GB2048407A

GB2048407A - Parking brake

Info

Publication number: GB2048407A
Application number: GB8011720A
Authority: GB
Original assignee: JI Case Co
Current assignee: Case LLC
Priority date: 1979-04-09
Filing date: 1980-04-09
Publication date: 1980-12-10
Also published as: DE3013894A1; FR2453761A1

Abstract

A parking brake 46 for a vehicle driven by a transmission system that includes at least one toothed sprocket wheel 40 has an engagement element 48 movable towards and away from wheel 40 along a path extending radially of the wheel 40; means (52) is provided for resiliently biasing the engagement element (48) into meshing engagement with the teeth of the wheel (40) such that, in the event of power being inadvertently applied while the brake is thus engaged, the bias can be overcome enabling the wheel (40) to rotate, step by step, but without component breakage or total release of the wheel 40. As shown, the engagement element 48 includes a slide portion 53 and a portion 56 comprising links 58, 62; slide portion 53 is acted on by the force absorption means 52 which comprises a helical spring 53. An operating mechanism 54 controls engagement and disengagement of the element 48. With the brake applied, disengagement followed by engagement under influence of means 52 creates a ratcheting sound to warn vehicle operator. <IMAGE>

Description

SPECIFICATION Parking brakes for vehicles The present invention relates generally to vehicles driven by a transmission system including at least one toothed sprocket wheel and, more particularly, to a parking brake for such vehicles. The invention is to some extent based on a braking mechanism of the type disclosed in U.S. Patent No. 3,840,094, to which reference is directed to the assignee of the present invention and incorporated herein by reference.

Parking brakes applied to the sprocket wheels of vehicles driven by chain gearing can become damaged if the vehicle is set in motion by applying power to the chain gearing. In addition, it is important to alert the operator that motion under power is being attempted with the parking brake engaged.

The brake mechanism described in U.S.

Patent No. 3,840,094 uses roller links emeshed into the teeth of a sprocket wheel powering the wheels of a skid steer vehicle. A lever is used to manually engage and disengage the brake. A problem with known parking brake mechanisms is that if overpowered, component damage can result. A feature of some existing brake mechanisms is the abso iue locking of the drive train. Since there is no force absorption capability in the brake system, machine parts can be overstressed to the point of failure.

The drive mechanisms for skid steer vehicles frequently employ a hydrostatic drive wherein a fixed or variable displacement motor driven by a variable displacement pump is interposed between the engine and the vehicle support wheels (hereinafter simply referred to as "the wheels"). Chain gearing is used to transmit power between the power unit and the wheels.

The hydraulic pump is essentially a positive displacement device. As is well-known, positive displacement pumps are characterized as being able to deliver the same flow at any pressure within the capability of the driver and the strength of the pump. Consequently, if the load on the hydraulic motor is very high (as would be the case when the parking brake is applied to the wheels of the skid steer vehicle), the hydraulic pump will put out higher and higher pressure, creating a greater and greater force on the chain gearing and the parking brake. Component damage usually occurs unless the vehicle operator is alerted to this situation and the parking brake disengaged or power to the wheels terminated.

In accordance with the present invention, a parking brake is provided for vehicles driven by a transmission system including at least one toothed sprocket wheel and a roller chain.

The drive may be locked by forcing into the sprocket wheels an engagement element movable along a path defined by a guide extending radially of the sprocket wheel. The engagement element is movable by an operating mechanism between a first position at which it resiliently meshes with the sprocket wheel teeth, and a second position at which it is disengaged. Means are provided for resiliently biasing the engagement element in a direction towards the sprocket wheel along said path such that when the sprocket is turned while the brake is engaged, the element must be forced away from the sprocket axis by the teeth. Thus, if the turning force is of sufficient magnitude to force the element out of meshing engagement it may turn step by step as the element engages and is disengaged from successive teeth.Shearing of the element or some other component failure rendering the brake inoperative is thereby avoided.

In a brake of the present invention, the engagement element is effectively spring loaded. Therefore, rotating the sprocket wheel with the parking brake applied will overcome the force of the spring and allow the engagement element to disengage. After passing over the crest of a sprocket tooth, spring pressure will automatically reinsert the element into the sprocket gear. Thus, the brake will be reapplied. However, the reinsertion will provide a clicking sound similar to that of a ratchet. Consequently, the operator will be alerted that he has applied power to the vehicle wheels with the parking brake engaged. He can then disengage the parking brake. When the parking brake is disengaged by the operator, the engagement element is sufficiently removed from the sprocket wheels so that free motion is possible without the reinsertion effect of the spring.

