Abstract:
The disclosure describes clutching arrangements for motor vehicle standard transmissions. The force required to clutch a vehicle transmission using a foot pedal is reduced by providing a compressed air actuated boost device attached to the clutch linkage. The degree of boost is selectable using a hand controlled air pressure regulator. Activation of the boost device is controlled by switches which are sensitive to clutch pedal position.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention:  
           [0002]    The present invention relates to motor vehicle standard transmission clutches and more particularly to an air assist system for reducing clutch pedal effort in a standard transmission equipped motor vehicle.  
           [0003]    2. Description of the Problem:  
           [0004]    Both standard and automatic shift transmissions are well know in the motor vehicle industry. Standard transmissions, sometimes called manual transmissions, remain common on light cars, trucks and busses, due to their mechanical simplicity, lower initial cost, lower weight and perceived efficiency relative to automatic transmissions. Standard transmissions typically provide a shift lever which is hand operated by the driver of a vehicle to move the transmission between the various available gear ratios provided in the transmission. The shift lever is connected with a linkage system to selectively engage a selected gear of an input shaft/counter-shaft standard transmission. During the disengagement of one gear ratio and the subsequent engagement of another gear ratio, a clutch is used to mechanically disengage the transmission from the vehicle&#39;s engine. Disengagement of the clutch is typically done by the driver depressing a clutch pedal located under the instrument dash board and against the vehicle dash panel. The clutch pedal is connected to a clutch lever using a clutch linkage.  
           [0005]    Standard transmissions installed on trucks can require excessive clutch effort on the part of some drivers or in stop and go situations. As a result, the driver can become tired or uncomfortable. The value in providing a mechanism to reduce the effort required to disengage clutches has long been recognized. U.S. Pat. No. 4,717,002 to Sasamura teaches one such clutch linkage power assist mechanism. Sasamura relies on pressurized air available on heavy duty trucks to drive a piston/cylinder arrangement which is connected to the linkage to provide a boost to the driver&#39;s leg pressure to disengage a clutch. The cylinder receives air from and discharges air through a control valve. Valve operation is controlled by being directly connected into the clutch linkage. Sasamura also describes prior art clutch linkage systems using a piston/cylinder boost arrangement to reduce driver clutch pedal effort. He describes such systems as having to time properly the assistance provided by the air cylinder by sensing the build up of force on the clutch pedal to provide air to the cylinder in direct proportion to the clutch pedal force. Such sensitivity to clutch pedal force is obtained by incorporating the valve into the clutch linkage, a feature which Sasamura retained. Splicing the valve into the linkage was seen as assuring the capability of operating the clutch in a purely manual mode without boost, should the vehicle air system be compromised or unavailable.  
         SUMMARY OF THE INVENTION  
         [0006]    An object of the present invention is to provide a clutch linkage requiring reduced effort for disengaging a standard transmission clutch.  
           [0007]    Another object of the present invention is allow operator selection of the clutch effort required for disengaging a clutch.  
           [0008]    Still another object of the present invention is to provide clutch linkage operation which is relatively immune to failure of the clutch disengaging boost system.  
           [0009]    The invention provides for these and other objects in a standard transmission for a vehicle. The transmission comprises a clutch having an engaged state and a disengaged state. The clutch is moved between engaged and disengaged states using a clutch pedal which is connected to the clutch by a linkage assembly. Depression of the clutch from a default position moves the linkage assembly which in turn moves the clutch from its engaged state to its disengaged state. A spring provides for return of the linkage assembly to the default position, which returns the clutch to its default engaged state.  
           [0010]    A powered actuator is coupled to the linkage assembly for generating a force urging the linkage assembly in the direction disengaging the clutch. Where the actuator is powered by compressed air, a relief valve operates to vent air from the powered actuator when open and to prevent venting when closed. The relief valve state is controlled by the position of the clutch pedal in a free travel. When the clutch pedal is in a first position in the free travel the valve is open and upon movement of the clutch pedal from the first position in the free travel the valve is closed. For compressed air systems the pressure assist is operator selected. An energization valve operates to deliver compressed air from the source of compressed air to the powered actuator when open, the energization valve being responsive to movement of the clutch pedal to a second position in the free travel.  
