Torque-limited electric servo system for deploying a vehicle snow chain traction system

A single unit of the new deployment system includes a housing to which an electric drive motor is externally mounted. The deployment system for each vehicle requires at least a pair of deployment units: one each for right and left wheels. Each unit includes a reversible electric drive motor having an armature shaft; an intermediate drive shaft; a worm axially affixed to the intermediate drive shaft; an output shaft; a shock damper affixed to the output shaft; a worm gear affixed to the shock damper, the worm gear meshing with the worm, and providing rotational locking for said output shaft; and a deployment arm coupled to the output shaft, the deployment arm having rotatably mounted thereto a friction drive disc, said friction drive disc having peripherally attached thereto a plurality of chain segments. Torque applied to the output shaft by the electric motor is limited either by a spring-loaded clutch axially mounted on the intermediate drive shaft or by a circuit which limits current drawn by the electric drive motor to a preset maximum.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to vehicle ice and chain traction systems which may be both rapidly deployed and rapidly retracted. More particularly, it relates to electrically-powered apparatuses for deploying a mounted system so that the components thereof are moved from a stowed configuration to an operable configuration.

2. Description of Related Art

Rapidly-deployable chain traction systems, which may be characterized generally as systems which fling short chain or cable segments beneath a road tire, have been known for some 90 years. Such a system is disclosed in U.S. Pat. No. 1,045,609 and in German Pat. No. No. 266,487 to W. H. Putnam for an ANTISKIDDING DEVICE. Throughout the years, various modifications and improvements have been made by numerous inventors. The following list is a representative list of a dozen other U.S. patents issued in this field:U.S. Pat. No. 1,150,148 for a TRACTION AND ANTISKIDDING DEVICE;U.S. Pat. No. 1,223,070 for an ANTISKIDDING DEVICE FOR VEHICLES;U.S. Pat. No. 1,374,252 for an ANTISKID DEVICE FOR AUTOMOBILES;U.S. Pat. No. 1,381,001 for a NON-SKID DEVICE FOR MOTOR AND OTHER VEHICLES;U.S. Pat. No. 1,975,325 for an ANTISKID CHAIN AND MEANS FOR APPLYING AND REMOVING SAME;U.S. Pat. No. 2,241,923 for an AUTOMATIC EMERGENCY TRACTION DEVICE FOR AUTOMOBILES;U.S. Pat. No. 2,264,466 for an ANTISKID DEVICE FOR VEHICLES;U.S. Pat. No. 2,277,036 for an ANTISKID DEVICE;U.S. Pat. No. 2,283,948 for an AUTOMOBILE TRACTION DEVICE;U.S. Pat. No. 2,442,322 for an ANTISKID DEVICE;U.S. Pat. No. 4,299,310 for an ANTISKID DEVICE FOR MOTOR VEHICLES;U.S. Pat. No. 4,800,992 for an ANTI-SKID DEVICE; andU.S. Pat. No. Des. 286,524 for ANTI SKID CHAIN UNIT FOR VEHICLE TIRES.

Referring now to the prior-art system ofFIG. 1, a modern rapidly-deployable chain traction system100is depicted in its deployed configuration in this rear elevational view drawing. The chain traction system100is removably affixed to a drive axle101which incorporates a differential unit102. Inner and outer road wheels (103A and103B, respectively) are mounted on the visible half of the drive axle101. On each road wheel (103A and103B) is mounted a rubber tire (104A and104B, respectively). The chain system100includes a friction drive disc105to which a plurality of chain segments106A,106B and106C are attached. Chain segment106A is depicted as being below the road surface114, which is normally covered with a layer of snow or ice when the chain system100is in the deployed configuration. The friction drive disc105is rotatably mounted on a spindle107which is affixed to a support member108which is pivotally mounted to a mounting bracket109. The mounting bracket is, in turn, bolted to the U-bolt shackles113which secure the suspension leaf springs112to the drive axle101. The chain system100also includes a pneumatic cylinder110that is bolted to the mounting bracket109. The pneumatic cylinder110has a slidable piston111that is held in a normally retracted position within cylinder110by spring biasing when pressure within cylinder108equals ambient pressure. The outer end of piston111is connected to support member108. In the deployed configuration, the outer rim of friction drive disc105is pressed against the sidewall of tire104A by a biasing force applied to support member108by piston111. The biasing force is provided by pneumatic pressure inside pneumatic cylinder110which overcomes the spring biasing and causes piston111to extend. As the tire104A rotates, the friction drive disc105also rotates with the chain segments106extended more or less radially therefrom. Thus each chain segment106is flung, sequentially, beneath the tread portion of tire104A. In order to retract the system and disengage the friction drive disc105from contact with the sidewall of tire104A, pneumatic pressure to pneumatic cylinder110is cut off, causing piston111to retract within cylinder110and raising the support member108, the rotatably attached friction drive disc105and the attached chain segments106. In the retracted configuration, the chain segments106do not touch the road surface114.

