Abstract:
A pseudo four-leg leveling system for a vehicle, such as a recreational vehicle or the like, includes four jacks in the form of hydraulic cylinders mounted in pairs at the front and rear of the vehicle. A power system supplies hydraulic fluid to extend and retract the jacks thereby adjusting the attitude of the vehicle relative to level. The front two jacks are driven in parallel and the rear jacks are driven separately and independent of the front jacks. When the power system is de-energized the front jacks are hydraulically isolated to improve the stability of the system when static. Pressure operated valves automatically control the isolation of the jacks driven in parallel, as well as return passage to the tank, without the need for additional electronically controlled valves.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of U.S. provisional application Ser. No. 60/331,864, filed Nov. 20, 2001. 

   STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates to a leveling system for use with a vehicle, such as a recreational vehicle. 
   2. Description of the Related Art 
   Various systems are known for leveling a vehicle such as a recreational vehicle. These systems are typically hydraulic powered systems that automatically level the vehicles to which there are attached in response to certain operator commands. Some such systems have four spring-biased hydraulic cylinders or “jacks” located one adjacent each corner of the vehicle. (See U.S. Pat. Nos. 4,061,309; 4,165,861; 4,597,584; 4,743,037; and 4,746,133). One problem with four independently operating jacks at each corner of the vehicle is that they tend to twist the vehicle frame during unsynchronized extension and retraction of the jacks. 
   U.S. Pat. No. 5,176,391, owned by the same assignee as the present application, discloses a vehicle leveling system having three jacks, two of which are located at the rearward end of the vehicle and one of which is located at the forward end of the vehicle. The use of a single front jack reduces twisting of the vehicle frame, however, it makes the system less stable because two corners of the vehicle are left unsupported. 
   U.S. Pat. No. 5,915,700, also owned by the assignee of the present application and incorporated by reference as though fully set forth herein, teaches a “pseudo four-leg” vehicle leveling system. That system has four jacks with one pair of jacks at one end of the vehicle driven in parallel and the other two jacks being driven independent of each other and the two jacks in parallel. The two jacks in parallel are in fluid communication with each other so that one end of the vehicle can “float” between the common jacks during extension and retraction. In other words, the hydraulic fluid will flow between the parallel jacks to provide more or less pressure in either jack depending on which side of the vehicle exerts more downward force, thereby reducing frame twisting. The stability of the system is also improved because all four corners of the vehicle are supported when the jacks are extended, however, because the hydraulic fluid can flow between the parallel jacks it is less stable than convention four leg systems when the jacks are static. 
   Accordingly, a vehicle leveling system with improved stability during static operation is needed. 
   SUMMARY OF THE INVENTION 
   In accordance with one aspect of the invention, a vehicle leveling system includes a control mechanism, a series of extendible and retractable jacks mounted to the frame of the vehicle and a power system interposed between the jacks and the control mechanism for supplying hydraulic fluid to selectively extend and retract the jacks. The system includes four jacks, two being located toward each end of the vehicle. Two of the jacks at one end of the vehicle are operated in tandem and the other two are operated independent of each other and the tandem pair to form a pseudo four-leg system. Each jack, including those in the tandem pair, is independently hydraulically lockable so that they can be locked after the leveling operation is performed, for example, when the system is de-energized. 
   Each jack is preferably in the form of a hydraulic cylinder assembly including a cylinder and an extendible and retractable piston mounted to the cylinder. A spring is interposed between the cylinder and the piston. Introduction of pressurized fluid into the cylinder causes extension of the piston against the force of the spring, and the spring causes retraction of the piston when fluid pressure within the cylinder is relieved. A shoe is connected to the extendible and retractable piston, and the spring is preferably interconnected between the cylinder and the shoe. 
   The power system is preferably a fluid power system consisting of a hydraulic fluid reservoir, a pump for selectively supplying fluid under pressure to the jacks from the reservoir, and a control valve interposed between the hydraulic fluid reservoir and each jack. Each control valve controls the supply of pressurized fluid to one or more of the jacks during operation of the pump, and also provides flow of fluid to the reservoir when the pump is not operating. 
