Displaceable Wheel Shifts Or Proportions Load Patents (Class 180/24.02)
-
Patent number: 7731208Abstract: A tag axle operating system comprises a gas circuit with gas at a prescribed pressure and a hydraulic circuit that delivers hydraulic fluid pressure to raise and establish the tag axle in an inactive condition and to lower and establish the tag axle in an active condition. The hydraulic circuit establishes a prescribed hydraulic pressure opposing the gas pressure and a resulting force forcing the tag axle tires to bear against a road surface and the tag axle to accept a predetermined load. A brake valve allows air pressure delivery to operate tag axle air brakes while the prescribed hydraulic pressure is maintained and prevents such delivery to disable the brakes when the prescribed hydraulic pressure is relieved. And the hydraulic circuit operates to relieve the prescribed hydraulic pressure to relieve the force on the tag axle and disable the brakes when the tag axle experiences a predetermined tilt angle.Type: GrantFiled: February 15, 2008Date of Patent: June 8, 2010Inventor: Brooks Strong
-
Patent number: 7677339Abstract: An arrangement for a suspension for a load carrying vehicle is provided. The suspension is provided with air springs and comprises at least one front axle and at least two rear axles, and each rear axle is provided with at least one pair of corresponding suspension air springs and at least one air spring is provided for lifting one of the rear axles. The suspension air springs for at least the rearmost axle is connected to the air spring for lifting one of the rear axles by a conduit for compressed air, which conduit is provided with a controllable valve, whereby the controllable valve is arranged to open during a vehicle loading process. A vehicle provided with the arrangement, and a method for carrying out a loading operation using the arrangement, are also described.Type: GrantFiled: March 1, 2006Date of Patent: March 16, 2010Assignee: Volvo Lastvagnar ABInventor: Christian Oscarsson
-
Patent number: 7635038Abstract: Presented is a heavy vehicle, such as a transport vehicle or civil engineering vehicle, of a mass greater than 500 metric tons configured to carry heavy loads and operable to generate a motive power. The vehicle includes tires of radial structure having a diameter greater than 3.5 meters and an axial width greater than 37 inches, a front steering axle coupled to at least two tires, at least one rear axle coupled to at least two tires and by which is transmitted at least part of the motive power, and a third, intermediate axle coupled to at least two tires. The intermediate axle is a steering axle and is moveable to a raised position. When the intermediate axle is in the raised position, the tires coupled to the intermediate axle are not in contact with the ground.Type: GrantFiled: January 11, 2006Date of Patent: December 22, 2009Assignee: Michelin Recherche et Technique S.A.Inventors: Jean-Marc Chamaillard, Pierre Durif
-
Publication number: 20090205884Abstract: A payload-carrying motor vehicle comprises a frame, a steer axle, tandem drive axles, at least one pusher axle located between the steer axle and drive axles, and a tag axle. The axles each have wheels with tires and a steer axle suspension system suspends the steer axle from the frame, a drive axle suspension system suspends the drive axles from the frame, a pusher axle suspension system including gas springs suspends the pusher axle from the frame, and a tag axle suspension system including a primary tag axle suspension and a secondary tag axle suspension suspends the tag axle from the frame behind the drive axles.Type: ApplicationFiled: February 15, 2008Publication date: August 20, 2009Inventor: Brooks Strong
-
Publication number: 20090205885Abstract: A payload-carrying motor vehicle comprises a steer axle, at least one drive axle and a tag axle. All of the axles have wheels with tires and brakes and a tag axle suspension system is adapted to suspend the tag axle in an active condition wherein the tag axle is pivotal about a first axis parallel to the other axles and also about a second axis located equidistant from the tag axle wheels and laying in a plane at right angles to the first axis and wherein the tag axle trails the drive axle and is forced to urge the tag axle tires against a road surface to aid in supporting the vehicle. A tag axle operating system is adapted to establish the tag axle in the active condition and relieve the force on the tag axle when the tag axle pivots about the second axis and reaches a predetermined tilt angle in maintaining contact of the tag axle tires with a road surface.Type: ApplicationFiled: February 15, 2008Publication date: August 20, 2009Inventor: Brooks Strong
-
