VEHICLE ENGINE SPEED INDICATOR CONTROL DEVICE

Abstract

An engine speed indicator control device (36) of a vehicle (10), comprising: a vehicle drive system (12) including an engine (20), a fluid-operated power transmission device (22), and an automatic transmission (24) having numerous gears, each providing different power transmission states; a manually operable transmission shift element (72) operable by a vehicle operator to place the automatic transmission into a selected gear; an accelerator pedal (62); an engine speed sensor (64) for detecting an actual value (RNe) of an operating speed (Ne) of the engine (20); and an engine speed indicator (44) for displaying a specific display value (DNe) of the operating speed (Ne) of the engine (20), wherein the engine speed indicator control device (36) is configured to determine the display value (Dne) of the operating speed (Rne) of the engine (20) to be displayed by the engine speed indicator (44), and comprising: a fluctuation limiting display control section (38) configured to execute fluctuation limiting display control when a shift operation of the manually operable gear shifting element (72) for garage parking is performed while the vehicle (10) is stationary and the accelerator pedal (62) is in an unoperated position, wherein the fluctuation limiting display control section (38) determines the display value (DNe) of the operating speed (Ne) of the engine (20) in the fluctuation limiting display control such that a fluctuation amount of the display value (Dne) is smaller than in a conventional display control in which the display value (Dne) is determined according to the actual value (RNe).

Description

FIELD OF THE INVENTIONThe present invention relates generally to a vehicle engine speed display control device, and more specifically to control of an operation speed display of a vehicle engine when a shift operation of a shift lever of the vehicle for garage parking is performed.BACKGROUND OF THE INVENTIONAn engine speed display control device of a vehicle is known, comprising: a vehicle drive system having an engine, a fluid-operated power transmission device, and an automatic transmission having multiple operating positions with different power transmission states; a manually operable transmission shift element operable by a vehicle operator to place the automatic transmission in a selected gear; an engine speed sensor for detecting an actual value of an operating speed of the engine; and an engine speed display for displaying a controlled value of the operating speed of the engine. The engine speed display control means is constructed such that the actual value of the engine speed is displayed as the controlled value of the engine speed by default. JP 2016-60 460 A discloses an example of an engine speed display control device. The engine speed display control means disclosed in this publication is configured to determine the engine speed based on a gear of the automatic transmission set after a shift operation and to display the thus determined value of the engine speed in the course of the shift operation of the automatic transmission. This engine speed display control means has an improved response to the shift operation of the automatic transmission.Incidentally, a so-called "garage parking" shift operation of the manually operated shift lever may be performed to shift the automatic transmission while the vehicle is stationary and an accelerator pedal of the vehicle is held at its unactuated position where the degree of operation of the accelerator pedal is zero. Also in this case, the motor is controlled to control its torque so that the operating speed coincides with a target value such as a predetermined engine idle value. Accordingly, the actual value of the engine speed is displayed as a controlled value. However, the shift operation of the automatic transmission in response to the shift operation of the manually operated garage parking shift lever causes a change in the power transmission state, i.e., a variation in a force acting on the engine and a consequent variation in the actual rotational speed, and a consequent variation in the controlled value of the engine rotational speed due to, for example, a small degree of response of torque control of the engine by feedback control. The operator may feel uncomfortable due to this variation in engine speed shown. Although it would be possible to control the engine torque so as to match the time course of the shifting operation of the automatic transmission, in consideration of the torque control behavior of the engine, it is difficult to sufficiently limit an amount of fluctuation of the actual rotation speed due to the fluctuations of the engine torque control behavior, a transmission shift control response, and the force acting on the engine caused by fluctuations of a coolant temperature of the engine and a working fluid temperature of the automatic transmission, a fluctuation of the viscosity of the working fluid, or fluctuations of the slip torque of clutches and brakes in the automatic transmission.DE 10 2014 118 271 A1 relates to an engine speed display device of a vehicle equipped with a continuously variable transmission having a manual shift mode in which the transmission is shifted according to the gear shift operation of a driver.From DE 11 2014 003 243 T5 a vehicle engine speed display device is known which is equipped with an engine speed detection unit which detects an engine speed, an engine speed display unit which displays an engine speed, and a display control unit which controls the engine speed display unit on the basis of the detected engine speed. The display control unit determines whether a phase of a shift operation is an inertia phase when shift control of an automatic transmission is executed, and sets the display responsiveness of a tachometer with respect to the detected engine speed to be higher than the display responsiveness to be set when the phase is not the inertia phase when it is determined that the phase of the shift operation is the inertia phase.JP 2017-213 942 A teaches those skilled in the art to display a pseudo rotational speed on a speed display corresponding to a current vehicle speed when the vehicle engine has been stopped and the vehicle is in a coasting state.BRIEF EXPLANATION OF THE INVENTIONThe present invention has been made in consideration of the above-described prior art. Therefore, an object of the present invention is to provide an engine speed display control means for controlling an engine speed display, the engine speed display control means having a lower possibility that the vehicle operator feels uncomfortable due to a variation in the engine speed displayed on an engine speed display in a shift operation for garage parking by a manually operable transmission shift member.The above object is achieved according to the following aspects of the present invention:According to a first aspect of the invention, there is provided an engine speed display control device of a vehicle, comprising: a vehicle drive system including an engine, a fluid-operated power transmission device, and an automatic transmission having multiple gear positions each establishing different power transmission states; a manually operated shift lever operable by a vehicle operator to place the automatic transmission in a selected gear; an accelerator pedal; an engine speed sensor for detecting an actual value of a speed of the engine; and an engine speed display for displaying a certain display value of the speed of the engine, wherein the engine speed display control means is configured to determine the display value of the operating speed of the engine to be displayed by the engine speed display, and comprises: a fluctuation limit display control portion configured to execute fluctuation limit display control when a shift operation of the manually operable shift lever for garage parking is performed while the vehicle is stationary and the accelerator pedal is in the unactuated position, wherein the fluctuation limit display control portion determines the display value of the speed of the engine in the fluctuation limit display control so that a fluctuation amount of the display value is less than in a conventional display control in which the display value is determined after the actual value.According to a second aspect of the invention, the fluctuation limit display control section determines the display value of the rotational speed of the engine according to a target value of the rotational speed used in the fluctuation limit display control instead of the actual value.According to a third aspect of the invention, the engine speed display control device according to the second aspect of the invention is configured such that the fluctuation limit display control portion gradually changes the display value of the operation speed of the engine within a phase between the conventional display control and the fluctuation limit display control.According to a fourth aspect of the invention, the engine speed display control device according to the first aspect of the invention is configured such that the fluctuation limit display control portion selects a higher degree of smoothing of the actual value of the rotational speed of the engine to reduce an amount of fluctuation of the display value in the fluctuation limit display control as compared with the conventional display control.According to a fifth aspect of the invention, the engine speed display control device according to any one of the first to fourth aspects of the invention is configured so that the fluctuation limit display control portion does not execute the fluctuation limit display control for limiting the fluctuation of the display value of the operation speed of the engine when an amount of deviation of the actual value of the speed of the engine from a target value of the speed is equal to or greater than a predetermined threshold value.According to a sixth aspect of the invention, the engine speed display control device according to any one of the first to fifth aspects