   The two jacks in tandem are in fluid communication with each other, and share a common control valve. The control valves are responsive to operation of the manually actuated switches for selectively adjusting the attitude of the vehicle relative to level in response to manual actuation by the operator. Each control valve is located on a valve block interconnected with a common line feeding the tandem jacks after their control valve splits at a location within the valve block. A single return line is interconnected with the reservoir and a return control valve, preferably a normally open pressure operated check valve, is disposed in the return line for controlling flow of fluid from the jacks to the reservoir. 
   These and still other advantages of the invention will be apparent from the detailed description and drawings. What follows is a preferred embodiment of the present invention. To assess the full scope of the invention the claims should be looked to as the preferred embodiment is not intended as the only embodiment within the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric view of a pseudo four-leg vehicle leveling system constructed according to the invention as installed on the frame of a vehicle such as a recreational vehicle; 
       FIG. 2  is one preferred schematic representation of the pseudo four-leg vehicle leveling system of  FIG. 1 ; and 
       FIG. 3  is another preferred schematic representation of the pseudo four-leg vehicle leveling system of FIG.  1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a vehicle leveling system  10  according to the invention mounted on the frame members of a vehicle, such as a recreational vehicle or the like. The system  10  includes four jack assemblies  12 ,  16 ,  20  and  312 . Jacks  312  and  16  are mounted near respective front and rear ends of a passenger side longitudinal frame member  18  and jacks  12  and  20  are similarly mounted to a driver side longitudinal frame member  22  connected to frame member  18  by two transverse frame members  14  and  28 . 
   The front jacks  12  and  312  are extended in parallel, and as such the system can be referred to as a pseudo four-leg vehicle leveling system. It should thus be appreciated that the pseudo four-leg system of  FIG. 1  can enhance the stability of the vehicle over a three-leg system. This form of the invention does not require that the pair of jacks operated in parallel be located towards the front of the vehicle, but it has been found that it is advantageous to do so. 
   The jacks  12 ,  16 ,  20  and  312  are identical, preferably being constructed as described in U.S. Pat. Nos. 5,100,105 or 5,915,700, both of which form a part of this disclosure. The jacks thus will not be described in great detail here, however, generally the jacks have a hydraulic cylinder assembly  30  with a sliding piston to which a circular shoe  34  is mounted. A top cap  46  mounted to the upper end of the cylinder has a fitting  48  for connecting a hydraulic fluid line  50 . A coil spring  54  extending between shoe  34  and a mounting plate  51  near the cap  46  biases the piston to slide into the cylinder. 
   The system also includes a manually operated control panel  26  mounted within the interior of the vehicle. Like the construction of the jacks, U.S. Pat. No. 5,915,700 describes in detail preferred electronic controls for manual and semi-automatic operation of the leveling system, and thus this will not be discussed at length here. Generally, however, the control panel  26  is preferably able to mount to the dashboard of the vehicle so that its manually operable front, rear, left and right actuator switches lie in a diamond pattern with its longitudinal axis parallel to the longitudinal axis of the vehicle so that each switch aligns with its corresponding side of the vehicle. 
   Referring now to  FIGS. 1 and 2 , a reservoir, pump and actuator assembly  24  includes a hydraulic fluid reservoir  94  and a pump and motor assembly  96 , both of which are mounted to a mounting block  98  disposed therebetween. A mounting bracket  100  is interconnected with pump and motor assembly  96  and block  98  for mounting the reservoir, pump and actuator assembly  24  to frame member  14 . 
   A valve block  102  is mounted to block  98 , and a series of supply/return control valves  104 ,  106  and  108  are mounted to valve block  102 . Supply/return control valves  104 ,  106 , and  108  are solenoid operated dual poppet bidirectional blocking valves, with a manual override, such as manufactured by Delta under its Part No. 86020151. 
