A SLIPPAGE PREVENTING APPARATUS FOR A VEHICLE WITH AN AUTOMATIC TRANSMISSION

Abstract: The output of the engine (6) is reduced by the slip control as a degree of slippage of the driven wheels (4,5) on pavement gets larger. Upon the slip control, the shift control of the automatic transmission (8) is brought into a state in which the speed stages are unlikely to be shifted.

Description: The present invention relates to a slip preventing system for a vehicle having the features stated in the preamble of claim 1 or claim 2. The prevention of excessive slip of the driven wheels on a road surface permits an effective provision of the required traction force of the vehicle and is further favourable from the standpoint of safety, that is to prevent the spinning of the vehicle. JP-A 16 948/1983 and 56 662/1985 disclose a slip control system wherein the torque on the driven wheels is decreased by applying a braking force to the driven wheels by means of the brake and by decreasing the torque output from the engine. More specifically, JP-A 16 948/1983 is directed to a slip control system wherein the driven wheels are braked only when the slip amount is smaller, on the one hand, and in addition, the torque output from the engine is decreased when the slip amount becomes greater, on the other hand. JP-A 56 662/1985 is directed to a slip control technology wherein, when one of the left and right driven wheels slips to a greater degree than the other, only the one driven wheel is braked and, when the left and right driven wheels both slip to a greater degree, the torque of the engine is reduced in addition to the braking of the driven wheels. An increasing number of automobiles is equipped with an automatic transmission of the multispeed stage type that is designed to transmit the output of the engine to the driven wheels. Such an automatic transmission can automatically shift the speed stages on the basis of shift characteristics which have been set in advance, wherein e.g. the vehicle speed and the throttle opening degree are used as parameters. A vehicle equipped with such an automatic transmission may be designed in such a way that the speed stages are shifted upon the slip control. In instances where the engine output is adjusted during the operation of the slip control the speed stages might be shifted when the throttle opening varies under the slip control, that is when the throttle opening, as being related to the engine output, is used as a parameter within the shift characteristic. Also the speed stages might be shifted during the slip control on account of an alteration in torque which is applied to the driven wheels, in case the torque is involved in the shift characteristic of the speed stages. Thus, for a vehicle having an automatic transmission it is likely that upshifting and downshifting of the speed stages is frequently repeated during the slip control on account of an interaction between the slip control and the shift characteristics of the automatic transmission. From US-A 46 82 667 a slip preventing system having the features of the preamble of claim 1 is known wherein the slip control is suspended during a transitional period when the engine is about to stall or the automatic transmission undergoes shifting. During that transitional period a series of steps of the slip control are skipped. This is to avoid any unfavourable operational condition of the engine, e.g. stalling, which might occur in the course of the slip control. However, during such transitional periods hazardous situations might occur, too, if the slip control is suspended under very bad road conditions, e.g. on slippery icy roads. From CH-A 526 417 a slip control system according to the preamble of claim 2 is known wherein shifting of the automatic transmission is definitely prevented as soon as an excessive slip of a driven wheel is detected. Shifting of the automatic transmission is allowed not earlier than until the excessive slipping has come to an end. Since, particularly on slippery icy roads, it is possible that the slip amount only slowly converges to a target slip amount and thus slipping may occur over an extended time period. Within this time period unfavourable operational engine conditions might come up which would require shifting of the automatic transmission which, however, is definitely prevented. In view of the prior art discussed above it is an object of the present invention to provide a slip preventing system for a vehicle having an automatic transmission which is adapted to control undesirable shift of the speed stages during the slip control. In a slip control system according to the preamble of claim 1, this object is achieved in one aspect of the present invention by the features according to the characterizing portion of claim 1. In a slip preventing system according to the preamble of claim 2 this object is achieved in an other aspect of the present invention by the features according to the characterizing portion of claim 2. The arrangement according to the invention prevents an interaction of the slip control with the shift of speed stages in order to control the automatic transmission so as to be unlikely to shift the speed stages during the slip control. The slip preventing system may contain a transmission control means, firstly, which may comprise a first shift characteric for ordinary drive operation, viz., for driving under ordinary conditions, without the slip control, and a second shift characteristic for the slip control. For the second shift characteristic the vehicle speed may be set as a sole parameter, thus enabling the slip control to exert no adverse influence at all