Abstract:
The purpose of the present invention is to provide a neutral control method and a neutral controller for an automatic transmission which improves fuel efficiency and driving characteristics. 
     According to the present invention, the neutral control method for the automatic transmission includes initiating the neutral control after every predetermined delay time, which begins with the neutral initiation conditions being satisfied, and continuing the neutral control as long as the neutral control initiation conditions remain satisfied. The neutral control ends when the neutral control initiation conditions are no longer satisfied.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a neutral controller for an automobile automatic transmission, and a method thereof. More particularly, the present invention relates to the neutral controller that initiate the neutral control after a predetermined period beginning when the neutral control initiation conditions are satisfied, and the method thereof. 
     2. Description of Prior Art 
     A neutral controller and a method thereof for an automobile automatic transmission are disclosed by Tokko No. Sho 63-33024, Tokko No. Sho 63-35869 and Tokko No. Sho 63-33585. The prior art is more specifically a neutral controller that automatically puts an automatic transmission into a neutral position when the accelerator is OFF, that is, the throttle is closed and the vehicle is stopped. In the prior art, an engine load and fuel consumption rate may be reduced by automatically putting a gear in a neutral position when the gear select lever is in the D (drive) position, the throttle valve is closed, and the vehicle is stopped. 
     For a general automatic transmission, application of the brake is added to the above-listed conditions to permit the vehicle to move during idling (so-called creeping). Then, the automatic transmission is put in the neutral position only when the brake is applied. Therefore, the conditions that cause the automatic transmission to initiate the neutral position (neutral control) include the gear select lever is in the D position, the throttle is closed completely, the vehicle is stopped, and the brake is applied. 
     It is generally known to program the neutral control so that it does not start for a predetermined delay time after all the conditions are satisfied. This is because it must be confirmed that the conditions are satisfied, and the automobile is not just in a temporary operation. This assumes the neutral control is not unintentionally initiated. 
     The neutral control is cancelled when any one of the above conditions is not satisfied, so that the operator may promptly accelerate the vehicle as he or she wishes. As mentioned above, the neutral control is initiated after the delay time beginning when the initiation conditions are satisfied, and is cancelled when any one condition is not satisfied. Thus, the vehicle may be operated according to the operator&#39;s intention. 
     In the prior art, it improves fuel efficiency to shorten the delay time as much as possible, that is, initiate the neutral control as soon as possible. Regarding real efficiency, the operator does not feel any inconsistency with a short delay time when he stops the vehicle at the traffic light and starts the vehicle again in his normal running conditions. This is because the vehicle stays still for a rather long time while waiting for the traffic light. 
     However, when slow running and stopping is alternately repeated, such as in a case of a traffic jam, the neutral control is initiated and cancelled during the stop. Under these conditions, the operator notices the vehicle&#39;s diminished driving characteristics because a transmitted torque change (a shift shock analogue) is often caused at the cancellation of the neutral control. The transmitted torque change is also often caused when the operator repeatedly operates the vehicle by creeping and brake pumping, such as when parking in a garage. 
     Even after the neutral control is initiated, such as when waiting for a stop traffic light to change, the neutral control may be cancelled when the operator unintentionally releases the brake. The neutral control is resumed when the operator applies the brake again, causing transmitted torque change. It is possible to avoid these by lengthening the delay time before the neutral control initiation. However, that diminishes the improving effect on the fuel efficiency. In the prior art, the improvement of fuel efficiency and the improvement of driving characteristics in the traffic congestion are mutually exclusive. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide a neutral control method for an automatic transmission that overcomes the drawback of the prior art, in particular, improves both fuel efficiency and driving characteristics. 
     The present invention of the neutral control method for the automatic transmission, including the step of initiating the neutral control after the predetermined delay time beginning when the neutral initiation conditions are satisfied, comprises the step of resetting the delay time depending on the vehicle running state (or operating conditions) before the neutral control initiation. 
     It is a purpose of the present invention to improve driving characteristics during a traffic jam by preventing the frequent neutral-control initiation-and-cancellation repetition. This is achieved by resetting (lengthening) the predetermined delay time after the controller determines that the vehicle is running in a traffic jam, with input. 