In preferred embodiments of the invention, the engagement element comprises a slide portion reciprocal along the axis of the guide: and a complementary portion carried by he slide portion for intermeshing with the sprocket wheel teeth. The complementary portion typically comprises a link pivoted on the slide portion; at least one roller supported by the link for engaging the sprocket wheel teeth, at least one roller being movable relative to the slide portion to engage the sprocket wheel teeth in any angular position of the sprocket wheel; and a stop on the slide portion defining the limits of pivotal movement of at least one link relative to the slide portion.

The invention will now be described by way of example and with reference to the accompanying drawings wherein: Figure 1 is a perspective view of a skidsteer vehicle suitable for incorporating a parking brake according to the present invention; and Figure 2 is a schematic illustration of the sprocket wheels and a parking brake accord ing to the invention.

Fig. 1 of the drawings shows an overall construction of a skid-steer vehicle that may have a parking brake of the present invention incorporated therein. Vehicle 10 has an elongated generally U-shaped body 1 2 that defines an engine space 14 at one end thereof and a forward space 1 6 at the opposite end with an operator's seat 1 8 located intermediate the ends. Engine 20 is located in the engine space 14 while forward space 1 6 is designed for the operator's legs.

Vehicle 10 further includes first and second sets of wheels 22 (only one side is shown), resectively located on the opposite sides of the body 1 2. Stanchions 24 project upwardly from the body on each side of the engine space and a lift arm 26 is connected by a pivot pin 28 to the upper end of each stanchion. The lift arms project forwardly adjacent opposite sides of the body and downwardly adjacent the forward end with-material handling member 30, such as a bucket, pivotally connected to the ends of the respective lift arms. A hydraulic fluid ram 32 is associated with each of the lift arms to raise and lower the lift arms while fluid rams 34 cooperate with bucket 30 to pivot the bucket on the lift arms.

Body 1 2 has side compartments 36 located on opposite sides thereof which house the drive mechanisms for the respective sets of wheels and the parking brake herein described below.

The drive mechanism includes a sprocket wheel 40 connected to one of the wheels 22 and a sprocket wheel 42 connected to a hydraulic motor (not shown) or other source of rotational force. The two sprocket wheels have sprocket teeth defined thereon and are joined by a roller chain 44 having a plurality of rollers interconnected by links.

A parking brake 46 according to the present invention is illustrated in Fig. 2 and includes the following components: an engagement element 48, a guide 50, a resilient biasing or force absorption means 52, and an operating mechanism 54.

Guide 50 is preferably a rectangular member rigidly attached to the body 1 2 of the vehicle in the side compartment 36 and has its centre line coinciding with a radius of sprocket wheel 40 so that its axis passes through the centre of the sprocket wheel. The engagement element 48 and the force absorption means 52 are fitted within the guide 50.

Thus, the guide acts to direct the motion of engagement element 48 to and from the sprocket wheel. Since the force absorption means 52 and engagement element 48 are fitted within the guide, the guide also acts as a housing to enclose and protect these components of the brake.

Engagement element 48 includes a slide portion 53 supported for sliding movement within the guide 50 and a complementary portion 56 immediately adjacent to the sprocket wheel 40. This complementary portion 56 is preferably in the form of a roller chain link identical to a link of roller chain 44 and includes a pair or rollers (not shown) supported by links 58 through pins 60. These pins 60 extend beyond the links 58 and have a pair of pin link plates or link means 62 supported thereon, the opposite ends of which are pivoted on pins 64 fixed to the slide portion 53. The spaced rollers have a size or diameter and a spacing substantially equal to the pitch of the teeth of sprocket wheel 40 so as to snugly fit within the teeth of the sprocket when the brake is engaged.

The slide portion 53 has a surface 55 facing the sprocket wheel. Links 62 have a length greater than the spacing between the surface 55 and the rollers in pins 60 so that surface 55 acts as a stop to define upper and lower limits of pivotal or relative movement of links 58 with respect to slide portion 53. This feature has an additional advantage of allowing the links 58 to mesh with the sprocket teeth for any position of angular rotation of the sprocket wheel relative to the slide portion 53.

Slide portion 53 is in turn coupled to the operating mechanism 54 by a shaft or tube 74 which has a pin 66 carried on one end.