Referring now to the side view of the modern prior-art modern rapidly-deployable chain traction system100ofFIG. 2, the pneumatic deployment components and the mounting system are shown in greater detail. The mounting system shown is designed for use on vehicles which have a beam or live axle (i.e., one which incorporates a differential)101. On each side of the vehicle, the apparatus mounts to U-bolt shackles which commonly secure the axle to a set of leaf springs112or an air bag assembly (not shown). If no U-bolts are present on the axle, a new set of U-bolts may be installed thereon and used to secure the system. In either case, the new mounting system is designed to be mounted directly to the exposed, threaded ends of the U-bolt shackles coupled to two sets of leaf springs (see112ofFIG. 1). Each leaf spring set is coupled to the beam axle or axle housing (in the case of a live axle) with a pair of U-bolt shackles113, which are tied together beneath the axle or axle housing with a flat tie plate114that is secured with four standard nuts115(two on each U-bolt). The mounting system is designed to be mounted directly to the exposed, threaded ends of the U-bolt shackles113.

Although various mechanical means, such as cables and gears, have been used in the past to deploy chain traction systems, the current genre of chain traction systems relies almost exclusively on pneumatic cylinders for deployment. The primary problem associated with chain traction systems deployed by pneumatic cylinders is that the system may be too bulky for certain applications, such as installation on light-duty pickup trucks. One major problem associated with prior art gear-driven deployment systems is that uneven road surfaces imposed a potentially destructive shock load on the gear train when the chain traction system was in a retracted state. The shock loads had a tendency to shear the teeth off of gears in the deployment gear train. The shock loads could also fracture the housing used to contain the gear train. Another major problem associated with gear-driven deployment systems is that of grit, water, and corrosion related to inadequate protection of the gear train. For a gear-driven deployment system to function reliably, it is essential that all gears and all bearings be completely sealed from the harsh environment beneath the vehicle. Without proper sealing, the life expectancy of such systems would likely be no more than one winter season. Gear driven deployment systems for a chain traction system, if not manually operated, require some type of motor for automatic operation. For most vehicles, the only type of motor that makes sense is an electric motor, as electric power is readily available from the vehicle's storage battery. Although the automotive industry has solved the problems related to operation of electric motors in a harsh environment (e.g. engine starter motors), in the case of an electric-powered chain traction system, there is still the problem of how to start and stop the electric motor at the appropriate times. If limit switches are to be used, they must be completely sealed in order to protect their delicate circuitry.

What is needed is an electric-powered, gear-driven deployment system for chain traction systems that: (1) is sufficiently compact for installation on a wide variety of vehicles; (2) is completely sealed from the environment; (3) is relatively simple to install and operate; (4) is not subject to damage from shock loads imposed by uneven road surfaces; and (5) solves the problems related to limiting the travel of the device during deployment and retraction.

SUMMARY OF THE INVENTION

The present invention answers the needs expressed in the foregoing section. A new electric-motor-powered, gear-driven deployment system for rapidly-deployable chain traction systems is provided that is compact, sealed from the environment, relatively simple to install and operate, protected from shock load damage to the gear train, and utilizes a timed deployment sequence to avoid the use of limit switches in the harsh environment beneath the vehicle. The deployment system for each vehicle requires at least a pair of deployment units: one each for right and left wheels. Torque applied to the output shaft of the deployment system by the electric motor is limited either by a spring-loaded clutch axially mounted on the intermediate drive shaft or by a circuit which limits current drawn by the electric drive motor to a preset maximum.