upon a variation in the engine output. As is conventional, the first shift characteristic may for example use, as a parameter, an opening degree of the throttle valve (hereinafter be referred to as a throttle opening), which may shift the speed stages in accordance with the engine output. The transmission control means may also comprise a system which fixes a speed stage at a particular position, for example, at the 2nd speed stage, during the slip control, thereby preventing the slip control from interacting with the shift of speed stages. It may further comprise only one shift characteristic of the type unlikely to cause the shift of the speed stages in accordance with a variation in the engine output. Such a shift characteristic may use, for example, an opening degree of an accelerator (hereinafter will be referred to as an accelerator opening) or a vehicle speed as a parameter. In other words, the accelerator opening does not virtually vary as the engine output is changed by the slip control, so that the shift of the speed stages which may arise upon the slip control can be prevented. It is further noted that the use of the accelerator opening as a parameter can shift the speed stages in response to requirements for acceleration or deceleration by the driver. The above and other objects, features and advantages of te present invention will become apparent from the description of preferred embodiments which will be hereinafter described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing one example of the slippage preventing apparatus according to the present invention. FIG. 2 is a diagram showing one example of a braking liquid pressure control circuit. FIGS. 3 through 7 are flowcharts each showing a control manner according to the present invention. FIG. 8 is a graph showing an example of the relationship of accelerator openings vs. throttle openings at the time when no slip control is under way. FIG. 9 is a graph showing one example of shift characteristics for ordinary drive operation. FIG. 10 is a graph showing one example of shift characteristics for the slip control. FIG. 11 is a graph showing the relationship of driving forces vs. slip ratios. FIGS. 12 and 14 each is a flowchart showing other examples of shift control according to the present invention. FIGS. 15 to 17 are graphs showing shift characteristics for holding mold. FIG. 18 is a block diagram showing the structure according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described by way of examples in conjunction with the drawings attached hereto. In the following embodiment, it is to be understood that a slippage of the driven wheel or wheels is controlled in such two ways as decreasing a torque to be generated by the engine and applying a braking force from the brake. Outline of Overall Construction In FIG. 1, an automobile 1 comprises left-hand and right-hand undriven front wheels 2 and 3 and left-hand and right-hand driven rear wheels 4 and 5, respectively. In this embodiment, the automobile 1 is of the FR (front engine rear wheel drive) type in which an engine 6 as a source of power is mounted in a forward portion thereof and an output or torque generated by the engine 6 is transmitted through a clutch 7, an automatic transmission 8 having forward three speed stages, a propeller shaft 9, a differential gear 10 and left-hand and right-hand drive shafts 11L and 11R to the respective left-hand and right-hand driven rear wheels 4 and 5. The engine 6 is designed to implement the load control, that is, a control of the output torque, by a throttle valve 13 mounted on an intake air passage 12. More specifically, the engine 6 is a gasoline engine of the type that the output torque varies with an amount of intake air. The amount of the intake air may be controlled by the throttle valve 13 that is electromagnetically opened or closed by a throttle actuator 14. Although a stepping motor is used as the throttle actuator 14 in this embodiment, there may be employed an appropriate means that may be electromagnetically controlled by a DC motor or by fluid pressures such as hydraulic pressures. The wheels 2 to 5 are provided with a brake 21, 22, 23 and 24, respectively, and the brakes 21 to 24 may be each a disk brake. As is known, the disk brake comprises a disk 25 rotatable with the corresponding wheel and a caliper 26. The caliper 26 is provided with a brake pad and a wheel cylinder, and the brake pad depresses the disk 5 by a braking force corresponding to an amount of a braking liquid pressure supplied to the wheel cylinder. A master cylinder 27 functioning as a source of generating the braking liquid pressure may be of the tandem type having two discharge outlets 27a and 27b. A brake pipe 28 extending from the discharge outlet 27a is branched at its middle portion along the line into branch pipes 28a and 28b, the branch pipe 28a being connected to the wheel cylinder of the brake 22 for the right-hand front wheel 3 and the branch pipe 28b being connected to the wheel cylinder of the brake 23 for the left-hand rear wheel 4. A brake pipe 29 extending from the discharge outlet 27b is branched at its middle portion along the line into branch pipes 29a and 29b, the branch pipe 29a being connected to the wheel cylinder of the brake 21 for the left-hand front wheel 2 and the branch pipe 29b being connected to that of the brake 24 for the right-hand rear wheel 5. As described hereinabove, the brake pipe system may be of a so-called 2-system X type. To the branch pipes 28a and 29a for the respective brakes 23 and 24 of the driven rear wheels 4 and 5 are connected, respectively, hydraulic pressure control valves 30 and 31 