           [0011]    The first and second points in the free travel of the clutch pedal are associated with first and second switches which are actuated by movement of the clutch pedal. First and second solenoid valve actuators provide for operating the relief valve and the energization valve, respectively, in response to changes in state of the first and second switches. The valves are arranged such that the energization valve has an inlet for receiving air from the source of compressed air, an exhaust port and an outlet to the compressed air powered actuator, the energization valve being operable in an open state to connect the inlet to the outlet and in the closed state for connecting the outlet to the exhaust port. The relief valve has an inlet connected to the exhaust port and an outlet, and being operable in a closed state to block communication between its inlet and its outlet and in an open state to connect its inlet to the outlet.  
           [0012]    Additional effects, features and advantages will be apparent in the written description that follows.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0014]    [0014]FIG. 1 is a perspective view of a truck on which the invention is practiced;  
         [0015]    [0015]FIG. 2 is a plan view of a truck chassis incorporating the standard transmission of the present invention;  
         [0016]    [0016]FIGS. 3A and B are diagrammatic illustrations of typical clutch linkage for contemporary standard transmissions; and  
         [0017]    [0017]FIGS. 4A and B are diagrammatic illustrations of clutching linkages for standard transmission modified to incorporate the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    Referring now to the figures and in particular to FIG. 1, where a truck  100  is illustrated. Truck  100  represents the class of vehicles with which the air assisted vehicle clutch linkage of the present invention is advantageously utilized. It is such vehicles which generally exhibit the highest clutch efforts.  
         [0019]    [0019]FIG. 2 is a plan view of truck  100  illustrating major components of the vehicle and invention and their approximate spatial relationship to one another. Truck  100  includes an engine  60  the output of which is coupled to rear end differentials  80  and rear axles  84  by a clutch  12 , a gear box  11  and a propeller shaft  82 . Clutch  12  is selectively engaged and disengaged to allow selection of a desired gear ratio in gear box  11 . Engagement of clutch  12  is controlled by the operator&#39;s use of a clutch pedal  14 , which is connected to the clutch  12  by a linkage  16 . Operator effort is minimized by an air boost system  45 . The amount of boost provided is adjustable using a dash panel mounted dial  48 . The boost system can also be provided by electrical or hydraulic systems. In an electrical system the voltage applied to a d.c. electric motor can be adjusted to vary the boost provided.  
         [0020]    [0020]FIGS. 3A and B illustrate a standard transmission  10  which includes a clutch  12  and a gear box  11 . Clutch linkage geometry can be arranged to be either a “pull” type clutch linkage  16  as illustrated in FIG. 3A or a push type linkage  116  as illustrated in FIG. 3B. Clutch  12  is moved between engaged and unengaged states by movement of clutch release lever  18 . In either case clutch release lever  18  is part of a linkage assembly  16 , which includes a pull link  22  connected between the clutch lever and a clutch pedal support linkage  20 . In the alternative geometry of FIG. 3B a push linkage  122  is substituted for pull linkage  22  and lever  18  is pushed rather than pulled to the disengaged position. Clutch pedal  14  is attached to one end of clutch pedal support linkage  20 . Clutch release lever  18  is biased toward its clutch engaging position by a spring  24  connected at one end to the lever and at its other end to a fixed point  26 . When clutch pedal  14  is depressed, as indicated by arrow “A”, the lower end of pedal support linkage  20  moves away from (FIG. 3A) or toward (FIG. 3B) clutch  12 , as indicated by arrow “B”, pulling link  22 , or pushing link  122 , in the same direction. At the same time, clutch lever  18 , as a result of return spring  24 , applies a force on the opposite end of linkage  22  and in the opposite direction. As a result, link  22  is placed under tension, as represented by arrow “C”. Link  122  is placed under compressive force as indicated by arrow “C”.  
         [0021]    The force required to depress clutch pedal  14  to move the clutch lever  18 , overcome any parasitic drag on the linkage assembly  16  and overcome the counter force generated by spring  24  is typically much greater on trucks than on passenger cars. As described above, pressurized air assisted systems providing supplemental force to a clutch linkage assembly are known in the art.  