A single unit of the new deployment system includes a housing to which an electric drive motor is externally mounted. By reversing the polarity of the electric current, the direction of revolution of the electric drive motor can be reversed. The output shaft of the drive motor extends through an input aperture within a wall of the housing. For a preferred embodiment of the invention, the output shaft is fitted with an 18-tooth drive spur pinion gear. The spur pinion gear drives a 72-tooth driven spur gear for a gear reduction ration of 4:1. The driven spur gear is mounted on an intermediate drive shaft that is rotatably mounted within the housing. For a first embodiment of the invention, torque applied to the output shaft is limited by a spring-loaded clutch axially mounted on the intermediate drive shaft that couples the driven spur gear to the intermediate drive shaft. For a second embodiment of the invention, the spring-loaded clutch is eliminated, altogether, and torque applied to the output shaft by the electric motor is limited by MOSFET H-Bridge circuit which limits current drawn by the electric drive motor to a preset maximum. For either embodiment, the spur gears may be replaced with a more costly helical-gear or bevel-gear train with a similar gear reduction ratio. The intermediate drive shaft incorporates a worm that is spaced from the driven spur gear and spring-loaded clutch. The worm operates on a worm gear that is coupled to an output shaft via a spring-loaded damper. The output shaft extends through a sealed output aperture in the housing. The deployment arm of a rapidly-deployable chain traction system (including the rotatably attached friction drive disc and associated chain segments) is rigidly affixed to the end of the output shaft that is external to the housing. The spring-loaded shock damper protects the gear train against shock loads imposed by rotational moments applied to the output shaft by the lever arm, which are caused primarily by forces attributable to uneven road surfaces acting on the rotationally unbalanced mass of the combined deployment arm, friction drive disc and associated chain segments. The spring constant of the coil spring employed within the shock damper is selected as a function of the moment of inertia of the rotationally unbalanced mass.

In order to deploy the first embodiment system, current is applied to the electric motor for a preset period of time. The time period is slightly greater than the measured time for full deployment from a fully retracted position. Slippage of the spring-loaded clutch on the intermediate drive shaft ensures that full deployment will occur. In order to retract the system, current of reverse polarity is applied to the electric motor for a preset time period that is slightly greater than the measured time for full retraction from a fully deployed position. As a practical matter, the time required for retraction is slightly greater than the time required for deployment, as the output of the motor is identical in both directions, gravity is working against the system during retraction, and the chain segments may need to be pulled from beneath the vehicle's tires.

PREFERRED EMBODIMENT OF THE INVENTION

In accordance with the present invention, a new gear-driven deployment system for a rapidly-deployable chain traction system is provided. A single unit of the new gear-driven deployment system will be described with reference to the attached drawing figures. It should be understood that a complete system requires the use of at least two units: one for each drive wheel. The drawing figures are intended for the purpose of illustrating a preferred embodiment of the invention only, and not for purpose of limiting the same.

Referring now toFIG. 3, a single unit300of the new gear-driven deployment system is shown mounted to a beam axle101using the mounting system shown inFIG. 2. It will be noted that the primary difference between the deployment system shown inFIG. 2and that shown inFIG. 3is that the pneumatic cylinder110ofFIG. 2has been replaced by a single gear-driven deployment unit300and the mounting bracket109ofFIG. 2has been replaced with a modified mounting bracket301, which incorporates an angle bracket extension302having a sealed ball-bearing race (not shown) installed therein. The sealed ball-bearing race functions as an end support for the output shaft (see item417ofFIG. 4) of the gear-driven deployment system unit300. The deployment arm303is affixed to the output shaft417.

