Ambulance

The invention relates to an ambulance car provided with a stretcher carrier, which stretcher carries is supported by a spring system with respect to the carriage work.

In many cases the natural spring frequency of ambulance cars ranges from 2.5 to 3 Hz. This frequency is too high for a person lying on the stretcher. In the ideal case the frequency should be about 0.5 Hz. Usually it is not possible to adapt the spring system of the car. In practice it is known to support the stretcher carrier with respect to that of the carriage work of the ambulance by means of a sophisticated spiral spring system. Thereby, it is true, the frequency at which the stretcher moves up and down may be reduced to about 0.5 Hz this however being accompagnied by an insufficient damping of the spring action so that a person lying on the stretcher experiences a heaving motion that may lead to nausea.

The object of the invention is to avoid the above drawback and to this end the ambulance mentioned abouve is characterized in that the spring system comprises at least one hydropneumatic spring element, a liquid filled part of which is connected to a pump and is separated by a membrane from a part filled with a pressurized gas.

In applying the invention the frequency of the movement of the stretcher may be reduced to about 0.5 Hz while the spring motion can also be damped sufficiently.

In order to accommodate the spring system at the side of the stretcher carrier within a side box of the ambulance and not underneath the stretcher carrier, the stretcher carrier is supported by two rotatable rods, each one of said rods being connected to a hinge lever, while each one of said hinge levers is connected to the liquid filled cylindrical part of a spring element by means of a connecting rod having a piston at the end thereof.

The system according to the invention offers the possibility to move the stretcher as a whole or at one of the two rods separately up or down.

In case of a difference in rotation between the hinge levers it will be required that one of said rotatable rods is operable to be shifted over a short distance with respect to the other rod.

The necessary damping of the springy action may be achieved in a simple manner if there is accommodated a damping element in the liquid filled part of each one of said spring elements.

Preferably each damping element consists of a disc in which two series of oblique traversing bores are provided, while at both sides of the disc there is mounted an elastic plate spaced at a short distance from said disc, a series of bores debouching between each one of said plates and said disc.

In an appropriate embodiment the hinge levers are in an L-shaped form while one of the arms of said levers is connected to a connecting rod by means of a ball and socket joint.

An easy supply and return of oil to and from each one of the spring elements separately may be achieved if the spring elements are both connected through an oil line to a common foot pump having two operating pedals.

The system according to the invention offers two possibilities to disengage the springy movement, that is by increasing the oil pressure so hig that the membrane comes to rest against the wall of the spring element or by completely dismissing the oil pressure. The non spring supported position is required when applying a heart massage.

The invention will now be elucidated further with reference to the drawings in which

• Fig. 1 represents a diagrammatic view of the spring system to be used in an ambulance according to the invention;
• Fig. 2 shows a cross section on an enlarged scale of a spring element to be employed in said system, and
• Fig. 3 shows a side elevation of the damping element forming part of a spring element.

In Fig. 1 there is shown an inserting plate 1 for a stretcher to be mounted in an ambulance. This plate serving as a stretcher carrier 1 is supported by two rods 2 and 3. The rod 2 is connected to the carrier 1 by means of two hing joints 4,5. The connection between the rod 3 and the carrier 1 is formed by two straps 6,7 within which the rod 3 is permitted to slide somewhat and also to rotate.

At the one end thereof the rods 2 and 3 are connected to an essentially L-shaped lever 8 and 9, respectively, said lever being connected to the carriage work of the ambulance by means of a hinge joint 11 or 12 respectively.

The arms 8a and 9a of the levers 8 and 9 are fastened to a connecting rod 14 by means of a ball and a socket joint 13 (see Fig. 2) said connecting rod being covered by a rubbery protecting bellows 15.

As will apparent from Fig. 2 there is mounted a piston 17 at the end of each connecting rod 14 which piston is slidably inserted in the cylindrical part of a hydropneumatic spring element 18 or 19, respectively.

Each one of said elements 18, 19 comprises an oil filled part 20 which part is connected by means of a line 21 or 22, respectively to a foot pump 23 having incorporated therein an excess pressure valve which part on the other hand is separated by means of a membrane 24 from a part 25, said latter part being filled with nitrogen at a pressure of about 8 atmospheres through a valve 26.