of the invention is configured such that the variation limitation display control portion switches a display control mode from the variation limitation display control to limit the variation of the display value of the speed of the engine to the conventional display control when a predetermined variation limitation time has elapsed after the time when the shift operation of the manually operated shift lever for garage parking was performed.According to a seventh aspect of the invention, the engine speed display control device according to any one of the first to sixth aspects of the invention is configured such that the vehicle further includes an idling speed control portion configured to execute idling speed fluctuation limiting control to control a torque of the engine in synchronization with a shift operation of the automatic transmission in response to the shift operation of the garage parking shift lever, and in consideration of a control response of the torque of the engine, so that an amount of deviation of the actual value of the speed of the engine from a target value of the speed during the shift operation of the automatic transmission is reduced to match the timing of the shift operation of the automatic transmission.In the engine speed display control device according to the first aspect of the invention, the fluctuation limit display control portion is configured to determine the display value of the speed of the engine in the fluctuation limit display control such that the fluctuation amount of the display value is smaller than in the conventional display control in which the display value is determined after the actual value when a shift operation for garage parking is performed. Therefore, the present engine speed display control means limits the change in the display speed so that even if the actual speed changes, the vehicle operator is less likely to feel uncomfortable by the display speed during a shift operation of the automatic transmission in response to the shift operation of the shift lever for garage parking due to a change in a load acting on the engine during the shift operation of the automatic transmission and an improper timing of the matching of control between the shift operation and the engine torque.According to the second aspect of the invention, in which the engine speed display control device according to the first aspect of the invention is configured to determine the display value of the operation speed of the engine from the target value of the operation speed used in place of the actual value in the fluctuation limitation display control, the fluctuation of the display value of the operation speed of the engine is sufficiently limited in spite of the fluctuation of the actual value, so that the driver is less likely to feel uncomfortable by the display value.According to the third aspect of the invention, in which the fluctuation limit display control portion gradually changes the display value of the operation speed of the engine during the phase between the conventional display control and the fluctuation limit display control, the driver is less likely to feel uncomfortable by the display value of the operation speed of the engine whose fluctuation is reduced within the phase between the conventional and the fluctuation limit display controls.According to the fourth aspect of the invention, in which the fluctuation limit display control portion selects the higher degree of smoothing of the actual value of the operation speed of the engine to reduce the amount of fluctuation of the display value in the fluctuation limit display control as compared with the conventional display control, a change rate and an amount of change of the actual value of the engine speed in the fluctuation limit display control are less or less than in the conventional display control, so that the driver is less likely to feel uncomfortable by the display value of the engine speed.According to the fifth aspect of the invention, the fluctuation limit display control section does not execute the fluctuation limit display control for limiting the fluctuation of the display value of the operating speed of the engine, whereas when the amount of deviation of the actual value of the operating speed of the engine from the target value of the operating speed is equal to or greater than the predetermined threshold value, it executes the conventional display control for determining the display value of the engine speed after the actual value. Namely, if the fluctuation limitation display control is executed when the amount of deviation of the actual value of the engine speed from the target value is equal to or greater than the threshold value, the driver may feel uncomfortable by the display value of the limited engine speed fluctuation because he feels a large difference between the display speed value and an engine speed value felt by him due to an operation noise of the engine. Accordingly, the conventional display control is executed to change the display rotational speed value according to a variation in the actual rotational speed value, so that the driver is very unlikely to feel uncomfortable due to the difference between the display rotational speed value and an engine rotational speed value felt by the driver based on the operating sound of the engine.According to the sixth aspect of the invention, wherein the fluctuation limit display control portion shifts the display control mode to the conventional display control when the predetermined fluctuation limit time has elapsed after the time of performing the shift operation of the garage parking shift lever, the fluctuation limit display control is executed to limit the fluctuation of the display speed value only during a period in which there is a possibility that the actual speed value fluctuates due to the shift operation of the garage parking shift lever. Accordingly, the present variation limitation display control portion makes it possible to reduce the possibility that the vehicle operator feels uncomfortable by the variation of the display rotational speed value while minimizing a period in which the display rotational speed value deviates from the actual value.According to the seventh aspect of the invention, the idle speed fluctuation limiting control is executed to control the torque of the engine in synchronization with the shifting operation of the automatic transmission in response to the shifting operation of the garage parking shift lever and in consideration of a delayed control response of the torque of the engine so that the amount of deviation of the actual speed value from the target value of the operating speed during the shifting operation of the automatic transmission is decreased to match the timing of the shifting operation of the automatic transmission. Usually, the fluctuation of the actual rotational speed value during the shift operation of the automatic transmission is reduced in response to the shift operation of the garage parking shift lever. However, it is difficult to always sufficiently limit the fluctuation of the actual rotational speed value due to fluctuations in the control response of the engine torque and the shift operation of the automatic transmission and the fluctuating engine load caused by temperature fluctuations of the coolant of the engine and the working fluid of the automatic transmission, the viscosity of the working fluid, and the slip torques of clutches and brakes of the automatic transmission. Thus, there is a possibility that the idle rotation variation limiting control causes a significant variation of the actual rotation speed value depending on the state of the vehicle immediately after the engine starts, for example. Accordingly, the fluctuation limit display control portion according to the seventh aspect of the invention has an advantage of reducing the fluctuation of the display rotational speed value in the garage parking shift operation and the possibility that the driver feels uncomfortable by the display rotational speed value.BRIEF EXPLANATION OF THE DRAWINGSFIG. 1 is a schematic view showing an arrangement of a vehicle and main parts of its control system provided with an engine speed display control device according to an embodiment of this invention; FIG. 2 is a schematic view showing an example of an automatic transmission shown in FIG. 1 ; FIG. 3 is a table indicating a relationship between various gears of the automatic transmission of FIG. 2 and respective combinations of friction clutch devices placed in engaged states to set the gears; FIG. 4 is a perspective view showing an example of a shift lever provided on the vehicle of FIG. 1 ; FIG. 5 is a view showing an example of a speedometer provided on the vehicle of FIG. 1 ; FIG. 6 is a flow chart illustrating a procedure of a shift control determination section of FIG. 1 for garage parking according to an embodiment of this invention; FIG. 7 is a flow chart illustrating an operation of a fluctuation limiting portion shown in FIG. 1 according to the first embodiment of this invention; FIG. 8 is a time chart indicating an example of changes in operating states of various portions of the vehicle when fluctuation limit display control of a display speed is executed by a speed fluctuation limit display control portion shown in FIG. 1 ; FIG. 9 is a time chart indicating an example of changes in operating states when a shift operation for garage parking of a shift lever is performed after starting an engine at a later timing than that in FIG. 8 ; FIG. 10 is a time chart indicating an example of changes in the operating states when the shift operation for garage parking is performed after starting an engine at a later timing than that in FIG. 9 ; FIG. 11 is a time chart indicating an example of changes in operating states when an actual rotational speed abruptly increases as compared with FIG. 10 due to the shift operation of the shift lever for garage parking; and FIG. 12 is a flow chart illustrating an operation of the fluctuation limiting portion of FIG. 1 according to a second embodiment