Transmission Neutralizing System

Technical Field

This invention relates to a system of neutralizing a transmission of a vehicle when the parking brake is set.

Background Art

Most vehicles in use today include parking • brakes which are adapted to be engaged whenever the vehicle is to remain stationary for any period of time. Because of the time lapse involved, all too frequently an inattentive operator will forget that the parking brakes have been set and will subsequently attempt to drive the vehicle under its own motive power while the parking brakes are set. This, of course, increases the wear rate of the brakes and, in some cases, may cause severe damage to the parking brakes to the point where they become inoperative.

As a consequence, many systems have been devised to provide some sort of indication to the operator of the vehicle that the parking brakes are engaged so that he will disengage them prior to driving the vehicle.

A problem can develop where it becomes necessary, as for example, during emergency situations, to override the system and drive the vehicle against the set parking brake. Where the system includes a positive interlock, preventing the vehicle transmission from being engaged in any situation, overriding of the interlock may be mechanically impossible. In other cases, where an interlock is not provided, a warning device may be included which if unheeded will permit

the operator to drive the vehicle against the engaged parking brake. In still other systems wherein the operator of the vehicle is positively provided with an indication that the parking brake is engaged, should he attempt to engage the transmission and drive the vehicle against the brakes, there may be no means to return the transmission to a neutral position as soon as the intentional overriding of the system is completed. And, in many cases, components utilized are unduly complicated and therefore quite expensive.

Disclosure of 'the Invention

The present invention is directed to overcoming one. or more of the above problems. in one aspect of the present invention, there is provided a transmission neutralizing system including a transmission control linkage movable between a neutral position and at least one drive position. A control element is movable between engaged and disengaged positions and interacts with one member of the transmission control linkage, under certain conditions, to return the transmission control linkage to a neutral position. Biasing means acting on the control element which causes the above interaction, is such as to allow movement of the transmission control linkage against the bias from the neutral position to a drive position to allow overriding of the neutralizing system. The force required to overcome the bias provides a perceptible indication to the operator of the fact that the parking brake is engaged. Means is provided for moving the control element out of engagement with the transmission control linkage when the oarkinq brake is in the isenraσed oosition.

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Brief Description of the Drawings

Fig. 1 is a side elevation of a dual housing arrangement and system diagram of a transmission neutralizing system according to the present invention; Fig. 2 is a vertical cross section of the transmission control positioner indicator portion of the system taken along line II-II of Fig. 1;;

Fig. 3 is an enlarged vertical cross section taken along line III-III of Fig. 2 through a shaft extending between the housings of Fig. 1;

Fig. 4 is a vertical cross section taken along line IV-IV of Fig. 1 showing the transmission shift control portion of the system; and

Fig. 5 is a somewhat enlarged vertical section taken along line V-V of Fig. 4 through a roller utilized in the transmission shift control.

Best Mode for Carrying Out the Invention

An exemplary embodiment of a transmission neutralizing system embodying the principles of the present invention is intended for use in vehicles having a hydraulic parking brake system generally indicated by the reference numeral 8. The parking brake automatically engages when hydraulic pressure in the system is relieved due to (i) actuation of the parking brake control by the operator, (ii) fluid leakage within the parking brake system, or (iii) vehicle shutdown. Typically, such brake systems employ spring engaged, hydraulically disengaged parking brake means.

With reference to Fig. 1, the parking brake system 8 includes a pair of linings 10 pivotally " r.r.ecr.aά -it. lever operated cam 14 is rotatable between the opposite ends of linings 10 to spread ^* hem outwardly against a brake drum, not shown. The cam is

operated between engaging and disengaging positions of the linings 10 by a fluid motor 16, having a piston 18. The piston 18 is connected via a link 20 to the cam 14, and a spring 22 normally urges piston 18 to a position such that the linings 10 will be spread to engage the brake drum. However, when fluid pressure is applied against piston 18, it is moved against the bias of spring 22 to disengage the linings 10 from the brake drum. Pressurized fluid for driving piston 18 in the above manner is supplied by a pump 24 via a manual brake control valve 26 and a line 27. It can be appreciated that whenever fluid pressure against the piston 18 is interrupted the parking brake will be actuated. Such interruption may occur when the valve 26 is shifted by the operator, when the vehicle engine is shutdown which will cause pump 24 to stop or by an accidental leak or rupture in one of the lines.

The transmission neutralizing system includes a transmission shift control mechanism, shown generally at 28 of Fig. 1, which is manipulated by an operator via control lever 30 and a conventional push-pull cable represented by the reference numeral 32.

As best seen in Fig. 2, a push-pull rod 34, housed in a protective sheath 36, is connected to a lever 38 by a pin 40, within a housing 42 of shift control mechanism 28. The housing 42 is secured to a second housing 44 of shift control mechanism 28, by a plurality of capscrews 46. As best shown in Fig. 3, lever 38 is secured to the first end of a shaft 48 by a capscrew 50. The shaft 48 is positioned in a hub 52 of housing 44 by a pair of needle bearings 54 which allow

A lever assembly 56 contained in housing 44, (Fig. 4) providing a first arm 58 and a control linkage blocker arm 60, is secured to the opposite end of shaft 48 by a capscrew 62. The first arm 58 is connected to a rod 64 by a pivot pin 66. The rod 64 shifts a control mechanism in a transmission, not shown. _^ The blocker arm 60 of lever assembly 56 carries a roller 70 by a pivot pin 71 for purposes hereinafter to be described. The housing 44 has a flange 68 which mounts the entire shift control mechanism 28 to the transmission.

