Swivel chair system
BACKGROUND OF THE INVENTION 
     A typical truck cab includes a door located at the left side of the driver through which he can exit the vehicle, by turning his body to the left and stepping down out of the cab. Another type of cabin that has been developed, includes a rear doorway at the rear of the cab, which is the principle avenue of ingress and egress to the cabin. This arrangement is described in U.S. patent application Ser. No. 351,495 filed Feb. 23, 1982 and Ser. No. 351,497 filed Feb. 23, 1982. When the driver wants to get out of the seat, or sit down while standing to the right of the seat, he finds it difficult to do so. This is because his feet lie at the same level as the floor of the cab, so he cannot easily support himself at a level just under the steering wheel to slide sidewardly under the steering wheel. A seat arrangement that facilitated getting up and sitting down by a driver who is leaving or entering through the rear of the cab, would facilitate operation of the vehicle. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the present invention, a seat is provided for use in a vehicle cab which has a doorway at the rear of the cab and a passageway that leads to a seat, and wherein a steering wheel lies closely over the driver&#39;s lap when he faces forwardly. The seat is mounted to pivot about a vertical axis between a forward position used during driving and a sideward position used during ingress and egress. An actuator is coupled to the seat to pivot it, and a control responsive to the state of the transmission controls the actuator, to force the seat to the forward position when the transmission is in a drive setting and to release the seat to pivot towards the sideward position when the transmission is in a neutral setting. The actuator can be constructed to bias the seat toward the sideward position when the transmission is in neutral, but with a torque that can be easily overcome by a seated person, so the seat remains in the sideward position for a driver entering the cab but can be pivoted by him to the forward position. 
     The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a right side perspective view of a vehicle constructed in accordance with the present invention. 
     FIG. 2 is a rear perspective view of the cab of the vehicle of FIG. 1. 
     FIG. 3 is a right side view of the cab of FIG. 2. 
     FIG. 4 is a bottom view of a portion of the cab of FIG. 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a yard tractor 10 which is used to move large containers 12 that can travel on railroad tracks, to move the containers around a railroad yard. The tractor vehicle has a cab 14 of small width and with large windows, to provide very good vision for the driver D. A passage or doorway 16 is formed in the back of the cab, and provides the main passageway for ingress and egress for the driver. The doorway 16 is normally not covered by any door, but there is no danger of the driver falling out, as there would be if the auxiliary side door 18 were left open. 
     As shown in FIG. 2, the driver&#39;s seat 20, which forms a seat area on the top of the seat, is placed at the left side of the cab, so the driver can easily exit through the left door 18, and an instrument console 22 is placed at the front and right side of the cab. A passageway 24, formed by the console and floor, is provided at the right side of the seat, for movement by the driver to and from the doorway 16. 
     In order for the driver to leave, he must slip from behind the steering wheel 26, which lies closely over the middle of his lap in the normal driving position. When a driver leaves through the side door 18, this is not too difficult because the driver can then place his left foot on a step located below cabin floor level and slide sidewardly from behind the steering wheel. However, it would be difficult to slide sidewardly under the steering wheel because the feet of the driver are so close to the floor 28 of the cabin. To ease ingress and egress, the seat 20 is pivotally mounted about a vertical axis 30 so it can pivot between the front position shown at 20f, and a side position indicated at 20s. 
     The seat 20 is held on a mount 32 that is pivotally supported by bearings 34 to the cab floor. A lever arm 36 (FIG. 4) fixed to the mount at a location under the cabin floor, is connected to an actuator 38. The actuator is operated by a control 40 which includes an air valve 41 and a switch 42 (FIG. 2) located adjacent to a transmission selector 43. When the transmission is in a neutral setting (often including two position labeled &#34;park&#34; and &#34;neutral&#34;) at which the running engine does not drive the wheels of the vehicle, the seat 20 can be pivoted to the sideward position 20s. When the transmission is in a drive setting (which may include &#34;first gear&#34;, &#34;second gear&#34;, etc.), at which the engine drives the vehicle wheels, the seat is securely held at the front position 20f. 