Referring now toFIG. 4, a single unit of the new deployment system300includes a housing401to which an electric drive motor402is externally mounted. The electric drive motor402is enclosed in a water-tight motor canister403. By reversing the polarity of the electric current applied to the electric drive motor402, the rotational direction of the electric drive motor402can be reversed. The electric drive motor402has an armature shaft404, which extends through an input aperture (not shown) within a side wall405of the housing401. For a preferred embodiment of the invention, the output shaft404is fitted with an 18-tooth drive spur pinion gear406. The spur pinion gear406drives a 72-tooth driven spur gear407for a gear reduction ration of 4:1. The driven spur gear407is mounted on an intermediate drive shaft408that is rotatably mounted within the housing401. For a first primary embodiment of the invention, the driven spur gear407rotates on the intermediate drive shaft408, and is coupled thereto via a spring-loaded clutch409, which has a biasing spring410and a driven disc411that is secured to the intermediate drive shaft with a first roll pin412. The compressed biasing spring410is sandwiched between a retainer washer413that is held in place on the intermediate drive shaft408by a second roll pin414, and the driven spur gear407. A paper friction disc415is placed between the driven spur gear407and the driven disc411. As an option, the spur gears406and407may be replaced with a more costly helical-gear or bevel-gear train with a similar gear reduction ratio. The intermediate drive shaft408incorporates a worm416that is spaced from the driven spur gear407and the spring-loaded clutch409.

Referring now to bothFIG. 4andFIG. 5, the worm416operates on a worm gear417that is coupled to an output shaft501via a spring-loaded damper502. The combination of the worm416and the worm gear417serve to lock the output shaft501in any position to which it is rotated. The spring-loaded damper502includes upper and lower nested, coaxial, closed-end cylinders (503and504, respectively), each of which has an arcuate portion of its cylindrical wall removed, and which, together, form a can in which is housed a coiled, normally-unloaded shock-absorbing spring505. The edges of the remaining cylindrical walls506R,506L,507R and507L act on the ends of the shock-absorbing spring505. Rotational moments applied to the output shaft501in either direction cause circumferential loading, as opposed to torsional loading, of the spring. The output shaft501extends through a sealed output aperture (not shown in this view) in the housing401. The deployment arm303of a rapidly-deployable chain traction system is rigidly affixed to the end of the output shaft that is external to the housing. The friction drive disc105is rotatably attached to the deployment arm303and a plurality of chain segments106A,106B and106C are attached to the friction drive disc105. The spring-loaded shock damper502protects the gear train against shock loads imposed by rotational moments applied to the output shaft501by the deployment arm303, which are caused primarily by forces attributable to uneven road surfaces acting on the rotationally unbalanced mass of the combined deployment arm303, friction drive disc105and associated chain segments. The spring constant of the shock-absorbing spring505(seeFIG. 6) employed within the shock damper502is selected as a function of the moment of inertia of the rotationally unbalanced mass. It will be noted that a pair of electrical terminals507U and507L are visible in this view. At least one of the terminals is insulated from the housing401. Electrical connections are made from these terminals507U and507L to the electric drive motor402through the inside of the housing401.

Referring now toFIG. 6, the shock-absorbing spring505is seen more completely in this view. It will be noted that the spring is circumferentially loaded by either spreading the ends601A and601B apart or squeezing them together.

Referring now to the isometric view ofFIG. 7, the housing401of a single unit of the new deployment system300includes a top cover (see item801ofFIG. 8) a perimetric wall portion701and a base702. The perimetric wall portion701may be formed as a single aluminum extrusion. The top cover801and the base702may be formed from a structural metal such as steel or aluminum. In this view, the shock damper502is visible in perspective. The output shaft501is axially welded to the upper closed-end cylinders503. The shock-absorbing spring505is also visible in this view. Mounting holes703are provided in the base702.

Referring now toFIG. 8, the top cover801has been bolted on the housing401of the deployment system unit300shown inFIG. 7.

Referring now toFIG. 9, the top view of the deployment system, unit300shows both mounting holes703and the top electrical terminal507U. An access plug901may be removed to expose the end of the intermediate drive shaft408, which may be equipped with a hex or splined socket which may be engaged with an appropriate wrench in order to raise or lower the traction system in the event of electrical failure.