The surface 68 of the slide portion is provided with a slot or channel 70 which is covered by a washer 72A secured to surface 68. Shaft 74 extends through an opening in washer 72A. Washer 72A is preferably attached to the slide portion 53 of the engagement element 48 by tack welding. The length of this slot 70 is at least equal to the distance the complementary portion 56 must move to go from full engagement to full disengagement so as to allow the sprocket wheel 40 to rotate.

Thus, the engagement element 48 is free to move towards and away from the sprocket wheel 40 without abutting into any fixed or rigid component.

The force absorption means 52 preferably consists of a cylindrical helical spring 73 telescoped on shaft 74 and held in compression between washer 72A and a second washer 72B held on shaft 74 by pin 76.

Shaft 74 has an eyelet 78 for coupling to the movement means 54. The magnitude of the force which holds the chain link in the sprocket wheel is determined by the preload on the spring and the spring constant. The diameter of the spring and washers is slightly less than the internal opening in the guide 50. Thus, the engagement element 48 and force absorption means 52 form a train of components in housing 50.

Briefly summarizing the force absorption means described to this point, pin 76 on shall: 74 defines a stop for washer 72B while pin 66 couples the opposite end of shaft 74 to the engagement means 48. Washer 72A is attached to the engagement means so that spring 53 is compressed between the two washers along shaft 74. Therefore, the engagement element can be said to freely float between engaged and disengaged positions if the sprocket wheel is set in motion with the brake in the engaged position.

The operating mechanism 54 displaces the force absorption means 52 and the engagement means 48 as a unit towards and away from the sprocket wheel 40 which may be defined as first and second positions. In the specific embodiment illustrated in Fig. 2, the operating mechanism consists of a combination of lever arms and connecting links. Lever arms 80 and 82 are attached to cross shaft 84 and act in bell crank fashion to change generally vertical movement from connecting rod 86 to generally horizontal movement.

Cross shaft 84 is pivotally fixed to the body 1 2 of the vehicle 10. Pin 79 joins shaft 74 of the force absorption means to lever arm 80 while pin 81 joins one end of connecting rod 86 to lever arm 82. To facilitate adjustment of the linkage, the opposite end of connecting rod 86 is joined to an eyenut 87 and locknut 89. The effective length of the connecting rod 86 and the positioning of shaft 74 may be changed by adjusting the eyenut 87.

Connecting rod 86 may be set into motion by a variety of methods but the preferred method is to use an overcentre cam lever mechanism. The overcentre cam lever mechanism includes a lever 88 having a pin 91 supported in an elongated slot 90 defined in a bracket 92 which is secured to top wall 96 of side compartment 36 by bolts 1 00. Lever 88 is joined to connecting rod 86 by a pin 93.

Connecting rod 86 extends through an opening 94 in top wall 96 of side compartment 36. Opening 94 has a diameter substantially equal to the diameter of connecting rod 86 so that the connecting rod is limited to axial or vertical motion.

A return (tension) spring 98 is attached to lever arm 82 and to a bracket 102 attached to wall 96. When the overcentre cam lever 88 is rotated counter-clockwise to disengage the mechanism, the return spring 98 provides a positive means to prevent the engagement element 48 from being driven accidentally into the sprocket wheel.

Thus, when the overcentre cam lever 88 is actuated by-rotating it clockwise, the connecting rod 86 is forced downward which rotates the two levers 82 and 80 on a cross shaft 84.

This rotation is converted to translational motion of shaft 74, slide 53 and spring 73 as a unit which slides a section of roller chain 58 into the sprocket wheel teeth thereby acting to prevent the sprocket wheel 40 from rotating.

It should be noted that in this position, illustrated in Fig. 2, pin 91 engages the right hand end of slot 90 and is located to the right of the axis of connecting rod 86. Therefore, the return-spring holds the brake in the engaged or first position.

If the torque on the wheel sprocket exceeds a specified magnitude, precompressed spring 73, which is located between shaft 74 and slide portion 53, is compressed further and allows the complementary portion 56 to slip past the sprocket teeth. Thus, the spring 73 acts as a movable joint between the engagement element 48 and the movement means 54. This prevents the structural failure of brake mechanism components.

Since the components are made of metallic materials this disengagement-engagement cycle under the influence of the force absbrption means will create a ratcheting sound alerting the vehicle operator that motion of the vehicle is attempted with the brake engaged. Thus, damage is prevented and the operator may disengage the parking brake.

