Abstract:
A method of selective, automatic application of one rear brake of a motor vehicle under appropriate vehicle operating conditions in response to intent of a driver to make a turn, whereby the rotational speed of the selected braked rear wheel is reduced so as to reduce the turn radius of the vehicle. Vehicle sensor outputs and calculated parameters in conjunction with vehicle systems such as, but not limited to, ESC, ABS, and traction control are used to determine if appropriate vehicle operating conditions exist to actuate the present invention. The method of the present invention is implemented via an algorithmic control, preferably within an ESC system.

Description:
TECHNICAL FIELD 
     The present invention relates generally to motor vehicle maneuverability and more specifically to a method of automatically controlling rear braking systems of a motor vehicle to reduce the turn radius. 
     BACKGROUND OF THE INVENTION 
     In the farm implements art, most farm tractors have separate left rear and right rear brake pedals, which respectively activate the left rear brake or the right rear brake separately of one another. For example, to make a very tight right turn (i.e., to reduce the turn radius of the tractor for a right turn), manual operation of the right rear brake pedal by the operator activates the right rear brake whereby the rotational speed of the braked right rear wheel is reduced, thereby reducing the turn radius of the braked right rear wheel by which the turn radius of the tractor is reduced, such that the tractor almost pivots about the right rear wheel. 
     In the automotive art, modern dual-circuit hydraulic braking systems for automotive applications typically include an operator-actuated brake actuation unit, such as a tandem master cylinder actuated by a booster-aided brake pedal, by which to supply a first pressurized fluid to each of a first pair of wheel brakes via a first or “primary” braking circuit, and a second pressurized fluid to each of a second pair of wheel brakes via a second or “secondary” braking circuit. The use of wholly redundant braking circuits for operating discrete pairs of wheel brakes ensures continued vehicle braking capability, notwithstanding a degradation of performance of one of the braking circuits. Alternatively, electric actuation of individual wheel brakes is possible as well by techniques well known in the art. 
     In order to achieve an “anti-lock” brake system (ABS), each braking circuit often features a normally-open electrically-operated inlet valve controlling the flow of pressurized fluid to each wheel brake, while a pressure relief line that includes a normally-closed electrically-operated outlet valve, a return pump, and a check valve controls the return of pressurized fluid from the wheel brake to the brake line upstream of the inlet valve. A “separation” or “isolation” valve, located in the brake line of each circuit upstream of the location at which the pressure relief line connects to the brake line, serves to isolate the brake line from the master cylinder during anti-lock operation. 
     Increasingly, such anti-lock brake systems are used in combination with wheel speed sensors in a traction control mode. The further addition of a steering angle sensor, a vehicle yaw rate sensor, and a lateral vehicle acceleration sensor in conjunction with vehicle speed, wheel speed, and wheel longitudinal slip enables such anti-lock brake systems to operate in an “electronic stability control” mode, wherein a braking system controller selectively energizes each circuit&#39;s electrically-operated valves when the controller identifies an opportunity to enhance vehicle stability through a selective application of the vehicle&#39;s brakes. Alternatively, a braking system controller may selectively energize individual wheel brakes through electric actuation. 
     In order to control the fluid pressure in traction control or vehicle stability control modes, a hydraulic pump is typically placed in the pressure relief line of each circuit downstream of the outlet valve to return pressurized fluid to the circuit&#39;s brake line. The pump also serves to provide an increasing rate of fluid pressure upon the closing of the isolation valve to provide a sufficient braking system response time when operating in a traction control mode, even at a time when the brake fluid has a relatively-high viscosity due, for example, to low brake fluid temperatures. 
     The prior art has recognized, however, that a quicker system response is desirable when the braking system is operated in a vehicle stability control mode. By way of example, a rapid pressure build up in one or the other braking circuit is particularly desirable upon commencing vehicle stability control in order to correct oversteer or understeer conditions. Accordingly, the prior art teaches the addition of a braking circuit pre-charging function to the brake actuation unit, i.e., to the vacuum booster of the master cylinder, in order to increase system response at the time such vehicle stability control is commenced. Alternatively, an additional pre-charging pump is provided in one or both braking circuits to ensure a sufficient increasing rate of fluid pressure at the commencement of vehicle stability control enhancement. 