of the electromagnetic type as means for controlling a braking force. The braking liquid pressure generated by the master cylinder 27 corresponds to an amount or force of a brake pedal 32 stepped down by the operator D. Braking Pressure Regulating Circuit As shown specifically in FIG. 2, the liquid pressure control valves 30 and 31 are provided each with a cylinder 41 and a piston 42 inserted slidably in the cylinder 41. The piston 42 divides the cylinder 41 into and defines a volume-variable chamber 43 and a control chamber 44. The volume-variable chambers 43 of the liquid pressure control valves 30 and 31 work as a passage of the braking liquid pressure to the brakes 23 and 24 from the master cylinder 27, respectively. Accordingly, the volume of the volume-variable chamber 43 can be varied by adjusting a position of displacement of the piston 42, thereby generating the braking liquid pressure to the brakes 23 and 24 and at the same time increasing, decreasing or retaining the braking liquid pressure generated. The piston 42 is constantly actuated by a return spring 45 to as to cause the volume in the volume-variable chamber 43 to be increased. The piston 42 is integrated with a check valve 46 that in turn is designed to close its inlet side to the volume-variable chamber 43 when the piston 42 is displaced in such a manner that the volume in the volume-variable chamber 43 is decreased. This arrangement allows the braking liquid pressure generated in the volume-variable chamber 43 to work only on the brakes 23 and 24 for the driven rear wheels 4 and 5 and not to act on the brakes 21 and 22 for the undriven front wheels 2 and 3, respectively. The position of displacement of the piston 42 is adjusted by regulation of the hydraulic pressure against the control chamber 44. More specifically, a supply pipe 48 extending from a reservoir 47 is branched at a middle portion thereof along the line into two branch pipes 48L and 48R, the branch pipe 48R being connected to the control chamber 44 for the valve 30 and the other branch pipe 48L being connected to the control chamber 44 for the valve 31. To the supply pipe 48 are connected a pump 49 and a relief valve 50. To the branch pipes 48L and 48R are connected supply valves SV3 and SV2, respectively, each consisting of an electromagnetically opening or closing valve. The control chambers 44 are additionally connected to the reservoir 47 through discharge piped 51L and 51R, to which discharge valve SV1 and SV4, respectively, each consisting of an electromagnetically opening of closing valve, are connected. When the braking is effected using the hydrualic pressure regulating valve 30 or 31 or during the slip control, on the one hand, the check valve 46 acts in such a manner that the brake does not basically work by means of operation of the brake pedal 32. When the braking liquid pressure to be generated by the hydraulic pressure regulating valve 30 or 31 is small or when the pressure is being decreased, on the other hand, the brake is allowed to work as the brake pedal 32 is stepped down. When no braking liquid presure for the slip control is generated by the hydrualic pressure regulating valves 30 and 31, the usual braking action that arises from operation of the brake pedal 27 is caused to work because the master cylinder 27 is allowed to be communicated with the brakes 23 and 24. A control of each of the valves SV1 to SV4, inclusive, is implemented by opening or closing by a brake control unit U B as will be described more in detail below. The table below demonstrates relationships of a state of the braking liquid pressure against the brakes 23 and 24 with operation of each of the valves SV1 to SV4, inclusive. Brakes Pressure VALVES SV1 SV2 SV3 SV4 24 Increase - - - - Opened Closed Decrease - - - - Closed Opened Retain - - - - Closed Closed 23 Increase Closed Opened - - - - Decrease Opened Closed - - - - Retain Closed Closed - - - - Outline of Control Units: Referring to FIG. 1, reference symbol U denotes generally a control unit group that consists roughly of a brake control unit U B , a throttle control unit U T , a slip control unit U S and a control unit U AT for shift control. The brake control unit U B is designed so as to control the opening or closing of each of the valves SV1 to SV4, inclusive, as have been described above, on the basis of signals from the slip control unit U S . The throttle control unit U T is to control the driving of the throttle actuator 14 on the basis of signals from the slip control unit U S . The slip control unit U S comprises a computer of the digital type such as a microcomputer. To the slip control unit U S are given signals output from each of sensors (or switches) 61 and 63 to 67, inclusive. The sensor 61 is to detect a degree of opening of the throttle valve 13. The sensors 63 and 64 are to detect rotational speeds of the respective left-hand and right-hand undriven front wheels 2 and 3, or a vehicle speed, and the sensors 65 and 66 are to detect rotational speeds of the respective left-hand and right-hand driven rear wheels 4 and 5. The sensor 67 is to detect an amount of operation of an accelerator 69, that is, a degree of accelerator opening. The control unit U S is designed to give an output to the control unit U AT for the shift control in such a manner, for example, that a "High" signal is produced when the slip control is implemented and a "Low" signal is produced when no slip control is under way. The control unit U AT may comprise a microcomputer. Into the control unit U AT are input a signal of a throttle opening from the sensor 61, a signal of the rotational number of the output shaft of the