     If the controller determines that the vehicle is running and stopping repeatedly in a regular traffic condition with input from the vehicle operation conditions, the delay time is set in an appropriate length (i.e. shorter than that in the traffic jam), before the neutral control initiation, so that the neutral control is promptly initiated. This altered delay time reduces the fuel consumption rate during a vehicle stop for a traffic light, since the duration of a traffic light stop may be forecast. 
     The vehicle operation conditions include the vehicle speed and the throttle opening degree. During a traffic jam, the vehicle speed tends to be lower than a certain value and the throttle opening degree tends to be less than a certain value. Therefore, it is possible to determine that the vehicle is operating in a traffic jam if the vehicle speed does not exceed a predetermined value (or threshold) or if the throttle opening degree is lower than a predetermined value (or threshold). Once determined that the vehicle operating an a traffic jam, the delay time may be reset longer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of the neutral control system according to a preferred embodiment of the present invention. 
     FIG. 2 is a schematic diagram of the system including the neutral controller of a preferred embodiment of the present invention. 
     FIG. 3 is a flow chart to set a delay time of a preferred embodiment of the present invention. 
     FIG. 4 is a flow chart to determine initiation of the neutral control according to a preferred embodiment of the present invention. 
     FIG. 5 is a flow chart for the neutral control of a preferred embodiment of the present invention. 
     FIG. 6 is a graph to show the relationship between the line pressure and the duty ratio signal to the line pressure solenoid. 
     FIG. 7 is a time chart for a preferred embodiment of the neutral control of the present invention. FIG.  7 (A) shows a change of the throttle opening degree (equivalent to the engine load) against time. FIG.  7 (B) shows a change of the vehicle speed against time. FIG.  7 (C) shows a change of the brake application against time. FIG.  7 (D) shows a change of the shift position against time. FIG.  7 (E) shows a change of the continuous time (or duration) when the neutral control initiation conditions are satisfied. FIG.  7 (F) shows a change between under-control and out-of control of the neutral control. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now in more detail to the drawings, in which like numerals refer to like elements throughout the several views, a preferred embodiment of the present invention is described. 
     The Whole System 
     A system block diagram of a preferred embodiment of the present invention is illustrated in FIG.  2 . The system comprises an automatic transmission  8 , an engine  2  which transmits driving force or torque to the automatic transmission  8 , and a main controller  1  which controls the automatic transmission  8 . The automatic transmission  8  is equipped with a shift position switch  5 , an input-shaft revolution sensor  11 , a vehicle speed sensor  4 , and an oil temperature sensor  10 . The automatic transmission  8  is also equipped with a line pressure solenoid  9 , a first shift solenoid  6 , a second shift solenoid  7 , and a lock-up solenoid  12 . 
     The engine  2  is equipped with an engine revolution sensor (crank angle sensor)  13  and a throttle opening degree sensor  3 . The main controller  1  receives a throttle opening degree signal from the throttle opening degree sensor  3  that detects throttle opening degree (equivalent to the load of the engine  2 ), a vehicle speed signal from the vehicle speed sensor  4  that detects the vehicle speed, a shift position signal from the shift position switch  5  that detects the shift position, an oil temperature signal from the oil temperature sensor  10  that detects the temperature of the hydraulic fluid, a revolution speed signal from the input-shaft revolution sensor  11  that detects the revolution speed of the input-shaft from the torque converter for the automatic transmission, engine revolution speed signal from the engine revolution speed sensor (crank angle sensor)  13  that detects an engine revolution speed, and a brake signal from the brake switch  14  that detects brake operation status. 
     The main controller transmits shift control signals to the first shift solenoid  6  and the second shift solenoid  7 . Then, each shift solenoid  6 ,  7  operates to select and engage certain friction elements of the automatic transmission  8  so that the automatic gear shifting may be controlled. During the neutral control described blew, the second gear is set in order to prevent rolling down the hill. Thus, the driving torque for forward travel is not transmitted, but reverse revolution caused by rolling back is prevented. 
     The main controller  1  transmits a line pressure control signal to the line pressure solenoid  9  to control the line pressure that controls each shift solenoid  6 ,  7 . Therefore, the line pressure is controlled for the engagement of the friction elements. 