     There are multiple Electronic Stability Control (ESC) system implementations on the road today. Although all of them attempt to perform the same task of helping the driver retain reasonable directional control under nonlinear vehicle dynamic conditions, these ESC systems have some distinct implementation differences and can be divided into four categories as defined and described in The Society of Automotive Engineers (SAE) Surface Vehicle Information Report, SAE J2564, “Automotive Stability Enhancement Systems”, revised June, 2004 and superceding version issued December, 2000, which report is hereby incorporated herein by reference in its entirety. 
     A system is defined as an ESC system in the above referenced report SAE J2564 if it: 
     a) is computer controlled and the computer contains a closed-loop algorithm designed to limit understeer and oversteer of the vehicle; 
     b) has a means to determine vehicle yaw velocity and side slip; 
     c) has a means to monitor driver steering input; 
     d) has a means of applying and adjusting the vehicle brakes to induce correcting yaw torques to the vehicle; and 
     e) is operational over the full speed range of the vehicle (except below a low-speed threshold where loss of control is unlikely). 
     Electronic Stability Control systems in use today can be divided into four categories, as follows. 
     Type A, comprised of two brake force channels used for yaw stability control (YSC) and three brake force channels used for ABS. Three speed sensors are used, one for each front wheel and one for detecting the average of the two rear wheels. 
     Type B, comprised of two brake force channels for YSC and traction control, four brake force channels for ABS. Four wheel speed sensors are used at each of the four corners (wheels). 
     Type C, comprised of four brake force channels for ABS, YSC and traction control. Four wheel speed sensors are used at each of the four corners. 
     Type D, comprised of a type C system with integrated preemptive control strategies and additional control channels that interface to other than the brake subsystem. These subsystems include, but are not limited to active driveline couplings, and active dampers and stabilizer bars and active steering. 
     For the vast majority of ESC systems, the corrective yaw moments that are developed by generating tire slip using the vehicle&#39;s brake corners are typically hydraulically actuated, but may also use electric actuators to generate the required corner brake force by techniques well known in the art. 
     Elements that all of these ESC systems have in common include ABS and the ability to sense steering wheel position; the ability to calculate vehicle speed; the ability to sense yaw velocity and lateral acceleration; and the ability to build and control braking force in the channels used for yaw stability control independent of the driver&#39;s input to the vehicle braking system. An example of the implementation of a vehicle hydraulic braking system utilizing a Type C or Type D ESC system is described in U.S. Pat. No. 6,896,338, which patent is hereby incorporated herein by reference in its entirety. 
     Returning now to the concept of minimizing turning radii, it is desirable to have minimization of the turning radius of a motor vehicle. Rear wheel steering, incorporated in vehicles with four wheel steering, can provide a small turning radius; however, four wheel steering is costly and requires a large packaging space around the rear wheels. 
     Accordingly, what is needed in the prior art is a method of automatically reducing the turn radius of motor vehicles which somehow mimics a farm tractor&#39;s ability to have a small turn radius via independently applying the brake of the wheel inside the turn radius by somehow adapting this model to an automotive ESC system. 
     SUMMARY OF THE INVENTION 
     The present invention is a method of selective automatic application of one rear brake of a motor vehicle actuated under appropriate vehicle operating conditions in response to sensing a turn, the turn being actualized by the vehicle operator whose intent is to make a left or right turn, wherein the motor vehicle incorporates a, preferably, Type C or Type D ESC system. 
     According to the methodology of the present invention, rotational speed of a selected rear wheel is reduced (within a range of allowed slip) by selective braking so as to reduce the turn radius of the motor vehicle. The selected rear wheel is that wheel which is on the inside of the turn (i.e. the right rear wheel in the case of a right turn). As an example, the present invention may be utilized to assist the operator of the motor vehicle in parking the vehicle. The capability of a Type C or Type D ESC system to apply all four brakes individually is utilized to automatically separately activate the left rear or right rear brake in order to enhance a reduction of the turn radius of motor vehicles equipped therewith. 
     The method according to present invention utilizes vehicle sensor outputs and calculated parameters available from the vehicle microprocessor or ESC system such as, but not limited to, vehicle speed, wheel speeds, steering wheel angle, steering hydraulic assist pressure, wheel slip, yaw velocity, lateral acceleration, gear position, throttle position, master cylinder brake pressure, wheel brake pressure, brake pedal position, and rate of change of wheel brake pressure. The aforementioned vehicle sensor outputs and calculated parameters are compared to predetermined parameter values obtained empirically or through simulation for a particular vehicle model to determine, in conjunction with vehicle systems such as, but not limited to, ESC, ABS, and traction control, whether appropriate vehicle operating conditions exist to actuate the present invention. The method of the present invention is implemented via an algorithmic control, preferably, by software within the ESC system. 