automatic transmission 8, i.e., a vehicle speed, from the sensor 71, a signal of a current gear position (shifting speed stages) of the automatic transmission 8 from the sensor 72, and a signal of implementation of or failure to implement the slip control from the control unit U S . The control unit U AT gives a shift solenoid 73 of the automatic transmission A a shift signal for providing a predetermined speed stage and, in this embodiment, the control unit U AT stores two shift characteristics, one being used during operation of the slip control only and the other being used during ordinary drive operation. The two shift characteristics are slected in accordance of absence or presence of the slip control. The slip control units U S and U AT basically comprises a CPU, ROM, RAM, and CLOCK. It is further provided with input and output interface as well as A/D or D/A converters in accordance with input or output signals. These are the same as a conventional one where a microcomputer is employed so that detailed description thereon will be omitted herein for the brevity of description. The control manner of the control unit group U will be described in the order as have been described hereinabove. It is noted that the driving force generally becomes the maximum in instances where a slip ratio S ranges from abnout 1.04 to 1.1. The slip ratio or amount S for the driven wheels may be defined by the following relationship (1): S = WD WL (1) where WD is an average of rotations of the left-hand and right-hand driven wheels 4 and 5; and WL is an average of rotations of the left-hand and right-hand undriven wheels 2 and 3 (a vehicle speed). Throttle Control The throttle control unit U T is designed to establish a feedbck of the throttle actuator 14 for the throttle valve 13 so as to give a target throttle opening. When no slip control is implemented during the throttle control, the target throttle opening is regulated so as to be proportional by a 1-to-1 ratio to an amount of operation of the accelerator 69 operated by the operator D. One example of the relationship of the throttle opening with the accelerator opening at this time is shown in FIG. 8. It is also noted herein that the throttle control unit U T is designed to implement the throttle control in such a manner that a target throttle opening T n operated by the slip control unit U S is given at the time of the slip control without following the characteristics as demonstrated in FIG. 8. The feedback of the throttle valve 13 using the throttle control unit U T is established in this embodiment by way of the PI-PD control so as to compensate for a variation in response speeds of the engine 6. More specifically, the opening of the throttle valve 13 is subjected to the PI-PD control during the slip control for the driven wheels in such a manner that the current slip value calculated by the above formula (1) corresponds with the target slip value. In other words, as will be apparent from the above formula (1), the throttle opening of the throttle valve 13 is controlled to satisfy the following relationship (2): WET = WL x ST (2) where WET is a driven wheel target rotational number; and ST is a target slip value. Brake Control During the time of the slip control, a feedback of the left-hand and right-hand driven wheels 4 and 5 is established using the control unit U B so as to allow their respective rotations or slippage to separately become a predetermined target slip value ST. It is possible that this slip value becomes a value different from the target slip value ST for the engine. In other words, the brake control is implemented by way of the feedback control such that a driven wheel rotational number WBT is determined by the following relationship (3): WBT = WL x ST (3) It is to be understood here that the driven wheel rotational number WBT in the formula (3) contains a correction in accordance with the steered angle of the steering wheel as the target driven wheel rotational speed WET in the formula (2) above. In this embodiment, the feedback is established by means of the I-PD control so as to satisfy the relationship as shown in the above formula (3). More specifically, an amount of operation of the brake Bn - an amount of operation of the piston 44 in the valve 30 or 31 - is subjected to the I-PD operation. It is noted that the braking liquid pressure is decreased when the operation amount of the brake Bn is larger than zero, viz., when it is positive, on the one hand, and the braking liquid pressure is increased when the operation amount of the brake Bn is equal to or lower than zero, on the other hand. The braking liquid pressure is increased or decreased by opening or closing the valves SV1 through SV4 as have been described above. Speeds of increasing or decreasing the braking liquid pressures are adjusted by ratios of the opening time to the closing time (duty ratios) of the valves SV1 to SV4, inclusive, that is, by means of the duty control. It is further noted herein that the duty control is conducted so as to be proportional to the absolute value of the operation amount of the brake Bn given by the relationship (3) above. Accordingly, the absolute value of the brake operation amount Bn leads to a proportion to a speed of a variation in the braking liquid pressures. On the contrary, the duty ratio determining the speed of increasing or decreasing the braking liquid pressures indicates the brake operation amount Bn. Shift Control The control unit U AT for the shift control stores the first shift characteristic as shown in FIG. 9 and the second shift characteristic as shown in FIG. 10. The first shift characteristic contains