     During the neutral control, the line pressure solenoid  9  provides a low clutch (not shown) with the hydraulic pressure, which has reduced pressure from the line pressure. With the pressure the low clutch is kept in a partially engaged state. Here, partially engaged is understood to mean to torque is partially transmitted by friction although opposing plates rotate with a differential revolution speed. When the vehicle runs at a constant speed greater than a threshold speed, the main controller  1  transmits a s torque-converter-direct-connection-clutch-control signal to the lock-up solenoid  12 . If the transmission is in third or fourth gear, the torque-converter-direct-connection clutch (not shown) is engaged. If the transmission is in first or second gear, the hydraulic pressure provided to the low clutch is alternatively controlled by normal line pressure or reduced line pressure mentioned above. 
     Main Controller 
     A block diagram of the main controller  1  of the preferred embodiment of the present invention is illustrated in FIG.  1 . The main controller  1  comprises a control-initiation-determination device (or a control-initiation-determination means)  1   b,  a vehicle-running-state-memory device (or a vehicle-running-state-memory means)  1   c,  a delay-time-setting device (or a delay-time-setting means)  1   d  that sets the delay time before the initiation of the neutral control, a neutral controller (or a neutral control means)  1   a  that conducts the neutral control from the information transmitted by these devices (or means)  1   b,    1   c,    1   d.  The control initiation determination device  1   b  determines whether the initiation conditions for the neutral control are satisfied with input including the throttle opening degree (engine load) detected by the throttle opening degree sensor  3 , the vehicle speed detected by the vehicle speed sensor  4 , the brake operation state determined from the brake switch  14 , and the shift position determined from the shift position switch  5 . 
     Further, the vehicle-running-state-memory device  1   c  determines whether the vehicle speed exceeds the predetermined value (or threshold) after the previous neutral control is cancelled or ended, and stores the results. The delay-time-setting device  1   d  sets the delay time based on the results determined by the vehicle-running-state-memory device  1   c.    
     The neutral controller  1   a  initiates the neutral control after the delay time set, beginning from when the neutral-control-initiation conditions mentioned above are satisfied and confirmed. Once the neutral control is initiated, a shift signal to shift the transmission to the second gear is transmitted to both the first shift solenoid  6  and the second shift solenoid  7 . Then, a signal to switch the line pressure provided for the low clutch from a normal line pressure to the reduced line pressure, is transmitted to the lock-up solenoid  12 . 
     The main controller  1  transmits a signal to the line pressure solenoid  9  to adjust the revolution speed difference closer to a certain value between the engine revolution speed (the input-shaft revolution speed of the torque converter) detected by the engine revolution sensor (crank angle sensor)  13  and the input shaft revolution speed (output-shaft revolution speed of the torque converter) detected by the input-shaft revolution sensor  11  of the automatic transmission  8 . 
     Actual Neutral Control 
     FIGS. 3,  4  and  5  are flow charts which illustrate the steps for the neutral control of the preferred embodiment according to the present invention. The process flow is repeatedly started at a certain interval to repeat the sequence of steps in a manner known to those skilled in the art. 
     Acquisition of the Vehicle Running State 
     The vehicle-running-state-memory device  1   c,  best illustrated in FIG. 1, first receives the vehicle-running-state information from each sensor. More specifically, as shown in FIG. 3, the throttle opening degree, which is equivalent to the engine load, is received from the signal transmitted by the throttle opening degree sensor  3  in the step S 100 . The vehicle speed information is determined from the signal transmitted by the vehicle speed sensor  4  in the step S 101 . The brake application state is determined from the signal transmitted by the brake switch  14  in step S 102 . The shift position is determined from the signal transmitted by the shift position switch  5  in step S 103 . The engine revolution speed is determined from the signal transmitted by the engine revolution sensor (crank angle sensor)  13  in the step S 104 . The input-shaft revolution speed of the automatic transmission  8  is determined from the signal transmitted by the input-shaft revolution sensor (turbine revolution sensor)  11  in step S 105 . 