     Accordingly, it is an object of the present invention to provide an ESC based independent application of an inside turn rear wheel brake to effect minimization of the turning radius of the motor vehicle. 
     This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an example of a functional pictorial view of a motor vehicle according to the present invention. 
         FIG. 2  is an example of an algorithmic method to implement the present invention. 
         FIG. 3  is a pictorial view of an implementation of a first parking example according to the present invention. 
         FIG. 4  is a pictorial view of an implementation of a second parking example according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is an example of a functional pictorial view  100  of a motor vehicle  102  implementing the present invention during a right hand turn  104 . The vehicle operator&#39;s intent to make a right hand turn  104  is sensed (detected) through either a steering wheel angle or steering hydraulic pressure sensor  106   a , the output of which being input to the ESC electronic control system  108 . Calculated parameters  106   b  are available to the ESC electronic control system  108  via the ESC controller  110  thereof. Vehicle sensor outputs  106   c  are input to the ESC electronic control system  108 . The calculated parameters  106   b  and vehicle sensor outputs  106   c  include, but are not limited to, vehicle speed, wheel speeds, steering wheel angle, steering hydraulic assist pressure, wheel slip, yaw velocity, lateral acceleration, gear position, throttle position, master cylinder brake pressure, wheel brake pressure, brake pedal position, and rate of change of wheel brake pressure 
     The ESC controller  110  of the ESC electronic control system  108  compares the vehicle sensor outputs and calculated parameters to predetermined parameter values obtained empirically or through simulation for a particular vehicle model to determine, in conjunction with vehicle systems such as, but not limited to, ESC, ABS, and traction control, whether vehicle chassis control activity is occurring, as for example a situation in which the operation of the vehicle is unstable. If vehicle chassis control chassis activity is occurring, brake controller  116  is notified via line  118  and selective rear brake controller  112  is notified via line  114 . 
     Otherwise, if vehicle chassis control chassis activity is not occurring, selective rear brake controller  112  is notified via line  114 . Selective rear brake controller  112  utilizes vehicle sensor outputs and calculated parameters available from the vehicle microprocessor or ESC system such as, but not limited to, vehicle speed, wheel speeds, steering wheel angle, steering hydraulic assist pressure, wheel slip, yaw velocity, lateral acceleration, gear position, throttle position, master cylinder brake pressure, wheel brake pressure, brake pedal position, and rate of change of wheel brake pressure. The selective rear brake controller  112  utilizes the aforementioned vehicle sensor outputs and calculated parameters in conjunction with predetermined parameter values obtained empirically or through simulation for a particular vehicle model to determine, in conjunction with vehicle systems such as, but not limited to, ESC, ABS, and traction control, whether appropriate vehicle operating conditions exist to actuate the present invention. If appropriate vehicle operating conditions do exist to actuate the present invention, then selective rear brake controller  112  determines appropriate rear brake parameters and selects the appropriate rear brake (the wheel at the inside of the turn) to activate (the rear right brake  122  of the rear right wheel  130  in the example of  FIG. 1 ), whereby brake controller  116  is notified via line  120 . 
     Brake controller  116  directs ESC hydraulic brake control unit  124  via line  126  to activate the appropriate rear brake (the rear right brake  122  in the example of  FIG. 1 ) via brake hydraulic line  128 , whereby the rotational speed of the selected braked rear wheel ( 130  in  FIG. 1 ) is selectively reduced, whereupon the right turn radius of the vehicle  102  is reduced. The selected braked rear wheel is that wheel which is on the inside of the turn (i.e., the right rear wheel  130  in the case of a right turn). 
     During and after activation of the appropriate rear brake ( 128  in  FIG. 1 ), selective rear brake controller  112  continuously monitors whether appropriate vehicle operating conditions continue to exist to actuate the present invention, as described hereinabove. If appropriate vehicle operating conditions continue to exist to actuate the present invention, selective rear brake controller  112  functions as previously described hereinabove. Otherwise, if appropriate vehicle operating conditions do not continue to exist to actuate the present invention, as described hereinabove, selective rear brake controller  112  notifies brake controller  116  via line  120  to deactivate the presently activated rear brake utilizing appropriate brake parameters. 
       FIG. 2  is an example of an algorithmic method  200  to implement the present invention. The predetermined parameter values obtained empirically or through simulation for a particular vehicle model utilized in  FIG. 2  are presented in Table I. 
     