Publication number: 20090205883Abstract: A payload-carrying motor vehicle comprises a steer axle, at least one drive axle and a tag axle. All of the axles have wheels with tires and air brakes and a tag axle suspension system is adapted to suspend the tag axle in an active condition wherein the tag axle is pivotal about a first axis parallel to the other axles and also about a second axis located equidistant from the tag axle wheels and laying in a plane at right angles to the first axis and wherein the tag axle is forced to urge the tag axle tires against a road surface to aid in supporting the vehicle. An air brake system is adapted to operate the air brakes of all the wheels and a tag axle operating system is adapted to establish the tag axle in the active condition while enabling operation of the air brakes of the tag axle wheels and to disable operation of the air brakes of the tag axle wheels when the tag axle pivots about the second axis and reaches a predetermined tilt angle in maintaining contact of the tag axle tires with a road surface.Type: ApplicationFiled: February 15, 2008Publication date: August 20, 2009Inventor: Brooks Strong
-
Patent number: 7549492Abstract: A trailing arm suspension unit for use on a vehicle including a ring bearing, a trailing arm, a spring and damper for providing large vertical wheel travel in a jounce and rebound suspension condition. The ring bearing may include external threads for rotationally connecting the trailing arm to a mounting plate or a hull of the vehicle. Further, supply lines for electrical and fluids may be passed through the opening in the ring bearings without the use of a slip ring and passed through a passage in the trailing arm to a wheel on the vehicle. The spring and damper may be located on top of the trailing arm and separately connected to the mounting plate to generate significant mechanical advantage. The geometry of the spring, damper, and trailing arm allow the spring in the suspension unit to be gas cylinder employing air.Type: GrantFiled: September 24, 2007Date of Patent: June 23, 2009Assignee: General DYnamics Land SystemsInventor: James Pond
-
Patent number: 7527118Abstract: A moveable axle assembly that can be moved into an operative position and retracted from an operative position and is constructed and arranged to be pivotally coupled to a motorized device, such as a skid steer loader. The axle assembly has a pair of wheels, an axle stabilizing assembly to securely support and stabilize the axle assembly and hydraulic actuator assemblies to move the moveable axle assembly in to and out of and operative position.Type: GrantFiled: May 17, 2004Date of Patent: May 5, 2009Inventor: Mark J. Bushinski
-
Patent number: 7527117Abstract: A vehicle with an actively adjustable axle system suitable for traveling over even or uneven terrain with a load is herein proposed.Type: GrantFiled: June 30, 2003Date of Patent: May 5, 2009Assignee: Integrated Vision, Inc.Inventor: Russell W. Strong
-
Patent number: 7503414Abstract: A movable subframe for a tractor-trailer includes a pair of elongated spaced-apart main members extending longitudinally relative to the tractor-trailer, at least one cross member extending between and being attached to the main members, and a retractable pin mechanism for selectively securing the position of the subframe relative to a body of the tractor-trailer. At least one of the main members includes at least one opening for receiving a pin of the retractable pin mechanism. The main member opening is formed in a shape, such as a D-shape, which reduces or minimizes distortion of the main member adjacent the top of the opening that is associated with forming of the main member.Type: GrantFiled: June 28, 2006Date of Patent: March 17, 2009Assignee: Hendrickson USA, L.L.C.Inventors: Phillippi R. Pierce, Kimm L. Carr, Greg Copeland
-
Patent number: 7398843Abstract: A robot including a robot body, a plurality of wheels on the robot body for propelling the robot body, and an axle for each wheel. Each wheel is configured to alternately attach to an axle at or proximate the center of the wheel for high efficiency mobility on flat terrain and also configured to attach to an axle at a position offset from the center of the wheel for better mobility on rougher terrain.Type: GrantFiled: August 30, 2005Date of Patent: July 15, 2008Assignee: Boston Dynamics, Inc.Inventors: Martin Buehler, Aaron Saunders, Felix Grimminger
-
Publication number: 20080053718Abstract: A system for providing a variable traction to a drive wheel of a vehicle includes a front axle for supporting the weight of the vehicle, a rear axle for supporting the weight of the vehicle, a middle axle for providing said variable traction to the drive wheel of the vehicle.Type: ApplicationFiled: September 6, 2006Publication date: March 6, 2008Inventor: Armen Shagbazyan
-
Patent number: 7273117Abstract: A trailing arm suspension unit for use on a vehicle including a ring bearing, a trailing arm, a spring and damper for providing large vertical wheel travel in a jounce and rebound suspension condition. The ring bearing may include external threads for rotationally connecting the trailing arm to a mounting plate or a hull of the vehicle. Further, supply lines for electrical and fluids may be passed through the opening in the ring bearings without the use of a slip ring and passed through a passage in the trailing arm to a wheel on the vehicle. The spring and damper may be located on top of the trailing arm and separately connected to the mounting plate to generate significant mechanical advantage. The geometry of the spring, damper, and trailing arm allow the spring in the suspension unit to be gas cylinder employing air.Type: GrantFiled: May 17, 2004Date of Patent: September 25, 2007Assignee: General Dynamics Land Systems, Inc.Inventor: James Pond