upshifting and downshifting characteristic lines using a throttle opening and a vehicle speed as parameters, as have generally been used in conventional manner. The second shift characteristic contains upshifting and downshifting characteristic lines using a vehicle speed only as a parameter. The first shift characteristic as shown in FIG. 9 is selected to carry out the shift control upon driving under ordinary conditions while the second shift characteristic as shown in FIG. 10 is selected for the shift control during the slip control. One example of the slip control according to the present invention will be described below in conjunction with the flowcharts attached hereto. FIG. 3 (Main Routine) As the key switch and the starter switch are turned on to thereby start the engine 6, the process is started from the step P1. At step P1, the overall system is initialized. At step P2, an output from each of the sensors 61, and 63 through 67 are read in. At step P3, a basic throttle opening TOB is computed from a map, as shown in FIG. 8, on the basis of the read-in data in accordance with an accelerator opening and, at step P4, a rotational speed of each of wheels 2 through 5 is computed. Then, at step P5, an average rotational speed SPB of the undriven wheels 2 and 3 is computed by adding the rotational speed of the left-hand undriven wheel 2 to that of the right-hand undriven wheel 3 and then dividing the sum by 2. After the step P5, the target slip value ST for the driven wheels is decided at step P7 by the basic vehicle speed SPB calculated in step P5. This decision is made on the basis of a map (not shown) prepared and stored in advance in such a manner that the target slip value ST for the driven wheel gets larger continuously as the basic vehicle speed SPB gets faster. Step P8 computes a basic target driven wheel rotational speed WB by multiplying the basic vehicle speed SPB by the target slip value ST computed at the step P7. The flow then proceeds to stp P10 for the slip control by the engine and step P11 for the slip control by the brake, as will be described more in detail. FIG. 4 (Slip Control by Engine) FIG. 4 illustrates the slip control by the engine and corresponds to the step P10 shown in FIG. 3. At step P21, an average ddriven wheel rotational speed SPR is computed by adding a rotational speed of the left-hand driven wheel 4 to that of the right-hand driven wheel 5 and then dividing the sum by 2. Step P22 computes a target throttle opening Tn necessary for the average driven wheel rotational speed SPR to reach the target slip value ST (target rotational number WB) by means of the PI-PD control. At step P23, it is judged whether or not the target throttle opening Tn computed at the step P22 is larger than the basic throttle opening TO B computed at the step P3 above. When NO at the step P23, on the one hand, the implementation of the slip control is required so that the flow advances to step P24 where the target throttle opening Tn computed at the step P22 is set intactly as a final target throttle opening Tn for the slip control. At step P25, the "High" signal indicative of the slip control being under way is output to the control unit U AT . When YES at the step P23, on the other hand, the basic throttle opening TOB is set as a final target throttle opening Tn for driving under ordinary conditions at step P26. And at step P27, the "Low" signal indicative of the slip control being not in the progress is output to the control unit U AT . FIG. 5 (Throttle Control) The flow chart shown in FIG. 6 may be designed to interrupt, for example, every 1 msec into the flow chart shown in FIG. 3. The processing in FIG. 5 is effected to realize the final target throttle opening Tn set at the step P24 or P25 in FIG. 4. At step P31, the current throttle opening is read in from a monitor as the stepping number THM of the stepping motor as the throttle actuator 14. At step P32, it is then judged whether or not the final target throttle opening Tn is equal to the current throttle opening THM. When YES at the step P32, no alteration of the throttle opening is required so that the control is finished. When NO at the step P32, the flow proceeds to step P33 and it is judged therein whether the final target throttle opening Tn is smaller than the current throttle opening THM. If it is judged NO at the step P33, the throttle opening THM is increased by one stepping at step P34 and the stepping number THM is counted up by one at step P35, on the one hand, and, if YES at the step P33, it is decreased by one stepping at step P36 and the stepping number THM is counted down by one at step P37, on the other hand. The counts at steps P35 and p37 are then read in at the step P31. FIG. 6 (Slip Control by Brake) FIG. 6 illustrates the slip control by the brake and corresponds to the step P11 in FIG. 3. Step P41 judges whether or not a predetermined degree of slippage occurs on the right-hand driven rear wheel 5. More specifically, whether or not the slip ratio for the right-hand rear wheel is larger than 12.5% of the vehicle speed is judged at te step P41. If YES at the step P41, the flow advances to step P42 where the operation amount Bn of the right-hand brake operated by means of the I-PD control is computed. Then, at step P43, the operation amount Bn computed at the step P42 is output whereby the braking force in an amount corresponding to the output operation amount Bn is applied to the right-hand driven rear wheel 5. If it is judged NO at the step P41, the flow proceeds to step P48 where the right-hand brake is released. After the steps P43 and P48, the flow proceeds to step P44 and it is judged therein