ENGINE SPEED CONTROL FOR IMPROVED SHIFTING

Abstract: A vehicle includes a powershift transmission (12) driven by an electronically controlled engine (10). A control system momentarily modifies a magnitude of an engine speed command signal SC during a shift of the power shift transmission (12) in order to make the shift smoother and less sensitive to achieving optimum clutch engagement pressure. It also prevents an engine governor from over-reacting and causing rough shifts.

Description: ENGINE SPEED CONTROL FOR IMPROVED SHIFTING The present invention relates to method and to a control system for a vehicle having a governor controlled engine which drives a power shift transmission, the power shift transmission having a gear box which is operated by a set of pressure operated clutches which are controlled by a corresponding set of solenoid operated shift control valves which are controlled by an electronic vehicle control unit (VCU) in response to the shift command signals generated by an operator controlled shift control lever mechanism, the engine being controlled by an electronic engine control unit (ECU) which receives a speed command signal from the VCU. Powershift transmissions change speeds by disengaging one or more clutches and then engaging one or more clutches, with no interruption of power during the shift. Shift smoothness is obtained by modulating the pressure of the oncoming clutches, i.e. engaging them at low pressure. Shift smoothness is very sensitive to having the optimum engagement pressure in relation to the load being transmitted by the transmission. If the engagement pressure is too low, the vehicle may drop load or speed during the shift, if the engagement pressure is too high, the shift will be aggressive, jumpy and harsh. Under lightly loaded conditions, the typical engine governor response contributes to the poor shift. For example, during an upshift, if the engaging clutch locks up quickly, it will bring the engine speed down rapidly. The engine governor typically over-reacts to this drop in speed by quickly increasing fuel to the engine. An excess amount of fuel may then cause the engine to quickly overshoot the commanded speed. The resulting acceleration-deceleration causes the vehicle to pitch fore and aft, and produces a "jumpy" feel. Accordingly, an object of this invention is to provide a transmission and engine control system and a related method which prevents such engine governor- caused rough shifts and improves the shift quality. Accordingly, another object of this invention is to provide a transmission and engine control system and a related method which makes shift smoothness less sensitive to modulating the oncoming clutch at the optimum pressure. These and other objects are achieved by the present invention according one of the claims 1 or 12. Further advantageous arrangements and developments of the invention appear from the dependent claims. In an advantageous embodiment of the present invention a method and a control system for a vehicle is provided. The vehicle includes an engine which drives a powershift transmission. The powershift transmission has a gear box which is operated by a set of pressure operated clutches which are controlled by a corresponding set of solenoid operated shift control valves. The valves are controlled by an electronic vehicle control unit (VCU) in response to the shift command signals generated by an operator controlled shift control lever mechanism. The engine is controlled by an electronic engine control unit (ECU) which receives a speed command signal from the VCU. During an upshift the control system depressurizes at least one off-going clutch and later pressurizes at least one on- going clutch. The VCU, during a shift, abruptly modifies the magnitude of the speed command signal while the off-going clutch is being de-pressurized, and then gradually returns the magnitude of the speed command signal back to its original magnitude when the on-going clutch is fully pressurized. During an upshift, the speed command signal SC is similarly momentarily decreased at the start of the clutch swap, and is then gradually increased or ramped up. During a downshift, the speed command signal SC is similarly momentarily increased at the start of the clutch swap, and is then gradually decreased or ramped down. This strategy allows the engine to accomplish most of the change in vehicle speed, and is less dependent on proper slipping of the oncoming clutch. This also causes the engine governor to react properly to the shift, and avoids governor over-reaction. The invention and further advantageous developments and arrangements of the invention will now be described and explained in more detail by way of example and with reference to the accompanying drawings in which: Fig. 1 is a simplified schematic diagram of a vehicle transmission/engine drive and control system of the present invention; and Fig. 2 is a signal timing diagram illustrating the time behavior of the speed command signal in relation to the operation of the transmission control clutches. As shown in FIG. 1 , a vehicle power train includes an engine 10 which drives a power shift transmission 12, which has an output shaft 13 which is connected to drive wheels (not shown). The power shift transmission 12 includes a transmission or gear box 18 which is operated by a set of pressure operated control elements or clutches 20 which are controlled by a corresponding set of solenoid operated shift control valves 22. The transmission 18 is preferably a powershift transmission such as a production John Deere 16 speed powershift transmission, which is controlled by an electronic vehicle control unit (VCU) 14, or such as described in US-A-5,011 ,465. The engine 10 is preferably an electronically controlled engine such as a production John Deere 8.1 liter governor controlled Diesel engine, and is controlled by a production electronic engine control unit (ECU) 16 in response to an engine speed or throttle command signal. The VCU 14 sends shift control signals to the shift control valves 22 in response to command signals it receives from an operator controlled shift control lever mechanism 24, such as the shift control mechanism of a production John Deere 8000 Series tractor. For example, Fig. 2 shows the behavior of the pressure (P-OFF) of an off-going clutch and P-ON of an on-going clutch during a typical upshift. According to the present invention, the VCU 14 controls or modifies the speed command or throttle command signal during upshifts and downshifts to improve the quality or smoothness of shifts. As best seen in Fig. 2, the VCU 14 momentarily reduces the magnitude of the speed command signal during an upshift of the power shift transmission 12. More specifically, during an upshift, the magnitude of the speed command signal, SC, is abruptly reduced when the pressure of the off-going clutch, P-OFF, is being reduced to zero. Preferably, the speed command signal SC is reduced to a value which would produce a lower engine speed corresponding to the change in gear ratio resulting from the upshift. Thereafter, the magnitude of the speed command signal SC is gradually increased as the pressure P-ON of the oncoming clutch is gradually increased, and so that the magnitude of the speed command signal SC is back up to its original magnitude when the on-going clutch pressure P-ON is at its full on pressure level. Thus, as described above, and as shown in Fig. 2, the speed command signal is modified in coordination with the changes to the transmission control clutch pressure. Similarly, although not illustrated, for a downshift, the speed command signal SC momentarily increased at the start of the clutch swap, and is then gradually decreased or ramped down. While the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.