-
Patent number: 7175189Abstract: A mounting bracket is attachable to a vehicle frame for pivotally connecting a booster axle assembly comprising a pair of spaced arms, each arm having a first end, a second end, and an axle connected therebetween. The mounting bracket includes a U-shaped portion having a base and a pair of spaced legs connected to the base and extending in a first direction generally normal to the base. The pair of spaced legs and base define a space for receiving the first end of one of the arms of the booster axle assembly. Each leg defines first and second spaced appendages that define a slot. A mounting plate is connected to the base of the U-shaped portion and extends in a second direction normal to the base to permit connection of the mounting bracket to the vehicle frame.Type: GrantFiled: March 15, 2004Date of Patent: February 13, 2007Assignee: Schwing America, Inc.Inventor: Thomas E. Eull
-
Patent number: 6921100Abstract: The present invention relates to a system for adjusting weight distribution throughout all axle groups of the truck and trailer. The trailer has at least one axle group mounted on a pair of rails attached to the frame of the trailer. These axle groups are locked in position on the rails by locking pins. The system for adjusting weight distribution according to the present invention measures the weight on every axle group on the truck and trailer. The measurement may be of weight directly by load cells etc. or indirectly, by taking measurements from the air suspension system to calculate weight. The measurements are delivered as an electrical signal to one or more microprocessors capable of receiving the electrical signals and calculating the optimum position of the axle group on the trailer. The position of the trailer axle groups relative to the rails is also determined and the position delivered to the microprocessor(s).Type: GrantFiled: December 30, 2002Date of Patent: July 26, 2005Assignee: Wheel Monitor Inc.Inventors: John Mantini, Dimitre Iankoulov
-
Patent number: 6883813Abstract: An auxiliary lift axle suspension of the parallelogram type is constructed for heavy duty operation by providing longitudinal control arms at the corners of a parallelogram configuration extending between the axle connecting member and the frame hanger bracket. A lift bellows is then located between two opposing rigidity providing, U-shaped members (called paddles or stabilizer members) located within the three dimensional parallelogram space, wherein the legs of one U-shaped member are connected to the axle connecting member and the legs of the opposing U-shaped member are connected to the hanger bracket, such that the lift bellows is located between the bases of the opposing paddles and expands bi-directionally to lift the wheels of the suspension from the road surface.Type: GrantFiled: February 26, 2003Date of Patent: April 26, 2005Assignee: The Boler CompanyInventor: Michael J. Gottschalk
-
Patent number: 6845989Abstract: A lift-type axle/suspension system of a heavy-duty vehicle includes ride air springs for providing vehicle load support when the system is lowered, and one or more lift air springs for selectively raising the system when such additional load support is unnecessary or when greater vehicle maneuverability is desired. An apparatus integrates and simultaneously controls the operating systems for the lift and ride air springs. The control apparatus includes a plurality of conduits and valves which enable pressurized air from the lift air springs to be rapidly provided to the ride air springs when the system is being lowered. The additional air supplements the normal source of air from the vehicle compressed air source to ensure sufficient and timely air for smooth and efficient operation of the ride air springs without excessive buckling or folding, thus maintaining adequate overall vehicle air pressure needed for operating other vehicle components.Type: GrantFiled: December 16, 2002Date of Patent: January 25, 2005Assignee: The Boler CompanyInventors: R. Scott Fulton, Jeffrey D. Beaver
-
Patent number: 6808035Abstract: Tandem rear axle air suspensions for trucks and truck-tractors wherein a non-reactive, roll compliant drive axle suspension equipped with wheel slip sensing and control apparatus is combined with a roll stable, non-drive tag or pusher axle suspension equipped with apparatus for transferring weight to the drive axle suspension. The preferred technology for the non-drive tag or pusher axle suspension is a rigid beam suspension. The wheel slip sensing and control apparatus and the weight transfer apparatus may be either automatically or manually operated.Type: GrantFiled: January 10, 1997Date of Patent: October 26, 2004Assignee: The Boler CompanyInventor: Michael J. Keeler