whether or not a predetermined degree of slippage occurs on the left-hand driven rear wheel 4 in substantially the same manner as at the step P41. When YES at the step P44, on the one hand, the operation amount Bn of the left-hand brake operated by means of the I-PD control is computed at step P45 and the resulting operation amount Bn is output at step P46, whereby the braking force in an amount corresponding to the output operation amount Bn is applied to the left-hand driven rear wheel 5. When NO at the step P44, on the other hand, the left-hand brake is forced to be released at step P47. FIG. 7 (Shift Control) The flowchart as shown in FIG. 7 is to process the interruption, for example, for every 20 msec. At step P51, signals from the sensors 61, 71 and 72 and a signal of implementation of or failure to implement the control unit U S are read in. In other words, a "High" or "Low" signal at the respective steps P25 and P27 in FIG. 4 is input. Step P52 judges whether or not the slip control is under way, that is, whether or not the "High" signal is output at the step P25. If it is judged YES at the step P52, on the one hand, the second shift characteristic for the slip control as shown in FIG. 10 is set at step P53, and if NO at the step P52, on the other hand. the first shift characteristic for ordinary drive operation as shown in FIG. 9 is set at step P54. After the step P53 or P54, a gear position CP (speed stages) to be shifted is determined on the basis of the shift characteristic set at the step P53 or P54. Then at step P56, the current gear position GPR is ste. At step P57, it is judged whether or not the gear position CP coincides with the current gear position GPR. When it is judged YES at step P57, on the one hand, no shift of speed stages is required so that the control is finished. When it it judged NO at the step P57, on the other, the flow advances to step P58 and it is then judged therein whether or not the gear position CP is larger than the current gearposition GPR. If YES at the step P58, an output is given to the shift solenoid 73 at step P59 and the speed stages are shifted up. If NO at the step P58, an output is given to the shift solenoid 73 at step P60 in order to downshift the speed stages. Second Embodiment FIG. 12 shows a second embodiment of the slippage preventing apparatus according to the present invention. In this embodiment, it is to be noted that the speed stage is fixed as the one immediately before the start-up of the slip control for a predetermined period of time, for example, for 60 seconds, and the shift is made after the elapse of the predetermined period of time. Given the foregoing, the flowchart shown in FIG. 12 will be described hereinbelow, provided that step P56 to P60 in FIG. 12 are substantially the same as the step P56 to P60 in FIG. 7 so that a description thereon will be omitted herein. At step R11, there are input data which are substantially the same as in the step P51 in FIG. 7. And at step R12 is read in a target gear position TGP that follows the shift characteristic by referring to the map in FIG. 9 representing the first shift characteristic involved with ordinary drive operation. At step R13, it is judged whether or not the slip control is currently in progress in substantially the same manner as at the step P52 in FIG. 7. If NO at the step R13, the target gear position TGP read in at the step R12 is set intactly as a final target gear position CP at step P14. Thereafter, the processing is effected at steps P56 to P60 in FIG. 12 to reach the target gear position CP by following the step P56 to P60 in FIG. 7. If YES at the step R13 and it is judged that the slip control is currently under way, it is further judged at step R20 whether or not the target gear position TGP at the step R12 is identical to the previous target gear position TGPL. If YES at the step R20, the flow proceeds to step R22 where a count value T of a timer for counting a period of time elapsed from the start-up of the slip control is counted up by one. Thereafter the processing of the steps P56 to P60 is effected. If NO at the step R20, it is then judged at step R23 whether or not the count value T for the timer is larger than 60 seconds. If NO at the step R21, the flow advances to the step R22 and subsequent steps which follow for further processing. If YES at the step R21, it is judged that the slip control elapsed 60 seconds from the commencement of the slip control. At this time, the target gear position TGP set at the step R12 is set at step R23 as a final target gear position CP. And at step R24, the count value T for the timer is then reset to zero at step P25. Then at step R25, the target gear position TGP at the step R12 is renewed as the previous target gear position TGPL. The final target gear position CP is then processed by steps P56 to P60 in the same manner as have been described hereinabove. Third Embodiment FIG. 13 relates to a third embodiment according to the present invention. In FIG. 13, steps P56 and P60 are substantially the same as shown in FIG. 7 so that a description thereon will be omitted herein for avoidance of duplicity. In this embodiment, the gear position is fixed at the 2nd speed stage during the slip control being under way. As the the 2nd speed stage generally may cover a speed range from the start-up to a high speed range faster than 100 km per hour, then this gear position is considered appropriate for restricting the shift of speed stages during the slip control and further avoiding problems with the drive which may arise upon restriction over the shift of speed stages. In this embodiment, it is to be noted that an indicator 