     Delay Time Setting 
     Now, the delay time setting is explained in detail. It is determined whether the vehicle speed exceeds the preset vehicle speed value V or whether the engine load exceeds the preset load value L in the step S 106 . If either value is exceeded, it is determined that the vehicle is not running in a traffic jam, and the program proceeds to the step S 107  to substitute the value 1(one) in a control flag F (let F=1) and further proceeds to the step S 108 . On the other hand, if at step S 106  neither value is exceeded, the program skips the step S 107  and proceeds to the step S 108 . This is because the vehicle may continuously creep in a heavy traffic. 
     Now, in steps S 108 , S 109  and S 110 , the delay time is determined by the value of F. When F=1, the delay time is set for the delay time DT 1 , which is rather short, since it is determined that the vehicle is not running in a traffic jam. When F=0, the delay time is set for the delay time DT 2 , which is rather long, since it is determined that the vehicle is caught in a traffic jam. Then, the program proceeds to the next step best illustrated in FIG.  4 . 
     Determination of Neutral Control Initiation Condition Satisfaction 
     As illustrated in FIG. 4, it is determined whether the neutral control initiation conditions are satisfied in steps S 111  through S 114 . More specifically, the control-initiation-determination-device determines whether the throttle opening degree is completely closed and the engine is in an idle state (step S 111 ), whether the vehicle is stopped (step S 112 ), whether the brake is applied (step S 113 ) and whether the shift lever is in the D position (step S 114 ). The neutral control initiation conditions are satisfied when the answer to each of these questions is “yes”. Otherwise, the neutral control initiation conditions are not satisfied. In determining the throttle opening degree, the completely closed state may include that state wherein the throttle opening degree is equal to or less than a certain value, as well as the completely closed state. The state wherein the vehicle is stopped may include when the vehicle speed is equal to or less than a certain value near 0 km/h as well as the completely stopped state. 
     If the neutral control initiation conditions are satisfied, the process proceeds to the step S 115  to count a duration time, i.e. the period of time when the conditions are satisfied (step S 115 ) and then proceeds to the next step S 117 . If the neutral-control-initiation conditions are not satisfied, the process proceeds to the step S 116  to reset the duration time and then proceeds to the step of return shown in FIG.  5 . When the neutral control initiation conditions are satisfied, it is determined whether the duration time exceeds a preset value of the delay time (step S 117 ). If the duration time exceeds the preset value, the process proceeds to the next step to initiate the neutral control. If it does not, the process proceeds to the step of return shown in FIG.  5 . 
     Neutral Control 
     In the step S 118  the control flag F is cleared (F=0) and the vehicle running state, after the neutral control is cancelled or ended, is stored in the vehicle running state memory device  1   c.  In the step S 119  the first shift solenoid is set OFF and the second shift solenoid is set ON so that the transmission may be put into second gear. In this manner, a one-way clutch operates to prevent the output-shaft from revolving backward so that the vehicle may be prevented from rolling back on the hill, although the creep torque is decreased due to the neutral control. 
     In the step S 120  the neutral controller  1   a  (shown in FIG. 1) transmits a control signal of 95% duty ratio to the lock-up solenoid, setting the line pressure greater if the duty ratio is higher. In this manner, the hydraulic pressure provided to the low clutch is switched from the regular line pressure to a slightly reduced line pressure. 
     The line pressure solenoid  9  (shown in FIGS. 1 and 2) is controlled in the steps S 121  through S 125 . In the step S 121 , it is first determined whether or not an absolute value of differential revolution speed, as calculated by the difference between the engine revolution speed and the input-shaft revolution speed of the shift gear mechanism (the differential revolution speed between the input- and output-shafts), is greater than a desired value. If the absolute value of differential revolution speed is greater than the desired value, it is determined that the hydraulic pressure provided to the low clutch is too high and the process proceeds to the step S 122  to decrease the control value for the line pressure and to reduce the hydraulic pressure provided to the low clutch. On the other hand, if the differential revolution speed is less than the desired value, it is determined that the hydraulic pressure provided to the low clutch is too low and the process proceeds to the step S 123  to increase the control value for the line pressure. Thus, the line pressure is feedback-controlled to bring the differential revolution speed between the input- and the output-shafts of the torque converter closer to the desired value so that the low clutch may be kept in a partially engaged state. 