   The hydraulic fluid power system for extending and retracting jacks  12 ,  16  and  20  as illustrated in  FIG. 2  is substantially similar to the hydraulic system shown in U.S. Pat. No. 5,176,391, owned by the same assignee as the present application, the disclosure of which is hereby incorporated by reference. Similarly, the construction of reservoir, pump and actuator assembly  24  is substantially identical to the reservoir, pump and actuator assembly as disclosed in U.S. Pat. No. 5,176,391, and reference is made to the description contained in U.S. Pat. No. 5,176,391 for a detailed explanation of the construction of reservoir, valve and actuator assembly  24 . 
   Referring to  FIG. 2 , supply/return control valves  104 ,  106 , and  108  are located in secondary supply/return passages  110 ,  112  and  114 , respectively. Valves  104 ,  106 , and  108  each include a rightward block having a double check valve and a leftward block providing free flow therethrough. Valves  104 ,  106 , and  108  are biased toward their closed position shown in  FIG. 2  in which their rightward blocks are located in passages  110 ,  112 , and  114 , respectively, so as to close off these passages and thereby isolate and hydraulically lock jacks  16  and  20  from each other and jacks  12  and  312  when the jacks are static. In accordance with known construction, valves  104 ,  106 , and  108  are shiftable rightwardly in response to supply of electrical current to a solenoid in response to operation of the corresponding switch(es) on the control panel  26 . In the event of an electrical failure, valves  104 ,  106 , and  108  can be manually shifted between their rightward and leftward positions. 
   Secondary supply/return passages  110 ,  112  and  114  each communicate with a primary supply/return passage  116 , which in turn communicates with reservoir  94  through a passage  118  and a line  120  extending between passage  118  and a line  122  interconnected with pump  124 , which forms a part of motor and pump assembly  96  (FIG.  1 ). Pump  124  is interconnected with reservoir  94  through a line  126 , and is driven by motor  128  which forms a further part of motor and pump assembly  96 . 
   A check valve  129  is mounted within passage  118  for providing one-way flow of fluid from pump  124  through line  120  to primary supply/return passage  116 . 
   A return passage  130  is formed in block  102 , communicating between primary supply/return passage  116  and a line  132  which interconnects with a return line  134  to provide return flow of fluid to reservoir  94  from primary supply/return passage  116 . A return control valve  136  is provided in passage  130  for controlling return flow of fluid from primary supply/return passage  116  to reservoir  94 . Return control valve  136  is a pressure operated valve biased in its normally open position shown in  FIG. 2  when pilot pressure at P 2  is at or near zero, such as when the pump is not energized, and allows flow in return passage  130  from primary supply/return passage  116  to line  132 . As pilot pressure P 2  raises from pressurization of the system the return control valve  136  automatically shifts to block flow through passage  130 . 
   A series of retraction restricting valves  137 ,  138  and  140  are located in passages  110 ,  112  and  114 , respectively between jacks  12 ,  16 ,  20  and supply/return control valves  104 ,  106 , and  108 , respectively. Retraction restricting valves  137 ,  138 , and  140  are generally constructed in accordance with the teachings of Schneider U.S. Pat. No. 4,704,947 entitled “Bidirectional Fluid Flow Valve”, owned by the same assignee as the present application, and the disclosure of which is hereby incorporated by reference. Valves  137 ,  138 , and  140  provide unrestricted flow in passages  110 ,  112 , and  114 , respectively, during supply of pressurized fluid from primary supply/return passage  116  to jacks  12 ,  16 ,  20 , respectively, to extend jacks  12 ,  16 ,  20  and  312 . On the other hand, when fluid pressure in primary supply/return passage  116  is relieved and flow control valves  104 ,  106 , and  108  are shifted rightwardly to provide retraction of jacks  12 ,  16 ,  20  and  312  retraction restricting valves  137 ,  138 , and  140  are shifted rightwardly to provide a restriction in the return flow of fluid from jacks  12 ,  16 ,  20  and  312  to primary supply/return passage  116 , until pressure on jacks  12 ,  16 ,  20  and  312  is relieved to a predetermined extent. For instance, retraction restricting valve  137  can be shifted to provide slow retraction of front jacks  12  and  312  until the front vehicle wheels engage the ground and relieve pressure on jacks  12  and  312 . When this occurs, retraction restricting valve  137  is shifted to its  FIG. 2  position to eliminate the restriction in flow through valve  137  and to provide full flow of fluid there across in secondary supply/return line  110  thus providing faster retraction of jacks  12  and  312 . In a similar manner, retraction restricting valves  138 ,  140  provide slow retraction of jacks  16 ,  20 , respectively until the rear tire set adjacent each jack engages the ground, and thereafter fast retraction of jacks  16 ,  20 . 
