Patent Publication Number: US-2002000699-A1

Title: Vehicle towing system

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates to a vehicle towing system for a towed vehicle having powered fluid suspension. The invention also relates to a vehicle adapted for use as the towed vehicle of such a vehicle towing system.  
       DESCRIPTION OF THE RELEVANT ART  
       [0002] A vehicle with a powered fluid suspension system requires the operation of a pump in order to maintain the suspension at the required height for driving. If the pump is not operated, the suspension will tend to deflate over time thereby reducing the ground clearance of the vehicle. Such a pump usually only operates when the engine of the vehicle is running.  
       [0003] During towing of such a vehicle, it is usual that the engine of the towed vehicle is not running. Therefore, up to now it has not been possible to tow a vehicle with powered fluid suspension, because the towed vehicle&#39;s suspension “deflates” during towing, thereby reducing ground clearance and causing damage to the vehicle.  
       SUMMARY OF THE INVENTION  
       [0004] It is an object of the invention to provide a vehicle towing system in which the above disadvantages are reduced or substantially obviated.  
       [0005] According to the broadest aspect of the present invention there is provided a vehicle towing system comprising a towing vehicle, and a towed vehicle, the towed vehicle having fluid suspension, a pump means for supplying pressurised fluid power to the fluid suspension, an electric motor for driving the pump means, the system further comprising an electrical connection between the towing vehicle and towed vehicle for supplying electrical power from the towing vehicle to the electric motor of the towed vehicle to enable the ride height of the towed vehicle to be maintained during the towing operation.  
       [0006] Preferably the pressurised fluid is pressurised hydraulic oil. Alternatively, the pressurised fluid may be water, which may be mixed with antifreeze or alcohol, or it may be compressed air.  
       [0007] Preferably the electrical connection is provided by a cable connected to the towing vehicle by means of a multi-pin connector socket and plug. The cable may be permanently connected to the electrical system of the towed vehicle, or the towed vehicle may have a further multi-pin connector socket and the cable may have corresponding multi-pin plugs at either end. Preferably the multi-pin connector socket and plug is a conventional seven pin trailer light sockets and plugs. A spur may be taken from the connecting cable to supply electrical power to a light board, which may be attached to the rear of the towed vehicle during towing.  
       [0008] The towed vehicle may have an electrical control unit connected to the electric motor for driving the pump means. Furthermore, sensors may be provided in the fluid suspension of the towed vehicle, which provide feedback to the electrical control unit for monitoring the status of the suspension system. If the electrical control unit detects deflation of the suspension system resulting in reduced ground clearance of the towed vehicle, the electrical control unit provides power to the electric motor which drives the pump means and restores the vehicle suspension to the required driving or towing height. As in normal driving operation of the vehicle, it is preferred that the sensors detect when the suspension system has been restored to the usual driving height. The electrical control unit may then cut off the electrical power supply to the electric motor for driving the pump means.  
       [0009] In accordance with a second aspect of the invention, there is provided a vehicle adapted for use as the towed vehicle of the vehicle towing system in accordance with the first aspect of the invention. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010] The invention will now be described, by way of example only, with reference to the accompanying drawings in which:  
     [0011]FIG. 1 shows a schematic plan of a vehicle towing system in accordance with the invention; and  
     [0012]FIG. 2 is a view similar to that of FIG. 1 but showing a modified vehicle towing system in accordance with the invention. 
    