Claims: Claims 1. Method for a vehicle having a governor controlled engine (10) which drives a power shift transmission (12), the power shift transmission (12) having a gear box (18) which is operated by a set of pressure operated clutches (20) which are controlled by a corresponding set of solenoid operated shift control valves (22) which are controlled by an electronic vehicle control unit (VCU) in response to the shift command signals generated by an operator controlled shift control lever mechanism (24), the engine (10) being controlled by an electronic engine control unit (ECU) which receives a speed command signal (SC) from the VCU, the method of improving shift quality comprising: momentarily modifying a magnitude of the speed command signal (SC) during a shift of the power shift transmission (12); and during said shift, abruptly modifying the magnitude of the speed command signal (SC) from a first magnitude to a second magnitude then gradually returning the speed command signal (SC) back to said first magnitude upon completion of said shift. 2. The method of claim 1 , wherein: the solenoid operated shift control valves (22) operate to vary pressures applied to the pressure operated clutches (20); and the magnitude of the speed command signal (SC) is momentarily modified in coordination with the variations of said clutch pressure. 3. The method according claim 1 or 2, wherein: during an upshift of the power shift transmission (12) the magnitude of the speed command signal (SC) is reduced. The method of claim 3, wherein: the magnitude of the speed command signal (SC) is momentarily reduced during said upshift. 5. The method of claim 3 or 4, wherein: during said upshift, the magnitude of the speed command signal (SC) is abruptly reduced and then gradually increased back to the first magnitude prior to said upshift. 6. The method according one of the claims 1 to 5, wherein: during a downshift of the power shift transmission (12), the magnitude of the speed command signal (SC) is increased. 7. The method of claim 6, wherein: the magnitude of the speed command signal (SC) is momentarily increased during said downshift. 8. The method of claim 6 or 7, wherein: during said downshift, the magnitude of the speed command signal (SC) is abruptly increased and then gradually decreased back to the first magnitude prior to said downshift. 9. The method according one of the claims 1 to 8, wherein: the speed command signal (SC) is modified to a value which produces a modified engine speed corresponding to a change in a gear ratio resulting from the shift. 10. The method of claim 9, wherein: during an upshift, the speed command signal (SC) is reduced to a value which produces a lower engine speed corresponding to a change in a gear ratio resulting from the upshift. 11. The method of claim 9 or 10, wherein: during a downshift, the speed command signal (SC) is increased to a value which produces a higher engine speed corresponding to a change in a gear ratio resulting from the downshift. 12. A control system for a vehicle having a governor controlled engine (10) which drives a power shift transmission (12), the power shift transmission (12) having a gear box which is operated by a set of pressure operated clutches (20) which are controlled by a corresponding set of solenoid operated shift control valves (22) which are controlled by an electronic vehicle control unit (VCU) in response to the shift command signals generated by an operator controlled shift control lever mechanism (24), the engine (10) being controlled by an electronic engine control unit (ECU) which receives a speed command signal (SC) from the VCU, comprising: a speed command modifier for momentarily modifying a magnitude of the speed command signal (SC) during a shift of the power shift transmission (12), and during said shift, the speed command modifier abruptly modifies the magnitude of the speed command signal (SC) from a first magnitude to a second magnitude, and then gradually returns the magnitude of the speed command signal (SC) back to the first magnitude upon completion of said shift. 13. The control system of claim 12, wherein: the solenoid operated shift control valves (22) operate to vary pressures applied to the pressure operated clutches (20); and the magnitude of the speed command signal (SC) is momentarily modified in coordination with the variations of said clutch pressure. 14. The control system according claim 12 or 13, wherein: the speed command modifier comprises means for modifying the magnitude of the speed command signal (SC) according the method of one of the claims 3 to 11.

Inventors: MEYER DUANE FREDERICK, MEYER, DUANE, FREDERICK
Applicants: DEERE & CO, DEERE & COMPANY
Application year: 2000
Main classification: B60K41
IPC codes: B60W10, F02D9, F02D29, F02D41, F16H59, F16H61, F16H63