1. Field of the Invention
The present invention relates generally to motor control systems and more particularly to control systems for motor brake retarders.
2. Description of the Prior Art
Numerous prior art approaches have been conceived to brake or retard a motor other than through use of wheel brakes. A brief discussion of such prior art approaches follows. Systems for varying valve timing are disclosed in Pelizzoni et al., U.S. Pat. No. 3,786,792. In Pelizzoni appears an excellent discussion of various prior art engine brakes and that discussion is repeated below:
Other devices for relieving compression to enhance starting are disclosed in the Jackson U.S. Pat. No. 1,172,362 and the Rounds U.S. Pat. No. 1,175,820. Here the exhaust cams are provided with an auxiliary relief or lobe which is circumferentially spaced from the main lobe which opens the exhaust valve during the exhaust stroke. During normal operation the exhaust valve is not raised by the auxiliary lobe, but during starting the exhaust valve gear train is manually expanded so that the auxiliary lobe raises the exhaust valve during a portion of the compression stroke. In addition, the Rounds patent shows apparatus for manually adjusting the timing of the inlet and exhaust valves.
The Saurer U.S. Pat. No. 934,762 discloses an engine brake in which the exhaust cam is shifted circumferentially from its normal position to open during the "expansion" stroke, ignition being discontinued, so that air is compressed during the compression and "exhaust" strokes, and necessarily dumped at the beginning of the inlet and "expansion" strokes, so that the energy of the compressed air is not returned to the drive train during the expansion stroke.
The Kirchensteiner U.S. Pat. No. 1,637,118 and the Loeffler U.S. Pat. No. 1,947,996 disclose engine brakes in which the cam shaft is axially shifted for braking to de-activate the inlet valve and to drive the exhaust valve by a special double lobe cam, one lobe opening the exhaust valve during the intake stroke, while the other lobe dumps the compressed air near the end of the compression stroke. A graduated degree of braking is available in the Kirchensteiner engine brake by selctively inserting wedge elements beneath predetermined ones of the exhaust rocker arms to prevent the corresponding exhaust valves from closing, thereby eliminating the braking effect in the corresponding cylinders.
The engine brake according to the Ucko U.S. Pat. No. 2,002,196 obtains the results of the Loeffler brake without axially shifting the cam shaft. Rather, the rocker arm shaft is shifted eccentrically to render the push rods (and the inlet and exhaust cams) ineffective. An auxiliary double lobe exhaust cam is hydraulically coupled to the exhaust valve through a master piston, which is driven by the double lobe cam, and a slave piston which drives the exhaust valve rocker arm to open the exhaust valve during the intake and expansion strokes. A graduated braking effect is obtained by sequentially converting groups of one or more cylinders to air compressors.
The Cummins U.S. Pat. No. 3,220,392 discloses another engine braking system employing hydraulically coupled master and slave pistons, the slave piston driving the exhaust valve rocker arm, and the master piston being driven by an auxiliary exhaust cam, the injector rocker arm of the corresponding cylinder, or by the inlet or exhaust rocker arm of another cylinder, so as to dump compressed air at or near the end of the compression stroke. Unlike Ucko, however, the Cummins mechanism for opening an exhaust valve at or near top dead center does not interfere with the actuation of the exhaust valve by the normal exhaust valve actuating mechanism. Nevertheless, the independent mechanism for actuating the exhaust valve for braking requires considerable additional structure, thus increasing the complexity and cost of that engine brake. Furthermore, hydraulic coupling between the exhaust rocker arm of one cylinder and the inlet or exhaust rocker arm of the appropriate other cylinder would be difficult to arrange with a V-8 engine.
In the engine brake according to the Jones et al U.S. Pat. No. 3,439,662 a single auxiliary cam sequentially drives the master pistons, which in turn actuate the corresponding slave pistons to open the exhaust valves at the end of the compression stroke. Apparatus is included to change the timing of the opening of the exhaust valves in accordance with the engine speed in order to increase the braking effect with increasing engine speed.
The Siegler U.S. Pat. No. 3,547,087 discloses another engine brake employing a mechanism external to the intake and exhaust valve gear train, but in this system a solenoid operated hydraulic valve remote from the engine brake mechanism is actuated to pump up a piston so as to block the return movement of the rocker arm, thereby holding the intake or exhaust valve partially open throughout the braking period.