       
         
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                 Parameter Name 
                 Function 
                 Range 
               
               
                   
               
             
             
               
                 NPMINGEARTIME 
                 Continuous time 
                 1 to 5 
               
               
                   
                 in a forward or 
                 seconds 
               
               
                   
                 reverse gear 
               
               
                 NPHWPOSITION 
                 Steering wheel 
                 Greater than 
               
               
                   
                 position 
                 95% to 98% 
               
               
                   
                   
                 of the 
               
               
                   
                   
                 maximum 
               
               
                   
                   
                 steering 
               
               
                   
                   
                 wheel 
               
               
                   
                   
                 angular 
               
               
                   
                   
                 position 
               
               
                 NPMINSPEED 
                 Lowest vehicle 
                 1 to 3 miles/ 
               
               
                   
                 speed 
                 hour 
               
               
                 NPMAXSPEED 
                 Highest vehicle 
                 4 to 8 miles/ 
               
               
                   
                 speed 
                 hour 
               
               
                 NPMINTHROT 
                 Lowest 
                 0 to 5% 
               
               
                   
                 accelerator 
               
               
                   
                 pedal position 
               
               
                 NPMAXTHROT 
                 Highest 
                 25% to 40% 
               
               
                   
                 accelerator 
               
               
                   
                 pedal position 
               
               
                 NPMAXPRESS 
                 Maximum applied 
                 200 psi to 
               
               
                   
                 brake pressure of 
                 1000 psi 
               
               
                   
                 activated 
               
               
                   
                 rear brake 
               
               
                 NPPRESSURERAMPUPRATE 
                 Rate of change of 
                 50 psi/sec to 
               
               
                   
                 brake pressure 
                 800 psi/sec 
               
               
                   
                 increase of 
               
               
                   
                 activated 
               
               
                   
                 rear brake 
               
               
                 NPPRESSURERAMPDOWNRATE 
                 Rate of change of 
                 50 psi/sec to 
               
               
                   
                 brake pressure 
                 800 psi/sec 
               
               
                   
                 decrease of 
               
               
                   
                 activated 
               
               
                   
                 rear brake 
               
               
                 QNPPRESSURERAMPDOWNRATE 
                 Quick brake 
                 Greater than 
               
               
                   
                 pressure release 
                 2000 psi/sec 
               
               
                   
                 of activated 
               
               
                   
                 rear brake 
               
               
                 NPBRKENABLEPRESS 
                 Maximum 
                 150 psi to 
               
               
                   
                 allowable brake 
                 400 psi 
               
               
                   
                 pedal induced 
               
               
                   
                 master brake 
               
               
                   
                 cylinder pressure 
               
               
                 NPMAXSLIP 
                 Maximum wheel 
                 15% to 70% 
               
               
                   
                 slip of selected 
               
               
                   
                 rear wheel 
               
               
                 NPMINSLIP 
                 Minimum wheel 
                 1% to 10% 
               
               
                   
                 slip of selected 
               
               
                   
                 rear wheel 
               
               
                   
               
             
          
         
       
     