   As mentioned, the second front jack  312  is operated in parallel with the first front jack assembly  12 . In particular, supply/return control valve  104  and retraction restricting valve  137  control the flow of hydraulic fluid through passage  110  in valve block  102  to both the first front jack assembly  12  and the second front jack assembly  312 . Common passage  110  has a branch point  314  from which hydraulic fluid is supplied to jack  12  through passage  316  and to jack  312  through passage  318 . There is a pressure operated control valve  320  along passage  318 . The control valve  20  is biased in its normally closed position shown in  FIG. 2  when pilot pressure at P 1  is at or near zero, such as when the pump is not energized. This blocks passage  318  and isolates jack  312  from jack  12  when the system is de-energized or in a static condition. Thus, all four jacks  12 ,  312 ,  16  and  20  are hydraulically locked independently of one another when not being raised or lowered. When the system is pressurized, such as during extension of the jacks, pilot pressure P 1  will shift the valve  320  to its open position allowing flow through passage  318 . Since there is no control valve in passage  316 , when valve  320  is open the hydraulic fluid pressure in the first front jack assembly  12  will equalize during operation with the hydraulic fluid pressure in the second front jack  312  to extend and retract the front jacks in unison. 
   In operation, to level the vehicle the operator first actuates a power ON/OFF switch (not shown) on the control panel  26  to energize the system. Energizing the system raises pilot pressure P 2  which closes off passage  130  so that the hydraulic fluid will flow to control valves  104 ,  106  and  108  and not back to the reservoir  94 . Manually or electronically the attitude of the vehicle relative to level is ascertained and the appropriate switches are activated to extend one or more of the jacks as needed, the front two jacks  12  and  312  extending together uniformly and each of the rear jacks  16  and  20  extending independently. The switches interconnected with valves  104 ,  106 , and  108  to provide selective extension of jacks  12 ,  16 ,  20  and  312 . Specifically, a front switch controls extension of both front jacks  12  and  312  in parallel; a rear switch controls extension of rear jacks; a left switch controls extension of driver side rear jack  20 ; and a right switch controls operation of passenger side rear jack  16 . Once the vehicle is properly leveled, the operator can again actuate the power switch to de-energize the system. This will lower pilot pressure P 1  to cause valve  320  to close and thus isolate and lock out jack  312  from jack  12 . Isolating these two jacks prevents redistribution of hydraulic fluid and thus pressure fluctuations between the jacks  12  and  312 , which thereby improves their stability. The other jacks  16  and  20  are each isolated and hydraulically locked by the closer of valves  106  and  108 . 
   A RETRACT ALL JACKS switch (not shown) is actuated by the operator when it is desired to move the vehicle. This switch is interconnected with valves  104 ,  106 , and  108  to shift them rightwardly, in order to provide retraction of jacks  12 ,  16 ,  20  and  312  under the influence of the springs of each jack. Note that pilot pressure P 2  lowers sufficiently to allow return control valve  136  to open and thus unblock passage  130  allowing hydraulic fluid to flow from passage  116  to passage  132 . 
   The system of the present invention is designed so that it can only be operated when the transmission of the vehicle is engaged in its neutral or park conditions and when the parking brake is engaged. If any one of these conditions is violated, the electronics of the system automatically provide retraction of jacks  12 ,  16 ,  20  and  312 . 