The Haviland U.S. Pat. No. 3,332,405 shows an engine brake in which the exhaust valve is opened at the end of the compression stroke by a separate engine braking cam when a plunger mounted in the rocker arm is hydraulically pumped up to engage the braking cam in response to a remote solenoid valve. In an effort to improve the response time of the system, a separate low pressure oil supply is required to keep the lines filled with oil.
The Jonsson U.S. Pat. No. 3,367,312 discloses an engine braking system in which the normal base circle of the exhaust cam is relieved to form an auxiliary base circle, the transition between the two base circles constituting an auxiliary ramp displaced circumferentially from the normal opening ramp, so that when the lash is removed from the exhaust valve train, the exhaust valve is opened by the auxiliary ramp at the end of the compression stroke. The lash is removed by a plunger mounted in the rocker arm which may be hydraulically extended when a remote valve is manually actuated to communicate the plunger with the lubrication pump. Inasmuch as there is no mechanism for hydraulically locking the plunger in the extended position, the rotating exhaust cam will reciprocate the plunger in its cylinder despite the hydraulic force supplied by the lubrication pump, thereby substantially impairing the performance of the engine brake. Furthermore, a very large force is applied to the exhaust valve and the plunger when the piston travels through its compression stroke, such force being a function of speed, exhaust valve opening, exhaust valve diameter and compression ratio. In a diesel engine such force would greatly exceed the opposite force on the plunger developed by the engine lubricating pump, so that the plunger would be collapsed and the desired braking effect minimized.
The Muir U.S. Pat. No. 3,525,317 discloses an engine brake providing a graduated braking effect by arranging a multiple-position switch for operation as the throttle pedal is retracted beyond the idling position. At the first position the fuel is cut off to create "motoring" friction, at the second position the exhaust valves are held continuously in a partially open position, and at the third position a butterfly valve in the exhaust mainfold is actuated to provide back pressure therein.
The Sweat U.S. Pat. No. 2,806,459 discloses an intricate device for changing the timing of motor valves in accordance with the speed of the motor by adjusting the position of the rocker arm fulcrum and thereby adjusting the clearance in the valve train and the amount of valve opening. The rocker arm fulcrum is driven by a motor, the electrical contacts for which are operated by a piston displaced by air pressure generated by a fan driven by the motor. The cam shaft is arranged to provide advanced timing when the clearance in the valve train is small, at high speeds, while at lower speeds the clearance is larger and the valve timing is thus retarded.
The Lieberherr U.S. Pat. No. 2,936,575 discloses apparatus for varying the valve timing of a supercharged gas engine in accordance with the pressure of the intake manifold or the governor fuel control shaft in an effort to obtain an approximately constant air-fuel ratio at all loads. The timing is varied by lateral displacement of the cam follower in response to the intake manifold pressure or the fuel control shaft.
The Ostborg U.S. Pat. No. 3,224,423 shows a valve timing system in which the timing of the inlet and exhaust valves is varied in accordance with the intake manifold pressure, the phase of the inlet and exhaust camshafts being shifted in opposite directions with respect to that of the crankshaft by means of planetary gear systems.
While all of the above prior art approaches provide for a plurality of different mechanical devices for retarding a motor, none of the above prior art approaches provide a system having a control for sequentially applying retardation to selected cylinders of the motor, for fully activating the brake retarder when the motor exceeds a predetermined high RPM, for deactivating the activated brake retarders when the motor drops below a predetermined low RPM, for automatically activating brake lights when retardation of the motor occurs, or for providing the operator of the motor with flexibility in controlling the degree of retardation.
The above features of the brake control system of the present invention substantially minimize the following problems which plague operators of large vehicles such as trucks. The problem of motor runaway and the ensuing mechanical damage to the motor is substantially prevented by the present invention in that whenever the speed of the motor exceeds a high predetermined RPM value, all cylinders of the motor are fully retarded. Should the present invention fail to detect the high RPM limit, the mechanical governor could function in the conventional fashion. Unfortunately, in the typical motor runaway situation, the mechanical governor flies apart and the motor then proceeds to destroy itself. The system of the present invention activates retardation prior to the activation of the mechanical governor and fully applies retardation to all cylinders. In addition, the present invention signals a warning to the operator or, if no operator is present, the system can optionally shut the motor down.