of this invention.DETAILED EXPLANATION OF A PREFERRED EMBODIMENTThe engine is used as a power source for vehicle drive, and is an internal combustion engine such as an Otto or diesel engine that generates a driving force by combustion of a fuel. The present invention is also applicable to a hybrid vehicle provided with a drive source including one or more electric motors besides the engine. Although a torque converter is preferably used as the fluid-operated power transmission device, a hydraulic clutch or any other type of fluid-operated power transmission device may be used. For example, the various speeds of the automatic transmission include at least two of: a forward speed D at which a driving force for forward travel can be transmitted; a reverse speed R at which a driving force for reverse travel can be transmitted; and a neutral speed N (parking position P) at which no driving force can be transmitted. The automatic transmission can be selected from various types, such as a stepped planetary gear type automatic transmission or a meshed transmission having at least two axles provided with numerous friction clutch devices selectively placed in engaged and released states, respectively, to set the numerous gears including forward gears, a reverse gear and a neutral gear; a reverse-to-reverse transmission; and a transmission which is a combination of, for example, a forward-to-reverse switching device and a belt-and-pulley type continuously variable transmission.The engine speed display indicating the display value of the operating speed of the engine may be of various types, such as: an analog display having a display panel in the form of a disc and a needle fixed at one end thereof to a rotatable central shaft for rotating the needle to display or indicate the display value of the engine speed; a digital display for displaying a numerical value corresponding to the display speed value; or a bar display having a variable-length display bar. The display speed value is determined according to the actual speed value or the target speed value. For example, the actual or target speed value is determined as the display speed value. Alternatively, the actual or target speed value is subjected to a smoothing or other processing process for determining or calculating the display speed.The shift operation of the manually operable transmission shift element (hereinafter also referred to as shift lever) for garage parking is an operation of the shift lever while the vehicle is stationary and the accelerator pedal is unactuated. A determination as to whether the accelerator pedal is unactuated may be made based on an opening angle of a throttle valve controlled according to an amount of actuation of the accelerator pedal. The fluctuation limit indication control of the indication rotational speed value may be performed in at least one of various shift operations of the shift lever, such as a shift operation from the neutral position to a forward or reverse gear, a shift operation from the forward or reverse gear to the neutral position, and a shift operation from the forward gear to the reverse gear or from the reverse gear to the forward gear. The fluctuation limit display control is executed such that a fluctuation amount of the display rotational speed value is smaller than in the conventional display control in which the display rotational speed value is determined by the actual rotational speed or the actual rotational speed, respectively. For example, the fluctuation limit display control is designed so that the display rotational speed value is determined by the target rotational speed value or by selecting a smoothing degree of the actual rotational speed which is higher than in the conventional display control for determining the display rotational speed value on the basis of the actual rotational speed value thus smoothed. Alternatively, the fluctuation limit display control is designed so as to limit the display rotational speed value within a predetermined range defined by upper and lower limit values determined based on the target rotational speed value.It is preferable to execute processing for gradually changing the display rotational speed value at, for example, a predetermined time interval or a predetermined change rate at a transition of the display control mode from the conventional display control to the fluctuation-limit display control or from the fluctuation-limit display control back to the conventional display control. However, the display control mode can be switched between the conventional display control and the fluctuation-limit display control without the display speed value gradual change processing. It is possible to prevent the transition of the display control mode from the conventional display control to the fluctuation limit display control if the amount of deviation of the actual rotational speed value from the target rotational speed value is larger than the predetermined threshold value. However, the display control mode may be switched from the conventional display control to the variation limitation display control regardless of the amount of deviation of the actual rotational speed value from the target rotational speed value. The limit value of the deviation amount may be kept constant or may be variable depending on the kind of garage parking shift operation of the shift lever or the state of the vehicle. The fluctuation limit display control portion is preferably configured to reset the display control mode to the conventional display control when a predetermined duration of a fluctuation limit time has elapsed after a time of shifting of the garage parking shift lever. However, the fluctuation limit display control portion may be configured to continue the fluctuation limit display control until a predetermined condition for resetting the display control mode to the conventional display control is satisfied, for example, until the accelerator pedal is operated or the vehicle is started. The fluctuation limiting time, which is preferably set as short as possible, includes at least a period in which the actual rotational speed value may fluctuate due to the garage parking shift. For example, the fluctuation limiting time is determined to change according to the kind of the garage parking shift and the state of the vehicle. However, the fluctuation limiting time may be determined to be a comparatively long predetermined time including the period in which the actual rotational speed value may fluctuate regardless of the type of the garage parking shift and the state of the vehicle.The present invention can be suitably applied to the vehicle provided with the idling speed control portion configured to execute the idling speed fluctuation limiting control for controlling the torque of the engine through feedforward control, for example, in synchronization with the shifting operation of the automatic transmission in consideration of the control behavior of the engine torque, so that the amount of deviation of the actual speed value from the target speed value during the shifting operation of the automatic transmission due to the shifting operation of the shift lever for garage parking is reduced. In this case, the fluctuation limit display control portion may be configured to forcibly execute the fluctuation limit display control of the display rotational speed value when the shift operation of the shift lever for garage parking is performed. However, alternatively, the fluctuation limit display control portion may be configured to execute the fluctuation limit display control only when the vehicle is placed in a state in which the timing of the control between the engine torque and the shift operation of the automatic transmission tends to be unstable, or in which the load acting on the engine tends to fluctuate, for example, only the temperature of the coolant of the engine or the working fluid of the automatic transmission is low. Alternatively, the fluctuation limit display control portion may be configured to execute the fluctuation limit display control only when the garage parking switching operation is performed for the first time after starting the engine or within a predetermined period of time after starting the engine. Furthermore, the present invention can also be applied to the vehicle in which the engine torque is feedback-controlled so that the actual rotational speed value coincides with the target value regardless of whether or not the shift operation of the shift lever for garage parking is performed. Also in this case, the fluctuation limit indication control according to the invention is effective because the aforementioned control of the engine torque can cause a fluctuation of the actual rotational speed value by a fluctuation of the engine load due to the garage parking shift operation when the control response of the engine torque is not high enough.EMBODIMENTSPreferred embodiments of the present invention will now be described in detail with reference to the drawings. Referring first to FIG. 1, which is a schematic view of a vehicle 10 and shows main portions of a control system provided with an engine speed display control means in the form of an engine speed display control portion 36 according to a first embodiment of this invention. The vehicle 10 is provided with a drive system 12 in which an engine 20, a torque converter (T / C) 22, and an automatic transmission 24 are connected to each other in series. The vehicle 10 is, for example, an FR type (front engine rear drive type) in which the drive system 12 is installed such that its axial direction is parallel to the longitudinal direction (traveling direction) of the vehicle 10. The engine 20 is a drive source of the vehicle 10 and an internal combustion engine such as a spark ignition engine that can be operated to generate a drive force by combustion of a fuel. Specifically, the vehicle 10 is an engine-driven vehicle provided only with the engine 20 as a drive source. The control system of the vehicle 10 includes an engine power control device 26 for controlling a