81 ( a lamp as shown in FIG. 1) is provided in order to show the driver the fact that a particular shift characteristic for exclusive use during the slip control is adopted. In this embodiment, a gear position fixing switch 82 (shown in FIG. 1) is disposed to thereby select an arbitrary gear position from the 1st to 3rd speed stages via manual operation by the driver. The gear position selected by the switch 82 is kept on being fixed during operation of the switch 82 regardless of whether the slip control is under way. Given the foregoing, a state of operation of the switch 82 is read in at step R31 in addition to the data as read in at the step P51 in FIG. 7. Then at step R32, it is judged whether or not the switch 82 is turned on. If YES at the step R32, the gear position selected by the switch 82 is set as the target gear position CP at steps R33 to R37. In other words, it is judged at step R33 whether or not the switch 82 selects a gear position for the 3rd speed stage. If YES at the sstep R33, the gear position for the 3rd speed stage is set at step R35 as the final target gear position CP. If NO at the step R33, it is then judged at step R34 whether or not the switch 82 selects a gear position for the 2nd speed stage. If YES at the step R34, the gear position selected by the switch 82 is set as the final target gear position CP at step R36. If NO at the step R34, the gear position for the 1st speed stage is set as the final target gear position CP at step R37. After the steps R35, R36 and R37, the indicator lamp 81 is turned off at step R38 and then the processing following steps P56 to P60 is effected in the same manner as in FIG. 7. If NO at the step R32, it is then judged at step R44 whether or not the slip control in progress. If NO at the step R44, the target gear position CP is read in at step R45 by referring to the shift characteristic shown in FIG. 9. Thereafter the processing of the steps P56 to P60 is effected in the same manner as above through the step R38 where the indicator lamp 81 is turned off in order to realize the target gear position CP read in at the step R45. If YES at the step R44, the target gear possition CP is set at the 2nd speed stage position at step R46. After the step R46, the indicator lamp 81 is turned on at step R47 and then the processing from the step P56 to the step P60 is effected to realize the gear position for the 2nd speed stage. Fourth Embodiment FIGS. 14 to 17 show a fourth embodiment according to the present invention. In this embodiment, there are selectively used a basic shift characteristic as shown in FIG. 9 and shift characteristics for a holding mode as shown in FIGS. 15 to 17. The shift characteristic for the holding mode may be selected by means of manual operation of a holding mode switch 83 (as shown in FIG. 1) by the driver. The speed stage is selected which follows the holding mode when the holding mode switch 83 is manually selected or during operation of the slip control. In other cases, the speed stage following the basic shift characteristic is selected. It is to be noted herein that, when the holding mode is selected, that is, for example, when a selection lever is held at the "D" range position, the shift characteristic as shown in FIG. 15 may be selected; when the selection lever is held at the "S" range position, the shift characteristic as shown in FIG. 16 may be selected; and when the lever is held at the "L" range position, the shift characteristic as shown in FIG. 17 may be seleclted. These shift characteristics are set each using only the vehicle speed as a parameter. The automatic transmission with such a holding mode is known so that a further description will be omitted herein. Referring now to FIG. 14, at step R51, there are read in a state of operation of the holding mode switch 83 as well as dada in the same manner as at the step P41 in FIG. 4. At step R52, it is judged whether or not the holding mode is selected, that is, whether or not the holding mode switch 83 is turned on. If YES at the step R52, the flow advances to step R60 and then the shift characteristic for the holding mode is selected from the shift characteristics as shown in FIGS. 15 to 17 on the basis of the "D", "S" or "L" range position and the target gear position CP is set in accordance with the shift characteristic selected at the step R60. The steps P56 to P60 are then processed until the target gear position CP is realized. If NO at the step R52, it is then judged whether or not the slip control is currently in progress at step R53. If YES at the step R53, the flow proceeds to the step R60 and the same proceeding as have been described hereinabove is repeated to provide the shift following the shift characteristic for the holding mode. If NO at the step R53, the target gear position CP is read in according to the basic shift characteristic as shown in FIG. 9. Although the foregoing embodiments relate to those where the torque to be applied to the driven wheels is adjusted by a control over both the engine output and the braking force by the brake, it is to be understood that the slip control can be conducted using adjustment of the engine output only. It is further understood that the engine output may be adjusted using changes in air-fuel ratios, ignition timings, supercharging pressures or the like or alterations in the number of operating cylinders. It is to be understood that the foregoing text and drawings relate to embodiments of the present invention given by way of examples but not limitation. Various other embodiments and variants are possible within the spirit and scope of the present invention as defined by the claims.