Another problem inherent to operators of large vehicles is that generally encountered while traveling down a steep incline such as those found in the mountains. In such situations, all cylinders are generally retarded to counteract the force of momentum of the truck down the hill. In the event that a wet, icy or sandy spot is encountered on the road, the motor, due to the retardation sometimes stalls. Such a stall is fatal to the operation of the vehicle because power is lost to all functions and the wheels skid. The following weight of the load, the retarding effect of the motor brake and the steering, shifting and/or wheel braking effort of the operator all contribute to a jack-knife condition causing destruction to the truck. The system of the present invention substantially prevents jack-knifing since if the speed of the motor drops below a low predetermined RPM value, the retarders are automatically and instantaneously released. Stalling therefore is prevented. When the speed of the motor regains it's normal operating speed, the retarders are sequentially activated to apply retardation. Another problem for operators of vehicles carrying large loads occurs when those loads are what is commonly termed "live". Live loads include loads containing live animals, liquids, or hanging and swinging loads. When carrying live loads, it is highly desirable to apply retardation in a sequential fashion after predetermined intervals have elapsed. The system of the present invention prevents damage to live loads by providing for the sequential application of retardation to the various cylinders of the motor.
Furthermore, since the present invention, provides for sequential application of retardation to the various cylinders, up and down shifting by the driver through the transmission is substantially eliminated since effective control of the power of the motor can be accomplished through the manual selection of the degree of retardation. For example, the operator of the present invention may selectively release retardation from six cylinders to four cylinders and then to two thereby increasing the power from the motor to the vehicle with each such selection. This is comparable to controlling the power delivery from the motor to the vehicle by controlling the shifting through the transmission. The system of the present invention is highly adaptable to situations involving "green" or inexperienced drivers who for the first time encounter situations, as in the mountains, of increased manual shifting of the transmission. Such provisions for inexperienced drivers are highly desirable since the accident rate of inexperienced drivers is much greater than that of experienced drivers. In addition, through the reduction of manual shifting (upshifting and downshifting), greater fuel economy is achieved and a great time savings is experienced in traveling from point to point through rugged and hilly terrain. These time and fuel savings continue in high population and traffic density areas.
Substantial reduction in maintenance costs is obtained with the motor brake control system of the present invention. In a typical application, as mentioned above, due to the fact that manual shifting is greatly reduced, decreased fuel consumption is obtained as well as increased savings in road and turn-around time. Due primarily to the fact that manual shifting is greatly reduced, there is less wear and tear on the drive train and motor resulting in a reduced number of expensive oil changes, less overhaul time in the repair shop, and considerable savings in relining the brakes and in replacing the tires since greater reliance and flexibility can be provided through engine retardation rather than wheel braking. Other advantages and features of the present invention include increased public safety due to the fact that jack-knifing, skidding, and engine stall are greatly reduced through use of the motor control system of the present invention. Such reduction of accident occurrences is especially valuable in loads including explosives, and chemicals wherein a single accident can affect numerous members of the public. Furthermore, since upshifting and downshifting is minimized through the teachings of this invention, less fuel is consumed and the various pollutants generated into the atmosphere from such excessive fuel consumption is minimized. This is especially true when the motor control system of the present invention is used to speed up and slow down vehicles while moving in heavy traffic conditions in a metropolitan area. And the public benefits from a reduction in the noise pollution that occurs when upshifting and downshifting to reach certain RPM's and when conventional brake retarders generate considerable "popping" noise due to the fuel lag problem wherein retardation occurs before the fuel within the fuel line system is fully combusted. Finally, the provision of a motor speed sensor and accompanying display provides a more accurate readout than currently obtainable with mechanical tachometers. However, the present invention contemplates the use of both the electronic display and the mechanical tachometer to operate in parallel thereby to provide a further safety feature for the operator of the vehicle in that he can visually compare the accuracy of the two readouts.