To release the brake, it is only necessary to rotate the lever 88 counterclockwise. The counterclockwise rotation of handle 88 raises rod 86 which moves the mechanism to the released or second position. Rotating handle 88 causes the pin 91 to travel to the left end of slot 90 and then back to the right end as the rod is raised to its highest position, where the connection 93 is above pin 91 and pin 91 is again in an overcentre position in the righthand end of slot 90. The spring 98 prevents the brake mechanism from engaging the sprocket 40 accidentally by maintaining a constant force to hold the brake mechanism in the released position.

Summarizing the invention, under the direction provided by the guide 50, the operating mechanism 54 drives the engagement element 48 in a generally radial direction towards and away from the sprocket wheel 40.

Should the engagement element 48 be emeshed in the sprocket wheel 40 when that wheel is set in motion by the roller chain 44, tangential forces acting upon the engagement element and force absorption means will cause the engagement means to retract. A component of the rotational energy causing retraction is stored in the force absorption means. When the sprocket wheel 40 has rotated through an arc corresponding to the pitch of the roller chain, the energy stored in the force absorption means 52 is released to redirect the engagement element 48 into the sprocket wheel 40 so as to mesh within the sprocket teeth and thus limit its continued rotation. This cycle of retraction followed by reinsertion is repeated until the vehicle operator terminates the power to the wheels or releases the brake.

Claims

1. A parking brake for a vehicle driven by a transmission system including at least one toothed sprocket wheel, which brake com prises a guide fixedly mounted on the body of the vehicle and defining a path extending radially of the sprocket wheel; an engagement element movable towards and away from the wheel along said path for selective meshing with the teeth of the sprocket wheel; means resiliently biasing the engagement element in a direction towards the sprocket wheel along said path; and an operating mechanism for moving the engagement element between a first position at which it resiliently meshes with the sprocket wheel teeth, and a second position at which it is disengaged.

2. A parking brake according to claim 1 wherein the operating mechanism includes an elongate rod guided for generally axial movement on the vehicle body frame and coupled to the engagement element, and a lever connected to the rod for moving same to operate the brake.

3. A parking brake according to claim 2 wherein the vehicle body is formed with a frame member having an elongate slot extending generally transversely of the rod with opposite ends located on opposite sides of the rod, and wherein the lever has a pin slidably supported in the slot between opposite ends, the pin being transversely offset from the connection between the rod and the lever in both the engaged and disengaged positions of the engagement element.

4. A parking brake according to any preceding claim wherein the operating mechanism includes a spring biasing the mechanism to move the engagement element to said second position.

5. A parking brake according to claim 4 wherein the mechanism includes an overcentre cam lever coupled to a bell crank, the cam lever being movable to overcome the bias of said spring, such movement operating the bell crank to the engagement element to said first position.

6. A parking brake according to any preceding claim wherein the guide is a rectangular member having its axis extending radially of the sprocket wheel.

7. A parking brake according to any preceding claim wherein the engagement element comprises a slide portion reciprocal along the axis of the guide: and a complementary portion carried by the slide portion for intermeshing with the sprocket wheel teeth.

8. A parking brake according to claim 7 wherein the complementary portion comprises a link pivoted on the slide portion; at least one roller supported by the link for engaging the sprocket wheel teeth, at least one roller being movable relative to the slide portion to engage the sprocket wheel teeth in any angular position of the sprocket wheel and a stop on the slide portion defining the limits of pivotal movement of at least one link relative to the slide portion.

9. A parking brake according to any preceding claim wherein biasing means comprises a shaft connecting operating mechanism to the engagement element along said path, and a spring telescoped on the shaft.

10. A parking brake according to claim 9 wherein the spring is mounted between two washers mounted on the shaft having a maximum spacing defined by steps on the shaft, one of the washers abutting against the engagement element and being slideable on the shaft.

11. A parking brake according to any preceding claim wherein the engagement element comprises a sliding portion having a slot to accept a pin to couple the biasing means to the operating mechanism and a complementary portion for engagement with the sprocket wheel teeth carried by said sliding portion.

12. A parking brake according to claim 8 wherein the length of said slot is at least equal to the distance the complementary portion must move to go from full engagement with the sprocket wheel teeth to full disengagement.

1 3. For a vehicle driven by a transmission system including at least one toothed sprocket wheel, a parking brake substantially as described herein with reference to and as illustrated by the accompanying drawing.

14. A vehicle driven by a transmission system including at least one toothed sprocket wheel and having a parking brake according to any preceding claim.