power of the engine 20. The engine power control device 26 is provided with an electronic throttle valve, a fuel injection device, and an ignition device, which are respectively controlled by control signals generated from an electronic controller 30 so that the power of the engine 20 is electrically controlled by the electronic controller 30.FIG. 2 is the schematic view showing examples of the torque converter 22 and the automatic transmission 24. The torque converter 22 includes a pump impeller 22 pconnected to a crankshaft 102 of the engine 20, a turbine impeller 22 tconnected to a driveshaft 122 of the automatic transmission 24, and a stator impeller 22 sconnected to a housing 106 of the automatic transmission 24 via a one-way clutch. The torque converter 22 is a fluidic power transmission device for transmitting a driving force of the engine 20 through a fluid to the automatic transmission 24. the drive system 12 further includes a direct connection in the form of a lock-up clutch 108 disposed between the pump impeller 22 pand the turbine impeller 22 t. This lock-up clutch 108 is electronically controlled to be placed in its engaged or released states by lock-up clutch control signals generated from the electronic controller 30, respectively, to control lock-up clutch control valves incorporated in a hydraulic control unit 28 shown in FIG. 1.The automatic transmission 24 is provided with a first shifting portion 114 substantially including a first planetary gear set 112 of a double-pinion type and a short and long-pinion type, respectively; and a second shifting portion 120 substantially including a second planetary gear set 116 of a single-pinion type and a third planetary gear set 118 of a double-pinion type. The first and second switching portions 114 and 120 are arranged coaxially with each other. The automatic transmission 24 includes the input shaft 122 and an output shaft 124, and is configured to transmit a rotational movement of the input shaft 122 to the output shaft 124 such that a gear ratio of the input shaft 122 with respect to the output shaft 124 is variable. The rotational motion of the output shaft 124 is transmitted to left and right drive wheels of the vehicle 10 through a final reduction device, not shown. The second and third planetary gear sets 116 and 118 are Ravigneaux type planetary gear sets whose carriers are integrally formed with each other and whose ring gears are also integrally formed, and in which a pinion of the second planetary gear set 116 and a second or outer pinion of the third planetary gear set 118 are formed as a single element.The automatic transmission 24 is provided with four clutches C1-C4 and two brakes B1 and B2 (hereinafter collectively referred to as "clutches C" and "brakes B" unless otherwise specified) as a friction hydraulic clutch device, each of which is selectively placed in a clutched or released state, and electromagnetically operable automatic transmission valves of the hydraulic control unit 28 are electronically controlled as appropriate to shift control signals generated by the electronic control device 30. The electromagnetically operable automatic transmission valves are provided for the clutches C1-C4 and brakes B1 and B2, respectively, so that each of these clutches C and brakes B is controlled to be selectively placed in the clutched or released state independently of each other. As shown in the table of FIG. 3, the automatic transmission 24 is placed in one of eight forward speeds "1" to "8" or one reverse speed "Rev" when a corresponding combination of two of the clutches C and brakes B is placed in the engaged state, and is placed in a neutral position and a neutral speed "N" when each clutch C and brake B is placed in the released state, respectively. Specifically, the automatic transmission 24 is selectively placed in a forward driving state "D" for driving the vehicle 10 in the forward direction in any one of the forward speeds "1" to "8", a reverse driving state "R" for driving the vehicle 10 in the reverse direction in the reverse speed "Rev", or a neutral position "N" in which the vehicle 10 cannot be driven because no power transmission is performed by the automatic transmission 24. Forward drive state "D", reverse drive state "R", and neutral position "N" are different power transmission states through the automatic transmission 24. Note that both the automatic transmission 24 and the torque converter 22 are each constructed substantially symmetrically about their axis, and the lower half is not shown in the schematic view of FIG. 2.The electronic control device 30 is provided as a controller that executes various controls of the vehicle 10 such as power control of the engine 20, shift control of the automatic transmission 24, and clutch or release control of the lock-up clutch 108. The electronic controller 30 is configured to receive output signals from various sensors required for executing various controls, such as an output signal of an accelerator operation degree sensor 60 representing an operation degree Acc of an accelerator pedal 62; an output signal of an engine speed sensor 64 representing an actual operation speed RNe of the engine 20 (actual speed RNe); an output signal of a turbine speed sensor 66 representing a turbine speed Nt represented by a rotational speed of the input shaft 122; an output signal of an output speed sensor 68 representing an output speed Nout represented by a rotational speed of the output shaft 124; and an output signal of a shift lever position sensor 70 representing a shift lever position Psh which is a currently selected gear of a shift lever 72 (shown in FIG. 4 ). Note that the accelerator pedal 62 is a manually operable vehicle accelerator, and the output rotational speed Nout corresponds to a travel speed V of the vehicle 10.As shown in FIG. 4, the shift lever 72 may be operated to select one of its three shift positions, namely, a neutral gear N, a reverse gear R, and a forward gear D. The shift lever 72 is placed in the neutral gear N, the reverse gear R, or the forward gear D to set the neutral gear N, the reverse gear Rev, or one of the forward gears 1st to 8th of the automatic transmission 24, respectively. The automatic transmission 24 is electronically controlled to be shifted to the neutral gear N, the reverse gear R or the forward gears 1st to 8th according to an operation of the shift lever 72 to be shifted to the neutral gear N, the reverse gear Rev or to one of the forward gears 1st to 8th, which is represented by the table of FIG. 3. When the shift lever 72 is placed in the forward speed D while the vehicle 10 is stationary, the automatic transmission 24 is placed in the first forward speed 1st having the largest gear ratio γ. In the forward speed D of the shift lever 72, the automatic transmission 24 is automatically shifted from the first forward speed 1st to a higher forward speed 2nd to 8th in accordance with a change in a running state of the vehicle 10 represented by the running speed V and the accelerator opening degree Acc. The shift lever 72 is operable from the forward speed D to an upshift position "+" and a downshift position "-". The automatic transmission 24 can be manually shifted up or down by operating the shift lever 72 to the upshift and downshift positions "+" and "-" respectively.Note that the shift lever 72 functions as a manually operable transmission shift element for shifting the automatic transmission 24.The electronic control device 30 is basically constituted by a so-called microcomputer, which includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), and an input / output interface (I / O), and performs signal processing operations according to control programs stored in the read only memory, using a temporary data storage function of the random access memory. As shown in FIG. 1, the electronic control device 30 has three control functions, namely, an engine control section 32, a transmission control section 34, and the engine speed display control section 36.The engine control portion 32 is configured to substantially control a torque Te of the engine 20 according to the accelerator operation amount Acc. The engine control section 32 includes an idle speed control section 33 for controlling the engine 20 while the accelerator pedal operation amount Acc is equal to or less than zero (Acc ≤ 0), i.e., while the accelerator pedal 62 is in its unactuated position. The idle speed control section 33 is configured to substantially feedback control the engine torque Te such that the actual speed RNe coincides with a predetermined target value TNe while the accelerator pedal 62 is in the unactuated position. The target value TNe is a target idle rotation speed value of the engine 20, for example, the target value TNe is changed according to an operating state of the engine 20 such as a cooling liquid temperature. However, the target value TNe may be a constant value.The transmission control section 34 is provided to perform the shift control of the automatic transmission 24, more specifically, to control the clutches C 1-C 4 (shown in the table of FIG. 3 ) and brakes B 1 and B 2 and the lock-up clutch 108 (shown in FIG. 2 ). During the forward running of the vehicle 10, the transmission control section 34 controls the electromagnetically operable automatic transmission valves of the hydraulic control unit 28 (shown in FIG. 1 ) for selectively placing the clutches C1-C4 and brakes B1 and B2 in the engaged or released state such that the automatic transmission 24 is placed in a selected forward speed from 1st to 8th according to a predetermined shift schedule. The shift map is designed, for example, such that the automatic transmission 24 is shifted based on the running speed V of the vehicle and a required driving force of the vehicle represented by the accelerator opening degree Acc, such that the gear ratio γ of the automatic transmission 24 decreases with an increase in the running speed V of the vehicle and increases with an increase in the required driving force of the vehicle, namely, such that the automatic