     FIG. 3  shows another preferred system for practicing the present invention. This system is similar to that described above having four identical jacks  12 ,  16 ,  20  and  312  and an identical reservoir, pump and actuator assembly  24  including a hydraulic fluid reservoir  94  interconnected with pump  124  through a line  126  and driven by motor  128 . As before, this assembly is connected via a supply line  120  and a return line  132  to a valve block  102  having a series of solenoid supply/return control valves  104 ,  106  and  108 . The supply/return control valves  104 ,  106 , and  108  are located in secondary supply/return passages  110 ,  112  and  114 , respectively, which communicate with a primary supply/return passage  116 . As before, when closed, the control valves  104 ,  106  and  108  isolate jacks  16  and  20  from each other and from jacks  12  and  312 . A check valve  129  is mounted within passage  118  for providing one-way flow of fluid from pump  124  through line  120  to primary supply/return passage  116 . 
   A return passage  130  is formed in block  102 , communicating between primary supply/return passage  116  and a line  132 . A check valve  136 A is provided in passage  130  for controlling return flow of fluid from primary supply/return passage  116  to reservoir  94 . Valve  136 A is a pressure operated one way check valve that is normally open in the return to tank direction as shown in  FIG. 3  when pilot pressure at P 3  is at or near zero, such as when the pump is not energized, to allow flow in return passage  130  from primary supply/return passage  116  to line  132 . As pilot pressure P 3  raises from pressurization of the system, valve  136 A automatically shifts to block flow through passage  130 . 
   Passage  314  branches from passage  110  downstream from control valve  104  to feed jack  312 . There are two normally closed, pressure operated one way check valves  350  and  351  in respective passages  110  and  314 . Both valves  350  and  351  open when pilot pressure P 4  is sufficient, such as when the system is energized. With both valves  350  and  351  open hydraulic fluid can flow to jacks  12  and  312  in parallel in which case the hydraulic fluid pressure in the first front jack assembly  12  will equalize with the hydraulic fluid pressure in the second front jack  312 . When the system is de-energized, valves  350  and  351  work to isolate and hydraulically lock jacks  12  and  312  from one another. Hydraulic fluid from jack  12  can flow back through line  316  and into line  314 , but then it is prevented by valve  351  from entering line  318  leading to jack  312 . Similarly, hydraulic fluid in line  318  can flow back through line  318  to line  314  where it is stopped by valve  350  so as not to flow into line  316 , which leads to jack  12 . Thus, valve  350  and  351 , in combination with control valves  104 ,  106  and  108  hydraulically lock each of the four jacks independent of one another when in a static condition. 
   However, interposed between valves  104 ,  106  and  108  are dual restricting valves  137 A,  138 A and  140 A in passages  110 ,  112  and  114 , respectively. There is an additional dual restricting valve  360  in passage  314 . Valves  137 A,  138 A,  140 A and  360  provide restricted flow in passages  110 ,  112 ,  114 , and  314  respectively, during supply of pressurized fluid from primary supply/return passage  116  to jacks  12 ,  16 ,  20 , and  312 , respectively, to extend jacks  12 ,  16 ,  20  and  312 . When fluid pressure in primary supply/return passage  116  is relieved and flow control valves  104 ,  106 , and  108  are shifted downwardly to provide retraction of jacks  12 ,  16 ,  20  and  312  valves  137 A,  138 A,  140 A and  360  shift downwardly by pilot pressure to allow restricted return flow of fluid from jacks  12 ,  16 ,  20  and  312  to primary supply/return passage  116  through valves  350  and  351 , until pressure on jacks  12 ,  16 ,  20  and  312  is relieved to a predetermined extent at which they return to their initial position. 
   It should be appreciated that preferred embodiments of the invention have been described above. However, many modifications and variations to these preferred embodiments will be apparent to those skilled in the art, which will be within the spirit and scope of the invention. Therefore, the invention should not be limited to the described embodiment. To ascertain the full scope of the invention, the following claims should be referenced.