Abstract:
A hill-hold method and system for a vehicle with manual transmission provides automated brake release timing when the vehicle&#39;s clutch is still disengaged to minimize or even prevent backward coasting of such a vehicle on a non-zero grade or hill by delaying full release of the brakes when the vehicle operator is in the transition of releasing the brake pedal and moving to the accelerator pedal.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to vehicular motion control. More particularly, the invention pertains to provision of an automated hill-hold function to inhibit backward coasting of a vehicle with a manual transmission. 
       BACKGROUND OF THE INVENTION 
       [0002]    A well-known problem with vehicles equipped with manual transmissions and clutches occurs when the vehicle comes to a stop on a hill or non-zero road grade. When the driver wishes to start out again in this circumstance, he/she must move one foot off the brake pedal to depress the accelerator while starting to engage the clutch. Often the brake will fully release before the clutch is engaged, resulting in undesired backward rolling of the vehicle down the hill. 
         [0003]    There is a need in the art for an automatically implemented hill-hold function for preventing undesired movement of a vehicle with a manual transmission upon brake release prior to full clutch activation. 
       SUMMARY OF THE INVENTION 
       [0004]    In one aspect of the invention, a method of providing a hill-hold function for a vehicle equipped with a manual transmission and clutch includes providing a selectively variable orifice in a brake hydraulic line of the vehicle, operative to fully close at zero vehicle speed and actuation of a brake pedal of the vehicle. The variable orifice is opened at a first rate upon detection of release of the brake pedal while the clutch is disengaged and the throttle is starting to increase. The variable orifice is then opened at a second rate higher than the first rate upon detection of clutch activation. 
         [0005]    In another aspect of the invention, an arrangement for providing a hill-hold function in a vehicle equipped with a manual transmission and clutch includes a selectively variable orifice positioned in a hydraulic brake fluid line of the vehicle. An auxiliary brake controller is coupled to a control input of the selectively variable orifice and is operative to open and close the selectively variable orifice at a rate determined by a signal presented to the control input. An electronic vehicle control module is coupled to a clutch pedal position sensor, a throttle sensor, a vehicle speed sensor and a brake pedal sensor, each coupled to a respective input of the electronic vehicle control module. The electronic vehicle control module is operative to activate and deactivate the auxiliary brake controller as a function of inputs received from one or more sensors coupled to the vehicle control module inputs. 
         [0006]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0008]      FIG. 1  is a block diagram of a system arranged for providing a vehicle hill-hold function is accordance with the teachings of the invention; 
           [0009]      FIG. 2  is a block diagram of an alternative embodiment of a system arranged for providing a vehicle hill-hold function in accordance with the teachings of the invention; 
           [0010]      FIG. 3  is a flow chart of a hill-hold method implemented by the system of  FIG. 1 ; and 
           [0011]      FIG. 4  is a flow chart of a hill-hold method implemented by the system of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0012]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0013]    The approach of the instant invention is to automatically hold the hydraulic brake line pressure for a predetermined time period when the brake pedal is initially released and to then modulate that line pressure down to zero as the brake pedal is fully released. As will be shown, this will require a selectively variable orifice, preferably an electrically variable orifice, associated with a brake hydraulic line in the vehicle which would be normally open, goes full closed at zero vehicle speed, opens at a reduced rate as throttle speed begins to increase and finally opens at a maximum rate when the clutch switch is triggered evidencing reengagement of the clutch. If the orifice response time is fast enough, it could open with the clutch switch deactivation. The clutch switch position should be calibrated to allow enough time for even a slower responding orifice to release the brakes. 
         [0014]    It may be possible to use current ABS hydraulics to serve such a function rather than adding a new single variable or on/off orifice upstream of the ABS circuit. However, ABS systems are not typically engineered to apply and hold hydraulic pressure for extended time periods. 
         [0015]    The basic embodiments are disclosed herein. The first is a more economical approach and does not use a grade sensor. The second uses a grade sensor and only activates an auxiliary brake control when a non-level road surface is detected. 
         [0016]    With reference to  FIG. 1 , the economical system is depicted. System  100  includes a selectively variable orifice  118  positioned in a hydraulic fluid line  116  of the vehicle. Variable orifice  118  has a control input  105  coupled to the orifice between the orifice and an auxiliary brake control unit  104 . 
         [0017]    A power train control module or a specialized electronic control module for the vehicle  108  activates and deactivates auxiliary brake control  104  in accordance with a vehicle speed sensor  102 , a clutch pedal sensor  110 , a throttle sensor  112  and a brake pedal sensor  114 , each of these sensors being coupled to an input of power train control module  108 . 