transmission 24 is upshifted as the running speed V of the vehicle increases and downshifted as the required driving force of the vehicle increases. Further, the transmission control section 34 is configured to control lockup clutch control valves of the hydraulic control unit 28 for selectively setting the lockup clutch 108 in the coupled or released state according to a predetermined lockup clutch shift schedule.The engine speed display control portion 36 is configured to control a display speed DNe that is the operation speed Ne of the engine 20 displayed on a tachometer 44 disposed in front of a driver seat in the vehicle 10 (shown in FIGS. 1 and 5 ). The engine speed display control section 36 is mainly configured to execute conventional display control for determining the display speed DNe based on the actual speed RNe. For example, the engine speed display control portion 36 may determine the actual speed RNe as the display speed DNe or calculate the display speed DNe by smoothing a change in the actual speed RNe. FIG. 5 shows an example of the tachometer 44 which is an analog speed indicator having a circular disc display 46 and an indicator needle 48 attached at one end thereof to a rotatable central shaft for rotating the indicator needle 48 to indicate the indicator speed DNe. Note that the engine speed display control portion 36 functions as the engine speed display control means of the present invention.When a shift operation of the garage parking shift lever 72 for shifting the automatic transmission 24 is performed while the vehicle 10 is stationary with the vehicle running speed V being equal to or less than zero (V≤0) and the accelerator pedal 62 is in the unactuated position with the accelerator pedal actuation amount Acc being equal to or less than zero (Acc≤0), the actual rotational speed RNe is likely to deviate from the target value TNe due to fluctuations of a load acting on the engine 20 during shift operations of the automatic transmission 24 despite the feedback control of the engine torque Te by the idling rotational speed control portion 33. When the automatic transmission 24 is placed in the neutral gear N in which the input shaft 122 and the output shaft 124 are separated from each other, the turbine impeller 22 tof the torque converter 22 is rotated, and the rotational motion of the pump impeller 22 pand the load of the engine 20 become relatively small. When the automatic transmission 24 is placed in the forward speed D or the reverse speed R of the shift lever 72 in which the automatic transmission 24 is placed in a power transmission state, the turbine impeller 22 tis placed in a non-moving state, while only the pump impeller 22 pis further rotated when the vehicle 10 is stationary (V=0). Accordingly, the engine load is increased due to a stirring resistance of an oil in the torque converter 22 so that the actual rotation speed RNe fluctuates despite the target rotation speed TNe kept constant if the engine torque Te has a weak feedback control response. Specifically, when the engine load increases from the neutral speed N to the forward speed D or the reverse speed R by operation of the shift lever 72, the actual rotational speed RNe can be temporarily lowered. On the other hand, when the engine load decreases from the forward speed D or the reverse speed R to the neutral speed N by operating the shift lever 72, the actual rotational speed RNe may increase temporarily. In this respect, it should be noted that the shift lever 72 is once placed in the neutral speed N when the shift lever 72 is operated between the forward speed D and the reverse speed R, so that the engine load may fluctuate temporarily, thereby causing the actual rotational speed RNe to fluctuate. If the display rotational speed DNe temporarily fluctuates without operation of the accelerator pedal 62 with the change in the actual rotational speed RNe, there is a possibility that the vehicle driver feels uncomfortable by the fluctuation of the display rotational speed DNe.In consideration of the above possibility, the idle speed control portion 33 is configured to execute idle speed variation limiting control that controls the engine torque Te in consideration of its control behavior in synchronization with the shift operation of the automatic transmission 24 so that an amount of deviation of the actual speed RNe from the target value TNe is decreased despite a change in the engine load in the shift operation of the shift lever 72 of the automatic transmission 24 for garage parking. That is, the idle speed control section 33 increases or decreases the engine torque Te by a predetermined amount at a proper timing in the shifting operation of the automatic transmission 24, which timing enables a decrease in the change of the actual engine speed RNe despite the change of the engine load. The timings and the amounts for increasing and decreasing the engine torque Te are determined through experiments corresponding to specific shift modes of the automatic transmission 24 performed in correspondence with respective different shift operations of the garage parking shift lever 72. Therefore, the idle rotation speed control portion 33 makes it possible to reduce the fluctuation amounts of the actual rotation speed RNe and the display rotation speed DNe due to the shift operation of the garage parking shift lever 72.However, conventional idle speed variation limiting control has difficulty in ensuring stable and adequate limiting of the variation of the actual speed RNe due to variations in control response of the engine torque Te and the shifts of the automatic transmission 24, and changes in engine load, the variations being caused by, for example, temperature variations of the coolant of the engine 20 and the viscosity of the working fluid of the automatic transmission 24, and drag torques of the clutches C and brakes B. There is a possibility that the actual rotational speed RNe largely fluctuates despite or just due to the idling speed fluctuation limiting control due to an inappropriate change timing of the engine torque Te or inappropriate amounts of increasing or decreasing the engine torque Te immediately after the engine 20 is started, in which the temperatures of the engine cooling liquid and the automatic transmission working liquid are low and the engine torque Te is unstable.The engine speed display control portion 36 includes a fluctuation limit display control portion 38 configured to limit a fluctuation amount of the display speed DNe regardless of a fluctuation of the actual speed RNe during the shift operation of the garage parking shift lever 72. This fluctuation limit display control section 38 includes a fluctuation limit display control determination section 40 and a fluctuation limit section 42. The fluctuation limit display control section 38 is configured to execute steps S1-S5 of a control routine shown in the flow chart of Fig. 6, and steps G1-1 to G1-7 of a control routine shown in the flow chart of Fig. 7. A part of the engine speed display control section 36 for executing the control routine of FIG. 6 (steps S1-S5) functions as the fluctuation limit display control determination section 40, whereas a part of the engine speed display control section 36 for executing the control routine of FIG. 7 (steps G1-1 to G1-7) functions as the fluctuation limit section 42.The control routine of FIG. 6 executed by the fluctuation limit display control determination section 40 is initiated with step S1 to determine whether the accelerator pedal operation amount Acc is equal to or less than zero (Acc ≤ 0) while the vehicle running speed V is equal to or less than zero (V ≤ 0), i.e., whether the accelerator pedal 62 is in the unactuated position while the vehicle 10 is stationary. If the accelerator pedal 62 is in the unactuated position while the vehicle 10 is stationary, control proceeds to step S 2 and subsequent steps. If the accelerator pedal 62 is operated with the operation amount Acc being greater than zero, or if the vehicle 10 is traveling at the traveling speed V being greater than zero, the control proceeds to step S 5 to make a negative determination for executing fluctuation limit display control in response to the shift operation of the garage parking shift lever 72. This negative determination to be made in step S 5 indicates the state of the vehicle 10 in which the fluctuation limit display control for limiting the fluctuation of the display rotational speed DNe corresponding to the fluctuation of the actual rotational speed RNe is not required, that is, the state of the vehicle 10 that allows the conventional display control to determine the display rotational speed DNe corresponding to the actual rotational speed RNe. Note that step S 1 corresponds to a function of a vehicle state determination section. The accelerator pedal operation amount Acc used for determining whether the accelerator pedal 62 is in the unactuated position may be replaced by any other parameter, such as an angle of an opening of an electronic throttle valve controlled according to the accelerator pedal operation amount Acc.Step S 2 is executed to determine whether the shift operation of the garage parking shift lever 72 has been performed to shift the automatic transmission 24, more specifically, whether the shift lever 72 has been shifted from the neutral gear N to the forward gear D or the reverse gear R, from the forward gear D or the reverse gear R to the neutral gear N, or alternatively, between the forward gear and the reverse gear D and R. If an affirmative determination is made in step S 2, the control flow proceeds to step S 3. On the other hand, if a negative determination is made in step S 2, the control flow proceeds to step S 5 to make the negative determination of the shift operation of the shift lever 72 for garage parking. Note that step S 2 corresponds to a function of a shift operation determination section for garage parking. When the shift lever 72 has a parking position P for parking the vehicle 10, the automatic transmission 24 is placed in its neutral gear N when the