    
     DETAILED DESCRIPTION  
     [0013] Referring to FIG. 1, a towing vehicle is indicated in dotted outline at  10 , and a towed vehicle is indicated in dotted outline at  12 . An electrical connector  16  is provided at the rear of the towing vehicle  10 , and is connected to a battery  14  of the vehicle by means of positive and negative wires  18 ,  20  respectively. A vehicle ignition switch  22  is provided in the positive wire  18 . When the ignition switch  22  is turned on, the battery  14  and connector  16 , are connected, and when the ignition switch is turned off, the battery and connector are disconnected.  
     [0014] A further electrical connector  24  is provided at the front of the towed vehicle  12 , which connector  24  is connected to the connector  16  of the towing vehicle  10  by positive and negative wires  26 ,  28 . The wires  26 ,  28  are most conveniently part of a single cable, fitted with conventional seven pin trailer cable plugs, and the connectors  16 ,  24  are correspondingly conventional seven pin sockets. A spur (not shown in FIG. 1 but see wires  41 ,  43  in FIG. 2) may be taken from the connecting cable to supply electrical power to a light board (not shown), which may be attached to the rear of the towed vehicle  12  during towing.  
     [0015] In normal driving operation of the towed vehicle  12 , an electrical control unit (ECU)  30  is connected to a vehicle battery  32  by means of positive and negative wires  34 ,  36 . The positive wire  34  is interrupted by the vehicle ignition switch  38 . Therefore, in usual driving conditions the ignition switch  38  must be switched on for power to be provided to the ECU  30 . However, the ECU  30  is also connected by positive and negative wires  40 ,  42  to the connector  24 . Consequently power can be provided to the ECU  30  when the ignition switch  38  of the towed vehicle is open. A switch (not shown) may be provided in the positive wire  40 , which is positioned in the passenger compartment of the vehicle (not shown).  
     [0016] The towed vehicle  12  has a fluid suspension system, which may be hydraulically or gas operated. The system described below is hydraulic, but the hydraulic components can be replaced with pneumatic components.  
     [0017] A hydraulic cylinder  44  is provided at each of the vehicle wheels  46 . The extension of the cylinders  44  determines the ride height of the vehicle. The hydraulic system further comprises a pump  48  having an integral electric motor, a reservoir of hydraulic oil  50  and a hydraulic control unit  52 . Hydraulic oil taken from the reservoir  50  via a line  54  is pressurised by the pump  48  and is provided to the hydraulic control unit  52  via a line  56 . Solenoid valves (not shown) in the hydraulic control unit  52  direct the pressurised oil to the cylinders  44  as necessary via lines  58 .  
     [0018] Height sensors  60  provided at each of the wheels  46  monitor the extension of the cylinders  44  and hence the ride height of the vehicle. Feedback from each height sensor  60  is provided to the ECU  30  by means of a cable  62 . The ECU is also electrically connected to the hydraulic control unit  52  and the motor of the pump  48  by means of cables  64 ,  66  respectively.  
     [0019] When the suspension system of the towed vehicle is powered up, either by the battery  32  through the ignition switch  38 , or via the connector  24 , the ECU  30  provides power to the motor of the pump  48  in order to pressurise the hydraulic system. The solenoid valves (not shown) in the hydraulic control unit  52  are opened and the hydraulic cylinders  44  are extended. Feedback from the height sensors  60  to the ECU  30  enables the ECU to determine when to close the solenoid valves of the hydraulic control unit  52 . The hydraulic cylinders  44  are thereby extended to a predetermined position for a required ride height. The ECU  30  accordingly switches off the motor of the pump  48 .  
     [0020] When a height sensor  60  detects deflation of its respective hydraulic cylinder  44 , that is, the ride height provided by that cylinder is reduced below the required level, then the ECU powers up the pump  48  and opens the necessary valve in the hydraulic control unit  52 . The cylinder  44  therefore extends and when the required predetermined ride height is restored, the valve is shut and the pump motor turned off. Any number of valves in the hydraulic control unit  52  may be open at any point in time as required. The extension of the cylinders  44  and the ride height is thereby maintained at the required predetermined level.  
     [0021] In an alternative embodiment of the invention, an accumulator  55 , shown in dotted outline in the Figures, is provided in the line  56  between the pump  48  and the hydraulic control unit  52 . This arrangement has the advantage that a smaller flow rate pump  48  can be utilised, and that the pump does not have to be turned on/off for every time that a detector  60  detects deflation of a respective cylinder  44 .  
     [0022] In this arrangement, a pressure detector (not shown) monitors the pressure in the accumulator  55 , and if the pressure drops below a certain threshold value, then the ECU  30  powers up the pump  48 . In this way, a minimum pressure level in the line  56  is maintained, enabling any of the cylinders  44  to be restored at any time by opening a respective valve in the hydraulic control unit  52  as previously described.  
     [0023] A driver is able to set the predetermined ride height according to a mode of travel, for example, off-road mode, road mode and towing mode, selected in the passenger compartment (not shown) by a controller (not shown) linked to the ECU  30 . In a further convenient arrangement of the invention, the ECU  30  is provided integral with the hydraulic control unit  52 .  
     [0024] A modification to the system of FIG. 1 is shown in FIG. 2, in which the same reference numbers have been used to denote components in common with FIG. 1. In the modified system shown in FIG. 2, the connection between the towed vehicle  12  and the towing vehicle  10  is effected by means of a cable permanently connected to the electrical system of the towed vehicle. The cable comprises positive and negative wires  27 ,  29  which are permanently connected to, or are an extension of, the positive and negative wires  40 ,  42  connected to the ECU  30  in the towed vehicle. The cable has a multi-pin plug  25  on its free end for connection with the socket  16  of the towing vehicle. In all other respects the modified system of FIG. 2 is the same as the system of FIG. 1.  
     [0025] Shown in chain dotted lines in FIG. 2 are spur wires  41 ,  43  which may be provided to supply electrical power a lighting board (not shown) for the towed vehicle  12  in a manner similar to that described above with reference to FIG. 1.  
     [0026] In a preferred embodiment, the towed vehicle is an amphibious vehicle adapted for travel on both land and water. In a particularly preferred embodiment, the towed vehicle is an amphibious vehicle having a suspension system comprising a suspension strut in accordance with the applicant&#39;s co-pending international patent application No. PCT/GB01/01334.