     In the step S 124 , the line pressure control value is converted to the control duty ratio as shown in FIG.  6 . The relation between the line pressure and the control duty ratio is not completely linear, but is non-linear in some region as illustrated in FIG.  6 . Therefore, if the line pressure is feedback-controlled directly with the control duty ratio, it is not easy to adjust a gain of the feedback control in every region since the line pressure rate of change varies at the same or different rate as the duty ratio rate of change. This is why the line pressure control value is converted to the control duty ratio (S 124 ). 
     In the step S 125 , the neutral controller  1   a  (shown in FIG. 1) transmits a control signal to the line pressure solenoid  9  according to the control duty ratio of the step S 124 . When the neutral control is not made, other controls (not shown) such as shift control, lock-up control, line pressure control and so on may be made separately. 
     Now, the neutral control operation will be described according to the time chart shown in FIG.  7 . The time chart illustrates a certain running state. At the time T 0 , the vehicle is determined to be in a normal running state and not in a traffic jam. When, the throttle is closed, the vehicle speed reduces to and becomes zero, which means the vehicle is stopped. Then, the neutral-control-initiation conditions are satisfied at the time T 1 . After the delay time DT 1 , the neutral control is initiated as shown by T 2  in FIG.  7 (E). The delay time DT 1  is the delay time for a non-traffic-jam state. The neutral control is ended due to the non-brake-application at the time T 3 . 
     Later, the neutral-control-initiation conditions are satisfied again at the time T 4 . Because neither the engine load exceeds the preset value L nor the vehicle speed exceeds the preset value V since the time T 3 , the vehicle is determined to be running in a traffic jam and the delay time is set for the delay time DT 2 . Therefore, the neutral control is not initiated at the time T 6 , when the neutral-control-initiation conditions are not satisfied, since it is before passing the delay time DT 2 . Regarding the neutral control system of the prior art, the neutral control could be made as shown in the dotted line from the time T 5  to T 6  in FIG.  7 (F) since the delay time is DT 1 . 
     Thus, according to the present invention, the neutral control is not made when the vehicle is stopped for a short period during the slow running and stopping of a traffic jam. The neutral-control-initiation conditions are satisfied at the time T 7 . Since the delay time is DT 2  like the previous case, the neutral control is initiated at the time T 8  after DT 2  is passed. The neutral control is ended at the time T 9  because the shift lever is in a position other than D. 
     As mentioned so far, the neutral control is not conducted when the vehicle is stopped for a short period during the slow running and stopping of a traffic jam. 
     In the preferred embodiment of the present invention, the vehicle is determined to be running in a traffic jam when neither the vehicle speed nor the throttle opening degree (engine load) exceeds certain preset values. Other means may be employed to determine whether the vehicle is running in a traffic jam or not. For example, traffic jam conditions may be determined when the average vehicle speed and the average engine load, which are averaged for a predetermined period of time before the neutral control initiation conditions are satisfied, are equal to or less than certain predetermined values (or thresholds). 
     Achievement 
     As described above, the period before initiating the neutral control should vary depending on the vehicle running state (e.g. slow running in a heavy traffic). Therefore, when the vehicle is stopped after running at speed more than a certain value like running in an uncongested area, the neutral control is started (or initiated) after a short delay time so as to improve the fuel efficiency. On the other hand, when extremely low speed running and stopping are alternately repeated, such as will occur during a traffic jam, the neutral control is not started (or initiated) for short stoppings. Thus, the driving torque change around the end of neutral control is much less frequently caused to keep good driving characteristics. According to the present invention, it becomes possible to improve both fuel efficiency and driving characteristics. 
     According to the present invention, it may be determined whether the vehicle is in normal running or traffic-jam conditions by determining the throttle opening degree and the vehicle speed according to the present invention. The throttle opening degree and the vehicle speed may be acquired from the throttle opening degree sensor and the vehicle speed sensor originally equipped for the conventional vehicle. Therefore, a new equipment such as a new sensor is not necessarily needed to perform the neutral control.