shift lever 72 is placed in the parking position P. In this connection, the parking position P may be considered to be equivalent to the neutral gear N with respect to the determination as to whether the shift operation of the garage parking shift lever 72 has been performed.Step S 3 is performed to determine whether a time period after a time of the positive determination in step S 2 at which the shift operation of the shift lever 72 for garage parking has been performed is within a predetermined time. This predetermined time is a fluctuation limit time Tgr during which the fluctuation limit display control is performed. The fluctuation limiting time Tgr, which is preferably set as short as possible, includes at least a period during which the actual rotational speed RNe can fluctuate according to the shifting of the automatic transmission 24 due to the shifting operation for garage parking. For example, the fluctuation limiting time Tgr (predetermined period) is set to change according to the type of shift of the garage parking shift lever 72, the state of the vehicle 10 such as the coolant temperature of the engine 20, or the working fluid temperature of the automatic transmission 24. If an affirmative determination is made in step S 3, i.e., the predetermined fluctuation limiting time Tgr has not elapsed after the time of the positive determination in step S 2, there is a possibility that the actual rotational speed RNe fluctuates during a shift operation of operations of the automatic transmission 24 due to the shift operation of the garage parking shift lever 72. In this case, the control flow proceeds to step S 4 and makes an affirmative determination to execute the fluctuation limit display control for fluctuation limiting the display rotational speed DNe despite fluctuation of the actual rotational speed RNe. If a negative determination is made in step S 3, that is, if the predetermined fluctuation limiting time Tgr has elapsed, execution of the fluctuation limiting display control for limiting the fluctuation of the display rotational speed DNe is not required. In this case, the control flow proceeds to step S 5 to make a negative determination for executing the fluctuation limit display control.The control routine of FIG. 7 executed by the fluctuation limiting part 42 is initiated with step G1-1 to determine whether the affirmative determination for executing the fluctuation limiting display control has been made. If an affirmative determination is made in step G1-1, the control flow proceeds to step G1-2. On the other hand, if a negative determination is made in step G1-1, the control flow proceeds to step G1-4. When the negative determination is made in step G 1- 1, execution of the fluctuation limit display control for limiting the fluctuation of the display rotational speed DNe is not required. In this case, step G1-4 is executed to execute the conventional display control in which the actual rotational speed RNe is determined as the display rotational speed DNe.In step G 1- 2 executed if the positive determination is made in step G 1- 1, a determination is made as to whether an amount of a rotational speed difference ΔNe between the actual rotational speed RNe and the target value TNe is less than a predetermined threshold α. If the rotational speed difference ΔNe is smaller than the threshold value α, the control flow proceeds to step G 1- 3 to set the target value TNe as the display rotational speed DNe, that is, to execute the fluctuation limitation display control in which the fluctuation of the display rotational speed DNe is limited despite the fluctuation of the actual rotational speed RNe, that is, the display rotational speed DNe is determined by the target rotational speed TNe.If a negative determination is made in step G1-2, that is, if the rotational speed difference ΔNe is not less than the threshold value α, the control flow proceeds to step G1-4 to determine the actual rotational speed RNe as the indication rotational speed DNe. In particular, if the rotational speed difference ΔNe is relatively large, the limitation on the variation of the display rotational speed DNe leads to a possibility that the vehicle operator feels uncomfortable due to the display rotational speed DNe whose variation is limited because the vehicle operator feels a large difference in the display rotational speed DNe from an engine rotational speed value estimated by him by an operating noise of the engine 20. Accordingly, when the rotational speed difference ΔNe is not less than the threshold value α (ΔNe≥α), step G 1- 4 is executed to execute the conventional display control in which the display rotational speed DNe is set corresponding to the actual rotational speed RNe so that the display rotational speed DNe fluctuates corresponding to a fluctuation of the actual rotational speed RNe. The threshold α may be a constant value or a variable that is changed depending on the state of the vehicle 10, such as the type of the shift operation of the automatic transmission 24 in response to the shift operation of the garage parking shift lever 72. The rotational speed difference ΔNe represents a deviation amount of the actual rotational speed RNe from the target value TNe.After the step G1-3 of setting the target rotation speed TNe as the display rotation speed DNe and the step G1-4 of setting the actual rotation speed RNe as the display rotation speed DNe, the step G1-5 of determining whether the fluctuation limit display control section 38 is in the transition phase of the engine rotation speed display control mode between the fluctuation limit display control for setting the target rotation speed TNe as the display rotation speed DNe and the conventional display control for setting the actual rotation speed RNe as the display rotation speed DNe follows. That is, a gradual change process is executed in step G 1- 6 before the display control mode of the engine speed is switched between the fluctuation limit display control and the conventional display control, as described below in detail. Therefore, step G1-5 is executed to determine whether the gradual change operation is performed. If an affirmative determination is made in step G1-5, the control flow proceeds to step G1-6, so that the gradual change operation is continued. The determination in step G 1- 5 may be performed by determining whether the determined display rotational speed DNe is substantially equal to the actual rotational speed RNe or the target rotational speed TNe. In the gradual change process in step G 1- 6, a change rate of the display rotational speed DNe is calculated based on a difference between the display rotational speed DNe and the actual rotational speed RNe or the target rotational speed TNe at a predetermined time interval, and the display rotational speed DNe is gradually changed at the calculated rate, so that the display rotational speed DNe thus gradually changed is displayed on the tachometer 44. The aforementioned time interval may be a constant value or a variable depending on whether the engine speed used for determining the display speed DNe is changed from the actual speed RNe to the target speed TNe or from the target speed TNe to the actual speed RNe or depending on the manner of shifting of the garage parking shift lever 72. The display rotational speed DNe may be gradually changed by a predetermined constant rate.If a negative determination is made in step G1-5, that is, if the gradual change operation in step S1-6 has been completed, that is, if the fluctuation limit display control section 38 is not in the transition process of the engine speed display control mode, the control flow proceeds to step G1-7, in which the display speed DNe determined based on the target speed TNe or the actual speed RNe is displayed. The display rotational speed DNe to be displayed on the tachometer 44 may be the target rotational speed TNe, the actual rotational speed RNe, or a value obtained by smoothing the target or actual rotational speed TNe or RNe.FIGS. 8 to 11 are the time charts showing examples of operating state changes of various portions of the vehicle 10 when the garage parking shift operation and the fluctuation limit display control of the display rotational speed DNe are executed along the flow charts of FIGS. 6 and 7. In the examples of FIGS. 8 to 11, the engine 20 is started with an operation of an ignition switch at a time t 1, and the shift operation of the shift lever 72 for garage parking from the neutral gear N to the forward gear D or the reverse gear R is performed at a time t 2 that is after a time t 1. A flag indicating "DEVIATION DETERMINATION" in FIGS. 8 to 11 is turned ON when ΔNe≥α, and is turned OFF when ΔNe<α. "RNe" of the "DISPLAY ROTATIONAL SPEED" indicates the conventional display control in which the actual rotational speed RNe is set as the display rotational speed DNe, while "TNe" indicates the fluctuation limit display control in which the target rotational speed TNe is set as the display rotational speed DNe. With respect to the "ROTATIONAL SPEEDS", the display rotational speed DNe, the actual rotational speed RNe, the turbine rotational speed Nt, and the target rotational speed TNe are respectively represented by a thick solid line, a thin solid line, a dash-dot line, and a broken line. The display rotational speed DNe is set equal to the actual rotational speed RNe or the target rotational speed TNe except for a period "ON" of the gradual change process of the display rotational speed DNe.In the example of FIG. 8, the shift operation of the garage parking shift lever 72 is performed after a comparatively short time from the start of the engine 20 at time t 1. At time t 2 at which the shift operation for garage parking is performed, the rotational speed difference ΔNe between the actual rotational speed RNe and the target rotational speed TNe is equal to or greater than the threshold value α, so that the negative determination is made in step G 1- 2. Accordingly, the actual rotation speed RNe is displayed as the display rotation speed DNe immediately after the