Method for controlling AMT system including after transmission gear change fuel control.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to vehicle automatic and semiautomatic power transmission systems providing a plurality of gear reduction ratios, such as automatic mechanical transmissions (i.e. "AMTs"), and, to control systems and methods therefor. In particular, the present invention relates to control systems and methods for automatic mechanical transmission systems wherein gear selection and shift decisions are made and/or executed based upon measured and/or calculated parameters such as vehicle or transmission output shaft speed, transmission input shaft speed, engine speed, throttle position, rate of change of throttle position, rate of change of vehicle and/or engine speed and the like. More particularly, the present invention relates to a method for controlling an AMT system after completion of a transmission gear change operation including controlling the rate and manner of returning control of the fuel supply to the engine to the vehicle operator.

Description of the Prior Art

The use of automatic transmissions of both the automatic mechanical type utilizing positive clutches and of the planetary gear type utilizing frictional clutches is well known in the prior art as are control systems therefor. Electronic control systems utilizing discrete logic circuits and/or software controlled microprocessors for automatic transmissions wherein gear selection and shift decisions are made based upon certain measured and/or calculated parameters such as vehicle speed (or transmission output shaft speed), transmission input shaft speed, engine speed, rate of change of vehicle speed, rate of change of engine speed, throttle position, rate of change of throttle position, full depression of the throttle (i.e. "kickdown"), actuation of the braking mechanism, currently engaged gear ratio, and the like are known in the prior art. Examples of such automatic /semiautomatic transmission control systems for vehicles may be seen by reference to U.S. Patent Nos. 4,36l,060; 4,­55l,802; 4,527,447; 4,493,228; 4,425,620; 4,463,427; 4,08l,­065; 4,073,203; 4,253,348; 4,038,889; 4,226,295; 3,776,048, 4,208,929; 4,039,06l; 3,974,720; 3,478,85l and 3,942,393, the disclosures of which are all hereby incorporated by reference.

Automatic control systems/subsystems for automatically controlling the engagement and disengagement of AMT system vehicle master clutches are known in the prior art as may be seen by reference to U.S. Patent Nos. 4,08l,065; 4,40l,­200; 4,4l3,7l4; 4,432,445, 4,509,625 and 4,576,263, the disclosures of all of which are hereby incorporated by reference. One control system for adjusting fuel control in view of throttle setting is, by way of example only, illustrated in U.S. Patent No. 4,493,228, the disclosure of which is hereby incorporated by reference.

While the above referenced automatic/semi- automatic transmission control systems are effective to control the supply of fuel to the engine under most conditions, under certain conditions, if fuel is allowed to be supplied to the engine in accordance with throttle pedal setting and/or if allowing operator control of the supply of fuel to the engine after a shift is not accomplished as rapidly as possible without causing driveline jolts, the control of the engine may be objectionably sluggish and/or may not provide acceptably smooth vehicle operation.

Summary of the Invention

In accordance with the present invention, the drawbacks of the prior art have been overcome or minimized by providing a control system, preferably an electronic control system, and control method, for automatic/semi-­automatic mechanical transmission systems wherein throttle setting decisions are made and/or executed based upon measured and/or calculated parameters including at least input signals indicative of throttle position, last throttle setting, engine speed and currently engaged gear ratio. Other inputs/parameters, such as signals indicative of transmission input shaft speed, transmission output shaft speed, rate of change of throttle position, condition of the master clutch, operation of the vehicle brakes, and the like are also utilized to make decisions for control of the AMT system.

The predetermined logic rules or programs by which the various input signals are processed include a method for detecting completion of a transmission gear change operation, the current throttle pedal setting, the current commanded throttle setting and for calculating a minimum allowable initial throttle setting value, such as the throttle setting necessary to maintain current engine speed under no load conditions.

The throttle setting is compared to the throttle pedal position. If throttle setting is equal to or greater than throttle pedal position, throttle setting is set equal to throttle pedal position.

If throttle pedal position is greater than throttle setting, throttle setting is first set equal to the lesser of the minimum allowable throttle setting value or throttle position and, thereafter, until throttle setting equals throttle pedal position, throttle setting is set equal to the lesser of throttle pedal position or the value of the sum of a constant related to currently engaged gear ratio added to the product of the last throttle setting multiplied by a constant greater than one. The control of fuel will remain in this mode until the throttle setting equals the throttle pedal position or until a different mode of fuel control is required due to initiation of a gear shift, or the like.

Accordingly, it is an object of the present invention to provide a new and improved control method for automatic mechanical transmission systems which involves sensing and identifying a return of engine fuel control to the operator and controlling the rate and manner of allowing the throttle setting command output signal to equal the throttle pedal position input signal.