In order to deploy the system, current is applied to the electric motor for a preset period of time. The time period is slightly greater than the measured time for full deployment from a fully retracted position. Slippage of the spring-loaded clutch on the intermediate drive shaft ensures that full deployment will occur. In order to retract the system, current of reverse polarity is applied to the electric motor for a preset time period that is slightly greater than the measured time for full retraction from a fully deployed position. As a practical matter, the time required for retraction is slightly greater than the time required for deployment, as the output of motor402is identical in both directions, gravity is working against the system during retraction, and the chain segments106may need to be pulled from beneath the vehicle's tires. The variation in times required for retraction and deployment may be made identical, or nearly so, by counterbalancing the deployment arm303.

Referring now toFIG. 10, graph A is representative of the voltage applied to the electric drive motor402, graph B is representative of the rate of rotation of the intermediate drive shaft408in radians per second, and graph C is representative of the rate of rotation of the clutch409with respect to the intermediate drive shaft408in radians per second, all as a function of time during system deployment. Time t=0 represents the instant that electrical power of positive 12-14 volts is applied to the terminals of the drive motor402. Time t=x represents the time when the friction disc105contacts the associated tire of the vehicle. At this instant, the intermediate shaft408stops turning and the clutch409begins slipping. The slippage time may be set to be long enough to compensate for wear of the system over its useful life, which may result in slower motor speed and increased friction among the mechanical components of the unit300.

Referring now toFIG. 11, graph A is representative of the voltage applied to the electric drive motor402, graph B is representative of the rate of rotation of the intermediate drive shaft408in radians per second, and graph C is representative of the rate of rotation of the clutch409with respect to the intermediate drive shaft408in radians per second, all as a function of time during system retraction. Time t=0 represents the instant that electrical power of negative 12-14 volts is applied to the terminals of the drive motor402. Time t=x represents the time when the deployment arm303reaches its limit stop. At this instant, the intermediate shaft408stops turning and the clutch409begins slipping. The slippage time may be set to be long enough to compensate for wear of the system over its useful life, which may result in slower motor speed and increased friction among the mechanical components of the unit300.

Referring now toFIG. 12, a second primary embodiment1200of the invention is similar to the first primary embodiment300shown inFIG. 4, with the exception that the clutch has been entirely eliminated and the driven spur gear407to be secured to the intermediate drive shaft408. The elimination of the clutch permits the housing1201to be somewhat shorter than the housing401of the first primary embodiment shown inFIG. 4. Rather than limiting the torque applied to the output shaft501with a spring-loaded clutch409, torque is limited by limiting the maximum amount of current that is supplied to the electric drive motor402. The fact that torque produced by the motor402is essentially a linear function of the amount of current drawn by the motor, torque may be limited by limiting the amount of current that is supplied to the motor to a preset value.

Referring now toFIG. 13, the detailed system wiring diagram shows how the current limiting circuits are integrated into a vehicle's wiring system. As with the first main embodiment of the rapidly-deployable chain traction system shown inFIGS. 3-11, a 12 or 24-volt vehicle battery1301provides power for the second main embodiment system. The main power switch (i.e., ignition switch)1302of the vehicle provides a switchable source of power from the battery1301to a dual motor controller1303, which incorporates current limiting circuitry. An electric drive motor402-R and402-L is provided for the traction chain deployment system positioned at the right and left rear wheel of the vehicle, respectively. Power is applied to each direct current electric drive motor402-R and402-L through the dual motor controller1303by activating a normally open forward/reverse switch1304. While power is being sent to the electric drive motors402-R and402-L, a light emitting diode (LED)1305positioned on the dash of the vehicle is illuminated. It will be noted that in this implementation of the invention, plug P1, which includes the wiring outside the vehicle passenger compartment from the vehicle battery1301and the wiring to the electric drive motors402-R and402-L, plugs into jack J1. Plug P2, which includes the wiring inside the vehicle passenger compartment from the forward/reverse switch1304and from the from the LED1305, plugs into jack J2. Both jack J1and jack J2are coupled to the dual motor controller1303.