time of the garage parking shift (immediately after the time t 2). At a time t3, the rotational speed difference ΔNe is decreased below the threshold value α by decreasing the actual rotational speed RNe to the target value TNe by feedback control of the engine torque Te. By lowering the rotational speed difference ΔNe below the threshold value α, step G 1- 3 for setting the target rotational speed TNe as the display rotational speed DNe is executed. Subsequently, steps G1-5 and G1-6 are executed to gradually change the display rotational speed DNe to the target rotational speed TNe. The gradual change operation is ended at time t 4 at which the display rotational speed DNe coincides with the target rotational speed TNe.At a time point t 5 in FIG. 8, the predetermined fluctuation limiting time Tgr has elapsed after the time point of the garage parking shift, and a flag indicating "DETERMINATION OF CHANGE-AMOUNT DISPLAY CONTROL" is turned OFF. Accordingly, step G 1- 4 follows step G 1- 1 to reset the display control mode of the fluctuation limit display control that determines the target rotation speed TNe as the display rotation speed DNe to the conventional display control that determines the actual rotation speed RNe as the display rotation speed DNe. In this case, too, the gradual change operation is performed based on the actual rotation speed RNe to gradually change the display rotation speed DNe. The gradual change operation to gradually change the display rotational speed DNe based on the actual rotational speed RNe is ended at time t 6.Note that the actual rotational speed RNe is temporarily decreased during a period between the times t 4 and t 5 during which a shift operation of the automatic transmission 24 occurs in response to the shift operation of the garage parking shift lever 72. In this period, the target rotational speed TNe is displayed as the display rotational speed DNe on the tachometer 44. Thus, the display rotational speed DNe is kept substantially constant despite a drop in the actual rotational speed RNe, so that there is a low possibility that the vehicle driver feels uncomfortable due to the display rotational speed DNe displayed on the speedometer 44. It is assumed that although the idle rotation fluctuation limiting control has been implemented by the idle rotation control section 33, the aforementioned drop of the actual rotation speed RNe occurs due to improper timing of the control and improper change amounts of the engine torque Te because the idle rotation fluctuation limiting control has been implemented immediately after the engine 20 is started, that is, while the temperatures of the coolant of the engine 20 and the working fluid of the automatic transmission 24 are still low and the engine torque Te is unstable.In the example of FIG. 9, the shifting operation of the shift lever 72 for garage parking is carried out at a later point in time (point in time t 2) than in the example of FIG. 8, wherein the rotational speed difference ΔNe between the actual rotational speed RNe and the target rotational speed TNe is less than the limit value α. In this case, the target rotation speed TNe is promptly set as the display rotation speed DNe, and the target rotation speed TNe is displayed as the display rotation speed DNe on the tachometer 44 after the gradual change process within the period between the times t 2 and t 3. In the example of FIG. 10, the shift operation for garage parking is performed at a later time (time t 2) than in the example of FIG. 9 after the actual rotational speed RNe has become substantially equal to the target rotational speed TNe. This example of Fig. 10 has substantially the same effect as the example of Fig. 9.In the example of FIG. 11, the garage parking shift operation is performed at substantially the same time as in the example of FIG. 10, but the actual rotation speed RNe is abruptly increased within the fluctuation limiting time Tgr (between the times t 2 and t 6) such that the rotation speed difference ΔNe between the actual rotation speed RNe and the target rotation speed TNe has reached the limit value α at the time t 4. It is also assumed that this change in the actual rotational speed RNe occurs by improper timing of the control of the engine torque Te, for example, despite the idling speed fluctuation limiting control that the idling speed control portion 33 has implemented immediately after the engine 20 is started, that is, the temperatures of the engine cooling liquid and the automatic transmission working liquid are still low and the engine torque Te is unstable. In this case, the display control mode is also reset within the fluctuation limit time Tgr from the fluctuation limit display control that determines the target rotation speed TNe as the display rotation speed DNe to the conventional display control that determines the actual rotation speed RNe as the display rotation speed DNe, and the display rotation speed DNe is gradually changed based on the actual rotation speed RNe within the period between the times t 4 and t 5.The engine speed display control portion 36 for displaying the operation speed of the engine 20 according to the present embodiment of the invention is configured to switch the engine speed display control mode from the conventional display control that determines the display speed DNe according to the actual speed RNe to the fluctuation limit display control that determines the display speed DNe according to the target speed TNe when the shift operation of the shift lever 72 for garage parking is performed. Accordingly, an amount of fluctuation of the display rotational speed DNe to be displayed on the speedometer 44 is reduced. Thus, the present engine speed display control portion 36 is configured to limit the variation of the display speed DNe so that the vehicle operator is less likely to feel uncomfortable due to the display speed DNe even when the actual speed RNe varies due to, for example, improper timing of control and improper amounts of change of the engine torque Te during a shift operation of the automatic transmission 24 in response to the shift operation of the garage parking shift lever 72 despite the idle speed variation limiting control executed by the idle speed control portion 33 immediately after starting the engine 20, that is, while the temperatures of the engine cooling liquid and transmission working liquid are still low and the engine torque Te is unstable.Further, the present embodiment is configured such that the fluctuation limit display control portion 38 gradually changes the display rotation speed DNe within the phase between the conventional display control that determines the actual rotation speed RNe as the display rotation speed DNe and the fluctuation limit display control that determines the target rotation speed TNe as the display rotation speed DNe. Accordingly, the vehicle operator is less likely to feel uncomfortable by the fluctuation of the display rotational speed DNe reduced within the phase between the conventional and fluctuation limit display control.The present embodiment is also configured such that the fluctuation limit display control portion 38 does not execute the fluctuation limit display control that limits the fluctuation of the display rotational speed DNe, whereas the conventional display control that determines the display rotational speed DNe according to the actual rotational speed RNe is executed within the period between the times t 4 and t 6 as illustrated in FIG. 11 while the rotational speed difference ΔNe between the actual rotational speed RNe and the target rotational speed TNe is equal to or greater than the predetermined limit value α. Although the vehicle operator would feel uncomfortable due to the difference between the display rotational speed DNe and the engine value estimated by him based on the operating sound of the engine 20, the fluctuation limit display control section 38 is configured to execute the conventional display control to change the display rotational speed DNe according to the fluctuation of the actual rotational speed RNe so that the vehicle operator is less likely to feel uncomfortable due to the difference between the display rotational speed DNe and the engine rotational speed value estimated by him based on the operating sound of the engine 20.Moreover, the present embodiment is configured such that the fluctuation limit display control portion 38 executes the fluctuation limit display control that determines the display rotation speed DNe according to the target rotation speed TNe so as to limit the fluctuation of the display rotation speed DNe only within the predetermined fluctuation limit time Tgr within which there is a possibility that the actual rotation speed RNe fluctuates by the shift operation of the shift lever 72 for garage parking. The fluctuation limit display control portion 38 switches the display control mode from the fluctuation limit display control to the conventional display control when the fluctuation limit time Tgr has elapsed. Accordingly, the fluctuation limit display control portion 38 makes it possible to reduce the possibility that the vehicle operator feels uncomfortable by reducing the fluctuation of the display rotational speed DNe, while minimizing a period of time within which the display rotational speed DNe other than the actual rotational speed RNe is displayed on the speedometer 44.Note that the idling speed control section 33 in the present embodiment is configured to execute the idling speed fluctuation limiting control for synchronously controlling the engine torque Te with the shifting operation of the automatic transmission 24 in consideration of the control behavior of the engine torque Te such that the amount of deviation of the actual rotational speed RNe from the target value TNe is decreased despite a change in the engine load in the shifting operation of the automatic transmission 24 due to the shifting operation of the garage parking shift lever 72. However, the idle speed control portion 33 may be configured to feedback control the engine