Claims: In a vehicle, wherein the output of an engine (6) is transmitted to a driven wheel by an automatic transmission (8), a slip preventing system comprising an output adjusting means (13) for adjusting the output of the engine (6), a slip amount detecting means (U S , step P23, Fig. 4) for detecting of the slip amount of the driven wheel (4, 5) on a road surface, an accelerator amount detecting means (67), a basic output adjusting means (U T ) for adjusting of said output adjusting means (13) on the basis of an accelerator amount signal from said accelerator amount detecting means (67), an output controlling means (U S ) adapted to reduce the engine output by controlling said output adjusting means (13) prior to said basic output adjusting means (U T ) in response to a signal of said slip amount detecting means (U S , step P23, Fig. 4) signalling excessive slip of the driven wheel (4, 5) and a shift control means (U AT ) adapted to control the shifting of the automatic transmission (8), characterized in that the shift control means (U AT ) is set so as to restrict the shifting of the speed stages of the automatic transmission (8) during a predetermined time period beginning from the initiation of the slip control implemented by said output controlling means (U S ). In a vehicle, wherein the output of an engine (6) is transmitted to a driven wheel by an automatic transmission (8), a slip preventing system comprising an output adjusting means (13) for adjusting the output of the engine (6), a slip amount detecting means (U S , step P23, Fig. 4) for detecting of the slip amount of the driven wheel (4, 5) on a road surface, an accelerator amount detecting means (67), a basic output adjusting means (U T ) for adjusting of said output adjusting means (13) on the basis of an accelerator amount signal from said accelerator amount detecting means (67), an output controlling means (U S ) adapted to reduce the engine output by controlling said output adjusting means (13) prior to said basic output adjusting means (U T ) in response to a signal of said slip amount detecting means (U S , step P23, Fig. 4) signalling excessive slip of the driven wheel (4, 5) and a shift control means (U AT ) adapted to control the shifting of the automatic transmission (8) in such a way that a shifting is not caused when the slip control is implemented by said output controlling means (U S ), characterized in that the shift controlling means (U AT ) controls the automatic transmission (8) by holding a predetermined speed stage thereof during a predetermined time period beginning from the initiation of the slip control. A slip preventing system as claimed in claim 1 or 2, characterized in that the shift control means (U AT ) controls the shift of the speed stages of the automatic transmission (8) on the basis of a shift characteristic which is defined by the engine output and the vehicle speed as parameters when the vehicle is driven under ordinary driving conditions. A slip preventing system as claimed in claim 1 or 2, characterized in that the shift control means (U AT ) controls the shift of the speed stages of the automatic transmission on the basis of a shift characteristic which is defined by the amount of operation of the accelerator (69) and the vehicle speed as parameters. A slip preventing system as claimed in claim 3 or 4, characterized by a first storing means for storing a first shift characteristic having the engine output and the vehicle speed as parameters, a second storing means for storing a second shift characteristic having the vehicle speed as the only parameter, shift characteristic selecting means (step P52, Fig. 7) for selecting the first shift characteristic during ordinary driving conditions and the second shift characteristic during the slip control, whereby the shift of the speed stages of the automatic transmission is caused according to the shift characteristic selected by said shift characteristic selecting means. A slip preventing system as claimed in claim 5, characterized in that the shift characteristic selecting means includes a manually operable holding mode selection means (83), whereby the shift characteristic selecting means selects said second shift characteristic when the holding mode selection means (83) is manually operated. A slip preventing system as claimed in claim 2, characterized in that the predetermined speed stage which is held during said predetermined time period is the speed stage immediately before the initiation of the slip control. A slip preventing system as claimed in claim 2, characterized in that the predetermined speed stage which is held during said predetermined time period is manually selectable. A slip preventing system as claimed in claim 2, characterized in that the predetermined speed stage is set as the second speed stage. A slip preventing system as claimed in any of claims 3 to 9, characterized in that the shift control means (U AT ) is set to provide a speed stage, during operation of the slip control, prior to the speed stage based on said shift characteristic, and includes an indicator means (81) to indicate that speed stage provided for the slip control. A slip preventing system as claimed in any of claims 1 to 10, characterized in that the output adjusting means comprises a throttle valve (13) adapted to adjust the intake air amount of the engine. A slip preventing system as claimed in any of claims 1 to 11, characterized in that it further comprises braking force adjusting means (27) to adjust the braking force to be applied to the driven wheel and slip control means (U B ) for the brake to control the braking force adjusting means (27) in response to a signal of said slip amount detecting means (U S , step P23, Fig. 4) signalling excessive slip of the driven wheel (4, 5). A slip preventing system as claimed in any of claims 1 to 12, characterized in that the slip amount detecting means (U S , step P23, Fig. 4) detects the slip amount on the basis of the rotational speed of the driven wheel and the rotational speed of an undriven wheel. A slip preventing system as claimed in any of claims 1 to 13, characterized in that the output controlling means (U S ) for the slip control subjects the output adjusting means (13) to a feedback control so as to converge the slip amount detected by the slip amount detecting means to a target slip amount. A slip preventing system as claimed in any of claims 1 to 14, characterized in that the output controlling means (U S ) further comprises a slip control amount determining means for determining a slip control value corresponding to a predetermined target slip amount, judgement means adapted to provide an output when said slip control value reaches a value so as to decrease the engine output in comparison with a basic control value by comparing said slip control value with the basic control value in said basic output adjusting means and control value selecting means adapted to provide said output adjusting means with said slip control value prior to said basic control value in response to an output from the judgement means.

Inventors: FUJITA, NAGAHISA
Applicants: MAZDA MOTOR CORPORATION
Application year: 1988
Main classification: B60K28
IPC codes: B60W10, F02D41, F02D45, B60T8, F02D29