Although it would be convenient to connect an electric motor directly to a chip that controls the power supplied to it, most integrated circuit (IC) chips cannot pass enough current or voltage to spin a motor. In addition, motors tend to generate electrical noise in the form of current spikes, and can slam power back into the control circuit when the motor direction or speed is changed. Consequently, specialized circuits have been developed to supply motors with power and to isolate the other ICs from electrical problems associated with the motor. A widely used circuit for driving DC motors (whether direct drive or geared) is called an H-bridge. It is given that name because it looks like the capital letter “H” on classic schematics. With an H-bridge circuit, the motor may be driven forward or backward at any speed, even using a completely independent power source. The primary features of a preferred H-bridge circuit are:Almost all voltage is delivered to the motor by MOSFET transistors;Schottky diodes are used to protect against overvoltage or undervoltage from the motor;TTL/CMOS compatible driver chips are used to protect the logic chips, isolate electrical noise, and prevent potential short-circuits inherently possible in a discrete H-bridge;Capacitors are employed to reduce electrical noise and provide spike protection to the driver chips; andPull-up resistors are employed to prevent unwanted motor movement while the microcontroller powers up or powers down.

Referring toFIG. 14, the dual motor controller1303ofFIG. 13is shown in greater detail. The dual motor controller1303includes a microcontroller1401, which for a preferred embodiment of the invention is a PIC16F870. The microcontroller1401is coupled to digital control logic1402via a bus1403. The digital control logic1402receives inputs from a pair of analog proportional, integral, derivative (PID) controllers1404-R and1404-L (one for each electric drive motor402-R and402-L). Each of the PID current limiter controllers1404-R and1404-L receives control signals from the microcontroller1401and an associated MOSFET H-bridge. A pair of H-bridge FET drivers1405-R and1405-L (one also for each electric drive motor) receive control signals from the digital control logic1402and drive a pair of MOSFET H-bridge circuits1406-R and1406-L (again, one for each electric drive motor). For a preferred embodiment of the invention, the H-bridge FET drivers1405-R and1405-L is each a HIP4081 component. The MOSFET H-bridge circuits1406-R and1406-L provide drive current to the electric drive motors402-R and402L. Each MOSFET H-bridge circuit1406-R and1406-L receives battery power through an over voltage protect circuit1407, which also provides voltage to a +5-volt regulator1408and to a +12-volt regulator1409, outputs from which are used to power the integrated circuitry of the dual motor controller1303. The microcontroller1401also provides a signal to an LED FET driver1410, which drives the LED1305.

Still referring toFIG. 14, the current supplied to each drive motor is varied independently by the FET driver, which is controlled via pulse width modulation. The digital control logic is controlled by dual pulse-width-modulated maximum power limiters, which are controlled by dual current sensors (once for each drive motor) in the dual MOSFET H-bridge circuit. For the preferred embodiment of the circuit, each of the two drive motors is controlled by a MOSFET H-bridge, which in turn is driven by an H-bridge FET driver. Each driver is activated by digital control logic that communicates with an analog current limit controller and a microcontroller. The H-bridge circuits are used to limit the current supplied to the electric drive motors (one drive motor for each drive wheel of the vehicle).

Spring loading of the deployment system is necessary due to the resiliency of the tires. Were it not for the spring loading of the output shaft, the system would not work nearly as well.

The drive motor controller circuits may be programmed so that the circuit remembers whether the chain system is deployed or retracted. A momentary toggle switch is used to send a deployment or retraction signal to the controller circuit. It is designed to require two inputs within a second or so for safety reasons in case the toggle switch is inadvertently bumped. By monitoring current applied to the motor402, the dual motor controller circuitry1400can tell where the mechanism is in the deployment process.

A primary feature of either embodiment of the system is that no electrical components, other than cables, are subjected to salt and slush. Only two wires connect to each drive motor.

Though only two embodiments of the invention have been disclosed and described herein, it will be obvious to those of ordinary skill in the art that modifications and changes may be made thereto without departing from the spirit and scope of the invention as hereinafter claimed.