         [0022]    As described below, the present invention allows the operator to select the amount of force which the boost system provides, and to hold boost with little or no effort. The linkage retains the fail-safe backup of a direct linkage between the clutch pedal and clutch lever.  
         [0023]    [0023]FIGS. 4A and B illustrate in detail the invention in a preferred embodiment. As in FIGS. 3A and B a standard transmission  10  is depicted including a clutch  12  and a gear box  11 . Clutch  12  is moveable between engaged and unengaged states by the positioning of clutch release lever  18 . Clutch release lever  18  is part of linkage assemblies  16  and  116 , which include links  22  and  122 , respectively, connected between the clutch lever and a clutch pedal support linkage  20 . Clutch pedal  14  is attached to one end of clutch pedal support linkage  20 . Clutch release lever  18  is biased toward its clutch engaging position by a spring  24  connected at one end to the lever and at its other end to a fixed point  26 . When clutch pedal  14  is depressed, the lower end of pedal support linkage  20  moves away from (FIG. 4A) or toward (FIG. 4B) clutch  12 , pulling link  22  or pushing link  122  in the same direction. At the same time, clutch lever  18 , as a result of return spring  24 , applies a force in the opposite direction on the opposite end of linkages  22  and  122 .  
         [0024]    Boost to moving linkage assembly  16  or  116  is provided from an air actuated reciprocating piston operating in a cylinder  38 , which is mounted at one end to a fixed point  27 . A piston rod  37  projects from the other end of cylinder  38  which is connected at its own exposed end to a clutch lever  18 . Air under pressure introduced to cylinder  38  may be used to force rod  37  in the direction indicated by the letter “D”, moving the lever in a direction for disengaging the clutch  12 . The details of air cylinder and clutch operation are well known in the art and are omitted here for the sake of simplicity. Those skilled in the art will recognize that a clutch which is disengaged is one which is not then mechanically coupling the engine and the gear box. A clutch which is in its engaged state is one which is mechanically coupling the output of the engine to the gear box. Clutches are routinely “disengaged” to allow the gear selection in the gear box to be changed.  
         [0025]    Pressurization and depressurization of cylinder  38  is provided through an air supply  47  and valves  40  and  42 . A conventional heavy duty truck air supply  47 , which typically includes compressors and compressed air storage tanks. Compressed air from air supply  47  is coupled to an energization valve  40  through a pressure regulator  50  in an air conduit  52 . Pressure regulator  50  is adjustable by hand using a manual adjustment controller  48  which may be conveniently positioned on the vehicle dashboard. By allowing control of the air pressure of air supplied to cylinder  38  an operator may provide exactly as much boost as he desires to achieve a personally comfortable clutch effort.  
         [0026]    Energization valve  40  controls the delivery of air to cylinder  38 . Valve  40  is opened or closed by an energization solenoid (S 2 )  53 , which in turn is controlled by an energization switch (SW 2 )  32 . Pressurized air is delivered to energization valve  40  via an inlet  41 . Inlet  41  is selectively connected to an outlet port  46  when valve  40  is “open”, that is when positioned to couple inlet  41  to outlet  46 . When valve  40  is closed inlet  41  is blocked. Inlet  39  to cylinder  38  is then connected via outlet  46  through valve  40  to exhaust port  45 . Exhaust port  45  is connected in turn to inlet  43  on relief valve  42 , which may or may not allow the compressed air in cylinder  38  to be vented, as described below. The default state for energization valve  40  is closed, allowing air to pass from cylinder  38  through the valve to relief valve  42 . The default state of cylinder  38  is to be unpressurized. The default states are associated with clutch pedal  14  being in its default state, i.e. not depressed.  
         [0027]    An enable or relief valve  42  has an inlet  43  and an exhaust  44 . When “open”, relief valve  42  allows communication between inlet  43  and exhaust  44 . When “closed”, relief valve  42  provides no outlet. The state of valve  42  is controlled by solenoid (S 1 )  55 , which in turn is controlled by the state of the signal from relief switch (SW 1 )  34 . The default condition of relief valve  42  is open, allowing venting of air from cylinder  38 .  