-
Publication number: 20040016579Abstract: A vehicle having a load frame with wheels, a drive frame, a drive wheel, a non-driven rigid castor wheel, and a pivot link assembly. The drive wheel and non-driven rigid castor wheel are each fixed to move with the drive frame. The pivot link assembly couples the drive frame to the load frame to permit the drive frame to move vertically relative to the load frame. The pivot link assembly also has a first pivot axis about which the drive frame is rotatable relative to the load frame.Type: ApplicationFiled: March 24, 2003Publication date: January 29, 2004Inventors: Jon L. Coveyou, Lewis R. Poole
-
Patent number: 6585071Abstract: A caster assembly is constructed and arranged to be coupled to a rear of skid steer loader. The skid steer loader has a pair of front wheels and a pair of rear wheels and a hydraulic system for driving at least the front wheels. The skid steer loader has an auxiliary hydraulic system. The caster assembly includes at least one caster mounted for rolling and swiveling motion and at least one actuator constructed and arranged to be connected with the auxiliary hydraulic system to cause movement of the caster with respect to the skid steer loader from an inoperative position, wherein the front and rear wheels are in a ground engaging position with the caster in a position so as not to engage the ground, to an operative position, wherein the caster and the front wheels are in a ground engaging position and the rear wheels are in a position so as not to engage the ground.Type: GrantFiled: July 24, 2002Date of Patent: July 1, 2003Inventor: Robert Meurer
-
Patent number: 6572124Abstract: A lift axle control system is provided for a vehicle that has fixed axles and a lift axle. The lift axle is configured to move between a raised position spaced apart from the ground and a lowered position in contact with the ground to reduce the load carried by the fixed axles. The lift axle control system is configured to control the raising and lowering of the lift axle. According to a preferred embodiment of the disclosure, the lift axle control system includes a housing and a valve configured to control the flow of air to a lower bag that lowers the lift axle into contact with the ground.Type: GrantFiled: February 28, 2001Date of Patent: June 3, 2003Assignee: SMC Corporation of AmericaInventors: Alexander M. Mlsna, Paul D. Mundie, Robert L. Thommen
-
Patent number: 6564890Abstract: A vehicle including a load frame, a drive assembly, and a pivot link assembly. The load frame includes castor wheels to rollingly support the load frame on a support surface. The drive assembly includes a drive frame, a drive wheel, and a rigid castor wheel wherein the drive wheel and rigid castor wheel are each mounted to the drive frame. The pivot link assembly couples the drive frame to the load frame and permits the drive frame to move vertically and angularly relative to the load frame.Type: GrantFiled: March 12, 2001Date of Patent: May 20, 2003Assignee: Jervis B. Webb CompanyInventor: Jon L. Coveyou
-
Patent number: 6523625Abstract: A system and method for improving the traction of a vehicle uses weight distribution control to improve wheel to driving surface friction. A driven axle and a non-driven axle support a vehicle load through adjustable suspension members. The suspension members are, for example, air bags. Actuators and controllers adjust the suspension members in a selectable predetermined manner. The selection can be based on operator preference, vehicle operating mode, or a sensed loss of traction. The driven axle carries a drive axle maximum rated load in order to maximize drive wheel traction at all times.Type: GrantFiled: December 20, 2000Date of Patent: February 25, 2003Assignee: Bendix Commercial Vehicle Systems LLCInventors: Charles E. Eberling, William P. Amato
-
Publication number: 20020179345Abstract: Tandem drive axles include a pair of drive axles interconnected by a thru-shaft. An inter-axle differential allows speed differentiation between the pair of axles. Differences in tire rolling radii and variations in axle load distribution between the pair of drive axles are examples of why axle differentiation is needed. By measuring and monitoring wheel speed and/or tire pressure, tire rolling radii differences can be determined and appropriate adjustments can be made to tire pressures to provide a common tire rolling radii range for all tires. In addition to tire pressure adjustment, by adjusting other axle parameters that affect axle performance, such as suspension height and weight distribution, the need for axle differentiation is eliminated.Type: ApplicationFiled: June 1, 2001Publication date: December 5, 2002Applicant: Meritor Heavy Vehicle Technology, LLCInventor: Dale K. Bell
-
