the lead vehicle 12 and the link 14 is available. The housing 102 is secured to a sphere 116 which is connected to the lead vehicle and cooperates with the ball hitch 46 to provide a pivotal connection between the lead vehicle and the headway link. This, of course, is a well-known method of attaching two devices together for relative angular displacement. 
     Lead Car 
     The lead car is equipped to provide accelerator and brake pedal information for direct mimic by the trail car servo mechanisms. In addition, turn signal, back-up lamp, and transmission selector position information is sensed for communication to the electronic control unit in the trail vehicle. Accelerator pedal angle and brake pedal force are monitored using the same type of transducers as used in the trail car. The transducer signal conditioning electronics are housed in a driver information package, and include conventional displays and annunciators, as shown in FIG. 16, which provide the driver with information regarding the status of the trail vehicle and certain critical system control parameters. Table 2 lists the various display and switch functions found in the driver information package which also contains an audio intercom which allows the lead car driver to listen to the operation of the trail car. This combination of aural and visual information closely duplicates the level of information available to a driver of a normally driven vehicle. 
     
                       Table 2                                                     
______________________________________                                    
Driver Information Package Functions                                      
______________________________________                                    
Oversteer: Warns driver that he is attempting                             
           to negotiate a turn of shorter                                 
           radius than system limits allow.                               
RPM:       Indication of trail car engine                                 
           overspeed or stall.                                            
Hdwy-Err:  Indication that the time integral                              
           of inter-vehicle axial forces is                               
           exceeding preset limits.                                       
Temp:      Repeats engine temperature lamp                                
           on trail car.                                                  
Alt:       Repeats alternator lamp on trail                               
           car.                                                           
Oil:       Repeats oil pressure lamp on                                   
           trail car.                                                     
Ack:       Allows driver to silence aural                                 
           alarm while retaining visual - indication.                     
Reset:     Allows reset of all alarm indi-                                
           cators if fault has been corrected.                            
Performance:                                                              
           Provides indication of relative                                
           signal levels required by the                                  
           pedal servo controllers to produce                             
           zero axial forces in the headway                               
           link.                                                          
Emerg. Stop:                                                              
           This is a direct control input                                 
           which the operator can introduce                               
           into the electronic control                                    
           system, and initiates the following                            
           sequence of events:                                            
           Disconnect primary vehicle (12-volt                            
           battery) power to the electronic                               
           control system.                                                
           Return the trail car accelerator                               
           pedal to the fully closed position.                            
           Turn off the trail car ignition                                
           system.                                                        
           Apply light brake pedal force in                               
           the trail car.                                                 
______________________________________                                    
 
    
     The emergency stop sequence is automatically initiated whenever an rpm alarm condition is received. In the event of multiple alarms occurring at the same time, the first alarm received causes that indicator to flash on and off while the remaining alarms are continuously on. This assists the driver in determining which fault initiated the alarm condition. 
     Basic Servo Control 
     The steer, accelerator, and brake actuating servos all utilize a common conventional control design consisting of a 12-volt DC permanent magnet gear motor, transistorized pulse width modulated (PWM) motor drive, and an associated feedback transducer. 
     Each of the three identical PWM motor drive electronic component sets are contained on separate, interchangeable printed circuit boards. These circuit boards are housed in a conventional manner in an electronic control unit, not shown. The PWM drive technique, in conjunction with DC servo motors, is used to minimize power loss between the vehicle 12-volt electrical system and the motors. Power pulses to the servo motors are width modulated at 330 Hz. The algebraic sum of incoming command and feedback signals is continuously compared to an internally generated triangle wave, and the resulting PWM pulse train is applied to four motor-drive transistors arranged in a conventional &#34;H&#34; bridge configuration. 
     The response characteristics of steering, accelerator pedal, and brake pedal will vary from vehicle to vehicle. These variations are accommodated in each motor-drive control through the use of adjustable gain and integral and rate feedback elements; thus allowing optimization of each servo loop to the vehicle in which it is installed. The servo control system is operational with conventional vehicle electrical system voltages ranging from 8 to 16 volts DC over an ambient temperature range of -10° to +70° C. Conventional automatic current limiting is included in each motor-drive control to provide motor and circuit element protection. 