Within the oil fillid part 20 there is accommodated a damping body 27 constituting a separation between the two parts 20a and 20b.

The damping body 27 consists of a disc (vide Fig. 3) in which there are provided two sets of obliquely extending bores. Spaced at a short distance from the two surfaces of the disc there are provided elastic plates 28a, 28b. The first set of bores extends from the lower surface of the disc beyond the reach of the lower plate 28b to the upper surface of the disc just below the upper plate 28a. The other set of bores extend from the other surface of the disc 27 beyond the reach of the upper plate 28a to the bottom surface of the disc just above the lower plate 28b.

The foot pump 23 is provided with two pedals one for operating the spring element 18 and the other for operating the spring element 19.

The operation of the above described system is as follows:

• Upon inserting a stretcher including a person lying thereon on the plate 1 the pedals of the foot pump 23 are operated for supplying oil to the elements 18 and 19.

The weight of the person and of the inserting plate 1 will cause a pressure on the piston directed towards the membrane. As long as the oil pressure within the room 20 of the spring element 18 or 19 is lower than this external pressure the membrane 24 will be displaced into the direction away from the piston 17 upon increasing the oil pressure whereby the gas pressure in the part 25 will increase. As soon as the oil pressure in the room 20 exceeds the external pressure the piston 17 will be pushed outward, whereby the hing lever will commence to rotate and the corresponding rod 2,3 will commence to move upwards. When both the rods 2 and 3 have reached about the intermediate part of their maximum strokes the operator will stop pumping. The spring system is then ready for a ride with the ambulance car.

In case the ambulance car hits a hole the hinges 11, 12 will move downwards together with the carriage work, while the pistons 17 will move away from the corresponding membranes 24, whereby the oil rooms will increase and the gas pressure in the parts 25 will decrease. The inserting plate will follow this downward movement of the carriage with some retardation whereby the pistons 17 will be pushed back again and the gas pressure will increase. This will lead to the springy effect. The damping of the spring motion is caused by the damping bodies 27, 28a, 28b. The oil flowing from the one oil filled room 20a (or 20b) to the other oil filled room 20b (or 20a) will loose part of its kinetic energy when impacting an elastic plate 28b (or 28a). This part of kinetic energy is converted into heat.

There is achieved the considerable advantage that the spring system may be adapted to the weight of the person lying on the stretcher. Moverover upon sufficient damping there is likewise assured a spring frequency of about 0.5 Hz. Even upon breaking there is achieved a good spring and dimping action while the center of gravity situated between the rods 2 and 3 will then move forwards. The front hinge lever 8 will be loaded additionally whereas the load on the back lever 9 will be decreased somewhat. Such movements are accommodated resiliently by the elements 18 and 19 while swing motions are damped.

Upon acceleration there happens of course the reverse with respect of breaking i.e. the center of gravity of the person will move backwards and the element 18 will additionally be loaded by means of the rod 3, the lever 9 and the connecting rod 14, whereas the element 19 will be somewhat relieved.

In order to permit differences in the hinge movements of the hinges 8 and 9 the rod 3 is permitted to slide on the straps 6 and 7.

. By making the oil pressure in the one hydropneumatic spring element higher than that in the other one the carrier 1 may be placed in any arbitrary oblique position, i.e. slanting forwards or slanting backwards (Trendelenburg position and anti-Trendelenburg position).

For carrying out a heart massage it is desired to nullify the spring action of the hydropneumatic elements 18, 19. This may be achieved in two ways: either by increasing the oil pressure so much (for instance to 80 atmospheres) that the membrane will come to rest against the wall of the corresponding hydropneumatic spring element, or by entirely releasing the oil pressure (by raising the pedals of the pump) whereby the piston will abut against a stop in the farmost retracted position.

The elements 18, 19, the levers 8,9 the lines 21, 22 and the pump 23 may be accommodated within a side box of the ambulance at the side of the carrier plate 1. Thus the normally available room in the ambulance will not be decreased by the application of the invention.

Within the scope of the main claim several modifications are possible.