Patent number: 6460641Abstract: A wheelchair has a plurality of central wheels which can be either power or manually driven, at least one rear caster wheel, and at least one resiliently biased ground engaging front wheel having a multiple suspension assembly. The wheelchair has improved tracking since the front wheel is maintained on the ground even on undulating, bumpy, or irregular surfaces. The wheelchair also has improved stability since the front ground engaging wheel also acts as a resiliently biased anti-tip wheel.Type: GrantFiled: June 29, 2000Date of Patent: October 8, 2002Assignee: Invacare CorporationInventor: Stephen L. Kral
-
Patent number: 6439332Abstract: A caster assembly is constructed and arranged to be coupled to a rear of skid steer loader. The skid steer loader has a pair of front wheels and a pair of rear wheels and a hydraulic system for driving at least the front wheels. The skid steer loader has an auxiliary hydraulic system. The caster assembly includes at least one caster mounted for rolling and swiveling motion and at least one actuator constructed and arranged to be connected with the auxiliary hydraulic system to cause movement of the caster with respect to the skid steer loader from an inoperative position, wherein the front and rear wheels are in a ground engaging position with the caster in a position so as not to engage the ground, to an operative position, wherein the caster and the front wheels are in a ground engaging position and the rear wheels are in a position so as not to engage the ground.Type: GrantFiled: July 13, 2001Date of Patent: August 27, 2002Inventor: Robert Meurer
-
Patent number: 6409192Abstract: A slider pin release mechanism for a slider suspension system of a semi-trailer which includes a trailer body and a slider suspension which is movable longitudinally forwardly and rearwardly relative to the trailer body. Locking pins carried on the slider suspension are movable laterally into and out of locking engagement with the slider suspension and the trailer body. A longitudinally extending pivot rod connects to the locking pins. A ratchet gear is affixed to the forward end of the pivot rod. A handle is mounted on the pivot rod for rotation relative to the ratchet gear. A drive pawl is mounted on the handle and engages the ratchet gear to drive the ratchet gear upon rotation of the handle. A holding pawl is engageable with said ratchet gear. A drive pawl release rod is connected to the drive pawl. The drive pawl includes a release tooth which is moved into contact with the holding pawl to disengage the holding pawl from the ratchet gear.Type: GrantFiled: August 9, 2000Date of Patent: June 25, 2002Assignee: Tuthill CorporationInventor: Robert D. Botts
-
Publication number: 20020066605Abstract: A proportional load transfer valve is disclosed to shift a predetermined ratio of approximately fifty percent (50%) of the weight on a tag axle to the drive axle. The load transfer valve acts in response to a pneumatic signal indicative of a traction event. The valve alters the ratio of supply port pressure associated with the air suspension bags of the drive axle that is forwarded to the delivery port associated with the air bag suspension assembly of the tag axle. As the weight imposed on the drive axle approaches a predetermined maximum, the load transfer valve transfers less weight so that the drive axle is not overloaded.Type: ApplicationFiled: June 15, 2001Publication date: June 6, 2002Applicant: Honeywell Commercial Vehicle Systems CompanyInventors: James McClelland, Charles E. Eberling, Dick W. McCreight
-
Patent number: 6371227Abstract: An automated auxiliary axle deployment control system for a load-hauling vehicle having a time-variable payload and one or more fluid-operated auxiliary support axles comprising one or more load sensing devices for determining the payload distribution of the vehicle in real-time. One or more automatically operable pressure modulation valves adjusts the pressure applied to the one or more auxiliary axles to adjust the load carrying capacity thereof based on payload distribution. A signal processing system receives input signals from the one or more load sensing devices and produces output control signals for operating the pressure modulation valve(s).Type: GrantFiled: September 24, 1999Date of Patent: April 16, 2002Assignee: McNeilus Truck and Manufacturing, Inc.Inventor: William P. Bartlett
-
Publication number: 20020014364Abstract: An automated auxiliary axle deployment control system for a load-hauling vehicle having a time-variable payload and one or more fluid-operated auxiliary support axles comprising one or more load sensing devices for determining the payload distribution of the vehicle in real-time. One or more automatically operable pressure modulation valves adjusts the pressure applied to the one or more auxiliary axles to adjust the load carrying capacity thereof based on payload distribution. A signal processing system receives input signals from the one or more load sensing devices and produces output control signals for operating the pressure modulation valve(s).Type: ApplicationFiled: September 24, 1999Publication date: February 7, 2002Inventor: WILLIAM P. BARTLETT
-
