Selective transmission speed control.

INTRODUCTION

This invention relates generally to vehicular transmissions and more particularly to vehicular transmissions for which vehicular speed is prevented from exceeding a prescribed amount only when particular predetermined transmission gear ratios are engaged.

BACKGROUND OF THE INVENTION

Transmissions have been a vital part of vehicular drive trains for many years as a means of insuring that sufficient torque is available to enable the vehicle drive train to operate efficiently over a prescribed ground speed range under design load factors.

Generally, such transmissions enable selection from a plurality of forward gear ratios as means of delivering high torque to drive the vehicle wheels to overcome inertia under start-up conditions by enabling the vehicle's engine output shaft to rotate at high speed relative to the rotational speed of the transmission output shaft speed and to then enable selection of gear ratios that offer higher transmission output shaft speeds relative the engine output shaft speed.

Such transmissions are generally of the manual, semi-­automatic, and automatic type well known to those skilled in the art and which generally include a neutral position, at least one reverse gear ratio and a plurality of forward gear ratios progressing from a lowest to a highest over a progressively increasing ground speed range prescribed for the vehicle.

Generally, manual transmissions require a clutch for disengaging the engine from the transmission during the time that a transmission gear is being engaged by an operator whereas such is automatically accomplished by speed controlled valves or electronically in an automatic transmission. Such transmissions may also be combinations of both manual and automatic operation for particular pre-selected speed ratios and may be of a compound design involving main and auxiliary transmissions coupled in series as is well known to those skilled in transmission design particularly heavy duty truck transmissions for providing a high number of forward gear ratios to select from due to torque, ground speed and load factor requirements. A variety of compound gear change transmissions are disclosed for example in United States Patents 3,283,6l3; 3,648,546; 3,799,002; 4,290,5l5; 4,440,037; and 4,527,447, the disclosures of all which are incorporated herein by reference.

In addition to transmissions, vehicles have, for various reasons, included engine speed control mechanisms such as engine speed governors well known to those skilled in the art for limiting the maximum ground speed and/or engine speed at which the vehicle is able to travel commonly for purposes of economy. Heretofor, however, speed control has been employed over the entire transmission gear ratio selection range to limit the ground speed of a vehicle and/or the rotational speed of the engine to a predetermined value regardless of the particular gear ratio being employed at the time. Such practice, however, imposes a torque limit upon the vehicle, particularly heavy duty trucks, by limiting engine speed in the lower gear speed ratios and thus deprives the vehicle of advantageous use of high engine speed power at low transmission gear ratios for overcoming inertia in start-up particularly when heavy load factors are involved.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide a vehicular speed control system that is operative only for certain predetermined transmission change gear ratios.

It is another object of this invention to provide a control system operative to enable high engine speed torque at low transmission gear speed ratios yet prevent vehicular speed from exceeding a predetermined amount at high gear speed ratios for purposes of economy, safety and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

<ul id="ul0001" list-style="none"><li>FIGURE l shows a schematic side elevation view of an embodiment of the speed control system of the invention; and</li><li>FIGURE 2 shows a graph of vehicular ground speed versus engine speed for a vehicle having its engine speed controlled by an embodiment of the speed control system of the invention.</li></ul>

DESCRIPTION OF SOME PREFERRED EMBODIMENTS

An embodiment of the control system of the invention for selectively controlling engine speed and/or vehicular ground speed is shown in FIGURE l in which rotational speed of an output shaft such as a drive shaft of a vehicular engine 2 such as a truck or passenger car gasoline or diesel engine is prevented from exceeding predetermined values and, as a result, limiting vehicular ground speed such as hereinafter described with respect to FIGURE 2.

The output or drive shaft of engine 2 is coupled to the input shaft of transmission 4 which may be manual, semi-­automatic, automatic or combinations of same as previously described.