     Steer Control Description 
     The basic steer control configuration is shown in the block diagram of FIG. 17. The minor control loop consists of a summing point 2, a PWM motor-drive control, the motor 18, the electromagnetic clutch 22, and the steer transducer 25. This minor loop receives command signals directly from a summing point 1. The front and rear link angle transducers 38 and 40 have fixed gain relationships to the trail vehicle&#39;s steering wheel 20, and ultimately to its front wheels. The geometry of the total system of lead car 12, headway link 14, and trail car 10, during turning maneuvers, is dictated by this gain relationship. Alignment of the link 14 and the trail car 10 is approximated by a direct 3:1 ratio between the angle of the angle transducer potentiometer 38 and the front wheel angle of the trail car. 
     Errors in this approximation are caused by vehicle steering ratio variations and lateral forces introduced into the vehicle by side wind or road slope. These errors are corrected by summing information from the rear link angle transducer in a negative direction at a ratio of 1:1. 
     The dual-car system may be driven in reverse to aid in parking or driving around obstacles. In order to maintain alignment of the trail car and the link, the sense of the steer command signal must be reversed. This is automatically accomplished whenever the lead car&#39;s transmission selector is placed in &#34;reverse&#34; by detecting the back-up lamp &#34;on&#34; condition, and inverting the signal path between summing points 1 and 2. 
     The clutch 22 shown in the steer control block diagram is automatically energized when the lead car&#39;s transmission is engaged in either &#34;drive&#34; or &#34;reverse&#34;. The drive motor is declutched from the steering wheel when the limit of the link rear pivot point is reached. This occurs simultaneously with mechanical latching of the pivot, and allows the trail vehicle&#39;s front wheels to castor normally. 
     Pedal Control 
     The pedal control block diagram shown in FIG. 18 is typical for both the accelerator pedal servo and the brake pedal servo. The link force transducer output is the only signal which is common to these two separate control loops. The following description will refer only to &#34;pedal&#34; actuation. The accelerator pedal is a conventional angular control, and the brake pedal is a conventional force control. 
     The minor control loop, beginning at summing point 3, acts to duplicate the lead vehicle&#39;s pedal activity in the trail car. This action is modified by a multiplier which adjusts the gain of the lead pedal transducer as required to produce trail vehicle performance consistent with zero axial forces in the headway link 14. 
     Prior to introduction to the multiplier, the link force signal is conditioned by an integrator whose time constant is several times longer than normal vehicle drive-train response times. In addition, the integrator is placed in a &#34;hold&#34; mode when a pedal is inactive. The resulting control action produces a trail vehicle response which averages out the transient effects of automatic transmission gear shifting and road roughness, while continuously nulling axial link forces. Placing the integrator in &#34;hold&#34; during periods of pedal inactivity allows the most recent loop gain requirements to be available for the next pedal actuation. An example of this is the pedal activity required for repeated vehicle accelerations alternated with full stops. 
     Summing point 2 introduces a constant bias to provide unity gain through the multiplier when the axial force signal impressed on the integrator by the force transducer 42 is at null. This bias also establishes unity multiplier gain when the system is first turned on at the start of a driving schedule. Since the magnitude of the integrator output signal is directly related to trail vehicle performance, this information is displayed to the lead car driver on the &#34;performance indicator&#34;. The performance indicator monitors the accelerator pedal control function only, and provides a subjective &#34;feel&#34; for relative trail car engine response changes over the life of a test program. 
     The total effectiveness of this control concept in the longterm maintenance of zero axial forces on either vehicle has been established. During initial operation of the system, both the lead and trail vehicles were fitted with rear wheels which had been strain-gauged to indicate the torque reaction developed between the vehicle and the road. This torque information was combined with speed information to produce vehicle power data which was used to compare vehicle efficiencies under various driving conditions. Two cars were operated on selected segments of the Federal Emission Durability Mileage Accumulation Schedule, both separately and while connected with the dual-car system. The test sequence was carefully controlled, using the same driver, roadway, and climate conditions for numerous consecutive repeats of the schedule. The test results demonstrated an average decrease in trail car power of 1.5 percent (at 55 km). The range of decreased power is zero percent at 10 km/h to 3 percent at 110 km/h. This decrease is for the trail car when operating in the dual-car mode, and is caused by the drafting effect produced by the lead vehicle. Effects on the lead car were consistently less than the overall variables encountered during the tests. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teaching. It is therefore to be understood, that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.