BRIEF DESCRIPTION OF THE DRAWINGS

<ul id="ul0001" list-style="none"><li>FIGURE l is a schematic illustration of the components and interconnections of the automatic mechanical transmission control system of the present invention.</li><li>FIGURES 2A-2B are symbolic illustrations, in the form of a flow chart, illustrating the preferred manner of practicing the method of the present invention.</li></ul>

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGURE l schematically illustrates an automatic mechanical transmission system l0 including an automatic multi-speed compound change gear transmission l2 driven by a throttle controlled engine l4, such as a well known diesel engine, through a master clutch l6. An engine brake, such as an exhaust brake l7 for retarding the rotational speed of engine l4 and/or an input shaft brake l8 which is effective to apply a retarding force to the input shaft upon disengagement of master clutch l6 may be provided as is known in the prior art. The output of automatic transmission l2 is output shaft 20 which is adopted for driving connection to an appropriate vehicle component such as the differential of a drive axle, a transfer case or the like as is well known in the prior art.

The above mentioned power train components are acted upon and monitored by several devices, each of which will be discussed in greater detail below. These devices include a throttle position or throttle opening monitor assembly 22 which senses the position of the operator controlled vehicle throttle or other fuel throttling device 24, a fuel control device 26 for controlling the amount of fuel to be supplied to engine l4, an engine speed sensor 28 which senses the rotational speed of the engine, a clutch operator 30 which engages and disengages clutch l6 and which also supplies information as to the status of the clutch, an input brake operator 3l, a transmission input shaft speed sensor 32, a transmission operator 34 which is effective to shift the transmission l2 into a selected gear ratio and to provide a signal indicative of current transmission status, and a transmission output shaft speed sensor 36. A vehicle brake monitor 38 senses actuation of vehicle brake pedal 40. Alternatively, the engaged gear ratio of transmission 11 may be calculated by comparing the input shaft speed signal to the output shaft speed signal.

The above mentioned devices supply information to and/or accept commands from a central processing unit or control 42. The central processing unit 42 may include analogue and/or digital electronic calculation and logic circuitry, the specific configuration and structure of which forms no part of the present invention. The central processing unit 42 also receives information from a shift control assembly 44 by which the vehicle operator may select a reverse (R), neutral (N), or forward drive (D) mode of operation of the vehicle. An electrical power source (not shown) and/or source of pressurized fluid (not shown) provides electrical and/or pneumatic power to the various sensing, operating and/or processing units. A fault indicator or alarm 46 may display the identity of a specific fault or simply signal the existence of an unidentified fault. Drive train components and controls therefor of the type described above are known in the prior art and may be appreciated in greater detail by reference to above-mentioned U.S. Patent Nos. 4,36l,060; 3,776,048; 4,038,889 and 4,226,295.

Sensors 22, 28, 32, 36, 38 and 44 may be of any known type or construction for generating analogue or digital signals proportional to the parameter monitored thereby. Similarly, operators l7, 31, 26, 30 and 34 may be of any known electrical, pneumatic or electropneumatic type for executing operations in response to command signals from processing unit 42. Fuel control 26 will normally supply fuel to engine l4 in accordance with the operator's setting of throttle 24 but may, to synchronize the transmission during an up or down shift or to provide a smooth start from stop operation, supply a lesser (fuel dip) or greater (fuel boost) amount of fuel in accordance with commands from control unit 42. If, at completion of a fuel dip or fuel boost operation, the setting "THCMD" of the fuel control 26 differs from the setting of "THL" throttle pedal 24, the fuel control will operate in the "recovery mode", to be described in greater detail below, and the command output signal "THCMD" will be ramped up or down, as appropriate, to match the throttle setting. One control system for adjusting fuel control in view of throttle setting is, by way of example only, illustrated in U.S. Patent No. 4,493,­228, the disclosure of which is hereby incorporated by reference.

The purpose of the central processing unit 42 is to select, in accordance with a program (i.e. predetermined logic rules) and current or stored parameters, the optimal gear ratio at which the transmission should be operating and, if necessary, to command a gear change, or shift, into the selected optimal gear ratio based upon the current and/or stored information.

The various functions to be performed by central processing unit 42, and a preferred manner of performing same may be seen in greater detail by reference to allowed pending U.S. Patent Application Serial No. 659,ll4 filed October l0, l984, and to published Society of Automotive Engineers SAE Paper No. 83l776 published November l983, the disclosures of which are hereby incorporated by reference.

Although a fully automatic AMT system 10 is illustrated, the present invention is also applicable to semi-automatic AMT systems where the system automatically executes driver selected gear changes.