         [0028]    Two clutch pedal  14  actuated switches  32  and  34  are provided for controlling solenoids  53  and  55  and to position valves  40  and  42 . Switches (SW 2  and SW 1 )  32  and  34  are active only if ignition switch  30  is closed. Switches  32  and  34  are positioned with respect to clutch pedal support linkage  20  to be actuated by movement of clutch pedal  14 . There exists a short, but distinct, free travel of clutch pedal  14  between the positions of contact with the relief switch  34  and the energization switch  32 . The free travel is defined by a slot  121  in a slotted head  21 , which is mounted on one end of clutch pedal linkage  20 . Clutch pedal  14  is an “L” shaped arm with a pawl  23  set near one end of the arm and a foot rest  94  mounted at the other end. Pawl  23  is fitted into a slot  121  located in slotted head  21 . A supplementary spring  124 , connected between clutch pedal  14  and a fixed point provides bias to return clutch pedal  14  to a position where pawl  23  is located in the bottom of slot  121 . Depression of clutch pedal  14  moves pawl  23  to the opposite end of slot  121  before linkage begins, or resumes movement.  
         [0029]    Relief switch  34  is positioned to be actuated as pawl  23  moves away from the bottom of the slot  121 . Energization (or pressurization) switch  32  is positioned to be thrown when pawl  23  reaches the top of the slot  121  and the clutch pedal  14  actually begin to engage clutch linkage  16 . The positioning of switches  34  and  32  with respect to slot  121  means that relief switch  34  changes state first during initial depression of clutch pedal  14 . This closes the switch and activates solenoid  55  to close relief valve  42 . With relief valve  42  closed, any boost added to cylinder  38  is held. Energization switch  32  is contacted by further depression of clutch pedal  14  sufficient to move pawl  23  to the top of slot  121 . Closure of switch  32  causes solenoid  53  to operate to open valve  40 , allowing pressurized air to pass through valve  40  from compressed air source  47  to cylinder  38  and thereby generating a force from cylinder  38  transmitted along piston shaft  37  urging clutch lever  18  toward a position disengaging clutch  12 .  
         [0030]    Release of clutch pedal  14  results in spring  124  acting to move the clutch pedal  14  away from a depressed position. Pawl  23  moves in slot  121  resetting switches  32  and  34  in that order. Return of pawl  23  to its start position returns valves  40  and  42  to their default states, in the reverse order from that occurring as the pedal was depressed. The relief of pressure in cylinder  38  allows spring  24  to return clutch linkage  16  to its default position, engaging the clutch  12 . The free travel in the pedal travel provided by slot  121  between actuation positions for the switches allows the operator to maintain, or even adjust, pressure in cylinder  38  by keeping clutch pedal  14  positioned so that pawl  23  does not return to the bottom of slotted head  21 . Under these circumstances air pressure is held in cylinder  38 .  
         [0031]    Air can be supplied from compressed air source  47  at sufficient pressure to move lever  18  without the driver moving pedal  14  past the point where switch  32  is contacted. Thus clutch  12  may be kept in a state of partial engagement by briefly allowing pressurization of cylinder  38  and then holding the clutch pedal  14  with pawl  23  floating in the slot  121  between contact positions with switches  32  and  34 . Because spring  124  has a low spring constant the leg effort required to keep pawl  23  floating is minimal. Spring  124  will always bias clutch pedal  14  in a direction to return pawl  23  to the bottom of the slot of slotted head  21 , where it activates relief valve  42  to return clutch  12  to full engagement. Briefly moving clutch pedal  14  to the limits of its free travel in slot  121  can be done to control the degree of engagement of clutch  12  by adding or releasing air from cylinder  38 . This feature should prove advantageous in reducing driver effort under conditions of heavy, stop and go traffic. The free travel in clutch pedal  14  provided by slot  121  will, with respect to the operator, move up and down depending upon the position of linkage  16 .  
         [0032]    The present invention provides a clutch linkage requiring reduced effort for disengaging a standard transmission clutch and allowing an operator to hold a partially engaged clutch with little to no effort. The operator can fully select a comfortable level clutch effort, even down to a level requiring essentially no clutch effort. The present invention fully preserves a conventional mechanical linkage so that failure of the air pressurization system has not effect on conventional use of the clutch. Those skilled in the art will now appreciate that clutch positioning mechanisms may be air powered, hydraulic or electro mechanical, among other systems.  
         [0033]    While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.