         [0018]    In production vehicles equipped with cruise control, the cruise disconnect switch associated with the clutch in a manual transmission could be used as the clutch pedal sensor. It will be apparent to those skilled in the art, however, that a separate clutch pedal activation sensor  110  could be provided. 
         [0019]    With the system as arranged in  FIG. 1 , the method for activating a hill-hold function is performed by power train control module  108  in accordance with the flow chart set forth in  FIG. 3 . The routine is entered at  302  and initially a test is performed to determine whether the brake pedal is beginning to release at step  304 . This test is maintained as long as the answer is no. If the brake pedal is beginning to release, then at step  306  a test is performed to determine whether the clutch is disengaged by monitoring clutch pedal sensor  110  of  FIG. 1 . This test is continued until the answer is yes, at which point in step  308  the controller  108  of  FIG. 1  monitors the throttle sensor  112  to determine if the throttle is beginning to increase. This test is continued until the answer is yes, at which point at step  310  the selectively variable orifice  118  of  FIG. 1  is opened at a first relatively slow rate. This can be accomplished via pulse width modulation of an actuation signal on control input  105 . While opening the orifice at the first rate in step  310 , controller  108  is monitoring for clutch engagement at step  312 . When it has been determined from clutch pedal sensor  110  of  FIG. 1  that the clutch has become engaged, then the variable orifice  118  is opened at a second faster rate than the first rate. Hence, during that transition period when the operator is switching from the brake pedal to the accelerator pedal, release of full braking is delayed to prevent undesirable backward rolling until the clutch is fully engaged. 
         [0020]    With reference to  FIG. 2 , a system is set forth which is only activated when a grade or hill is detected beneath the vehicle. This requires an additional grade or wheel sensor  206  which is monitored by power train control module  208 . Similarly to  FIG. 1 , the remaining elements are a hydraulic brake line  216  containing a variable orifice  218  which is selectively opened and closed in accordance with a signal appearing at control input  205  emanating from auxiliary brake controller  204 . 
         [0021]    Power train control module  208  implements the hill-hold function in accordance with various vehicle states as presented by vehicle speed sensor  102 , clutch pedal sensor  210 , throttle sensor  212  and brake pedal sensor  214 . 
         [0022]    Power train control module  208  of system  200  of  FIG. 2  implements a hill-hold function in accordance with the method set forth in the flow chart of  FIG. 4 . The routine is entered at  402  and controller  208  monitors for initiation of brake pedal release at step  404 . For as long as the answer is no, the test continues. Upon detection of brake pedal release, the routine proceeds to step  406  where a test is made for clutch disengagement by monitoring clutch pedal sensor  210  of  FIG. 2 . This test is likewise continued until the answer is yes, whereupon at step  408  controller  208  monitors throttle sensor  212  to determine if the throttle is beginning to increase. Upon a positive result of the test at  408 , the routine proceeds to step  410  where the grade or wheel sensor  206  is monitored by a control unit  208  to determine if the vehicle is presently on a level road surface. This test may be implemented using either a grade sensor or a wheel sensor for detecting reverse motion of the vehicle&#39;s wheels. For example, existing ABS wheel speed sensors could be utilized thus avoiding the necessity for inclusion of an additional grade sensor into the system. Using the reverse wheel motion detection approach would allow a slight amount of rollback which could be a driver irritant. On the other hand, such slight rollback could be justified by arguing that drivers are used to manual transmission cars rolling backwards on a hill, and that they could get used to the feature and even appreciate the fact that the hill-hold function is being implemented by the small amount of rollback which would then cease. 
         [0023]    In any event, whichever approach is used, if a level road surface is detected then the routine skips to the last step  416  where the variable orifice  218  would be opened at the second higher rate immediately. If a level road surface is not present as detected by test  410 , then at step  412  orifice  218  is opened at the first slow rate in effect activating the hill-hold function. This first rate is maintained during test  414  for so long as the clutch has not reengaged. If the clutch has engaged, then the routine proceed to step  416  for opening the orifice  218  at the faster rate. 
         [0024]    Under either the economical or the more complicated approaches set forth above, when the brake pedal is released and the clutch pedal is still depressed the hill-hold algorithms would maintain caliper pressure by tuning the first and second orifice release rates to the engine speed acceleration rate from idle. 
         [0025]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.