     The algorithm is initiated at Block  202  and proceeds to Block  204 . If the engine is running at Block  204 , control passes to Block  206 . If the brake pedal induced master brake cylinder pressure at Block  206  is less than NPBRKENABLEPRESS, control passes to Block  208 . If there is no chassis control activity, as determined by, for example, the ESC, ABS, or traction control systems, control passes to Block  210 . In the case where the engine is not running at Block  204  or the brake pedal induced master brake cylinder pressure at Block  206  is greater than NPBRKENABLEPRESS or a chassis control activity at Block  208  is occurring wherein an electronic control (i.e., ESC, ABS, or traction control systems) of the motor vehicle is sensing a tracking instability for which the electronic control provides a pre-programmed stability control response, control is passed to Block  212 . At Block  212 , the inside rear brake is released at QNPPRESSURERAMP-DOWNRATE and control then passes to Block  204 . 
     At Block  210 , if the time in a forward or reverse gear is greater than NPMINGEARTIME, control passes to Block  214 . At Block  214 , if the steering wheel position is greater than NPHWPOSITION, control passes to Block  216 . At Block  216 , if the vehicle speed is between NPMINSPEED and NPMAXSPEED, control passes to Block  218 . At Block  218 , if the throttle position is between NPMINTHROT and NPMAXTHROT, control passes to Block  220 . 
     However, if at Block  210  the time in a forward or reverse gear is less than NPMINGEARTIME or at Block  214  the steering wheel position is less than NPHWPOSITION or at Block  216  the vehicle speed is not between NPMINSPEED and NPMAXSPEED or at Block  218  the throttle position is not between NPMINTHROT and NPMAXTHROT, control passes to Block  222 . At Block  222 , the inside rear brake is released at NPPRESSURE-RAMPDOWNRATE and control then passes to Block  204 . 
     At Block  220 , the appropriate rear wheel to brake, the inside rear wheel of the turn, is selected using, for example, steering wheel angle position, and control passes to Block  223 . 
     At Block  223 , if the wheel slip of the selected rear wheel to brake is greater than NPMAXSLIP, then control passes to Block  222  whereat the inside rear brake is released at NPPRESSURE-RAMPDOWNRATE and control then passes to Block  204 ; if not, control passes to Block  224 . In this regard, “wheel slip” of a wheel during vehicle movement ranges between 100 percent when the wheel is locked (nonrotating) and zero percent when the wheel is freely rotating, and is defined by the expression: (wheel free rotation speed minus actual wheel rotation speed) divided by wheel free rotation speed. 
     At Block  224 , if the wheel slip of the selected rear wheel to brake is not between NPMINSLIP and NPMAXSLIP, then control passes to Block  226 . 
     At Block  226 , if the estimated brake pressure is less than NPMAXPRESS, control passes to Block  228 . At Block  228 , the brake of the selected rear wheel is applied at NPPRESSURERAMPUPRATE. The estimated brake pressure and wheel slip of the selected rear wheel to brake are calculated by the ESC control system. The ESC control system uses the master brake cylinder pressure sensor, valve control information, and wheel speed sensors to continuously estimate these parameters. 
     At Block  224 , if the wheel slip of the selected rear wheel to brake is between NPMINSLIP and NPMAXSLIP, control passes to Block  230  whereat the brake pressure of the selected rear wheel to brake is held at its present level and control then passes to Block  204 . At Block  226 , if the estimated brake pressure is greater than NPMAXPRESS, control passes to Block  232  whereat the brake pressure of the selected rear wheel to brake is held at NPMAXPRESS and control then passes to Block  204 . 
       FIG. 3  is a pictorial view of an implementation of a first parking example  300  according to the present invention. In  FIG. 3 , a motor vehicle  302  is shown pulling forward into a parking place  304 . The method according to the present invention shortens the turn radius of the vehicle  302  depicted by solid line curved path  306  as compared to a conventional turn radius depicted by dashed line curved path  308  which otherwise would be traversed by the vehicle. 
       FIG. 4  is a pictorial view of an implementation of a second parking example  400  according to the present invention. In  FIG. 4 , a motor vehicle  402  is shown backing into a parking place  404 . The method according to the present invention shortens the turn radius of the vehicle  402  depicted by solid line curved path  406  as compared to a conventional turn radius depicted by dashed line curved path  408  which otherwise would be traversed by the vehicle. 
     To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.