torque Te simply so that the actual speed RNe matches the target value TNe. In this case, the fluctuation limit display control by the fluctuation limit display control portion 38 is also effective. For example, when the shift operation of the shift lever 72 for garage parking is performed from the neutral gear N to the forward or reverse gear D or R, the load 20 acting on the engine increases during the shift operation of the automatic transmission 24, and the actual rotational speed RNe temporarily fluctuates (decreases) as exemplarily shown in the time charts of FIGS. 8 to 10, so that there is a possibility that the vehicle operator feels uncomfortable due to the fluctuation of the display rotational speed DNe corresponding to the fluctuation of the actual rotational speed RNe. However, the variation of the display rotational speed DNe can be reduced by the variation limitation display control executed by the variation limitation display control portion 38 for setting the display rotational speed DNe corresponding to the target rotational speed TNe, and the vehicle operator is less likely to feel uncomfortable by the display rotational speed DNe displayed on the speedometer 44.Also, the present embodiment is configured to switch the display control mode from the conventional display control that determines the display rotation speed DNe according to the actual rotation speed RNe to the fluctuation limit display control that determines the display rotation speed DNe according to the target rotation speed TNe, so that the fluctuation amount of the display rotation speed DNe displayed on the speedometer 44 is decreased. However, it is possible to reduce the fluctuation amount of the display rotational speed DNe by selecting a high degree of smoothing of the actual rotational speed RNe to set the display rotational speed RNe as shown in the flow chart of FIG. 12 according to a second embodiment of this invention. A control routine shown in the flow chart of Fig. 12 is executed in place of the control routine shown in the flow chart of Fig. 7 according to the first embodiment. Steps G2-1 and G2-2 in the control routine of FIG. 12 are identical to steps G1-1 and G1-2 in the control routine of FIG. 7. If an affirmative determination is made in step G2-1, the control flow proceeds to step G2-2. On the other hand, if a negative determination is made in step G2-1, the control flow proceeds to step G2-4. When the negative determination is made in step G 2- 1, it is not necessary to execute the fluctuation limit display control for limiting the fluctuation of the display rotational speed DNe. In this case, the step G2-4 is executed to execute the conventional display control in which the display rotational speed DNe is set corresponding to the actual rotational speed RNe, concretely, by smoothing the actual rotational speed RNe. In this step G 2- 4, a small degree of smoothing of the actual rotational speed RNe is selected to calculate the display rotational speed DNe so that a rate and a variation amount of the calculated or determined display rotational speed DNe are relatively close to those of the actual rotational speed RNe. The degree of smoothing in step S 2- 4 may be zero, so that the actual rotational speed RNe is displayed as the display rotational speed DNe on the tachometer 44.In step G 2- 2 executed if the positive determination is made in step G 2- 1, a determination is made as to whether the amount of the rotational speed difference ΔNe between the actual rotational speed RNe and the target value TNe is less than the predetermined threshold value α. If the rotational speed difference ΔNe is smaller than the threshold value α, the control flow proceeds to a step G 2- 3. That is, if the rotational speed difference ΔNe is smaller than the threshold value α after performing the shift operation of the garage parking shift lever 72, step G 2- 3 of executing the fluctuation limit display control is executed in which a higher degree of smoothing of the actual rotational speed RNe than in the conventional display control is selected in step G 2- 4 of calculating the display rotational speed DNe, and the display rotational speed DNe thus calculated is displayed on the speedometer 44. The higher degree of smoothing of the actual rotational speed RNe for calculating the display rotational speed DNe enables a lower rate of fluctuation and a lower amount of fluctuation of the display rotational speed DNe than in the conventional display control in which the lower degree of smoothing is selected. Accordingly, the vehicle driver is less likely to feel uncomfortable due to the variation in the display rotation speed DNe.While the preferred embodiments and modifications have been described for illustrative purposes only, it is to be understood that the present invention may be embodied with various other changes and improvements apparent to those skilled in the art.LIST OF REFERENCE CHARACTERS10 Vehicle 12 Vehicle drive system 20 Engine (internal combustion engine, spark ignition engine) 22 Torque converter (fluid-operated power transmission device) 24 Automatic transmission 30 Electronic controller 33 Idling speed control part (idling speed control section) 36 Engine speed display control section (engine speed display control means) 38 Fluctuation limit display control section 44 Tachometer (engine speed display) 64 Engine speed sensor 72 Shift lever (manually operable transmission shift element) RNe Actual speed TNe Target speed DNe Display speed (display value) ΔNe Speed difference (amount of speed deviation) α Limit value Tgr Fluctuation limit time Ne Operating speed

Claims

An engine speed indication control means (36) of a vehicle (10) comprising: a vehicle propulsion system (12) including an engine (20), a fluid operated power transfer device (22), and an automatic transmission (24) having multiple gears each establishing different power transfer conditions; a manually operable transmission shift element (72) operable by a vehicle operator to place the automatic transmission in a selected gear; an accelerator pedal (62); an engine speed sensor (64) for sensing an actual value (RNe) of an operating speed (Ne) of the engine (20); and an engine speed indicator (44) for indicating a particular indication value (DNe) of the operating speed (Ne) of the engine (20), the engine speed indication control means (36) being configured to:, determining the display value (Dne) of the operation speed (Rne) of the engine (20) to be displayed by the engine speed display (44), and comprising: a fluctuation limit display control section (38) configured to execute fluctuation limit display control when a shift operation of the manually operable transmission shift element (72) is performed for garage parking while the vehicle (10) is stationary and the accelerator pedal (62) is in an unactuated position, wherein the fluctuation limit display control section (38) determines the display value (DNe) of the operation speed (Ne) of the engine (20) in the fluctuation limit display control such that a fluctuation amount of the display value (Dne) is smaller than in conventional display control, in which the display value (Dne) is determined in accordance with the actual value (RNe).The engine speed display control device (36) according to claim 1, wherein the fluctuation limit display control section (38) determines the display value (Dne) of the operation speed (Ne) of the engine according to a target value (TNe) of the operation speed (Ne) used in place of the actual value (RNe) in the fluctuation limit display control.The engine speed display control device (36) according to claim 2, wherein the fluctuation limit display control section (38) gradually changes the display value (Dne) of the operation speed (Ne) of the engine (20) within a phase between the conventional display control and the fluctuation limit display control.The engine speed display control device (36) according to claim 1, wherein the fluctuation limit display control section (38) selects a higher degree of smoothing of the actual value (Rne) of the operation speed (Ne) of the engine (20) to reduce an amount of fluctuation of the display value in the fluctuation limit display control as compared with the conventional display control.The engine speed display control device (36) according to any one of claims 1 to 4, wherein the fluctuation limit display control section (38) does not execute the fluctuation limit display control for limiting a fluctuation of the display value (Dne) of the operation speed (Ne) of the engine (20) when a deviation amount (ΔNe) of the actual value (Rne) of the operation speed (Ne) of the engine (20) from a target value (TNe) of the operation speed (Ne) is equal to or greater than a predetermined threshold value (α).The engine speed display control device (36) according to any one of claims 1 to 5, wherein the fluctuation limit display control portion (38) switches a display control mode from the fluctuation limit display control for limiting the fluctuation of the display value (Dne) of the operation speed (Ne) of the engine (20) to the conventional display control when a predetermined fluctuation limit time (Tgr) has elapsed after a time point at which the shift operation of the manually operable transmission shift element (72) for garage parking has been performed.The engine speed display control device (36) according to any one of claims 1 to 6, wherein the vehicle (10) further includes an idling speed control portion (33) configured to execute idling speed fluctuation limiting control to control a torque (Te) of the engine (20) in synchronization with a shift operation of the automatic transmission (24) in response to the shift operation of the manually operable transmission shift element (72) for garage parking and in consideration of a control response of the torque of the engine (20) so as to reduce an amount of deviation of the actual value (RNe) of the operating speed of the engine (20) from a target value (TNe) of the operating speed during the shift operation of the automatic transmission (24).

Images