Patent number: 6315311Abstract: A wheeled support structure reversibly deployable from a stowed condition on the bed of a trailer to aid in rolling support of a load thereupon is provided. The support structure includes a frame, pivotable through a range of motion exceeding 90 degrees and having forward and rearward portions, and an actuator assembly capable of reversibly deploying the frame from a stowed condition on the bed of the trailer. The rearward frame portion includes a tag axle assembly and means for limiting energy transfer from the tag axle assembly to the frame as when the wheeled support structure is deployed to aid in rolling support of a load being hauled by the trailer. The actuator assembly cooperatively links the trailer to the forward portion of the frame.Type: GrantFiled: September 12, 2000Date of Patent: November 13, 2001Assignee: R and G Construction Co.Inventor: Reinhold P. Mathiowetz
-
Patent number: 6308793Abstract: A proportional load transfer valve is disclosed to shift a predetermined ratio of approximately fifty percent (50%) of the weight on a tag axle to the drive axle. The load transfer valve acts in response to a pneumatic signal indicative of a traction event. The valve alters the ratio of supply port pressure associated with the air suspension bags of the drive axle that is forwarded to the delivery port associated with the air bag suspension assembly of the tag axle. As the weight imposed on the drive axle approaches a predetermined maximum, the load transfer valve transfers less weight so that the drive axle is not overloaded.Type: GrantFiled: March 22, 1999Date of Patent: October 30, 2001Assignee: AlliedSignal Truck Brake Systems Co.Inventor: Charles E. Eberling
-
Patent number: 6247196Abstract: A bogie construction includes at least two stiff axles interconnected by a rocking lever. The rocking lever is pivoted in its middle so that it can move in its longitudinal direction as a result of steering movements. The rocking lever is preferably connected to the bogie axle that turns the least, by a joint of an ear, and thus this axle determines the longitudinal displacement of the rocking lever. The rocking lever is connected to the other axles which turn more by suspension rods. A suspension rod pivoted below the axle is used, and thus the suspension rod can be made as long as possible. Consequently, the suspension rod tilts less as a result of the longitudinal movement of the rocking lever.Type: GrantFiled: July 12, 1999Date of Patent: June 19, 2001Assignee: Sandvik ABInventor: Risto Jurmu
-
Patent number: 6247712Abstract: A vehicle comprising a body having a front end and a rear end, front wheels carried by a front axle mounted to the body proximate the front end of the vehicle, rear wheels carried by a rear axle mounted to the body proximate the rear end of the vehicle, a cargo body mounted to the body for carrying a load, a framework having an inner end pivotally mounted to the rear end of the vehicle and having an outer end, wheels mounted for rotation to a trailing axle, the trailing axle mounted to the outer end of the framework for transverse pivotal movement relative the cargo body, the trailing axle movable between an extended orientation wherein the trailing axle is located generally outboard of the outer end of the framework and a retracted orientation wherein the trailing axle is located generally inboard of the outer end of the framework, and a pair of lifting arms for moving the framework relative the cargo body of the vehicle from an operative position wherein the trailing axle is positionable in the extended oriType: GrantFiled: July 14, 1997Date of Patent: June 19, 2001Inventors: Fred P. Smith, Jack Mitchell
-
Patent number: 6217044Abstract: Wheel assemblies for attachment to a carriage or a vehicle. The wheel assemblies can be configured for four wheel steering, locked in predetermined directions, or free pivoting. The wheel assemblies further include an apparatus for retracting and extending the wheels of the carriage to support the carriage on fixed length supports.Type: GrantFiled: April 15, 1999Date of Patent: April 17, 2001Assignee: Beeche Systems, Corp.Inventors: Gregory L. Beeche, Roy Scrafford
-
Patent number: 6206119Abstract: An electrical wheelchair includes a chassis on which a seat is mounted. The chassis has a double-framed structure including a primary frame and a secondary frame pivotally connected to each other so as to be rotatable with respect to each other about a first rotational axis. Two driving wheels are mounted to the primary frame and independently driven by motors. Two rear guide wheels are rotatably and swivellingly mounted to the primary frame. The secondary frame has a front edge frontward extending beyond the primary frame with two front guide wheels rotatably and swivellingly mounted thereto whereby the front guide wheels are capable to orbit about the driving wheels by means of the pivotal connection between the primary and secondary frames so as to provide the front guide wheels and the driving wheels with excellent surface compliance when the wheelchair is moving on an uneven surface.Type: GrantFiled: May 5, 1999Date of Patent: March 27, 2001Inventor: Donald P. H. Wu