The housing 44 also contains a control element or shiftable blocker member 72 pivoted therein by a pin 74. The. element 72 has a cam surface 73 and is positioned by two forces acting on it. One force is supplied by a fluid motor means 76 having a piston 78 and a rod 80 secured to the piston 78. A branch line 27a directs pressurized fluid from the parking brake mechanism 8, disclosed in Fig. 1, to motor 76 and against the piston 78. The piston 78 and rod 80 combination reacts, against a lobe 82 of element 72 to pivot element 72 counterclockwise against the bias of a spring means 84. The spring means engages a stop 86 pivoted on element 72 by a pin 88. In so doing, element 72 is pivoted counterclockwise out of the way to allow free pivoting of arm 60 of lever assembly 56 to either one or the other of the phantom positions of roller 70, shown in Fig. 4. A first phantom position 90 represents a forward shift of the transmission and a second phantom position 92 represents a reverse shift of the transmission.

Should fluid pressure in line 27a be lost for any reason, bias of spring means 84 will pivot element 72 clockwise. If the lever assembly 56 is shifted so that roller 70 is in the first phantom position 90, a

cam surface 94 of element 72 will contact roller 70 and cause the lever assembly 56 to pivot to the neutral position shown. Similarly, if lever assembly 56 is shifted so that roller 70 is in the second phantom position 92, a cam surface 96 of element 72 will contact roller 70 and also return the lever assembly 56 to the neutral position shown. The relationship of roller 70 to the cam surfaces 94 and 96 is depicted in Fig. 5. As shown in Fig. 2, the lever 38 has a first means or lobe 98 and a second means or lobe 100 machined thereon. When lever 38 is shifted in a counterclockwise, or forward position, the lobe 98 will contact the roller 102 of a conventional microswitch 104 to indicate to the operator that the transmission is shifted by activating a lamp 106 in the operator's cab. When lever 38 is shifted in a clockwise, or reverse position, the lobe 98 will contact a roller 108 of a microswitch 110 which will activate a conventional reverse alarm means 112, and lobe 100 will contact roller 102 to also activate lamp 106 in the operator's cab, as a double indication that the transmission has been shifted to the reverse condition.

Industrial Applicability

Whenever the operator disengages the parking brake mechanism 8 by shifting the control valve 26 to the off position, pressurized fluid will be directed to the fluid motor 16 to cause the brake to be disengaged. It will similarly direct fluid to the fluid motor means 76 to cause the control element 72 to be moved counterclockwise to the disengaged position. At this time, the shift control linkage is relatively freely 7θ D-_.3 Dβtween its drive and r.e zl positions as commanαeα by the operator of the vehicle without

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expending undue effort in operating the handle 30. This, of course, is highly desirable during normal operation of the vehicle which would be the case when the parking brake is disengaged. Conversely, when the parking brake mechanism 8 is engaged for any reason, whether it be by operation of the valve 26, inoperability of the pump 24 due to failure thereof, the shutdown of the vehicle engine, or a major leak in the fluid system so that there is inefficient pressure to disengage the parking brake, fluid pressure will also be lost from fluid motor means 76. This allows the bias of spring 84 to -move the control element 72 clockwise into its engaging position. This will also cause the shift control mechanism 28 to be shifted to its neutral position and will shift the transmission to a neutral condition.

Should the operator of the vehicle forget that the parking brake is engaged, and attempt to engage the transmission through operation of the handle 30, he will be immediately appraised of the fact that the parking brake is engaged by reason of the additional resistance to movement of the shift control mechanism 28 provided by the bias of the spring means 84 applied against the control element 72. Should an emergency arise wherein it is desirable to move the vehicle, notwithstanding the parking brake being engaged, and it is impossible to disengage the brake through the fluid system or by other means, the operator may nonetheless engage the transmission through the operation of the control handle 30. This is due to the fact that the control element 72, and thus the shift control mechanism 28, is not positively restrained in the engaged position whenever the parking brake is engaged, but is only resiliently urged to that position by the bias of the

spring means 84. By applying a sufficient force to the handle 30, the shift control mechanism 28 can be moved to either of its drive positions against the bias of the spring means 84. However, as soon as the operator has moved the machine and takes his hand off of the control lever 30 the bias of spring means 84 will again return the shift control mechanism 28, and thereby the transmission, to the neutral position.

From the foregoing it will be appreciated that a vehicle transmission neutralizing system made according to the present invention is simple and easily fabricated. It possesses the distinct advantage of automatically returning the transmission shift control mechanism to its neutral position whenever the brake is engaged and an intentional effort to override the system is not being made. Yet, in the event of emergency the system can be overriden as required.

Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.