The recovery mode of fuel control 26 operation is a transition mode used to pass from one of the modes wherein the CPU 42 controls the engine fuel supply regardless of the amount of fuel requested by the operator, as would occur during a synchronization operation, to the follow mode wherein fuel control is returned to the operator, i.e. the THCMD command output signal is equal to the THL pedal position input.

Both the THCMD throttle setting command output signal and the THL throttle pedal position input signal have values which may be considered as ranging from zero percent (0%) which corresponds to the amount of fuel required to maintain the engine 14 at idle speed under no-load conditions (i.e. clutch 16 disengaged and/or transmission 12 in neutral) to one hundred percent (100%) corresponding to maximum or wide open supply of fuel to the engine.

In the recovery mode of fuel control, the control of the supply of fuel to the engine is returned to the vehicle operator as quickly as possible, to provide acceptable vehicle performance, while minimizing or eliminating unwanted driveline jerk and/or vehicle surge.

In the recovery mode of fuel control, if the throttle demand signal THL is less than the current throttle command output signal THCMD (as would be typical on a braking or coasting downshift) the throttle command output signal THCMD is set to equal the demand input signal THL and the recovery mode sequence is completed.

If the throttle demand signal THL exceeds the current fuel control command output signal THCMD (as is typical after an upshift or after a power downshift), the THCMD is first set to a calculated minimum value which is a function of current engine speed N. Preferably, this minimum value is about the magnitude of the THCMD signal required to maintain the engine 14 at current speed N under no-load conditions and is thus a safe value to begin to smoothly ramp THCMD up to THL without the necessity of starting at a zero or minimum fuel control setting.

In subsequent loops, until the command output signal THCMD equals the demand input signal THL, which signals the completion of the recovery mode of fuel control, the THCMD signal is the lesser of demand input THL or     TMCMB_C = [THCMD_L*K] + KGR where:     THCMD_L = the value of the last fuel control command output signal,     K = a weighting factor having a value greater than unity,     KGR = a weighting factor dependent upon currently engaged gear ratio, and     THCMD_C = a calculated maximum value for next fuel control command output signal.

Generally, K has a value of slightly greater than unity, such as about 1.01 to 1.10, to provide a smooth ramping up of THCMD towards THL. KGR has a relatively high value in the lower transmission gear ratios, a relatively low value in the intermediate transmission gear ratios and a relatively high value in the high transmission gear ratios. By way of example, in a twelve forward speed transmission, first through fourth gear ratios would be low gear ratios, fifth through eighth gears would be intermediate gear ratios, while ninth through twelfth would be the high gear ratios.

Briefly, in the low gear ratios, a vehicle requires a significant torque to accelerate and relatively rapid increases in fuel supply are unlikely to cause vehicle learching. Similarly, in the high gear ratios the driveline gear reduction is comparatively low and thus relatively rapidly increased fuel to the engine is unlikely to have undesireable effects on the vehicle. However, in the intermediate ratios, the gear reduction is significant and rapidly increased engine fueling, if permitted, is likely to cause torque increases of a magnitude likely to exceed that needed to smoothly accelerate the vehicle resulting in vehicle learching, driveline jolt or the like.

Accordingly, it may be seen that a method of controlling the rate at which control of fueling the engine is returned from the control logic to the vehicle operator is provided which will provide for a smooth but rapid increase of the fuel control command output signal THCMD towards the value of the demand input signal THL. If the value of the demand input signal THL exceeds the value of the command fuel control output signal THCMD, the rate of increasing the command output signal THCMD is dependent upon the currently engaged gear ratio GR and begins from a value dependent upon the then existing engine speed N. Of course, during this recovery mode, the throttle command output THCMD never exceeds the value of the operator demand input signal THL.

Although the AMT system l0 has been described as utilizing a microprocessor based control 42 and the methods and operations carried out as software modes or algorithms, it is clear that the operations can also be carried out in electronic/fluidic logic circuits comprising discrete hardware components.

Clutch operator 30 is preferably controlled by the central processing unit 42 and engages and disengages master clutch l6 generally as described in above-mentioned U.S. Pat. No. 4,08l,065. Transmission l2 may include synchronizing means, such as an accelerator and/or a brake mechanism as described in U.S. Pat. No. 3,­478,85l, hereby incorporated by reference. The transmission l2 is preferably, but not necessarily, of the twin countershaft type as is seen in U.S. Pat. No. 3,l05,395, hereby incorporated by reference.

Although the present invention has been set forth with a certain degree of particularity, it is understood the various modifications are possible without departing from the spirit and scope of the invention as hereinafter claimed.