     The torque applied to the seat at 20f to hold it in its forward orientation when the transmission is in a drive position, is great enough to avoid accidental turning of the seat and thereby lock the seat in position. A torque of more than about twenty foot pounds should be used. This prevents unintended swiveling of the seat away from the forward position, which could startle the driver and lead to an accident. When the transmission is in a neutral position, the seat is released from the forward position, and is preferably biased toward the sideward position at 20s. With the seat at the sideward position, it is much easier for the driver to stand up, since the steering wheel is not directly over his legs. When the driver reenters the cab, it is desirable for him to encounter the seat in the sideward position, so he can easily sit down, without having to slide his body sidewardly between the seat and the steering wheel. Instead, after he sits in the seat, the driver can apply relatively small torque to turn to the forward position. The actuator 38 is constructed to apply a low biasing force on the order of ten foot pounds that urges the seat to the sideward position at 20s when the transmission is in a neutral setting. This assures that the seat will remain in the sideward position to facilitate sitting by the driver. Of course, the actuator could be constructed with the pneumatic cylinder and spring as two separate parts. 
     FIG. 4 shows some additional details of the apparatus or means for pivoting the seat 20. The apparatus 44 includes a support plate 45 fixed to the underside of the cab floor, and supporting the actuator 38 and control 40. The control 40 has an inlet 46 which receives a constant supply of pressured air from a pump, which can be the same pump that supplies air to the brakes of an air brake system. A hose 48 connects the air valve 41 to the actuator 38 which is a pneumatic cylinder. When air pressure is applied to the cylinder, the piston moves to the position shown at 50, so the mount and seat are pivoted to the forward position shown at 20f and held there by a torque proportional to the air pressure supplied to the control valve inlet 46. A suffient pressure is applied to hold the seat securely in the forward position against the level of jars that are expected to be encountered. When the transmission is in neutral, the control valve 41 is closed so no air is applied to the actuator 38. Then, a spring 52 in the actuator pushes the piston to pivot the lever arm 36, to pivot the seat to the sideward position 20s. A much smaller torque is applied to the seat to hold it in a sideward position, than in the forward position. This allows the driver to sit in the seat and apply suffient torque to pivot the seat toward the forward position before starting the engine and/or shifting the transmission to a drive setting. It also allows a driver entering or leaving through the door 18 to hold the seat forward. The control valve 41 is an electrically operated type which has conductors 54 that extend to the transmission switch 42 (FIG. 2) so the valve is operated according to the position of the transmission. The angle A between the forward and side positions of the seat is preferable at least 30°, and in this case is about 60°. 
     In order to further aid the driver in entering and leaving the seat 20, the seat mount 32 is constructed, as shown in FIG. 3, to move up and down, as from the downward position shown at 20 to the upper position shown at 20u. The mount 32 includes an upper tube 60 which slides vertically within a lower tube 62. Splines 64 prevent the tube from rotating, while allowing the upper tube that is fixed to the seat to move up and down. A spring 66 urges the seat and upper tube in an upward direction. When the driver pivots to the side position, the spring urges the chair upwardly, to help lift the driver off the seat and stand up. When a driver sits, his weight overcomes the force of the spring, which is less than one hundred pounds, to lower the seat so that it lies low enough below the rear of the steering wheel 26 to enable the driver&#39;s legs to comfortablly fit under the steering wheel. 
     Thus, the invention provides a swivel chair system which is especially useful in a vehicle cab having a rearward entrance, which facilitates ingress and egress of the driver. An actuator is operated by a control to pivot the seat to a forward position and hold it thereat when the vehicle transmission is in a drive position, and to release the seat so it can pivot to the side when the transmission is in a neutral position. The actuator also can be constructed to bias the seat to the side when the transmission is in neutral, but with a low enough force to enable a seated driver to turn the seat to a forward position. 
     Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.