Transmission 4 is provided with a plurality of selectable forward change gear ratios progressively increasing from a lowest to a highest over a progressively increasing ground speed range prescribed for the particular vehicle. The particular number of forward gear speed ratios involved depends generally upon the particular vehicle and load factors involved and may range, for example, from typically three to five forward gear ratios for passenger cars to as many as eight or even as high as sixteen or more forward gear ratios for trucks using compound transmissions as previously described. The particular gear ratios of transmission 4 are selected by positioning shift arm 6 according to a prescribed pattern which differs according to whether the transmission is manual, semi-automatic or automatic, as is well known to those skilled in the art.

Transmission 4 is provided with a gear ratio position sensor 8 that is adapted to provide a second signal l0 to logic means l2 such as a suitable electronic logic circuit only when certain predetermined transmission 4 gear ratios are engaged. Sensor 8 may, for example, be a magnetic pick-­up or direct electrical contact arrangement operable to provide an electrical signal when shift control arm 6 is placed in certain gear ratio positions. Alternatively, sensor 8 may be operable to provide a signal indicative of each and every forward gear speed ratio position which is then distinguished by logic means l2 for particular positions as hereinafter described.

The particular gear speed ratios for which it is desired to control engine and ground speed is preferably the highest within the range available and thence the next highest such as hereinafter discussed with respect to FIGURE 2 but not all and certainly not the lowest forward gear speed ratio available from transmission 4 for such would limit the desired start-up power requirements previously described. In one embodiment, for example, the control system of the invention is operable to limit vehicular speed for the three highest forward gear ratios provided by the transmission.

In addition to second signal l0, logic means l2 receives a first signal l6 from engine 2 provided by engine speed sensor member l4 that is adapted to monitor engine speed. Sensor member l4 may, for example, be a Hall-effect type sensor adapted to provide a signal corresponding to engine speed by counting teeth of a rotating gear driven by engine 2. Since engine speed and vehicular speed are related, the term "vehicular speed" as used herein means either engine speed or vehicular ground speed as shown for example in FIGURE l where vehicle speed sensor 3 may be alternately employed to provide a signal 5 indicative of vehicle ground speed to control means l2.

Logic means l2 may be any logic circuitry operable to receive and process signals l0 and l6 or 5 and provide in response an output control signal l8 to a speed control device 20 such as a governor or suitable throttle stop well known to those skilled in the art that limits fuel supply to prevent engine speed and ultimately vehicular ground speed from exceeding a prescribed value whenever the particular predetermined gear ratios of transmission 4 are selected.

An example of the application of the vehicular speed control system of the invention to a heavy duty truck having eight forward gear ratios is shown in graph form in FIGURE 2. In FIGURE 2, the maximum desirable engine rpm is 2200 regardless of the gear ratio engaged. Of the eight gear ratios only the highest gear ratio 8 and the next highest gear ratio 7 trigger an upper limit control upon the engine speed. Thus, the engine speed is not prevented from reaching 2200 rpm for the first six gear ratios for a ground speed of from 0 to about 40 mph but once the seventh gear ratio is engaged, logic means l2 is operative to provide a signal to engine speed control means such as a governor preventing engine speed from exceeding l700 whenever gear ratio 7 is engaged and l500 whenever gear ratio 8 is engaged resulting in fuel saving economy for ground speeds of 50 mph and higher while enabling high engine speed at lower gear ratio to provide power for overcoming inertia, climbing inclines and the like.

In addition, engine and/or ground speed sensing may include an acceleration term dv/dt well known to those skilled in the art of devices operative to provide precise control over engine and/or vehicular ground speed since the first derivative of velocity with respect to time provides information relative to the slow down or speed up of vehicular speed.

Further to control of highest engine and/or ground speed for particular selected gear ratios, the control system of the invention may further include cruise control means that is operative to maintain vehicular speed about a desired value selected within the vehicular speed range provided by the predetermined gear ratios selected for upper limit vehicular speed control.

Generally, the vehicular speed control system of the invention is particularly advantageous for use by over the road trucks which spend a good portion of their time at higher speeds resulting in good performance and fuel efficiency whilst allowing full performance of the engine under start-up and lower speed conditions.